Epidermal Growth Factor Receptor Variant III Research Articles

IMMU-67. INTRACRANIAL IL12 SECRETING CAR-T CELLS OBVIATE THE NEED FOR LYMPHODEPLETION AND COMBAT HETEROGENEITY VIA MICROGLIAL INTERACTIONS

Abstract INTRODUCTION Epidermal growth factor receptor variant III (EGFRvIII) is a tumor-specific antigen distinctively expressed in glioblastoma multiforme (GBM). However, its heterogeneous expression in GBM complicates its application as a target for Chimeric Antigen Receptor (CAR) T cells. Additionally, Interleukin-12 (IL12) has recently been identified as a potent cytokine in the treatment of solid tumors. In this study, we investigate the potential synergy between CAR-T cells and IL12 in targeting heterogeneous tumor antigens. METHODS To model tumor heterogeneity, mice were injected with a 50/50 mix of CT2A and CT2A EGFRvIII+ cells. EGFRvIII-specific third-generation CAR T cells, engineered with or without single-chain IL12, were cloned using an MSGV retrovirus backbone and transduced into murine T cells. The antitumor efficacy of CAR-T cells was evaluated through survival analysis. Additionally, the capability of CAR-T cells with or without IL12 to prolong survival and alter the tumor microenvironment was analyzed using single-cell sequencing. RESULTS EGFRvIII CARs alone were insufficient to cure mice with heterogeneous tumors, whereas EGFRvIII CARs co-expressing IL12 achieved a 60% cure rate. Interestingly, EGFRvIII CARs secreting IL12 demonstrated longer persistence in vivo compared to EGFRvIII CARs alone and did not require lymphodepletion before administration. We found that EGFRvIII CARs expressing IL12 promoted the elimination of EGFRvIII-negative tumor cells by recruiting endogenous CD8 T cells. Furthermore, among all Antigen Presenting Cell (APC) populations in the tumor microenvironment, we found that IL12 primarily acted on microglia to enhance antigen presentation pathways and support epitope spreading. CONCLUSION EGFRvIII CARs engineered to secrete IL12 effectively treat antigen-heterogeneous tumors by modulating local APCs and recruiting endogenous T cells. IL12-secreting CARs demonstrate longer persistence without the need for lymphodepletion compared to traditional EGFRvIII CARs. Employing CAR-T cells that secrete IL12 is a promising strategy to address tumor heterogeneity, offering therapeutic potential against GBM in clinical settings.

Enhancing anti-EGFRvIII CAR T cell therapy against glioblastoma with a paracrine SIRPγ-derived CD47 blocker

A significant challenge for chimeric antigen receptor (CAR) T cell therapy against glioblastoma (GBM) is its immunosuppressive microenvironment, which is densely populated by protumoral glioma-associated microglia and macrophages (GAMs). Myeloid immune checkpoint therapy targeting the CD47-signal regulatory protein alpha (SIRPα) axis induces GAM phagocytic function, but CD47 blockade monotherapy is associated with toxicity and low bioavailability in solid tumors. In this work, we engineer a CAR T cell against epidermal growth factor receptor variant III (EGFRvIII), constitutively secreting a signal regulatory protein gamma-related protein (SGRP) with high affinity to CD47. Anti-EGFRvIII-SGRP CAR T cells eradicate orthotopic EGFRvIII-mosaic GBM in vivo, promoting GAM-mediated tumor cell phagocytosis. In a subcutaneous CD19+ lymphoma mouse model, anti-CD19-SGRP CAR T cell therapy is superior to conventional anti-CD19 CAR T. Thus, combination of CAR and SGRP eliminates bystander tumor cells in a manner that could overcome main mechanisms of CAR T cell therapy resistance, including immune suppression and antigen escape.

Enhanced Anticancer Activity of 7MeERT over Ertredin: A Comparative Study on Cancer Cell Proliferation and NDUFA12 Binding.

We have previously identified Ertredin (3-(2-amino-5-bromophenyl) quinoxalin-2(1H)-one) as a compound that suppresses 3D spheroid formation and tumorigenesis in NIH3T3 cells induced by Epidermal Growth Factor Receptor variant III (EGFRvIII) transduction. One of its targets has been shown to be NDUFA12 (NADH Dehydrogenase (Ubiquinone) 1 Alpha Subcomplex Subunit 12), a component protein of oxidative phosphorylation complex I. In this report, we compared the growth inhibitory activity of Ertredin with its methylated analogue 7MeERT (3-(2-amino-5-bromophenyl)-7-methylquinoxalin-2(1H)-one) on human cancer cells. 7MeERT induced the inhibition of the proliferation of various cancer cells similarly to Ertredin and showed higher activity in glioblastoma cells, A431 cells overexpressing EGFR (wild type), and multiple myeloma cells. Molecular docking analysis and a Cellular Thermal Shift Assay (CETSA) suggested that 7MeERT binds to NDUFA12 similarly to Ertredin. The binding of 7MeERT and Ertredin to NDUFA12 in glioblastoma was further supported by the inhibition of the oxygen consumption rate. These results suggest that 7MeERT also binds to NDUFA12, inhibits oxidative phosphorylation, and has a higher anti-cancer cell growth inhibitory activity than Ertredin.

