IDH-mutant Tumors Research Articles

P10.09.A BLOOD-BASED CLASSIFICATION OF IDH-STATUS OF NON-ENHANCING GLIOMAS: A MACHINE LEARNING APPROACH

Abstract BACKGROUND Non-invasive determination of IDH mutational status in patients with glioma could offer significant therapeutic opportunities. While IDH wildtype tumors (e.g., GBM) typically show enhancement on MRI, IDH mutant tumors often lack this enhancement. However, relying solely on anatomic radiology may lead to misclassification, and currently, tissue acquisition is the primary method for assessing IDH status in gliomas. This limitation hampers the development of neoadjuvant or intraoperative therapeutic strategies based on IDH status; thus, more minimally invasive methods to determine IDH status are needed. In this study, we assessed immune cell proportions, which vary by glioma subtype, from pre-surgery peripheral blood samples as an alternative method of classifying the IDH status in gliomas without enhancement. MATERIAL AND METHODS First, we employed a highly accurate large language model (GPT-4-Turbo-128k) with over 99% accuracy to read radiology notes and exclude patients with enhancing gliomas. Then, we identified twelve immune cell subtypes from whole blood using deconvolution algorithms based on DNA methylation data. These immune cell subtypes, along with patient age, were integrated into a machine learning model (random forest) to predict IDH status (wildtype vs. mutant), leveraging conditional Generative Adversarial Networks to generate synthetic data and mitigate bias in the datasets. Two independent datasets were included for training and validating the model. RESULTS The random forest model had an area under the ROC curve (AUC) of 0.90 and accurately identified IDH status in 81% of a training set of 287 gliomas (65 wildtype and 222 mutant tumors at varied time points after diagnosis). In an independent validation data set of 99 gliomas (6 wildtype and 93 mutant) from pre-surgery blood samples, the AUC was 0.93, and accuracy predicted IDH status in 92% of cases with a sensitivity of 93% and specificity of 83%. CONCLUSION We could accurately predict IDH status in pre-surgical peripheral blood samples from patients with non-enhancing gliomas. This minimally invasive approach is a promising step toward reducing risk and exploring opportunities for earlier therapies based on IDH status.

Sex differences in the molecular profile of adult diffuse glioma are shaped by IDH status and tumor microenvironment.

Sex differences in adult diffuse glioma (ADG) are well-established clinically, yet the underlying molecular mechanisms remain inadequately understood. Here, we aim to reveal molecular features and cellular compositions unique to each sex in ADG to comprehend the role of sex in disease etiology. We quantified sex differences in transcriptome of ADG using multiple independent glioma patient datasets. Next, we delved into the single-cell landscape to examine sex differences in gene expression and cellular composition. To explore how sex influences disease progression, we analyzed paired samples from primary and recurrent ADG cases, aiming to identify sex-specific differences in molecular and cellular features. Our analysis revealed that mutations in isocitrate dehydrogenase (IDH) genes and the tumor microenvironment emerged as primary influencers of sex-differential molecular enrichments. In IDHwt tumors, genes in neuronal signaling pathway are found to be enriched in male tumors, while genes in hypoxia and inflammatory response pathways are enriched in female tumors. This pattern was reversed in IDHmut gliomas. We hypothesized that these distinctions could be attributed to heterogeneous cellular composition between sexes. Using single-cell data, we observed distinctive patterns of sex differences in cell states, cell composition and cell-cell interaction in IDHwt and IDHmut tumors separately. Further, by comparing molecular changes in paired primary and recurrent ADG samples, we identified sex-specific differences in molecular characteristics and cellular compositions of recurrent tumors. Our results provide a comprehensive multi-level characterization of sex differences in ADG, such findings provide novel insights into glioma disease progression in each sex.

Integrated electrophysiological and genomic profiles of single cells reveal spiking tumor cells in human glioma

Prior studies have described the complex interplay that exists between glioma cells and neurons; however, the electrophysiological properties endogenous to glioma cells remain obscure. To address this, we employed Patch-sequencing (Patch-seq) on human glioma specimens and found that one-third of patched cells in IDH mutant (IDHmut) tumors demonstrate properties of both neurons and glia. To define these hybrid cells (HCs), which fire single, short action potentials, and discern if they are of tumoral origin, we developed the single cell rule association mining (SCRAM) computational tool to annotate each cell individually. SCRAM revealed that HCs possess select features of GABAergic neurons and oligodendrocyte precursor cells, and include both tumor and non-tumor cells. These studies characterize the combined electrophysiological and molecular properties of human glioma cells and describe a cell type in human glioma with unique electrophysiological and transcriptomic properties that may also exist in the non-tumor brain.

