chlorin-p6 and Colonic-Neoplasms

Effect of varying extracellular pH on mode of cell death induced by photodynamic action of chlorin p6 was investigated in human colon carcinoma (Colo-205) cells. At an extracellular pH of 7.4, compared to cells treated with chlorin p6 in dark, the photodynamically treated cells showed reduction in mitochondrial membrane potential, an increase in ADP/ATP ratio (1:2) and a large percentage of cells with chromatin condensation. In contrast, when photodynamic treatment and post irradiation incubation was carried out in acidic medium (pH 6.5), total loss of mitochondrial membrane potential, a marked increase in ADP/ATP ratio (1:33) and increased damage to plasma membrane were observed. Further, cells subjected to photodynamic treatment in a medium of pH 7.4 showed twofold increase in caspase-3 activity as compared to photodynamic treatment at pH 6.5. These results suggest that chlorin p6 mediated photodynamic action induces apoptotic cell death when extracellular pH is 7.4 whereas necrosis is more predominant under condition when extracellular pH is 6.5.

Topics: Adenocarcinoma; Adenosine Diphosphate; Adenosine Triphosphate; Apoptosis; Caspase 3; Caspases; Cell Line, Tumor; Colonic Neoplasms; Extracellular Space; Humans; Hydrogen-Ion Concentration; Membrane Potentials; Mitochondria; Photochemotherapy; Porphyrins

The effect of reducing the extracellular pH from 7.4 to 6.0 on the uptake and photosensitivity of chlorin p6, a potential photosensitising drug, has been investigated using two mammalian cell lines, human colon (Colo-205) and breast (MCF-7) adenocarcinoma cells. In Colo-205 cells, the uptake and phototoxicity of chlorin p6 was observed to increase as the pH of the incubation medium decreased. For light doses of up to [similar]6 kJ m(-2), although there was no evidence of mitochondrial damage, a significant reduction in Neutral Red uptake was observed, signifying damage to lysosomes. At higher light doses, significant mitochondrial damage was observed, accompanied by saturation of the lysosomal damage. This suggests light-induced relocalization of the photosensitizer from lysosomes to mitochondria. Furthermore, it was found that for a given light dose, lysosomes exhibit greater photosensitivity at lower pH. Since chlorin p6 is known to aggregate at pH 6.0, this observation suggests that the dye accumulation in these cells mainly takes place through endocytosis. In contrast, no significant variation in uptake, photosensitivity, and sites of photodamage was observed for MCF-7 cells at different extracellular pH. Additionally, the lower photosensitivity of lysosomes as compared to mitochondria in these cells suggests chlorin p6 is taken up through diffusion rather than endocytosis.

Topics: Adenocarcinoma; Breast Neoplasms; Cell Line, Tumor; Cell Survival; Colonic Neoplasms; Dermatitis, Phototoxic; Humans; Hydrogen-Ion Concentration; Mitochondria; Neutral Red; Oxidoreductases; Photochemistry; Photochemotherapy; Photosensitizing Agents; Porphyrins; Spectrometry, Fluorescence