MAYTANSINOID DERIVATIVES

The present invention provides maytansinoid derivatives, including maytansinoid derivatives for linking to antigen binding unit and maytansinoid drug linked with antigen binding unit, for targeted delivery to disease cells. Also provided are related compositions and methods for treating diseases, such as cancers and immunological disorders.

BACKGROUND

Maytansinoids are highly cytotoxic compounds which inhibit the formation of microtubule protein polymerization (Remillard, et al., Science 189, 1002-1005 (1975)). Maytansine was first isolated by Kupchan et al. (J. Am. Chem. Sci 94:1354-1356 (1972)) from the east African shrub Maytenus serrata. Maytansinoids including maytansinol and C-3 esters of maytansinol were also produced by certain microbes (U.S. Pat. No. 4,151,042). Various analogues of maytansinol with different cytotoxicity have also been prepared by synthetic chemistry (for review see Chem. Pharm. Bull. 52(1) 1-26 (2004)). Examples of mytansinoids include maytansine, mertansine (DM1), DM3 and DM4. Maytansine is a strong mitotic inhibitor and shows significant inhibitory activity against multiple tumors including Lewis lung carcinoma and B-16

melanocarcinoma solid murine tumor models. Maytansine was reported to inhibit the human acute lymphoblastic leukemia line C.E.M. at concentrations as low as 10 ^"7 μg/mL (Wolpert- DeFillippes et al., Biochem. Pharmacol. 1735-1738 (1975)). It also showed to be 100- to 1000- fold more cytotoxic than conventional chemotherapeutic agents like methotrexate, daunorubicin, and vincristine (U.S. Pat. No. 3,896,111).

Ansamitocins, the bacterial maytansinoids, show an activity spectrum and effective dosage range similar to maytansine. They inhibit P388 leukemia at daily doses as low as 0.8 μg/kg.

Ansamitocin P3 (AP3) was also shown to be effective against multiple cancer cell lines (for review see Alkaloids, vol. 2, 149-204 (1984); Chem. Pharm. Bull. 52(1) 1 -26 (2004)). The maytansinol C-3 esters with N-methyl-L-alanine derivatives are found to be much more cytotoxic than the corresponding esters of simple carboxylic acid and to be 100 times more cytotoxic than their epimers corresponding to N-methyl-D-alanine (U.S. Pat. Nos. 4,137,230; 4,260,608; Kawai, et al., Chem. Pharm. Bull. 32: 3441-3451 (1984); Widdison, et al., J. Med. Chem. 49: 4392-4408 (2006)). Maytansinoids were expected to have the capacity to treat many different cancers due to their highly toxic nature and the in vitro activities against multiple cancer cell lines. However, the toxicity also made this class of compounds not favorable in human clinical trials as the side effects were intolerable for many patients (Issel et al., Cancer Treat. Rev. 199-207 (1978)).

Accordingly, targeted delivery of cytotoxic compounds to cancer cells by conjugating toxic drugs to monoclonal antibodies (ADC for antibody drug conjugate) is proposed in order to reduce the side effects. Certain conjugates of cytotoxic drugs such as maytansinoids, auristatins, anthracyclins, duocarmycins, etc. with antibodies are being evaluated in preclinical or clinical studies in the treatment of diseases.

Antibody drug conjugates (ADCs) are composed of three key elements: antibody, linker, and drug. The selection of a particular antibody and drug will have a great impact on the efficacy and safety depending on the particular disease. Linker stability and the method by which the drug is conjugated to the antibody plays a critical role in the success or failure of the ADC drug development.

The efficacy of an ADC depends in part on combination of a variety of parameters, involving not only the specificity of the antibody and the potency of drugs, but also the linker's stability or sensitivity to cleavage, the cell surface triggered the internalization, trafficking, and subsequent release of the active cytotoxic payload. Thus, ADC comprising different drug linkers or with different antibodies against the same target can vary significantly in their utility.

SUMMARY OF THE INVENTION

The present invention provides maytansinoid drug derivatives which can be linked to a antigen binding unit (Abu), and maytansinoid drug linked with antigen binding unit (Drug-Linker- Antigen binding Unit: D-L-Abu), for targeted delivery to disease cells or tissues. D-L-Abu, D- L-Abu derivatives, and methods relating to the use of such drug conjugates to treat antigen positive cells in cancers and immunological disorders are also provided. The antigen binding unit, Abu, such as an antibody, or other targeting moiety in the D-L-Abu, binds to an antigen in the disease cells or tissues. A drug conjugated to the Abu exerts a cytotoxic, cytostatic, or immunosuppressive effect on the antigen-expressing cells to treat or prevent recurrence of antigen-positive cancers or immunological disorders. The present technology provides drug- linker-antigen binding unit exerting cellular inhibitory or killing effect on the antigen positive cells, while minimizing the undesirable side effects, such as bystander killing effects on antigen negative cells.

In one aspect, provided are maytansinoid derivative compounds capable of conjugation to an antigen binding unit via a linker that is not acid labile, not peptidase cathepsin sensitive, and does not contain a disulfide bond. Such derivatives may also be referred to as "drug-linkers." In some embodiments, the linker modified maytansinoid compounds is a maytansinoid N ₂ '- deacetyl- N ₂ '-(6-maleimido-l-oxo-hexyl) maytansine, or its derivatives, wherein the linker is not acid labile, not peptidase cathepsin sensitive, and does not contain a disulfide bond. Such linkers are contemplated to provide stability to the D-L-Abu prior to endocytosis, such as during circulation, to prevent premature degradation of D-L-Abu and release of the toxic drug, thus minimizes the toxic effect of the drug.

In some embodiments, provided herein is a maytansinoid derivative of Formula I or I-l, formula II or II-l :

or a salt thereof,

wherein

X is hydrogen or halo;

Y is selected from the group consisting of hydrogen, Ci - C ₆ alkyl, C ₃ - C ₆ cycloalkyl, and -C(=0)R ⁵ ;

R ¹ is selected from the group consisting of hydrogen, -OH, -OC(=0)R ⁵ and -OR ⁵ ;

R ² is hydrogen or Ci - C ₆ alkyl;

R ³ is methyl, -CH ₂ OH, or -CH ₂ C(=0)R ⁶ ;

R ⁴ is -OH or -SH;

R ⁵ is Ci - C ₆ alkyl or benzyl;

R ⁶ is Ci - C ₆ alkyl, phenyl or benzyl;

R ⁷ is hydrogen, C1-C6 alkyl or an amino acid side chain;

R ⁸ is hydrogen or Ci _-6 alkyl;

each Z is independently hydrogen or C ₁ -C4 alkyl, or the two Z with the carbon atom to which they are attached form a C=0; and L is selected from optionally substituted C1-C2 ₀ alkylene, C ₃ -C ₈ cycloalkylene, optionally substituted C1-C20 alkylene wherein one or more of the -CH ₂ - groups are

independently replaced with C ₃ -C ₈ cycloalkylene, -0-, -S-, -NR ⁸ -, -C(O)- , -C(=0)NR ⁸ -, -NR ⁸ C(=0)-, -S0 ₂ NR ⁸ -, or -NR ⁸ S0 ₂ -; preferably L is -(CH ₂ ) _m -, wherein m is selected from an integer of 1 to 20, preferably 1 to 10, more preferably 5 to 10;

substituted Ci-C ₂₀ alkylene is Ci-C ₂₀ alkylene substituted with 1 to 4 -SO ₃ H, -P(0)(OH) ₂ or R ²³ , wherein each R ²³ is independently Ci _-6 alkyl optionally substituted with 1 or 2 substituents independently selected from the group consisting of -SH, -S-C1-4 alkyl, - CONR ⁿ R ⁿ , -C0 ₂ H, and -NR ⁿ R ^u , wherein each R ¹¹ is independently hydrogen, alkyl, aryl, cycloalkyl, cycloalkenyl, heteroaryl, and heterocyclic, or the two R ¹¹ together with the nitrogen form a heterocyclic, wherein the heterocyclic is optionally substituted with one or two oxo.

In another aspect, provided is a composition comprising the above-described maytansinoid compound and an antigen binding unit capable of being conjugated with each other.

In another aspect, provided is an antigen binding unit conjugated with a maytansinoid compound, wherein the maytansinoid compound is modified, and linked to an antigen binding unit via a linker that is not acid labile, not peptidase cathepsin sensitive, and does not contain a disulfide bond.

In some embodiments, provided herein is a maytansinoid linker antigen binding unit conjugate of Formula la, Ia-1, Ila or IIa-1 :

la

or a pharmaceutically acceptable salt or solvate thereof,

wherein

X is hydrogen or halo;

Y is selected from the group consisting of hydrogen, Ci - Ce alkyl, C3 - Ce cycloalkyl, and -C(=0)R ⁵ ;

R ¹ is selected from the group consisting of hydrogen, -OH, -OC(=0)R ⁵ and -OR ⁵ ; R ² is hydrogen or Ci - C ₆ alkyl;

R ³ is methyl, -CH ₂ OH, or -CH ₂ C(=0)R ⁶ ;

R ⁴ is -OH or -SH;

R ⁵ is Ci - C ₆ alkyl or benzyl;

R ⁶ is Ci - Ce alkyl, phenyl or benzyl;

R ⁷ is hydrogen, Ci-C ₆ alkyl or an amino acid side chain;

R ⁸ is hydrogen or Ci _-6 alkyl;

p is selected from 1 , 2, 3, 4, 5, 6, 7, 8, 9, and 10;

each Z is independently hydrogen or Ci-C ₄ alkyl, or the two Z with the carbon atom to which they are attached form a C=0;

L is selected from optionally substituted Ci-C ₂₀ alkylene, C ₃ -C ₈ cycloalkylene, optionally substituted Ci-C ₂ o alkylene wherein one or more of the -CH ₂ - groups are

independently replaced with C ₃ -C ₈ cycloalkylene, -0-, -S-, -NR ⁸ -, -C(O)- , -C(=0)NR ⁸ -, -NR ⁸ C(=0)-, -S0 ₂ NR ⁸ -, or -NR ⁸ S0 ₂ -; Preferably L is -(CH ₂ ) _m -, wherein m is selected from an integer of 1 to 20, preferably 1 to 10, more preferably 5 to 10;

substituted Ci-C ₂₀ alkylene is Ci-C ₂₀ alkylene substituted with 1 to 4 -S0 ₃ H, -P(0)(OH) ₂ or R ²³ , wherein each R ²³ is independently Ci _-6 alkyl optionally substituted with 1 or 2 substituents independently selected from the group consisting of -SH, -S-Ci _-4 alkyl, - CONR ⁿ R ⁿ , -C0 ₂ H, and -NR ⁿ R ^u , wherein each R ¹¹ is independently hydrogen, alkyl, aryl, cycloalkyl, cycloalkenyl, heteroaryl, and heterocyclic, or the two R ¹¹ together with the nitrogen form a heterocyclic, wherein the heterocyclic is optionally substituted with one or two oxo; and

Abu is an antigen binding unit. embodiments, provided are compounds of the formula:

a pharmaceutically acceptable salt or solvate thereof. In another aspect, provided is a composition comprising the above-described maytansinoid linker antigen binding unit conjugate.

In another aspect, provided is a method of preparing the above-described maytansinoid linker antigen binding unit conjugate which method comprises contacting an antigen binding unit with one or more maytansinoid compounds described herein capable of being conjugated to the antigen binding unit.

In another aspect, disclosed herein is a compound of Formula lb, Ib-1, lib or nb-1 :

or a salt thereof,

wherein

X is hydrogen or halo;

Y is selected from the group consisting of hydrogen, Ci - C ₆ alkyl, C ₃ - C ₆ cycloalkyl, and -C(=0)R ⁵ ;

R ¹ is selected from the group consisting of hydrogen, -OH, -OC(=0)R ⁵ and -OR ⁵ ;

R ² is hydrogen or Ci - C ₆ alkyl;

R ³ is methyl, -CH ₂ OH, or -CH ₂ C(=0)R ⁶ ;

R ⁴ is -OH or -SH;

R ⁵ is Ci - C ₆ alkyl or benzyl;

R ⁶ is Ci - C ₆ alkyl, phenyl or benzyl;

R ⁷ is hydrogen, C1-C6 alkyl or an amino acid side chain;

R ⁸ is hydrogen or Ci _-6 alkyl;

each Z is independently hydrogen or C ₁ -C4 alkyl, or the two Z with the carbon atom to which they are attached form a C=0; L is selected from optionally substituted C ₁ -C ₂₀ alkylene, C ₃ -C ₈ cycloalkylene, optionally substituted C1-C20 alkylene wherein one or more of the -CH ₂ - groups are

independently replaced with C ₃ -C ₈ cycloalkylene, -0-, -S-, -NR ⁸ -, -C(O)- , -C(=0)NR ⁸ -, -NR ⁸ C(=0)-, -S0 ₂ NR ⁸ -, or -NR ⁸ S0 ₂ -; preferably L is -(CH ₂ ) _m -, wherein m is selected from an integer of 1 to 20, preferably 1 to 10, more preferably 5 to 10;

substituted Ci-C ₂₀ alkylene is Ci-C ₂₀ alkylene substituted with 1 to 4 -SO ₃ H, -P(0)(OH) ₂ or R ²³ , wherein each R ²³ is independently Ci _-6 alkyl optionally substituted with 1 or 2 substituents independently selected from the group consisting of -SH, -S-C ₁ -4 alkyl, - CONR ⁿ R ⁿ , -C0 ₂ H, and -NR ⁿ R ^u , wherein each R ¹¹ is independently hydrogen, alkyl, aryl, cycloalkyl, cycloalkenyl, heteroaryl, and heterocyclic, or the two R ¹¹ together with the nitrogen form a heterocyclic, wherein the heterocyclic is optionally substituted with one or two oxo; and

AA is an amino acid, such as a cysteine or a thiolated amino acid, such as a thiolated lysine. embodiments, provided are compounds of the formula:

or a pharmaceutically acceptable salt or solvate thereof.

In another aspect, provided is a composition comprising the above-described maytansinoid compound of Formula lb, Ib-1 , lib or lib- 1.

In another aspect, provided is a method for targeting a maytansinoid to antigen positive cells or tissues with an antigen binding unit conjugated with maytansinoid described herein.

In another aspect, provided is an antigen binding unit, Bat0206 comprising an anti-EGFR light chain having an amino acid sequence of SEQ ID NO: 1 and an anti-EGFR heavy chain having an amino acid sequence of SEQ ID NO: 2. In another aspect, provided is a maytansinoid linker antigen binding unit conjugate wherein the antigen binding unit is Bat0206.

In another aspect, provided is a method for treatment of proliferative disorders such as tumors, inflammatory or immunologic diseases such as graft rejections, and other diseases that can be treated by targeted therapy in a subject in need of the treatment, wherein the disease is characterized by cells comprising an antigen that binds to an antigen binding unit, said method comprising administering to the subject an effective amount of the antigen binding unit conjugated with one or more maytansinoid compound described herein.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 shows Sephadex G25(M) chromatograph of purification of Batansine-0206.

Fig. 2 shows Sephadex G25(M) chromatograph of purification of Batansine-1206.

Fig. 3 shows Phenyl Sepharose FF column separation of Batansine-0206.

Fig. 4 shows Sephadex G25(M) column separation of Batansine-0606.

Fig. 5 shows Phenyl Sepharose FF column separation of Batansine-0606.

Fig. 6 shows the effects of the metabolites of prodrug antibody maytansinoid conjugates on the tubulin polymerization.

Fig. 7 shows that Bat0206 and Batansine-0206 inhibited tumor cell growth.

Fig. 8 shows that Bat0206, cetuximab, Batansine-0206 has no inhibitory effect on EGFR negative cells.

Fig. 9 shows the inhibitory effect of D-Lmcc-Bat0206 towards MDA-MB-468 cells.

Fig. 10 shows that Bat0206, cetuximab, D-Lmcc-Bat0206 has no inhibitory effect on EGFR negative cells.

Fig. 11 and 12 shows that D-Lmcc-Bat0206 eradicated A431 tumor xenographs. Fig. 13 shows that D-Lmcc-Bat0206 and D-Lspp-Bat0206 inhibited A431 tumor cells.

Fig. 14 shows D-Lmcc-Bat0206 and D-Lspp-Bat0206 inhibited A549 tumor cells.

Fig. 15 A and 15B show the amino acid sequences of anti-EGFR antibody.

Fig. 16 and 17 show the processing of D-Lmcc-bat0606 and Batanine-0606 using Sephadex G- 25.

Fig. 18 and 19 show the size exclusion chromatograph of D-Lmcc-bat0606 and Batanine-0606 respectively.

Fig. 20 shows the inhibitory effects of Bat0606 and Batanine-0606 on Her2 (SK-BR-3) cells.

Fig. 21 shows that Bat0606 and Batanine-0606 did not inhibit A549.

Fig. 22 shows the inhibitory effect of D-Lmcc-Bat0606 on SK-BR-3.

Fig. 23 shows that Bat0606 and D-Lmcc-Bat0606 did not inhibit A549 cells.

Fig. 24 shows the inhibitory effects of Batl206 and Batansine-1206 on Raji cells.

Fig. 25 shows that Batl206 and Batansine-1206 had no effects on A431 cells.

Fig. 26 shows that D-Lmcc-Batl 206 inhibited Raji cell growth.

Fig. 27 shows the purification of Batansine-1206 on SEC-HPLC.

Fig. 28 shows the non-reduced SDS-PAGE of Batl206 and D-Lmcc-Batl 206.

Fig. 29 shows Batansine-0606 eradicated human NCI-N87 tumor in mouse xenografts.

Fig. 30 shows Batansine-0606 eradicated human BT474 tumor in mouse xenografts.

Fig. 31 shows the ESI-MS spectra of the metabolite (Batansine-Cysteine) from the prodrug Batansine-0606 . Fig. 32 shows the ESI-MS spectra of the two diastereomeric metabolites (MDC-MCC-Lysine) from the prodrug D-Lmcc-Bat0606.

DETAILED DESCRIPTION OF THE INVENTION

Definitions

As used herein, the following definitions shall apply unless otherwise indicated.

As used herein, unless otherwise stated, the singular forms "a," "an," and "the" include plural reference. Thus, for example, a reference to "a compound" includes a plurality of compounds.

As used herein, "about" will be understood by persons of ordinary skill in the art and will vary to some extent depending upon the context in which it is used. If there are uses of the term which are not clear to persons of ordinary skill in the art, given the context in which it is used, "about" will mean up to plus or minus 10% or plus or minus 5%, or plus or minus 1% of the particular term.

As used herein, the term "comprising" is intended to mean that the compositions and methods include the recited elements, but not excluding others. "Consisting essentially of when used to define compositions and methods, shall mean excluding other elements of any essential significance to the combination. For example, a composition consisting essentially of the elements as defined herein would not exclude other elements that do not materially affect the basic and novel characteristic(s) of the claimed invention. "Consisting of shall mean excluding more than trace amount of other ingredients and substantial method steps recited. Embodiments defined by each of these transition terms are within the scope of this invention.