Mutant IDH Modulates Suppressive Myeloid Populations in Malignant Glioma.

Mutations in the isocitrate dehydrogenase (IDH) genes IDH1 and IDH2 have critical diagnostic and prognostic significance in diffuse gliomas. Neomorphic mutant IDH activity has been previously implicated in T-cell suppression; however, the effects of IDH mutations on intratumoral myeloid populations remain underexplored. In this study, we investigate the influence of IDH status on the myeloid compartment using human glioma specimens and preclinical models. We performed RNA sequencing and quantitative immunofluorescence on newly diagnosed, treatment-naive IDH-mutant grade 4 astrocytoma and IDH-wild-type (IDH-WT) glioblastoma (GBM) specimens. We also generated a syngeneic murine model, comparing transcriptomic and cell-level changes in paired isogenic glioma lines that differ only in IDH mutational status. Among patient samples, IDH-mutant tumors displayed an underrepresentation of suppressive myeloid transcriptional signatures, which was confirmed at the cellular level with decreased numbers of intratumoral M2-like macrophages and myeloid-derived suppressor cells. Introduction of the mutant IDH enzyme into murine glioma was sufficient to recapitulate the transcriptomic and cellular shifts observed in patient samples. We provide transcriptomic and cellular evidence that mutant IDH is associated with a quantitative reduction of suppressive myeloid cells in gliomas and that introduction of the mutant enzyme is sufficient to result in corresponding cellular changes using an in vivo preclinical model. These data advance our understanding of high-grade gliomas by identifying key myeloid cell populations that are reprogrammed by mutant IDH and may be targetable through therapeutic approaches.

Valproic acid targets IDH1 mutants through alteration of lipid metabolism

Histone deacetylases (HDACs) have a wide range of targets and can rewire both the chromatin and lipidome of cancer cells. In this study, we show that valproic acid (VPA), a brain penetrant anti-seizure medication and histone deacetylase inhibitor, inhibits the growth of IDH1 mutant tumors in vivo and in vitro, with at least some selectivity over IDH1 wild-type tumors. Surprisingly, genes upregulated by VPA showed no enhanced chromatin accessibility at the promoter, but there was a correlation between VPA-downregulated genes and diminished promoter chromatin accessibility. VPA inhibited the transcription of lipogenic genes and these lipogenic genes showed significant decreases in promoter chromatin accessibility only in the IDH1 MT glioma cell lines tested. VPA inhibited the mTOR pathway and a key lipogenic gene, fatty acid synthase (FASN). Both VPA and a selective FASN inhibitor TVB-2640 rewired the lipidome and promoted apoptosis in an IDH1 MT but not in an IDH1 WT glioma cell line. We further find that HDACs are involved in the regulation of lipogenic genes and HDAC6 is particularly important for the regulation of FASN in IDH1 MT glioma. Finally, we show that FASN knockdown alone and VPA in combination with FASN knockdown significantly improved the survival of mice in an IDH1 MT primary orthotopic xenograft model in vivo. We conclude that targeting fatty acid metabolism through HDAC inhibition and/or FASN inhibition may be a novel therapeutic opportunity in IDH1 mutant gliomas.

Targeting Isocitrate Dehydrogenase (IDH) in Solid Tumors: Current Evidence and Future Perspectives.

The isocitrate dehydrogenase 1 and 2 (IDH1 and IDH2) enzymes are involved in key metabolic processes in human cells, regulating differentiation, proliferation, and oxidative damage response. IDH mutations have been associated with tumor development and progression in various solid tumors such as glioma, cholangiocarcinoma, chondrosarcoma, and other tumor types and have become crucial markers in molecular classification and prognostic assessment. The intratumoral and serum levels of D-2-hydroxyglutarate (D-2-HG) could serve as diagnostic biomarkers for identifying IDH mutant (IDHmut) tumors. As a result, an increasing number of clinical trials are evaluating targeted treatments for IDH1/IDH2 mutations. Recent studies have shown that the focus of these new therapeutic strategies is not only the neomorphic activity of the IDHmut enzymes but also the epigenetic shift induced by IDH mutations and the potential role of combination treatments. Here, we provide an overview of the current knowledge about IDH mutations in solid tumors, with a particular focus on available IDH-targeted treatments and emerging results from clinical trials aiming to explore IDHmut tumor-specific features and to identify the clinical benefit of IDH-targeted therapies and their combination strategies. An insight into future perspectives and the emerging roles of circulating biomarkers and radiomic features is also included.

