To investigate the effect of glycolysis and the tissue redox state on P-gp expression in multicellular
tumor spheroids derived from prostate
adenocarcinoma cells (DU-145),
glioma cells (Gli36), and the human cervix
carcinoma cell line KB-3-1 transfected with a P-gp-EGFP fusion gene that allows monitoring of P-gp expression in living cells. During cell culture of DU-145, Gli36, and KB-3-1
tumor spheroids P-gp expression was observed as well as increased
lactate and decreased
pyruvate levels and expression of glycolytic
enzymes. Inhibition of glycolysis for 24 h by either iodoacetate (IA) or
2-deoxy-D-glucose (2-DDG) downregulated P-gp expression which was reversed upon coincubation with the radical scavenger
ebselen as shown by semi-quantitative immunohistochemisty in DU-145 and Gli36
tumor spheroids, and by EGFP fluorescence in KB-3-1
tumor spheroids. Consequently endogenous ROS generation in DU-145
tumor spheroids was increased in the presence of either IA or 2-DDG, which was abolished upon coincubation with
ebselen. Exogenous addition of
pyruvate significantly reduced ROS generation, increased P-gp expression as well as efflux of the P-gp substrate
doxorubicin.
Doxorubicin transport was significantly blunted by 2-DDG and IA, indicating that inhibition of glycolysis reversed the multidrug resistance phenotype. In summary our data demonstrate that P-gp expression in
tumor spheroids is closely related to the glycolytic metabolism of
tumor cells and can be downregulated by glycolysis inhibitors via mechanisms that involve changes in the cellular redox state.