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Radiation responses of HMV-I human malignant melanoma cells grown in vitro as multicellular spheroids.

HMV-I cells, derived from human malignant melanoma, were cultured in spinner flask as multicellular spheroids. The growth in vitro was exponential for 9 days and then the growth rate gradually decreased. Central necrosis was detected by histological examination in the 400-500 μm diameter spheroids. Radiation survival curve obtained for spheroids of approximately 400 pm diameters consisted of an initial steeper component and a shallower one. The Do values were 1.2 Gy and 3.5 Gy for radiosensitive and radioresistant component, respectively. It was considered that this radioresistance was due to hypoxic cells which were located in the inner region adjacent to the central necrosis in the spheroids. These results suggest that HMV-I spheroids provide an useful in vitro human tumor model which is capable of contributing much to a better knowledge of cancer therapy.