Expert opinion on translational research for advanced glioblastoma treatment

Malignant gliomas are known to be one of the most difficult diseases to diagnose and treat because of the infiltrative growth pattern,rapid progression,and poor prognosis.Many antitumor drugs are not ideal for the treatment of gliomas due to the blood-brain barrier.Temozolomide(TMZ)is a DNA alkylating agent that can cross the blood-brain barrier.As the only first-line chemotherapeutic drug for malignant gliomas at present,TMZ is widely utilized to provide a survival benefit;however,some patients are inherently insensitive to TMZ.In addition,patients could develop acquired resistance during TMZ treatment,which limits antitumor efficacy.To clarify the mechanism underlying TMZ resistance,numerous studies have provided multilevel solutions,such as improving the effective concentration of TMZ in tumors and developing novel small molecule drugs.This review discusses the in-depth mechanisms underlying TMZ drug resistance,thus aiming to provide possibilities for the establishment of personalized therapeutic strategies against malignant gliomas and the accelerated development and transformation of new targeted drugs.

Identification of the E2F1-RAD51AP1 axis as a key factor in MGMT-methylated GBM TMZ resistance

Objective:Epidermal growth factor receptor variant III(EGFRvIII)is a constitutively-activated mutation of EGFR that contributes to the malignant progression of glioblastoma multiforme(GBM).Temozolomide(TMZ)is a standard chemotherapeutic for GBM,but TMZ treatment benefits are compromised by chemoresistance.This study aimed to elucidate the crucial mechanisms leading to EGFRvIII and TMZ resistance.Methods:CRISPR-Cas13a single-cell RNA-seq was performed to thoroughly mine EGFRvIII function in GBM.Western blot,realtime PCR,flow cytometry,and immunofluorescence were used to determine the chemoresistance role of E2F1 and RAD51-associated protein 1(RAD51AP1).Results:Bioinformatic analysis identified E2F1 as the key transcription factor in EGFRvIII-positive living cells.Bulk RNA-seq analysis revealed that E2F1 is a crucial transcription factor under TMZ treatment.Western blot suggested enhanced expression of E2F1 in EGFRvIII-positive and TMZ-treated glioma cells.Knockdown of E2F1 increased sensitivity to TMZ.Venn diagram profiling showed that RAD51AP1 is positively correlated with E2F1,mediates TMZ resistance,and has a potential E2F1 binding site on the promoter.Knockdown of RAD51AP1 enhanced the sensitivity of TMZ;however,overexpression of RAD51AP1 was not sufficient to cause chemotherapy resistance in glioma cells.Furthermore,RAD51AP1 did not impact TMZ sensitivity in GBM cells with high O6-methylguanine-DNA methyltransferase(MGMT)expression.The level of RAD51AP1 expression correlated with the survival rate in MGMT-methylated,but not MGMT-unmethylated TMZ-treated GBM patients.Conclusions:Our results suggest that E2F1 is a key transcription factor in EGFRvIII-positive glioma cells and quickly responds to TMZ treatment.RAD51AP1 was shown to be upregulated by E2F1 for DNA double strand break repair.Targeting RAD51AP1 could facilitate achieving an ideal therapeutic effect in MGMT-methylated GBM cells.

TGFβ signaling-induced miRNA participates in autophagic regulation by targeting PRAS40 in mesenchymal subtype of glioblastoma

