Isocitrate Dehydrogenase Mutation Research Articles

Comprehensive multicentre retrospective analysis for predicting isocitrate dehydrogenase‐mutant lower‐grade gliomas

AbstractObjectiveTo differentiate glioma grading and determine isocitrate dehydrogenase (IDH) mutation status, which are crucial for prognosis assessment and treatment planning in glioma patients.MethodsThis retrospective study included patients diagnosed with adult diffuse glioma from 1 January, 2018 to 31 July, 2023 in two independent institutions. It documented and analysed clinical and radiographic features. A nomogram model was constructed using stepwise regression to predict lower‐grade gliomas and IDH mutation status.ResultsA total of 383 adult patients with diffuse glioma were included in the study, with Cohort A (297 patients) serving as the training set and Cohort B (86 patients) serving as the validation cohort. Consistent with previous reports, the Hyper fluid‐attenuated inversion recovery (FLAIR) rim sign exhibited higher sensitivity in lower‐grade gliomas for IDH mutant gliomas compared with the T2‐FLAIR mismatch sign. However, the Hyper FLAIR rim sign was also present in Grade 4 gliomas, and thus, the T2‐FLAIR mismatch sign exhibited better clinical efficacy in predicting glioma grade and IDH mutation compared with the Hyper FLAIR rim sign in clinical applications. Meanwhile, preoperative magnetic resonance spectroscopy (MRS) indicators, particularly the Cho/Cr ratio, have shown excellent performance in predicting glioma grade and IDH mutation status. The nomogram developed through stepwise regression demonstrated excellent predictive capabilities in distinguishing glioma grade and IDH mutation status.InterpretationCombining imaging and molecular features, the predictive model established in this study offers a reliable non‐invasive tool for predicting glioma grading and IDH mutation status, aiding the clinical decision‐making process and improving patient management.

Multimodal MRI and 1H-MRS for Preoperative Stratification of High-Risk Molecular Subtype in Adult-Type Diffuse Gliomas

Isocitrate dehydrogenase (IDH) and O6-methylguanine-DNA methyltransferase (MGMT) genes are critical molecular markers in determining treatment options and predicting the prognosis of adult-type diffuse gliomas. Objectives: this study aimed to investigate whether multimodal MRI enables the differentiation of genotypes in adult-type diffuse gliomas. Methods: a total of 116 adult-type diffuse glioma patients (61 males, 51.5 (37, 62) years old) who underwent multimodal MRI before surgery were retrospectively analysed. Multimodal MRI included conventional MRI, proton magnetic resonance spectroscopy (1H-MRS), and diffusion tensor imaging (DTI). Conventional visual features, N-acetyl-aspartate (NAA)/Creatine (Cr), Choline (Cho)/Cr, Cho/NAA, fractional anisotropy (FA), mean diffusivity (MD), and diffusion histogram parameters were extracted on the whole tumour. Multimodal MRI parameters of IDH-mutant and IDH-wildtype gliomas were compared using the Mann–Whitney U test, Student’s t-test, or Pearson chi-square tests. Logistic regression was used to select the MRI parameters to predict IDH-mutant gliomas. Furthermore, multimodal MRI parameters were selected to establish models for predicting MGMT methylation in the IDH-wildtype gliomas. The performance of models was evaluated by the receiver operating characteristics curve. Results: a total of 56 patients with IDH-mutant gliomas and 60 patients with IDH-wildtype glioblastomas (GBM) (37 with methylated MGMT and 17 with unmethylated MGMT) were diagnosed by 2021 WHO classification criteria. The enhancement degree (OR = 4.298, p < 0.001), necrosis/cyst (OR = 5.381, p = 0.011), NAA/Cr (OR = 0.497, p = 0.037), FA-Skewness (OR = 0.497, p = 0.033), MD-Skewness (OR = 1.849, p = 0.035), FAmean (OR = 1.924, p = 0.049) were independent factors for the multimodal combined prediction model in predicting IDH-mutant gliomas. The combined modal based on conventional MRI, 1H-MRS, DTI parameters, and histogram performed best in predicting IDH-wildtype status (AUC = 0.890). However, only NAA/Cr (OR = 0.17, p = 0.043) and FA (OR = 0.38, p = 0.015) were associated with MGMT methylated in IDH-wildtype GBM. The combination of NAA/Cr and FA-Median is more accurate for predicting MGMT methylation levels than using these elements alone (AUC, 0.847 vs. 0.695/0.684). Conclusions: multimodal MRI based on conventional MRI, 1H-MRS, and DTI can provide compound imaging markers for stratified individual diagnosis of IDH mutant and MGMT promoter methylation in adult-type diffuse gliomas.

The Correlation Patterns of miRNA Expression with Targeted mRNA Transcripts in Glioma Patients with Wild-Type and Mutated Isocitrate Dehydrogenase (IDH) Genotypes.

Low-grade gliomas are divided into two main genetic phenotypes based on the presence or absence of mutations in the isocitrate dehydrogenase (IDH) genes. The mutated IDH phenotype (IDHmut), in contrast to the wild-type phenotype (IDHwt), is characterized by a more positive response to pharmacological intervention and a significantly longer survival time. In this study, we analyzed the differential co-expression of 225,000 microRNA-mRNA pairs at the level of correlations between microRNA levels and their potential mRNA targets. Analysis of the associative relationships of individual representatives of the selected pairs revealed that the level of mRNAs encoded by the ELN, ARL4C, C9orf64, PLAT, and FKBP9 genes associated with aggressive progression of glioma was increased in the IDHwt group. Meanwhile, the levels of miRNA-182, miRNA-455, and miRNA-891a associated with the negative prognosis in glioma were generally increased in the IDHmut group. Most (16/21) of the detected 21 microRNA-mRNA pairs with significant difference in regulation between IDHwt and IDHmut glioma samples had a weak or moderate positive correlation in IDHmut samples and a negative correlation in IDHwt samples. Therefore, our findings indicate that glioma samples from the IDHmut group with a positive prognosis potentially have a significantly less pronounced ability to microRNA-mediated regulation. We further suggest that such physiological disorders can lead to reduced tumor viability, resulting in an increased ability of the host to resist the spread of a malignant transformation of this genetic phenotype.

