The impact of tumor treating fields (TTFields) on the transcriptome and the secretome of cancer stem-like cells isolated from the sub-ventricular zone of glioblastoma patients

Glioblastoma (GBM) is the most aggressive brain tumor in adults that almost inevitably recurs despite radical treatments. Recurrence is driven by residual disease, which is extremely difficult to identify and target. We were the first to identify and characterize specific anatomic/functional areas of residual disease in GBM patients, including the sub-ventricular zone (SVZ), the most well-characterized neurogenic area in the mammalian brain. Specifically, we showed that the SVZ is a reservoir of cancer stem-like cells (CSCs) seeding recurrence. Thus, the SVZ holds the key to identifying novel therapeutic targets for GBM patients. We previously evaluated the impact of Tumor Treating Fields (TTFields) - electric fields exerting physical forces on tumor cells - on the morphology and proliferation of CSCs isolated from the SVZ of GBM patients. We observed that the proliferation of CSCs resistant to Temozolomide and ionizing radiation is significantly inhibited by TTFields when cells are exposed for 48 hours to the optimized frequency for GBM (200 kHz). Moreover, we observed that this antiproliferative effect of TTFields is maintained among patients. In our recent work, we examined the impact of TTFields on the transcriptome and secretome of CSCs isolated from the SVZ of GBM patients using single-cell transcriptomics and functional phenotyping. First, we isolated and characterized 10 CSCs. These cells were maintained in conditions that preserve the molecular profile of the original patient tumor, thus representing bona fide models to study the impact of TTFields on GBM residual disease. Second, we used the 10x Genomics platform and the Bruker single-cell proteomic barcoding solution to perform single-cell transcriptomics and functional phenotyping. Our results indicate changes in the transcriptomic profile of CSCs after TTFields compared with matched untreated cells. Specifically, TTFields altered the expression of genes related to cell cycle and GBM cell states. Moreover, functional phenotyping analysis of the innate immune cytokine secretome revealed that CSCs treated with TTFields secrete less VEGF and more soluble CD137 (sCD137) than untreated cells. CD137 is a member of the TNF family contributing to the activation of cytotoxic responses in T cells, while sCD137 exhibits immunoinhibitory functions. Clinical trials involving agonistic anti-CD137 antibodies(Abs) that also counteract sCD137-mediated immunoinhibition are currently underway in patients with advanced tumors. Combined with TTFields, these Abs offer a novel therapeutic opportunity for the treatment of GBM. Collectively, our results point to the effectiveness of TTFields in GBM and identify a novel therapeutic target in GBM residual disease.