Objective:Mesenchymal subtype of glioblastoma(mesGBM)is a refractory disease condition characterized by therapeutic failure and tumor recurrence.Hyperactive transforming growth factor-β(TGF-β)signaling could be a signature event in mesGBM,which leads to dysregulation of downstream targets and contribute to malignant transformation.In this study we aimed to investigate the hyperactive TGFβsignaling-mediated pathogenesis and possible downstream targets for the development of novel therapeutic interventions for mesGBM.Methods:GBM-BioDP is an online resource for accessing and displaying interactive views of the TCGA GBM data set.Transcriptomic sequencing followed by bioinformatic analysis was performed to identify dysregulated microRNAs.Target prediction by MR-microT and dual luciferase reporter assay were utilized to confirm the predicted target of novel_miR56.CCK-8 assays was used to assesse cell viability.The miRNA manipulation was proceeded by cell transfection and lentivirus delivery.A plasmid expressing GFP-LC3 was introduced to visualize the formation of autophagosomes.Orthotopic GBM model was constructed forin vivo study.Results:TGFβ1 and TGFβreceptor type II(TβRII)were exclusively upregulated in mesGBM(P<0.01).Dysregulated miRNAs were identified after LY2109761(a TβRI/II inhibitor)treatment in a mesGBM-derived cell line,and novel_miR56 was selected as a promising candidate for further functional verification.Novel_miR56 was found to potentially bind to PRAS40 via seed region complementarity in the 3'untranslated region,and we also confirmed that PRAS40 is a direct target of novel_miR56 in glioma cells.In vitro,over expression of novel_miR56 in tumor cells significantly promoted proliferation and inhibited autophagy(P<0.05).The expression levels of P62/SQSTM was significantly increased accompanied by the decrease of BECN1 and LC3B-II/I,which indicated that autophagic activity was reduced after novel_miR56 treatment.In addition,over expression of novel_miR56 also promoted tumor growth and inhibited autophagyin vivo,which is associated with worse prognosis(P<0.05).Conclusions:In summary,we provide novel insight into TGFβsignaling-mediated pathogenesis in mesGBM and TGFβsignaling-induced novel_miR56 may be a novel target for mesGBM management.

Blockage of EGFR/AKT and mevalonate pathways synergize the antitumor effect of temozolomide by reprogramming energy metabolism in glioblastoma

Background Metabolism reprogramming plays a vital role in glioblastoma(GBM)progression and recurrence by producing enough energy for highly proliferating tumor cells.In addition,metabolic reprogramming is crucial for tumor growth and immune-escape mechanisms.Epidermal growth factor receptor(EGFR)amplification and EGFR-vIII mutation are often detected in GBM cells,contributing to the malignant behavior.This study aimed to investigate the functional role of the EGFR pathway on fatty acid metabolism remodeling and energy generation.Methods Clinical GBM specimens were selected for single-cell RNA sequencing and untargeted metabolomics analysis.A metabolism-associated RTK-fatty acid-gene signature was constructed and verified.MK-2206 and MK-803 were utilized to block the RTK pathway and mevalonate pathway induced abnormal metabolism.Energy metabolism in GBM with activated EGFR pathway was monitored.The antitumor effect of Osimertinib and Atorvastatin assisted by temozolomide(TMZ)was analyzed by an intracranial tumor model in vivo.Results GBM with high EGFR expression had characteristics of lipid remodeling and maintaining high cholesterol levels,supported by the single-cell RNA sequencing and metabolomics of clinical GBM samples.Inhibition of the EGFR/AKT and mevalonate pathways could remodel energy metabolism by repressing the tricarboxylic acid cycle and modulating ATP production.Mechanistically,the EGFR/AKT pathway upregulated the expressions of acyl-CoA synthetase short-chain family member 3(ACSS3),acyl-CoA synthetase long-chain family member 3(ACSL3),and long-chain fatty acid elongation-related gene ELOVL fatty acid elongase 2(ELOVL2)in an NF-κB-dependent manner.Moreover,inhibition of the mevalonate pathway reduced the EGFR level on the cell membranes,thereby affecting the signal transduction of the EGFR/AKT pathway.Therefore,targeting the EGFR/AKT and mevalonate pathways enhanced the antitumor effect of TMZ in GBM cells and animal models.Conclusions Our findings not only uncovered the mechanism of metabolic reprogramming in EGFR-activated GBM but also provided a combinatorial therapeutic strategy for clinical GBM management.