INNV-07. IVOSIDENIB AND BEVACIZUMAB IN HEAVILY PRETREATED PATIENTS WITH IDH1 MUTANT GLIOMAS

Abstract Isocitrate dehydrogenase 1 (IDH1) inhibitors are transforming the treatment of patients with non-enhancing IDH1 mutant gliomas that have only undergone surgical resection. Questions remain on the utility of IDH1 inhibitors in patients that have received prior therapies such as radiation therapy (RT) and chemotherapy (e.g. temozolomide (TMZ)) and have progressive disease. We evaluated the safety and efficacy of ivosidenib, an oral IDH1 inhibitor, in combination with bevacizumab (BEV), a monoclonal antibody targeting VEGF-A, in IDH1 mutant glioma patients that were heavily pretreated. Fourteen patients received combination ivosidenib and bevacizumab starting between February 2021 to July 2023. In our small cohort, patient age range was 26 to 73 years with seven female patients and seven male patients. Diagnoses represented were astrocytoma, IDH1 mutant (n=10) and oligodendroglioma, IDH1 mutant (n=4). At the time of IDH1 therapy initiation, the majority of patients (n=10) had a grade 3 tumor. All patients (n=14) had canonical IDH1 mutation (p.Arg132His) and had enhancing disease. Therapies initiated prior to ivosidenib therapy included: prior RT (n=12), prior TMZ (n=14) and prior BEV (n=10). The median number of progressions prior to initiation of ivosidenib combination therapy was 3 (range 2 to 6). All patients received ivosidenib dosed at 500 mg daily with bevacizumab doses varying from 5 to 15 mg/kg IV dosed every 2 to 3 weeks. Combination therapy was well tolerated with minimal patients experiencing toxicities requiring dose interruptions; diarrhea (n=2), creatine phosphokinase elevations (n=1), QTc prolongation (n=1), and thrombocytopenia (n=1). The median treatment duration on ivosidenib combination therapy was 4.42 months (range 0.69 to 11.4 months). In this cohort, the combination of ivosidenib and bevacizumab was well tolerated. More information is needed on the benefit of ivosidenib in combination with other therapies and in heavily pretreated patients with IDH1 mutant gliomas.

NIMG-36. PERFUSION, DIFFUSION, AND ANATOMICAL MRI BIOMARKERS FOR ASSESSING HISTOLOGICALLY-CONFIRMED MALIGNANT TRANSFORMATION IN MOLECULAR SUBTYPES OF IDH-MUTANT GLIOMAS

Abstract BACKGROUND Isocitrate dehydrogenase-mutant (IDHm) gliomas often initially present as low-grade (grade 2) gliomas but are expected to later progress into more aggressive higher-grade (grade 3-4) gliomas through malignant transformation (MT). MT is often determined non-invasively by emergence of contrast-enhancement on post-contrast T1-weighted magnetic resonance imaging (MRI), but contrast-enhancement is an imperfect surrogate for histologically-confirmed MT. This study explored perfusion, diffusion, and anatomical MRI biomarkers besides contrast-enhancement to study histologically-confirmed MT in IDHm 1p/19q-intact astrocytomas (IDHm-A) and IDHm 1p/19q-co-deleted oligodendrogliomas (IDHm-O). METHODS N=64 patients with initial histopathological grade 2 IDH-mutant glioma diagnosis who underwent repeated tissue sampling and were classified as histologically-confirmed MT (n=35) or non-MT (n=29) were retrospectively studied. Pre-surgical anatomical MRI (n=64) and, if available, diffusion-weighted imaging (n=61) and dynamic susceptibility contrast perfusion MRI (n=53) were analyzed. Tumor volumes of interest were segmented on the whole T2/FLAIR-hyperintense tumor. Measurable contrast enhancement (>1000mm3), tumor volume, sphericity, median apparent diffusion coefficient (ADC), and normalized relative cerebral blood volume (nrCBV) were compared between MT vs. non-MT IDHm-A and IDHm-O. RESULTS 81% of contrast-enhancing IDHm-A and 100% of contrast-enhancing IDHm-O underwent MT, while 41% of MT IDHm-A and 62% of MT IDHm-O were non-enhancing. Tumor volumes were significantly larger in the MT vs. non-MT groups for both IDHm-A (P=0.02) and IDHm-O (P=0.04). Whole tumor nrCBV was significantly higher (P=0.002), whole tumor ADC trended lower (P=0.06), and non-enhancing tumor sphericity was significantly lower (P=0.03) in MT vs. non-MT IDHm-A. There were no significant differences in ADC, nrCBV, nor sphericity when comparing MT vs. non-MT IDHm-O (P>0.05). CONCLUSIONS Many MT IDHm-gliomas remain non-enhancing. Tumor volumes can determine MT for both IDHm-A and IDHm-O. Diffusion and perfusion MRI show differences for MT in IDHm-A but not IDHm-O, which may reflect the different tumor biology of these IDHm molecular subtypes and their need for separate imaging biomarkers.

