FIELD OF INVENTION

This invention relates to in vivo tumour imaging and therapy, an more particularly to a novel reagent for use therein, diagnostic an therapeutic compositions containing that reagent, and methods of tumou imaging and therapy utilising the reagent.

BACKGROUND INFORMATION AND PRIOR ART In the cause of improving the diagnosis and treatment of cance numerous attempts have been made to target imaging agents, e.g radioactive isotopes, and therapeutic reagents onto tumours in viv using anti-tumour monoclonal antibodies, Mabs, see for exampl published International Applications WO 89/00583 and W0 90/09197 Because of the size of the average Mab, diffusion rates of, fo example, a radio-labelled antibody to the site of a tumour are ver low, and the same applies to conjugates formed from a cytotoxic reagen and an anti-tumour antibody.

Tumour imaging and therapy using Mabs is therefore inherently slow process, often taking several hours, whereas ideally one woul like to have the process complete in minutes, rather than hours particularly in the case of tumour imaging and diagnosis.

In J. Immunol., 145, No. 1, 59-67, 1990, Shimizu et al hav reported on the co-stimulation of proliferative responses of restin CD4U ^t T-cells by the interaction of the extracellular matrix (ECM proteins fibronectin (FN) and laminin (LN) with the VLA integrins VLA- and VLA-5 (in the case of fibronectin) or VLA-6 (in the case o laminin) expressed by resting human T-lymphocytes, and have shown inte alia that the 12-amino acid peptide

L H G P E I D V- P S T ( leu-his-gly-pro-glu-ile-leu-asp-val-pro-ser-thr )

is an effective T-cell adhesion inhibitor and an effective blockin agent for 0KT3/FN T-cell proliferation, but does not go beyond a mer investigation into the role of cell adhesion molecules (CAMs ) in T-cell recognition and activation . Thus , Shimizu et al suggest no practical

outcome or industrial utility resulting from their inve tigations.

In J. Biol. Chem., 266, No. 6, 3579-3585, 1991, Mould et al ha reported their studies of the inhibition of the interaction of t integrin heterodimer α^β* with the CS1 and CS5 sites in the IIICS regi of fibronectin, which interaction is believed to play an important rol in melanoma cell adhesion, and have shown that the tripeptide X-asp- where X is glycine, leucine or glutamic acid, and Y is serine o valine, represents a minimum recognition sequence within the CS1 sit of the fibronectin for the integrin α^β.. Inter alia, those studie utilised synthetic CS1 and KKT-CS1-VQK peptides, viz:

CS1

D E L P Q L V T L P H P N L H G P asp-glu-Ieu-pro-gln-leu-val-thr-leu-pro-his-pro-asn-leu-his- gly-pro- E I L D V P S T glu-ile-leu-asp-val-pro-ser-thr

KKT-GS1-VQK K K T D E L P Q L V T L P H P N L lys-lys-thr-asp-glu-leu-pro-gln-leu-val-thr-leu-pro-his-pro- asn-leu- H G P E I L D V P S T V Q K his-gly-pro-glu-ile-leu-asp-val-pro-ser-thr-val-gln-lys

but again no consequential commercial utility is suggested for such LD (leu-asp-val) containing peptides.

Subsequent studies of similar kind confirming the significance of the LDV triplet as the minimum recognition site for the α^β. integrin, as opposed to the RGDS sequence which constitutes the minimum recognition site for the αi-β. integrin, those two minimum recognition sites occuring in different domains of the fibronectin (FN) molecule, viz. the alternatively spliced type III connecting segment (IIICS) and the central cell binding domain respectively, are reported by Komoriya et al in J. Biol. Chem., 266, No. 23, 15075-15079, 1991, but published after the present priority date. Earlier studies into the cell binding activity of fibronectin are reported by Pierschbacher and Ruoslahti (Nature, 309, 30-33, 1984) and by Kloczewiak et al in Biochemistry, 28, 2915-2919, 1989.

