Identification of molecular characteristics correlated with glioblastoma sensitivity to EGFR kinase inhibition through use of an intracranial xenograft test panel

Factors Influencing the Central Nervous System (CNS) Distribution of the Ataxia Telangiectasia Mutated and Rad3-Related Inhibitor Elimusertib (BAY1895344): Implications for the Treatment of CNS Tumors

Glioblastoma (GBM) is a disease of the whole brain, with infiltrative tumor cells protected by an intact blood-brain barrier (BBB). GBM has a poor prognosis despite aggressive treatment, in part due to the lack of adequate drug permeability at the BBB. Standard of care GBM therapies include radiation and cytotoxic chemotherapy that lead to DNA damage. Subsequent activation of DNA damage response (DDR) pathways can induce resistance. Various DDR inhibitors, targeting the key regulators of these pathways such as ataxia telangiectasia mutated and Rad3-related (ATR), are being explored as radio- and chemosensitizers. Elimusertib, a novel ATR kinase inhibitor, can prevent repair of damaged DNA, increasing efficacy of DNA-damaging cytotoxic therapies. Robust synergy was observed in vitro when elimusertib was combined with the DNA-damaging agent temozolomide; however, we did not observe improvement with this combination in in vivo efficacy studies in GBM orthotopic tumor-bearing mice. This in vitro-in vivo disconnect was explored to understand factors influencing central nervous system (CNS) distribution of elimusertib and reasons for lack of efficacy. We observed that elimusertib is rapidly cleared from systemic circulation in mice and would not maintain adequate exposure in the CNS for efficacious combination therapy with temozolomide. CNS distribution of elimusertib is partially limited by P-glycoprotein efflux at the BBB, and high binding to CNS tissues leads to low levels of pharmacologically active (unbound) drug in the brain. Acknowledging the potential for interspecies differences in pharmacokinetics, these data suggest that clinical translation of elimusertib in combination with temozolomide for treatment of GBM may be limited. SIGNIFICANCE STATEMENT: This study examined the disconnect between the in vitro synergy and in vivo efficacy of elimusertib/temozolomide combination therapy by exploring systemic and central nervous system (CNS) distributional pharmacokinetics. Results indicate that the lack of improvement in in vivo efficacy in glioblastoma (GBM) patient-derived xenograft (PDX) models could be attributed to inadequate exposure of pharmacologically active drug concentrations in the CNS. These observations can guide further exploration of elimusertib for the treatment of GBM or other CNS tumors.

Imaging extrachromosomal DNA (ecDNA) in cancer

Extrachromosomal DNA (ecDNA) are circular regions of DNA that are found in many cancers. They are an important means of oncogene amplification, and correlate with treatment resistance and poor prognosis. Consequently, there is great interest in exploring and targeting ecDNA vulnerabilities as potential new therapeutic targets for cancer treatment. However, the biological significance of ecDNA and their associated regulatory control remains unclear. Light microscopy has been a central tool in the identification and characterisation of ecDNA. In this review we describe the different cellular models available to study ecDNA, and the imaging tools used to characterise ecDNA and their regulation. The insights gained from quantitative imaging are discussed in comparison with genome sequencing and computational approaches. We suggest that there is a crucial need for ongoing innovation using imaging if we are to achieve a full understanding of the dynamic regulation and organisation of ecDNA and their role in tumourigenesis.

From bedside to bench: New insights in epilepsy-associated tumors based on recent classification updates and animal models on brain tumor networks

Low-grade neuroepithelial tumors (LGNTs), particularly those with glioneuronal histology, are highly associated with pharmacoresistant epilepsy. Increasing research focused on these neoplastic lesions did not translate into drug discovery; and anticonvulsant or antitumor therapies are not available yet. During the last years, animal modeling has improved, thereby leading to the possibility of generating brain tumors in mice mimicking crucial genetic, molecular and immunohistological features. Among them, intraventricular in utero electroporation (IUE) has been proven to be a valuable tool for the generation of animal models for LGNTs allowing endogenous tumor growth within the mouse brain parenchyma. Epileptogenicity is mostly determined by the slow-growing patterns of these tumors, thus mirroring intrinsic interactions between tumor cells and surrounding neurons is crucial to investigate the mechanisms underlying convulsive activity. In this review, we provide an updated classification of the human LGNT and summarize the most recent data from human and animal models, with a focus on the crosstalk between brain tumors and neuronal function.

Docetaxel targets aggressive methylation profiles and serves as a radiosensitizer in high-risk meningiomas

BACKGROUND

Meningioma is the most common primary intracranial tumor in adults. A subset of these tumors recur and invade the brain, even after surgery and radiation, resulting in significant disability. There is currently no standard-of-care chemotherapy for meningiomas. As genomic DNA methylation profiling can prognostically stratify these lesions, we sought to determine whether any existing chemotherapies might be effective against meningiomas with high-risk methylation profiles.

METHODS

A previously published dataset of meningioma methylation profiles was used to screen for clinically significant CpG methylation events and associated cellular pathways. Based on these results, patient-derived meningioma cell lines were used to test candidate drugs in vitro and in vivo, including efficacy in conjunction with radiotherapy.

RESULTS

We identified 981 genes for which methylation of mapped CpG sites was related to progression-free survival in meningiomas. Associated molecular pathways were cross-referenced with FDA-approved cancer drugs, which nominated Docetaxel as a promising candidate for further preclinical analyses. Docetaxel arrested growth in 17 meningioma cell sources, representing all tumor grades, with a clinically favorable IC50 values ranging from 0.3 nM to 10.7 mM. The inhibitory effects of this medication scaled with tumor doubling time, with maximal benefit in fast-growing lesions. The combination of Docetaxel and radiation therapy increased markers of apoptosis and double-stranded DNA breaks, and extended the survival of mice engrafted with meningioma cells relative to either modality alone.

CONCLUSIONS

Global patterns of DNA methylation may be informative for the selection of chemotherapies against meningiomas, and existing drugs may enhance radiation sensitivity in high-risk cases.

EGFR, the Lazarus target for precision oncology in glioblastoma

The Lazarus effect is a rare condition that happens when someone seemingly dead shows signs of life. The epidermal growth factor receptor (EGFR) represents a target in the fatal neoplasm glioblastoma (GBM) that through a series of negative clinical trials has prompted a vocal subset of the neuro-oncology community to declare this target dead. However, an argument can be made that the core tenets of precision oncology were overlooked in the initial clinical enthusiasm over EGFR as a therapeutic target in GBM. Namely, the wrong drugs were tested on the wrong patients at the wrong time. Furthermore, new insights into the biology of EGFR in GBM vis-à-vis other EGFR-driven neoplasms, such as non-small cell lung cancer, and development of novel GBM-specific EGFR therapeutics resurrects this target for future studies. Here, we will examine the distinct EGFR biology in GBM, how it exacerbates the challenge of treating a CNS neoplasm, how these unique challenges have influenced past and present EGFR-targeted therapeutic design and clinical trials, and what adjustments are needed to therapeutically exploit EGFR in this devastating disease.

Modeling Therapy-Driven Evolution of Glioblastoma with Patient-Derived Xenografts

Adult-type diffusely infiltrating gliomas, of which glioblastoma is the most common and aggressive, almost always recur after treatment and are fatal. Improved understanding of therapy-driven tumor evolution and acquired therapy resistance in gliomas is essential for improving patient outcomes, yet the majority of the models currently used in preclinical research are of therapy-naïve tumors. Here, we describe the development of therapy-resistant IDH-wildtype glioblastoma patient-derived xenografts (PDX) through orthotopic engraftment of therapy naïve PDX in athymic nude mice, and repeated in vivo exposure to the therapeutic modalities most often used in treating glioblastoma patients: radiotherapy and temozolomide chemotherapy. Post-temozolomide PDX became enriched for C>T transition mutations, acquired inactivating mutations in DNA mismatch repair genes (especially MSH6), and developed hypermutation. Such post-temozolomide PDX were resistant to additional temozolomide (median survival decrease from 80 days in parental PDX to 42 days in a temozolomide-resistant derivative). However, temozolomide-resistant PDX were sensitive to lomustine (also known as CCNU), a nitrosourea which induces tumor cell apoptosis by a different mechanism than temozolomide. These PDX models mimic changes observed in recurrent GBM in patients, including critical features of therapy-driven tumor evolution. These models can therefore serve as valuable tools for improving our understanding and treatment of recurrent glioma.

Targeted profiling of human extrachromosomal DNA by CRISPR-CATCH

Extrachromosomal DNA (ecDNA) is a common mode of oncogene amplification but is challenging to analyze. Here, we adapt CRISPR-CATCH, in vitro CRISPR-Cas9 treatment and pulsed field gel electrophoresis of agarose-entrapped genomic DNA, previously developed for bacterial chromosome segments, to isolate megabase-sized human ecDNAs. We demonstrate strong enrichment of ecDNA molecules containing EGFR, FGFR2 and MYC from human cancer cells and NRAS ecDNA from human metastatic melanoma with acquired therapeutic resistance. Targeted enrichment of ecDNA versus chromosomal DNA enabled phasing of genetic variants, identified the presence of an EGFRvIII mutation exclusively on ecDNAs and supported an excision model of ecDNA genesis in a glioblastoma model. CRISPR-CATCH followed by nanopore sequencing enabled single-molecule ecDNA methylation profiling and revealed hypomethylation of the EGFR promoter on ecDNAs. We distinguished heterogeneous ecDNA species within the same sample by size and sequence with base-pair resolution and discovered functionally specialized ecDNAs that amplify select enhancers or oncogene-coding sequences.