NCMP-01. EARLY RECURRENCE OF GLIOBLASTOMA MULTIFORM INVOLVING MULTIPLE BRAIN REGIONS ASSOCIATED WITH MUTATIONS IN EXON 4 OF ISOCITRATE DEHYDROGENASE 1 COMPLICATED BY GADOLINIUM-INDUCED ACUTE KIDNEY FAILURE: A CASE REPORT

Abstract BACKGROUND Glioblastoma multiform (GBM) remains one of the most aggressive primary brain tumors with high recurrence rates. Case presentation We present a case of a 43-year-old female, Yira, diagnosed with early recurrence of GBM involving multiple brain regions, accompanied by mutations in exon 4 of isocitrate dehydrogenase 1 (IDH1), a marker associated with poor prognosis. Additionally, this case was complicated by gadolinium-induced acute kidney failure on postoperative day 3. The patient initially presented with progressive neurological symptoms, including headache and cognitive decline. Multiplanar multiecho MRI of the brain was performed with IV contrast in orthogonal plane and revealed a moderate sized multilobulated heterogeneously and predominantly peripherally enhancing mass lesion with irregular margins and central non enhancing areas of necrosis arising from the right corona radiata, insular cortex, external capsule, lentiform nucleus, temporal, and frontal white matter with blood products. Perilesional edema was seen. Effacement of sulcal spaces. Right sylvian fissure, compression over right ventricle and midline shift of 8mm toward left side. There was dilatation of the left lateral ventricle with periventricular cerebrospinal fluid ooze. Uncal herniation was right side. On MR spectroscopy large choline, creatinine levels were seen in the lesion with reduced N-acetyl aspartate levels as compared to the normal parenchyma. Findings were suggestive of neoplastic lesion mostly high-grade glioma. Polymerase chain reaction sequencing confirmed missense mutation R132H in exon 4 of isocitrate dehydrogenase 1 gene. Despite maximal safe surgical resection, the patient developed recurrent GBM within three months, with gadolinium-based contrast agent exposure leading to acute kidney injury. CONCLUSION The combination of aggressive tumor behavior and complications from contrast agent administration highlights the challenges in managing recurrent GBM. This case underscores the importance of vigilant monitoring for complications in GBM patients, particularly those with IDH1 mutations, and the need for further research into novel therapeutic strategies.

TMIC-26. IMMUNE CELL DYNAMICS WITHIN GLIOMAS: THE INFLUENCE OF GRADE AND IDH STATUS

Abstract Mutations in isocitrate dehydrogenase (IDH) are known to significantly impact the prognosis and biology of diffuse gliomas. A number of studies have compared the immune microenvironment of IDH-wildtype glioma versus IDH-mutant glioma, and have also characterized the impact of mutant-IDH on lymphocytes. However, few studies have explored how mutant-IDH may affect tumors as they progress and increase in grade, or have delved into the myeloid immune cell compartment. Thus, we sought to understand whether tumor progression affected intratumoral immune cell composition within IDH-mutant glioma, and aimed to compare IDH-mutant versus IDH-wildtype glioma in both humans and mice. Using bulk RNA sequencing, we compared paired samples from patients with IDH-mutant glioma before and after progression, focusing on differentially-expressed immunological genes and relative immune cell proportions. We also compared grade 4 IDH-mutant astrocytoma cases to IDH-wildtype glioblastoma, performing both transcriptomic and cellular analyses. Finally, we engineered murine glioma cells to test the effect of mutant-IDH alone in the tumor microenvironment. We found that multiple immune-related genes distinguish low- and high-grade IDH-mutant glioma, and that high-grade tumors contain greater proportions of suppressive myeloid cells. When comparing IDH-wildtype to IDH-mutant glioma, we found enrichment of suppressive macrophages and myeloid-derived suppressor cells (MDSC) in IDH-wildtype tumors. Finally, our murine model of IDH-wildtype versus IDH-mutant glioma mirrored many of the myeloid cell shifts observed in human tumors. Our data show that progression of IDH-mutant tumors is a significant immunological phenomenon, associated with marked alterations in the tumor immune microenvironment. We also show that IDH-mutant glioma harbors greater inflammatory signatures and fewer suppressive myeloid cells than IDH-wildtype glioma, and that engineering mutant IDH into murine tumors is sufficient to model these differences. These findings improve our understanding of key intratumoral cell populations that may be harnessed by future immunotherapeutic strategies.

INNV-23. UNDERSTANDING THE BURDEN OF MIDH1/2 DIFFUSE GLIOMA AND THE COMPLEXITY OF NAVIGATING THE PATIENT PATHWAY: INSIGHTS FROM PATIENTS AND CAREGIVERS

Abstract Diffuse gliomas with mutations in isocitrate dehydrogenase 1 or 2 (mIDH1/2) are characterized by a slow-progressing yet life-limiting disease predominantly in young people. We report interim findings from a qualitative study to describe the mIDH1/2 diffuse glioma patient pathway, experience of the disease, and treatment approaches. Patients, caregivers, and patient-association group (PAG) representatives undertook individual interviews, with patients also completing standardized exercises as pre-work. Materials were developed in collaboration with the International Brain Tumour Alliance. Patients were aged ≥12 years with mIDH1/2 glioma and last resection ≥6 months before enrollment, either undergoing active observation or receiving chemotherapy/radiotherapy. Caregivers were living with the patient. PAG representatives were active members of a brain tumor PAG. From November 2023 to March 2024, 30 patients (Australia: n=10; China: n=6; France, UK: n=5 each; Canada, Japan: n=2 each), two caregivers (China, Australia: n=1 each) and one PAG (UK) participated. Median age of patients was 41.5 years, with 17 astrocytoma and 13 oligodendroglioma diagnoses. Presentation symptoms, circumstances of diagnosis and treatment, access to care, and navigation in the healthcare system differed per patient and within countries. Surgical resection was perceived as a crucial stage, both feared and desired. A second opinion was more often sought for surgery than for subsequent treatment approaches. Patients undergoing chemotherapy/radiotherapy (n=17) or active observation (n=13) expressed substantial physical, socioeconomic, financial, and psychological burden. Patients receiving active observation experienced strong and ongoing anxiety, as the uncertainty of tumor recurrence took a toll on their emotional wellbeing in the long term. The experience of people living with mIDH1/2 diffuse glioma is heterogeneous regarding their pathway and complexity navigating the healthcare system, with a substantial psychological and socioeconomic impact. Improved education, as well as facilitating early navigation and prioritizing shared decision-making along the disease pathway, will better support people living with mIDH1/2 diffuse glioma.

