Long-term survival in patients with brain-only metastatic non-small cell lung cancer undergoing upfront intracranial stereotactic radiosurgery and definitive treatment to the thoracic primary site

BACKGROUND AND PURPOSE

To evaluate modern clinical outcomes for patients with brain-only metastatic non-small cell lung cancer (NSCLC) treated with intracranial stereotactic radiosurgery (SRS) with or without definitive treatment of the primary site.

MATERIALS AND METHODS

Patients with synchronously diagnosed NSCLC and brain-only metastatic disease treated with intracranial SRS at a single institution were retrospectively identified. Patients were stratified based on whether they did (A) or did not (B) receive definitive primary site treatment. Patient characteristics and clinical outcomes were compared.

RESULTS

From 2008 to 2022, 103 patients were identified, 53 of whom received definitive primary site treatment. Median follow-up was 2.1 y (A) and 0.8 y (B) (p < 0.001). 28 (53 %) patients in Group A received immune checkpoint inhibitor (ICI) therapy versus 19 (38 %) in Group B (p = 0.13) and there were no other statistically significant baseline or treatment characteristic differences between the groups. 5-year local-PFS was 34.5 % (A) versus 0 % (B) (p < 0.001). 5-year regional-PFS was 33.0 % (A) versus 0 % (B) (p < 0.001). 5-year distant body-PFS was 34.0 % (A) versus 0 % (B) (p < 0.001). 5-year CNS-PFS was 14.7 % (A) versus 0 % (B) (p = 0.12). 5-year OS was 40.2 % (A) versus 0 % (B) (p = 0.001). 5-year CSS was 67.6 % (A) versus 0 % (B) (p = 0.002). On multivariable analysis, lack of definitive treatment to the primary site (HR = 2.40), AJCC T3-4 disease (HR = 2.73), and lack of ICI therapy (HR = 2.86) were significant predictors of death.

CONCLUSION

Definitive treatment to the thoracic primary site in patients with brain-only metastatic NSCLC after intracranial radiosurgery was associated with slower progression of disease and improved survival.

Metabolomic Profiles of Human Glioma Inform Patient Survival

Aims: Targeting tumor metabolism may improve the outcomes for patients with glioblastoma (GBM). To further preclinical efforts targeting metabolism in GBM, we tested the hypothesis that brain tumors can be stratified into distinct metabolic groups with different patient outcomes. Therefore, to determine if tumor metabolites relate to patient survival, we profiled the metabolomes of human gliomas and correlated metabolic information with clinical data. Results: We found that isocitrate dehydrogenase-wildtype (IDHwt) GBMs are metabolically distinguishable from IDH mutated (IDHmut) astrocytomas and oligodendrogliomas. Survival of patients with IDHmut gliomas was expectedly more favorable than those with IDHwt GBM, and metabolic signatures can stratify IDHwt GBMs subtypes with varying prognoses. Patients whose GBMs were enriched in amino acids had improved survival, while those whose tumors were enriched for nucleotides, redox molecules, and lipid metabolites fared more poorly. These findings were recapitulated in validation cohorts using both metabolomic and transcriptomic data. Innovation: Our results suggest the existence of metabolic subtypes of GBM with differing prognoses, and further support the concept that metabolism may drive the aggressiveness of human gliomas. Conclusions: Our data show that metabolic signatures of human gliomas can inform patient survival. These findings may be used clinically to tailor novel metabolically targeted agents for GBM patients with different metabolic phenotypes. Antioxid. Redox Signal. 39, 942-956.

Exploiting Enhanced Lipid Metabolism in Glioblastoma through Diet Modification

PURPOSE/OBJECTIVE(S)

Enhanced lipid metabolism has emerged as a central metabolic node in glioblastoma, serving as a 'gain of function' that allows these cells to efficiently adapt to their dynamic tumor microenvironment. Seemingly contradictory to this, pre-clinical studies have demonstrated anti-tumor activity in mice fed a high-fat/low-carbohydrate ketogenic diet (KD), both alone and in combination with radiation therapy (RT). In this study, we sought to identify mechanisms underlying the antitumor activity of a KD in glioblastoma from a metabolic perspective to better understand factors contributing to this apparent disconnect.

MATERIALS/METHODS

Immunocompromised and immunocompetent mice were injected orthotopically with human and mouse-derived glioblastoma cell lines and randomized to four treatment arms. Mice were fed ad libitum a standard diet (SD), KD (Bio-Serve), or a modified unsaturated fatty acid (uFA) rich diet (MD; 60/30/10: fat/protein/carb) alone or in combination with hypofractionated RT (6 Gy x 3). Global metabolomic profiling of tumors and serum were carried out using LC/GC-MS. Lipid droplets were analyzed by flow cytometer and confocal microscopy using BODIPY staining and free fatty acids were measured using a commercially available kit.

RESULTS

A KD demonstrated independent anti-tumor activity and potent synergy with RT in two aggressive glioblastoma models. Metabolomic profiling of tumors revealed significant changes in tumor metabolism in KD-fed mice when compared to SD, with an accumulation of uFAs being a key finding. We therefore sought to determine if this accumulation of fatty acids in KD mice contributed towards the observed anti-tumor activity. Consistent with in vivo results, in vitro studies using the uFA linoleic acid demonstrated anti-proliferative activity, reduced clonogenic capacity, and potent synergy when combined with RT in glioblastoma cells. Through a series of investigations, we went on to determine that this anti-tumor activity was attributed to the ability of uFA to override lipid storage homeostasis in glioblastoma cells, resulting in lipotoxicity. Based on these findings, we hypothesized high fat concentrations, rather than carbohydrate restriction, contributed to the anti-tumor activity of a KD. To test this, we generated a MD rich in uFA that did not require carbohydrate restriction. Similar to a KD, mice fed a MD demonstrated both independent anti-tumor activity and potent synergy when combined with RT.

CONCLUSION

High concentrations of uFA represents a key factor underlying the anti-tumor activity of a KD in glioblastoma by targeting lipid homeostasis. A MD consisting of high concentrations of uFA without carbohydrate restriction demonstrates promising anti-tumor activity in glioblastoma models. As a major limitation of a KD is tolerability, particularly in glioblastoma patients, a MD represents a promising form of dietary modification that may be translated clinically.

Long-Term Survival in Patients with Brain-Only Metastatic Lung Cancer Undergoing Upfront Intracranial Stereotactic Radiosurgery and Definitive Treatment to the Thoracic Primary Site

PURPOSE/OBJECTIVE(S)

To evaluate modern clinical outcomes for patients with brain-only metastatic lung cancer treated with intracranial stereotactic radiosurgery (SRS) with or without definitive treatment of the primary site.

MATERIALS/METHODS

Patients with new diagnosis of lung cancer and synchronous brain-only metastatic disease treated with intracranial SRS were identified in a prospectively maintained, single institution database. Patients were stratified based on whether they did (Group A) or did not receive (Group B) definitive primary site treatment, defined by surgical resection or radiation therapy (RT) to a dose > 40 Gy. Patient demographics and treatment details were recorded. Intrathoracic, distant body, and intracranial progression, as well as overall survival (OS) and cancer-specific survival (CSS) were recorded, with 2- and 5-y rates estimated using the Kaplan-Meier method. Univariate (UVA) and multivariate analysis (MVA) were performed to determine predictors of OS.

RESULTS

From 2008-2022, 107 patients were identified. 57 patients received definitive primary site treatment, of whom forty received upfront and seventeen received consolidative treatment at a median 9 months after diagnosis. 45 patients underwent fractionated RT to a median dose of 60 Gy (range 45-74 Gy), 9 underwent SBRT to a median dose of 50 Gy in 5 fractions (range 40-60 Gy), and 3 had lobectomy. Median follow-up was 2.7 y (A) and 1.2 y (B) (p<0.01). Median number of brain metastases was 1 (range 1-17; 82% 1-3 and 18% ≥ 4). There were no significant differences in patient age, sex, race, smoking status, histology, targetable mutations, AJCC T- or N-stage, receipt of systemic therapy, number or volume of brain metastases, neurologic deficits, or resected brain metastases between the groups. 82% (A) and 72% (B) of patients were T1-4N1-3, while 16% (A) and 24% (B) were T1-3N0. 32 (56%) patients in Group A received immunotherapy (ICI) versus 19 (38%) in Group B (p = 0.048). There were no differences in intracranial progression-free survival (PFS) (p = 0.17) or CNS-related death (p = 0.30) between groups. 2- and 5-y estimates for OS were 61.4% and 38.5% (A) versus 28.3% and 0% (B) (p = 0.002). 2- and 5-y CSS were 83.8% and 64.2% (A) versus 48.6% and 0% (B) (p = 0.002). 2- and 5-year intrathoracic PFS were 90% and 75% (A) versus 55% and 55% in (B) (p<0.01). 2- and 5-y distant body PFS were 49.3% and 32% (A) versus 17.3% and 0% (B) (p = 0.001). On UVA, definitive primary site treatment, receipt of immunotherapy, and young age were significant predictors of OS, and each of these remained significant on MVA.

CONCLUSION

Definitive treatment to the thoracic primary site in patients with brain-only metastatic lung cancer after intracranial radiosurgery was associated with not only reduced rates of intrathoracic progression but also lower rates of distant systemic progression and improved overall and cancer-specific survival.

Quinolinate promotes macrophage-induced immune tolerance in glioblastoma through the NMDAR/PPARγ signaling axis

There has been considerable scientific effort dedicated to understanding the biologic consequence and therapeutic implications of aberrant tryptophan metabolism in brain tumors and neurodegenerative diseases. A majority of this work has focused on the upstream metabolism of tryptophan; however, this has resulted in limited clinical application. Using global metabolomic profiling of patient-derived brain tumors, we identify the downstream metabolism of tryptophan and accumulation of quinolinate (QA) as a metabolic node in glioblastoma and demonstrate its critical role in promoting immune tolerance. QA acts as a metabolic checkpoint in glioblastoma by inducing NMDA receptor activation and Foxo1/PPARγ signaling in macrophages, resulting in a tumor supportive phenotype. Using a genetically-engineered mouse model designed to inhibit production of QA, we identify kynureninase as a promising therapeutic target to revert the potent immune suppressive microenvironment in glioblastoma. These findings offer an opportunity to revisit the biologic consequence of this pathway as it relates to oncogenesis and neurodegenerative disease and a framework for developing immune modulatory agents to further clinical gains in these otherwise incurable diseases.