As used herein, "maytansinoid" refers to a maytansine analogue, including stereoisomers thereof. Maytansine can be isolated from plants of the genus Maytenus U.S. Pat. No. 3,896,111). It is of the formula:

25

Maytansinoids are compounds having the ring structure of maytansine with one or more modifications of the substituents on the ring.

"Alkyl" refers to monovalent saturated aliphatic hydrocarbyl groups having from 1 to 10 carbon atoms and preferably 1 to 6 carbon atoms. C _v alkyl wherein v is an integer represents an alkyl having v carbons. This term includes, by way of example, linear and branched hydrocarbyl groups such as methyl (CH ₃ -), ethyl (CH ₃ CH ₂ -), ^-propyl (CH ₃ CH ₂ CH ₂ -), isopropyl

((CH ₃ ) ₂ CH-), 77-butyl (CH ₃ CH ₂ CH ₂ CH ₂ -), isobutyl ((CH ₃ ) ₂ CHCH ₂ -), sec-butyl

((CH ₃ )(CH ₃ CH ₂ )CH-), t-butyl ((CH ₃ ) ₃ C-), «-pentyl (CH ₃ CH ₂ CH ₂ CH ₂ CH ₂ -), and neopentyl ((CH ₃ ) ₃ CCH ₂ -). "Alkylene" is a divalent saturated aliphatic hydrocarbyl groups having from 1 to 10 carbon atoms and preferably 1 to 6 carbon atoms.

"Alkenyl" refers to straight or branched hydrocarbyl groups having from 2 to 6 carbon atoms and preferably 2 to 4 carbon atoms and having at least 1 and preferably from 1 to 2 sites of vinyl (>C=C<) unsaturation. Such groups are exemplified, for example, by vinyl, allyl, and but-3-en-l-yl. Included within this term are the cis and trans isomers or mixtures of these isomers.

"Alkynyl" refers to straight or branched monovalent hydrocarbyl groups having from 2 to 6 carbon atoms and preferably 2 to 3 carbon atoms and having at least 1 and preferably from 1 to 2 sites of acetylenic (-C≡C-) unsaturation. Examples of such alkynyl groups include acetylenyl (-C≡CH), and propargyl (-CH ₂ C≡CH). "Amino" refers to the group -NR'R" where R' and R" are independently selected from the group consisting of hydrogen, alkyl, substituted alkyl, alkenyl, substituted alkenyl, alkynyl, substituted alkynyl, aryl, substituted aryl, cycloalkyl, substituted cycloalkyl, cycloalkenyl, substituted cycloalkenyl, heteroaryl, substituted heteroaryl, heterocyclic, substituted heterocyclic, and wherein R' and R" are optionally joined, together with the nitrogen bound thereto to form a heterocyclic or substituted heterocyclic group, provided that R' and R" are both not hydrogen, and wherein alkyl, substituted alkyl, alkenyl, substituted alkenyl, alkynyl, substituted alkynyl, cycloalkyl, substituted cycloalkyl, cycloalkenyl, substituted cycloalkenyl, aryl, substituted aryl, heteroaryl, substituted heteroaryl, heterocyclic, and substituted heterocyclic are as defined herein. When R' is hydrogen and R" is alkyl, the substituted amino group is sometimes referred to herein as alkylamino. When R' and R" are alkyl, the substituted amino group is sometimes referred to herein as dialkylamino. When referring to a monosubstituted amino, it is meant that either R' and R" is hydrogen but not both. When referring to a disubstituted amino, it is meant that neither R' and R" are hydrogen.

"Amino acid" refers any compound, whether natural, unnatural or synthetic, which comprises both an amino group and a carboxy group. Examples of amino acid include, but are not limited to glycine (NH ₂ CH ₂ COOH), cysteine, alanine, N-methyl-L-alanine, including both the D and L optical isomers. "Amino acid side chain" refers to the substituent that replaces a hydrogen of the methylene group of glycine or glycine derivatives, such as N-alkylglycine or glycine esters.

Examples of an amino acid side chain include, but are not limited to the side chains of the natural amino acids, alkyl, substituted alkyl, alkenyl, substituted alkenyl, alkynyl, substituted alkynyl, aryl, substituted aryl, cycloalkyl, substituted cycloalkyl, cycloalkenyl, substituted cycloalkenyl, heteroaryl, substituted heteroaryl, heterocyclic, and substituted heterocyclic.

"Aryl" or "Ar" refers to a monovalent aromatic carbocyclic group of from 6 to 14 carbon atoms having a single ring (e.g., phenyl) or multiple condensed rings (e.g., naphthyl or anthryl) which condensed rings may or may not be aromatic (e.g., 2-benzoxazolinone,

2H-l ,4-benzoxazin-3(4H)-one-7-yl, and the like) provided that the point of attachment is at an aromatic carbon atom. Preferred aryl groups include phenyl and naphthyl.

"Carbonyl" refers to the divalent group -C(O)- which is equivalent to -C(=0)-. "Carboxy" or "carboxyl" refers to -COOH or C0 ₂ H or salts thereof.

"Carboxylic acid" refers to a compound having at least one carboxy. "Cyano" refers to the group -CN.

"Cycloalkyl" refers to cyclic alkyl groups of from 3 to 10 carbon atoms having single or multiple cyclic rings including fused, bridged, and spiro ring systems. One or more of the rings can be aryl, heteroaryl, or heterocyclic provided that the point of attachment is through the non-aromatic, non-heterocyclic ring carbocyclic ring. Examples of suitable cycloalkyl groups include, for instance, adamantyl, cyclopropyl, cyclobutyl, cyclopentyl, and cyclooctyl. Other examples of cycloalkyl groups include bicycle[2,2,2,]octanyl, norbornyl, and spirobicyclo groups such as spiro[4.5]dec-8-yl:

Cycloalkylene refers to a cyclic alkylene.

"Cycloalkenyl" refers to non-aromatic cyclic alkyl groups of from 3 to 10 carbon atoms having single or multiple cyclic rings and having at least one >C=C< ring unsaturation and preferably from 1 to 2 sites of >C=C< ring unsaturation.

"Halo" or "halogen" refers to fluoro, chloro, bromo and iodo and preferably is fluoro or chloro.

"Haloalkyl" refers to alkyl groups substituted with 1 to 5, 1 to 3, or 1 to 2 halo groups, wherein alkyl and halo are as defined herein.

"Hydroxy" or "hydroxyl" refers to the group -OH.

"Heteroaryl" refers to an aromatic group of from 1 to 10 carbon atoms and 1 to 4 heteroatoms selected from the group consisting of oxygen, nitrogen and sulfur within the ring. Such heteroaryl groups can have a single ring (e.g., pyridinyl or furyl) or multiple condensed rings (e.g., indolizinyl or benzothienyl) wherein the condensed rings may or may not be aromatic and/or contain a heteroatom provided that the point of attachment is through an atom of the aromatic heteroaryl group. In one embodiment, the nitrogen and/or the sulfur ring atom(s) of the heteroaryl group are optionally oxidized to provide for the N-oxide (N→0), sulfinyl, or sulfonyl moieties. Preferred heteroaryls include pyridinyl, pyrrolyl, indolyl, thiophenyl, and furanyl.

"Heterocycle" or "heterocyclic" or "heterocycloalkyl" or "heterocyclyl" refers to a saturated or partially saturated, but not aromatic, group having from 1 to 10 ring carbon atoms and from 1 to 4 ring heteroatoms selected from the group consisting of nitrogen, sulfur, or oxygen.

Heterocycle encompasses single ring or multiple condensed rings, including fused bridged and spiro ring systems. In fused ring systems, one or more the rings can be cycloalkyl, aryl, or heteroaryl provided that the point of attachment is through the non-aromatic ring. In one embodiment, the nitrogen and/or sulfur atom(s) of the heterocyclic group are optionally oxidized to provide for the N-oxide, sulfinyl, or sulfonyl moieties.

Examples of heterocycle and heteroaryls include, but are not limited to, azetidine, pyrrole, imidazole, pyrazole, pyridine, pyrazine, pyrimidine, pyridazine, indolizine, isoindole, indole, dihydroindole, indazole, purine, quinolizine, isoquinoline, quinoline, phthalazine,

naphthylpyridine, quinoxaline, quinazoline, cinnoline, pteridine, carbazole, carboline, phenanthridine, acridine, phenanthroline, isothiazole, phenazine, isoxazole, phenoxazine, phenothiazine, imidazolidine, imidazoline, piperidine, piperazine, indoline, phthalimide, 1,2,3,4-tetrahydroisoquinoline, 4,5,6,7-tetrahydrobenzo[b]thiophene, thiazole, thiazolidine, thiophene, benzo[b]thiophene, morpholinyl, thiomorpholinyl (also referred to as

thiamorpholinyl), 1 ,1 -dioxothiomorpholinyl, piperidinyl, pyrrolidine, and tetrahydrofuranyl.

"Substituted alkyl," "substituted alkenyl," "substituted alkynyl," "substituted cycloalkyl," "substituted cycloalkenyl," "substituted aryl," "substituted heteroaryl" or "substituted heterocyclic" refers to alkyl, alkenyl, alkynyl, cycloalkyl, cycloalkenyl, aryl, heteroaryl or heterocyclic groups, respectively, which are substituted with 1 to 5, preferably 1 to 3, or more preferably 1 to 2 substituents selected from the group consisting of alkyl, halo alkyl, -O-R ²⁰ , -S- R ²⁰ , alkenyl, alkynyl, -C(=0)R ²⁰ , -C(=S)R ²⁰ , -C(=0)OR ²⁰ , -

NR ²⁰ C(=O)R ²¹ , -OC(=0)R ²¹ , -NR ²⁰ R ²⁰ , -C(=O)NR ²⁰ R ²⁰ , -C(=S)NR ²⁰ R ²⁰ , -NR ²⁰ C(=O)NR ²⁰ R ²⁰ , - NR ²⁰ C(=S)NR ²⁰ R ²⁰ , -OC(=O)NR ²⁰ R ²⁰ , -SO ₂ NR ²⁰ R ²⁰ , -OSO ₂ NR ²⁰ R ²⁰ , -NR ²⁰ SO ₂ NR ²⁰ R ²⁰ , -C(=N R ^2U )NR ^2U R , aryl, -NR ^2U C(=0)OR , -OC(=0)OR , cyano, cycloalkyl,

cycloalkenyl, -NR ²⁰ C(=NR ²⁰ )NR ²⁰ R ²⁰ , halo, hydroxy, heteroaryl, heterocyclic, nitro, -S0 ₃ H, - S0 ₂ R , and -OS0 ₂ R , wherein each R is selected from the group consisting of hydrogen, alkyl, alkenyl, alkynyl, aryl, cycloalkyl, cycloalkenyl, heteroaryl, and heterocyclic or two R ²⁰ with the atom(s) bound thereto form a heterocyclic ring, and R ²¹ is selected from the group consisting of alkyl, alkenyl, alkynyl, aryl, cycloalkyl, cycloalkenyl, heteroaryl, and heterocyclic.

"Nitro" refers to the group -N0 ₂ .

"Oxo" refers to the atom (=0) or (-0 ^" ).

"Spiro ring systems" refers to bicyclic ring systems that have a single ring carbon atom common to both rings.

"Thiol" refers to the group -SH.

"Thiocarbonyl" refers to the divalent group -C(S)- which is equivalent to -C(=S)-. "Thione" refers to the atom (=S).

"Compound" or "compounds" as used herein is meant to include the stereoiosmers and tautomers of the indicated formulas.

"Stereoisomer" or "stereoisomers" refer to compounds that differ in the chirality of one or more stereocenters. Stereoisomers include enantiomers and diastereomers.

"Tautomer" refer to alternate forms of a compound that differ in the position of a proton, such as enol-keto and imine-enamine tautomers, or the tautomeric forms of heteroaryl groups containing a ring atom attached to both a ring -NH- moiety and a ring =N- moiety such as pyrazoles, imidazoles, benzimidazoles, triazoles, and tetrazoles.

"Solvate" refer to an association of a solvent with a compound, in the crystalline form. The solvent association is typically due to use of the solvent in the synthesis, crystallization, and/or recrystallization of the compound. "Solvate" includes hydrate which is an association of water with a compound, in the crystalline form. "Patient" or "subject" refers to mammals and includes humans and non-human mammals.

"Pharmaceutically acceptable salt" refers to pharmaceutically acceptable salts of a compound, which salts are derived from a variety of organic and inorganic counter ions well known in the art and include, by way of example only, when the molecule contains an acidic functionality, salts of organic or inorganic bases, such as sodium, potassium, calcium, magnesium, ammonium, isopropylamine, trimethylamine, diethylamine, triethylamine, tripropylamine, ethanolamine, 2- dimethylaminoethanol, 2-diethylaminoethanol, dicyclohexylamine, lysine, arginine, histidine, caffeine, procaine, hydrabamine, choline, betaine, ethylenediamine, glucosamine,

methylglucamine, theobromine, purines, piperazine, piperidine, N-ethylpiperidine, polyamine resins and tetraalkylammonium, and the like; and when the molecule contains a basic

functionality, salts of organic or inorganic acids, such as hydrochloride, hydrobromide, tartrate, mesylate, acetate, maleate, and oxalate. Other non-limiting examples of acids include sulfuric acid, nitric acid, phosphoric acid, propionic acid, glycolic acid, pyruvic acid, malonic acid, succinic acid, fumaric acid, tartaric acid, citric acid, benzoic acid, cinnamic acid, mandelic acid, methanesulfonic acid, ethanesulfonic acid, p-toluenesulfonic acid, salicyclic acid and the like.

"Treating" or "treatment" of a disease in a patient refers to (1) preventing the disease from occurring in a patient that is predisposed or does not yet display symptoms of the disease; (2) inhibiting the disease or arresting its development; or (3) ameliorating or causing regression of the disease.

"Effective amount" is intended to mean an amount of an active compound or pharmaceutical agent that elicits the biological or medicinal response in a tissue, system, animal, individual or human that is being sought by a researcher, veterinarian, medical doctor or other clinician, which includes treating a disease.

Drug Derivatives for Conjugation with an Antigen Binding Unit

In one aspect, disclosed herein is a maytansinoid derivative having a linking group capable of conjugating to an antigen binding unit (Abu), by forming a linker that is not acid labile, not peptidase cathepsin sensitive, and does not contain a disulfide bond.

Maytansinoids suitable for attaching the linking group include maytansinol and maytansinol analogues and can be isolated from natural sources according to known methods, produced using biotechnologies (see e.g., Yu et al., 99 PNAS 7968-7973 (2002)), or prepared synthetically according to known methods (see e.g., Cassady et al., Chem. Pharm. Bull. 52(1) 1-26 (2004)).

Certain examples of suitable maytansinol analogues include:

(1) C-19-dechloro (U.S. Pat. No. 4,256,746) (prepared by LAH reduction of ansamytocin P2);

(2) C-20-hydroxy (or C-20-demethyl)+/-C-19-dechloro (U.S. Pat. Nos. 4,361,650 and 4,307,016) (prepared by demethylation using Streptomyces or Actinomyces or dechlorination using lithium aluminium hydride (LAH));

(3) C-20-demethoxy, C-20-acyloxy (-OCOR), +/-dechloro (U.S. Pat. No. 4,294,757) (prepared by acylation using acyl chlorides);

(4) C-9-SH (U.S. Pat. No. 4,424,219) (prepared by the reaction of maytansinol with H ₂ S or P ₂ S ₅ );

(5) C-14-hydroxymethyl (CH ₂ OH) or acyloxymethyl (CH ₂ OC(=0)phenyl or

CH ₂ OC(=0)(Ci -C ₅ alkyl)) (U.S. Pat. No. 4,331,598) (prepared from Nocardia);

(6) C-15-hydroxy/acyloxy (U.S. Pat. No. 4,364,866) (prepared by the conversion of maytansinol by Streptomyces);

(7) C-15-methoxy (U.S. Pat. Nos. 4,313,946 and 4,315,929) (isolated from Trewia nudlflora);

(8) C-18-N-demethyl (U.S. Pat. Nos. 4,362,663 and 4,322,348) (prepared by the demethylation of maytansinol by Streptomyces); and

(9) 4,5-deoxy (U.S. Pat. No. 4,371 ,533) (prepared by the titanium trichloride/LAH reduction of maytansinol).

Many positions on maytansinol can be useful as the linkage position, depending upon the type of linker. For example, for forming an ester linkage, the C-3 position having a hydroxyl group, the C-14 position modified with hydroxymethyl, the C-15 position modified with a hydroxyl group and the C-20 position having a hydroxyl group are all suitable. In some embodiments, the linkage position is the C-3 position.

In some embodiments, provided herein is a maytansinoid derivative of Formula I or 1-1 :

or a salt thereof,

wherein

X is hydrogen or halo;

Y is selected from the group consisting of hydrogen, Ci - C ₆ alkyl, C ₃ - C ₆ cycloalkyl, and -C(=0)R ⁵ ;

R ¹ is selected from the group consisting of hydrogen, -OH, -OC(=0)R ⁵ and -OR ⁵ ;

R ² is hydrogen or Ci - C ₆ alkyl;

R ³ is methyl, -CH ₂ OH, or -CH ₂ C(=0)R ⁶ ;

R ⁴ is -OH or -SH;

R ⁵ is Ci - C ₆ alkyl or benzyl;

R ⁶ is Ci - C ₆ alkyl, phenyl or benzyl;

R ⁷ is hydrogen, C1-C6 alkyl or an amino acid side chain;

R ⁸ is hydrogen or Ci _-6 alkyl;

each Z is independently hydrogen or C ₁ -C4 alkyl, or the two Z with the carbon atom to which they are attached form a C=0; and L is selected from optionally substituted C ₁ -C ₂₀ alkylene, C ₃ -C ₈ cycloalkylene, optionally substituted C1-C20 alkylene wherein one or more of the -CH ₂ - groups are

independently replaced with C ₃ -C ₈ cycloalkylene, -0-, -S-, -NR ⁸ -, -C(O)- , -C(=0)NR ⁸ -, -NR ⁸ C(=0)-, -S0 ₂ NR ⁸ -, or -NR ⁸ S0 ₂ -; preferably L is -(CH ₂ ) _m -, wherein m is selected from an integer of 1 to 20, preferably 1 to 10, more preferably 5 to 10;

substituted Ci-C ₂₀ alkylene is Ci-C ₂₀ alkylene substituted with 1 to 4 -SO ₃ H, -P(0)(OH) ₂ or R ²³ , wherein each R ²³ is independently Ci _-6 alkyl optionally substituted with 1 or 2 substituents independently selected from the group consisting of -SH, -S-C ₁ -4 alkyl, - CONR ⁿ R ⁿ , -C0 ₂ H, and -NR ⁿ R ^u , wherein each R ¹¹ is independently hydrogen, alkyl, aryl, cycloalkyl, cycloalkenyl, heteroaryl, and heterocyclic, or the two R ¹¹ together with the nitrogen form a heterocyclic, wherein the heterocyclic is optionally substituted with one or two oxo. embodiments, the compound of Formula I is

In some embodiments, the compound of Formula I is the isomer:

In some embodiments, the compound of Formula I-l is the isomer:

or a salt thereof,

wherein

X is hydrogen or halo;

Y is selected from the group consisting of hydrogen, Ci - C ₆ alkyl, C ₃ - C ₆ cycloalkyl, and -C(=0)R ⁵ ;

R ¹ is selected from the group consisting of hydrogen, -OH, -OC(=0)R ⁵ and -OR ⁵ ;

R ² is hydrogen or Ci - C ₆ alkyl;

R ³ is methyl, -CH ₂ OH, or -CH ₂ C(=0)R ⁶ ;

R ⁴ is -OH or -SH;

R ⁵ is Ci - C ₆ alkyl or benzyl;

R ⁶ is Ci - Ce alkyl, phenyl or benzyl;

R ⁷ is hydrogen, Ci-C ₆ alkyl or an amino acid side chain;

R ⁸ is hydrogen or Ci _-6 alkyl;

each Z is independently hydrogen or Ci-C ₄ alkyl, or the two Z with the carbon atom to which they are attached form a C=0; and

L is selected from optionally substituted Ci-C ₂₀ alkylene, C ₃ -C ₈ cycloalkylene, optionally substituted Ci-C ₂₀ alkylene wherein one or more of the -CH ₂ - groups are independently replaced with C3-C8 cycloalkylene, -0-, -S-, -NR ⁸ -, -C(O)- , -C(=0)NR ⁸ -, -NR ⁸ C(=0)-, -S0 ₂ NR ⁸ -, or -NR ⁸ S0 ₂ -; Preferably L is -(CH ₂ ) _m -, wherein m is selected from an integer of 1 to 20, preferably 1 to 10, more preferably 5 to 10;

substituted Ci-C ₂₀ alkylene is Ci-C ₂₀ alkylene substituted with 1 to 4 -SO ₃ H, -P(0)(OH) ₂ or R ²³ , wherein each R ²³ is independently Ci _-6 alkyl optionally substituted with 1 or 2 substituents independently selected from the group consisting of -SH, -S-Ci _-4 alkyl, - CONR ⁿ R ⁿ , -CO2H, and -NR ⁿ R ^u , wherein each R ¹¹ is independently hydrogen, alkyl, aryl, cycloalkyl, cycloalkenyl, heteroaryl, and heterocyclic, or the two R ¹¹ together with the nitrogen form a heterocyclic, wherein the heterocyclic is optionally substituted with one or two oxo.

