Sarkaria, Jann N.

Abstract Background Glioblastoma (GBM) represents the most common and aggressive central nervous system malignancy where overall survival is a dismal 14.6 months despite an aggressive standard of care treatment regimen that includes maximally safe surgical resection, radiotherapy, and temozolomide. It has recently been established that GBM tumors have increased transferrin receptor expression and iron content which corresponds with worse patient prognosis. This has led to the hypothesis that iron metabolism is a viable therapeutic target. An emergent therapeutic strategy to target GBM iron metabolism is gallium maltolate (GaM), which is an orally bioavailable form of Ga3+ that functions as a redox inactive iron mimic to disrupt iron metabolism. As mitochondrial iron metabolism serves as a central connection point between iron and DNA metabolism, the goal of this study was to determine if GaM could disrupt this system. Methods The effects of GaM on GBM cells were interrogated using conventional techniques including colony formation assays to assess clonogenicity, alkaline comet assays to evaluate DNA damage induction, and MitoFerro Green analysis to evaluate mitochondrial iron content. The effects of GaM on tumor growth in vivo were evaluated using a subcutaneous flank xenograft model system to determine the induction of DNA damage and an orthtopic model system to evaluate the combinatorial effects of GaM, radiation, and temozolomide on murine survival. Results This study uncovered that maintenance of high mitochondrial iron content corresponds with increased proliferative capacity in GBM cells. This study also shows that GaM can deplete mitochondrial iron to induce DNA damage both in vitro and in a subcutaneous xenograft model. Furthermore, GaM enhances the efficacy of radiation and temozolomide when delivered concomitant and adjuvantly in an orthotopic GBM model system. Conclusion These results suggest that GaM warrants further consideration for use in combination with standard of care GBM therapy.

ABSTRACT Extracellular vesicles (EVs) are increasingly recognized as mediators of intercellular communication in cancer. We previously demonstrated that re‐expression of the leucine‐rich domain (LRD) of neurofibromin (NF1) suppresses glioblastoma (GBM) invasion and limits microglia/macrophage infiltration into the tumor microenvironment (TME). Given the central role of tumor‐associated microglia/macrophages (TAMs) in GBM progression, we investigated whether NF1‐LRD‐containing EVs (NF1‐LRD‐EVs) could modulate TAM function and remodel the TME. Our results showed that NF1‐LRD‐EVs attenuated microglia and macrophage recruitment in migration assays, consistent with reduced microglia/macrophage recruitment observed in vivo . In parallel, treatment with NF1‐LRD‐EVs enhanced phagocytic activity of both microglia and iPSC‐derived macrophages, accompanied by induction of pro‐inflammatory cytokines TNF‐α, IL‐6, and IL‐1β, and downregulation of immunosuppressive mediators such as Arginase‐1 and IL‐10. Mechanistically, NF1‐LRD‐EVs induced ADAM17‐associated inflammatory signaling, accompanied by NF‐κB activation. Pharmacological inhibition of ADAM17 reduced TNF‐α release and attenuated NF‐κB activation, supporting a role for ADAM17‐dependent signaling in amplifying this inflammatory response. Together, these findings show that NF1‐LRD‐EVs reprogram TAMs toward a pro‐inflammatory phenotype and modulate the GBM immune microenvironment. These results provide a framework for understanding NF1‐LRD‐EV‐mediated immune regulation and support further investigation of EV‐mediated immune modulation of the TME.

