RAS mutation-specific responses to paralog- and state-selective RAS inhibitors.

A high therapeutic index, defined as potent inhibition of oncogenic signaling in tumor cells with minimal effects on normal cells, is critical for effective cancer therapies. Recent advances have introduced diverse RAS-targeting inhibitors, including mutant-specific inhibitors such as KRAS G12C and KRAS G12D, as well as paralog- and state-selective inhibitors. Non-mutant-specific RAS inhibition can be achieved by: (1) guanine nucleotide exchange-OFF inhibitors that indirectly inactivate RAS by targeting SHP2 or SOS1, (2) KRAS-OFF inhibitors that spare NRAS and HRAS, and (3) active-state RAS(ON) inhibitors that directly block binding of effector RAF. However, the signaling inhibition index (SII)-the differential suppression of oncogenic signaling between RAS-mutant and normal cells-remains poorly defined for these approaches. We evaluated the SII for state- and paralog-selective RAS inhibitors across diverse RAS-mutant and RAS-wild-type models. Guanine nucleotide exchange-OFF inhibitors exhibited neutral or negative values, with reduced MAPK suppression in KRAS G12X cells compared to wild-type cells. KRAS G13D models, especially with NF1 loss, showed low sensitivity. SHP2 plus MEK inhibition resulted in low selectivity, and RAS Q61X models were resistant due to MEK inhibitor-induced NRAS reactivation and altered SHP2 conformations. KRAS-OFF inhibitors demonstrated higher selectivity, while active-state RAS(ON) inhibitors showed broader activity but narrow selectivity. Sensitivity to mutant-specific inhibitors largely overlapped with sensitivity to state-selective agents, suggesting that most RAS-mutant tumors will respond poorly to any currently available RAS inhibitor. Implications: Determining the signaling inhibition index (SII) can inform the design and clinical application of RAS-targeted therapies to improve tumor selectivity and therapeutic outcomes.