AB020. Flagellin synergistically enhances anti-tumor effect of EGFRvIII peptide in a glioblastoma-bearing mouse brain tumor model.

Glioblastoma (GBM) is the most aggressive type of brain tumor with heterogeneity and strong invasive ability. Treatment of GBM has not improved significantly despite the progress of immunotherapy and classical therapy. Epidermal growth factor receptor variant III (EGFRvIII), one of GBM-associated mutants, is regarded as an ideal therapeutic target in EGFRvIII-expressed GBM patients because it is a tumor-specific receptor expressed only in tumors. Flagellin B (FlaB) originated from Vibrio vulnificus, is known as a strong adjuvant that enhances innate and adaptive immunity in various vaccine models. This study investigated whether FlaB synergistically could enhance the anti-tumor effect of EGFRvIII peptide (PEGFRvIII). EGFRvIII-GL261/Fluc cells were used for GBM-bearing mouse brain model. Cell-bearing mice were inoculated with phosphate-buffered saline (PBS), FlaB alone, PEGFRvIII alone, and PEGFRvIII plus FlaB. Tumor growth based on magnetic resonance imaging (MRI) and the survival rate was investigated. T cell population was examined by flow cytometry analysis. Both cleaved caspase-3 and CD8+ lymphocytes were shown by immunohistochemistry (IHC) staining. The PEGFRvIII plus FlaB group showed delayed tumor growth and increased survival rate when compared to other treatment groups. As evidence of apoptosis, cleaved caspase-3 expression and DNA disruption were more increased in the PEGFRvIII plus FlaB group than in other groups. In addition, the PEGFRvIII plus FlaB group showed more increased CD8+ T cells and decreased Treg cells than other treatment groups in the brain. FlaB can enhance the anti-tumor effect of PEGFRvIII by increasing CD8+ T cell response in a mouse brain GBM model.

Synergistic effect of chimeric antigen receptor modified with Bcl-2 on enhanced solid tumour targeting.

Engineered T cells expressing chimeric antigen receptors (CARs) have shown remarkable therapeutic effects on haematological malignancies. However, CART cells are less effective on solid tumours mainly due to their weak persistence, which might be caused by activation-induced cell death (AICD). To overcome this limitation, CART cell with the antigen, Epidermal growth factor receptor variant III (EGFRvIII), targeting was modified to carry the anti-apoptotic molecule B cell lymphoma 2 (Bcl-2), and the final construct was named as EGFRvIII·CART-Bcl2 cells. Compared with the EGFRvIII·CART cells, EGFRvIII·CART-Bcl2 cells revealed higher capacities of proliferation, anti-apoptosis and tumour cell killing in vitro. Moreover, EGFRvIII·CART-Bcl2 cells had a longer persistence rate and exerted better anti-tumour effects than EGFRvIII·CART cells in cervical carcinoma xenograft model. Taken together, our findings suggest that incorporating anti-apoptotic molecules into CART cells may enhance its therapeutic effects against solid tumours.

Overexpressing Bcl-2 enhances murine chimeric antigen receptor T cell therapy against solid tumor.

Chimeric antigen receptor T (CART) cell therapy has demonstrated promising potential in the treatment of hematologic malignancies. However, its application to solid tumors is limited due to the restrictive nature of the tumor microenvironment, resulting in functional failure and poor persistence of CART cells. Overexpression of Bcl-2 in human CART cells (hCART) has been found to significantly enhance their anti-apoptotic effects both in vitro and in vivo. Nevertheless, the evaluation of hCART cells in preclinical studies has predominantly relied on immunodeficient mice xenograft tumor models, making it challenging to assess the impact of hCART cells on normal tissues and the immune system. We established a murine CART (mCART) that overexpresses Bcl-2 and targets the epidermal growth factor receptor variant III (EGFRvIII), named EGFRvIII·mCART-Bcl2. It demonstrated superior proliferation, cytotoxicity, and anti-apoptotic capabilities in vitro. In an immunocompetent mouse model of abdominal metastasis of colorectal cancer, EGFRvIII·mCART-Bcl2 exhibited improved survival of CART in the abdomen, increased tumor clearance, and significantly prolonged overall mouse survival. In summary, our study provides evidence that the introduction of Bcl-2 into mCART cells can enhance their therapeutic efficacy against solid tumors while ensuring safety.

