Cytotoxicity of Liposomal C6-Ceramide in Oral Squamous Cell Carcinoma Cells

Objectives: C6-ceramide is a sphingolipid metabolite, with antiproliferative and proapoptotic activity in vitro and in vivo.  Its use as a therapeutic agent has been limited because of its insolubility. In this study, we have utilized liposomes as a drug carrier to deliver C6-ceramide to target cells. Survivin is a known inhibitor of apoptosis and is overexpressed in oral squamous cell carcinoma (OSCC) cells. Recent studies with C6-ceramide have shown the down-regulation of survivin in large granular lymphocytic leukemia. We therefore investigated the cytotoxicity and anti-survivin activity of liposomal C6-ceramide in HSC-3 OSCC cells as a potential novel therapeutic agent.

Methods: Palmitoyloleoylphosphatodylcholine (POPC):dioleoylphosphatidylethanolamine (DOPE) or POPC:DOPE:C6-ceramide liposomes were added to HSC-3 cells in the concentration range 0.1–50 µM of C6-ceramide. After incubation for 24 h at 37°C, cell survival was evaluated by the Alamar Blue assay. Survivin levels were measured by ELISA. The morphology of the treated and control cells were examined by scanning and transmission electron microscopy, and phase contrast microscopy.

Results: Cells treated with liposomal C6-ceramide resulted in dose-dependent, decreased cell viability, measured by the Alamar Blue. The viability with plain POPC:DOPE liposomes was 93±5% of the control. For 5 and 10 μM liposomal C6 ceramide, the viability was reduced to 72±3% and 44±0% of untreated cells. Survivin levels decreased from 1226±5 ng/mg protein to 346±6 ng/mg protein at 10 µM C6-ceramide. Electron microscopy indicated deformation of nucleoli by C6 ceramide treatment.

Conclusions: HSC-3 cells are vulnerable to liposomal C6 ceramide in a dose-dependent manner. Liposomal C6-ceramide reduced cell proliferation in HSC-3 cells probably because of a decrease in the levels of the anti-apoptotic protein, survivin. Further studies will focus on whether liposomal C6 ceramide and the reduced survivin levels will increase the susceptibility of HSC-3 cells to various anti-cancer agents such as doxorubicin and tamoxifen.