CDKI-83 is a potent CDK9 and CDK1 inhibitor with K i values of 21 nM and 72 nM for CDK9/T1 and CDK1/B, respectively. CDKI-83 demonstrates effective anti-proliferative activity in human tumour cell lines with a GI 50 <1 μM. CDKI-83 effectively induces apoptosis in A2780 human ovarian cancer cells. CDKI-83 reduces phosphorylation at Ser-2 of RNA polymerase II (RNAPII) by inhibiting cellular CDK9 activity, and down-regulates Mcl-1 and Bcl-2. CDKI-83 has the potential for anti-cancer research.