Preparation and evaluation of the PD0721‑DOX antibody‑drug conjugate targeting EGFRvIII to inhibit glioblastoma

Preparation and evaluation of the PD0721‑DOX antibody‑drug conjugate targeting EGFRvIII to inhibit glioblastoma

Abstract 5496: Multi-omic spatial analysis of the tumor microenvironment in gliomas

Abstract Introduction: The diverse tumor environment of high-grade glioma, which remains refractory to treatment, demands new innovative, multi-omic approaches to characterize tumor heterogeneity and expression profiles associated with progression and therapeutic response. Approach: We have applied an integrated, multi-omic approach using paired spatial in situ sequencing (Xenium) and protein profiling (PhenoCycler® Fusion) of glioma tissue to identify distinct glioma cellular phenotypes, activation states and metabolic pathways at true single cell resolution. Our multi-omic approach used hundreds of phenotypic RNA target probes and >50 antibodies in an unbiased single-cell analysis of primary, recurrent, and IDH1 mutant/wild type tumors with a range of heterogeneity. Summary: We were able to distinguish differentially regulated genes and pathways between aggregated primary and recurrent GBM, including cell cycle pathways being upregulated in primary vs recurrent GBM glial cell clusters and a down regulation of ERBB4 signaling in vascular cell clusters in primary GBMs. Our data also suggests that SOX11, known to be involved in tumorigenesis, is >2-fold upregulated in annotated tumor cells in primary compared to recurrent tumors. We were also able to quantitatively localize the expression of Epidermal Growth Factor Receptor, variant III (EGFRvIII) to specific tumor-cell sub-types, which is important given its association with therapeutic resistance. Further, we have been able to establish the cellular neighborhoods and cell-cell and receptor-ligand relationships within the tumors. Our spatial protein analysis identified distinct tumor and immune phenotypes with varying abundance of myeloid and lymphoid populations in IDH1 wt and mt tumors. Moreover, spatial proximity analyses and cellular neighborhood analyses revealed differences in higher order organizational landscapes that may contribute to the differential outcomes across wt and mt tumor subtypes. Conclusion: Multiomic spatial analysis enables deeper characterization of the glioma cellular and functional landscape to broaden our understanding of the key TME features that contribute to disease pathogenesis and prognoses. Our study provides an analytical framework to combine RNA and protein-based spatial data for a holistic investigation into a variety of glioma subtypes and aid in the identification of novel biomarkers, spatial neighborhoods, and functional states that drive glioma progression. Citation Format: Dmytro Klymyshyn, Vaibhav Jain, Lauren Whaley, Emily Hocke, Bassem Ben Cheikh, Alan Smith, Karen Abramson, Nadine Nelson, Diane Satterfield, Elizabeth Thomas, Giselle Lopez, Seetha Hariharan, Michael Brown, Niyati Jhaveri, Roger McLendon, David Ashley, Matthew Waitkus, Simon Gregory. Multi-omic spatial analysis of the tumor microenvironment in 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 5496.

Formation of EGFRwt/EGFRvIII homo- and hetero-dimers in glioblastoma cells as detected by single molecule localization microscopy.

Super-resolution microscopy has been used to show the formation of receptor clusters and adapted lipid organization of cell membranes for many members of the ErbB receptor family. The clustering behaviour depends on the receptor size and shape, possibly ligand binding or expression activity. Using single molecule localization microscopy (SMLM), we also showed this typical clustering for the epidermal growth factor receptor variant III (EGFRvIII) in glioblastoma multiforme (GBM) cells. EGFRvIII is co-expressed with the wild type (EGFRwt) and both receptors are assumed to preferentially form hetero-dimers leading to transactivation and elevated oncogenic EGFR-signalling in GBM cells. Here, we analysed EGFRvIII and EGFRwt co-localization using our already described model system of the glioblastoma cell line DKMG, displaying endogenous EGFRvIII expression. Using EGFRvIII and EGFRwt specific antibodies, EGFR localization and their potential for dimerization in a given membrane cluster were analysed by dual colour SMLM supported by novel approaches of mathematic evaluations including Ripley statistics, persistent homology and similarity algorithms. Surprisingly, cluster analysis, Ripley point-to-point distance statistics for cluster geometry and persistent homology comparing cluster topology, revealed that both EGFRvIII and EGFRwt do primarily not form hetero-dimers but the results support the hypothesis that they tend to form homo-dimers. The ratio of homo-dimers obtained by this calculation was significantly higher (>5σ, standard deviation) than expected from randomly arranged points. In comparison, hetero-dimer formation was only slightly increased. We confirmed these data by immunoprecipitation, which show no co-precipitation of EGFRvIII and EGFRwt. Furthermore, we showed that the topology of the clusters was more similar among the same type than among the different types of receptors. Taken together, these data indicate that EGFRvIII does induce oncogenic signalling by homo-dimerisation and not preferentially by hetero-dimer formation with EGFRwt. These data offer a new perspective on EGFRvIII signalling which will lead to a better understanding of this tumour associated receptor variant in GBM.

