In silico driven redesign of a clinically relevant antibody for the treatment of GD2 positive tumors

Anti-OAcGD2 antibody in combination with ceramide kinase inhibitor mediates potent antitumor cytotoxicity against breast cancer and diffuse intrinsic pontine glioma cells

O-acetylated GD2 (OAcGD2) is a cancer-related antigen that is currently being explored for therapeutic use. Exploring the intricate mechanisms behind OAcGD2 synthesis in cancer cells has long been a challenge. Leveraging state-of-the-art high-throughput RNAi screening and confocal imaging technologies, our study delves into the genetic network orchestrating OAcGD2 synthesis in breast cancer cells. By conducting a comprehensive siRNA screen targeting the OAcGD2 phosphatome/kinome, we identified 43 genetic modulators, with 25 downregulating and 18 upregulating OAcGD2 synthesis. Among these, our study focused on CERK, the gene-encoding ceramide kinase, a pivotal player in glycosphingolipid metabolism. Through meticulous experimentation utilizing anti-CERK inhibitor and siRNAs, we made a significant discovery: CERK inhibition robustly upregulates OAcGD2 in both neuroblastoma and breast cancer cells, concurrently dampening cell migration. Furthermore, our findings highlight an exciting prospect: augmenting the antibody-dependent cell cytotoxicity of the chimeric human/mouse anti-OAcGD2 IgG1 monoclonal antibody (c8B6 mAb) against breast cancer and diffuse intrinsic pontine glioma cell lines in combination with specific CERK inhibitors. These results underscore the pivotal role of CERK inhibition in bolstering OAcGD2 synthesis, thus, presenting a promising strategy to increase the efficacy of anti-OAcGD2-based immunotherapy in patients with neuroectodermal tumors. By shedding light on this intricate interplay, our study paves the way for innovative therapeutic strategies poised to revolutionize the treatment landscape for these aggressive malignancies.

Chimeric antigen receptor natural killer cells: a promising antitumor immunotherapy

Chimeric antigen receptor (CAR) T cells have been successfully used in adoptive cell therapy for malignancies. However, some obstacles, including side effects such as graft-versus-host disease and cytokine release syndrome, therapy resistance, limited sources, as well as high cost, limited the application of CAR T cells. Recently, CAR natural killer (NK) cells have been pursued as the effector cells for adoptive immunotherapy for their attractive merits of strong intrinsic antitumor activity and relatively mild side effects. Additionally, CAR NK cells can be available from various sources and do not require strict human leukocyte antigen matching, which suggests them as promising "off-the-shelf" products for clinical application. Although the use of CAR NK cells is restrained by the limited proliferation and impaired efficiency within the immunosuppressive tumor microenvironment, further investigation in optimizing CAR structure and combination therapies will overcome these challenges. This review will summarize the advancement of CAR NK cells, CAR NK cell manufacture, the clinical outcomes of CAR NK therapy, the challenges in the field, and prospective solutions. Besides, we will discuss the emerging application of other immune cells for CAR engineering. Collectively, this comprehensive review will provide a valuable and informative summary of current progress and evaluate challenges and future opportunities of CAR NK cells in tumor treatment.

High-throughput analysis system of interaction kinetics for data-driven antibody design

Surface plasmon resonance (SPR) is widely used for antigen-antibody interaction kinetics analysis. However, it has not been used in the screening phase because of the low throughput of measurement and analysis. Herein, we proposed a high-throughput SPR analysis system named "BreviA" using the Brevibacillus expression system. Brevibacillus was transformed using a plasmid library containing various antibody sequences, and single colonies were cultured in 96-well plates. Sequence analysis was performed using bacterial cells, and recombinant antibodies secreted in the supernatant were immobilized on a sensor chip to analyze their interactions with antigens using high-throughput SPR. Using this system, the process from the transformation to 384 interaction analyses can be performed within a week. This system utility was tested using an interspecies specificity design of an anti-human programmed cell death protein 1 (PD-1) antibody. A plasmid library containing alanine and tyrosine mutants of all complementarity-determining region residues was generated. A high-throughput SPR analysis was performed against human and mouse PD-1, showing that the mutation in the specific region enhanced the affinity for mouse PD-1. Furthermore, deep mutational scanning of the region revealed two mutants with > 100-fold increased affinity for mouse PD-1, demonstrating the potential efficacy of antibody design using data-driven approach.

