Protoporphyrin IX fluorescence photobleaching is a useful tool to predict the response of rat ovarian cancer following hexaminolevulinate photodynamic therapy

Objective: Accurate dosimetry was shown to be critical to achieve effective photodynamic therapy (PDT). This study aimed to assess the reliability of in vivo protoporphyrin IX (PpIX) fluorescence photobleaching as a predictive tool of the hexaminolevulinate PDT (HAL-PDT) response in a rat model of advanced ovarian cancer. Materials and Methods: Intraperitoneal 10(6) NuTu 19 cells were injected in 26 female rats Fisher 344. Peritoneal carcinomatosis was obtained 26 days post-tumor induction. Four hours post-intraperitoneal HAL (Photocure ASA, Oslo, Norway) injection, a laparoscopic procedure (D-light Auto-Fluorescence system, Karl Storz endoscope, Tuttlingen, Germany) and a fluorescence examination were made for 22 rats. The first group (LASER group, n = 26) was illuminated with laser light using a 532 nm KTP laser (Laser Quantum, Stockport, UK) on 1 cm(2) surface at 45 J/cm(2) The second group (NO LASER group, n = 26) served as controls. Biopsies were taken 24 hours after PDT. Semi-quantitative histology was performed and necrosis value was determined: 0-no necrosis to 4-full necrosis. Fluorescence was monitored before and after illumination on complete responders (NV = 3-4; n = 20) and non-responders (NV = 02; n = 6). Results: High PpIX photobleaching corresponded with complete responders whereas low photobleaching corresponded with non-responders (P<0.05). A direct linear correlation was shown between photobleaching and necrosis (R-2 = 0.89). Conclusion: In vivo PpIX fluorescence photobleaching is useful to predict the tissue response to HAL-PDT.