Abstract A040: Characterization of a humanized monoclonal antibody targeting cancer-expressed EGFR

Abstract The epidermal growth factor receptor (EGFR), an established oncology target, is a transmembrane protein highly expressed on the surface of malignant tumors such as glioblastoma, lung, liver, bladder and breast cancers. In addition to overexpression, EGFR mutants are frequently associated with malignancy. For example, EGFR variant III (EGFRvIII), deletion of exons 2-7, is only expressed on cancer cells and is associated with poor prognosis and chemotherapy resistance. To target cancer-expressed EGFR, including EGFRvIII, we generated the 40H3 monoclonal antibody which is reactive with the 287-302 loop that is fully exposed on the extracellular domain of EGFRvIII. The 40H3 antibody also showed strong reactivity for cells expressing gene-amplified EGFR but little or no reactivity for cells expressing normal levels of wild type EGFR. When conjugated with toxic payloads (either tesirine or deruxtecan), the resulting antibody-drug conjugates (ADCs) exhibited antitumor activity in several xenograft models. To improve its utility as a clinical candidate, we humanized the variable portions of the heavy and light chains of 40H3, without changing the original CDRs. The variable regions of 40H3, heavy and light chains, were compared to the closest human immunoglobulin families and then framework residues were altered to produce candidate humanized antibodies. The humanized variable chains were then fused with a human IgG1 heavy chain and a kappa light chain to generate full-sized humanized antibodies. A total of 9 humanized antibodies were generated by pairing 3 variable humanized heavy chains (VH1, VH2, VH3) with 3 variable humanized light chains (VL1, VL2, VL3). To evaluate the binding activity of humanized antibodies, we used either immobilized EGFRvIII (by ELISA or Octet) or various cancer cells expressing either EGFR or EGFRvIII (by flow cytometry). All humanized antibodies retained binding activity to immobilized EGFRvIII but bound with different apparent affinities to cells overexpressing EGFR or cells transfected with EGFRvIII. The ‘A10’ antibody was the best candidate. Mutations introduced in A10 preserved the binding affinity of the 40H3 antibody but exhibited an increased affinity compared to the corresponding chimeric antibody constructed with the original mouse VH and VL. The other eight antibodies retained EGFRvIII binding activity, albeit with a lower cell binding affinity. Specifically, A10 showed improved binding to cells with EGFR gene amplification including two TNBC lines, MDA-MB-468 and BT-20, epithelial cancer cells, A431, head and neck squamous carcinoma, UMSCC17B, as well to cells expressing EGFRvIII, F98npEGFRvIII. No binding of A10 was detected to cell lines expressing wild type EGFR, WI-38 or U87MG. In summary, humanized candidates of the 40H3 monoclonal antibody retained EGFR binding. Of 9 antibodies, A10 exhibited the best cell binding activity elevating it to our top clinical candidate for the production of ADCs or similar antibody-based therapeutics. Citation Format: Tamara G Fernandes Costa, Robert Sarnovsky, Maria Teresa Bilotta, Antonella Antignani, David FitzGerald. Characterization of a humanized monoclonal antibody targeting cancer-expressed EGFR [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr A040.

CTIM-24. REPEATED PERIPHERAL INFUSIONS OF ANTI-EGFRVIII CAR T CELLS IN COMBINATION WITH PEMBROLIZUMAB REMODELS THE TUMOR MICROENVIRONMENT IN DE NOVO GLIOBLASTOMA