Biology of GD2 ganglioside: implications for cancer immunotherapy

Part of the broader glycosphingolipid family, gangliosides are composed of a ceramide bound to a sialic acid-containing glycan chain, and locate at the plasma membrane. Gangliosides are produced through sequential steps of glycosylation and sialylation. This diversity of composition is reflected in differences in expression patterns and functions of the various gangliosides. Ganglioside GD2 designates different subspecies following a basic structure containing three carbohydrate residues and two sialic acids. GD2 expression, usually restrained to limited tissues, is frequently altered in various neuroectoderm-derived cancers. While GD2 is of evident interest, its glycolipid nature has rendered research challenging. Physiological GD2 expression has been linked to developmental processes. Passing this stage, varying levels of GD2, physiologically expressed mainly in the central nervous system, affect composition and formation of membrane microdomains involved in surface receptor signaling. Overexpressed in cancer, GD2 has been shown to enhance cell survival and invasion. Furthermore, binding of antibodies leads to immune-independent cell death mechanisms. In addition, GD2 contributes to T-cell dysfunction, and functions as an immune checkpoint. Given the cancer-associated functions, GD2 has been a source of interest for immunotherapy. As a potential biomarker, methods are being developed to quantify GD2 from patients' samples. In addition, various therapeutic strategies are tested. Based on initial success with antibodies, derivates such as bispecific antibodies and immunocytokines have been developed, engaging patient immune system. Cytotoxic effectors or payloads may be redirected based on anti-GD2 antibodies. Finally, vaccines can be used to mount an immune response in patients. We review here the pertinent biological information on GD2 which may be of use for optimizing current immunotherapeutic strategies.

GD2 CAR-T cells in combination with Nivolumab exhibit enhanced antitumor efficacy

Glioblastoma (GBM) is a common primary brain tumor with poor clinical prognosis. Although CAR-T therapy has been trialed for treatment of GBM, the outcomes are sub-optimal possibly due to exhaustion of T cells and life-threatening neurotoxicity. To address these issues, a combined therapeutic strategy was tested in the current study using GD2 CAR-T together with Nivolumab - an anti-PD-1 monoclonal antibody. An effector-to-target co-culture system was established to evaluate the short-term and long-term cytotoxicity of CAR-T, as well as to investigate the inhibitory activity and T cell exhaustion associated with the PD-1/PD-L1 signaling pathway. Orthotopic NOD/SCID GBM animal models were generated to evaluate the safety and efficacy of the combined therapeutic strategy at various dosages of GD2 CAR-T with Nivolumab. GD2 CAR-T exhibited significant antigen-specific cytotoxicity in a dose-dependent manner in vitro. The persistence of cytotoxicity of GD2 CAR-T could be enhanced by addition of Nivolumab in the co-culture system. Animal studies suggested that GD2 CAR-T effectively infiltrated into tumor tissue and significantly hampered tumor progression. The optimal therapeutic outcome was obtained via using the medium dosage of CAR-T with Nivolumab, which displayed the highest efficacy in extending the survival up to 60 days. Further investigation of toxicity revealed that high-dosage of GD2 CAR-T could induce tumor apoptosis through p53/caspase-3/PARP signaling pathway. This study suggests that GD2 CAR-T in combination with Nivolumab may offer an improved therapeutic strategy for treatment of GBM.

Structure-Based Affinity Maturation of Antibody Based on Double-Point Mutations

Structure-based site-directed affinity maturation of antibodies can be expanded by multiple-point mutations to obtain various mutants. However, selecting the appropriate number of promising mutants for experimental evaluation from the vast number of combinations of multiple-point mutations is challenging. In this report, we describe how to narrow candidate mutants using the so-called weak interaction analysis such as CH-π and CH-O in addition to widely recognized interactions such as hydrogen bonds.

Harnessing Antibody Polyspecificity for Cancer Immunotherapy

Targeting the diverse glycan repertoire expressed on tumor cells is considered a viable therapeutic strategy to deal with tumor cell heterogeneity. Inherently polyspecific, natural, glycan-reactive antibodies are purported to be protective in thwarting infections and in cancer immunotherapy. Tumor-associated carbohydrate antigens (TACAs) are related to pathogen glycans, to which nascent or natural antibodies exist and IgM responses are elicited. To capture the polyspecific nature of anticarbohydrate responses, we have focused on the rational design of carbohydrate mimetic peptides (CMPs) cross-reactive with TACA reactive antibodies. In particular, we have focused on the development of CMPs that display reactivity to GD2 and Lewis Y (LeY) reactive monoclonal antibodies. They would serve as templates for pan-immunogens inducing biosimilar polyreactive antibodies. In the design, we relied on structural analyses of CMP's enhanced binding to the templates using molecular modeling. Glycan reactivity patterns of affinity CMP-purified human antibodies further refined specificity profiles in comparison with the immune response to the CMP in clinical trials. In this study, we further define the molecular characteristics for this mimicry by considering the polyspecificity of LeY and GD2 reactive antibodies binding to the lacto-ceramide core Galβ(1,4)Glcβ(1-1')Cer. Binding to this minimum building block can be capitalized on for cancer therapy and diagnostics and illustrates a new approach in designing cancer vaccines taking advantage of the latent polyspecificity of antibodies and the relevance of natural antibodies in antigen discovery and design.