Introduce a rotational robust optimization framework for spot-scanning proton arc (SPArc) therapy

Objective. Proton dosimetric uncertainties resulting from the patient's daily setup errors in rotational directions exist even with advanced image-guided radiotherapy techniques. Thus, we developed a new rotational robust optimization SPArc algorithm (SPArc_rot) to mitigate the dosimetric impact of the rotational setup error in Raystation ver. 6.02 (RaySearch Laboratory AB, Stockholm, Sweden).Approach.The initial planning CT was rotated ±5° simulating the worst-case setup error in the roll direction. The SPArc_rotuses a multi-CT robust optimization framework by taking into account of such rotational setup errors. Five cases representing different disease sites were evaluated. Both SPArc_originaland SPArc_rotplans were generated using the same translational robust optimized parameters. To quantitatively investigate the mitigation effect from the rotational setup errors, all plans were recalculated using a series of pseudo-CT with rotational setup error (±1°/±2°/±3°/±5°). Dosimetric metrics such as D98% of CTV, and 3D gamma analysis were used to assess the dose distribution changes in the target and OARs.Main results.The magnitudes of dosimetric changes in the targets due to rotational setup error were significantly reduced by the SPArc_rotcompared to SPArc in all cases. The uncertainties of the max dose to the OARs, such as brainstem, spinal cord and esophagus were significantly reduced using SPArc_rot. The uncertainties of the mean dose to the OARs such as liver and oral cavity, parotid were comparable between the two planning techniques. The gamma passing rate (3%/3 mm) was significantly improved for CTV of all tumor sites through SPArc_rot.Significance.Rotational setup error is one of the major issues which could lead to significant dose perturbations. SPArc_rotplanning approach can consider such rotational error from patient setup or gantry rotation error by effectively mitigating the dose uncertainties to the target and in the adjunct series OARs.

TMET-11. QUINOLINATE PROMOTES ALTERNATIVELY ACTIVATED MACROPHAGE-INDUCED IMMUNE TOLERANCE IN GLIOBLASTOMA THROUGH THE NMDA/PPARG SIGNALING AXIS

There has been considerable interest in understanding the biological consequence and therapeutic implications of aberrant tryptophan metabolism in brain tumors and neurodegenerative diseases. An overwhelming majority of this work has focused on the first-step of tryptophan metabolism (kynurenine); however, this has yet to result in clinical application. Using global metabolomic profiling on &gt;100 patient-derived brain tumors, we identified a 64-fold accumulation of quinolinate (QA), a downstream metabolic intermediate of the tryptophan pathway, in glioblastoma when compared to low-grade glioma. As several metabolites in the tryptophan pathway have been implicated in immune modulation, we sought to determine the impact of QA on the immune microenvironment. We identified the capacity of QA to strongly skew macrophage polarization towards the “pro-tumorigenic” M2-phenotype with suppressive properties, which recent studies suggest play a dominant role in the immune microenvironment in glioblastoma. Intriguingly, QA conferred an “M2-like” phenotype to M1 macrophages and microglia, attenuating their phagocytosis efficiency. We went on to systematically delineate a novel mechanism of macrophage polarization through QA-induced NMDA receptor activation and Foxo1/PPARg signaling. We then determined that tumor cells and host macrophages/microglia work in concert to complete both upstream and downstream metabolism of tryptophan, respectively, resulting in the accumulation of QA. We discovered a very strong positive feedback loop involving the expression of kynureninase (KYNU) in macrophages, an enzyme involved in the downstream metabolism of tryptophan and QA production, making this a lead candidate for targeting this pathway. As this represents a novel target and agents designed to inhibit this enzyme are not commercially available, we generated a Kynu-/- knockout mouse model. Intriguingly, consistent with in vitro data, tumors grown in Kynu-/- mice had a ~50% reduction in M2 macrophages, increased immune activation, decreased growth, and improved overall survival in two orthotopic glioblastoma models, supporting the therapeutic potential of targeting this pathway.

TMET-22. ENHANCED LIPID METABOLISM IN BRAIN TUMORS: AN EXPLOITABLE METABOLIC VULNERABILITY THROUGH DIET-INDUCED KETOSIS

Enhanced lipid metabolism contributes towards carcinogenesis at multiple levels, serving as a "gain of function" in several cancers, including glioblastoma. Seemingly paradoxical to these findings, pre-clinical investigations have demonstrated anti-tumor activity in mice fed a high fat/low carbohydrate ketogenic diet (KD), both alone and in combination with conventional therapy. Therefore, we sought to define mechanistic underpinnings contributing towards this apparent disconnect. Consistent with previous reports, mice fed a KD demonstrated independent anti-tumor activity and potent synergy with RT when tested in an aggressive glioblastoma orthotopic model. To provide a window into metabolic consequences of a KD in glioblastoma, we performed global metabolomic profiling on tumors and serum from mice fed a standard diet and KD. Although ketosis was confirmed, no change in glucose was observed in serum of KD mice, suggesting presence/absence of carbohydrates might not be contributing to the observed anti-tumor activity. Interestingly, profound intra-tumoral metabolic changes were observed in intracranial tumors from mice fed a KD, with an accumulation of unsaturated fatty acids emerging as a central metabolic node. Intriguingly, recapitulating these findings in culture conditions in vitro, polyunsaturated fatty acid linoleic acid demonstrated anti-proliferative activity, decreased clonogenic capacity, and synergy with RT in GBM cells, recapitulating in vivo findings. This was not observed when cultured with the monounsaturated fatty acid oleic acid. Through a series of investigations, we went on to identify lipid storage homeostasis and lipotoxicity associated with free fatty acid accumulation played a contributory role in the differential activity of these different classes of fatty acids. Importantly, PUFA-rich modified diet showed potent antitumor activity in combination with RT in our preliminary investigation. These studies collectively reaffirm and provide mechanistic underpinnings of the anti-tumor activity of a KD, suggesting that enhanced lipid metabolism in brain tumors may serve as an exploitable metabolic vulnerability through diet modification.

TMET-13. SEX DIFFERENCES IN GLUCOSE METABOLISM AND MITOCHONDRIAL FUNCTION IN GLIOBLASTOMA IMPLICATE HYPOXIA-INDUCIBLE FACTOR 1 ALPHA (HIF1A) ACTIVITY

Glioblastoma (GBM) is the most common and aggressive primary brain tumor in adults. It is more prevalent in males and female patients have better survival. Investigating the molecular mechanisms underlying this disparity is imperative for understanding its development and progression as well as developing novel treatment paradigms. Carbohydrate (namely glucose) metabolism is a critical GBM nutrient source for biosynthesis, energetics, and reducing equivalents. Previously, our group discovered that elevated glycolytic activity uniquely predicted the outcomes of male, but not female, lower grade glioma patients. Our goal was to characterize sex differences in GBM carbohydrate metabolism and their effects on cellular phenotype. First, we discovered that male transformed murine astrocytes were more susceptible to glucose deprivation than females. We confirmed this phenotype with irreversible inhibition of hexokinase with 2-deoxyglucose as well as a GLUT1-selective inhibitor. Time-resolved stable isotope tracing of cell metabolism with carbon-13 glucose in transformed astrocytes further supported these findings; male cells had significantly higher rates of glucose uptake and metabolism than female cells. These results were validated with stable isotope metabolomics datasets from human cancer cell lines. Using additional assays of cellular metabolism, we discovered that male transformed astrocytes had a higher glycolytic rate, higher pyruvate kinase activity, higher mitochondrial respiration, and higher mitochondrial mass compared to females. This was validated by a TCGA pancancer analysis that revealed significantly higher expression of nuclear genes involved in mitochondrial regulation in males than in females. This prompted us to identify possible regulators of this metabolic phenotype. We discovered that HIF1A had robust hypoxia-inducible expression that was significantly higher in male transformed astrocytes. Moreover, HIF1A expression as well as its target transcripts were significantly higher in TCGA pancancer tumor datasets. Together, our data underscore the potential for developing sex-specific metabolic targeting approaches for patients with GBM.

MODL-02. GLIOMA ORGANOID MODEL PHENOTYPICALLY RECAPITULATES KEY ASPECTS OF MALIGNANT TRANSFORMATION IN GLIOBLASTOMA

Glioblastoma (GBM) displays extensive intra-tumoral heterogeneity, serving as a major obstacle for effective treatment. The identification of molecular subtypes offered promise for personalized treatment regimens in GBM, however, it has seen been determined these subtypes are reflective of intra- rather than inter-tumoral heterogeneity, with proneural (PN) and mesenchymal (MES) subtypes corresponding to the infiltrative edge and peri-necrotic core of a tumor, respectively. Further, plasticity between subtypes has been identified, with PN-to-MES transition being described as a mode of resistance. Our laboratory utilizes patient-derived, subtype-specific GBM neurospheres as a model to understand GBM heterogeneity and have previously demonstrated that these models faithfully recapitulate human disease, with PN-neurospheres expressing Olig2, having a metabolic phenotype consistent with low-grade glioma, and an indolent growth pattern in vivo when compared to aggressive, CD44 expressing MES-neurospheres. In parallel, our group demonstrated 3D-organoid models of GBM recapitulate the tumor ecology of this malignancy ex vivo. Therefore, we sought to determine if this model could be utilized to provide a window into the plasticity of GBM molecular subtypes. Consistent with their phenotype when grown as neurospheres, MES-organoids had a homogeneous distribution of proliferating cells and retained CD44 expression. In contrast, cellular heterogeneity emerged in PN organoids that could be morphologically divided into an outer, cell-dense rim and an inner core with a lower cell density. The outer rim, recapitulating a perivascular niche, contained proliferating cells, and the inner core contained necrotic cells, mimicking the hypoxic microenvironment of GBM. Intriguingly, PN organoids retained Olig2 expression in the edge, however, actively transitioned into a MES-like state in the core, expressing CD44 and metabolic reprogramming consistent with malignant transformation. Collectively, these finding support that microenvironment contributes towards PN-MES transition and PN organoid models may serve as a tool to provide a window into specific molecular and metabolic factors contributing towards transformation.