Abstract Treatment efficacy with chimeric antigen receptor (CAR) T cell therapy in glioblastoma (GBM) is undermined by an immunosuppressive tumor microenvironment (TME). We previously showed that CAR T cell therapy targeting epidermal growth factor receptor variant III (EGFRvIII) produces anti-tumor activity against recurrent GBM and causes upregulation of programmed death-ligand 1 (PD-L1) in the TME. Here, we conducted a phase I trial to study the safety and tolerability of CART-EGFRvIII cells administered concomitantly with the PD-1 inhibitor pembrolizumab in patients with newly diagnosed, EGFRvIII+ GBM (n = 7). Treatment was well tolerated without incidence of dose-limiting toxicity. However, no signal of efficacy was detected with a median progression-free survival of 5.2 months (90% CI, 2.9 – 6.0 months) and overall survival of 11.8 months (90 % CI, 9.2 – 14.2 months). We aimed to elucidate reasons for limited efficacy through correlative analyses. Using BBZ qPCR, we found circulating CAR T cells in 5 out of 7 patients at the time of repeat resection, but only in one patient in the tumor. However, shared TCRs were found between the infusion product and the relapsed tumors, which could indicate an infiltration but lack of persistence of the CART. We further compared the tumor microenvironment of the tumors harvested before and after CAR+aPD1 administration using single cell RNAseq, and observed comparable proportions of the major immune cell subsets. However, the myeloid and T cells infiltrating the tumors significantly evolved, with more exhausted, regulatory and IFN-stimulated T cells at the relapse. At that time, the amount of IFN-stimulated T cells positively correlated with time from relapse to death. Together, these findings suggest that the combination of CAR T cells and PD-1 inhibition in GBM is safe and biologically active but, given the lack of efficacy, also indicate a need to consider alternative immunotherapeutic strategies. ClinicalTrials.gov registration: NCT03726515.

STEM-06. OSMR INTERACTOME MAPPING REVEALS THE SIGNIFICANCE OF A CHLORIDE CHANNEL IN CYTOKINE REGULATION AND BRAIN TUMOUR STEM CELL SELF-RENEWAL

Abstract Oncostatin M Receptor (OSMR) is a key regulator of brain tumour stem cell (BTSC) self-renewal and glioblastoma (GB) tumourigenesis. This receptor is found in a complex with Epidermal Growth Factor Receptor variant III (EGFRvIII) and orchestrates a positive feedback loop with STAT3. OSMR also regulates oxidative phosphorylation and participates in promoting the transition of cells towards mesenchymal-like glioma states. How OSMR drives GB tumorigenesis via multiple mechanisms remains largely unclear. Here, we map OSMR interactome in different GB subtypes using the Mammalian Membrane Two Hybrid High Throughput Screen (MaMTH-HTS). Analysis of these data followed by functional validation has uncovered distinct OSMR interactome in a context dependent manner. Follow up investigations, however, have led to the discovery of the Chloride Intracellular Channel 1 (CLIC1), essential in the regulation of OSMR cytokine signaling and GB progression independently of the genetic profile of the GB tumour. CLIC1 forms a complex with OSMR to promote BTSC self-renewal and knockout of CLIC1 or pharmacological inhibitors to CLIC1 impairs OSM mediated STAT3 phosphorylation. Our work suggests that CLIC1 and OSMR form a complex in BTSCs and functionally interact to activate STAT3.

CTIM-09. PHASE 1/1B TRIAL OF FC-ENGINEERED ANTI-CD40 AGONIST MONOCLONAL ANTIBODY (2141-V11) INFUSED WITH D2C7-IT IN ENHANCING DISEASE BY CONVECTION-ENHANCED DELIVERY (CED) FOR RECURRENT MALIGNANT GLIOMA (RMG)

Abstract BACKGROUND D2C7-IT is a dual-specific immunotoxin. Recombinant antibody fragments bind the wild-type epidermal growth factor receptor (EGFRwt) and its mutant EGFR variant III (EGFRvIII), triggering internalization and intracellular delivery of the Pseudomonas exotoxin, D2C7-IT cell-killing component. Single intratumoral delivery of D2C7-IT in animals generates an antitumor response by directly killing tumor cells and indirectly activating an adaptive T-cell response. However, tumor-associated macrophages (TAMs)-mediated immunosuppression limits its efficacy. Eliminating MG immunosuppression via CD40 co-stimulation enhances D2C7-IT-induced antitumor responses by activating a TAMs proinflammatory phenotype and promoting long-term tumor-specific CD8+ T-cell immunity. We initiated a phase 1 trial of D2C7-IT+2141-V11 (Fc-engineered anti-CD40 agonist) administered via CED in rMG patients. METHODS Eligibility includes adult patients with solitary supratentorial rMG (WHO grade 3/4); ≥ 4weeks after chemotherapy, bevacizumab, or investigational agent; adequate organ function; and KPS ≥70%. Cohorts of 3 patients were treated with increasing doses of 2141-V11 to determine the recommended phase 2 dose (RP2D) when administered sequentially following D2C7-IT (166,075ng) via CED. Five dose levels (DLs) were evaluated (2141-V11 at: DL1: 0.70mg; DL2: 2.0mg; DL2**: 3.0mg; DL2*: 4.0mg; DL3: 7.0mg). RESULTS As of June 5, 2023, 27 patients had been treated (3 patients on DL1 and DL2; 2 on DL3 and DL2*; 17 on DL2**). No dose-limiting toxicities were observed; however, lower DLs were added due to higher frequency of adverse events (AEs) expected with D2C7-IT+2141-V11 within DL3 and DL2* (fever, neurologic symptoms). 13/27 patients remain alive (range 4-22months after therapy). No grade 4 or 5 AEs related to D2C7-IT+2141-V11 were observed, while grade 3 related AEs include one each of: dysphasia, encephalopathy, headache, hydrocephalus, paresthesia, and pyramidal tract disorder. CONCLUSIONS The RP2D for intratumoral infusion of D2C7-IT+2141-V11 via CED is identified. The protocol was amended to evaluate the addition of cervical perilymphatic injections of 2141-V11 post CED of D2C7-IT+2141-V11.