Pierschbacher et al recognise the importance of the RGDS sequence a recognition site in the cell adhesion activity of fibronectin, report that they were unable to obtain any inhibition of cell adhes using either soluble fibronectin or by peptides not containing the R sequence. Similarly Kloczewiak et al, investigating the essential r of the terminal region of the fibrinogen γ-chain in the interaction human fibrinogen with activated platelets, showed that the synthe dodecapaptide:

H H L Q L L K Q L L D V his-his-leu-gln-leu-leu-lys-gln-leu-leu-asp-val

being an analogue of the γ400-411 FN residue, and containing the triplet, achieved 50% inhibition of fibrinogen binding to activa platelets, but only at concentrations greater than 500μM.

In contrast to both Shimizu et al and Mould et al, EP-A-0428 identifies as potential anti-cancer agents, peptides based on functional domains of fibronectin, more particularly the cell bind domains and the heparin binding domains, amino acid residues 1239-1 and 1690-1960 respectively (EP-A-0428266, SEQ ID Nos. 2 and According to EP-A-0428266, these fibronectin fragments show anti-can activity in mice by inhibiting metastasis, and may be used singly or the form of a chimeric peptide comprising both sequences 1 inked b linker, e.g. a methionine residue, EP-A-0428266 SEQ ID No. 4. either event, the peptide fragment is of substantial size: 277 am acid residue in the case of the cell binding domain FN fragment, 271 in the case of the heparin binding FN fragment, making a total 549 amino acid residues in the chimeric peptide. Such fragments therefore still of substantial size compared to the oligopeptides u in the present invention, and can be expected still to show many of disadvantages of the Mab based anti-cancer agents, namely low diffus and clearance rates. Not only that, but n- ^~ ne of the FN fragme disclosed as anti-cancer agents in EP-A-0428266 contain the amino a triplet which is characteristic of the oligopeptides used in accorda with the present invention, that is to say the leu-asp-val (L triplet.

More recently, in published International Patent Application

90/15858, the present inventor has disclosed novel peptides comprising an RGD sequence (i.e. the sequence: arg-gly-asp) primarily for in vivo thrombus imaging, but also potentially useful for in vivo tumour imaging and therapy, and capable of binding to tumours in vivo via RGD binding sites on the surface of the tumour. In the case of thrombus imaging the peptide binds to RGD recognition and binding sites in the

GPIIb/IIIa (glycoprotein-fibrinogen receptor) complex present on the membrane surface of activated platelets, and which contain the fibrinogen binding domains and which are involved in the aggregation of the activated platelets to form the thrombus.

OBJECTS OF THE PRESENT INVENTION

The present invention seeks to overcome the above-mentioned disadvantages of monoclonal antibody (Mab) based cytotoxic and diagnostic reagents by providing novel oligopeptide based reagents having specific binding properties to tumour associated binding sites, and which are rapidly transported to the tumour site following injection, with equally rapid clearance of unbound reagent from the body following administration, thus considerably reducing treatment times and reducing the effective dosage of potentially highly toxic reagents, whether administered for diagnostic or therapeutic purposes.

Further objects of the present invention are to provide tumour diagnostic and therapeutic compositions containing such reagents, and methods of diagnostically imaging or treatment of tumours using such reagents.

SUMMARY OF PRESENT INVENTION

In accordance with the present invention the above objectives are achieved using a synthetic oligopeptide of from 4 to about 50 peptide units and containing the sequence

L D V leu-asp-val

referred to herein as the LDV sequence, which sequence binds the oligopeptide in vivo to LDV binding sites on the tumour.

Because of their relatively small size, such oligopeptides

diffuse rapidly throughout the body and, equally importantly, ar rapidly cleared from the body by ordinary metabolic and/or excretor processes, leaving behind only bound oligopeptide bound to the tumou or to other tissue structures containing an LDV binding site. Thi rapid clearance of unbound oligopeptide from the body is particularl important in the case of tumour imaging using a radio-labelle oligopeptide, since it permits visualisation of local concentrations o bound radio-labelled oligopeptide by conventional radiologica techniques within a relatively short period of time followin intravenous administration of the diagnostic reagent, i.e. the radio labelled oligopeptide.