In some embodiments, the compound of Formula II is

In some embodiments, the compound of Formula II is the isomer:

In some embodiments, X is hydrogen. In some embodiments, X is chloro. In some

embodiments, Y is hydrogen. In some embodiments, R ¹ is hydrogen. In some embodiments, R ² is methyl. In some embodiments, R ³ is methyl. In some embodiments, R ⁴ is -OH. In some embodiments, R ⁷ is an amino acid side chain. In some embodiments, R ⁷ is methyl. In some embodiments, R ⁸ is methyl.

In some embodiments, L is unsubstituted C1-C2 ₀ alkylene. In some embodiments, L is substituted C1-C2 ₀ alkylene. In some embodiments, L is unsubstituted Ci-Cio alkylene. In some embodiments, L is substituted Ci-Cio alkylene. In some embodiments, L is -(CH ₂ ) ₅ -. In some embodiments, L is unsubstituted Ci-C ₂₀ alkylene wherein one or two of the -CH ₂ - groups are independently replaced with C ₃ -C ₈ cycloalkylene, -0-, -S-, -NR ⁸ -, -C(=0)NR ⁸ -, -NR ⁸ C(=0)-, - S0 ₂ NR ⁸ -, or -NR ⁸ S0 ₂ -. In some embodiments, L is substituted Ci-C ₂₀ alkylene wherein one or two of the -CH ₂ - groups are independently replaced with C3-C8 cycloalkylene, -0-, -S-, -NR ⁸ - , -C(=0)NR -, -NR*C(=0)-, -SO ₂ NR -, or -NR*S0 ₂ -. In some embodiments, when more than one -CH ₂ - groups are replaced, the-CH ₂ - groups are not adjacent to each other.

In some embodiments, provided is a compound of Formula ΙΠ or ΙΠ-1 :

or a salt thereof,

wherein

X is H or CI;

Y is H or methyl;

R ⁷ is hydrogen, Ci-C ₆ alkyl or an amino acid side chain;

R ⁸ is hydrogen or Ci-C ₆ alkyl; and

L is selected from C1-C20 alkylene, C ₃ -C ₈ cycloalkylene, and C1-C20 alkylene wherein or more of the -CH ₂ - groups are independently replaced with C ₃ -C ₈ cycloalkylene, 0-, -S-, -NR ⁸ -, -C(=0)NR ⁸ -, -NR ⁸ C(=0)-, -S0 ₂ NR ⁸ -, or -NR ⁸ S0 ₂ -.

In some embodiments, the compound is of Formula IV or IV- 1

or a salt thereof,

wherein

X is H or CI;

Y is H or methyl;

R ⁷ is hydrogen, Ci-C ₆ alkyl or an amino acid side chain;

R ⁸ is hydrogen or C1-C6 alkyl; and

m is selected from an integer of 1 to 20, preferably 1 to 10, more preferably 5 to 10.

In some embodiments, the compound is N ₂ -deacetyl-N ₂ -(6-maleimido-l-oxo-hexyl)maytansine, named batansine, or a salt thereof Batansine is represented by Formula V:

and

or a salt thereof.

Drug Linker Antigen Binding Unit Conjugates

In another aspect, disclosed herein is a maytansinoid conjugated with an antigen binding unit (Abu) via a linker (drug linker Abu conjugate).

In exemplary embodiments, the drug linker Abu conjugate is a maytansinoid conjugated to an antibody via a linker that is neither acid-labile, cathepsin sensitive, nor containing a disulfide bond.

In some embodiments, provided herein is a maytansinoid linker antigen binding unit conjugate Formula la or Ia-1 :

or a pharmaceutically acceptable salt or solvate thereof,

wherein

X is hydrogen or halo;

Y is selected from the group consisting of hydrogen, Ci - C ₆ alkyl, C ₃ - C ₆ cycloalkyl, and -C(=0)R ⁵ ;

R ¹ is selected from the group consisting of hydrogen, -OH, -OC(=0)R ⁵ and -OR ⁵ ;

R ² is hydrogen or Ci - C ₆ alkyl;

R ³ is methyl, -CH ₂ OH, or -CH ₂ C(=0)R ⁶ ;

R ⁴ is -OH or -SH;

R ⁵ is Ci - C ₆ alkyl or benzyl;

R ⁶ is Ci - Ce alkyl, phenyl or benzyl;

R ⁷ is hydrogen, Ci-C ₆ alkyl or an amino acid side chain;

R ⁸ is hydrogen or Ci _-6 alkyl;

p is selected from 1 , 2, 3, 4, 5, 6, 7, 8, 9, and 10;

each Z is independently hydrogen or Ci-C ₄ alkyl, or the two Z with the carbon atom to which they are attached form a C=0;

L is selected from optionally substituted Ci-C ₂₀ alkylene, C ₃ -C ₈ cycloalkylene, optionally substituted Ci-C ₂ o alkylene wherein one or more of the -CH ₂ - groups are independently replaced with C ₃ -C ₈ cycloalkylene, -0-, -S-, -NR ⁸ -, -C(O)- , -C(=0)NR ⁸ -, -NR ⁸ C(=0)-, -S0 ₂ NR ⁸ -, or -NR ⁸ S0 ₂ -; Preferably L is -(CH ₂ ) _m -, wherein m is selected from an integer of 1 to 20, preferably 1 to 10, more preferably 5 to 10; substituted C ₁ -C ₂₀ alkylene is C ₁ -C ₂₀ alkylene substituted with 1 to 4 -S0 ₃ H, -P(0)(OH) ₂ or R ²³ , wherein each R ²³ is independently Ci-6 alkyl optionally substituted with 1 or 2 substituents independently selected from the group consisting of -SH, -S-Ci _-4 alkyl, - CONR ⁿ R ⁿ , -C0 ₂ H, and -NR ⁿ R ^u , wherein each R ¹¹ is independently hydrogen, alkyl, aryl, cycloalkyl, cycloalkenyl, heteroaryl, and heterocyclic, or the two R ¹¹ together with the nitrogen form a heterocyclic, wherein the heterocyclic is optionally substituted with one or two oxo; and

Abu is an antigen binding unit.

In some embodiments, the compound of Formula la or Ia-1 is

In some embodiments, the compound of Formula la is:

or a pharmaceutically acceptable salt or solvate thereof,

wherein

X is hydrogen or halo;

Y is selected from the group consisting of hydrogen, Ci - C ₆ alkyl, C ₃ - C ₆ cycloalkyl, and -C(=0)R ⁵ ;

R ¹ is selected from the group consisting of hydrogen, -OH, -OC(=0)R ⁵ and -OR ⁵ ;

R ² is hydrogen or Ci - C ₆ alkyl;

R ³ is methyl, -CH ₂ OH, or -CH ₂ C(=0)R ⁶ ;

R ⁴ is -OH or -SH;

R ⁵ is Ci - C ₆ alkyl or benzyl;

R ⁶ is Ci - C ₆ alkyl, phenyl or benzyl;

R ⁷ is hydrogen, Ci-C ₆ alkyl or an amino acid side chain;

R ⁸ is hydrogen or Ci _-6 alkyl;

p is selected from 1 , 2, 3, 4, 5, 6, 7, 8, 9, and 10;

each Z is independently hydrogen or Ci-C ₄ alkyl, or the two Z with the carbon atom to which they are attached form a C=0;

L is selected from optionally substituted Ci-C ₂₀ alkylene, C ₃ -C ₈ cycloalkylene, optionally substituted Ci-C ₂₀ alkylene wherein one or more of the -CH ₂ - groups are independently replaced with C3-C8 cycloalkylene, -0-, -S-, -NR ⁸ -, -C(O)- , -C(=0)NR ⁸ -, -NR ⁸ C(=0)-, -S0 ₂ NR ⁸ -, or -NR ⁸ S0 ₂ -; Preferably L is -(CH ₂ ) _m -, wherein m is selected from an integer of 1 to 20, preferably 1 to 10, more preferably 5 to 10; substituted C ₁ -C ₂₀ alkylene is C ₁ -C ₂₀ alkylene substituted with 1 to 4 -S0 ₃ H, -P(0)(OH) ₂ or R ²³ , wherein each R ²³ is independently Ci-6 alkyl optionally substituted with 1 or 2 substituents independently selected from the group consisting of -SH, -S-Ci _-4 alkyl, - CONR ⁿ R ⁿ , -C0 ₂ H, and -NR ⁿ R ^u , wherein each R ¹¹ is independently hydrogen, alkyl, aryl, cycloalkyl, cycloalkenyl, heteroaryl, and heterocyclic, or the two R ¹¹ together with the nitrogen form a heterocyclic, wherein the heterocyclic is optionally substituted with one or two oxo; and

Abu is an antigen binding unit. embodiments, the compound of Formula Ila or IIa-1 is

In some embodiments, the compound of Formula Ila is:

The compound of Formula IIa-1 is:

In some embodiments, X is hydrogen. In some embodiments, X is chloro. In some

embodiments, Y is hydrogen. In some embodiments, R ¹ is hydrogen. In some embodiments, R ² is methyl. In some embodiments, R ³ is methyl. In some embodiments, R ⁴ is -OH. In some embodiments, R ⁷ is an amino acid side chain. In some embodiments, R ⁷ is methyl. In some embodiments, R ⁸ is methyl.

In some embodiments, L is unsubstituted C ₁ -C ₂ 0 alkylene. In some embodiments, L is substituted C ₁ -C ₂ 0 alkylene. In some embodiments, L is unsubstituted Ci-Cio alkylene. In some embodiments, L is substituted Ci-Cio alkylene. In some embodiments, L is -(CH ₂ ) ₅ -. In some embodiments, L is unsubstituted Ci-C ₂ o alkylene wherein one or two of the -CH ₂ - groups are independently replaced with C ₃ -C ₈ cycloalkylene, -0-, -S-, -NR ⁸ -, -C(=0)NR ⁸ -, -NR ⁸ C(=0)-, - S0 ₂ NR ⁸ -, or -NR ⁸ S0 ₂ -. In some embodiments, L is substituted Ci-C ₂₀ alkylene wherein one or two of the -CH ₂ - groups are independently replaced with C ₃ -C ₈ cycloalkylene, -0-, -S-, -NR ⁸ - , -C(=0)NR -, -NR*C(=0)-, -SO ₂ NR -, or -NR*S0 ₂ -. In some embodiments, when more than one -CH ₂ - groups are replaced, the replaced -CH ₂ - groups are not adjacent to each other.

In some embodiments, provided is a compound of Formula Ilia or IIIa-1 :

or a pharmaceutically acceptable salt or solvate thereof,

wherein

X is H or CI;

Y is H or methyl;

R ⁷ is hydrogen, C1-C6 alkyl or an amino acid side chain;

R ⁸ is hydrogen or Ci-C ₆ alkyl;

p is selected from 1 , 2, 3, 4, 5, 6, 7, 8, 9, and 10;

L is selected from optionally substituted C ₁ -C ₂₀ alkylene, C ₃ -C ₈ cycloalkylene, optionally substituted C ₁ -C ₂₀ alkylene wherein one or more of the -CH ₂ - groups are independently replaced with C ₃ -C ₈ cycloalkylene, -0-, -S-, -NR ⁸ -, -C(O)- , -C(=0)NR ⁸ -, -NR ⁸ C(=0)-, -SO ₂ NR ⁸ -, or -NR ⁸ S0 ₂ -; preferably L is -(CH ₂ ) _m -, wherein m is selected from an integer of 1 to 20, preferably 1 to 10, more preferably 5 to 10;

substituted Ci-C ₂ o alkylene is Ci-C ₂ o alkylene substituted with 1 to 4 -S0 ₃ H, -P(0)(OH) ₂ or R ²³ , wherein each R ²³ is independently Ci _-6 alkyl optionally substituted with 1 or 2 substituents independently selected from the group consisting of -SH, -S-C1-4 alkyl, - CONR ⁿ R ⁿ , -CO ₂ H, and -NR ⁿ R ^u , wherein each R ¹¹ is independently hydrogen, alkyl, aryl, cycloalkyl, cycloalkenyl, heteroaryl, and heterocyclic, or the two R ¹¹ together with the nitrogen form a heterocyclic, wherein the heterocyclic is optionally substituted with one or two oxo; and

Abu is an antigen binding unit.

In some embodiments, the compound is of Formula IVa or IVa-1

harmaceutically acceptable salt or solvate thereof,

wherein

X is H or CI; Y is H or methyl;

R ⁷ is hydrogen, C1-C6 alkyl or an amino acid side chain;

R ⁸ is hydrogen or Ci-C ₆ alkyl;

p is selected from 1 , 2, 3, 4, 5, 6, 7, 8, 9, and 10;

m is selected from an integer of 1 to 20, preferably 1 to 10, more preferably 5 to 10; and Abu is an antigen binding unit.

In some embodiments, the compound is of Formula Va:

or a pharmaceutically acceptable salt or solvate thereof.

In some embodiments, the compound of Formula la or Ia-1 is selected from:

Via

In some embodiments, the compound of Formula la or Ia-1 is selected from:

harmaceutically acceptable salt thereof. The maytansinoid component of the maytansinoid derivatives having a linking group capable of conjugating to an antigen binding unit (Abu) or the maytansinoid linker antigen binding unit conjugates can be substituted by other suitable cytotoxic agents, for example, an auristatin, a DNA minor groove binding agent, a DNA minor groove alkylating agent, an enediyne, a lexitropsin, a duocarmycin, a taxane, a puromycin, a dolastatin, and a vinca alkaloid. Other suitable cytotoxic agents include anti-tubulin agents, such as an auristatin, a vinca alkaloid, a podophyllotoxin, a taxane, a baccatin derivative, a cryptophysin, a maytansinoid, a

combretastatin, or a dolastatin. In some embodiments, the cytotoxic agent is AFP, MMAF, MMAE, AEB, AEVB, auristatin E, vincristine, vinblastine, vindesine, vinorelbine, VP-16, camptothecin, paclitaxel, docetaxel, epothilone A, epothilone B, nocodazole, colchicines, colcimid, estramustine, cemadotin, discodermolide, maytansine, DM-1, DM-3, DM-4, or eleutherobin. Suitable immunosuppressive agents include, for example, gancyclovir, etanercept, cyclosporine, tacrolimus, rapamycin, cyclophosphamide, azathioprine, mycophenolate mofetil, methotrexate, Cortisol, aldosterone, dexamethasone, a cyclooxygenase inhibitor, a 5- lipoxygenase inhibitor, or a leukotriene receptor antagonist. In some embodiments, the cytotoxic agent is AFP, MMAF, MMAE, AEB, AEVB, auristatin E, paclitaxel, docetaxel, CC-1065, SN-38, topotecan, mo holino-doxorubicin, rhizoxin, cyanomorpholino-doxorubicin, dolastatin- 10, echinomycin, combretatstatin, chalicheamicin, maytansine, DM-1, DM-3, DM-4, or netropsin.

The maytansinoid component of the maytansinoid derivatives having a linking group capable of conjugating to an antigen binding unit (Abu) and the maytansinoid linker antigen binding unit conjugates can also be substituted by a suitable immunosuppressive agent, for example, gancyclovir, etanercept, cyclosporine, tacrolimus, rapamycin, cyclophosphamide, azathioprine, mycophenolate mofetil, methotrexate, Cortisol, aldosterone, dexamethasone, a cyclooxygenase inhibitor, a 5 -lipoxygenase inhibitor, or a leukotriene receptor antagonist.

Antigen Binding Units

The antigen binding units may be of any kind presently known, or that become known, and include peptides and non-peptides. Generally, these can be antibodies (for example, monoclonal antibodies), lymphokines, hormones, growth factors, vitamins, nutrient-transport molecules (such as transferrin), or any other cell-binding molecules or substances that specifically bind a target, derived from antibodies, antibody fragments, cell specific ligands, derived from peptides, carbohydrates, natural or synthetic chemical compounds; or a pharmaceutically acceptable salt or solvate thereof.

Antigen binding units include ragments of antibodies (polyclonal and monoclonal) such as Fab, Fab', F(ab') ₂ , and Fv (see, e.g., Parham, J. Immunol. 131 :2895-2902 (1983); Spring et al., J.

Immunol. 113:470-478 (1974); Nisonoff et al., Arch. Biochem. Biophys. 89:230-244 (I960)); domain antibodies (dAbs) and antigen-binding fragments thereof, including camelid antibodies (see, e.g., Desmyter et al., Nature Struct. Biol, 3:752 (1996)); shark antibodies called new antigen receptors (IgNAR) (see, e.g., Greenberg et al., Nature, 374:168 (1995); Stanfield et al. Science 305:1770-1773 (2004)).

Monoclonal antibody techniques allow for the production of antigen binding unit in the form of specific monoclonal antibodies. Particularly well known in the art are techniques for creating monoclonal antibodies produced by immunizing mice, rabbits, or any other mammal with the antigen of interest such as the tumor specific antigens isolated from the target cell. Another method of creating antigen binding unit is using phage libraries of scFv (single chain variable region), specifically human scFv (see, e.g., Griffiths et al., U.S. Pat. Nos. 5,885,793 and

5,969,108; McCafferty et al., WO 92/01047; Liming et al., WO 99/06587), or domain antibodies using yeast selection system (see, e.g., U.S. Pat. No. 7,195,595). In addition, resurfaced antibodies such as those disclosed in U.S. Pat. No. 5,639,641 may also be used, as may chimerized or humanized antibodies.

