Identification of 1-(3-(6,7-Dimethoxyquinazolin-4-yloxy)phenyl)-3-(5-(1,1,1-trifluoro-2-methylpropan-2-yl)isoxazol-3-yl)urea Hydrochloride (CEP-32496), a Highly Potent and Orally Efficacious Inhibitor of V-RAF Murine Sarcoma Viral Oncogene Homologue B1 (BRAF) V600E

The Ras/RAF/MEK/ERK mitogen-activated protein kinase (MAPK) signaling pathway plays a central role in the regulation of cell growth, differentiation, and survival. Expression of mutant BRAF^V600E results in constitutive activation of the MAPK pathway, which can lead to uncontrolled cellular growth. Herein, we describe an SAR optimization campaign around a series of quinazoline derived BRAF^V600E inhibitors. In particular, the bioisosteric replacement of a metabolically sensitive <i>tert</i>-butyl group with fluorinated alkyl moieties is described. This effort led directly to the identification of a clinical candidate, compound <b>40</b> (CEP-32496). Compound <b>40</b> exhibits high potency against several BRAF^V600E-dependent cell lines and selective cytotoxicity for tumor cell lines expressing mutant BRAF^V600E versus those containing wild-type BRAF. Compound <b>40</b> also exhibits an excellent PK profile across multiple preclinical species. In addition, significant oral efficacy was observed in a 14-day BRAF^V600E-dependent human Colo-205 tumor xenograft mouse model, upon dosing at 30 and 100 mg/kg BID