The rapid clearance of unbound oligopeptide from the body is als invaluable in reducing possible toxic side effects of cytotoxic drug used in tumour therapy regimes and administered, in accordance with th concepts of this invention, as a conjugate formed from the cytotoxic reagent and an oligopeptide of from 4 to about 50 peptide units an containing the sequence

L D V leu-asp-val

BRIEF DESCRIPTION OF DRAWINGS

The binding capacity of radio-labelled peptides according to the invention to tumour cells, both in vitro and in vivo is illustrated by the accompanying drawings, in which:

Figure 1 is a bar chart illustrating the binding capacity of the radio-labelled peptide ¹²⁵ I-YLDVY to tumour cells from cell lines T47D, LoVo, HT29, HT1080, HEp-2, EJ28 and A431, in vitro;

Figure 2 presents similar data in respect of the radio-labelled peptide ¹²⁵ I-YGGLDVGLDVGGY;

Figure 3 presents similar data in respect of the radio-labelled peptide ^,25 I-LDVGGGGSY; and

Figure 4 is a bar chart illustrating the in vivo retention of the radio-labelled peptide ¹²⁵ I-YGGLDVGLDVGGY by nude mice bearing HEp-2 and HT29 tumours.

DETAILED DESCRIPTION

In accordance with this invention, therefore, there are provided diagnostic and therapeutic reagents, primarily for in vivo tumour imaging and therapy, but also useful in targeting other pathological tissues containing an LDV-binding site, such reagents comprising an oligopeptide of from 4 to about 50 peptide units and containing as a triplet therein the sequence

D leu-asp-val

and to which oligopeptide there is attached either a radioactive label or cytotoxin.

As to the actual size of the oligopeptide used in accordance with the present invention, this will be determined largely by economic considerations: generally in the construction of oligopeptides on a peptide synthesizer cost is directly proportional to length. For synthetic oligopeptides therefore, 50 peptide units represents the maximum chain length that is likely to be viable economically, although in practice very much shorter chain lengths are the more likely, e.g. from 4 to 30, down to 4 to 20 or 4 to 15, or as little as 4 to 10. Particularly preferred sequences are the CS1 sequence of fibronectin, i.e. a 25-unit oligopeptide having the sequence SEQ ID No. 1, and sub- units thereof containing the LDV triplet. Other suitable oligopeptides include the five unit peptide:

Y L D V Y tyr-1eu-asp-val-tyr

the nine unit peptide:

L D V G G G G S Y leu-asp-val-gly-gly-gly-gly-ser-tyr

and the thirteen unit peptide: SEQ ID No. 2. The CS1 sequence of fibronectin, SEQ ID No. 1, is known to bind to the cell adhesion molecule (CAM) VLA-4 expressed in vitro by many tumour cells and by resting CD4 ^f T-cells (see Shimizu et al above). It

is now established that the CS1 sequence of fibronectin and other LD containing peptides bind strongly to tumour cells in vivo, th providing a method of targeting imaging or therapeutic reagents on those cells. A variety of different techniques are available for attaching radioactive label to the oligopeptide, and a variety of differe labels are available for this purpose. Amongst those there may mentioned, in particular: technetium-99m, iodine-123 or iodine-125 a indium-111. In order to attach the label (or for that matter, cytotoxic reagent) the oligopeptide will usually be provided with reactive terminal amino acid residue such as a terminal tyrosin histidine, lysine or cysteine residue. When using Tc as the lab this may be attached via a cysteine residue, 125I via a tyrosi residue, and In via a lysine residue. Attachment of I to a oligopeptide via a tyrosine residue is described in WO 90/15818, an the same procedure may be used herein. Other suitable techniques ar described in Science 220, 613-615; Int. J. Nucl. Med. Biol., 12, 3-8 J. Nucl. Med., 26, 293-299 and J. Nucl, Med., 27, 685-693, incorporate herein by reference. In the alternative, there may be attached to the oligopeptide, i place of the radioactive label, a cytotoxic agent, such as ricin or derivative or component thereof, particularly the ricin A-chain Methods of attaching a cytotoxic agent, such as ricin A-chain, to th oligopeptide will depend on the particular cytotoxin to be used, an the functional groups contained therein and by means of which th cytotoxin can be chemically coupled to functional groups in th oligopeptide, either directly or by means of a di-functional couplin agent. The choice of coupling agent or method will be well within th abilities of the ordinary person skilled in the art, see for example W 88/00583 incorporated herein by reference, so also will be othe suitable cytotoxic reagents besides the ricin and ricin derivative already mentioned.