Signaling pathways and therapeutic approaches in glioblastoma multiforme (Review)

Glioblastoma multiforme (GBM) is the most aggressive type of primary brain tumor and is associated with a poor clinical prognosis. Despite the progress in the understanding of the molecular and genetic changes that promote tumorigenesis, effective treatment options are limited. The present review intended to identify and summarize major signaling pathways and genetic abnormalities involved in the pathogenesis of GBM, as well as therapies that target these pathways. Glioblastoma remains a difficult to treat tumor; however, in the last two decades, significant improvements in the understanding of GBM biology have enabled advances in available therapeutics. Significant genomic events and signaling pathway disruptions (NF‑κB, Wnt, PI3K/AKT/mTOR) involved in the formation of GBM were discussed. Current therapeutic options may only marginally prolong survival and the current standard of therapy cures only a small fraction of patients. As a result, there is an unmet requirement for further study into the processes of glioblastoma pathogenesis and the discovery of novel therapeutic targets in novel signaling pathways implicated in the evolution of glioblastoma.

Methods for intratumoral microdialysis probe targeting and validation in murine brain tumor models

BACKGROUND

Microdialysis is a well validated sampling technique that can be used for pharmacokinetic studies of oncological drugs targeting the central nervous system. This technique has also been applied to evaluate tumor metabolism and identify pharmacodynamic biomarkers of drug activity. Despite the potential utility of microdialysis for therapeutic discovery, variability in tumor size and location hamper routine use of microdialysis as a preclinical tool. Quantitative validation of microdialysis membrane location relative to radiographically evident tumor regions could facilitate rigorous preclinical studies. However, a widely accessible standardized workflow for preclinical catheter placement and validation is needed.

NEW METHOD

We provide methods for a workflow to yield tailored placement of microdialysis probes within a murine intracranial tumor and illustrate in an IDH1-mutant patient-derived xenograft (PDX) model. This detailed workflow uses a freely available on-line tool built within 3D-slicer freeware to target microdialysis probe placement within the tumor core and validate probe placement fully within the tumor.

RESULTS

We illustrate use of this workflow to validate microdialysis probe location relative to implanted IDH1-mutant PDXs, using the microdialysis probes to quantify levels of extracellular onco-metabolite D-2 hydroxyglutarate.

COMPARISON WITH EXISTING METHODS

Previous methods have used 3D slicer to reliably measure tumor volumes. Prior microdialysis studies have targeted expected tumor locations without validation.

CONCLUSIONS

The new method offers a streamlined and freely available workflow in 3D slicer to optimize and validate microdialysis probe placement within a murine brain tumor.

Quantitative Analysis of Tyrosine Phosphorylation from FFPE Tissues Reveals Patient-Specific Signaling Networks

Human tissue samples commonly preserved as formalin-fixed paraffin-embedded (FFPE) tissues after diagnostic or surgical procedures in the clinic represent an invaluable source of clinical specimens for in-depth characterization of signaling networks to assess therapeutic options. Tyrosine phosphorylation (pTyr) plays a fundamental role in cellular processes and is commonly dysregulated in cancer but has not been studied to date in FFPE samples. In addition, pTyr analysis that may otherwise inform therapeutic interventions for patients has been limited by the requirement for large amounts of frozen tissue. Here we describe a method for highly sensitive, quantitative analysis of pTyr signaling networks, with hundreds of sites quantified from one to two 10-μm sections of FFPE tissue specimens. A combination of optimized magnetic bead-based sample processing, optimized pTyr enrichment strategies, and tandem mass tag multiplexing enabled in-depth coverage of pTyr signaling networks from small amounts of input material. Phosphotyrosine profiles of flash-frozen and FFPE tissues derived from the same tumors suggested that FFPE tissues preserve pTyr signaling characteristics in patient-derived xenografts and archived clinical specimens. pTyr analysis of FFPE tissue sections from breast cancer tumors as well as lung cancer tumors highlighted patient-specific oncogenic driving kinases, indicating potential targeted therapies for each patient. These data suggest the capability for direct translational insight from pTyr analysis of small amounts of FFPE tumor tissue specimens. SIGNIFICANCE: This study reports a highly sensitive method utilizing FFPE tissues to identify dysregulated signaling networks in patient tumors, opening the door for direct translational insights from FFPE tumor tissue banks in hospitals.

Epidermal growth factor receptor as a molecular determinant of glioblastoma response to dopamine receptor D2 inhibitors

BACKGROUND

There are ongoing clinical trials exploring the efficacy of dopamine receptor D2 (DRD2) inhibition against glioblastomas, the most common primary brain tumor. Here we examine potential molecular determinants of this efficacy.

METHODS

The Cancer Genome Atlas glioblastoma database and other published mRNA profiles were used to analyze the DRD2 and epidermal growth factor receptor (EGFR) expression pattern. In vitro and in vivo responses to DRD2 inhibitors were determined using patient-derived xenograft (PDX) glioblastoma models. Immunohistochemical studies were performed on clinically annotated glioblastoma samples derived from patients treated with ONC201.

RESULTS

Analysis of clinical glioblastoma specimens derived from independent patient cohorts revealed an inverse correlation between EGFR and DRD2 mRNA expression, with implication that signaling mediated by these proteins shares overlapping functions. In independent panels of PDX glioblastoma lines, high EGFR expression was associated with poor in vitro and in vivo response to DRD2 inhibitors, including haloperidol and ONC201. Moreover, ectopic expression of a constitutively active EGFR, variant (v)III, suppressed glioblastoma sensitivity to ONC201. DRD2 expression positively correlated with expression of rate-limiting enzymes for dopamine synthesis as well as dopamine secretion, suggesting contribution of autocrine DRD2 signaling. Analysis of specimens from patients treated with ONC201 (n = 15) showed an inverse correlation between the intensity of EGFR staining and clinical response. The median overall survival for patients with high and low EGFR staining was 162 and 373 days, respectively (0.037).

CONCLUSIONS

High EGFR expression is a determinant of poor glioblastoma response to DRD2. This finding should inform future clinical trial designs.

EGFRvIII tumorigenicity requires PDGFRA co-signaling and reveals therapeutic vulnerabilities in glioblastoma

Focal amplification of epidermal growth factor receptor (EGFR) and its ligand-independent, constitutively active EGFRvIII mutant form are prominent oncogenic drivers in glioblastoma (GBM). The EGFRvIII gene rearrangement is considered to be an initiating event in the etiology of GBM, however, the mechanistic details of how EGFRvIII drives cellular transformation and tumor maintenance remain unclear. Here, we report that EGFRvIII demonstrates a reliance on PDGFRA co-stimulatory signaling during the tumorigenic process in a genetically engineered autochthonous GBM model. This dependency exposes liabilities that were leveraged using kinase inhibitors treatments in EGFRvIII-expressing GBM patient-derived xenografts (PDXs), where simultaneous pharmacological inhibition of EGFRvIII and PDGFRA kinase activities is necessary for anti-tumor efficacy. Our work establishes that EGFRvIII-positive tumors have unexplored vulnerabilities to targeted agents concomitant to the EGFR kinase inhibitor repertoire.

In Vivo Efficacy of Tesevatinib in EGFR-Amplified Patient-Derived Xenograft Glioblastoma Models May Be Limited by Tissue Binding and Compensatory Signaling

Tesevatinib is a potent oral brain penetrant EGFR inhibitor currently being evaluated for glioblastoma therapy. Tesevatinib distribution was assessed in wild-type (WT) and Mdr1a/b^(-/-)Bcrp^(-/-) triple knockout (TKO) FVB mice after dosing orally or via osmotic minipump; drug-tissue binding was assessed by rapid equilibrium dialysis. Two hours after tesevatinib dosing, brain concentrations in WT and TKO mice were 0.72 and 10.03 μg/g, respectively. Brain-to-plasma ratios (Kp) were 0.53 and 5.73, respectively. With intraperitoneal infusion, brain concentrations were 1.46 and 30.6 μg/g (Kp 1.16 and 25.10), respectively. The brain-to-plasma unbound drug concentration ratios were substantially lower (WT mice, 0.03-0.08; TKO mice, 0.40-1.75). Unbound drug concentrations in brains of WT mice were 0.78 to 1.59 ng/g. In vitro cytotoxicity and EGFR pathway signaling were evaluated using EGFR-amplified patient-derived glioblastoma xenograft models (GBM12, GBM6). In vivo pharmacodynamics and efficacy were assessed using athymic nude mice bearing either intracranial or flank tumors treated by oral gavage. Tesevatinib potently reduced cell viability [IC₅₀ GBM12 = 11 nmol/L (5.5 ng/mL), GBM6 = 102 nmol/L] and suppressed EGFR signaling in vitro However, tesevatinib efficacy compared with vehicle in intracranial (GBM12, median survival: 23 vs. 18 days, P = 0.003) and flank models (GBM12, median time to outcome: 41 vs. 33 days, P = 0.007; GBM6, 44 vs. 33 days, P = 0.007) was modest and associated with partial inhibition of EGFR signaling. Overall, tesevatinib efficacy in EGFR-amplified PDX GBM models is robust in vitro but relatively modest in vivo, despite a high brain-to-plasma ratio. This discrepancy may be explained by drug-tissue binding and compensatory signaling.