Mutant IDH1 inhibition induces dsDNA sensing to activate tumor immunity.

Isocitrate dehydrogenase 1 (IDH1) is the most commonly mutated metabolic gene across human cancers. Mutant IDH1 (mIDH1) generates the oncometabolite (R)-2-hydroxyglutarate, disrupting enzymes involved in epigenetics and other processes. A hallmark of IDH1-mutant solid tumors is T cell exclusion, whereas mIDH1 inhibition in preclinical models restores antitumor immunity. Here, we define a cell-autonomous mechanism of mIDH1-driven immune evasion. IDH1-mutant solid tumors show selective hypermethylation and silencing of the cytoplasmic double-stranded DNA (dsDNA) sensor CGAS, compromising innate immune signaling. mIDH1 inhibition restores DNA demethylation, derepressing CGAS and transposable element (TE) subclasses. dsDNA produced by TE-reverse transcriptase (TE-RT) activates cGAS, triggering viral mimicry and stimulating antitumor immunity. In summary, we demonstrate that mIDH1 epigenetically suppresses innate immunity and link endogenous RT activity to the mechanism of action of a US Food and Drug Administration-approved oncology drug.

The IDH paradox: Meta-analysis of alkylating chemotherapy in IDH-wild type and -mutant lower grade gliomas.

IDH-wild type (-wt) status is a prerequisite for the diagnosis of glioblastoma (GBM); however, IDH-wt gliomas with low-grade or anaplastic morphology have historically been excluded from GBM trials and may represent a distinct prognostic entity. While alkylating agent chemotherapy improves overall survival (OS) and progression-free survival (PFS) for IDH-wt GBM and also IDH-mutant gliomas, irrespective of grade, the benefit for IDH-wt diffuse histologic lower-grade gliomas is unclear. We performed a meta-analysis of randomized clinical trials for World Health Organization (WHO) grades 2-3 gliomas (2009 to present) to determine the effect of alkylating chemotherapy on IDH-wt and -mutant gliomas using a random-effects model with inverse-variance pooling. We identified 6 trials with 1204 patients (430 IDH-wt, 774 IDH-mutant) that evaluated alkylating chemoradiotherapy versus radiotherapy alone, allowing us to perform an analysis focused on the value of adding alkylating chemotherapy to radiotherapy. For patients with IDH-wt tumors, alkylating chemotherapy added to radiotherapy was associated with improved PFS (HR:0.77 [95% CI: 0.62-0.97], P = .03) but not OS (HR:0.87 [95% CI: 0.64-1.18], P = .17). For patients with IDH-mutant tumors, alkylating chemotherapy added to radiotherapy improved both OS (HR:0.52 [95% CI: 0.42-0.64], P < .001) and PFS (HR = 0.47 [95% CI: 0.39-0.57], P < .001) compared to radiotherapy alone. The magnitude of benefit was similar for IDH-mutant gliomas with or without 1p19q-codeletion. Alkylating chemotherapy reduces mortality by 48% and progression by 53% for patients with IDH-mutant gliomas. Optimal management of IDH-wt diffuse histologic lower-grade gliomas remains to be determined, as there is little evidence supporting an OS benefit from alkylating chemotherapy.

The biological significance of tumor grade, age, enhancement, and extent of resection in IDH-mutant gliomas: How should they inform treatment decisions in the era of IDH inhibitors?

The 2016 and 2021 World Health Organization 2021 Classification of central nervous system tumors have resulted in a major improvement in the classification of isocitrate dehydrogenase (IDH)-mutant gliomas. With more effective treatments many patients experience prolonged survival. However, treatment guidelines are often still based on information from historical series comprising both patients with IDH wild-type and IDH-mutant tumors. They provide recommendations for radiotherapy and chemotherapy for so-called high-risk patients, usually based on residual tumor after surgery and age over 40. More up-to-date studies give a better insight into clinical, radiological, and molecular factors associated with the outcome of patients with IDH-mutant glioma. These insights should be used today for risk stratification and for treatment decisions. In many patients with IDH-mutant grades 2 and 3 glioma, if carefully monitored postponing radiotherapy and chemotherapy is safe, and will not jeopardize the overall outcome of patients. With the INDIGO trial showing patient benefit from the IDH inhibitor vorasidenib, there is a sizable population in which it seems reasonable to try this class of agents before recommending radio-chemotherapy with its delayed adverse event profile affecting quality of survival. Ongoing trials should help to further identify the patients that are benefiting from this treatment.

