Identification of the Epitope for the Epidermal Growth Factor Receptor-specific Monoclonal Antibody 806 Reveals That It Preferentially Recognizes an Untethered Form of the Receptor

Development of CAR-T cell therapy for NF1/SWN-related nerve sheath tumor treatment

Neurofibromatosis type 1 (NF1) and schwannomatosis (SWN) are rare genetic disorders with distinct genetic etiologies. Both syndromes are predominantly characterized by the development of multiple benign nerve sheath tumors, which typically arise from cranial/peripheral nerves. The management of NF1/SWN-associated benign nerve sheath tumors pose a substantial clinical challenge. In recent years, immunotherapy has demonstrated significant efficacy in treating various tumors, but its application to NF1/SWN has not been explored. In this study, we first evaluated the feasibility of chimeric antigen receptor (CAR)-T cell therapy for the treatment of benign NF1/SWN-related nerve sheath tumor by analyzing the expression of multiple antigens in 85 tumor samples. Our findings revealed that epidermal growth factor receptor (EGFR/HER1) was highly expressed in most samples, indicating its potential as an ideal target for CAR-T cell therapy. Additionally, TGFβ1 and PDL1, key inhibitory regulators of T cell function within solid tumor microenvironment (TME), were universally overexpressed in these samples, highlighting the immunosuppressive nature of NF1/SWN tumors. To target HER1, we constructed CARs using three distinct scFvs (806, E2 and NEC). All three types of CAR-T cells demonstrated significant tumor-eliminating capability against NF1/SWN tumor cell lines, with 806 CAR-T cells showing the highest efficacy. Considering the immunosuppressive TME, we knocked out TGFBR2 and/or PDCD1 in 806 CAR-T cells using CRISPR/Cas9. Their anti-tumor efficacy was further evaluated using a 3D tumor spheroid model, and the gene-edited 806 CAR-T cells exhibited superior anti-tumor efficacy. In conclusion, we identified HER1 as a target for CAR-T cell therapy in NF1/SWN-related nerve sheath tumors, and developed anti-HER1 CAR-T cells that effectively eliminated NF1/SWN tumor cells, providing a promising therapeutic strategy for patients with these conditions.

Generation of binder-format-payload conjugate-matrices by antibody chain-exchange

The generation of antibody-drug conjugates with optimal functionality depends on many parameters. These include binder epitope, antibody format, linker composition, conjugation site(s), drug-to-antibody ratio, and conjugation method. The production of matrices that cover all possible parameters is a major challenge in identifying optimal antibody-drug conjugates. To address this bottleneck, we adapted our Format Chain Exchange technology (FORCE), originally established for bispecific antibodies, toward the generation of binder-format-payload matrices (pair-FORCE). Antibody derivatives with exchange-enabled Fc-heterodimers are combined with payload-conjugated Fc donors, and subsequent chain-exchange transfers payloads to antibody derivatives in different formats. The resulting binder-format-conjugate matrices can be generated with cytotoxic payloads, dyes, haptens, and large molecules, resulting in versatile tools for ADC screening campaigns. We show the relevance of pair-FORCE for identifying optimal HER2-targeting antibody-drug conjugates. Analysis of this matrix reveals that the notion of format-defines-function applies not only to bispecific antibodies, but also to antibody-drug conjugates.

Analysis of EGFR binding hotspots for design of new EGFR inhibitory biologics

The epidermal growth factor (EGF) receptor (EGFR) is activated by the binding of one of seven EGF-like ligands to its ectodomain. Ligand binding results in EGFR dimerization and stabilization of the active receptor conformation subsequently leading to activation of downstream signaling. Aberrant activation of EGFR contributes to cancer progression through EGFR overexpression/amplification, modulation of its positive and negative regulators, and/or activating mutations within EGFR. EGFR targeted therapeutic antibodies prevent dimerization and interaction with endogenous ligands by binding the ectodomain of EGFR. However, these antibodies have had limited success in the clinic, partially due to EGFR ectodomain resistance mutations, and are only applicable to a subset of patients with EGFR-driven cancers. These limitations suggest that alternative EGFR targeted biologics need to be explored for EGFR-driven cancer therapy. To this end, we analyze the EGFR interfaces of known inhibitory biologics with determined structures in the context of endogenous ligands, using the Rosetta macromolecular modeling software to highlight the most important interactions on a per-residue basis. We use this analysis to identify the structural determinants of EGFR targeted biologics. We suggest that commonly observed binding motifs serve as the basis for rational design of new EGFR targeted biologics, such as peptides, antibodies, and nanobodies.

Structural insights into the role and targeting of EGFRvIII

The epidermal growth factor receptor (EGFR) is a well-known oncogenic driver in lung and other cancers. In glioblastoma multiforme (GBM), the EGFR deletion variant III (EGFRvIII) is frequently found alongside EGFR amplification. Agents targeting the EGFR axis have shown limited clinical benefits in GBM and the role of EGFRvIII in GBM is poorly understood. To shed light on the role of EGFRvIII and its potential as a therapeutic target, we determined X-ray crystal structures of a monomeric EGFRvIII extracellular region (ECR). The EGFRvIII ECR resembles the unliganded conformation of EGFR, including the orientation of the C-terminal region of domain II. Domain II is mostly disordered, but the ECR structure is compact. We selected a nanobody with preferential binding to EGFRvIII relative to EGFR and structurally defined an epitope on domain IV that is occluded in the unliganded intact EGFR. These findings suggest new avenues for EGFRvIII targeting in GBM.

Radiolabeling and Preclinical Evaluation of Therapeutic Efficacy of 225Ac-ch806 in Glioblastoma and Colorectal Cancer Xenograft Models

The epidermal growth factor receptor (EGFR) protein is highly expressed in a range of malignancies. Although therapeutic interventions directed toward EGFR have yielded therapeutic responses in cancer patients, side effects are common because of normal-tissue expression of wild-type EGFR. We developed a novel tumor-specific anti-EGFR chimeric antibody ch806 labeled with 225Ac and evaluated its in vitro properties and therapeutic efficacy in murine models of glioblastoma and colorectal cancer. Methods: 225Ac-ch806 was prepared using different chelators, yielding [225Ac]Ac-macropa-tzPEG3Sq-ch806 and [225Ac]Ac-DOTA-dhPzPEG4-ch806. Radiochemical yield, purity, apparent specific activity, and serum stability of 225Ac-ch806 were quantified. In vitro cell killing effect was examined. The biodistribution and therapeutic efficacy of 225Ac-ch806 were investigated in mice with U87MG.de2-7 and DiFi tumors. Pharmacodynamic analysis of tumors after therapy was performed, including DNA double-strand break immunofluorescence of γH2AX, as well as immunohistochemistry for proliferation, cell cycle arrest, and apoptosis. Results: [225Ac]Ac-macropa-tzPEG3Sq-ch806 surpassed [225Ac]Ac-DOTA-dhPzPEG4-ch806 in radiochemical yield, purity, apparent specific activity, and serum stability. [225Ac]Ac-macropa-tzPEG3Sq-ch806 was therefore used for both in vitro and in vivo studies. It displayed a significant, specific, and dose-dependent in vitro cell-killing effect in U87MG.de2-7 cells. 225Ac-ch806 also displayed high tumor uptake and minimal uptake in normal tissues. 225Ac-ch806 significantly inhibited tumor growth and prolonged survival in both U87MG.de2-7 and DiFi models. Enhanced γH2AX staining was observed in 225Ac-ch806-treated tumors compared with controls. Reduced Ki-67 expression was evident in all 225Ac-ch806-treated tumors. Increased expression of p21 and cleaved caspase 3 was shown in U87MG.de2-7 and DiFi tumors treated with 225Ac-ch806. Conclusion: In glioblastoma and colorectal tumor models, 225Ac-ch806 significantly inhibited tumor growth via induction of double-strand breaks, thereby constraining cancer cell proliferation while inducing cell cycle arrest and apoptosis. These findings underscore the potential clinical applicability of 225Ac-ch806 as a potential therapy for EGFR-expressing solid tumors.

