Abstract

In the present study dopaminergic neuroblastoma B65 cells were exposed to Camptothecin (CPT) (0.5-10 mu M), either alone or in the presence of roscovitine (ROSC). The results show that CPT induces apoptosis through the activation of ataxia telangiectasia mutated (ATM)-induced cell-cycle alteration in neuroblastoma B65 cells. The apoptotic process is mediated through the activation of cystein proteases, namely calpain/caspases. However, whereas a pan-caspase inhibitor, zVADfmk, inhibited CPT-mediated apoptosis, a calpain inhibitor, calpeptin, did not prevent cell death. Interestingly, CPT also induces CDK5 activation and ROSC (25 mu M) blocked CDK5, ATM activation and apoptosis (as measured by caspase-3 activation). By contrast, selective inhibition of ATM, by KU55933, and non-selective inhibition, by caffeine, did not prevent CPT-mediated apoptosis. Thus, we conclude that CDK5 is activated in response to DNA damage and that CDK5 inhibition prevents ATM and p53ser15 activation. However, pharmacological inhibition of ATM using KU55933 and caffeine suggests that ATM inhibition by ROSC is not the only mechanism that might explain the anti-apoptotic effects of this drug in this apoptosis model. Our findings have a potential clinical implication, suggesting that combinatory drugs in the treatment of cancer activation should be administered with caution.