Preliminary study of verteporfin photodynamic therapy in a canine prostate model

Photodynamic therapy (PDT) mediated with verteporfin was investigated as an alternative modality for the treatment of prostate cancer. Materials and Methods: Vertoporfin-mediated photodynamic effects on the prostate and its adjacent structures (underlying colon and bladder) were evaluated in a healthy canine model. Interstitial prostate PDT was performed by irradiating individual lobes with a diode laser (689 nm) and 1-cm cylindrical diffuser fibers at various light doses and drug-light intervals (DLI) to activate the IV administrated photosensitizer (0.5 or 2 mg/kg). The sensitivity of the adjacent tissues to Vertoporfin-PDT was determined by superficially irradiating the serosal surface of the bladder and colon with a microlens fiber. The prostate and adjacent tissues were harvested one-week after the treatment and subjected to histopathological examination. Results: Histopathological examinations confirmed that verteporfin PDT could destroy a clinically significant volume of prostatic tissue in the animal model. At the drug dose of 0.5 mg/kg, the light irradiation of 100 J/cm could induce a lesion diameter of 2 cm at DLI of 15 min and 1.2 cm at DLI of 3 hrs, respectively. This implies a strong influence of DLI on the lesion volume. The shorter DLI might produce stronger vascular effect and therefore more severe tissue damage. The colon was more sensitive to verteporfin PDT than the bladder. At the possible light dose level caused by light scattering during intra-prostate irradiation, the damage to the bladder and colon were superficial and minimal. Conclusions: The preliminary results clearly demonstrate that verteporfin PDT could be an effective means to destroy prostate gland and its usefulness for the treatment of prostate cancer is worth further investigation.