BARKER, Michael Gordon (4 Millbeck Cottages, Millbeck, Keswick CA12 4PT, GB)
ALMOND, Andrew (Flat 2, 814 Wilmslow Road, Manchester M20 2RN, GB)
BLUNDELL, Charles Douglas (23 Chatsworth Road, Eccles, Manchester M30 9DZ, GB)
BARKER, Michael Gordon (4 Millbeck Cottages, Millbeck, Keswick CA12 4PT, GB)
ALMOND, Andrew (Flat 2, 814 Wilmslow Road, Manchester M20 2RN, GB)
| Claims 1 . A compound of formula I (I) wherein represents an optional double bond; Ri is selected from the group consisting: =N-ORa; -CH2-0-Ra; -CH2-NRaRb; -C(0)0-Ra; -C(0)NRaRb; or -0-N=CRaRb; wherein Ra and Rb are each independently selected from hydrogen or (1 -3C)alkyl optionally substituted by one or more substituents independently selected from hydroxyl, amino, nitro, cyano, fluoro, CF3, methoxy or carboxy; R2 is selected from the group consisting of (1 -10C)alkyl, (2-10C)alkenyl, (2-10C)alkynyl, (3- 8C)cycloalkyl, (3-8C)cycloalkyl-(1 -2C)alkyl or aryl, wherein said aryl group is optionally substituted by 1 , 2 or 3 (1 -3C) alkyl groups; R3 is selected from the group consisting of hydrogen, hydroxyl, (1 -3C)alkyl optionally substituted by one or more hydroxyl groups, or a mono- or di-saccharide moiety; R4 is selected from the group consisting of hydroxyl or (1 -3C)alkyl optionally substituted by one or more hydroxyl groups; R5 is selected from the group consisting of hydroxyl or (1 -3C)alkyl optionally substituted by one or more hydroxyl groups; or a pharmaceutically acceptable salt thereof; for use as a positive allosteric modulator of the a7 nicotinic acetylcholine receptor. 2. A compound according to claim 1 , wherein is =N-ORa (wherein Ra is hydrogen or methyl). 3. A compound according to claim 2, wherein is =N-0-CH3. 4. A compound according to any one of the preceding claims, wherein R2 is selected from the group consisting of (1 -8C)alkyl or (2-8C)alkenyl. 5. A compound according to claim 4, wherein R2 is -C(CH3)=CH-CH(CH3)2. 6. A compound according to any one of the preceding claims, wherein R3 is selected from hydrogen, hydroxyl or methyl. 7. A compound according to claim 6, wherein R3 is hydrogen. 8. A compound according to any one of the preceding claims, wherein R4 is selected from hydroxyl or (1 -3C)alkyl. 9. A compound according to claim 8, wherein R4 is methyl. 10. A compound according to any one of the preceding claims, wherein R5 is selected from hydroxyl or (1 -3C)alkyl. 1 1 . A compound according to claim 10, wherein R5 is methyl. 12. A compound according to claim 1 , which is moxidectin or a pharmaceutically acceptable salt or solvate thereof. 13. A pharmaceutical composition comprising a compound according to any one of claims 1 to 12 together, or a pharmaceutically acceptable salt or solvate thereof, with a pharmaceutically acceptable diluent or excipient for use as a positive allosteric modulator of the alpha-7 nicotinic acetylcholine receptor. 14. A method of providing a positive allosteric modulation effect to the alpha-7 nicotinic acetylcholine receptors in an individual, said method comprising administering to said individual an effective amount of a compound of formula I, or a pharmaceutically acceptable salt thereof, as defined in any one of claims 1 to 12 or a pharmaceutically acceptable salt or solvate thereof, or a pharmaceutical composition as defined in claim 13. 15. A compound according to any one of claims 1 to 12 or a pharmaceutically acceptable salt or solvate thereof, or a pharmaceutical composition according to claim 13, for use in the treatment of a disease or condition associated with a decline in alpha-7 nicotinic acetylcholine receptor activity. 16. A compound or a pharmaceutically acceptable salt or solvate thereof or a pharmaceutical composition according to claim 15, wherein said disease or condition is selected from Alzheimer's disease, schizophrenia, nicotine and other drug addiction, pain, anxiety and depression. 17. A method of treating a disease or condition associated with a decline in alpha-7 nicotinic acetylcholine receptor activity in a patient in need of such treatment, the method comprising administering a therapeutically effective amount of a compound of formula I or a pharmaceutical salt thereof as defined in any one of claims 1 to 12, or a pharmaceutical composition as defined in claim 13, to an individual in need of such treatment. 18. A method according to claim 17, wherein said disease or condition is selected from Alzheimer's disease, schizophrenia, nicotine and other drug addiction, pain, anxiety and depression. |
[0001] The present invention relates to a new therapeutic use of milbemycin derivatives. More specifically, the present invention relates to the use of certain milbemycin derivatives as positive allosteric modulators of the alpha-7 nicotinic acetylcholine receptor.
