Role of PARP Inhibitors in Glioblastoma and Perceiving Challenges as Well as Strategies for Successful Clinical Development

Glioblastoma multiform is the most aggressive primary type of brain tumor, representing 54% of all gliomas. The average life span for glioblastoma multiform is around 14-15 months instead of treatment. The current treatment for glioblastoma multiform includes surgical removal of the tumor followed by radiation therapy and temozolomide chemotherapy for 6.5 months, followed by another 6 months of maintenance therapy with temozolomide chemotherapy (5 days every month). However, resistance to temozolomide is frequently one of the limiting factors in effective treatment. Poly (ADP-ribose) polymerase (PARP) inhibitors have recently been investigated as sensitizing drugs to enhance temozolomide potency. However, clinical use of PARP inhibitors in glioblastoma multiform is difficult due to a number of factors such as limited blood-brain barrier penetration of PARP inhibitors, inducing resistance due to frequent use of PARP inhibitors, and overlapping hematologic toxicities of PARP inhibitors when co-administered with glioblastoma multiform standard treatment (radiation therapy and temozolomide). This review elucidates the role of PARP inhibitors in temozolomide resistance, multiple factors that make development of these PARP inhibitor drugs challenging, and the strategies such as the development of targeted drug therapies and combination therapy to combat the resistance of PARP inhibitors that can be adopted to overcome these challenges.

YTHDF2 promotes temozolomide resistance in glioblastoma by activation of the Akt and NF-κB signalling pathways via inhibiting EPHB3 and TNFAIP3

Objectives

Temozolomide (TMZ) resistance is a key factor that restricts the therapeutic effect of glioblastoma (GBM). YTH‐domain family member 2 (YTHDF2) is highly expressed in GBM tissues, while the mechanism of YTHDF2 in TMZ resistance in GBM remains not fully elucidated.

Methods

The YTHDF2 expression in TMZ‐resistant tissues and cells was detected. Kaplan–Meier analysis was employed to evaluate the prognostic value of YTHDF2 in GBM. Effect of YTHDF2 in TMZ resistance in GBM was explored via corresponding experiments. RNA sequence, FISH in conjugation with fluorescent immunostaining, RNA immunoprecipitation, dual‐luciferase reporter gene and immunofluorescence were applied to investigate the mechanism of YTHDF2 that boosted TMZ resistance in GBM.

Results

YTHDF2 was up‐regulated in TMZ‐resistant tissues and cells, and patients with high expression of YTHDF2 showed lower survival rate than the patients with low expression of YTHDF2. The elevated YTHDF2 expression boosted TMZ resistance in GBM cells, and the decreased YTHDF2 expression enhanced TMZ sensitivity in TMZ‐resistant GBM cells. Mechanically, YTHDF2 bound to the N6‐methyladenosine (m⁶A) sites in the 3′UTR of EPHB3 and TNFAIP3 to decrease the mRNA stability. YTHDF2 activated the PI3K/Akt and NF‐κB signals through inhibiting expression of EPHB3 and TNFAIP3, and the inhibition of the two pathways attenuated YTHDF2‐mediated TMZ resistance.

Conclusion

YTHDF2 enhanced TMZ resistance in GBM by activation of the PI3K/Akt and NF‐κB signalling pathways via inhibition of EPHB3 and TNFAIP3.

Transcription Factors with Targeting Potential in Gliomas

Gliomas portray a large and heterogeneous group of CNS tumors, encompassing a wide range of low- to high-grade tumors, as defined by histological and molecular characteristics. The identification of signature mutations and other molecular abnormalities has largely impacted tumor classification, diagnosis, and therapy. Transcription factors (TFs) are master regulators of gene expression programs, which ultimately shape cell fate and homeostasis. A variety of TFs have been detected to be aberrantly expressed in brain tumors, being highly implicated in critical pathological aspects and progression of gliomas. Herein, we describe a selection of oncogenic (GLI-1/2/3, E2F1–8, STAT3, and HIF-1/2) and tumor suppressor (NFI-A/B, TBXT, MYT1, and MYT1L) TFs that are deregulated in gliomas and are subsequently associated with tumor development, progression, and migratory potential. We further discuss the current targeting options against these TFs, including chemical (Bortezomib) and natural (Plumbagin) compounds, small molecules, and inhibitors, and address their potential implications in glioma therapy.

