LAUSR

Increased activation of the RAS/RAF/MEK/ERK signaling pathway, through mutations in upstream activators or in components of the pathway, can lead to uncontrolled cellular growth and proliferation leading to tumor development. BRAF mutations are present in more than 50% of melanoma patients as well as in colorectal (5-10%), thyroid carcinomas (25-45%), hairy-cell leukemia (~100%) and less commonly in ovarian and lung malignancies. Specifically, activating BRAF mutation V600E in the kinase domain of BRAF accounts for almost 50% of melanoma. Although, FDA-approved RAF inhibitors vemurafenib and dabrafenib have elicited remarkable responses and improved survival of melanoma patients with BRAFV600E/K mutations, acquired resistance limits their effectiveness as patients relapse. Several studies have demonstrated that resistance in melanoma and other tumors involve increased formation of RAF dimers that are not effectively inhibited by clinical inhibitors. Hence, underscoring the need for improved RAF inhibitors. Toward this goal, we developed an in-cell-western assay to screen for small molecule kinase inhibitors of the ERK signaling pathway, using melanoma cells that express BRAFV600E monomers and dimers. Because several inhibitors have been identified to inhibit ERK signaling that led us to investigate the precise mechanism of inhibition. We performed structural characterization and biochemical analysis of the RAS/RAF/MEK/ERK signaling pathway in cells with different RAS/BRAF mutational background, expressing BRAF monomers and dimers. Our study enabled us to identify a kinase inhibitor that potently inhibits BRAF monomers and dimers, with distinct structural properties compared to current RAF inhibitors. Further development of this new class of RAF kinase inhibitor may lead to more effective ERK signaling inhibition and improved treatments for BRAF-dependent tumors. Citation Format: Xiomaris M. Cotto Rios, Paul Agianian, Yang Wu, Evripidis Gavathiotis. Discovery of a new kinase inhibitor targeting BRAF monomers and dimers [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2017 Oct 26-30; Philadelphia, PA. Philadelphia (PA): AACR; Mol Cancer Ther 2018;17(1 Suppl):Abstract nr LB-A35.