DAUNORUBICIN-INDUCED INTERNUCLEOSOMAL DNA FRAGMENTATION IN ACUTE MYELOID CELL-LINES

The study was designed to evaluate the implication of apoptosis in mye loid leukemic cell death induced by daunorubicin (DNR) and to identify the possible factors which may influence this process. DNR-induced ap optosis was characterized by morphology and DNA fragmentation in six l eukemic myeloid cell lines which expressed different differentiation p henotypes. In phenotypically mature HL-60 and U937 cells, DNR induced typical apoptosis with characteristic morphological changes and intens e internucleosomal DNA fragmentation within a narrow concentration ran ge (0.5-2 mu M). When these cells were treated with higher doses of DN R, large DNA fragments (100 kbp), but not internucleosomal fragments, were identified. DNR-induced DNA fragmentation in HL-60 and U937 was i nhibited by antioxidants such as N-acetylcysteine (N-ac) or pyrrolidin e-dithiocarbamate (PDTC). In the phenotypically immature KG1a, KG1, HE L and ML1 cell lines DNR induced no characteristic apoptotic morpholog ical features as well as very low levels of internucleosomal DNA fragm entation, whereas large DNA fragments (200 kbp) were observed in KG1a treated with 7 mu M DNR. Since the latter expressed P-glycoprotein (P- gp), the role of P-gp in the lack of apoptotic response to DNR was inv estigated. One P-gp inhibitor (verapamil) slightly improved DNR-induce d DNA fragmentation in KG1a cells whereas the combination of verapamil and buthionine-sulfoximine (BSO), which depletes glutathion store, fu rther increased internucleosomal DNA fragmentation. In conclusion, DNR induced internucleosomal DNA fragmentation in some but not all AML ce lls; the magnitude of this process being influenced by both intracellu lar drug concentration and oxidative balance.