Modulation of effector caspase cleavage determines response of breast and lung tumor cell lines to chemotherapy.

In spite of compelling evidence-implicating caspases in drug-induced apoptosis, how tumors modulate caspase expression and activity to overcome the cytotoxicity of anticancer agents is not fully understood. To address this issue, we investigated the role of caspases-3 and caspase-7 in determining the response of breast and lung tumor cell lines to chemotherapy. We found that an early and late apoptotic response correlated with weak and strong cellular caspase-activation, respectively. The results highlight an underappreciated relationship of temporal apoptotic response with caspase-activation and drug resistance. Moreover, the extent of tumor growth restoration after drug withdrawal was dependent on the degree of endogenous blockage of caspase-3 and caspase-7 cleavages. This points to an unrecognized role of caspase modulation in tumor recurrence and suggests that targeting caspase cleavage is a rational approach to increasing potency of cancer drugs.