Glyceollins Modulate Tumor Development and Growth in a Mouse Xenograft Model of Human Colon Cancer in a p53-Dependent Manner

Glyceollins are soybean-derived phytoalexins that induce the nuclear factor (erythroid-derived 2)-like 2 (Nrf2) signaling pathway, which is involved in the detoxification of carcinogens and the removal of reactive oxygen species (ROS). Recent studies, however, have indicated that Nrf2 induction stimulates the development of pre-existing tumors and confers resistance to chemotherapy by elevating drug metabolism and by efficient scavenging of ROS produced by the Warburg effect, which is regulated, in turn, by the p53 tumor suppressor. This study, therefore, aimed at examining whether glyceollins could accelerate tumor growth in the presence of active p53, using a xenograft BALB/c nude mouse model transplanted subcutaneously with p53 wild-type and p53 null HCT116 human colon cancer cells. Glyceollins were orally administered at a dose of either 1 or 4 mg/kg body weight after xenografting HCT116 cells, and tumor growth and volume were monitored for 2 weeks. A high dose of glyceollins resulted in a significant increase in the average volume of p53 wild-type HCT116 xenografts, but not of p53 null HCT116 xenografts. However, a low dose of glyceollins had no effect on the tumor growth regardless of p53 presence. Interestingly, antioxidant enzymes, including heme oxygenase-1 (HO-1) and NAD(P)H: quinone oxidoreductase, were prominently induced by glyceollins in p53 wild-type xenografts, compared with p53 null xenografts. These results suggest that a high dose of glyceollins possibly promotes the growth of p53 wild-type colon cancer through activation of the Nrf2-mediated signaling pathway and, in particular, strong induction of HO-1 expression. Therefore, the consumption of Nrf2 activators, including glyceollins, should be carefully monitored for patients suffering from certain types of cancer and/or receiving chemotherapy.