CN-3 increases TMZ sensitivity and induces ROS-dependent apoptosis and autophagy in TMZ-resistance glioblastoma

Many glioma patients develop resistance to temozolomide (TMZ) treatment, resulting in reduced efficacy and survival rates. TMZ-resistant cell lines SHG44R and U87R, which highly express O₆ -methylguanine DNA methyltransferase (MGMT) and P-gp, were established. CN-3, a new asterosaponin, showed cytotoxic effects on TMZ-resistant cells in a dose- and time-dependent manner via reactive oxygen species (ROS)-mediated apoptosis and autophagy. Transmission electron microscopy and monodansylcadaverine (MDC) staining showed turgidity of the mitochondria and autophagosomes in CN-3-treated SHG44R and U87R cells. The autophagy inhibitor 3-methyladenine was used to confirm the important role of autophagy in CN-3 cytotoxicity in TMZ-resistant cells. The ROS scavenger N-acetyl- l-cysteine (NAC) attenuated the levels of ROS induced by CN-3 and, therefore, rescued the CN-3 cytotoxic effect on the viability of SHG44R and U87R cells by Cell Counting Kit-8 assays and JuLI-Stage videos. MDC staining also confirmed that NAC rescued an autophagosome increase in CN-3-treated SHG44R and U87R cells. Western blotting revealed that CN-3 increased Bax, cleaved-caspase 3, cytochrome C, PARP-1, LC3-Ⅱ, and Beclin1, and decreased P-AKT, Bcl-2, and p62. Further rescue experiments revealed that CN-3 induced apoptosis and autophagy through ROS-mediated cytochrome C, cleaved-caspase 3, Bcl-2, P-AKT, PARP-1, and LC3-Ⅱ. In addition, CN-3 promoted SHG44R and U87R cells sensitive to TMZ by reducing the expression of P-gp, MGMT, and nuclear factor kappa B p65, and it had a synergistic cytotoxic effect with TMZ. Moreover, CN-3 disrupted the natural cycle arrest and inhibited the migration of SHG44R and U87R cells by promoting cyclin E1 and D1, and by decreasing P21, P27, N-cadherin, β-catenin, transforming growth factor beta 1, and Smad2.

MicroRNAs Regulate Cell Cycle and Cell Death Pathways in Glioblastoma

Glioblastoma (GBM), a grade IV brain tumor, is known for its heterogenicity and its resistance to the current treatment regimen. Over the last few decades, a significant amount of new molecular and genetic findings has been reported regarding factors contributing to GBM’s development into a lethal phenotype and its overall poor prognosis. MicroRNA (miRNAs) are small non-coding sequences of RNA that regulate and influence the expression of multiple genes. Many research findings have highlighted the importance of miRNAs in facilitating and controlling normal biological functions, including cell differentiation, proliferation, and apoptosis. Furthermore, miRNAs’ ability to initiate and promote cancer development, directly or indirectly, has been shown in many types of cancer. There is a clear association between alteration in miRNAs expression in GBM’s ability to escape apoptosis, proliferation, and resistance to treatment. Further, miRNAs regulate the already altered pathways in GBM, including P53, RB, and PI3K-AKT pathways. Furthermore, miRNAs also contribute to autophagy at multiple stages. In this review, we summarize the functions of miRNAs in GBM pathways linked to dysregulation of cell cycle control, apoptosis and resistance to treatment, and the possible use of miRNAs in clinical settings as treatment and prediction biomarkers.

A novel polymerase β inhibitor from phage displayed peptide library augments the anti-tumour effects of temozolomide on colorectal cancer

The therapeutic efficacy of TMZ, a common used drug for chemotherapy, is limited by the resistance from colorectal cancer cells. Base excision repair (BER) pathway has been identified as one of the reasons for drug resistance. By blocking Polβ-dependent BER (Base Excision Repair) pathway, the efficacy of TMZ treatment can be improved greatly. Several Polβ inhibitors that have been identified could not become approved drugs due to lack of potency or specificity. To find therapeutic candidates with exquisite specificity and high affinity to Polβ, phage display technology was used in the current research. We screened out a candidate Polβ inhibitor, 10 D, that can inhibit the activity of Polβand SP-BER (Short-Patch Base excision Repair) pathway. Co-treatment with 10 D enhanced the sensitivity of colorectal cancer (CRC) cells to TMZ both in vitro and in vivo. Our data suggested that the novel Polβ inhibitor we identified can improve TMZ efficacy and optimize CRC chemotherapy.

