Mutant IDH inhibitors induce lineage differentiation in IDH-mutant oligodendroglioma

A subset of patients with IDH-mutant glioma respond to inhibitors of mutant IDH (IDHi), yet the molecular underpinnings of such responses are not understood. Here, we profiled by single-cell or single-nucleus RNA-sequencing three IDH-mutant oligodendrogliomas from patients who derived clinical benefit from IDHi. Importantly, the tissues were sampled on-drug, four weeks from treatment initiation. We further integrate our findings with analysis of single-cell and bulk transcriptomes from independent cohorts and experimental models. We find that IDHi treatment induces a robust differentiation toward the astrocytic lineage, accompanied by a depletion of stem-like cells and a reduction of cell proliferation. Furthermore, mutations in NOTCH1 are associated with decreased astrocytic differentiation and may limit the response to IDHi. Our study highlights the differentiating potential of IDHi on the cellular hierarchies that drive oligodendrogliomas and suggests a genetic modifier that may improve patient stratification.

Cancer vaccine strategies for the treatment of diffusely infiltrating gliomas

Diffusely infiltrating gliomas - including glioblastoma (GBM), isocitrate dehydrogenase (IDH) mutant gliomas, and histone 3 (H3) altered gliomas - are primary brain tumors with an invariably fatal outcome. Despite advances in the understanding of their biology, standard, targeted and immune checkpoint inhibitor immunotherapies have proven ineffective in arresting their inexorable progression and associated morbidity and mortality. Recognizing the unique aspects of the immunogenicity of cancer cells, the last decade has seen the development and evaluation of vaccine-based therapies for the treatment of solid tumors, including gliomas. Here we review the current vaccine strategies for the treatment of GBM, IDH-mutant gliomas and diffuse midline glioma H3 K27M-altered. We discuss potential benefits and challenges of vaccine therapies in these specific patient populations.

Epigenetic silencing of HTATIP2 in glioblastoma contributes to treatment resistance by enhancing nuclear translocation of the DNA repair protein MPG

Glioblastoma, the most malignant brain tumor in adults, exhibits characteristic patterns of epigenetic alterations that await elucidation. The DNA methylome of glioblastoma revealed recurrent epigenetic silencing of HTATIP2, which encodes a negative regulator of importin β-mediated cytoplasmic-nuclear protein translocation. Its deregulation may thus alter the functionality of cancer-relevant nuclear proteins, such as the base excision repair (BER) enzyme N-methylpurine DNA glycosylase (MPG), which has been associated with treatment resistance in GBM. We found that induction of HTATIP2 expression in GBM cells leads to a significant shift of predominantly nuclear to cytoplasmic MPG, whereas depletion of endogenous HTATIP2 results in enhanced nuclear MPG localization. Reduced nuclear MPG localization, prompted by HTATIP2 expression or by depletion of MPG, yielded less phosphorylated-H2AX-positive cells upon treatment with an alkylating agent. This suggested reduced MPG-mediated formation of apurinic/apyrimidinic sites, leaving behind unrepaired DNA lesions, reflecting a reduced capacity of BER in response to the alkylating agent. Epigenetic silencing of HTATIP2 may thus increase nuclear localization of MPG, thereby enhancing the capacity of the glioblastoma cells to repair treatment-related lesions and contributing to treatment resistance.

[Mobilization of Medical Students, UNIL, during the COVID-19 Pandemic]

Medical students from the University of Lausanne volunteered rapidly and in great number to bolster health facilities across Switzerland in response to the COVID-19 pandemic. At Unisanté, Center for general practice and public health, University of Lausanne, students recruited as interns discovered the different aspects of primary care. This extraordinary period naturally involves considerable challenges but represents also a precious learning opportunity for future doctors.

CBIO-13. EPIGENETIC DEREGULATION OF NUCLEAR TRANSLOCATION - A NOVEL MECHANISM FOR TREATMENT RESISTANCE IN GLIOBLASTOMA

In a genome-wide DNA methylation analysis of glioblastoma we identified aberrant methylation of the HIV-1 Tat interactive protein 2 (HTATIP2) gene promotor. This was strongly correlated with downregulation of HTATIP2 gene expression, suggesting a potential tumor suppressor function in glioblastoma. HTATIP2 has been shown to inhibit nuclear translocation through interaction with β-importins. We hypothesize that deregulation of HTATIP2 expression inhibits nuclear entry of cancer-relevant proteins, thereby disturbing their specific function in the nucleus. We identified N-Methylpurine-DNA Glycosylase (MPG) as a potential cancer relevant candidate with the observation of nuclear and/or cytoplasmic localization in glioblastoma. MPG is a DNA repair protein that recognizes DNA lesions (N7-meG, N3-meA) and initiates base excision repair. We have shown that nuclear MPG expression contributes to resistance of glioblastoma to treatment with the alkylating agent temozolomide. Here we investigated the effect of HTATIP2 on cellular localization of MPG using (i) an inducible system (TET-ON) to express HTATIP2 in non-expressing glioblastoma cells, and (ii) HTATIP2-targeting siRNAs to knock down HTATIP2 in cells with endogenous expression. Results from confocal microscopy or Imagestream analyses showed a significant cytoplasmic retention of MPG in presence of HTATIP2, while knock-down of HTATIP2 resulted in nuclear MPG localization. Cytoplasmic retention of MPG in the presence of HTATIP2 was associated with a significant increase in γ-H2Ax signal after treatment with the alkylating agent: methyl methanesulfonate (MMS), suggesting increase in DNA damage. Mechanistically, we found that HTATIP2 co-localizes with importin β1, and excludes MPG localization. Furthermore, HTATIP2 displayed a similar effect on cytoplasmic retention of MPG as pharmacologic inhibition of Importin β 1. Taken together, these results suggest that epigenetic silencing of HTATIP2 may increase nuclear localization of MPG, thereby increasing the capacity of the tumor cells to repair treatment related lesions and thereby contributing to treatment resistance.