Manipulation of DNA damage checkpoint signaling in cancer cells by antioxidant biofactor (AOB)

Antioxidant biofactor (AOB) is one of the fermented grain food supplements commercially available in Japan and other countries. Herein, we investigated the effect of AOB on the UVC (254 nm) induced DNA damage in A549 cells. Both distilled water and MeOH extracts of AOB did not show any significant cell toxicity. However, the UV (25-75 J m(-2)) induced cell death was amplified in the presence of these extracts, especially the MeOH extract. When the DNA damage was evaluated by comet assay, the AOB water extract prevented the UV induced DNA damage at the initial stage but significantly inhibited the repair process, especially in the cells exposed to a high dose of UV. The retardation of DNA repair was significantly higher in the presence of the MeOH extract, concentrating such components as caffeine and polyphenols, and thus the damage was enhanced both in the cells irradiated by low and high doses of UV. The DNA damage profile was consistent with the inhibitory profile of ATR, a key kinase of DNA damage checkpoint signaling. The AOB MeOH extract markedly reduced the phosphorylation level of the checkpoint proteins activated by UV, such as p53, SMC1 and Chk1, together with ATR. The inhibitory effect of the AOB water extract was less effective as compared to the MeOH extract, but was dose-dependent both in the cells irradiated with high and low doses of UV. The dual role of AOB as an antioxidant and a checkpoint modulator suggests its beneficial use in complementary medicine as a potential sensitizer of anticancer treatment.