Photodynamic Therapy Using a Diode Laser with Mono‐l‐aspartyl Chlorin e6 for Implanted Fibrosarcoma in Mice

We have developed a new high‐power red (664 nm) laser diode system for photodynamic therapy (PDT) with mono‐L‐aspartyl chlorin e6 (NPe6). Meth‐A fibrosarcoma cells (1X106) were implanted subcutaneously in the right hind leg of 4‐week‐old BALB/c female mice. One week later, diode laser irradiation was applied 5 h after the intravenous administration of NPe6 to each tumor‐bearing mouse. In the first study, the time course of intratumor temperature increase during PDT was measured by using a 23‐guage thermocouple hypodermic needle at a depth of 2 mm from the tumor surface. In the second study, 6 groups of 10 to 17 tumor‐bearing mice were treated with the diode laser 5 h after intravenous administration of NPe6 at the dose of 1.25, 2.5, 5.0 or 7.5 mg/kg i.v. per mouse. Total photoirradiation ranged from 0 to 150 J/cm2 and the dose rate was adjusted to 100 mW/cm2. Percentages of cures were determined from numbers of mice apparently disease‐free 50 days after treatment. The results showed that this diode laser is effective in PDT of implanted fibrosarcoma after NPe6 administration. It also confirmed that the therapeutic effects of PDT were not due to hyperthermia. Moreover, the diode laser beam was demonstrated by CCD technology to be uniform in intensity throughout the photoirradiated field.