Studies of tin ethyl etiopurpurin photodynamic therapy of the canine prostate

Purpose: Previous studies have demonstrated the technical feasibility of de stroying prostate tissue using photodynamic therapy for benign and malignan t disease. A series of canine studies was performed to evaluate the systemi c uptake and distribution of the photosensitizer tin ethyl etiopurpurin (Sn ET2) in the prostate and surrounding tissues, and determine the optimal com bination of drug dose, light dose and time interval between drug and light administration using transurethral and transperineal interstitial light del ivery. Materials and Methods: Adult male mongrel source dogs received intravenous bolus injections of 0.5 or 1.0 mg./kg. SnET2 in 4 studies. In the first stu dy the concentration of SnET2 in the prostate and surrounding tissue was me asured at various time points after dosing. In the second study a tissue do se response relationship of SnET2-PDT was studied after transperineal inter stitial light application The third and fourth studies evaluated the tissue effects of combined transurethral and transperineal interstitial light app lication on SnET2 sensitized prostates. Results: Substantial amounts of SnET2 were measured in the prostate between 24 and 168 hours after infusion. Drug and light dose dependent prostatic t issue necrosis and volume reduction were documented in the dose response re lationship study. The combination of transurethral and transperineal light resulted in the extensive destruction of glandular epithelium with minimal damage to surrounding structures. Average prostate volume decreased 52%. Tr ansperineal interstitial light delivery with multiple diffusers resulted in substantial glandular destruction of the prostate. An average volume reduc tion of more than 60% was achieved. Conclusions: SnET2-PDT is a viable minimally invasive treatment modality fo r prostate tissue destruction.