An anion exchange membrane sensor detects EGFR and its activity state in plasma CD63 extracellular vesicles from patients with glioblastoma

We present a quantitative sandwich immunoassay for CD63 Extracellular Vesicles (EVs) and a constituent surface cargo, EGFR and its activity state, that provides a sensitive, selective, fluorophore-free and rapid alternative to current EV-based diagnostic methods. Our sensing design utilizes a charge-gating strategy, with a hydrophilic anion exchange membrane functionalized with capture antibodies and a charged silica nanoparticle reporter functionalized with detection antibodies. With sensitivity and robustness enhancement by the ion-depletion action of the membrane, this hydrophilic design with charged reporters minimizes interference from dispersed proteins, thus enabling direct plasma analysis without the need for EV isolation or sensor blocking. With a LOD of 30 EVs/μL and a high relative sensitivity of 0.01% for targeted proteomic subfractions, our assay enables accurate quantification of the EV marker, CD63, with colocalized EGFR by an operator/sample insensitive universal normalized calibration. We analysed untreated clinical samples of Glioblastoma to demonstrate this new platform. Notably, we target both total and "active" EGFR on EVs; with a monoclonal antibody mAb806 that recognizes a normally hidden epitope on overexpressed or mutant variant III EGFR. Analysis of samples yielded an area-under-the-curve (AUC) value of 0.99 and a low p-value of 0.000033, surpassing the performance of existing assays and markers.

Targeted Therapy in Mesotheliomas: Uphill All the Way

Mesothelioma (MM) is an aggressive and lethal disease with few therapeutic opportunities. Platinum-pemetrexed chemotherapy is the backbone of first-line treatment for MM. The introduction of immunotherapy (IO) has been the only novelty of the last decades, allowing an increase in survival compared to standard chemotherapy (CT). However, IO is not approved for epithelioid histology in many countries. Therefore, therapy for relapsed MM remains an unmet clinical need, and the prognosis of MM remains poor, with an average survival of only 18 months. Increasing evidence reveals MM complexity and heterogeneity, of which histological classification fails to explain. Thus, scientific focus on possibly new molecular markers or cellular targets is increasing, together with the search for target therapies directed towards them. The molecular landscape of MM is characterized by inactivating tumor suppressor alterations, the most common of which is found in CDKN2A, BAP1, MTAP, and NF2. In addition, cellular targets such as mesothelin or metabolic enzymes such as ASS1 could be potentially amenable to specific therapies. This review examines the major targets and relative attempts of therapeutic approaches to provide an overview of the potential prospects for treating this rare neoplasm.

An engineering strategy to target activated EGFR with CAR T cells

Chimeric antigen receptor (CAR) T cells have shown remarkable response rates in hematological malignancies. In contrast, CAR T cell treatment of solid tumors is associated with several challenges, in particular the expression of most tumor-associated antigens at lower levels in vital organs, resulting in on-target/off-tumor toxicities. Thus, innovative approaches to improve the tumor specificity of CAR T cells are urgently needed. Based on the observation that many human solid tumors activate epidermal growth factor receptor (EGFR) on their surface through secretion of EGFR ligands, we developed an engineering strategy for CAR-binding domains specifically directed against the ligand-activated conformation of EGFR. We show, in several experimental systems, that the generated binding domains indeed enable CAR T cells to distinguish between active and inactive EGFR. We anticipate that this engineering concept will be an important step forward to improve the tumor specificity of CAR T cells directed against EGFR-positive solid cancers.

Detection of EGFR and its Activity State in Plasma CD63-EVs from Glioblastoma Patients: Rapid Profiling using an Anion Exchange Membrane Sensor

We present a novel quantitative immunoassay for CD63 EVs (extracellular vesicles) and a constituent surface cargo, EGFR and its activity state, that provides a sensitive, selective, fluorophore-free and rapid alternative to current EV-based diagnostic methods. Our sensing design utilizes a charge-gating strategy, with a hydrophilic anion exchange membrane and a charged silica nanoparticle reporter. With sensitivity and robustness enhancement by the ion-depletion action of the membrane, this hydrophilic design with charged reporters minimizes interference from dispersed proteins and fluorophore degradation, thus enabling direct plasma analysis. With a limit of detection of 30 EVs/μL and a high relative sensitivity of 0.01% for targeted proteomic subfractions, our assay enables accurate quantification of the EV marker, CD63, with colocalized EGFR by an operator/sample insensitive universal normalized calibration. Glioblastoma necessitates improved non-invasive diagnostic approaches for early detection and monitoring. Notably, we target both total and "active" EGFR on EVs; with a monoclonal antibody mAb806 that recognizes a normally hidden epitope on overexpressed or mutant variant III EGFR. This approach offers direct glioblastoma detection from untreated human patient samples. Analysis of glioblastoma clinical samples yielded an area-under-the-curve (AUC) value of 0.99 and low p-value of 0.000033, significantly surpassing the performance of existing assays and markers.

Confinement of unliganded EGFR by tetraspanin nanodomains gates EGFR ligand binding and signaling

The epidermal growth factor receptor (EGFR) is a central regulator of cell physiology. EGFR is activated by ligand binding, triggering receptor dimerization, activation of kinase activity, and intracellular signaling. EGFR is transiently confined within various plasma membrane nanodomains, yet how this may contribute to regulation of EGFR ligand binding is poorly understood. To resolve how EGFR nanoscale compartmentalization gates ligand binding, we developed single-particle tracking methods to track the mobility of ligand-bound and total EGFR, in combination with modeling of EGFR ligand binding. In comparison to unliganded EGFR, ligand-bound EGFR is more confined and distinctly regulated by clathrin and tetraspanin nanodomains. Ligand binding to unliganded EGFR occurs preferentially in tetraspanin nanodomains, and disruption of tetraspanin nanodomains impairs EGFR ligand binding and alters the conformation of the receptor's ectodomain. We thus reveal a mechanism by which EGFR confinement within tetraspanin nanodomains regulates receptor signaling at the level of ligand binding.

EGFR, the Lazarus target for precision oncology in glioblastoma

The Lazarus effect is a rare condition that happens when someone seemingly dead shows signs of life. The epidermal growth factor receptor (EGFR) represents a target in the fatal neoplasm glioblastoma (GBM) that through a series of negative clinical trials has prompted a vocal subset of the neuro-oncology community to declare this target dead. However, an argument can be made that the core tenets of precision oncology were overlooked in the initial clinical enthusiasm over EGFR as a therapeutic target in GBM. Namely, the wrong drugs were tested on the wrong patients at the wrong time. Furthermore, new insights into the biology of EGFR in GBM vis-à-vis other EGFR-driven neoplasms, such as non-small cell lung cancer, and development of novel GBM-specific EGFR therapeutics resurrects this target for future studies. Here, we will examine the distinct EGFR biology in GBM, how it exacerbates the challenge of treating a CNS neoplasm, how these unique challenges have influenced past and present EGFR-targeted therapeutic design and clinical trials, and what adjustments are needed to therapeutically exploit EGFR in this devastating disease.

Control of cell metabolism by the epidermal growth factor receptor

The epidermal growth factor receptor (EGFR) triggers the activation of many intracellular signals that control cell proliferation, growth, survival, migration, and differentiation. Given its wide expression, EGFR has many functions in development and tissue homeostasis. Some of the cellular outcomes of EGFR signaling involve alterations of specific aspects of cellular metabolism, and alterations of cell metabolism are emerging as driving influences in many physiological and pathophysiological contexts. Here we review the mechanisms by which EGFR regulates cell metabolism, including by modulation of gene expression and protein function leading to control of glucose uptake, glycolysis, biosynthetic pathways branching from glucose metabolism, amino acid metabolism, lipogenesis, and mitochondrial function. We further examine how this regulation of cell metabolism by EGFR may contribute to cell proliferation and differentiation and how EGFR-driven control of metabolism can impact certain diseases and therapy outcomes.

Radiation enhances the efficacy of EGFR-targeted CAR-T cells against triple-negative breast cancer by activating NF-κB/Icam1 signaling

Triple-negative breast cancer (TNBC) is the most aggressive breast cancer subtype, with limited treatment options. Epidermal growth factor receptor (EGFR) is reported to be expressed in 50%-75% of TNBC patients, making it a promising target for cancer treatment. Here we show that EGFR-targeted chimeric antigen receptor (CAR) T cell therapy combined with radiotherapy provides enhanced antitumor efficacy in immunocompetent and immunodeficient orthotopic TNBC mice. Intriguingly, this combination therapy resulted in a substantial increase in the number of tumor-infiltrating CAR-T cells. The efficacy of this combination was independent of tumor radiosensitivity and lymphodepleting preconditioning. Cytokine profiling showed that this combination did not increase the risk of cytokine release syndrome (CRS). RNA sequencing (RNA-seq) analysis revealed that EGFR-targeting CAR-T therapy combined with radiotherapy increased the infiltration of CD8+ T and natural killer (NK) cells into tumors. Mechanistically, radiation significantly increased Icam1 expression on TNBC cells via activating nuclear factor κB (NF-κB) signaling, thereby promoting CAR-T cell infiltration and killing. These results suggest that CAR-T therapy combined with radiotherapy may be a promising strategy for TNBC treatment.