Treatments of gliosarcoma of the brain: a systematic review and meta-analysis

Gliosarcoma (GSM) is a rare central nervous system tumor. Clinical management of it is similar to glioblastoma (GBM). However, due to a few comparative studies exist, uncertainty and disagreements remain in the literatures. To assess the available evidence on the value of different treatments and to carry out an up-to-date evaluation to summarize the evidence for the optimal treatment in GSM patients. Free words were used to search for the relevant studies without language limitations in electronic databases including PubMed, Ovid EMBASE, Cochrane Central Register of Controlled Trials from inception to September 15, 2019. Pooled hazard ratio (HR) with 95% confidence interval (CI) were calculated using a random-effects model. The main endpoint was all-cause mortality. Overall, 10 studies published between 2008 and 2018 including 803 patients were selected for the meta-analysis. Temozolomide (TMZ)-dominated chemotherapy was associated with a reduced risk of overall survival (OS), with HR 0.49 (95% CI 0.37-0.66). The pooled HR of OS was 0.40 (95% CI 0.29-0.56) between radiotherapy and without radiotherapy. The pooled HR (0.52, 95% CI 0.32-0.85) indicated gross total resection (GTR) had a positive impact on OS in GSM. In patients with GSM, survival benefits as currently performed are associated with TMZ-dominated chemotherapy and high-dose radiotherapy. Our systematic review and meta-analysis also demonstrate GTR is associated with a reduction in all-cause mortality in patients with primary GSM.

The PI3K Inhibitor XH30 Enhances Response to Temozolomide in Drug-Resistant Glioblastoma via the Noncanonical Hedgehog Signaling Pathway

Glioblastoma multiforme (GBM) is the most common malignant tumor of the central nervous system. Temozolomide (TMZ)-based adjuvant treatment has improved overall survival, but clinical outcomes remain poor; TMZ resistance is one of the main reasons for this. Here, we report a new phosphatidylinositide 3-kinase inhibitor, XH30; this study aimed to assess the antitumor activity of this compound against TMZ-resistant GBM. XH30 inhibited cell proliferation in TMZ-resistant GBM cells (U251/TMZ and T98G) and induced cell cycle arrest in the G1 phase. In an orthotopic mouse model, XH30 suppressed TMZ-resistant tumor growth. XH30 was also shown to enhance TMZ cytotoxicity both in vitro and in vivo. Mechanistically, the synergistic effect of XH30 may be attributed to its repression of the key transcription factor GLI1 via the noncanonical hedgehog signaling pathway. XH30 reversed sonic hedgehog-triggered GLI1 activation and decreased GLI1 activation by insulin-like growth factor 1 via the noncanonical hedgehog signaling pathway. These results indicate that XH30 may represent a novel therapeutic option for TMZ-resistant GBM.

Temozolomide abrogates the aggressiveness of urothelial carcinoma cells by enhancing senescence and depleting the side population

Patients with advanced urothelial carcinoma (UC) generally have poor prognoses due to therapeutic resistance. Furthermore, there are limited treatment options for advanced UC. Therefore, novel or effective chemotherapeutic agents are needed to improve patient survival. The present study was conducted to investigate the effect of temozolomide (TMZ) on UC cells so as to identify a potential method to overcome therapeutic resistance. TMZ is an alkylating agent with a target different from that of other anticancer drugs used to treat UC, such as cisplatin. TMZ enhanced the autophagic response and senescence, which was mediated via the p53 and p21 pathways. Inhibiting the autophagic response using chloroquine synergistically augmented the cytotoxic effect of TMZ on UC cells. TMZ significantly reduced the invasiveness of UC cells. Notably, the abundance of side population fraction was also significantly reduced following TMZ treatment. Considering that side population fraction is known to confer therapeutic resistance, it is noteworthy that the TMZ treatment markedly decreased side population fraction. Altogether, TMZ may have the potential to be applied as a part of an alternative treatment strategy to reduce the malignancy of UC cells.

Accurately Controlled Delivery of Temozolomide by Biocompatible UiO-66-NH2 Through Ultrasound to Enhance the Antitumor Efficacy and Attenuate the Toxicity for Treatment of Malignant Glioma

Background

Glioma is the most common and malignant primary brain tumour in adults and has a dismal prognosis. Temozolomide (TMZ) is the only clinical first-line chemotherapy drug for malignant glioma up to present. Due to poor aqueous solubility and toxic effects, TMZ is still inefficient and limited for clinical glioma treatment.

