Aptamers: ushering in new hopes in targeted glioblastoma therapy

Glioblastoma, a formidable brain cancer, has remained a therapeutic challenge due to its aggressive nature and resistance to conventional treatments. Recent data indicate that aptamers, short synthetic DNA or RNA molecules can be used in anti-cancer therapy due to their better tumour penetration, specific binding affinity, longer retention in tumour sites and their ability to cross the blood-brain barrier. With the ability to modify these oligonucleotides through the selection process, and using rational design to modify them, post-SELEX aptamers offer several advantages in glioblastoma treatment, including precise targeting of cancer cells while sparing healthy tissue. This review discusses the pivotal role of aptamers in glioblastoma therapy and diagnosis, emphasising their potential to enhance treatment efficacy and also highlights recent advancements in aptamer-based therapies which can transform the landscape of glioblastoma treatment, offering renewed hope to patients and clinicians alike.

Rapid P-TEFb-dependent transcriptional reorganization underpins the glioma adaptive response to radiotherapy

Dynamic regulation of gene expression is fundamental for cellular adaptation to exogenous stressors. P-TEFb-mediated pause-release of RNA polymerase II (Pol II) is a conserved regulatory mechanism for synchronous transcriptional induction in response to heat shock, but this pro-survival role has not been examined in the applied context of cancer therapy. Using model systems of pediatric high-grade glioma, we show that rapid genome-wide reorganization of active chromatin facilitates P-TEFb-mediated nascent transcriptional induction within hours of exposure to therapeutic ionizing radiation. Concurrent inhibition of P-TEFb disrupts this chromatin reorganization and blunts transcriptional induction, abrogating key adaptive programs such as DNA damage repair and cell cycle regulation. This combination demonstrates a potent, synergistic therapeutic potential agnostic of glioma subtype, leading to a marked induction of tumor cell apoptosis and prolongation of xenograft survival. These studies reveal a central role for P-TEFb underpinning the early adaptive response to radiotherapy, opening avenues for combinatorial treatment in these lethal malignancies.

Zotiraciclib (TG02) for newly diagnosed glioblastoma in the elderly or for recurrent glioblastoma: The EORTC 1608 STEAM trial

BACKGROUND

Zotiraciclib (TG02) is an oral multi-cyclin dependent kinase (CDK) inhibitor thought to inhibit tumor growth via CDK-9-dependent depletion of survival proteins such as c-MYC and MCL-1 which are frequently overexpressed in glioblastoma.

METHODS

EORTC 1608 (NCT03224104) (STEAM) had a three parallel group (A,B,C) phase Ib, open-label, non-randomized, multicenter design in IDH wild-type newly diagnosed glioblastoma or anaplastic astrocytoma. Groups A and B explored the maximum tolerated dose (MTD) of TG02 in elderly patients, in combination with hypofractionated radiotherapy alone (group A) or temozolomide alone (group B), according to O6-methylguanine DNA methyltransferase promoter methylation status determined centrally. Group C explored single agent activity of TG02 at first relapse after temozolomide chemoradiotherapy with a primary endpoint of progression-free survival at 6 months (PFS-6). Tumor expression of CDK-9, c-MYC and MCL-1 was determined by immunohistochemistry.

RESULTS

The MTD was 150 mg twice weekly in combination with radiotherapy alone (group A) or temozolomide alone (group B). Two dose-limiting toxicities were observed at 150 mg: one in group A (grade 3 seizure), one in group B (multiple grade 1 events). Main toxicities included neutropenia, gastrointestinal disorders and hepatotoxicity. PFS-6 in group C was 6.7%. CDK-9, c-MYC and MCL-1 were confirmed to be expressed and their expression was moderately cross-correlated. High protein levels of MCL-1 were associated with inferior survival.

CONCLUSIONS

TG02 exhibits overlapping toxicity with alkylating agents and low single agent clinical activity in recurrent glioblastoma. The role of CDK-9 and its down-stream effectors as prognostic factors and therapeutic targets in glioblastoma warrants further study.

Exploiting the therapeutic vulnerability of IDH-mutant gliomas with zotiraciclib

Isocitrate dehydrogenase (IDH)-mutant gliomas have distinctive metabolic and biological traits that may render them susceptible to targeted treatments. Here, by conducting a high-throughput drug screen, we pinpointed a specific susceptibility of IDH-mutant gliomas to zotiraciclib (ZTR). ZTR exhibited selective growth inhibition across multiple IDH-mutant glioma in vitro and in vivo models. Mechanistically, ZTR at low doses suppressed CDK9 and RNA Pol II phosphorylation in IDH-mutant cells, disrupting mitochondrial function and NAD+ production, causing oxidative stress. Integrated biochemical profiling of ZTR kinase targets and transcriptomics unveiled that ZTR-induced bioenergetic failure was linked to the suppression of PIM kinase activity. We posit that the combination of mitochondrial dysfunction and an inability to adapt to oxidative stress resulted in significant cell death upon ZTR treatment, ultimately increasing the therapeutic vulnerability of IDH-mutant gliomas. These findings prompted a clinical trial evaluating ZTR in IDH-mutant gliomas towards precision medicine ( NCT05588141 ).

