In the recent past immense research has been dedicated to the discovery and understanding of the structure and functions of enzymes and bio-molecules associated with various diseases. One such important class of enzymes that has been the subject of extensive research is Protein Kinase.
In general, protein kinases represent a set of structurally related phosphoryl transferases having conserved structures and catalytic functions. These enzymes modify proteins by chemically adding phosphate groups (phosphorylation). Phosphorylation involves the removal of a phosphate group from ATP and covalently attaching it to amino acids that have a free hydroxyl group such as serine, threonine or tyrosine. Phosphorylation usually results in a functional change of the target protein (substrate) by altering enzyme activity, cellular localization or association with other proteins. Up to 30% of all proteins may be modified by kinase activity.
This class of proteins are classified into subsets depending upon the substrate they act upon such as tyrosine kinase, serine/theronine kinase, histidine kinase and the like. These proteins can also be classified based on their localization into receptor tyrosine kinases (RTKs) or non-receptor tyrosine kinases.
Receptor tyrosine kinases (RTKs) have an extracellular portion, a transmembrane domain, and an intracellular portion, while non-receptor tyrosine kinases are entirely intracellular. Receptor tyrosine kinase mediated signal transduction is typically initiated by an extracellular interaction with a specific growth factor (ligand), followed by receptor dimerization, stimulation of the intrinsic protein tyrosine kinase activity, and phosphorylation of amino acid residues. The ensuing conformational change leads to the formation of complexes with a spectrum of cytoplasmic signalling molecules and facilitates a myriad of responses such as cell division, differentiation, metabolic effects, and changes in the extracellular microenvironment.
Protein kinases are known to control a wide variety of biological processes such as cell growth, survival and differentiation, organ formation and morphogenesis, neovascularisation, tissue repair and regeneration. In addition to their functions in normal tissues/organs, many protein kinases also play specialized roles in a host of human diseases including cancer. A subset of protein kinases (also referred to as oncogenic protein kinases), when dysregulated, can cause tumor formation and growth and contribute to tumor maintenance and progression (Blume-Jensen P et al, Nature 2001, 411(6835):355-365). Thus far, oncogenic protein kinases represent one of the largest and most attractive groups of protein targets for therapeutic intervention and drug development.
Both receptor and non-receptor protein kinases have been found to be attractive targets for small molecule drug discovery due to their impact on cell physiology and signalling. Dysregulation of protein kinase activity thus leads to altered cellular responses including uncontrolled cell growth associated with cancer. In addition to oncological indications, altered kinase signalling is implicated in numerous other pathological diseases. These include, but are not limited to immunological disorders, cardiovascular diseases, inflammatory diseases, and degenerative diseases.
Modulation (particularly inhibition) of cell proliferation and angiogenesis, the two key cellular processes needed for tumor growth and survival is an attractive goal for development of small-molecule drugs (Matter A. Drug Disc Technol 2001, 6, 1005-1024). Anti-angiogenic therapy represents a potentially important approach for the treatment of solid tumors and other diseases associated with dysregulated vascularisation including ischemic coronary artery disease, diabetic retinopathy, psoriasis and rheumatoid arthritis. Similarly, cell antiproliferative agents are desirable to slow or inhibit the growth of tumors.
Phosphatidylinositol (hereinafter abbreviated as “PI”) is one of a number of phospholipids found in cell membranes. In recent years it has become clear that PI plays an important role in intracellular signal transduction. Cell signaling via 3′-phosphorylated phosphoinositides has been implicated in a variety of cellular processes, e.g., malignant transformation, growth factor signaling, inflammation, and immunity (Rameh et al (1999) J. Biol Chem, 274:8347-8350). The enzyme responsible for generating these phosphorylated signaling products, phosphatidylinositol 3-kinase (also referred to as PI 3-kinase or PI3K), was originally identified as an activity associated with viral oncoproteins and growth factor receptor tyrosine kinases that phosphorylate phosphatidylinositol (PI) and its phosphorylated derivatives at the 3′-hydroxyl of the inositol ring (Panayotou et al (1992) Trends Cell Biol 2:358-60).
