Pharmacological SOS1 inhibitor BI-3406 demonstrates in vivo anti-tumor activity comparable to SOS1 genetic ablation in KRAS mutant tumors

Resistance to KRASmut inhibitors frequently arises, warranting further searches for anti-RAS cancer therapies. We evaluated the tolerability and efficacy of SOS1 pharmacological inhibition in comparison to genetic ablation in different KRAS-dependent tumor settings. Contrary to the rapid lethality caused by SOS1 genetic ablation in SOS2KO mice, SOS1 pharmacological inhibition by its specific inhibitor BI-3406 did not significantly affect animal weight/viability nor cause noteworthy systemic toxicity. In BI-3406-treated KRASmut MEFs, we observed significantly reduced RAS-GTP levels and RAS downstream signaling, as well as decreased tumor burden and slower disease progression resulting from tumor-intrinsic and extrinsic therapeutic drug effects. In vivo analyses of KRASG12D allografts in immunocompromised mice and KRASG12D-driven lung adenocarcinomas in immunocompetent mice showed that systemic BI-3406 treatment impaired tumor growth and downmodulated components of the tumor microenvironment comparably to the KRASG12D inhibitor MRTX1133. Markedly stronger synergistic antitumor effects were observed upon concomitant BI-3406+MRTX113 treatment, confirming SOS1 as an actionable therapy target in RAS-dependent cancers.