Photodynamic therapy of C3H tumours in mice: Effect of drug/light dose fractionation and misonidazole

C3H mammary carcinomas transplanted to the feet of mice were treated with haematoporphyrin derivative (HPD) or Photofrin II(PII) and laser light at 630 nm. While fluence rates lower than 100 mW cm⁻² gave minimal hyperthermic effects, a slight but significant growth delay was observed in unsensitized tumours exposed to a fluence rate of 150 mW cm⁻² which induced tumour temperatures in the range 40–50°C. Different modes of fractionation of the light fluence and of the HPD dose were tested but were found to give poorer rather than better results than the application of a single light exposure 24 h after intraperitoneal injection of HPD. Different PII doses were applied together with different light fluences, keeping the product of the drug dose and light fluence constant. In the dose range 6.25–50 mg/kg body weight the resulting effect on tumours was constant, allowing for a slight effect of hyperthermia at the highest light fluences, and possibly a photodegradation of PII. Misonidazole given before photodynamic treatment (PDT) slightly reduced the effect of PDT on the tumour growth. When given after PDT, however, misonidazole improved the therapeutic results significantly.