Single-cell analysis of 5-aminolevulinic acid intraoperative labeling specificity for glioblastoma

OBJECTIVE

Glioblastoma (GBM) is the most common and aggressive malignant primary brain tumor, and resection is a key part of the standard of care. In fluorescence-guided surgery (FGS), fluorophores differentiate tumor tissue from surrounding normal brain. The heme synthesis pathway converts 5-aminolevulinic acid (5-ALA), a fluorogenic substrate used for FGS, to fluorescent protoporphyrin IX (PpIX). The resulting fluorescence is believed to be specific to neoplastic glioma cells, but this specificity has not been examined at a single-cell level. The objective of this study was to determine the specificity with which 5-ALA labels the diversity of cell types in GBM.

METHODS

The authors performed single-cell optical phenotyping and expression sequencing-version 2 (SCOPE-seq2), a paired single-cell imaging and RNA sequencing method, of individual cells on human GBM surgical specimens with macroscopically visible PpIX fluorescence from patients who received 5-ALA prior to surgery. SCOPE-seq2 allowed the authors to simultaneously image PpIX fluorescence and unambiguously identify neoplastic cells from single-cell RNA sequencing. Experiments were also conducted in cell culture and co-culture models of glioma and in acute slice cultures from a mouse glioma model to investigate cell- and tissue-specific uptake and secretion of 5-ALA and PpIX.

RESULTS

SCOPE-seq2 analysis of human GBM surgical specimens revealed that 5-ALA treatment resulted in labeling that was not specific to neoplastic glioma cells. The cell culture further demonstrated that nonneoplastic cells could be labeled by 5-ALA directly or by PpIX secreted from surrounding neoplastic cells. Acute slice cultures from mouse glioma models showed that 5-ALA preferentially labeled GBM tumor tissue over nonneoplastic brain tissue with significant labeling in the tumor margins, and that this contrast was not due to blood-brain barrier disruption.

CONCLUSIONS

Together, these findings support the use of 5-ALA as an indicator of GBM tissue but question the main advantage of 5-ALA for specific intracellular labeling of neoplastic glioma cells in FGS. Further studies are needed to systematically compare the performance of 5-ALA to that of potential alternatives for FGS.

Biologically-informed deep neural networks provide quantitative assessment of intratumoral heterogeneity in post-treatment glioblastoma

Intratumoral heterogeneity poses a significant challenge to the diagnosis and treatment of glioblastoma (GBM). This heterogeneity is further exacerbated during GBM recurrence, as treatment-induced reactive changes produce additional intratumoral heterogeneity that is ambiguous to differentiate on clinical imaging. There is an urgent need to develop non-invasive approaches to map the heterogeneous landscape of histopathological alterations throughout the entire lesion for each patient. We propose to predictively fuse Magnetic Resonance Imaging (MRI) with the underlying intratumoral heterogeneity in recurrent GBM using machine learning (ML) by leveraging image-localized biopsies with their associated locoregional MRI features. To this end, we develop BioNet, a biologically-informed neural network model, to predict regional distributions of three tissue-specific gene modules: proliferating tumor, reactive/inflammatory cells, and infiltrated brain tissue. BioNet offers valuable insights into the integration of multiple implicit and qualitative biological domain knowledge, which are challenging to describe in mathematical formulations. BioNet performs significantly better than a range of existing methods on cross-validation and blind test datasets. Voxel-level prediction maps of the gene modules by BioNet help reveal intratumoral heterogeneity, which can improve surgical targeting of confirmatory biopsies and evaluation of neuro-oncological treatment effectiveness. The non-invasive nature of the approach can potentially facilitate regular monitoring of the gene modules over time, and making timely therapeutic adjustment. These results also highlight the emerging role of ML in precision medicine.

OGDH and Bcl-xL loss causes synthetic lethality in glioblastoma

Glioblastoma (GBM) remains an incurable disease, requiring more effective therapies. Through interrogation of publicly available CRISPR and RNAi library screens, we identified the α-ketoglutarate dehydrogenase (OGDH) gene, which encodes an enzyme that is part of the tricarboxylic acid (TCA) cycle, as essential for GBM growth. Moreover, by combining transcriptome and metabolite screening analyses, we discovered that loss of function of OGDH by the clinically validated drug compound CPI-613 was synthetically lethal with Bcl-xL inhibition (genetically and through the clinically validated BH3 mimetic, ABT263) in patient-derived xenografts as well neurosphere GBM cultures. CPI-613-mediated energy deprivation drove an integrated stress response with an upregulation of the BH3-only domain protein, Noxa, in an ATF4-dependent manner, as demonstrated by genetic loss-of-function experiments. Consistently, silencing of Noxa attenuated cell death induced by CPI-613 in model systems of GBM. In patient-derived xenograft models of GBM in mice, the combination treatment of ABT263 and CPI-613 suppressed tumor growth and extended animal survival more potently than each compound on its own. Therefore, combined inhibition of Bcl-xL along with disruption of the TCA cycle might be a treatment strategy for GBM.

A pharmacological toolkit for human microglia identifies Topoisomerase I inhibitors as immunomodulators for Alzheimer's disease

While efforts to identify microglial subtypes have recently accelerated, the relation of transcriptomically defined states to function has been largely limited to in silico annotations. Here, we characterize a set of pharmacological compounds that have been proposed to polarize human microglia towards two distinct states - one enriched for AD and MS genes and another characterized by increased expression of antigen presentation genes. Using different model systems including HMC3 cells, iPSC-derived microglia and cerebral organoids, we characterize the effect of these compounds in mimicking human microglial subtypes in vitro. We show that the Topoisomerase I inhibitor Camptothecin induces a CD74high/MHChigh microglial subtype which is specialized in amyloid beta phagocytosis. Camptothecin suppressed amyloid toxicity and restored microglia back to their homeostatic state in a zebrafish amyloid model. Our work provides avenues to recapitulate human microglial subtypes in vitro, enabling functional characterization and providing a foundation for modulating human microglia in vivo.

Glioma-Induced Alterations in Excitatory Neurons are Reversed by mTOR Inhibition

Gliomas are highly aggressive brain tumors characterized by poor prognosis and composed of diffusely infiltrating tumor cells that intermingle with non-neoplastic cells in the tumor microenvironment, including neurons. Neurons are increasingly appreciated as important reactive components of the glioma microenvironment, due to their role in causing hallmark glioma symptoms, such as cognitive deficits and seizures, as well as their potential ability to drive glioma progression. Separately, mTOR signaling has been shown to have pleiotropic effects in the brain tumor microenvironment, including regulation of neuronal hyperexcitability. However, the local cellular-level effects of mTOR inhibition on glioma-induced neuronal alterations are not well understood. Here we employed neuron-specific profiling of ribosome-bound mRNA via 'RiboTag,' morphometric analysis of dendritic spines, and in vivo calcium imaging, along with pharmacological mTOR inhibition to investigate the impact of glioma burden and mTOR inhibition on these neuronal alterations. The RiboTag analysis of tumor-associated excitatory neurons showed a downregulation of transcripts encoding excitatory and inhibitory postsynaptic proteins and dendritic spine development, and an upregulation of transcripts encoding cytoskeletal proteins involved in dendritic spine turnover. Light and electron microscopy of tumor-associated excitatory neurons demonstrated marked decreases in dendritic spine density. In vivo two-photon calcium imaging in tumor-associated excitatory neurons revealed progressive alterations in neuronal activity, both at the population and single-neuron level, throughout tumor growth. This in vivo calcium imaging also revealed altered stimulus-evoked somatic calcium events, with changes in event rate, size, and temporal alignment to stimulus, which was most pronounced in neurons with high-tumor burden. A single acute dose of AZD8055, a combined mTORC1/2 inhibitor, reversed the glioma-induced alterations on the excitatory neurons, including the alterations in ribosome-bound transcripts, dendritic spine density, and stimulus evoked responses seen by calcium imaging. These results point to mTOR-driven pathological plasticity in neurons at the infiltrative margin of glioma - manifested by alterations in ribosome-bound mRNA, dendritic spine density, and stimulus-evoked neuronal activity. Collectively, our work identifies the pathological changes that tumor-associated excitatory neurons experience as both hyperlocal and reversible under the influence of mTOR inhibition, providing a foundation for developing therapies targeting neuronal signaling in glioma.

Consensus scHPF Identifies Cell Type-Specific Drug Responses in Glioma by Integrating Large-Scale scRNA-seq

Single-cell transcriptomic analyses now frequently involve elaborate study designs including samples from multiple individuals, experimental conditions, perturbations, and batches from complex tissues. Dimensionality reduction is required to facilitate integration, interpretation, and statistical analysis. However, these datasets often include subtly different cellular subpopulations or state transitions, which are poorly described by clustering. We previously reported a Bayesian matrix factorization algorithm called single-cell hierarchical Poisson factorization (scHPF) that identifies gene co-expression patterns directly from single-cell RNA-seq (scRNA-seq) count matrices while accounting for transcript drop-out and noise. Here, we describe consensus scHPF, which analyzes scHPF models from multiple random initializations to identify the most robust gene signatures and automatically determine the number of factors for a given dataset. Consensus scHPF facilitates integration of complex datasets with highly multi-modal posterior distributions, resulting in factors that can be uniformly analyzed across individuals and conditions. To demonstrate the utility of consensus scHPF, we performed a meta-analysis of a large-scale scRNA-seq dataset from drug-treated, human glioma slice cultures generated from surgical specimens across three major cell types, 19 patients, 10 drug treatment conditions, and 52 samples. In addition to recapitulating previously reported cell type-specific drug responses from smaller studies, consensus scHPF identified disparate effects of the topoisomerase poisons etoposide and topotecan that are highly consistent with the distinct roles and expression patterns of their respective protein targets.