Characterization and Potential Mitigation of Corneal Effects in Nonclinical Toxicology Studies in Animals Administered Depatuxizumab Mafodotin

Purpose: To characterize the ocular toxicity of an antibody-drug conjugate (ADC), depatuxizumab mafodotin (Depatux-m), in nonclinical species and to evaluate the effects of drug-antibody ratios (DARs), variations of the ADC construct, and potential methods for mitigation of the corneal toxicity. Depatux-m contains the potent cytotoxic agent monomethyl auristatin F as the ADC payload. Methods: Depatux-m was administered intravenously to cynomolgus monkeys at doses up to 30 mg/kg and to mice up to 100 mg/kg. Ocular toxicity was evaluated by clinical ophthalmic examinations and histopathology. Potential mitigation was tested through agents to block target engagement and multiple topical ophthalmic treatments (antioxidant, vasoconstrictor, tear stimulant). Results: Effects primarily involved corneal epithelium and were dose-dependent with respect to onset, severity, and time to reversal in both monkeys and mice. On slit lamp biomicroscopy, the initial effect in monkeys was superficial multifocal punctate opacities (granularity), which migrated axially and were followed by pigmentation and multifocal punctate fluorescein staining. Microscopically, findings were characterized by single-cell necrosis, pigmentation, disordered basilar layer, and thinning of the corneal epithelium. Increased toxicity was associated with a higher DAR or more stably attached linker. Treatment with agents to block target engagement did not affect toxicity, and none of the topical treatments was successful. Conclusions: The corneal findings observed were similar to the effects described in clinical trials with Depatux-m and other ADCs. Collectively, these studies and available literature support the hypothesis that ADC-mediated toxicity is driven primarily by mechanism of action of the payload.

Radiolabeled Antibodies for Cancer Imaging and Therapy

Radioimmunoconjugates consist of a monoclonal antibody (mAb) linked to a radionuclide. Radioimmunoconjugates as theranostics tools have been in development with success, particularly in hematological malignancies, leading to approval by the US Food and Drug Administration (FDA) for the treatment of non-Hodgkin's lymphoma. Radioimmunotherapy (RIT) allows for reduced toxicity compared to conventional radiation therapy and enhances the efficacy of mAbs. In addition, using radiolabeled mAbs with imaging methods provides critical information on the pharmacokinetics and pharmacodynamics of therapeutic agents with direct relevance to the optimization of the dose and dosing schedule, real-time antigen quantitation, antigen heterogeneity, and dynamic antigen changes. All of these parameters are critical in predicting treatment responses and identifying patients who are most likely to benefit from treatment. Historically, RITs have been less effective in solid tumors; however, several strategies are being investigated to improve their therapeutic index, including targeting patients with minimal disease burden; using pre-targeting strategies, newer radionuclides, and improved labeling techniques; and using combined modalities and locoregional application. This review provides an overview of the radiolabeled intact antibodies currently in clinical use and those in development.

Isolation of Single-Domain Antibodies to Transmembrane Proteins Using Magnetized Yeast Cell Targets

The isolation of binding ligands from yeast-displayed combinatorial libraries has typically relied on the use of a soluble, recombinantly expressed form of the target protein when performing magnetic selections or fluorescence-activated cell sorting. When identifying binding ligands, appropriate target protein expression and subsequent purification represents a significant bottleneck. As an alternative, we describe the use of target proteins expressed on the surface of magnetized yeast cells in the selection of yeast-displayed nanobody libraries. In this approach, yeast cells displaying the target protein also co-express an iron oxide-binding protein; incubation with iron oxide nanopowder results in magnetization of target-displaying cells. Alternatively, target-displaying cells are magnetized by nonspecific adsorption of iron oxide nanopowder. Subsequently, any library cells that interact with the magnetized target cells can be isolated using a magnet. Here, we detail protocols for the isolation of binders to membrane protein targets from a yeast display nanobody library using magnetized yeast cell targets. We provide guidance on how to generate magnetic yeast cell targets as well as library selection conditions to bias the isolation of high affinity binders. We also discuss how to assess the affinity and specificity of the isolated nanobodies using flow cytometry.

Antibody Drug Conjugates in Glioblastoma - Is There a Future for Them?

Glioblastoma (GBM) is an aggressive and fatal malignancy that despite decades of trials has limited therapeutic options. Antibody drug conjugates (ADCs) are composed of a monoclonal antibody which specifically recognizes a cellular surface antigen linked to a cytotoxic payload. ADCs have demonstrated superior efficacy and/or reduced toxicity in a range of haematological and solid tumors resulting in nine ADCs receiving regulatory approval. ADCs have also been explored in patients with brain tumours but with limited success to date. While earlier generations ADCs in glioma patients have had limited success and high toxicity, newer and improved ADCs characterised by low immunogenicity and more effective payloads have shown promise in a range of tumour types. These newer ADCs have also been tested in glioma patients, however, with mixed results. Factors affecting the effectiveness of ADCs to target the CNS include the blood brain barrier which acts as a physical and biochemical barrier, the pro-cancerogenic and immunosuppressive tumor microenvironment and tumour characteristics like tumour volume and antigen expression. In this paper we review the data regarding the ongoing the development of ADCs in glioma patients as well as potential strategies to overcome these barriers to maximise their therapeutic potential.

A Phase 1 and Biodistribution Study of ABT-806i, an 111In-Radiolabeled Conjugate of the Tumor-Specific Anti-EGFR Antibody ABT-806

ABT-806 is a tumor-specific antibody targeting the epidermal growth factor receptor (EGFR). This study assessed safety, biodistribution, and pharmacokinetics of ¹¹¹In-radiolabeled ABT-806 (ABT-806i) and effects of repeated doses of ABT-806 on receptor occupancy. Methods: Eligible patients had advanced tumors likely to express EGFR/EGFRvIII; adequate performance status and organ function; and measurable disease by RECIST 1.1. In cohort 1, 6 patients received a bolus administration of ABT-806i and underwent SPECT followed by whole-body planar scans. In cohort 2, 12 patients were imaged similarly as in 1 initially; thereafter, they received 3 doses of unlabeled ABT-806, before another dose of ABT-806i with associated SPECT and whole-body planar scans. At the end of both cohorts, patients who had stable or responding disease were able to enroll into an extension study (M12-326) in which they received unlabeled ABT-806 every 2 wk until disease progression, withdrawal of consent, or intolerable toxicity. Results: No toxicity related to ABT-806i infusion was observed. ABT-806i showed minimal uptake in normal tissues and cleared gradually from blood with a half-life of 6.0 ± 1.5 d. The mean effective dose of ABT-806i was 0.137 mSv/MBq for males and 0.183 mSv/MBq for females. ABT-806i tumor uptake varied and did not correlate with archived tumor EGFR expression. No change in ABT-806i uptake was observed after interval ABT-806 treatment, indicating stable EGFR expression in tumor. The patient with highest tumor uptake of ABT-806i had advanced head and neck cancer and experienced a partial response. Conclusion: ABT-806i allows for real-time imaging of EGFR conformational expression in tumors, has an acceptable radiation dosimetry, and provides important additional information about antigen expression compared with standard approaches using archival tissue. Its role to assist in patient selection for EGFR-based therapeutics and investigate treatment resistance should be further investigated.

