Humanisation of a claudin-1-specific monoclonal antibody for clinical prevention and cure of HCV infection without escape

Tight Junctions, the Key Factor in Virus-Related Disease

Tight junctions (TJs) are highly specialized membrane structural domains that hold cells together and form a continuous intercellular barrier in epithelial cells. TJs regulate paracellular permeability and participate in various cellular signaling pathways. As physical barriers, TJs can block viral entry into host cells; however, viruses use a variety of strategies to circumvent this barrier to facilitate their infection. This paper summarizes how viruses evade various barriers during infection by regulating the expression of TJs to facilitate their own entry into the organism causing infection, which will help to develop drugs targeting TJs to contain virus-related disease.

Targeting claudins in cancer: diagnosis, prognosis and therapy

Increasing evidence has linked claudins to signal transduction and tumorigenesis. The expression of claudins is frequently dysregulated in the context of neoplastic transformation, suggesting their promise as biomarkers for diagnosis and prognosis or targets for treatment. Claudin binders (Clostridium perfringens enterotoxin and monoclonal antibody) have been tested in preclinical experiments, and some of them have progressed into clinical trials involving patients with certain cancers. However, the clinical development of many of these agents has not advanced to clinical applications. Herein, I review the current status of preclinical and clinical investigations of agents targeting claudins for diagnosis, prognosis and therapy. I also discuss the potential of combining claudin binders with other currently approved therapeutic agents.

Identification of Interferon Receptor IFNAR2 As a Novel HCV Entry Factor by Using Chemical Probes

Upon sensing pathogen-associated patterns and secreting interferons (IFNs) into the environment, host cells perceive extracellular type I IFNs by the IFNα/β receptors IFNAR1 and IFNAR2 to stimulate downstream innate immune signaling cascades. Through the use of chemical probes, we demonstrated that IFNAR2 facilitates hepatitis C virus (HCV) entry. Silencing of IFNAR2 significantly attenuated HCV proliferation. IFNAR2 binds infectious HCV virions through a direct interaction of its D2 domain with the C-terminal end of apolipoprotein E (apoE) on the viral envelope and facilitates virus entry into host cells. The antibody against the IFNAR2 D2 domain attenuates IFNAR2-apoE interaction and impairs HCV infection. The recombinant IFNAR2 protein and the chemical probe potently inhibit major HCV genotypes in various human liver cells in vitro. