BET inhibitors repress expression of interferon-stimulated genes and synergize with HDAC inhibitors in glioblastoma

Abstract

Background The development of rational combination therapies is key to overcome inherent treatment resistance of glioblastoma. We aim at identifying new druggable targets by disturbing glioblastoma cells with inhibitors of Bromodomain and Extra-Terminal motif (BET) proteins to reveal cancer relevant vulnerabilities that may sensitize to a second drug. BET-proteins are epigenetic modulators and have been associated with proto-oncogene overexpression in cancer. Methods A glioblastoma derived sphere-line was treated with the BET inhibitor JQ1 over a time-course of 48h, followed by RNA-sequencing. Four chromatin marks were investigated by chromatin immunoprecipitation followed by sequencing (ChIP-seq). Signatures of interest were functionally validated in vitro and in orthotopic xenografts. Combination therapies were evaluated for synergistic effects. Results Cancer relevant pathways significantly modulated by JQ1 comprised interferon-alpha (IFN-α) response genes and response signatures to histone deacetylase inhibitors (HDACi). The IFN-signature was reminiscent of a glioblastoma-derived IFN-signature comprising CD274 (PD-L1). Functional pathway analysis suggested that JQ1 was acting directly on the transcriptional level of IFN-response genes and not via the canonical JAK-STAT pathway. This was in line with JQ1 modulated expression and BRD4 and POL2 occupancy at IFN-signature genes, supporting a direct mechanistic interaction. Finally, we showed that combining HDACi with JQ1 acts synergistically in reducing cell viability of GS-lines. Conclusions Our approach identified BETi-induced vulnerabilities in cancer relevant pathways, potentially amenable to synergistic combinatorial therapy, such as combination with HDACi. The direct inhibitory effect of BETi on IFN-responsive genes in GBM cells, including CD274, indicates modulation of the tumor immune landscape and warrants further studies.

BET protein inhibition sensitizes glioblastoma cells to temozolomide treatment by attenuating MGMT expression

“…The RNA-seq data reported in Gusyatiner et al [ 6 ] served as input and was obtained in the GBM derived sphere line LN-2683GS upon treatment with 1 μM JQ1 or DMSO over a time course of 48 h with three biological replicates. Differential gene expression analysis used a model with full interaction between treatment and time (edgeR package).…”

Metabolic and transcriptomic profiles of glioblastoma invasion revealed by comparisons between patients and corresponding orthotopic xenografts in mice

“…The next day 10 5 cells were transplanted stereotactically in a volume of 5 µl (Hanks’ balanced salt solution, HBBS, with phenol red, no calcium, no magnesium; Thermo Fisher Scientific) into the striatum (coordinates: bregma 0.5 mm anterior, 2 mm lateral and 3 mm ventral)[ 58 ] of male immunocompromised mice (n = 3–6/patient; age, 6–8 weeks; NOD-SCID gamma knock-out mice, NOD.Cg-Prkdcscid II2rgtm1Wjl/SzJ, bred in-house) using a micro pump (injection rate 5 µl/1 min, Stoelting). For the procedure, anesthetized mice were placed into a stereotactic frame, and fixed with a mouth piece (Stoelting) as previously described [ 19 ]. Mice were checked daily and sacrificed at first signs of neurologic symptoms (lethargy, ataxia and seizures) or body weight loss (> 10%).…”

Glioblastoma Microenvironment: From an Inviolable Defense to a Therapeutic Chance

“…Another recent research investigated RNA expression of GBM-derived sphere-line treated with the BET inhibitor JQ1. The inhibition of BET resulted in a significant modulation of genes responding to Interferon-alpha (enhanced in about 50% of GBM) through a direct transcriptional inhibition more than interference to the JAK (Janus Kinase) -STAT (Signal transducer and activator of transcription) pathway ( 39 ).…”

“…These two factors act through proteins belonging to the BET family. To date, BET inhibitors have been assessed on phase I trials with more of them showing a safety profile (39)(40)(41)(42)(43)(44)(45)(46)(47). A further investigation of these agents could be important for patients with GBM.…”