IDH1 mutation is associated with improved resection rates, progression-free survival and overall survival in patients with anaplastic astrocytomas.

The introduction of molecular markers in to the diagnosis of gliomas has changed the therapeutic approach to this tumors. The aim of this study was to examine the impact of surgery on anaplastic astrocytomas (AA), which has not previously been fully elucidated. This was a retrospective study involving a total of 143 patients who underwent surgery for primary AA in our department between 1995 and 2020. Total tumor resection was achieved more often in patients with IDH-mutant tumors (41.09%) than in patients with IDH-wildtype tumors (30.76%). The median PFS was 1876 days for patients with IDH1 mutations and 238 days for patients with IDH-wildtype tumors. The 1-, 3-, 5- and 10-year PFS were longer in patients with total tumor resection and IDH-mutant AA (86.2%, 69%, 65.5% and 44.8%, respectively) than in patients with subtotal tumor resection and IDH-mutant AA (83.3%, 55.6%, 41.7% and 25%, respectively) and even longer compared to all IDH-wildtype tumors. The median OS was 2472 days for patients with IDH1 mutations and 434 days for patients with IDH-wildtype tumors. The 3-, 5- and 10-year OS times were longer in patients with total tumor resection and IDH-mutant AA (89.2%, 85.2% and 72.6%, respectively) than in patients with subtotal tumor resection and IDH-mutant AA (85.9%, 73.7% and 52.6%, respectively) and were even longer compared to all IDH-wildtype tumors. Total tumor resection is more common with IDH-mutant AA than with IDH-wildtype tumors. Patients with IDH-mutant AA had significantly better PFS and OS after total tumor resection than after subtotal tumor resection and biopsy.

HGG-21. DISTRIBUTION AND MUTATIONAL PATTERNS OF TP53 ALTERATIONS ACROSS SUBTYPES OF PEDIATRIC HIGH-GRADE GLIOMAS

Abstract Inactivating alterations of tumor suppressor gene TP53 are a hallmark of tumor progression in various cancer entities. Unfortunately, TP53 inactivation has not yet provided an actionable vulnerability. To investigate distribution, mutational pattern and impact of TP53 alterations in pediatric high-grade gliomas (pedHGG), we investigated TP53 alterations in 407 pedHGG by analyzing genomic sequencing and survival data collected through the INFORM and MNP molecular diagnostic pipelines. Nearly half of pedHGG (47%) showed signs of genomic TP53 inactivation. A second hit suggesting complete loss of function was observed in 84% of tumors, with loss of heterozygosity as the most common mechanism (70%). The frequency of TP53 alterations ranged from 97% in H3 G34-mutated tumors, 70% in IDH-mutated tumors and 61% in H3 K27-mutated tumors down to 40% in H3-/IDH-wildtype subtypes and none in infant-type hemispheric gliomas. Alterations in TP53 were associated with significantly shorter mean overall survival of 11 vs. 15 months in patients diagnosed with H3 K27-mutated tumors. Previously described TP53 hotspot mutations, such as amino acid substitutions at position 17, 248, 273, 282 and 342 were also prominent in the studied cohort (NM_000546). Mutations at position 342 were enriched in H3 G34-mutated tumors, with one-third carrying a stopgain mutation at this position rarely seen in other pedHGG. G34-mutated tumors also showed an abundance of nonsense, splicing or frameshift mutations in contrast to the predominance of missense mutations in other subtypes. The functional impact of these differences is currently under investigation. Lastly, we observed potential evidence for a genotype-phenotype link with Li-Fraumeni syndrome (LFS)-associated (constitutional) TP53 mutations in pedHGG, including an absence of the R248 hotspot mutation in 15 LFS-associated tumors.

CDKN2A deletion and radiation sensitivity in IDH-mutant astrocytomas.

