Abstract A5: Tivozanib, a selective VEGFR TKI, potently blocks angiogenesis and growth in tumors that express a high level of VEGF-C and are refractory to VEGF-A blockade.

Abstract

Abstract Background: Scientific understanding of the role of VEGF-A in tumor angiogenesis has led to the development of antiangiogenic therapies, such as bevacizumab, that selectively target VEGF-A. However, clinical trials across multiple cancer types have resulted in limited positive outcomes. VEGF-C is thought to be a potent lymphangiogenic growth factor and plays a role in tumor angiogenesis through VEGFR3; it has also been shown to bind to VEGFR2, which is important in tumor angiogenesis. Nevertheless, a direct role of VEGF-C in driving tumor angiogenesis has not been established. To explore the potential of VEGF-C as a driver of tumor angiogenesis and its implication in developing antiangiogenic therapies, we assessed the activity of tivozanib, a potent and selective TKI for VEGFR1, 2 and 3, and a VEGF-A targeted antibody in animal tumor models that exhibit distinct VEGF-C and VEGF-A expression. Method: A total of 107 independently derived murine breast tumors were expanded in vivo to establish population-based primary tumor models. The tumors were characterized for their angiogenesis phenotypes, including expression of angiogenic factors, microvasculature (demonstrated by quantitative CD31 IHC analysis), and myeloid infiltration, a previously identified mediator of tivozanib resistance. To examine the role of VEGF-C vs. VEGF-A in tumor angiogenesis and in affecting response to anti-VEGF therapies, a panel of representative tumors were tested with the cross species anti-VEGF-A antibody B20–4.1 and tivozanib. Tivozanib was also compared with B20–4.1 in blocking VEGF-C stimulated VEGFR2 or VEGFR3 activation in endothelial cells, and in VEGF-C stimulated in vivo angiogenesis in matrigel assay. Results: Three distinct subtypes of tumors were identified: those that expressed high level of VEGF-A and low VEGF-C, or high VEGF-C and low VEGF-A, or both high VEGF-A and high VEGF-C. These tumors exhibited characteristic VEGF driven microvasculature. When treated with systemic administration of B20–4.1 or tivozanib, the tumors expressing high VEGF-A showed comparable response to both agents, while the tumors expressing high VEGF-C but low VEGF-A only responded to tivozanib. In tumors that express both high VEGF-A and high VEGF-C, B20–4.1 treatment resulted in only modest response, while tivozanib completely blocked tumor progression accompanied by vast central necrosis. Pharmacodynamic analysis in representative tumors revealed tumor death associated with progressive hypoxia in tivozanib-treated tumors, consistent with antiangiogenic mechanism of action. Consistent with these findings, tivozanib, but not B20–4.1, potently blocked VEGF-C stimulated VEGFR2 and VEGFR3 activation in endothelial cells, and effectively blocked VEGF-C induced in vivo angiogenesis in a matrigel assay. Conclusion: These data suggest that VEGF-C can play a direct role in tumor angiogenesis, and that tumor expressing high level of VEGF-C are sensitive to VEGFR TKI tivozanib but are refractory to VEGF-A targeted antibodies. These findings provides further scientific evidence that pan-VEGFR TKIs may have broader activity than agents that selectively target VEGF-A. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2011 Nov 12-16; San Francisco, CA. Philadelphia (PA): AACR; Mol Cancer Ther 2011;10(11 Suppl):Abstract nr A5.