MGMT Promoter Methylation Predicts Overall Survival after Chemotherapy for 1p/19q-Codeleted Gliomas

PURPOSE

While MGMT promoter methylation (mMGMT) is predictive of response to alkylating chemotherapy and guides treatment decisions in glioblastoma, its role in grade 2 and 3 glioma remains unclear. Recent data suggest that mMGMT is prognostic of progression-free survival in 1p/19q-codeleted oligodendrogliomas, but an effect on overall survival (OS) has not been demonstrated.

EXPERIMENTAL DESIGN

We identified patients with newly diagnosed 1p/19q-codeleted gliomas and known MGMT promoter status in the National Cancer Database from 2010 to 2019. Multivariable Cox proportional hazards regression modeling was used to assess the effect of mMGMT on OS after adjusting for age, sex, race, comorbidity, grade, extent of resection, chemotherapy, and radiotherapy.

RESULTS

We identified 1,297 eligible patients, 938 (72.3%) of whom received chemotherapy in their initial course of treatment. The MGMT promoter was methylated in 1,009 (77.8%) patients. Unmethylated MGMT (uMGMT) was associated with worse survival compared with mMGMT [70% {95% confidence interval (CI), 64%-77%} vs. 81% (95% CI, 78%-85%); P < 0.001; adjusted HR (aHR), 2.35 (95% CI, 1.77-3.14)]. uMGMT was associated with worse survival in patients who received chemotherapy [63% (95% CI, 55-73%) vs. 80% (95% CI, 76%-84%); P < 0.001; aHR, 2.61 (95% CI, 1.89-3.60)] but not in patients who did not receive chemotherapy [P = 0.38; HR, 1.31 (95% CI, 0.71-2.42)]. Similar results were observed regardless of World Health Organization grade and after single- or multiagent chemotherapy.

CONCLUSIONS

Our study demonstrates an association between mMGMT and OS in 1p/19q-codeleted gliomas. MGMT promoter status should be considered as a stratification factor in future clinical trials of 1p/19q-codeleted gliomas that use OS as an endpoint.

MGMT Promoter Methylation Predicts Survival in 1p19q-Codeleted Gliomas after Chemotherapy

PURPOSE/OBJECTIVE(S)

MGMT promoter methylation (mMGMT) is predictive of response to alkylating chemotherapy in glioblastomas and used to guide treatment decisions. However, the role of MGMT promoter status in low-grade and anaplastic gliomas remains unclear due to molecular heterogeneity and the lack of sufficiently large datasets. We recently found that MGMT promoter methylation predicts progression-free survival in 1p19q-codeleted gliomas after alkylating chemotherapy in a meta-analysis of three prospective cohorts. There were not enough deaths to determine the effect on overall survival. Here, we query a large national database to determine the association between MGMT promoter methylation and overall survival in patients with 1p19q-codeleted gliomas.

MATERIALS/METHODS

We identified all patients with newly diagnosed gliomas in the National Cancer Database (NCDB) from 2010-2016 with 1p19q-codeletion and information on MGMT promoter methylation status. The cohort was stratified based on receipt of chemotherapy. Multivariable Cox proportional hazards regression modeling was used to assess the effect of MGMT promoter methylation status on overall survival after adjusting for age, sex, race, co-morbidity, grade, extent of resection, chemotherapy, and radiotherapy.

RESULTS

We identified 530 eligible patients, 373 (70.4%) of whom received chemotherapy in their initial course of treatment. The MGMT promoter was methylated in 400 (75.5%) patients. For all patients, unmethylated MGMT (uMGMT) was associated with poorer survival compared to mMGMT (75% survival time [75%ST] 45 months vs. not reached, P = .003, adjusted hazard ratio [aHR] 2.36 [95% confidence interval (95% CI) 1.53-3.62]). uMGMT was associated with poorer survival in patients who received chemotherapy (75%ST 22 vs. 66 months, P<.001, aHR 2.55 [95% CI 1.60-4.06]) but not in patients who did not receive chemotherapy (75%ST 110 months vs. not reached, P = 0.7, HR 1.24 [95% CI 0.40-3.81]).

CONCLUSION

To our knowledge, this is the first study to demonstrate an association between overall survival and MGMT promoter status in 1p19q-codeleted gliomas. MGMT promoter status should be used as a stratification factor in future clinical trials of 1p19q-codeleted gliomas that use overall survival as an endpoint.

Persistent Deficits in Bone Quality in Treated Acromegaly: Evidence From Assessments of Microstructure

Purpose

Fractures are increased in patients with acromegaly, both before and after successful acromegaly treatment. Abnormalities of bone microstructure, which may underlie this fragility, are present in active acromegaly but to what extent these improve with acromegaly treatment or persist despite biochemical remission remains unclear. To examine these questions, we studied the effects of acromegaly treatment and remission on bone quality.

Methods

Sixty-five women and men with acromegaly were studied. Subgroups underwent assessments of areal bone mineral density by dual x-ray absorptiometry, trabecular bone score (TBS), and volumetric bone mineral density, microarchitecture, stiffness and failure load of the distal radius and tibia by high-resolution peripheral quantitative tomography in a longitudinal study before and after acromegaly treatment and in a cross-sectional study in which patients were compared to sex-, age-, and body mass index-matched healthy controls.

Results

In the longitudinal study, significant increases in total, cortical, and trabecular densities at the radius and tibia and increased stiffness and failure load of the tibia occurred with acromegaly treatment. In the cross-sectional study, patients in biochemical remission after surgery had larger bones, lower trabecular and cortical volumetric density, and disrupted trabecular microarchitecture compared to controls. TBS did not change with acromegaly treatment but correlated with some microstructural parameters.

Conclusion

We show, for the first time, that volumetric bone mineral density and microarchitecture of the peripheral skeleton improve with acromegaly treatment but remain abnormal in patients in remission after surgery compared to controls. These abnormalities, known to be associated with fractures in other populations, may play a role in the pathogenesis of persistent fragility in treated acromegaly.

Association of MGMT Promoter Methylation With Survival in Low-grade and Anaplastic Gliomas After Alkylating Chemotherapy

Importance

O6-methylguanine-DNA methyltransferase (MGMT [OMIM 156569]) promoter methylation (mMGMT) is predictive of response to alkylating chemotherapy for glioblastomas and is routinely used to guide treatment decisions. However, the utility of MGMT promoter status for low-grade and anaplastic gliomas remains unclear due to molecular heterogeneity and the lack of sufficiently large data sets.

Objective

To evaluate the association of mMGMT for low-grade and anaplastic gliomas with chemotherapy response.

Design, Setting, and Participants

This cohort study aggregated grade II and III primary glioma data from 3 prospective cohort studies with patient data collected from August 13, 1995, to August 3, 2022, comprising 411 patients: MSK-IMPACT, EORTC (European Organization of Research and Treatment of Cancer) 26951, and Columbia University. Statistical analysis was performed from April 2022 to January 2023.

Exposure

MGMT promoter methylation status.

Main Outcomes and Measures

Multivariable Cox proportional hazards regression modeling was used to assess the association of mMGMT status with progression-free survival (PFS) and overall survival (OS) after adjusting for age, sex, molecular class, grade, chemotherapy, and radiotherapy. Subgroups were stratified by treatment status and World Health Organization 2016 molecular classification.

Results

A total of 411 patients (mean [SD] age, 44.1 [14.5] years; 283 men [58%]) met the inclusion criteria, 288 of whom received alkylating chemotherapy. MGMT promoter methylation was observed in 42% of isocitrate dehydrogenase (IDH)-wild-type gliomas (56 of 135), 53% of IDH-mutant and non-codeleted gliomas (79 of 149), and 74% of IDH-mutant and 1p/19q-codeleted gliomas (94 of 127). Among patients who received chemotherapy, mMGMT was associated with improved PFS (median, 68 months [95% CI, 54-132 months] vs 30 months [95% CI, 15-54 months]; log-rank P < .001; adjusted hazard ratio [aHR] for unmethylated MGMT, 1.95 [95% CI, 1.39-2.75]; P < .001) and OS (median, 137 months [95% CI, 104 months to not reached] vs 61 months [95% CI, 47-97 months]; log-rank P < .001; aHR, 1.65 [95% CI, 1.11-2.46]; P = .01). After adjusting for clinical factors, MGMT promoter status was associated with chemotherapy response in IDH-wild-type gliomas (aHR for PFS, 2.15 [95% CI, 1.26-3.66]; P = .005; aHR for OS, 1.69 [95% CI, 0.98-2.91]; P = .06) and IDH-mutant and codeleted gliomas (aHR for PFS, 2.99 [95% CI, 1.44-6.21]; P = .003; aHR for OS, 4.21 [95% CI, 1.25-14.2]; P = .02), but not IDH-mutant and non-codeleted gliomas (aHR for PFS, 1.19 [95% CI, 0.67-2.12]; P = .56; aHR for OS, 1.07 [95% CI, 0.54-2.12]; P = .85). Among patients who did not receive chemotherapy, mMGMT status was not associated with PFS or OS.

Conclusions and Relevance

This study suggests that mMGMT is associated with response to alkylating chemotherapy for low-grade and anaplastic gliomas and may be considered as a stratification factor in future clinical trials of patients with IDH-wild-type and IDH-mutant and codeleted tumors.