IMMU-05. THE INFLUENCE OF THE KETOGENIC DIET ON THE IMMUNE TOLERANT MICROENVIRONMENT IN GLIOBLASTOMA

Glioblastoma (GBM) represents a particularly aggressive and immune-resistant cancer. Preclinical investigations have identified the anti-tumor activity of a ketogenic diet (KD) in GBM, potentially being used as a tool to target its glycolytic phenotype. Since immune cells in the tumor have a similar reliance upon nutrients to perform their individual functions, we sought to determine if the KD influenced the immune landscape of GBM. Utilizing genetically-engineered murine GBM tumor cells orthotopically implanted in immune-competent mice, we demonstrate that KD improved survival in GBM. Immunophenotyping of tumors identified a novel role KD plays in macrophage polarization, with a paradoxical 50% increase in immune-suppressive M2-macrophages and a decrease in pro-inflammatory M1-macrophages. We recapitulated KD in vitro using a modified cell culture based on comprehensive metabolomic profiling of serum in KD-fed mice. Consistent with in vivo studies, murine macrophages cultured in these conditions skewed polarization towards the M2-phenotype with immune-suppressive properties. We went on to mechanistically link these findings to the activation of transcription factor PPARg. Although anti-tumor activity was observed in mice fed a KD, we hypothesized this parallel increase in M2 macrophage polarization tempered its potential therapeutic benefit. Colony-stimulating factor 1 (CSF-1) plays a central role in macrophage differentiation, and CSF-1R inhibition is actively being investigated as a strategy to skew their polarization towards an M1-phenotype. Therefore, we tested a combination of KD with the brain-penetrant CSF-1R inhibitor BLZ945. Consistent with our hypothesis, this combination demonstrated a striking improvement in survival (p = 0.0004), with 50% of mice achieving long-term survival ( &gt; 50 days). Correlative studies confirmed the capacity of BLZ945 to normalize KD-induced increases in M2s, and the combination induced an increase of anti-tumor iNOS+M1s. Combinatorial strategies using agents designed to modulate macrophage polarization represent a rational approach to improve the anti-tumor activity of KD in GBM.

Sex differences in brain tumor glutamine metabolism reveal sex-specific vulnerabilities to treatment

BACKGROUND

Brain cancer incidence and mortality rates are greater in males. Understanding the molecular mechanisms that underlie those sex differences could improve treatment strategies. Although sex differences in normal metabolism are well described, it is currently unknown whether they persist in cancerous tissue.

METHODS

Using positron emission tomography (PET) imaging and mass spectrometry, we assessed sex differences in glioma metabolism in samples from affected individuals. We assessed the role of glutamine metabolism in male and female murine transformed astrocytes using isotope labeling, metabolic rescue experiments, and pharmacological and genetic perturbations to modulate pathway activity.

FINDINGS

We found that male glioblastoma surgical specimens are enriched for amino acid metabolites, including glutamine. Fluoroglutamine PET imaging analyses showed that gliomas in affected male individuals exhibit significantly higher glutamine uptake. These sex differences were well modeled in murine transformed astrocytes, in which male cells imported and metabolized more glutamine and were more sensitive to glutaminase 1 (GLS1) inhibition. The sensitivity to GLS1 inhibition in males was driven by their dependence on glutamine-derived glutamate for α-ketoglutarate synthesis and tricarboxylic acid (TCA) cycle replenishment. Females were resistant to GLS1 inhibition through greater pyruvate carboxylase (PC)-mediated TCA cycle replenishment, and knockdown of PC sensitized females to GLS1 inhibition.

CONCLUSION

Our results show that clinically important sex differences exist in targetable elements of metabolism. Recognition of sex-biased metabolism may improve treatments through further laboratory and clinical research.

FUNDING

This work was supported by NIH grants, Joshua's Great Things, the Siteman Investment Program, and the Barnard Research Fund.

Abstract 632: The immune consequences of a ketogenic diet in GBM and its therapeutic implications

Glioblastoma (GBM) is one of the most complex, deadly, and immune-resistant cancers. Recent investigations have identified a ketogenic diet (KD) as a nutritional intervention in GBM. KD is a high-fat diet with a low carbohydrate intake. It is postulated that a KD dramatically shifts nutritional bioavailability in both tumors and its microenvironment. Since immune cells also rely upon similar nutrients for performing their functions, we hypothesized that a KD might also influence their anti-tumor activity. Consistent with previous publications, utilizing genetically engineered murine GBM tumor cells orthotopically implanted in immune-competent mice, we demonstrated improved survival in mice fed a KD when compared to mice fed a standard diet (p=0.043). To begin to understand the immune consequences of a KD in GBM, we immunophenotyped these tumors. Of the immune cells analyzed, we discovered that KD played an important role in influencing macrophage polarization, which recent investigations suggest play a critical role in inducing a potent immune suppression in GBM. Specifically, anti-tumor activity was observed in mice fed a KD, there was a paradoxical 50% increase in immune suppressive M2 macrophages (CD45+CD11b+F4/80+CD206+) coupled with a decrease in pro-inflammatory M1 macrophages (CD45+CD11b+F4/80+CD80hi). To extend these findings, we recapitulated KD in vitro using a modified cell culture media. Consistent with in vivo studies, murine macrophages cultured in these conditions skewed polarization towards the M2 phenotype with immune suppressive properties and we went on to mechanistically link these findings to activation of transcription factor PPARγ. Although anti-tumor activity was observed in mice fed a KD, we hypothesized this parallel increase in M2 macrophage polarization tempered its potential therapeutic benefit. Colony-stimulating factor 1 (CSF-1) plays a central role in macrophage differentiation and CSF-1 receptor inhibition is actively being investigated as a strategy to skew their polarization towards an M1 anti-tumor phenotype. To test this hypothesis, we performed investigations combining KD with the brain penetrant, clinically relevant CSF-1R inhibitor BLZ945. Consistent with our hypothesis, this combination demonstrated a striking improvement in survival in comparison to KD or BLZ945 alone (p=0.0004) with 50% of mice achieving long term survival (&gt;50 days). Correlative studies confirmed the capacity of BLZ945 to normalize KD-induced increases in M2s and the combination induced an increase of iNOS+ M1s, which are responsible for performing pro-inflammatory functions in tumors. Collectively, although anti-tumor activity was observed with a KD, parallel increases in M2 macrophage tempered its therapeutic benefit. Combinatorial strategies using agents designed to modulate macrophage polarization represent a rational approach to improve the anti-tumor activity of a KD in GBM.

Citation Format: Pravin Kesarwani, Shiva Kant, Yi Zhao, C. Ryan Miller, Prakash Chinnaiyan. The immune consequences of a ketogenic diet in GBM and its therapeutic implications [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 632.

Redefine the Role of Spot-Scanning Proton Beam Therapy for the Single Brain Metastasis Stereotactic Radiosurgery

Purpose

To explore the role of using Pencil Beam Scanning (PBS) proton beam therapy in single lesion brain stereotactic radiosurgery (SRS), we developed and validated a dosimetric in silico model to assist in the selection of an optimal treatment approach among the conventional Volumetric Modulated Arc Therapy (VMAT), Intensity Modulated Proton Therapy (IMPT) and Spot-scanning Proton Arc (SPArc).

Material and Methods

A patient’s head CT data set was used as an in silico model. A series of targets (volume range from 0.3 cc to 33.03 cc) were inserted in the deep central and peripheral region, simulating targets with different sizes and locations. Three planning groups: IMPT, VMAT, and SPArc were created for dosimetric comparison purposes and a decision tree was built based on this in silico model. Nine patients with single brain metastases were retrospectively selected for validation. Multiple dosimetric metrics were analyzed to assess the plan quality, such as dose Conformity Index (CI) (ratio of the target volume to 100% prescription isodose volume); R50 (ratio of 50% prescription isodose volume to the target volume); V_12Gy (volume of brain tissue minus GTV receiving 12 Gy), and mean dose of the normal brain. Normal tissue complication probability (NTCP) of brain radionecrosis (RN) was calculated using the Lyman-Kutcher-Burman (LKB) model and total treatment delivery time was calculated. Six physicians from different institutions participated in the blind survey to evaluate the plan quality and rank their choices.

Results

The study showed that SPArc has a dosimetric advantage in the V_12Gy and R50 with target volumes > 9.00 cc compared to VMAT and IMPT. A significant clinical benefit can be found in deep centrally located lesions larger than 20.00 cc using SPArc because of the superior dose conformity and mean dose reduction in healthy brain tissue. Nine retrospective clinical cases and the blind survey showed good agreement with the in silico dosimetric model and decision tree. Additionally, SPArc significantly reduced the treatment delivery time compared to VMAT (SPArc 184.46 ± 59.51s vs. VMAT: 1574.78 ± 213.65s).

Conclusion

The study demonstrated the feasibility of using Proton beam therapy for single brain metastasis patients utilizing the SPArc technique. At the current stage of technological development, VMAT remains the current standard modality of choice for single lesion brain SRS. The in silico dosimetric model and decision tree presented here could be used as a practical clinical decision tool to assist the selection of the optimal treatment modality among VMAT, IMPT, and SPArc in centers that have both photon and proton capabilities.