The effects of palbociclib in combination with radiation in preclinical models of aggressive meningioma

BACKGROUND

Meningiomas are the most common tumor arising within the cranium of adults. Despite surgical resection and radiotherapy, many meningiomas invade the brain, and many recur, often repeatedly. To date, no chemotherapy has proven effective against such tumors. Thus, there is an urgent need for chemotherapeutic options for treating meningiomas, especially those that enhance radiotherapy. Palbociclib is an inhibitor of cyclin-dependent kinases 4 and 6 that has been shown to enhance radiotherapy in preclinical models of other cancers, is well-tolerated in patients, and is used to treat malignancies elsewhere in the body. We, therefore, sought to determine its therapeutic potential in preclinical models of meningioma.

METHODS

Patient-derived meningioma cells were tested in vitro and in vivo with combinations of palbociclib and radiation. Outputs included cell viability, apoptosis, clonogenicity, engrafted mouse survival, and analysis of engrafted tumor tissues after therapy.

RESULTS

We found that palbociclib was highly potent against p16-deficient, Rb-intact CH157 and IOMM-Lee meningioma cells in vitro, but was ineffective against p16-intact, Rb-deficient SF8295 meningioma cells. Palbociclib also enhanced the in vitro efficacy of radiotherapy when used against p16-deficient meningioma, as indicated by cell viability and clonogenic assays. In vivo, the combination of palbociclib and radiation extended the survival of mice bearing orthotopic p16 deficient meningioma xenografts, relative to each as a monotherapy.

CONCLUSIONS

These data suggest that palbociclib could be repurposed to treat patients with p16-deficient, Rb-intact meningiomas, and that a clinical trial in combination with radiation therapy merits consideration.

Crosstalk between microglia and patient-derived glioblastoma cells inhibit invasion in a three-dimensional gelatin hydrogel model

BACKGROUND

Glioblastoma is the most common and deadly form of primary brain cancer, accounting for more than 13,000 new diagnoses annually in the USA alone. Microglia are the innate immune cells within the central nervous system, acting as a front-line defense against injuries and inflammation via a process that involves transformation from a quiescent to an activated phenotype. Crosstalk between GBM cells and microglia represents an important axis to consider in the development of tissue engineering platforms to examine pathophysiological processes underlying GBM progression and therapy.

METHODS

This work used a brain-mimetic hydrogel system to study patient-derived glioblastoma specimens and their interactions with microglia. Here, glioblastoma cells were either cultured alone in 3D hydrogels or in co-culture with microglia in a manner that allowed secretome-based signaling but prevented direct GBM-microglia contact. Patterns of GBM cell invasion were quantified using a three-dimensional spheroid assay. Secretome and transcriptome (via RNAseq) were used to profile the consequences of GBM-microglia interactions.

RESULTS

Microglia displayed an activated phenotype as a result of GBM crosstalk. Three-dimensional migration patterns of patient-derived glioblastoma cells showed invasion was significantly decreased in response to microglia paracrine signaling. Potential molecular mechanisms underlying with this phenotype were identified from bioinformatic analysis of secretome and RNAseq data.

CONCLUSION

The data demonstrate a tissue engineered hydrogel platform can be used to investigate crosstalk between immune cells of the tumor microenvironment related to GBM progression. Such multi-dimensional models may provide valuable insight to inform therapeutic innovations to improve GBM treatment.

Driving Neuronal Differentiation through Reversal of an ERK1/2-miR-124-SOX9 Axis Abrogates Glioblastoma Aggressiveness

Identifying cellular programs that drive cancers to be stem-like and treatment resistant is critical to improving outcomes in patients. Here, we demonstrate that constitutive extracellular signal-regulated kinase 1/2 (ERK1/2) activation sustains a stem-like state in glioblastoma (GBM), the most common primary malignant brain tumor. Pharmacological inhibition of ERK1/2 activation restores neurogenesis during murine astrocytoma formation, inducing neuronal differentiation in tumorspheres. Constitutive ERK1/2 activation globally regulates miRNA expression in murine and human GBMs, while neuronal differentiation of GBM tumorspheres following the inhibition of ERK1/2 activation requires the functional expression of miR-124 and the depletion of its target gene SOX9. Overexpression of miR124 depletes SOX9 in vivo and promotes a stem-like-to-neuronal transition, with reduced tumorigenicity and increased radiation sensitivity. Providing a rationale for reports demonstrating miR-124-induced abrogation of GBM aggressiveness, we conclude that reversal of an ERK1/2-miR-124-SOX9 axis induces a neuronal phenotype and that enforcing neuronal differentiation represents a therapeutic strategy to improve outcomes in GBM.

Leukemia-Associated Rho Guanine Nucleotide Exchange Factor and Ras Homolog Family Member C Play a Role in Glioblastoma Cell Invasion and Resistance

Glioblastoma (GBM) is the most common primary malignant brain cancer in adults. A hallmark of GBM is aggressive invasion of tumor cells into the surrounding normal brain. Both the current standard of care and targeted therapies have largely failed to specifically address this issue. Therefore, identifying key regulators of GBM cell migration and invasion is important. The leukemia-associated Rho guanine nucleotide exchange factor (LARG) has previously been implicated in cell invasion in other tumor types; however, its role in GBM pathobiology remains undefined. Herein, we report that the expression levels of LARG and ras homolog family members C (RhoC), and A (RhoA) increase with glial tumor grade and are highest in GBM. LARG and RhoC protein expression is more prominent in invading cells, whereas RhoA expression is largely restricted to cells in the tumor core. Knockdown of LARG by siRNA inhibits GBM cell migration in vitro and invasion ex vivo in organotypic brain slices. Moreover, siRNA-mediated silencing of RhoC suppresses GBM cell migration in vitro and invasion ex vivo, whereas depletion of RhoA enhances GBM cell migration and invasion, supporting a role for LARG and RhoC in GBM cell migration and invasion. Depletion of LARG increases the sensitivity of GBM cells to temozolomide treatment. Collectively, these results suggest that LARG and RhoC may represent unappreciated targets to inhibit glioma invasion.

TROY signals through JAK1-STAT3 to promote glioblastoma cell migration and resistance

Glioblastoma (GBM) is the most common primary malignant brain tumor in adults and carries a discouraging prognosis. Its aggressive and highly infiltrative nature renders the current standard treatment of maximal surgical resection, radiation, and chemotherapy relatively ineffective. Identifying the signaling pathways that regulate GBM migration/invasion and resistance is required to develop more effective therapeutic regimens to treat GBM. Expression of TROY, an orphan receptor of the TNF receptor superfamily, increases with glial tumor grade, inversely correlates with patient overall survival, stimulates GBM cell invasion in vitro and in vivo, and increases resistance to temozolomide and radiation therapy. Conversely, silencing TROY expression inhibits GBM cell invasion, increases sensitivity to temozolomide, and prolongs survival in a preclinical intracranial xenograft model. Here, we have identified for the first time that TROY interacts with JAK1. Increased TROY expression increases JAK1 phosphorylation. In addition, increased TROY expression promotes STAT3 phosphorylation and STAT3 transcriptional activity that is dependent upon JAK1. TROY-mediated activation of STAT3 is independent of its ability to stimulate activity of NF-κB. Inhibition of JAK1 activity by ruxolitinib or knockdown of JAK1 expression by siRNA significantly inhibits TROY-induced STAT3 activation, GBM cell migration, and decreases resistance to temozolomide. Taken together, our data indicate that the TROY signaling complex may represent a potential therapeutic target with the distinctive capacity to exert effects on multiple pathways mediating GBM cell invasion and resistance.

Pediatric bithalamic gliomas have a distinct epigenetic signature and frequent EGFR exon 20 insertions resulting in potential sensitivity to targeted kinase inhibition

Brain tumors are the most common solid tumors of childhood, and the genetic drivers and optimal therapeutic strategies for many of the different subtypes remain unknown. Here, we identify that bithalamic gliomas harbor frequent mutations in the EGFR oncogene, only rare histone H3 mutation (in contrast to their unilateral counterparts), and a distinct genome-wide DNA methylation profile compared to all other glioma subtypes studied to date. These EGFR mutations are either small in-frame insertions within exon 20 (intracellular tyrosine kinase domain) or missense mutations within exon 7 (extracellular ligand-binding domain) that occur in the absence of accompanying gene amplification. We find these EGFR mutations are oncogenic in primary astrocyte models and confer sensitivity to specific tyrosine kinase inhibitors dependent on location within the kinase domain or extracellular domain. We initiated treatment with targeted kinase inhibitors in four children whose tumors harbor EGFR mutations with encouraging results. This study identifies a promising genomically-tailored therapeutic strategy for bithalamic gliomas, a lethal and genetically distinct brain tumor of childhood.