CTIM-07. A PHASE II, OPEN LABEL, SINGLE ARM STUDY OF NIVOLUMAB FOR RECURRENT OR PROGRESSIVE IDH MUTANT GLIOMAS WITH PRIOR EXPOSURE TO ALKYLATING AGENTS

Abstract BACKGROUND Somatic mutations in isocitrate dehydrogenase 1 (IDH1) are an important prognostic factor in patients with gliomas. IDH-mutant gliomas are prone to develop hypermutation after exposure to alkylating agents; in other solid tumors, hypermutation may be a predictive biomarker for PD-1 inhibitor response. In this study, we hypothesize that this specific subgroup of patients would clinically benefit from nivolumab as measured by overall response rate (ORR), duration of response (DOR), median progression-free survival (PFS), and overall survival (OS). METHODS Patients aged 18 years and older with recurrent/progressive IDH-mutant (WHO Grades 2-4) gliomas and prior exposure to alkylating agents were included. Nivolumab was given 240 mg q2w for 8 cycles, then 480 mg q4w until progression, toxicity, study withdrawal, or completion at 2 years. Efficacy was evaluated by ORR of partial (PR) and complete responses (CR) per RANO criteria; low-grade glioma RANO criteria was used for patients with non-enhancing disease. Secondary endpoints included median PFS, median OS, DOR. Toxicity and survival were followed every 3 months until death/study completion. RESULTS Thirty-three patients (66.7% male) were evaluable at study completion. Histology consisted of oligodendroglioma (N=11; 55% Grade 3) and astrocytoma (N=22; 36% Grade 3, 32% Grade 4). Median number of prior lines of systemic therapy was 1 (range 1-6). Median dexamethasone dose at screening was 0 mg (range 0-4). ORR was 9% with two PR and one CR, median DOR 33 months. 11 (32%) patients had stable disease (7 stable for 6+ months) with median PFS 2.2 months and median OS 29.1 months. There were two treatment-related Grade 3 adverse events (lymphopenia and hypotension). One patient discontinued treatment for Grade 2 transaminitis. CONCLUSIONS Though the primary endpoint was not met, three patients have ongoing CR and PR at 54+, 33+ and 24+ months. Future combination therapies with PD-1 inhibitors may increase efficacy in recurrent IDH-mutant gliomas.

NIMG-28. HYPERPOLARIZED13C IMAGING OF D-2-HYDROXYGLUTARATE-INDUCED DOWNREGULATION OF PYRUVATE DEHYDROGENASE ACTIVITY PROVIDES AN EARLY READOUT OF RESPONSE TO VORASIDENIB IN MUTANT IDH GLIOMAS

Abstract Mutations in isocitrate dehydrogenase (IDHm) define a distinct class of gliomas. IDHm converts a-ketoglutarate (a-KG) to D-2-hydroxyglutarate (D-2HG), which inhibits a-KG-dependent histone/DNA demethylases and induces epigenetic alterations that drive tumorigenesis. The IDHm inhibitor vorasidenib extends progression-free survival in IDHm glioma patients and is expected to be widely used for this patient population. However, not all patients respond to vorasidenib, and magnetic resonance imaging (MRI) does not assess whether a patient is responding to vorasidenib. Therefore, the goal of this study was to identify metabolic alterations induced by D-2HG that can be leveraged for non-invasive imaging of IDHm gliomas. Using clinically relevant patient-derived models (BT257, BT142, BT54, SF10417, SF10602), we show that D-2HG downregulates the activity of pyruvate dehydrogenase (PDH), the rate-limiting enzyme for oxidation of glucose-derived pyruvate via the tricarboxylic acid cycle, by multiple mechanisms. Drug affinity target stability assays show that D-2HG directly binds to and inhibits PDH activity. D-2HG also inhibits a-KG-dependent prolyl hydroxylases that target hypoxia-inducible factor 1-a (HIF-1a) for degradation. As a result, D-2HG stabilizes HIF-1a and drives expression of pyruvate dehydrogenase kinase 3, which phosphorylates and inhibits PDH activity. Suppressing D-2HG using vorasidenib upregulates PDH activity in IDHm glioma cells and intracranial tumors. Next, we examined whether hyperpolarized 13C-MRS, which is an advanced MRI-based method of imaging metabolic activity, monitors PDH activity in IDHm gliomas. Following administration of hyperpolarized [2-13C]-pyruvate, metabolic conversion to [5-13C]-glutamate provides a readout of PDH activity. Our studies indicate that [5-13C]-glutamate production from hyperpolarized [2-13C]-pyruvate is upregulated in IDHm glioma cells treated with vorasidenib. Importantly, [5-13C]-glutamate production is elevated within 5 days of treatment with vorasidenib in rats bearing intracranial BT257 or BT142 xenografts, when changes cannot be observed by MRI. Collectively, our studies identify hyperpolarized [2-13C]-pyruvate as a unique probe of D-2HG-induced metabolic rewiring and highlight its ability to assess IDHm glioma response to therapy, which is a challenge in the clinic.

