A Frizzled-Like Cysteine-Rich Domain in Glypican-3 Mediates Wnt Binding and Regulates Hepatocellular Carcinoma Tumor Growth in Mice

The Glypican proteoglycans show intrinsic interactions with Wnt-3a in human prostate cancer cells that are not always associated with cascade activation

Background

Prostate cancer occurs through multiple steps until advanced metastasis. Signaling pathways studies can result in the identification of targets to interrupt cancer progression. Glypicans are cell surface proteoglycans linked to the membrane through glycosylphosphatidylinositol. Their interaction with specific ligands has been reported to trigger diverse signaling, including Wnt. In this study, prostate cancer cell lines PC-3, DU-145, and LNCaP were compared to normal prostate RWPE-1 cell line to investigate glypican family members and the activation of the Wnt signaling pathway.

Results

Glypican-1 (GPC1) was highly expressed in all the examined cell lines, except for LNCaP, which expressed glypican-5 (GPC5). The subcellular localization of GPC1 was detected on the cell surface of RWPE-1, PC-3, and DU-145 cell lines, while GPC5 suggested cytoplasm localization in LNCaP cells. Besides glypican, flow cytometry analysis in these prostate cell lines confirmed the expression of Wnt-3a and unphosphorylated β-catenin. The co-immunoprecipitation assay revealed increased levels of binding between Wnt-3a and glypicans in cancer cells, suggesting a relationship between these proteoglycans in this pathway. A marked increase in nuclear β-catenin was observed in tumor cells. However, only PC-3 cells demonstrated activation of canonical Wnt signaling, according to the TOPFLASH assay.

Conclusions

GPC1 was the majorly expressed gene in all the studied cell lines, except for LNCaP, which expressed GPC5. We assessed by co-immunoprecipitation that these GPCs could interact with Wnt-3a. However, even though nuclear β-catenin was found increased in the prostate cancer cells (i.e., PC-3, DU-145 and LNCaP), activation of Wnt pathway was only found in PC-3 cells. In these PC-3 cells, GPC1 and Wnt-3a revealed high levels of colocalization, as assessed by confocal microscopy studies. This suggests a localization at the cellular surface, where Frizzled receptor is required for downstream activation. The interaction of Wnt-3a with GPCs in DU-145 and LNCaP cells, which occurs in absence of Wnt signaling activation, requires further studies. Once non-TCF-LEF proteins can also bind β-catenin, another signaling pathway may be involved in these cells with regulatory function.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12860-021-00361-x.

Shed antigen-induced blocking effect on CAR-T cells targeting Glypican-3 in Hepatocellular Carcinoma

BACKGROUND

Glypican-3 (GPC3), a cell surface glycoprotein that is pathologically highly expressed in hepatocellular carcinoma (HCC), is an attractive target for immunotherapies, including chimeric antigen receptor (CAR) T cells. The serum GPC3 is frequently elevated in HCC patients due to the shedding effect of cell surface GPC3. The shed GPC3 (sGPC3) is reported to block the function of cell-surface GPC3 as a negative regulator. Therefore, it would be worth investigating the potential influence of antigen shedding in anti-GPC3 CAR-T therapy for HCC.

METHODS

In this study, we constructed two types of CAR-T cells targeting distinct epitopes of GPC3 to examine how sGPC3 influences the activation and cytotoxicity of CAR-T cells in vitro and in vivo by introducing sGPC3 positive patient serum or recombinant sGPC3 proteins into HCC cells or by using sGPC3-overexpressing HCC cell lines.

RESULTS

Both humanized YP7 CAR-T cells and 32A9 CAR-T cells showed GPC3-specific antitumor functions in vitro and in vivo. The existence of sGPC3 significantly inhibited the release of cytokines and the cytotoxicity of anti-GPC3 CAR-T cells in vitro. In animal models, mice carrying Hep3B xenograft tumors expressing sGPC3 exhibited a worse response to the treatment with CAR-T cells under both a low and high tumor burden. sGPC3 bound to CAR-T cells but failed to induce the effective activation of CAR-T cells. Therefore, sGPC3 acted as dominant negative regulators when competed with cell surface GPC3 to bind anti-GPC3 CAR-T cells, leading to an inhibitory effect on CAR-T cells in HCC.

CONCLUSIONS

We provide a proof-of-concept study demonstrating that GPC3 shedding might cause worse response to CAR-T cell treatment by competing with cell surface GPC3 for CAR-T cell binding, which revealed a new mechanism of tumor immune escape in HCC, providing a novel biomarker for patient enrolment in future clinical trials and/or treatments with GPC3-targeted CAR-T cells.

