Abstract 2522: Identification and characterization of new highly selective and potent BRAF inhibitors

Aberrant activation of the MAPK-mediated pathway components, RAF-MEK-ERK, is frequently found in human cancers and clearly contributes to oncogenesis. In particular, one of the three isoforms of RAF, BRAF, presents activating somatic mutations in 70% of melanomas, 50% of thyroid cancers, 10% of colon and 20% ovarian carcinomas. The most common BRAF mutation, substitution of glutamic acid for valine at position 600 within the activation segment of the kinase domain, accounts for 90% of mutated BRAF cases, and results in elevated kinase activity with consequent enhanced promotion of cell survival and proliferation. Here we describe the in vitro and in vivo properties of a novel class of potent and selective BRAF inhibitors. Starting from a series of arylpyrazole derivatives that were found to be active against wild-type and mutated BRAF, an expansion and optimization program was undertaken. This led to the identification of both inhibitors of the active conformation and inhibitors of the inactive conformation of the enzyme, as confirmed by co-crystallography studies. Among the former category, a sub-series endowed with high potency and selectivity was identified, with compounds possessing low nM affinity for BRAF V600E and negligible cross-reactivity against a panel of 44 kinases. Members of this sub-series inhibited 72-hour proliferation of cell lines harboring the BRAF V600E mutation with IC 50 s below 100 nM and with greater than 100-fold selectivity compared to lines with wild-type BRAF. Consistent with this observation, inhibition of the MAPK signal transduction pathway was highly selective for cell lines with mutated BRAF. Biochemical profile, potency in cell proliferation assays, and cellular mechanism of action compared favorably among the sub-series to a reference BRAF inhibitor, PLX-4720, tested in parallel. The most potent compounds (e.g. NMS-P730 and NMS-P383) were selected for in vivo evaluation. In vivo, potent tumor growth inhibition was observed in the A375 xenograft model following oral administration, with no overt toxicity, and with corresponding modulation of the MAPK pathway, consistent with expected mechanism of action. Selection of candidates most suitable for further development is underway. 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 2522.