Evaluating the Efficacy of Current and Novel Chemotherapeutic Agents for the Treatment of Glioma

Abstract

Glioblastoma (GBM) is the most common and aggressive tumour of the central nervous system. Currently, GBM remains an incurable tumour characterized by a poor prognosis with a median survival time of 15 months. Both hypoxia and inflammation are central hallmarks of the GBM microenvironment leading to therapy resistance, however, research studies on GBM are rarely undertaken in hypoxic conditions. A lack of progress in the development of novel treatments has led to repurposing of existing licensed drugs as an alternative option. Research has suggested a role for aspirin, a non-steroidal anti-inflammatory drug, in the treatment and prevention of GBM. However, widespread aspirin
usage is challenging due to side effects which has led to the development of several novel aspirin analogues with the aim of producing the same or better anti- cancer effects accompanied with safer toxicity profiles.

This study has investigated the effects of one such analogue, PN517, in addition to aspirin, cisplatin, and temozolomide either as monotherapy or combined therapy on the U87-MG glioblastoma and non- cancerous SVG-p12 cell lines under normoxic and
hypoxic conditions. Multiple assays were performed including cell viability assay, proliferation and cell cycle analysis, wound healing assay, mitopotential and cell death assays, metabolic activity assays as well as western blot analysis for several proteins. In addition, U87-MG hypoxia-adapted cell lines and 3D spheroid models were generated and employed to examine the effect of the drug treatments in models that better mimic the GBM microenvironment.
Results found that PN517 and aspirin decreased cell viability under normoxia and hypoxia in a time and concentration dependent manner with similar efficacy to cisplatin in the U87-MG glioblastoma cell line.
Interestingly, data suggested different mechanism of actions for PN517 and aspirin, with PN517 being consistently more efficacious. PN517 significantly inhibited cell proliferation, wound healing and GAPDH enzymatic activity. Additionally, PN517 induced significant alterations in the metabolic network of the cells by simultaneously reducing glycolytic and mitochondrial activities leading ultimately to apoptosis. Furthermore, PN517 significantly enhanced the efficacy of cisplatin and temozolomide where the combination of PN517 and temozolomide always produced the greatest efficacy among all drug treatments. Most importantly, the enhanced therapeutic efficacy of the combined therapy as compared to the monotherapy was also observed in the hypoxia-adapted cell lines and 3D spheroid cultures, and the combination of PN517 and temozolomide remained the most effective drug treatment.

In conclusion, these results have suggested possible mechanisms of action for the effects of PN517 and aspiring in GBM and highlighted PN517 as an effective and potentially well-tolerated treatment which could have potential therapeutic value for the future treatment of GBM by enhancing temozolomide efficacy and increasing the patients’ tolerance to the chemotherapy. Therefore, this study supports the further investigation of the combined therapy of PN517 with standard drugs in vivo using animal models of GBM in order to confirm its efficacy and ability to cross the blood brain barrier.