Targeting Glycogen Phosphorylase as a Potential Therapeutic Strategy for Glioblastoma

Abstract

Glioblastoma (GB) is one of the most aggressive malignancies of the brain and spinal cord. The current standard of care has remained surgical resection of the tumour, followed by radiotherapy and/or chemotherapy. Crucial challenges in the effective treatment of GB include resistance to the main chemotherapeutic, temozolomide. Prognosis is poor with median survival remaining at 14.6 months. A now established hallmark of cancer is the ability of malignant cells to “modify, or reprogram, cellular metabolism”, such as glycogenolysis upregulation. This hallmark could suggest the potential of targeting a specific metabolic component within glycolysis, thus reducing energy production, resulting in possible apoptosis or suppressed proliferation. Studies suggest that glycogen phosphorylase (GP), an enzyme in glycogenolysis, could be inhibited for a therapeutic effect in GB. In this project, GP levels across the three different isoforms (PYGB, PYGL, and PYGM) and the effect of the GP inhibitor CP-91149 was investigated across three different GB cell lines. Cell viability of T98G, U251, and U87 glioblastoma cell lines and SVGp12 human foetal glial cell line was measured after administration of CP-91149 for 24, 48, and 72 hours. Migration of T98G and U251 cells following treatment with CP-91149 was measured in a wound healing assay. Visualisation of the three GP isoforms was achieved through western blotting and confirmed by immunocytochemistry. Flow cytometry was utilised to expand analysis on GP inhibition by assessing the cell cycle before and after treatments. Results showed that CP-91149 had a significant dose- and time-dependent effect in vitro on all GB cell lines. Inhibition of GP caused a reduction in cell viability and cell migration. Western blot and immunocytochemistry analysis showed that PYGL is the most predominant isoform of GP. There was no clear effect on the cell cycle following treatment with CP-91149. Inhibition of glycogenolysis by targeting GP shows potential as a novel therapeutic approach in the treatment of glioblastoma.