Selection of a particular antigen binding unit is a matter of choice that depends upon the disease type, cells and tissues that are to be targeted.

In some embodiments, the antigen binding unit is human monoclonal antibody.

Antigen binding units that have specificity to a tumor antigen can be used. A "tumor antigen" as used herein, refers to an antigenic substance produced in tumor cells, i.e., it triggers an immune response in the host. Tumor antigens are useful in identifying tumor cells and are potential candidates for use in cancer therapy. Normal proteins in the body are not antigenic. Certain proteins, however, are produced or overexpressed during tumorigenesis and thus appear "foreign" to the body. This may include normal proteins that are well sequestered from the immune system, proteins that are normally produced in extremely small quantities, proteins that are normally produced only in certain stages of development, or proteins whose structure is modified due to mutation.

An abundance of tumor antigens are known in the art and new tumor antigens can be readily identified by screening. Non-limiting examples of tumor antigens include EGFR, Her2, EpCAM, CD20, CD30, CD33, CD47, CD52, CD133, CEA, gpA33, Mucins, TAG-72, CTX, PSMA, folate-binding protein, GD2, GD3, GM2, VEGF, VEGFR, Integrin, νβ3, 5β1, ERBB2, ERBB3, MET, IGF1R, EPHA3, TRAILR1, TRAILR2, RANKL, FAP and Tenascin.

Hormones and cellular factors can be tumor antigents. Non-limiting examples include lymphokines such as IL-2, IL-3, IL-4, IL-6, hormones such as insulin, thyrotropin releasing hormone (TRH), melanocyte-stimulating hormone (MSH), steroid hormones such as androgens and estrogens; growth factors and colony-stimulating factors such as EGF, TGF-alpha, FGF, VEGF, G-CSF, M-CSF and GM-CSF (see, e.g., Burgess, Immunology Today 5:155-158 (1984)), transferrin (see, e.g., O'Keefe et al., J. Biol. Chem. 260:932-937 (1985)); and vitamins, such as folate.

Antigen binding units having specificity to a protein that is overexpressed on a tumor cell as compared to a corresponding non-tumor cell can also be used. A "corresponding non-tumor cell" as used here, refers to a non-tumor cell that is of the same cell type as the origin of the tumor cell. It is noted that such proteins are not necessarily different from tumor antigens. Non-limiting examples include carcinoembryonic antigen (CEA), which is overexpressed in most colon, rectum, breast, lung, pancreas and gastrointestinal tract carcinomas; heregulin receptors (F£ER-2, neu or c-erbB-2), which is frequently overexpressed in breast, ovarian, colon, lung, prostate and cervical cancers; epidermal growth factor receptor (EGFR), which is highly expressed in a range of solid tumors including those of the breast, head and neck, non-small cell lung and prostate; asialoglycoprotein receptor; transferrin receptor; serpin enzyme complex receptor, which is expressed on hepatocytes; fibroblast growth factor receptor (FGFR), which is overexpressed on pancreatic ductal adenocarcinoma cells; vascular endothelial growth factor receptor (VEGFR), for anti-angiogenesis gene therapy; folate receptor, which is selectively overexpressed in 90% of nonmucinous ovarian carcinomas; cell surface glycocalyx; carbohydrate receptors; and polymeric immunoglobulin receptor, which is useful for gene delivery to respiratory epithelial cells and attractive for treatment of lung diseases such as cystic fibrosis.

It is contemplated that antigen binding units can be modified to introduce an amino acid sequence having improved antibody-dependent cellular cytotoxicity (ADCC). For instance, an IgG2 antibody can be modified to include an Fc and/or hinge region from an IgGl antibody to achieve improved ADCC. Examples of IgGl -Fc that mediates improved ADCC, as well as methods of screening for such sequences, are known in the art (e.g., Stewart et al. Protein Eng Des Sel. 24(9):671-8, 2011).

One particular example of such an antigen binding unit, Bat0206, having improved ADCC has been tested in the present disclosure. Bat0206 includes an anti-EGFR light chain having an amino acid sequence of SEQ ID NO: 1 and an anti-EGFR heavy chain having an amino acid sequence of SEQ ID NO: 2. As shown in Table 1, SEQ ID NO NO: 2 includes a fragment (not underlined) derived from an IgG2 antibody which is fused with an Fc fragment of an IgGl antibody (underlined and bold).

Table 1. Amino acid sequences of exemplifying antigen binding units

SEQ ID NO: Amino acid sequence and name

1 Bat0202 (Anti-EGFR Light Chain 1)

DIQMTQSPSSLSASVGDRVTITCQASQDISNYLNWYQQKPGKAPKLLIYD ASNLETGVPSRFSGSGSGTDFTFTISSLQPEDIATYFCQHFDHLPLAFGG GTKVEIKRTVAAPSVFIFPPSDEQLKSGTASWCLLNNFYPREAKVQWKV DNALQSGNSQESVTEQDSKDSTYSLSSTLTLSKADYEKHKVYACEVTHQG LSSPVTKSFNRGEC

Bat0204 (Anti-EGFR heavy Chain 1)

QVQESGPGLVKPSETLSLTCTVSGGSVSSGDYYWTWIRQSPGKGLEWIGH IYYSGNTNYNPSLKSRLTISIDTSKTQFSLKLSSVTAADTAIYYCVRDRV TGAFDIWGQGTLVTVSSASTKGPSVFPLAPSSKSTSGGTAALGCLVKDYF PEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSWTVPSSSLGTQTYIC NVNHKPSNTKVDKKVEPKSCDKTHTCPPCPAPELLGGPSVFLFPPKPKDT L ISRTPEVTCVWDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQYNSTY RWSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREPQVYT LPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPPVLDS DGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK

Cetuximab Light Chain

DILLTQSPVILSVSPGERVSFSCRASQSIGTNIHWYQQRTNGSPRLLIKY ASESISGIPSRFSGSGSGTDFTLSINSVESEDIADYYCQQNNNWPTTFGA GTKLELKRTVAAPSVFIFPPSDEQLKSGTASWCLLNNFYPREAKVQWKV DNALQSGNSQESVTEQDSKDSTYSLSSTLTLSKADYEKHKVYACEVTHQG LSSPVTKSFNRGA

Cetuximab heavy Chain

QVQLKQSGPGLVQPSQSLSITCTVSGFSLTNYGVHWVRQSPGKGLEWLGV IWSGGNTDYNTPFTSRLSINKDNSKSQVFFKMNSLQSNDTAIYYCARALT YYDYEFAYWGQGTLVTVSAASTKGPSVFPLAPSSKSTSGGTAALGCLVKD YFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSWTVPSSSLGTQTY ICNVNHKPSNTKVDKRVEPKSPKSCDKTHTCPPCPAPELLGGPSVFLFPP KPKDTLMISRTPEVTCVWDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQ YNSTYRWSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPRE PQVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTP PVLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSP GK

EGF-ABXL (Anti-EGFR Light Chain 3)

DIQMTQSPSSLSASVGDRVTITCQASQDISNYLNWYQQKPGKAPKLLIYD ASNLETGVPSRFSGSGSGTDFTFTISSLQPEDIATYFCQHFDHLPLAFGG GTKVEIKRTVAAPSVFIFPPSDEQLKSGTASWCLLNNFYPREAKVQWKV DNALQSGNSQESVTEQDSKDSTYSLSSTLTLSKADYEKHKVYACEVTHQG LSSPVTKSFNRGEC EGF-ABXH (Anti-EGFR Heavy Chain 3 )

QLQESGPGLVKPSETLSLTCTVSGGSVSSGDYYWTWIRQSPGKGLEWIGH IYYSGNTNYNPSLKSRLTISIDTSKTQFSLKLSSVTAADTAIYYCVRDRV TGAFDIWGQGTMVTVSSASTKGPSVFPLAPCSRSTSESTAALGCLVKDYF PEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSWTVPSSNFGTQTYTC NVDHKPSNTKVDERKCCVECPAGPSVFLFPPKPKDTLMISRTPEVTCVW DVSHEDPEVQFNWYVDGVEVHNAKTKPREEQFNSTFRWSVLTWHQDWL NGKEYKCKVSNKGLPAPIEKTISKTKGQPREPQVYTLPPSREEMTKNQVS LTCLVKGFYPSDIAVEWESNGQPENNYKTTPPMLDSDGSFFLYSKLTVDK SRWQQGNVFSCSVMHEALHNHYTQKSLSLSPGK

Nimotuzumab Light Chain

DIQMTQSPSSLSASVGDRVTITCRSSQNIVHSNGNTYLDWYQQTPGKAPK LLIYKVSNRFSGVPSRFSGSGSGTDFTFTISSLQPEDIATYYCFQYSHVP WTFGQGTKLQITREVAAPSVFIFPPSDEQLKSGTASWCLLNNFYPREAK VQWKVDNALQSGNSQESVTEQDSKDSTYSLSSTLTLSKADYEKHKVYACE VTHQGLSSPVTKSFNRGEC

Nimotuzumab Heavy Chain

QVQLQQSGAEVKKPGSSVKVSCKASGYTFTNYYIYWVRQAPGQGLEWIGG INPTSGGSNFNEKFKTRVTITADESSTTAYMELSSLRSEDTAFYFCTRQG LWFDSDGRGFDFWGQGTTVTVSSASTKGPSVFPLAPSSKSTSGGTAALGC LVKDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSVVTVPSSSLG TQTYICNVNHKPSNTKVDKKVP

Matuzumab Light Chain

QVDIQMTQSPSSLSASVGDRVTITCSASSSVTYMYWYQQKPGKAPKLLIY DTSNLASGVPSRFSGSGSGTDYTFTISSLQPEDIATYYCQQWSSHIFTFG QGTKVEIKRTVAAPSVFIFPPSDEQLKSGTASWCLLNNFYPREAKVQWK VDNALQSGNSQESVTEQDSKDSTYSLSSTLTLSKADYEKHKVYACEVTHQ GLSSPVTKSFNRGE

Matuzumab Heavy Chain

QVQLVQSGAEVKKPGASVKVSCKASGYTFTSHWMHWVRQAPGQGLEWIGE FNPSNGRTNYNEKFKSKATMTVDTSTNTAYMELSSLRSEDTAVYYCASRD YDYDGRYFDYWGQGTLVTVSSASTKGPSVFPLAPSSKSTSGGTAALGCLV KDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSWTVPSSSLGTQ TYICNVNHKPSNTKVDKKVEPKS 11 Trastuzumab Light Chain

DIQMTQSPSSLSASVGDRVTITCRASQDVNTAVAWYQQKPGKAPKLLIYS ASFLYSGVPSRFSGSRSGTDFTLTISSLQPEDFATYYCQQHYTTPPTFGQ GTKVEIKRTVAAPSVFIFPPSDEQLKSGTASWCLLNNFYPREAKVQWKV DNALQSGNSQESVTEQDSKDSTYSLSSTLTLSKADYEKHKVYACEVTHQG LSSPVTKSFNRGEC

12 Trastuzumab Heavy Chain

EVQLVESGGGLVQPGGSLRLSCAASGFNIKDTYIHWVRQAPGKGLEWVAR IYPTNGYTRYADSVKGRFTISADTSKNTAYLQMNSLRAEDTAVYYCSRWG GDGFYAMDYWGQGTLVTVSSASTKGPSVFPLAPSSKSTSGGTAALGCLVK DYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSWTVPSSSLGTQT YICNVNHKPSNTKVDKKVEPPKSCDKTHTCPPCPAPELLGGPSVFLFPPK PKDTLMISRTPEVTCVWDVSHEDPEVKFNWYVDGVEVHNAKTKPREEQY NSTYRVVSVLTVLHQDWLNGKEYKCKVSNKALPAPIEKTISKAKGQPREP QVYTLPPSRDELTKNQVSLTCLVKGFYPSDIAVEWESNGQPENNYKTTPP VLDSDGSFFLYSKLTVDKSRWQQGNVFSCSVMHEALHNHYTQKSLSLSPG

K

13 Rituxamab light chain (Anti-CD20 Light Chain)

QIVLSQSPAILSASPGEKVTMTCRASSSVSYIHWFQQKPGSSPKPWIYAT SNLASGVPVRFSGSGSGTSYSLTISRVEAEDAATYYCQQWTSNPPTFGGG TKLEIKRTVAAPSVFIFPPSDEQLKSGTASVVCLLNNFYPREAKVQWKVD NALQSGNSQESVTEQDSKDSTYSLSSTLTLSKADYEKHKVYACEVTHQGL SSPVTKSFNRGEC

14 Rituxamab heavy chain (Anti-CD20 Heavy Chain)

QVQLQQPGAELVKPGASVKMSCKASGYTFTSYNMHWVKQTPGRGLEWIGA IYPGNGDTSYNQKFKGKATLTADKSSSTAYMQLSSLTSEDSAVYYCARST YYGGDWYFNVWGAGTTVTVSAASTKGPSVFPLAPSSKSTSGGTAALGCLV KDYFPEPVTVSWNSGALTSGVHTFPAVLQSSGLYSLSSWTVPSSSLGTQ TYICNVNHKPSNTKVDKKVEPKSC

Another example of the antigen binding unit is Cetuximab which is a chimeric (mouse/human) monoclonal antibody targeting epidermal growth factor receptor (EGFR). The light and heavy chain sequences of Cetuximab are provided as SEQ ID NO: 3 and 4, respectively, shown in Table 1. Another anti-EGFR antibody is Panitumumab which is a fully human monoclonal antibody. Still another anti-EGFR antibody is Nimotuzumab, and the light and heavy chain sequences of Nimotuzumab are provided as SEQ ID NO: 7 and 8; still another anti-EGFR antibody is Matuzumab, and the light and heavy chain sequences of Matuzumab are provided as SEQ ID NO: 9 and 10. EGFR is over expressed in many cancer tissues such as metastatic colorectal cancer and head and neck cancer.

Rituximab is a chimeric monoclonal antibody against the protein CD20, which is primarily found on the surface of B cells. Rituximab specifically binds to and destroys B cells, and is therefore used to treat diseases which are characterized by excessive numbers of B cells, overactive B cells, or dysfunctional B cells. This includes many lymphomas, leukemias, transplant rejection, and some autoimmune disorders. The light chain and heavy chain sequences of Rituximab are provided in Table 1 as SEQ ID NO: 13 and 14, respectively.

Similarly, the monoclonal antibody trastuzumab (marketed as Herceptin®) is a chimeric monoclonal antibody against the protein Her2, that interfering with the Her2/neu receptor. The light chain and heavy chain sequences of trastuzumab are provided in Table 1 as SEQ ID NO: 11 and 12, respectively. In some cancers, notably some breast cancers, Her2 is over-expressed, and causes breast cells to reproduce uncontrollably. Trastuzumab is used to treat certain breast cancers and gastric cancers.

Additional examples of antigen binding units and their sequences are provided in Table 1 , without limitation.

Non-antibody molecules can also be used an antigen binding unit to target specific cell populations. For example, GM-CSF, which binds to myeloid cells, can be used as a cell-binding agent to target diseased cells from acute myelogenous leukemia. In addition, IL-2, which binds to activated T-cells, can be used for prevention of transplant graft rejection, for therapy and prevention of graft-versus-host disease, and for treatment of acute T-cell leukemia. MSH, which binds to melanocytes, can be used for the treatment of melanoma. Folic acid can be used to target the folate receptor expressed on ovarian and other tumors. Epidermal growth factor (EGF) can be used to target squamous cancers such as lung and head and neck. Somatostatin can be used to target neuroblastomas and other tumor types. Cancers of the breast and testes can be successfully targeted with estrogen (or estrogen analogues) or androgen (or androgen analogues) respectively as cell-binding agents.

In some embodiments, the antibody is an equivalent of any one of the antibodies described herein. Equivalents of antibody include those having at least about 80 % homology or identity or alternatively, at least about 85 %, or alternatively at least about 90 %, or alternatively at least about 95 %, or alternatively 98 % homology with nepenthesin, or alternatively a polypeptide or protein encoded by a polynucleotide that hybridizes under stringent conditions to the nucleotide sequence encoding nepenthesin or its complement, while maintaining the desired structure and exhibiting at least part of the antigen binding activity of the antibody.

In another aspect, provided is a D-L-Abu which is one or more of maytansinoid lined with Bat0206, wherein Bat0206 comprises an anti-EGFR light chain having an amino acid sequence of SEQ ID NO: 1 and an anti-EGFR heavy chain having an amino acid sequence of SEQ ID NO: 2, or an equivalent thereof.

In some embodiments, provided herein is a maytansinoid linker Bat0206 conjugate of Formula Id or nd:

or a pharmaceutically acceptable salt or solvate thereof,

wherein

X is hydrogen or halo;

Y is selected from the group consisting of hydrogen, Ci - C ₆ alkyl, C ₃ - C ₆ cycloalkyl, and -C(=0)R ⁵ ;

R ¹ is selected from the group consisting of hydrogen, -OH, -OC(=0)R ⁵ and -OR ⁵ ;

R ² is hydrogen or Ci - C ₆ alkyl;

R ³ is methyl, -CH ₂ OH, or -CH ₂ C(=0)R ⁶ ;

R ⁴ is -OH or -SH; and

R ⁵ is Ci - C ₆ alkyl or benzyl;

R ⁶ is Ci - C ₆ alkyl, phenyl or benzyl;

R ⁷ is hydrogen, C1-C6 alkyl or an amino acid side chain;

R is hydrogen or Ci _-6 alkyl;

p is selected from 1 , 2, 3, 4, 5, 6, 7, 8, 9, and 10; and

L ^b is selected from Ci-C ₂ o alkylene optionally substituted with Ci-C ₄ alkyl, -S0 ₃ H or - P(0)(OH) ₂ , C ₃ -C ₈ cycloalkylene optionally substituted with Ci-C ₄ alkyl, and Ci-C ₂₀ alkylene which is optionally substituted with Ci-C ₄ alkyl -S0 ₃ H or -P(0)(OH) ₂ and wherein one or more of the -CH ₂ - groups are independently replaced with C ₃ -C ₈ cycloalkylene, -0-, -S-, -S-S-, -NR ⁸ -, -C(=0)NR ⁸ -, -NR ⁸ C(=0)-, -S0 ₂ NR ⁸ -, or -NR ⁸ S0 ₂ , 3-8 membered heterocycloalkylene optionally substituted with one or more C ₁ -C4 alkyl or oxo.

In some embodiments, L ^b is Ci-C ₂₀ alkylene which is optionally substituted with Ci-C alkyl, -

S0 ₃ H or -P(0)(OH) ₂ and wherein one or more of the -CH ₂ - groups are independently replaced with -S-, -S-S-, -C(=0)NR ⁸ -, -NR ⁸ C(=0)-,

In some embodiments, the compound of Formula Id is selected from:

or a pharmaceutically acceptable salt or solvate thereof, wherein

X is H or CI;

Y is H or methyl;

R ⁷ is hydrogen, Ci-C ₆ alkyl or an amino acid side chain;

R ⁸ is hydrogen or Ci-C ₆ alkyl;

p is selected from 1 , 2, 3, 4, 5, 6, 7, 8, 9, and 10.

