BACKGROUND OF THE INVENTION

The present invention relates to amide substituted indazoles which are inhibitors of the enzyme poly(ADP-ribose)polymerase (PARP), previously known as poly(ADP-ribose)synthase and poly(ADP-ribosyl)transferase. The compounds of the present invention are useful as mono-therapies in tumors with specific defects in DNA-repair pathways and as enhancers of certain DNA-damaging agents such as anticancer agents and radiotherapy. Further, the compounds of the present invention are useful for reducing cell necrosis (in stroke and myocardial infarction), down regulating inflammation and tissue injury, treating retroviral infections and protecting against the toxicity of chemotherapy.

Poly(ADP-ribose) polymerase (PARP) constitute a super family of eighteen proteins containing PARP catalytic domains (Bioessays (2004) 26:1148). These proteins include PARP-1, PARP-2, PARP-3, tankyrase-1, tankyrase-2, vaultPARP and TiPARP. PARP-1, the founding member, consists of three main domains: an amino (N)-terminal DNA-binding domain (DBD) containing two zinc fingers, the automodification domain, and a carboxy (C)-terminal catalytic domain.

PARP are nuclear and cytoplasmic enzymes that cleave NAD⁺to nicotinamide and ADP-ribose to form long and branched ADP-ribose polymers on target proteins, including topoisomerases, histones and PARP itself (Biochem. Biophys. Res. Commun. (1998) 245:1-10).

Poly(ADP-ribosyl)ation has been implicated in several biological processes, including DNA repair, gene transcription, cell cycle progression, cell death, chromatin functions and genomic stability.

The catalytic activity of PARP- 1 and PARP-2 has been shown to be promptly stimulated by DNA strand breakages (see Pharmacological Research (2005) 52:25-33). In response to DNA damage, PARP-1 binds to single and double DNA nicks. Under normal physiological conditions there is minimal PARP activity, however, upon DNA damage an immediate activation of PARP activity of up to 500-fold occurs. Both PARP-1 and PARP-2 detect DNA strand interruptions acting as nick sensors, providing rapid signals to halt transcription and recruiting the enzymes required for DNA repair at the site of damage. Since radiotherapy and many chemotherapeutic approaches to cancer therapy act by inducing DNA damage, PARP inhibitors are useful as chemo- and radiosensitizers for cancer treatment. PARP inhibitors have been reported to be effective in radio sensitizing hypoxic tumor cells (U.S. Pat. Nos. 5,032,617, 5,215,738 and 5,041,653).

Most of the biological effects of PARP relate to this poly (ADP-ribosyl)ation process which influences the properties and function of the target proteins; to the PAR oligomers that, when cleaved from poly(ADP-ribosyl)ated proteins, confer distinct cellular effects; the physical association of PARP with nuclear proteins to form functional complexes; and the lowering of the cellular level of its substrate NAD⁺(Nature Review (2005) 4:421-440).

Besides being involved in DNA repair, PARP may also act as a mediator of cell death. Its excessive activation in pathological conditions such as ischemia and reperfusion injury can result in substantial depletion of the intercellular NAD⁺, which can lead to the impairment of several NAD⁺dependent metabolic pathways and result in cell death (see Pharmacological Research (2005) 52:44-59). As a result of PARP activation, NAD⁺levels significantly decline. Extensive PARP activation leads to severe depletion of NAD⁺in cells suffering from massive DNA damage. The short half-life of poly(ADP-ribose) results in a rapid turnover rate, as once poly(ADP-ribose) is formed, it is quickly degraded by the constitutively active poly(ADP-ribose) glycohydrolase (PARG). PARP and PARG form a cycle that converts a large amount of NAD⁺to ADP-ribose, causing a drop of NAD⁺and ATP to less than 20% of the normal level. Such a scenario is especially detrimental during ischemia when deprivation of oxygen has already drastically compromised cellular energy output. Subsequent free radical production during reperfusion is assumed to be a major cause of tissue damage. Part of the ATP drop, which is typical in many organs during ischemia and reperfusion, could be linked to NAD⁺depletion due to poly(ADP-ribose) turnover. Thus, PARP inhibition is expected to preserve the cellular energy level thereby potentiating the survival of ischemic tissues after insult. Compounds which are inhibitors of PARP are therefore useful for treating conditions which result from PARP mediated cell death, including neurological conditions such as stroke, trauma and Parkinson's disease.