Cooperative Blockade of PKCα and JAK2 Drives Apoptosis in Glioblastoma

The mTOR signaling is dysregulated prominently in human cancers including glioblastoma, suggesting mTOR as a robust target for therapy. Inhibitors of mTOR have had limited success clinically, however, in part because their mechanism of action is cytostatic rather than cytotoxic. Here, we tested three distinct mTOR kinase inhibitors (TORKi) PP242, KU-0063794, and sapanisertib against glioblastoma cells. All agents similarly decreased proliferation of glioblastoma cells, whereas PP242 uniquely induced apoptosis. Apoptosis induced by PP242 resulted from off-target cooperative inhibition of JAK2 and protein kinase C alpha (PKCα). Induction of apoptosis was also decreased by additional on-target inhibition of mTOR, due to induction of autophagy. As EGFR inhibitors can block PKCα, EGFR inhibitors erlotinib and osimertinib were tested separately in combination with the JAK2 inhibitor AZD1480. Combination therapy induced apoptosis of glioblastoma tumors in both flank and in patient-derived orthotopic xenograft models, providing a preclinical rationale to test analogous combinations in patients. SIGNIFICANCE: These findings identify PKCα and JAK2 as targets that drive apoptosis in glioblastoma, potentially representing a clinically translatable approach for glioblastoma.

Glioblastoma Multiforme: An Overview of Emerging Therapeutic Targets

Glioblastoma multiforme (GBM) is the most common and aggressive malignant primary brain tumour in humans and has a very poor prognosis. The existing treatments have had limited success in increasing overall survival. Thus, identifying and understanding the key molecule(s) responsible for the malignant phenotype of GBM will yield new potential therapeutic targets. The treatment of brain tumours faces unique challenges, including the presence of the blood brain barrier (BBB), which limits the concentration of drugs that can reach the site of the tumour. Nevertheless, several promising treatments have been shown to cross the BBB and have shown promising pre-clinical results. This review will outline the status of several of these promising targeted therapies.

Hyaluronic acid-functionalized gelatin hydrogels reveal extracellular matrix signals temper the efficacy of erlotinib against patient-derived glioblastoma specimens

Therapeutic options to treat primary glioblastoma (GBM) tumors are scarce. GBM tumors with epidermal growth factor receptor (EGFR) mutations, in particular a constitutively active EGFRvIII mutant, have extremely poor clinical outcomes. GBM tumors with concurrent EGFR amplification and active phosphatase and tensin homolog (PTEN) are sensitive to the tyrosine kinase inhibitor erlotinib, but the effect is not durable. A persistent challenge to improved treatment is the poorly understood role of cellular, metabolic, and biophysical signals from the GBM tumor microenvironment on therapeutic efficacy and acquired resistance. The intractable nature of studying GBM cell in vivo motivates tissue engineering approaches to replicate aspects of the complex GBM tumor microenvironment. Here, we profile the effect of erlotinib on two patient-derived GBM specimens: EGFR + GBM12 and EGFRvIII GBM6. We use a three-dimensional gelatin hydrogel to present brain-mimetic hyaluronic acid (HA) and evaluate the coordinated influence of extracellular matrix signals and EGFR mutation status on GBM cell migration, survival and proliferation, as well as signaling pathway activation in response to cyclic erlotinib exposure. Comparable to results observed in vivo for xenograft tumors, erlotinib exposure is not cytotoxic for GBM6 EGFRvIII specimens. We also identify a role of extracellular HA (via CD44) in altering the effect of erlotinib in GBM EGFR + cells by modifying STAT3 phosphorylation status. Taken together, we report an in vitro tissue engineered platform to monitor signaling associated with poor response to targeted inhibitors in GBM.

Potent Antineoplastic Effects of Combined PI3Kα-MNK Inhibition in Medulloblastoma

Medulloblastoma is a highly malignant pediatric brain tumor associated with poor outcome. Developing treatments that target the cancer stem cell (CSC) population in medulloblastoma are important to prevent tumor relapse and induce long-lasting clinical responses. We utilized medulloblastoma neurospheres that display CSC characteristics and found activation of the PI3K/AKT pathway in sphere-forming cells. Of all class IA PI3Ks, only the PI3Kα isoform was required for sphere formation by medulloblastoma cells. Knockdown of p110α, but not p110β or p110δ, significantly disrupted cancer stem cell frequencies as determined by extreme limiting dilution analysis (ELDA), indicating an essential role for the PI3Kα catalytic isoform in medulloblastoma CSCs. Importantly, pharmacologic inhibition of the MAPK-interacting kinase (MNK) enhanced the antineoplastic effects of targeted PI3Kα inhibition in medulloblastoma. This indicates that MNK signaling promotes survival in medulloblastoma, suggesting dual PI3Kα and MNK inhibition may provide a novel approach to target and eliminate medulloblastoma CSCs. We also observed a significant reduction in tumor formation in subcutaneous and intracranial mouse xenograft models, which further suggests that this combinatorial approach may represent an efficient therapeutic strategy for medulloblastoma. IMPLICATIONS: These findings raise the possibility of a unique therapeutic approach for medulloblastoma, involving MNK targeting to sensitize medulloblastoma CSCs to PI3Kα inhibition.

A cell type-selective apoptosis-inducing small molecule for the treatment of brain cancer

We have completed a screen of ∼10⁶ small molecules to identify compounds that induce cell death in multipotent glioblastoma multiforme (GBM) cancer stem cells (CSCs). This resulted in the identification of a hit class (RIPGBM) that was found to induce apoptosis in GBM CSCs in a cell type-selective manner. Metabolite profiling experiments led to the identification of a proapoptotic derivative of RIPGBM (cRIPGBM), which was found to be selectively formed in GBM CSCs. Mechanistic studies revealed that cRIPGBM induces apoptosis by binding to receptor-interacting protein kinase 2 (RIPK2) in a mode that results in the formation of a proapoptotic RIPK2/caspase 1 complex. In a physiologically relevant orthotopic intracranial GBM CSC tumor xenograft mouse model, RIPGBM was found to significantly inhibit in vivo tumor formation.

Glioblastoma multiforme (GBM; grade IV astrocytoma) is the most prevalent and aggressive form of primary brain cancer. A subpopulation of multipotent cells termed GBM cancer stem cells (CSCs) play a critical role in tumor initiation, tumor maintenance, metastasis, drug resistance, and recurrence following surgery. Here we report the identification of a small molecule, termed RIPGBM, from a cell-based chemical screen that selectively induces apoptosis in multiple primary patient-derived GBM CSC cultures. The cell type-dependent selectivity of this compound appears to arise at least in part from redox-dependent formation of a proapoptotic derivative, termed cRIPGBM, in GBM CSCs. cRIPGBM induces caspase 1-dependent apoptosis by binding to receptor-interacting protein kinase 2 (RIPK2) and acting as a molecular switch, which reduces the formation of a prosurvival RIPK2/TAK1 complex and increases the formation of a proapoptotic RIPK2/caspase 1 complex. In an orthotopic intracranial GBM CSC tumor xenograft mouse model, RIPGBM was found to significantly suppress tumor formation in vivo. Our chemical genetics-based approach has identified a drug candidate and a potential drug target that provide an approach to the development of treatments for this devastating disease.

Tumor treating fields increases membrane permeability in glioblastoma cells

Glioblastoma is the most common yet most lethal of primary brain cancers with a one-year post-diagnosis survival rate of 65% and a five-year survival rate of barely 5%. Recently the U.S. Food and Drug Administration approved a novel fourth approach (in addition to surgery, radiation therapy, and chemotherapy) to treating glioblastoma; namely, tumor treating fields (TTFields). TTFields involves the delivery of alternating electric fields to the tumor but its mechanisms of action are not fully understood. Current theories involve TTFields disrupting mitosis due to interference with proper mitotic spindle assembly. We show that TTFields also alters cellular membrane structure thus rendering it more permeant to chemotherapeutics. Increased membrane permeability through the imposition of TTFields was shown by several approaches. For example, increased permeability was indicated through increased bioluminescence with TTFields exposure or with the increased binding and ingress of membrane-associating reagents such as Dextran-FITC or ethidium D or with the demonstration by scanning electron microscopy of augmented number and sizes of holes on the cellular membrane. Further investigations showed that increases in bioluminescence and membrane hole production with TTFields exposure disappeared by 24 h after cessation of alternating electric fields thus demonstrating that this phenomenom is reversible. Preliminary investigations showed that TTFields did not induce membrane holes in normal human fibroblasts thus suggesting that the phenomenom was specific to cancer cells. With TTFields, we present evidence showing augmented membrane accessibility by compounds such as 5-aminolevulinic acid, a reagent used intraoperatively to delineate tumor from normal tissue in glioblastoma patients. In addition, this mechanism helps to explain previous reports of additive and synergistic effects between TTFields and other chemotherapies. These findings have implications for the design of combination therapies in glioblastoma and other cancers and may significantly alter standard of care strategies for these diseases.