A Transcriptome-Based Precision Oncology Platform for Patient-Therapy Alignment in a Diverse Set of Treatment-Resistant Malignancies

Predicting in vivo response to antineoplastics remains an elusive challenge. We performed a first-of-kind evaluation of two transcriptome-based precision cancer medicine methodologies to predict tumor sensitivity to a comprehensive repertoire of clinically relevant oncology drugs, whose mechanism of action we experimentally assessed in cognate cell lines. We enrolled patients with histologically distinct, poor-prognosis malignancies who had progressed on multiple therapies, and developed low-passage, patient-derived xenograft models that were used to validate 35 patient-specific drug predictions. Both OncoTarget, which identifies high-affinity inhibitors of individual master regulator (MR) proteins, and OncoTreat, which identifies drugs that invert the transcriptional activity of hyperconnected MR modules, produced highly significant 30-day disease control rates (68% and 91%, respectively). Moreover, of 18 OncoTreat-predicted drugs, 15 induced the predicted MR-module activity inversion in vivo. Predicted drugs significantly outperformed antineoplastic drugs selected as unpredicted controls, suggesting these methods may substantively complement existing precision cancer medicine approaches, as also illustrated by a case study.

SIGNIFICANCE

Complementary precision cancer medicine paradigms are needed to broaden the clinical benefit realized through genetic profiling and immunotherapy. In this first-in-class application, we introduce two transcriptome-based tumor-agnostic systems biology tools to predict drug response in vivo. OncoTarget and OncoTreat are scalable for the design of basket and umbrella clinical trials. This article is highlighted in the In This Issue feature, p. 1275.

Re-convolving the compositional landscape of primary and recurrent glioblastoma reveals prognostic and targetable tissue states

Glioblastoma (GBM) diffusely infiltrates the brain and intermingles with non-neoplastic brain cells, including astrocytes, neurons and microglia/myeloid cells. This complex mixture of cell types forms the biological context for therapeutic response and tumor recurrence. We used single-nucleus RNA sequencing and spatial transcriptomics to determine the cellular composition and transcriptional states in primary and recurrent glioma and identified three compositional 'tissue-states' defined by cohabitation patterns between specific subpopulations of neoplastic and non-neoplastic brain cells. These tissue-states correlated with radiographic, histopathologic, and prognostic features and were enriched in distinct metabolic pathways. Fatty acid biosynthesis was enriched in the tissue-state defined by the cohabitation of astrocyte-like/mesenchymal glioma cells, reactive astrocytes, and macrophages, and was associated with recurrent GBM and shorter survival. Treating acute slices of GBM with a fatty acid synthesis inhibitor depleted the transcriptional signature of this pernicious tissue-state. These findings point to therapies that target interdependencies in the GBM microenvironment.

Long-term Outcome of Body Composition, Ectopic Lipid, and Insulin Resistance Changes With Surgical Treatment of Acromegaly

Context

Acromegaly presents a unique pattern of lower adiposity and insulin resistance in active disease but reduction in insulin resistance despite a rise in adiposity after surgery. Depot-specific adipose tissue masses and ectopic lipid are important predictors of insulin resistance in other populations, but whether they are in acromegaly is unknown. Long-term persistence of body composition changes after surgery is unknown.

Objective

To determine how depot-specific body composition and ectopic lipid relate to insulin resistance in active acromegaly and whether their changes with surgery are sustained long-term.

Methods

Cross-sectional study in patients with active acromegaly and longitudinal study in newly diagnosed patients studied before and in long-term follow-up, 3 (1-8) years (median, range), after surgery. Seventy-one patients with active acromegaly studied cross-sectionally and 28 with newly diagnosed acromegaly studied longitudinally. Main outcome measures were visceral (VAT), subcutaneous (SAT), and intermuscular adipose tissue masses by whole-body magnetic resonance imaging; intrahepatic lipid (IHL) by proton magnetic resonance spectroscopy; insulin resistance measures derived from fasting; and oral glucose tolerance test insulin and glucose levels.

Results

SAT and insulin-like growth factor 1 level, but not VAT or IHL, were independent predictors of insulin resistance in active acromegaly. VAT, SAT, and IHL gains were sustained long-term after surgery. VAT mass rise with surgery correlated inversely with rise in QUICKI while SAT rise correlated with fall in the Homeostatic Model Assessment score.

Conclusion

SAT and disease activity are important predictors of insulin resistance in active acromegaly. Adiposity gains are sustained long-term after surgical treatment and impact on the accompanying improvement in insulin resistance.

Dietary restriction of cysteine and methionine sensitizes gliomas to ferroptosis and induces alterations in energetic metabolism

Ferroptosis is mediated by lipid peroxidation of phospholipids containing polyunsaturated fatty acyl moieties. Glutathione, the key cellular antioxidant capable of inhibiting lipid peroxidation via the activity of the enzyme glutathione peroxidase 4 (GPX-4), is generated directly from the sulfur-containing amino acid cysteine, and indirectly from methionine via the transsulfuration pathway. Herein we show that cysteine and methionine deprivation (CMD) can synergize with the GPX4 inhibitor RSL3 to increase ferroptotic cell death and lipid peroxidation in both murine and human glioma cell lines and in ex vivo organotypic slice cultures. We also show that a cysteine-depleted, methionine-restricted diet can improve therapeutic response to RSL3 and prolong survival in a syngeneic orthotopic murine glioma model. Finally, this CMD diet leads to profound in vivo metabolomic, proteomic and lipidomic alterations, highlighting the potential for improving the efficacy of ferroptotic therapies in glioma treatment with a non-invasive dietary modification.

A cell state specific metabolic vulnerability to GPX4-dependent ferroptosis in glioblastoma

Glioma cells hijack developmental transcriptional programs to control cell state. During neural development, lineage trajectories rely on specialized metabolic pathways. However, the link between tumor cell state and metabolic programs is poorly understood in glioma. Here we uncover a glioma cell state-specific metabolic liability that can be leveraged therapeutically. To model cell state diversity, we generated genetically engineered murine gliomas, induced by deletion of p53 alone (p53) or with constitutively active Notch signaling (N1IC), a pathway critical in controlling cellular fate. N1IC tumors harbored quiescent astrocyte-like transformed cell states while p53 tumors were predominantly comprised of proliferating progenitor-like cell states. N1IC cells exhibit distinct metabolic alterations, with mitochondrial uncoupling and increased ROS production rendering them more sensitive to inhibition of the lipid hydroperoxidase GPX4 and induction of ferroptosis. Importantly, treating patient-derived organotypic slices with a GPX4 inhibitor induced selective depletion of quiescent astrocyte-like glioma cell populations with similar metabolic profiles.

Scalable co-sequencing of RNA and DNA from individual nuclei

The ideal technology for directly investigating the relationship between genotype and phenotype would analyze both RNA and DNA genome-wide and with single-cell resolution. However, existing tools lack the throughput required for comprehensive analysis of complex tumors and tissues. We introduce a highly scalable method for jointly profiling DNA and expression following nucleosome depletion (DEFND-seq). In DEFND-seq, nuclei are nucleosome-depleted, tagmented, and separated into individual droplets for mRNA and genomic DNA barcoding. Once nuclei have been depleted of nucleosomes, subsequent steps can be performed using the widely available 10x Genomics droplet microfluidic technology and commercial kits without experimental modification. We demonstrate the production of high-complexity mRNA and gDNA sequencing libraries from thousands of individual nuclei from both cell lines and archived surgical specimens for associating gene expression phenotypes with both copy number and single nucleotide variants.

C-Terminal p53 Palindromic Tetrapeptide Restores Full Apoptotic Function to Mutant p53 Cancer Cells In Vitro and In Vivo

We previously demonstrated that a synthetic monomer peptide derived from the C-terminus of p53 (aa 361−382) induced preferential apoptosis in mutant p53 malignant cells, but not normal cells. The major problem with the peptide was its short half-life (half-life < 10 min.) due to a random coil topology found in 3D proton NMR spectroscopy studies. To induce secondary/tertiary structures to produce more stability, we developed a peptide modelled after the tetrameric structure of p53 essential for activation of target genes. Starting with the above monomer peptide (aa 361−382), we added the nuclear localization sequence of p53 (aa 353−360) and the end of the C-terminal sequence (aa 383−393), resulting in a monomer spanning aa 353−393. Four monomers were linked by glycine to maximize flexibility and in a palindromic order that mimics p53 tetramer formation with four orthogonal alpha helices, which is required for p53 transactivation of target genes. This is now known as the 4 repeat-palindromic-p53 peptide or (4R-Pal-p53p). We explored two methods for testing the activity of the palindromic tetrapeptide: (1) exogenous peptide with a truncated antennapedia carrier (Ant) and (2) a doxycycline (Dox) inducer for endogenous expression. The exogenous peptide, 4R-Pal-p53p-Ant, contained a His tag at the N-terminal and a truncated 17aa Ant at the C-terminal. Exposure of human breast cancer MB-468 cells and human skin squamous cell cancer cells (both with mutant p53, 273 Arg->His) with purified peptide at 7 µM and 15 µM produced 52% and 75%, cell death, respectively. Comparatively, the monomeric p53 C-terminal peptide-Ant (aa 361−382, termed p53p-Ant), at 15 µM and 30 µM induced 15% and 24% cell death, respectively. Compared to the p53p-Ant, the exogenous 4R-pal-p53p-Ant was over five-fold more potent for inducing apoptosis at an equimolar concentration (15 µM). Endogenous 4R-Pal-p53p expression (without Ant), induced by Dox, resulted in 43% cell death in an engineered MB468 breast cancer stable cell line, while endogenous p53 C-terminal monomeric peptide expression produced no cell death due to rapid peptide degradation. The mechanism of apoptosis from 4R-Pal-p53p involved the extrinsic and intrinsic pathways (FAS, caspase-8, Bax, PUMA) for apoptosis, as well as increasing reactive oxygen species (ROS). All three death pathways were induced from transcriptional/translational activation of pro-apoptotic genes. Additionally, mRNA of p53 target genes (Bax and Fas) increased 14-fold and 18-fold, respectively, implying that the 4R-Pal-p53p restored full apoptotic potential to mutant p53. Monomeric p53p only increased Fas expression without a transcriptional or translational increase in Fas, and other genes and human marrow stem cell studies revealed no toxicity to normal stem cells for granulocytes, erythrocytes, monocytes, and macrophages (CFU-GEMM). Additionally, the peptide specifically targeted pre-malignant and malignant cells with mutant p53 and was not toxic to normal cells with basal levels of WT p53.