PARP inhibitors have been demonstrated as being useful for the specific killing of BRCA-1 and BRCA-2 deficient tumors (Nature (2005) 434:913-916 and 917-921; and Cancer Biology & Therapy (2005) 4:934-936).

PARP inhibitors have been shown to enhance the efficacy of anticancer drugs (Pharmacological Research (2005) 52:25-33), including platinum compounds such as cisplatin and carboplatin (Cancer Chemother Pharmacol (1993) 33:157-162 and Mol Cancer Ther (2003) 2:371-382). PARP inhibitors have been shown to increase the antitumor activity of topoisomerase I inhibitors such as Irinotecan and Topotecan (Mol Cancer Ther (2003) 2:371-382; and Clin Cancer Res (2000) 6:2860-2867) and this has been demonstrated in in vivo models (J Natl Cancer Inst (2004) 96:56-67).

PARP inhibitors have been shown to restore susceptibility to the cytotoxic and antiproliferative effects of temozolomide (TMZ) (see Curr Med Chem (2002) 9:1285-1301 and Med Chem Rev Online (2004) 1:144-150). This has been demonstrated in a number of in vitro models (Br J Cancer (1995) 72:849- 856; Br J Cancer (1996) 74:1030-1036; Mol Pharmacol (1997) 52:249-258; Leukemia (1999) 13:901-909; Glia (2002) 40:44-54; and Clin Cancer Res (2000) 6:2860-2867 and (2004) 10:881-889) and in vivo models (Blood (2002) 99:2241-2244; Clin Cancer Res (2003) 9:5370-5379 and J Natl Cancer Inst (2004) 96:56-67). PAPR inhibitors have also been shown to prevent the appearance of necrosis induced by selective N3-adenine methylating agents such as MeOSO₂(CH₂)-lexitropsin (Me-Lex) (Pharmacological Research (2005) 52:25-33).

PARP inhibitors have been shown to act as radiation sensitizers. PARP inhibitors have been reported to be effective in radiosensitizing (hypoxic) tumor cells and effective in preventing tumor cells from recovering from potentially lethal (Br. J. Cancer (1984) 49(Suppl. VI):34-42; and Int. J. Radiat. Bioi. (1999) 75:91-100) and sub-lethal (Clin. Oncol. (2004) 16(1):29-39) damage of DNA after radiation therapy, presumably by their ability to prevent DNA strand break rejoining and by affecting several DNA damage signaling pathways.

PARP inhibitors have also been shown to be useful for treating acute and chronic myocardial diseases (see Pharmacological Research (2005) 52:34-43). For instance, it has been demonstrated that single injections of PARP inhibitors have reduced the infarct size caused by ischemia and reperfusion of the heart or skeletal muscle in rabbits. In these studies, a single injection of 3-amino-benzamide (10 mg/kg), either one minute before occlusion or one minute before reperfusion, caused similar reductions in infarct size in the heart (32-42%) while 1,5-dihydroxyisoquinoline (1 mg/kg), another PARP inhibitor, reduced infarct size by a comparable degree (38-48%). These results make it reasonable to assume that PARP inhibitors could salvage previously ischemic heart or reperfusion injury of skeletal muscle tissue (PNAS (1997) 94:679-683). Similar findings have also been reported in pigs (Eur. J. Pharmacol. (1998) 359:143-150 and Ann. Thorac. Surg. (2002) 73:575-581) and in dogs (Shock. (2004)21:426-32).

PARP inhibitors have been demonstrated as being useful for treating certain vascular diseases, septic shock, ischemic injury and neurotoxicity (Biochim. Biophys. Acta (1989) 1014:1-7; J. Clin. Invest. (1997) 100: 723-735). Oxygen radical DNA damage that leads to strand breaks in DNA, which are subsequently recognized by PARP, is a major contributing factor to such disease states as shown by PARP inhibitor studies (J. Neurosci. Res. (1994) 39:38-46 and PNAS (1996) 93:4688-4692). PARP has also been demonstrated to play a role in the pathogenesis of hemorrhagic shock (PNAS (2000) 97:10203-10208).