2041 Background: IDH-mutant astrocytomas represent the most prevalent primary tumors in younger adults (&lt;45yo). A substantial minority of these tumors exhibit the deletion of CDKN2A (Cyclin-Dependent Kinase Inhibitor Gene 2A). Homozygous deletion of this gene– which encodes the tumor suppressor protein p16 – is associated with a malignant phenotype and poorer prognosis in IDH-mutant astrocytoma. CDKN2A deletions are primarily observed in tumors that have received radiation therapy (RT), suggesting a potential mechanistic relationship between RT and deletion. This observation gives rise to two alternative hypotheses: either RT is causing DNA damage in irradiated cells, leading to the induction of subclonal CDKN2A deletion, or a subset of cells already possesses the CDKN2A deletion and is resistant to RT, resulting in the treatment selecting for the subsequent emergence of these cells. Here, we sought to ascertain the influence of CDKN2A deletion on IDH-mutant astrocytoma cellular response to RT. Methods: The antitumor effect of RT was evaluated in vitro using patient-derived IDH-mutant astrocytoma cells, MGG152. A homozygous CDKN2A deletion was engineered in this parental line, creating a paired line to permit an isogenic comparison between CDKN2A intact versus CDKN2A deleted tumor cells. A photon irradiator was used to deliver a range of clinically-relevant RT doses spanning from 0 to 20 gray (Gy). Differences in cell viability after a predetermined incubation period were examined and relevant statistical comparisons performed. Results: Dose-response curves in response to radiation therapy, comparing CDKN2A intact and deleted cell lines, were generated (Table). Both CDKN2A intact and deleted cell lines exhibited significant reductions in viability following radiation exposure at and above 2Gy (p &lt; 0.001). CDKN2A-deleted cells displayed a small but significantly greater sensitivity than CDKN2A-intact at 1, 2, and 5Gy (Table). Conclusions: Our findings offer evidence indicating that p16 loss does not bestow radioresistance in IDH-mutant astrocytomas. These findings align with a hypothesis that radiotherapy (RT) might promote DNA damage, and consequently, subclonal CDKN2A deletion, in irradiated IDH-mutant tumors. [Table: see text]

Comprehensive analysis of the REST transcription factor regulatory networks in IDH mutant and IDH wild-type glioma cell lines and tumors

The RE1-silencing transcription factor (REST) acts either as a repressor or activator of transcription depending on the genomic and cellular context. REST is a key player in brain cell differentiation by inducing chromatin modifications, including DNA methylation, in a proximity of its binding sites. Its dysfunction may contribute to oncogenesis. Mutations in IDH1/2 significantly change the epigenome contributing to blockade of cell differentiation and glioma development. We aimed at defining how REST modulates gene activation and repression in the context of the IDH mutation-related phenotype in gliomas. We studied the effects of REST knockdown, genome wide occurrence of REST binding sites, and DNA methylation of REST motifs in IDH wild type and IDH mutant gliomas. We found that REST target genes, REST binding patterns, and TF motif occurrence proximal to REST binding sites differed in IDH wild-type and mutant gliomas. Among differentially expressed REST targets were genes involved in glial cell differentiation and extracellular matrix organization, some of which were differentially methylated at promoters or gene bodies. REST knockdown differently impacted invasion of the parental or IDH1 mutant glioma cells. The canonical REST-repressed gene targets showed significant correlation with the GBM NPC-like cellular state. Interestingly, results of REST or KAISO silencing suggested the interplay between these TFs in regulation of REST-activated and repressed targets. The identified gene regulatory networks and putative REST cooperativity with other TFs, such as KAISO, show distinct REST target regulatory networks in IDH-WT and IDH-MUT gliomas, without concomitant DNA methylation changes. We conclude that REST could be an important therapeutic target in gliomas.

Determining the Underlying Mechanisms of Glioma Progression and Recurrence

INTRODUCTION: Gliomas are the most common malignant brain tumour. Despite standard-of-care therapy, these tumours inevitably recur. Recurrent tumours are often treatment-resistant and associated with a poor prognosis, and there is an urgent need for novel treatments. METHODS: The epigenome-wide methylome, transcriptome, and proteome was analyzed in a total of 271 samples from 176 patients with gliomas, including 166 primary (pre-treatment) and 105 recurrent (post-treatment) tumours. Included is a unique cohort of 81 patients with paired tumour samples collected at both pre- and post- treatment. RESULTS: Epigenomics accounted for the majority of observed variance between samples and was driven by IDH status. Paired analyses identified epigenetic stability in IDH wildtype tumours at recurrence, compared to a loss of methylation at recurrence in IDH mutant tumours. Loss of methylation in IDH mutant gliomas at recurrence was driven by astrocytomas undergoing malignant transformation. Integrated, multi-platform analyses of paired samples undergoing malignant transformation identified novel genetic markers and pathways of transformation. Finally, a novel subgroup of IDH wildtype GBM with improved survival and a distinct proteomics signature was discovered. Multi-platform analyses characterized this novel subgroup as exhibiting hypermethylation, increased DNA mismatch repair and cell cycle regulation, and an altered tumour microenvironment. CONCLUSIONS: In conclusion, this study identifies targetable molecular factors that promote malignant transformation in IDH mutant gliomas and classifies a novel subgroup of IDH wildtype GBM with improved prognosis.