The detailed preparation of radioactively labelled peptide according to this invention is illustrated by the following example:

EXAMPLE

P Prreparation of radioactivelv labelled ^t25 I-YLDVY. ^t25 I-LDVGGGGSY. an 125 'I-YGGLDVGLDVGGY

The oligopeptides YLDVY, LDVGGGGSY (corresponding amino aci sequences, see above), and YGGLDVGLDVGGY (amino acid sequence, see SE ID No. 2), were synthesised by standard procedures using an automati peptide synthesizer.

Iodogen tubes were prepared by dissolving Iodogen (1,3,4,6

Tetrachloro-3α,6α-diphenylglycouril) in chloroform at a concentratio of 1 mg.ml . Aliquots of 50μl (50μg Iodogen) were dispensed int polypropylene cryo-tubes and the chloroform evaporated to dryness

These tubes were then stored desiccated at -20°C until required.

Prior to radio-labelling the peptides were dissolved in phosphat buffered saline (PBS) at a concentration of 50μg.ml ^" . Iodogen tubes were equilibrated to room temperature before th addition of 200μl peptide solution and 1-10μl of I (in aqueou solution). The reaction mixture was then left for 15 minutes at roo temperature with occasional shaking. Following the incubation perio the reaction mixture was removed and passed through a Sephadex G10 column which had been equilibrated with PBS. The column, which separates radio-labelled peptide from free iodine was eluted with PBS and 2ml fractions collected. radioactivity in the fractions was measured and the eluted peptides, represented by the first radioactive peak from the column, collected and stored at 4 ^° C until required. At this point, it may be mentioned that, in accordance with the usual convention on the representation of labelled peptides, the representation I-YLDVY, for example, merely indicates that the

125 peptide YLDVY has been labelled with I. It is not intended to indicate either the position of attachment of the label or the actual number of radioactive iodine atoms attached to the peptide molecule.

The capacity of the radioactively labelled peptides to bind to tumour cells in vitro and in vivo is illustrated by the following experiments, the results of which are illustrated in the accompanying drawings.

EXPERIMENT 1

Tumour cells from tumour cell lines T47D, LoVo, HT29, HT1080,

HEp-2, EJ28 and A431 were grown to confluence on separate microtitr plates, fixed with glutaraldehyde and then incubated for 1 hour at roo

I? ¹ * temperature with varying concentrations of the three I-labelle peptides ^,25 I-YLDVY, ¹²⁵ I-LDVGGGGSY and ¹²⁵ 1-YGGLDVGLDVGGY. The plate were then washed to remove unbound reagent and the cell residue containing the bound label were removed from each well and the residua radioactivity of the bound label measured. From the known level o radioactivity possessed by the radio-labelled peptide,the molar amoun of bound peptide was determined. The results are presented in Figure 1 to 3.

EXPERIMENT 2

In vivo experiments were performed in nude mice bearing HEp-2 an HT29 tumours obtained by injecting the nude mice subcutaneously in bot flanks with from 2 to 5 x 10 ^* HEp-2 and HT29 tumour cells and th tumours allowed to grow for three weeks.

