SLC9A1 and cancer: This specific metabolism of hypoxic cancer cells leads to a marked extra-cellular acidosis due to both increased H+ production and increased H+ efflux through hypoxia-inducible factor 1 (HIF-1) mediated trans-activation of transporters such as carboanhydrase IX, monocarboxylic transporter 4 (MCT4) and Na+/H+ exchanger 1 (NHE1) [43].