Hypoxic Fraction and Repair of Potentially Lethal Radiation Damage in Two Human Melanomas Transplanted into Nude Mice

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Abstract
The radiosensitivity of 2 human cell lines, Ma-11 and Be-11, each arising from a human melanoma, was studied. The tumors were transplanted into nude mice and irradiated in situ; the colony-forming ability was tested in vitro. The DO [mean lethal dose] values obtained under these conditions were 4.22 and 5.85 Gy [gray] for Ma-11 and Be-11, respectively. The surviving fraction of irradiated cells increased when tumor excision was delayed for 6 h. The Be-11 line contained 40% hypoxic cells; the corresponding figure for Ma-11 was 62%. These figures, like that previously determined for another melanoma (85%), are among the highest reported in the literature. For solid tumors, only 10% of tumors have a hypoxic cell fraction greater than 40%; this high fraction may partially explain the radioresistance of human melanomas.