Amrubicin, a completely synthetic 9-aminoanthracycline derivative, inhibits cell growth by stabilizing a
topoisomerase II-
DNA complex. This study was designed to examine the apoptosis induced in human
leukemia U937 cells by
amrubicin and its active metabolite
amrubicinol.
Amrubicin,
amrubicinol and other
antitumor agents, such as
daunorubicin and
etoposide, induced typical apoptosis with characteristic nuclear morphological change and DNA fragmentation. Measuring the population of sub-G(1) phase cells, it was found that under conditions where cell growth was inhibited by either
amrubicin or
amrubicinol, U937 cells underwent apoptotic cell death in a dose-dependent manner accompanied by an arrest of the cell cycle at G(2)/M. Furthermore,
amrubicin- and
amrubicinol-induced apoptosis was mediated by the activation of
caspase-3/7, but not caspase-1, preceding a loss of mitochondrial membrane potential. These results indicate that both a reduction in mitochondrial membrane potential and the activation of
caspase-3/7 are key events in the apoptosis induced by
amrubicin and
amrubicinol as well as the other
antitumor agents. In addition, studies with
oligomycin suggested that the apoptosis induced by
amrubicin and
amrubicinol involved substantially different pathways from that triggered by
daunorubicin and
etoposide.
Oligomycin blocked the
etoposide-induced increase in the number of sub-G(1) phase cells without preventing the activation of
caspase-3/7, and had no inhibitory effect on the expansion of the sub-G(1) population in
daunorubicin-treated cells, whereas apoptosis-related changes caused by
amrubicin and
amrubicinol were suppressed in the presence of
oligomycin.