Tumor Response Research Articles

Abstract A018: Alternative Polyadenylation Regulates Pancreatic Cancer Fibroblast Metabolism

Abstract Dense, fibrotic stroma is a defining feature of pancreatic ductal adenocarcinoma (PDAC), comprising up to 90% of tumor volume. Multiple studies have shown that this stroma strongly influences cancer progression and response to treatment. Cancer Associated Fibroblasts (CAFs) make up the majority of the Tumor Microenvironment (TME) and directly alter the tumor landscape and response to therapeutics. CAFs are a heterogenous population comprising of a mixture of inflammatory, myofibroblastic, and antigen-presenting CAFs, with both pro- and anti- tumorigenic functions. While we have been able to define CAFs phenotypically, we lack a deeper understanding of the mechanisms underlying their transcriptional heterogeneity and ultimately their contribution to driving PDAC progression. Our lab has previously shown 3’UTR-Alternative Polyadenylation (APA) to be an important driver of genetic dysregulation in PDAC. APA is an important process regulating mRNA stability, protein localization, and expression, ultimately determining cellular processes such as proliferation, metastasis, and migration. We have also shown that increased 3’ UTR shortening is associated with the pro- tumorigenic inflammatory CAF subtype. However, how APA regulates CAF function is unknown. We are now trying to understand the possible mechanisms of these changes in vitro using human-derived CAF cell lines and treating them with a known pharmacological modulator of APA. We performed PAC-Seq analyses on these samples and show that important drivers of CAF metabolism are hindered by APA, ultimately affecting the ability of CAFs to support cancer cell growth. We find that inhibition of APA drives CAF migration and senescence phenotype and alters gene expression of critical genes required for CAF function, and metabolism. We identified a novel mechanism by which a key metabolic gene SLC7A11 is regulated by APA. To our knowledge, our work is one of the first studies to study how APA is an important regulator of CAF function. Citation Format: Aditi H Chaubey, Michael E Feigin, Eric J Wagner. Alternative Polyadenylation Regulates Pancreatic Cancer Fibroblast Metabolism [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: RNAs as Drivers, Targets, and Therapeutics in Cancer; 2024 Nov 14-17; Bellevue, Washington. Philadelphia (PA): AACR; Mol Cancer Ther 2024;23(11_Suppl):Abstract nr A018.

Metabolic Reprogramming of Immune Cells in the Tumor Microenvironment

Metabolic reprogramming of immune cells within the tumor microenvironment (TME) plays a pivotal role in shaping tumor progression and responses to therapy. The intricate interplay between tumor cells and immune cells within this ecosystem influences their metabolic landscapes, thereby modulating the immune evasion tactics employed by tumors and the efficacy of immunotherapeutic interventions. This review delves into the metabolic reprogramming that occurs in tumor cells and a spectrum of immune cells, including T cells, macrophages, dendritic cells, and myeloid-derived suppressor cells (MDSCs), within the TME. The metabolic shifts in these cell types span alterations in glucose, lipid, and amino acid metabolism. Such metabolic reconfigurations can profoundly influence immune cell function and the mechanisms by which tumors evade immune surveillance. Gaining a comprehensive understanding of the metabolic reprogramming of immune cells in the TME is essential for devising novel cancer therapeutic strategies. By targeting the metabolic states of immune cells, it is possible to augment their anti-tumor activities, presenting new opportunities for immunotherapeutic approaches. These strategies hold promise for enhancing treatment outcomes and circumventing the emergence of drug resistance.

Transarterial Chemoembolization in Locally Advanced Rectal Cancer: A Systematic Review

Background: Locally advanced rectal cancer (LARC) presents a significant treatment challenge. Transarterial chemoembolization (TACE) has emerged as a potential adjunctive treatment, offering targeted delivery of chemotherapeutic agents to the tumor site, minimizing systemic exposure. This systematic review aims to assess the current literature on this novel technique and evaluate the safety and efficacy profile of TACE in treating this complex cohort of patients. Methods: A comprehensive literature search was conducted across multiple databases, including PubMed, EMBASE, and Cochrane Library, to identify studies evaluating TACE in LARC. Inclusion criteria encompassed clinical trials, cohort studies, and case series reporting on outcomes such as tumor response rate, overall survival (OS), progression-free survival (PFS), and treatment-related adverse events. Results: A total of eight studies involving 543 patients met the inclusion criteria. The studies varied in design, with five prospective and three retrospective studies. A higher prevalence of male participants (68.7%) was noted, with a median age of 60.3 years. The studies primarily evaluated the efficacy and safety of TACE in LARC treatment. Pathological response rates, tumor reduction, and survival outcomes varied across studies, with TACE showing promise in reducing tumor size, improving survival, and controlling metastasis. Major complications were rare, reported in 6.0% of cases. Conclusions: TACE is a promising therapeutic option for patients with LARC, demonstrating favorable tumor response rates and manageable toxicity profiles. Further large-scale, randomized controlled trials are warranted to confirm these findings and better define the role of TACE in the multimodal treatment of LARC.