Novel organic assisted Ag-ZnO photocatalyst for atenolol and acetaminophen photocatalytic degradation under visible radiation: performance and reaction mechanism

This study is on photocatalytic degradation of pharmaceutical residues of atenolol (ATL) and acetaminophen (ACT) present in secondary effluent under visible light irradiation stimulated by Ag doped ZnO (Ag-ZnO) photocatalyst. Lawsonia inermis leaf extract was used for reduction of Zinc sulphate to ZnO nanoparticles (NPs). Further, ZnO NPs were doped with Ag and characterized by XRD, FT-IR, SEM-EDX, surface area analyzer, UV-Vis, and photoluminescence spectrometry to analyze the structure, morphology, chemical composition, and optical property. FT-IR analysis revealed major functional groups such as OH, C=O, and SEM analysis depicted the polyhedron shape of the NPs with size range of 100 nm. Ag-ZnO NPs were used in the photocatalytic degradation of ATL and ACT, and its removal was evaluated by varying initial contaminant concentration, catalyst dosage, and initial pH. Findings indicate that Ag-ZnO NPs demonstrated relative narrow bandgap and efficient charge separation that resulted in enhanced photocatalytic activity under visible light illumination. The photocatalytic degradation of ATL and ACT fitted well with pseudo-first-order kinetic model. Further, it was found that under optimal conditions of 5 mg/L of contaminants, pH of 8.5, and catalyst dose of 1 g/L, degradation efficiency of 70.2% (ATL) and 90.8% (ACT) was achieved for a reaction time of 120 min. More than 60% reduction in TOC was observed for both contaminants and OH• pathway was found to be the major removal process. Ag-ZnO photocatalyst showed good recycling performance, and these findings indicate that it could be cost effectively employed for removing emerging contaminants under visible light radiation.

Hypofractionated stereotactic re-irradiation with pembrolizumab and bevacizumab in patients with recurrent high-grade gliomas: results from a phase I study

BACKGROUND

Radiotherapy may synergize with programmed cell death 1 (PD1)/PD1 ligand (PD-L1) blockade. The purpose of this study was to determine the recommended phase II dose, safety/tolerability, and preliminary efficacy of combining pembrolizumab, an anti-PD1 monoclonal antibody, with hypofractionated stereotactic irradiation (HFSRT) and bevacizumab in patients with recurrent high-grade gliomas (HGGs).

METHODS

Eligible subjects with recurrent glioblastoma or anaplastic astrocytoma were treated with pembrolizumab (100 or 200 mg based on dose level Q3W) concurrently with HFSRT (30 Gy in 5 fractions) and bevacizumab 10 mg/kg Q2W.

RESULTS

Thirty-two patients were enrolled (bevacizumab-naïve, n = 24; bevacizumab-resistant, n = 8). The most common treatment-related adverse events (TRAEs) were proteinuria (40.6%), fatigue (25%), increased alanine aminotransferase (25%), and hypertension (25%). TRAEs leading to discontinuation occurred in 1 patient who experienced a grade 3 elevation of aspartate aminotransferase. In the bevacizumab-naïve cohort, 20 patients (83%) had a complete response or partial response. The median overall survival (OS) and progression-free survival (PFS) were 13.45 months (95% CI: 9.46-18.46) and 7.92 months (95% CI: 6.31-12.45), respectively. In the bevacizumab-resistant cohort, PR was achieved in 5 patients (62%). Median OS was 9.3 months (95% CI: 8.97-18.86) with a median PFS of 6.54 months (95% CI: 5.95-18.86). The majority of patients (n = 20/26; 77%) had tumor-cell/tumor-microenvironment PD-L1 expression <1%.

CONCLUSIONS

The combination of HFSRT with pembrolizumab and bevacizumab in patients with recurrent HGG is generally safe and well tolerated. These findings merit further investigation of HFSRT with immunotherapy in HGGs.

Low Dose Brain Irradiation Reduces Amyloid-β and Tau in 3xTg-AD Mice

We have previously reported that low doses of external beam ionizing irradiation reduced amyloid-β (Aβ) plaques and improved cognition in APP/PS1 mice. In this study we investigated the effects of radiation in an age-matched series of 3xTg-AD mice. Mice were hemibrain-irradiated with 5 fractions of 2 Gy and sacrificed 8 weeks after the end of treatment. Aβ and tau were assessed using immunohistochemistry and quantified using image analysis with Definiens Tissue Studio. We observed a significant reduction in Aβ plaque burden and tau staining; these two parameters were significantly correlated. This preliminary data is further support that low doses of radiation may be beneficial in Alzheimer's disease.

Pulsed radiation therapy for the treatment of newly diagnosed glioblastoma

BACKGROUND

Pulsed radiation therapy (PRT) has shown effective tumor control and superior normal-tissue sparing ability compared with standard radiotherapy (SRT) in preclinical models and retrospective clinical series. This is the first prospective trial to investigate PRT in the treatment of patients with newly diagnosed glioblastoma (GBM).

METHODS

This is a single-arm, prospective study. Patients with newly diagnosed GBM underwent surgery, followed by 60 Gy of PRT with concurrent temozolomide (TMZ). Each day, a 2-Gy fraction was divided into ten 0.2-Gy pulses, separated by 3-minute intervals. Patients received maintenance TMZ. Neurocognitive function (NCF) and quality of life (QoL) were monitored for 2 years using the Hopkins Verbal Learning Test‒Revised and the European Organisation for Research and Treatment of Cancer QLQ-C30 QoL questionnaire. Change in NCF was evaluated based on a minimal clinically important difference (MCID) threshold of 0.5 standard deviation.

RESULTS

Twenty patients were enrolled with a median follow-up of 21 months. Median age was 60 years. Forty percent underwent subtotal resection, and 60% underwent gross total resection. One patient had an isocitrate dehydrogenase (IDH)-mutated tumor. Median progression-free survival (PFS) and overall survival (OS) were 10.7 and 20.9 months, respectively. In a post-hoc comparison, median OS for the prospective cohort was longer, compared with a matched cohort receiving SRT (20.9 vs 14 mo, P = 0.042). There was no decline in QoL, and changes in NCF scores did not meet the threshold of an MCID.

CONCLUSIONS

Treatment of newly diagnosed GBM with PRT is feasible and produces promising effectiveness while maintaining neurocognitive function and QoL. Validation of our results in a larger prospective trial warrants consideration.

FSMP-19. SEX DIFFERENCES IN REDOX REGULATION UNDERLIE GLUTAMINE DEPENDENCY IN MALE GLIOBLASTOMA

Glioblastoma (GBM) is the most aggressive primary brain tumor in adults. GBM occurs more commonly in males but female patients survive significantly longer. Understanding the molecular mechanisms underlying this clinical sex disparity could support novel treatment strategies to improve outcomes for GBM patients. In this regard, we found that male and female GBM patient tissues differ in their metabolite profiles and that male GBM exhibit a higher abundance of amino acid metabolites. We confirmed these findings in a murine model of GBM. Furthermore, we found that male GBM cells are more sensitive to amino acid deprivation. This male-specific dependency on amino acids is almost entirely driven by amino acids involved in reactive oxygen species (ROS) regulation and glutathione synthesis. We found that male GBM cells are more sensitive to depletion of glutathione, which resulted in a significant increase in ROS and cell death in male GBM cells. Moreover, assays of glutathione oxidation demonstrated that male GBM cells exist in a chronically oxidized state. GLS1 mediates the conversion from glutamine to glutamate, a crucial component of glutathione. We found that male GBM cells are more sensitive to GLS1 inhibition with the clinical inhibitor CB-839. This correlated with significantly increased ROS and glutathione levels as well as significantly decreased TCA cycle metabolites in male GBM. Lastly, we found that the TCA cycle metabolite α-ketoglutarate rescues the effects of CB-839 in male GBM cells. Together, these data suggest that (1) male and female GBM differ in their amino acid requirements, (2) male GBM are more dependent on glutathione to regulate ROS levels, and (3) male GBM increase glutathione synthesis at the expense of TCA cycle metabolites upon GLS1 inhibition, suggesting an increased susceptibility to drugs targeting the glutamate/glutathione axis in male GBM. Our data underline the importance of considering sex in metabolic targeting approaches.

Ethical Allocation of Proton Therapy and the Insurance Review Process

PURPOSE

The purpose of this study was to delineate a scoring system to maximize the ethical allocation of proton beam therapy (PBT) and determine what factors are associated with receipt of PBT, including the role of specific insurance providers.

METHODS AND MATERIALS

Our scoring system was developed in collaboration with a multidisciplinary panel of experts. Patients submitted for PBT consideration were assigned a score by committee at a weekly peer-reviewed session at a time when our center was operating at capacity. Univariate analysis and multivariable analysis of initial and final insurance response were performed.

RESULTS

One hundred ninety-seven patients were prospectively reviewed. Ninety-three percent of patients with Medicaid coverage, 88% of patients with Medicare, and 78% of patients with private insurance were ultimately approved for PBT. Median time to final insurance response was 12 days (interquartile range, 9-18 days) for patients who were ultimately denied PBT coverage. Having primary provider C (odds ratio [OR], 14; 95% confidence interval [CI], 1.20-1.96; P = .033) or third party providers A (OR, 4.22; 95% CI, 1.71-10.9; P = .002) or B (OR, 5.28; 95% CI, 1.56-17.2; P = .006) was significantly associated with final insurance denial for PBT on univariate analysis. Total score (OR, 0.79; 95% CI, 0.67-0.90; P = .002) and having coverage through third party provider A (OR, 24.2; 95% CI, 9.51-68.9; P < .001) were associated with final insurance response on multivariable analysis.

CONCLUSIONS

Our scoring system was significantly associated with receipt of proton beam therapy. Certain insurance providers are less likely to approve PBT for patients, all else being equal. Such a scoring system could be implemented effectively at other PBT facilities, and additional work is needed in ensuring patients with the most to gain from PBT will be approved by their insurance providers.