293 The Impact of Tumor Mutational Status on Protoporphyrin IX Accumulation in Tumor-Associated Macrophages in Glioblastoma Patients

INTRODUCTION: Immunotherapies provide promising new treatment options for lung cancer and melanoma, however success in glioblastoma (GBM) patients has been much rarer and uneven. Identifying candidates with GBM that are most likely to benefit from immunotherapy remains a challenge. The abundance of tumor-associated macrophages (TAMs) correlates response to immunotherapy in GBM patients. Here we leverage a new imaging technique for quantifying TAMs via tandem stimulated Raman histology (SRH) and two-photon excitation fluorescence microscopy (TPEF) to assess the impact of genetic classification on the abundance of TAMs. METHODS: We conducted tandem SRH and TPEF on specimens from 79 patients undergoing high-grade glioma resection with 5-ALA. We trained a MaskR-CNN deep neural network to identify TAMs and compute their density in each specimen. Corresponding clinical, demographic, genomic and methylomic data were collected for each patient. Independent sample t-tests were used to identify significant correlations between genetic markers, treatment, and TAM density. RESULTS: We analyzed 3,121,524 300 x 300 micron fields of view, from 151 fresh specimens, enabling segmentation of 611,789 TAMs. IDH-mutant tumors had significantly lower TAM density than IDH-wildtype tumors (p &lt; 0.01). The absence of MGMT promoter hypermethylation was associated with significantly higher TAM density (p = 0.03). Tumors with EGFR amplification averaged significantly lower TAM density than EGFR wildtype specimens (p &lt; 0.01). Recurrent tumors possessed 31.5% lower TAM density than primary resections. CONCLUSIONS: Tandem SRH and TPEF can estimate variations in TAM density in human GBMs. We found TAM density to be associated with IDH status, MGMT promoter methylation, and EGFR amplification. This imaging technique creates a new avenue for forecasting response to immunotherapy in GBM patients.

Next Generation Sequencing Mutational Profiles of Gliomas Reveal Clinical and Genetic Factors Predicting Refractory Postoperative Seizures

INTRODUCTION: Postoperative seizures are a common complication of gliomas following resection, but little is known about their course and the role of tumor biology in their development. METHODS: Single-center retrospective review of adults who underwent surgical management of glioma with targeted next generation sequencing of tumor samples obtained 2017-2020. Univariate analysis for relevant cohort characteristics and adjustment with multivariate regression was performed. RESULTS: Among 341 patients with at least 3 months of follow-up, 174 (51.0%) experienced postoperative seizures and 89 (26.1%) had refractory seizures, defined as seizures occurring monthly or more frequently. Patients with refractory seizures were younger, presented with seizure, had IDH-mutated tumors, and had recurrent tumors. Postoperative refractory seizures had a median length of 9.4 months. In a multivariate analysis adjusting for age, seizures at presentation, newly diagnosed or recurrent status, WHO grade, and IDH status, PIK3R1 mutation emerged as an independent predictor of increased odds of developing refractory seizures (log(OR) 0.89 [0, 1.8], p = 0.044) with PIK3CA mutations trending towards significance (log(OR) 0.66 [-0.12, 1.4], p = 0.09). In another stratified multivariate analysis, CKD4 (log(OR) 1.9 [0.42, 3.4], p = 0.014), PIK3CA (log(OR) 1.3 [0.15, 2.4], p = 0.026) emerged as predictors of refractory seizure among recurrent tumors while presenting with seizure (log(OR) 0.81, [0.08, 1.5], p = 0.03) was the only significant predictor among newly diagnosed tumors. CONCLUSIONS: PIK3R1 and PIK3CA mutations were independent predictors of increased odds of postoperative refractory seizures, with CDK4 mutations as an additional predictor among recurrent tumors. Seizures at presentation predicted refractory postoperative seizures in newly diagnosed tumors, suggesting the need for close clinical follow-up in these patients. Future analysis of this cohort will enable better characterization of the influence of tumor mutational profile on postoperative seizure activity.

