Apoptosis as a mechanism of cell death induced by different chemotherapeutic drugs in human leukemic T-lymphocytes

The involvement of apoptosis in the mechanism of cell death induced by six clinically relevant anticancer drugs [methotrexate (MTX), doxorubicin (ADR), daunorubicin (DNR), vincristine (VCR), 6-mercaptopurine (6MP), and prednisolone (PRD)] in human leukemic T-lymphocytes (CCRF-CEM and Jurkat) was investigated by analysing changes in cell size and morphology, changes in membrane integrity, alterations in [Ca2+]i and induction of DNA fragmentation. MTX, ADR, and DNR showed pronounced dose- and time-dependent cytotoxic effects on both cell lines, whereas cell viability was not considerably reduced by 6MP or PRD. On the other hand, the cytotoxic activity of VCR was much higher on Jurkat cells than on CEM cells. With the exception of 6MP and PRD, all the other compounds induced extensive chromatin condensation, nuclear fragmentation, plasma membrane blebbing, and formation of apoptotic bodies and fragmentation of DNA in both cell lines. Occurrence of DNA fragmentation always preceded loss of membrane integrity. These observation are consistent with cell death being mediated by apoptosis. Significant increases in [Ca2+]i were only observed in CEM cells preincubated with MTX or DNR (10 microM). In contrast, MTX as well as VCR induced a reduction in the basal intracellular Ca2+ concentration in Jurkat T-cells. Although the ability to induce changes in [Ca2+]i correlated with higher cytotoxic potency of the anticancer drugs, a causal relationship between increased [Ca2+] and induction of apoptosis could not be clearly established. These results, therefore, suggest no determinant role for Ca2+ in triggering the process of endonucleolytic cleavage of genomic DNA in these leukemic T-lymphocytes.