In some embodiments, the compound of Formula Id is selected from:

(Batansine-0206),

and

harmaceutically acceptable salt or solvate thereof.

Conjugation of a drug to an antigen binding unit

As discussed, a drug (e.g., a maytansinoid drug derivative) can be conjugated to an antigen binding unit through a linker. In one embodiment, the antigen binding unit can be modified with appropriate bifunctional modifying agent. In some embodiments, a group comprising a thiol (SH) group (also referred to as thio-comprising group) can be introduced to the side-chain of an amino acid residue, such as the side-chain of a lysine, on the antigen binding unit. For example, the amino group of a lysine residue on the antigen binding unit can be converted to a thiol- comprising group by reaction with 2-iminothiolane (Traut's Reagent), or with N-succinimidyl 3- (2-pyridyldithio)propanoate (SPDP), N-succinimidyl 4-(2-pyridyldithio)butanoate (SPDB), etc and followed by reduction with a reducing reagent, such as 2-mercaptoethanol, dithiothreitol (DTT) or tris(2-carboxyethyl)phosphine (TCEP).

Non-limiting examples of thiol-comprising group that can replace the side-chain amino group of a lysine residue include -NHC(=NH)(CH ₂ ) _n SH and -NHC(0)(CH ₂ ) _n SH, wherein n is 1 , 2, 3, 4, 5 or 6. When a thiol-comprising group is introduced to an amino acid residue, the amino acid residue is referred to as thiolated amino acid. For example, when the side-chain amino group of a lysine residue is converted to a thio-comprising group, the lysine residue is referred to as thiolated lysine. The number of free thiol (SH) group introduced in an antigen binding unit may vary, such as between 1 and about 20, or 5 to 15, and or 5 to 12. The linkers or drug-linkers can form bonds with the free thiol (SH) group of a thiolated lysine residue on the antigen binding unit. In some embodiments, the number of linkers or drug-linkers that form bonds with thiolated lysine residues in the antigen binding unit is between 1 and about 10. In some embodiments, the number of such formed bonds is at least 1 , or alternatively at least 2, or 3, or 4, or 5. In some embodiments, the number of such formed bonds is no more than 10, or alternatively no more than 9, or 8, or 7, or 6, or 5, or 4. In some embodiments, each antigen binding unit, on average, is conjugated with 3-5 drug molecules.

In another embodiment, a drug-linker can be conjugated to an antigen binding unit by binding to the thiol group of a cysteine residue. Each antigen binding unit typically contains multiple cysteines, but many, if not all, of them form disulfite bonds between each other, and thus are not available for such conjugation. In some embodiments, therefore, one or more of the disufite bonds of the antigen binding unit can be broken to form free thiol (SH) groups by reaction with a reducing reagent, such as 2-mercaptoethanol, dithiothreitol (DTT) or tris(2- carboxyethyl)phosphine (TCEP), for instance. The reaction can be monitored and/or controlled so that a sufficient number of disulfite bonds are broken to allow conjugation while maintaining a sufficient number of disulfide bonds to keep the structure stability of the antigen binding unit. In some embodiments, the number of bonds formed between the drug-linker and cysteine residue on the antigen binding unit is from 1 to 10. In one embodiment, the number of such bonds is at least 1 , or alternatively at least 2, or 3, or 4, or 5. In some embodiments, the number of such formed bonds is no more than 10, or alternatively no more than 9, or 8, or 7, or 6, or 5, or 4. In one embodiment, each antigen binding unit, on average, is conjugated with 3-5 drug molecules through cysteines.

In some embodiments, drug molecules are conjugated to the antigen binding unit through a mixture of lysine and cysteine residues.

An antigen binding unit can be modified, by way of, e.g., site-specific mutagenesis, to introduce additional thiolated lysine or cysteine residues to allow suitable conjugation. Amino acid modification methods are well known in the art. Modified antigen binding units can then be experimentally examined for their stability and antigen binding capability. In one embodiment, at least one thiolated lysine or cysteine residue is introduced by such modification. In another embodiment, at least two thiolated lysine or cysteine residues are introduced by such

modification.

Drug Load

The drug load on an antigen binding unit may vary depending on many factors, such as the potency of the drug, the size, stability of the antigen binding unit, conjugatable groups available on the antigen binding unit, etc. In some embodiments, 1 to 10 maytansinoid drug molecules are conjugated with 1 antigen binding unit molecule. In some embodiments, an average of 3 to 5 maytansinoid drug molecules are conjugated with 1 antigen binding unit molecule. In some embodiments, an average of 3.5 maytansinoid drug molecules are conjugated with 1 antigen binding unit molecule.

Preparation of Drug Linker Antigen Binding Unit Conjugates

In another aspect, provided are methods of preparing a maytansinoid drug linker antigen binding unit conjugate compound comprising contacting a compound of any one of Formula 1, 1-1, II, II- 1, ΠΙ, ΠΙ-1, IV, IV- 1 and V with an antigen binding unit. In some embodiments, the compound of any one of Formula 1, 1-1, II, Π-1, III, III-l , IV, IV- 1 and V and an antigen binding unit are dissolved in an aqueous solution. In some embodiments, the solution comprises a buffer, such as a phosphate buffer.

Metabolites of Drug Linker Antigen Binding Unit Conjugates

While not wishing to be bound to any theories, it is contemplated that upon endocytosis, compounds of any one of Formula Ia-Va is degraded by intracellular proteins to degradation products comprising the maytansinoid moiety which are cytotoxic.

In another aspect, disclosed herein is a compound of Formula lb or Ib-1 :

or a salt thereof,

wherein

X is hydrogen or halo;

Y is selected from the group consisting of hydrogen, Ci - C ₆ alkyl, C ₃ - C ₆ cycloalkyl, and -C(=0)R ⁵ ;

R ¹ is selected from the group consisting of hydrogen, -OH, -OC(=0)R ⁵ and -OR ⁵ ; R ² is hydrogen or Ci - C ₆ alkyl;

R ³ is methyl, -CH ₂ OH, or -CH ₂ C(=0)R ⁶ ;

R ⁴ is -OH or -SH;

R ⁵ is Ci - C ₆ alkyl or benzyl;

R ⁶ is Ci - Ce alkyl, phenyl or benzyl;

R ⁷ is hydrogen, Ci-C ₆ alkyl or an amino acid side chain;

R ⁸ is hydrogen or Ci _-6 alkyl;

each Z is independently hydrogen or C ₁ -C4 alkyl, or the two Z with the carbon atom to which they are attached form a C=0;

L is selected from optionally substituted Ci-C ₂₀ alkylene, C ₃ -C ₈ cycloalkylene, optionally substituted Ci-C ₂₀ alkylene wherein one or more of the -CH ₂ - groups are

independently replaced with C3-C8 cycloalkylene, -0-, -S-, -NR ⁸ -, -C(O)- , -C(=0)NR ⁸ -, -NR ⁸ C(=0)-, -S0 ₂ NR ⁸ -, or -NR ⁸ S0 ₂ -; Preferably L is -(CH ₂ ) _m -, wherein m is selected from an integer of 1 to 20, preferably 1 to 10, more preferably 5 to 10;

substituted Ci-C ₂₀ alkylene is Ci-C ₂₀ alkylene substituted with 1 to 4 -SO ₃ H, -P(0)(OH) ₂ or R ²³ , wherein each R ²³ is independently Ci _-6 alkyl optionally substituted with 1 or 2 substituents independently selected from the group consisting of -SH, -S-C ₁ -4 alkyl, - CONR ⁿ R ⁿ , -C0 ₂ H, and -NR ⁿ R ^u , wherein each R ¹¹ is independently hydrogen, alkyl, aryl, cycloalkyl, cycloalkenyl, heteroaryl, and heterocyclic, or the two R ¹¹ together with the nitrogen form a heterocyclic, wherein the heterocyclic is optionally substituted with one or two oxo; and

AA is an amino acid, such as a cysteine or a thiolated amino acid, such as a thiolated lysine. embodiments, the compound is:

In some embodiments, provided herein is a compound of Formula lib or IIb-1

wherein

X is hydrogen or halo;

Y is selected from the group consisting of hydrogen, Ci - C ₆ alkyl, C ₃ - C ₆ cycloalkyl, and -C(=0)R ⁵ ;

R ¹ is selected from the group consisting of hydrogen, -OH, -OC(=0)R ⁵ and -OR ⁵ ;

R ² is hydrogen or Ci - C ₆ alkyl;

R ³ is methyl, -CH ₂ OH, or -CH ₂ C(=0)R ⁶ ;

R ⁴ is -OH or -SH;

R ⁵ is Ci - Ce alkyl or benzyl;

R ⁶ is Ci - C ₆ alkyl, phenyl or benzyl;

R ⁷ is hydrogen, Ci-Ce alkyl or an amino acid side chain;

R ⁸ is hydrogen or G-6 alkyl;

each Z is independently hydrogen or C1-C4 alkyl, or the two Z with the carbon atom to which they are attached form a C=0;

L is selected from optionally substituted Ci-C ₂₀ alkylene, C ₃ -C ₈ cycloalkylene, optionally substituted Ci-C ₂ o alkylene wherein one or more of the -CH ₂ - groups are independently replaced with C ₃ -C ₈ cycloalkylene, -0-, -S-, -NR -, -C(O)- , -C(=0)NR ⁸ -, -NR ⁸ C(=0)-, -S0 ₂ NR ⁸ -, or -NR ⁸ S0 ₂ -; preferably L is -(CH ₂ ) _m -, wherein m is selected from an integer of 1 to 20, preferably 1 to 10, more preferably 5 to 10;

substituted Ci-C ₂ o alkylene is Ci-C ₂ o alkylene substituted with 1 to 4 -SO3H, -P(0)(OH) ₂ or R ²³ , wherein each R ²³ is independently Ci _-6 alkyl optionally substituted with 1 or 2 substituents independently selected from the group consisting of -SH, -S-C1-4 alkyl, - CONR ⁿ R ⁿ , -C0 ₂ H, and -NR ⁿ R ^u , wherein each R ¹¹ is independently hydrogen, alkyl, aryl, cycloalkyl, cycloalkenyl, heteroaryl, and heterocyclic, or the two R ¹¹ together with the nitrogen form a heterocyclic, wherein the heterocyclic is optionally substituted with one or two oxo; and

AA is an amino acid, such as a cysteine or a thiolated amino acid, such as a thiolated lysine.

In some embodiments, X is hydrogen. In some embodiments, X is chloro. In some

embodiments, Y is hydrogen. In some embodiments, R ¹ is hydrogen. In some embodiments, R ² is methyl. In some embodiments, R ³ is methyl. In some embodiments, R ⁴ is -OH. In some embodiments, R ⁷ is an amino acid side chain. In some embodiments, R ⁷ is methyl. In some embodiments, R ⁸ is methyl.

In some embodiments, L is unsubstituted Ci-C ₂₀ alkylene. In some embodiments, L is substituted Ci-C ₂₀ alkylene. In some embodiments, L is unsubstituted C1-C1 ₀ alkylene. In some embodiments, L is substituted C1-C1 ₀ alkylene. In some embodiments, L is -(CH ₂ ) ₅ -. In some embodiments, L is unsubstituted Ci-C ₂₀ alkylene wherein one or two of the -CH ₂ - groups are independently replaced with C ₃ -C ₈ cycloalkylene, -0-, -S-, -NR ⁸ -, -C(=0)NR ⁸ -, -NR ⁸ C(=0)-, - S0 ₂ NR ⁸ -, or -NR ⁸ S0 ₂ -. In some embodiments, L is substituted Ci-C ₂₀ alkylene wherein one or two of the -CH ₂ - group is independently replaced with C ₃ -C ₈ cycloalkylene, -0-, -S-, -NR ⁸ - , -C(=0)NR ⁸ -, -NR ⁸ C(=0)-, -S0 ₂ NR ⁸ -, or -NR ⁸ S0 ₂ -. In some embodiments, when more than one -CH ₂ - groups are replaced, the-CH ₂ - groups are not adjacent to each other.

In some embodiments, provided is a compound of the formula:

or a salt thereof,

wherein

X is H or CI;

Y is H or methyl;

R ⁷ is hydrogen, Ci-C ₆ alkyl or an amino acid side chain;

R ⁸ is hydrogen or Ci-C ₆ alkyl;

L is selected from optionally substituted C1-C2 ₀ alkylene, C ₃ -C ₈ cycloalkylene, optionally substituted C1-C2 ₀ alkylene wherein one or more of the -CH ₂ - groups are independently replaced with C3-C8 cycloalkylene, -0-, -S-, -NR ⁸ -, -C(O)- , -C(=0)NR ⁸ -, -NR ⁸ C(=0)-, -S0 ₂ NR ⁸ -, or -NR ⁸ S0 ₂ -; preferably L is -(CH ₂ ) _m -, wherein m is selected from an integer of 1 to 20, preferably 1 to 10, more preferably 5 to 10;

substituted Ci-C ₂₀ alkylene is Ci-C ₂₀ alkylene substituted with 1 to 4 -SO ₃ H, -P(0)(OH) ₂ or R ²³ , wherein each R ²³ is independently Ci _-6 alkyl optionally substituted with 1 or 2 substituents independently selected from the group consisting of -SH, -S-C1-4 alkyl, - CONR ⁿ R ⁿ , -C0 ₂ H, and -NR ⁿ R ^u , wherein each R ¹¹ is independently hydrogen, alkyl, aryl, cycloalkyl, cycloalkenyl, heteroaryl, and heterocyclic, or the two R ¹¹ together with the nitrogen form a heterocyclic, wherein the heterocyclic is optionally substituted with one or two oxo; and

AA is an amino acid, such as a cysteine or a thiolated amino acid, such as a thiolated lysine. In some embodiments, the compound is of Formula IVb or IVb-1 :

or a salt thereof,

wherein

X is H or CI;

Y is H or methyl;

R ⁷ is hydrogen, Ci-C ₆ alkyl or an amino acid side chain;

R ⁸ is hydrogen or C1-C6 alkyl;

m is an integer of 1 to 20, preferably 1 to 10, more preferably 5 to 10; and

AA is an amino acid, such as a cysteine or a thiolated amino acid, such as a thiolated lysine.

In some embodiments, the compound is of Formula Vb:

or a salt thereof.

In some embodiments, AA is, but not limited to:

represents point of connection to the rest of the molecule.

In some embodiments, the compound of Formula lb is selected from:

a salt thereof. While not wishing to be bound to any theories, it is contemplated that upon endocytosis, compounds of any one of Formula Ia-Va, formula Va-XIIa is degraded by intracellular proteins to degradation products comprising the maytansinoid moiety which are cytotoxic.

In another aspect, disclosed herein is a compound of Formula Vc:

In another aspect, disclosed herein are compounds degraded by intracellular proteins to degradation products comprising the maytansinoid moiety which are cytotoxic, and these compounds include but not limited to:

Methods of Treatment

In another aspect, provided herein is a method of treating a proliferative, inflammatory or immunologic disease or condition in a patient in need thereof comprising administering an effective amount of one or more compounds as described herein, for example, a compound of any one of Formula Ia-Va, Id and formula Va-XIVc.

The compounds can be formulated as pharmaceutical compositions and administered to the patient in a variety of forms adapted to the chosen route of administration, i.e., orally or parenterally, by intravenous, intramuscular, topical or subcutaneous routes. The amount of the compounds will vary depend on the nature of the drug, linker, drug load, degree of cell surface triggered the internalization, trafficking, and release of the drug, the disease being treated, the conditions of the patient, such as age, gender, weight, etc. and can be determined by methods known to the art, for example, see U.S. Pat. No. 4,938,949, and will be ultimately at the discretion of the attendant physician or clinician.

In general, a suitable dose will be in the range of from about 0.1 to about 200 mg/kg, e.g., from about 0.5 to about 50 mg/kg of body weight IV infusion over 30-90 min every 1-4 week for 52 weeks, about 1.0 to about 25 mg/kg of body weight IV infusion over 30-90 min every 1 -4 week for 52 weeks, about 1.5 to about 15 mg/kg body weight IV infusion over 30-90 min every 1-4 week for 52 weeks, or in the range of about 1 to 10 mg/kg body weight IV infusion over 30-90 min every 1 -4 week. In some embodiments, the dose is from about 1.0 mg to about 100 mg/day, e.g., from about 2 mg to about 5 g per day, about 10 mg to about 1 g per day, about 20 to about 500 mg per day, or in the range of about 50 to 100 mg per day. The compounds can be administered daily, weekly, monthly, such as once a day, every 1-3 weeks, or month.

Alternatively, the compounds can be administered in cycles, such as administered daily for a number of days, for example, 5 days to 21 days, with a period, such as one day to seven days, wherein no drug is being administered.

In some embodiments, the compound is administered at an initial dose of 1-4 mg/kg over 30-90 minute IV infusion, followed by 1 -2 mg/kg over 30 minute IV infusion weekly or every 1-4 weeks for 52 weeks. In some embodiments, the compound is administered at an initial dose of 2-10 mg/kg over 30-90 minutes IV infusion, followed by 1 -5 mg/kg over 30-90 minutes IV infusion every 1-4 weeks for 52 weeks.

In some embodiments, the compounds are administered in conjunction with another therapy. For example, the compounds can be co-administered with another therapy for treating cancer, for example, radiation therapy or another anticancer agent known in the art.

In another aspect, provided herein is a method of treating a proliferative, inflammatory or immunologic disease or condition in a patient in need thereof comprising administering an effective amount of a compound of Formula lb, wherein the compound of Formula lb is generated as a result of a metabolic chemical reaction following administration of a compound of Formula la, or a pharmaceutically acceptable salt thereof, to the individual. Metabolic chemical reaction refers to a reaction occurring inside the body, for example, cells, of the subject, in which a chemical compound is converted to another chemical compound. The conversion can be by metabolic and/or chemical processes and can occur in one step or through a series of two or more steps. Metabolic chemical reactions include reactions of degrading a protein or peptide component of a maytansinoid linker antigen binding unit conjugate, such as an antibody or antibody fragment, by proteins inside a cell.

In some embodiments, provided herein is a method of treating a proliferative, inflammatory or immunologic disease or condition in a patient in need thereof comprising administering an effective amount of a compound of Formula lib, wherein the compound of Formula lib is generated as a result of a metabolic chemical reaction following administration of a compound of Formula Ila, or a pharmaceutically acceptable salt thereof, to the patient.

In some embodiments, provided herein is a method of treating a proliferative, inflammatory or immunologic disease or condition in a patient in need thereof comprising administering an effective amount of a compound of Formula mb, wherein the compound of Formula nib is generated as a result of a metabolic chemical reaction following administration of a compound of Formula Ilia, or a pharmaceutically acceptable salt thereof, to the patient.

In some embodiments, provided herein is a method of treating a proliferative, inflammatory or immunologic disease or condition in a patient in need thereof comprising administering an effective amount of a compound of Formula VIb, wherein the compound of Formula VIb is generated as a result of a metabolic chemical reaction following administration of a compound of Formula Via, or a pharmaceutically acceptable salt thereof, to the patient.