Structure-based design and discovery of novel anti-tissue factor antibodies with cooperative double-point mutations, using interaction analysis

The generation of a wide range of candidate antibodies is important for the successful development of drugs that simultaneously satisfy multiple requirements. To find cooperative mutations and increase the diversity of mutants, an in silico double-point mutation approach, in which 3D models of all possible double-point mutant/antigen complexes are constructed and evaluated using interaction analysis, was developed. Starting from an antibody with very high affinity, four double-point mutants were designed in silico. Two of the double-point mutants exhibited improved affinity or affinity comparable to that of the starting antibody. The successful identification of two active double-point mutants showed that a cooperative mutation could be found by utilizing information regarding the interactions. The individual single-point mutants of the two active double-point mutants showed decreased affinity or no expression. These results suggested that the two active double-point mutants cannot be obtained through the usual approach i.e. a combination of improved single-point mutants. In addition, a triple-point mutant, which combines the distantly located active double-point mutation and an active single-point mutation collaterally obtained in the process of the double-point mutation strategy, was designed. The triple-point mutant showed improved affinity. This finding suggested that the effects of distantly located mutations are independent and additive. The double-point mutation approach using the interaction analysis of 3D structures expands the design repertoire for mutants, and hopefully paves a way for the identification of cooperative multiple-point mutations.

Structure guided maturation of a novel humanized anti-HBV antibody and its preclinical development

We have reported that E6F6, a mouse monoclonal antibody, is a promising treatment option for patients with chronic hepatitis B (CHB). A humanized E6F6 antibody B11 with affinity loss was obtained by CDR-grafting approach. To address this issue, in silico affinity maturation through scanning mutagenesis using CHARMM force field methods was performed on an predicted immune complex model of the B11:HBsAg. We chose four variants with top increased interaction energy for further characterization. The antibody huE6F6-1 within two point mutations (Heavy Chain: Asp65Val; His66Leu) was identified to restore the parental antibody's high binding affinity, neutralization activity, and potent efficacy of viral suppression in vivo. Crystal structure (1.8 Å resolution) based molecular docking proved more stabilized and compact hydrogen bond interactions formed in huE6F6-1.The smaller and dispersed HBV immune complexes of huE6F6-1 by electron microscopy suggested it will have the same therapeutic efficacy as the parental E6F6 mAb. Preclinical study and pharmacokinetics of huE6F6-1 demonstrated that it is a stable and desirable lead candidate to improve the clinical management of CHB. Notably, our structure guided approach may facilitate the humanization and affinity maturation of other rodent antibody candidates during drug development.

The terminal sialic acid of stage-specific embryonic antigen-4 has a crucial role in binding to a cancer-targeting antibody

Cancer remains a leading cause of morbidity and mortality worldwide, requiring ongoing development of targeted therapeutics such as monoclonal antibodies. Carbohydrates on embryonic cells are often highly expressed in cancer and are therefore attractive targets for antibodies. Stage-specific embryonic antigen-4 (SSEA-4) is one such glycolipid target expressed in many cancers, including breast and ovarian carcinomas. Here, we defined the structural basis for recognition of SSEA-4 by a novel monospecific chimeric antibody (ch28/11). Five X-ray structures of ch28/11 Fab complexes with the SSEA-4 glycan headgroup, determined at 1.5-2.7 Å resolutions, displayed highly similar three-dimensional structures indicating a stable binding mode. The structures also revealed that by adopting a horseshoe-shaped conformation in a deep groove, the glycan headgroup likely sits flat against the membrane to allow the antibody to interact with SSEA-4 on cancer cells. Moreover, we found that the terminal sialic acid of SSEA-4 plays a dominant role in dictating the exquisite specificity of the ch28/11 antibody. This observation was further supported by molecular dynamics simulations of the ch28/11-glycan complex, which show that SSEA-4 is stabilized by its terminal sialic acid, unlike SSEA-3, which lacks this sialic acid modification. These high-resolution views of how a glycolipid interacts with an antibody may help to advance a new class of cancer-targeting immunotherapy.

Epigenetic hypomethylation and upregulation of GD3s in triple negative breast cancer

Background

Breast cancer remains a major health problem in the world. Triple-negative breast cancer (TNBC) is an aggressive subtype with very poor prognosis. Up to now, the mechanism behind TNBC's activity is still unclear and no candidate drug target has been identified. Thus, it is of critical importance to elucidate the pathways in TNBC and identify the relevant biomarkers. Recent studies showed that ganglioside D3 synthase (GD3s) played a very important role in development of cancers. However, the physiological functions and associated pathways of GD3s in TNBC are still unclear.

