Metabolic alterations and mitochondrial dysfunction underlie hepatocellular carcinoma cell death induced by a glycogen metabolic inhibitor

Hepatocellular carcinoma (HCC) is one of the leading causes of cancer-related deaths. There is an urgent need for new targets to treat HCC due to limited treatment options and drug resistance. Many cancer cells are known to have high amount of glycogen than their tissue of origin and inhibition of glycogen catabolism induces cancer cell death by apoptosis. To further understand the role of glycogen in HCC and target it for pharmacotherapy, we studied metabolic adaptations and mitochondrial function in HepG2 cells after pharmacological inhibition of glycogen phosphorylase (GP) by CP-91149 (CP). GP inhibition increased the glycogen levels in HepG2 cells without affecting overall glucose uptake. Glycolytic capacity and importantly glycolytic reserve decreased significantly. Electron microscopy revealed that CP treatment altered mitochondrial morphology leading to mitochondrial swelling with less defined cristae. A concomitant decrease in mitochondrial oxygen consumption and mitochondria-linked ATP generation was observed. Metabolomics and enzyme activity / expression studies showed a decrease in the pentose phosphate pathway. In addition, CP treatment decreased the growth of HepG2 3D tumor spheroids in a dose- and time-dependent manner. Taken together, our study provides insights into metabolic alterations and mitochondrial dysfunction accompanying apoptosis in HepG2 cells upon GP inhibition. Our study can aid in the understanding of the mechanism and development of metabolic inhibitors to treat HCC.