TMET-12. TARGETING AMINO ACID METABOLIC VULNERABILITIES IN GLIOMAS

Abstract Isocitrate dehydrogenase (IDH) wild-type gliomas and IDH mutant gliomas are similar in histologic appearance but differ in their genetic and metabolic backgrounds. This study aimed to reveal the difference in metabolites between IDH-wildtype glioma and IDH-mutant glioma, and to find the effective treatment according to the status of IDH in gliomas. Two artificial cell lines made from human astrocyte were used: NHAE6E7hTERTRas (IDH-wildtype) and NHAE6E7hTERTIDHmut (IDH-mutant). Using capillary electrophoresis- and ion chromatography–coupled mass spectrometry, the amount of asparagine was lower in NHAE6E7hTERTRas cells compared with NHAE6E7hTERTIDHmut cells, whereas the amount of glutamine, glutamate and 2-oxoglutarate in NHAE6E7hTERTIDHmut cells was lower than NHAE6E7hTERTRas cells. L-asparaginase, which converts asparagine into aspartate, was more effective in NHAE6E7hTERTRas cells than NHAE6E7hTERTIDHmut cells. L-asparaginase induced autophagy and inhibition of autophagy by 3-MA suppressed L-asparaginase-induced antitumor effect, which meant that the antitumor effect was at least partially due to the L-asparaginase-induced autophagy. Pharmacological or genetical inhibition of GLUD1 which converts glutamate to 2-oxoglutarate, suppressed proliferation of the cells by inducing ROS and apoptosis in NHAE6E7hTERTIDHmut cells. ROS inhibitor, NAC suppressed GLUD1 inhibitor-induced ROS, apoptosis, and cytotoxicity in NHAE6E7hTERTIDHmut cells, revealing that cytotoxicity by GLUD1 inhibitor was at least partially due to the inhibitor-induced ROS. The experiments using mutant IDH1 overexpressed glioma cell line showed similar sensitivity to GLUD1 inhibitor to NHAE6E7hTERTIDHmut, which suggested that the difference of sensitivity to GLUD1 inhibitor was due to the status of mutant IDH. In vivo experiments, L-asparaginase suppressed the growth of xenografted glioma cells without mutant IDH, whereas GLUD1 inhibitor inhibited the proliferation of xenografted glioma cells with overexpressed mutant IDH1. In conclusion, L-asparaginase and Glud1 inhibitor will be new therapeutic option for IDH-wildtype glioma and IDH-mutant glioma, respectively.

CTNI-47. A PHASE 1, RANDOMIZED, PERIOPERATIVE TRIAL OF VORASIDENIB AND IVOSIDENIB IN IDH1-MUTANT DIFFUSE GLIOMA: UPDATED RESULTS

Abstract BACKGROUND Vorasidenib (VOR) and ivosidenib (IVO) showed clinical activity in subjects with isocitrate dehydrogenase mutant (mIDH) gliomas. We evaluated both agents in a phase 1, randomized, open-label perioperative trial (NCT03343197). Pharmacodynamics, pharmacokinetics, and preliminary objective response rate (ORR) data as of 29-April-2020 were previously reported (Mellinghoff et al. Nat Med. 2023). Progression-free survival (PFS) data were not mature at publication time. We report here longer-term follow-up results, including mature PFS. METHODS Participants with grade 2/3 non-enhancing mIDH1 R132H mutant gliomas were randomized to VOR (50 or 10 mg QD), IVO (500 or 250 mg BID), or no treatment (control) for 4 weeks prior to planned surgery, with the option to continue treatment with VOR or IVO post-surgery. Secondary objectives included PFS, ORR assessed by Investigator in the post-surgery period, and safety profile of VOR and IVO. RESULTS Enrollment completed in April-2019. 49 participants were randomized, of which 46 participants (24 oligodendroglioma, 20 astrocytoma, 1 anaplastic oligodendroglioma, 1 anaplastic oligoastrocytoma) received treatment with either VOR (N=24) or IVO (N=22) after surgery. As of 23-September-2023 data cutoff, 11 (46%) and 5 (20%) participants remain on treatment for VOR and IVO, respectively. Median (range) post-operative treatment duration was 44.7 months (0.9–62.7) for VOR, 23.9 months (0–62.7) for IVO. Median (95% CI) PFS was 41.4 months (9.3, NE) for VOR and 38.6 months (18.3, NE) for IVO. ORR per Response Assessment in Neuro-Oncology in low-grade gliomas (RANO-LGG) was 46% for VOR and 27% for IVO. Longer safety follow up will also be presented. CONCLUSION These results provide further evidence of prolonged response using IVO and VOR immediately following surgery in predominantly non-enhancing gliomas. This longer-term follow-up is consistent with Phase 3 INDIGO study results where VOR demonstrated PFS benefit with manageable safety compared with placebo in participants with non-enhancing mIDH gliomas.

BIOM-76. EXPLORING CSF MICRORNA SIGNATURES AS DIAGNOSTIC BIOMARKERS IN IDH-WILDTYPE DIFFUSE GLIOMAS

Abstract The most prevalent malignant tumors of the central nervous system are adult-type diffuse gliomas. Isocitrate dehydrogenase (IDH) mutations are identified in a subset of diffuse gliomas, leading to two distinct subtypes of gliomas: IDH-wildtype and IDH-mutant. In comparison to IDH-mutant gliomas, IDH-wildtype gliomas tend to be associated with a more rapid progression and lower overall survival rates. The analysis of differentially expressed microRNAs (DE-miRNAs) in cerebrospinal fluid (CSF) of IDH-wildtype diffuse gliomas could provide an effective and non-invasive approach to assist in the early diagnosis, classification, and management of the disease. Extracellular vesicle (EV)-derived miRNAs obtained from the CSF of 11 patients with IDH-wildtype diffuse gliomas and 8 controls were analyzed by microRNA sequencing (miRNA-seq). DE-miRNAs were defined using p-value≤0.05 and absolute log2 fold change (log2FC) ≥1. Candidate DE-miRNAs were validated by qRT-PCR in 24 samples (15 IDH-wildtype vs. 9 control) using the 2-ΔΔCT method, followed by receiver operating characteristic (ROC) curve analysis. Hsa-miR-24-3p was used as the internal control. miRNA-seq analysis identified hsa-miR-484, hsa-miR-223-3p, hsa-miR-1246, hsa-miR-323a-3p, hsa-miR-106b-3p, hsa-miR-21-5p, hsa-miR-15a-5p, has-miR-15b-5p, and hsa-miR-92a-3p among the top 20 upregulated miRNAs in the CSF of patients with IDH-wildtype diffuse gliomas. Further analysis by qPCR showed that patients with IDH-wildtype diffuse gliomas had significantly higher levels of has-miR-21-5p (2.28 ± 2.33) compared to control subjects (-2.22e-007 ± 1.08, p=0.012). The ROC curve analysis revealed an area under the curve (AUC) of 0.84 (95% CI, 0.68-1.0) for has-miR-21-5p CSF levels in distinguishing IDH-wildtype diffuse gliomas from control subjects. EV-derived miRNAs in CSF, including has-miR-21-5p, have the potential to distinguish IDH-wildtype diffuse gliomas from control individuals in a minimally-invasive manner and serve as diagnostic biomarkers.