Methods

In silico analysis of the expression of GD3s in TNBC was conducted using The Cancer Genome Atlas (TCGA) and Oncomine databases. The proliferation of breast cancer cells was measured by MTT assay, colony formation by the soft agar method, and migration and invasion using Boyden chamber inserts. The methylation level of the gene encoding GD3s, ST8SIA1, in specimens was assessed by qMS-PCR and in silico using the UCSC gene browser. Protein expression was examined via immunohistochemistry (IHC), qRT-PCR and Western immunoblotting.

Results

In silico analysis showed a higher GD3s expression in ER^- than ER⁺ breast cancers and GD3s was also highly expressed in TNBC compared to other types of breast cancers. The elevated GD3s expression in TNBC cells and tissues was associated with hypomethylation of the ST8SIA1 gene. Overexpression of GD3s in human breast cancer cells increased their proliferation, migration, invasion and colony formation ability. GD3s expression in breast cancers was closely associated with relapse-free survival (RFS) and overall survival (OS).

Conclusions

In summary, these results suggest that GD3s may be a potential biomarker and drug target in treatment of TNBC.

Trends in therapeutic antibody affinity maturation: From in-vitro towards next-generation sequencing approaches

Current advances in antibody engineering driving the strongest growth area in biotherapeutic agents development. Affinity improvement that is mainly important for biological activity and clinical efficacy of therapeutic antibodies, has still remained a challenging task. In the human body, during a course of immune response affinity maturation increase antibody activity by several rounds of somatic hypermutation and clonal selection in the germinal center. The final outputs are antibodies representing higher affinity and specificity against a particular antigen. In the realm of biotechnology, exploring of mutations which improve antibody affinity while preserving its specificity and stability is an extremely time-consuming and laborious process. Recent advances in computational algorithms and DNA sequencing technologies help researchers to redesign antibody structure to achieve desired properties such as improved binding affinity. In this review, we briefly described the principle of affinity maturation and different corresponding in vitro techniques. Also, we recapitulated the most recent advancements in the field of antibody affinity maturation including computational approaches and next-generation sequencing (NGS).

Anti-GD2 immunotherapy for neuroblastoma

INTRODUCTION

Current therapeutic approaches for high-risk neuroblastoma (HR-NB) include high-dose chemotherapy, surgery and radiotherapy; interventions that are associated with long and short-term toxicities. Effective immunotherapy holds particular promise for improving survival and quality of life by reducing exposure to cytotoxic agents. GD2, a surface glycolipid is the most common target for immunotherapy. Areas covered: We review the status of anti-GD2 immunotherapies currently in clinical use for neuroblastomas and novel GD2-targeted strategies in preclinical development. Expert commentary: Anti-GD2 monoclonal antibodies are associated with improved survival in patients in their first remission and are increasingly being used for chemorefractory and relapsed neuroblastoma. As protein engineering technology has become more accessible, newer antibody constructs are being tested. GD2 is also being targeted by natural killer cells and T-cells. Active immunity can be elicited by anti-GD2 vaccines. The rational combination of currently available and soon-to-emerge immunotherapeutic approaches, and their integration into conventional multimodality therapies will require further investigation to optimize their use for HR-NB.

Therapeutic Antibodies to Ganglioside GD2 Evolved from Highly Selective Germline Antibodies

Antibodies play a crucial role in host defense and are indispensable research tools, diagnostics, and therapeutics. Antibody generation involves binding of genomically encoded germline antibodies followed by somatic hypermutation and in vivo selection to obtain antibodies with high affinity and selectivity. Understanding this process is critical for developing monoclonal antibodies, designing effective vaccines, and understanding autoantibody formation. Prior studies have found that antibodies to haptens, peptides, and proteins evolve from polyspecific germline antibodies. The immunological evolution of antibodies to mammalian glycans has not been studied. Using glycan microarrays, protein microarrays, cell binding studies, and molecular modeling, we demonstrate that therapeutic antibodies to the tumor-associated ganglioside GD2 evolved from highly specific germline precursors. The results have important implications for developing vaccines and monoclonal antibodies that target carbohydrate antigens. In addition, they demonstrate an alternative pathway for antibody evolution within the immune system that is distinct from the polyspecific germline pathway.

