Abstract 1975: PHuDock®, a computational discovery and development platform for novel PH domain-binding agents, identifies a novel antitumor AKT/PDPK1 inhibitor, PHT- 427

The PH (pleckstrin homology) domain is a highly conserved phosphatidylinositol-3-phosphate (PtdIn-3-P) binding 3D superfold found in approximately 40 high value protein targets that are components of signal transduction pathways regulating cancer cell growth, survival and metabolism. PHuDock® is a computational platform that integrates high-throughput molecular docking coupled to large chemical and biological databases, with high-performance computing clusters allowing computationally intensive calculations and virtual screening to be conducted for the discovery and development of PH-domain targeted anticancer agents. The platform is integrated with about 10 million curated drug-like compounds, more than 100 PH domain proteins for selectivity evaluation, and over 6000 other proteins for off-target and toxicity modeling. When no protein crystal structure exists for a PH domain, homology modeling is used to build 3D structures. Surface plasmon resonance spectroscopy is used to determine the binding affinities of inhibitors to expressed PH domains. Using this approach we have identified PHT-427 a dual PDKP1 and AKT inhibitor. Both are members of the PtdIns-3-kinase (PI-3-K) signaling pathway that plays a critical role in activating survival and anti-apoptotic signaling in cancer cells. The pathway is constitutively activated in many different cancer types. Emerging evidence suggest that AKT and PDKP1 play complimentary yet independent roles in signaling by the pathway. Thus a dual inhibitor should have advantages over an inhibitor of either target alone. Our data show that PHT-427 binds to the expressed PH domains of AKT and PDPK1 and inhibits AKT and PDPK1 signaling in cells and tumor xenografts with decreased activation of downstream signaling targets for both. PHT-427 also inhibits the translocation of AKT and PDPK1-tagged GFP constructs from the cytoplasm to the plasma membrane in cancer cells. PHT-427 given orally on a twice-daily schedule at doses of 125 to 250 mg/kg inhibited the growth rate of human tumor xenografts in scid mice with up to an 80% inhibition of tumor growth. Tumors with PIK3CA mutation were among the most sensitive while tumors with a K-Ras mutation were less sensitive. Combination antitumor studies showed that PHT-427 has greater than additive activity with both paclitaxel in MCF-7 breast cancer and erlotinib in orthotopic NCI-H441 non-small cell lung cancer. There was minimal toxicity of PH-427 at doses that gave antitumor activity. In summary, we have used PHuDock® to efficiently identify a novel orally active PH domain binding inhibitor of PDPK1/AKT signaling showing minimal toxicity and antitumor activity against human tumor xenografts. 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 1975.