Highlights

Zotiraciclib (ZTR), a CDK9 inhibitor, hinders IDH-mutant glioma growth in vitro and in vivo . ZTR halts cell cycle, disrupts respiration, and induces oxidative stress in IDH-mutant cells.ZTR unexpectedly inhibits PIM kinases, impacting mitochondria and causing bioenergetic failure.These findings led to the clinical trial NCT05588141, evaluating ZTR for IDH-mutant gliomas.

The "Superoncogene" Myc at the Crossroad between Metabolism and Gene Expression in Glioblastoma Multiforme

The concept of the Myc (c-myc, n-myc, l-myc) oncogene as a canonical, DNA-bound transcription factor has consistently changed over the past few years. Indeed, Myc controls gene expression programs at multiple levels: directly binding chromatin and recruiting transcriptional coregulators; modulating the activity of RNA polymerases (RNAPs); and drawing chromatin topology. Therefore, it is evident that Myc deregulation in cancer is a dramatic event. Glioblastoma multiforme (GBM) is the most lethal, still incurable, brain cancer in adults, and it is characterized in most cases by Myc deregulation. Metabolic rewiring typically occurs in cancer cells, and GBM undergoes profound metabolic changes to supply increased energy demand. In nontransformed cells, Myc tightly controls metabolic pathways to maintain cellular homeostasis. Consistently, in Myc-overexpressing cancer cells, including GBM cells, these highly controlled metabolic routes are affected by enhanced Myc activity and show substantial alterations. On the other hand, deregulated cancer metabolism impacts Myc expression and function, placing Myc at the intersection between metabolic pathway activation and gene expression. In this review paper, we summarize the available information on GBM metabolism with a specific focus on the control of the Myc oncogene that, in turn, rules the activation of metabolic signals, ensuring GBM growth.

Rapid PTEFb-dependent transcriptional reorganization underpins the glioma adaptive response to radiotherapy

Dynamic regulation of gene expression is fundamental for cellular adaptation to exogenous stressors. PTEFb-mediated pause-release of RNA polymerase II (Pol II) is a conserved regulatory mechanism for synchronous transcriptional induction in response to heat shock, but this pro-survival role has not been examined in the applied context of cancer therapy. Using model systems of pediatric high-grade glioma, we show that rapid genome-wide reorganization of active chromatin facilitates PTEFb-mediated nascent transcriptional induction within hours of exposure to therapeutic ionizing radiation. Concurrent inhibition of PTEFb disrupts this chromatin reorganization and blunts transcriptional induction, abrogating key adaptive programs such as DNA damage repair and cell cycle regulation. This combination demonstrates a potent, synergistic therapeutic potential agnostic of glioma subtype, leading to a marked induction of tumor cell apoptosis and prolongation of xenograft survival. These studies reveal a central role for PTEFb underpinning the early adaptive response to radiotherapy, opening new avenues for combinatorial treatment in these lethal malignancies.

Interferon-beta inhibits human glioma stem cell growth by modulating immune response and cell cycle related signaling pathways

Malignant Glioma is characterized by strong self-renewal potential and immature differentiation potential. The main reason is that malignant glioma holds key cluster cells, glioma stem cells (GSCs). GSCs contribute to tumorigenesis, tumor progression, recurrence, and treatment resistance. Interferon-beta (IFN-β) is well known for its anti-proliferative efficacy in diverse cancers. IFN-β also displayed potent antitumor effects in malignant glioma. IFN-β affect both GSCs and Neural stem cells (NSCs) in the treatment of gliomas. However, the functional comparison, similar or different effects of IFN-β on GSCs and NSCs are rarely reported. Here, we studied the similarities and differences of the responses to IFN-β between human GSCs and normal NSCs. We found that IFN-β preferentially inhibited GSCs over NSCs. The cell body and nucleus size of GSCs increased after IFN-β treatment, and the genomic analysis revealed the enrichment of the upregulated immune response, cell adhesion genes and down regulated cell cycle, ribosome pathways. Several typical cyclin genes, including cyclin A2 (CCNA2), cyclin B1 (CCNB1), cyclin B2 (CCNB2), and cyclin D1 (CCND1), were significantly downregulated in GSCs after IFN-β stimulation. We also found that continuous IFN-β stimulation after passage further enhanced the inhibitory effect. Our study revealed how genetic diversity resulted in differential effects in response to IFN-β treatment. These results may contribute to improve the applications of IFN-β in anti-cancer immunotherapy. In addition, these results may also help to design more effective pharmacological strategies to target cancer stem cells while protecting normal neural stem cells.

