Figure 5.

The effect of the checkpoint inhibitors on oxaliplatin-mediated p53 stabilization and p21 up-regulation. (A) HCT116 wild-type (WT) and checkpoint kinase 2 (CHK2) KO cells were left either untreated (UT) or treated with either oxaliplatin (Ox), CHK2 II, debromohymenialdisine (DBH) or with a combination of the inhibitor and a 1 h pulse treatment of oxaliplatin. Inhibitors were added 24 h prior to, and continuously after, oxaliplatin treatment. The levels of p53 or p21 were assessed by western blotting. Actin was used as a protein-loading control. The western blot depicted is representative of three independent experiments. (B) Chou and Talalay combination index (CI) values following fixed drug concentration-ratios of oxaliplatin and either CHK2 II or DBH. CI values are representative of the IC₅₀, IC₇₅ and IC₉₀ effective doses. WT, CHK2 KO and p53 KO cells were treated with oxaliplatin for 1 h. Inhibitors were added 24 h before and continuously following platinum treatment. Data shown are for the average of three independent experiments.