Abstract 4472: NVP-BKM120, a pan class I PI3K inhibitor impairs microvascular permeability and tumor growth as detected by DCE-MRI and IFP measurements via radio-telemetry: Comparison with NVP-BEZ235

Abstract

Abstract Tumor blood vessels are distinctly abnormal in structure and function. When compared to normal vessels, they are enlarged and tortuous and 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-BKM120, a novel, synthetic low molecular mass compound, which potently inhibits class I PI3K 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 with a variety of technologies: dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI), tumor interstitial fluid pressure (IFP) measurements in conscious animals via radio-telemetry and a modified Miles assay, representing non invasive, minimally invasive and invasive methods, respectively. Tumor histology and western blots were used to confirm pathway inhibition. For comparison, the effect of NVP-BEZ235, a potent pan class I PI3K and mTOR activity inhibitor, was assessed head-to-head in the same experiments. BKM120 induced significant decreases in VEGF-induced vascular leakage in normal and tumor tissues. These effects were similar to those obtained following BEZ235 treatment. Western blot of total ear lysates from treated mice clearly demonstrated pathway inhibition. The inhibition of vessel permeability observed with BEZ235 and BKM120 correlated with their respective anti-tumor activities, IFP change and Ktrans (vascular permeability transfer constant measured by DCE-MRI) decrease. In conclusion, our data demonstrate that in BN472 tumors, BKM120 significantly decreases tumor microvascular leakage similar to BEZ235 at equipotent antitumor dose. Changes in Ktrans may be a useful independent clinical surrogate biomarker for NVP-BKM120 efficacy. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 4472.