Prostate cancer cells elevate glycolysis and G6PD in response to caffeic acid phenethyl ester-induced growth inhibition

Background: Caffeic acid phenethyl ester (CAPE) is the main bioactive component of poplar type propolis. We previously reported that treatment with caffeic acid phenethyl ester (CAPE) suppressed the cell proliferation, tumor growth, as well as migration and invasion of prostate cancer (PCa) cells via inhibition of signaling pathways of AKT, c-Myc, Wnt and EGFR. We also demonstrated that combined treatment of CAPE and docetaxel altered the genes involved in glycolysis and tricarboxylic acid (TCA) cycle. We therefore suspect that CAPE treatment may interfere glucose metabolism in PCa cells. Methods: Seahorse Bioenergetics platform was applied to analyzed the extra cellular acidification rate (ECAR) and oxygen consumption rate (OCR) of PCa cells under CAPE treatment. UPLC-MSMS with Multiple Reaction Monitoring (MRM), PCR, and western blot were used to analyze the effects of CAPE on metabolites, genes, and proteins involved in glycolysis, TCA cycle and pentose phosphate pathway in PCa cells. Flow cytometry and ELISA were used to determine the level of reactive oxygen species in PCa cells being treated with CAPE. Results: Seahorse Bioenergetics analysis revealed that ECAR, glycolysis, OCR, and ATP production were elevated in C4-2B cells under CAPE treatment. Protein levels of glucose-6-phosphate dehydrogenase (G6PD), phosphogluconate dehydrogenase (PGD), glutaminase (GLS), phospho-AMPK Thr172 as well as abundance of pyruvate, lactate, ribulose-5-phosphate, and sedoheptulose-7-phosphate were increased in CAPE-treated C4-2B cells. ROS level decreased 48 h after treatment with CAPE. Co-treatment of AMPK inhibitor with CAPE exhibited additive growth inhibition on PCa cells. Conclusions: Our study indicated that PCa cells attempted to overcome the CAPE-induced stress by upregulation of glycolysis and G6PD but failed to impede the growth inhibition caused by CAPE. Concurrent treatment of CAPE and inhibitors targeting glycolysis may be effective therapy for advanced PCa.