Syndecan receptors: pericellular regulators in development and inflammatory disease

The syndecans are the major family of transmembrane proteoglycans, usually bearing multiple heparan sulfate chains. They are present on virtually all nucleated cells of vertebrates and are also present in invertebrates, indicative of a long evolutionary history. Genetic models in both vertebrates and invertebrates have shown that syndecans link to the actin cytoskeleton and can fine-tune cell adhesion, migration, junction formation, polarity and differentiation. Although often associated as co-receptors with other classes of receptors (e.g. integrins, growth factor and morphogen receptors), syndecans can nonetheless signal to the cytoplasm in discrete ways. Syndecan expression levels are upregulated in development, tissue repair and an array of human diseases, which has led to the increased appreciation that they may be important in pathogenesis not only as diagnostic or prognostic agents, but also as potential targets. Here, their functions in development and inflammatory diseases are summarized, including their potential roles as conduits for viral pathogen entry into cells.

Comparative two-dimensional GPC3 overexpressing SK-Hep1 cell membrane chromatography /C18/ time-of-flight mass spectrometry for screening selective GPC3 inhibitor components from Scutellariae Radix

Screening active components targeting membrane proteins is important for drug discovery from traditional Chinese medicine. Cell membrane chromatography (CMC) has achieved a wide application in screening active components on pathological cells due to its high sensitivity and effectiveness. However, it is hard to clarify the specific target protein through simply using pathological and normal cells. In this study, a novel comparative two-dimensional (2D) cell membrane chromatography system was established. Based on the construction of hepatocellular carcinoma cell line SK-Hep1-GPC3 with high expression of protein Glypican-3 (GPC3), SK-Hep1-GPC3/CMC column was loaded to screen selective antitumor components from Scutellariae Radix according to the retention behaviors on column. Viscidulin I was retained on SK-Hep1-GPC3/CMC column, and showed 4.33 μM affinity to GPC3 according to surface plasmon resonance (SPR). The IC₅₀ of viscidulin I on SK-Hep1-GPC3 cells was 18.01 μM in cell proliferation assay. Thus, this method can be applied to screen complex herbal medicines for ligands bound to specific target protein receptor related to hepatic carcinoma.

Identification of the atypical cadherin FAT1 as a novel glypican-3 interacting protein in liver cancer cells

Glypican-3 (GPC3) is a cell surface heparan sulfate proteoglycan that is being evaluated as an emerging therapeutic target in hepatocellular carcinoma (HCC). GPC3 has been shown to interact with several extracellular signaling molecules, including Wnt, HGF, and Hedgehog. Here, we reported a cell surface transmembrane protein (FAT1) as a new GPC3 interacting protein. The GPC3 binding region on FAT1 was initially mapped to the C-terminal region (Q14517, residues 3662-4181), which covered a putative receptor tyrosine phosphatase (RTP)-like domain, a Laminin G-like domain, and five EGF-like domains. Fine mapping by ELISA and flow cytometry showed that the last four EGF-like domains (residues 4013-4181) contained a specific GPC3 binding site, whereas the RTP domain (residues 3662-3788) and the downstream Laminin G-2nd EGF-like region (residues 3829-4050) had non-specific GPC3 binding. In support of their interaction, GPC3 and FAT1 behaved concomitantly or at a similar pattern, e.g. having elevated expression in HCC cells, being up-regulated under hypoxia conditions, and being able to regulate the expression of EMT-related genes Snail, Vimentin, and E-Cadherin and promoting HCC cell migration. Taken together, our study provides the initial evidence for the novel mechanism of GPC3 and FAT1 in promoting HCC cell migration.

Beta-catenin activation and immunotherapy resistance in hepatocellular carcinoma: mechanisms and biomarkers

Mutations involving CTNNB1, the gene encoding beta-catenin, and other molecular alterations that affect the Wnt/beta-catenin signaling pathway are exceptionally common in hepatocellular carcinoma. Several of these alterations have also been associated with scarcity of immune cells in the tumor microenvironment and poor clinical response to immune checkpoint inhibitor therapy. In light of these associations, tumor biomarkers of beta-catenin status could have the potential to serve as clinical predictors of immunotherapy outcome. This editorial review article summarizes recent pre-clinical and clinical research pertaining to associations between beta-catenin activation and diminished anti-tumor immunity. Potential non-invasive biomarkers that may provide a window into this oncogenic mechanism of immune evasion are also presented and discussed.