Impact of Tumor Response After Neoadjuvant Treatment on Overall Survival Among Patients With Pancreatic Ductal Adenocarcinoma: National Cancer Database Analysis

Impact of Tumor Response After Neoadjuvant Treatment on Overall Survival Among Patients With Pancreatic Ductal Adenocarcinoma: National Cancer Database Analysis

Polyradiculitis as a Neurological Complication Associated with Adagrasib: A Case Report

Introduction: Adagrasib is an upcoming anticancer treatment for KRAS G12C-mutated non-small-cell lung carcinoma, colorectal cancer and potentially other solid tumors harboring this mutation. It is generally well-tolerated and reports of neurological adverse events so far have been limited. Case Presentation: We present to our best knowledge the first case of a 70-year-old woman who was admitted with polyradiculitis as a treatment-related complication of adagrasib. Symptoms resolved after treatment with prednisone and therapy interruption of adagrasib followed by a permanent dose reduction. After the dose reduction, there was an ongoing effective tumor response at follow-up, and serum concentrations of adagrasib remained within the therapeutic index. Conclusion: Through this case report, we aim to bring attention to the possibility of this side effect, as we believe it is important to be aware of it for future patients undergoing treatment with adagrasib.

INNV-12. CUTANEOUS TOXICITIES OF MITOGEN-ACTIVATED PROTEIN KINASE INHIBITORS IN CHILDREN AND YOUNG ADULTS WITH NEUROFIBROMATOSIS-1

Abstract BACKGROUND Neurofibromatosis type 1 (NF1) is an autosomal dominant disorder which commonly causes neoplasms leading to disfigurement or dysfunction. Mitogen-activated protein kinase inhibitors (MEKi) are generally well-tolerated treatments which target neural tumor progression in patients with NF1. Cutaneous adverse events (CAEs) are common and may hinder patients’ abilities to remain on treatment, particularly in children. We aim to characterize CAEs secondary to MEKi treatment in pediatric and young adult patients with NF1. METHODS We reviewed institutional medical records of patients under 30 years with a diagnosis of “NF1,” “NF2,” or “other neurofibromatoses” on MEKi therapy between January 1, 2019 and June 1, 2022. We recorded the time-to-onset, type, and distribution of CAEs, non-cutaneous adverse events (AEs), AE management, and tumor response. RESULTS The median age of 40 patients with NF1 was 14 years old. Tumor types included low-grade gliomas (51%) and plexiform neurofibromas (38%). MEKi used included selumetinib (69%), trametinib (25%), and mirdametinib (6%) (Table 1). A total of 74 CAEs occurred, with 28 cases of acneiform rash (38%) (Figure 1). Twenty-three out of the 28 cases of acneiform eruption were in post-pubertal patients (82.1%). Other common CAEs were paronychia, seborrheic dermatitis, eczema, xerosis, and oral mucositis. The most common treatments included oral antibiotics and topical corticosteroids. Most patients had clinical (stable or improved) tumor response (71%) while 29% had tumor progression while on a MEKi (Table 2). There was no significant association between CAE presence and tumor response (p=0.39). CONCLUSIONS MEK inhibitors have been demonstrated as a valuable treatment, but CAEs complicate the ability to stay on the treatment. Most patients in our cohort developed a CAE, demonstrating its prevalence in this population. Improvement in characterization of MEKi toxicities and their management is important to develop treatment guidelines for pediatric and young adult patients with NF1 on MEKi therapy.

CTIM-13. D2C7-IT IN COMBINATION WITH AN FC-ENGINEERED ANTI-HUMANCD40 MONOCLONAL ANTIBODY (2141-V11) ADMINISTERED INTRATUMORALLY VIA CONVECTION-ENHANCED DELIVERY (CED) FOLLOWED BY CERVICAL PERILYMPHATIC INJECTIONS (CPLIS) OF 2141-V11 IN PATIENTS WITH RECURRENT GLIOBLASTOMA (RGBM)

