Discernment between candidate mechanisms for KRAS G13D colorectal cancer sensitivity to EGFR inhibitors
Thomas McFall1, Noah K Schomburg2, Kent L Rossman2
1Integrative Biology Laboratory, Salk Institute for Biological Studies, 10010 N. Torrey Pines Rd, La Jolla, CA, 92037, USA.
Abstract:
Phase three clinical trial evidence suggests that colorectal cancers with the KRAS G13D mutation may benefit from EGFR inhibitors, like cetuximab, in contrast to the other most common KRAS mutations. A mechanism to explain why this mutation behaves differently from other KRAS mutations had long been lacking. Two recent studies have reproduced KRAS G13D specific sensitivity to cetuximab in cellular models, and both have implicated the tumor suppressor NF1 as a critical variable in determining sensitivity and resistance. One study proposes a mechanism that focuses on the inhibition of active, GTP-bound wild-type RAS, which is proposed to occur to a greater extent in KRAS G13D tumors due to the inability of KRAS G13D to bind NF1 well. The other study suggests NF1 can convert GTP-bound KRAS G13D to inactive, GDP-bound KRAS G13D. Here, we report an inability to reproduce cellular and biophysical studies that suggested NF1 has strong GTPase activity on KRAS G13D. We also report additional data that further suggests only WT RAS-GTP levels are reduced with EGFR inhibition and that KRAS G13D is impaired in binding to NF1. These new experiments further support a mechanism in which cetuximab inhibits wild-type (HRAS and NRAS) signals in KRAS G13D colorectal cancers. Video Abstract.
Insights
Colorectal cancers with KRAS G13D mutations may respond to EGFR inhibitors. This study challenges the proposed role of NF1 in this sensitivity, suggesting cetuximab primarily impacts wild-type RAS signaling in these tumors.
Area of Science:
- Oncology
- Molecular Biology
- Cancer Genetics
Background:
- Phase III trials indicate KRAS G13D mutations in colorectal cancer may benefit from EGFR inhibitors, unlike other KRAS mutations.
- The underlying mechanism for KRAS G13D-specific sensitivity to EGFR inhibitors has remained unclear.
- Recent studies implicated the tumor suppressor NF1 in mediating sensitivity or resistance to EGFR inhibitors in KRAS G13D colorectal cancers.
Purpose of the Study:
- To investigate the proposed mechanisms by which NF1 influences sensitivity to EGFR inhibitors in KRAS G13D colorectal cancer.
- To determine if NF1 exhibits GTPase activity on KRAS G13D.
- To elucidate the signaling pathways affected by EGFR inhibition in KRAS G13D colorectal cancer.
Main Methods:
- Reproduced cellular and biophysical experiments from previous studies.
- Assessed NF1's GTPase activity on KRAS G13D.
- Measured wild-type RAS-GTP levels following EGFR inhibition.
- Evaluated the binding affinity between KRAS G13D and NF1.
Main Results:
- Failed to reproduce studies suggesting NF1 possesses significant GTPase activity on KRAS G13D.
- Observed that EGFR inhibition reduces wild-type RAS-GTP levels, not KRAS G13D-GTP.
- Demonstrated that KRAS G13D exhibits impaired binding to NF1.
- Supported a mechanism where cetuximab inhibits wild-type (HRAS, NRAS) signaling in KRAS G13D colorectal cancers.
Conclusions:
- The proposed mechanism involving NF1's direct GTPase activity on KRAS G13D is not supported by these findings.
- EGFR inhibitors like cetuximab likely exert their therapeutic effect in KRAS G13D colorectal cancer by inhibiting wild-type RAS signaling pathways.
- Further research is needed to fully understand the complex interplay between KRAS mutations, NF1, and EGFR inhibitor response.
