The benzoacronycine derivative
S23906-1 is a highly potent
antitumor agent with a broad spectrum of activity against different human solid
tumor xenografts. The marked cytotoxic potential of this
drug may be the result of its interaction with
DNA but the precise mechanism of action remains unclear at present. We have investigated the induction of apoptosis in human promyelocytic
leukemia HL-60 and murine
melanoma B16 cells treated with
S23906-1. With both cell lines, the
drug induces cell cycle perturbations (G2/M arrest) and triggers apoptosis as revealed by the externalization of
Annexin V-targeted PS residues at the periphery of the cells. But the biochemical pathways leading to apoptosis are different for the two
cancer cell lines. In HL-60 cells, the
drug induces significant variations of the Delta Psi(mt), measured by flow cytometry using the
fluorochromes JC-1 and cm-X-ros. Activation of
caspase-3 and
chromatin condensation in HL-60 cells exposed to submicromolar concentrations of
S23906-1 for 24hr were also clearly seen by flow cytometry and confocal microscopy experiments. In contrast, the extent of apoptosis induced by
S23906-1 was found to be much more limited in B16 cells. No significant variations of Delta Psi(mt) and no cleavage of the fluorescent
caspase-3 substrate GDEVDGI (PhiPhiLux-G(1)D(2) probe) could be detected by cytometry in B16 cells exposed to
S23906-1. In addition, we characterized the mitochondrial production of
reactive oxygen species (ROS) using the probe
dihydroethidine (HE) and the variations of the mitochondrial mass using the
cardiolipin-interacting probe nonyl
acridine orange (
NAO).
S23906-1 stimulates the production of ROS in both cell lines but the number of mitochondria seems to increase only in
drug-treated B16 cells. Collectively these findings identify
S23906-1 as a potent inducer of cell apoptosis in the
leukemia cells and to a lower extent in the
melanoma cells. The results help to understand the downstream cytotoxic actions of this new
anticancer agent which is currently undergoing preclinical development.