Characterisation of Glycogen Phosphorylase as a Potential Molecular Target for Novel Anti-Glioblastoma therapy

Abstract

Glioblastoma (GB) is the most aggressive primary malignancy of the Central Nervous System. Even in patients receiving standard treatment, the median survival duration is only 15 months. However, current anti-glioblastoma treatments are often ineffective with several side effects. Hence, newer GB treatments are needed. One hallmark of cancer cells is metabolic reprogramming, characterised by increased demand for glucose. Some cancers meet this increased glucose demand by metabolizing glycogen. The enzyme glycogen phosphorylase (GP) catalyses the rate-limiting step in glycogen breakdown, making GP an appealing pharmacological target in GB through its inhibition. The last decade has seen the development of several GP inhibitors for the treatment of diabetes. However, recent studies have shown the therapeutic roles of these inhibitors in various cancers. This study aimed to dissect the role of GP inhibition with GP inhibitors, baicalein and CP-91149 in the survival and migration of GB cells using resazurin viability assay and wound healing assay. Also, demonstrate the expression of GP isoforms in normal astrocyte cell lines (SVG) and three GB cell lines using western blotting. This study showed that GP inhibitors inhibited the growth of U87-MG and T98G cells in a concentration-, dose- and cell line-dependent manner with superior potency to standard therapy (temozolomide). However, the effects of the GP inhibitors on the migration and intracellular glycogen of T98G cells were less potent. Furthermore, the expression of the brain (PYGB), muscle (PYGM), and liver (PYGL) isoforms of GP varied in untreated-GB cells. SVG cells expressed only PYGB and PYGL GP isoforms, while the three isoforms of GP were upregulated in T98G cells and downregulated in U87-MG cells. Meanwhile, U51 cells had upregulated PYGB and PYGM. Therefore, this in vitro study validates GP as a potential pharmacological target in GB.