BACKGROUND
[0002] The alpha-7 nicotinic acetyl choline receptor is a member of the family of ligand-gated ion channels, which mediate "fast" (millisecond timescale) synaptic transmission or signalling (Lindstrom, 1997). It is a pentameric protein comprised of five polypeptide subunits, aligned around a channel or pore that traverses the membrane lipid bilayer.
[0003] The binding of the ligand agonist acetylcholine increases the probability of receptor activation, and the transient opening of the channel to permit cationic conductance to occur. After activation, the channel enters a refractory state during which it is insensitive to acetylcholine and is unable to conduct cations.
[0004] In addition to the agonist binding site, there are distinct allosteric modulatory sites that can influence the probability of receptor activation in response to acetylcholine (Albuquerque et at., 1997). Allosteric modulators can also influence the kinetics of receptor activation and desensitisation and the duration of this refractory state.
[0005] Importantly, in diseases such as Schizophrenia and Alzheimer's disease there is a diminished expression of functional alpha-7 nicotinic acetylcholine receptors (Deutsch et at., 2005). There are defects in sensory gating linked to the alpha-7 nicotinic acetylcholine receptor that contribute to the cognitive and attention deficits of Schizophrenia. There is also evidence to suggest that activation of the alpha-7 nicotinic acetylcholine receptor is neuroprotective against β-amyloid peptide Αβ1 -42 neurotoxicity (Buckingham et at., 2009), which is thought to play a causal role in Alzheimer's disease. The alpha-7 nicotinic acetylcholine receptor is also thought to be involved in nicotine and other drug addiction (Salas et at., 2007), pain (Bertrand & Gopalakrishnan, 2007), anxiety and depression (Nomikos et al., 2000 & Levin et al., 2006).
[0006] Positive allosteric modulators (PAMs) of the alpha-7 nicotinic acetylcholine receptor may improve defective signal transduction in these CNS conditions by increasing the frequency and duration of channel opening. In particular, it is hoped that PAMs of the alpha-7 nicotinic acetylcholine receptor will help maintain the lower number of functional receptors in Alzheimer's disease and schizophrenia patients in a responsive state, whilst at the same time preserving the integrity of cholinergic neuronal transmission.
[0007] The molecule ivermectin belongs to the avermectin family of compounds, which are widely used as insecticides by the agricultural industry. In addition to its primary pesticidal activity, ivermectin is coincidentally also known to be a weak PAM of alpha-7 nicotinic acetylcholine receptor (Sattelle et al., 2009).
[0008] It is an object of the present invention to provide compounds that are potent PAMs of the alpha-7 nicotinic acetylcholine receptor.
[0009] It is a further object of the invention to provide compounds that are PAMs that are potential therapeutic agents for the treatment of diseases or conditions that are associated with a decline in alpha-7 nicotinic acetylcholine receptor function, including diseases such as, for example, Alzheimer's disease and schizophrenia.
BRIEF SUMMARY OF THE DISCLOSURE
[0010] Thus, the present invention provides, in a first aspect, a compound of formula I
(I)
wherein
represents an optional double bond;
Ri is selected from the group consisting of:
=N-OR a ; -CH 2 -0-R a ;
-CH 2 -NR a R b ;
-C(0)0-R a ;
-C(0)NR a R b ; or
-0-N=CR a R b ;
wherein R a and R b are each independently selected from hydrogen or (1 -3C)alkyl which is optionally substituted by one or more substituents independently selected from hydroxyl, amino, nitro, cyano, fluoro, CF 3 , methoxy or carboxy;
R 2 is selected from the group consisting of (1 -10C)alkyl, (2-10C)alkenyl, (2-10C)alkynyl, (3- 8C)cycloalkyl, (3-8C)cycloalkyl-(1 -2C)alkyl or aryl, wherein said aryl group is optionally substituted by 1 , 2 or 3 (1 -3C)alkyl groups;
R 3 is selected from the group consisting of hydrogen, hydroxyl, (1 -3C)alkyl optionally substituted by one or more hydroxyl groups, or a mono- or di-saccharide moiety;
R 4 is selected from the group consisting of hydroxyl or (1 -3C)alkyl optionally substituted by one or more hydroxyl groups;
R 5 is selected from the group consisting of hydroxyl or (1 -3C)alkyl optionally substituted by one or more hydroxyl groups;
or a pharmaceutically acceptable salt or solvate thereof;
for use as a positive allosteric modulator of the alpha-7 nicotinic acetylcholine receptor.
[0011 ] The compounds of formula I are surprisingly potent PAMs of the alpha-7 nicotinic acetylcholine receptor.
[0012] The compounds of formula I are milbemycin derivatives. Milbemycin derivatives are chemically related to the avermectins, such as ivermectin, and are also used primarily as insecticides or antiparasitic agents. One particular milbemycin derivative of formula I is moxidectin (or milbemycin B), which is registered worldwide as a veterinary antiparasitic agent for use in companion and farm animals (brand names include: ProHeart®, Cydectin®, Quest®, Equest®). Moxidectin is also currently being developed for use as a human therapeutic to treat onchocerciasis, the disease caused by the parasitic filaria worm that eventually gives rise to river blindness.
