Photodynamic therapy with a diode laser for implanted fibrosarcoma in mice employing mono-L-aspartyl chlorin E6

The authors performed photodynamic therapy (PDT), avoiding any hyperthermic effects, using a newly developed diode laser and photosensitizer, mono-L-aspartyl chlorin e6 (NPe6), of Meth-A fibrosarcoma implanted in mice and achieved tumor therapeutic benefit. The photodynamic light treatment was performed 5 h following the photosensitizer administration. With 5.0 mg/kg NPe6 and light doses of 50, 100, 150 and 200 J/cm2, the tumor cure rates were 20, 50, 70 and 90%, respectively. With 100 J/cm2 laser exposure and NPe6 doses of 1.25, 2.5, 5.0, 7.5 and 10.0 mg/kg, the tumor cure rates were 0, 20, 50, 70 and 90%, respectively. A charge-coupled device (CCD) camera system was employed to measure the NPe6 fluorescence intensity correlating with the residual amount of the photosensitizer at deferent depth from the tumor surface. The ratios of the NPe6 fluorescence intensity at 3 mm from the tumor surface following 50, 100, 150 and 200 J/cm2 laser exposure to no laser exposure were 0.73, 0.36, 0.22 and 0.16, respectively. With samples sectioned at 1 mm depth, after 50 J/cm2 and the same photosensitizer dose (5 mg/kg) this ratio was 0.19. These results suggest that a certain increase in the tumor tissue level of NPe6 and a certain increase of laser light dose reaching deeper layer of tumor caused an increase in percent cure. In addition, the effectiveness of PDT depends on the total laser dose reaching deeper layers of tumors. Furthermore, the effectiveness of PDT tends to correlate with the amount of NPe6 photobleaching by PDT.