AKT1 and colonic neoplasm: Herein, we report that increasing the tetrahydrobiopterin:dihydrobiopterin ratio and recoupling nitric oxide synthase with sepiapterin in the colon cancer cell lines, HCT116 and HT29, inhibit their proliferation and enhance cell death, in part, by Akt/GSK-3β–mediated downregulation of β-catenin.