Synergistic effect of CDKI-73 combined with olaparib on the survival and growth of ovarian cancer cells. A-D. Cytotoxic effect of CDKI-73 and olaparib, either as monotherapy or in combination, on ovarian cancer cells (HO8910, OVCAR-5, and OVCAR-8). The synergistic effect of the combination was judged according to the combination index (CI) and fraction affected (FA). DMSO was used as a vehicle. Values are shown as the mean ± S.D. representative of three independent experiments. *P < 0.05 vs CDK9i; **P < 0.01 vs CDK9i. E, F. The proliferation inhibitory effect of CDKI-73 (0.25 μM) and olaparib (0.5 μM) on HO8910 and OVCAR-5 cells was determined with a clonogenic assay. DMSO was used as a vehicle. Values are shown as the mean ± S.D. representative of three independent experiments. *P < 0.05; **P < 0.01; ***P < 0.001 (Student’s t-test).