GP7(4-[4"-(2", 2", 6",6"-tetramethyl-l-piperi-dinyloxy) aminol-4-demethyl epipodophyllotoxin). a new spin-labeled derivative of podophylIotoxin, is a promising antlcancer drug of podophyllotoxin class The primary effect of GP7 is the anticancer activity on transplanted mouse tumors and cultured tumor cells. However. its molecular mechanism of action IS still obscure In this study. we investigated the activity ofGP7 to induce apoptosis in human leukemia HL-60 and Jurkat cells Apoptosis was determined by detection of DNA fragmentation in agarose gel electrophoresis GP7 induced apoptotic DNA fragmentation of HL-60 and Jurkat ceils in time-and dose-dependent manner. We further investigated the activity ofcaspase-3 in GP7-induced apoptotic DNA fragmentation of HL-60 and Jurkat cells GP7 also induced time-and dose-dependent caspase-3 activation in both cell lines, and the kinetics of caspase-3 activation induced by GP7 was well correlated with that of apoptotic DNA fragmentation. To determine the role of cilspase-3 in GP7-induced apoptotic DNA fragmentation, we examined the effect of specific caspase-3 inhibitor, Ac-DEVD-CHO, on GP7-induced apoptotic DNA fragmentation Ac-DEVD-CHO prevented GP7-induced caspase-3 activation in both HL-60 and Jurkat cells, however, it only inhibited GP7-induced apoptonc internucleosomal DNA fragmentation in HL-60 cells We then employed L-carnitine to investigate the role of caspase-3 in GP7-induced apoptotic DNA fragmentation L-carnitine treatment prevented GP7-induced caspase-3 activation in both cell lines in a dose-dependent manner Similar to Ac-DEVD-CHO. L-camitine only inhibited GP7-induced apoptotic internucleosomal DNA fragmentation in HL-60 cells. These findings suggest that GP7 exems an anti-leukemic erfect by both caspase-3-dependent and-independent apoptotic signaling pathways