Abstract BACKGROUND The combination of D2C7-IT, an antibody toxin conjugate, and anti-mouseCD40 via CED generates robust antitumor immunity by killing tumor cells, activating microglia, reversing glioma-associated microglia and macrophage (GAMM)-mediated immune suppression, and empowering polyfunctional tumor antigen-specific CD8 T cells in glioma models. In addition to reprogramming GAMMs, anti-CD40 also activated dendritic cells and induced glioma-specific T cell responses in tumor draining lymph nodes. After establishing the phase 2 dose of the combination of D2C7-IT+2141-V11 when infused via CED, we initiated an assessment of the safety and efficacy of the combination of D2C7-IT+2141-V11 CED followed by repeated subcutaneous CPLIs of 2141-V11 ipsilateral to the tumor in patients with rGBM, IDH wild-type (NCT04547777). METHODS Eligible are adult patients with solitary supratentorial rGBM; ≥4weeks after chemotherapy, bevacizumab, or investigational agent; adequate organ function; and KPS ≥70%. Patients are treated with D2C7-IT (166μg) and 2141-V11 (3mg), both infused via CED, followed by CPLI of 2141-V11 at 2mg at weeks 2 and 4 post D2C7-IT+2141-V11 CED, followed by every 3 weeks for 1 year and then every 4-6 weeks. RESULTS As of May 22, 2024, 18 patients with rGBM (median age of 54) were treated with D2C7-IT+2141-V11 CED followed by CPLIs of 2141-V11. 83% patients remain alive (range 3.3-14.8 months from start of D2C7-IT CED infusion) with a median of 8 CPLIs of 2141-V11 received (range 3-19). No study related grade 4 or 5 adverse events (AEs) were observed. Grade 3 AEs related to D2C7-IT and/or 2141-V11 include one each of hydrocephalus, headache, seizure, and cerebral edema. AEs related exclusively to CPLIs of 2141-V11 consist of grade 1 injection site reaction (n=16). CONCLUSIONS The addition of CPLIs of 2141-V11 post CED of D2C7-IT+2141-V11 is feasible and has shown an acceptable toxicity profile. The safety and efficacy results will be updated.

CTIM-29. TUMOR RESPONSES IN A RANDOMIZED PHASE IIB TRIAL OF A CMV VACCINE IMMUNOTHERAPEUTIC CANDIDATE (VBI-1901) IN RECURRENT GLIOBLASTOMAS

Abstract Cytomegalovirus (CMV) antigens have been reported in over 90% of GBMs. CD4+ and CD8+ T cells are most frequently directed against the gB and pp65 antigens, respectively, which are immunogenic targets in a CMV-based GBM immunotherapeutic. First-recurrent GBM patients were enrolled, with Karnofsky Performance Status of at least 70, to receive VBI-1901 (a gB/pp65 enveloped virus-like particle [eVLP]) adjuvanted with GM-CSF and given intradermally (NCT03382977). Patients were vaccinated with VBI-1901 every 4 weeks, with surveillance brain MRI scans every 6 weeks. Among 16 subjects receiving the highest dose of VBI-1901 in the Phase I/IIa portion of the study, the disease control rate was 44%, including 2 durable partial responses, which translated into a mOS of 12.9 months. Based on these results, the study was amended into a randomized study. Approximately 60 adult subjects (18 years or older) with first recurrence of WHO 2016 grade IV Glioblastoma, IDH-wildtype will be randomized at a 1:1 ratio to two open-label cohorts to receive: VBI-1901 or standard of care (SOC) treatment with lomustine or carmustine. Only subjects with a CD4/CD8 ratio ≥1 or a CD4 count of ≥ 400/uL at screening are eligible, as people with a preserved immune system are more likely to respond to immunization with VBI-1901 based on the initial phases of the study. As of May 15, 2024, 23 patients have been randomized across 6 sites. Among evaluable patients (n=13), disease control rates of 43% and 0% have been observed in the VBI-1901 and SOC arms, respectively, including 1 partial response in the VBI-1901 arm. Full enrollment (n=60) is anticipated by the end of the year across 11 sites, and updated tumor response data and select biomarkers associated previously with tumor responses will be presented.

CTNI-09. TYPE II RAF INHIBITOR TOVORAFENIB IN RELAPSED/REFRACTORY (R/R) PEDIATRIC LOW-GRADE GLIOMA (PLGG): RESULTS FROM PATIENTS ON A DRUG HOLIDAY (DH) IN THE PHASE 2 FIREFLY-1 TRIAL