Inhibition of Colony-Stimulating Factor-1 Receptor Enhances the Efficacy of Radiotherapy and Reduces Immune Suppression in Glioblastoma

AIM

To use inhibition of colony-stimulating factor-1 receptor (CSF-1R) to target tumor-associated macrophages (TAMs) and improve the efficacy of radiotherapy in glioblastoma (GBM).

MATERIALS AND METHODS

The CSF-1R inhibitor BLZ-945 was used to examine the impact of CSF-1R inhibition on M2 polarization in vitro. Using an orthotopic, immunocompetent GBM model, mice were treated with vehicle, RT, BLZ-945, or RT plus BLZ-945.

RESULTS

BLZ-945 reduced M2 polarization in vitro. BLZ-945 alone did not improve median overall survival (mOS=29 days) compared to control mice (mOS=27 days). RT improved survival (mOS=45 days; p=0.02), while RT plus BLZ-945 led to the longest survival (mOS=not reached; p=0.005). Resected tumors had a relatively large population of M2 TAMs in GBM at baseline, which was increased in response to RT. BLZ-945 reduced RT-induced M2 infiltration.

CONCLUSION

Inhibition of CSF-1R improved response to RT in the treatment of GBM and may represent a promising strategy to improve RT-induced antitumor immune responses.

TBIO-01. SEX DIFFERENCES IN REDOX STATE UNDERLIE GLUTAMINE DEPENDENCY IN MALE GLIOBLASTOMA

Glioblastoma (GBM) is an aggressive brain tumor in children and adults. It occurs more commonly in males, but female patients survive significantly longer. Understanding the molecular mechanisms that underlie those sex differences could support novel treatment strategies. In this regard, we found that male and female GBM patient samples differ in their metabolite abundance and that males exhibit a significantly higher abundance of amino acid metabolites. We confirmed those findings in a murine model of GBM, which has previously yielded important insights into sexual dimorphism in GBM. Furthermore, we found that male GBM cell cultures are significantly more sensitive to amino acid deprivation, which was almost entirely driven by amino acids involved in the synthesis of the antioxidant glutathione. Glutaminase 1 (GLS1) mediates the conversion from glutamine to glutamate, a crucial component of glutathione. We found that male GBM cells exhibited higher levels of GLS1, suggesting they are more dependent on glutamate. Indeed, we found that male GBM cells are more sensitive to pharmacological GLS1 inhibition with the clinical inhibitor CB-839. This correlated with significantly increased reactive oxygen species (ROS) in males compared to females. We further confirmed sex differences in redox state through pharmacological depletion of glutathione that resulted in a significant increase in ROS and cell death in male GBM. Together, these data indicate that male GBM cells are more dependent on glutamine to regulate ROS levels. This reveals novel sex-specific metabolic targets for GBM and underlines the importance of considering sex in metabolic targeting approaches.

TAMI-37. SEX DIFFERENCES IN REDOX STATE UNDERLIE GLUTAMINE DEPENDENCY IN MALE GLIOBLASTOMA

Glioblastoma (GBM) is the most aggressive primary brain tumor in adults. GBM occurs more commonly in males but female patients survive significantly longer. Understanding the molecular mechanisms underlying this clinical sex disparity could support novel treatment strategies to improve outcomes for GBM patients. In this regard, we found that male and female GBM patient tissues differ in their metabolite profiles and that male GBM exhibit a higher abundance of amino acid metabolites. We confirmed these findings in a murine model of GBM. Furthermore, we found that male GBM cells are more sensitive to amino acid deprivation. This male-specific dependency on amino acids is almost entirely driven by amino acids involved in the synthesis of the antioxidant glutathione. Glutaminase 1 (GLS1) mediates the conversion from glutamine to glutamate, a crucial component of glutathione. We found that male GBM cells are more sensitive to GLS1 inhibition with the clinical inhibitor CB-839. This correlated with significantly increased reactive oxygen species (ROS) in male GBM. We further confirmed sex differences in redox state through pharmacological depletion of glutathione, which resulted in a significant increase in ROS and cell death in male GBM cells. Moreover, assays of glutathione oxidation demonstrated that male GBM cells exist in a chronically oxidized state. Finally, we found that mitochondrial structure and function, including TCA cycle flux, NADH levels, and antioxidant activity, differ between male and female GBM cells. Together, these data suggest that (1) male and female GBM differ in their amino acid requirements, (2) male GBM are more dependent on glutamine to regulate ROS levels, and (3) sex differences in mitochondrial physiology may result in ROS accumulation and increased susceptibility to drugs targeting the redox state in male GBM. Our data reveal novel metabolic targets for GBM and underline the importance of considering sex in metabolic targeting approaches.

Perhexiline Demonstrates FYN-mediated Antitumor Activity in Glioblastoma

Glioblastoma is the most common primary malignant brain tumor in adults. Despite aggressive treatment, outcomes remain poor with few long-term survivors. Therefore, considerable effort is being made to identify novel therapies for this malignancy. Targeting tumor metabolism represents a promising therapeutic strategy and activation of fatty acid oxidation (FAO) has been identified as a central metabolic node contributing toward gliomagenesis. Perhexiline is a compound with a long clinical track record in angina treatment and commonly described as an FAO inhibitor. We therefore sought to determine whether this compound might be repurposed to serve as a novel therapy in glioblastoma. Perhexiline demonstrated potent in vitro cytotoxicity, induction of redox stress and apoptosis in a panel of glioblastoma cell lines. However, the antitumor activity of perhexiline was distinct when compared with the established FAO inhibitor etomoxir. By evaluating mitochondrial respiration and lipid dynamics in glioblastoma cells following treatment with perhexiline, we confirmed this compound did not inhibit FAO in our models. Using in silico approaches, we identified FYN as a probable target of perhexiline and validated the role of this protein in perhexiline sensitivity. We extended studies to patient samples, validating the potential of FYN to serve as therapeutic target in glioma. When evaluated in vivo, perhexiline demonstrated the capacity to cross the blood-brain barrier and antitumor activity in both flank and orthotopic glioblastoma models. Collectively, we identified potent FYN-dependent antitumor activity of perhexiline in glioblastoma, thereby, representing a promising agent to be repurposed for the treatment of this devastating malignancy.

Integrative cross-platform analyses identify enhanced heterotrophy as a metabolic hallmark in glioblastoma

BACKGROUND

Although considerable progress has been made in understanding molecular alterations driving gliomagenesis, the diverse metabolic programs contributing to the aggressive phenotype of glioblastoma remain unclear. The aim of this study was to define and provide molecular context to metabolic reprogramming driving gliomagenesis.

METHODS

Integrative cross-platform analyses coupling global metabolomic profiling with genomics in patient-derived glioma (low-grade astrocytoma [LGA; n = 28] and glioblastoma [n = 80]) were performed. Identified programs were then metabolomically, genomically, and functionally evaluated in preclinical models.

RESULTS

Clear metabolic programs were identified differentiating LGA from glioblastoma, with aberrant lipid, peptide, and amino acid metabolism representing dominant metabolic nodes associated with malignant transformation. Although the metabolomic profiles of glioblastoma and LGA appeared mutually exclusive, considerable metabolic heterogeneity was observed in glioblastoma. Surprisingly, integrative analyses demonstrated that O6-methylguanine-DNA methyltransferase methylation and isocitrate dehydrogenase mutation status were equally distributed among glioblastoma metabolic profiles. Transcriptional subtypes, on the other hand, tightly clustered by their metabolomic signature, with proneural and mesenchymal tumor profiles being mutually exclusive. Integrating these metabolic phenotypes with gene expression analyses uncovered tightly orchestrated and highly redundant transcriptional programs designed to support the observed metabolic programs by actively importing these biochemical substrates from the microenvironment, contributing to a state of enhanced metabolic heterotrophy. These findings were metabolomically, genomically, and functionally recapitulated in preclinical models.

CONCLUSION

Despite disparate molecular pathways driving the progression of glioblastoma, metabolic programs designed to maintain its aggressive phenotype remain conserved. This contributes to a state of enhanced metabolic heterotrophy supporting survival in diverse microenvironments implicit in this malignancy.

Clinical Outcomes in Patients with Recurrent Glioblastoma Treated with Proton Beam Therapy Reirradiation: Analysis of the Multi-Institutional Proton Collaborative Group Registry

Purpose

As a means of limiting normal tissue toxicity, proton-beam therapy (PBT) is an emerging radiation modality for glioblastoma (GBM) reirradiation. However, data for recurrent GBM treated with PBT reirradiation is limited. Therefore, we analyzed treatment patterns, toxicities, and clinical outcomes of patients with recurrent GBM treated with PBT reirradiation using the multi-institutional Proton Collaborative Group registry.

Methods and Materials

Prospectively collected data for patients with recurrent GBM who underwent PBT while enrolled in Proton Collaborative Group study 01-009 (NCT01255748) were analyzed. We evaluated overall survival (OS), progression-free survival (PFS), and toxicity. Toxicities were scored per the Common Terminology Criteria for Adverse Events, version 4.0. Descriptive statistics were used to report patient, tumor, and treatment characteristics. Multivariable analyses (MVA) for toxicity were conducted using logistic regression. The Kaplan-Meier method was used to calculate OS and PFS. MVA for OS and PFS was conducted using Cox proportional-hazards models. The SAS statistical software was used for the analysis.

Results

We identified 45 recurrent patients with GBM who underwent PBT reirradiation between 2012 and 2018. The median time between initial GBM diagnosis and recurrence was 20.2 months. The median follow-up time from PBT reirradiation was 10.7 months. Median PFS was 13.9 months (95% confidence interval [CI], 8.23-20.0 months) and median OS was 14.2 months (95% CI, 9.6-16.9 months) after PBT reirradiation. One patient experienced an acute grade 3 toxicity, 4 patients experienced late grade 3 toxicity (no grade ≥4 toxicities). MVA revealed that prior surgery was associated with a 91.3% decreased hazard of death (hazard ratio: 0.087; 95% CI, 0.02-0.42; P < .01). No explanatory variables were associated with PFS or grade 3 toxicities.