CAR T Cell-Based Immunotherapy for the Treatment of Glioblastoma

Glioblastoma multiforme (GBM) is the most common and aggressive malignant primary brain tumor in adults. Current treatment options typically consist of surgery followed by chemotherapy or more frequently radiotherapy, however, median patient survival remains at just over 1 year. Therefore, the need for novel curative therapies for GBM is vital. Characterization of GBM cells has contributed to identify several molecules as targets for immunotherapy-based treatments such as EGFR/EGFRvIII, IL13Rα2, B7-H3, and CSPG4. Cytotoxic T lymphocytes collected from a patient can be genetically modified to express a chimeric antigen receptor (CAR) specific for an identified tumor antigen (TA). These CAR T cells can then be re-administered to the patient to identify and eliminate cancer cells. The impressive clinical responses to TA-specific CAR T cell-based therapies in patients with hematological malignancies have generated a lot of interest in the application of this strategy with solid tumors including GBM. Several clinical trials are evaluating TA-specific CAR T cells to treat GBM. Unfortunately, the efficacy of CAR T cells against solid tumors has been limited due to several factors. These include the immunosuppressive tumor microenvironment, inadequate trafficking and infiltration of CAR T cells and their lack of persistence and activity. In particular, GBM has specific limitations to overcome including acquired resistance to therapy, limited diffusion across the blood brain barrier and risks of central nervous system toxicity. Here we review current CAR T cell-based approaches for the treatment of GBM and summarize the mechanisms being explored in pre-clinical, as well as clinical studies to improve their anti-tumor activity.

Expression of EGFR and conformational forms of EGFR in malignant pleural mesothelioma and its impact on survival

AIM

Conformational forms of the epidermal growth factor receptor (EGFR) are pro-tumorigenic. The prevalence and impact of conformational forms of EGFR in malignant mesothelioma (MM) is unknown. We investigated expression of EGFR and conformational forms of EGFR by immunohistochemistry using EGFR-targeting monoclonal antibodies (mAb). In addition, EGFR gene amplification was investigated by fluorescent in-situ hybridization (FISH). Findings were correlated with survival.

METHODS

Patients treated between 1988 and 2014 were identified from the thoracic surgery database of the Austin Hospital, Melbourne, Australia. Tissue microarrays (TMAs) were constructed, subjected to wild type (wt) EGFR IHC staining and FISH analysis. Conformational and mutation forms of EGFR were detected by IHC using mAb806, and LMH-151 which detects EGFRVIII. `H-scores` were derived and EGFR expression correlated with survival by Kaplan-Meier and log rank analysis.

RESULTS

WtEGFR expression was seen in 93 % (299/321) of cases with overexpression (defined as an H-score ≥200) seen in more than half of cases (64 %). EGFR overexpression in MM was seen more commonly in the epithelioid subtype. EGFR overexpression was not associated with true EGFR amplification, although multiple copies were appreciated in samples with polysomy. EGFR expression did not correlate with survival. A conformational form of EGFR associated with EGFR dysregulation was found in 8.2 % of cases, and patients with these tumors had a trend towards a poorer outcome. No cases of the EGFRVIII mutation were identified.

CONCLUSION

MM consistently demonstrated high expression of EGFR, with a subset of tumors showing conformational EGFR forms consistent with EGFR dysregulation, but withoutEGFR amplification or EGFR VIII mutation. wtEGFR expression did not influence survival. The impact of EGFR conformation on survival warrants further investigation.

Targeting and Efficacy of Novel mAb806-Antibody-Drug Conjugates in Malignant Mesothelioma

Epidermal growth factor receptor (EGFR) is highly overexpressed in malignant mesothelioma (MM). MAb806 is a novel anti-EGFR antibody that selectively targets a tumor-selective epitope. MAb806-derived antibody drug conjugates (ADCs), ABT-414, ABBV-221 and ABBV-322, may represent a novel therapeutic strategy in MM. EGFR and mAb806 epitope expressions in mesothelioma cell lines were evaluated using an array of binding assays, and the in vitro cell effects of ABT-414 and ABBV-322 were determined. In vivo therapy studies were conducted in mesothelioma xenograft and patient-derived xenograft (PDX) tumor models. We also performed biodistribution and imaging studies to allow the quantitative targeting of MM by mAb806 using a 89Zr-labeled immunoconjugate-ch806. A high EGFR expression was present in all mesothelioma cell lines evaluated and mAb806 binding present in all cell lines, except NCIH-2452. ABT-414 and ABBV-322 resulted in significant tumor growth inhibition in MM models with high EGFR and mAb806 epitope expressions. In contrast, in an EGFR-expressing PDX model that was negative for the mAb806 epitope, no growth inhibition was observed. We demonstrated the specific targeting of the mAb806 epitope expressing MM tumors using 89Zr-based PET imaging. Our data suggest that targeting EGFR in MM using specific ADCs is a valid therapeutic strategy and supports further investigation of the mAb806 epitope expression as a predictive biomarker.

Olaparib Suppresses MDSC Recruitment via SDF1α/CXCR4 Axis to Improve the Anti-tumor Efficacy of CAR-T Cells on Breast Cancer in Mice

A hostile tumor microenvironment is one of the major obstacles for the efficacy of chimeric antigen receptor modified T (CAR-T) cells, and combination treatment might be a potential way to overcome this obstacle. Poly(ADP-ribose) polymerase inhibitor (PARPi) has demonstrated tremendous potential in breast cancer. In this study, we explored the possible combination of the PAPRi olaparib with EGFRvIII-targeted CAR (806-28Z CAR) T cells in immunocompetent mouse models of breast cancer. The results indicated that the administration of olaparib could significantly enhance the efficacy of 806-28Z CAR-T cells in vivo. Interestingly, we observed that olaparib could suppress myeloid-derived suppressor cell (MDSC) migration and promote the survival of CD8⁺ T cells in tumor tissue. Mechanistically, olaparib was shown to reduce the expression of SDF1α released from cancer-associated fibroblasts (CAFs) and thereby decreased MDSC migration through CXCR4. Taken together, this study demonstrated that olaparib could increase the antitumor activities of CAR-T cell therapy at least partially through inhibiting MDSC migration via the SDF1α/CXCR4 axis. These findings uncover a novel mechanism of PARPi function and provide additional mechanistic rationale for combining PARPi with CAR-T cells for the treatment of breast cancer.

A Head Start: CAR-T Cell Therapy for Primary Malignant Brain Tumors

OPINION STATEMENT

Oncology is the midst of a therapeutic renaissance. The realization of immunotherapy as an efficacious and expanding treatment option has empowered physicians and patients alike. However, despite these remarkable advances, we have only just broached the potential immunotherapy has to offer and have yet to successfully expand these novel modalities to the field of neuro-oncology. In recent years, exciting results in preclinical studies of immune adjuvants, oncolytic viruses, or cell therapy have been met with only fleeting signs of response when taken to early phase trials. Although many have speculated why these innovative approaches result in impaired outcomes, we are left empty-handed in a field plagued by a drought of new therapies. Herein, we will review the recent advances across cellular therapy for primary malignant brain tumors, an approach that lends itself to overcoming the inherent resistance mechanisms which have impeded the success of prior treatment attempts.

Femtosecond Plasmonic Laser Nanosurgery (fs-PLN) mediated by molecularly targeted gold nanospheres at ultra-low pulse fluences

Plasmonic Laser Nanosurgery (PLN) is a novel photomodification technique that exploits the near-field enhancement of femtosecond (fs) laser pulses in the vicinity of gold nanoparticles. While prior studies have shown the advantages of fs-PLN to modify cells, further reduction in the pulse fluence needed to initiate photomodification is crucial to facilitate deep–tissue treatments. This work presents an in-depth study of fs-PLN at ultra-low pulse fluences using 47 nm gold nanoparticles, conjugated to antibodies that target the epithelial growth factor receptor and excited off-resonance using 760 nm, 270 fs laser pulses at 80 MHz repetition rate. We find that fs-PLN can optoporate cellular membranes with pulse fluences as low as 1.3 mJ/cm², up to two orders of magnitude lower than those used at lower repetition rates. Our results, corroborated by simulations of free-electron generation by particle photoemission and photoionization of the surrounding water, shed light on the off-resonance fs-PLN mechanism. We suggest that photo-chemical pathways likely drive cellular optoporation and cell damage at these off-resonance, low fluence, and high repetition rate fs-laser pulses, with clusters acting as local concentrators of ROS generation. We believe that the low fluence and highly localized ROS-mediated fs-PLN approach will enable targeted therapeutics and cancer treatment.