The phosphoinositide 3-kinases (PI3Ks) are a family of enzymes that regulate diverse biological functions in every cell type by generating phosphoinositide second-messenger molecules. As the activity of these phosphoinositide second messengers is determined by their phosphorylation state, the kinases and phosphatises that act to modify these lipids are central to the correct execution of intracellular signaling events. Phosphoinositide 3-kinases (PI3K) phosphorylate lipids at the 3-hydroxyl residue of an inositol ring (Whitman et al (1988) Nature, 332:664) to generate phosphorylated phospholipids (PIP3s) which act as second messengers recruiting kinases with lipid binding domains (including plekstrin homology (PH) regions), such as Akt and phosphoinositide-dependent kinase-1 (PDK1). Binding of Akt to membrane PIP3s causes the translocation of Akt to the plasma membrane, bringing Akt into contact with PDK1, which is responsible for activating Akt. The tumor-suppressor phosphatase, PTEN, dephosphorylates PIPS and therefore acts as a negative regulator of Akt activation. The PI3-kinases Akt and PDK1 are important in the regulation of many cellular processes including cell cycle regulation, proliferation, survival, apoptosis and motility and are significant components of the molecular mechanisms of diseases such as cancer, diabetes and immune inflammation (Vivanco et al (2002) Nature Rev. Cancer 2:489; Phillips et al (1998) Cancer 83:41).
The PI3K family is constituted by four different classes: classes I, II and III are lipid kinases while members of class IV are Ser/Thr protein kinases.
The members of the class I family of PI3Ks are dimers of a regulatory and a catalytic subunit. The class I family consists of four isoforms, determined by the catalytic subunits α, β, γ and δ (see Engelman J A, Nat Rev Genet. 2006; 7:606-19; Carnero A, Curr Cancer Drug Targets 2008; 8:187-98; Vanhaesebroeck B, Trends Biochem Sci 2005; 30:194-204). Class I can be subdivided into two subclasses: Ia, formed by the combination of p110 α β and δ and a regulatory subunit (p85, p55 or p50) and Ib, formed by p110 γ and p101 regulatory subunits. The regulatory subunit p85 contains Src homology 2 domains, which bind to phosphotyrosines and bring the attached catalytic subunit p110 into the complexes located in the membrane around the receptor. The activation of PI3K is induced by growth factors and insulin targeting the catalytic subunit to the membrane where it is in close proximity with its substrates, mainly PIP2. Alternatively, GTP-bound Ras can bind and activate p110 subunits in a p85-independent manner. Class I phosphoinositide 3-kinases (PI3Ks) are lipid kinases that phosphorylate phosphatidyl-inositide lipids (PI) at the D3 position of the inositol ring producing lipid second messengers (PIPs). The products of PI3K activity, mainly PI(3,4,5)-P3 (PIP3), are present in very low level in quiescent cells but are rapidly produced during cell stimulation and are involved in the regulation of several biological responses including mitogenesis, apoptosis, vesicular trafficking and cytoskeleton rearrangement. The result of rising PIP3 levels is the activation of 3-phosphoinositide-dependent protein kinase-1 and its substrate AKT, which triggers most of the biological activities of the pathway. Phosphatase and tensin homolog in chromosome 10 (PTEN) is a lipidic phosphatase which constitutes the main negative regulator of the route by dephosphorylating PIP3 to PI(4,5)-P2 (PIP2). Class II displays the ability to phosphorylate PI and PI-4 phosphate in vitro. Class III, composed by Vps34 only member, phosphorylates PI at position 3 generating PI 3-phosphate. Vps34 has been implicated in Golgi trafficking of proteins, autophagy and activation of mammalian target of rapamycin (mTOR) by amino acids (see Backer J M. Biochem J 2008; 410:1-17) these classes are generally resistant to class I PI3K inhibitors. Class IV, however, is important because it constitutes the major cross-activity proteins for class I inhibitors. This class includes enzymes involved in signal transduction and DNA damage response such as mTOR, DNA-dependent protein kinase (DNA-PK) or ATM. This fourth class of PI3K-related enzymes contains a catalytic core similar to the PI3K, which can account for the cross-inhibition by class I ‘selective’ compounds. However, small differences, especially in the hinge region, and the solving of the PI3K-related structures might lead to the fine tuning of different paralog selective PI3K-members. (see Expert Opin. Investig. Drugs (2009) 18(9): 1265-1277)
