Milind.N. Doshi et al. / Journal of Pharmacy Research 2012,5(8),4140-4142 Review Article Available online through ISSN: 0974-6943 http://jprsolutions.info Inhibitors as Novel Target for Treatment of

Milind.N. Doshi*, Savita. J. Yadav, Rajkumar Dube Dr. L. H. Hiranandani College of Pharmacy, C.H.M. Campus,Opp. Ulhasnagar Railway Station, Ulhasnagar – 421003, Maharashtra, India Received on:14-05-2012; Revised on: 17-06-2012; Accepted on:28-07-2012

ABSTRACT refers to a new generation of anti cancer drugs that are designed to interfere with a specific molecular target, usually a with a critical role in tumour growth or progression. This approach differs from the more empirical approach used in conventional cytotoxic , which has remained the main stay of anti cancer drug used over the past several decades. Targeted therapy has the potential to reduce or eliminate many of the present problems in the field of cytotoxic chemotherapy, such as the production of serious host cell toxicity. In recent years, Tyrosine kinases have been recognized as central players and regulators of cancer cell proliferation, and angiogenesis, and are therefore considered suitable potential targets for anti cancer therapies. Inhibitors of Tyrosine kinases are thus an important new class of targeted therapy that interfere with specific cell signaling pathways and thus allow target specific therapy for selected malignancies. Tyrosine kinases are an especially important target because they play an important role in the modulation of growth factor signaling.

Key words: Tyrosine kinase, angiogenesis, anti-cancer. INTRODUCTION Multicellular organisms live in a complex milieu where signaling pathways Classification contribute to critical links, for their existence. Tyrosine kinases are important Tyrosine kinases are primarily classified as (RTK) mediators of this signal transduction process, leading to cell proliferation, e.g. EGFR, PDGFR, FGFR and the IR and non-receptor tyrosine kinase differentiation, migration, metabolism and programmed cell death. Tyrosine (NRTK) e.g. SRC, ABL, FAK and . The receptor tyrosine kinases are a family of enzymes, which catalyzes phosphorylation of select kinases are not only cell surface transmembrane receptors, but are also tyrosine residues in target , using ATP. This covalent post- enzymes having kinase activity. The kinase domain has regulatory sequence translational modification is a pivotal component of normal cellular both on the N and C terminal end. [6,7] communication and maintenance of homeostasis. [1,2] NRTK are cytoplasmic proteins, exhibiting considerable structural variability. With the deciphering of the Human Genome Project more than 90 tyrosine The NRTK have a kinase domain and often possess several additional kinases have been found out. Tyrosine kinases represent a major portion of signaling or protein-protein interacting domains such as SH2, SH3 and the all oncoprotein that play a transforming role in a plethora of . Hence PH domain. the identification and development of therapeutic agents for disease states that are linked to abnormal activation of tyrosine kinases due to enhanced Mechanism of Action expression, mutation or autocrine stimulation leading to abnormal Activation of transmembrane PTKs is typically initiated by binding of a downstream oncogenic signaling have taken a centre stage as a potent target ligand (e.g., hormone or growth factor) to a specific site within the extracellular for cancer therapy. [3,4] domain of the receptor. Upon ligand binding, these receptors commonly undergo dimerization, resulting in autophosphorylation of tyrosine residues Tyrosine Kinase within the cytoplasmic domain. [8,9] Tyrosine kinases have been identified as signaling molecules and prototypic oncogenes, and shown to play an important role in the development of Autophosphorylation of a receptor (e.g., Epidermal Growth Factor Receptor) many diseases, including cancer.