Malignant Glioma

This chapter provides a comprehensive overview of malignant gliomas, the most common primary brain tumor in adults. These tumors are varied in their cellular origin, genetic profile, and morphology under the microscope, but together they share some of the most dismal prognoses of all neoplasms in the body. Although there is currently no cure for malignant glioma, persistent efforts to improve outcomes in patients with these tumors have led to modest increases in survival, and researchers worldwide continue to strive toward a deeper understanding of the factors that influence glioma development and response to treatment. In addition to well-established epidemiology, clinical manifestations, and common histopathologic and radiologic features of malignant gliomas, this section considers recent advances in molecular biology that have led to a more nuanced understanding of the genetic changes that characterize the different types of malignant glioma, as well as their implications for treatment. Beyond the traditional classification of malignant gliomas based on histopathological features, this chapter incorporates the World Health Organization's 2016 criteria for the classification of brain tumors, with special focus on disease-defining genetic alterations and newly established subcategories of malignant glioma that were previously unidentifiable based on microscopic examination alone. Traditional therapeutic modalities that form the cornerstone of treatment for malignant glioma, such as aggressive surgical resection followed by adjuvant chemotherapy and radiation therapy, and the studies that support their efficacy are reviewed in detail. This provides a foundation for additional discussion of novel therapeutic methods such as immunotherapy and convection-enhanced delivery, as well as new techniques for enhancing extent of resection such as fluorescence-guided surgery.

Benign and Malignant Tumors of the Pineal Region

Pineal region tumors fall into five broad categories: benign pineal region tumors, glial tumors, papillary tumors, pineal parenchymal tumors, and germ cell tumors. Genetic and transcriptional studies have identified key chromosomal alterations in germinomas (RUNDC3A, ASAH1, LPL) and in pineocytomas/pineoblastomas (DROSHA/DICER1, RB1). Pineal region tumors generally present with symptoms of hydrocephalus including nausea, vomiting, papilledema, and the classical Parinaud's triad of upgaze paralysis, convergence-retraction nystagmus, and light-near pupillary dissociation. Workup requires neuroimaging and tissue diagnosis via biopsy. In germinoma cases, diagnosis may be made based on serum or CSF studies for alpha-fetoprotein or beta-HCG making the preferred treatment radiosurgery, thereby preventing the need for unnecessary surgeries. Treatment generally involves three steps: CSF diversion in cases of hydrocephalus, biopsy through endoscopic or stereotactic methods, and open surgical resection. Multiple surgical approaches are possible for approach to the pineal region. The original approach to the pineal region was the interhemispheric transcallosal first described by Dandy. The most common approach is the supracerebellar infratentorial approach as it utilizes a natural anatomic corridor for access to the pineal region. The paramedian or lateral supracerebellar infratentorial approach is another improvement that uses a similar anatomic corridor but allows for preservation of midline bridging veins; this minimizes the chance for brainstem or cerebellar venous infarction. Determination of the optimal approach relies on tumor characteristics, namely location of deep venous structures to the tumor along with the lateral eccentricity of the tumor. The immediate post-operative period is important as hemorrhage or swelling can cause obstructive hydrocephalus and lead to rapid deterioration. Adjuvant therapy, whether chemotherapy or radiation, is based on tumor pathology. Improvements within pineal surgery will require improved technology for access to the pineal region along with targeted therapies that can effectively treat and prevent recurrence of malignant pineal region tumors.

Benign Glioma

Benign glioma broadly refers to a heterogeneous group of slow-growing glial tumors with low proliferative rates and a more indolent clinical course. These tumors may also be described as "low-grade" glioma (LGG) and are classified as WHO grade I or II lesions according to the Classification of Tumors of the Central Nervous System (CNS) (Louis et al. in Acta Neuropathol 114:97-109, 2007). Advances in molecular genetics have improved understanding of glioma tumorigenesis, leading to the identification of common mutation profiles with significant treatment and prognostic implications. The most recent WHO 2016 classification system has introduced several notable changes in the way that gliomas are diagnosed, with a new emphasis on molecular features as key factors in differentiation (Wesseling and Capper in Neuropathol Appl Neurobiol 44:139-150, 2018). Benign gliomas have a predilection for younger patients and are among the most frequently diagnosed tumors in children and young adults (Ostrom et al. in Neuro Oncol 22:iv1-iv96, 2020). These tumors can be separated into two clinically distinct subgroups. The first group is of focal, well-circumscribed lesions that notably are not associated with an increased risk of malignant transformation. Primarily diagnosed in pediatric patients, these WHO grade I tumors may be cured with surgical resection alone (Sturm et al. in J Clin Oncol 35:2370-2377, 2017). Recurrence rates are low, and the prognosis for these patients is excellent (Ostrom et al. in Neuro Oncol 22:iv1-iv96, 2020). Diffuse gliomas are WHO grade II lesions with a more infiltrative pattern of growth and high propensity for recurrence. These tumors are primarily diagnosed in young adult patients, and classically present with seizures (Pallud et al. Brain 137:449-462, 2014). The term "benign" is a misnomer in many cases, as the natural history of these tumors is with malignant transformation and recurrence as grade III or grade IV tumors (Jooma et al. in J Neurosurg 14:356-363, 2019). For all LGG, surgery with maximal safe resection is the treatment of choice for both primary and recurrent tumors. The goal of surgery should be for gross total resection (GTR), as complete tumor removal is associated with higher rates of tumor control and seizure freedom. Chemotherapy and radiation therapy (RT), while not typically a component of first-line treatment in most cases, may be employed as adjunctive therapy in high-risk or recurrent tumors and in some select cases. The prognosis of benign gliomas varies widely; non-infiltrative tumor subtypes generally have an excellent prognosis, while diffusely infiltrative tumors, although slow-growing, are eventually fatal (Sturm et al. in J Clin Oncol 35:2370-2377, 2017). This chapter reviews the shared and unique individual features of the benign glioma including diffuse glioma, pilocytic astrocytoma and pilomyxoid astrocytoma (PMA), subependymal giant cell astrocytoma (SEGA), pleomorphic xanthoastrocytoma (PXA), subependymoma (SE), angiocentric glioma (AG), and chordoid glioma (CG). Also discussed is ganglioglioma (GG), a mixed neuronal-glial tumor that represents a notable diagnosis in the differential for other LGG (Wesseling and Capper 2018). Ependymomas of the brain and spinal cord, including major histologic subtypes, are discussed in other chapters.

Convection-enhanced delivery of immunomodulatory therapy for high-grade glioma

The prognosis for glioblastoma has remained poor despite multimodal standard of care treatment, including temozolomide, radiation, and surgical resection. Further, the addition of immunotherapies, while promising in a number of other solid tumors, has overwhelmingly failed in the treatment of gliomas, in part due to the immunosuppressive microenvironment and poor drug penetrance to the brain. Local delivery of immunomodulatory therapies circumvents some of these challenges and has led to long-term remission in select patients. Many of these approaches utilize convection-enhanced delivery (CED) for immunological drug delivery, allowing high doses to be delivered directly to the brain parenchyma, avoiding systemic toxicity. Here, we review the literature encompassing immunotherapies delivered via CED-from preclinical model systems to clinical trials-and explore how their unique combination elicits an antitumor response by the immune system, decreases toxicity, and improves survival among select high-grade glioma patients.

MODL-28. DEVELOPING A STRATEGY FOR MODELING HIGH-GRADE GLIOMA IN GӦTTINGEN MINIPIGS

BACKGROUND

The current literature does not describe a reproducible large animal model of intracranial high-grade glioma (HGG). Prior work has demonstrated the feasibility of inducing HGG de-novo in rodents by targeting specific oncogenic pathways. Here we report our approach to the production of supratentorial HGG in a series of minipigs through lentiviral gene transfer and subsequent initial characterization of a porcine glioma cell line.

METHODS

Four minipigs received injections into the subcortical white matter using a combination of lentiviral vectors expressing platelet-derived growth factor beta (PDGF-B), HRAS, and shRNA-p53. Animals underwent behavioral monitoring through porcine neurobehavioral scoring (PNS) and veterinary monitoring. Magnetic resonance imaging (MRI) was conducted at endpoint prior to necropsy. Post-mortem tissue biopsies underwent tissue culture and neuropathologic evaluation with hematoxylin and eosin (H&E) staining, immunohistochemistry, and immunofluorescent staining. Data are presented using appropriate statistical tests where relevant and descriptive statistics.

RESULTS

Two pigs received 50ul injections and reached endpoint by the end of post-operative week 1 and 2. Two pigs received 25 ul injections and were asymptomatic until a pre-determined endpoint of 4 weeks. MRI scans at endpoint demonstrated contrast enhancing, mass forming lesions at the site of injection with evidence of hemorrhage and perilesional edema, consistent with high-grade glioma. On H&E staining high-grade glioma growth was identified in 100% of animals. We observed immunopositivity for tumor markers GFAP, OLIG2, NG2, SOX2, and PDGFRA, as well as redox markers, and microenvironmental features consistent with high-grade glioma. Porcine glioma cell cultures were found to have significantly greater proliferative rate compared to control, and demonstrated GFAP, OLIG2, PDGFRA, and CD68 immunopositivity.

