NMS-E973 is a selective inhibitor of CDK7 (cyclin-dependent kinase 7), a key regulator in the transcription and cell cycle processes. It is primarily used in cancer research to study the role of CDK7 in tumor growth, especially in transcriptionally driven cancers such as certain types of leukemia, ovarian, and breast cancers. By inhibiting CDK7, NMS-E973 disrupts the phosphorylation of the RNA polymerase II C-terminal domain, leading to reduced transcription of key oncogenes like MYC. This results in cell cycle arrest and apoptosis in cancer cells. Due to its mechanism, NMS-E973 serves as a valuable tool compound for validating CDK7 as a therapeutic target and for guiding the development of more advanced CDK inhibitors. It is not used clinically but plays a critical role in preclinical studies exploring targeted cancer therapies.