Free and conjugated chlorin E6 in the photodynamic therapy of human bladder carcinoma cells

Abstract

Photodynamic therapy is an experimental modality for treatment of superficial bladder cancer, and consists of the administration of a photosensitizer and subsequent tumor-irradiation with light. Presently hematoporphyrin derivative (HPD) is the only photosensitizer in experimental clinical use in the United States. Because of the high nonspecific phototoxicity of HPD, new methods of photosensitization have been sought. In this study we compared chlorin e6, free and conjugated to 1-micron.-diameter latex microspheres. Phototoxicity was evaluated on MGH-U1 cells derived from a human bladder carcinoma. MGH-U1 cells were preincubated for 18 hours either with free Ce6 (0.43 microM) or Ce6-microspheres (0.43 microM equivalent in Ce6) and irradiated with an argon-laser-pumped dye laser emitting at 659 nm., over the radiant-exposure range of 5-50 J/cm. At 24 hours after light exposure the cells were observed microscopically for morphological alteration and evaluated for cell death by trypan blue exclusion. Cultures incubated with Ce6-microspheres and subsequently irradiated showed morphologic evidence of cell damage, apparent after irradiation with five J/cm. and a light dose dependent decrease in cell survival. In contrast, cells incubated with free Ce6 at the same concentration of 0.43 microM and subsequently irradiated demonstrated neither detectable morphologic alteration nor change in cell survival. Only cells preincubated with free Ce6 at higher concentration showed morphologic changes. Thus, Ce6-microsphere conjugate was much more efficient at inducing photodynamic destruction of bladder carcinoma cells than was free Ce6.