Enhancement of photodynamic therapy due to hyperbaric hyperoxia: an experimental study of Walker 256 tumors in rats

摘要

Abstract: Photodynamic therapy (PDT), which is now an approved treatment for many types of cancers, is based on the simultaneous involvement of three factors, namely: tumor tissue retention of a specific photosensitizer; local illumination of the lesion with a visible light source and the occurrence of oxygen in the triplet state. Theoretically, a change in any one of these factors may be compensated by a change in the other two factors, leading to the same therapeutic result. In practice, this is not true, since we are dealing with living tissue, but we may expect to find an ideal combination of these three factors which may give the best clinical results. In this work we present experimental results of PDT under Hyperbaric hyperoxia (HBO) in tumor masses of the dorsal subcutaneous tissue of rats. These tumors were created by previous inoculation of 'Walker 256' neoplastic cells Hematoporphyrin Ester (HpE) was administered as the photosensitizer. The rats were pressurized at up to 3 atm with a 100 percent continuous oxygen ventilation environment in a specially designed hyperbaric chamber. The skin area above the tumor was photosensitized for 45 minutes with a 7 mw HeNe laser. Twenty four hours later, the tumor was removed for study. In all the animals treated with PDT/HBO histology revealed a very important reduction in the number of tumor cells as compared with the PDT controls in normal atmospheric condition, showing numerous apoptotic as well as necrotic cells at the border of the radiated area. The observed enhancement in the PDT for this situation is, of course, related to the extra oxygen in the circulatory system. !13