Discovery of a potent and orally available SOS1 inhibitor with antitumor efficacy in KRAS-mutant colorectal cancers.

As a key guanine nucleotide exchange factor, SOS1 is an attractive therapeutic target for KRAS-driven colorectal cancer. In this study, based on the co-crystal structure of SOS1 in complex with BI-68BS, we developed a high-affinity fluorescent tracer TRR2 (K = 0.134 μM), and established a robust fluorescence polarization assay for the profiling of SOS1 inhibitors. Subsequent structure-based optimization yielded a series of SOS1 inhibitors, among which SL43 emerged as the most promising candidate. SL43 demonstrated superior binding affinity to SOS1 (K = 0.16 μM), potently disrupted the SOS1-KRAS interaction (IC = 13.0 nM) and broadly inhibited SOS1-mediated nucleotide exchange on multiple KRAS mutants (G12C, G12V and G12D; IC = 13.4-29.1 nM). Biologically, SL43 exhibited potent and selective antiproliferative activity against KRAS-mutant colorectal cancer cells (IC = 0.028-0.238 μM), achieving over 100-fold selectivity over KRAS wild-type cells. in Balb/c mice, SL43 displayed a favorable profile with a moderate half-life (T = 4.6 h) and high oral bioavailability (F = 56.8%). In an HCT116 xenograft model, oral administration of SL43 (20 and 40 mg/kg) also significantly suppressed tumor growth (TGI = 57.2% and 74.9%, respectively), outperforming MRTX0902 (60 mg/kg, TGI = 47.1%) with no observable systemic toxicity. In conclusion, SL43 represents a potent and orally bioavailable SOS1 inhibitor that effectively suppresses KRAS signaling and exerts strong antitumor efficacy, highlighting its potential as a promising candidate for KRAS-mutant colorectal cancer.