Discovery of a novel, dual mechanism anti-angiogenic and anti-proliferative agent with oral anti-tumor activity

4558 Angiogenesis, the growth of new microvessels, is considered critical for the growth of most solid tumors and their metastatic spread. Agents that inhibit tumor-induced angiogenesis generally either target processes involved in activating endothelial cell (EC) and/or smooth muscle cell (SMC) proliferation (typically growth factors such as VEGF, PDGF, bFGF) or block other functional steps in the angiogenesis process (e.g. EC migration, adhesion, alignment and tube formation), but without directly affecting tumor cell growth. While pure angiogenesis inhibitors have been demonstrated pre-clinically and clinically to produce anti-tumor activity when administered as monotherapy, the current thinking is that the more effective anti-cancer therapy might be anti-angiogenic therapeutics used in combination with cytotoxic or directed cytostatic agents that also target the proliferating tumor cells. An agent that simultaneously targets both the angiogenic process and the tumor cell compartment by combining both anti-angiogenic and tumor cell anti-proliferative activites into a single molecule would be highly desirable and would represent a novel class of oncology therapeutics. By cross-screening potent anti-angiogenic PDGFR-kinase inhibitors for tumor cell anti-proliferative activity, dual mechanism compounds with novel properties were identified. Using this strategy, we identified ATP-competitive inhibitors of PDGF receptor tyrosine kinase that exhibit both anti-angiogenic and tumor cell anti-proliferative activities. One such compound potently inhibits PDGFR-β kinase with an IC50 of 0.002 μM and displays relatively good selectivity versus a large panel of serine/threonine and other tyrosine kinases. In cell-based assays, the compound exhibits potent, concentration-dependent inhibition of PDGF-BB-stimulated SMC proliferation (IC50 = 0.003 μM) and it directly inhibits the in vitro growth of 9 of 11 human tumor cell lines in culture (IC50s= 0.007 –0.033 μM). The selected compound exhibits potent anti-angiogenic activity in vitro in the rat aortic ring assay of microvessel outgrowth (IC50 = 0.015 μM) and is active in vivo following oral dosing at 30 mg/kg in the matrigel mouse model of PDGF-BB-stimulated angiogenesis. When administered orally as a single agent to nude mice bearing human tumor xenografts, the compound produces significant, dose-dependent (25-100 mg/kg, BID) growth inhibition against four different human tumors (LoVo colon, A375 melanoma, H460 lung and MDA-MB-231 breast) suggesting broad anti-tumor activity. The primary pharmacology of this interesting dual mechanism compound will be presented.