Abstract BACKGROUND Tovorafenib, a selective, CNS-penetrant, type II RAF inhibitor, received US FDA accelerated approval for r/r BRAF-altered pLGG. Results from the ongoing FIREFLY-1 (NCT04775485) phase 2 study (Kilburn LK, et al. Nat Med. 2023) in this population showed clinically meaningful tumor responses and a manageable safety profile. METHODS Patients in FIREFLY-1 treated for ≥26 cycles (~24 months) who entered a DH period were routinely assessed every 3 cycles; once-weekly tovorafenib 420 mg/m2 (not to exceed 600 mg) could be restarted if there was radiographic and/or clinical evidence of new disease progression. RESULTS As of the April 19, 2024 data cutoff, 26 patients (BRAF fusion: 22; BRAF V600E mutation: 4) (33.8%) of 77 patients in arm 1 (pLGG registrational) had completed 2 years of treatment and started a DH. No patients on a DH withdrew. Twenty-four patients (92.3%) remain on a DH, of which 22 were evaluable for response (duration range: 0.6-10.9 months); duration of response off-treatment ranged from 0.0-8.5 months. (Ranges exclude 2 non-evaluable patients treated beyond radiographic progression who remained on treatment in first 26 cycles due to ongoing clinical benefit; both remain on DH without clinical progression.) Two patients had tumor progression while on a DH and restarted treatment; 1 patient with a BRAF V600E mutation progressed (≥25% in tumor size) after 1 month (rebound growth per O’Hare P., et al. Neuro-Oncol. 2024: ≥25% increase [per RANO-LGG] w/in 6 months of stopping treatment) and has been on retreatment for 4 months; 1 patient with a BRAF fusion progressed after 9 months and has been on retreatment for 3 months. Treatment-related adverse events of any grade experienced by patients on retreatment were alopecia and rash (1 each). Independent radiographic analysis for response during retreatment is ongoing. CONCLUSIONS Tovorafenib provided durable tumor responses off-treatment in patients with r/r pLGG on a DH in FIREFLY-1.

IMMU-40. INVESTIGATING THE ROLE OF MUTATIONAL BURDEN IN TUMOR IMMUNOGENICITY USING A PRE-CLINICALMLH1-DEFICIENT GLIOBLASTOMA MODEL

Abstract BACKGROUND Although there is an established correlation between tumor mutational burden (TMB) and response to immune checkpoint inhibition (ICI) in many cancers, such an association has not been definitively shown in high-grade gliomas. Most studies of ICI therapy in gliomas, including glioblastoma (GBM), have failed to demonstrate efficacy, with the exception of hypermutated cases resulting from rare inherited defects in mismatch repair (MMR) genes. We sought to investigate the association of TMB to immune response using a syngeneic murine model with a spectrum of mutational burdens. METHODS We used CRISPR-Cas9 to knockout the MMR gene Mlh1 in the murine glioma model SB28, an ICI-resistant cell line with a very low mutational burden (108 non-synonymous mutations). RESULTS Single-cell sorted Mlh1 knockout SB28 clones revealed a two- to six-fold increase in TMB. Importantly, loss of Mlh1 also brought about global changes in immune- and inflammatory-related gene expression in vitro, without correlation to increasing TMB. While all clones had the same rate of in vitro proliferation, flank injection of a high TMB vs a low TMB SB28 Mlh1 knockout clone resulted in similar survival benefits compared to Mlh1 wildtype SB28. CONCLUSIONS These preliminary results suggest that, although disruption of the MMR system may result in heightened tumor immunogenicity, elevated TMB may not be the sole significant determinant. We are currently investigating tumor proliferation after flank injection in immunocompromised mice to confirm that slowed growth is immune-related, as well as clone-specific response to ICI treatment. We are also exploring the role of specific cytokines/chemokines in conferring this survival advantage and potential immune response. By generating a GBM model of varied mutational burdens and immune profiles and comparing to the baseline SB28 cell line, we can interrogate the relative significance of TMB in tumor immunogenicity and ICI response.

TMET-04. METABOLOMICS ANALYSIS IN FUNCTIONING AND SILENT CORTICOTROPH ADENOMAS USING A TWO-DIMENSIONAL NANOMATERIAL HIGH-THROUGHPUT PLATFORM

Abstract Functioning pituitary corticotroph adenomas (CAs) originated from T-PIT lineage with an ACTH-positive staining cause Cushing’s Disease. However, silent CAs (SCAs) baring the same histological features present clinically non-functioning with more aggressive courses. Metabolites within the tumor microenvironment play critical roles in regulating tumor behaviors and responses to therapy. Understanding their distribution and concentration provides valuable insights for diagnosis and treatment. This study investigated metabolite patterns in functioning and silent CAs. We developed a novel two-dimensional nanomaterial platform for enhanced surface-assisted laser desorption/ionization mass spectrometry. Utilizing this platform, we analyzed the metabolomes of three functioning CAs and three SCAs. Our platform exhibited exceptional sensitivity and stability in detecting metabolite molecules. Analysis of the metabolomes revealed distinct spatial distributions and peak intensity of various metabolites, including carbohydrates, amino acids, organic acids, nucleotides, and their precursors. Notably, certain metabolites such as tryptophol, clopidogrel carboxylic acid, DG(20:4(8Z,11Z,14Z,17Z)-2OH(5S,6R)/0:0/i-16:0), S-(-)-ureidoglycolate, and PC(20:4(5Z,7E,11Z,14Z)-OH(9)/14:1(9Z)) were significantly enriched in functioning CAs compared to SCAs, while others, including Cer(d18:1/16:0), Dihydrocytochalasin B, and LysoPC(O-18:0/0:0), exhibited higher peak intensity in SCAs. Overall, our findings underscored the existence of unique metabolomic signatures distinguishing functioning CAs and SCAs. Heterogeneous metabolite distributions among functioning CAs and SCAs were revealed by our novel nanomaterial high-throughput platform, and unique metabolic signatures were identified. Metabolomics analysis holds promise for precise biomedical diagnostics and individualized therapeutic strategies in functioning and silent CAs.

