Photodynamic effects using a diode laser with mono-L-aspartyl Chlorin e6 for implanted mice tumor

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Photodynamic therapy (PDT) using the photosensitizer drug Photofrin has recently been approved for the treatment of early stage lung cancer, esophageal cancer, gastric cancer, uterine cancer and uterine dysplasia by the Japanese Ministry of Health and Welfare. The authors performed photodynamic therapy, avording any hyperthermic effects, using a diode laser and another photosensitizer mono-L-aspartyl chlorin e6 (NPe6) in an implanted fibrosarcoma in mice and achieved tumor therapeutic effects. The tissue temperature rise was 3.8ﾟC when 100mW/cm^2 light was delivered, this temperature being below the temperature range of hyperthermia. In the present study, PDT was performed 5 hours following the administration of 5.0 mg/kg NPe6. With 50,100,150 and 200 J/cm^2, tumor cure rates were 20,50,70 and 90%, respectively. In addition, when PDT was performed with administration of 1.25,2.5,5.0,7.5 and 10.0 mg/kg NPe6 with 100 J/cm^2 laser exposure, tumor cure rates were 0,20,50,70 and 90%, respectively. In some arimals, tumor recurrence seemed to occur from deeper layr of tumors. Therefore, the relationship between the effects of PDT and residual amounts of NPe6 in the deeper level of tumors following the PDT procedure were examined. We used a CCD camera system to measure the fluorescence intensity to evaluate the residual amount of NPe6 at 3mm from the tumor surface. The ratio of the residual amount of NPe6 following 50,100,150 and 200J/cm^2 laser exposure to no laser exposure were 73.4,36.0,22.0 and 15.9% respectively. These results suggest that a certain increase in the tumor tissue level of NPe6 and a certain increase of laser light dose reaching deeper layr of tumor caused an increase in percent cure. In addition, the effectiveness of PDT and also tumor recurrence following PDT depend to some extent on the total laser laser dose reaching deeper layrs of tumors. Furthermore, the effectiveness of PDT tends to correlate with the amount of photobleaching by PDT.