[0013] In a further aspect, the present invention provides a method of providing a positive allosteric modulation effect to alpha-7 nicotinic acetylcholine receptors in an individual, said method comprising administering to said individual an effective amount of a compound of formula I, or a pharmaceutically acceptable salt thereof, as defined herein. [0014] In a further aspect, the present invention provides the use of a compound of formula I, or a pharmaceutically acceptable salt thereof, in the manufacture of a medicament for use as a positive allosteric modulator of the alpha-7 nicotinic acetylcholine receptor.
[0015] In another aspect, the present invention provides a compound of formula I, or a pharmaceutically acceptable salt thereof, for use in the treatment of a disease or condition associated with a decline in alpha-7 nicotinic acetylcholine receptor activity.
[0016] In another aspect, the present invention provides a pharmaceutical composition comprising a compound of formula I, or a pharmaceutically acceptable salt thereof, as defined herein, together with a pharmaceutically acceptable excipient for use in the treatment of a disease or condition associated with a decline in alpha-7 nicotinic acetylcholine receptor activity.
[0017] In another aspect the present invention provides a method of treating a condition associated with a decline in alpha-7 nicotinic acetylcholine receptor activity in a subject in need of such treatment, the method comprising administering a therapeutically effective amount of a compound of formula I, or a pharmaceutically acceptable salt thereof, as defined herein, or a pharmaceutical composition as defined herein, to said subject.
[0018] In another aspect, the present invention provides the use of a compound of formula I, or a pharmaceutically acceptable salt thereof, as defined herein in the manufacture of a medicament for use in the treatment of a disease or condition associated with a decline in alpha-7 nicotinic acetylcholine receptor activity.
DETAILED DESCRIPTION Definitions
[0019] In this specification the following definitions apply to the following terms, unless they are defined otherwise elsewhere in the specification:
[0020] The term "alkyl" includes both straight and branched chain alkyl groups. For example, "(1 -3C)alkyl" includes methyl, ethyl, propyl and isopropyl. References to individual alkyl groups such as "propyl" are specific for the straight chain version only and references to individual branched chain alkyl groups such as "isopropyl" are specific for the branched chain version only.
[0021 ] The terms "alkenyl" and "alkynyl" also include both straight and branched alkenyl or alkenyl chains respectively.
[0022] The term "(3-8C)cycloalkyl" means a hydrocarbon ring containing from 3 to 8 carbon atoms, for example, cyclopropyl, cyclobutyl, cyclopentyl, cyclohexyl or bicyclo[2.2.1 ]heptyl. [0023] The term "(3-8C)cycloalkyl-(1 -2C)alkyl" means a substituent group comprising a cycloalkyi group moiety having 3 to 8 carbon atoms linked via a methylene or ethylene linker group. Suitable examples of such substituents include cyclopropylmethyl, cyclopropylethyl, cyclobutylmethyl and/or cyclopentylmethyl.
[0024] The term "monosaccharide moiety" refers to any known monosaccharide sugar unit. Examples of monosaccharides include glucose, fructose, galactose, xylose and ribose.
[0025] The term "disaccharide moiety" refers to carbohydrates formed by the covalent bonding of two monosaccharide units. Examples of disaccharides include sucrose, lactulose, lactose, maltose and trehalose.
[0026] The term "aryl" means phenyl and naphthyl, especially phenyl.
[0027] References to "treatment" herein include prophylaxis as well as the alleviation of established symptoms of a condition. Hence, "treating" or "treatment" of a state, disorder or condition includes: (1 ) preventing or delaying the appearance of clinical symptoms of the state, disorder or condition developing in a human that may be afflicted with or predisposed to the state, disorder or condition but does not yet experience or display clinical or subclinical symptoms of the state, disorder or condition, (2) inhibiting the state, disorder or condition, i.e. arresting, reducing or delaying the development of the disease or a relapse thereof (in case of maintenance treatment) or at least one clinical or subclinical symptom thereof, or (3) relieving or attenuating the disease, i.e. causing regression of the state, disorder or condition or at least one of its clinical or subclinical symptoms.
Milbemycin derivatives
[0028] As stated above, the present invention relates to milbemycin derivatives of formula I as defined herein, which are potent PAMs of the alpha-7 nicotinic acetylcholine receptor.