Methods

UiO-66-NH₂ nanoparticle is a zirconium-based framework, constructed by Zr and 2-amino-1,4-benzenedicarboxylic acid (BDC-NH₂) with octahedral microporous structure, which can be decomposed by the body into an ionic form to discharge. We prepared the nanoscale metal-organic framework (MOF) of UiO-66-NH₂ to load TMZ for therapy of malignant glioma, TMZ is released from UiO-66-NH₂ through a porous structure. The ultrasound accelerates its porous percolation and promotes the rapid dissolution of TMZ through low-frequency oscillations and cavitation effect. The biological safety and antitumor efficacy were evaluated both in vitro and in vivo.

Results

The prepared TMZ@MOF exhibited excellent biocompatibility and biosafety due to minimal drug leakage without ultrasound intervention. We further used the flank model of glioblastoma to verify the in vivo therapeutic effect. TMZ@UiO-66-NH₂ nanocomposites could be well delivered to the tumour tissue, which led to local enrichment of the TMZ concentration. Furthermore, TMZ@UiO-66-NH₂ nanocomposites under ultrasound demonstrated much more efficient inhibition for tumor growth than TMZ@UiO-66-NH₂ nanocomposites and TMZ alone. Meanwhile, the bone marrow suppression side effects of TMZ were significantly reduced by TMZ@UiO-66-NH₂ nanocomposites.

Conclusion

In this work, TMZ@UiO-66-NH₂ nanocomposites with ultrasound mediation could effectively improve the killing effect of malignant glioma and decrease TMZ-induced toxicity in normal tissues, demonstrating great potential for the delivery of TMZ in the clinical treatment of malignant gliomas.

ATR inhibition reverses the resistance of homologous recombination deficient MGMTlow/MMRproficient cancer cells to temozolomide

The therapeutic efficacy of temozolomide (TMZ) is hindered by inherent and acquired resistance. Biomarkers such as MGMT expression and MMR proficiency are used as predictors of response. However, not all MGMTlow/-ve/MMRproficient patients benefit from TMZ treatment, indicating a need for additional patient selection criteria. We explored the role of ATR in mediating TMZ resistance and whether ATR inhibitors (ATRi) could reverse this resistance in multiple cancer lines. We observed that only 31% of MGMTlow/-ve/MMRproficient patient-derived and established cancer lines are sensitive to TMZ at clinically relevant concentrations. TMZ treatment resulted in DNA damage signaling in both sensitive and resistant lines, but prolonged G2/M arrest and cell death were exclusive to sensitive models. Inhibition of ATR but not ATM, sensitized the majority of resistant models to TMZ and resulted in measurable DNA damage and persistent growth inhibition. Also, compromised homologous recombination (HR) via RAD51 or BRCA1 loss only conferred sensitivity to TMZ when combined with an ATRi. Furthermore, low REV3L mRNA expression correlated with sensitivity to the TMZ and ATRi combination in vitro and in vivo. This suggests that HR defects and low REV3L levels could be useful selection criteria for enhanced clinical efficacy of an ATRi plus TMZ combination.

Identifying the optimal cutoff point for MGMT promoter methylation status in glioblastoma

Aim: To define the optimal cutoff point for determining methylation status of O6-methylguanine-DNA methyltransferase (MGMT) by pyrosequencing in glioblastoma. Patients & methods: A retrospective study of 109 glioblastoma patients was performed to determine the optimal cutoff point for MGMT methylation status. Results: Receiver operating characteristic (ROC) analysis revealed 21% as the optimal cutoff (sensitivity: 68%; specificity: 59%) for MGMT methylation corresponding with the highest likelihood ratio of 1.66 and accuracy of 0.65. Methylation status (hazard ratio: 0.453; 95% CI: 0.279-0.735; p = 0.001) was associated with better overall survival. The crude model indicated linearity between methylation percent and survival rate; an increase of 10% of methylation resulted in a reduction of risk of death by 20% (p = 0.004). Conclusion: ROC analysis determined 21% as the optimal cutoff point for MGMT methylation status by pyrosequencing.