There is now considerable evidence indicating that Class Ia PI3K enzymes contribute to tumourigenesis in a wide variety of human cancers, either directly or indirectly (Vivanco and Sawyers, Nature Reviews Cancer, 2002, 2, 489-501). For example, the pi 10a subunit is amplified in some tumours such as those of the ovary (Shayesteh et al, Nature Genetics. 1999, 21: 99-102) and cervix (Ma et al, Oncogene, 2000, 19: 2739-2744). More recently, activating mutations within the catalytic site of pi 10a have been associated with various other tumours such as those of the colorectal region and of the breast and lung (Samuels et al, Science, 2004, 304, 554). Tumour-related mutations in p85α have also been identified in cancers such as those of the ovary and colon (Philp et al., Cancer Research, 2001, 61, 7426-7429). In addition to direct effects, it is believed that activation of Class Ia PI3K contributes to tumourigenic events that occur upstream in signalling pathways, for example by way of ligand-dependent or ligand-independent activation of receptor tyrosine kinases, GPCR systems or integrins (Vara et al, Cancer Treatment Reviews, 2004, 30, 193-204). Examples of such upstream signalling pathways include over-expression of the receptor tyrosine kinase Erb2 in a variety of tumours leading to activation of PI3K-mediated pathways (Harari et al., Oncogene, 2000, 19, 6102-6114) and over-expression of the oncogene Ras (Kauffmann-Zeh et al., Nature, 1997, 385, 544-548). In addition, Class Ia PBKs may contribute indirectly to tumourigenesis caused by various downstream signalling events. For example, loss of the effect of the PTEN tumour-suppressor phosphatase that catalyses conversion of PI(3,4,5)P3 back to PI(4,5)P2 is associated with a very broad range of tumours via deregulation of PI3K-mediated production of PI(3,4,5)P3 (Simpson and Parsons, Exp. Cell Res. 2001, 264, 29-41). Furthermore, augmentation of the effects of other PI3K-mediated signalling events is believed to contribute to a variety of cancers, for example by activation of Akt (Nicholson and Anderson, Cellular Signalling, 2002, H, 381-395).
In addition to a role in mediating proliferative and survival signalling in tumour cells, there is also good evidence that Class Ia PI3K enzymes will also contribute to tumourigenesis via its function in tumour-associated stromal cells. For example, PI3K signalling is known to play an important role in mediating angiogenic events in endothelial cells in response to pro-angiogenic factors such as VEGF (Abid et al., Arterioscler. Thromb. Vase. Biol., 2004, 24, 294-300). As Class I PI3K enzymes are also involved in motility and migration (Sawyer, Expert Opinion Investig. Drugs, 2004, JJ., 1-19), PI3K inhibitors should provide therapeutic benefit via inhibition of tumour cell invasion and metastasis.
In addition, Class I PI3K enzymes play an important role in the regulation of immune cells with PI3K activity contributing to pro-tumourigenic effects of inflammatory cells (Coussens and Werb, Nature, 2002, 420, 860-867). These findings suggest that pharmacological inhibitors of Class I PI3K enzymes should be of therapeutic value for treatment of the various forms of the disease of cancer comprising solid tumours such as carcinomas and sarcomas and the leukaemias and lymphoid malignancies. In particular, inhibitors of Class I PI3K enzymes should be of therapeutic value for treatment of, for example, cancer of the breast, colorectum, lung (including small cell lung cancer, non-small cell lung cancer and bronchioalveolar cancer) and prostate, and of cancer of the bile duct, bone, bladder, head and neck, kidney, liver, gastrointestinal tissue, oesophagus, ovary, pancreas, skin, testes, thyroid, uterus, cervix and vulva, and of leukaemias (including ALL and CML), multiple myeloma and lymphomas.