CONCLUSIONS

Lentiviral gene transfer represents a feasible strategy for glioma modeling in the Gӧttingen minipig. With our described methodology, we present a realistic strategy for reproducible modeling of intracranial glioma as a platform for preclinical neurosurgical development programs.

Chronic convection-enhanced delivery of topotecan for patients with recurrent glioblastoma: a first-in-patient, single-centre, single-arm, phase 1b trial

BACKGROUND

Topotecan is cytotoxic to glioma cells but is clinically ineffective because of drug delivery limitations. Systemic delivery is limited by toxicity and insufficient brain penetrance, and, to date, convection-enhanced delivery (CED) has been restricted to a single treatment of restricted duration. To address this problem, we engineered a subcutaneously implanted catheter-pump system capable of repeated, chronic (prolonged, pulsatile) CED of topotecan into the brain and tested its safety and biological effects in patients with recurrent glioblastoma.

METHODS

We did a single-centre, open-label, single-arm, phase 1b clinical trial at Columbia University Irving Medical Center (New York, NY, USA). Eligible patients were at least 18 years of age with solitary, histologically confirmed recurrent glioblastoma showing radiographic progression after surgery, radiotherapy, and chemotherapy, and a Karnofsky Performance Status of at least 70. Five patients had catheters stereotactically implanted into the glioma-infiltrated peritumoural brain and connected to subcutaneously implanted pumps that infused 146 μM topotecan 200 μL/h for 48 h, followed by a 5-7-day washout period before the next infusion, with four total infusions. After the fourth infusion, the pump was removed and the tumour was resected. The primary endpoint of the study was safety of the treatment regimen as defined by presence of serious adverse events. Analyses were done in all treated patients. The trial is closed, and is registered with ClinicalTrials.gov, NCT03154996.

FINDINGS

Between Jan 22, 2018, and July 8, 2019, chronic CED of topotecan was successfully completed safely in all five patients, and was well tolerated without substantial complications. The only grade 3 adverse event related to treatment was intraoperative supplemental motor area syndrome (one [20%] of five patients in the treatment group), and there were no grade 4 adverse events. Other serious adverse events were related to surgical resection and not the study treatment. Median follow-up was 12 months (IQR 10-17) from pump explant. Post-treatment tissue analysis showed that topotecan significantly reduced proliferating tumour cells in all five patients.

INTERPRETATION

In this small patient cohort, we showed that chronic CED of topotecan is a potentially safe and active therapy for recurrent glioblastoma. Our analysis provided a unique tissue-based assessment of treatment response without the need for large patient numbers. This novel delivery of topotecan overcomes limitations in delivery and treatment response assessment for patients with glioblastoma and could be applicable for other anti-glioma drugs or other CNS diseases. Further studies are warranted to determine the effect of this drug delivery approach on clinical outcomes.

FUNDING

US National Institutes of Health, The William Rhodes and Louise Tilzer Rhodes Center for Glioblastoma, the Michael Weiner Glioblastoma Research Into Treatment Fund, the Gary and Yael Fegel Foundation, and The Khatib Foundation.

Lactate is an epigenetic metabolite that drives survival in model systems of glioblastoma

Lactate accumulates to a significant amount in glioblastomas (GBMs), the most common primary malignant brain tumor with an unfavorable prognosis. However, it remains unclear whether lactate is metabolized by GBMs. Here, we demonstrated that lactate rescued patient-derived xenograft (PDX) GBM cells from nutrient-deprivation-mediated cell death. Transcriptome analysis, ATAC-seq, and ChIP-seq showed that lactate entertained a signature of oxidative energy metabolism. LC/MS analysis demonstrated that U-13C-lactate elicited substantial labeling of TCA-cycle metabolites, acetyl-CoA, and histone protein acetyl-residues in GBM cells. Lactate enhanced chromatin accessibility and histone acetylation in a manner dependent on oxidative energy metabolism and the ATP-citrate lyase (ACLY). Utilizing orthotopic PDX models of GBM, a combined tracer experiment unraveled that lactate carbons were substantially labeling the TCA-cycle metabolites. Finally, pharmacological blockage of oxidative energy metabolism extended overall survival in two orthotopic PDX models in mice. These results establish lactate metabolism as a novel druggable pathway for GBM.

Dissecting the treatment-naive ecosystem of human melanoma brain metastasis

Melanoma brain metastasis (MBM) frequently occurs in patients with advanced melanoma; yet, our understanding of the underlying salient biology is rudimentary. Here, we performed single-cell/nucleus RNA-seq in 22 treatment-naive MBMs and 10 extracranial melanoma metastases (ECMs) and matched spatial single-cell transcriptomics and T cell receptor (TCR)-seq. Cancer cells from MBM were more chromosomally unstable, adopted a neuronal-like cell state, and enriched for spatially variably expressed metabolic pathways. Key observations were validated in independent patient cohorts, patient-derived MBM/ECM xenograft models, RNA/ATAC-seq, proteomics, and multiplexed imaging. Integrated spatial analyses revealed distinct geography of putative cancer immune evasion and evidence for more abundant intra-tumoral B to plasma cell differentiation in lymphoid aggregates in MBM. MBM harbored larger fractions of monocyte-derived macrophages and dysfunctional TOX+CD8+ T cells with distinct expression of immune checkpoints. This work provides comprehensive insights into MBM biology and serves as a foundational resource for further discovery and therapeutic exploration.

Abstract 984: Dissecting the ecosystem of treatment-naïve melanoma brain metastasis using multi-modal single-cell analysis

Brain metastases are the most frequent malignancies in the brain and are associated with significant morbidity and mortality. Melanoma brain metastases (MBM) occur in most patients with advanced melanoma and are challenging to treat. Our understanding of the treatment-naïve landscape of MBM is still rudimentary, and there are no site-specific molecular therapies available. To gain comprehensive insights into the niche-specific biology of MBM, we performed multi-modal profiling of fresh and frozen samples using single-cell RNA-seq, single-cell TCR-seq, single-nuclei RNA-seq, and spatial transcriptional profiling. We evolved single-nucleus RNA-seq processing methods to enable profiling of minute amounts of archival, frozen specimens and compared data quality and structure between matched fresh and frozen MBM. We curated a treatment-naïve single-transcriptome atlas of MBM, collected either fresh samples over 1 year or profiled frozen samples dating back more than 15 years, and compared these samples to extracranial melanoma metastases (ECMM). In total, we profiled 25 samples with more than 114,000 transcriptomes. We identified more than 20 different cell types, including diverse tumor-infiltrating T-cell subsets and rare dendritic cell types, and tissue-specific cell types, such as activated microglia. Tumor cells in MBM showed an increase in copy number alterations (CNAs) compared to ECMM, which we validated using an external dataset of whole exome sequencing (WES) data including both MBM and ECMM. MBM-derived tumor cells show enrichment of genes involved in neuronal development and function, and site-specific metabolic programs (e.g., oxidative phosphorylation). Comparison with an external bulk RNA-seq dataset validated enriched key genes in MBM and ECMM as putative dependencies. We recovered cell-cell interactions between tumor and brain-resident cells involved in brain development, homeostasis, and disease. Similar to ECMM, the tumor microenvironment of MBM contained CD8+ T cells across a spectrum of differentiation, exhaustion and expansion, which was associated with loss of TCF7 expression and adoption of a TOX+ cell state. CD4+ T cells included T regulatory, T helper and T follicular-helper-like expression profiles. Plasma cells showed spatially localized expansion and limited heterogeneity. Myeloid cells largely adopted pro-tumorigenic cell states, including microglia, the brain-resident myeloid cells, which showed an activation trajectory characterized by expression of SPP1 (osteopontin). Spatial transcriptional analysis revealed restricted expression of antigen presentation genes with only a subset of these locations showing a type I interferon response. In summary, this work presents a multi-modal single-cell approach to dissect and compare the landscape of treatment-naïve MBM and ECMM.

Citation Format: Johannes C. Melms, Jana Biermann, Amit Dipak Amin, Yiping Wang, Somnath Tagore, Massimo Andreatta, Ajay Nair, Meri Rogava, Patricia Ho, Lindsay A. Caprio, Zachary H. Walsh, Shivem Shah, Daniel H. Vacarro, Blake Caldwell, Adrienne M. Luoma, Joseph Driver, Matthew Ingham, Suthee Rapisuwon, Jennifer Wargo, Craig L. Slinguff, Evan Z. Macosco, Fei Chen, Richard Carvajal, Michael B. Atkins, Michael A. Davies, Elham Azizi, Santiago J. Carmona, Hanina Hibshoosh, Peter D. Canoll, Jeffrey N. Bruce, Wenya L. Bi, Gary K. Schwartz, Benjamin Izar. Dissecting the ecosystem of treatment-naïve melanoma brain metastasis using multi-modal single-cell analysis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 984.

Pineal region ganglioglioma: A neoplasm with a bimodal age distribution

Background:

Gangliogliomas arise very rarely in the pineal region, where their natural histories and pathologic features are poorly understood.

Case Description:

In this report, we describe a 36-year-old woman who presented with a seizure followed by worsening headache, dizziness, confusion, and intermittent left facial numbness over the next few weeks. A head CT scan showed a partially calcified pineal region mass with hydrocephalus. After an endoscopic third ventriculostomy, the patient underwent a resection of the tumor that contained dysplastic ganglion cells and piloid glial cells. Molecular profiling of this CNS WHO Grade 1 ganglioglioma revealed polysomies of chromosomes 7 and 9, and a BUB1 variant of uncertain significance, without known MAP kinase pathway alterations. From a review of the literature, we found two distinct age distributions for pineal ganglioglioma, with modes at 1 and 36 years of age.

