Figure 4: High energy metabolite transport across the membrane supports tumor metabolism balance. The monocarboxylate transporter (MCT) proteins are responsible for moving lactate and pyruvate across the membrane, supplying pyruvate for lactate dehydrogenase to convert to lactate. Lactate is one of the chief molecules responsible for acidifying the tumor extracellular space. Additionally, carbonic anhydrase IX is also known to regulate intracellular pH, acidifying the extracellular microenvironment in the process. Both MCT proteins and CAIX can be targeted by agents whose efficacy could be measured by quantifying changes in the tumor extracellular pH.