Photodynamic therapy with PAD-S31, a new hydrophilic chlorin photosensitizer, in an orthotopic rat bladder tumor model

Purpose: PAD-S31 (13,17-bis (1-carboxypropion) carbamoylethyl-3-thenyl-8- thoxyiminoethylidene-7-hydroxy-2,7,12,18-tetramethyl-porphyrin sodium) (Photochemical Co., Ltd., Okayama, Japan), 1 of the latest second-generation photosensitizers, has hydrophilic characteristics and excitation wave-lengths of around 670 nm. Using an orthotopic rat bladder tumor model we investigated the biodistribution of PAD-S31 and assessed the antitumor effects of photodynamic therapy (PDT) with PAD-S31. Materials and Methods: An orthotopic rat bladder tumor was established by implanting AY-27 cells in the bladder wall. After intravenous PAD-S31 administration the accumulation of PAD-S31 in the tumor and normal bladder wall was investigated by a fluorometric technique. One or 3 hours after intravenous administration of PAD-S31 (5 mg/kg) bladder tumors in rats were transurethrally irradiated at 100 mW/cm² with a light dose of 50 to 200 J/cm². The efficacy of PDT was evaluated 7 days later by observation with an ultrathin cystoscope and histopathological examination. Results: The ratio of PAD-S31 concentration in tumor tissue to that in normal bladder wall was more than 1 at all time points and it achieved a maximum (more than 10) 150 to 240 minutes after PAD-S31 administration. All rats that were irradiated at 100 J/cm² 3 hours after PAD-S31 administration showed more than 50% tumor destruction. When the light dose was more than 150 J/cm ², more than half of the rats showed complete tumor eradication, of which the average size was 6 mm. Conclusions: We report that PDT using PAD-S31 is effective for destroying bladder tumors in an orthotopic rat model. These experimental results suggest that this therapy could be a clinically promising method for the treatment of patients with bladder cancer.