BS-181 is a highly selective CDK7 inhibitor with IC50 of 21 nM. It is more than 40-fold selective for CDK7 than CDK1, 2, 4, 5, 6, or 9. BS-181 promotes cell cycle arrest and inhibits the cancer cell growth of a range of tumor types, including breast, lung, prostate and colorectal cancer with IC50 in the range of 11.5-37 uM. In MCF-7 cells, BS-181 inhibits the phosphorylation of the CDK7 substrate RNA polymerase II COOH-terminal domain (CTD), and promotes cell cycle arrest and apoptosis to inhibit the growth of cancer cell lines. BS-181 is stable in vivo with a plasma elimination half-life in mice of 405 minutes after i.p. administration of 10 mg/kg. BS-181 inhibits the growth of MCF-7 xenografts in the nude mice model in a dose-dependent manner, with 25% and 50% reduction in tumor growth after 2 weeks of treatment at 10 mg/kg/day and 20 mg/kg/day, respectively without apparent toxicity. BS-181 demonstrated the anticancer activities in BGC823 cells, suggesting that CDK7 may serve as a novel therapeutic target or the treatment of GC. It has being shown that selective inhibition of CDK7 by BS-181 ameliorates experimental arthritis in mice.