DDEL-03. INTRANASAL DELIVERY OF PDGFRA-TARGETED NANOTHERAPEUTICS FOR THE TREATMENT OF PEDIATRIC HIGH-GRADE GLIOMA

Abstract Pediatric high-grade glioma (pHGG) is the most common cause of cancer-related death in children, of which the most malignant and devastating tumors include diffuse midline glioma (DMG). Its anatomical location in the brainstem, infiltrative nature, and blood-brain barrier (BBB) limit surgical resection and the distribution of systemically administered drugs. Intranasal delivery (IND) is a noninvasive method that bypasses the BBB, by leveraging the unique anatomic connections of the olfactory and trigeminal nerve pathways with the nasal cavity. We previously demonstrated the efficacy of IND of nanoliposomal (LS) formulation of the active metabolite of the DNA topoisomerase I inhibitor, irinotecan, LS-SN-38, in orthotopic human brainstem xenograft models. The specificity of liposomes can be enhanced by using immunoliposome (iLS) formulation, which are coated with antibodies specific to the tumor cells leading to targeted drug delivery and reduced toxicity to normal cells. Platelet-derived growth factor receptor alpha (PDGFRA) plays a role in DMG oncogenesis and is expressed in as much as 70% of DMG by immunohistochemistry. In this study, we evaluated the effect of anti-PDGFRA monoclonal antibody-conjugated immunoliposome encapsulated SN-38 (PDGFRA-iLS-SN-38) in pHGG cell lines. PDGFRA signals were assessed in pHGG cells using western blotting. Cells were treated with rhodamine (Rho)-labeled PDGFRA-iLS and cellular uptake was confirmed with a fluorescent microscope. PDGFRA-iLS-SN38 had the additive effect on the LS-SN-38 in DIPG007 cells (PDGFRA positive), but not in SF8628 cells (PDGFRA negative) in vitro. We treated mice bearing human DMG xenografts with IND of PDGFRA-iLS-SN38. Tumor growth and response to therapy are quantitatively measured by bioluminescence imaging, and efficacy is assessed by survival analysis. Results of survival analysis will be reported at the meeting. PDGFRA-targeted nanotherapeutics represented a specific effect on glioma cells expressing PDGFRA, providing a promising therapeutic approach for targeting pHGG.

NIMG-55. DEVELOPING A COMPUTATIONAL PIPELINE TO FORECAST AND SPATIALLY MAP HIGH-GRADE GLIOMA RESPONSE TO RADIOTHERAPY USING BIOPHYSICAL MODELS AND DATA-DRIVEN STATISTICAL ANALYSIS

Abstract High-grade glioma (HGG) presents significant treatment challenges, particularly in identifying less responsive tumor areas to target with adaptive radiotherapy (RT). This study introduces a patient-specific computational pipeline designed to predict and spatially map HGG response to RT, focusing on regions demonstrating resilience to RT. Our computational pipeline is centered around a family of 3D biophysical models describing tumor cell invasion, proliferation, and response to RT which can be personalized for individual patients using longitudinal multiparametric MRI data. Utilizing longitudinal multiparametric MRI data reporting on cell density (diffusion weighted MRI) and the extent of disease (T2-FLAIR and contrast-enhanced T1-weighted MRIs) from 21 patients, ranging from baseline to three weeks into RT, we calibrated a family of biophysical models to forecast tumor cell density up to the final week of RT and one-month follow-up. By employing pareto tail analysis on empirical cumulative distribution function fits of voxel-wise changes in apparent diffusion coefficient maps (ΔADC) between the future images (end of RT, one-month follow-up) and pre-treatment images, we identified areas of increased tumor cellularity on both the ground truth and model predicted cellularity maps. The analysis differentiated tumor voxels into “non-responding” and “responding” categories, based on cutoffs determined through ROC analysis across various conditions—including assessments of both enhancing and non-enhancing tumor regions at different time points. Optimal ΔADC cutoffs for predicted and measured data were established, leading to high area under curve (AUC; ranging from 0.803 to 0.934) values and significant Youden’s index scores (ranging from 0.526 to 0.765) across all conditions. Our findings demonstrate the feasibility of this novel pipeline in delineating biologically relevant RT targets, offering a potential tool for enhancing the efficacy of adaptive RT strategies in treating HGG.