[5] There is strong evidence that during or phosphorylation of a receptor associated adapter such as Shc allows tumor progression, the hyperactivation of tyrosine kinases leads to the Grb2 to bind to these proteins via its SH2 domain. The SH3 domain of continuous activation of downstream signaling cascades that block cellular Grb2 then binds to the proline-rich C-terminal tail of Sos and recruits Sos to apoptosis, promote cellular proliferation. the membrane-bound complex. Sos, a GTP/GDP exchange factor, activates Ras by exchanging GTP for GDP on the Ras molecule. The GTP-bound PTKs represent a diverse and rapidly expanding superfamily of proteins, form of Ras then binds to Raf (a MAPK kinase kinase) including both transmembrane receptor tyrosine kinases (RTK). Receptor isoforms, including C-Raf-1, B-Raf and A-Raf. This interaction results in Tyrosine Kinases are single pass transmembrane proteins that account for targeting of Raf to the membrane where its protein kinase activity is increased almost two thirds of the genes coding for tyrosine kinases. RTKs possess by phosphorylation, thereby allowing it to activate other signaling molecules. a common functional kinase domain that is able to translate extracellular signals into active intracellular cues. Under physiological conditions, these Tyrosine Kinase: Targets For Anticancer Drugs receptors are activated only upon ligand binding. The role of tyrosine kinases in cancer molecular pathogenesis is immense and recently kinases have come in vogue as potential anticancer drug targets. *Corresponding author. Recent understanding of the molecular pathophysiology of cancer have Milind.N. Doshi highlighted that many tyrosine kinases are found upstream or downstream Dr. L. H. Hiranandani College of Pharmacy, of epidemiologically relevant oncogenes or tumor suppressor, in particular C.H.M. Campus, Ulhasnagar – 421003, the receptor tyrosine kinases. Maharashtra, India

Journal of Pharmacy Research Vol.5 Issue 8.August 2012 4140-4142 Milind.N. Doshi et al. / Journal of Pharmacy Research 2012,5(8),4140-4142 Site of Targeting In past two decades, inhibitors of angiogenesis have been developed for Inhibiting the activity of tyrosine kinases by low molecular weight clinical use. Antiangiogenic drugs stops new vessels from forming around a compounds capable of interfering with either ligand binding (in the case of tumor and break up the existing network of abnormal capillaries that feeds receptor tyrosine kinases) [10] or with protein substrate (in case of non the cancerous mass, thus shrinks the tumor by limiting blood supply. receptor tyrosine kinase) has proved to be difficult. The ATP inhibitors Antiangiogenic therapy does not induce acquired drug resistance and hence appear to be the target of choice. can prove valuable for long-term maintenance therapy. [20]

Small Molecule Inhibitors Tyrosine Kinase Inhibitors Low molecular weight tyrosine phosphorylation inhibitors (tyrphostins) These include , which inhibits the nonreceptor tyrosine kinases have been proposed to be prospective anti-proliferating agents. By late BCR-ABL and KIT, as well as receptor tyrosine kinase inhibitors targeting 1980s it was proved that low molecular weight EGFR inhibitors could epidermal growth factor receptor (EGFR) (ErbB/HER) family members, block EGF dependent cell proliferation. [11] vascular endothelial growth factor receptors (VEGFR), and platelet-derived growth factor receptors (PDGFR) (a and ß). Most of these molecules can be categorized into four groups: Imatinib Mesylate (STI571; Gleevec) (i)ATP-competitive inhibitors, which bind predominantly to the This translocation results in the formation of the BCR-ABL oncogene by ATP-binding site of the kinase when this site is in the active conformation; way of fusing the BCR gene on chromosome 22 and the ABL tyrosine (ii)inhibitors that recognize and bind to the non-active conformation of the kinase gene located on chromosome 9. Imatinib mesylate is a protein-tyrosine ATP-binding