Liver regeneration: biological and pathological mechanisms and implications

The liver is the only solid organ that uses regenerative mechanisms to ensure that the liver-to-bodyweight ratio is always at 100% of what is required for body homeostasis. Other solid organs (such as the lungs, kidneys and pancreas) adjust to tissue loss but do not return to 100% of normal. The current state of knowledge of the regenerative pathways that underlie this 'hepatostat' will be presented in this Review. Liver regeneration from acute injury is always beneficial and has been extensively studied. Experimental models that involve partial hepatectomy or chemical injury have revealed extracellular and intracellular signalling pathways that are used to return the liver to equivalent size and weight to those prior to injury. On the other hand, chronic loss of hepatocytes, which can occur in chronic liver disease of any aetiology, often has adverse consequences, including fibrosis, cirrhosis and liver neoplasia. The regenerative activities of hepatocytes and cholangiocytes are typically characterized by phenotypic fidelity. However, when regeneration of one of the two cell types fails, hepatocytes and cholangiocytes function as facultative stem cells and transdifferentiate into each other to restore normal liver structure. Liver recolonization models have demonstrated that hepatocytes have an unlimited regenerative capacity. However, in normal liver, cell turnover is very slow. All zones of the resting liver lobules have been equally implicated in the maintenance of hepatocyte and cholangiocyte populations in normal liver.

Glypican-3: A molecular marker for the detection and treatment of hepatocellular carcinoma☆

Hepatocellular carcinoma (HCC) is a malignant tumor with a fairly poor prognosis (5-year survival of less than 50%). Using sorafenib, the only food and drug administration (FDA)-approved drug, HCC cannot be effectively treated; it can only be controlled at most for a couple of months. There is a great need to develop efficacious treatment against this debilitating disease. Glypican-3 (GPC3), a member of the glypican family that attaches to the cell surface by a glycosylphosphatidylinositol anchor, is overexpressed in HCC cases and is elevated in the serum of a large proportion of patients with HCC. GPC3 expression contributes to HCC growth and metastasis. Furthermore, several different types of antibodies targeting GPC3 have been developed. The aim of this review is to summarize the current literatures on the GPC3 expression in human HCC, molecular mechanisms of GPC3 regulation and antibodies targeting GPC3.

Assembling custom side chains on proteoglycans to interrogate their function in living cells

Proteoglycans (PGs) are composed of a core protein and one or more chains of glycosaminoglycans (GAGs). The highly heterogeneous GAG chains play an irreplaceable role in the functions of PGs. However, the lack of an approach to control the exact structure of GAG chains conjugated to PGs tremendously hinders functional studies of PGs. Herein, by using glypican-3 as a model, we establish an aldehyde tag-based approach to assemble PGs with specific GAG chains on the surface of living cells. We show that the engineered glypican-3 can regulate Wnt and Hedgehog signaling like the wild type. Furthermore, we also present a method for studying the interaction of PGs with their target glycoproteins by combining the assembly of PGs carrying specific GAG chains with metabolic glycan labeling, and most importantly, we obtain evidence of GPC3 directly interacting with Frizzled. In conclusion, this study provides a very useful platform for structural and functional studies of PGs with specific GAG chains.

Currently, it is not possible to generate proteoglycans displaying glycosaminoglycan chains with specific structures. Here the authors show that by using an aldehyde tag-based methodology it is possible to insert these specific chains onto proteoglycans expressed on the cell surface.

Generation of fully human anti-GPC3 antibodies with high-affinity recognition of GPC3 positive tumors

The acceleration of therapeutic antibody development has been motivated by the benefit to and their demand for human health. In particular, humanized transgenic antibody discovery platforms, combined with immunization, hybridoma fusion and/or single cell DNA sequencing are the most reliable and rapid methods for mining the human monoclonal antibodies. Human GPC3 protein is an oncofetal antigen, and it is highly expressed in most hepatocellular carcinomas and some types of squamous cell carcinomas. Currently, no fully human anti-GPC3 therapeutic antibodies have been reported and evaluated in extensive tumor tissues. Here, we utilized a new humanized transgenic mouse antibody discovery platform (CAMouse) that contains large V(D)J -regions and human gamma-constant regions of human immunoglobulin in authentic configurations to generate fully human anti-GPC3 antibodies. Our experiments resulted in four anti-GPC3 antibodies with high-specific binding and cytotoxicity to GPC3 positive cancer cells, and the antibody affinities are in the nanomolar range. Immunohistochemistry analysis demonstrated that these antibodies can recognize GPC3 protein on many types of solid tumors. In summary, the human anti-human GPC3 monoclonal antibodies described here are leading candidates for further preclinical studies of cancer therapy, further, the CAMouse platform is a robust tool for human therapeutic antibody discovery.