In these experiments the nude tumour bearing mice divided int five groups were each injected subcutaneously with the 171I-labelle peptide

125 I-YGGLDVGLDVGGY

(SEQ ID No. 2), and the uptake of labelled peptide measured againsl time. For this purpose the five groups were killed at intervals of minutes, 30 minutes, 1 hour, 3 hours, and 6 hours after injection. A this time the blood and tumours were separately removed, weighed an counted for radioactivity, as well as samples taken from all majo organs. Figure 4 shows the retention level at intervals of 30 minutes, 1 hour, 3 hours and 6 hours expressed as a fraction of the percentag injected dose (id) per gram relative to the five minute time point. At this point peptide uptake was 10.3% id per gram in blood, 4.5% id per gram in HEp-2 tumour and 3.0% id per gram in HT29 tumour.

The data presented clearly indicates the capacity of the LDV- containing oligopeptides of this invention to bind to tumour associated LDV binding sites in vivo and therefore potentially to provide useful transport agents for the targeting of imaging and therapeutic reagents onto tumours in vivo. Not only that, but transportation and clearance

rates are rapid enabling shortened diagnosis times in the case o tumour imaging and shortened treatment times in the case of tumou therapy.

For diagnostic purposes, the radioactively labelled oligopeptide of this invention are designed for intravenous administration in suitable liquid carrier at a single dosage rate of no more than abou 100 microgra s as a practical upper limit, more usually in the range 1 to 50 μg. For therapeutic purposes, the cytotoxic oligopeptides o this invention, i.e. the LDV-containing carrier peptide conjugated o chemically linked to a cytotoxic agent, such as the ricin A-chain, wil usually be employed at dosage rates in the range 1mg to 1g depending o tumour size and/or bodyweight, and will usually be administrate serially over a period of time ranging from a few hours to a few days, or in some cases over a period of several weeks. Placing these figure in perspective, and given an average human plasma volume of 2.5L, single diagnostic injection of 100μg represents a maximum peptid plasma concentration of from about 0.078μM to about 0.15μM depending o the molecular weight of the peptide, even assuming no clearance of the peptide from the body. Correspondingly a therapeutic dosage of 1mg represents a maximum peptide plasma concentration of from about 0.78uM to about 1.5μM, again assuming no clearance of peptide from the body. At these extremely low peptide plasma concentrations, which in practice will never be attained due to the systemic clearance rates of the peptide from the body, it is highly surprising that any significant amount of LDV peptide remains bound to the tumour, let aJone a sufficient amount to permit effective imaging or treatment of the tumour. Those peptide plasma concentrations may indeed be contrasted quite remarkably with the >500μM concentration recorded by Kloczewiak et al, loc. cit., as necessary to obtain 50% inhibition of fibronectin binding to activated platelets using the peptide HHLQLLKQLLDV and which figure would indicate a very low level of binding of the LDV-containing peptide to the activated platelets. In contrast to that, the LDV- containing peptides used in the present invention show a quite exceptional and quite unexpected high level of affinity for tumour cells in vivo.

Whether for diagnostic or chemotherapeutic purposes, the labelled or cytotoxic oligopeptides of this invention will be formulated in a

suitable liquid carrier for intravenous administration. Suitabl carriers for this purpose include physiological saline, sterilize water, various other buffer and/or sugar or salt solutions as known i the art. For convenience of administration the concentration o labelled or cytotoxic peptide in the injectable carrier liquid wil usually be in the range 1 to 30% by weight, more usually 1 to 10% b weight.

APPENDIX

Peptide sequence details.

SEQ ID No. 1

Sequence Type Amino acid

Sequence Length 25

Strandedness Single

Topology Linear

Molecular Type Peptide

Original Source Fibronectin CS1-sequence

Original Organism Human

Immediate Experimental Source Synthetic

Sequence Description:

D E L P Q L V T L P asp-glu-leu-pro-gln-leu-val-thr-leu-pro- H P L L H G P E I L his-pro-leu-leu-his-gly-pro-glu-ile-leu-

J) V P S T asp-val-pro-ser-thr

SEQ ID No. 2

Sequence Type Amino acid

Sequence Length 13

Strandedness Single

Topology Linear

Molecular Type Peptide

Original Source

Original Organism

Immediate Experimental Source Synthetic

Sequence Description:

Y G G L D V D V tvr-εly-gly-leu-asp-val-gly-leu-asp-val- G G Y gly-gly-tyr