PARP inhibitors have been demonstrated as being useful for treatment of inflammation diseases (see Pharmacological Research (2005) 52:72-82 and 83-92).

It has also been demonstrated that efficient retroviral infection of mammalian cells is blocked by the inhibition of PARP activity. Such inhibition of recombinant retroviral vector infections has been shown to occur in various different cell types (J. Virology, (1996) 70(6):3992-4000). Inhibitors of PARP have thus been developed for use in anti-viral therapies and in cancer treatment (WO 91/18591).

In vitro and in vivo experiments have demonstrated that PARP inhibitors can be used for the treatment or prevention of autoimmune diseases such as Type I diabetes and diabetic complications (Pharmacological Research (2005) 52:60-71).

PARP inhibition has been speculated as delaying the onset of aging characteristics in human fibroblasts (Biochem. Biophys. Res. Comm. (1994) 201(2):665-672 and Pharmacological Research (2005) 52:93-99). This may be related to the role that PARP plays in controlling telomere function (Nature Gen., (1999) 23(1):76-80).

The vast majority of PARP inhibitors to date interact with the nicotinamide binding domain of the enzyme and behave as competitive inhibitors with respect to NAD⁺(Expert Opin. Ther. Patents (2004) 14:1531-1551). Structural analogues of nicotinamide, such as benzamide and derivatives were among the first compounds to be investigated as PARP inhibitors. However, these molecules have a weak inhibitory activity and possess other effects unrelated to PARP inhibition. Thus, there is a need to provide potent inhibitors of the PARP enzyme.

Structurally related PARP inhibitors have previously been described. WO 1999/59973 discloses amide substituted benzene rings fused to 5 membered heteroaromatic rings; WO02001/85687 discloses amide substituted indoles; WO 1997/04771, WO 2000/26192, WO 2000/32579, WO 2000/64878, WO 2000/68206, WO 2001/21615, WO 2002/068407, WO 2003/106430 and WO 2004/096793 disclose amide substituted benzoimidazoles; WO 2000/29384 discloses amide substituted benzoimidazoles and indoles; and EP 0879820 discloses amide substituted benzoxazoles.

It has now surprisingly been discovered that amide substituted indazoles of the present invention exhibit particularly high levels of inibition of the activity of poly(ADP-ribose)polymerase (PARP). Thus the compounds of the present invention are particularly useful as inhibitors of PARP- 1 and/or PARP-2. They also show particularly good levels of cellular activity, demonstrating good anti-proliferative effects in BRCA1 and BRCA2 deficient cell lines.

The present invention provides compounds of formula I:

wherein:

- R¹is hydrogen or fluorine; and
- R²is hydrogen or fluorine; or pharmaceutically acceptable salts, stereoisomers or tautomers thereof.
- In an embodiment R¹is hydrogen.
- In another embodiment R¹is fluorine.
- In an embodiment R2 is hydrogen.
- In another embodiment R²is fluorine.
- In an embodiment R¹is hydrogen and R²is hydrogen or fluorine.
- In another embodiment R¹is fluorine and R²is hydrogen or fluorine.
- In another embodiment R¹is hydrogen and R²is hydrogen.
- In another embodiment R¹is hydrogen and R²is fluorine.
- In another embodiment R¹is fluorine and R²is fluorine.
- In another embodiment R¹is hydrogen or fluorine and R²is hydrogen.
- In another embodiment R¹is hydrogen or fluorine and R²is fluorine.
- The present invention also provides compounds of formula II:

wherein R¹and R²are as defined above; or pharmaceutically acceptable salts, stereoisomers or tautomers thereof.

The present invention also provides compounds of formula III:

wherein R¹and R²are as defined above; or pharmaceutically acceptable salts or tautomers thereof.

The present invention also provides compounds of formula IV:

wherein R¹and R²are as defined above; or pharmaceutically acceptable salts or tautomers thereof.

The preferred identities with reference to formulae II, III and IV are as defined previously for formula I mutatis mutandis.