INNV-14. OUTCOMES OF PATIENTS WITH ISOCITRATE DEHYDROGENASE-MUTANT WHO GRADE 4 ASTROCYTOMA TREATED WITH TUMOR TREATING FIELDS (TTFIELDS) THERAPY: A REAL-WORLD ANALYSIS

Abstract BACKGROUND Tumor Treating Fields (TTFields) therapy is approved for the treatment of patients with newly diagnosed glioblastoma, based on the EF-14 study which demonstrated improvement in progression free survival and overall survival (OS). EF-14 included patients with the isocitrate dehydrogenase (IDH) mutation (IDHmut), which has since been reclassified as IDHmut WHO grade 4 astrocytoma (Astrocytoma IDHmut/G4) and confers a more favorable prognosis than IDH wild type. However, large real-world datasets are lacking. Here, we report real-world outcomes of patients with Astrocytoma IDHmut/G4 treated with TTFields in the US. METHODS Utilizing electronic health records from the xCures real-world data platform, patients with newly diagnosed Astrocytoma IDHmut/G4 receiving TTFields in the US from January 1 to December 31, 2019 were analyzed and IDH-mut status was confirmed. Survival was analyzed based on IDH-mut status and TTFields usage, with patients categorized into 2 usage groups (minimum 30 days treatment): high (≥50%) and low (<50%) usage. RESULTS Among 1285 patients with known IDH status, 82 had an IDH-mut and were included. The median (range) age of patients was 40.6 (21–75) years, with the majority being men (n=58/71%) and with methylguanine-methyltransferase-promoter methylation (n=48/59%). Median TTFields therapy duration and usage were 9.4 months and 76.8%, respectively. OS at 2 and 4 years was 66% (95% CI: 56–77%) and 44% (34–57%), respectively. Patients with high TTFields usage had increased OS compared to low usage (HR: 0.53 [0.28–1.02], P=0.057, n=80). Among 22 patients with a minimum 4 years of survival, 5 were still on therapy as of the data cutoff. CONCLUSIONS These findings demonstrate the utility of the xCures platform in systematically assessing outcomes for a rare glioma subtype in the real-world setting, and suggests that patients with Astrocytoma IDHmut/G4 may benefit from TTFields therapy. Additional patient follow-up and correlative data will be presented.

BIOM-50. SERIAL INTRACRANIAL CEREBROSPINAL CELL-FREE DNA FOR DISEASE MONITORING IN PATIENTS WITH GLIOMAS

Abstract Improved response assessment methods are needed for patients with gliomas. Intracranial cerebrospinal fluid (CSF) is longitudinally accessible and provides an abundance source of candidate biomarkers, such as cell-free DNA (cfDNA), for disease monitoring. To evaluate the clinical feasibility of molecular profiling from longitudinal intracranial CSF, CSF was acquired from patients with CSF access devices, including Ommaya reservoirs and ventriculoperitoneal shunts. cfDNA was extracted and analyzed via PredicineCARE (Next Generation sequencing) or PredicineSCORE (low pass whole genome sequencing). Five patients (2 females, 3 males; median age: 40 years, range 32-64 years) underwent longitudinal intracranial CSF collection via Ommaya reservoirs (n=4) or VP shunt (n=1). In total, forty-eight CSF samples were obtained (median volume: 4.00 mL; 0.5-5 mL), with 39 samples (81.3%) yielding sufficient cfDNA for variant profiling. Our initial findings suggest that tumor fraction increased by 6.28x, 2.87x, and 8.31x with radiographic progression in three patients. Tumor fraction decreased by 0.08x and 0.04x in two patients with paired immediate pre-versus-post chemoradiation samples. Despite ongoing pseudoprogression in one patient, tumor fraction decreased to unmeasurable levels from a post-resection baseline of 0.26. Patient-specific tumor-associated variant allelic frequencies (VAFs), including TP53, PTEN, TERT, and CDKN2A/B, decreased within individual patients after resection and chemoradiation. In two patients with isocitrate dehydrogenase (IDH) mutant gliomas, decreasing IDH1 VAF after resection and chemoradiation correlated with decreased CSF D-2-hydroxyglutarate (D-2-HG) levels (0.64x and 0.62x, respectively, for the first patient, and 0.01x and 0.07x for the other patient). Both CSF IDH1 VAF and CSF D-2-HG increased a patient who had radiographic progression (2.56x and 9.21x, respectively). Moreover, CNB decreased below the limit of quantification during treatment and increased above the limit at progression. In conclusion, longitudinal CSF cfDNA can feasibly be obtained via CSF access devices in patients with gliomas during their disease course toward evaluating candidate monitoring biomarkers.