Chemosensitization of Temozolomide-Resistant Pediatric Diffuse Midline Glioma Using Potent Nanoencapsulated Forms of a N(3)-Propargyl Analogue

The lack of clinical response to the alkylating agent temozolomide (TMZ) in pediatric diffuse midline/intrinsic pontine glioma (DIPG) has been associated with O6-methylguanine-DNA-methyltransferase (MGMT) expression and mismatch repair deficiency. Hence, a potent N(3)-propargyl analogue (N3P) was derived, which not only evades MGMT but also remains effective in mismatch repair deficient cells. Due to the poor pharmacokinetic profile of N3P (t1/2 < 1 h) and to bypass the blood-brain barrier, we proposed convection enhanced delivery (CED) as a method of administration to decrease dose and systemic toxicity. Moreover, to enhance N3P solubility, stability, and sustained distribution in vivo, either it was incorporated into an apoferritin (AFt) nanocage or its sulfobutyl ether β-cyclodextrin complex was loaded into nanoliposomes (Lip). The resultant AFt-N3P and Lip-N3P nanoparticles (NPs) had hydrodynamic diameters of 14 vs 93 nm, icosahedral vs spherical morphology, negative surface charge (-17 vs -34 mV), and encapsulating ∼630 vs ∼21000 N3P molecules per NP, respectively. Both NPs showed a sustained release profile and instant uptake within 1 h incubation in vitro. In comparison to the naked drug, N3P NPs demonstrated stronger anticancer efficacy against 2D TMZ-resistant DIPG cell cultures [IC50 = 14.6 (Lip-N3P) vs 32.8 μM (N3P); DIPG-IV) and (IC50 = 101.8 (AFt-N3P) vs 111.9 μM (N3P); DIPG-VI)]. Likewise, both N3P-NPs significantly (P < 0.01) inhibited 3D spheroid growth compared to the native N3P in MGMT+ DIPG-VI (100 μM) and mismatch repair deficient DIPG-XIX (50 μM) cultures. Interestingly, the potency of TMZ was remarkably enhanced when encapsulated in AFt NPs against DIPG-IV, -VI, and -XIX spheroid cultures. Dynamic PET scans of CED-administered zirconium-89 (89Zr)-labeled AFt-NPs in rats also demonstrated substantial enhancement over free 89Zr radionuclide in terms of localized distribution kinetics and retention within the brain parenchyma. Overall, both NP formulations of N3P represent promising approaches for treatment of TMZ-resistant DIPG and merit the next phase of preclinical evaluation.

Should temozolomide be used on the basis of O6-methylguanine DNA methyltransferase status in patients with advanced neuroendocrine tumors? A systematic review and meta-analysis

BACKGROUND

Temozolomide (TEM) is an active treatment in metastatic neuroendocrine tumors (NETs). Patients affected by glioblastoma multiforme or advanced melanoma treated with TEM who have deficiency of O⁶-methylguanine DNA methyltransferase (MGMT) have a better responses and survival. However, the predictive role of MGMT in patients with NETs treated with TEM is still debated.

METHODS

We conducted a systematic review of the literature and meta-analysis, based on PRISMA methodology, searching in the main databases (PubMed, Embase, Scopus, Web of Science, Cochrane Library and clinical trial.gov) and the proceedings of the main international congresses, until April 26, 2021.

RESULTS

Twelve out of 616 articles were selected for our analysis, regarding a total of 858 NET patients treated with TEM-based chemotherapy. The status of MGMT had been tested in 513 (60%) patients, using various methods. The pooled overall response rate (ORR) was higher in MGMT-deficient compared with MGMT-proficient NETs, with a risk difference of 0.31 (95% confidence interval, CI: 0.13-0.50; p < 0.001; I²: 73%) and risk ratio of 2.29 (95% CI: 1.34-3.91; p < 0.001; I²: 55%). The pooled progression free survival (PFS) (hazard ratio, HR = 0.56; 95% CI: 0.43-0.74; p < 0.001) and overall survival (OS) (HR = 0.41; 95% CI: 0.20-0.62; p = 0.011) were longer in MGMT-deficient versus MGMT-proficient NETs.

CONCLUSIONS

Our meta-analysis suggested that MGMT status may be predictive of TEM efficacy. However, due to the high heterogeneity of the evaluated studies the risk of biases should be considered. On this hypothesis future homogeneous prospective studies are warranted.

SD-36 promotes growth inhibition and induces apoptosis via suppression of Mcl-1 in glioma

Glioma is one of the most commonly observed tumours, representing approximately 75% of brain tumours in the adult population. Generally, glioma therapy includes surgical resection followed by radiotherapy and chemotherapy. The transcription factor STAT3 (signal transducer and activator of transcription 3) is a promising target for the treatment of cancer and several other diseases. At nanomolar concentrations, SD‐36 induces rapid cellular degradation of STAT3 but cannot degrade other STAT proteins. The current study demonstrates the therapeutic efficacies of the STAT3 degraders SD‐36 against glioma, as well as understanding the elucidating mechanisms and identifying molecular markers that determine cell sensitivity to STAT3 degraders. Glioma cell lines possessed similar response patterns to SD‐36 but different responses to the STAT3 inhibitor Stattic. SD‐36 potently induced apoptosis in glioma cells along with a reduction in Mcl‐1 levels, which are critical for mediating the induction of apoptosis and enhancing TMZ‐induced apoptosis. Accordingly, SD‐36 sensitizes the antitumour effect of TMZ in patient‐derived xenograft. In addition, the downregulation of Mcl‐1 expression‐mediated antitumour effect of SD‐36 was analysed in cell‐derived xenograft. These observations need to be validated clinically to confirm the efficacy of STAT3 degraders in glioma.