SURG-48. LASER INTERSTITIAL THERMAL THERAPY REMODELS THE TUMOR IMMUNE LANDSCAPE IN A MOUSE GLIOMA MODEL

Abstract BACKGROUND Laser interstitial thermal therapy (LITT), a minimally invasive surgical technique for tumor ablation, is increasingly being used to treat primary and recurrent glioma. While the primary goal of using LITT has been to destroy tumor tissue, little is known about the impact of LITT on the overall immune response. To investigate changes in the tumor immune landscape, we utilized a mouse model of LITT and applied it to a poorly immunogenic mouse model of glioma. METHODS SB28 glioma cells were implanted in the right frontal lobe of C57BL/6 mice, and on day 7, an optical fiber is inserted into the tumor, paired with a thermocouple for real-time temperature monitoring. A 30W laser was activated in pulses to maintain a peri-lesional temperature of 44C for 150-180 seconds. The tumor and LITT-associated immune response was analyzed by multiparameter flow cytometry, single cell RNA-seq, and multiplex immunofluorescence. RESULTS LITT (versus sham control) triggered an increase in neutrophils in the tumor during the acute phase at day 3 following treatment. Total immune cell numbers increased over time in both sham- and LITT-treated mice, but there was a significant increase at post-LITT day 7 in select adaptive immune cell populations including type 1 conventional dendritic cells, NK cells, and gamma delta T cells. Monocytes/macrophages comprised the majority of the immune infiltrate, and multiplex immunofluorescence revealed these populations localized to the perimeter of the LITT lesion. scRNA-seq also revealed enrichment of a Fabp5- and Gpnmb-expressing macrophage subset following LITT. CONCLUSIONS LITT modifies the tumor immune infiltrate with increases in neutrophils as well as select adaptive cell and macrophage subsets. Future studies will explore adjunct therapies to further augment the immune response in the setting of LITT.

PATH-03. SPATIAL-RESOLVED METABOLOMICS ANALYSIS IN HISTOLOGICAL AND MOLECULAR GLIOBLASTOMAS USING A MOF/MXENE-ASSISTED LDI-MSI PLATFORM

Abstract Glioblastoma (GBM) is a highly aggressive primary brain tumor encompassing both histological and molecular subtypes. Metabolites within the tumor microenvironment play critical roles in regulating tumor behavior and response to therapy. Understanding their spatial distribution provides valuable insights for diagnosis and treatment. We investigated metabolite patterns of histological GBMs (hist-GBMs) and molecular GBMs (mol-GBMs) by developing a novel MOF/MXene platform for enhanced surface-assisted laser desorption/ionization mass spectrometry. Utilizing this platform, we analyzed the metabolomes of three hist-GBMs and three mol-GBMs. Our platform exhibited exceptional sensitivity, repeatability, and stability in detecting metabolite molecules. Analysis of the metabolomes revealed distinct spatial distributions and concentrations of various metabolites, including carbohydrates, amino acids, organic acids, nucleotides, and their precursors. Notably, certain metabolites such as TG(15:0/20:3n6/20:5(5Z,8Z,11Z,14Z,17Z)), PG(20:3(6,8,11)-OH(5)/i-21:0), and SM(d20:1/20:3(6,8,11)-OH(5)) were significantly enriched in hist-GBMs compared to mol-GBMs, while others, including lithocholic acid glycine conjugate, PE(P-16:0/14:1(9Z)), and CE(11:1D5), exhibited higher peak intensity in mol-GBMs. Overall, our findings underscore the existence of unique metabolomic signatures distinguishing hist-GBMs from mol-GBMs. In conclusion, heterogeneous metabolite distributions among hist-GBMs and mol-GBMs were revealed by our novel MOF/MXene assisted LDI-MSI platform, and unique metabolic signatures were identified. Advanced metabolomics analysis holds promise for precise biomedical diagnostics and individualized therapeutic strategies in GBMs.