Conclusions

This is the largest series to date reporting outcomes for PBT reirradiation of patients with recurrent GBM. Our analysis indicates that PBT is well tolerated and offers efficacy rates comparable with previously reported photon reirradiation.

Enhanced fatty acid oxidation provides glioblastoma cells metabolic plasticity to accommodate to its dynamic nutrient microenvironment

Despite advances in molecularly characterizing glioblastoma (GBM), metabolic alterations driving its aggressive phenotype are only beginning to be recognized. Integrative cross-platform analysis coupling global metabolomic and gene expression profiling on patient-derived glioma identified fatty acid β-oxidation (FAO) as a metabolic node in GBM. We determined that the biologic consequence of enhanced FAO is directly dependent upon tumor microenvironment. FAO serves as a metabolic cue to drive proliferation in a β-HB/GPR109A dependent autocrine manner in nutrient favorable conditions, while providing an efficient, alternate source of ATP only in nutrient unfavorable conditions. Rational combinatorial strategies designed to target these dynamic roles FAO plays in gliomagenesis resulted in necroptosis-mediated metabolic synthetic lethality in GBM. In summary, we identified FAO as a dominant metabolic node in GBM that provides metabolic plasticity, allowing these cells to adapt to their dynamic microenvironment. Combinatorial strategies designed to target these diverse roles FAO plays in gliomagenesis offers therapeutic potential in GBM.

IMMU-19. QUINOLINATE-INDUCED IMMUNE SUPPRESSION IN GLIOBLASTOMA

Glioblastoma continues to be an invariably fatal malignancy with limited treatment options. We performed integrative cross-platform analyses coupling global metabolomic profiling with genomics in patient-derived tumors to provide insight into metabolic programs that may be driving the aggressive phenotype of this malignancy. A persistent theme that emerged was the interplay between metabolic remodeling and immune response. Most notable was a 64-fold accumulation of quinolinate, which represents a downstream intermediary of tryptophan metabolism, in glioblastoma, when compared to low-grade astrocytoma. We discovered a dynamic interaction between cells within the tumor microenvironment that contributes to the generation of quinolinate. Specifically, neither tumor cells nor immune cells demonstrated the capacity to completely metabolize tryptophan. Tumor cells were required to metabolize tryptophan to kynurenine, while only cells of monocyte lineage, including M1/M2 macrophages and microglial cells, demonstrated the capacity to generate quinolinate from tumor-generated kynurenine. We next sought to determine if the observed accumulation of quinolinate in glioblastoma had immune consequences. We discovered a novel role quinolinate plays in increasing (~50%) immunosuppressive M2 macrophage (CD45+CD11b+F4/80+ and CD206+) polarization and promoting a suppressive molecular phenotype (IL4Rα +). These findings were functionally recapitulated, with quinolinate-induced M2 macrophages demonstrating potent inhibition of CD8+T-cell proliferation. Intriguingly, quinolinate also skewed M1 polarization towards an “M2-like” phenotype both molecularly (CD45+CD11b+F4/80+CD206+) and functionally, by inhibiting CD8+T-cell proliferation and decreasing phagocytosis efficiency. Targeting quinolinate’s upstream enzyme kynurenine-3-monooxygenase (KMO) inhibited M2 polarization in vitro and deceased M2 macrophage levels in vivo by 60%. This was unique to KMO, as targeting tryptophan metabolism by inhibiting the more established, upstream target IDO1 did not influence M2 macrophage levels. As emerging studies suggest M2 macrophages play a central role in contributing towards the potent immunosuppressive microenvironment in glioblastoma, therapeutic strategies designed to target quinolinate metabolism may serve as a novel immuno-metabolic checkpoint with direct clinical implications in this malignancy.

CBMT-28. FATTY ACID OXIDATION PROVIDES METABOLIC PLASTICITY TO MAINTAIN GROWTH IN THE DYNAMIC MICROENVIRONMENT OF GLIOBLASTOMA

Glioblastoma represents an aggressive, primary brain tumor with limited treatment options. Despite advances in molecularly characterizing glioblastoma, metabolic alterations driving its aggressive phenotype are only beginning to be recognized. Integrative cross-platform analyses coupling global metabolomic and gene expression profiling identified alterations in fatty acid β-oxidation (FAO) as a key metabolic node differentiating glioblastoma from low-grade astrocytoma, which was defined by an accumulation of acylcarnitines. Metabolic heterogeneity was observed within glioblastoma that could further define tumors as FAO ‘high’ and ‘low’, which were enriched with mesenchymal and proneural subtypes of glioblastoma, respectively. These findings were metabolomically and functionally recapitulated in molecular subtype-specific preclinical models, with the majority of baseline mitochondrial oxygen consumption being a result of enhanced FAO in these cells. The biologic consequence of enhanced FAO in glioblastoma is directly dependent upon tumor microenvironment. FAO serves as a metabolic cue to drive proliferation in a β-HB/GPR109A/cAMP-dependent autocrine manner in nutrient favorable conditions while providing an efficient, alternate source of ATP only in nutrient unfavorable conditions. Accordingly, inhibiting FAO alone in glioblastoma cells with etomoxir only led to modest anti-proliferative activity and minimal cytotoxicity. However, rational combinatorial strategies designed to target the dynamic roles FAO plays in gliomagenesis resulted in metabolic synthetic lethality in glioblastoma. Specifically, dual targeting of FAO (etomoxir) and glycolysis (2DG) resulted in robust energetic stress, necroptosis mediated cell death, and a significant improvement in survival in an orthotopic glioblastoma mouse model. In summary, we identified FAO as a dominant metabolic node in glioblastoma that provides metabolic plasticity, allowing these cells to adapt to their dynamic microenvironment. Combinatorial strategies designed to target these diverse roles FAO plays in gliomagenesis offers therapeutic potential in glioblastoma.

CBMT-27. ABERRANT AMINO ACID METABOLISM EXPOSE NOVEL FUNCTIONAL VULNERABILITIES IN GLIOBLASTOMA

Despite advances in molecularly characterizing glioblastoma, metabolic alterations driving its aggressive phenotype are only beginning to be recognized. Integrative cross-platform analyses coupling global metabolomic and gene expression profiling identified aberrant amino acid (AA) metabolism as a central node in glioblastoma. This metabolic phenotype was recapitulated in preclinical models and through a series of investigations designed to determine the biologic consequence of individual AA, we identified branched chain AA (BCAA) and glutamine as the only indispensable AA in glioblastoma, serving as the sole source of nucleotide pools and glutathione, respectively. Although molecularly and/or chemically perturbing these pathways resulted in cytotoxicity in glioblastoma, normal astrocytes demonstrated a similar response, suggesting therapeutic limitations in targeting these core metabolic pathways in cancer. As the glioblastoma microenvironment typically represents a nutrient-deprived state, we went on to determine the capacity of these cells to adapt to AA restricted conditions by only providing these cells with the above-identified indispensable AA. Intriguingly, glioblastoma cells had the unique ability to revert a state of metabolic dormancy. In addition to triggering a reversible proliferative arrest, this dormant phenotype displayed a near-complete shutdown of glycolysis that allowed these cells to adapt and maintain survival in glucose-deprived conditions and elicited profound resistance to ionizing radiation. Studies designed to systemically understand molecular underpinnings driving this unique metabolically dormant state uncovered a functional reliance upon mTOR/p21 signaling to maintain proliferative arrest in nutrient unfavorable conditions. Consistent with these findings, p21 expression was differentially expressed in the perinecrotic core of glioblastoma when compared to the peripheral edge in patient samples. Targeting this novel functional vulnerability through p21 inhibition, thereby, ‘forcing’ proliferation of these cells in nutrient unfavorable conditions, led to robust cytotoxicity specific to dormant cells and enhanced radiation response. Targeting functional vulnerabilities in otherwise therapeutically resistant cells represents a promising clinical strategy in glioblastoma.

CBMT-45. SEX-SPECIFIC METABOLIC ADAPTIONS IN GLIOBLASTOMA

Glioblastoma (GBM) is the most common and aggressive brain tumor in adults. GBM occurs more commonly in males, but female patients survive significantly longer. Understanding the molecular mechanisms that underlie those sex differences could support novel treatment strategies. In this regard, we found that male and female GBM patient samples differ in their metabolite abundance and that male patients exhibit a significantly higher abundance of TCA cycle metabolites. We confirmed those findings in a murine model of GBM, which has previously yielded important insights into sexual dimorphism in GBM. Strikingly, sex differences in TCA cycle flux were entirely driven by glutamine flux, not glucose flux, suggesting a sex-specific role for glutamine in GBM. Metabolic manipulation through glutamine deprivation resulted in a greater growth inhibition in male GBM cells. Glutamine itself can be utilized for anabolic reactions or it can be converted to glutamate by glutaminase. Only male GBM cells were sensitive to pharmacological glutaminase inhibition with BPTES or CB-839, suggesting that male GBM cells are glutamate dependent while female GBM cells are not. Concordantly, we found significantly higher glutaminase levels in male GBM cells. Furthermore, we found that numerous metabolites (including NADH, ATP, and glutathione) involved in cellular processes downstream of glutamate were more abundant in male GBM cells. In contrast, female GBM cells were resistant to low glutamine conditions and glutaminase inhibitors unless glutamine-synthase activity was disrupted, suggesting that glutamine synthesis might play a more prominent role in female GBM. Together, these data indicate that male and female GBM differ in their metabolic adaptions. Male GBM utilize glutamate to fuel the TCA cycle and mitochondrial activity while female GBM synthesize and utilize glutamine itself. This sexual dimorphism in metabolic reprogramming reveals novel sex specific metabolic targets for GBM and underlines the importance of considering sex in metabolic targeting approaches.

