Targeting Hif-1α by Zebularine for the Treatment of Colorectal Cancers

Colorectal cancer (CRC) is the second leading cause of cancer-related death in males and females in the world. Hypoxia and accumulation of hypoxia-inducible factor HIF-1α in solid tumor tissues, including CRC, have been reported to associate with resistance to anticancer therapy and poor prognosis. Therefore, targeting HIF-1α might provide clinical benefits to CRC. Zebularine (Zeb), a stable DNA methyltransferase (DNMT) inhibitor, has been shown to preferentially kill cancer cells and exhibits low toxicity in normal cells and mice. Our preliminary results demonstrated that Zeb inhibit HIF-1α expression human colorectal HCT116 cells, suggesting that Zeb might have clinical activity toward CRC. Indeed, Zeb showed anticancer effect in HCT116 cells and in mice colitis-associated colon cancer. Autophagy is a physiological process involved in the turnover of proteins or intracellular organelles. It serves as a temporary survival mechanism during starvation where self-digestion becomes an alternative energy source. It has been recently reported that HIF-1α-dependent autophagy protects cells from anticancer drug-induced apoptosis in hypoxia. However, severe hypoxia or anoxia could induce HIF-1α-independent autophagic cell death through activation of AMPK and unfolded protein response (UPR). In addition to HIF-1α inhibition, Zeb also induced AMPK activation, UPR/ER stress and autophagy in HCT116 cells. Therefore, we hypothesized that Zeb treatment will switch HIF-1α-dependent cytoprotective autophagy to HIF-1α-independent autophagic cell death in hypoxia, which could abrogate hypoxia-induced anticancer drug resistance. In this four-year research project, we plan to incorporate the preliminary results to test the following SPECIFIC AIMS: (1) To investigate the in vitro and in vivo anticancer effect of Zeb toward colorectal cancers. (Year 1) (2) To elucidate the molecular mechanisms of Zeb-mediated HIF-1α inhibition. (Year 1~2) (3) To elucidate the molecular mechanisms of Zeb-induced autophagy. (Year 2~3) (4) To investigate the effect of Zeb on hypoxia-mediated drug resistance. (Year 3)