Ceramide regulates gemcitabine-induced senescence and apoptosis in human pancreatic cancer cell lines.
Bioactive sphingolipids are potent intracellular signaling molecules having profound effects on cell death, growth, and differentiation. Pharmacologic manipulation of sphingolipid levels could have a significant effect on the induction of apoptosis by anticancer agents, and thus, improve treatment efficacy. We observed that gemcitabine cannot completely kill AsPc1 and Panc1 human pancreatic cancer cells in culture; even at high concentrations of gemcitabine, 30% to 40% of the cells remain viable. By adding sphingomyelin to the culture medium, gemcitabine-induced cell death increased synergistically to >90%. Panc1 cells that survived high concentrations of gemcitabine had an increase in beta-galactosidase activity, a marker of senescence. The inclusion of sphingomyelin with gemcitabine reduced beta-galactosidase activity, as compared with cells treated with gemcitabine alone. Expression of p21(waf1/cip1) in both cell lines exposed to sphingomyelin, gemcitabine, and gemcitabine + sphingomyelin varied relative to the untreated group. C(8)-ceramide induced both cell death and senescence in a dose-dependent manner. These results indicate that gemcitabine induces senescence in pancreatic cancer cells and that sphingomyelin-enhanced chemosensitivity is achieved through reducing the induction of senescence by redirecting the cell to enter the apoptotic pathway. Ceramide levels seem to be critical to this decision, with cell cycle progression being uninhibited at low ceramide levels, senescence induced at moderate levels, and apoptosis initiated at high levels. Our results provide further evidence that targeting the sphingolipid metabolism is a means of enhancing the efficacy of chemotherapeutic agents.
Modrak
David E
DE
Garden State Cancer Center, Center for Molecular Medicine and Immunology, Belleville, NJ 07109, USA. dmodrak@gscancer.org
Leon
Evelyn
E
Goldenberg
David M
DM
Gold
David V
DV
D000964:Antimetabolites, Antineoplastic / Q000494:pharmacology; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects*; D002453:Cell Cycle / Q000187:drug effects; D018797:Cell Cycle Proteins / Q000378:metabolism; D045744:Cell Line, Tumor; D002470:Cell Survival; D016922:Cellular Senescence / Q000187:drug effects; D002518:Ceramides / Q000008:administration & dosage / Q000494:pharmacology*; D003841:Deoxycytidine / Q000008:administration & dosage / Q000031:analogs & derivatives* / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D004357:Drug Synergism; D006801:Humans; D010190:Pancreatic Neoplasms / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D013109:Sphingomyelins / Q000378:metabolism; D000093542:Gemcitabine
D000964:Antimetabolites, Antineoplastic; D018797:Cell Cycle Proteins; D002518:Ceramides; D013109:Sphingomyelins; D003841:Deoxycytidine; D000093542:Gemcitabine