a. The effect of olaparib on CPT toxicity. DLD-1 cells were treated with 1 μM of olaparib and various cocentrations of CPT for 6 h. Values shown are the mean ± standard error of the mean. b. The relationship between concentrations of olaparib and sensitizing effects to CPT in DLD-1 cells. Cells were treated with 0.01 μM of CPT and various concentrations of olaparib for 6 h. Values shown are the mean ± standard error of the mean.