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Preclinical evaluation of an anti-a5b1 integrin antibody as a novel anti-angiogenic agent
Vanitha Ramakrishnan, Vinay Bhaskar, Debbie A. Law, Melanie H.L. Wong, Robert B. DuBridge, Danna Breinberg, Christopher O’Hara, David B. Powers, Gao Liu, Jennifer Grove, Peter Hevezi, Kellie M. Cass, Susan Watson, Ferdinand Evangelista, Rick A. Powers, Barbara Finck, Margaret Wills, Ingrid Caras, Yuni Fang, Donald McDonald, Dale Johnson, Richard Murray, and Ursula Jeffry

Integrin a5b1, the principal fibronectin receptor, is an important survival factor, playing a key role in angiogenesis. Angiogenesis is critical for tumor growth, and anti-angiogenic therapies have met clinical success. To validate the therapeutic potential of an anti-a5b1 strategy, we generated volociximab (M200) a chimeric human IgG4 version of the a5b1 function blocking murine antibody IIA1; and F200, the Fab derivative. Volociximab, F200 and IIA1 showed similar activity by ELISA (EC50= 0.2nM), Biacore (Kd= 0.1- 0.4nM) and inhibition of fibronectin binding (IC50= 2- 3nM). The inhibitory potential of a5b1 antibodies was compared to HuMV833, an anti-VEGF antibody. Both volociximab and HuMV833 inhibited HUVEC proliferation (IC50 of volociximab = 0.2-0.5nM; IC50 of HuMV833 = 45nM). However, IIA1, volociximab and F200 were also potent inhibitors of an in vitro model of angiogenesis (HUVEC tube formation assay), unlike HuMV833. Additionally, volociximab inhibited in vitro tube formation induced by VEGF and/or bFGF, suggesting a mechanism of action independent of growth factor stimulus. In fact, inhibition of a5b1 function by volociximab induced apoptosis of actively proliferating, but not resting, endothelial cells. Volociximab does not cross-react with rodent a5b1, therefore in vivo validation of an anti-a5b1 approach was conducted in a cynomolgus model of choroidal revascularization. Volociximab and F200 were potent inhibitors of neovessel formation in this model. These data demonstrate that volociximab has therapeutic potential in diseases in which new vessel formation is a component of the pathology.

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