A recent review by Romina Marone et. al., describes the activation of the PI3K signalling cascade having a positive effect on cell growth, survival and proliferation. Constitutive up-regulation of PI3K signaling can have a deleterious effect on cells leading to uncontrolled proliferation, enhanced migration and adhesion-independent growth. These events favor not only the formation of malignant tumors, but also the development of inflammatory and autoimmune disease indicating the role of PI3K in various diseases including chronic inflammation & allergy, Cardiovascular diseases, cancer and metabolic disorders. (see Biochimica et Biophysica Acta 1784 (2008) 159-185).
Several components of the PI3-kinase/Akt/PTEN pathway are implicated in oncogenesis. In addition to growth factor receptor tyrosine kinases, integrin-dependent cell adhesion and G-protein coupled receptors activate PI3-kinase both directly and indirectly through adaptor molecules. Functional loss of PTEN (the most commonly mutated tumor-suppressor gene in cancer after p53), oncogene mutations in PI3 kinase (Samuels et al (2004) Science 304:554), amplification of PI3-kinase and overexpression of Akt have been established in many malignancies. In addition, persistent signaling through the PI3-kinase/Akt pathway by stimulation of the insulin-like growth factor receptor is a mechanism of resistance to epidermal growth factor receptor inhibitors such as AG1478 and trastuzumab. Oncogenic mutations of p110alpha have been found at a significant frequency in colon, breast, brain, liver, ovarian, gastric, lung, and head and neck solid tumors. PTEN abnormalities are found in glioblastoma, melanoma, prostate, endometrial, ovarian, breast, lung, head and neck, hepatocellular, and thyroid cancers.
The levels of phosphatidylinositol-3,4,5-triphosphate (PIP3), the primary product of PI3-kinase activation, increase upon treatment of cells with a variety of agonists. PI3-kinase activation, therefore, is believed to be involved in a range of cellular responses including cell growth, differentiation, and apoptosis (Parker et al (1995) Current Biology, 5:577-99; Yao et al (1995) Science, 267:2003-05). Though the downstream targets of phosphorylated lipids generated following PI3 kinase activation have not been well characterized, emerging evidence suggests that pleckstrin-homology domain- and FYVE-finger domain-containing proteins are activated when binding to various phosphatidylinositol lipids (Sternmark et al (1999) J Cell Sci, 112:4175-83; Lemmon et al (1997) Trends Cell Biol, 7:237-42). In vitro, some isoforms of protein kinase C (PKC) are directly activated by PIPS, and the PKC-related protein kinase, PKB, has been shown to be activated by PI3 kinase (Burgering et al (1995) Nature, 376:599-602).
PI3 kinase also appears involved in leukocyte activation. A p85-associated PI3 kinase activity has been shown to physically associate with the cytoplasmic domain of CD28, which is an important costimulatory molecule for the activation of T-cells in response to antigen (Pages et al (1994) Nature, 369:327-29; Rudd, (1996) Immunity 4:527-34). Activation of T cells through CD28 lowers the threshold for activation by antigen and increases the magnitude and duration of the proliferative response. These effects are linked to increases in the transcription of a number of genes including interleukin-2 (IL2), an important T cell growth factor (Fraser et al (1991) Science, 251:313-16). Mutation of CD28 such that it can no longer interact with PI3 kinase leads to a failure to initiate IL2 production, suggesting a critical role for PI3 kinase in T cell activation.