Glutathione S-Transferase M3 Is Associated with Glycolysis in Intrinsic Temozolomide-Resistant Glioblastoma Multiforme Cells

Glioblastoma multiforme (GBM) is a malignant primary brain tumor. The 5-year relative survival rate of patients with GBM remains <30% on average despite aggressive treatments, and secondary therapy fails in 90% of patients. In chemotherapeutic failure, detoxification proteins are crucial to the activity of chemotherapy drugs. Usually, glutathione S-transferase (GST) superfamily members act as detoxification enzymes by activating xenobiotic metabolites through conjugation with glutathione in healthy cells. However, some overexpressed GSTs not only increase GST activity but also trigger chemotherapy resistance and tumorigenesis-related signaling transductions. Whether GSTM3 is involved in GBM chemoresistance remains unclear. In the current study, we found that T98G, a GBM cell line with pre-existing temozolomide (TMZ) resistance, has high glycolysis and GSTM3 expression. GSTM3 knockdown in T98G decreased glycolysis ability through lactate dehydrogenase A activity reduction. Moreover, it increased TMZ toxicity and decreased invasion ability. Furthermore, we provide next-generation sequencing-based identification of significantly changed messenger RNAs of T98G cells with GSTM3 knockdown for further research. GSTM3 was downregulated in intrinsic TMZ-resistant T98G with a change in the expression levels of some essential glycolysis-related genes. Thus, GSTM3 was associated with glycolysis in chemotherapeutic resistance in T98G cells. Our findings provide new insight into the GSTM3 mechanism in recurring GBM.

Oxidative Stress Activated by Sorafenib Alters the Temozolomide Sensitivity of Human Glioma Cells Through Autophagy and JAK2/STAT3-AIF Axis

The development of temozolomide (TMZ) resistance in glioma leads to poor patient prognosis. Sorafenib, a novel diaryl urea compound and multikinase inhibitor, has the ability to effectively cross the blood-brain barrier. However, the effect of sorafenib on glioma cells and the molecular mechanism underlying the ability of sorafenib to enhance the antitumor effects of TMZ remain elusive. Here, we found that sorafenib could enhance the cytotoxic effects of TMZ in glioma cells in vitro and in vivo. Mechanistically, the combination of sorafenib and TMZ induced mitochondrial depolarization and apoptosis inducing factor (AIF) translocation from mitochondria to nuclei, and this process was dependent on STAT3 inhibition. Moreover, the combination of sorafenib and TMZ inhibited JAK2/STAT3 phosphorylation and STAT3 translocation to mitochondria. Inhibition of STAT3 activation promoted the autophagy-associated apoptosis induced by the combination of sorafenib and TMZ. Furthermore, the combined sorafenib and TMZ treatment induced oxidative stress while reactive oxygen species (ROS) clearance reversed the treatment-induced inhibition of JAK2/STAT3. The results indicate that sorafenib enhanced the temozolomide sensitivity of human glioma cells by inducing oxidative stress-mediated autophagy and JAK2/STAT3-AIF axis.

NBM-BMX, an HDAC8 Inhibitor, Overcomes Temozolomide Resistance in Glioblastoma Multiforme by Downregulating the β-Catenin/c-Myc/SOX2 Pathway and Upregulating p53-Mediated MGMT Inhibition