Off the Clock: the Non-canonical Roles of Cyclin-Dependent Kinases in Neural and Glioma Stem Cell Self-Renewal

Glioma stem cells (GSCs) are thought to drive growth and therapy resistance in glioblastoma (GBM) by "hijacking" at least a subset of signaling pathways active in normal neural stem cells (NSCs). Though the origins of GSCs still remain elusive, uncovering the mechanisms of self-renewing division and cell differentiation in normal NSCs has shed light on their dysfunction in GSCs. However, the distinction between self-renewing division pathways utilized by NSC and GSC becomes critical when considering options for therapeutically targeting signaling pathways that are specifically active or altered in GSCs. It is well-established that cyclin-dependent kinases (CDKs) regulate the cell cycle, yet more recent studies have shown that CDKs also play important roles in the regulation of neuronal survival, metabolism, differentiation, and self-renewal. The intimate relationship between cell cycle regulation and the cellular programs that determine self-renewing division versus cell differentiation is only beginning to be understood, yet seems to suggest potential differential vulnerabilities in GSCs. In this timely review, we focus on the role of CDKs in regulating the self-renewal properties of normal NSCs and GSCs, highlighting novel opportunities to therapeutically target self-renewing signaling pathways specifically in GBM.

CD95 gene deletion may reduce clonogenic growth and invasiveness of human glioblastoma cells in a CD95 ligand-independent manner

CD95 (Fas/APO-1) is a multifunctional cell surface receptor with antithetic roles. First described to mediate cell death, interactions of CD95 with its natural ligand, CD95L, have also been described to induce tumor-promoting signaling leading to proliferation, invasion and stem cell maintenance, mainly in cancer cells that are resistant to CD95-mediated apoptosis. While activation of CD95-mediated apoptosis in cancer cells may not be clinically practicable due to toxicity, inhibition of tumor-promoting CD95 signaling holds therapeutic potential. In the present study, we characterized CD95 and CD95L expression in human glioma-initiating cells (GIC), a glioblastoma cell population with stem cell features, and investigated the consequences of CRISPR-Cas9-mediated CD95 or CD95L gene deletion. In vitro, GIC expressed CD95 but not CD95L and were sensitive to CD95-mediated apoptosis. Upon genetic deletion of CD95, GIC acquired resistance to CD95L-induced apoptosis but exhibited inferior clonogenic growth, sphere-forming capacity, and invasiveness compared with control cells, suggesting the existence of CD95L-independent constitutive CD95 signaling with tumor-promoting properties in GIC. In vivo, GIC expressed CD95 and a non-canonical form of CD95L lacking the CD95-binding region. CD95 genetic deletion did not prolong survival in immunocompromised GIC-bearing mice. Altogether, these data indicate that canonical CD95L may not be expressed in human GIC and suggest the existence of a CD95L-independent CD95-signaling pathway that maintains some malignancy traits of GIC. The lack of altered survival of tumor-bearing mice after genetic deletion of CD95 suggests that CD95 signaling is not essential to maintain the growth of human GIC xenografted into the brains of nude mice. The ligand-independent tumor-promoting role of constitutive CD95 in our GIC models in vitro highlights the complexity and challenges associated with targeting CD95 with therapeutic intent.

Quantitative proteomic landscapes of primary and recurrent glioblastoma reveal a protumorigeneic role for FBXO2-dependent glioma-microenvironment interactions

BACKGROUND

Recent efforts have described the evolution of glioblastoma from initial diagnosis to post-treatment recurrence on a genomic and transcriptomic level. However, the evolution of the proteomic landscape is largely unknown.

METHODS

Sequential window acquisition of all theoretical fragment ion spectra mass spectrometry (SWATH-MS) was used to characterize the quantitative proteomes of two independent cohorts of paired newly diagnosed and recurrent glioblastomas. Recurrence-associated proteins were validated using immunohistochemistry and further studied in human glioma cell lines, orthotopic xenograft models, and human organotypic brain slice cultures. External spatial transcriptomic, single-cell, and bulk RNA sequencing data were analyzed to gain mechanistic insights.

RESULTS

Although overall proteomic changes were heterogeneous across patients, we identified BCAS1, INF2, and FBXO2 as consistently upregulated proteins at recurrence and validated these using immunohistochemistry. Knockout of FBXO2 in human glioma cells conferred a strong survival benefit in orthotopic xenograft mouse models and reduced invasive growth in organotypic brain slice cultures. In glioblastoma patient samples, FBXO2 expression was enriched in the tumor infiltration zone and FBXO2-positive cancer cells were associated with synaptic signaling processes.

CONCLUSIONS

These findings demonstrate a potential role of FBXO2-dependent glioma-microenvironment interactions to promote tumor growth. Furthermore, the published datasets provide a valuable resource for further studies.