Abstract 5259: Fatty acid oxidation represents a metabolic vulnerability in glioblastoma in nutrient-deprived conditions

Glioblastoma represents an aggressive, primary brain tumor with limited treatment options. We performed an integrative, cross-platform analysis coupling global metabolomics and gene expression profiling in &gt;100 patient-derived gliomas to begin to understand the diverse metabolic programs driving the aggressive phenotype of this malignancy. Alterations in fatty acid β-oxidation (FAO) emerged as a key metabolic node differentiating glioblastoma from low-grade astrocytoma, as demonstrated by an accumulation of acylcarnitines. Metabolic heterogeneity was observed within glioblastoma that could further define tumors as FAO ‘high’ and ‘low’. Integrative analyses identified these metabolic subtypes to be enriched with mesenchymal (MES) and proneural (PN) glioblastoma subtypes, respectively. These findings were metabolomically and functionally recapitulated in molecular subtype-specific preclinical models. Analysis of gene expression profiles from these lines uncovered an orchestrated transcriptional program designed to promote fatty acid uptake, activation, and mitochondrial oxidation. Studies designed to determine the biologic consequence of enhanced FAO in glioblastoma only identified a role in glucose-deprived conditions, where it served as a vital, alternate source for ATP synthesis. Based on these findings, we tested the hypothesis that dual targeting of glycolysis and FAO would elicit energetic stress-mediated cell death in glioblastoma. Accordingly, the glycolysis inhibitor 2DG and the FAO inhibitor etomoxir only demonstrated anti-proliferative activity in MES glioblastoma cell lines when used as single agents in vitro, while the combination resulted in robust, necroptosis-mediated cell death. Synergistic anti-tumor activity was observed following combined glycolysis and FAO inhibition when extended in vivo in an orthotopic model. Collectively, our findings suggest FAO provides metabolic plasticity in MES glioblastoma, allowing these cells to adapt to nutrient-deprived microenvironments. Combinatorial strategies designed to inhibit glycolysis and FAO represents an attractive therapeutic approach in glioblastoma.

Citation Format: Shiva Kant, Antony Dayalan, Pravin Kesarwani, Prakash Chinnaiyan. Fatty acid oxidation represents a metabolic vulnerability in glioblastoma in nutrient-deprived conditions [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 5259.

Abstract 5280: Branched chain amino acids represent indispensible metabolic substrates in glioblastoma

Glioblastoma (GBM) is an aggressive brain tumor with limited treatment options. Considerable advances have been made in understanding the genetic alterations driving these tumors, however, the metabolic alterations and mechanisms underlying these aggressive phenotypes remain unclear. We performed global metabolomic profiling of patient derived low-grade astrocytoma (LGA, n= 28) and GBM (n=80). Hierarchical clustering (HC) identified amino acid (AA) metabolism as a dominant metabolic node in GBM compared to LGA. Considerable inter-tumoral heterogeneity of AA metabolism was observed in GBM, with HC identifying two clearly distinct metabolic subtypes consisting of increased and decreased concentrations of AA and their metabolic intermediates. VIP analysis identified the accumulation of branched chain amino acids (BCAA)- leucine, valine and isoleucine as the top ranked metabolites differentiating these subtypes. Based on this, GBMs were classified as BCAA-high and BCAA-low. BCAA-high GBM was enriched with mesenchymal and classical subtypes while BCAA-low GBM was enriched with proneural and neural subtypes. Integrative analysis coupling these metabolic signatures with gene expression profiling performed on matched tissue demonstrated upregulation of BCAA metabolism-associated genes in BCAA-high GBM, along with global transcriptional programs designed to activate cell cycle progression. When extended into molecular subtype specific preclinical models, we demonstrated that BCAA were indispensible for survival of mesenchymal GBM cells, which was independent of the presence or absence of other non-essential and essential amino acids. Further, these cells were able to maintain long-term survival in a dormant state when grown in media devoid of all essential and non-essential AA other than BCAA and glutamine. Knockdown of key enzymes in BCAA metabolism led to robust cytotoxicity in this model, underscoring the importance of BCAA in GBM survival. Ongoing studies are designed to determine the biologic consequence and intermediary metabolism of BCAA in GBM. Collectively these results identify BCAA metabolism as a therapeutic target in GBM.

Citation Format: Antony H. Prabhu, Shiva Kant, Pravin Kesarwani, Prakash Chinnaiyan. Branched chain amino acids represent indispensible metabolic substrates in glioblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 5280.

Metabolic remodeling contributes towards an immune-suppressive phenotype in glioblastoma

Glioblastoma (GBM) is one of the most aggressive tumors. Numerous studies in the field of immunotherapy have focused their efforts on identifying various pathways linked with tumor-induced immunosuppression. Recent research has demonstrated that metabolic reprogramming in a tumor can contribute towards immune tolerance. To begin to understand the interface between metabolic remodeling and the immune-suppressive state in GBM, we performed a focused, integrative analysis coupling metabolomics with gene-expression profiling in patient-derived GBM (n = 80) and compared them to low-grade astrocytoma (LGA; n = 28). Metabolic intermediates of tryptophan, arginine, prostaglandin, and adenosine emerged as immuno-metabolic nodes in GBM specific to the mesenchymal and classical molecular subtypes of GBM. Integrative analyses emphasized the importance of downstream metabolism of several of these metabolic pathways in GBM. Using CIBERSORT to analyze immune components from the transcriptional profiles of individual tumors, we demonstrated that tryptophan and adenosine metabolism resulted in an accumulation of Tregs and M2 macrophages, respectively, and was recapitulated in mouse models. Furthermore, we extended these findings to preclinical models to determine their potential utility in defining the biologic and/or immunologic consequences of the identified metabolic programs. Collectively, through integrative analysis, we uncovered multifaceted ways by which metabolic reprogramming may contribute towards immune tolerance in GBM, providing the framework for further investigations designed to determine the specific immunologic consequence of these metabolic programs and their therapeutic potential.

Improving dosimetric outcome for hippocampus and cochlea sparing whole brain radiotherapy using spot-scanning proton arc therapy

This feasibility study shows that Spot-scanning Proton Arc therapy (SPArc) is able to significantly reduce the dose to the hippocampus and cochlea compared to both Volumetric Modulated Arc Photon Therapy (VMAT) and the robust optimized Intensity Modulated Proton Therapy (ro-IMPT) plans in whole brain radiotherapy. Furthermore, SPArc not only improves plan robustness but could potentially deliver a treatment as efficient as ro-IMPT when proton system's energy layer switch time is less than 1 s.

A multicenter phase II study of temozolomide plus disulfiram and copper for recurrent temozolomide-resistant glioblastoma

PURPOSE

Preclinical studies have suggested promising activity for the combination of disulfiram and copper (DSF/Cu) against glioblastoma (GBM) including re-sensitization to temozolomide (TMZ). A previous phase I study demonstrated the safety of combining DSF/Cu with adjuvant TMZ for newly diagnosed GBM. This phase II study aimed to estimate the potential effectiveness of DSF/Cu to re-sensitize recurrent GBM to TMZ.

METHODS

This open-label, single-arm phase II study treated recurrent TMZ-resistant GBM patients with standard monthly TMZ plus concurrent daily DSF 80 mg PO TID and Cu 1.5 mg PO TID. Eligible patients must have progressed after standard chemoradiotherapy and within 3 months of the last dose of TMZ. Known isocitrate dehydrogenase (IDH) mutant or secondary GBMs were excluded. The primary endpoint was objective response rate (ORR), and the secondary endpoints included progression-free survival (PFS), overall survival (OS), clinical benefit (response or stable disease for at least 6 months), and safety.

RESULTS

From March 2017 to January 2018, 23 recurrent TMZ-resistant GBM patients were enrolled across seven centers, and 21 patients were evaluable for response. The median duration of DSF/Cu was 1.6 cycles (range: 0.1-12.0). The ORR was 0%, but 14% had clinical benefit. Median PFS was 1.7 months, and median OS was 7.1 months. Only one patient (4%) had dose-limiting toxicity (grade three elevated alanine transaminase).

CONCLUSIONS

Addition of DSF/Cu to TMZ for TMZ-resistant IDH-wild type GBM appears well tolerated but has limited activity for unselected population.

A randomized phase II study of everolimus in combination with chemoradiation in newly diagnosed glioblastoma: results of NRG Oncology RTOG 0913

Background

This phase II study was designed to determine the efficacy of the mammalian target of rapamycin (mTOR) inhibitor everolimus administered daily with conventional radiation therapy and chemotherapy in patients with newly diagnosed glioblastoma.

Methods

Patients were randomized to radiation therapy with concurrent and adjuvant temozolomide with or without daily everolimus (10 mg). The primary endpoint was progression-free survival (PFS) and the secondary endpoints were overall survival (OS) and treatment-related toxicities.

Results

A total of 171 patients were randomized and deemed eligible for this study. Patients randomized to receive everolimus experienced a significant increase in both grade 4 toxicities, including lymphopenia and thrombocytopenia, and treatment-related deaths. There was no significant difference in PFS between patients randomized to everolimus compared with control (median PFS time: 8.2 vs 10.2 mo, respectively; P = 0.79). OS for patients randomized to receive everolimus was inferior to that for control patients (median survival time: 16.5 vs 21.2 mo, respectively; P = 0.008). A similar trend was observed in both O6-methylguanine-DNA-methyltransferase promoter hypermethylated and unmethylated tumors.

Conclusion

Combining everolimus with conventional chemoradiation leads to increased treatment-related toxicities and does not improve PFS in patients with newly diagnosed glioblastoma. Although the median survival time in patients receiving everolimus was comparable to contemporary studies, it was inferior to the control in this randomized study.

Histologically defined intratumoral sequencing uncovers evolutionary cues into conserved molecular events driving gliomagenesis

Background

Glioblastoma represents an archetypal example of a heterogeneous malignancy. To understand the diverse molecular consequences of this complex tumor ecology, we analyzed RNA-seq data generated from commonly identified intratumoral structures in glioblastoma enriched using laser capture microdissection.