[0029] Particular milbemycin derivatives of the invention include, for example, derivatives of formula I, or pharmaceutically acceptable salts thereof, wherein, unless otherwise stated, each of R 1 ; R 2 , R 3 , R 4 , R 5 , R a and R b have any of the meanings defined hereinbefore or in paragraphs (a) to (z) hereinafter:
(a) Ri is selected from the group consisting of:
=N-OR a ;
-CH 2 -0-R a ;
-CH 2 -NR a R b ;
-C(0)0-R a ; -C(0)NR a R b ; or
-0-N=CR a R b ;
wherein R a and R b are each independently selected from hydrogen or (1 -3C)alkyl;
(b) Ri is selected from the group consisting of:
=N-OR a ;
-CH 2 -0-R a ;
-CH 2 -NR a R b ;
-C(0)0-R a ;
-C(0)NR a R b ; or
wherein R a and R b are each independently selected from hydrogen or (1 -3C)alkyl which is optionally substituted by one or more substituents independently selected from hydroxyl, amino, fluoro, CF 3 , or methoxy;
(c) Ri is selected from the group consisting of:
=N-OR a ;
-CH 2 -0-R a ;
-CH 2 -NR a R b ;
-C(0)0-R a ;
-C(0)NR a R b ; or
wherein R a and R b are each independently selected from hydrogen or (1 -3C)alkyl;
(d) Ri is selected from the group consisting:
=N-OR a ;
-CH 2 -0-R a ;
-CH 2 -NR a R b ;
-C(0)0-R a ;
-C(0)NR a R b ; or
wherein R a and R b are each independently selected from hydrogen or methyl;
(e) Ri is =N-OR a (wherein R a is hydrogen or methyl);
(f) Ri is =N-OR a (wherein R a is methyl); (g) R 2 is selected from the group consisting of (1 -8C)alkyl, (2-8C)alkenyl, (2-8C)alkynyl, (3- 6C)cycloalkyl, (3-6C)cycloalkyl-(1 -2C)alkyl or phenyl, wherein said phenyl group is optionally substituted by 1 , 2 or 3 (1 -2C)alkyl groups;
(h) R 2 is selected from the group consisting of (1 -6C)alkyl, (2-6C)alkenyl, (2-6C)alkynyl, (3- 6C)cycloalkyl, (3-6C)cycloalkyl-(1 -2C)alkyl or phenyl, wherein said phenyl group is optionally substituted by 1 or 2 (1 -2C)alkyl groups;
(i) R 2 is selected from the group consisting of (1 -6C)alkyl, (2-6C)alkenyl, (2-6C)alkynyl, (3- 6C)cycloalkyl, (3-6C)cycloalkyl-(1 -2C)alkyl or toluenyl;
(j) R 2 is selected from the group consisting of (1 -6C)alkyl or (2-6C)alkenyl or (3- 6C)cycloalkyl;
(k) R 2 is (2-8C)alkenyl;
(I) R 2 is -C(CH 3 )=CH-CH(CH 3 ) 2 ;
(m) R 3 is selected from the group consisting of hydrogen, hydroxyl, (1 -3C)alkyl, or a mono- or di-saccharide moiety
(n) R 3 is selected from hydrogen, hydroxyl, or (1 -3C)alkyl;
(o) R 3 is selected from hydrogen, hydroxyl or methyl;
(p) R 3 is hydrogen;
(q) R 4 is selected from hydroxyl or (1 -3C)alkyl optionally substituted by hydroxyl;
(r) R 4 is (1 -3C)alkyl optionally substituted by hydroxyl;
(s) R 4 is (1 -3C)alkyl;
(t) R 4 is methyl;
(u) R 5 is selected from hydroxyl or (1 -3C)alkyl;
(v) R 5 is (1 -3C)alkyl;
(w) R 5 is methyl;
(x) R a is hydrogen or methyl;
(y) R a is methyl;
(z) R b is hydrogen or methyl.
[0030] In a group of compounds of formula I, and where appropriate given the nature of the Ri substituent group, the optional double bond represented by is a double bond. [0031] In a particular group of compounds of formula I, the optional double bond represented by is a single bond.
[0032] In a particular group of compounds of formula I, the carbon atom to which is attached is sp 2 hybridised.
[0033] In a particular group of compounds of formula I, is a moiety that functions as a hydrogen bond acceptor.
[0034] In a particular group of compounds of the present invention, the optional double bond represented by is a single bond and is =N-0-CH 3 ; i.e. the compounds have the structural formula IA shown below:
IA
wherein R 2 , R 3 , R 4 and R 5 each have any one of the definitions set out hereinbefore.
[0035] A particular example of a compound of formula I is:
Moxidectin or a pharmaceutically acceptable salt or solvate thereof.
[0036] A particularly preferred compound of formula I is moxidectin or a pharmaceutically acceptable salt or solvate thereof.
[0037] Moxidectin has previously shown a good safety and tolerability profile in human clinical trials (Cotreau et al., 2003) for its use as an antiparasitic, making it an ideal candidate drug for the treatment of long-term chronic CNS conditions too.
