BS-181 is a highly selective CDK7 inhibitor with an IC₅₀ of 21 nM, showing 40-fold selective over CDK1, 2, 4, 5, 6, or 9. IC50 & Target: IC50: 21 nM (CDK7)^[1] In Vitro: BS-181 promotes cell cycle arrest and inhibits cancer cell growth, and growth is inhibited for all cell lines tested, with IC₅₀ values ranging from 11.5 to 37 μM. BS-181 inhibits RB phosphorylation at Ser⁷⁹⁵ and Ser⁸²¹ with an apparent IC₅₀ of 15 μM, similar to the IC₅₀ obtained for P-Ser2 inhibition. BS-181 treatment of MCF-7 cells leads to G1 arrest at and apoptosis^[1]. BS-181 inhibits GC cell and normal gastric epithelial RGM-1 cell line growth with inhibitory concentration (IC₅₀) ranging from 17 to 22 μM and 6.5 μM, respectively. BS-181 significantly inhibits cell migration and invasion ability in a dose-dependent manner^[2]. In Vivo: BS-181 (5 mg/kg, 10 mg/kg, i.p.) inhibits the growth of MCF-7 tumors in nude mice. Intravenous (i.v) and i.p administration of 10 mg/kg BS-181 shows rapid clearance^[1]. BS-181 (10 mg/kg/d or 20 mg/kg/d, i.p.) significantly inhibits the growth of tumor in a dose-dependent manner compared to the control group^[2].