Combinatorial therapies improve the therapeutic efficacy of nanoliposomal ceramide for pancreatic cancer

Poor prognosis cancers, such as pancreatic cancer, represent inherent challenges for ceramide-based nanotherapeutics due to metabolic pathways which neutralize ceramide to less toxic or pro-oncogenic metabolites. We have recently developed a novel 80 nanometer diameter liposomal formulation that incorporates 30 molar percent C-6-ceramide, a bioactive lipid that is pro-apoptotic to many cancer cells, but not to normal cells. In this manuscript, we evaluated the efficacy of combining nanoliposomal C-6-ceramide (Lip-C-6) with either gemcitabine or an inhibitor of glucosylceramide synthase. We first assessed the biological effect of Lip-C-6 in PANC-1 cells, a gemcitabine-resistant human pancreatic cancer cell line, and found that low doses alone did not induce cell toxicity. However, cytotoxicity was achieved by combining Lip-C-6 with either non-toxic sub-therapeutic concentrations of gemcitabine or with the glucosylceramide synthase inhibitor D-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol (PDMP). Furthermore, these combinations with Lip-C-6 cooperatively inhibited PANC-1 tumor growth in vivo. Mechanistically, Lip-C-6 inhibited pro-survival Akt and Erk signaling, whereas the nucleoside analog gemcitabine did not. Furthermore, by including PDMP within the nanoliposomes, which halted ceramide neutralization as evidenced by LC-MS/MS/MS, the cytotoxic effects of Lip-C-6 were enhanced. Collectively, we have demonstrated that nanoliposomal ceramide can be an effective anti-pancreatic cancer therapeutic in combination with gemcitabine or an inhibitor of ceramide neutralization.