PDT effects of m-THPC and ALA, phototoxicity and apoptosis

The purpose of this study was to estimate the efficacy of an endogenous sensitizer (-aminolevulinic acid (or ALA) induced protoporphyrin IX (or PpIX)) and an exogenous sensitizer (meta(tetrahydroxyphenyl)chlorin or m-THPC) on two different cell lines, rat colon adenocarcinoma PROb cells and murine melanoma B16A45 (B16) cells, in apoptosis production. After sensitizer incubation, cells were irradiated with an argon dye laser. LD₅₀ with m-THPC was 2.8 g/ml and 4.7 g/ml under irradiation of 25 J/cm² respectively for PROb and B16 cells. With ALA, LD₅₀ was 150 g/ml and 175 g/ml under 25 J/cm² respectively for PROb and B16 cells. Apoptosis induction by m-THPC or ALA-PDT was detected by DNA gel electrophoresis and quantified using an ELISA assay 24 h after PDT. The maximal apoptosis enrichment factor (MAEF) was reached for 6 g/ml m-THPC at 10 J/cm² for PROb and B16 cells and for 50 g/ml ALA at 25 J/cm² for PROb or B16 cells. Both m-THPC and PpIX are efficient photosensitizers and apoptosis inducers. However, MAEF is obtained by sensitizer or laser doses inducing very different phototoxic effects: MAEF was obtained after m-THPC-PDT with LD₇₈ for PROb cells and LD₃₀ for B16 cells and after ALA-PDT with LD₂₂ for PROb cells and LD₁₈ for B16 cells. However the overall m-THPC/PDT apoptotic induction (under the curve surface analysis) was not different whatever the cell line for 10 and 25 J/cm². On the contrary, ALA-PpIX/PDT apoptotic induction was twice for 25 J/cm² as compared to 50 J/cm² (p < 0.01) for both the PROb and B16 cells. These results indicate that the apoptosis rate in PDT cell killing varies considerably according to cell type and sensitizer.