Combined Pan-RAF and MEK Inhibition Overcomes Multiple Resistance Mechanisms to Selective RAF Inhibitors.
Abstract
RAF and MEK inhibitors are effective in BRAF-mutant melanoma but not in BRAF-mutant colorectal cancer. To gain additional insights into this difference, we performed a genome-scale pooled shRNA enhancer screen in a BRAF-mutant, RAF inhibitor-resistant colorectal cancer cell line exposed to the selective RAF inhibitor PLX4720. We identified multiple genes along the receptor tyrosine kinase (RTK)/mitogen-activated protein kinase (MAPK) signaling axis that, when suppressed, either genetically or pharmacologically, sensitized cells to the selective RAF inhibitor through sustained inhibition of MAPK signaling. Strikingly, CRAF was a key mediator of resistance that could be overcome by the use of pan-RAF inhibitors in combination with a MEK inhibitor. Furthermore, the combination of pan-RAF and MEK inhibitors displayed strong synergy in melanoma and colorectal cancer cell lines with RAS-activating events such as RTK activation, KRAS mutation, or NF1 loss-of-function mutations. Combinations of selective RAF inhibitors, such as PLX4720 or dabrafenib, with MEK inhibitors did not incur such profound synergy, suggesting that inhibition of CRAF by pan-RAF inhibitors plays a key role in determining cellular response. Importantly, in contrast to the modest activity seen with single-agent treatment, dual pan-RAF and MEK inhibition results in the induction of apoptosis, greatly enhancing efficacy. Notably, combined pan-RAF and MEK inhibition can overcome intrinsic and acquired resistance to single-agent RAF/MEK inhibition, supporting dual pan-RAF and MEK inhibition as a novel therapeutic strategy for BRAF- and KRAS-mutant cancers.
Collections
Subject
Cell Line, Tumor
Humans
Colorectal Neoplasms
Sulfonamides
Indoles
MAP Kinase Kinase Kinases
raf Kinases
Proto-Oncogene Proteins B-raf
Protein Kinase Inhibitors
Apoptosis
MAP Kinase Signaling System
Drug Resistance, Neoplasm
Mutation
Proto-Oncogene Proteins p21(ras)
Research team
Molecular Drug Resistance
Language
eng
Date accepted
2015-08-30
License start date
2015-12
Citation
Molecular cancer therapeutics, 2015, 14 (12), pp. 2700 - 2711
Publisher
AMER ASSOC CANCER RESEARCH
Except where otherwise noted, this item's license is described
as
https://creativecommons.org/licenses/by/4.0
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