Although histone deacetylase 8 (HDAC8) plays a role in glioblastoma multiforme (GBM), whether its inhibition facilitates the treatment of temozolomide (TMZ)-resistant GBM (GBM-R) remains unclear. By assessing the gene expression profiles from short hairpin RNA of HDAC8 in the new version of Connectivity Map (CLUE) and cells treated by NBM-BMX (BMX)-, an HDAC8 inhibitor, data analysis reveals that the Wnt signaling pathway and apoptosis might be the underlying mechanisms in BMX-elicited treatment. This study evaluated the efficacy of cotreatment with BMX and TMZ in GBM-R cells. We observed that cotreatment with BMX and TMZ could overcome resistance in GBM-R cells and inhibit cell viability, markedly inhibit cell proliferation, and then induce cell cycle arrest and apoptosis. In addition, the expression level of β-catenin was reversed by proteasome inhibitor via the β-catenin/ GSK3β signaling pathway to reduce the expression level of c-Myc and cyclin D1 in GBM-R cells. BMX and TMZ cotreatment also upregulated WT-p53 mediated MGMT inhibition, thereby triggering the activation of caspase-3 and eventually leading to apoptosis in GBM-R cells. Moreover, BMX and TMZ attenuated the expression of CD133, CD44, and SOX2 in GBM-R cells. In conclusion, BMX overcomes TMZ resistance by enhancing TMZ-mediated cytotoxic effect by downregulating the β-catenin/c-Myc/SOX2 signaling pathway and upregulating WT-p53 mediated MGMT inhibition. These findings indicate a promising drug combination for precision personal treating of TMZ-resistant WT-p53 GBM cells.

Immune System-Related Changes in Preclinical GL261 Glioblastoma under TMZ Treatment: Explaining MRSI-Based Nosological Imaging Findings with RT-PCR Analyses

Glioblastomas (GB) are brain tumours with poor prognosis even after aggressive therapy. Previous work suggests that magnetic resonance spectroscopic imaging (MRSI) could act as a biomarker of efficient immune system attack onto GB, presenting oscillatory changes. Glioma-associated microglia/macrophages (GAMs) constitute the most abundant non-tumour cell type within the GB and can be polarised into anti-tumour (M1) or pro-tumour (M2) phenotypes. One of the mechanisms to mediate immunosuppression in brain tumours is the interaction between programmed cell death-1 ligand 1 (PD-L1) and programmed cell death-1 receptor (PD-1). We evaluated the subpopulations of GAMs in responding and control GB tumours to correlate PD-L1 expression to GAM polarisation in order to explain/validate MRSI-detected findings. Mice were evaluated by MRI/MRSI to assess the extent of response to treatment and with qPCR for GAMs M1 and M2 polarisation analyses. M1/M2 ratios and PD-L1 expression were higher in treated compared to control tumours. Furthermore, PD-L1 expression was positively correlated with the M1/M2 ratio. The oscillatory change in the GAMs prevailing population could be one of the key causes for the differential MRSI-detected pattern, allowing this to act as immune system activity biomarker in future work.

From Laboratory Studies to Clinical Trials: Temozolomide Use in IDH-Mutant Gliomas

In this review, we discuss the use of the alkylating agent temozolomide (TMZ) in the treatment of IDH-mutant gliomas. We describe the challenges associated with TMZ in clinical (drug resistance and tumor recurrence) and preclinical settings (variabilities associated with in vitro models) in treating IDH-mutant glioma. Lastly, we summarize the emerging therapeutic targets that can potentially be used in combination with TMZ.

Phosphoglycerate mutase 1 (PGAM1) overexpression promotes radio- and chemoresistance in gliomas by activating the DNA damage response

The glycolytic enzyme PGAM1 is overexpressed in gliomas where it efficiently facilitates the repair of DNA damage. Mechanistically, PGAM1 prevents inactivation of the ataxia-telangiectasia mutated (ATM) signaling pathway by sequestering the wild-type p53-induced phosphatase 1 (WIP1) in the cytoplasm. Genetic inhibition of PGAM1 expression subsequently sensitizes glioma cells against irradiation and chemotherapy-induced DNA damage.

The Role of Mismatch Repair in Glioblastoma Multiforme Treatment Response and Resistance

Mismatch repair (MMR) is a highly conserved DNA repair pathway that is critical for the maintenance of genomic integrity. This pathway targets base substitution and insertion-deletion mismatches, which primarily arise from replication errors that escape DNA polymerase proof-reading function. Here, the authors review key concepts in the molecular mechanisms of MMR in response to alkylation damage, approaches to detect MMR status in the clinic, and the clinical relevance of this pathway in glioblastoma multiforme treatment response and resistance.