Implementation of a combined CDK inhibition and arginine-deprivation approach to target arginine-auxotrophic glioblastoma multiforme cells

Constitutive activation of cyclin-dependent kinases (CDKs) or arginine auxotrophy are hallmarks of Glioblastoma multiforme (GBM). The latter metabolic defect renders tumor cells vulnerable to arginine-depleting substances, such as arginine deiminase from Streptococcus pyogenes (SpyADI). Previously, we confirmed the susceptibility of patient-derived GBM cells towards SpyADI as well as CDK inhibitors (CDKis). To improve therapeutic effects, we here applied a combined approach based on SpyADI and CDKis (dinaciclib, abemaciclib). Three arginine-auxotrophic patient-derived GBM lines with different molecular characteristics were cultured in 2D and 3D and effects of this combined SpyADI/CDKi approach were analyzed in-depth. All CDKi/SpyADI combinations yielded synergistic antitumoral effects, especially when given sequentially (SEQ), i.e., CDKi in first-line and most pronounced in the 3D models. SEQ application demonstrated impaired cell proliferation, invasiveness, and viability. Mitochondrial impairment was demonstrated by increasing mitochondrial membrane potential and decreasing oxygen consumption rate and extracellular acidification rate after SpyADI/abemaciclib monotherapy or its combination regimens. The combined treatment even induced autophagy in target cells (abemaciclib/SpyADI > dinaciclib/SpyADI). By contrast, the unfolded protein response and p53/p21 induced senescence played a minor role. Transmission electron microscopy confirmed damaged mitochondria and endoplasmic reticulum together with increased vacuolization under CDKi mono- and combination therapy. SEQ-abemaciclib/SpyADI treatment suppressed the DSB repair system via NHEJ and HR, whereas SEQ-dinaciclib/SpyADI treatment increased γ-H2AX accumulation and induced Rad51/Ku80. The latter combination also activated the stress sensor GADD45 and β-catenin antagonist AXIN2 and induced expression changes of genes involved in cellular/cytoskeletal integrity. This study highlights the strong antitumoral potential of a combined arginine deprivation and CDK inhibition approach via complex effects on mitochondrial dysfunction, invasiveness as well as DNA-damage response. This provides a good starting point for further in vitro and in vivo proof-of-concept studies to move forward with this strategy.

Cyclin-dependent kinase inhibitor fadraciclib (CYC065) depletes anti-apoptotic protein and synergizes with venetoclax in primary chronic lymphocytic leukemia cells

Fadraciclib (CYC065) is a second-generation aminopurine CDK2/9 inhibitor with increased potency and selectivity toward CDK2 and CDK9 compared to seliciclib (R-roscovitine). In chronic lymphocytic leukemia (CLL), a disease that depends on the over-expression of anti-apoptotic proteins for its survival, inhibition of CDK9 by fadraciclib reduced phosphorylation of the C-terminal domain of RNA polymerase II and blocked transcription in vitro; these actions depleted the intrinsically short-lived anti-apoptotic protein Mcl-1 and induced apoptosis. While the simulated bone marrow and lymph node microenvironments induced Mcl-1 expression and protected CLL cells from apoptosis, these conditions did not prolong the turnover rate of Mcl-1, and fadraciclib efficiently abrogated the protective effect. Further, fadraciclib was synergistic with the Bcl-2 antagonist venetoclax, inducing more profound CLL cell death, especially in samples with 17p deletion. While fadraciclib, venetoclax, and the combination each had distinct kinetics of cell death induction, their activities were reversible, as no additional cell death was induced upon removal of the drugs. The best combination effects were achieved when both drugs were maintained together. Altogether, this study provides a rationale for the clinical development of fadraciclib in CLL, either alone or in combination with a Bcl-2 antagonist.

CDK9 Inhibitors in Cancer Research

Cyclin dependent kinase 9 (CDK9) played an essential role in regulating transcriptional elongation. Aberrations in CDK9 activity have been observed in various cancers, which made CDK9 was an attractive therapeutic...

Targeting of cyclin-dependent kinases in atypical teratoid rhabdoid tumors with multikinase inhibitor TG02

OBJECTIVE

Atypical teratoid rhabdoid tumors (ATRTs) are aggressive pediatric brain tumors with no current standard of care and an estimated median patient survival of 12 to 18 months. Previous genetic analyses have implicated cyclin D1 and enhancer of zeste homolog 2 (EZH2), a histone methyltransferase that is implicated in many cancers, as key drivers of tumorigenicity in ATRTs. Since the effects of EZH2 and cyclin D1 are facilitated by a host of cyclin-dependent kinases (CDKs), the authors sought to investigate the potential therapeutic effects of targeting CDKs in ATRTs with the multi-CDK inhibitor, TG02.

METHODS

Human ATRT cell lines BT12, BT37, CHLA05, and CHLA06 were selected for investigation. The effects of TG02 on cell viability, proliferation, clonogenicity, and apoptosis were assessed via Cell Counting Kit-8 assays, cell counting, clonogenic assays, and flow cytometry, respectively. Similar methods were used to determine the effects of TG02 combined with radiation therapy (RT) or cisplatin. Synergism indices for TG02-cisplatin combination therapy were calculated using CompuSyn software.

