Glioblastoma multiforme (GBM), the most aggressive central nervous system cancer, is highly angiogenetic and infiltrative with high potential of resistance to chemotherapy and radio therapy. The median survival of primary GBM patients is approximately 14.6 months, despite patients receiving aggressive treatment with surgery, radiotherapy, and alkylating chemotherapy drugs such as temozolomide (TMZ). Some research results point out more than 90% of patients show no response after the second cycle of current GBM chemotherapy. Glutathione S-transferase (GST) is an important detoxification protein family that highly correlates with drug inactivation and multidrug resistance.
In our study, we generated TMZ-resistant glioblastoma GBM8401 cells (GBM8401-TMZ-R) over a 130-day period. We compared TMZ resistance level in TMZ-sensitive cell lines U87MG, A172 and GBM8401 with TMZ-resistant cell lines GBM8401-TMZ-R, T98G and U138 through cell toxicity assays and O-6-Methylguanine-DNA Methyltransferase (MGMT) expression. Moreover, we investigated the mRNA profiles of GBM8401, GBM8401-TMZ-R, and T98G cells by using next generation sequencing (NGS) for analyzing.
We found GBM8401-TMZ-R cells with significantly higher MGMT expression and increased TMZ tolerance. GSTM subfamily proteins, which are located in human chromosome 1, showed different basal expressions in the GBM cell lines we tested. Surprisingly, GBM8401-TMZ-R cells showed higher GST activity and increased GSTM1 and GSTM5 protein levels than GBM8401. GBM8401-TMZ-R cells also displayed higher glycolytic capacity in a Seahorse extracellular flux (XF) analyzer. We also analyzed the expression of GST subfamilies and drug resistance-related genes by NGS.
From these results, we theorized that certain GST proteins may play a key role in TMZ-resistant glioblastoma cells. We hope this study will provide potential therapeutic targets for TMZ-resistant GBM patients.
Clinical trial identification
Legal entity responsible for the study
National Sun Yat-sen University.
Ministry of Science and Technology, R.O.C (Taiwan).
All authors have declared no conflicts of interest.