C-RAF Mutations Confer Resistance to RAF Inhibitors

Abstract

Melanomas that contain B-RAFV600E mutations respond transiently to RAF and MEK inhibitors; however, resistance to these agents remains a formidable challenge. Although B- or C-RAF dysregulation represents prominent resistance mechanisms, resistance-associated point mutations in RAF oncoproteins are surprisingly rare. To gain insights herein, we conducted random mutagenesis screens to identify B- or C-RAF mutations that confer resistance to RAF inhibitors. Whereas bona fide B-RAFV600E resistance alleles were rarely observed, we identified multiple C-RAF mutations that produced biochemical and pharmacologic resistance. Potent C-RAF resistance alleles localized to a 14-3-3 consensus binding site or a separate site within the P loop. These mutations elicited paradoxical upregulation of RAF kinase activity in a dimerization-dependent manner following exposure to RAF inhibitors. Knowledge of resistance-associated C-RAF mutations may enhance biochemical understanding of RAF-dependent signaling, anticipate clinical resistance to novel RAF inhibitors, and guide the design of “next-generation” inhibitors for deployment in RAF- or RAS-driven malignancies. Cancer Res; 73(15); 4840–51. ©2013 AACR.

Oncogenic and sorafenib-sensitive ARAF mutations in lung adenocarcinoma

“…To the best of our knowledge, the ARAF and RAF1 mutations profiled in this study have not been characterized previously as oncogenic somatic mutation hot spots in clinical cancer samples. Interestingly, one group has recently associated derived RAF1 p.S257P mutations with in vitro PLX-4720 resistance in BRAF p.V600E mutant melanoma cells (18); however, all of the TCGA samples from patients with lung cancer analyzed in the current study were treatment naive.…”

Targeting cancer with kinase inhibitors

“…To date, the majority of putative resistance mechanisms involve reactivation or hyperactivation of the MAPK pathway itself (on-pathway resistance). The molecular mechanisms include amplification, mutation, or gene fusions of upstream (NRAS), parallel (CRAF; encoded by RAF1), or downstream (MEK1 and MEK2; MAP2K1 and MAP2K2, respectively) pathway components (71)(72)(73). As such, combined blockade of BRAF together with its immediate effectors, MEK1 and MEK2, has been examined in advanced clinical trials (74,75).…”

The RAF-MEK-ERK Pathway: Targeting ERK to Overcome Obstacles of Effective Cancer Therapy

“…However, through random mutagenesis screening in BRAF V600E melanomas that developed resistance to BRAFi, it was the first time to identify multiple CRAF mutations that produced biochemical and pharmacological resistance. Those CRAF mutations localized in a 14-3-3 consensus binding site or a separate site within the phosphate-binding loop (P loop), which explained paradoxical upregulation of RAF kinase activity in a dimerization-dependent manner [96].…”