RESULTS

TG02 was observed to significantly impair ATRT cell growth in vitro by limiting cell proliferation and clonogenicity, and by inducing apoptosis. TG02 inhibited ATRT cell proliferation and decreased cell viability in a dose-dependent manner with nanomolar half maximal effective concentration (EC50) values (BT12, 207.0 nM; BT37, 127.8 nM; CHLA05, 29.7 nM; CHLA06, 18.7 nM). TG02 (150 nM) dramatically increased the proportion of apoptotic ATRT cells 72 hours posttreatment (TG02 8.50% vs control 1.52% apoptotic cells in BT12, p < 0.0001; TG02 70.07% vs control 15.36%, p < 0.0001). Combination therapy studies revealed that TG02 acted as a potent radiosensitizer in ATRT cells (BT12 surviving fraction, RT 51.2% vs RT + TG02 21.7%). Finally, CompuSyn analysis demonstrated that TG02 acted synergistically with cisplatin against ATRT cells at virtually all therapeutic doses. These findings were consistent in cell lines that cover all three molecular subgroups of ATRTs.

CONCLUSIONS

The results of this investigation have established that TG02 is an effective therapeutic against ATRTs in vitro. Given the lack of standard therapy for ATRTs, these findings help fill an unmet need and support further study of TG02 as a potential therapeutic option for patients with this deadly disease.

Targeting CDK9 for the Treatment of Glioblastoma

Glioblastoma is the most common and aggressive primary malignant brain tumor, and more than two-thirds of patients with glioblastoma die within two years of diagnosis. The challenges of treating this disease mainly include genetic and microenvironmental features that often render the tumor resistant to treatments. Despite extensive research efforts, only a small number of drugs tested in clinical trials have become therapies for patients. Targeting cyclin-dependent kinase 9 (CDK9) is an emerging therapeutic approach that has the potential to overcome the challenges in glioblastoma management. Here, we discuss how CDK9 inhibition can impact transcription, metabolism, DNA damage repair, epigenetics, and the immune response to facilitate an anti-tumor response. Moreover, we discuss small-molecule inhibitors of CDK9 in clinical trials and future perspectives on the use of CDK9 inhibitors in treating patients with glioblastoma.

Cyclin-dependent kinase inhibitors in head and neck cancer and glioblastoma-backbone or add-on in immune-oncology?

Cyclin-dependent kinases (CDK) control the cell cycle and play a crucial role in oncogenesis. Pharmacologic inhibition of CDK has contributed to the recent clinical approval of dual CDK4/6 inhibitors for the treatment of breast and small cell lung cancer. While the anticancer cell effects of CDK inhibitors are well-established, preclinical and early clinical studies describe additional mechanisms of action such as chemo- and radiosensitization or immune stimulation. The latter offers great potential to incorporate CDK inhibitors in immune-based treatments. However, dosing schedules and accurate timing of each combination partner need to be respected to prevent immune escape and resistance. In this review, we provide a detailed summary of CDK inhibitors in the two solid cancer types head and neck cancer and glioblastoma multiforme; it describes the molecular mechanisms of response vs. resistance and covers strategies to avoid resistance by the combination of immunotherapy or targeted therapy.

Endoglin and TGF-β signaling in glioblastoma

Microvascular proliferation is a key feature of glioblastoma and neovascularization has been implicated in tumor progression. Glioblastomas use pro-angiogenic factors such as vascular endothelial growth factor (VEGF) for new blood vessel formation. Yet, anti-VEGF therapy does not prolong overall survival so that alternative angiogenic pathways may need to be explored as drug targets. Both glioma cells and glioma-associated endothelial cells produce TGF-β superfamily ligands which bind TGF-β receptors (TGF-βR). The TGF-βR type III endoglin (CD105), is a marker of proliferating endothelium that has already been studied as a potential therapeutic target. We studied endoglin expression in glioblastoma tissue and in glioma-associated endothelial cells in a cohort of 52 newly diagnosed and 10 recurrent glioblastoma patients by immunohistochemistry and by ex vivo single-cell gene expression profiling of 6 tumors. Endoglin protein levels were similar in tumor stroma and endothelium and correlated within tumors. Similarly, endoglin mRNA determined by ex vivo single-cell gene expression profiling was expressed in both compartments. There was positive correlation between endoglin and proteins of TGF-β superfamily signaling. No prognostic role of endoglin expression in either compartment was identified. Endoglin gene silencing in T98G glioma cells and in human cerebral microvascular endothelial cells (hCMEC) did not affect constitutive or exogenous TGF-β superfamily ligand-dependent signaling, except for a minor facilitation of pSmad1/5 signaling in hCMEC. These observations challenge the notion that endoglin might become a promising therapeutic target in glioblastoma.