In silico and in vitro inhibition of cytochrome P450 3A by synthetic stilbenoids

Inhibition of cytochrome P450 3A4 (CYP3A4), the major drug metabolizing enzyme, by dietary compounds has recently attracted increased attention. Evaluating the potency of the many known inhibitory compounds is a tedious and time consuming task, yet it can be achieved using computing tools. Here, CDOCKER and Glide served to design model inhibitors in order to characterize molecular features of an inhibitor. Assessing nitro-stilbenoids, both approaches suggested nitrostilbene to be a weaker inhibitor of CYP3A4 than resveratrol, and stronger than dimethoxy-nitrostilbene. Nitrostilbene and resveratrol, but not dimethoxy-nitrostilbene, engage electrostatic interactions in the enzyme cavity, and with the haem. In vitro assessment of the inhibitory capacity supported the in silico predictions, suggesting that evaluating the electrostatic interactions of a compound with the prosthetic group allows the prediction of inhibitory potency. Since both programs yielded related results, it is suggested that for CYP3A4, computing tools may allow rapid identification of potent dietary inhibitors.

Emerging and investigational therapies for neuroblastoma

INTRODUCTION

Treatment for children with clinically aggressive, high-risk neuroblastoma remains challenging. Less than 50% of patients with high-risk neuroblastoma will survive long-term with current therapies, and survivors are at risk for serious treatment-related late toxicities. Here, we review new and evolving treatments that may ultimately improve outcome for children with high-risk neuroblastoma with decreased potential for late adverse events.

AREAS COVERED

New strategies for treating high-risk neuroblastoma are reviewed including: radiotherapy, targeted cytotoxics, biologics, immunotherapy, and molecularly targeted agents. Recently completed and ongoing neuroblastoma clinical trials testing these novel treatments are highlighted. In addition, we discuss ongoing clinical trials designed to evaluate precision medicine approaches that target actionable somatic mutations and oncogenic cellular pathways.

EXPERT OPINION

Advances in genomic medicine and molecular biology have led to the development of early phase studies testing biologically rational therapies targeting aberrantly activated cellular pathways. Because many of these drugs have a wider therapeutic index than standard chemotherapeutic agents, these treatments may be more effective and less toxic than current strategies. However, to effectively integrate these targeted strategies, robust predictive biomarkers must be developed that will identify patients who will benefit from these approaches and rapidly match treatments to patients at diagnosis.

Antibody recognition of aberrant glycosylation on the surface of cancer cells

Carbohydrate-binding antibodies and carbohydrate-based vaccines are being actively pursued as targeted immunotherapies for a broad range of cancers. Recognition of tumor-associated carbohydrates (glycans) by antibodies is predominantly towards terminal epitopes on glycoproteins and glycolipids on the surface of cancer cells. Crystallography along with complementary experimental and computational methods have been extensively used to dissect antibody recognition of glycan epitopes commonly found in cancer. We provide an overview of the structural biology of antibody recognition of tumor-associated glycans and propose potential rearrangements of these targets in the membrane that could dictate the complex biological activities of these antibodies against cancer cells.

Activation of human naïve Th cells increases surface expression of GD3 and induces neoexpression of GD2 that colocalize with TCR clusters

CD4+ T helper lymphocytes (Th) orchestrate the immune response after their activation by antigen-presenting cells. Activation of naïve Th cells is reported to generate the reduction in surface epitopes of sialic acid (Sia) in α2,3 and α2,6 linkages. In this work, we report that in spite of this glycophenotype, anti-CD3/anti-CD28-activated purified human naïve Th cells show a significant increase in surface Sia, as assessed by metabolic labeling, compared with resting naïve Th cells, suggesting an increased flux of Sia toward Siaα2,8 glycoconjugates. To understand this increase as a result of ganglioside up-regulation, we observed that very early after activation, human naïve Th cells show an increased expression in surface GD3 and neoexpression of surface GD2 gangliosides, the latter clustering with the T cell receptor (TCR). Also, we report that in contrast to GM2/GD2 synthase null mice, lentiviral vector-mediated silencing of the GM2/GD2 synthase in activated human naïve Th cells reduced efficient TCR clustering and downstream signaling, as assessed by proliferation assays and IL-2 and IL-2R expression, pointing to an important role of this enzyme in activation of human naive Th cells.

Structural Basis of GD2 Ganglioside and Mimetic Peptide Recognition by 14G2a Antibody

Monoclonal antibodies targeting GD2 ganglioside (GD2) have recently been approved for the treatment of high risk neuroblastoma and are extensively evaluated in clinics in other indications. This study illustrates how a therapeutic antibody distinguishes between different types of gangliosides present on normal and cancer cells and informs how synthetic peptides can imitate ganglioside in its binding to the antibody. Using high resolution crystal structures we demonstrate that the ganglioside recognition by a model antibody (14G2a) is based primarily on an extended network of direct and water molecule mediated hydrogen bonds. Comparison of the GD2-Fab structure with that of a ligand free antibody reveals an induced fit mechanism of ligand binding. These conclusions are validated by directed mutagenesis and allowed structure guided generation of antibody variant with improved affinity toward GD2. Contrary to the carbohydrate, both evaluated mimetic peptides utilize a "key and lock" interaction mechanism complementing the surface of the antibody binding groove exactly as found in the empty structure. The interaction of both peptides with the Fab relies considerably on hydrophobic contacts however, the detailed connections differ significantly between the peptides. As such, the evaluated peptide carbohydrate mimicry is defined primarily in a functional and not in structural manner.