site of the kinase, thus making activation energetically kinase inhibitor that inhibits the bcr-abl tyrosine kinase, the constitutive unfavorable; abnormal tyrosine kinase created by the (iii) allosteric inhibitors, that bind outside of the ATP-binding site, modifying abnormality in chronic myeloid (CML). It inhibits proliferation the tridimensional structure of the receptor and disrupting the interaction and induces apoptosis in bcr-abl positive cell lines as well as fresh leukemic between the ATP and the kinase pocket; and cells from Philadelphia chromosome positive chronic myeloid leukemia. (iv) covalent inhibitors, that bind irreversibly by covalently bonding to the Imatinib is also an inhibitor of the receptor tyrosine kinases for platelet- ATP-binding site of the target kinase. [12] derived growth factor (PDGF) and stem cell factor (SCF), c-, and inhibits PDGF- and SCF-mediated cellular events. Monoclonal Antibody Immunotherapy is based on the production of humanized monoclonal antibodies (mAbs) that bind with high specificity to secreted proteins or to Gefitinib acts completively at the ATP-binding site of the EGFR on the the extracellular domain of membrane-bound proteins. So far, there are surface of cancer cell to inhibit ligand-induced tyrosine phosphorylation, several mechanisms described by which they exert their therapeutic effects; thereby blocking ligand-induced activation of the receptor and downstream among them are:binding to the ligand or to receptor, thus preventing ligand- pathways1, Gefitinib is the first selective inhibitor of epidermal growth receptor interaction; disrupting receptor internalization[13], promoting factor receptor's (EGFR) tyrosine kinase domain. Thus gefitinib is an EGFR receptor internalization [14], shedding of the extracellular portion of the inhibitor. The target protein (EGFR) is also sometimes referred to as Her1 receptor [14,15], preventing receptor dimerization and activation [16], and or ErbB-1 depending on the literature source. induction of apoptosis. However, it is believed that each mAb acts through more than one mechanism. Gefitinib inhibits EGFR tyrosine kinase by binding to the adenosine triphosphate (ATP)-binding site of the enzyme. Thus the function of the Antibody Drug Complex EGFR tyrosine kinase in activating the anti-apoptotic Ras signal transduction The efficacy of the antibodies that targets specific molecules expressed by cascade is inhibited, and malignant cells are inhibited.[21] tumor cells can be increased by attaching toxins to them. [17] Existing immunotoxins are based on bacterial toxins like pseudomonas exotoxin, plant exotoxin like ricin or radio-nucleotides. The toxins are chemically Although erlotinib’s mechanism of action is not fully understood,it is thought conjugated to a specific ligand such as the variable domain of the heavy or to reversibly bind to the adenosine triphosphate (ATP) binding site of the light chain of the monoclonal antibody. Normal cells lacking the cancer tyrosine kinase domain associated with HER1/EGFR, located on the surface specific antigens are not targeted by the targeted antibody. of normal and cancer cells. This binding inhibits the phosphorylation of the tyrosine kinase, interfering with cell communication, signal transduction, Heat Shock Proteins and, ultimately, cellular growth. [22,23] The heat shock protein family is a group of related proteins that act as molecular chaperons to aid and stabilize the correct folding of proteins. (GW-572016) Most kinases require molecular chaperons to maintain their activation Lapatinib is a reversible and specific receptor tyrosine kinase inhibitor of competent conformation. Hsp-s interacts with and stabilizes various both ErbB1 and ErbB2 and has been shown to have activity against ErbB1 kinases. [18] The result being the proteosomal degradation of the misfolded and ErbB2, as well as Akt-overexpressing human tumor xenografts. kinases, thus diminishing the level