The Role of Proteoglycans in Cancer Metastasis and Circulating Tumor Cell Analysis

Circulating tumor cells (CTCs) are accessible by liquid biopsies via an easy blood draw. They represent not only the primary tumor site, but also potential metastatic lesions, and could thus be an attractive supplement for cancer diagnostics. However, the analysis of rare CTCs in billions of normal blood cells is still technically challenging and novel specific CTC markers are needed. The formation of metastasis is a complex process supported by numerous molecular alterations, and thus novel CTC markers might be found by focusing on this process. One example of this is specific changes in the cancer cell glycocalyx, which is a network on the cell surface composed of carbohydrate structures. Proteoglycans are important glycocalyx components and consist of a protein core and covalently attached long glycosaminoglycan chains. A few CTC assays have already utilized proteoglycans for both enrichment and analysis of CTCs. Nonetheless, the biological function of proteoglycans on clinical CTCs has not been studied in detail so far. Therefore, the present review describes proteoglycan functions during the metastatic cascade to highlight their importance to CTCs. We also outline current approaches for CTC assays based on targeting proteoglycans by their protein cores or their glycosaminoglycan chains. Lastly, we briefly discuss important technical aspects, which should be considered for studying proteoglycans.

Roles of Proteoglycans and Glycosaminoglycans in Cancer Development and Progression

The extracellular matrix (ECM) spatiotemporally controls cell fate; however, dysregulation of ECM remodeling can lead to tumorigenesis and cancer development by providing favorable conditions for tumor cells. Proteoglycans (PGs) and glycosaminoglycans (GAGs) are the major macromolecules composing ECM. They influence both cell behavior and matrix properties through direct and indirect interactions with various cytokines, growth factors, cell surface receptors, adhesion molecules, enzymes, and glycoproteins within the ECM. The classical features of PGs/GAGs play well-known roles in cancer angiogenesis, proliferation, invasion, and metastasis. Several lines of evidence suggest that PGs/GAGs critically affect broader aspects in cancer initiation and the progression process, including regulation of cell metabolism, serving as a sensor of ECM's mechanical properties, affecting immune supervision, and participating in therapeutic resistance to various forms of treatment. These functions may be implemented through the characteristics of PGs/GAGs as molecular bridges linking ECM and cells in cell-specific and context-specific manners within the tumor microenvironment (TME). In this review, we intend to present a comprehensive illustration of the ways in which PGs/GAGs participate in and regulate several aspects of tumorigenesis; we put forward a perspective regarding their effects as biomarkers or targets for diagnoses and therapeutic interventions.

New Advances in Canonical Wnt/β-Catenin Signaling in Cancer

Wnt/β-catenin-mediated signaling is a key pathway regulating tissue growth and development, and tumorigenesis, and has received increasing attention in recent years. In addition to participating in healthy tissue and organ development, ectopic activation of the pathway can cause a variety of tumors and other pathologies. The pathway plays a critical role in many processes such as proliferation, differentiation, apoptosis, migration, invasion, epithelial–mesenchymal transition and cancer cell stemness. The importance of the Wnt signal is self-evident. This review describes the underlying mechanism of Wnt signaling pathway and highlights the latest findings on the relationship between Wnt signaling pathway and tumorigenesis. In addition, the potential relationship between miRNAs and Wnt signaling is presented. Furthermore, we discuss the intrinsic link between Wnt signaling and cancer cell stemness, which shed light on the malignant progression of tumor cells. Finally, cancer treatment strategies based on the canonical Wnt signaling pathway are summarized, hoping to help clinical development.

32A9, a novel human antibody for designing an immunotoxin and CAR-T cells against glypican-3 in hepatocellular carcinoma

Background

Treatment of hepatocellular carcinoma (HCC) using antibody-based targeted therapies, such as antibody conjugates and chimeric antigen receptor T (CAR-T) cell therapy, shows potent antitumor efficacy. Glypican-3 (GPC3) is an emerging HCC therapeutic target; therefore, antibodies against GPC3 would be useful tools for developing immunotherapies for HCC.

