Compared with seliciclib (IC50 = 13.3 μM), fadraciclib is more selective for CDK2 (IC50 = 5 nM) and CDK9 (IC50 = 26 nM).105 Fadraciclib exhibited an approximately 34-fold anti-proliferative activity than that of seliciclib in a human tumor cell line panel.105 Fadraciclib induced a rapid and robust decrease in pSer2-RNAP II, loss of MCL-1, and decrease in RB pThr821 (a potential target of CDK2), and then led to cell death within a few hours.105 Percentage of cells in sub-G1 increases significantly 24 h after fadraciclib treatment in Colo205 cells. Here, CDK9 is linked to neoplasm.