Depatuxizumab Mafodotin (ABT-414)-induced Glioblastoma Cell Death Requires EGFR Overexpression, but not EGFRY1068 Phosphorylation

Glioblastomas commonly (40%) exhibit epidermal growth factor receptor (EGFR) amplification; half of these tumors carry the EGFRvIII deletion variant characterized by an in-frame deletion of exons 2-7, resulting in constitutive EGFR activation. Although EGFR tyrosine kinase inhibitors had only modest effects in glioblastoma, novel therapeutic agents targeting amplified EGFR or EGFRvIII continue to be developed.Depatuxizumab mafodotin (ABT-414) is an EGFR-targeting antibody-drug conjugate consisting of the mAb 806 and a toxic payload, monomethyl auristatin F. Because glioma cell lines and patient-derived glioma-initiating cell models expressed too little EGFR in vitro to be ABT-414-sensitive, we generated glioma sublines overexpressing EGFR or EGFRvIII to explore determinants of ABT-414-induced cell death.Overexpression of EGFRvIII induces sensitization to ABT-414 more readily than overexpression of EGFR in vitro and in vivo Exposure to ABT-414 in vivo eliminated EGFRvIII-expressing tumor cells, and recurrent tumors were devoid of EGFRvIII expression. There is no bystander killing of cells devoid of EGFR expression. Surprisingly, either exposure to EGF or to EGFR tyrosin kinase inhibitors reduce EGFR protein levels and are thus not strategies to promote ABT-414-induced cell killing. Furthermore, glioma cells overexpressing kinase-dead EGFR or EGFRvIII retain binding of mAb 806 and sensitivity to ABT-414, allowing to dissociate EGFR phosphorylation from the emergence of the "active" EGFR conformation required for ABT-414 binding.The combination of EGFR-targeting antibody-drug conjugates with EGFR tyrosine kinase inhibitors carries a high risk of failure. Promoting EGFR expression rather than phosphorylation should result in glioblastoma cell sensitization to ABT-414.

Epidermal growth factor receptor (EGFR) involvement in epithelial-derived cancers and its current antibody-based immunotherapies

The epidermal growth factor receptor (EGFR) is a transmembrane glycoprotein that is part of the family of tyrosine kinase receptors. The binding of EGFR to its cognate ligands leads to its autophosphorylation and subsequent activation of the signal transduction pathways involved in regulating cellular proliferation, differentiation, and survival. Accordingly, this receptor carries out both redundant and restricted functions in the germline development of mammals and in the maintenance of various adult tissues. Correspondingly, the loss of EGFR regulation results in many human diseases, with the most notable cancer. This receptor is overexpressed and/or mutated in multiple epithelial-derived tumors, and associated with poor prognosis and survival in cancer patients. Here, we discuss in detail the role of EGFR in specific epithelial-derived cancer pathologies; these include lung cancer, colorectal cancer, and squamous cell carcinomas. The development of multiple anticancer agents against EGFR diminished the progression and metastasis of tumors. Some of the most versatile therapeutic anti-EGFR agents include the monoclonal antibodies (mAbs), demonstrating success in clinical settings when used in combination with cytotoxic treatments, such as chemotherapy and/or radiation. We thus discuss the development and application of two of the most notable therapeutic mAbs, cetuximab, and panitumumab, currently utilized in various EGFR-related epithelial cancers.

EGFR806-CAR T cells selectively target a tumor-restricted EGFR epitope in glioblastoma

Targeting solid tumor antigens with chimeric antigen receptor (CAR) T cell therapy requires tumor specificity and tolerance toward variability in antigen expression levels. Given the relative paucity of unique cell surface proteins on tumor cells for CAR targeting, we have focused on identifying tumor-specific epitopes that arise as a consequence of target protein posttranslational modification. We designed a CAR using a mAb806-based binder, which recognizes tumor-specific untethered EGFR. The mAb806 epitope is also exposed in the EGFRvIII variant transcript. By varying spacer domain elements of the CAR, we structurally tuned the CAR to recognize low densities of EGFR representative of non-gene amplified expression levels in solid tumors. The appropriately tuned short-spacer 2nd generation EGFR806-CAR T cells showed efficient in vitro cytokine secretion and glioma cell lysis, which was competitively blocked by a short peptide encompassing the mAb806 binding site. Unlike the nonselective Erbitux-based CAR, EGFR806-CAR T cells did not target primary human fetal brain astrocytes expressing wild-type EGFR, but showed a similar level of activity compared to Erbitux-CAR when the tumor-specific EGFRvIII transcript variant was overexpressed in astrocytes. EGFR806-CAR T cells successfully treated orthotopic U87 glioma implants in NSG mice, with 50% of animals surviving to 90 days. With additional IL-2 support, all tumors were eradicate without recurrence after 90 days. In a novel human induced pluripotent stem cell (iPSC)-derived teratoma xenograft model, EGFR806-CAR T cells infiltrated but were not activated in EGFR+ epidermal cell nests as assessed by Granzyme B expression. These results indicate that EGFR806-CAR T cells effectively and selectively target EGFR-expressing tumor cells.

Screening Yeast Display Libraries against Magnetized Yeast Cell Targets Enables Efficient Isolation of Membrane Protein Binders

When isolating binders from yeast displayed combinatorial libraries, a soluble, recombinantly expressed form of the target protein is typically utilized. As an alternative, we describe the use of target proteins displayed as surface fusions on magnetized yeast cells. In our strategy, the target protein is coexpressed on the yeast surface with an iron oxide binding protein; incubation of these yeast cells with iron oxide nanoparticles results in their magnetization. Subsequently, binder cells that interact with the magnetized target cells can be isolated using a magnet. Using a known binder-target pair with modest binding affinity (K_D ≈ 400 nM), we showed that a binder present at low frequency (1 in 10⁵) could be enriched more than 100-fold, in a single round of screening, suggesting feasibility of screening combinatorial libraries. Subsequently, we screened yeast display libraries of Sso7d and nanobody variants against yeast displayed targets to isolate binders specific to the cytosolic domain of the mitochondrial membrane protein TOM22 (K_D ≈ 272-1934 nM) and the extracellular domain of the c-Kit receptor (K_D ≈ 93 to K_D > 2000 nM). Additional studies showed that the TOM22 binders identified using this approach could be used for the enrichment of mitochondria from cell lysates, thereby confirming binding to the native mitochondrial protein. The ease of expressing a membrane protein or a domain thereof as a yeast cell surface fusion-in contrast to recombinant soluble expression-makes the use of yeast-displayed targets particularly attractive. Therefore, we expect the use of magnetized yeast cell targets will enable efficient isolation of binders to membrane proteins.

EGFR mutations are associated with response to depatux-m in combination with temozolomide and result in a receptor that is hypersensitive to ligand

Background

The randomized phase II INTELLANCE-2/EORTC_1410 trial on EGFR-amplified recurrent glioblastomas showed a trend towards improved overall survival when patients were treated with depatux-m plus temozolomide compared with the control arm of alkylating chemotherapy only. We here performed translational research on material derived from this clinical trial to identify patients that benefit from this treatment.

Methods

Targeted DNA-sequencing and whole transcriptome analysis was performed on clinical trial samples. High-throughput, high-content imaging analysis was done to understand the molecular mechanism underlying the survival benefit.

Results

We first define the tumor genomic landscape in this well-annotated patient population. We find that tumors harboring EGFR single-nucleotide variations (SNVs) have improved outcome in the depatux-m + TMZ combination arm. Such SNVs are common to the extracellular domain of the receptor and functionally result in a receptor that is hypersensitive to low-affinity EGFR ligands. These hypersensitizing SNVs and the ligand-independent EGFRvIII variant are inversely correlated, indicating two distinct modes of evolution to increase EGFR signaling in glioblastomas. Ligand hypersensitivity can explain the therapeutic efficacy of depatux-m as increased ligand-induced activation will result in increased exposure of the epitope to the antibody-drug conjugate. We also identified tumors harboring mutations sensitive to "classical" EGFR tyrosine-kinase inhibitors, providing a potential alternative treatment strategy.

Conclusions

These data can help guide treatment for recurrent glioblastoma patients and increase our understanding into the molecular mechanisms underlying EGFR signaling in these tumors.

'Characterization of monoclonal antibodies generated to the 287-302 amino acid loop of the human epidermal growth factor receptor'

BACKGROUND

The dysregulation of epidermal growth factor receptor (EGFR) has been implicated in the oncogenesis of various malignancies including glioblastoma and some epithelial cancers. Oncogenesis occurs from the overexpression of EGFR, often linked to gene amplification or receptor mutagenesis. The 287-302 loop in the extracellular domain is exposed completely on EGFR variant III (EGFRvIII), partially exposed on some cancers but cryptic on normal cells. We report on the generation of antibodies to this loop.

