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Characterize Disease-related Mutants of RAF Family Kinases by Using a Set of Practical and Feasible Methods
Published on: July 17, 2019
Combined Pan-RAF and MEK Inhibition Overcomes Multiple Resistance Mechanisms to Selective RAF Inhibitors
Steven R Whittaker1, Glenn S Cowley2, Steve Wagner3
1Department of Medical Oncology, Dana-Farber Cancer Institute, Boston, Massachusetts. The Broad Institute, Cambridge, Massachusetts. Division of Cancer Therapeutics, Institute of Cancer Research, London, United Kingdom.
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.
Insights
Pan-RAF and MEK inhibitors overcome resistance in BRAF-mutant colorectal cancer by targeting CRAF. This combination therapy shows promise for BRAF- and KRAS-mutant cancers, inducing apoptosis and enhancing efficacy.
Area of Science:
- Oncology
- Molecular Biology
- Cancer Signaling Pathways
Background:
- RAF and MEK inhibitors are effective against BRAF-mutant melanoma but show limited efficacy in BRAF-mutant colorectal cancer.
- Understanding the molecular mechanisms underlying this differential response is crucial for developing effective cancer therapies.
Purpose of the Study:
- To investigate the genetic basis of resistance to RAF inhibitors in BRAF-mutant colorectal cancer.
- To identify therapeutic strategies that can overcome resistance and enhance treatment efficacy in BRAF-mutant and other RAS-driven cancers.
Main Methods:
- Genome-scale pooled shRNA enhancer screen in a BRAF-mutant, RAF inhibitor-resistant colorectal cancer cell line.
- Treatment with selective RAF inhibitor PLX4720.
- Genetic and pharmacological suppression of genes within the receptor tyrosine kinase (RTK)/mitogen-activated protein kinase (MAPK) signaling axis.
- Combination therapy studies using pan-RAF inhibitors, selective RAF inhibitors, and MEK inhibitors.
Main Results:
- Suppression of multiple genes in the RTK/MAPK pathway sensitized colorectal cancer cells to RAF inhibitors.
- CRAF was identified as a key mediator of resistance, which could be overcome by combining pan-RAF inhibitors with MEK inhibitors.
- Dual pan-RAF and MEK inhibition demonstrated strong synergy in melanoma and colorectal cancer cell lines with RAS-activating events (e.g., RTK activation, KRAS mutation, NF1 loss).
- Pan-RAF/MEK inhibition induced apoptosis and overcame both intrinsic and acquired resistance to single-agent RAF/MEK inhibitors.
Conclusions:
- Dual inhibition of pan-RAF and MEK is a potent therapeutic strategy for BRAF- and KRAS-mutant cancers.
- Targeting CRAF with pan-RAF inhibitors in combination with MEK inhibitors is critical for overcoming resistance in colorectal cancer.
- This combination approach significantly enhances anti-cancer efficacy compared to single-agent treatments.
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