SEPTEMBER 16, 2008 -- The September issue of BJU (British Journal of Urology) International reports the results of "the largest study to date" of Tookad (padoporfin, WST09), a minimally invasive vascular-targeted photodynamic (VTP) therapy agent. The study suggests that Tookad can help men with recurring cancer of the prostate. Tookad was developed by researchers at the Weizmann Institute of Science (Rehovot, Israel), which has also worked to advance adaptive optics for tissue imaging.
Dr. John Trachtenberg of the Ontario Cancer Institute/Prince Margaret Hospital (Toronto, Ontario, Canada) led a team of Canadian and Israeli investigators in the work to evaluate the photodynamic therapy (PDT) approach. Patients received a fixed photosensitizer dose of 2 mg/kg and patient-specific light doses as determined by computer-aided treatment planning. Up to six cylindrical light-diffusing delivery fibers were placed transperineally in the prostate under ultrasonographic guidance. The treatment response was assessed by measuring serum prostate-specific antigen (PSA) levels, lesion formation (avascular areas of tissue) measured on 7-day gadolinium-enhanced T1-weighted magnetic resonance imaging (MRI) and a 6-month biopsy.
The team reports that treatment of the whole prostate was possible with minimal effects on surrounding organs. An increased light dose improved the tissue response, with MRI-detectable avascular lesions, encompassing up to 80% of the prostate in some patients. A complete response, as determined by the 6-month biopsy, required that patients received light doses of at least 23 J/cm2 in 90% of the prostate volume (D90 > 23 J/cm2). Of the 13 patients who received at least this light dose, eight were biopsy-negative at 6 months. In this group of eight patients, PSA levels decreased and did so to negligible levels for those patients with a baseline PSA level of <5 ng/mL.
Side-effects were modest and self-limited in most patients, the researchers say. The study concluded that Tookad, a novel palladium-bacteriopheophorbide photosensitizer, can produce large avascular regions in the irradiated prostate, and result in a complete negative-biopsy response at high light doses. A response rate of more than half for those patients receiving the highest light doses shows the clinical potential of Tookad to manage recurrence of prostatic carcinoma after external beam radiation therapy (EBRT).