Abstract Background Meningiomas lack effective therapies for recurrent or aggressive disease. NF2 inactivation, commonly in meningioma, may sensitize tumors to FAK inhibition and interact with MAPK signaling. This study investigated the therapeutic activity of defactinib (FAK inhibitor) and avutometinib (RAF/MEK inhibitor) alone and in combination in preclinical meningioma models. Methods MAPK-altered meningioma cell lines, IOMM-Lee (NF2 wild-type, BRAF p.V600E) and CH157-MN (NF2 mutant, NRAS p.Q61K), BenMen-1 (NF2 mutant, MAPK wild-type), and three patient-derived NF2 mutant cell lines were cultured in matrigel and treated with defactinib and avutometinib in 3D cell viability assays. In vivo, flank and intracranial xenograft models of IOMM-Lee and CH157-MN were treated with VS-4718 (FAK inhibitor, superior pharmokinetics in mice), avutometinib, or combination. Tumor growth, survival, and pharmacokinetic/pharmacodynamic properties were assessed. Results In vitro, combination therapy showed synergistic or additive effects in CH157-MN and IOMM-Lee cells, respectively. Defactinib alone demonstrated activity in NF2-mutant patient-derived and BenMen-1 cells, while avutometinib did not. In vivo, avutometinib monotherapy suppressed tumor growth and extended survival in both flank and intracranial xenograft models, with evidence of favorable pharmacokinetic properties and target pathway inhibition in intracranial tumors. Combination therapy provided enhanced and sustained control of flank CH157-MN meningioma compared to avutometinib alone but did not significantly improve survival over avutometinib alone in intracranial models. Conclusions Avutometinib demonstrated robust anti-tumor effects in flank and intracranial models of MAPK-altered meningioma. Combination benefits were context dependent. Defactinib activity in NF2-mutant patient-derived cells without targetable MAPK-kinase alterations highlights the importance of genomic biomarkers to guide personalized strategies.

Temozolomide (TMZ) remains the cornerstone of chemotherapeutic agent for glioblastoma (GBM), yet intrinsic and acquired resistance severely limits its clinical benefit. While O6-methylguanine-DNA methyltransferase (MGMT)–mediated repair of TMZ-induced O6-methylguanine (O6-meG) lesions has been extensively studied, the DNA mismatch repair (MMR) pathway is increasingly recognized as a key determinant of TMZ cytotoxicity. Canonical MMR, mediated by MutSα (MSH2–MSH6) and MutLα (MLH1–PMS2) complexes, recognizes O6-meG: thymine mispairs generated during replication and initiates futile repair cycles that culminate in replication stress, replication fork collapse, and apoptotic signaling; intact canonical MMR is, therefore, required for TMZ-induced cell death. Disruption of canonical MMR, frequently via acquired MSH6 mutations, confers TMZ tolerance and drives hypermutated recurrent GBM. Beyond mismatch correction, MMR proteins perform non-canonical functions in DNA damage signaling, replication stress responses, transcriptional regulation, chromatin dynamics, and immune modulation. These activities may shift the outcome from cytotoxic futile repair toward replication stress adaptation, Translesion synthesis (TLS)-mediated lesion tolerance, immune remodeling, and therapeutic resistance. Notably, partial attenuation or functional diversion of MMR may decouple lesion recognition from cytotoxic signaling, enabling TLS-mediated lesion tolerance without complete loss of MMR activity. This review integrates current insights into canonical and non-canonical MMR functions in GBM, defines their distinct contributions to TMZ sensitivity and resistance, and highlights therapeutic opportunities to exploit MMR-associated dependencies, including synthetic lethal strategies and immunotherapeutic vulnerabilities linked to MMR deficiency-driven hypermutation.

Abstract Glioblastoma (GBM) remains a deadly cancer driven in part by invasion of tumor cells into the brain. Transcriptomic analyses have identified distinct molecular subtypes, but mechanistic differences that account for clinical differences are not clear. In this study, we show that, as predicted by the motor-clutch model of cell migration, mesenchymal glioma cells are more spread, generate larger traction forces, and migrate faster in brain tissue compared with proneural cells. Despite their rapid migration and comparable proliferation rates in vitro, mice with mesenchymal tumors survive longer than those with proneural tumors. This improved survival correlated with an immune response in mesenchymal tumors, including T cell–mediated. Consistently, inducing mesenchymal tumors in immunodeficient mice resulted in shorter survival, supporting a protective immune role in mesenchymal tumors. Thus, mesenchymal tumors have aggressive migration but are immunologically “hot,” which suppresses net proliferation. These two features counteract each other and may explain the lack of a strong survival difference between subtypes clinically, while also opening up new opportunities for subtype-specific therapies. Significance: This study highlights new mechanical and immunologic insights into GBM molecular subtypes using an integrated modeling–genome engineering strategy, which can potentially facilitate GBM subtype-specific therapeutic strategies.

