Abstract 3743: NVP-BYL719, a selective inhibitor of the class Ia PI3K isoform alpha impairs angiogenesis and microvascular permeability.

Abstract

Abstract Tumor blood vessels are distinctly abnormal in structure and function. When compared to normal vessels, they are enlarged, tortuous, leaky, poorly covered by pericytes and with a defective basement membrane. VEGF is a prominent cytokine responsible for the hyperpermeable state of tumor microvasculature to plasma macromolecules. The phosphatidylinositol 3-kinase (PI3K)-Akt signaling pathway functions downstream of VEGF and can activate the production of the free radical gas nitric oxide (NO) through the enzyme endothelial NO synthase (eNOS), a key player for the in vivo biological activity of VEGF. In the present study, we investigated the effect of NVP-BYL719, a novel, synthetic low molecular mass compound, which potently and selectively inhibits class I PI3K isoform alpha activity, on vascular leakage in tumors and its impact on tumor progression in an orthotopic breast cancer model (BN472) in syngeneic rats. Effects on the vasculature were investigated in normal and tumor tissues via tumor interstitial fluid pressure (IFP) measurements in conscious animals via radio-telemetry and a modified Miles assay. The antiangiogenic effect of NVP-BYL719 and its impact on tumor progression was also assessed in an U87MG glioblastoma subcutaneous xenograft tumor model. Pathway inhibition was confirmed using tumor histology and Reverse Phase Protein Array (RPPA) approaches. NVP-BYL719 inhibits VEGF driven tissue formation as well as neo-vascularization of the newly formed tissue. Moreover, the compound strongly inhibited microvessel permeability in normal tissue as determined in the modified miles assay. Similarly, tumor interstitial fluid pressure (IFP), a phenomenon that is directly dependent on tumor vessel permeability, was significantly reduced (up to 43%) by NVP-BYL719 in a dose-dependent manner, upon oral administration in BN472 mammary carcinoma grown orthotopically in syngeneic rats. Concomitantly, tumor growth was significantly inhibited in BN472 mammary carcinoma and U87MG xenografts. The compound was well tolerated with no significant body weight loss at any tested dose. In conclusion, our data suggest that NVP-BYL719, a Class I PI3K selective inhibitor of p110 alpha, interferes with the tumor vasculature system. Thus, the anti-angiogenic proprieties of NVP-BYL719 might participate to the antitumor activity (or efficacy) of the compound. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3743. doi:1538-7445.AM2012-3743