Photodynamic therapy of oral cancer with liposomal zinc phthalocyanine

Objectives: Photodynamic therapy (PDT) is a medical treatment that uses photosensitizer molecules activated with light to kill cancer cells. Liposomes are nanoparticles used for transporting the photosensitizer into the target cells. We investigated the use of free or liposome-encapsulated zinc phthalocyanine (ZnPc), as a photosensitizer for PDT against CAL27 cells derived from a squamous cell carcinoma of the tongue.Methods: Liposomes were prepared by hydration of dry lipid films in isotonic buffer, either followed or not by extrusion through polycarbonate membranes. Two types of liposomes were prepared: (1) palmitoyloleoyl phosphatidylcholine (POPC) with palmitoyloleoyl phosphatidylglycerol (POPG), and (2) dioleoyl PE (DOPE) with POPG. Cells incubated with free ZnPc, and extruded and non-extruded liposomal ZnPc, were exposed to light (660 nm) for 30 min. To evaluate dark toxicity, the treated cells were shielded from light. Cells incubated with medium or drug-free liposomes were used as controls. Cell viability was assessed using the Alamar Blue assay. Results: At 0.1, 0.5 and 1 µM, free ZnPc reduced CAL27 cell viability to ~82, 38 and 24%, respectively. Extruded POPG:POPC:ZnPc liposomes were more effective than free ZnPc only at 1 µM, reducing cell viability to 14%. Non-extruded POPG:POPC:ZnPc liposomes were less effective than free ZnPc, reducing cell viability to 60% at 1 µM. The phototoxic effect of extruded and non-extruded POPG:DOPE:ZnPC liposomes was insignificant. Both free and liposomal ZnPc did not cause dark toxicity. Conclusions: PDT against CAL27 cells is effective using free ZnPc in a dose-dependent manner, following irradiation. Extruded POPG:POPC:ZnPc liposomes are more effective than non-extruded liposomes. Future studies will address the apparent resistance of cells to POPG:DOPE:ZnPc to PDT, the intracellular localization of liposomes labeled with fluorescent lipids, and the effect of PDT on other oral cancer cell lines including FaDu (squamous cell carcinoma of the pharynx)