ABSTRACT Glioblastoma (GBM) is a highly aggressive brain tumor with a five-year survival rate of less than 5%. The current standard of care established 20 years ago includes maximal surgical resection and administration of alkylating agent temozolomide (TMZ). GBM is highly invasive, and GBM cells that evade surgical resection can become resistant to TMZ and develop new aggressive secondary tumors. Post-relapse there are few treatment options available to patients. Tissue engineering approaches suggest the opportunity to develop in vitro models of the GBM tumor microenvironment that may accelerate the discovery of novel therapies for GBM. Here, we report the adaptation of hydrogel microdroplets (microgels) to encapsulate GBM cells in a tailorable 3D matrix to assess patters of growth and to screen TMZ drug response using patient-derived xenograft (PDX) specimens. We exploit a unique aspect of the microgel system to account for the cellular heterogeneity within the tumor microenvironment (TME). We combine cell-laden microgels generated from TMZ-resistant and TMZ responsive variants of the same PDX specimens to create heterogeneous populations with varying levels of drug sensitivity. We demonstrate a range of drug resistance phenotypes as a function of the ratio of TMZ-responsive to resistance cells and identify the population required for TMZ-resistance to overtake take the response. We then investigate the influence of tumor mimetic shifts in hyaluronic acid bioavailability and hypoxia on patterns of TMZ resistance. We show exposure to matrix-bound hyaluronan increases TMZ resistance and the glioma stem cell population in both cell variants. Lastly, we report an increase in TMZ sensitivity but divergent changes in the GSC subfraction for TMZ resistant vs responsive GBM in the presence of hypoxia. Together, we demonstrate the versatility of cell-laden microgel approach to replicate heterogenous tumor populations, model shifts in the tumor microenvironment, and rapidly screen therapeutic response.

Glioblastoma (GBM) is a devastating cancer with a dismal prognosis. Current treatment includes temozolomide (TMZ), which is more effective in about 50% of GBMs that have O 6 - methylguanine DNA methyltransferase ( MGMT ) promoter methylation. MGMT is a DNA repair protein that reverses TMZ-induced DNA damage. EGFR is a prime oncogene in GBM. Here, we report that EGFR inhibition induced the down-regulation of MGMT in GBM cells, revealing a previously unidentified link between EGFR signaling and response to TMZ. EGFR inhibition led to activation of two transcription factors, activator protein-1 (AP-1), which repressed MGMT transcription, and nuclear factor κB (NF-κB), which up-regulated MGMT transcription. EGFR inhibition also induced AP-1–mediated transcription of miR-616. miR-616 inhibited both MGMT translation and NF-κB activation. Thus, the overall effect of EGFR inhibition was down-regulation of MGMT expression. In addition, we provided an explanation for the prior failure of clinical trials that used concomitant EGFR tyrosine kinase inhibitors (TKIs) and TMZ. TMZ up-regulated MGMT, and concomitant treatment with EGFR TKIs and TMZ failed to down-regulate MGMT. However, pretreatment with EGFR TKIs followed by TMZ efficiently down-regulated MGMT and enhanced TMZ sensitivity in experimental models. Posttreatment tumor tissues from two clinical trials were used to validate these findings. We demonstrated that EGFR inhibitors induced down-regulation of MGMT in posttreatment resected tumor tissues from patients with GBM and the failure of EGFR inhibition to down-regulate MGMT if TMZ was used concomitantly. These data support using EGFR TKIs before TMZ treatment as a therapeutic approach in MGMT unmethylated GBM.

