Photodynamic therapy (PDT) has been demonstrated to be efficacious in the treatment of cancer and has exhibited promising results in the treatment of HIV, laryngeal papillomas and atherosclerotic placque. However, the concomitant long-term skin photosensitivity limits the clinical usefulness of this therapy. Pilot experiments in mice have shown that the clearance rate of Photofrin, which is the photosensitizing dye approved for use in humans, can be increased with the ingest of ethanol. While the operative mechanism behind this effect is not known, it is conceivable that the increased clearance rate of Photofrin will result in a reduced or insignificant long-term skin photosensitivity.
The specific aims of the work proposed in this grant application are to (1) determine the mechanism by which ethanol treatment increases the rate of Photofrin clearance and (2) determine the effect of combined PDT- ethanol treatment on the efficacy of cancer kill and on skin photosensitivity by the ingestion of ethanol or some other compound that causes an increased rate of Photofrin clearance. We hypothesize that several different biologic phenomenon may be operative in PDT-ethanol therapy; they are: ingested ethanol causes (a) an impaired gastrointestinal absorption of Photofrin (b) an inhibition of the cellular uptake or retention of Photofrin (c) a reduction in the vasoconstrictive effect of Photofrin and (d) increases the skin clearance rate of Photofrin resulting in reduced post-PDT skin photosensitivity. To test these hypotheses, a series of in vivo and in vitro experiments will be done. A radiation induced fibrosarcoma mouse footpad model and a mammary adenocarcinoma rat dorsal skin-flap window-chamber model will be used for the in vivo experiments. These animals will undergo PDT and ethanol treatments using various protocols, and Photofrin concentrations in tissues will be determined at various times post-treatment using the techniques of high-performance liquid chromatography and absorption or fluorescence spectrophotometry. Mass spectroscopy will be used to examine the chemical makeup of the excreted dye. Tumor kill efficacy will be determined by physical measurements of tumor size while skin photosensitivity will be measured by morphometric analysis, laser doppler blood-flow measurements, and the wet/dry weight ratio of biopsied tissue. Vascular effects of PDT and ethanol treatment will be studied by videomicroscopy and reluctance spectrophotometry in a skin-flap window- chamber model. In vitro experiments will involve fibrosarcoma and adenocarcinoma cell cultures, as well as a normal human skin culture. These cells will be treated with PDT and ethanol therapy using various protocols, and assayed at various times post-treatment for Photofrin concentrations and cell survival.