METHODS

The 286-303 peptide was coupled chemically to keyhole limpet hemocyanin. After immunizations, sera were assayed for reactivity to the peptide. Mice with high titers were used for hybridoma production. Purified antibodies were isolated from hybridoma supernatants, while V regions were cloned and sequenced. Receptor binding was characterized using enzyme-linked immunosorbent assay and flow cytometry. A recombinant immunotoxin was generated from the 40H3 antibody and its cytotoxic activity characterized on relevant cancer cell lines.

RESULTS

Seven monoclonal antibodies were generated to the 287-302 loop and characterized further. Each one reacted with EGFRvIII but not wild-type EGFR. Based on reactivity with the immunizing peptide, antibodies were mapped to one of three subgroups. One antibody, 40H3, also exhibited binding to MDA-MB-468 and A431 cells but not to non-cancerous WI-38 cells. Because of its unusual binding characteristics, a recombinant immunotoxin was generated from 40H3, which proved to be cytotoxic to MDA-MB-468, A431 and F98npEGFRvIII expressing cells.

CONCLUSIONS

Immunization with a peptide corresponding to a cryptic epitope from EGFR can produce tumor cell-binding antibodies. The 40H3 antibody was engineered as a cytotoxic recombinant immunotoxin and could be further developed as a therapeutic agent.

Therapeutic anti-cancer activity of antibodies targeting sulfhydryl bond constrained epitopes on unglycosylated RON receptor tyrosine kinase

Recepteur d'origine nantais (RON) receptor tyrosine kinase (RTK) and its ligand, serum macrophage-stimulating protein (MSP), are well-established oncogenic drivers for tumorigenesis and metastasis. RON is often found to be alternatively spliced resulting in various isoforms that are constitutively active. RON is therefore an attractive target for cancer therapeutics, including small molecular inhibitors and monoclonal antibodies. While small molecule inhibitors of RON may inhibit other protein kinases including the highly similar MET kinase, monoclonal antibodies targeting RON are more specific, potentially inducing fewer side effects. Although anti-RON monoclonal antibody therapies have been developed and tested in clinical trials, they were met with limited success. Cancer cells have been associated with aberrant glycosylation mechanisms. Notably for RON, the loss of N-bisected glycosylation is a direct cause for tumorigenesis and poorer prognosis in cancer patients. Particularly in gastric cancer, aberrant RON glycosylation augments RON activation. Here, we present a novel panel of monoclonal antibodies which potentially widens the specific targeting of not only the glycosylated RON, but also unglycosylated and aberrantly glycosylated RON. Our antibodies can bind strongly to deglycosylated RON from tunicamycin treated cells, recognise RON in IHC/IF and possess superior therapeutic efficacy in RON expressing xenograft tumours. Our most potent antibody in xenograft assays, is directed to the RON alpha chain and targets a sulfhydryl bond constrained epitope that appears to be cryptic in the crystal structure. This establishes the paradigm that such constrained and cryptic epitopes represent good targets for therapeutic antibodies.

Oncogenic mutations at the EGFR ectodomain structurally converge to remove a steric hindrance on a kinase-coupled cryptic epitope

Epidermal growth factor receptor (EGFR) signaling is initiated by a large ligand-favored conformational change of the extracellular domain (ECD) from a closed, self-inhibited tethered monomer, to an open untethered state, which exposes a loop required for strong dimerization and activation. In glioblastomas (GBMs), structurally heterogeneous missense and deletion mutations concentrate at the ECD for unclear reasons. We explore the conformational impact of GBM missense mutations, combining elastic network models (ENMs) with multiple molecular dynamics (MD) trajectories. Our simulations reveal that the main missense class, located at the I-II interface away from the self-inhibitory tether, can unexpectedly favor spontaneous untethering to a compact intermediate state, here validated by small-angle X-ray scattering (SAXS). Significantly, such intermediate is characterized by the rotation of a large ECD fragment (N-TR1), deleted in the most common GBM mutation, EGFRvIII, and that makes accessible a cryptic epitope characteristic of cancer cells. This observation suggested potential structural equivalence of missense and deletion ECD changes in GBMs. Corroborating this hypothesis, our FACS, in vitro, and in vivo data demonstrate that entirely different ECD variants all converge to remove N-TR1 steric hindrance from the 806-epitope, which we show is allosterically coupled to an intermediate kinase and hallmarks increased oncogenicity. Finally, the detected extraintracellular coupling allows for synergistic cotargeting of the intermediate with mAb806 and inhibitors, which is proved herein.

Antitumor efficacy of chimeric antigen receptor T cells against EGFRvIII-expressing glioblastoma in C57BL/6 mice

Chimeric antigen receptor (CAR) T cell therapy has shown remarkable success in hematological tumors. However, many challenges remain in improving the efficacy of CAR T cells in solid tumors. The epidermal growth factor receptor variant III (EGFRvIII) is only expressed in tumors but barely found in normal tissues, making it a good target for CAR T therapy. It is reported that 31-64% of glioblastoma (GBM) patients are EGFRvIII positive. Here we report the robust antitumor activities of CAR T cells targeting EGFRvIII-expressing mouse GBM cells. In vitro and in vivo, 806-28Z CAR T cells were able to lyse GL261/EGFRvIII cellsin a dose-dependent manner. A low dose of 806-28Z CAR T cells suppressed GL261/EGFRvIII tumor growth, whereas a high dose of 806-28Z CAR T cells completely eradicated xenograft tumors. Higher concentrations of granzyme B in mice plasma were correlated with increased CAR T cells infusion. Enhanced CD8⁺ T cells infiltration within the tumors were detected by immunohistochemistry in sections from the mice treated by CAR T cells. The 806-28Z CAR T cells can also inhibit the growth of antigenic heterogeneous GBM tumors. More importantly, additional rechallenge experiments indicated that GL261/EGFRvIII cells or parental GL261 cells could not grow in the cured mice. Therefore, the cell dose is a crucial determinant for CAR T efficacy against EGFRvIII-expressing GBM and granzyme B release is a predictive marker for the antitumor efficacy of CAR T cells.

RN765C, a low affinity EGFR antibody drug conjugate with potent anti-tumor activity in preclinical solid tumor models

Epidermal growth factor receptor (EGFR) is a clinically validated target and often overexpressed in some solid tumors. Both EGFR tyrosine kinase inhibitors and ligand-blocking antibodies have been approved for treatment of NSCLC, head and neck cancers and colorectal cancers. However, clinical response is limited and often accompanied by significant toxicities due to normal tissue expression. To improve the effectiveness of targeting EGFR while minimizing the toxicities on normal tissues, we developed a low-affinity anti-EGFR antibody drug conjugate (ADC), RN765C. Potent in vitro cytotoxicity of RN765C, with nanomolar to subnanomolar EC50, was observed on a panel of cancer cell lines expressing moderate to high level of EGFR. In contrast, RN765C was less effective in killing normal human keratinocytes, presumably due to its lower receptor expression. Mechanistically, RN765C has multiple modes of action: inducing payload mediated mitotic arrest and cell death, blocking EGFR pathway signal and mediating antibody dependent cell cytotoxicity. In preclinical studies, a single dose of RN765C at 1.5-3 mg/kg was generally sufficient to induce tumor regression in multiple cell line and patient-derived xenograft models, including those that are resistant to EGFR-directed tyrosine kinase inhibitors. Our data support further investigation of RN765C in the clinic to treat EGFR expressing solid tumors.

Allosteric regulation of epidermal growth factor (EGF) receptor ligand binding by tyrosine kinase inhibitors

The epidermal growth factor (EGF) receptor is a classical receptor tyrosine kinase with an extracellular ligand-binding domain and an intracellular kinase domain. Mutations in the EGF receptor have been shown to drive uncontrolled cell growth and are associated with a number of different tumors. Two different types of ATP-competitive EGF receptor tyrosine kinase inhibitors have been identified that bind to either the active (type I) or inactive (type II) conformation of the kinase domain. Despite the fact that both types of inhibitors block tyrosine kinase activity, they exhibit differential efficacies in different tumor types. Here, we show that in addition to inhibiting kinase activity, these inhibitors allosterically modulate ligand binding. Our data suggest that the conformations of the EGF receptor extracellular domain and intracellular kinase domain are coupled and that these conformations exist in equilibrium. Allosteric regulators, such as the small-molecule tyrosine kinase inhibitors, as well as mutations in the EGF receptor itself, shift the conformational equilibrium among the active and inactive species, leading to changes in EGF receptor-binding affinity. Our studies also reveal unexpected positive cooperativity between EGF receptor subunits in dimers formed in the presence of type II inhibitors. These findings indicate that there is strong functional coupling between the intracellular and extracellular domains of this receptor. Such coupling may impact the therapeutic synergy between small-molecule tyrosine kinase inhibitors and monoclonal antibodies in vivo.

