Comparison of red and green light for treating non‐muscle invasive bladder cancer in rats using singlet oxygen‐cleavable prodrugs with PPIX‐PDT

Abstract It has been 30 years since Photofrin‐PDT was approved for the treatment of bladder cancer in Canada. However, Photofrin‐PDT failed to gain popularity due to bladder complications. The PDT with red light and IV‐administered Photofrin could permanently damage the bladder muscle. We have been developing a new combination strategy of PpIX‐PDT with singlet oxygen‐cleavable prodrugs for NMIBC with minimal side effects, avoiding damage to the bladder muscle layer. PpIX can be excited by either green (532 nm) or red (635 nm) light. Red light could be more efficacious in vivo due to its deeper tissue penetration than green light. Since HAL preferentially produces PpIX in tumors, we hypothesized that illuminating PpIX with red light might spare the muscle layer. PpIX‐PDT was used to compare green and red laser efficacy in vitro and in vivo. The IC 50 of in vitro PpIX‐PDT was 18 mW/cm 2 with the red laser and 22 mW/cm 2 with the green laser. The in vivo efficacy of the red laser with 50, 75, and 100 mW total dose was similar to the same dose of green laser in reducing tumor volume. Combining PpIX‐PDT with prodrugs methyl‐linked mitomycin C (Mt‐L‐MMC) and rhodamine‐linked SN‐38 (Rh‐L‐SN‐38) significantly improved efficacy (tumor volume comparison). PpIX‐PDT or PpIX‐PDT + prodrug combination did not cause muscle damage in histological analysis. Overall, a combination of PpIX‐PDT and prodrug with 635 nm laser is promising for non‐muscle invasive bladder cancer treatment.