Ceramide Is Involved in Temozolomide Resistance in Human Glioblastoma U87MG Overexpressing EGFR.

Glioblastoma multiforme (GBM) is the most frequent and deadly brain tumor. Many sphingolipids are crucial players in the regulation of glioma cell growth as well as in the response to different chemotherapeutic drugs. In particular, ceramide (Cer) is a tumor suppressor lipid, able to induce antiproliferative and apoptotic responses in different types of tumors including GBM, most of which overexpress the epidermal growth factor receptor variant III (EGFRvIII). In this paper, we investigated whether Cer metabolism is altered in the U87MG human glioma cell line overexpressing EGFRvIII (EGFR+ cells) to elucidate their possible interplay in the mechanisms regulating GBM survival properties and the response to the alkylating agent temozolomide (TMZ). Notably, we demonstrated that a low dose of TMZ significantly increases Cer levels in U87MG cells but slightly in EGFR+ cells (sensitive and resistant to TMZ, respectively). Moreover, the inhibition of the synthesis of complex sphingolipids made EGFR+ cells sensitive to TMZ, thus involving Cer accumulation/removal in TMZ resistance of GBM cells. This suggests that the enhanced resistance of EGFR+ cells to TMZ is dependent on Cer metabolism. Altogether, our results indicate that EGFRvIII expression confers a TMZ-resistance phenotype to U87MG glioma cells by counteracting Cer increase.

CHCHD2 mediates glioblastoma cell proliferation, mitochondrial metabolism, hypoxia‑induced invasion and therapeutic resistance.

Glioblastoma (GBM) is the most common and malignant primary brain tumor affecting adults and remains incurable. The mitochondrial coiled‑coil‑helix‑coiled‑coil‑helix domain‑containing protein 2 (CHCHD2) has been demonstrated to mediate mitochondrial respiration, nuclear gene expression and cell migration; however, evidence of this in GBM is lacking. In the present study, it was hypothesized that CHCHD2 may play a functional role in U87 GBM cells expressing the constitutively active epidermal growth factor receptor variant III (EGFRvIII). The amplification of the CHCHD2 gene was found to be associated with a decreased patient overall and progression‑free survival. The CHCHD2 mRNA levels were increased in high‑vs. low‑grade glioma, IDH‑wt GBMs, and in tumor vs. non‑tumor tissue. Additionally, CHCHD2 protein expression was greatest in invasive, EGFRvIII‑expressing patient‑derived samples. The CRISPR‑Cas9‑mediated knockout of CHCHD2 in EGFRvIII‑expressing U87 cells resulted in an altered mitochondrial respiration and glutathione status, in decreased cell growth and invasion under both normoxic and hypoxic conditions, and in an enhanced sensitivity to cytotoxic agents. CHCHD2 was distributed in both the mitochondria and nuclei of U87 and U87vIII cells, and the U87vIII cells exhibited a greater nuclear expression of CHCHD2 compared to isogenic U87 cells. Incubation under hypoxic conditions, serum starvation and the reductive unfolding of CHCHD2 induced the nuclear accumulation of CHCHD2 in both cell lines. Collectively, the findings of the present study indicate that CHCHD2 mediates a variety of GBM characteristics, and highlights mitonuclear retrograde signaling as a pathway of interest in GBM cell biology.