The activated conformation of integrin β7 is a novel multiple myeloma-specific target for CAR T cell therapy

Cancer-specific cell-surface antigens are ideal targets for monoclonal antibody (mAb)-based immunotherapy but are likely to have previously been identified in transcriptome or proteome analyses. Here, we show that the active conformer of an integrin can serve as a specific therapeutic target for multiple myeloma (MM). We screened >10,000 anti-MM mAb clones and identified MMG49 as an MM-specific mAb specifically recognizing a subset of integrin β₇ molecules. The MMG49 epitope, in the N-terminal region of the β₇ chain, is predicted to be inaccessible in the resting integrin conformer but exposed in the active conformation. Elevated expression and constitutive activation of integrin β₇ conferred high MMG49 reactivity on MM cells, whereas MMG49 binding was scarcely detectable in other cell types including normal integrin β₇⁺ lymphocytes. T cells transduced with MMG49-derived chimeric antigen receptor (CAR) exerted anti-MM effects without damaging normal hematopoietic cells. Thus, MMG49 CAR T cell therapy is promising for MM, and a receptor protein with a rare but physiologically relevant conformation can serve as a cancer immunotherapy target.

Recombinant Immunotoxin Therapy of Glioblastoma: Smart Design, Key Findings, and Specific Challenges

Recombinant immunotoxins (RITs) refer to a group of recombinant protein-based therapeutics, which consists of two components: an antibody variable fragment or a specific ligand that allows RITs to bind specifically to target cells and an engineered toxin fragment that kills the target cells upon internalization. To date, over 1,000 RITs have been generated and significant success has been achieved in the therapy of hematological malignancies. However, the immunogenicity and off-target toxicities of RITs remain as significant barriers for their application to solid tumor therapy. A group of RITs have also been generated for the treatment of glioblastoma multiforme, and some have demonstrated evidence of tumor response and an acceptable profile of toxicity and safety in early clinical trials. Different from other solid tumors, how to efficiently deliver the RITs to intracranial tumors is more critical and needs to be solved urgently. In this article, we first review the design and expression of RITs, then summarize the key findings in the preclinical and clinical development of RIT therapy of glioblastoma multiforme, and lastly discuss the specific issues that still remain to forward RIT therapy to clinical practice.

Highly Specific and Effective Targeting of EGFRvIII-Positive Tumors with TandAb Antibodies

To harness the cytotoxic capacity of immune cells for the treatment of solid tumors, we developed tetravalent, bispecific tandem diabody (TandAb) antibodies that recognize EGFRvIII, the deletion variant III of the epidermal growth factor receptor (EGFR), and CD3 on T-cells, thereby directing immune cells to eliminate EGFRvIII-positive tumor cells. Using phage display, we identified scFv antibodies selectively binding to EGFRvIII. These highly EGFRvIII-specific, fully human scFv were substantially improved by affinity maturation, achieving K_Ds in the picomolar range, and were used to construct a set of bispecific EGFRvIII-targeting TandAbs with a broad range of binding and cytotoxic properties. These antibodies exhibited an exquisite specificity for a distinguished epitope in the N-terminal portion of EGFRvIII, as shown on recombinant antigen in Western Blot, SPR, and ELISA, as well as on antigen-expressing cells in FACS assays, and did not bind to the wild-type EGFR. High-affinity EGFRvIII/CD3 TandAbs were most potent in killing assays, displaying cytotoxicity toward EGFRvIII-expressing CHO, F98 glioma, or human DK-MG cells with EC₅₀ values in the range of 1-10 pM in vitro. They also demonstrated dose-dependent growth control in vivo in an EGFRvIII-positive subcutaneous xenograft tumor model. Together with the tumor-exclusive expression of EGFRvIII, the EGFRvIII/CD3 TandAbs' high specificity and strictly target-dependent activation with no off-target activity provide an opportunity to target tumor cells and spare normal tissues, thereby reducing the side effects associated with other anti-EGFR therapies. In summary, EGFRvIII/CD3 TandAbs are highly attractive therapeutic antibody candidates for selective immunotherapy of EGFRvIII-positive tumors.

Targeting a Cancer-Specific Epitope of the Epidermal Growth Factor Receptor in Triple-Negative Breast Cancer

BACKGROUND

Triple-negative breast cancers (TNBCs) are typically more aggressive and result in poorer outcomes than other breast cancers because treatment options are limited due to lack of hormone receptors or amplified human epidermal growth factor receptor 2 (HER2). Many TNBCs overexpress the epidermal growth factor receptor (EGFR) or manifest amplification of theEGFRgene, supporting EGFR as a therapeutic target. While EGFR-directed small molecule inhibitors have shown limited effectiveness in clinical settings, use of EGFR as a mechanism of delivering enzymatic cytotoxins to TNBC has not been demonstrated.

METHODS

Using the single-chain variable fragment (scFv) of the 806 antibody that binds only cells with overexpressed, misfolded, or mutant variants of the EGFR, a recombinant immunotoxin was engineered through gene fusion withPseudomonas aeruginosaExotoxin A (806-PE38). The potency of 806-PE38 on reducing TNBC cell growth in vitro and in xenograft models (n ≥ 6) was examined for six TNBC cell lines. All statistical tests were two-sided.

RESULTS

806-PE38 statistically significantly reduced the viability of all tested TNBC lines, with IC50values below 10 ng/mL for three of six cell lines, while not affecting cells with wild-type EGFR (IC50>300 ng/mL). Systemic treatments with 806-PE38 vs vehicle resulted in statistically significantly reduced tumor burdens (806-PE38 mean = 128 mm(3)[SD = 46 mm(3)] vs vehicle mean = 749 mm(3)[SD = 395 mm(3)], P = .001) and increased median survival (806-PE38 median = 82 days vs vehicle median = 50 days,P= .01) in a MDA-MB-468 TNBC mouse xenograft. Deletion of the catalytic residue eliminated both cytotoxic activity in vitro and the reduction in tumor burden and survival (P= .52).

CONCLUSIONS

These data support the further development of the 806-PE38 immunotoxin as a therapeutic agent for the treatment of patients with EGFR-positive TNBC. Follow-up experiments with combination therapies will be attempted to achieve full remissions.

Immunotoxin Therapies for the Treatment of Epidermal Growth Factor Receptor-Dependent Cancers

Many epithelial cancers rely on enhanced expression of the epidermal growth factor receptor (EGFR) to drive proliferation and survival pathways. Development of therapeutics to target EGFR signaling has been of high importance, and multiple examples have been approved for human use. However, many of the current small molecule or antibody-based therapeutics are of limited effectiveness due to the inevitable development of resistance and toxicity to normal tissues. Recombinant immunotoxins are therapeutic molecules consisting of an antibody or receptor ligand joined to a protein cytotoxin, combining the specific targeting of a cancer-expressed receptor with the potent cell killing of cytotoxic enzymes. Over the decades, many bacterial- or plant-based immunotoxins have been developed with the goal of targeting the broad range of cancers reliant upon EGFR overexpression. Many examples demonstrate excellent anti-cancer properties in preclinical development, and several EGFR-targeted immunotoxins have progressed to human trials. This review summarizes much of the past and current work in the development of immunotoxins for targeting EGFR-driven cancers.

Epidermal growth factor receptor targeting and challenges in glioblastoma

With the evolution of technology, there is now a deeper understanding of glioblastoma as an inter- and intraheterogeneous disease comprising a multitude of genetically and epigenetically different cancer cells. Greater characterization of glioblastoma at the molecular level has improved its initial pathophysiological staging and classification. With this knowledge comes the hope that more efficacious therapies to combat this highly lethal disease are on the horizon. One possibility for intervention is represented by the targeting of epidermal growth factor receptor (EGFR), which is amplified and mutated in a large subset of patients. In this review, we provide a brief overview of EGFR and its mutated form, EGFR variant III, describing the downstream cellular pathways activated by each receptor, available animal models, therapeutic strategies to inhibit the receptor, and possible intervention routes to efficiently target this receptor and prevent the emergence of resistant mechanisms which to date have hampered a successful therapeutic outcome.