YAP and MRTF-A, transcriptional co-activators of RhoA-mediated gene expression, are critical for glioblastoma tumorigenicity

The role of YAP (Yes-associated protein 1) and MRTF-A (myocardin-related transcription factor A), two transcriptional co-activators regulated downstream of GPCRs (G protein-coupled receptors) and RhoA, in the growth of glioblastoma cells and in vivo glioblastoma multiforme (GBM) tumor development was explored using human glioblastoma cell lines and tumor-initiating cells derived from patient-derived xenografts (PDX). Knockdown of these co-activators in GSC-23 PDX cells using short hairpin RNA significantly attenuated in vitro self-renewal capability assessed by limiting dilution, oncogene expression, and neurosphere formation. Orthotopic xenografts of the MRTF-A and YAP knockdown PDX cells formed significantly smaller tumors and were of lower morbidity than wild-type cells. In vitro studies used PDX and 1321N1 glioblastoma cells to examine functional responses to sphingosine 1-phosphate (S1P), a GPCR agonist that activates RhoA signaling, demonstrated that YAP signaling was required for cell migration and invasion, whereas MRTF-A was required for cell adhesion; both YAP and MRTF-A were required for proliferation. Gene expression analysis by RNA-sequencing of S1P-treated MRTF-A or YAP knockout cells identified 44 genes that were induced through RhoA and highly dependent on YAP, MRTF-A, or both. Knockdown of F3 (tissue factor (TF)), a target gene regulated selectively through YAP, blocked cell invasion and migration, whereas knockdown of HBEGF (heparin-binding epidermal growth factor-like growth factor), a gene selectively induced through MRTF-A, prevented cell adhesion in response to S1P. Proliferation was sensitive to knockdown of target genes regulated through either or both YAP and MRTF-A. Expression of TF and HBEGF was also selectively decreased in tumors from PDX cells lacking YAP or MRTF-A, indicating that these transcriptional pathways are regulated in preclinical GBM models and suggesting that their activation through GPCRs and RhoA contributes to growth and maintenance of human GBM.

PDZ-RhoGEF Is a Signaling Effector for TROY-Induced Glioblastoma Cell Invasion and Survival

Glioblastoma multiforme (GBM) is the most common type of malignant brain tumors in adults and has a dismal prognosis. The highly aggressive invasion of malignant cells into the normal brain parenchyma renders complete surgical resection of GBM tumors impossible, increases resistance to therapeutic treatment, and leads to near-universal tumor recurrence. We have previously demonstrated that TROY (TNFRSF19) plays an important role in glioblastoma cell invasion and therapeutic resistance. However, the potential downstream effectors of TROY signaling have not been fully characterized. Here, we identified PDZ-RhoGEF as a binding partner for TROY that potentiated TROY-induced nuclear factor kappa B activation which is necessary for both cell invasion and survival. In addition, PDZ-RhoGEF also interacts with Pyk2, indicating that PDZ-RhoGEF is a component of a signalsome that includes TROY and Pyk2. PDZ-RhoGEF is overexpressed in glioblastoma tumors and stimulates glioma cell invasion via Rho activation. Increased PDZ-RhoGEF expression enhanced TROY-induced glioma cell migration. Conversely, silencing PDZ-RhoGEF expression inhibited TROY-induced glioma cell migration, increased sensitivity to temozolomide treatment, and extended survival of orthotopic xenograft mice. Furthermore, depletion of RhoC or RhoA inhibited TROY- and PDZ-RhoGEF-induced cell migration. Mechanistically, increased TROY expression stimulated Rho activation, and depletion of PDZ-RhoGEF expression reduced this activation. Taken together, these data suggest that PDZ-RhoGEF plays an important role in TROY signaling and provides insights into a potential node of vulnerability to limit GBM cell invasion and decrease therapeutic resistance.

Bioluminescence imaging and two-photon microscopy guided laser ablation of GBM decreases tumor burden

Brain tumor delineation and treatment are the main concerns of neurosurgeons in neurosurgical operations. Bridging the gap between imaging/diagnosis and treatment will provide great convenience for neurosurgeons. Here, we developed an optical theranostics platform that helps to delineate the boundary and quantitatively analyze glioblastoma multiforms (GBMs) with bioluminescence imaging (BLI) to guide laser ablation, and we imaged the GBM cells with two-photon microscopy (TPM) to visualize the laser ablation zone in vivo.

Methods: Laser ablation, using the method of coupled ablated path planning with the guidance of BLI, was implemented in vivo for mouse brain tumors. The mapping relationship between semi-quantitative BLI and the laser ablation path was built through the quantitative tumor burden. The mapping was reflected through coupled ablated path planning. The BLI quantitatively and qualitatively evaluated treatment using laser ablation with the appropriate laser parameters and laser-tissue parameters. These parameters were measured after treatment. Furthermore, histopathological analysis of the brain tissue was conducted to compare the TPM images before and after laser ablation and to evaluate the results of in vivo laser ablation. The local recurrences were measured with three separate cohorts. The weights of all of the mice were measured during the experiment.

Results: Our in vivo BLI data show that the tumor cell numbers were significantly attenuated after treatment with the optical theranostics platform, and the delineation of GBM margins had clear views to guide the laser resection; the fluorescence intensity in vivo of GBMs quantitatively analyzed the rapid progression of GBMs. The laser-tissue parameters under guidance of multimodality imaging ranged between 1.0 mm and 0.1 mm. The accuracy of the laser ablation reached a submillimeter level, and the resection ratio reached more than 99% under the guidance of BLI. The histopathological sections were compared to TPM images, and the results demonstrated that these images highly coincided. The weight index and local recurrence results demonstrated that the therapeutic effect of the optical theranostics platform was significant.

Conclusion: We propose an optical multimodality imaging-guided laser ablation theranostics platform for the treatment of GBMs in an intravital mouse model. The experimental results demonstrated that the integration of multimodality imaging can precisely guide laser ablation for the treatment of GBMs. This preclinical research provides a possibility for the precision treatment of GBMs. The study also provides some theoretical support for clinical research.

Characterizing Glioblastoma Heterogeneity via Single-Cell Receptor Quantification

Dysregulation of tyrosine kinase receptor (RTK) signaling pathways play important roles in glioblastoma (GBM). However, therapies targeting these signaling pathways have not been successful, partially because of drug resistance. Increasing evidence suggests that tumor heterogeneity, more specifically, GBM-associated stem and endothelial cell heterogeneity, may contribute to drug resistance. In this perspective article, we introduce a high-throughput, quantitative approach to profile plasma membrane RTKs on single cells. First, we review the roles of RTKs in cancer. Then, we discuss the sources of cell heterogeneity in GBM, providing context to the key cells directing resistance to drugs. Finally, we present our provisionally patented qFlow cytometry approach, and report results of a "proof of concept" patient-derived xenograft GBM study.

Influence of Hyaluronic Acid Transitions in Tumor Microenvironment on Glioblastoma Malignancy and Invasive Behavior

The extracellular matrix (ECM) is critical in tumor growth and invasive potential of cancer cells. In glioblastoma tumors, some components of the native brain ECM such as hyaluronic acid (HA) have been suggested as key regulators of processes associated with poor patient outlook such as invasion and therapeutic resistance. Given the importance of cell-mediated remodeling during invasion, it is likely that the molecular weight of available HA polymer may strongly influence GBM progression. Biomaterial platforms therefore provide a unique opportunity to systematically examine the influence of the molecular weight distribution of HA on GBM cell activity. Here we report the relationship between the molecular weight of matrix-bound HA within a methacrylamidefunctionalized gelatin (GelMA) hydrogel, the invasive phenotype of a patient-derived xenograft GBM population that exhibits significant in vivo invasivity, and the local production of soluble HA during GBM cell invasion. Hyaluronic acid of different molecular weights spanning a range associated with cell-mediated remodeling (10, 60, and 500 kDa) was photopolymerized into GelMA hydrogels, with cell activity compared to GelMA only conditions (-HA). Polymerization conditions were tuned to create a homologous series of GelMA hydrogels with conserved poroelastic properties (i.e., shear modulus, Poisson's ratio, and diffusivity). GBM migration was strongly influenced by HA molecular weight; while markers associated with active remodeling of HA (hyaluronan synthase and hyaluronidase) were found to be uninfluenced. These results provide new information regarding the importance of local hyaluronic acid content on the invasive phenotype of GBM.