NIMG-44. ELEVATED TRANSLOCATOR PROTEIN 18KDA BINDING IN LOW MEAN DIFFUSIVITY CLUSTERS IS A FEATURE OF THE TRANSFORMING GLIOMA AND IDH MUTANT GLIOMA MICROENVIRONMENT

Abstract Around 95% of low-grade gliomas undergo anaplastic de-differentiation into high-grade gliomas, a process only partially understood from in vivo clinical imaging. 11 patients with suspected transforming gliomas underwent a combined magnetic resonance imaging (MRI) and positron emission tomography (PET) protocol, incorporating post-contrast T1-weighted/FLAIR acquisition for tumour delineation and diffusion tensor imaging. The PET radiotracer [11C]-(R)-PK11195 assessed translocator protein 18kDa (TSPO) distribution, whose upregulation is associated with inflammation/glioma progression. [11C]-(R)-PK11195 binding potential (BPND) maps were generated using the simplified reference tissue model, with the grey-matter cerebellar time-activity curve serving as the reference tissue input function. KMeans clustering of mean diffusivity (MD) intensity values defined spatially distinct “habitats” of high/low MD voxels within the glioma microenvironment. BPND values within high/low MD clustering habitats were evaluated, across glioma grades and isocitrate dehydrogenase (IDH) mutational status. Across all grade 2 and 3 gliomas (n= 6), mean TSPO BPND values in low MD habitats (0.0383 ±0.102) were significantly greater than high MD habitats (-0.045 ±0.142) (p= 0.003). In grade 4 gliomas (n= 5), no significant difference was observed in mean BPND values between low (0.514 ±0.176) and high (0.465 ±0.296) MD habitats (p= 0.543). IDH mutant gliomas (n= 7) exhibited significantly higher mean BPND in low MD habitats (0.116 ±0.225), relative to high habitats (0.052 ±0.287) (p= 0.021). IDH wildtype gliomas (n= 4) showed no significant differences between BPND values in low (0.498 ±0.199) and high MD habitats (0.424 ±0.325) (p= 0.467). Our novel findings demonstrate spatial heterogeneity in TSPO expression within 2/3/IDH mutant gliomas, a characteristic absent from grade 4/IDH wildtype varieties. Regions of restricted diffusion with high TSPO signal in grade 2/3/IDH mutant tumours indicate the heterogenous distribution of active TSPO-expressing immune/neoplastic cell populations, contrasting the homogenous distribution in grade 4/IDH wildtype gliomas, highlighting differences between their inflammatory profile and pathological features.

CTNI-66. IDH-MUTANT GLIOMA PATIENTS TREATED WITH VORASIDENIB: ONGOING DATA FROM THE VORASIDENIB EXPANDED ACCESS PROGRAM

Abstract BACKGROUND Vorasidenib (VOR) is an oral, brain-penetrant dual inhibitor of mutant isocitrate dehydrogenase 1/2 (mIDH1/2) demonstrating clinical efficacy and safety in patients with mIDH1/2 glioma in the phase 3 INDIGO study (NCT04164901). Servier launched an expanded access program (EAP, NCT05592743) in November 2022 designed to provide access to VOR for patients with mIDH1/2 glioma. Early clinical outcomes of patients treated in this EAP are presented. METHODS Eligible participants were aged ≥12 years with mIDH1/2 glioma and, in the opinion of the treating oncologist, would potentially benefit from treatment with VOR. Safety assessments occur every two weeks for the first two 28-day cycles, then monthly for the duration of treatment. RESULTS As of the March 31, 2024 data cutoff, 71 participants have initiated treatment with VOR. Mean (SD) age was 42.7 (14.8) years; 39 (55%) were male; and 34 (48%) with astrocytoma. mIDH mutation status was 46 (65%) mIDH1. One participant had separate tumors with either mIDH1 or mIDH2 identified. The majority of participants had grade 2 gliomas (n=51 [72%]) and non-contrast–enhancing disease (n=49 [69%]). As of the data cutoff, 62 (87%) participants remain on treatment, with the majority initiating treatment within the past 6 months (n=49 [69%]). Nine (13%) participants have discontinued treatment due to: radiographic progressive disease (n=3); clinical progressive disease (n=4); adverse event (AE) unrelated to treatment (n=1); or other reason (n=1). Three participants have died (disease progression [n=2], unrelated infection [n=1]). At least one AE of any grade was seen in 35 (49%) participants, with 4 (6%) experiencing unrelated serious AEs. Eight (11%) patients had AEs of special interest (defined as grade 2 or higher ALT/AST elevations). Ten (14%) patients had AEs that led to dose interruption and one (1%) patient had dose reduction. Additional treatment duration and various subgroup analyses will be presented.

DDDR-24. REAL WORLD EXPERIENCE USING THE IDH INHIBITOR IVOSIDENIB IN IDH MUTANT GLIOMA: TOLERABILITY AND OUTCOMES

Abstract BACKGROUND Mutant isocitrate dehydrogenase (IDHm) inhibitors represent a novel therapeutic strategy for treating IDHm glioma, though their optimal use outside of clinical trials remains undefined. This study describes real world utilization of the IDH1 inhibitor, ivosidenib, in patients with IDHm glioma. METHODS We retrospectively reviewed clinical and radiographic data from IDHm glioma patients treated with ivosidenib monotherapy at Dana-Farber Cancer Institute and Massachusetts General Hospital from 2020-2024. Patients with a baseline MRI at ivosidenib initiation and at least 2 subsequent scans while on ivosidenib were included in radiographic response analysis (452 scans). RESULTS This cohort included 77 patients (39 males) age 17-75 years (median 41). Thirty-eight patients (49%) had astrocytomas and 39 (51%) had oligodendrogliomas; 48 (62%) had grade 2, 26 (34%) grade 3, and 3 (4%) grade 4 gliomas. Twenty-four patients (31%) received ivosidenib as first-line therapy and 53 (69%) received ivosidenib after failing prior treatments. Among those in the radiographic analysis, 4 (6%) demonstrated partial response, 4 (6%) minor response, 44 (62%) stable disease, and 19 (27%) progressive disease (PD). Significantly higher PD rates were seen in those with enhancing disease (p<0.001) or received ivosidenib as subsequent-line therapy (p=0.002); PD rate was similar between grades 2 and 3 in the first-line group (p=0.64). One-year progression free survival was 100% in the first-line group and 66% in the subsequent-line group. At the time of our analyses, 4 patients (5%) had died (all in the subsequent-line group). Infrequent side effects included CK elevation, QTc prolongation, transaminitis, and diarrhea. One patient (1%) was dose reduced and 3 (4%) discontinued drug due to side effects. CONCLUSIONS In this real world IDHm glioma cohort, ivosidenib was well-tolerated. Better response rates were seen in patients without enhancing disease at ivosidenib initiation and those who received the drug as first-line therapy.

