A High Rate of Glycolysis Participates in the Resistance of Glioblastoma to Temozolomide Chemotherapy

Glioblastomas (GBM) account for more than 50% of all brain tumors in humans. Temozolomide (TMZ) is an orally available alkylating agent that was initially developed for brain cancer. It is a prodrug and its conversion is entirely pH dependent. Methyltransferase MGMT can further modulate the activity of TMZ by specifically demethylating O6-MeG. Because a glycolytic metabolism can induce extracellular acidification and thereby potentially interfere with the activation mechanism of the drug, we aimed to understand whether metabolic changes could provide resistance to TMZ in GBM. Cell viability was measured using a SpectraMax MiniMax300 analyzer, glucose consumption and lactate release with a CMA600 enzymatic analyzer, and extracellular acidification with a Seahorse bioenergetic analyzer.We generated isogenic TMZ-resistant and sensitive T98G and U373 human GBM cell lines. Metabolic analyses revealed an increased glycolytic rate in resistant cells. Enhanced glycolysis was associated to higher expression of transcription factor HIF-1a and to an increased extracellular acidification rate. TMZ-resistant cells also overexpressed MGMT, but MGMT silencing with siRNAs did not restore sensitivity to TMZ. Interestingly, extracellular acidification rate was maintained when MGMT was silenced, indicating that glycolysis per se plays an important role in TMZ resistance. Our findings indicate that resistance to TMZ in glioblastoma is linked to increased glycolysis independently from MGMT expression.

Study supported by ERC Starting Grant 243188 TUMETABO, FRS-FNRS and Télévie.