S961 acetate is an high-affinity and selective insulin receptor (IR) antagonist with IC50s of 0.048, 0.027, and 630 nM for HIR-A, HIR-B, and human insulin-like growth factor I receptor (HIGF-IR) in SPA-assay, respectively.In Vitro: S961 also shows high-affinity to Rat IR and Pig IR with IC50s of 0.056 nM and 0.084 nM in PEG-assay, respectively.