LRIG1 extracellular domain: structure and function analysis

We have expressed and purified three soluble fragments of the human LRIG1-ECD (extracellular domain): the LRIG1-LRR (leucine-rich repeat) domain, the LRIG1-3Ig (immunoglobulin-like) domain, and the LRIG1-LRR-1Ig fragment using baculovirus vectors in insect cells. The two LRIG1 domains crystallised so that we have been able to determine the three-dimensional structures at 2.3Å resolution. We developed a three-dimensional structure for the LRIG1-ECD using homology modelling based on the LINGO-1 structure. The LRIG1-LRR domain and the LRIG1-LRR-1Ig fragment are monomers in solution, whereas the LRIG1-3Ig domain appears to be dimeric. We could not detect any binding of the LRIG1 domains or the LRIG1-LRR-1Ig fragment to the EGF receptor (EGFR), either in solution using biosensor analysis or when the EGFR was expressed on the cell surface. The FLAG-tagged LRIG1-LRR-1Ig fragment binds weakly to colon cancer cells regardless of the presence of EGFRs. Similarly, neither the soluble LRIG1-LRR nor the LRIG1-3Ig domains nor the full-length LRIG1 co-expressed in HEK293 cells inhibited ligand-stimulated activation of cell-surface EGFR.

A bivalent recombinant immunotoxin with high potency against tumors with EGFR and EGFRvIII expression

EGFR and EGFRvIII are overexpressed in various types of cancer, serving as optimal targets for cancer therapy. Capitalizing on the high specificity of humanized antibody 806 (mAb806) to the EGFR and EGFRvIII overexpressed in cancer, we designed and generated a bivalent recombinant immunotoxin (RIT, DT390-BiscFv806) by fusing the mAb806-derived bivalent single-chain variable fragment with a diphtheria toxin fragment, DT390. In vitro, DT390-BiscFv806 efficiently internalized into the cells and exhibited high cytotoxicity against the U87 glioblastoma cells and the EGFRvIII-transfected U87 (U87-EGFRvIII) cells with a half maximal inhibition concentration (IC50) of 1.47 nM and 2.26 × 10(-4) nM, respectively. Notably, DT390-BiscFv806 was 4 orders of magnitude more potent against the U87-EGFRvIII cells than against the parent U87 cells. The cytotoxicity against a group of 6 head and neck squamous cell carcinoma cell lines were further analyzed, showing an IC50 ranging from 0.24 nM to 156 nM, depending on the expression level of EGFR/EGFRvIII. In animals, the U87-EGFRvIII tumor xenografts grew extremely faster than the parental U87, and systemic administration of DT390-BiscFv806 significantly inhibited the growth of established U87-EGFRvIII and U87 tumor xenografts, showing a growth inhibition rate of 76.3% (59.82-96.2%) and 59.4% (31.5-76.0%), respectively. In pathology, the RIT-treated tumors exhibited a low mitotic activity and a large number of degenerative tumor cells, compared with the control tumors. The results indicate that DT390-BiscFv806 is promising for treatment of various types of cancer, especially for those with high EGFR expression or with EGFR and EGFRvIII co-expression.

mAb806 binding to epidermal growth factor receptor: a computational study

The epidermal growth factor receptor (EGFR) is an important target in the treatment of cancer. A very potent antibody, mAb806, has been developed against overexpressed EGFR and was found to be particularly active in brain tumors. Structural studies reveal that it binds to an epitope on the extracellular region of the EGFR. However, this epitope is cryptic/buried in crystal structures of the active (untethered) and inactive (tethered) EGFR, and it is unclear as to how the antibody interacts with this region. To explore this interaction, we combined molecular docking, steered molecular dynamics, and equilibrium molecular dynamics simulations. Our computational models reveal that the antibody induces local unfolding around the epitope to form the antibody-EGFR complex. In addition, regions in the vicinity of the epitope also modulate the interaction, which are in accordance with several other known antibody-antigen interactions, and offers new possibilities for the design of antibodies with increased potency and specificity for this receptor.

High throughput identification of monoclonal antibodies to membrane bound and secreted proteins using yeast and phage display

Antibodies are ubiquitous and essential reagents for biomedical research. Uses of antibodies include quantifying proteins, identifying the temporal and spatial pattern of expression in cells and tissue, and determining how proteins function under normal or pathological conditions. Specific antibodies are only available for a small portion of the proteome, limiting study of those proteins for which antibodies do not exist. The technologies to generate target-specific antibodies need to be improved to obtain high quality antibodies to the proteome at reasonable cost. Here we show that renewable, validated, and standardized monoclonal antibodies can be generated at high throughput, without the need for antigen production or animal immunizations. In this study, 60 protein domains from 24 selected secreted proteins were expressed on the surface of yeast and used for selection of phage antibodies, over 400 monoclonal antibodies were identified within 3 weeks. A subset of these antibodies was validated for binding to cancer cells that overexpress the target protein by flow cytometry or immunohistochemistry. This approach will be applicable to many of the membrane-bound and the secreted proteins, 20–40% of the proteome, accelerating the timeline for Ab generation while reducing the cost.

MR signal amplification for imaging of the mutant EGF receptor in orthotopic human glioma model

PURPOSE

To investigate the potential of targeted MR signal amplification strategy for imaging of EGF receptor variant III (EGFRvIII) overexpression associated with the infiltrating margin of aggressive orthotopic brain tumors.

PROCEDURES

F(ab')2 fragments of humanized anti-EGFRvIII monoclonal antibody (EMD72000) were linked to deglycosylated horseradish peroxidase (HRP) and glucose oxidase (GOX). Detection of the F(ab')2 conjugate pair colocalization in vivo was enabled by a subsequent IV injection of a low molecular weight paramagnetic substrate of HRP, diTyr-GdDTPA.

RESULTS

The delivery of the targeted fragments to the tumor was validated using SPECT/CT imaging of radiolabeled anti-EGFRvIII F(ab')2 conjugates. Further, by using 3 T MRI, we observed time-dependent differences in tumor signal intensity and signal retention at the endpoint depending on whether or not the animals were pre-injected with the anti-EGFRvIII F(ab')2 conjugates.

CONCLUSIONS

Imaging of EGFRvIII expression in vivo was enabled by consecutive administration of targeted F(ab')2 conjugates and a paramagnetic substrate resulting in a tumor-specific receptor detection with high specificity and resolution.

Global protein profiling reveals anti-EGFR monoclonal antibody 806-modulated proteins in A431 tumor xenografts

An important mediator of tumorigenesis, the epidermal growth factor receptor (EGFR) is expressed in almost all non-transformed cell types, associated with tumor progression, angiogenesis and metastasis. The significance of the EGFR as a cancer therapeutic target is underscored by the clinical development of several different classes of EGFR antagonists, including monoclonal antibodies (mAb) and tyrosine kinase inhibitors. Extensive preclinical studies have demonstrated the anti-tumor effects of mAb806 against tumor xenografts overexpressing EGFR. EGF stimulation of A431 cells induces rapid tyrosine phosphorylation of intracellular signalling proteins which regulate cell proliferation and apoptosis. Detailed understanding of the intracellular signalling pathways and components modulated by mAbs (such as mAb806) to EGFR, and other growth factor receptors, remain limited. The use of fluorescence 2D difference gel electrophoresis (2D DIGE), coupled with sensitive MS-based protein profiling in A431 tumor (epidermoid carcinoma) xenografts, in combination with mAb806, revealed proteins modulating endocytosis, cell architecture, apoptosis, cell signalling pathways and cell cycle regulation, including Dynamin-1-like protein, cofilin-1 protein, and 14-3-3 protein zeta/delta. Further, we report various proteins, including Interferon-induced protein 53 (IFI53), and Oncogene EMS1 (EMS1) which have roles in the tumor microenvironment, regulating cancer cell invasiveness, angiogenesis and formation of metastases. These findings contribute to understanding the underlying biological processes associated with mAb806 therapy of EGFR-positive tumors, and identifying further potential protein markers that may contribute in assessment of the treatment response.

Targeting the ERBB family in cancer: couples therapy

The ERBB family of receptor tyrosine kinases has a central role in the tumorigenesis of many types of solid tumour. Various therapeutics targeting these receptors have been approved for the treatment of several cancers. Considerable preclinical data have shown that the administration of two inhibitors against an individual ERBB family member--particularly epidermal growth factor receptor (EGFR) or ERBB2--leads to markedly higher antitumour activity than the administration of single agents. This Opinion article describes the preclinical and clinical performance of these dual-targeting approaches, discusses the key mechanisms that mediate their increased efficacy and highlights areas for ongoing investigation.