1238 Next Generation Sequencing of Gliomas to Identify Predictors of Time to Postoperative Epilepsy

INTRODUCTION: Seizures during the course of disease for patients with diffuse gliomas is common. As genetic characterization of gliomas has improved, how a tumors mutational profile influences the timing of postoperative seizures, and if postoperative seizures relate to survival and tumor progression, is poorly understood. METHODS: A retrospective review of consecutive adults from 2017 to 2020 who underwent resection of gliomas with next generation sequencing of tumors at a single institution was performed. Cox proportional hazards regression was performed to identify factors associated with time to postoperative seizures. Seizures within 72 hours of surgery were excluded. RESULTS: 363 patients with newly diagnosed or recurrent tumor tissue genotyped via next generation sequencing were included. Median follow-up time was 37.4 months, median time to seizure after surgery was 39.2 months (95% CI 34.6 – 60.8), and IDH-mutant tumors comprised 38.3% of the cohort. Patients with IDH-mutant tumors were more likely to have non-immediate postoperative seizures (p = 0.031) and more persistent postoperative seizures (p = 0.004) compared to IDH-wildtype tumors. PDGFRA mutation was associated with shorter time to seizure in IDH-mutant gliomas (p = 0.033), with no such genetic factors in IDH-wildtype tumors. Among IDH-mutant and wildtype tumors, patients with shorter seizure freedom had significantly shorter overall and progression-free survival. CONCLUSIONS: PDGFRA mutation is associated with earlier seizures after resection of IDH-mutant diffuse gliomas. Earlier first non-immediate postoperative seizure after resection is associated with worse overall and progression-free survival.

1242 Metabologenomic Characterization Uncovers Heterogeneity Amongst IDH Mutant Gliomas

INTRODUCTION: Mutations in isocitrate dehydrogenase (IDH) enzymes are recognised to drive the molecular footprint of diffuse gliomas through the accumulation of oncometabolite R-2-hydroxyglutarate which drives the widespread restructuring of the DNA methylome; however, beyond R-2-hydroxyglutarate, a comprehensive metabologenomic characterization of IDH-mutant gliomas has yet to be performed. METHODS: Glioma samples from a cohort of 154 patients underwent multiplatform molecular analysis, including metabolomic studies, genome-wide DNA methylation profiling and bulk RNA sequencing. A integrative analysis was performed, including hierarchical clustering and principal component analysis of identified metabolites, differentially methylated probes, copy number alteration and bulk mRNA data. Survival analysis as well as multivariable hazard ratios for clinical variables were calculated by fitting Cox Proportional Hazards Models. RESULTS: We discovered a group of IDH-mutant gliomas whose metabolic profile highly resembled IDH wildtype tumors. Notably, these IDH-mutant gliomas with dysregulated metabolism were distinguished from their IDH-mutant counterparts by significantly shorter overall survival (median OS 118.9 months vs 173.6 months, p=0.048). The IDH-mutant tumors with dysregulated metabolism harbored distinct epigenetic alterations that converged to drive proliferative and stem-like transcriptional profiles. The prognostic relevance of dysregulated metabolism complements, but was not wholly explained by canonically recognized prognostic classifications in IDH-mutant gliomas including 1p/19q codeletion, glioma CpG Island Hypermethylator (GCIMP) status and CDKN2A homozygous deletion. CONCLUSIONS: Utilizing a cross-platform analysis we have uncovered a novel subtyping of IDH-mutant gliomas with dysregulated cellular metabolism with similar survival to IDH-wildtype tumors. The metabolic profile provides unique information on glioma phenotypes, which may facilitate a more comprehensive understanding of glioma biology, and provide a window to target novel dependencies.

Abstract 6819: Exploring the impact of IDH1-mutations on antitumor immunity in intrahepatic cholangiocarcinoma

