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Modification of Radiosensitivity by Porphyrins

II. Transplanted Rhabdomyosarcoma in Mice¹

Department of Experimental Medicine and Cancer Research, Medical School, Hebrew University, Jerusalem, Israel, and Department of Medicine University of Minnesota, Minneapolis, Minnesota

Eight days after i.m. injection of rhabdomyosarcoma into the thighs of mice, the tumors were irradiated with 2750 r. Three hr before X-irradiation the mice were given injections i.p. of 0.5 ml of 0.75% sodium bicarbonate alone or of 0.01, 0.05, 0.25, or 1.25 mg of crude "hematoporphyrin," a copper "hematoporphyrin," or a copper "hematoporphyrin" nitrate. The tumor response varied significantly with the dose of porphyrin given: tumors of all 27 mice (100%) who received 0.05 mg of "hematoporphyrin" or its copper complex showed grossly complete regression 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 receiving 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 administered. Little, if any, modification of radiosensitivity was produced by the copper "hematoporphyrin" nitrate. Other findings related to the observed porphyrin dose-dependent response curve are discussed.

¹ These studies were performed in the Department of Experimental Medicine and Cancer Research, Hebrew University, Jerusalem, as part of the Sabbatical Year program of S. Schwartz. A report of these studies was submitted by L. Cohen to the faculty of the Medical School in partial fulfillment of the requirements for a Master of Science Degree. The study was supported by grants from the American Cancer Society (T-190A) and the USPHS (GM-K3-14,086 Cl-A).

² Research Career Awardee of USPHS.

Received 3/23/64. Revised 3/14/66.