Next generation sequencing and molecular imaging identify EGFR mutation and amplification in a glioblastoma multiforme patient treated with an EGFR inhibitor: a case report

Epidermal growth factor receptor (EGFR) mutations and amplifications are frequently reported in glioblastoma multiforme (GBM) patients. In this case report, we utilize next-generation sequencing (NGS) and EGFR molecular imaging to investigate intratumoral heterogeneity in a male patient presenting with GBM. Further, we describe the patient's clinical course as well as outcomes of targeted EGFR therapy with erlotinib, an EGFR tyrosine kinase inhibitor (TKI). NGS demonstrated the presence of an EGFR mutation and amplification in our patient. Molecular imaging revealed a heterogeneous expression pattern of EGFR in the frontal and temporal lobes. This patient briefly responded to erlotinib therapy. However, the patient relapsed and died from progressive neurological deterioration. Partial response and acquired secondary resistance may be attributed to intratumoral heterogeneity. Combination of NGS and EGFR molecular imaging may be helpful in understanding intratumoral molecular heterogeneity and may aid in developing individualized GBM treatments, thereby improving outcomes.

EGFRvIII-Stat5 Signaling Enhances Glioblastoma Cell Migration and Survival

Glioblastoma multiforme (GBM) is the most common brain malignancies in adults. Most GBM patients succumb to the disease less than 1 year after diagnosis due to the highly invasive nature of the tumor, which prevents complete surgical resection and gives rise to tumor recurrence. The invasive phenotype also confers radioresistant and chemoresistant properties to the tumor cells; therefore, there is a critical need to develop new therapeutics that target drivers of GBM invasion. Amplification of EGFR is observed in over 50% of GBM tumors, of which half concurrently overexpress the variant EGFRvIII, and expression of both receptors confers a worse prognosis. EGFR and EGFRvIII cooperate to promote tumor progression and invasion, in part, through activation of the Stat signaling pathway. Here, it is reported that EGFRvIII activates Stat5 and GBM invasion by inducing the expression of a previously established mediator of glioma cell invasion and survival: fibroblast growth factor-inducible 14 (Fn14). EGFRvIII-mediated induction of Fn14 expression is Stat5 dependent and requires activation of Src, whereas EGFR regulation of Fn14 is dependent upon Src-MEK/ERK-Stat3 activation. Notably, treatment of EGFRvIII-expressing GBM cells with the FDA-approved Stat5 inhibitor pimozide blocked Stat5 phosphorylation, Fn14 expression, and cell migration and survival. Because EGFR inhibitors display limited therapeutic efficacy in GBM patients, the EGFRvIII-Stat5-Fn14 signaling pathway represents a node of vulnerability in the invasive GBM cell populations.Implications: Targeting critical effectors in the EGFRvIII-Stat5-Fn14 pathway may limit GBM tumor dispersion, mitigate therapeutic resistance, and increase survival. Mol Cancer Res; 16(7); 1185-95. ©2018 AACR.

Repositioning chlorpromazine for treating chemoresistant glioma through the inhibition of cytochrome c oxidase bearing the COX4-1 regulatory subunit

Patients with glioblastoma have one of the lowest overall survival rates among patients with cancer. Standard of care for patients with glioblastoma includes temozolomide and radiation therapy, yet 30% of patients do not respond to these treatments and nearly all glioblastoma tumors become resistant. Chlorpromazine is a United States Food and Drug Administration-approved phenothiazine widely used as a psychotropic in clinical practice. Recently, experimental evidence revealed the anti-proliferative activity of chlorpromazine against colon and brain tumors. Here, we used chemoresistant patient-derived glioma stem cells and chemoresistant human glioma cell lines to investigate the effects of chlorpromazine against chemoresistant glioma. Chlorpromazine selectively and significantly inhibited proliferation in chemoresistant glioma cells and glioma stem cells. Mechanistically, chlorpromazine inhibited cytochrome c oxidase (CcO, complex IV) activity from chemoresistant but not chemosensitive cells, without affecting other mitochondrial complexes. Notably, our previous studies revealed that the switch to chemoresistance in glioma cells is accompanied by a switch from the expression of CcO subunit 4 isoform 2 (COX4-2) to COX4-1. In this study, chlorpromazine induced cell cycle arrest selectively in glioma cells expressing COX4-1, and computer-simulated docking studies indicated that chlorpromazine binds more tightly to CcO expressing COX4-1 than to CcO expressing COX4-2. In orthotopic mouse brain tumor models, chlorpromazine treatment significantly increased the median overall survival of mice harboring chemoresistant tumors. These data indicate that chlorpromazine selectively inhibits the growth and proliferation of chemoresistant glioma cells expressing COX4-1. The feasibility of repositioning chlorpromazine for selectively treating chemoresistant glioma tumors should be further explored.

LPA signaling is regulated through the primary cilium: a novel target in glioblastoma

The primary cilium is a ubiquitous organelle presented on most human cells. It is a crucial signaling hub for multiple pathways including growth factor and G-protein coupled receptors. Loss of primary cilia, observed in various cancers, has been shown to affect cell proliferation. Primary cilia formation is drastically decreased in glioblastoma (GBM), however, the role of cilia in normal astrocyte or glioblastoma proliferation has not been explored. Here, we report that loss of primary cilia in human astrocytes stimulates growth rate in a lysophosphatidic acid (LPA)-dependent manner. We show that lysophosphatidic acid receptor 1 (LPAR1) is accumulated in primary cilia. LPAR1 signaling through Gα12/Gαq was previously reported to be responsible for cancer cell proliferation. We found that in ciliated cells, Gα12 and Gαq are excluded from the cilium, creating a barrier against unlimited proliferation, one of the hallmarks of cancer. Upon loss of primary cilia, LPAR1 redistributes to the plasma membrane with a concomitant increase in LPAR1 association with Gα12 and Gαq. Inhibition of LPA signaling with the small molecule compound Ki16425 in deciliated highly proliferative astrocytes or glioblastoma patient-derived cells/xenografts drastically suppresses their growth both in vitro and in vivo. Moreover, Ki16425 brain delivery via PEG-PLGA nanoparticles inhibited tumor progression in an intracranial glioblastoma PDX model. Overall, our findings establish a novel mechanism by which primary cilium restricts proliferation and indicate that loss of primary cilia is sufficient to increase mitogenic signaling, and is important for the maintenance of a highly proliferative phenotype. Clinical application of LPA inhibitors may prove beneficial to restrict glioblastoma growth and ensure local control of disease.

New therapeutic approaches for brainstem tumors: a comparison of delivery routes using nanoliposomal irinotecan in an animal model

Despite the advances in imaging, surgery and radiotherapy, the majority of patients with brainstem gliomas die within 2 years after initial diagnosis. Factors that contribute to the dismal prognosis of these patients include the infiltrative nature and anatomic location in an eloquent area of the brain, which prevents total surgical resection and the presence of the blood-brain barrier (BBB), which reduces the distribution of systemically administered agents. The development of new therapeutic approaches which can circumvent the BBB is a potential path to improve outcomes for these children. Convection-enhanced delivery (CED) and intranasal delivery (IND) are strategies that permit direct drug delivery into the central nervous system and are an alternative to intravenous injection (IV). We treated rats bearing human brainstem tumor xenografts with nanoliposomal irinotecan (CPT-11) using CED, IND, and IV. A single treatment of CED irinotecan had a similar effect on overall survival as multiple treatments by IV route. IND CPT-11 showed significantly increased survival of animals with brainstem tumors, and demonstrated the promise of this non-invasive approach of drug delivery bypassing the BBB when combined with nanoliposomal chemotherapy. Our results indicated that using CED and IND of nanoliposomal therapy increase likelihood of practical therapeutic approach for the treatment of brainstem gliomas.

A Novel Signaling Complex between TROY and EGFR Mediates Glioblastoma Cell Invasion

Glioblastoma is the most frequent primary brain tumor in adults and a highly lethal malignancy with a median survival of about 15 months. The aggressive invasion of the surrounding normal brain makes complete surgical resection impossible, increases the resistance to radiation and chemotherapy, and assures tumor recurrence. Thus, there is an urgent need to develop innovative therapeutics to target the invasive tumor cells for improved treatment outcomes of this disease. Expression of TROY (TNFRSF19), a member of the tumor necrosis factor (TNF) receptor family, increases with increasing glial tumor grade and inversely correlates with patient survival. Increased expression of TROY stimulates glioblastoma cell invasion in vitro and in vivo and increases resistance to temozolomide and radiation therapy. Conversely, silencing TROY expression inhibits glioblastoma cell invasion, increases temozolomide sensitivity, and prolongs survival in an intracranial xenograft model. Here, a novel complex is identified between TROY and EGFR, which is mediated predominantly by the cysteine-rich CRD3 domain of TROY. Glioblastoma tumors with elevated TROY expression have a statistically positive correlation with increased EGFR expression. TROY expression significantly increases the capacity of EGF to stimulate glioblastoma cell invasion, whereas depletion of TROY expression blocks EGF stimulation of glioblastoma cell invasion. Mechanistically, TROY expression modulates EGFR signaling by facilitating EGFR activation and delaying EGFR receptor internalization. Moreover, the association of EGFR with TROY increases TROY-induced NF-κB activation. These findings substantiate a critical role for the TROY-EGFR complex in regulation of glioblastoma cell invasion.Implications: The TROY-EGFR signaling complex emerges as a potential therapeutic target to inhibit glioblastoma cell invasion. Mol Cancer Res; 16(2); 322-32. ©2017 AACR.

