Enitociclib, a selective CDK9 inhibitor: in vitro and in vivo preclinical studies in multiple myeloma

• Targeting CDK9 with enitociclib induces apoptotic cell death in multiple myeloma and demonstrates synergy in drug combinations

• Enitociclib may be an effective treatment for multiple myeloma as a single agent or in combination therapies in future clinical studies

Multiple myeloma (MM) is a cancer of the plasma cells that remains incurable despite advances in treatment options. In this study, a library of 216 clinically feasible small-molecule inhibitors was screened to identify agents that selectively inhibit MM cell proliferation. Enitociclib, a CDK9-specific small-molecule inhibitor, was found to be highly effective at decreasing cell viability and inducing apoptosis in four MM cell lines. Enitociclib inhibited the phosphorylation of the CTD of RNA Pol II at Ser2/Ser5 and repressed the protein expression of oncogenes c-Myc, Mcl-1, and PCNA in MM cells. Additionally, enitociclib demonstrated synergistic effects with several anti-MM agents, including bortezomib, lenalidomide, pomalidomide, and venetoclax. These results suggest that enitociclib may represent a promising therapeutic option for the treatment of MM, either as a single agent or in combination with other anti-MM agents.