In some embodiments, provided herein is a method of treating a proliferative, inflammatory or immunologic disease or condition in a patient in need thereof comprising administering an effective amount of a compound of Formula Vb, wherein the compound of Formula Vb is generated as a result of a metabolic chemical reaction following administration of a compound of Formula Va, or a pharmaceutically acceptable salt thereof, to the patient.

In some embodiments, provided herein is a method of treating a proliferative, inflammatory or immunologic disease or condition in a patient in need thereof comprising administering an effective amount of a compound of Formula Vc, wherein the compound of Formula Vc is generated as a result of a metabolic chemical reaction following administration of a compound of Formula Va, Via, or Vila, or a pharmaceutically acceptable salt thereof, to the patient.

In some embodiments, provided herein is a method of treating a proliferative, inflammatory or immunologic disease or condition in a patient in need thereof comprising administering an effective amount of a compound of Formula VIIIc, wherein the compound of Formula Vnic is generated as a result of a metabolic chemical reaction following administration of a compound of Formula Villa, or a pharmaceutically acceptable salt thereof, to the patient.

In some embodiments, provided herein is a method of treating a proliferative, inflammatory or immunologic disease or condition in a patient in need thereof comprising administering an effective amount of a compound of Formula rXc, wherein the compound of Formula IXc is generated as a result of a metabolic chemical reaction following administration of a compound of Formula rXa, or a pharmaceutically acceptable salt thereof, to the patient.

In some embodiments, provided herein is a method of treating a proliferative, inflammatory or immunologic disease or condition in a patient in need thereof comprising administering an effective amount of a compound of Formula Xc, wherein the compound of Formula Xc is generated as a result of a metabolic chemical reaction following administration of a compound of Formula Xa, or a pharmaceutically acceptable salt thereof, to the patient.

In some embodiments, provided herein is a method of treating a proliferative, inflammatory or immunologic disease or condition in a patient in need thereof comprising administering an effective amount of a compound of Formula XIc, wherein the compound of Formula XIc is generated as a result of a metabolic chemical reaction following administration of a compound of Formula XIa, or a pharmaceutically acceptable salt thereof, to the patient.

In some embodiments, provided herein is a method of treating a proliferative, inflammatory or immunologic disease or condition in a patient in need thereof comprising administering an effective amount of a compound of Formula XIIc, wherein the compound of Formula XIIc is generated as a result of a metabolic chemical reaction following administration of a compound of Formula Xlla, or a pharmaceutically acceptable salt thereof, to the patient.

In some embodiments, provided herein is a method of treating a proliferative, inflammatory or immunologic disease or condition in a patient in need thereof comprising administering an effective amount of a compound of Formula XIVc, wherein the compound of Formula XIVc is generated as a result of a metabolic chemical reaction following administration of a compound of Formula XlVa, or a pharmaceutically acceptable salt thereof, to the patient.

The diseases being treated can be determined by the antigen binding unit of the conjugate. In some embodiments, the disease a proliferative disease, such as a cancer, including melanoma, breast cancer, bladder cancer, lung cancer, thyroid cancer, prostate cancer, ovarian cancer, mast cell leukemia, germ cell tumors, small-cell lung carcinoma, gastrointestinal stromal tumors, acute myelogenous leukemia (AML), B-chronic lymphatic leukemia (B-CLL), and non-Hodgkin lymphoma (NF£L), neuroblastoma, or pancreatic cancer. In some embodiments, the disease an inflammatory disease, or an immunologic disease, such as graft rejections, and autoimmune diseases, such as type 1 diabetes, rheumatoid arthritis, systemic lupus erythematosus, and inflammatory bowel disease. Pharmaceutical Compositions

In a further aspect, provided are pharmaceutical compositions comprising one or more compounds as described herein, for example, a compound of any one of Formula Ia-Va, and one or more pharmaceutically acceptable carriers. Such compositions should contain at least 0.1% of active compound. The percentage of the compositions may vary and may be between about 2 to about 90% of the weight of a given unit dosage form. The amount of active compound in such therapeutically useful compositions is such that an effective dosage level will be obtained.

Examples of compositions for oral administration include, but are not limited to, ingestible tablets, buccal tablets, troches, capsules, elixirs, suspensions, syrups, solutions, wafers, and the like. Compositions suitable for injection or infusion can include sterile aqueous solutions or dispersions in a pharmaceutically acceptable liquid carrier or vehicle, or sterile powders comprising the active ingredient which are adapted for the extemporaneous preparation of sterile injectable or infusible solutions or dispersions, optionally encapsulated in liposomes. Other forms of pharmaceutical compositions include topical formulations, such as gel, ointments, creams, lotions or transdermal patches, etc.

The pharmaceutical compositions include using techniques well known to those in the art.

Suitable pharmaceutically-acceptable carriers, outside those mentioned herein, are known in the art; for example, see Remington, The Science and Practice of Pharmacy, 20th Edition, 2000, Lippincott Williams & Wilkins, (Editors: Gennaro, A. R., et al.).

In a further aspect, provided are methods of producing a pharmaceutical composition comprising admixing a compound as described herein, for example, a compound of any one of Formula Ia- Va and Id, and a pharmaceutically acceptable carrier. Methods of admixing an active ingredient with a pharmaceutically acceptable carrier are generally known in the art, for example, uniformly mixing the active compound(s) with liquids or finely divided solid carriers, or both, in the required proportions, and then, if necessary, forming the resulting mixture into a desired shape.

In some embodiments, a compound of any one of Formula Ia-Va and Id is formulated as an injectable, for example, at a concentration of 2-50 mg/mL in an aqueous solution comprising 4- 10 mg/mL sodium chloride and/or 5-12 mg/mL sodium acetate, or alternatively at a

concentration of 2-50 mg/mL in an aqueous solution comprising 5-10 mg/mL sodium chloride, 1-5 mg/rnL sodium phosphate dibasic heptahydrate, 0.1-0.5 mg/mL sodium phosphate monobasic monohydrate.

Other examples of formulations of a compound of any one of Formula Ia-Va and Id include an injectable formulation having a concentration of 2-100 mg/mL of the compound in an aqueous solution comprising 0.5-1.0% sodium chloride, 0.05-0.10% monobasic sodium phosphate dihydrate, 1.0-2.0% dibasic sodium phosphate dihydrate, 0.01-0.05% sodium citrate, 0.10-0.20% citric acid monohydrate, 1.0-2.0% mannitol, 0.1%-0.2 polysorbate 80, and Water for Injection, USP. Sodium hydroxide added as necessary to adjust pH.

Methods

The compounds of this invention can be prepared from readily available starting materials using the following general methods and procedures. It will be appreciated that where typical or preferred process conditions (i.e., reaction temperatures, times, mole ratios of reactants, solvents, pressures, etc) are given, other process conditions can also be used unless otherwise stated. Optimum reaction conditions may vary with the particular reactants or solvent used, but such conditions can be determined by one skilled in the art by routine optimization procedures.

Additionally, as will be apparent to those skilled in the art, conventional protecting groups may be necessary to prevent certain functional groups from undergoing undesired reactions. Suitable protecting groups for various functional groups as well as suitable conditions for protecting and deprotecting particular functional groups are well known in the art. For example, numerous protecting groups are described in T. W. Greene and G. M. Wuts, Protecting Groups in Organic Synthesis, Third Edition, Wiley, New York, 1999, and references cited therein.

Furthermore, the compounds of this invention may contain one or more chiral centers.

Accordingly, if desired, such compounds can be prepared or isolated as pure stereoisomers, i.e., as individual enantiomers or diastereomers, or as stereoisomer-enriched mixtures. All such stereoisomers (and enriched mixtures) are included within the scope of this invention, unless otherwise indicated. Pure stereoisomers (or enriched mixtures) may be prepared using, for example, optically active starting materials or stereoselective reagents well-known in the art. Alternatively, racemic mixtures of such compounds can be separated using, for example, chiral column chromatography, chiral resolving agents and the like. The starting materials for the following reactions are generally known compounds or can be prepared by known procedures or obvious modifications thereof. For example, many of the starting materials are available from commercial suppliers such as Aldrich Chemical Co.

(Milwaukee, Wisconsin, USA), Bachem (Torrance, California, USA), Emka-Chemce or Sigma (St. Louis, Missouri, USA). Others may be prepared by procedures, or obvious modifications thereof, described in standard reference texts such as Fieser and Fieser's Reagents for Organic Synthesis, Volumes 1 -15 (John Wiley and Sons, 1991), Rodd's Chemistry of Carbon Compounds, Volumes 1-5 and Supplemental (Elsevier Science Publishers, 1989), Organic Reactions, Volumes 1-40 (John Wiley and Sons, 1991), March's Advanced Organic Chemistry, (John Wiley and Sons, 4 ^th Edition), and Larock's Comprehensive Organic Transformations (VCH Publishers Inc., 1989).

The various starting materials, intermediates, and compounds of the invention may be isolated and purified where appropriate using conventional techniques such as precipitation, filtration, crystallization, evaporation, distillation, and chromatography. Characterization of these compounds may be performed using conventional methods such as by melting point, mass spectrum, nuclear magnetic resonance, and various other spectroscopic analyses.

Coupling reagents include carbodiimide, amininum and phosphonium based reagents.

Carbodiimide type reagents include dicyclohexylcarbodiimide (DCC), diisopropylcarbodiimide (DIC), and l-ethyl-3-(3-dimethylaminopropyl)-dicarbodiimide (EDC), etc. Aminium salts include N-[(dimethylamino)-lH-l ,2,3-triazolo[4,5-b]pyridine-l-ylmethylene]-N- methylmethanaminium hexafluorophosphate N-oxide (HATU), N-[(lH-benzotriazol-l - yl)(dimethylamino)methylene]-N-methylmethanaminium hexafluorophosphate N-oxide (HBTU), N- [( 1 H-6-chlorobenzotriazol- 1 -yl)(dimethylamino)methylene] -N-methylmethanaminium hexafluorophosphate N-oxide (HCTU), N-[(lH-benzotriazol-l -yl)(dimethylamino)methylene]- N-methylmethanaminium tetrafluoroborate N-oxide (TBTU), and N-[(lH-6-chlorobenzotriazol- l-yl)(dimethylamino)methylene]-N-methylmethanaminium tetrafluoroborate N-oxide (TCTU). Phosphonium salts include 7-azabenzotriazol-l -yl-N-oxy-tris(pyrrolidino)phosphonium hexafluorophosphate (PyAOP) and benzotriazol-l-yl-N-oxy-tris(pyrrolidino)phosphonium hexafluorophosphate (PyBOP). Amide formation step may be conducted in a polar solvent such as dimethylformamide (DMF) and may also include an organic base such as

diisopropylethylamine (DIEA) or dimethylaminopyridine (DMAP). The following examples are provided to illustrate certain aspects of the present invention and to aid those of skill in the art in practicing the invention. These examples are in no way to be considered to limit the scope of the invention.

EXAMPLES

The examples below as well as throughout the application, the following abbreviations have the following meanings. If not defined, the terms have their generally accepted meanings.

ACN = acetonitrile

Ala = alanine

aq. = aqueous

brs = broad singlet

calc. = calculated

d = doublet

DCM = dichloromethane

dd = double doublet

DIEA = N,N-diisopropylethylamine

DMA = N,N-dimethylacetamide

DMAP = dimethylaminopyridine

DMF = dimethylformamide

DMSO = dimethylsulfoxide

DTT = dithiothreitol

EDTA = ethylenediaminetetraacetate or salt

Et = ethyl

EtOAc = ethyl acetate

g = gram

h = hour

HC1 = hydrochloric acid

HPLC = high- pressure liquid chromatography

Hz = hertz

J = coupling constant

LC-MS = liquid chromatography mass spectroscopy

m = multiplet

MDC = maytansinol

Me = methyl

MeOH = methanol

MHz = megahertz

min = minute

mL = milliliter

mm = millimeter

m.p. = melting point

OTf = inflate (trifluoromethanesulfonate)

N = normal

r.t. = room temperature PBS = phosphate buffered saline

Rt = retention time

s = singlet

t = triplet

TLC = thin layer chromatography

vol = volume

= microliter

μηι = micrometer

MATERIALS AND METHODS: NMR specetra were recorded on a Bruker AM 400 (400 MHz) spectrometer. Chemical shifts in CDC1 ₃ are reported in ppm relative to residual CHC1 ₃ as an internal standard. UV spectra were recorded on a Beckman DU-640 spectrophotometer. Mass spectra were acquired on a ThermoFinnigan LCQ DECA XP+ instrument using electrospray ionization. HPLC was performed using an Agilent HPLC 1100 system equipped with a diode array detector and a Kromasil reverse phase C-18 5 μιη, 250x4.6 mm column, eluting with a gradient of acetonitrile: water (50-95% CH ₃ CN 0-10 min, 95% CH ₃ CN 10-15 min, flow rate = 1.0 mL/min. Silica gel for flash column chromatography was from Branch of Qiangdao Haiyang Chemical Co., Ltd.. Maytansinol was prepared from ansamitocin P-3 (which in turn was obtained from the fermentation of the microorganism Actinosynnema pretiosum) as previously described (Widdison, et al. (2006) J. Med. Chem. 49: 4392-4408). Dichloromethane was dried by distillation over calcium hydride. Dimethylformamide was dried by distillation over calcium hydride under reduced pressure. All other solvents used are reagent grade or HPLC grade.

EXAMPLE 1

Esterification of Maytansinol with Fmoc-N-methyl-L-alanine (Fmoc-N-Me-D/L-Ala-MDC)

(Fmoc-N-Me-L-Ala-MDC) (Fmoc-N-Me-D-Ala-MDC)

A mixture of maytansinol (0.600 g, 1.062 mmol), Fmoc-N-Me-L-Ala (6.911 g, 21.24 mmol), Sc(OTf) ₃ (0.314 g, 0.637 mmol) and DMAP (0.389 g, 3.186 mmol) in CH ₂ C1 ₂ (100 mL) was stirred for 0.5 h at -8 °C. DIC (2.949 g, 23.37 mmol) was added dropwise, stirred for 0.5 h, warmed to r.t. slowly, filtered to recover the Lewis acid catalyst, the filtrate was quenched with diluted HCl and extracted with CH ₂ C1 ₂ . The combined organic phase was washed with NaHCC aq, brine, dried over anhydrous Na ₂ S0 ₄ . The solvent was removed under reduced pressure. Chromatography (silica gel, CH ₂ Cl ₂ MeOH 30:1) gave the desired product as a mixture of diastereomer Fmoc-N-Me-D L-Ala-MDC: white solid (0.8385 g, 90.5%). Further column chromatography (silica gel, CH ₂ Cl ₂ /MeOH 100:1 to 20:1) gave two fractions as pure diastereomer. The higher Rf fraction was determined to be the D-aminoacyl ester diastereomer (Fmoc-N-Me-D-Ala-MDC), while the lower Rf fraction was the desired L-aminoacyl ester (Fmoc-N-Me-L-Ala-MDC). Fmoc-N-Me-L-Ala-MDC: white solid (0.4262 g, 46.0% yield), 1H NMR (400 MHz, CDC1 ₃ ): 50.77 (3H, s), 1.22-1.32 (6H, m),1.40-1.48 (lH, m), 1.63 (3H, s), 2.13 (1H, dd, J= 14.4, 2.8 Hz), 2.53 (1H, dd, J= 14.4, 10.8 Hz), 2.64 (3H, s), 2.88 (3H, s), 3.00 (1H, d, J = 9.6 Hz), 3.07 (1H, d, J = 12.4 Hz), 3.35 (3H, s), 3.48 (1H, d, J = 8.8 Hz), 3.59 (1H, d, J = 11.2 Hz), 3.97 (3H, s), 4.13-4.19 (1H, m), 4.15 (1H, s), 4.24 (1H, t, J= 10.8 Hz), 4.72-4.77 (2H, m), 5.03 (1H, q, J= 6.8 Hz), 5.65 ( 1H, dd, J= 15.2, 9.2 Hz), 6.29 (1H, br), 6.41 (1H, dd, J = 15.2 , 11.2 Hz), 6.52 (1H, d, J= 1.2Hz), 6.70 (1H, d, J= 10.8 Hz), 6.79 (1H, d, J = 1.2 Hz), 7.33 (1H, t, J = 7.6 Hz), 7.36 (1H, t, J = 7.6 Hz), 7.39 (1H, d, J = 7.6 Hz), 7.49 (1H, d, J = 7.6 Hz), 7.70 (1H, d, J= 7.6 Hz), 7.72 (1H, d, J= 7.6 Hz). LC-MS (M+Na ⁺ ) calc : 894.3, found: 894.3. Fmoc-N-Me-D- Ala-MDC : white solid (0.3993 g, 43.1% yield), ^X H NMR (400 MHz, CDC1 ₃ ): 50.84 (3H, s), 1.22-1.27 (3H, m), 1.40-1.48 (1H, m), 1.51 (3H, d, J= 7.6 Hz), 1.67 (3H, s), 2.20 (1H, dd, J=14.4, 2.8 Hz ), 2.63 (1H, dd, J= 14.4, 12.4 Hz), 2.85 (1H, d, J = 9.6 Hz), 2.96 (3H, s), 3.17 (3H, s), 3.20 (1H, s), 3.24 (3H, s), 3.40 (1H, d, J= 9.2 Hz), 3.51 (1H, d, J = 12.8 Hz), 3.99 (3H, s), 4.20-4.28 (2H, m), 4.38-4.43 (2H, m), 4.80-4.98 (2H, m), 5.80 ( 1H, dd, J= 15.2, 11.2 Hz), 6.18 (1H, s), 6.25 (1H, d, J= 10.8 Hz), 6.40 (1H, dd, J= 15.2 , 11.2 Hz), 6.79 (1H, d, J = 1.6 Hz), 6.84 (1H, d, J = 1.6 Hz ), 7.32 (2H, t, J =7.6 Hz), 7.41 (2H, t, J =7.6 Hz), 7.61 (2H, d, J =7.6 Hz), 7.77 (2H, d, J=7.6 Hz). LC-MS (M+Na ⁺ ) calc: 894.3, found: 894.3.

EXAMPLE 2

Deprotection of Fmoc-N-Me-D/L-Ala-MDC ( -Me-D/L-Ala-MDC)

(Fmoc-N-Me-L-Ala-MDC) (Fmoc-N-Me-D-Ala-MDC)

i-L-Ala-MDC) (N-Me-D-Ala-MDC)

Into Fmoc-N-Me-D/L-Ala-MDC (0.463 g, 0.5307 mmol) in ACN (200 mL) was added piperidine (0.865 g, 10.15 mmol). The mixture was stirred at r.t. for 4 h, quenched with water and extracted with CH ₂ C1 ₂ . The combined organic phase was washed with brine and dried over Na ₂ SC>4. The solvent was removed under reduced pressure to give the crude product, which was used in the next step without further purification. LC-MS (M+tT) calc: 650.3, found: 650.3. Rt: 3.96 min. EXAMPLE 3

Deprotection of Fmoc-N-Me-L-Ala-MDC (N-Me-L-Ala-MDC)

(Fmoc-N-Me-L-Ala-MDC) (N-Me-L-Ala-MDC)

Into Fmoc-N-Me-L-Ala-MDC (0.463 g, 0.5307 mmol) in ACN (200 mL) was added piperidine (0.865 g, 10.15 mmol). The mixture was stirred at r.t. for 4 h, quenched with water and extracted with CH ₂ C1 ₂ . The combined organic phase was washed with brine and dried over Na ₂ S0 ₄ . The solvent was removed under reduced pressure to give the crude product, which was used in the next step without further purification. LC-MS (Μ+ΐί) calc : 650.3, found: 650.3. Rt: 3.96 min.

