The connection between abnormal protein phosphorylation and the cause or consequence of diseases has been known for over 20 years. Accordingly, protein kinases have become a very important group of drug targets. See Cohen, Nature, 1:309-315 (2002). Various protein kinase inhibitors have been used clinically in the treatment of a wide variety of diseases, such as cancer and chronic inflammatory diseases, including diabetes and stroke. See Cohen, Eur. J. Biochem., 268:5001-5010 (2001).
The protein kinases are a large and diverse family of enzymes that catalyze protein phosphorylation and play a critical role in cellular signaling. Protein kinases may exert positive or negative regulatory effects, depending upon their target protein. Protein kinases are involved in specific signaling pathways which regulate cell functions such as, but not limited to, metabolism, cell cycle progression, cell adhesion, vascular function, apoptosis, and angiogenesis. Malfunctions of cellular signaling have been associated with many diseases, the most characterized of which include cancer and diabetes. The regulation of signal transduction by cytokines and the association of signal molecules with protooncogenes and tumor suppressor genes have been well documented. Similarly, the connection between diabetes and related conditions, and deregulated levels of protein kinases, has been demonstrated. See e.g., Sridhar et al. Pharmaceutical Research, 17(11):1345-1353 (2000). Viral infections and the conditions related thereto have also been associated with the regulation of protein kinases. Park et al. Cell 101 (7), 777-787 (2000).
Protein kinases can be divided into broad groups based upon the identity of the amino acid(s) that they target (serine/threonine, tyrosine, lysine, and histidine). For example, tyrosine kinases include receptor tyrosine kinases (RTKs), such as growth factors and non-receptor tyrosine kinases, such as the src kinase family. There are also dual-specific protein kinases that target both tyrosine and serine/threonine, such as cyclin dependent kinases (CDKs) and mitogen-activated protein kinases (MAPKs). Any particular cell contains many protein kinases, some of which phosphorylate other protein kinases. Some protein kinases phosphorylate many different proteins, others phosphorylate only a single protein. Not surprisingly, there are numerous classes of protein kinases. Upon receiving a signal, some proteins may also undergo auto-phosphorylation.
The protein tyrosine kinases (PTKs) compose a large family of kinases that regulate cell to cell signals involved in growth, differentiation, adhesion, motility, and death. Robinson et al., Oncogene 19:5548-5557 (2000). Members of the tyrosine kinase include, but are not limited to, Yes, BMX, Syk, EphA1, FGFR3, RYK, MUSK, JAK1 and EGFR. Tyrosine kinases are distinguished into two classes, i.e., the receptor type and non-receptor type tyrosine kinases. Interestingly, the entire of family of tyrosine kinases is quite large—consisting of at least 90 characterized kinases with at least 58 receptor type and at least 32 nonreceptor type kinases comprising at least 30 total subfamilies. Robinson et al., Oncogene 19:5548-5557 (2000). Tyrosine kinases have been implicated in a number of diseases in humans, including diabetes and cancer. Robinson et al. at page 5548. Tyrosine kinases are often involved in most forms of human malignancies and have been linked to a wide variety of congenital syndromes. Robertson et al., Trends Genet. 16:265-271 (2000).
The non-receptor tyrosine kinases represent a group of intracellular enzymes that lack extracellular and transmembrane sequences. Currently, over 32 families of non-receptor tyrosine kinases have been identified. Robinson et al., Oncogene 19:5548-5557 (2000). Examples are Src, Btk, Csk, ZAP70, Kak families. In particular, the Src family of non-receptor tyrosine kinase family is the largest, consisting of Src, Yes, Fyn, Lyn, Lck, Blk, Hck, Fgr and Yrk protein tyrosine kinases. The Src family of kinases have been linked to oncogenesis, cell proliferation and tumor progression. A detailed discussion of non-receptor protein tyrosine kinases is available in Oncogene 8:2025-2031 (1993). Many of these protein tyrosine kinases have been found to be involved in cellular signaling pathways involved in various pathological conditions including but not limited to cancer and hyperproliferative disorders and immune disorders.
