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), doxorub icin (ADR), daunorubicin (DNR), vincristine (VCR), 6-mercaptopurine (6 MP), and prednisolone (PRD)] in human leukemic T-lymphocytes (CCRF-CEM and Jurkat) was investigated by analysing changes in cell size and mo rphology, changes in membrane integrity, alterations in [Ca2+](i) and induction of DNA fragmentation. MTX, ADR, and DNR showed pronounced do se- and time-dependent cytotoxic effects on both cell lines, whereas c ell viability was not considerably reduced by 6MP or PRD. On the other hand, the cytotoxic activity of VCR was much higher on Jurkat cells t han on CEM cells. With the exception of 6MP and PRD, all the other com pounds induced extensive chromatin condensation, nuclear fragmentation , plasma membrane blebbing, and formation of apoptotic bodies and frag mentation of DNA in both cell lines. Occurrence of DNA fragmentation a lways preceded loss of membrane integrity. These observations are cons istent with cell death being mediated by apoptosis. Significant increa ses in [Ca2+](i) were only observed in CEM cells preincubated with MTX or DNR (10 mu M). In contrast, MTX as well as VCR induced a reduction in the basal intracellular Ca2+ concentration In Jurkat T-cells. Alth ough the ability to induce changes in [Ca2+](i) correlated with higher cytotoxic potency of the anticancer drugs, a causal relationship betw een increased [Ca2+](i) and induction of apoptosis could not be clearl y established. These results, therefore, suggest no determinant role f or Ca2+ in triggering the process of endonucleolytic cleavage of genom ic DNA in these leukemic T-lymphocytes.