Whole-bladder wall photodynamic therapy (PDT) is a promising treatment for carcinoma in situ (CIS) and diffuse premalignant changes of the bladder. After the results of our clinical studies showing that intravesical hypericin selectively accumulates in superficial bladder tumors, we investigated the hypericin-PDT efficacy in an AY-27 orthotopic transitional cell carcinoma rat bladder tumor model. After the instillation of hypericin (30 microM, 2 hr) in the bladder, tumors were irradiated (25-50 mW/cm 6-48 J/cm(2)) using 595 nm laser light. Data demonstrate that light doses of 12-48 J/cm(2) resulted in selective PDT-induced urothelial tumor damage without damaging detrusor musculature. Histological assessment of bladder sections 2 days after PDT showed tumor destruction, with tumor cells shrinking and detaching from the bladder wall. There were tumor regrowth 1-3 weeks after treatment. The in vivo/in vitro clonogenic assay results revealed up to 98% of tumor cell kill by hypericin PDT. In conclusion, hypericin PDT can be used to safely induce a selective urothelial tumor damage without damaging detrusor musculature, when optimum hypericin concentration and light fluences are used. A small percentage (2-5%) of tumor cells that survive the photodynamic treatment resulting in tumor regrowth after a prolonged period of time is likely due to oxygen depletion during light irradiation.
Copyright 2003 Wiley-Liss, Inc.