Bacteriopheophorbide molecules are second-generation photosensitizers with promise for PHotodynamic Therapy applications due largely to their absorption peaks in the near-Infrared region. Palladium bcteriopheophorbide, also called TOOKAD, has been successfully evaluated in several pre-clinical animal models. In this study the effect on tumor and normal vasculature was evaluated using an intravital vascular model on mouse cremaster muscle implanted with the RIF tumor. For tumor response studies, the same RIF tumor was implanted intradermally on the right flank and regression was evaluated for 42 days or until the tumor reached a 12 mm diameter.
A light dose 300 J/cm2 were delivered at 763 nm with power density of 100 mW/cm2. Photosensitizer dose was 4 mg/kg body weight. Mice were treated immediately, 10 minutes, 30 minutes, or 24 hours after injection. Only the higher light dose (300 J/cm2) delivered 10 minutes after injection produced a reproducible and complete vascular and tumor response after PDT in these animals. In the cremaster-tumor model, arterioles and venules partially shutdown as early as 40 minutes after the beginning of treatment, while tumor neovasculature was irreversibly closed within 20 minutes of treatment. Tumor response studies demonstrated that the magnitude of vascular stasis correlates with tumor regression studies. Further studies using this photosensitizer are warranted, given its short clearance time and its near-Infrared activation wavelength.