149 Metformin as adjuvant in PDT in squamous cell carcinoma

Abstract

Photodynamic therapy (PDT) is used for the treatment of several types of Non-Melanoma Skin Cancer (NMSC) although sometimes resistant cells responsible for the relapses may appear after treatment. Normal differentiated cells depend primarily on mitochondrial oxidative phosphorylation to generate energy, but cancer cells change this metabolism to an aerobic glycolysis (Warburg effect), which could influence in the response to antitumor drugs. Here, we have evaluated the expression of different proteins implicated in the energetic metabolism in the resistance to PDT of squamous cell carcinoma (SCC) in vitro and in vivo. In addition, we have evaluated the use of metformin, an antidiabetic type II compound, to destroy in vitro the resistant cells, alone or in combination with PDT, and in SKH-1 hairless mice exposed chronically to UV in the prevention of the development of tumors. For in vitro experiments, the cell lines SCC-13 and A431 were used. The cells, called parental (P), were subjected to 10 PDT cycles to obtain resistant cells that were inoculated in immunosuppressed mice; the induced tumors were sub-cultured by explants and a cell population called 10GT was obtained. On these cultures we have evaluated the combined treatment of PDT with metformin. For in vivo experiments, the SCC carcinomas induced in SKH-1 mice exposed to UV were treated with PDT, metformin or combination of both. The results obtained in vitro, showed a significant increase in cell death after the combined PDT-metformin treatment when compared to those obtained after PDT or metformin alone. In SCC carcinomas induced in SKH-1 hairless mice, after 28 weeks exposed to UV the number of lesions in the UV group was greater than that of the groups: UV+PDT, UV+metf or UV+metf+PDT. To analyse the molecular mechanism of metformin in combination with PDT, we have finally evaluated the expression elements that participate in the mTOR pathway after the treatments, in vitro and in tumors generated in mice.