Effects of radioprotectors on DNA repair capacity of tumor cells

Abstract

Three cell lines, CHO, L929 and B16 which are non-tumorigenic, tumorigenic and cancer cells, respectively, were first tested for their survival in the presence of radioprotective ginseng protein fraction(GPF). The influence of three radioprotectors-GPF, cysteamine, and 1-Methyl-2-bis[(2- methylthio)vinyl] quinolinium iodide (MVQI) on DNA repair capacity of UV damaged cells was also investigated by measuring 3H-thymidine incorporation of PUVA treated cells. In cell survival test, the GPF showed higher cytotoxicity in L929 and B16 than in CHO cells. However, the degree of cell killing was not high enough to consider it as an antitumorigenic agent. Variable results were obtained in the effects on DNA repair capacity depending on the protectors and cell lines used. In pretreatment, the presence of GPF and MVQI brought about a significant increase in the capacity in both CHO and B16 cells. However, in L929, the enhancing effect was not shown. In all three cell lines, cysteamine showed lower repair capacity than control, suggesting the primary damage reduction to occur, rather than repair enhancement. In posttreatment, GPF and MVQI resulted in stronger enhancing effects in L929 and B16 cells, while it was weaker in CHO cells. Here also cysteamine showed a very little or no increase in the capacity in all three cell lines. These results demonstrate that GPF has mild cytotoxicity in tumorigenic cells and that GPF and MVQI enhance DNA repair capacity of UV damaged cells, whether they are tumorigenic or not. On the other hand, cysteamine shows only damage reduction effect. Cells of different genetic origin seem to give different responses to the modifier and different modifiers may possibly work by different mechanisms.