Overexpression Of GPD1 Enhances The Anticancer Effects Of Metformin

Cancer cell has its specific metabolic reprogramming to meet the energy requirements of rapid proliferation and metastasis.It has been suggested a“Warburg effect”that their energy sources still rely on glycolysis under aerobic conditions,with high glucose uptake rate and high production of lactic acid.Therefore,metabolic therapy of cancer cells has attracted much attentions nowadays,and many clinical trials have shown that it has positive effects on cancer treatment.Metformin,as a first-line oral hypoglycemic drug,has been widely used in cancer research because of its inhibitory effect on glycolysis,good tolerance and few side effects.However,although numerous studies demonstrated metformin exerts great values in cancer treatment,it's still not an anticancer drug in guidelines.On the other hand,according to the cancer heterogeneity,cell subpopulations show different sensitivity to drugs,and even develop drug resistance after a long-term treatment.The effective methods and the underlying mechanisms on how to improve the anticancer activity of metformin remain unknown.Previous study had demonstrated that metformin can directly target glycerol-3-phosphate dehydrogenase 2(GPD2),reducing the level of intracellular oxidative phosphorylation and inhibiting gluconeogenesis.Although glycerol-3-phosphate dehydrogenase 1(GPD1)belongs to the Glycerol-3-phosphate dehydrogenase(GPDH)family as well,but it did not show the similar effect to GPD2.We observed that GPD1 and metformin can influence the production of glycerol-3-phosphate(G3P),which is lie at the crossroad of glycolipid metabolism.In this study,we preliminary found that GPD1 shows a low mRNA expression level in many cancers in GEPIA public database.We identified GPD1 mRNA expression level was inversely correlated with half maximal inhibitory concentration(IC50)of metformin in 15 cancer cell lines,using RT-qPCR and CCK-8 assay.Further in vivo and in vitro experiments showed that overexpression of GPD1 can significantly inhibit cancer growth and promote the anticancer ability of metformin.Mechanically,combination of GPD1 overexpression and metformin treatment can significantly block G3P shuttle and increase the total cellular concentration of G3P.Using Seahorse assay,we identified that overgeneration of G3P can inhibit mitochondrial function and reduce mitochondrial-ATP production.Eventually,imbalance of NAD~+/NADH,increase of reactive oxygen species and the damage of mitochondrial structure were observed in GPD1 overexpressing cell lines combined with metformin treatment.In conclusion,we demonstrated for the first time that overexpression of GPD1 enhances the anticancer effects of metformin and it has potential to be a synergist of metformin on cancer treatment.The cancer patients with high GPD1expression may have a new selection for receiving metformin treatment.