ORCID

https://orcid.org/https://orcid.org/0000-0003-0924-5701

Date of Award

2021

Document Type

Dissertation

Degree Name

Philosophy (Ph.D)

Department

Pharmaceutical Sciences

First Advisor

Vikas Dukhande

Second Advisor

Ketan Patel

Third Advisor

Sandra E Reznik

Abstract

Metabolic reprogramming is one of the important features of cancers, and there has been growing interest in targeting metabolic proteins to treat cancer. Glycogen is a polymer of glucose and serves as its storage unit in cells. Glycogen can provide energy to cells during the situations of high energy demand. A number of tumors are known to contain high levels of glycogen than their normal tissue counterparts. The liver plays an essential role in maintaining glucose homeostasis in the body via storing it into glycogen. The significance of glycogen metabolism in patients suffering from hepatocellular carcinoma (HCC) has not been clearly understood. In this study, we investigated the effects of a metabolic inhibitor targeting glycogen catabolism in HCC cells on the survival, proliferation, mechanism of cell death, metabolic changes, and synergistic effect on multikinase inhibitors. Inhibition of glycogen phosphorylase (GP), a rate-limiting enzyme in glycogen catabolism, was achieved using pharmacological inhibitor CP-91149. GP inhibition caused an increase in glycogen level and changed the expression of proteins involved in various metabolic processes. Mitochondrial metabolism was affected significantly whereas glucose entry and glycolysis were relatively unchanged. Determination of levels of different metabolites showed GP inhibition causes reduction in levels of many intermediates of pentose phosphate pathway (PPP). In addition, increase in ROS levels, cell cycle inhibition, decrease in oxygen consumption rate, and decreased mitochondrial membrane potential was observed. CP-91149 treatment resulted in the activation of intrinsic apoptotic pathways and cell death in HCC cells and HepG2 3D spheroids. Also, GP inhibition potentiated the effects of multikinase inhibitors sorafenib and regorafenib, which are key drugs in advanced-stage HCC therapy. Our study provides mechanistic insights into cell death by perturbating glycogen metabolism and highlights GP inhibition as a potential HCC pharmacotherapy target.

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