Our research uncovers a role for ATR in responding to ECM stiffness and promoting epithelial-to-mesenchymal transition (EMT) and metastasis. ATR, when deubiquitinated and upregulated by USP21 under enhanced ECM stiffness conditions, phosphorylates the nuclear protein SUN2, which promotes β-catenin nuclear translocation and EMT. ATM-mediated EMT promotes polymorphonuclear myeloid-derived suppressor cell recruitment and inhibits CD103 + dendritic cells, fostering an immunosuppressive tumor milieu. ATR inhibition disrupts this malignant cascade by promoting mesenchymal-to-epithelial transition to enhance antitumor immunity and mitigate metastases. Consistently, circulating HLA-DR + dendritic cells were also enhanced following treatment with the ATR inhibitor berzosertib in patients with therapeutically resistant early-stage breast cancer. Our data suggest that ATR-targeted therapy may be optimized by considering both DNA damage–dependent and EMT-inducing effects of ATR ATR promotes metastasis and immunosuppression through EMT process

ABSTRACT Truncating mutations in the tumor suppressor STAG2 , which encodes a component of the cohesin complex, are prevalent across diverse human cancers. Here, we report that acute reconstitution of physiological STAG2 levels in STAG2 -mutant human glioblastoma multiforme cancer cells triggers a rapid reduction in the size of chromatin loops genome-wide. Despite this global change in chromatin loop size, early transcriptional responses to STAG2 restoration are limited to a small number of genes, most of which are induced by STAG2 reconstitution. Notably, the growth-suppressor EFEMP1 (Fibulin-3), a secreted glycoprotein that functions as an extracellular matrix-associated inhibitor of glioblastoma growth and invasion, was the only gene consistently induced across all experimental models. The most robust and conserved STAG2-induced genes all reside within intense chromatin loops whose anchors and overall intensity did not appear to change in response to STAG2 reconstitution. These findings suggest that inactivating mutations of STAG2 promote neoplastic transformation by alleviating a restriction on chromatin loop size, allowing for an expanded range of chromatin interactions that disrupts the maintenance of a tumor-suppressive transcriptome.

Abstract Background Upstream regulators of the homologous recombination (HR) repair pathway are promising targets for overcoming temozolomide (TMZ) resistance. We investigated whether pharmacologic inhibition of Retinoblastoma Binding Protein 4 (RBBP4)/p300-mediated HR activity by CCS1477 or NEO2734 sensitizes glioblastoma (GBM) to TMZ. Methods Lentiviral-mediated shRNA was used to silence RBBP4 and EP300 (p300). A fluorescence-based multiplex flow-cytometric host cell reactivation assay was used to measure DNA repair activity, while TMZ-induced double-strand breaks (DSBs) were assessed using a comet assay and γ-H2AX foci formation. Cytotoxicity was monitored using an Incucyte device, and survival analysis was performed to evaluate efficacy in orthotopic tumor models. Drug distribution was assessed using liquid chromatography-mass spectrometry (LC-MS/MS) and acetylation of lysine 27 of histone H3 (H3K27Ac) immunofluorescence for target inhibition. Promoter occupancy was determined using chromatin immunoprecipitation. Results GBM patient-derived xenograft tumors with high RBBP4 expression showed elevated levels of 6 HR genes (RAD51, RAD50, BRCA1, BARD1, BRIP1, and FIGNL1), with RAD51 and BRIP1 correlating strongly with RBBP4 and p300. Silencing RBBP4 or p300 decreased HR and microhomologous-mediated end joining (MMEJ) activity and delayed repair of TMZ-induced DSBs. CCS1477 and NEO2734 suppressed RAD51 and MYC in a concentration-dependent manner, prolonged γ-H2AX foci, and enhanced TMZ sensitivity. Both compounds inhibited H3K27Ac and were detectable in orthotopic tumors by LC-MS/MS and significantly extended survival alone and in combination with TMZ. Conclusion These findings suggest that the RBBP4/p300-axis is a key regulator of HR-mediated repair of TMZ-induced DSBs, and inhibition by either CCS1477 or NEO2734 may be beneficial as monotherapy, but further studies are needed to determine the benefit of combining these agents with TMZ.