The novel roles of virus infection-associated gene CDKN1A in chemoresistance and immune infiltration of glioblastoma

Chemoresistance is a common limitation for successful treatment of glioblastoma multiforme (GBM). Recently, virus infections have been demonstrated to be associated with tumorigenesis and chemoresistance in tumors. However, the role of infection-related genes in GBM haven’t been clearly demonstrated. Here, we explored the roles and mechanisms of human T-lymphotropic virus type-1 (HTLV-1) infections in tumorigenesis and chemoresistance in GBM. Four candidate genes, CDKN1A, MSX1, MYC and CHEK2, were identified to be the codifferentially expressed genes between three temozolomide (TMZ) chemotherapy datasets and one HTLV-1 infection gene set. Next, comprehensive bioinformatics data from several databases indicated that only CDKN1A was significantly upregulated in both GBM tissues and cells and showed the greatest prognostic value in GBM patients. Clinical data identified the correlations between CDKN1A expression and clinicopathological parameters of GBM patients. Moreover, CDKN1A was found to be involved in AKT-mediated TMZ resistance of glioma cells. In addition, KEGG analysis of CDKN1A-associated coexpression genes showed that CDKN1A was potentially involved in complement and coagulation cascades pathways in GBM. Finally, TISIDB database was used to investigate the role of CDKN1A in tumor-immune system interactions in GBM. These findings enhanced our understanding of the roles of CDKN1A in tumorigenesis and therapy response in GBM.

Extracellular vesicles derived from hypoxic glioma stem-like cells confer temozolomide resistance on glioblastoma by delivering miR-30b-3p

Rationale: Glioma stem-like cells (GSCs) contribute to temozolomide (TMZ) resistance in gliomas, although the mechanisms have not been delineated. Methods: In vitro functional experiments (colony formation assay, flow cytometric analysis, TUNEL assay) were used to assess the ability of extracellular vesicles (EVs) from hypoxic GSCs to promote TMZ resistance in glioblastoma (GBM) cells. RNA sequencing and quantitative Reverse Transcription-PCR were employed to identify the functional miRNA in hypoxic EVs. Chromatin immunoprecipitation assays were performed to analyze the transcriptional regulation of miRNAs by HIF1α and STAT3. RIP and RNA pull-down assays were used to validate the hnRNPA2B1-mediated packaging of miRNA into EVs. The function of EV miR-30b-3p from hypoxic GSCs was verified by in vivo experiments and analysis of clinical samples. Results: Hypoxic GSC-derived EVs exerted a greater effect on GBM chemoresistance than those from normoxic GSCs. The miRNA profiling revealed that miR-30b-3p was significantly upregulated in the EVs from hypoxic GSCs. Further, HIF1α and STAT3 transcriptionally induced miR-30b-3p expression. RNA immunoprecipitation and RNA-pull down assays revealed that binding of miR-30b-3p with hnRNPA2B1 facilitated its transfer into EVs. EV-packaged miR-30b-3p (EV-miR-30b-3p) directly targeted RHOB, resulting in decreased apoptosis and increased proliferation in vitro and in vivo. Our results provided evidence that miR-30b-3p in CSF could be a potential biomarker predicting resistance to TMZ. Conclusion: Our findings indicated that targeting EV-miR-30b-3p could provide a potential treatment strategy for GBM.

Oncolytic herpes simplex virus and temozolomide synergistically inhibit breast cancer cell tumorigenesis in vitro and in vivo

The oncolytic herpes simplex virus (HSV) G47Δ can selectively eliminate glioblastoma cells via viral replication and temozolomide (TMZ) has been clinically used to treat glioblastoma. However, the combined effect of G47Δ and TMZ on cancer cells, particularly on breast cancer cells, remains largely unknown. The objective of the present study was to investigate the role and underlying mechanism of G47Δ and TMZ, in combination, in breast cancer cell tumorigenesis. The human breast cancer cell lines SK-BR-3 and MDA-MB-468 were treated with G47Δ and TMZ individually or in combination. Cell viability, flow cytometry, reverse transcription quantitative-PCR and western blotting were performed to investigate the synergy between G47Δ and TMZ in regulating breast cancer cell behavior in vitro. The role of G47Δ and TMZ in suppressing tumorigenesis in vivo was investigated in a xenograft mouse model. G47Δ and TMZ served a synergistic role resulting in decreased breast cancer cell viability, induction of cell cycle arrest, promotion of tumor cell apoptosis and enhancement of DNA damage response in vitro. The combined administration of G47Δ and TMZ also effectively suppressed breast cancer cell-derived tumor growth in vivo, compared with the administration of G47Δ or TMZ alone. Synergy between G47Δ and TMZ was at least partially mediated via TMZ-induced acceleration of G47Δ replication, and such a synergy in breast cancer cells in vitro and in vivo provides novel insight into the future development of a therapeutic strategy against breast cancer.