Alteration of Electrostatic Surface Potential Enhances Affinity and Tumor Killing Properties of Anti-ganglioside GD2 Monoclonal Antibody hu3F8

Ganglioside GD2 is highly expressed on neuroectodermal tumors and an attractive therapeutic target for antibodies that have already shown some clinical efficacy. To further improve the current antibodies, which have modest affinity, we sought to improve affinity by using a combined method of random mutagenesis and in silico assisted design to affinity-mature the anti-GD2 monoclonal antibody hu3F8. Using yeast display, mutants in the Fv with enhanced binding over the parental clone were FACS-sorted and cloned. In silico modeling identified the minimal key interacting residues involved in the important charged interactions with the sialic acid groups of GD2. Two mutations, D32H (L-CDR1) and E1K (L-FR1) altered the electrostatic surface potential of the antigen binding site, allowing for an increase in positive charge to enhance the interaction with the negatively charged GD2-pentasaccharide headgroup. Purified scFv and IgG mutant forms were then tested for antigen specificity by ELISA, for tissue specificity by immunohistochemistry, for affinity by BIACORE, for antibody-dependent cell-mediated cytotoxicity (ADCC) and complement-mediated cytotoxicity in vitro, and for anti-tumor efficacy in xenografted humanized mice. The nearly 7-fold improvement in affinity of hu3F8 with a single D32H (L-CDR1) mutation translated into a ∼12-fold improvement in NK92MI-transfected CD16-mediated ADCC, a 6-fold improvement in CD32-mediated ADCC, and a 2.5-fold improvement in complement-mediated cytotoxicity while maintaining restricted normal tissue cross-reactivity and achieving substantial improvement in tumor ablation in vivo. Despite increasing GD2 affinity, the double mutation D32H (L-CDR1) and E1K (L-FR1) did not further improve anti-tumor efficacy.

Structural biology of antibody recognition of carbohydrate epitopes and potential uses for targeted cancer immunotherapies

Monoclonal antibodies represent the most successful class of biopharmaceuticals for the treatment of cancer. Mechanisms of action of therapeutic antibodies are very diverse and reflect their ability to engage in antibody-dependent effector mechanisms, internalize to deliver cytotoxic payloads, and display direct effects on cells by lysis or by modulating the biological pathways of their target antigens. Importantly, one of the universal changes in cancer is glycosylation and carbohydrate-binding antibodies can be produced to selectively recognize tumor cells over normal tissues. A promising group of cell surface antibody targets consists of carbohydrates presented as glycolipids or glycoproteins. In this review, we outline the basic principles of antibody-based targeting of carbohydrate antigens in cancer. We also present a detailed structural view of antibody recognition and the conformational properties of a series of related tissue-blood group (Lewis) carbohydrates that are being pursued as potential targets of cancer immunotherapy.

Disialoganglioside GD2 as a therapeutic target for human diseases

INTRODUCTION

Ganglioside GD2 is found in vertebrates and invertebrates, overexpressed among pediatric and adult solid tumors, including neuroblastoma, glioma, retinoblastoma, Ewing's family of tumors, rhabdomyosarcoma, osteosarcoma, leiomyosarcoma, liposarcoma, fibrosarcoma, small cell lung cancer and melanoma. It is also found on stem cells, neurons, some nerve fibers and basal layer of the skin.

AREAS COVERED

GD2 provides a promising clinical target for radiolabeled antibodies, bispecific antibodies, chimeric antigen receptor (CAR)-modified T cells, drug conjugates, nanoparticles and vaccines. Here, we review its biochemistry, normal physiology, role in tumorigenesis, important characteristics as a target, as well as anti-GD2-targeted strategies.

EXPERT OPINION

Bridging the knowledge gaps in understanding the interactions of GD2 with signaling molecules within the glycosynapses, and the regulation of its cellular expression should improve therapeutic strategies targeting this ganglioside. In addition to anti-GD2 IgG mAbs, their drug conjugates, radiolabeled forms especially when genetically engineered to improve therapeutic index and novel bispecific forms or CARs to retarget T-cells are promising candidates for treating metastatic cancers.