Methods

Raw gene-level values of fragments per kilobase of transcript per million reads mapped and the associated clinical data were acquired from the publicly available Ivy Glioblastoma Atlas Project database and analyzed using MetaboAnalyst (v3.0). The database includes gene expression data generated from multiple structural features commonly identified in glioblastoma enriched by laser capture microdissection.

Results

We uncovered a relationship between subtype heterogeneity in glioblastoma and its unique tumor microenvironment, with infiltrating cells harboring a proneural signature while the mesenchymal subtype was enriched in perinecrotic regions. When evaluating the tumors' transcriptional profiles in the context of their derived structural regions, there was a relatively small amount of intertumoral heterogeneity in glioblastoma, with individual regions from different tumors clustering tightly together. Analyzing the transcriptional profiles in the context of evolutionary progression identified unique cellular programs associated with specific phases of gliomagenesis. Mediators of cell signaling and cell cycle progression appear to be critical events driving proliferation in the tumor core, while in addition to a multiplex strategy for promoting angiogenesis and/or an immune-tolerant environment, transformation to perinecrotic zones involved global metabolic alterations.

Conclusion

These findings suggest that intratumoral heterogeneity in glioblastoma is a conserved, predictable consequence to its complex microenvironment, and combinatorial approaches designed to target these unequivocally present tumor biomes may lead to therapeutic gains.

Abstract 3474: Integrative metabolomic and genomic analysis identifies fatty acid oxidation as a metabolic node in glioblastoma

Glioblastoma (GBM) represents an aggressive brain tumor with limited treatment options. Although considerable progress has been made in understanding molecular alterations unique to these tumors, the diverse metabolic programs driving their aggressive phenotype are only beginning to be recognized. As an initial investigation, using a library consisting of over 3000 biochemicals, we performed global metabolomic profiling in patient-derived GBM (n=80) and low-grade glioma (LGG; n=28). Alterations in fatty acid β-oxidation (FAO) emerged as a key metabolic node differentiating GBM from LGG, as demonstrated by an accumulation of acyl carnitines. Metabolic heterogeneity was observed within GBM that could further define tumors as FAO ‘high' and ‘low'. To begin to understand the molecular underpinnings of this metabolic heterogeneity, gene expression profiling on matched tumor samples was performed. We determined that established molecular subtypes of GBM correspond with FAO phenotypes, with FAO ‘high' and ‘low' tumors enriched with mesenchymal (MES) and proneural (PN) GBM subtypes, respectively. These findings were metabolomically and functionally recapitulated in molecular subtype-specific preclinical models, with an accumulation of acyl carnitines and enhanced FAO, contributing to nearly 60% of baseline cellular respiration, in MES glioma tumor initiating cells when compared to PN cells. Analysis of gene expression profiles from these lines uncovered an orchestrated transcriptional program designed to promote fatty acid uptake and activation. Consistent with gene expression findings, BODIPY labeling and fluorescent microscopy uncovered the unique capacity of MES cells to uptake fatty acids from the media, which was perturbed following FATP inhibition. Chemical and molecular inhibition of mediators of FAO, including fatty acid uptake, acylation, and CPT-1 demonstrated selective inhibition of proliferation in MES cells and inhibition of FAO using etomoxir demonstrated anti-tumor activity in vivo in an orthotopic model. Studies designed to determine the biologic consequence of enhanced FAO in GBM were not able to attribute this metabolic node to ATP synthesis. Systemic evaluation of the intermediary metabolism of FAO identified accumulation of the endogenous HDAC inhibitor 3HB and histone acetylation as consequence to enhanced FAO in GBM, which was also elevated in patient samples. The addition of 3HB rescued MES cells from the anti-proliferative effects of FAO inhibition and gene expression profiling identified FAO-mediated transcriptional programs contributing to the aggressive phenotype of MES in GBM. Collectively, our findings suggest that FAO represents a metabolic phenotype in GBM driven by enhanced fatty acid uptake and acylation, providing insight into both mechanisms driving the aggressive phenotype of this tumor and novel therapeutic targets.

Citation Format: Shiva Kant, Antony Prabhu, Pravin Kesarwani, Praveen Kumar, Stewart F. Graham, Prakash Chinnaiyan. Integrative metabolomic and genomic analysis identifies fatty acid oxidation as a metabolic node in glioblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3474.

Abstract 2763: Tryptophan metabolism contributes to radiation-induced immune checkpoint reactivation in glioblastoma

Glioblastoma (GBM) is an aggressive brain tumor with limited treatment options. Immune checkpoint inhibitors designed to revert tumor-induced immune suppression have emerged as potent anti-cancer therapies. We performed cross-platform analyses coupling global metabolomic and gene-expression profiling in patient-derived gliomas. We identified aberrant tryptophan metabolism as a metabolic node in glioblastoma, which represents an emerging immune checkpoint. Specifically, GBM demonstrated an accumulation of tryptophan and kynurenine when compared to low-grade glioma (LGG), while kynurenate, a metabolite immediately downstream of kynurenine, was significantly lower in glioblastoma, resulting kynurenine/kynurenate ratio demonstrating &gt;90% accuracy in discriminating between GBM and LGG. These metabolic findings were corroborated by increased expression of indoleamine-2,3-dioxygenase-1 (IDO1) in GBM, a key enzyme involved in tryptophan metabolism and kynurenine production. Cross-platform analysis using gene expression arrays allowed for molecular subtyping of GBM, demonstrated that aberrant tryptophan metabolism was specific to classical and mesenchymal subtypes, while kynurenate accumulation, the metabolite elevated in LGG, was only evident in the proneural subtype. This metabolic phenotype was recapitulated in GBM preclinical models, which demonstrated robust IFNγ-induced IDO1 pathway activation and kynurenine production. The novel IDO1 inhibitor GDC-0919 demonstrated potent inhibition of tryptophan metabolism in our model and importantly, effectively crossed the blood-brain barrier. To explore the immune consequence of aberrant tryptophan metabolism in GBM, we extended investigations to an adult astrocytic, genetically engineered mouse (GEM) cell line to allow for in vivo studies using immune competent mice. Using this orthotopic mouse model, we demonstrated that although GDC-0919 as a single agent did not have anti-tumor activity, it had strong potential for enhancing radiation response in glioblastoma, which was further augmented when using a hypofractionated regimen. The immunological evaluation demonstrated that radiation response in glioblastoma involves immune stimulation, reflected by an increase in activated and cytotoxic T-cells, which is balanced by immune checkpoint reactivation, reflected by an increase in IDO1 expression and immunosuppressive regulatory T cells. GDC-0919 mitigated radiation-induced immune suppression and enhanced immune activation. These findings support clinical efforts designed to combine IDO1 inhibition with hypofractionated radiation in glioblastoma, offering the promise of harnessing a patient's immune system to attack these otherwise recalcitrant tumors.

Citation Format: Pravin Kesawani, Antony Prabhu, Shiva Kant, Praveen Kumar, Stewart F. Graham, Katie Buelow, George Wilson, C Ryan Miller, Prakash Chinnaiyan. Tryptophan metabolism contributes to radiation-induced immune checkpoint reactivation in glioblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 2763.

Abstract 3478: Integrative metabolomic and genomic analysis of glioblastoma

Normal 0 false false false EN-US JA X-NONE /* Style Definitions */ table.MsoNormalTable {mso-style-name:"Table Normal"; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-parent:""; mso-padding-alt:0in 5.4pt 0in 5.4pt; mso-para-margin:0in; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:12.0pt; font-family:Cambria; mso-ascii-font-family:Cambria; mso-ascii-theme-font:minor-latin; mso-hansi-font-family:Cambria; mso-hansi-theme-font:minor-latin;} Despite considerable progress in understanding the molecular alterations in Glioblastoma (GBM), the diverse metabolic programs driving their aggressive phenotype remains unclear. We performed global metabolomic profiling in patient-derived GBM (n=80) and low-grade glioma (LGG; n=28). Hierarchical clustering of profiles identified clear metabolic programs differentiating LGG from GBM. GBM had an accumulation of metabolites that appeared mutually exclusive compared to LGG, a majority of which was involved in lipid and peptide metabolism. We next examined metabolic heterogeneity within GBM. Hierarchical clustering identified unique metabolic subtypes in GBM. The first subtype, which represented &lt;10% of the tumors analyzed, was defined by an accumulation of lysolipids, a second subtype, by alterations in amino acid, nucleotide, and lipid metabolism. The third subtype, which comprised the majority of tumors, had a unique accumulation of dipeptides in addition to a heterogeneous accumulation of the metabolites of the first two subtypes. To understand the molecular underpinnings of the metabolic heterogeneity in GBM, integrative analysis using gene expression profiles of matched tumors was performed. Preliminary analyses determined that metabolic heterogeneity in GBM is associated with known molecular subtypes, demonstrating mutual exclusivity of the proneural and mesenchymal metabolic profiles, consistent with their molecular signatures. MGMT methylated and IDH mutated tumors were evenly distributed within the metabolic subtypes, indicating that conserved metabolic programs associated with phenotypic changes are required for gliomagenesis. As aberrant fatty acid metabolism, amino acid metabolism, and accumulation of dipeptides represented core metabolic pathways differentiating LGG from GBM and appeared to contribute towards metabolic heterogeneity, we studied these pathways in further detail. Integrated cross-platform analyses uncovered a tightly orchestrated and highly redundant transcriptional program designed to drive the observed metabolic phenotype, also observed in preclinical models. Collectively, integrated metabolomic and genomic analyses helps in both, understanding biologic processes associated with gliomagenesis and identification of novel therapeutic targets.

Citation Format: Antony Dayalan, Pravin Kesarwani, Shiva Kant, Prakash Chinnaiyan. Integrative metabolomic and genomic analysis of glioblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 3478.