The treatment of esophageal cancer by vascular-targeted photodynamic therapy (VTP) using orthotopic rat model.

Abstract

91 Background: Vascular targeted photodynamic therapy (VTP) based on local sensitization of circulating WST11, a water-soluble derivative of Pd-bacteriochlorophyll, enables effective focal ablation of solid tumors. Highly toxic oxygen radicals are produced in the vascular lumen upon illumination with near infra-red light (755nm), leading to irreversible occlusion of tumor feeding arteries and veins. WST11 clears rapidly from the circulation and does not accumulate in the body, providing high level of safety and minimizing adverse effects. WST11-VTP completed Phase II clinical trials in USA and Phase III in Europe for the treatment of early localized prostate cancer as a first line monotherapy with above 80% complete response rate. Here we evaluate its’ safety and efficacy for the treatment of esophageal cancer aiming at development of clinically translatable treatment protocol. Methods: We developed an orthotopic model in which esophageal cancer cells are implanted in the mid esophagus using endoscopy guided procedure. Established tumors are illuminated with cylindrical diffuser deployed through the custom built endoscopy guided system following infusion of WST11. For assessment of treatment safety and tissue recovery normal esophagus tissue was subjected to WST11-VTP using the same treatment set up. Selectivity and efficacy were evaluated histologically by examining sections of treated tumors and normal esophageal tissues under various treatment conditions. Results: Safety control VTP procedures on healthy esophageal tissues have shown a confined destruction only at the illuminated zone while collateral damage to neighboring tissues was not observed. The impact runs as deep as the muscularis propria without signs of perforation or death as a result of the procedure. The VTP protocol was able to ablate implanted and established tumors as opposed to the control group with light illumination alone without the sensitizer (WST11). Conclusions: VTP could be safely applied to treat esophageal tumors, with transient and mild adverse effects. Importantly, VTP effectively eradicated established esophageal tumors in tested set up that could be translated into a clinical treatment protocol.