Identification of PLX4032‐resistance mechanisms and implications for novel RAF inhibitors

Abstract

Summary BRAF inhibitors improve melanoma patient survival, but resistance invariably develops. Here we report the discovery of novel BRAF mutation that confers resistance to PLX4032 employing whole-exome sequencing of drug-resistant BRAFV600K melanoma cells, BRAF Leu505 to His substitution (BRAFL505H) and describe a new screening approach, a genome-wide piggyBac mutagenesis screen that revealed clinically relevant aberrations (N-terminal BRAF truncations and CRAF overexpression). The BRAFL505H is the first resistance-conferring second-site mutation identified in BRAF mutant cells. The mutation replaces a small nonpolar amino acid at the BRAF-PLX4032 interface with a larger polar residue. Moreover, we show that BRAFL505H, found in human prostate cancer, is itself a MAPK-activating, PLX4032-resistant oncogenic mutation. Lastly, we demonstrate that the PLX4032-resistant melanoma cells are sensitive to novel, next-generation BRAF inhibitors, especially the “paradox-blocker” PLX8394, supporting its use in clinical trials for treatment of melanoma patients with BRAF-mutations.

KRAS: The Critical Driver and Therapeutic Target for Pancreatic Cancer

“…Several pan-RAF inhibitors are currently in phase I clinical trials. Another second-generation RAF inhibitor is the “paradox breaker” PLX8394 that also effectively inhibits CRAF and BRAF (Basile et al 2014; Choi et al 2014; Zhang et al 2015). PLX8394 effectively blocked ERK activation and growth of RAS -mutant, vemurafenib-resistant melanoma cells.…”

Recent progress on MAP kinase pathway inhibitors

“…It is also reportedly able to inhibit vemurafenib-resistant melanoma cells, which acquire their resistance via a Leu505 to His substitution in the B-RAF protein (B-RAF L505H ). 17 This mutation replaces a small nonpolar amino acid at the B-RAF-vemurafenib interface with a larger polar residue and is itself a MAPK-activating oncogenic mutation. Acquired resistance to vemurafenib and dabrafenib is also frequently driven by expression of mutation B-RAF splice variants.…”

Genomically Driven Tumors and Actionability across Histologies:BRAF-Mutant Cancers as a Paradigm

“…However, some activating mutations in BRAF have been shown to be less sensitive or even resistant to BRAF inhibitors in preclinical studies. For example, the activating BRAF L505H mutation appears to be resistant to vemurafenib (70). In addition, some mutations in BRAF, including substitutions at codon 466, are inactivating (18); BRAF inhibitors are predicted to be ineffective for such mutations.…”