Localization and photodynamic efficacy of two cationic porphyrins varying in charge distributions

Effects of subcellular localization pattern of PpIX on photodynamic efficiency in esophageal cancer cells

AIM: To study the effects of subcellular localization pattern of PpIX on photodynamic efficiency in esophageal cancer cell lines.

METHODS: KYSE-450, KYSE-70 and Het-1A cells were treated with ALA, exogenous PpIX and MitoTracker, respectively. The subcellular localization patterns of PpIX were observed using fluorescence microscopy. Mitochondrial transmembrane potential (ΔΨm) after ALA-PDT and PpIX-PDT was measured using JC-1 flow cytometry. The morphological study of mitochondria after ALA-PDT and PpIX-PDT was performed with electron microscopy. MTS was used to examine the cell survival rate.

RESULTS: The granular patterns and distribution of fluorescence in the extranuclear fraction of the cells were similar for both ALA-derived endogenous PpIX and the MitoTracker in all cell lines; however, exogenous PpIX was diffusely distributed in the whole cytoplasm of cells. After 12 h of ALA-based PDT, the percentages were increased to 22%, 52% and 33% in the KYSE-450, KYSE-70 and Het-1A cell lines, respectively; where only 15%, 14% and 18% of the depolarized cell fractions were seen following PDT with exogenous PpIX. As early as 1 h after photodynamic treatment, some of the mitochondria were already damaged by ALA-PDT with unclear cristae, vacuoles and swelling; while the mitochondrial ultrastructure was still well preserved 1 h later following PDT with exogenous PpIX. ALA-mediated PDT was significantly more efficient than PDT with exogenous PpIX in killing cells in all the 3 cell lines.

CONCLUSION: Different subcellular location of photosensitizer may affect the PDT efficacy. Mitochondria are more sensitive and may be important targets for PDT. This finding suggests that new photosensitizers with mitochondrially-localizing property may be designed for improvement of PDT effectiveness in the future.