Resistance to the KRASG12D Inhibitor MRTX1133 is Associated with Aberrant Histone Acetylation and Increased Sensitivity to BET Inhibition

Inhibition of the histone acetyltransferase EP300 reversed the drug-resistant phenotype in vitro, which subsequent RNA sequencing experiments determined was associated with the suppression of pro-survival FOSL1 signaling. Accordingly, siFOSL1 reversed the MRTX1133-resistant phenotype with similar effects on pro-survival signaling. Given the lack of clinically useful EP300 or FOSL1 inhibitors, we next explored whether inhibitors of the acetylation scanning BET proteins would be similarly effective.

The addition of BET inhibitors re-sensitized several highly resistant cell lines to MRTX1133 and impaired FOSL1-mediated survival signaling in vitro. In murine models of MRTX1133-resistant PDAC, BET inhibition cooperated with MRTX1133 to markedly extend overall survival. As BET inhibitors are currently under clinical testing, the combination of MRTX1133 and BET inhibitors warrants further investigation, particularly in tumors that have developed resistance to KRAS inhibition.