The ability of cells to regenerate GSH from oxidized glutathione (GSSG) is dependent upon the availability of NADPH, which in turn is regenerated from NADP by utilizing different substrates: glucose in particular is the main source of NADPH in cancer cells when metabolized through the pentose phosphate pathway (PPP), under the control of G6pd and Pgd (Fig 3A; Patra & Hay, 2014). This evidence concerns the gene PGD and cancer.