The cyclin dependent kinases CDKs represent a group of intracellular enzymes that control progression through the cell cycle and have essential roles in cell proliferation. See Cohen, Nature, 1:309-315 (2002). Examples of CDKs include, but are not limited to, cyclin dependent kinase 2 (CDK2), cyclin dependent kinase 7 (CDK7), cyclin dependent kinase 6 (CDK6) and cell division control 2 protein (CDC2). CDKs have been implicated in the regulation of transitions between different phases of the cell cycle, such as the progression from a quiescent stage in G1 (the gap between mitosis and the onset of DNA replication for a new round of cell division) to S (the period of active DNA synthesis), or the progression from G2 to M phase, in which active mitosis and cell division occur. See e.g., the articles compiled in Science, vol. 274 (1996), pp. 1643-1677; and Ann. Rev. Cell Dev Biol., vol. 13 (1997), pp. 261-291. CDK complexes are formed through association of a regulatory cyclin subunit (e.g., cyclin A, B1, B2, D1, D2, D3, and E) and a catalytic kinase subunit (e.g., cdc2 (CDK1), CDK2, CDK4, CDK5, and CDK6). As the name implies, CDKs display an absolute dependence on the cyclin subunit in order to phosphorylate their target substrates, and different kinase/cyclin pairs function to regulate progression through specific portions of the cell cycle. CDKs have been implicated in various disease states, including but not limited to, those displaying the cancer phenotype, various neoplastic disorders and in neurological disorders. Hunter, Cell 100:113-127 (2000).
The mitogen activated protein (MAP) kinases participate in the transduction of signals to the nucleus of the cell in response to extracellular stimuli. Examples of MAP kinases include, but are not limited to, mitogen activated protein kinase 3 (MAPK3), mitogen-activated protein kinase 1 (ERK2), mitogen-activated protein kinase 7 (MAPK7), mitogen-activated protein kinase 8 (JNK1), mitogen-activated protein kinase 14 (p38 alpha), mitogen-activated protein kinase 10 (MAPK10), JNK3 alpha protein kinase, stress-activated protein kinase JNK2 and mitogen-activated protein kinase 14 (MAPK14). MAP kinases are a family of proline-directed serine/threonine kinases that mediate signal transduction from extracellular receptors or heath shock, or UV radiation. See Sridhar et al., Pharmaceutical Research, 17:11 1345-1353 (2000). MAP kinases activate through the phosphorylation of theonine and tyrosine by dual-specificity protein kinases, including tyrosine kinases such as growth factors. Cell proliferation and differentiation have been shown to be under the regulatory control of multiple MAP kinase cascades. See Sridhar et al., Pharmaceutical Research, 17:11 1345-1353 (2000). As such, the MAP kinase pathway plays critical roles in a number of disease states. For example, defects in activities of MAP kinases have been shown to lead to aberrant cell proliferation and carcinogenesis. See Hu et al., Cell Growth Differ. 11:191-200 (2000); and Das et al., Breast Cancer Res. Treat. 40:141 (1996). Moreover, MAP kinase activity has also been implicated in insulin resistance associated with type-2 diabetes. See Virkamaki et al., J. Clin. Invest. 103:931-943 (1999).
The p90 ribosomal S6 kinases (Rsk) are serine/threonine kinases. The Rsk family members function in mitogen-activated cell growth and proliferation, differentiation, and cell survival. Examples of members of the Rsk family of kinases include, but are not limited to, ribosomal protein S6 kinase, 90 kDa, polypeptide 2 (Rsk3), ribosomal protein S6 kinase, 90 kDa, polypeptide 6 (Rsk4), ribosomal protein S6 kinase, 90 kDa, polypeptide 3 (Rsk2) and ribosomal protein S6 kinase, 90 kDa, polypeptide 1 (Rsk 1/p90Rsk). The Rsk family members are activated by extracellular signal-related kinases 1/2 and phosphoinositide-dependent protein kinase 1. Frodin and Gammeltoft, Mol. Cell. Endocrinol. 151:65-77 (1999). Under basal conditions, RSK kinases are localized in the cytoplasm of cells and upon stimulation by mitogens, the activated (phosphorylated by extracellular-related kinase) RSK transiently translocates to the plasma membrane where they become fully activated. The fully activated RSK phosphorylates substrates that are involved in cell growth, proliferation, differentiation, and cell survival. Richards et al., Curr. Biol. 9:810-820 (1999); Richards et al., Mol. Cell. Biol. 21:7470-7480 (2001). RSK signaling pathways have also been associated with the modulation of the cell cycle. Gross et al., J. Biol. Chem. 276(49): 46099-46103 (2001). Current data suggests that small molecules that inhibit Rsk may be useful therapeutic agents for the prevention and treatment of cancer and inflammatory diseases.
