Modification of radiosensitivity by porphyrins. II. Transplanted rhabdomyosarcoma in mice.

response varied significantly with the dose of porphyrin given: tumors of all 27 mice (100%) who received 0.05 mg of "hemato porphyrin" or its copper complex showed grossly complete re gression and did not recur during the following 84-86-day study period, while such regression was seen in only 5 of 126 mice (4%) treated by injection with the other dose levels of porphyrin or with vehicle alone prior to X-irradiation. Normal mice re ceiving total body X-irradiation showed no similar porphyrin effect, suggesting an increase in the therapeutic ratio (cancer effect/whole body effect) by the 0.05 mg of porphyrin admin istered. Little, if any, modification of radiosensitivity was pro duced by the copper "hematopoqjhyrin" nitrate. Other findings related to the observed porphyrin dose-dependent response curve are discussed.