IMMU-12. TRANSLATING COMBINED PD1 AND LAG3 INHIBITION FROM PRECLINICAL MODELS TO PATIENTS WITH REFRACTORY, DNA REPLICATION REPAIR DEFICIENT (RRD) GLIOBLASTOMA: AN IRRDC STUDY

Abstract BACKGROUND AND AIMS RRD-glioblastoma harbour high tumor mutation burden (TMB) and respond to anti-PD1 immune-checkpoint inhibition (ICI). However, not all respond, and the majority progress, highlighting the need for combinatorial therapies for sustained immune-surveillance. METHODS We performed transcriptomic analyses of human RRD-glioblastoma specimens for immune checkpoint expression, and accordingly, tested combined ICI in immunocompetent murine models. Based on these preclinical data, we treated refractory patients using a combination of anti-PD1+anti-LAG3 through single-patient trial/compassionate access. Complimentary immuno-genomic biomarker analyses including circulating tumor DNA (ctDNA) were performed to investigate mechanisms and track responses. RESULTS Human RRD-glioblastoma (n=80) demonstrated high LAG3 expression, providing a strong rationale for therapeutic targeting. We tested combined anti-PD1+anti-LAG3 inhibition in three immunocompetent RRD-glioblastoma murine models. In the anti-PD1-responsive (Nestin-CreMSH2LoxP/LoxP-POLES459F/+) model, anti-PD1+anti-LAG3 resulted in universal tumor response and superior survival to ICI-monotherapy. In the anti-PD1 resistant models (Mlh1-/-/NestinCre+/Trp53LoxP/LoxP and therapy-induced hypermutant ENU/Trp53-/- gliomas), anti-PD1+antiLAG3 improved survival, overcoming the lack of response to ICI-monotherapy. Biologically, high LAG3 expression and immune-exhaustion observed in CD8 T-cells after treatment with anti-PD1 was ablated following the addition of anti-LAG3. Serially transplanted, post-anti-PD1 treated tumors showed response, confirming, in-vivo, that resistance to anti-PD1 could be abrogated by anti-PD1+anti-LAG3. Seven children with refractory RRD-glioblastoma who had progressed after anti-PD1 treatment were treated using anti-PD1+anti-LAG3, resulting in objective radiological responses and prolonged ongoing survival. Tolerability was better than a previous study of combined CTLA4 and PD1 inhibition for similar patients. Paired immuno-genomic tumor analyses, serial blood flow-cytometry, T-cell receptor clonotype, and CSF ctDNA analyses provided novel insights into the mechanisms of immunological invigoration and first-in-human, radiological responses. CONCLUSIONS LAG3 is an effective target in refractory RRD-glioblastoma. Combined inhibition with anti-PD1 inhibition demonstrated radiological response, prolonged survival and manageable toxicities in patients, and unearthered mechanisms of immune-responses. The combination will now be tested in biomarker-driven clinical trials in RRD-glioblastoma and other immune-inflamed solid tumors.

CTIM-14. EARLY SAFETY DATA FROM A RANDOMIZED, MULTICENTER, DOUBLE-BLIND, PHASE 2B STUDY OF IGV-001, AN AUTOLOGOUS CELL IMMUNOTHERAPY, VERSUS PLACEBO, IN NEWLY DIAGNOSED GLIOBLASTOMA (NDGBM)

Abstract Standard of care (SOC) for ndGBM begins with maximal safe resection followed by adjuvant radiotherapy and temozolomide, and maintenance temozolomide. IGV-001 is an autologous biologic-device combination immunotherapy for the treatment of ndGBM that consists of autologous GBM tumor cells and an antisense oligonucleotide against IGF-1R mRNA, irradiated and administered via biodiffusion chambers implanted in the abdomen. In a phase 1b study, IGV-001 was well tolerated without unexpected adverse events in subjects with ndGBM. Multiple efficacy signals were observed, including significant improvements in progression-free survival (PFS), overall survival (OS), radiographic evidence of tumor response, and changes in immune response biomarkers. Here, we present early safety data from the phase 2b randomized, multicenter, double-blind, placebo-controlled study (NCT04485949) designed to assess efficacy and safety of IGV-001 in subjects with ndGBM across 20 sites in the United States. After surgical resection, subjects were randomized 2:1 and treated with IGV-001 or placebo followed by SOC. The primary outcome is PFS, defined as the time from randomization to first progression, as determined by blinded central radiology review, or death. Secondary outcomes include OS, defined as the time from randomization to death due to any cause, and safety. As of May 22, 2024, 99 subjects were randomized and 95 implanted with IGV-001 or placebo plus SOC. A total of 39/45 (86.7%) subjects had sufficient follow-up time after initiated treatment with concurrent radiation and temozolomide. Nine of 72 randomized (12.5%) discontinued treatment, including 7 who stopped during the SOC treatment period. None ceased treatment for adverse events, protocol deviations, or death. A total of 11/72 (15.3%) randomized subjects discontinued the study after randomization. A review of blinded safety data did not show any emerging risk and supports no change to the benefit-risk profile of IGV-001 versus placebo. Updated data will be presented.