EXAMPLE 4

Condensation of N-Me-D/L- Ala-MDC with MA-ACP (D-3AA-MDC and L-3AA-MDC)

(L-3AA-MDC) (D-3AA-MDC)

Into above prepared N-Me-D/L- Ala-MDC (0.5307 mmol) and MA-ACP (0.448 g, 2.123 mmol) in DMF (25 mL) under 0 °C was added EDC (0.407 g, 2.123 mmol). The mixture was stirred at r.t. overnight, quenched with water, extracted with EtOAc, washed with brine, and dried over Na ₂ S0 ₄ . The solvent was removed under reduced pressure. Chromatography (silica gel:

CH ₂ Cl ₂ MeOH 30:1) gave the crude product. Further purification by preparative HPLC on a YMC C-18 column (250x20 mm, S 10 μιτι) gave two fractions (Rt = 6.59 min and 6.98 min) as white solid. The higher Rt fraction was determined to be the D-aminoacyl ester diastereomer (D- 3AA-MDC, 45.2%), while the lower Rt fraction was the desired L-aminoacyl ester (L-3AA- MDC, 54.8%). L-3AA-MDC: white solid (0.1364 g, 30.5% overall yield over two steps), 1H NMR (400 MHz, CDC1 ₃ ): 50.79 (3H, s), 1.17-1.32 (3H, m), 1.27 (3H, s), 1.29 (3H, s),1.40-1.76 (7H, m), 2.12-2.23 (2H, m), 2.31-2.45 (1H, m), 2.59 (1H, t, J= 12.8 Hz), 2.82 (3H, s), 3.01 (1H, d, J = 9.6 Hz), 3.10 (1H, d, J = 8.8 Hz), 3.17 (3H, s), 3.34 (3H, s), 3.42 (2H, t, J = 6.8Hz), 3.48 (2H, d, J = 6.8 Hz), 3.62 (1H, d, J = 12.8 Hz), 3.97 (3H, s), 4.27 (1H, t, J = 11.2 Hz), 4.76 (lH,d, J = 11.6 Hz), 5.36 (1H, q, J= 6.8 Hz), 5.65 ( 1H, dd, J = 15.2, 9.2 Hz), 6.25 (1H, s), 6.41 (1H, dd, J = 15.2 , 11.2 Hz), 6.64 (1H, s), 6.65 (2H, s), 6.72 (1H, d, J = 11.2 Hz), 6.82 (1H, s). LC-MS (M+Na ⁺ ) calc: 865.3, found: 865.3. Rt: 6.59 min. D-3AA-MDC: white solid (0.1128 g, 25.2% overall yield over two steps), 1H NMR (400 MHz, CDC1 ₃ ): 50.86 (3H, s), 1.22-1.38 (4H, m),

I .25 (3H, d, J= 9.2 Hz), 1.38-1.45 (1H, m), 1.48 (3H, d, J = 7.6 Hz), 1.56-1.70 (4H, m),1.68 (3H, s), 1.75 (1H, d, J = 13.6 Hz), 2.19 (1H, dd, J =14 A, 2.8 Hz), 2.28-2.36 (2H, m), 2.65 (1H, dd, J = 14.2, 12.0 Hz), 2.80 (1H, d, J = 9.6Hz), 3.01 (3H, s), 3.19 (1H, d, J= 13.2 Hz), 3.32 (3H, s), 3.42 (1H, d, J= 9.6 Hz), 3.47-3.54 (3H, m), 3.98 (3H, s), 4.29 (1H, t, J = 10.4 Hz), 4.88 (lH,dd, J =

I I .8, 3.2 Hz), 5.07 (1H, q, J = 7.6 Hz), 5.84 ( 1H, dd, J = 15.2, 9.2 Hz), 6.23 (1H, d, J = 11.2 Hz), 6.27 (1H, s), 6.41 (1H, dd, J= 15.2 , 1 1.2 Hz), 6.69 (2H, s), 6.79 (1H, d, J= 1.2 Hz), 6.84 (1H, d, J= 1.2 Hz). LC-MS (M+Na ⁺ ) calc: 865.3, found: 865.3. Rt: 6.98 min.

EXAMPLE 5

Condensation of N-Me-L-Ala-MDC with MA-ACP (L-3AA-MDC)

(N-Me-L-Ala-M DC)

(L-3AA-MDC)

Into above prepared N-Me-L-Ala-MDC (0.5307 mmol) and MA-ACP (0.448 g, 2.123 mmol) in DMF (25 mL) under 0 °C was added EDC (0.407 g, 2.123 mmol). The mixture was stirred at r.t. overnight, quenched with water, extracted with EtOAc, washed with brine, dried over Na ₂ S0 ₄ . The solvent was removed under reduced pressure. Chromatography (silica gel: CH ₂ Cl ₂ MeOH 30:1) gave the crude product. Further purification by preparative HPLC on a YMC C-18 column (250x20 mm, S 10 μιη) gave the desired L-3AA-MDC: white solid (0.280 g, 62.6% overall yield over two steps), 1H NMR (400 MHz, CDC1 ₃ ): 50.79 (3H, s), 1.17-1.32 (3H, m), 1.27 (3H, s), 1.29 (3H, s),1.40-1.76 (7H, m), 2.12-2.23 (2H, m), 2.31-2.45 (1H, m), 2.59 (1H, t, J = 12.8 Hz), 2.82 (3H, s), 3.01 (IH, d, J= 9.6 Hz), 3.10 (IH, d, J = 8.8 Hz), 3.17 (3H, s), 3.34 (3H, s), 3.42 (2H, t, J = 6.8Hz), 3.48 (2H, d, J= 6.8 Hz), 3.62 (IH, d, J = 12.8 Hz), 3.97 (3H, s), 4.27 (IH, t, J = 11.2 Hz), 4.76 (lH,d, J = 11.6 Hz), 5.36 (IH, q, J = 6.8 Hz), 5.65 ( IH, dd, J = 15.2, 9.2 Hz), 6.25 (IH, s), 6.41 (IH, dd, J= 15.2 , 1 1.2 Hz), 6.64 (IH, s), 6.65 (2H, s), 6.72 (IH, d, J= 11.2 Hz), 6.82 (IH, s). LC-MS (M+Na ⁺ ) calc: 865.3, found: 865.3. Rt: 6.59 min.

EXAMPLE 6

The effect of the metabolites of prodrug antibody maytansinoid conjugates on the tubulin polymerization

The effect of 3AA-MDC, 206-3 AA-MDC and the metabolites (Cys-3AA-MDC and Lys-mcc- MDC) of prodrug antibody maytansinoid conjugates on the tubulin polymerization in vitro was assessed by HTS-Tubulin Polymerization Assay Kit (BK004P, Cytoskeleton, Inc., USA).

According to the instruction of kit, pre-warm the 96-well plate to 37 °C for 30 min prior to starting the assay. At the same time, the spectrophotometer (SpectraMax, Molecular Devices, USA) was set as follow: wavelength, 405 nm; temperature, 37 ^° C ; Kinetic, 31 cycles of 1 reading per minute. Make cold G-PEM buffer (990 General Tubulin Buffer + \ 0 μΐ, GTP Stock) and keep it on ice. Prepare 4 mg/mL tubulin, 1 μM L-3AA-MDC (N ₂ '-deacetyl-N ₂ '-(6-maleimido-l - oxo-hexyl)maytansine), 1 μΜ 206-3 AA-MDC, 1 μΜ cys-3 AA-MDC, 1 μΜ lys-mcc-MDC, 100 μΜ Paclitaxel, and 100 μΜ Nocodazole. Add 10 μΐ, G-PEM, 3 AA-MDC, 206-3 AA-MDC, cys- 3 AA-MDC, lys-mcc-MDC, Paclitaxel, Nocodazole into the wells, and then add 100 μί 4 mg/ml tubulin to each well. Immediately place the plate into the spectrophotometer and start recording using the kinetic setup described above. As show in the Fig. 6, compared with the PBS buffer, 3 AA-MDC, Cys-3 AA-MDC, Lys-mcc-MDC and 206-3 AA-MDC more significantly inhibited the tubulin polymerization (Fig. 6). Nocodazole, the tubulin polymerization inhibitor, was set as a negative control. The metabolite Cys-3 AA-MDC was prepared by reaction of 3 AA-MDC with cysteine under the base DIEA in CH ₂ C1 ₂ . LC-MS (M+Ff) calc : 964.5, found: 964.2. Rt: 12.97 min. The metabolite Lys-MCC-MDC was prepared by reaction of SMCC-MDC with lysine under the base DIEA in DMF. LC-MS (M+H ⁺ ) calc : 1 103.7, found: 1 103.2. Rt: 13.00 and 13.18 min.

EXAMPLE 7

Recombinant Antibody Expression and Purification

The monoclonal antibodies, Bat0206, Bat0606 (trastuzumab), Batl206 (rituximab), which specifically bind the extracellular domain of EGFR, Her2, CD20 respectively were produced as described in CHO cells essentially as described in Wood et al., J Immunol. 145 :3011 (1990). Briefly, each of the antibody genes were constructed with molecular biology techniques (Molecular Cloning: A Laboratory Manual, 3 ^rd edition J. Sambrook et al., Cold spring Harbor Laboratory Press) . A derivative of Chinese hamster ovary cell lines CHOK1 was grown in CD- CHO media (GIBCO). Transfections were facilitated using electroporation. Healthy mid-log CHO-K1 cells were pelleted by centrifuge and were resuspended in fresh CD-CHO media to achieve cell densities of approximately 1 ^χ 10 ⁷ cells (600 mL) per cuvette. Suspensions of cells containing 40 μg of linearized plasmid DNA were electroporated, seeding 10 ³ cells per well in 96-well tissue culture plates containing suitable selection drug. The antibody expression level in the culture supernatant of clones isolated on 96-well tissue culture plates was determined by an enzyme-linked immunosorbent assay (ELIS A). On the basis of the antibody titer in the supernatant, clones with high-level expression were transferred to 24-well plate (Corning) containing suitable media. Specific antibody productivity (qAb) and specific growth rate (μ) were further analyzed by seeding cells at 2* 10 ⁵ cells per well containing 5 ml of medium in six- well tissue culture plates, culturing for 2 and 4 days, and usually 20-30 high-producing clones (parental clones) were transferred to shake flask for successive selection, and 5-8 highest producer clones were chosen to be further subcloned, and tested for expression.

The purification was carried out by centrifuging cell suspension and harvesting the supernatant, which was further cleared by centrifuging. Protein A affinity columns such as Mab Select SuRe (GE Healthcare) and ion exchange such as Capto S (GE) were used to purify the expressed antibodies).

EXAMPLE 8

Conjugation of Bat0206 with SMCC-MDC

The drug-linker SMCC-MDC was prepared in the following reactions: (1) 3-mercaptopropanoic acid (MPr) was reacted with N-succinimidyl 4-(maleimidomethyl)cyclohexane-l -carboxylate (SMCC) in the presence of DIEA, giving the MPr-SMCC at a yield of over 95%; Secondly, condensation of N-Me-L-Ala-MDC, which was prepared by deprotection of Fmoc-N-Me-Ala- MDC under a base piperidine in CH ₃ CN, with MPr-SMCC under a coupling reagent EDC, giving the desired coupled product SMCC-MDC in 60-70% yield over two steps. Antibody Bat0206 (Abu) was diluted to 2.5 mg/mL in solution A (50 mM potassium phosphate, 50 mM NaCl, and 2 mM EDTA, pH 6.5). SMCC-MDC was added to give a ratio of SMCC-MDC to antibody of 7: 1 mole equivalent. Then DMA was added to 15% (v/v) to the reaction and reaction was mixed by stirring for 4 h at ambient temperature. D-Lmcc-Bat0206 conjugate was purified from excess unreacted or hydrolyzed reagent and excess SMCC-MDC using a G25 gel filtration column equilibrated in pH 7.4 phosphate buffer (aqueous). The conjugate was then dialyzed overnight into pH 7.4 phosphate buffer (aqueous) and then filtered through a 0.22 μιτι filter for final storage. The number of SMCC-MDC molecule per Abu molecule in the final conjugate was measured by determining absorbance of the conjugate at 252 and 280 nm and using known extinction coefficients for SMCC-MDC and antibody at these two wavelengths. A ratio of maytansinoid compound to antibody of 3.5 : 1.0 was normally obtained.

EXAMPLE 9

Conjugation of Bat0206 with Batansine

Antibody Bat0206 was diluted to 8.0 mg/mL in solution B (50 mM potassium phosphate, 50 mM NaCl, and 2 mM EDTA, pH 8.0). Partial reduction was carried out with (6 moles equivalent) DTT. After incubation at 37 °C for 60 minutes, the buffer was exchanged by elution through Sephadex G-25 resin with solution B. The thiol-antibody value was determined from the reduced monoclonal antibody (mAb) concentration determined from 280-nm absorbance, and the thiol concentration was determined by reaction with DTNB (5,5'-dithiobis(2-nitrobenzoic acid); Aldrich) and absorbance measured at 412 nm.

The conjugation reaction was carried out with 10% DMA. The batansine (3AA-MDC) was prepared as in Example 4 and 5 above. The volume of batansine solution was calculated to contain 1.5-mol batansine (3AA-MDC) per mol thiol equivalent. Batansine solution was added rapidly with mixing to the cold-reduced antibody solution, and the mixture was stirred at r.t. for 3 hours, and continued for additional 1 h after adding 5 mM cysteine. The reaction mixture was concentrated by centrifugal ultrafiltration and buffer-exchanged by elution through Sephadex G25 equilibrated in PBS. The conjugate was then filtered through a 0.2-μιτι filter under sterile conditions and stored at -80 °C for analysis and testing. The Batansine-0206 was further analyzed for drug/antibody ratio by measuring unreacted thiols with DTNB, and 3.5:1 ratio of drug/antibody was often obtained. Batansine-0206 was further characterized for concentration by UV absorbance, aggregation by size-exclusion chromatography, and residual free drug by reverse-phase HPLC. All mAbs and ADCs used in these studies exceeded 98 % monomeric protein.

EXAMPLE 10

Characterization of Batansine-0206

The growth inhibitory characteristics of Bat0206 and Batansine-0206 were evaluated using the EGFR positive breast tumor cell line, MDA-MB-468 and EGFR negative cell line BT474 (Shanghai Cell Collections, Ltd. Co., Shanghai, China). Briefly, cells were detached by using 0.25% (vol/vol) trypsin and suspended in complete medium. Aliquots of 100 containing 10,000 cells were plated into 96-well microplates. The cells were allowed to adhere overnight at 37 °C, and 100 of media containing various concentrations of Bat0206 and Batansine-0206 was then added. After 72 hours, plates were washed twice with PBS (pH 7.5), and analyzed for relative cell proliferation with Cell Counting Kit-8 (CCK-8, Dojindo Molec. Technologies, Japan) reagent. Drug conjugate Batansine-0206 significantly inhibited the EGFR positive cell proliferation at much lower concentration than naked Bat0206 and naked Cetuximab (Fig. 7). Neither naked antibodies Bat0206, naked marked antibody Cetuximab, nor drug conjugate Batansine-0206 inhibited the growth of EGFR negative cell line BT474 (Fig. 8).

EXAMPLE 11

Preparation of Antibody-Drug Conjugates: D-Lmcc-Bat0206

Antibody Bat0206 was diluted to 2.5 mg/mL in solution A (50 mM potassium phosphate, 50 mM NaCl, and 2 mM EDTA, pH 6.5). SMCC-MDC was added to give a ratio of SMCC-MDC to antibody of 7: 1 mole equivalent. Then DMA was added to 15% to the reaction and reaction was mixed by stirring for 4 h at ambient temperature. D-Lmcc-Bat0206 conjugate was purified from excess unreacted or hydrolyzed reagent and excess SMCC-MDC using a G25 gel filtration column equilibrated in pH 7.4 phosphate buffer (aqueous). The conjugate was then dialyzed overnight into pH 7.4 phosphate buffer (aqueous) and then filtered through a 0.22 μιτι filter for final storage. The number of SMCC-MDC molecule per Abu molecule in the final conjugate was measured by determining absorbance of the conjugate at 252 and 280 nm and using known extinction coefficients for SMCC-MDC and antibody at these two wavelengths. A ratio of maytansinoid compound to antibody of 2-5 to 1 was normally obtained. The growth inhibitory characteristics of D-Lmcc-Bat0206 were also evaluated using the EGFR positive breast tumor cell line, MDA-MB-468 and EGFR negative cell line BT474. Briefly, cells were detached by using 0.25 % (vol/vol) trypsin and suspended in complete medium. Aliquots of 100 \JLL containing 10,000 cells were plated into 96-well microplates. The cells were allowed to adhere overnight at 37 °C, and 100 \JLL of media containing various concentrations of Bat0206 and D-Lmcc-bat0206 was then added. After 72 hours, plates were washed twice with PBS (pH 7.5), and analyzed for relative cell proliferation with CCK-8 reagent. Drug conjugate D-Lmcc- Bat0206, as in the case of Batansine-0206, significantly inhibited the EGFR positive cell proliferation at much lower concentration than naked Bat0206 and naked Cetuximab ( Fig. 10).

EXAMPLE 12

D-Lmcc-Bat0206 Eradicates Human A431 Tumor Xenografts

In Vivo Tumor Studies: The effects of D-Lmcc-Bat0206 on the growth of established tumors were examined on human A431 tumor xenografts. Human A431 cells (ATCC, CRL-7907) were cultured in DMEM medium supplemented with 10% fetal bovine serum, 2mM glutamine and antibiotics. Female BALB/c nude mice, 4-6 weeks old, were injected subcutaneously with 4x10 ⁶ tumor cells in the dorsal area in a volume of 100 uL. When the tumor xenografts reaches a size of 80-200 mm ³ (calculated as 0.5 (length x width ² ), animals were then treated with Bat0206, D- Lmcc-Bat0206, or a control buffer. Bat0206 and D-Lmcc-Bat0206 were administered at the doses of 5 mg/kg. Animals were dosed every 3 days for a total of 8 doses i.p. in a volume of 100 μ Each group consisted of 12 mice. Tumor size was determined at 3 days intervals. Twenty four days after tumor cell inoculation, animals were euthanized and tumors were removed and weighed. As shown in Fig. 1 1 and 12, at 5 mg/kg dose tested, Bat0206 and D-Lmcc-Bat0206 markedly suppressed tumor growth as assessed by tumor weight measurements 24 days after drug treatment.

