ABSTRACT
The small-molecule drug ralimetinib was developed as an inhibitor of the kinase p38α, and it has advanced to phase 2 clinical trials in oncology. Here, we apply a multi-modal approach to demonstrate that ralimetinib’s anti-cancer activity occurs due to its ability to inhibit EGFR, rather than p38α. We find that cancer cell lines driven by EGFR mutations exhibit the greatest sensitivity to ralimetinib treatment, and ralimetinib phenocopies established EGFR inhibitors in pharmacogenomic profiling experiments. We further demonstrate that ralimetinib inhibits EGFR kinase activity in vitro and in cellulo, albeit at >30-fold higher concentrations than it inhibits p38α. Finally, while deletion of the gene encoding p38α has no effect on ralimetinib sensitivity, expression of the EGFR-T790M gatekeeper mutation confers resistance to ralimetinib treatment. These findings suggest that future clinical trials involving ralimetinib could incorporate EGFR mutation status as a biomarker to identify sensitive patients. Moreover, our results demonstrate that a compound’s anti-cancer effects should not necessarily be attributed to the protein that it inhibits most strongly, and instead, comprehensive cellular and genetic profiling is required to understand a drug’s mechanism-of-action.
Competing Interest Statement
J.C.S. is a co-founder of Meliora Therapeutics, a member of the advisory board of Surface Ventures, and an employee of Google, Inc. This work was performed outside of her affiliation with Google and used no proprietary knowledge or materials from Google. J.M.S. has received consulting fees from Merck, Pfizer, Ono Pharmaceuticals, and Highside Capital Management, is a member of the advisory board of Tyra Biosciences and the Chemical Probes Portal, and is a co-founder of Meliora Therapeutics. Meliora Therapeutics is seeking to develop new strategies to characterize the MOAs of anti-cancer compounds, and a research grant from Meliora Therapeutics supported some of the work described in this manuscript.