Abstract Intrahepatic cholangiocarcinoma (CCA) is an aggressive biliary tract cancer that carries unfavorable prognosis. 10-20% of intrahepatic CCAs harbor a mutation in IDH1 that can be targeted with mutant IDH1-specific inhibitors. However, objective and durable responses to treatment with mutant IDH1 inhibitors are rare in CCA. Mutant IDH1 has neomorphic enzymatic activity that produces the oncometabolite D-2-hydroxyglutarate (D-2-HG). D-2-HG promotes biliary tumor formation through cancer cell-intrinsic mechanisms but is also a paracrine factor in the tumor microenvironment (TME). Our group and others have identified that IDH1-mutant CCAs are not responsive to immunotherapy treatment approaches in part due to decreased CD8+ T cell infiltration and an increase in immunosuppressive macrophage cells in the TME. To better understand the immunosuppressive features of the IDH1-mutant CCA TME, we generated an isogenic cell line panel of IDH1-mutant (MUT) and IDH1-wild type (WT) mouse cholangiocarcinoma cells in the SB1 cell line background through a CRISPR homology directed repair approach. Compared to IDH1-WT cells, IDH1-MUT cells produce high levels of D-2-HG and both cell line panels readily form tumors in immunocompetent C57BL/6 mice. Tumors formed from IDH1-mut cells have reduced CD8+ T cell infiltration compared to IDH1-WT tumors, a finding that correlates with analysis of human CCA samples. Using cytometry by time of flight (CyTOF), we identified that CD8+ T cells in IDH1-MUT tumors have decreased expression of key regulators of the antitumor immune response including EOMES, TBET, and GZMB compared to those isolated from IDH1-WT tumors. Analysis of secreted factors from these IDH1-MUT and IDH1-WT cells identified that IDH1-MUT cells release increased levels of CCL2, a chemokine shown to diminish the antitumor immune response across multiple cancer types, compared to IDH1-WT cells. Further, IDH1-MUT tumors grown in syngeneic, immunocompetent mice have increased CCL2 staining by IHC compared to IDH1-WT tumors. CCL2 expression is also increased in a preliminary analysis of IDH1-mutant human CCA primary tumors. Treatment of mice harboring orthotopic liver tumors formed from IDH1-MUT cells with a CCL2 neutralizing antibody resulted in decreased tumor size compared to isotype control. Together, our data suggest that CCL2 is a mediator of immunosuppression in the IDH1-mutant CCA TME and that modulation of CCL2 activity may improve outcomes in this rare disease subtype. Further work to understand the mechanisms through which IDH1 mutations regulate CCL2 levels in these tumors is underway. Citation Format: Emma Kartalia, James M. Leatherman, Jae W. Lee, Kiyoko Yoshima, Daniel J. Zabransky, Mark Yarchoan. Exploring the impact of IDH1-mutations on antitumor immunity in intrahepatic cholangiocarcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6819.

Abstract 6304: Seizure self-report and monitoring: Agreement between patient and clinician report and implications for care in patients with IDH-mutant and IDH-wild type gliomas

Abstract Primary brain tumor (PBT) patients commonly experience seizures, which can be measured and monitored by a variety of tools. Here, we explore the concordance between 2 tools and their use in reporting seizures over time among PBT patients enrolled in a natural history study (NCT02851706, PI: T. Armstrong). Patients complete the M.D. Anderson Symptom Inventory - Brain Tumor (MDASI-BT), which measures symptom severity (including seizure) within the last 24 hours from 0-10; and, as part of the same visit, pairs of clinicians and patients complete the Seizure Control Composite Index (RANO-SCCI), which includes the questions ‘Have you ever had a seizure’ (RANO-SCCIQ1) and ‘Have you had a seizure since your last clinic visit’ (RANO-SCCIQ2). Responses to each measure are reported in aggregate and by IDH status. Participants included 89 patients with gliomas who were primarily white (84%) males (62%) with a median age of 48 years (range: 27-78) and KPS ≥ 90 (85%). Based on patient reports, 65% endorsed ever having a seizure (RANO-SCCIQ1), 17% had a recent seizure (RANO-SCCIQ2), and 12% had a seizure within the last 24 hours (MDASI-BT). For the RANO-SCCIQ1 data, patients and clinicians generally agreed except for 6 pairs (7%) where clinicians indicated a seizure but patients did not. Of the 59 who reported recent seizures (RANO-SCCIQ2), two pairs (3%) disagreed, with patients indicating a recent seizure but clinicians not endorsing a seizure had occurred. Good overall agreement (86%) was observed between the RANO-SCCIQ2 and MDASI-BT for both clinician and patient responses, with 3 and 2 paired disagreements respectively, in which seizures were indicated in the last 24 hours but not recorded as a recent seizure on the (RANO-SCCIQ2). Comparing clinician report of seizures in those with IDH-mutated (n=39) to IDH-wildtype (n=15) tumors, 85% (33/39) versus 47% (7/15) reported ever having a seizure and 7 of 33 (21%) with IDH-mutant and 1 of 7 (14%) with IDH-wild type (IDH-WT) tumors respectively reported a seizure since the last visit. Disparities in recognition of seizures between patient and clinician highlights a need for patient education to increase awareness of events and recognition of ongoing risk. Although those with IDH-mutated tumors are at higher risk of having seizures, nearly half of those with IDH-WT reported ever having seizures, underscoring the need for all patients to be educated on recognizing and assessing seizure symptoms. Citation Format: Hope Miller, Ewa Grajkowska, Alvina Acquaye-Mallory, Anna Choi, Jennifer Reyes, Mark R. Gilbert, Edward K. Avila, Terri S. Armstrong, Elizabeth Vera. Seizure self-report and monitoring: Agreement between patient and clinician report and implications for care in patients with IDH-mutant and IDH-wild type gliomas [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 6304.