Methods

We isolated a novel human monoclonal antibody, 32A9, by phage display technology. We determined specificity, affinity, epitope and anti-tumor activity of 32A9, and developed 32A9-based immunotherapy technologies for evaluating the potency of HCC treatment in vitro or in vivo.

Results

32A9 recognized human GPC3 with potent affinity and specificity. The epitope of 32A9 was located in the region of the GPC3 protein core close to the modification sites of the HS chain and outside of the Wnt-binding site of GPC3. The 32A9 antibody significantly inhibited HCC xenograft tumor growth in vivo. We then pursued two 32A9-based immunotherapeutic strategies by constructing an immunotoxin and CAR-T cells. The 32A9 immunotoxin exhibited specific cytotoxicity to GPC3-positive cancer cells, while 32A9 CAR-T cells efficiently eliminated GPC3-positive HCC cells in vitro and caused HCC xenograft tumor regressions in vivo.

Conclusions

Our study provides a rationale for 32A9 as a promising GPC3-specific antibody candidate for HCC immunotherapy.

Glucometabolic Reprogramming in the Hepatocellular Carcinoma Microenvironment: Cause and Effect

Hepatocellular carcinoma (HCC) is a tumor that exhibits glucometabolic reprogramming, with a high incidence and poor prognosis. Usually, HCC is not discovered until an advanced stage. Sorafenib is almost the only drug that is effective at treating advanced HCC, and promising metabolism-related therapeutic targets of HCC are urgently needed. The “Warburg effect” illustrates that tumor cells tend to choose aerobic glycolysis over oxidative phosphorylation (OXPHOS), which is closely related to the features of the tumor microenvironment (TME). The HCC microenvironment consists of hypoxia, acidosis and immune suppression, and contributes to tumor glycolysis. In turn, the glycolysis of the tumor aggravates hypoxia, acidosis and immune suppression, and leads to tumor proliferation, angiogenesis, epithelial–mesenchymal transition (EMT), invasion and metastasis. In 2017, a mechanism underlying the effects of gluconeogenesis on inhibiting glycolysis and blockading HCC progression was proposed. Treating HCC by increasing gluconeogenesis has attracted increasing attention from scientists, but few articles have summarized it. In this review, we discuss the mechanisms associated with the TME, glycolysis and gluconeogenesis and the current treatments for HCC. We believe that a treatment combination of sorafenib with TME improvement and/or anti-Warburg therapies will set the trend of advanced HCC therapy in the future.

The Role of Glypicans in Cancer Progression and Therapy

Glypicans are a family of heparan sulfate proteoglycans that are attached to the cell membrane via a glycosylphosphatidylinositol anchor. Glypicans interact with multiple ligands, including morphogens, growth factors, chemokines, ligands, receptors, and components of the extracellular matrix through their heparan sulfate chains and core protein. Therefore, glypicans can function as coreceptors to regulate cell proliferation, cell motility, and morphogenesis. In addition, some glypicans are abnormally expressed in cancers, possibly involved in tumorigenesis, and have the potential to be cancer-specific biomarkers. Here, we provide a brief review focusing on the expression of glypicans in various cancers and their potential to be targets for cancer therapy.

Development of Glypican-3 Targeting Immunotoxins for the Treatment of Liver Cancer: An Update

Hepatocellular carcinoma (HCC) accounts for most liver cancers and represents one of the deadliest cancers in the world. Despite the global demand for liver cancer treatments, there remain few options available. The U.S. Food and Drug Administration (FDA) recently approved Lumoxiti, a CD22-targeting immunotoxin, as a treatment for patients with hairy cell leukemia. This approval helps to demonstrate the potential role that immunotoxins can play in the cancer therapeutics pipeline. However, concerns have been raised about the use of immunotoxins, including their high immunogenicity and short half-life, in particular for treating solid tumors such as liver cancer. This review provides an overview of recent efforts to develop a glypican-3 (GPC3) targeting immunotoxin for treating HCC, including strategies to deimmunize immunotoxins by removing B- or T-cell epitopes on the bacterial toxin and to improve the serum half-life of immunotoxins by incorporating an albumin binding domain.

Persistent Polyfunctional Chimeric Antigen Receptor T Cells That Target Glypican 3 Eliminate Orthotopic Hepatocellular Carcinomas in Mice

BACKGROUND AND AIMS

Glypican 3 (GPC3) is an oncofetal antigen involved in Wnt-dependent cell proliferation that is highly expressed in hepatocellular carcinoma (HCC). We investigated whether the functions of chimeric antigen receptors (CARs) that target GPC3 are affected by their antibody-binding properties.

