Apoptosis induced by doxorubicin in neurotumor cells is divorced from drugeffects on ceramide accumulation and may involve cell cycle-dependent caspase activation

Doxorubicin (0.5 mu g/ml) induced caspase-dependent apoptosis in SH-SY5Y ne uroblastoma and CHP-100 neuroepithelioma cells. The apoptotic response star ted to be evident similar to 15 h after drug administration and, as monitor ed over a 48-h period, was more pronounced in CHP-100 than in SH-SY5Y cells . In both systems, apoptosis was accompanied by elevation of intracellular ceramide levels. Ceramide accumulation was blocked by the ceramide synthase inhibitor fumonisin B-1 (25 mu M); this compound, however, did not prevent drug-induced apoptosis, Untreated cells from both lines expressed negligib le p53 levels; on the other hand, whereas p53 and p21(Cip1/Waf1) were rapid ly up-regulated in doxorubicin-treated SH-SY5Y cells, such a response was n ot observed in CHP-100 cells. Doxorubicin induced a G(2)/M phase block in b oth cell lines, but whereas the G(1) phase was markedly depleted in CHP-100 cells, it was substantially retained in SH-SY5Y cells. in the latter syste m, double G(1) and G(2)/M block largely preceded cell death; however, as ap optosis underwent completion, it selectively targeted late S and G(2)/M cel ls. Moreover, apoptosis suppression by caspase inhibition did not result in a recovery of the G(1) cell population. These results support the notion t hat doxorubicin-induced apoptosis and ceramide elevation are divorced event s in neuroectodermal tumors and that p53 function is at least dispensable f or apoptosis completion, Indeed, as G(1) cells appear to be refractory to d oxorubicin-induced apoptosis, p53 up-regulation and p21(Cip1/Waf1) expressi on may provide an unfavorable setting for the apoptotic action of the drug.