The present invention also includes within its scope N-oxides of the compounds of formula I above. In general, such N-oxides may be formed on any available nitrogen atom. The N-oxides may be formed by conventional means, such as reacting the compound of formula I with oxone in the presence of wet alumina.

The present invention includes within its scope prodrugs of the compounds of formula I above. In general, such prodrugs will be functional derivatives of the compounds of formula I which are readily convertible in vivo into the required compound of formula I. Conventional procedures for the selection and preparation of suitable prodrug derivatives are described, for example, in â€œDesign of Prodrugsâ€ , ed. H. Bundgaard, Elsevier, 1985.

A prodrug may be a pharmacologically inactive derivative of a biologically active substance (the â€œparent drugâ€ or â€œparent moleculeâ€ ) that requires transformation within the body in order to release the active drug, and that has improved delivery properties over the parent drug molecule. The transformation in vivo may be, for example, as the result of some metabolic process, such as chemical or enzymatic hydrolysis of a carboxylic, phosphoric or sulphate ester, or reduction or oxidation of a susceptible functionality.

The present invention includes within its scope solvates of the compounds of formula I and salts thereof, for example, hydrates.

The compounds of the present invention may have asymmetric centers, chiral axes, and chiral planes (as described in: E. L. Eliel and S. H. Wilen, Stereochemistry of Carbon Compounds, John Wiley & Sons, New York, 1994, pages 1119-1190), and occur as racemates, racemic mixtures, and as individual diastereomers, with all possible isomers and mixtures thereof, including optical isomers, all such stereoisomers being included in the present invention. In addition, the compounds disclosed herein may exist as tautomers and both tautomeric forms are intended to be encompassed by the scope of the invention, even though only one tautomeric structure is depicted.

The compounds may exist in different isomeric forms, all of which are encompassed by the present invention.

The compounds may exist in a number of different polymorphic forms.

As used herein, C_1-6alkyl represents a branched, straight-chain and cyclic saturated aliphatic hydrocarbon group containing 1, 2, 3, 4, 5 or 6 carbon atoms. For example, â€œC_1-6alkylâ€ specifically includes methyl, ethyl, n-propyl, i-propyl, n-butyl, t-butyl, i-butyl, pentyl, hexyl, cyclopropyl, cyclobutyl, cyclopentyl and cyclohexyl and so on. Preferred alkyl groups are methyl and ethyl.

Particular compounds within the scope of the present invention are:

3-{4-[7-(Aminocarbonyl)-2H-indazol-2-yl]phenyl} piperidinium chloride;
2-{4-[(3R)-Piperidin-3-yl]phenyl}-2H-indazole-7-carboxamide;
2-{4-[(3S)-Piperidin-3-yl]phenyl}-2H-indazole-7-carboxamide;
3-{4-[7-(Aminocarbonyl)-5-fluoro-2H-indazol-2-yl]phenyl}piperidinium trifluoroacetate;
5-Fluoro-2-(3-fluoro-4-piperidin-3-ylphenyl)-2H-indazole-7-carboxamide trifluoroacetate;
3-{4-[7-(Aminocarbonyl)-2H-indazol-2-yl]phenyl}piperidinium trifluoroacetate;
5-Fluoro-2-(4-piperidin-3-ylphenyl)-2H-indazole-7-carboxamide;
(3S)-3-{4-[7-(Aminocarbonyl)-2H-indazol-2-yl]phenyl}piperidinium chloride;
(3R)-3-{4-[7-(Aminocarbonyl)-2H-indazol-2-yl]phenyl}piperidinium chloride;
(R)-5-Fluoro-2-(4-piperidin-3-ylphenyl)-2H-indazole-7-carboxamide;
(S)-5-Fluoro-2-(4-piperidin-3-ylphenyl)-2H-indazole-7-carboxamide;
(R)-5-Fluoro-2-{3-fluoro-4-piperidin-3-ylphenyl}-2H-indazole-7-carboxamide;
(S)-5-Fluoro-2-{3-fluoro-4-piperidin-3-ylphenyl}-2H-indazole-7-carboxamide;
and pharmaceutically acceptable salts, free bases or tautomers thereof. Stereosiomers thereof of these compounds are also provided.