by Dorothy Williams | Mar 19 2012
Introduction: The VEGFR pathway
The VEGF pathway is the mechanism by which a mammalian system regulates the growth of vascular structures, such as blood vessels and lymphatic vessels. There exists three iso-forms of VEGFR spread across the cellular membrane of mostly endothelial cells, with a head in the extracellular medium and a tail in the cytosole. Ligand activity dimerizes the receptor and causes conformational changes to be transferred down the protein structure into the tail section where tyrosine kinase binding domains are revealed. There exists seven know ligands for the VEGF receptors known simple as VEGF-A, B, C, D, E, F or G [2;3]. VEGF-A binds only to VEGFR 1 or 2 and it is reported that this is predominately regulates the formation and maintenance of the vascular system. VEGFR1 doesn’t appear to have a direct function of cellular response but has been suggested that it regulates VEGFR2 activity [4;5]. VEGFR3 is less well known and only discovered recently, it appears to bind only to VEGF-C or D regulating the lymphatic system. Inhibition of the VEGFR focuses mainly on the isoforms VEGFR2 since this receptor is 90% responsible for all activity in this pathway . Pazopanib is a small molecule that inhibits all VEGFR isoforms and has demonstrated anti-tumor activity .
Pazopanib: Properties and availability
The Pazopanib VEGFR inhibitor is under development by the Pharmaceutical Company GlaxoSmithKline and is assigned the trade names of Armala and Votrient. Its original research code name was GW786034B and it is supplied as the hydrochloride salt. Pazopanib is multi-kinase inhibitor with specificity towards VEGFR 1,2&3 isoforms, in addition Pazopanib has activity against cKIT, PDGFR (α&β) and cFMS. Pazopanib IC50’s for inhibition of the 1,2&3 VEGF isoforms are in the 30±17 nM range, where as the other activities have IC50 ten fold higher. Pazopanib structure consists of three main sections; a benzene sulphonamide and a dimethyl indazol linked together by pyrimidine giving Pazopanib its unique activity. The Pazopanib solubility is poor in both aqueous and alcoholic solutions, surprisingly Pazopanib is soluble to DMSO only up to 8.3 mg/ml, presenting significant problems in preparation of cell culture buffers. Maximum aqueous concentrations are estimated to be in the 10-20 µM range and only the addition of protein to the buffered preparation will keep this compound in solution.Pazopanib stability of the solid material is estimated at 2 years if kept at -20°C, however, caution should taken in the freezing of stock solutions since Pazopanib can be difficult to get back in solution on defrosting. To buy Pazopanib is relatively easy and many Pazopanib suppliers exist for research material. The Pazopanib price of 25 mg vial range between $62 and $395 although purity remains consistent between suppliers.
Pazopanib: Preclinical Investigation
Initial investigations in multiple myeloma for activity of Pazopanib demonstrated a reduction of angiogenesis and an increase apoptotic cell death in both the tumor and the endothelial cells . In renal cell carcinoma and other solid tumors Pazopanib has demonstrated apoptotic effects, linked to the key role VEGF plays in these diseases. In hematological conditions VEGF also is instrumental in the uncontrolled cell survival, Pazopanib proved to equally effective in reducing tumor mass and inducing cell death. Pharmacokinetic (PK) and pharmacodynamic (PD) parameters for tyrosine kinase inhibitors like Pazopanib have been recognized as indicating eventual human sensitivity and efficacy of these drugs. In murine model systems the PK and PD parameters were determined. For an initial phase 1 screening PK and PD parameters were measured and demonstrating direct correlation to the murine model [10-12]. The extensive preclinical testing demonstrate a clear potential use for this molecule in renal cell carcinoma and phase I clinical trials were fast tracked by FDA approval [13-21]. In 2009 Pazopanib was approved for first line use in treatment of renal cell carcinoma barely 3 years since its first introduction into the clinical testing phase.
Pazopanib: Clinical Status
In addition to extensive phase II and Phase III in all forms of renal cell carcinomaPazopanib clinical trials have been initiated in tumors where VEGFR plays a pivotal role. In conditions such as breast cancer [22;23], prostate cancer [24;25], liver cancer , thyroid cancer, soft cell sarcoma  and NSCLC [28-30]VEGFR has been observed to be elevated, promoting cell survival.
1. Cross MJ, Claesson-Welsh L. FGF and VEGF function in angiogenesis: signalling pathways, biological responses and therapeutic inhibition. Trends Pharmacol Sci 2001; 22(4):201-207.
2. Flaherty KT. Sorafenib: delivering a targeted drug to the right targets. Expert Rev Anticancer Ther 2007; 7(5):617-626.
3. Shinkaruk S, Bayle M et al. Vascular endothelial cell growth factor (VEGF), an emerging target for cancer chemotherapy. Curr Med Chem Anticancer Agents 2003; 3(2):95-117.
4. Schwartz JD, Rowinsky EK et al. Vascular endothelial growth factor receptor-1 in human cancer: concise review and rationale for development of IMC-18F1 (Human antibody targeting vascular endothelial growth factor receptor-1). Cancer 2010; 116(4 Suppl):1027-1032.
5. Holmes K, Roberts OL et al. Vascular endothelial growth factor receptor-2: structure, function, intracellular signalling and therapeutic inhibition. Cell Signal 2007; 19(10):2003-2012.