EXAMPLE 13

Preparation of Antibody-Drug Conjugate D-LSPP-bat0206

Antibody Bat0206 (8 mg/mL) was modified using 8-fold molar excess of N-succinimidyl-4-(2- pyridyldithio) pentanoate (SPP) to introduce dithiopyridyl groups. The reaction was carried out in 95% v/v Buffer A (50 mM potassium phosphate, 50 mM NaCl, 2 mM EDTA, pH 6.5) and 5% v/v DMA for 2 h at room temperature. The slightly turgid reaction mixture was gel-filtered through a Sephadex G25 column (equilibrated in Buffer A). The degree of modification was determined by measuring the absorbance of the antibody and the 2-mercaptopyridine (Spy) released by DTT respectively at 280 and 343 nm. Modified Bat0206 was then conjugated at 2.5 mg/mL using a 1.7-fold molar excess of N2'-deacetyl-N2'-(3-mercapto-l -oxopropyl)-maytansine over SPy. The reaction was carried out with DMA (5% v/v) in Buffer A (see above). The reaction was incubated at room temperature overnight for 17 h. The conjugated antibody was cleared by centrifugation and then further purified through gel-filteration with a Sephadex G25 column equilibrated with PBS pH 6.5. The conjugate was sterile-filtered using a 0.22 μΜ

Millex-GV filter. The number of drug molecules linked per Bat0206 molecule was determined by measuring the absorbance at both 252 nm and 280 nm of the filtered material. The drug to antibody ratio was found to be about 4.5. The conjugated antibody was further biochemically characterized by size exclusion chromography (SEC) and found to be over 96% monomer.

The growth inhibitory characteristics of D-Lspp-Bat0206 were evaluated using the EGFR positive tumor cell line A431 and A549. Briefly, cells were detached by using 0.25 % (vol/vol) trypsin and suspended in complete medium. Aliquots of cells were plated into 96-well microdilution plates. The cells were allowed to adhere overnight at 37 °C, and 100 μΐ. of media containing various concentrations of Bat0606 and D-Lspp-Bat0206 was then added. After 72 hours, plates were washed twice with PBS (pH 7.5), and analyzed for relative cell proliferation with CCK-8 reagent. Drug conjugate D-Lspp-Bat0206 significantly inhibited the A431 positive cell proliferation at much lower concentration than naked Bat0206 (Fig. 13), and furthermore, D- Lspp-bat0206 effectively inhibited the growth of A549 cells, which is resistant to treatment by naked Bat0206 as a result of Kras mutation (Fig. 14).

The IC ₅ o values of certain compounds are presented in Tables 1 and 2. The data in Table 2 are obtained with conjugates having different drug loads and using different experimental conditions.

Batansine-0206 and D-Lmcc-Bat0206 significantly increased the activity of the naked antibody agasint EGFR positive tumor cell lines. Compared with the di-sulfide comprising drug-linker- antibody D-Lspp-Bat0206, Batansine-0206 and D-Lmcc-Bat0206 exhibited significant improvement in selectivity against EGFR positive tumor cell lines A431 and MDA-MB-468. Surprisingly, Batansine-0206 and D-Lmcc-Bat0206 also exhibited significant improvement in selectivity against EGFR positive tumor cell lines A431 and MDA-MB-468 over the naked antibody.

Table 1

Table 2

EXAMPLE 14

Batansine-0606 Eradicates Human BT474 Tumor Xenografts

In Vivo Tumor Studies: The effects of batansine-0606 (3AA-MDC-trastuzumab) on the growth of established tumors were examined on human BT474 tumor xenografts. Human BT474 cells (ATCC, HTB-20) were cultured in DMEM medium supplemented with 10% fetal bovine serum, 2 mM glutamine and antibiotics. Female BALB/c nude mice, 8-9 weeks old, were injected subcutaneously with 1 x 10 ⁷ tumor cells in the dorsal area in a volume of 100 μί. When the tumor xenografts reaches a size of 150-200 mm ³ (calculated as 0.5 ^χ (length ^χ width ² ), animals were then treated with Bat0606 (5 or 15 mg/kg), batansine-0606 (5 or 15 mg/kg), or control antibody (Rituximab, 15 mg/kg). Animals were dosed every 3 weeks for a total of 3 doses i.v. in a volume of 100 μ Each group consisted of 10 mice. Tumor size was determined at 3 days intervals. 49 days after tumor cell inoculation, animals were euthanized and tumors were removed and weighed. As shown in Fig. 30 , Rapid tumor shrinkage was seen by batansine-0606 (15 mg/kg) from day 7. From day 10 onwards batansine-0606 (15 mg/kg) treated tumors had shrunken to non-palpable. Compared to the unconjugated Bat0606, batansine-0606 more significantly inhibited the tumor growth as assessed by tumor weight measurements 49 days after drug treatment.

EXAMPLE 15

Preparation of Antibody-Drug Conjugates: D-Lmcc-Bat0606

Antibody Bat0606 was diluted to 2.5 mg/mL in solution A (50 mM potassium phosphate, 50 mM NaCl, and 2 mM EDTA, pH 6.5). SMCC-MDC was added to give a ratio of SMCC-MDC to antibody of 7: 1 mole equivalent. Then DMA was added to 15% to the reaction and reaction was mixed by stirring for 4 h at ambient temperature. D-Lmcc-bat0606 conjugate was purified from excess unreacted or hydrolyzed reagent and excess SMCC-MDC using a G25 gel filtration column equilibrated in pH 7.4 phosphate buffer (aqueous). The conjugate was then dialyzed overnight into pH 7.4 phosphate buffer (aqueous) and then filtered through a 0.22 μιτι filter for final storage. The number of SMCC-MDC molecule per Abu molecule in the final conjugate was measured by determining absorbance of the conjugate at 252 and 280 nm and using known extinction coefficients for SMCC-MDC and antibody at these two wavelengths. A ratio of maytansinoid compound to antibody of 3.5:1.0 was normally obtained.

EXAMPLE 16

Preparation of Antibody-Drug Conjugates: Batansine-0606

Antibody Bat0606 was diluted to 8.0 mg/mL in solution B (50 mM potassium phosphate, 50 mM NaCl, and 2 mM EDTA, pH 8.0). Partial reduction was carried out with (6 moles equivalent) DTT. After incubation at 37 °C for 60 minutes, the buffer was exchanged by elution through Sephadex G-25 resin with solution B. The thiol-antibody value was determined from the reduced monoclonal antibody (mAb) concentration determined from 280-nm absorbance, and the thiol concentration was determined by reaction with DTNB (5,5'-dithiobis(2-nitrobenzoic acid); Aldrich) and absorbance measured at 412 nm.

The conjugation reaction was carried out with 10% DMA. The volume of batansine solution was calculated to contain 1.5-mol batansine (3AA-MDC) per mol equivalent of free thiol on the antibody. Batansine solution was added rapidly with mixing to the cold-reduced antibody solution, and the mixture was stirred at r.t. for 3 hours, and continued for additional 1 h after adding 5 mM cysteine. The reaction mixture was concentrated by centrifugal ultrafiltration and buffer-exchanged by elution through Sephadex G25 equilibrated in PBS. The conjugate was then filtered through a 0.2-μιτι filter under sterile conditions and stored at -80 °C for analysis and testing. The Batansine-0606 was further analyzed for drug/antibody ratio by measuring unreacted thiols with DTNB, and 3.5:1.0 ratio of drug/antibody was often obtained. Batansine- 0206 was further characterized for concentration by UV absorbance, aggregation by size- exclusion chromatography, and residual free drug by reverse-phase HPLC. All mAbs and ADCs used in these studies exceeded 98 % monomeric protein.

EXAMPLE 17

Characterization of Anti-ErbB2 Antibody Drug Conjugate Batansine-0606

The growth inhibitory characteristics of Bat0606 and Batansine-0606 were evaluated using the Her2 positive breast tumor cell line, SK-BR-3 (see Hudziak et al. Molec. Cell. Biol. 9(3): 1 165 1172 (1989) and Her2 negative cell line A549 [Shanghai Cell Collections, Ltd., Co., Shanghai, China]. Briefly, cells were detached by using 0.25 % (vol/vol) trypsin and suspended in complete medium. Aliquots of 100 μΐ, containing 10,000 cells for SK-BR-3 cell line and 8,000 cells for A549 cell line were plated into 96-well microdilution plates. The cells were allowed to adhere overnight at 37 °C, and 100 μΐ. of media containing various concentrations of Bat0606 and Batansine-0606 was then added. After 72 hours, plates were washed twice with PBS (pH 7.5), and analyzed for relative cell proliferation with CCK-8 reagent. Drug conjugate Batansine-0606 more significantly inhibited the Her2 positive cell proliferation than naked Bat0606 (Fig. 20). Neither naked antibody Bat0606 nor drug conjugate Batansine-0606 inhibited the growth of Her2 negative cell line A549 (Fig. 21).

EXAMPLE 18

Characterization of Anti-ErbB2 Antibody Drug Conjugate D-Lmcc-Bat0606

The growth inhibitory characteristics of D-Lmcc-bat0606 were evaluated using the Her2 positive breast tumor cell line, SK-BR-3 (see Hudziak et al. Molec. Cell. Biol. 9(3):1165 1172 (1989) and Her2 negative cell line A549. Briefly, cells were detached by using 0.25 % (vol/vol) trypsin and suspended in complete medium. Aliquots of 100 μΐ. containing 10,000 cells for SK-BR-3 cell line and 8,000 cells for A549 cell line were plated into 96-well microdilution plates. The cells were allowed to adhere overnight at 37 °C, and 100 μΐ. of media containing various

concentrations of Bat0606 and D-Lmcc-Bat0606 was then added. After 72 hours, plates were washed twice with PBS (pH 7.5), and analyzed for relative cell proliferation with CCK-8 reagent. Drug conjugate D-Lmcc-Bat0606 strongly inhibited the Her2 positive cell proliferation (Fig. 22). Neither naked antibody Bat0606 nor drug conjugate D-Lmcc-Bat0606 inhibited the growth of Her2 negative cell line A549 (Fig. 23).

EXAMPLE 19

The stability studies of Batansine-0606 were evaluated in Sprague-Dawley rats. Sprague-Dawley rats were administered 10 mg/kg Batansine-0606 (based on the antibody component) by tail vein injection. Blood samples were collected from each mouse via the saphenous vein at 0 h, 10 min, 30 min, lh, 2h, 4h, 8h, 24h, 36 h, day 2, day 3, day 4, day 7, day 14, day 21 , day 28 after injection. Blood was collected into heparin coated tubes followed by centrifugation (14,000 ^χ g, 3 minutes) to isolate plasma. Plasma concentrations of total Anti-Erb B/neu and antibody-drug conjugates were measured by ELISA. Total antibody concentration in the serum samples was measured as follows: 96-well ELISA plates were coated with FIER2 ECD in 2 μg/mL

carbonate/bicarbonate buffer (pH 9.6) at 4 ^° C overnight. After removal of the coat solution, nonspecific binding sites were blocked by incubating with blocking solution (PBS, 1% BSA, 0.05% Tween 20) at room temperature for 1 hour. The plates were then washed with wash buffer (0.05% Tween in PBS), and standards or samples diluted in PBS were added. After a 2h incubation, plates were washed and mouse anti-human IgG-horseradish peroxidase conjugate (Sigma, St. Louis, MO) was added for an additional 2 h. Plates were then washed again.

Subsequently, 100 μΐ. of 3,3,5, 5-tetramethylbenzidine (Sigma, St. Louis, MO) were added to each well, and upon color development, the reaction was stopped with 100 of 1 N sulfuric acid. Absorbance was measured using a VMax Kinetic Microplate reader (Molecular Devices, Sunnyvale, CA) at 490 nm. For measurement of antibody-drug conjugates concentration, wells were coated with HER2 ECD and serum samples added as above. After the 2-h sample incubation, the plates were washed, rabbit anti-maytansine antibody was added to each well, and the plates were incubated for 1 h. Plates were then washed, and HRP-conjugated goat anti-rabbit IgG (Sigma) was added for an additional lh incubation. Color detection and measurement were performed as described above. Noncompartmental pharmacokinetic parameters were calculated with WinNonlin (Pharsight, Mountain View, CA). The time-concentration curves of antibody component of Batansine-0606 and the drug component of Batansine-0606 appeared to follow bi- exponential declines. The terminal half-life of antibody component of Batansine-0606 was 571.07, and the terminal half-life of drug component of Batansine-0606 was 88.36 hours.

EXAMPLE 20

Batansine-0606 Eradicates Human NCI-N87 Tumor Xenografts

In Vivo Tumor Studies: The effects of batansine-0606 (3AA-MDC-trastuzumab) on the growth of established tumors were examined on human NCI-N87 tumor xenografts. Human NCI-N87 cells (ATCC, CRL-5822) were cultured in DMEM medium supplemented with 10% fetal bovine serum, 2 mM glutamine and antibiotics. Female BALB/c nude mice, 4-8 weeks old, were injected subcutaneously with 5xl0 ⁶ tumor cells in the dorsal area in a volume of 100 uL. When the tumor xenografts reaches a size of 100-200 mm ³ (calculated as 0.5 ^χ (length ^χ width ² )), animals were then treated with Bat0606 (5 or 15 mg/kg, i.v), batansine-0606 (5 or 15 mg/kg, i.v), or control antibody (Rituximab, 15 mg/kg, i.v). Animals were dosed once per week for a total of 5 doses i.v. in a volume of 100 μ Bat0606 treatment of NCI-N87 xenografts was discontinued on day 15 and switched to batansine-0606 (5 or 15 mg/kg, i.v.) from the day 21 onwards. Each group consisted of 10 mice. Tumor size was determined at 3 days intervals. 42 days after tumor cell inoculation, animals were euthanized and tumors were removed and weighed. As shown in Fig. 29, rapid tumor shrinkage was seen by batansine-0606 (5 or 15 mg/kg) from day 1 1. From day 32 onwards batansine-0606 (5 or 15 mg/kg) treated tumors had shrunken to non-palpable. Compared to the unconjugated Bat0606, at 5 or 15 mg/kg dose tested, batansine-0606 more significantly inhibited the tumor growth as assessed by tumor weight measurements 35 days after drug treatment.

EXAMPLE 21

Preparation of Antibody-Drug Conjugates: D-Lmcc-Batl206

Antibody Batl206 was diluted to 2.5 mg/mL in solution A (50 mM potassium phosphate, 50 mM NaCl, and 2 mM EDTA, pH 6.5). SMCC-MDC was added to give a ratio of SMCC-MDC to antibody of 7: 1 mole equivalent. Then DMA was added to 15% to the reaction and reaction was mixed by stirring for 4 h at ambient temperature. D-Lmcc-Batl206 conjugate was purified from excess unreacted or hydrolyzed reagent and excess SMCC-MDC using a G25 gel filtration column equilibrated in pH 7.4 phosphate buffer (aqueous). The conjugate was then dialyzed overnight into pH 7.4 phosphate buffer (aqueous) and then filtered through a 0.22 μιτι filter for final storage. The number of SMCC-MDC molecule per Abu molecule in the final conjugate was measured by determining absorbance of the conjugate at 252 and 280 nm and using known extinction coefficients for SMCC-MDC and antibody at these two wavelengths. A ratio of maytansinoid compound to antibody of 2-5 to 1 was normally obtained.

EXAMPLE 22

Preparation of Anti-CD20 Antibody Drug Conjugate Batansine-1206

Antibody Batl206 was diluted to 8.0 mg/mL in solution B (50 mM potassium phosphate, 50 mM NaCl, and 2 mM EDTA, pH 8.0). Partial reduction was carried out with ( 6 moles equivalent ) DTT. After incubation at 37 °C for 60 minutes, the buffer was exchanged by elution through Sephadex G-25 resin with solution B. The thiol-antibody value was determined from the reduced monoclonal antibody (mAb) concentration determined from 280-nm absorbance, and the thiol concentration was determined by reaction with DTNB (5,5'-dithiobis(2-nitrobenzoic acid);

Aldrich) and absorbance measured at 412 nm. The conjugation reaction was carried out with 10% DMA. The volume of batansine solution was calculated to contain 1.5-mol batansine (3AA- MDC) per mol equivalent of free thiol on the antibody. Batansine solution was added rapidly with mixing to the cold-reduced antibody solution, and the mixture was stirred at r.t. for 3 hours, and continued for additional 1 h after adding 5 mM cysteine. The reaction mixture was concentrated by centrifugal ultrafiltration and buffer-exchanged by elution through Sephadex G25 equilibrated in PBS. The conjugate was then filtered through a 0.2-μιτι filter under sterile conditions and stored at -80 °C for analysis and testing. The Batansine-1206 was further analyzed for drug/antibody ratio by measuring unreacted thiols with DTNB, and 3.5:1 ratio of drug/antibody was often obtained. Batansine-1206 was further characterized for concentration by UV absorbance, aggregation by size-exclusion chromatography, and residual free drug by reverse-phase HPLC.

EXAMPLE 23

Study on the Effect of Batl206 and D-Lmcc-Batl206 on the Growth of Raji Cells

The effect of Batl206 and D-Lmcc-Batl206 on the growth of Raji cell (Shanghai Cell Collection. Ltd., Co. Shanghai, China) was determined using the method described by Ishiyama et al. (Biol. Pharmacol. Bull., 19: 1518-1520, 1996). Briefly, 10 thousands cells in 100 of DMEM:F12 (GBICO, CA) culture medium without serum were seeded into each well of a 96-well plate.

Twice-fold serial dilutions of antibodies or conjugated form were prepared and each diluted antibodies were added in triplicate to the wells and the cultures were incubated at 37°C for 3 days. The controls consisted of either medium alone or medium containing of Raji cell. After incubation, CCK-8 was added to each well and the absorbance at 450 nm of each well was determined in a Spectra Max spectrophotometer (Molecular Devices, Sunnyvale, CA). As shown in Figure 26, D-Lmcc-Batl206 more effectively inhibited CD20 positive cell growth than non conjugated anti-CD20 antibody Batl206.

EXAMPLE 24

Cellular Metabolites of Batansine-0206 and D-Lmcc-Bat0206

Cellular metabolites of Batansine-0206 and D-Lmcc-Bat0206 were assayed as described in Erickson, et al. Cancer Res 66:4426-4433 (2006). Briefly, A431 cells (6xl0 ⁶ ) suspended in 3 mL culture medium containing Batansine-0206 at a concentration of 10-7 mol/L of conjugated antibody were incubated at 37 °C for 3 to 30 hours. The cells and the medium were then separated by centrifugation (2,000 g, 5 minutes). The supernatant (3 mL) was chilled on ice, mixed with 4 mL ice-cold acetone, and kept at -80 °C for at least 1 hour or until further processing. Precipitated protein was removed by centrifugation at 2,500 g and the supematants were acidified with 5% acetic acid and evaporated to dryness. The samples were dissolved in 0.12 mL of 20% aqueous CH ₃ CN containing 0.025% trifluoroacetic acid (TFA), aliquots of 0.1 mL were submitted to LC-MS. The metabolite of Batansine-0206: LC-MS (M+Ff) calc : 964.5, found: 964.2. The metabolite of D-Lmcc-Bat0206: LC-MS (M+Ff) calc : 1103.7, found:l 103.3.