AB029. Mitochondrial dysfunction and impaired growth of glioblastoma cell lines caused by antimicrobial agents inducing ferroptosis

Background: Glioblastoma, a malignant tumor, has no curative treatment. Mitochondria have been reported to be involved in tumorigenesis and drug resistance in various cancers. Recently, mitochondria have been considered a potential target for treating glioblastoma. We are developing a new treatment for glioblastoma targeting mitochondria. The microenvironment of glioblastoma is reported to be a low-nutrition and hypoxic condition. We focused our research on how mitochondria work under tumor circumstances.

Methods: In this research, we used cell lines including U87, LN229, U373, T98G, and two patient-derived stem-like cells. First, we investigated the efficacy of mitochondria-targeted glioblastoma therapy in cell lines under glucose-starved conditions and the mechanism of cell death caused by mitochondria-targeted therapy. Second, we developed a treatment effective for cells with more glucose, because we believe that there is some lesion with higher glucose concentration in the tumor considering the heterogeneity of the tumor.

Results: We discovered that under glucose-starved conditions, mitochondria-related proteins and oxidative phosphorylation activity increased in glioblastoma cells, and in this condition, glioblastoma cells strongly depended on mitochondria. Administration of agents causing mitochondrial dysfunction including chloramphenicol was very effective and it led to cell death. The mechanism of cell death was not apoptosis but ferroptosis which is a recently discovered type of cell death caused by iron accumulation. In normoglycemic conditions, the effect of chloramphenicol was poor for the short term, however, for the long term, it was effective and caused cell death. Although both chloramphenicol alone and combined treatment using 2-DG (glycolysis inhibitor) and chloramphenicol had poor effects on cells in glucose-sufficient conditions, combined treatment was very effective for the short term under normal glucose conditions. These results suggest the importance of controlling glucose concentration. The effect of combined treatment was also confirmed in hypoxic conditions and for patient-derived neurosphere cells. And the mechanism of cell death was ferroptosis, too.

Conclusions: Our mitochondria-targeted treatment was effective for cells with both glucose-starved conditions and normoglycemic conditions. It is necessary to investigate its effectiveness in vivo in the future. However, chloramphenicol has already been used, and therefore, this treatment can be used for humans safely. This discovery is expected to make a major contribution to the development of treatments for glioblastomas.

Keywords: Glioblastoma; mitochondria; chloramphenicol; ferroptosis