Radiation and/or hyperthermia sensitivity of human melanoma cells after several days of incubation in media lacking serum or certain serum components

Purpose: Complete serum and single growth factors have been reported to protect cells against the effects of hyperthermia. The phenomenon is not very well understood, especially with regard to the relative importance of the various serum components. There is also a need to clarify the possible involvement of changes in proliferation. The influence of serum and growth factors on radiation sensitivity has not been studied in detail. The present communication is an attempt to at least partly fill these gaps. Cells were exposed to X-rays and/or heat after incubation in sufficiently supplemented medium and media lacking certain serum components. Differences in clonogenic survival were recorded and related to the proliferative status under the various conditions. Methods and Materials: Human melanoma cells (MeWo) were used throughout. Cells were incubated for 3 or 6 days (a) in Ham’s F12 medium with 20% fetal calf serum; (b) in medium without serum, but supplemented with the following components: insulin, transferrin, Na-selenite, and a lipid–protein complex; (c) to (f) in media lacking one or the other of these components; (g) in unsupplemented medium. Colony formation ability served as a measure of cell survival after exposure to radiation (250 kV X-rays) and/or hyperthermia (heating at 43°C). In parallel, cell proliferation was characterized by the bromodeoxyuridine (BrdU) labeling index and the Ki-67 growth fraction, both determined by two-parameter flow cytometry. Results and Conclusions: Sensitivity was hardly influenced by 3 days of incubation in medium containing no supplement at all, whereas after 6 days under the same conditions survival curves both of irradiated and hyperthermia-treated cells had a strongly reduced shoulder or were considerably steeper. Experiments with media lacking only one or the other serum component, showed that deprivation of insulin, transferrin, and sodium selenite led to no more than a modest increase in cell killing, whereas the effects in medium lacking lipid–protein complex were about the same as in medium containing no supplement at all. Sensitivity changes did not seem to be due to the lack of serum or certain of its components per se, but were very well correlated with changes in proliferation as characterized by BrdU labeling index or the Ki-67 growth fraction.