METHODS

We collected peripheral blood mononuclear cells from healthy donors and patients with HCC and used them to create CAR T cells, based on the humanized YP7 (hYP7) and HN3 antibodies, which have high affinities for the C-lobe and N-lobe of GPC3, respectively. NOD/SCID/IL-2Rgcnull (NSG) mice were given intraperitoneal injections of luciferase-expressing (Luc) Hep3B or HepG2 cells and after xenograft tumors formed, mice were given injections of saline or untransduced T cells (mock control), or CAR (HN3) T cells or CAR (hYP7) T cells. In other NOD/SCID/IL-2Rgcnull (NSG) mice, HepG2-Luc or Hep3B-Luc cells were injected into liver, and after orthotopic tumors formed, mice were given 1 injection of CAR (hYP7) T cells or CD19 CAR T cells (control). We developed droplet digital polymerase chain reaction and genome sequencing methods to analyze persistent CAR T cells in mice.

RESULTS

Injections of CAR (hYP7) T cells eliminated tumors in 66% of mice by week 3, whereas CAR (HN3) T cells did not reduce tumor burden. Mice given CAR (hYP7) T cells remained tumor free after re-challenge with additional Hep3B cells. The CAR T cells induced perforin- and granzyme-mediated apoptosis and reduced levels of active β-catenin in HCC cells. Mice injected with CAR (hYP7) T cells had persistent expansion of T cells and subsets of polyfunctional CAR T cells via antigen-induced selection. These T cells were observed in the tumor microenvironment and spleen for up to 7 weeks after CAR T-cell administration. Integration sites in pre-infusion CAR (HN3) and CAR (hYP7) T cells were randomly distributed, whereas integration into NUPL1 was detected in 3.9% of CAR (hYP7) T cells 5 weeks after injection into tumor-bearing mice and 18.1% of CAR (hYP7) T cells at week 7. There was no common site of integration in CAR (HN3) or CD19 CAR T cells from tumor-bearing mice.

CONCLUSIONS

In mice with xenograft or orthoptic liver tumors, CAR (hYP7) T cells eliminate GPC3-positive HCC cells, possibly by inducing perforin- and granzyme-mediated apoptosis or reducing Wnt signaling in tumor cells. GPC3-targeted CAR T cells might be developed for treatment of patients with HCC.

Engineered Anti-GPC3 Immunotoxin, HN3-ABD-T20, Produces Regression in Mouse Liver Cancer Xenografts Through Prolonged Serum Retention

BACKGROUND AND AIMS

Treatment of hepatocellular carcinomas using our glypican-3 (GPC3)-targeting human nanobody (HN3) immunotoxins causes potent tumor regression by blocking protein synthesis and down-regulating the Wnt signaling pathway. However, immunogenicity and a short serum half-life may limit the ability of immunotoxins to transition to the clinic.

APPROACH AND RESULTS

To address these concerns, we engineered HN3-based immunotoxins to contain various deimmunized Pseudomonas exotoxin (PE) domains. This included HN3-T20, which was modified to remove T-cell epitopes and contains a PE domain II truncation. We compared them to our previously reported B-cell deimmunized immunotoxin (HN3-mPE24) and our original HN3-immunotoxin with a wild-type PE domain (HN3-PE38). All of our immunotoxins displayed high affinity to human GPC3, with HN3-T20 having a KD value of 7.4 nM. HN3-T20 retained 73% enzymatic activity when compared with the wild-type immunotoxin in an adenosine diphosphate-ribosylation assay. Interestingly, a real-time cell growth inhibition assay demonstrated that a single dose of HN3-T20 at 62.5 ng/mL (1.6 nM) was capable of inhibiting nearly all cell proliferation during the 10-day experiment. To enhance HN3-T20's serum retention, we tested the effect of adding a streptococcal albumin-binding domain (ABD) and a llama single-domain antibody fragment specific for mouse and human serum albumin. For the detection of immunotoxin in mouse serum, we developed a highly sensitive enzyme-linked immunosorbent assay and found that HN3-ABD-T20 had a 45-fold higher serum half-life than HN3-T20 (326 minutes vs. 7.3 minutes); consequently, addition of an ABD resulted in HN3-ABD-T20-mediated tumor regression at 1 mg/kg.

CONCLUSION

These data indicate that ABD-containing deimmunized HN3-T20 immunotoxins are high-potency therapeutics ready to be evaluated in clinical trials for the treatment of liver cancer.