TMET-14. ENOLASE 2 IS A UNIQUE METABOLIC VULNERABILITY INDUCED BY THE 1P19Q CODELETION IN OLIGODENDROGLIOMAS

Abstract Gliomas are devastating primary brain tumors in adults. The presence of an isocitrate dehydrogenase mutation combined with a chromosomal 1p/19q codeletion discriminates oligodendrogliomas from astrocytomas. The goal of this study was to leverage metabolic vulnerabilities induced by the 1p/19q codeletion for oligodendroglioma therapy. The 1p19q codeletion results in loss of enolase 1 (ENO1), which converts 2-phosphoglycerate to phosphoenolpyruvate during glycolysis. Here, we show that enolase 2 (ENO2) is upregulated in patient-derived oligodendroglioma (SF10417, BT88, BT54) models relative to astrocytoma (BT142, SF10602) and normal human astrocytes. ENO2 is also elevated in oligodendroglioma patient biopsies relative to astrocytoma or gliosis. Mechanistic studies indicate that inhibiting MEK1 or ERK1 abrogates ENO2 expression, suggesting that the MAPK pathway upregulates ENO2 in oligodendrogliomas. Next, we examined the therapeutic potential of targeting ENO2 in oligodendrogliomas. Genetic ablation of ENO2 or pharmacological inhibition using POMHEX inhibited the viability of SF10417 and BT88 cells with IC50 values of ~50 nM. In contrast, the IC50 for BT142 and SF10602 astrocytoma cells was ~5-8 uM, highlighting the exquisite dependence of oligodendrogliomas on ENO2. However, ENO2 inhibition did not lead to cytotoxicity in patient-derived oligodendroglioma cells or intracranial tumor xenografts. To assess the metabolic consequences of ENO2 inhibition and identify potential compensatory alterations, we traced [U-13C]-glucose metabolism in vivo in mice bearing intracranial SF10417 tumors. Although POMHEX abrogated glycolytic metabolism downstream of 2-phosphoglycerate, it shunted glucose towards biosynthesis of serine, glycine, methionine and purine nucleotides, an effect that was driven by phosphoglycerate dehydrogenase (PHGDH), the rate-limiting enzyme for serine biosynthesis. Importantly, the novel PHGDH inhibitor PHGDH-D8 was synthetically lethal in combination with POMHEX in oligodendroglioma cells and the combination induced apoptosis in mice bearing intracranial SF10417 tumors. Collectively, we exploit a mechanistic understanding of metabolic vulnerabilities induced by the 1p19q codeletion to identify combined inhibition of ENO2 and PHGDH as a novel therapeutic opportunity for oligodendrogliomas.

TMIC-53. USE OF CEREBRAL OPEN-FLOW MICROPERFUSION TO IDENTIFY POTENTIAL ONCOMETABOLITE, L-2-HYDROXYGLUTARATE, IN GLIOBLASTOMA CHEMOTHERAPY ADAPTATION

Abstract Glioblastoma (GBM) is among the most prevalent and lethal brain tumors, comprising nearly half of all central nervous system malignancies and imparting a median overall survival of only 18-20 months. One major challenge in curing this disease is the limited understanding of how GBM cells biologically respond to treatments like radiotherapy and chemotherapy, including temozolomide (TMZ), in real-time. A significant challenge is observing changes within the tumor interstitial fluid (ISF), which mediates adaptive intercellular signaling between tumor cells and their surrounding tumoral and stromal neighbors. Microfluidic sampling methods, such as cerebral microdialysis and microperfusion, have started to provide valuable insights into the ISF signaling dynamics. These methods enable real-time biomolecular monitoring of this often-neglected component of the tumor microenvironment (TME). We have performed in vivo cerebral open-flow microperfusion (cOFM) pilot studies to identify metabolomic and proteomic changes within the tumor ISF resulting from differential treatment with either TMZ or vehicle control. Among these metabolite and protein changes, we identified an increase in 2-hydroxyglutarate (2-HG). While D-2-HG is a hallmark metabolite of isocitrate dehydrogenase mutant (IDH-mut) tumors, our model utilized the IDH wild-type (IDH-WT) CT2A mouse-syngeneic glioma model. Subsequent analysis of enantiomeric confirmation characterized this to be predominantly L-2-HG. Follow-up in vitro studies have shown that elevated L-2-HG plays a functional role in IDH-WT patient-derived glioma cells via non-canonical HIF1α stabilization and subsequent expression of HRE genes. This suggested that L-2-HG may play a similar role in IDH-WT GBM as D-2-HG plays in IDH-mutant tumors. This study demonstrates the potential of L-2-HG to function as a chemo-responsive oncometabolite in the TME of highly aggressive IDH-WT glioblastoma. By targeting the metabolic and signaling properties of L-2-HG, it may be possible to prevent chemo-resistant adaptations mounted by GBM cells when treated with TMZ.