OSMR INTERACTOME MAPPING REVEALS THE SIGNIFICANCE OF A CHLORIDE CHANNEL IN CYTOKINE REGULATION AND BRAIN TUMOUR STEM CELL SELF-RENEWAL

Abstract Oncostatin M Receptor (OSMR) is a key regulator of brain tumour stem cell (BTSC) self-renewal and glioblastoma (GB) tumourigenesis. This receptor is found in a complex with Epidermal Growth Factor Receptor variant III (EGFRvIII) and orchestrates a positive feedback loop with STAT3. OSMR also regulates oxidative phosphorylation and participates in promoting the transition of cells towards mesenchymal-like glioma states. How OSMR drives GB tumorigenesis via multiple mechanisms remains largely unclear. Here, we map OSMR interactome in different GB subtypes using the Mammalian Membrane Two Hybrid High Throughput Screen (MaMTH-HTS). Analysis of these data followed by functional validation has uncovered distinct OSMR interactome in a context dependent manner. Follow up investigations, however, have led to the discovery of the Chloride Intracellular Channel 1 (CLIC1), essential in the regulation of OSMR cytokine signaling and GB progression independently of the genetic profile of the GB tumour. CLIC1 forms a complex with OSMR to promote BTSC self-renewal and knockout of CLIC1 or pharmacological inhibitors to CLIC1 impairs OSM mediated STAT3 phosphorylation. Our work suggests that CLIC1 and OSMR forms a complex in BTSCs and functionally interact to activate STAT3.

Chimeric Antigen Receptor T Cells in Glioblastoma-Current Concepts and Promising Future.

Glioblastoma (GBM) is a highly aggressive primary brain tumor that is largely refractory to treatment and, therefore, invariably relapses. GBM patients have a median overall survival of 15 months and, given this devastating prognosis, there is a high need for therapy improvement. One of the therapeutic approaches currently tested in GBM is chimeric antigen receptor (CAR)-T cell therapy. CAR-T cells are genetically altered T cells that are redirected to eliminate tumor cells in a highly specific manner. There are several challenges to CAR-T cell therapy in solid tumors such as GBM, including restricted trafficking and penetration of tumor tissue, a highly immunosuppressive tumor microenvironment (TME), as well as heterogeneous antigen expression and antigen loss. In addition, CAR-T cells have limitations concerning safety, toxicity, and the manufacturing process. To date, CAR-T cells directed against several target antigens in GBM including interleukin-13 receptor alpha 2 (IL-13Rα2), epidermal growth factor receptor variant III (EGFRvIII), human epidermal growth factor receptor 2 (HER2), and ephrin type-A receptor 2 (EphA2) have been tested in preclinical and clinical studies. These studies demonstrated that CAR-T cell therapy is a feasible option in GBM with at least transient responses and acceptable adverse effects. Further improvements in CAR-T cells regarding their efficacy, flexibility, and safety could render them a promising therapy option in GBM.

Identification of the E2F1-RAD51AP1 axis as a key factor in MGMT-methylated GBM TMZ resistance.

Epidermal growth factor receptor variant III (EGFRvIII) is a constitutively-activated mutation of EGFR that contributes to the malignant progression of glioblastoma multiforme (GBM). Temozolomide (TMZ) is a standard chemotherapeutic for GBM, but TMZ treatment benefits are compromised by chemoresistance. This study aimed to elucidate the crucial mechanisms leading to EGFRvIII and TMZ resistance. CRISPR-Cas13a single-cell RNA-seq was performed to thoroughly mine EGFRvIII function in GBM. Western blot, real-time PCR, flow cytometry, and immunofluorescence were used to determine the chemoresistance role of E2F1 and RAD51-associated protein 1 (RAD51AP1). Bioinformatic analysis identified E2F1 as the key transcription factor in EGFRvIII-positive living cells. Bulk RNA-seq analysis revealed that E2F1 is a crucial transcription factor under TMZ treatment. Western blot suggested enhanced expression of E2F1 in EGFRvIII-positive and TMZ-treated glioma cells. Knockdown of E2F1 increased sensitivity to TMZ. Venn diagram profiling showed that RAD51AP1 is positively correlated with E2F1, mediates TMZ resistance, and has a potential E2F1 binding site on the promoter. Knockdown of RAD51AP1 enhanced the sensitivity of TMZ; however, overexpression of RAD51AP1 was not sufficient to cause chemotherapy resistance in glioma cells. Furthermore, RAD51AP1 did not impact TMZ sensitivity in GBM cells with high O6-methylguanine-DNA methyltransferase (MGMT) expression. The level of RAD51AP1 expression correlated with the survival rate in MGMT-methylated, but not MGMT-unmethylated TMZ-treated GBM patients. Our results suggest that E2F1 is a key transcription factor in EGFRvIII-positive glioma cells and quickly responds to TMZ treatment. RAD51AP1 was shown to be upregulated by E2F1 for DNA double strand break repair. Targeting RAD51AP1 could facilitate achieving an ideal therapeutic effect in MGMT-methylated GBM cells.

