CDK9 and neoplasm: In high-CDK9 TNBC cell lines (MDA-MB-231 and MDA-MB-453), atuveciclib markedly reduced the number and size of colonies in a dose-dependent manner (Figure 4); whereas no such anti-tumor effects were observed for a low-CDK9 TNBC cell line (HCC1937) (Supplementary Figure 4).