Toxic pulmonary effects of photodynamic therapy (PDT) in a mouse model

A major limitation of PDT for Barrett's esophagus is the development of esophageal strictures. This report summarizes the effects of PDT delivered to mouse esophagus. Sixty-two C3H/Nsd mice were injected with Photofrin (2-10mg/Kg) intraperitoneally. Forty-eight hours later a I cm laser probe was passed orally to the mid-esophagus. Light energy (630nm) ranged from 0 to 400 Joules/cm (J). Animals were sacrificed if death was imminent, otherwise at 6 weeks and 3 months. Gross and microscopic exams were performed on paraffin embedded esophagus and lung specimens. Exposure to 400J as a single fraction, 125 X 3 or 150 X 3 fractions resulted in a lethal pulmonary injury in 90% of mice within 48 hours. There was no esophageal mucosal damage at this early time point. Lower doses caused minor pulmonary injury allowing long-term survival but no change in the esophageal endothelium and no stricture. In the mouse, this histopathologic study demonstrates that pulmonary toxicity is the limiting factor following esophageal PDT. At lower PDT doses, minimal pulmonary damage occurred but no effect was observed on the esophagus. We believe the 5 mm depth of PDT injury leads to lethal pulmonary damage preventing subsequent study of the effects on the esophagus.