[0038] It is to be understood that, insofar as certain of the compounds of formula I defined above may exist in optically active or racemic forms by virtue of one or more asymmetric carbon atoms, the invention includes in its definition any such optically active or racemic form which possesses the above-mentioned positive allosteric modulation activity at the alpha-7 nicotinic acetylcholine receptor. The synthesis of optically active forms may be carried out by standard techniques of organic chemistry well known in the art, for example by synthesis from optically active starting materials or by resolution of a racemic form. Similarly, the above-mentioned positive allosteric modulation activity at the alpha-7 nicotinic acetylcholine receptor may be evaluated using the standard laboratory techniques referred to in the accompanying Example.
[0039] It is to be understood that certain compounds of formula I defined above may exhibit the phenomenon of tautomerism. It is to be understood that the present invention includes in its definition any such tautomeric form, or a mixture thereof, which possesses the above-mentioned activity and is not to be limited merely to any one tautomeric form utilised within the formulae drawings or named in the Example.
[0040] A suitable pharmaceutically-acceptable salt of a compound of the formula I is, for example, an acid-addition salt of a compound of the formula I, for example an acid-addition salt with an inorganic or organic acid such as hydrochloric, hydrobromic, sulphuric, trifluoroacetic, citric or maleic acid; or, for example, a salt of a compound of the formula I which is sufficiently acidic, for example an alkali or alkaline earth metal salt such as a calcium or magnesium salt, or an ammonium salt, or a salt with an organic base such as methylamine, dimethylamine, trimethylamine, piperidine, morpholine or tris-(2-hydroxyethyl)amine. A further suitable pharmaceutically-acceptable salt of a compound of the formula I is, for example, a salt formed within the human or animal body after administration of a compound of the formula I.
[0041 ] The compounds of formula I may exist in a suitable solvated form. A suitable pharmaceutically-acceptable solvate of a compound of the formula I is, for example, a hydrate such as a hemi-hydrate, a mono-hydrate, a di-hydrate or a tri-hydrate or an alternative hydration quantity thereof.
[0042] The compounds of formula I may be administered in the form of a pro-drug, which is a compound that is broken down in the human or animal body to release a compound of the invention. A pro-drug may be used to alter the physical properties and/or the pharmacokinetic properties of a compound of the invention. A pro-drug can be formed when the compound of the invention contains a suitable group or substituent to which a property-modifying group can be attached. Examples of pro-drugs include in vivo cleavable ester derivatives that may be formed at a carboxy group or a hydroxy group in a compound of the formula I and in vivo cleavable amide derivatives that may be formed at a carboxy group or an amino group in a compound of the formula I.
[0043] Accordingly, the present invention includes those compounds of the formula I as defined hereinbefore when made available by organic synthesis and when made available within the human or animal body by way of cleavage of a pro-drug thereof. Accordingly, the present invention includes those compounds of the formula I that are produced by organic synthetic means and also such compounds that are produced in the human or animal body by way of metabolism of a precursor compound, that is a compound of the formula I may be a synthetically-produced compound or a metabolically-produced compound.
[0044] A suitable pharmaceutically-acceptable pro-drug of a compound of the formula I is one that is based on reasonable medical judgement as being suitable for administration to the human or animal body without undesirable pharmacological activities and without undue toxicity.
[0045] Various forms of pro-drug have been described, for example in the following documents :- a) Methods in Enzymoloqy, Vol. 42, p. 309-396, edited by K. Widder, et al. (Academic Press, 1985); b) Design of Pro-drugs, edited by H. Bundgaard, (Elsevier, 1985);
c) A Textbook of Drug Design and Development, edited by Krogsgaard-Larsen and H. Bundgaard, Chapter 5 "Design and Application of Pro-drugs", by H. Bundgaard p. 1 13-191 (1991 );
d) H. Bundgaard, Advanced Drug Delivery Reviews, 8, 1 -38 (1992);
e) H. Bundgaard, et al., Journal of Pharmaceutical Sciences, 77, 285 (1988);
f) N. Kakeya, et al., Chem. Pharm. Bull., 32, 692 (1984);
g) T. Higuchi and V. Stella, "Pro-Drugs as Novel Delivery Systems", A.C.S. Symposium Series, Volume 14; and
h) E. Roche (editor), "Bioreversible Carriers in Drug Design", Pergamon Press, 1987.
[0046] A suitable pharmaceutically-acceptable pro-drug of a compound of the formula I that possesses a carboxy group is, for example, an in vivo cleavable ester or amide thereof. Suitable pharmaceutically-acceptable esters for carboxy include (1 -6C)alkyl esters such as methyl, ethyl and terf-butyl esters and suitable amides include amides formed with an amine such as ammonia, a (1 -4C)alkylamine such as methylamine, a di-(1 -4C)alkylamine such as dimethylamine, A/-ethyl-/V-methylamine or diethylamine.
[0047] A suitable pharmaceutically-acceptable pro-drug of a compound of the formula I that possesses a hydroxy group is, for example, an in vivo cleavable ester or ether thereof. Suitable pharmaceutically-acceptable ester forming groups for a hydroxy group include inorganic esters such as phosphate esters (including phosphoramidic cyclic esters).