Conclusion:

Although very rare, this tumor should be considered in the differential diagnosis of pineal region tumors in children and young adults.

Thoracic low grade glial neoplasm with concurrent H3 K27M and PTPN11 mutations

We present the case of a 41-year-old man who developed worsening mid-thoracic back pain and imaging revealed a well-circumscribed intramedullary tumor in the thoracic spinal cord. Subtotal resection was performed, and histopathological analysis showed a cytologically bland, minimally proliferative glial neoplasm. Sequencing revealed H3 K27M and an activating PTPN11 mutation. Serial imaging revealed slow tumor regrowth over a three year period which prompted a second resection. The recurrent tumor displayed a similar low grade-appearing histology and harbored the same H3 K27M and PTPN11 mutations as the primary. While the prognostic importance of isolated H3 K27M in spinal gliomas is well-known, the combination of these two mutations in spinal low grade glioma has not been previously reported. Importantly, PTPN11 is a component of the MAPK signaling pathway. Thus, as building evidence shows that low grade-appearing gliomas harboring H3 K27M mutations along with BRAF or FGFR1 mutations have a relatively more favorable course compared to isolated H3 K27M-mutant midline gliomas, the present case provides new evidence for the prognostic importance of activating mutations in other components of the MAPK signaling pathway. This case further highlights the importance of clinico-radio-pathologic correlation when incorporating evolving genetic data into the integrated diagnosis of rare neuroepithelial tumors.

BIOM-31. ERK1/2 PHOSPHORYLATION PREDICTS SURVIVAL FOLLOWING ANTI-PD-1 IMMUNOTHERAPY IN RECURRENT GLIOBLASTOMA

PD-1 checkpoint inhibition has led to remarkable clinical responses in several cancer types. Whereas PD-1 blockade has not shown an overall survival (OS) benefit for glioblastoma (GBM) patients, a subset of them exhibit long-term responses to this immunotherapy. Previously, we reported an enrichment of BRAF/PTPN11 activating mutations in 30% of recurrent GBMs that responded to PD-1 blockade, but the molecular profile of the majority of responders remained elusive. Given that BRAF and PTPN11 promote MAPK/ERK signaling, we investigated whether activation of this pathway is associated with response to PD-1 inhibitors in recurrent GBM, including patients that do not harbor BRAF/PTPN11 mutations. Immunohistochemistry for ERK1/2 phosphorylation (p-ERK), a marker of MAPK/ERK pathway activation, was performed in a discovery cohort including pre-treatment specimens of 29 recurrent GBM patients treated with adjuvant PD-1 blockade, and 33 patients who did not undergo immunotherapy. p-ERK was predictive of response and OS following PD-1 blockade. Yet p-ERK was not associated with OS in patients not treated with immunotherapy. p-ERK was also associated with OS in a validation GBM cohort treated with adjuvant anti-PD-1 therapy. Single-cell RNA-seq and multiplex-immunofluorescence analyses revealed that p-ERK was mainly localized in tumor cells and high p-ERK GBMs contained tumor-infiltrating myeloid cells and microglia with elevated expression of MHC class II and associated genes. Thus, our findings indicate that ERK1/2 activation in recurrent GBM is predictive of response to PD-1 blockade and is associated with a distinct myeloid cell phenotype.

TAMI-70. METABOLIC VULNERABILITY TO GPX4 INHIBITION AND FERROPTOSIS OF QUIESCENT ASTROCYTE-LIKE GLIOMA CELL POPULATIONS

Diversity is a key feature in the glioma ecosystem. Adaptation to a changing tumor microenvironment is achieved through cellular and metabolic plasticity. Here we show that slow-cycling, astrocyte-like glioma cell subpopulations activate distinct metabolic programs, rendering them susceptible to novel treatments. We performed multi-omics analysis on transgenic murine glioma models to characterize cellular heterogeneity. Bulk RNAseq on targeted time-dependent biopsies combined with scRNAseq uncovered distinct tumor cell populations, including a quiescent, astrocyte-like population relatively insensitive to conventional chemotherapy targeting proliferating cells. Using scRNAseq, we identified a persistently conserved astrocytic population in human IDH1-mt/wt high-grade gliomas. This astrocytic tumor population was more abundant in mouse models with constitutive Notch activation, however it was associated with alterations in several other transcriptional programs, suggesting that targeted therapies would likely be ineffective at eradicating it. Gene ontology analysis revealed enrichment in mitochondrial genes specifically regulating oxidative phosphorylation and tricarboxylic acid cycle. Energetic, lipidomic and metabolomic analyses revealed significant mitochondrial β-fatty acid oxidation and lipid catabolism, with less effective oxygen consumption rate and higher basal oxidative stress. Furthermore, this astrocytic tumor population had depleted levels of basal GSH and was more sensitive to reactive oxygen species. Leveraging this metabolic vulnerability, we performed drug screens and found that therapeutic inhibition of complex I or GPX4 was highly effective and synergistic. GPX4 inhibition induced ferroptosis, a newly-discovered form of programmed non-necroptotic cell death mediated by iron-driven lipid peroxidation. Using scRNAseq and RNAscope on ex vivo slice cultures from murine and human gliomas, we found that GPX4 inhibition and ferroptosis induction in the glioma microenvironment selectively eradicated the quiescent astrocytic subpopulation whereas proliferating glioma were less sensitive. Our data therefore supports a novel treatment paradigm, employing metabolic strategies, such as ferroptosis, in conjunction with chemotherapy and RT to target distinct tumor cell populations with different therapeutic vulnerabilities.

TAMI-57. INDUCTION OF FERROPTOSIS PROMOTES IMMUNOGENIC CELL DEATH AND ACTIVATION OF THE IMMUNE MICROENVIRONMENT IN GLIOMA

Gliomas are immune cold tumors. Effective therapeutic strategies capable of inducing an immune response are lacking.Here we present evidence that ferroptosis, a form of iron-mediated lipid peroxidation-based cell death, may promote anti-tumor immunity via stimulation of phagocytosis and pro-inflammatory activities in microglia. While ferroptosis has shown promise in induction of glioma cell death, the immunogenic and microenvironmental effects of glioma ferroptosis are poorly understood. First, we tested the in vitro effects of the glutathione peroxidase 4 (GPX4) inhibitor RSL3, a ferroptosis inducer, on murine glioma cell lines. Using flow cytometry, we discovered that RSL3 treatment led to membrane translocation of the pro-phagocytic antigen calreticulin, known hallmark of immunogenic cell death, by an average log2-fold-change of 2.53 (p= 0.03) compared to DMSO-treated controls. This effect correlated with lipid peroxidation, as assessed by BODIPY-C11 staining. To further test the effects of ferroptosis on glioma cell-microglia crosstalk, we prepared acute brain tumor slices from both mouse and human glioma samples, and treated them with RSL3. Quantification of immunofluorescent staining from three independent human slice cultures after RSL3 treatment demonstrated a significant increase in calreticulin abundance as compared to control (p &lt; 0.001). Importantly, this effect was significantly diminished with addition of ferrostatin, an inhibitor of ferroptosis, demonstrating that ferroptosis induction was directly responsible for calreticulin translocation. Single-cell RNAseq on mouse and human acute glioma slice cultures treated with RSL3 demonstrated significant overexpression of calreticulin in the tumor population, and positive enrichment of interferon signaling, antigen presentation, and phagocytosis ontologies in both tumor and myeloid compartments. These findings suggest that ferroptosis-induced translocation of calreticulin on the surface of glioma cells promotes activation of the local immune microenvironment by increasing tumor antigen presentation and pro-inflammatory cytokine release by tumor-associated microglia. Thus, ferroptosis-inducing drugs may promote anti-tumor immunity through the activation of immunogenic cell death signals.

Rosette-Forming Glioneuronal Tumor in the Pineal Region: A Series of 6 Cases and Literature Review

Resected lesions from the pineal region are rare specimens encountered by surgical pathologists, and their heterogeneity can pose significant diagnostic challenges. Here, we reviewed 221 pineal region lesions resected at New York-Presbyterian Hospital/Columbia University Irving Medical Center from 1994 to 2019 and found the most common entities to be pineal parenchymal tumors (25.3%), glial neoplasms (18.6%), and germ cell tumors (17.6%) in this predominantly adult cohort of patients. Six cases of a rare midline entity usually found exclusively in the fourth ventricle, the rosette-forming glioneuronal tumor, were identified. These tumors exhibit biphasic morphology, with a component resembling pilocytic astrocytoma admixed with variable numbers of small cells forming compact rosettes and perivascular pseudorosettes. Targeted sequencing revealed a 100% co-occurrence of novel and previously described genetic alterations in the mitogen-activated protein kinase (MAPK) and phosphoinositide 3-kinase (PI3K) signaling pathways, suggesting a synergistic role in tumor formation. The most common recurrent mutation, PIK3CA H1047R, was identified in tumor cells forming rosettes and perivascular pseudorosettes. A review of the literature revealed 16 additional cases of rosette-forming glioneuronal tumors in the pineal region. Although rare, this distinctive low-grade tumor warrants consideration in the differential diagnosis of pineal region lesions.

