A non-conserved histidine residue on KRAS drives paralog selectivity of the KRAS G12D inhibitor MRTX1133

The discovery of small molecule inhibitors against mutant KRAS protein was a recent breakthrough in targeted therapy. Understanding the mechanism of selectivity by KRAS inhibitors and the mechanism of resistance to them can guide the future development of KRAS inhibitors. MRTX1133 was the first non-covalent inhibitor against the KRAS G12D mutant that demonstrated specificity and potency in pre-clinical tumor models. We used isogenic cell lines expressing a single RAS allele to evaluate the selectivity of this compound. We found that in addition to KRAS G12D, MRTX1133 shows significant activity against several other KRAS mutants as well as wildtype KRAS protein. In contrast, MRTX1133 exhibits no activity against both G12D and wildtype forms of HRAS and NRAS proteins. Functional analysis revealed that the selectivity of MRTX1133 towards KRAS is associated with its binding to histidine 95 on KRAS, a residue that is not conserved in HRAS and NRAS. Reciprocal mutation of amino acid 95 among the three RAS paralogs resulted in reciprocal change in their sensitivity towards MRTX1133. Thus, histidine 95 is an essential selectivity handle for MRTX1133 towards KRAS. This knowledge could aid the development of future KRAS-selective inhibitors.