[0048] A suitable pharmaceutically-acceptable pro-drug of a compound of the formula I that possesses an amino group is, for example, an in vivo cleavable amide derivative thereof. Suitable pharmaceutically-acceptable amides from an amino group include, for example an amide formed with (1 -10C)alkanoyl groups such as an acetyl or benzoyl.
Synthesis
[0049] The compounds of the present invention can be sourced commercially or otherwise prepared by techniques known in the art. In particular, various alternative derivatives of compounds of formula I can be made by chemically modifying compounds sourced commercially to introduce different substituent groups. Pharmaceutical compositions
[0050] Compounds of the invention intended for pharmaceutical use may be administered as crystalline or amorphous products. They may be obtained, for example, as solid plugs, powders, or films by methods such as precipitation, crystallization, freeze drying, or spray drying, or evaporative drying. Microwave or radio frequency drying may be used for this purpose.
[0051 ] They may be administered alone or in combination with one or more other compounds of the invention or in combination with one or more other drugs. Generally, they will be administered as a formulation in association with one or more pharmaceutically acceptable excipients.
[0052] Thus, according to an aspect of the invention there is provided a pharmaceutical composition which comprises a compound of the formula I, or a pharmaceutically acceptable salt thereof, as defined hereinbefore in association with a pharmaceutically acceptable excipient for use in the positive allosteric modulation of the alpha-7 nicotinic acetylcholine receptor.
[0053] In a further aspect of the invention, there is provided a pharmaceutical composition which comprises a compound of the formula I, or a pharmaceutically acceptable salt thereof, as defined hereinbefore in association with a pharmaceutically acceptable excipient for use in the treatment of a disease or condition associated with a decline in alpha-7 nicotinic acetylcholine receptor activity.
[0054] Pharmaceutically acceptable excipients include one or more of: fillers, diluents, antioxidants, colourants, flavouring agents, preservatives and taste-masking agents.
[0055] Pharmaceutical compositions suitable for the delivery of compounds of the present invention and methods for their preparation will be readily apparent to those skilled in the art. Such compositions and methods for their preparation may be found, for example, in 'Remington's Pharmaceutical Sciences', 19th Edition (Mack Publishing Company, 1995). The formulation of tablets is discussed in "Pharmaceutical Dosage Forms: Tablets, Vol. 1 ", by H. Lieberman and L. Lachman, Marcel Dekker, N.Y., N.Y., 1980 (ISBN 0-8247-6918-X).
[0056] The methods by which the compounds may be administered include oral administration by capsule, bolus, tablet, powders, lozenges, chews, multi and nanoparticulates, gels, solid solution, films, sprays, or liquid formulation. Liquid forms include suspensions, solutions, and syrups. Such formulations may be employed as fillers in soft or hard capsules and typically comprise a carrier, for example, water, ethanol, polyethylene glycol, propylene glycol, methylcellulose, or a suitable oil, and one or more emulsifying agents and/or suspending agents. Liquid formulations may also be prepared by the reconstitution of a solid preparation, for example, from a sachet.
[0057] The compounds can also be administered parenterally, or by injection directly into the blood stream, muscle or into an internal organ. Suitable means for parenteral administration include intravenous, intraarterial, intraperitoneal, intrathecal, intraventricular, intraurethral, intrasternal, intracranial, intramuscular and subcutaneous. Suitable devices for parenteral administration include needle (including microneedle) injectors, needle-free injectors and infusion techniques.
[0058] Formulations may be immediate and/or modified controlled release. Controlled release formulations include: delayed-, sustained-, and pulsed-release formulations.
[0059] The amount of active ingredient that is combined with one or more excipients to produce a single dosage form will necessarily vary depending upon the host treated and the particular route of administration. For example, a formulation intended for oral administration to humans will generally contain, for example, from 0.5 mg to 0.5 g of active agent (more suitably from 0.5 to 100 mg, for example from 1 to 30 mg) compounded with an appropriate and convenient amount of excipients which may vary from about 5 to about 98 percent by weight of the total composition.
[0060] The size of the dose for therapeutic or prophylactic purposes of a compound of the formula I will naturally vary according to the nature and severity of the conditions, the age and sex of the animal or patient and the route of administration, according to well known principles of medicine.
Therapeutic Uses
[0061 ] The alpha-7 nicotinic acetylcholine receptor is located in the brain, where activation yields post- and pre-synaptic excitation, mainly by increased Ca 2+ permeability. Accordingly, the positive allosteric modulation of this receptor is potentially useful therapeutically for the treatment of diseases or conditions of the central nervous system associated with a decrease in alpha-7 nicotinic acetylcholine receptor activity.
[0062] Particular diseases or conditions in which the positive allosteric modulation of the alpha-7 nicotinic acetylcholine receptor is potentially beneficial therefore include Alzheimer's disease (Deutsch et al, 2005 & Buckingham et al, 2009), schizophrenia (Deutsch et al, 2005), nicotine and other drug addiction (Salas et al, 2007), pain (Bertrand & Gopalakrishnan, 2007), anxiety and depression (Nomikos et al. 2000, Levin et al. 2006).