Sensitivity of human meningioma cells to the cyclin-dependent kinase inhibitor, TG02

Standards of care for meningioma include surgical resection and radiotherapy whereas pharmacotherapy plays almost no role in this disease. We generated primary cultures from surgically removed meningiomas to explore the activity of a novel cyclin-dependent kinase inhibitor, TG02, in meningioma cell cultures. Tumor and cell cultures were characterized by mutation profiling and DNA methylation profiling. DNA methylation data were used to allot each sample to one out of six previously established meningioma methylation classes: benign (ben)-1, 2, 3, intermediate (int)-A, B, and malignant (mal). Four tumors assigned to the methylation class ben-2 showed the same class in culture whereas cultures from five non-ben-2 tumors showed a more malignant class in four patients. Cell cultures were uniformly sensitive to TG02 in the nanomolar range. Assignment of the cell cultures to a more malignant methylation class appeared to be more closely associated with TG02 sensitivity than assignment to a higher WHO grade of the primary tumors. Primary cell cultures from meningioma facilitate the investigation of the anti-meningioma activity of novel agents. TG02, an orally available cyclin-dependent kinase (CDK) inhibitor, warrants further exploration.

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Standards of care for meningioma include surgical resection and radiotherapy whereas pharmacotherapy plays almost no role.

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Primary cultures were established to explore the activity of a novel cyclin-dependent kinase inhibitor, TG02.

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DNA methylation data were used to assign each sample to one out of six previously established methylation classes.

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Cell cultures were uniformly sensitive to TG02 in the nanomolar range.

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Methylation class of cell cultures was associated stronger with TG02 sensitivity than WHO grade of the primary tumor.

MGMT-inhibitor in combination with TGF-βRI inhibitor or CDK 4/6 inhibitor increases temozolomide sensitivity in temozolomide-resistant glioblastoma cells

BACKGROUND

Glioblastoma (GB) remains an incurable and deadly brain malignancy that often proves resistant to upfront treatment with temozolomide. Nevertheless, temozolomide remains the most commonly prescribed FDA-approved chemotherapy for GB. The DNA repair protein methylguanine-DNA methyl transferase (MGMT) confers resistance to temozolomide. Unsurprisingly temozolomide-resistant tumors tend to possess elevated MGMT protein levels or lack inhibitory MGMT promotor methylation. In this study, cultured human temozolomide resistance GB (43RG) cells were introduced to the MGMT inhibitor O⁶-benzylguanine combined with temozolomide and either LY2835219 (CDK 4/6 inhibitor) or LY2157299 (TGF-βRI inhibitor) seeking to overcome GB treatment resistance.

METHODS

Treatment effects were assessed using MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide) assay, western blot, cell viability, and cell cycle progression.

RESULTS

Our in vitro study demonstrated that sequential treatment of O⁶-Benzylguanine with either LY2385219 or LY2157299-enhanced temozolomide enhanced sensitivity in MGMT+ 43RG cells. Importantly, normal human neurons and astrocytes remained impervious to the drug therapies under these conditions. Furthermore, LY2835219 has additional anti-proliferative effects on cell cycling, including induction of an RB-associated G (1) arrest via suppression of cyclin D-CDK4/6-Rb pathway. LY2157299 enhances anti-tumor effect by disrupting TGF-β-dependent HIF-1α signaling and by activating both Smad and PI3K-AKT pathways towards transcription of S/G2 checkpoints.

CONCLUSION

This study establishes the groundwork for the development of a combinatorial pharmacologic approach by using either LY2385219 or LY2157299 inhibitor plus O⁶-Benzylguanine to augment temozolomide response in temozolomide-resistant GB cells.

Interferon-β exposure induces a fragile glioblastoma stem cell phenotype with a transcriptional profile of reduced migratory and MAPK pathway activity

Background

Type I interferons (IFN-α/β) are cytokines that are typically expressed in response to double-stranded RNA associated with viral infections. Glioblastomas are the most common malignant primary brain tumors, characterized by an infiltrative growth pattern and prominent angiogenic activity, and thought to be maintained by a subpopulation of glioma-initiating (stem-like) cells (GICs). The growth of human GIC lines is highly sensitive to IFN-β.

Methods

Repetitive pulse stimulation with IFN-β1a (IS) was used to generate IS sublines that had acquired resistance to IFN-β-induced suppression of sphere formation. These cell lines were characterized by analyses of type 1 IFN signaling, growth patterns, and transcriptomic profiles.

Results

Here we report that repetitive IFN-β1a stimulation (IS) induces a stable phenotype (referred to as IS) at the level of maintaining sphere formation, although classical IFN signaling defined by the expression of both IFN receptors, myxovirus resistance protein A (MxA) accumulation, and STAT1 induction is unaffected. Furthermore, this stably altered IS phenotype is characterized by constitutively decreased sphere formation capacity and morphological features of senescence and autophagy. Transcriptional profiling reveals increased type I IFN signaling in these IS cells, but decreased expression of genes involved in receptor signaling and cell migration.