Targeting human leukocyte antigen G with chimeric antigen receptors of natural killer cells convert immunosuppression to ablate solid tumors

Background

Immunotherapy against solid tumors has long been hampered by the development of immunosuppressive tumor microenvironment, and the lack of a specific tumor-associated antigen that could be targeted in different kinds of solid tumors. Human leukocyte antigen G (HLA-G) is an immune checkpoint protein (ICP) that is neoexpressed in most tumor cells as a way to evade immune attack and has been recently demonstrated as a useful target for chimeric antigen receptor (CAR)-T therapy of leukemia by in vitro studies. Here, we design and test for targeting HLA-G in solid tumors using a CAR strategy.

Methods

We developed a novel CAR strategy using natural killer (NK) cell as effector cells, featuring enhanced cytolytic effect via DAP12-based intracellular signal amplification. A single-chain variable fragment (scFv) against HLA-G is designed as the targeting moiety, and the construct is tested both in vitro and in vivo on four different solid tumor models. We also evaluated the synergy of this anti-HLA-G CAR-NK strategy with low-dose chemotherapy as combination therapy.

Results

HLA-G CAR-transduced NK cells present effective cytolysis of breast, brain, pancreatic, and ovarian cancer cells in vitro, as well as reduced xenograft tumor growth with extended median survival in orthotopic mouse models. In tumor coculture assays, the anti-HLA-G scFv moiety promotes Syk/Zap70 activation of NK cells, suggesting reversal of the HLA-G-mediated immunosuppression and hence restoration of native NK cytolytic functions. Tumor expression of HLA-G can be further induced using low-dose chemotherapy, which when combined with anti-HLA-G CAR-NK results in extensive tumor ablation both in vitro and in vivo. This upregulation of tumor HLA-G involves inhibition of DNMT1 and demethylation of transporter associated with antigen processing 1 promoter.

Conclusions

Our novel CAR-NK strategy exploits the dual nature of HLA-G as both a tumor-associated neoantigen and an ICP to counteract tumor spread. Further ablation of tumors can be boosted when combined with administration of chemotherapeutic agents in clinical use. The readiness of this novel strategy envisions a wide applicability in treating solid tumors.

BOLD Asynchrony Elucidates Tumor Burden in IDH-Mutated Gliomas

BACKGROUND

Gliomas comprise the most common type of primary brain tumor, are highly invasive, and often fatal. IDH-mutated gliomas are particularly challenging to image and there is currently no clinically accepted method for identifying the extent of tumor burden in these neoplasms. This uncertainty poses a challenge to clinicians who must balance the need to treat the tumor while sparing healthy brain from iatrogenic damage. The purpose of this study was to investigate the feasibility of using resting-state blood oxygen level dependent (BOLD) functional magnetic resonance imaging (fMRI) to detect glioma-related asynchrony in vascular dynamics for distinguishing tumor from healthy brain.

METHODS

Twenty-four stereotactically localized biopsies were obtained during open surgical resection from ten treatment-naïve patients with IDH-mutated gliomas who received standard of care preoperative imaging as well as echo-planar resting-state BOLD fMRI. Signal intensity for BOLD asynchrony and standard of care imaging was compared to cell counts of total cellularity (H&E), tumor density (IDH1 & Sox2), cellular proliferation (Ki67), and neuronal density (NeuN), for each corresponding sample.

RESULTS

BOLD asynchrony was directly related to total cellularity (H&E, p = 4 x 10 -5), tumor density (IDH1, p = 4 x 10 -5; Sox2, p = 3 x 10 -5), cellular proliferation (Ki67, p = 0.002), and as well as inversely related to neuronal density (NeuN, p = 1 x 10 -4).

CONCLUSIONS

Asynchrony in vascular dynamics, as measured by resting-state BOLD fMRI, correlates with tumor burden and provides a radiographic delineation of tumor boundaries in IDH-mutated gliomas.

Right occipital transtentorial approach for a pineal malignant germ cell tumor

Germ cell tumors account for up to 53% of the malignant lesions found in the pineal region and are typically managed with a combination of radiation therapy and chemotherapy. Malignant somatic transformation of intracranial germ cell tumors is exceedingly rare and has only been reported on two other occasions. Here the authors present the case of a pineal yolk sac tumor that failed optimum first-line treatment and underwent malignant somatic transformation to an enteric mucinous adenocarcinoma requiring surgical intervention. This video demonstrates the technical nuances of the occipital transtentorial approach and the safe microsurgical dissection of lesions within the pineal region. The video can be found here: https://stream.cadmore.media/r10.3171/2021.4.FOCVID2151.

The Sledgehammer in Precision Medicine: Dexamethasone and Immunotherapeutic Treatment of Glioma

Understanding dexamethasone's effect on the immune microenvironment in glioma patients is of key importance. We performed a comprehensive literature review using the NCBI PubMed database for all articles meeting the following search criteria. ((dexamethasone[All Fields]) AND (glioma or glioblastoma)[Title/Abstract]) AND (immune or T cell or B cell or monocyte or neutrophil or macrophage). Forty-three manuscripts were deemed relevant to the topic at hand. Multiple clinical studies have linked dexamethasone use to decreased overall survival while preclinical studies in murine glioma models have demonstrated decreased tumor-infiltrating lymphocytes after dexamethasone administration.

Rationale and Clinical Implications of Fluorescein-Guided Supramarginal Resection in Newly Diagnosed High-Grade Glioma

Current standard of care for glioblastoma is surgical resection followed by temozolomide chemotherapy and radiation. Recent studies have demonstrated that >95% extent of resection is associated with better outcomes, including prolonged progression-free and overall survival. The diffusely infiltrative pattern of growth in gliomas results in microscopic extension of tumor cells into surrounding brain parenchyma that makes complete resection unattainable. The historical goal of surgical management has therefore been maximal safe resection, traditionally guided by MRI and defined as removal of all contrast-enhancing tumor. Optimization of surgical resection has led to the concept of supramarginal resection, or removal beyond the contrast-enhancing region on MRI. This strategy of extending the cytoreductive goal targets a tumor region thought to be important in the recurrence or progression of disease as well as resistance to systemic and local treatment. This approach must be balanced against the risk of impacting eloquent regions of brain and causing permanent neurologic deficit, an important factor affecting overall survival. Over the years, fluorescent agents such as fluorescein sodium have been explored as a means of more reliably delineating the boundary between tumor core, tumor-infiltrated brain, and surrounding cortex. Here we examine the rationale behind extending resection into the infiltrative tumor margins, review the current literature surrounding the use of fluorescein in supramarginal resection of gliomas, discuss the experience of our own institution in utilizing fluorescein to maximize glioma extent of resection, and assess the clinical implications of this treatment strategy.

Single-cell characterization of macrophages in glioblastoma reveals MARCO as a mesenchymal pro-tumor marker

BACKGROUND

Macrophages are the most common infiltrating immune cells in gliomas and play a wide variety of pro-tumor and anti-tumor roles. However, the different subpopulations of macrophages and their effects on the tumor microenvironment remain poorly understood.

METHODS

We combined new and previously published single-cell RNA-seq data from 98,015 single cells from a total of 66 gliomas to profile 19,331 individual macrophages.

RESULTS

Unsupervised clustering revealed a pro-tumor subpopulation of bone marrow-derived macrophages characterized by the scavenger receptor MARCO, which is almost exclusively found in IDH1-wild-type glioblastomas. Previous studies have implicated MARCO as an unfavorable marker in melanoma and non-small cell lung cancer; here, we find that bulk MARCO expression is associated with worse prognosis and mesenchymal subtype. Furthermore, MARCO expression is significantly altered over the course of treatment with anti-PD1 checkpoint inhibitors in a response-dependent manner, which we validate with immunofluorescence imaging.

CONCLUSIONS

These findings illustrate a novel macrophage subpopulation that drives tumor progression in glioblastomas and suggest potential therapeutic targets to prevent their recruitment.

Asynchrony in Peritumoral Resting-State Blood Oxygen Level-Dependent fMRI Predicts Meningioma Grade and Invasion

BACKGROUND AND PURPOSE

Meningioma grade is determined by histologic analysis, with detectable brain invasion resulting in a diagnosis of grade II or III tumor. However, tissue undersampling is a common problem, and invasive parts of the tumor can be missed, resulting in the incorrect assignment of a lower grade. Radiographic biomarkers may be able to improve the diagnosis of grade and identify targets for biopsy. Prior work in patients with gliomas has shown that the resting-state blood oxygen level-dependent fMRI signal within these tumors is not synchronous with normal brain. We hypothesized that blood oxygen level-dependent asynchrony, a functional marker of vascular dysregulation, could predict meningioma grade.

MATERIALS AND METHODS

We identified 25 patients with grade I and 11 patients with grade II or III meningiomas. Blood oxygen level-dependent time-series were extracted from the tumor and the radiographically normal control hemisphere and were included as predictors in a multiple linear regression to generate a blood oxygen level-dependent asynchrony map, in which negative values signify synchronous and positive values signify asynchronous activity relative to healthy brain. Masks of blood oxygen level-dependent asynchrony were created for each patient, and the fraction of the mask that extended beyond the contrast-enhancing tumor was computed.

RESULTS

The spatial extent of blood oxygen level-dependent asynchrony was greater in high (grades II and III) than in low (I) grade tumors (P < 0.001) and could discriminate grade with high accuracy (area under the curve = 0.88).

CONCLUSIONS

Blood oxygen level-dependent asynchrony radiographically discriminates meningioma grade and may provide targets for biopsy collection to aid in histologic diagnosis.

Deconvolution of cell type-specific drug responses in human tumor tissue with single-cell RNA-seq

BACKGROUND

Preclinical studies require models that recapitulate the cellular diversity of human tumors and provide insight into the drug sensitivities of specific cellular populations. The ideal platform would enable rapid screening of cell type-specific drug sensitivities directly in patient tumor tissue and reveal strategies to overcome intratumoral heterogeneity.