Extracellular Hyaluronic Acid Influences the Efficacy of EGFR Tyrosine Kinase Inhibitors in a Biomaterial Model of Glioblastoma

3D biomaterial models have potential to explore the influence of the tumor microenvironment on aberrant signaling pathways and compensatory signals using patient-derived cells. Glioblastoma (GBM) tumors are highly heterogeneous, with both cell composition and extracellular matrix biophysical factors seen as key regulators of malignant phenotype and treatment outcomes. Amplification, overexpression, and mutation of the epidermal growth factor receptor (EGFR) tyrosine kinase have been identified in 50% of GBM patients. Here, hyaluronic acid (HA) decorated methacrylamide-functionalized gelatin (GelMA) hydrogels are used to examine the synergies between microenvironmental factors and a model EGFR tyrosine kinase inhibitor (TKI) using patient-derived xenograft cells. The in vitro behavior of 3 patient-derived xenografts that reflect a clinically relevant range of EGFR variants is characterized: GBM10 (EGFR, wild type), GBM12 (EGFR+), and GBM6 (EGFRvIII). GelMA hydrogels support xenograft culture; cells remain viable, active, respond to matrix-immobilized HA, and upregulate genes associated with matrix remodeling and tumor growth. Interestingly, matrix-immobilized HA alters the response of GBM cells to a model tyrosine kinase inhibitor, erlotinib. While constitutively activated EGFRvIII cells are sensitive to TKI in gelatin hydrogels, hyaluronic acid mediated adhesive signaling interacts with EGFRvIII signaling to increase cell metabolic activity, increase soluble hyaluronic acid synthesis, and modify response to erlotinib exposure.

Developing chemotherapy for diffuse pontine intrinsic gliomas (DIPG)

Prognosis of diffuse intrinsic pontine glioma (DIPG) is poor, with a median survival of 10 months after radiation. At present, chemotherapy has failed to show benefits over radiation. Advances in biotechnology have enabled the use of autopsy specimens for genomic analyses and molecular profiling of DIPG, which are quite different from those of supratentorial high grade glioma. Recently, combined treatments of cytotoxic agents with target inhibitors, based on biopsied tissue, are being examined in on-going trials. Spontaneous DIPG mice models have been recently developed that is useful for preclinical studies. Finally, the convection-enhanced delivery could be used to infuse drugs directly into the brainstem parenchyma, to which conventional systemic administration fails to achieve effective concentration. The WHO glioma classification defines a diffuse midline glioma with a H3-K27M-mutation, and we expect increase of tissue confirmation of DIPG, which will give us the biological information helping the development of a targeted therapy.

Synergistic inhibition of glioma cell proliferation by Withaferin A and tumor treating fields

Glioblastoma (GBM) is the most aggressive and lethal form of brain cancer. Standard therapies are non-specific and often of limited effectiveness; thus, efforts are underway to uncover novel, unorthodox therapies against GBM. In previous studies, we investigated Withaferin A, a steroidal lactone from Ayurvedic medicine that inhibits proliferation in cancers including GBM. Another novel approach, tumor treating fields (TTFields), is thought to disrupt mitotic spindle formation and stymie proliferation of actively dividing cells. We hypothesized that combining TTFields with Withaferin A would synergistically inhibit proliferation in glioblastoma. Human glioblastoma cells (GBM2, GBM39, U87-MG) and human breast adenocarcinoma cells (MDA-MB-231) were isolated from primary tumors. The glioma cell lines were genetically engineered to express firefly luciferase. Proliferative potential was assessed either by bioluminescence imaging or cell counting via hemocytometer. TTFields (4 V/cm) significantly inhibited growth of the four cancer cell lines tested (n = 3 experiments per time point, four measurements per sample, p < 0.02 at least; 2-way ANOVA, control vs. treatment). The combination of Withaferin A (10-100 nM) with TTFields significantly inhibited the growth of the glioma cells to a degree beyond that of Withaferin A or TTFields alone. The interaction of the Withaferin A and TTFields on glioma cells was found to be synergistic in nature (p < 0.01, n = 3 experiments). These findings were validated by both bioluminescence and hemocytometric measurements. The combination of Withaferin A with TTFields represents a novel approach to treat GBM in a manner that is likely better than either treatment alone and that is synergistic.

Spatially graded hydrogels for preclinical testing of glioblastoma anticancer therapeutics

While preclinical models such as orthotopic tumors generated in mice from patient-derived specimens are widely used to predict sensitivity or therapeutic interventions for cancer, such xenografts can be slow, require extensive infrastructure, and can make in situ assessment difficult. Such concerns are heightened in highly aggressive cancers, such as glioblastoma (GBM), that display genetic diversity and short mean survival. Biomimetic biomaterial technologies offer an approach to create ex vivo models that reflect biophysical features of the tumor microenvironment (TME). We describe a microfluidic templating approach to generate spatially graded hydrogels containing patient-derived GBM cells to explore drug efficacy and resistance mechanisms.

Heterogeneous Binding and Central Nervous System Distribution of the Multitargeted Kinase Inhibitor Ponatinib Restrict Orthotopic Efficacy in a Patient-Derived Xenograft Model of Glioblastoma

This study investigated how differences in drug distribution and free fraction at different tumor and tissue sites influence the efficacy of the multikinase inhibitor ponatinib in a patient-derived xenograft model of glioblastoma (GBM). Efficacy studies in GBM6 flank (heterotopic) and intracranial (orthotopic) models showed that ponatinib is effective in the flank but not in the intracranial model, despite a relatively high brain-to-plasma ratio. In vitro binding studies indicated that flank tumor had a higher free (unbound) drug fraction than normal brain. The total and free drug concentrations, along with the tissue-to-plasma ratio (Kp) and its unbound derivative (Kp,uu), were consistently higher in the flank tumor than the normal brain at 1 and 6 hours after a single dose in GBM6 flank xenografts. In the orthotopic xenografts, the intracranial tumor core displayed higher Kp and Kp,uu values compared with the brain-around-tumor (BAT). The free fractions and the total drug concentrations, hence free drug concentrations, were consistently higher in the core than in the BAT at 1 and 6 hours postdose. The delivery disadvantages in the brain and BAT were further evidenced by the low total drug concentrations in these areas that did not consistently exceed the in vitro cytotoxic concentration (IC₅₀). Taken together, the regional differences in free drug exposure across the intracranial tumor may be responsible for compromising efficacy of ponatinib in orthotopic GBM6.

Anti-GD2-ch14.18/CHO coated nanoparticles mediate glioblastoma (GBM)-specific delivery of the aromatase inhibitor, Letrozole, reducing proliferation, migration and chemoresistance in patient-derived GBM tumor cells

Aromatase is a critical enzyme in the irreversible conversion of androgens to oestrogens, with inhibition used clinically in hormone-dependent malignancies. We tested the hypothesis that targeted aromatase inhibition in an aggressive brain cancer called glioblastoma (GBM) may represent a new treatment strategy. In this study, aromatase inhibition was achieved using third generation inhibitor, Letrozole, encapsulated within the core of biodegradable poly lactic-co-glycolic acid (PLGA) nanoparticles (NPs). PLGA-NPs were conjugated to human/mouse chimeric anti-GD2 antibody ch14.18/CHO, enabling specific targeting of GD2-positive GBM cells. Treatment of primary and recurrent patient-derived GBM cells with free-Letrozole (0.1 μM) led to significant decrease in cell proliferation and migration; in addition to reduced spheroid formation. Anti-GD2-ch14.18/CHO-NPs displayed specific targeting of GBM cells in colorectal-glioblastoma co-culture, with subsequent reduction in GBM cell numbers when treated with anti-GD2-ch14.18-PLGA-Let-NPs in combination with temozolomide. As miR-191 is an estrogen responsive microRNA, its expression, fluctuation and role in Letrozole treated GBM cells was evaluated, where treatment with premiR-191 was capable of rescuing the reduced proliferative phenotype induced by aromatase inhibitor. The repurposing and targeted delivery of Letrozole for the treatment of GBM, with the potential role of miR-191 identified, provides novel avenues for target assessment in this aggressive brain cancer.