6. Epstein RJ. VEGF signaling inhibitors: more pro-apoptotic than anti-angiogenic. Cancer Metastasis Rev 2007; 26(3-4):443-452.
7. Melichar B, Studentova H et al. Pazopanib: a new multiple tyrosine kinase inhibitor in the therapy of metastatic renal cell carcinoma and other solid tumors. J BUON 2011; 16(2):203-209.
8. Hamberg P, Verweij J et al. (Pre-)clinical pharmacology and activity of pazopanib, a novel multikinase angiogenesis inhibitor. Oncologist 2010; 15(6):539-547.
9. Podar K, Tonon G et al. The small-molecule VEGF receptor inhibitor pazopanib (GW786034B) targets both tumor and endothelial cells in multiple myeloma. Proc Natl Acad Sci U S A 2006; 103(51):19478-19483.
10. Kumar R, Knick VB et al. Pharmacokinetic-pharmacodynamic correlation from mouse to human with pazopanib, a multikinase angiogenesis inhibitor with potent antitumor and antiangiogenic activity. Mol Cancer Ther 2007; 6(7):2012-2021.
11. Podar K, Anderson KC. Inhibition of VEGF signaling pathways in multiple myeloma and other malignancies. Cell Cycle 2007; 6(5):538-542.
12. Sonpavde G, Hutson TE. Pazopanib: a novel multitargeted tyrosine kinase inhibitor. Curr Oncol Rep 2007; 9(2):115-119.
13. Hutson TE. Targeted therapy for renal cell carcinoma: a new treatment paradigm. Proc (Bayl Univ Med Cent ) 2007; 20(3):244-248.
14. Heng DY, Bukowski RM. Anti-angiogenic targets in the treatment of advanced renal cell carcinoma. Curr Cancer Drug Targets 2008; 8(8):676-682.
15. Sloan B, Scheinfeld NS. Pazopanib, a VEGF receptor tyrosine kinase inhibitor for cancer therapy. Curr Opin Investig Drugs 2008; 9(12):1324-1335.
16. Sonpavde G, Hutson TE et al. Pazopanib, a potent orally administered small-molecule multitargeted tyrosine kinase inhibitor for renal cell carcinoma. Expert Opin Investig Drugs 2008; 17(2):253-261.
17. Bastien L, Culine S et al. Targeted therapies in metastatic renal cancer in 2009. BJU Int 2009; 103(10):1334-1342.
18. Castaneda CA, Gomez HL. Pazopanib: an antiangiogenic drug in perspective. Future Oncol 2009; 5(9):1335-1348.
19. Limvorasak S, Posadas EM. Pazopanib: therapeutic developments. Expert Opin Pharmacother 2009; 10(18):3091-3102.
20. Sonpavde G, Hutson TE et al. Pazopanib for the treatment of renal cell carcinoma and other malignancies. Drugs Today (Barc ) 2009; 45(9):651-661.
21. Bukowski RM. Pazopanib: a multikinase inhibitor with activity in advanced renal cell carcinoma. Expert Rev Anticancer Ther 2010; 10(5):635-645.
22. Amiri-Kordestani L, Tan AR et al. Pazopanib for the treatment of breast cancer. Expert Opin Investig Drugs 2012; 21(2):217-225.
23. Gril B, Palmieri D et al. Pazopanib reveals a role for tumor cell B-Raf in the prevention of HER2+ breast cancer brain metastasis. Clin Cancer Res 2011; 17(1):142-153.
24. Kutikov A, Makhov P et al. Interleukin-6: a potential biomarker of resistance to multitargeted receptor tyrosine kinase inhibitors in castration-resistant prostate cancer. Urology 2011; 78(4):968-11.
25. Ward JE, Karrison T et al. A randomized, phase II study of pazopanib in castrate-sensitive prostate cancer: a University of Chicago Phase II Consortium/Department of Defense Prostate Cancer Clinical Trials Consortium study. Prostate Cancer Prostatic Dis 2011.
26. Tan AR, Dowlati A et al. Phase I study of pazopanib in combination with weekly paclitaxel in patients with advanced solid tumors. Oncologist 2010; 15(12):1253-1261.
27. Sleijfer S, Ray-Coquard I et al. Pazopanib, a multikinase angiogenesis inhibitor, in patients with relapsed or refractory advanced soft tissue sarcoma: a phase II study from the European organisation for research and treatment of cancer-soft tissue and bone sarcoma group (EORTC study 62043). J Clin Oncol 2009; 27(19):3126-3132.
28. Nikolinakos PG, Altorki N et al. Plasma cytokine and angiogenic factor profiling identifies markers associated with tumor shrinkage in early-stage non-small cell lung cancer patients treated with pazopanib. Cancer Res 2010; 70(6):2171-2179.
29. Scagliotti G, Govindan R. Targeting angiogenesis with multitargeted tyrosine kinase inhibitors in the treatment of non-small cell lung cancer. Oncologist 2010; 15(5):436-446.
30. Ulahannan SV, Brahmer JR. Antiangiogenic agents in combination with chemotherapy in patients with advanced non-small cell lung cancer. Cancer Invest 2011; 29(4):325-337.