Retargeting T cells to GD2 pentasaccharide on human tumors using Bispecific humanized antibody

Anti-disialoganglioside GD2 IgG antibodies have shown clinical efficacy in solid tumors that lack human leukocyte antigens (e.g., neuroblastoma) by relying on Fc-dependent cytotoxicity. However, there are pain side effects secondary to complement activation. T-cell retargeting bispecific antibodies (BsAb) also have clinical potential, but it is thus far only effective against liquid tumors. In this study, a fully humanized hu3F8-BsAb was developed, in which the anti-CD3 huOKT3 single-chain Fv fragment (ScFv) was linked to the carboxyl end of the anti-GD2 hu3F8 IgG1 light chain, and was aglycosylated at N297 of Fc to prevent complement activation and cytokine storm. In vitro, hu3F8-BsAb activated T cells through classic immunologic synapses, inducing GD2-specific tumor cytotoxicity at femtomolar EC50 with >10⁵-fold selectivity over normal tissues, releasing Th1 cytokines (TNFα, IFNγ, and IL2) when GD2⁺ tumors were present. In separate murine neuroblastoma and melanoma xenograft models, intravenous hu3F8-BsAb activated T cells in situ and recruited intravenous T cells for tumor ablation, significantly prolonging survival from local recurrence or from metastatic disease. Hu3F8-BsAb, but not control BsAb, drove T cells and monocytes to infiltrate tumor stroma. These monocytes were necessary for sustained T-cell proliferation and/or survival and contributed significantly to the antitumor effect. The in vitro and in vivo antitumor properties of hu3F8-BsAb and its safety profile support its further clinical development as a cancer therapeutic, and provide the rationale for exploring aglycosylated IgG-scFv as a structural platform for retargeting human T cells.

Structure Based Refinement of a Humanized Monoclonal Antibody That Targets Tumor Antigen Disialoganglioside GD2

Disialoganglioside GD2 is an important target on several pediatric and adult cancer types including neuroblastoma, retinoblastoma, melanoma, small-cell lung cancer, brain tumors, sarcomas, and cancer stem cells. We have utilized structural and computational methods to refine the framework of humanized monoclonal antibody 3F8, the highest affinity anti-GD2 antibody in clinical development. Two constructs (V3 and V5) were designed to enhance stability and minimize potential immunogenicity. Construct V3 contained 12 point mutations and had higher thermal stability and comparable affinity and in vitro tumor cells killing as the parental hu3F8. Construct V5 had nine point mutations to minimize potential immunogenicity, but resulted in weaker thermal stability, weaker antigen binding, and reduced tumor killing potency. When construct V3 was combined with the single point mutation HC:G54I, the resulting V3-Ile construct had enhanced stability, antigen binding, and a nearly sixfold increase in tumor cell killing. The resulting product is a lead candidate for clinical development for the treatment of GD2-positive tumors.

Dielectrophoretic capture and genetic analysis of single neuroblastoma tumor cells

Our understanding of the diversity of cells that escape the primary tumor and seed micrometastases remains rudimentary, and approaches for studying circulating and disseminated tumor cells have been limited by low throughput and sensitivity, reliance on single parameter sorting, and a focus on enumeration rather than phenotypic and genetic characterization. Here, we utilize a highly sensitive microfluidic and dielectrophoretic approach for the isolation and genetic analysis of individual tumor cells. We employed fluorescence labeling to isolate 208 single cells from spiking experiments conducted with 11 cell lines, including 8 neuroblastoma cell lines, and achieved a capture sensitivity of 1 tumor cell per 10⁶ white blood cells (WBCs). Sample fixation or freezing had no detectable effect on cell capture. Point mutations were accurately detected in the whole genome amplification product of captured single tumor cells but not in negative control WBCs. We applied this approach to capture 144 single tumor cells from 10 bone marrow samples of patients suffering from neuroblastoma. In this pediatric malignancy, high-risk patients often exhibit wide-spread hematogenous metastasis, but access to primary tumor can be difficult or impossible. Here, we used flow-based sorting to pre-enrich samples with tumor involvement below 0.02%. For all patients for whom a mutation in the Anaplastic Lymphoma Kinase gene had already been detected in their primary tumor, the same mutation was detected in single cells from their marrow. These findings demonstrate a novel, non-invasive, and adaptable method for the capture and genetic analysis of single tumor cells from cancer patients.

GD2-targeted immunotherapy and radioimmunotherapy

Ganglioside GD2 is a tumor-associated surface antigen found in a broad spectrum of human cancers and stem cells. They include pediatric embryonal tumors (neuroblastoma, retinoblastoma, brain tumors, osteosarcoma, Ewing sarcoma, rhabdomyosarcoma), as well as adult cancers (small cell lung cancer, melanoma, soft tissue sarcomas). Because of its restricted normal tissue distribution, GD2 has been proven safe for antibody targeting. Anti-GD2 antibody is now incorporated into the standard of care for the treatment of high-risk metastatic neuroblastoma. Building on this experience, novel combinations of antibodies, cytokines, cells, and genetically engineered products all directed at GD2 are rapidly moving into the clinic. In this review, past and present immunotherapy trials directed at GD2 will be summarized, highlighting the lessons learned and the future directions.