Identification of aurintricarboxylic acid as a selective inhibitor of the TWEAK-Fn14 signaling pathway in glioblastoma cells

The survival of patients diagnosed with glioblastoma (GBM), the most deadly form of brain cancer, is compromised by the proclivity for local invasion into the surrounding normal brain, which prevents complete surgical resection and contributes to therapeutic resistance. Tumor necrosis factor-like weak inducer of apoptosis (TWEAK), a member of the tumor necrosis factor (TNF) superfamily, can stimulate glioma cell invasion and survival via binding to fibroblast growth factor-inducible 14 (Fn14) and subsequent activation of the transcription factor NF-κB. To discover small molecule inhibitors that disrupt the TWEAK-Fn14 signaling axis, we utilized a cell-based drug-screening assay using HEK293 cells engineered to express both Fn14 and a NF-κB-driven firefly luciferase reporter protein. Focusing on the LOPAC1280 library of 1280 pharmacologically active compounds, we identified aurintricarboxylic acid (ATA) as an agent that suppressed TWEAK-Fn14-NF-κB dependent signaling, but not TNFα-TNFR-NF-κB driven signaling. We demonstrated that ATA repressed TWEAK-induced glioma cell chemotactic migration and invasion via inhibition of Rac1 activation but had no effect on cell viability or Fn14 expression. In addition, ATA treatment enhanced glioma cell sensitivity to both the chemotherapeutic agent temozolomide (TMZ) and radiation-induced cell death. In summary, this work reports a repurposed use of a small molecule inhibitor that targets the TWEAK-Fn14 signaling axis, which could potentially be developed as a new therapeutic agent for treatment of GBM patients.

Transgenic Expression of IL15 Improves Antiglioma Activity of IL13Rα2-CAR T Cells but Results in Antigen Loss Variants

Glioblastoma (GBM) is the most aggressive primary brain tumor in adults and is virtually incurable with conventional therapies. Immunotherapy with T cells expressing GBM-specific chimeric antigen receptors (CAR) is an attractive approach to improve outcomes. Although CAR T cells targeting GBM antigens, such as IL13 receptor subunit α2 (IL13Rα2), HER2, and EGFR variant III (EGFRvIII), have had antitumor activity in preclinical models, early-phase clinical testing has demonstrated limited antiglioma activity. Transgenic expression of IL15 is an appealing strategy to enhance CAR T-cell effector function. We tested this approach in our IL13Rα2-positive glioma model in which limited IL13Rα2-CAR T-cell persistence results in recurrence of antigen-positive gliomas. T cells were genetically modified with retroviral vectors encoding IL13Rα2-CARs or IL15 (IL13Rα2-CAR.IL15 T cells). IL13Rα2-CAR.IL15 T cells recognized glioma cells in an antigen-dependent fashion, had greater proliferative capacity, and produced more cytokines after repeated stimulations in comparison with IL13Rα2-CAR T cells. No autonomous IL13Rα2-CAR.IL15 T-cell proliferation was observed; however, IL15 expression increased IL13Rα2-CAR T-cell viability in the absence of exogenous cytokines or antigen. In vivo, IL13Rα2-CAR.IL15 T cells persisted longer and had greater antiglioma activity than IL13Rα2-CAR T cells, resulting in a survival advantage. Gliomas recurring after 40 days after T-cell injection had downregulated IL13Rα2 expression, indicating that antigen loss variants occur in the setting of improved T-cell persistence. Thus, CAR T cells for GBM should not only be genetically modified to improve their proliferation and persistence, but also to target multiple antigens.Summary: Glioblastoma responds imperfectly to immunotherapy. Transgenic expression of IL15 in T cells expressing CARs improved their proliferative capacity, persistence, and cytokine production. The emergence of antigen loss variants highlights the need to target multiple tumor antigens. Cancer Immunol Res; 5(7); 571-81. ©2017 AACR.

Integrating the glioblastoma microenvironment into engineered experimental models

Glioblastoma (GBM) is the most lethal cancer originating in the brain. Its high mortality rate has been attributed to therapeutic resistance and rapid, diffuse invasion - both of which are strongly influenced by the unique microenvironment. Thus, there is a need to develop new models that mimic individual microenvironmental features and are able to provide clinically relevant data. Current understanding of the effects of the microenvironment on GBM progression, established experimental models of GBM and recent developments using bioengineered microenvironments as ex vivo experimental platforms that mimic the biochemical and physical properties of GBM tumors are discussed.

An LXR-Cholesterol Axis Creates a Metabolic Co-Dependency for Brain Cancers

Small-molecule inhibitors targeting growth factor receptors have failed to show efficacy for brain cancers, potentially due to their inability to achieve sufficient drug levels in the CNS. Targeting non-oncogene tumor co-dependencies provides an alternative approach, particularly if drugs with high brain penetration can be identified. Here we demonstrate that the highly lethal brain cancer glioblastoma (GBM) is remarkably dependent on cholesterol for survival, rendering these tumors sensitive to Liver X receptor (LXR) agonist-dependent cell death. We show that LXR-623, a clinically viable, highly brain-penetrant LXRα-partial/LXRβ-full agonist selectively kills GBM cells in an LXRβ- and cholesterol-dependent fashion, causing tumor regression and prolonged survival in mouse models. Thus, a metabolic co-dependency provides a pharmacological means to kill growth factor-activated cancers in the CNS.

Large-scale assessment of the gliomasphere model system

BACKGROUND

Gliomasphere cultures are widely utilized for the study of glioblastoma (GBM). However, this model system is not well characterized, and the utility of current classification methods is not clear.

METHODS

We used 71 gliomasphere cultures from 68 individuals. Using gene expression-based classification, we performed unsupervised clustering and associated gene expression with gliomasphere phenotypes and patient survival.

RESULTS

Some aspects of the gene expression-based classification method were robust because the gliomasphere cultures retained their classification over many passages, and IDH1 mutant gliomaspheres were all proneural. While gene expression of a subset of gliomasphere cultures was more like the parent tumor than any other tumor, gliomaspheres did not always harbor the same classification as their parent tumor. Classification was not associated with whether a sphere culture was derived from primary or recurrent GBM or associated with the presence of EGFR amplification or rearrangement. Unsupervised clustering of gliomasphere gene expression distinguished 2 general categories (mesenchymal and nonmesenchymal), while multidimensional scaling distinguished 3 main groups and a fourth minor group. Unbiased approaches revealed that PI3Kinase, protein kinase A, mTOR, ERK, Integrin, and beta-catenin pathways were associated with in vitro measures of proliferation and sphere formation. Associating gene expression with gliomasphere phenotypes and patient outcome, we identified genes not previously associated with GBM: PTGR1, which suppresses proliferation, and EFEMP2 and LGALS8, which promote cell proliferation.

CONCLUSIONS

This comprehensive assessment reveals advantages and limitations of using gliomaspheres to model GBM biology, and provides a novel strategy for selecting genes for future study.

Inhibition of DNA damage repair by the CDK4/6 inhibitor palbociclib delays irradiated intracranial atypical teratoid rhabdoid tumor and glioblastoma xenograft regrowth

BACKGROUND

Radiation therapy is the most commonly used postsurgical treatment for primary malignant brain tumors. Consequently, investigating the efficacy of chemotherapeutics combined with radiation for treating malignant brain tumors is of high clinical relevance. In this study, we examined the cyclin-dependent kinase 4/6 inhibitor palbociclib, when used in combination with radiation for treating human atypical teratoid rhabdoid tumor (ATRT) as well as glioblastoma (GBM).

METHODS

Evaluation of treatment antitumor activity in vitro was based upon results from cell proliferation assays, clonogenicity assays, flow cytometry, and immunocytochemistry for DNA double-strand break repair. Interpretation of treatment antitumor activity in vivo was based upon bioluminescence imaging, animal subject survival analysis, and staining of tumor sections for markers of proliferation and apoptosis.

RESULTS

For each of the retinoblastoma protein (RB)-proficient tumor models examined (2 ATRTs and 2 GBMs), one or more of the combination therapy regimens significantly (P < .05) outperformed both monotherapies with respect to animal subject survival benefit. Among the combination therapy regimens, concurrent palbociclib and radiation treatment and palbociclib treatment following radiation consistently outperformed the sequence in which radiation followed palbociclib treatment. In vitro investigation revealed that the concurrent use of palbociclib with radiation, as well as palbociclib following radiation, inhibited DNA double-strand break repair and promoted increased tumor cell apoptosis.

CONCLUSIONS

Our results support further investigation and possible clinical translation of palbociclib as an adjuvant to radiation therapy for patients with malignant brain tumors that retain RB expression.

Network Modeling Identifies Patient-specific Pathways in Glioblastoma

Glioblastoma is the most aggressive type of malignant human brain tumor. Molecular profiling experiments have revealed that these tumors are extremely heterogeneous. This heterogeneity is one of the principal challenges for developing targeted therapies. We hypothesize that despite the diverse molecular profiles, it might still be possible to identify common signaling changes that could be targeted in some or all tumors. Using a network modeling approach, we reconstruct the altered signaling pathways from tumor-specific phosphoproteomic data and known protein-protein interactions. We then develop a network-based strategy for identifying tumor specific proteins and pathways that were predicted by the models but not directly observed in the experiments. Among these hidden targets, we show that the ERK activator kinase1 (MEK1) displays increased phosphorylation in all tumors. By contrast, protein numb homolog (NUMB) is present only in the subset of the tumors that are the most invasive. Additionally, increased S100A4 is associated with only one of the tumors. Overall, our results demonstrate that despite the heterogeneity of the proteomic data, network models can identify common or tumor specific pathway-level changes. These results represent an important proof of principle that can improve the target selection process for tumor specific treatments.