[Analysis of drug-induced apoptosis in human leukemic cell line (HL-60)].

: Cell death plays an essential role in cell homeostasis and the pathological process in cancer. Apoptosis has been identified by the internucleosomal DNA cleavage which appears to be associated with endonuclease activation. Proteolysis is considered to be an early event in apoptosis. We studied the effects of proteolysis on early apoptotic events, such as chromatin condensation, nuclear breakdown, DNA breakage and sensitivity to denaturation induced by anticancer drugs (camptothecin: CAM, 5-azacytidine: AZA) on HL-60 cells. CAM induced apoptosis on S phase and AZA on G1 phase. The internucleosomal DNA cleavage shown by both the presence of DNA fragments during gel electrophoresis and a large number of in situ DNA strands breaks (revealed in high intensity fluorescence FITC of cells in the TdT reaction) was prevented by the protease inhibitor, TPCK (N-tosyl-L-phenylalanine chlorometyl-ketone), as well as by an inhibitor of the apoptosis-associated endonuclease, ZnSO4. The protective effects were observed under conditions in which apoptosis was induced by agents with a different mechanism of action, such as the DNA damaging drug. CAM (topo-isomerase inhibitor), and an RNA antimetabolite, AZA. The protease inhibitor inhibits early events of apoptosis such as chromatin condensation, nuclear breakdown, DNA breakage and sensitivity to denaturation, which have different structures and a different mechanism of interaction with drugs. The results suggest that control of protease inhibitor may be a useful strategy to treat cancers.