Conclusions

Altogether, these data suggest a role for promoting IFN-β signaling in glioblastoma and might provide clues to design future therapeutic approaches.

Depatuxizumab Mafodotin (ABT-414)-induced Glioblastoma Cell Death Requires EGFR Overexpression, but not EGFRY1068 Phosphorylation

Glioblastomas commonly (40%) exhibit epidermal growth factor receptor (EGFR) amplification; half of these tumors carry the EGFRvIII deletion variant characterized by an in-frame deletion of exons 2-7, resulting in constitutive EGFR activation. Although EGFR tyrosine kinase inhibitors had only modest effects in glioblastoma, novel therapeutic agents targeting amplified EGFR or EGFRvIII continue to be developed.Depatuxizumab mafodotin (ABT-414) is an EGFR-targeting antibody-drug conjugate consisting of the mAb 806 and a toxic payload, monomethyl auristatin F. Because glioma cell lines and patient-derived glioma-initiating cell models expressed too little EGFR in vitro to be ABT-414-sensitive, we generated glioma sublines overexpressing EGFR or EGFRvIII to explore determinants of ABT-414-induced cell death.Overexpression of EGFRvIII induces sensitization to ABT-414 more readily than overexpression of EGFR in vitro and in vivo Exposure to ABT-414 in vivo eliminated EGFRvIII-expressing tumor cells, and recurrent tumors were devoid of EGFRvIII expression. There is no bystander killing of cells devoid of EGFR expression. Surprisingly, either exposure to EGF or to EGFR tyrosin kinase inhibitors reduce EGFR protein levels and are thus not strategies to promote ABT-414-induced cell killing. Furthermore, glioma cells overexpressing kinase-dead EGFR or EGFRvIII retain binding of mAb 806 and sensitivity to ABT-414, allowing to dissociate EGFR phosphorylation from the emergence of the "active" EGFR conformation required for ABT-414 binding.The combination of EGFR-targeting antibody-drug conjugates with EGFR tyrosine kinase inhibitors carries a high risk of failure. Promoting EGFR expression rather than phosphorylation should result in glioblastoma cell sensitization to ABT-414.

Cyclin-dependent kinase inhibitors in brain cancer: current state and future directions

Cyclin-dependent kinases (CDKs) are important regulatory enzymes in the normal physiological processes that drive cell-cycle transitions and regulate transcription. Virtually all cancers harbour genomic alterations that lead to the constitutive activation of CDKs, resulting in the proliferation of cancer cells. CDK inhibitors (CKIs) are currently in clinical use for the treatment of breast cancer, combined with endocrine therapy. In this review, we describe the potential of CKIs for the treatment of cancer with specific focus on glioblastoma (GBM), the most common and aggressive primary brain tumour in adults. Despite intense effort to combat GBM with surgery, radiation and temozolomide chemotherapy, the median survival for patients is 15 months and the majority of patients experience disease recurrence within 6-8 months of treatment onset. Novel therapeutic approaches are urgently needed for both newly diagnosed and recurrent GBM patients. In this review, we summarise the current preclinical and clinical findings emphasising that CKIs could represent an exciting novel approach for GBM treatment.

Interferon-β sensitizes human glioblastoma cells to the cyclin-dependent kinase inhibitor, TG02

Novel treatments for glioblastoma, the most common malignant primary brain tumor, are urgently required. Type I interferons (IFN) are natural cytokines primarily involved in the defense against viral infections, which may also serve a role in the control of cancer, notably in the suppression of the cancer stem cell phenotype. TG02 is a novel orally available cyclin-dependent kinase 9 inhibitor which induces glioma cell apoptosis without profound caspase activation, which is currently explored in early clinical trials in newly diagnosed and recurrent glioblastoma. In the present study, human glioma-initiating cell line models were used to explore whether IFN-β modulates the anti-glioma activity of TG02. The present study employed immunoblotting to assess protein levels, several viability assays and gene silencing strategies to assess gene function. Pre-exposure to IFN-β sensitized human glioma models to a subsequent exposure to TG02. Combination treatment was associated with increased DEVD-amc cleaving caspase activity that was blocked by the anti-apoptotic protein, BCL2. However, BCL2 did not protect from the synergistic effects of IFN and TG02 on glioma cell growth. Furthermore, although IFN strongly induced pro-apoptotic XIAP-associated factor (XAF) expression, disrupting XAF expression did not abrogate the synergy with TG02. Consistent with that, caspase 3 gene silencing did not abrogate the effects of TG02 or IFN-β alone or in combination. Finally, it was observed that IFN-β may indeed modulate the effects of TG02 upstream in the signaling cascade since inhibition of RNA polymerase II phosphorylation, a direct readout of the pharmacodynamic activity of TG02, was facilitated when glioma cells were pre-exposed to IFN-β. In summary, these data suggest that type I IFN may be combined with TG02 to limit glioblastoma growth, but that the well characterized effects of IFN and TG02 on apoptotic signaling are dispensable for synergistic tumor growth inhibition. Instead, exploring how IFN signaling primes glioma cells for TG02-mediated direct target inhibition may help to design novel and effective pharmacological approaches to glioblastoma.

