Abstract 387: Development of a model of acquired resistance to a multi targeted VEGFR TKI and strategies to target resistance mechanisms through combination

Proceedings: AACR 101st Annual Meeting 2010‐‐ Apr 17‐21, 2010; Washington, DC Anti angiogenic agents that target the VEGF pathway (bevacizumab, sorafenib and sunitinib (SU)) have demonstrated improved clinical benefit as single agents or in combination with chemotherapy in a variety of solid tumor types. Although this class of agents has provided an improved treatment option to certain tumor types, it is evident that some patients do not respond to therapy or will relapse despite an initial response to treatment due to an acquired resistance. To better understand this mode of acquired resistance to this class of agents, a model of Renal Cell Carcinoma (RCC) which has shown regression, eventually developed evasive resistance during long term administration of the single agent sunitinib (a small-molecule inhibitor of the VEGF-1, 2, 3, PDGF-α,β, KIT, CSF-1R and FLT-3 receptor tyrosine kinases). Despite the observation that resistant tumors under continuous treatment with sunitinib (60 mg/kg PO, QD) demonstrated a gross phenotypic reduction of micro-vascular density (MVD), they continued to show a progressive increase in size. Because the observed low MVD phenotype was suggestive of an ability of resistant tumor cells to survive in an increasingly hypoxic environment with a reduced functional vasculature, emphasis was placed on identifying tumor cell derived resistance factors. Gene expression and/or proteomic profiling studies accompanied by confirmatory immunoblotting indicated a subset of differentially expressed genes and/or proteins in resistant vs. sensitive treated tumors. Although profiling studies did not clearly elucidate definitive resistance mechanisms, the dysregulation of EGFR, FGFR1, & TGFB1 pathways and downstream signaling through PI3K and MEK were potentially implicated. Comparative genomic hybridization studies did not identify any resistance mechanisms at the cytogenetic level. Sunitinib combination studies designed to target pathways potentially involved in resistance (SU + a PI3K/mTOR inhibitor; SU + a MEK inhibitor) demonstrated the ability to restore sensitivity in the sunitinib resistance model. The ability to identify and characterize resistance mechanisms and circumvent resistance through combination approaches may have utility in developing future combination regimens for anti angiogenic therapies. 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 387.