G6PD deficiency sensitizes metastasizing melanoma cells to oxidative stress and glutaminolysis

The pentose phosphate pathway is a major source of NADPH for oxidative stress resistance in cancer cells but there is limited insight into its role in metastasis, when some cancer cells experience high levels of oxidative stress. To test this, we mutated the substrate binding site of Glucose-6-phosphate dehydrogenase (G6PD), which catalyzes the first step of the pentose phosphate pathway, in patient-derived melanomas. G6PD mutant melanomas had significantly decreased G6PD enzymatic activity and depletion of intermediates in the oxidative branch of the pentose phosphate pathway. Reduced G6PD function had little effect on the formation of primary subcutaneous tumors but when these tumors spontaneously metastasized the frequency of circulating melanoma cells in the blood and metastatic disease burden were significantly reduced. G6PD mutant melanomas exhibited increased levels of reactive oxygen species (ROS), decreased NADPH levels, and depleted glutathione as compared to control melanomas. G6PD mutant melanomas compensated for this increase in oxidative stress by increasing the production of NADPH through glutaminolysis. This generated a new metabolic vulnerability as G6PD mutant melanomas were more dependent upon glutamine as compared to control melanomas. The oxidative pentose phosphate pathway and compensatory glutaminolysis thus confer layered protection against oxidative stress during metastasis. Significance Melanoma metastasis is limited by oxidative stress. Cells that enter the blood experience high levels of ROS and usually die of ferroptosis. We found that melanoma cells become more dependent upon the oxidative branch of the pentose phosphate pathway to manage oxidative stress during metastasis. When pentose phosphate pathway function was disabled by G6PD mutation, the melanoma cells increased their utilization of malic enzyme, fueled by increased consumption of glutamine in the tricarboxylic acid cycle. Melanoma cells thus have redundant and layered protection against oxidative stress.