METHODS

We combine multiplexed drug perturbation in acute slice culture from freshly resected tumors with single-cell RNA sequencing (scRNA-seq) to profile transcriptome-wide drug responses in individual patients. We applied this approach to drug perturbations on slices derived from six glioblastoma (GBM) resections to identify conserved drug responses and to one additional GBM resection to identify patient-specific responses.

RESULTS

We used scRNA-seq to demonstrate that acute slice cultures recapitulate the cellular and molecular features of the originating tumor tissue and the feasibility of drug screening from an individual tumor. Detailed investigation of etoposide, a topoisomerase poison, and the histone deacetylase (HDAC) inhibitor panobinostat in acute slice cultures revealed cell type-specific responses across multiple patients. Etoposide has a conserved impact on proliferating tumor cells, while panobinostat treatment affects both tumor and non-tumor populations, including unexpected effects on the immune microenvironment.

CONCLUSIONS

Acute slice cultures recapitulate the major cellular and molecular features of GBM at the single-cell level. In combination with scRNA-seq, this approach enables cell type-specific analysis of sensitivity to multiple drugs in individual tumors. We anticipate that this approach will facilitate pre-clinical studies that identify effective therapies for solid tumors.

Prognostic value of nadir GH levels for long-term biochemical remission or recurrence in surgically treated acromegaly

CONTEXT

Outcome of acromegaly surgery is assessed by IGF-1 and glucose-suppressed GH, but whether the latter provides additional clinically relevant information when IGF-1 is normal is unclear. The role of GH suppression testing after surgery requires clarification.

METHODS

We studied 97 acromegaly patients with normal IGF-1 after surgery by measuring GH after oral glucose longitudinally, initially at ≥ 3 months after surgery and repeated one or more times ≥ 1 year later. Nadir GH was categorized as normal or abnormal relative to the 97.5th percentile of nadir GH in 100 healthy subjects, which were ≤ 0.14 µg/L (DSL IRMA) or ≤ 0.15 µg/L(IDS iSYS). Signs and symptoms scores and insulin resistance were followed longitudinally.

RESULTS

Of 68 patients with initial normal GH suppression 63 (93%) remained in remission and of 29 with initial abnormal GH suppression, 9 (31%) recurred. Recurrence was more common in patients with abnormal suppression (P < 0.001). A total of 14 patients recurred, including 5 with normal GH suppression progressing to abnormal and then recurrence. Overall, serial signs and symptoms and insulin resistance assessments did not identify patients with abnormal suppression or recurrence.

CONCLUSION

Risk of recurrence after surgery is increased for patients with a normal IGF-1 level, but abnormal GH suppression. We newly find, using both our and others' cut-offs, that while normal suppression predicts long-term remission in most patients, some can progress from normal to abnormal suppression and then recurrence after many years of follow up. Nadir GH levels are of prognostic value in acromegaly patients with normal IGF-1 levels after surgery.

Convection-enhanced drug delivery for glioblastoma: a review

INTRODUCTION

Convection-enhanced delivery (CED) is a method of targeted, local drug delivery to the central nervous system (CNS) that bypasses the blood-brain barrier (BBB) and permits the delivery of high-dose therapeutics to large volumes of interest while limiting associated systemic toxicities. Since its inception, CED has undergone considerable preclinical and clinical study as a safe method for treating glioblastoma (GBM). However, the heterogeneity of both, the surgical procedure and the mechanisms of action of the agents studied-combined with the additional costs of performing a trial evaluating CED-has limited the field's ability to adequately assess the durability of any potential anti-tumor responses. As a result, the long-term efficacy of the agents studied to date remains difficult to assess.

MATERIALS AND METHODS

We searched PubMed using the phrase "convection-enhanced delivery and glioblastoma". The references of significant systematic reviews were also reviewed for additional sources. Articles focusing on physiological and physical mechanisms of CED were included as well as technological CED advances.

RESULTS

We review the history and principles of CED, procedural advancements and characteristics, and outcomes from key clinical trials, as well as discuss the potential future of this promising technique for the treatment of GBM.

CONCLUSION

While the long-term efficacy of the agents studied to date remains difficult to assess, CED remains a promising technique for the treatment of GBM.

Body Composition Changes with Long-term Pegvisomant Therapy of Acromegaly

Context

In active acromegaly, the lipolytic and insulin antagonistic effects of growth hormone (GH) excess alter adipose tissue (AT) deposition, reduce body fat, and increase insulin resistance. This pattern reverses with surgical therapy. Pegvisomant treats acromegaly by blocking GH receptor (GHR) signal transduction and lowering insulin-like growth factor 1 (IGF-1) levels. The long-term effects of GHR antagonist treatment of acromegaly on body composition have not been studied.

Methods

We prospectively studied 21 patients with active acromegaly who were starting pegvisomant. Body composition was examined by whole body magnetic resonance imaging, proton magnetic resonance spectroscopy of liver and muscle and dual-energy x-ray absorptiometry, and endocrine and metabolic markers were measured before and serially during 1.0 to 13.4 years of pegvisomant therapy. The data of patients with acromegaly were compared with predicted and to matched controls.

Results

Mass of visceral AT (VAT) increased to a peak of 187% (1.56-229%) (P < .001) and subcutaneous AT (SAT) to 109% (–17% to 57%) (P = .04) of baseline. These remained persistently and stably increased, but did not differ from predicted during long-term pegvisomant therapy. Intrahepatic lipid rose from 1.75% to 3.04 % (P = .04). Although lean tissue mass decreased significantly, skeletal muscle (SM) did not change. IGF-1 levels normalized, and homeostasis model assessment insulin resistance and HbA1C were lowered.

Conclusion

Long-term pegvisomant therapy is accompanied by increases in VAT and SAT mass that do not differ from predicted, stable SM mass and improvements in glucose metabolism. Long-term pegvisomant therapy does not produce a GH deficiency-like pattern of body composition change.

Gonadotroph tumours with a low SF-1 labelling index are more likely to recur and are associated with enrichment of the PI3K-AKT pathway

AIMS

The gonadotroph tumour (GT) is the most frequently resected pituitary neuroendocrine tumour. Although many symptomatic GT are successfully resected, some recur. We sought to identify histological biomarkers that may predict recurrence and explore biological mechanisms that explain this difference in behaviour.

METHODS

SF-1 immunohistochemistry of 51 GT, a subset belonging to a longitudinal prospective cohort study (n = 25), was reviewed. Four groups were defined: Group 1-recently diagnosed GT (n = 20), Group 2-non-recurrent GT with long-term follow up (n = 11), Group 3-initial resections of GT that recur (n = 7) and Group 4-recurrent GT (n = 13). The percentage of SF-1 immunolabelling in the lowest staining fields (SF-1 labelling index (SLI)) was assessed and RNA sequencing was performed on 5 GT with SLI <80% and 5 GT with SLI >80%.

RESULTS

Diffuse, strong SF-1 immunolabelling was the most frequent pattern in Groups 1/2, whereas patchy SF-1 staining predominated in Groups 3/4. There was a lower median SLI in Groups 3/4 than 1/2. Overall, GT with SLI <80% recurred earlier than GT with SLI >80%. Differential expression analysis identified 89 statistically significant differentially expressed genes (FDR <0.05) including over-expression of pituitary stem cell genes (SOX2, GFRA3) and various oncogenes (e.g. BCL2, ERRB4) in patchy SF-1 GT. Gene set enrichment analysis identified significant enrichment of genes involved in the PI3K-AKT pathway.

CONCLUSIONS

We speculate that patchy SF-1 labelling in GT reflects intratumoural heterogeneity and are less differentiated tumours than diffusely staining GT. SF-1 immunolabelling patterns may have prognostic significance in GT, but confirmatory studies are needed for further validation.

Focused Ultrasound-Mediated Blood-Brain Barrier Opening Increases Delivery and Efficacy of Etoposide for Glioblastoma Treatment

PURPOSE

Glioblastoma (GBM) is a devastating disease. With the current treatment of surgery followed by chemoradiation, outcomes remain poor, with median survival of only 15 months and a 5-year survival rate of 6.8%. A challenge in treating GBM is the heterogeneous integrity of the blood-brain barrier (BBB), which limits the bioavailability of systemic therapies to the brain. There is a growing interest in enhancing drug delivery by opening the BBB with the use of focused ultrasound (FUS). We hypothesize that an FUS-mediated BBB opening can enhance the delivery of etoposide for a therapeutic benefit in GBM.

METHODS AND MATERIALS

A murine glioma cell line (Pdgf⁺, Pten^-/-, P53^-/-) was orthotopically injected into B6(Cg)-Tyrc-2J/J mice to establish the syngeneic GBM model for this study. Animals were treated with FUS and microbubbles to open the BBB to enhance the delivery of systemic etoposide. Magnetic resonance (MR) imaging was used to evaluate the BBB opening and tumor progression. Liquid chromatography tandem mass spectrometry was used to measure etoposide concentrations in the intracranial tumors.

RESULTS

The murine glioma cell line is sensitive to etoposide in vitro. MR imaging and passive cavitation detection demonstrate the safe and successful BBB opening with FUS. The combined treatment of an FUS-mediated BBB opening and etoposide decreased tumor growth by 45% and prolonged median overall survival by 6 days: an approximately 30% increase. The FUS-mediated BBB opening increased the brain tumor-to-serum ratio of etoposide by 3.5-fold and increased the etoposide concentration in brain tumor tissue by 8-fold compared with treatment without ultrasound.

CONCLUSIONS

The current study demonstrates that BBB opening with FUS increases intratumoral delivery of etoposide in the brain, resulting in local control and overall survival benefits.