Enhancement of sensitivity of human squamous carcinoma cells to radiation by epidermal growth factor.

Experiments were done to determine the effect of murine epidermal growth factor (EGF) on the radiation responses of the human squamous carcinoma cell line CaSki grown as an exponential monolayer culture. The radiation responses studied included recovery from potentially lethal damage (PLDR) and recovery from sublethal damage (SLDR). The presence of EGF in the cell culture either after irradiation (during the clonogenic assay period) or continuously before, during, and after irradiation enhanced the radiosensitivity of the cells and reduced their plating efficiency (PE). However, these effects were not as great when EGF was present in the cell culture only before and during irradiation. This enhancement of radiosensitivity was associated with a reduction in the shoulder region of the cell survival curves. The PE reduction and radiosensitivity enhancement were maximum with 10 ng of EGF/mL. However, EGF present continuously in the cell culture, including during the 6-hour repair period, had no effect on cellular PLDR or SLDR. The single-stranded DNA breaks present in large numbers in cells immediately after irradiation returned to control levels by 6 hours. Moreover, EGF present in cell cultures for the 48 hours before irradiation and during the 6-hour repair period had no effect on the DNA alkaline elution profiles of either control or irradiated cells. EGF did not affect the growth of unirradiated cells; however, it extended the lag-phase period for growth of irradiated cells. In summary, this EGF-induced radiosensitivity enhancement was not correlated with the effects of EGF on PE, cell growth, PLDR, or SLDR.