Tumor Microenvironment: Extracellular Matrix Alterations Influence Tumor Progression

The tumor microenvironment (TME) is composed of various cell types embedded in an altered extracellular matrix (ECM). ECM not only serves as a support for tumor cell but also regulates cell-cell or cell-matrix cross-talks. Alterations in ECM may be induced by hypoxia and acidosis, by oxygen free radicals generated by infiltrating inflammatory cells or by tumor- or stromal cell-secreted proteases. A poorer diagnosis for patients is often associated with ECM alterations. Tumor ECM proteome, also named cancer matrisome, is strongly altered, and different ECM protein signatures may be defined to serve as prognostic biomarkers. Collagen network reorganization facilitates tumor cell invasion. Proteoglycan expression and location are modified in the TME and affect cell invasion and metastatic dissemination. ECM macromolecule degradation by proteases may induce the release of angiogenic growth factors but also the release of proteoglycan-derived or ECM protein fragments, named matrikines or matricryptins. This review will focus on current knowledge and new insights in ECM alterations, degradation, and reticulation through cross-linking enzymes and on the role of ECM fragments in the control of cancer progression and their potential use as biomarkers in cancer diagnosis and prognosis.

Isolation of rabbit single domain antibodies to B7-H3 via protein immunization and phage display

Single domain antibodies have certain advantages including their small size, high stability and excellent tissue penetration, making them attractive drug candidates. Rabbit antibodies can recognize diverse epitopes, including those that are poorly immunogenic in mice and humans. In the present study, we established a method to isolate rabbit VH single domain antibodies for potential cancer therapy. We immunized rabbits with recombinant human B7-H3 (CD276) protein, made a phage-displayed rabbit VH single domain library with a diversity of 7 × 10⁹, and isolated two binders (A1 and B1; also called RFA1 and RFB1) from phage panning. Both rabbit VH single domains exhibited antigen-dependent binding to B7-H3-positive tumor cell lines but not B7-H3 knockout tumor cell lines. Our study shows that protein immunization followed by phage display screening can be used to isolate rabbit single domain antibodies. The two single domain antibodies reported here may have potential applications in cancer immunotherapy.

Ancient species offers contemporary therapeutics: an update on shark VNAR single domain antibody sequences, phage libraries and potential clinical applications

The antigen binding variable domain (VNAR) of the shark immunoglobulin new antigen receptor (IgNAR) evolved approximately 500 million years ago and it is one of the smallest antibody fragments in the animal kingdom with sizes of 12-15 kDa. This review discusses the current knowledge of the shark VNAR single domain sequences and ongoing development of shark VNARs as research tools as well as potential therapeutics, in particular highlighting the recent next-generation sequencing analysis of 1.2 million shark VNAR sequences and construction of a large phage displayed shark VNAR library from six naïve adult nurse sharks (Ginglymostoma cirratum). The large phage-displayed VNAR single domain library covers all the four known VNAR types (Types I-IV) and many previously unknown types. Ongoing preclinical development will help define the utility of shark VNAR single domains as a potentially new family of drug candidates for treating cancer and other human diseases.

Next-Generation Antibody Therapeutics: Discovery, Development and Beyond: highlights of the third annual conference of the Chinese Antibody Society

The Chinese Antibody Society (CAS) convened the third annual conference in Cambridge, Massachusetts, USA on April 7, 2019. More than 600 global members attended the meeting. The theme of this conference was Next-Generation Antibody Therapeutics: Discovery, Development and Beyond. The meeting covered a vast variety of topics including cancer immunotherapy, single-domain antibodies as well as bispecific antibodies, immunotoxins, transgenic mouse platforms for next-generation monoclonal antibody discovery and antibody chemistry, manufacturing and controls (CMCs). Two hot topics were comprehensively discussed by the prestigious panelists and hosts at the panel discussions during the conferences, i.e., bispecific antibodies and antibody CMC.

Statement of Significance: The Chinese Antibody Society convened the third annual conference in Cambridge, Massachusetts, USA on 7 April 2019. The meeting covered a variety of topics, including cancer immunotherapy, single-domain antibody, bispecific antibody, immunotoxin, transgenic mouse platforms for next-generation monoclonal antibody discovery and antibody CMC.

Cobalt Chloride Induced Apoptosis by Inhibiting GPC3 Expression via the HIF-1α/c-Myc Axis in HepG2 Cells

Purpose

To investigate the role of glypican-3 (GPC3) in cobalt chloride (CoCl₂)-induced cell apoptosis in hepatocellular carcinoma.