Novel approaches for glioblastoma treatment: Focus on tumor heterogeneity, treatment resistance, and computational tools

BACKGROUND

Glioblastoma (GBM) is a highly aggressive primary brain tumor. Currently, the suggested line of action is the surgical resection followed by radiotherapy and treatment with the adjuvant temozolomide, a DNA alkylating agent. However, the ability of tumor cells to deeply infiltrate the surrounding tissue makes complete resection quite impossible, and, in consequence, the probability of tumor recurrence is high, and the prognosis is not positive. GBM is highly heterogeneous and adapts to treatment in most individuals. Nevertheless, these mechanisms of adaption are unknown.

RECENT FINDINGS

In this review, we will discuss the recent discoveries in molecular and cellular heterogeneity, mechanisms of therapeutic resistance, and new technological approaches to identify new treatments for GBM. The combination of biology and computer resources allow the use of algorithms to apply artificial intelligence and machine learning approaches to identify potential therapeutic pathways and to identify new drug candidates.

CONCLUSION

These new approaches will generate a better understanding of GBM pathogenesis and will result in novel treatments to reduce or block the devastating consequences of brain cancers.

Enhanced Efficacy of Temozolomide Loaded by a Tetrahedral Framework DNA Nanoparticle in the Therapy for Glioblastoma

Glioblastoma (GBM) is one of the deadliest primary brain malignant tumors with a bleak prognosis. Craniotomy surgical resection followed by radiotherapy and chemotherapy was still the standard therapeutic strategy for GBM. As a target alkylating agent, temozolomide (TMZ) was utilized in the therapy of GBM for decades. However, effective treatment for GBM is stymied by rapid acquired resistance and bone marrow suppression. Here, we synthesize a tetrahedral framework nucleic acid (tFNA) nanoparticle that can carry TMZ to enhance the lethality on four GBM cell lines via activating the cell apoptosis and autophagy pathway. Our nanoparticle, namely, tFNA-TMZ, shows a more obvious efficacy in killing TMZ-sensitive cells (A172 and U87) than single-agent TMZ. Besides, tFNA-TMZ was able to attenuate drug resistance in TMZ-resistant cells (T98G and LN-18) via downregulating the expression of O6-methylguanine-DNA-methyltransferase. Furthermore, we modified the tFNA with GS24, a DNA aptamer that can specially bind to transferrin receptor in the cerebral vascular endothelial cell of mouse and enable the tFNA nanoparticle to cross the blood-brain barrier. In summary, our results demonstrated that tFNA-TMZ has a promising role as a nanoscale vehicle to deliver TMZ to enhance the efficacy of GBM.

Therapeutic Targeting of TGFβ Ligands in Glioblastoma Using Novel Antisense Oligonucleotides Reduces the Growth of Experimental Gliomas

PURPOSE

Transforming growth factor (TGF)-β is expressed at high levels by glioma cells and contributes to the malignant phenotype of glioblastoma. However, its therapeutic targeting remains challenging. Here, we examined an alternative therapeutic approach of TGFβ inhibition using two novel phosphorothioate-locked nucleic acid (LNA)-modified antisense oligonucleotide gapmers, ISTH1047 and ISTH0047, which specifically target TGFβ₁ and TGFβ₂.

EXPERIMENTAL DESIGN

We characterized the effects of ISTH1047 and ISTH0047 on TGFβ_1/2 expression, downstream signaling and growth of human LN-308, LN-229, and ZH-161 cells as well as murine SMA-560 glioma cells in vitro. Furthermore, we assessed their target inhibition and effects on survival in orthotopic xenogeneic and syngeneic rodent glioma models in vivo.

RESULTS

Both antisense oligonucleotides specifically silenced their corresponding target and abrogated SMAD2 phosphorylation in several glioma cell lines. Moreover, inhibition of TGFβ₁ or TGFβ₂ expression by ISTH1047 or ISTH0047 reduced the migration and invasiveness of LN-308 and SMA-560 glioma cells. Systemic antisense oligonucleotide administration to glioma-bearing mice suppressed TGFβ₁ or TGFβ₂ mRNA expression as well as the expression of the downstream target PAI-1 in orthotopic gliomas. Glioma-bearing mice had significantly prolonged survival upon systemic treatment with ISTH1047 or ISTH0047, which was associated with a reduction of intratumoral SMAD2 phosphorylation and, in a fully immunocompetent model, with increased immune cell infiltration.

CONCLUSIONS

Targeting TGFβ expression with the novel LNA antisense oligonucleotides ISTH1047 or ISTH0047 results in strong antiglioma activity in vitro and in vivo, which may represent a promising approach to be examined in human patients with glioma.