Objective: Glioblastoma (GBM) is the most prevalent and aggressive adult primary cancer in the central nervous system. Therapeutic approaches for GBM treatment are under intense investigation, including the use of emerging immunotherapies. Here, we propose an alternative approach to treat GBM through reprogramming proliferative GBM cells into non-proliferative neurons. Methods: Retroviruses were used to target highly proliferative human GBM cells through overexpression of neural transcription factors. Immunostaining, electrophysiological recording, and bulk RNA-seq were performed to investigate the mechanisms underlying the neuronal conversion of human GBM cells. An in vivo intracranial xenograft mouse model was used to examine the neuronal conversion of human GBM cells. Results: We report efficient neuronal conversion from human GBM cells by overexpressing single neural transcription factor Neurogenic differentiation 1 (NeuroD1), Neurogenin-2 (Neurog2), or Achaete-scute homolog 1 (Ascl1). Subtype characterization showed that the majority of Neurog2-and NeuroD1-converted neurons were glutamatergic, while Ascl1 favored GABAergic neuron generation. The GBM cell-converted neurons not only showed pan-neuronal markers but also exhibited neuron-specific electrophysiological activities. Transcriptome analyses revealed that neuronal genes were activated in glioma cells after overexpression of neural transcription factors, and different signaling pathways were activated by different neural transcription factors. Importantly, the neuronal conversion of GBM cells was accompanied by significant inhibition of GBM cell proliferation in both in vitro and in vivo models. Conclusions: These results suggest that GBM cells can be reprogrammed into different subtypes of neurons, leading to a potential alternative approach to treat brain tumors using in vivo cell conversion technology.

Glioblastoma (GBM) is the most prevalent and aggressive adult primary cancer in the central nervous system (CNS). Therapeutic approaches for glioblastoma are under intense investigation, such as the emerging immunotherapy, but so far only marginal progress has been made due to the heterogeneity and highly invasive nature of glioblastoma. Here, we propose an alternative approach to tackle GBM through reprogramming proliferative GBM cells into non-proliferative neurons. We report efficient neuronal conversion from human GBM cells by overexpressing single neural transcription factor Neurogenic differentiation 1 (NeuroD1), Neurogenin-2 (Neurog2) or Achaete-scute homolog 1 (Ascl1). Subtype characterization reveals that the majority of Neurog2- and NeuroD1-converted neurons are glutamatergic, while Ascl1 favors GABAergic neuron generation. The GBM cell-converted neurons not only express pan-neuronal markers, such as NeuN and MAP2, but also exhibit neuron-specific electrophysiological activities. We further conducted transcriptome analyses to investigate the underlying cell conversion mechanism. Our RNA-seq analyses discover that neuronal genes are activated among glioma cells after overexpression of neural transcription factors, and different signaling pathways are activated by different neural transcription factors. Importantly, the neuronal conversion of GBM cells is accompanied by significant inhibition of GBM cell proliferation in both in vitro and in vivo models. Therefore, these results suggest that GBM cells can be reprogrammed into different subtypes of neurons, leading to a potential alternative approach to treat brain tumor.

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Background: Glioblastoma is one of the most severe primary cancer types in the central nervous system. Because of genomic and epigenetic heterogeneity, GBM is infiltrative and resistant to conventional treatments such as radiation, chemotherapy and molecular targeting drugs. Glioblastoma often arises from astrocytes, which can be directly converted into neurons according to our earlier work, so we hypothesize that glioblastoma cells might also be converted into non-proliferating neurons. This trans-differentiation therapy might provide a unique approach for glioblastoma treatment. Methods: NeuroD1 was chosen as one of the candidate factors in this study because we have shown its critical roles in astrocyte-to-neuron conversion. Neurog2 and Ascl1 were also tested to understand possible different conversion mechanisms. Single transcription factor or GFP was overexpressed via retrovirus in human glioblastoma cells. Twelve hours after virus infection, culture medium was changed into differentiation medium containing neurotropic factors for neuronal maturation. Immuostainng and other tests were conducted at different days post infection. Results: Retrovirus yielded high infection efficiency in fast-proliferating glioblastoma cells. All three factors tested were capable of converting glioblastoma cells into neuron-like cells efficiently. Besides morphological change, robust pan-neuronal markers were expressed during the conversion, such as immature neuronal markers DCX, Tuj1 and mature neuronal makers MAP2, NeuN. Majority of the converted cells from glioma were immunopositive for glutamatergic neuron marker vGluT1 and hippocampal neuron marker Prox1. Reactive astroglial marker GFAP decreased after conversion, but cancer marker EGFR and IL13Ra2 remained during conversion. Cell proliferation was inhibited during conversion indicated by Ki67 and BrdU. Robust synaptic puncta along dendrites were found in glioma-converted cells, indicated by SV2 immunostaining. Patch-clamp recordings revealed that most of the converted neurons could fire multiple action potentials or single action potential. Conclusion: Our data suggest that several neuronal transcription factors are capable to convert human glioblastoma cells into neuron-like cells efficiently. The converted cells obtained a variety of neuron-specific markers with functional synaptic networks and active electrophysiological properties. This neuronal conversion was also confirmed by reduction of reactive astroglial marker GFAP. Although some cancer markers remain in the converted neurons, glioblastoma cells stopped proliferating once being converted. In summary, our study suggests that converting human glioblastoma cells into neurons could be a potential therapeutic approach for glioblastoma treatment to at least control cancer cell proliferation and inhibit tumor progression. Citation Format: Xin Wang, Zifei Pei, Aasma Hossain, Tania T. Barnatan, Yuting Bai, Gong Chen. Conversion of human glioblastoma cells into neurons by neuronal transcription factors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 5224.