Photodynamic therapy of pharyngeal cancer with liposomal aluminum phthalocyanine chloride

Objective: Photodynamic therapy (PDT) utilizes visible light to activate photosensitizer molecules, which then generate singlet oxygen and other reactive oxygen species that can cause cytotoxicity. Head and neck squamous cell carcinomas may be amenable to PDT. We investigated the efficacy of PDT with free or liposome-encapsulated aluminum phthalocyanine chloride (AlPc) as the photosensitizer on FaDu pharyngeal carcinoma and HPV16+ 2A3 cells.Method: Liposomes comprising phosphatidyalglycerol (PG), palmitoyloleoylphosphatidylcholine (POPC), and AlPc (5:5:0.1) were prepared by thin film hydration and extrusion through polycarbonate membranes. FaDu and 2A3 cells were incubated with free and liposomal AlPc in the concentration range 0.1–1 µM for 24 h at 37°C. They were then exposed to light (690 nm) from a 9.8V High Power LED Multi Chip Emitter for 20 min, at a total light dose of 3.6 J/cm2. Cell survival was evaluated by the Alamar Blue assay. Result: Treatment of the cells with AlPc resulted in a dose dependent decrease in cell viability. In the case of free AlPc at 0.1, 0.5, and 1 μM, the viabilities of FaDu cells were reduced to 87.5±14%, 24.8±15%, and 0% of untreated controls, respectively. With 0.1, 0.5, and 1 μM liposomal AlPc, the viabilities were reduced to 1.4± 0.3%, 0%, and 0%, respectively. With 2A3 cells treated with free AlPc, the viabilities were 104.0±0.4%, 66.7±14.3%, and 51.6±12.5, and with liposomal AlPc they were 45.9±10.5%, 24.4±2.9%, and 15.5±6.1%, respectively. Conclusion: In FaDu cells, even at the lowest concentration, liposomal AlPc was 63-fold more effective than the free photosensitizer. PDT was not as effective in 2A3 cells, although liposomal AlPc could reduce the viability to 15% of untreated controls and was 3-fold more effective than the free drug. Whether the lower susceptibility of the HPV16+ cells is related to the viral proteins expressed in these cells is yet to be determined