Description: Atuveciclib (formerly known as BAY-1143572) is novel, potent, oral and highly selective PTEFb/CDK9 inhibitor with antitumor activity. It is more than 100-fold more selective for CDK9 over CDK2, and it inhibits CDK9/CycT1 with an IC50 of 13 nM. With IC50 values of 45 nM for GSK3α and 87 nM for GSK3β, respectively, it also inhibits GSK3 kinase. A Phase I clinical trial for ateveciclib is presently underway. One promising new strategy in cancer therapy is selective inhibition of exclusively transcription-regulating PTEFb/CDK9. The orally available clinical candidate atuveciclib (BAY1143572) was ultimately identified through lead optimization efforts that began with lead compound BAY-958 and strictly focused on kinase selectivity, physicochemical, and DMPK properties. BAY 1143572, which is structurally distinguished by an uncommon benzyl sulfoximine group, demonstrated the best overall profile both in vitro and in vivo, demonstrating good tolerability and high efficacy in mice and rat xenograft models. Among the PTEFb/CDK9 inhibitors in clinical trials for cancer treatment, BAY 1143572 is the most potent and highly selective inhibitor.