[0063] Accordingly, compounds of formula I defined herein are potentially useful agents for the treatment of Alzheimer's disease, schizophrenia, nicotine and other drug addiction, pain, anxiety and depression.
[0064] Therefore, in an embodiment, the present invention provides a method of treating Alzheimer's disease, schizophrenia, nicotine and other drug addiction, pain, anxiety and depression in a patient in need of such treatment, the method comprising administering a therapeutically effective amount of a compound of formula I or a pharmaceutical salt thereof, or a pharmaceutical composition as defined herein, to an individual in need of such treatment.
[0065] In a further embodiment, the present invention provides a compound of formula I or a pharmaceutically acceptable salt thereof, or a pharmaceutical composition as defined herein, for use in the treatment of Alzheimer's disease, schizophrenia, nicotine and other drug addiction, pain, anxiety and depression.
[0066] In yet another embodiment, the present invention provides the use of a compound of formula I or a pharmaceutically acceptable salt thereof, or a pharmaceutical composition as defined herein, in the manufacture of a medicament for use in the treatment of Alzheimer's disease, schizophrenia, nicotine and other drug addiction, pain, anxiety and depression.
[0067] In an embodiment, the compound of formula I is for the treatment of Alzheimer's disease.
[0068] In an embodiment, the compound of formula I is for the treatment of schizophrenia.
[0069] In an embodiment, the compound of formula I is for the treatment of nicotine or other drug addiction.
[0070] In an embodiment, the compound of formula I is for the treatment of pain.
[0071 ] In an embodiment, the compound of formula I is for the treatment of anxiety.
[0072] In an embodiment, the compound of formula I is for the treatment of depression
[0073] In using a compound of the formula I for therapeutic or prophylactic purposes it will generally be administered so that a daily dose in the range, for example, 0.1 mg/kg to 75 mg/kg body weight is received, given, if required, in divided doses. In general lower doses will be administered when a parenteral route is employed. Thus, for example, for intravenous or intraperitoneal administration, a dose in the range, for example, 0.1 mg/kg to 30 mg/kg body weight will generally be used. Similarly, for administration by inhalation, a dose in the range, for example, 0.05 mg/kg to 25 mg/kg body weight will be used. Oral administration may also be suitable, particularly in tablet form. Typically, unit dosage forms will contain about 0.5 mg to 0.5 g of a compound of this invention. EXAMPLES
[0074] The invention will now be described in more detail in relation to the following illustrative examples.
Example 1
Materials
[0075] Ivermectin and moxidectin were both sourced commercially from Sigma (Poole, UK). Methods
[0076] To test the relative activity of ivermectin (comparator) and moxidectin (compound of formula I), both compounds were tested in a cell-based assay employing patch-clamp electrophysiology on xenopus oocytes expressing human alpha-7 nicotinic acetylcholine receptor. This assay has been well validated and is able to discriminate between agonists and positive allosteric modulators with high reproducibility and sensitivity (Sattelle et al, 2009).
[0077] The following experimental protocol was followed:
[0078] The vectors pcDNA3.1 /Zeo+ (Invitrogen) encoding human a 7 nicotinic acetyl choline receptor or C. elegans ric-3 (whose co-expression is required for the maturation of the al receptor) were linearised to provide templates for cRNA synthesis with the T7 (pCDNA3.1 ) mMESSAGE mMACHINE kits (Ambion).
[0079] Mature stage IV or V Xenopus laevis oocytes were manually defolliculated after incubation for 1 h in 2 mg/ml collagenase (Sigma type IV) in calcium-free oocyte saline (OS) containing 100 mM NaCI, 2mM KCI, 1 .8mM CaCI 2 , 1 mM MgCI 2 , 5mM HEPES, adjusted to pH 7.6 with 5 M NaOH.
[0080] Following defolliculation, the cytoplasm of each oocyte was injected with 50 nl 1 ng/nl containing a 5:1 ratio of alpha-7 receptor cRNA:ric-3 cRNA in RNAase-free dH 2 0. Oocytes were incubated for 2-7 days in filter-sterilized culture medium consisting of OS supplemented with 100 units/ml of penicillin, 100 mg/ml of streptomycin and 50 mg/ml gentamycin sulphate and 2.5 mM sodium pyruvate, the medium being changed daily.
[0081 ] After 2-7 days incubation, injected oocytes were transferred to a recording chamber (Warner type RC-3Z) for electrophysiological analysis. Oocytes were impaled with two glass microelectrodes (3 M KCI, resistance 0.5-1 MV in OS) and held under voltage clamp at -100 mV. Standard two-electrode voltage clamp was achieved using an Axon Axoclamp 900A amplifier under the control of a laboratory PC. Signals were acquired at 1 kHz. Saline and drugs were applied through a gravity-fed perfusion system (Valvelink 8.2) using computer-controlled pinch valves.
