gms | German Medical Science

Objective: Invariably, malignant glioma develops resistance against temozolomide (TMZ) chemotherapy during the course of the disease through clonal selection of resistant cells. Autocrine glutamate signalling via metabotropic glutamate receptors (mGluR) was reported to sustain malignant hallmarks, however the extent to which chemoresistance is supported by glutamate signalling remained unknown. Here we aimed to evaluate the potential of mGluR3 blockade therapy as a potential add-on to TMZ in patients suffering from primary glioblastoma.

Methods: Three different primary GBM cell lines were analysed by IncuCyte^® Live-Cell Analysis in order to monitor cellular response in the presence of TMZ, LY341495 or the combination of both drugs. Treatment response was validated in vitro and a human neocortical slice model. Visual assessment of cell viability & apoptosis was performed using a polarity sensitive kinetic apoptosis assay under live-imaging conditions. Cell viability assay and BrdU proliferation assay with TMZ, LY341495 and an alternative mGluR3 inhibitor, ß-NAAG were carried out for further validation. Gene expression analysis was performed to investigate down-stream transcription effects.

Results: In two of our three cell lines TMZ resistant clones remained after 48 hours TMZ treatment which were lost by mGluR inhibition (LY34149) in the in-vitro and neocortical slice model. We showed that autocrine release of glutamate was increased under hypoxic conditions but inhibition of mGluR reduces the hypoxic resistance. Single cell profiling revealed a heterogeneous distribution of mGluR associated with stem-cell markers. Further characterizing the mGluR family we found that TMZ-resistance is mediated by mGluR3 signalling and downstream upregulation of NFkB signalling.

Conclusion: Autocrine glutamate signalling via mGluR3 is crucial for tumour cell metabolism and affects chemotherapeutic efficacy by altered intracellular signalling. In particular, the specific inhibition of mGluR3 with a selective antagonist like LY341495 could sensitize primary glioblastoma tumour cells for TMZ-induced cytotoxicity – which may constitute a promising new therapeutic strategy in the field of translational glioblastoma research.