Modification of ceramide metabolism increases cancer cell sensitivity to cytotoxics

In the preceding report we demonstrated that MCF-7-AdrR cells (adriamycin r esistant) were insensitive to ceramide, whereas MCF-7 wild-type cells were sensitive. It was also shown that the drug resistant cells had an increased capacity to convert ceramide to glucosylceramide. Here we demonstrate that blocking the conversion of ceramide to glucosylceramide increases MCF-7-Ad rR cell sensitivity to ceramide as well as to antitumor agents. Treatment o f MCF-7 cells with adriamycin elicited a 5-fold increase in ceramide, and c aused oligonucleosomal fragmentation, characteristic to apoptosis. Under si milar treatment conditions, ceramide was not generated in MCF-7-AdrR cells. In MCF-7-AdrR cells neither C-6-ceramide nor tamoxifen was cytotoxic; howe ver, the addition of tamoxifen to the C-6-ceramide treatment regimen reduce d cell viability to 42% and elicited apoptosis. Treatment of MCF-7-AdrR cel ls with Adriamycin promoted an increase in ceramide only if tamoxifen was p resent, in which case ceramide increased 7-fold, and cell viability decreas ed to 50%. The employment of another agent, RU486 (Mifepristone), which blo cks ceramide glycosylation, increased MCF-7-AdrR cell sensitivity to adriam ycin in a dose-dependent manner. Our data show that agents that block ceram ide glycosylation potentiate cellular sensitivity to ceramide and to chemot herapeutic drugs, and suggest that the ceramide metabolic pathway is an imp ortant target for anticancer drug development.