Members of the checkpoint protein kinase family are serine/threonine kinases that play an important role in cell cycle progression. Examples of members of the checkpoint family include, but are not limited to, CHK1 and CHK2. Checkpoints are control systems that coordinate cell cycle progression by influencing the formation, activation and subsequent inactivation of the cyclin-dependent kinases. Checkpoints prevent cell cycle progression at inappropriate times, maintain the metabolic balance of cells while the cell is arrested, and in some instances can induce apoptosis (programmed cell death) when the requirements of the checkpoint have not been met. See e.g., O'Connor, Cancer Surveys, 29: 151-182 (1997); Nurse, Cell, 91: 865-867 (1997); Hartwell et al., Science, 266: 1821-1828 (1994); Hartwell et al., Science, 246: 629-634 (1989). Members of the checkpoint family of kinases have been implicated in cell proliferative disorders, cancer phenotypes and other diseases related to DNA damage and repair. Kohn, Mol. Biol. Cell 10:2703-2734 (1999); Ohi and Gould, Curr. Opin. Cell Biol. 11:267-273 (1999); Peng, et al., Science 277:1501-1505 (1997).
Aurora kinases are a family of multigene mitotic serine-threonine kinases that functions as a class of novel oncogenes. These kinases comprise aurora-A and aurora-B members. Aurora kinases are hyperactivated and/or over-expressed in several solid tumors including but not limited to, breast, ovary, prostate, pancreas, and colorectal cancers. In particular aurora-A is a centrosome kinase that plays an important role cell cycle progression and cell proliferation. Aurora-A is located in the 20q13 chromosome region that is frequently amplified in several different types of malignant tumors such as colorectal, breast and bladder cancers. There is also a high correlation between aurora-A and high histo-prognostic grade aneuploidy, making the kinase a potential prognostic vehicle. Inhibition of aurora kinase activity could help to reduce cell proliferation, tumor growth and potentially tumorigenesis. A detailed description of aurora kinase function is reviewed in Oncogene 21:6175-6183 (2002).
The Rho-associated coiled-coil-containing protein serine/threonine kinases ROCK-I and ROCK-II are thought to play a major role in cytoskeletal dynamics by serving as downstream effectors of the Rho/Rac family of cytokine- and growth factor-activated small GTPases. ROCKS phosphorylate various substrates, including, but not limited to, myosin light chain phosphatase, myosin light chain, ezrin-radixin-moesin proteins and LIM (for Linl1, Isl1 and Mec3) kinases. ROCKS also mediate the formation of actin stress fibers and focal adhesions in various cell types. ROCKs have an important role in cell migration by enhancing cell contractility. They are required for tail retraction of monocytes and cancer cells, and a ROCK inhibitor has been used to reduce tumor-cell dissemination in vivo. Recent experiments have defined new functions of ROCKS in cells, including centrosome positioning and cell-size regulation, which might contribute to various physiological and pathological states. See Nature Reviews Mol. Cell. Biol. 4, 446-456 (2003). The ROCK family members are attractive intervention targets for a variety of pathologies, including cancer and cardiovascular disease. For example, Rho kinase inhibitors can be useful therapeutic agents for hypertension, angina pectoris, and asthma. Furthermore, Rho is expected to play a role in peripheral circulation disorders, arteriosclerosis, inflammation, and autoimmune disease and as such, is a useful target for therapy.
The 70 kDa ribosomal S6 kinase (p70S6K) is activated by numerous mitogens, growth factors and hormones. Activation of p70S6K occurs through phosphorylation at a number of sites and the primary target of the activated kinase is the 40S ribosomal protein S6, a major component of the machinery involved in protein synthesis in mammalian cells. In addition to its involvement in regulating translation, p70S6K activation has been implicated in cell cycle control, neuronal cell differentiation, regulation of cell motility and a cellular response that is important in tumor metastases, immunity and tissue repair. Modulation of p70S6 kinase activity may have therapeutic implications in disorders such as cancer, inflammation, and various neuropathies. A detailed discussion of p70S6K kinases can be found in Prog. Cell Cycle Res. 1:21-32 (1995), and Immunol Cell Biol. 78(4):447-51 (2000).
Glycogen synthase kinase 3 (GSK-3) is a ubiquitously expressed constitutively active serine/threonine kinase that phosphorylates cellular substrates and thereby regulates a wide variety of cellular functions, including development, metabolism, gene transcription, protein translation, cytoskeletal organization, cell cycle regulation, and apoptosis. GSK-3 was initially described as a key enzyme involved in glycogen metabolism, but is now known to regulate a diverse array of cell functions. Two forms of the enzyme, GSK-3α and GSK-3β, have been previously identified. The activity of GSK-3β is negatively regulated by protein kinase B/Akt and by the Wnt signaling pathway. Small molecules inhibitors of GSK-3 may, therefore, have several therapeutic uses, including the treatment of neurodegenerative diseases, diabetes type II, bipolar disorders, stroke, cancer, and chronic inflammatory disease. Reviewed in Role of glycogen synthase kinase-3 in cancer: regulation by Wnts and other signaling pathways (Adv Cancer Res.; 84:203-29, 2002); Glycogen synthase kinase 3 (GSK-3) inhibitors as new promising drugs for diabetes, neurodegeneration, cancer, and inflammation (Med Res Rev.; 22(4):373-84, 2002); Role of glycogen synthase kinase-3 in the phosphatidylinositol 3-Kinase/Akt cell survival pathway. (J. Biol. Chem., 273(32):19929-32, 1998).