of many kinases. Lapatinib inhibits receptor signal processes by binding to the ATP-binding Angiogenesis Inhibitors pocket of the EGFR/HER2 protein kinase domain, preventing self- [24] Angiogenesis, the growth of new vessels from preexisting vasculature, is a phosphorylation and subsequent activation of the signal mechanism. critical step in tumor progression. [19] New blood vessels are required to Canertinib (CI-1033) support the growth of a tumor beyond the size of about 1–2 mm3, to Canertinib is an irreversible nonselective EGFR inhibitor. This characteristic supply oxygen and nutrients to proliferating tumor cells and for metastasis may result in a greater efficacy and broader spectrum of antitumor activity. formation. Canertinib has been shown to have activity against a variety of human

Journal of Pharmacy Research Vol.5 Issue 8.August 2012 4140-4142 Milind.N. Doshi et al. / Journal of Pharmacy Research 2012,5(8),4140-4142 breast carcinomas in both in vitro and in vivo tumor xenograft models. [25] 7. Hunter, T. Protein kinases and phosphatases: The yin and yang of protein phosphorylation and signalling. Cell, 1995. 80: 225- 236. Vatalanib is a protein kinase inhibitor that inhibits 8. Weiss, A. and Schlessinger, J. (1998) Cell 94, 277. angiogenesis. It is being studied as a possible treatment for several types 9. Lemmon, M.A. and Schlessinger, J. (1998) Meth. Mol. Biol. 84, of cancer, particularly cancer that is at an advanced stage or has not responded 49. to chemotherapy. Vatalanib is orally active, that is, it is effective when 10. Bennasroune A, Gardin A, Aunis D, Cremel G, Hubert P. Tyrosine taken by mouth. kinase receptors as attractive targets for cancer therapy. Crit Rev Oncol Hematol. 2004; 50(1):23-38. 11. Yaish, P., Gazit, A., Gilon, C., and Levitzki, A. Blocking of EGF- Sunitinib inhibits cellular signaling by targeting multiple receptor tyrosine dependent cell proliferation by EGF receptor kinase inhibitors. kinases (RTKs). These include all receptors for platelet-derived growth Science, 1988. 242: 933-935. factor (PDGF-Rs) and vascular endothelial growth factor receptors 12. Zhang J, Yang PL, Gray NS: Targeting cancer with small molecule (VEGFRs), which play a role in both tumor angiogenesis and tumor cell kinase inhibitors. Nat Rev Cancer 2009, 9:28-39. proliferation. It inhibits the growth of a variety of mouse tumor cells and 13. Wheeler DL, Huang S, Kruser TJ, Nechrebecki MM, Armstrong xenograft models . [26] The simultaneous inhibition of these targets therefore EA, Benavente S, Gondi V, Hsu KT, Harari PM: Mechanisms of leads to both reduced tumor vascularization and cancer cell death, and acquired resistance to : role of HER (ErbB) family ultimately tumor shrinkage. members. Oncogene 2008, 27:3944-3956. 14. Petrelli A, Circosta P, Granziero L, Mazzone M, Pisacane A, Fenoglio S, Comoglio PM, Giordano S: Ab-induced ectodomain Sorafenib is a multikinase inhibitor that shows high efficacy against the shedding mediates hepatocyte growth factor receptor down- wide variety of cancers. The effectiveness and strength of this molecule has regulation and hampers biological activity. Proc Natl Acad Sci been proved in various preclinical trials.[27] Sorafenib can inhibit the cell USA 2006, 103:5090-5095. proliferation and angiogenesis by inhibiting the threonine and serine kinase 15. Molina MA, Codony-Servat J, Albanell J, Rojo F, Arribas J, system (c-RAF, and mutant and wild-type BRAF). This molecule also Baselga J: (herceptin), a humanized anti-Her2 inhibits the receptor tyrosine kinases and vascular endothelial growth factor receptor monoclonal antibody, inhibits basal and activated Her2 receptor2, 3, platelet derived growth factor receptor (PDGFR), c-KIT and ectodomain cleavage in cells. Cancer Res 2001, FLT3, etc. [27,28] 61:4744-4749. 