Methods

HepG2 cells were treated with CoCl₂ in the absence or presence of GPC3 plasmid transfection. Cell viability and apoptosis were assessed by MTT assay and flow cytometry, respectively. The expression of GPC3, hypoxia-inducible factor 1α (HIF-1α), c-myc, sp1, poly-ADP-ribose polymerase (PARP) and caspase-3 was determined by real-time PCR, Western blotting, and immunofluorescence after the cells were treated with different concentrations of CoCl₂ or siRNA targeting HIF-1α.

Results

CoCl₂ significantly inhibited the proliferation of HepG2 cells and induced apoptosis. Additionally, the expression of GPC3 mRNA and protein was decreased, and overexpression of GPC3 attenuated the tumour inhibiting effects. Further studies showed that CoCl₂ increased the expression of HIF-1α while reducing the expression of sp1 and c-myc; knockdown of HIF-1α elevated the expression of GPC3, sp1, and c-myc.

Conclusion

CoCl₂ inhibited the growth of HepG2 cells through downregulation of GPC3 expression via the HIF-1α/c-myc axis.

Glypican-6 stimulates intestinal elongation by simultaneously regulating Hedgehog and non-canonical Wnt signaling

We report here that Glypican-6 (GPC6)-null mice display at birth small intestines that are 75% shorter than those of normal littermates. Notably, we demonstrate that the role of GPC6 in intestinal elongation is mediated by both Hedgehog (Hh) and non-canonical Wnt signaling. Based on results from in vitro experiments, we had previously proposed that GPC6 stimulates Hh signaling by interacting with Hh and Patched1 (Ptc1), and facilitating/stabilizing their interaction. Here we provide strong support to this hypothesis by showing that GPC6 binds to Ptc1 in the mesenchymal layer of embryonic intestines. This study also provides experimental evidence that strongly suggests that GPC6 inhibits the activity of Wnt5a on the intestinal epithelium by binding to this growth factor, and reducing its release from the surrounding mesenchymal cells. Finally, we show that whereas the mesenchymal layer of GPC6-null intestines displays reduced cell proliferation and a thinner smooth muscle layer, epithelial cell differentiation is not altered in the mutant gut.

Glypican 3-Targeted Therapy in Hepatocellular Carcinoma

Glypican-3 (GPC3) is an oncofetal glycoprotein attached to the cell membrane by a glycophosphatidylinositol anchor. GPC3 is overexpressed in some kinds of tumors, particularly hepatocellular carcinoma (HCC). The prognostic significance of serum GPC3 levels and GPC3 immunoreactivity in tumor cells has been defined in patients with HCC. In addition to its usefulness as a biomarker, GPC3 has attracted attention as a novel therapeutic target molecule, and clinical trials targeting GPC3 are in progress. The major mechanism of anti-GPC3 antibody (GPC3Ab) against cancer cells is antibody-dependent cellular cytotoxicity and/or complement-dependent cytotoxicity. Since GPC3Ab is associated with immune responses, a combination of protocols with immune checkpoint inhibitors has also been investigated. Moreover, some innovative approaches for GPC3-targeting therapy have emerged in recent years. This review introduces the results of recent clinical trials targeting GPC3 in HCC and summarizes the latest knowledge regarding the role of GPC3 in HCC progression and clinical application targeting GPC3.

The Role of Glypican-3 in Regulating Wnt, YAP, and Hedgehog in Liver Cancer

Glypican-3 (GPC3) is a cell-surface glycoprotein consisting of heparan sulfate glycosaminoglycan chains and an inner protein core. It has important functions in cellular signaling including cell growth, embryogenesis, and differentiation. GPC3 has been linked to hepatocellular carcinoma and a few other cancers, however, the mechanistic role of GPC3 in cancer development remains elusive. Recent breakthroughs including the structural modeling of GPC3 and GPC3-Wnt complexes represent important steps toward deciphering the molecular mechanism of action for GPC3 and how it may regulate cancer signaling and tumor growth. A full understanding of the molecular basis of GPC3-mediated signaling requires elucidation of the dynamics of partner receptors, transducer complexes, and downstream players. Herein, we summarize current insights into the role of GPC3 in regulating cancer development through Wnt and other signaling pathways, including YAP and hedgehog cascades. We also highlight the growing body of work which underlies deciphering how GPC3 is a key player in liver oncogenesis.