43P Pre-clinical evaluation of potent and orally bioavailable next-generation inhibitors targeting the family of mutants that drive oncogenic BRAF dimer formation

Abstract

The canonical BRAF V600E (class I) mutation is a potent oncogene which is uniquely active as a RAS-independent monomer, and which has been successfully targeted by several FDA-approved inhibitors. While active against monomeric BRAF V600E, these first generation BRAF inhibitors induce paradoxical activation of RAS-driven BRAF dimers in cells expressing wild-type RAF, and this can lead to secondary malignancies. More recently, numerous non-canonical BRAF oncogenic mutations including BRAF-fusions have been described as oncogenes that drive RAS-independent (class II) or RAS-dependent (class III) dimers. These non-canonical dimeric BRAF oncogenes are resistant to the first-generation drugs, effective only against the monomeric BRAF V600E mutation. Discovery of an inhibitor directed against the family of dimeric BRAF oncogenic mutations which avoids paradoxical activation is a major unmet need. We applied our proprietary Mutation-Allostery-Pharmacology (MAP) platform technology developed by Black Diamond Therapeutics to identify and validate a group of previously uncharacterized non-canonical oncogenic class II and class III BRAF mutation clusters. We further demonstrate that this ensemble of both novel and previously validated non-canonical oncogenic BRAF mutants can form the basis of a differentiated drug discovery program aimed at identifying small molecules that potently and selectively target this family of dimeric BRAF mutations. Herein, we describe a series of small molecule inhibitors with potent anti-proliferative activity directed against tumor cells harboring dimer-inducing BRAF oncogenic mutations and which are devoid of paradoxical RAF activation. Leading exemplars of BDTX compounds are orally available inhibitors that achieve target engagement of BRAF dimer oncogenes in vivo and robust anti-tumor efficacy in xenograft models in mice. These data support continued development of rationally designed molecules targeting a broad range of non-canonical BRAF dimer-promoting mutations to extend the prospect of precision medicine in patients with BRAF mutant tumors.