NIMG-89. MULTI-THRESHOLD VOLUMETRIC MAPPING OF18F-FLUOROETHYLTYROSINE POSITRON EMISSION TOMOGRAPHY (18F-FET PET) IMPROVES TUMOR DETECTION IN PRIMARY MALIGNANT BRAIN TUMOR PATIENTS

Abstract PURPOSE The purpose of this study was to determine whether additional volumetric measurements yielded significant prognostic information than typically reported tumor-to-brain ratio thresholds (TBRmax) alone for accurately distinguishing progressive disease from treatment induced changes. METHODS Hybrid 18F-FET PET/MRI was obtained on pathology confirmed high-grade glioma in sixty patients from August 6th, 2022 to March 9th, 2023 at one US institution. We compared the diagnostic accuracy of various TBR thresholds and volumetric measurement combinations in identifying progressive disease. Specifically, we assessed TBR >1.6, 2.0, 2.5, 3.0, 3.5, 4, 4.5, and 5.0 alone and in combination with volumetric measurements greater than 1 mL. Survival data for all patients were analyzed using Kaplan-Meier curves. RESULTS Our analysis revealed that TBR > 2.5 and >1 mL yielded the highest diagnostic accuracy (100%) in distinguishing progressive disease from treatment induced changes. This was followed by the combination TBR >2.0 and >1 mL (98%), TBR > 2.5 alone (98%), TBR > 2.0 alone (86%), TBR >1.6 and >1 mL (84%), and TBR >1.6 alone (77%). TBR >3.0, 3.5, 4.0, 4.5, and 5.0 with and without volumetric measurements showed accuracies of 100%. Kaplan-Meier survival analysis showed significant results for all thresholds: TBR >1.6 alone (p = 0.047), TBR >1.6 and 1 mL (p = 0.003), TBR > 2.0 alone (p = 0.019), TBR >2.0 and >1 mL (p < 0.001), TBR >2.5 alone (p < 0.001), and TBR >2.5 and >1 mL (p = 0.002). CONCLUSION Our findings suggest that although TBRmax > 2.5 alone continues to be a reliable metric for distinguishing progressive disease from treatment induced changes, TBRmax >2.5 when volume is greater than 1 mL shows the greatest accuracy in detecting disease progression. Understanding the volumetric contribution to static FET TBRmax is important for tumor response assessment at TBRmax thresholds above 1.6 TBRmax.

Prediction of tumor response to neoadjuvant chemotherapy in high-grade osteosarcoma using clustering-based analysis of magnetic resonance imaging: an exploratory study

Prediction of tumor response to neoadjuvant chemotherapy in high-grade osteosarcoma using clustering-based analysis of magnetic resonance imaging: an exploratory study

CNSC-14. GLIOBLASTOMA MULTIFORME TUMOR VOLUME AND PERSISTENCE OF CHIMERIC ANTIGEN RECEPTOR T CELLS FOLLOWING TREATMENT

Abstract Glioblastoma Multiforme (GBM) is one of the most common and aggressive high-grade primary brain tumors that arises from the glial cells of the central nervous system and occurs most often in the frontal and temporal lobes. Despite current treatment options, long-term prognosis of GBM remains low with no significant improvement rates. Chimeric antigen receptor (CAR)-expressing T cells target the B cell marker CD19 and have shown increased efficacy in B cell lymphomas, and lymphoblastic leukemias suggesting benefits in GBM. This study aims to quantify the persistence of CAR-T cells in the context of GBM tumor volume following neurosurgical debulking procedure. A radiology software known as the mint Lesion was utilized to provide Tumor Response Assessment by Criteria (TRAC) reports that consist of volumetric measurements of the tumor lesions (target enhancing lesions, non-target enhancing lesions, and non-target non-enhancing lesions). Fluorescence-activated cell sorting (FACS) analysis takes a sample mixture of cells and sorts them into different populations based on specific biomarkers and characteristics. B7-H3 CAR-T cell persistence was increased in patients with a larger post-surgical tumor volume (3.04% Subject 001 with 2438 mm² volume and 2.38% Subject 003 with 224 mm² tumor volume). However, the number of CAR-T cells per 1 mm² was significantly reduced in patients with a larger post-surgical tumor volume (0.0012 cells/mm² Subject 001 and 0.010 cells/mm² Subject 003). This study shows that although there is an overall increased CAR-T cell persistence for a larger tumor volume, the number of CAR-T cells per 1 mm² is significantly smaller for larger tumor volumes, while illustrating that a larger post-surgical tumor bulk volume is correlated with an increased CAR-T cell persistence within 1-week post-infusion. These findings provide novel information and complement other correlative studies as part of the Phase 1 interventional clinical trial for glioblastoma patients.