Because protein kinases regulate nearly every cellular process, including metabolism, cell proliferation, cell differentiation, and cell survival, they are attractive targets for therapeutic intervention for various disease states. For example, cell-cycle control and angiogenesis, in which protein kinases play a pivotal role are cellular processes associated with numerous disease conditions such as but not limited to cancer, inflammatory diseases, abnormal angiogenesis and diseases related thereto, atherosclerosis, macular degeneration, diabetes, obesity, and pain.
Protein kinases have become attractive targets for the treatment of cancers. Fabbro et al., Pharmacology & Therapeutics 93:79-98 (2002). It has been proposed that the involvement of protein kinases in the development of human malignancies may occur by: (1) genomic rearrangements (e.g., BCR-ABL in chronic myelogenous leukemia), (2) mutations leading to constitutively active kinase activity, such as acute myelogenous leukemia and gastrointestinal tumors, (3) deregulation of kinase activity by activation of oncogenes or loss of tumor suppressor functions, such as in cancers with oncogenic RAS, (4) deregulation of kinase activity by over-expression, as in the case of EGFR and (5) ectopic expression of growth factors that can contribute to the development and maintenance of the neoplastic phenotype. Fabbro et al., Pharmacology & Therapeutics 93:79-98 (2002).
Certain cancers are associated with angiogenesis. Angiogenesis is the growth of new capillary blood vessels from pre-existing vasculature. Risau, W., Nature 386:671-674 (1997). It has been shown that protein kinases can contribute to the development and maintenance of the neoplastic phenotype. Fabbro et al., Pharmacology & Therapeutics 93:79-98 (2002). For example, VEGF A-D and their four receptors have been implicated in phenotypes that involve neovascualrization and enhanced vascular permeability, such as tumor angiogenesis and lymphangiogenesis. Matter, A., Drug Discov. Today 6:1005-1023 (2001).
Cardiovascular disease (“CVD”) accounts for nearly one quarter of total annual deaths worldwide. Vascular disorders such as atherosclerosis and restenosis result from dysregulated growth of the vessel walls and the restriction of blood flow to vital organs. Various kinase pathways, e.g. JNK, are activated by atherogenic stimuli and regulated through local cytokine and growth factor production in vascular cells. Yang et al., Immunity 9:575 (1998). Ischemia and ischemia coupled with reperfusion in the heart, kidney or brain result in cell death and scar formation, which can ultimately lead to congestive heart failure, renal failure or cerebral dysfunction. In organ transplantation, reperfusion of previously ischemic donor organs results in acute leukocyte-mediated tissue injury and delay of graft function. Ischemia and reperfusion pathways are mediated by various kinases. For example, the JNK pathway has been linked to leukocyte-mediated tissue damage. Li et al., Mol. Cell. Biol. 16:5947-5954 (1996). Finally, enhanced apoptosis in cardiac tissues has also been linked to kinase activity. Pombo et al., J. Biol. Chem. 269:26546-26551 (1994).
The elucidation of the intricacy of protein kinase pathways and the complexity of the relationship and interaction among and between the various protein kinases and kinase pathways highlights the importance of developing pharmaceutical agents capable of acting as protein kinase modulators, regulators or inhibitors that have beneficial activity on multiple kinases or multiple kinase pathways.
It has therefore been suggested that due to the complexity of intracellular signaling cascades of protein kinase pathways, agents that affect multiple pathways simultaneously may be required for meaningful clinical activity. Indeed, it is known that some kinase drugs, such as Gleevec®, do target several kinases at once. Gleevec® primarily targets a mutant fusion protein containing the abl kinase, which is created by a 9:22 chromosomal translocation event; Gleevec® also targets c-kit, a tyrosine kinase implicated in gastrointestinal stromal tumors (GIST). However, in recent clinical trials, patients have developed resistance to Gleevec® or have shown incomplete response to treatment.
Accordingly, there remains a need for new kinase modulators.
Citation or identification of any reference in Section 2 of this application is not to be construed as an admission that the reference is prior art to the present application.