Samuraciclib hydrochloride is a potent, selective, ATP competitive and oral active CDK7 inhibitor with IC50 of 41 nM. The selectivity of Samuraciclib hydrochloride is 45-, 15-, 230- and 30-fold higher than CDK1, CDK2 (IC50 is 578 nM), CDK5 and CDK9 respectively. Samuraciclib hydrochloride inhibits the growth of breast cancer cell lines with GI50 values between 0.2-0.3 µM. Samuraciclib hydrochloride has anti-tumor effects.