The localization of
photosensitizers in the subcellular compartments during
photodynamic therapy (
PDT) plays a major role in the cell destruction; therefore, the aim of this study was to investigate the intracellular localization of
Chlorin e6-PVP (Photolon™) in malignant and normal cells. Our study involves the characterization of the structural determinants of subcellular localization of
Photolon, and how subcellular localization affects the selective toxicity of
Photolon towards
tumor cells. Using confocal
laser scanning microscopy (CLSM) and fluorescent organelle probes; we examined the subcellular localization of Photolon™ in the murine colon
carcinoma CT-26 and normal fibroblast (NHLC) cells. Our results demonstrated that after 30 min of incubation, the distribution of
Photolon was localized mainly in the cytoplasmic organelles including the mitochondria, lysosomes, Golgi apparatus, around the nuclear envelope and also in the nucleus but not in the endo-plasmic reticulum whereas in NHLC cells,
Photolon was found to be localized minimally only in the nucleus not in other organelles studied. The relationship between subcellular localization of
Photolon and
PDT-induced apoptosis was investigated. Apoptotic cell death was judged by the formation of known apoptotic hallmarks including, the
phosphatidylserine externalization (PS), PARP cleavage, a substrate for
caspase-3 and the formation of apoptotic nuclei. At the irradiation dose of 1 J/cm2, the percentage of apoptotic cells was 80%, respectively. This study provided substantial evidence that
Photolon preferentially localized in the subcellular organelles in the following order: nucleus, mitochondria, lysosomes and the Golgi apparatus and subsequent photodamage of the mitochondria and lyso-somes played an important role in
PDT-mediated apoptosis CT-26 cells. Our results based on the cytoplasmic organelles and the intranuclear localization extensively enhance the efficacy of
PDT with appropriate
photosensitizer and light dose and support the idea that
PDT can contribute to elimination of malignant cells by inducing apoptosis, which is of physiological significance.