[0082] Relatively high perfusion rates (5 ml/min), low saline levels in the chamber and a short distance between the perfusion manifold and the chamber, were used to achieve consistent amplitude, rapid onset responses in oocytes expressing the rapidly desensitizing alpha-7 nicotinic acetylcholine receptor. Agonists were applied for 10 s, and the effects of allosteric modulators were assessed by applying the drug for 10 s immediately prior to a 10 s test application of agonist in the continued presence of modulator. Agonist challenges were at 2 min intervals to minimize any effects of desensitization. Oocytes were only used in experiments if the amplitudes of responses to successive challenges of agonist differed by 10% or less.
Results
[0083] The amplitude of the response for ivermectin modulation relative to the control (agonist alone - 100μΜ acetyl choline) is shown in Figure 1 . The amplitude of the response for moxidectin modulation relative to the control (agonist alone - 100μΜ acetyl choline) is shown in Figure 2. It is evident from the data shown in Figures 1 and 2 that moxidectin is a much more potent positive allosteric modulator (PAM) for the alpha-7 nicotinic acetylcholine receptor when compared to ivermectin.
[0084] The level of signal induction with agonist alone (100μΜ acetyl choline) gave a baseline response that was set at 100%. In the presence of the known PAM ivermectin (at 20μΜ), signalling activity in response to the agonist was on average 170% of the baseline level (a 0.7- fold increase). In contrast, co-incubation with moxidectin (also at 20μΜ) gave an average response that was approximately 500% above baseline (a 5-fold increase). The PAM activity of moxidectin on the response of alpha-7 nicotinic acetylcholine receptor to the natural agonist acetyl choline is therefore six times greater than that of ivermectin at the concentrations tested.
[0085] The activity profile shows no alteration to the duration of signalling or the subsequent refractory period, which is consistent with moxidectin being a particularly potent Type I PAM.
[0086] The results for moxidectin showed a surprisingly high level of alpha-7 nicotinic acetylcholine receptor PAM activity compared to ivermectin in cell-based bioassays.
Example 2
Materials
[0087] Ivermectin and moxidectin were sourced commercially from Sigma (Poole, UK). Nemadectin was sourced commercially from Bioaustralis (Smithfield, Australis). Methods
[0088] Further testing of the relative activity of ivermectin (comparator) and moxidectin (a compound of formula I) was carried out using a protocol similar to that described above in Example 1 (see below). Nemadactin (an additional comparator) was also tested.
[0089] Oocytes were injected with mRNA encoding human alpha-7 nAChr. After 3-5 days' incubation at ~\ 8°C oocytes were used for assay using two electrode voltage clamp. Oocytes were secured in a low volume chamber (<0.1 ml) designed for the rapid bath-application of ACh required for accurate measurements of alpha-7-mediated responses and perfused at ~5ml/min with Standard Oocyte Saline (SOS). Oocytes were impaled with two electrodes (resistance about 1 mQ when filled with 3M KCI) and voltage clamped at -100mV. Oocytes were exposed to 7s applications of 100μΜ ACh every 2 min. Test compounds diluted from DMSO stock to 30μΜ were applied for 60s before challenging the oocyte with ACh along with the test compound. The peak amplitude of the ACh-induced current in the presence of the test compound was divided by the mean of the peak amplitudes of the flanking ACh challenges to reduce the effects of rundown or other slow changes in responsiveness of the oocytes.
[0090] The amplitude of the response observed with agonist alone (100μΜ acetyl choline), an agonist wash, and the agonist plus compound (ivermectin, moxidectin or nemadectin) was assessed.
Results
[0091 ] The results are shown in Table 1 below. The results are expressed as the mean ratio (+/- the standard error) of the amplitude of the response detected following the application of agonist plus compound (i.e. acetylcholine (100μΜ) with ivermectin, nemadectin or moxidectin) relative to the mean amplitude observed with the agonist alone. Hence, a ratio of 1 indicates that the mean response amplitudes are the same and the compound has no effect on the acetylcholine response. A ratio of greater than 1 indicates an enhancement of the response and a ratio less than 1 indicates a reduction.
Table 1
Compound Mean ratio (+/- SEM)
Ivermectin 3.2 (+/- 1 .5)
Nemadectin 0.9 (+/- 0.1 )
Moxidectin 6.1 (+/- 2.3) [0092] The results for moxidectin showed a surprisingly high level of alpha-7 nicotinic acetylcholine receptor PAM activity compared to ivermectin and nemadectin in this cell-based bioassay.
[0093] In conclusion, the inventors have identified an additional medical use for milbemycin compounds and in particular moxidectin, as novel human therapeutics for treating defects in alpha-7 nicotinic acetylcholine receptor signalling including Alzheimer's disease, schizophrenia, nicotine and other drug addiction, the control of pain, anxiety and depression.
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