16. Hudziak RM, Lewis GD, Winget M, Fendly BM, Shepard HM, CONCLUSION Ullrich A: p185HER2 monoclonal antibody has antiproliferative The role of tyrosine kinase in the control of cellular growth and differentiation effects in vitro and sensitizes human breast tumor cells to tumor is central to all organisms and has been found to participate in human necrosis factor. Mol Cell Biol 1989, 9:1165-1172. neoplastic diseases. Tyrosine kinase inhibitors and their potential in clinical 17. Colaco, CALS. : simple cell biology? application are well documented by dramatic examples like, Gleevec, Iressa Trends Mol Med. 2003. 12:515-516. and Herceptin. With all of the advances in this new category of drugs, one 18. Yarden, Y., and Sliwkowsky, MX. Untangling the ErbB signaling can expect many promising results to emerge from the current clinical trials network. Nature Rev Mol Cell Biol., 2001. 2: 127-137. and future developments to come. With the various combinations of specific- 19. Bergers G, Benjamin LE (2003) Tumorigenesis and the angiogenic target Tyrosine Kinase inhibitor drugs, several types of cancer can be reduced, switch. Nat Rev Cancer 3:401 410 retarded, or eliminated through concentrated chemotherapy regimens. With 20. Boehm, T., Folkman, J., Browder, T., and O’Reilly, MS. Tyrosene Kinase inhibitors, patients with cancer are given more options Antiangiogenic therapy of experimental cancer does not induce and better choices for managing the disease without disrupting their quality acquired drug resistance. Nature, 1997. 27:404-407. of life to the degree that previous treatments have. Several tyrosine kinase 21. Takimoto CH, Calvo E. ”Principles of Oncologic inhibitors are undergoing human trials and several are in the pipeline of drug Pharmacotherapy” in Pazdur R, Wagman LD, Camphausen KA, discovery. The activities of these drugs are restricted to cancers with Hoskins WJ (Eds) Cancer Management: A Multidisciploinary alterations in kinase targets, hence broad application of this treatment Approach . 11 ed. 2008. strategy are challenging. The quick selection of epidemiologically relevant, 22. Tarceva® (erlotinib) tablets (package insert). OSI (Melville, NY) drugable tyrosine kinase targets coupled to efficient lead finding and and (South San Francisco, CA), 2004. Available at: optimization needs more intervention in the area of highthroughput cancer www. tarceva.com/ tarceva/docs/PI.pdf. Accessed January 4, 2005. genome based molecular therapeutics. All these concerted effort may pave 23. Clinical experience with Tarceva® (erlotinib) in non–small cell the silverlining to tailor made personalised cancer therapeutics. lung cancer. Genentech, 2004. 24. Nelson MH, Dolder CR (February 2006). “Lapatinib: a novel REFERENCES dual tyrosine kinase inhibitor with activity in solid tumors”. Ann 1. Hunter, T. Signaling-2000 and Beyond. Cell, 2000. 100: 113-127. Pharmacother 40 (2): 261-9 doi:10.1345/aph.1G387 .PMID 2. Schlessinger, J. Cell Signaling by receptor tyrosine kinases. Cell, 16418322 2000. 103: 211-225. 25. Allen LF, Lenehan PF, Eiseman IA, Elliott WL, and Fry DW 3. Workman, P. Paul workman on the challenges of cancer drug (2002) Potential benefits of the irreversible pan-erbB inhibitor, development. Drug Disc Today, 2003. 8: 775-777. CI-1033, in the treatment of breast cancer. Semin Oncol 29:11– 4. Sawyers, CL. Rational therapeutic intervention in cancer: kinases 21. as drug targets. Curr Opin Gen Develop. 2002. 12: 111-115. 26. Traxler P, Allegrini PR, and Brandt R (2004) A dual family epidermal 5. Robertson SC, Tynan J, Donoghue DJ: RTK mutations and human growth factor receptor/ErbB2 and vascular endothelial growth syndromes: when good receptors turn bad. Trends Genet 2000, factor receptor tyrosine kinase inhibitor with antitumor and 16:368. antiangiogenic activity. Cancer Res 64:4931–4941. 6. Schlessinger, J. Cell Signaling by receptor tyrosine kinases. Cell, 27. Cancer Res 2004; 64: 7099–109. 2000. 103: 211-225. 28. J Natl Cancer Inst 2006; 98: 326–34.

Source of support: Nil, Conflict of interest: None Declared Journal of Pharmacy Research Vol.5 Issue 8.August 2012 4140-4142