Structural design of disialoganglioside GD2 and CD3-bispecific antibodies to redirect T cells for tumor therapy

Antibody-based immunotherapy has proven efficacy for patients with high-risk neuroblastoma. However, despite being the most efficient tumoricidal effectors, T cells are underutilized because they lack Fc receptors. Using a monovalent single-chain fragment (ScFv) platform, we engineered tandem scFv bispecific antibodies (BsAbs) that specifically target disialoganglioside (GD2) on tumor cells and CD3 on T cells. Structural variants of BsAbs were constructed and ranked based on binding to GD2, and on competency in inducing T-cell-mediated tumor cytotoxicity. In vitro thermal stability and binding measurements were used to characterize each of the constructs, and in silico molecular modeling was used to show how the orientation of the variable region heavy (VH) and light (VL) chains of the anti-GD2 ScFv could alter the conformations of key residues responsible for high affinity binding. We showed that the VH-VL orientation, the (GGGGS)3 linker, disulfide bond stabilization of scFv, when combined with an affinity matured mutation provided the most efficient BsAb to direct T cells to lyse GD2-positive tumor cells. In vivo, the optimized BsAb could efficiently inhibit melanoma and neuroblastoma xenograft growth. These findings provide preclinical validation of a structure-based method to assist in designing BsAb for T-cell-mediated therapy.

Chimeric antibody c.8B6 to O-acetyl-GD2 mediates the same efficient anti-neuroblastoma effects as therapeutic ch14.18 antibody to GD2 without antibody induced allodynia

Background

Anti-GD2 antibody is a proven therapy for GD2-postive neuroblastoma. Monoclonal antibodies against GD2, such as chimeric mAb ch14.18, have become benchmarks for neuroblastoma therapies. Pain, however, can limit immunotherapy with anti-GD2 therapeutic antibodies like ch14.18. This adverse effect is attributed to acute inflammation via complement activation on GD2-expressing nerves. Thus, new strategies are needed for the development of treatment intensification strategies to improve the outcome of these patients.

Methodology/Principal Findings

We established the mouse-human chimeric antibody c.8B6 specific to OAcGD2 in order to reduce potential immunogenicity in patients and to fill the need for a selective agent that can kill neuroblastoma cells without inducing adverse neurological side effects caused by anti-GD2 antibody immunotherapy. We further analyzed some of its functional properties compared with anti-GD2 ch14.18 therapeutic antibody. With the exception of allodynic activity, we found that antibody c.8B6 shares the same anti-neuroblastoma attributes as therapeutic ch14.18 anti-GD2 mAb when tested in cell-based assay and in vivo in an animal model.

Conclusion/Significance

The absence of OAcGD2 expression on nerve fibers and the lack of allodynic properties of c.8B6–which are believed to play a major role in mediating anti-GD2 mAb dose-limiting side effects–provide an important rationale for the clinical application of c.8B6 in patients with high-risk neuroblastoma.

Engineering anti-GD2 monoclonal antibodies for cancer immunotherapy

Ganglioside GD2 is highly expressed on neuroectoderm-derived tumors and sarcomas, including neuroblastoma, retinoblastoma, melanoma, small cell lung cancer, brain tumors, osteosarcoma, rhabdomyosarcoma, Ewing's sarcoma in children and adolescents, as well as liposarcoma, fibrosarcoma, leiomyosarcoma and other soft tissue sarcomas in adults. Since GD2 expression in normal tissues is restricted to the brain, which is inaccessible to circulating antibodies, and in selected peripheral nerves and melanocytes, it was deemed a suitable target for systemic tumor immunotherapy. Anti-GD2 antibodies have been actively tested in clinical trials for neuroblastoma for over the past two decades, with proven safety and efficacy. The main limitations have been acute pain toxicity associated with GD2 expression on peripheral nerve fibers and the inability of antibodies to treat bulky tumor. Several strategies have been developed to reduce pain toxicity, including bypassing complement activation, using blocking antibodies, or targeting of O-acetyl-GD2 derivative that is not expressed on peripheral nerves. To enhance anti-tumor efficacy, anti-GD2 monoclonal antibodies and fragments have been engineered into immunocytokines, immunotoxins, antibody drug conjugates, radiolabeled antibodies, targeted nanoparticles, T-cell engaging bispecific antibodies, and chimeric antigen receptors. The challenges of these approaches will be reviewed to build a perspective for next generation anti-GD2 therapeutics in cancer therapy.