Inhibition of class I PI3 kinase induces apoptosis, blocks tumor induced angiogenesis in vivo, and increases the radiosensitivity of certain tumors. At least two compounds, LY294002 and wortmannin, have been widely used as PI3 kinase inhibitors. These compounds, however, are nonspecific PI3K inhibitors, as they do not distinguish among the four members of Class I PI3 kinases. For example, the IC50 values of wortmannin (U.S. Pat. No. 6,703,414) against each of the various Class I PI3 kinases are in the range of 1-10 nanomolar (nM). LY294002 (2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one) is a well known specific inhibitor of class I PI3 kinases and has anti-cancer properties (Chiosis et al (2001) Bioorganic & Med. Chem. Lett. 11:909-913; Vlahos et al (1994) J. Biol. Chem. 269(7):5241-5248; Walker et al (2000) Mol. Cell. 6:909-919; Fruman et al (1998) Ann Rev Biochem, 67:481-507).
Patent literature belonging to various research groups around the world includes several such patents and/or patent applications viz., U.S. Pat. Nos. 6,608,056; 6,608,053; 6,838,457; 6,770,641; 6,653,320; 6,403,588; WO 2004017950; US 2004092561; WO 2004007491; WO 2004006916; WO 2003037886; US 2003149074; WO 2003035618; WO 2003034997; US 2003158212; EP 1417976; US 2004053946; JP 2001247477; JP 08175990; JP 08176070). WO 97/15658, U.S. Pat. Nos. 7,173,029; 7,037,915; 6,703,414; WO 2006/046031; WO 2006/046035; WO 2006/046040; WO 2007/042806; WO 2007/042810; WO 2004/017950; US 2004/092561; WO 2004/007491; WO2004/006916; WO 2003/037886; US 2003/149074; WO 2003/035618; WO 2003/034997; including p110 alpha binding activity US 2008/0207611; US 2008/0039459; US 2008/0076768; WO 2008/073785; WO 2008/070740; US20090270430A1; US2006270673 A1; WO2009129211A1; US2009 0263398A1; US20090263397A1; WO2009129259A2; U.S. Pat. Nos. 7,605,160; 7,605,155; 7,608,622; US20090270621; US20090270445; US20090247567A1; U.S. Pat. No. 7,592,342; US2009 0239847A1; U.S. Pat. No. 7,595,320; US20090247538A1; US20090239936A1; U.S. Pat. No. 7,595,330; US20090239859A1; WO2009117482A1; WO2009117097A1; US20090247565A1; WO2009 120094A2; US20090258852A1; U.S. Pat. No. 7,601,724; WO2009126635A1; U.S. Pat. Nos. 7,601,718; 7,598,245; US20090239859A1; US20090247554; US20090238828; WO2009114874A2; WO2009114870A2; US20090234132A1; WO2009112565A1; US20090233950A1; US20090233926A1; U.S. Pat. No. 7,589,101; WO2009111547A1; WO2009111531A1; WO2009109867A2 and WO2009105712A1.
reviews and studies regarding PI3K and related protein kinase pathways have been given by Pixu Liu et. al. (Nature Reviews Drug Discovery, 2009, 8, 627-644); Nathan T. et. al. (Mol Cancer Ther., 2009; 8 (1) January, 2009); Romina Marone et, al. (Biochimica et Biophysica Acta 1784 (2008) 159-185) and B. Markman et. al. (Annals of oncology Advance access published August 2009). All of these patents and/or patent applications and literature disclosures are incorporated herein as reference in their entirety for all purposes.
Despite the advances made in the area of kinases and in particular the role that PI3K and related protein kinases play in human diseases, challenges remain in terms of the complexities of the target involved, the protein structure of the kinases, specificity issues for various kinase inhibitors, side effects and desired clinical benefits expected form the PI3K inhibitors. Accordingly, there still remains an unmet and dire need for small molecule kinase modulators in order to regulate and/or modulate transduction of kinases, particularly PI3K and related protein kinase for the treatment of diseases and disorders associated with kinases-mediated events.
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