Abstract LB097: Armored bicistronic CAR T cells with dominant-negative TGF-β receptor II to alleviate antigenic heterogeneity and suppressive immune microenvironment in glioblastoma

Abstract Introduction: We have completed two CAR T cell clinical trials for glioblastoma (GBM) and have identified several key challenges to therapeutic efficacy, including the inherently heterogenous genomic landscape and the immunosuppressive tumor microenvironment (TME) found in GBM. Our previous study showed that EGFR variant III (EGFRvIII)-targeting monovalent CAR T cells reduced target-positive tumor cell populations, but tumor recurrence resulted from target-negative tumor cells, highlighting the limitation of single-target approaches in heterogenous tumors. With regards to the highly immunosuppressive TME in GBM, we found that transforming growth factor-β (TGFβ) was present in the GBM TME as a major driver of suppression of the anti-GBM response in clinical samples. TGFb is consistently highly expressed in both GBM tumor cell lines and patient tumor tissues. Methods: We used two parallel scFv constructs, independently targeting both IL13Rα2 and EGFRvIII, in combination with a truncated dominant negative (dn) TGFβ receptor II. This trivalent construct was designed to explore possible additive effects in both in vitro and in vivo GBM model systems to limit tumor escape and overcome the immunosuppressive GBM TME. The CART-EGFR-IL13Rα2-dnTGFb construct broadened the targeted tumor cell repertoire, blocked TGFβ signaling, and served as a sink for free TGFβ in the GBM TME to overcome the suppressive function of TGFβ. Results: The tri-modular CAR T construct had an enhanced proliferative response when compared with the CART-EGFR-IL13Rα2 construct, in vitro. In co-culture assays, this construct led to reduced PD-1 expression and increased central memory phenotype, when compared to the bicistronic CAR T construct, which suggested a lower fraction of exhausted T cells. Tri-modular CAR T cells blocked the suppressive pSmad2/3 signaling pathway, leading to the increased tumor killing activity in co-culture experiments with both adherent and suspension GBM cell lines. In an immunodeficient mouse model, tri-modular CAR T cells eradicated tumor cells efficiently and mice had a longer median survival when compared those treated with the bicistronic CART-EGFR-IL13Rα2 cells, lacking the dnTGFb receptor II. Conclusion: Overcoming the adaptive changes in the local TME and addressing antigen heterogeneity will be required to improve the clinical efficacy of CAR T-directed strategies. Our combination work showed that bicistronic CART constructs cooperate with truncated TGFβ receptor II efficiently. In summary, the dominant-negative TGFβ RII CART-EGFR-IL13Rα2 structure is a promising strategy to address the clinical challenges of antigenic heterogeneity and the immunosuppressive TME in GBM we have observed in our two GBM CART cell trials at UPenn. Citation Format: Nannan Li, Jesse Rodriguez, Zev Binder, Donald O’Rourke. Armored bicistronic CAR T cells with dominant-negative TGF-β receptor II to alleviate antigenic heterogeneity and suppressive immune microenvironment in glioblastoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2023; Part 2 (Clinical Trials and Late-Breaking Research); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(8_Suppl):Abstract nr LB097.

IGFBP3 induced by the TGF-β/EGFRvIII transactivation contributes to the malignant phenotype of glioblastoma

Dual or multi-targets therapy targeting epidermal growth factor receptor variant III (EGFRvIII) and other molecular may relax the constraint for glioblastoma (GBM), putting forward the urgent requirement of finding candidate molecules. Here, the insulin-like growth factor binding protein-3 (IGFBP3) was considered a candidate, whereas the mechanisms of IGFBP3 production remain unclear. We treated GBM cells with exogenous transforming growth factor β (TGF-β) to simulate the microenvironment. We found that TGF-β and EGFRvIII transactivation induced the activation of transcription factor c-Jun, which specifically bound to the promoter region of IGFBP3 through Smad2/3 and ERK1/2 pathways and promoted the production and secretion of IGFBP3. IGFBP3 knockdown inhibited the activation of TGF-β and EGFRvIII signals and the malignant behaviors triggered by them invitro and invivo. Collectively, our results indicated a positive feedback loop of p-EGFRvIII/IGFBP3 under administration of TGF-β, blocking IGFBP3 may be an additional target in EGFRvIII-expressing GBM-selective therapeutic strategy.