Growth and radiosensitivity of malignant melanoma multicellular spheroids initiated directly from surgical specimens of tumours in man.

The growth and radiosensitivity of multicellular spheroids initiated directly from disaggregated surgical specimens of four human malignant melanomas were studied. The spheroids were grown in liquid-overlay culture for up to 6 passages. Cell survival following irradiation was measured by using the Courtenay soft agar colony assay. The four melanomas formed spherical, densely packed spheroids. The volumetric growth rate as well as the plating efficiency in soft agar usually increased with increasing passage number. The radiosensitivity differed significantly among the melanomas. The survival curves for single cells from disaggregated spheroids in the first passage were always similar to those for single cells isolated directly from the surgical specimens. Two of the melanomas showed a significant contact effect as spheroids whereas the other two did not. The spheroids of two of the melanomas showed lower D0 in the third and the sixth passage than in the first passage, whereas the spheroids of the other two melanomas showed similar survival curves in the first and the third passage. There was no clear relationship between the changes in radiosensitivity and the changes in growth rate or plating efficiency. It is concluded that spheroids in the first passage, but not spheroids in later passages, may have the potential to identify differences in clinical radioresponsiveness among tumours.