Structural and Biophysical Characterization of Aminobenzo[d]isothiazole 1,1-Dioxide SOS1 Ligands.

SOS1 is a guanine nucleotide exchange factor that promotes KRAS activation by catalyzing GDP release and GTP loading, making SOS1-mediated nucleotide exchange an attractive therapeutic target in KRAS-driven cancers. Herein, we report the synthesis, biophysical characterization, and structural analysis of aminobenzo-[d]-isothiazole 1,1-dioxide SOS1 ligands. Compound 6f engaged SOS1 with a KD of 570 nM by microscale thermophoresis, supported by surface plasmon resonance. X-ray crystal structures of SOS1 bound to compounds 6b and 6f refined previous binding hypotheses regarding pocket engagement. Rather than being dominated by sulfone-mediated contacts, SOS1 recognition is primarily driven by hydrophobic and aromatic packing within the canonical pocket, a conserved ligand NH hydrogen bond to Asn879, and π-π stacking with Tyr884, recapitulating key features of BI-3406 binding. Comparative analysis further delineates vector requirements for productive engagement of KRAS-facing regions, providing a structure-based framework for future optimization of aminobenzo-[d]-isothiazole 1,1-dioxide SOS1 ligands.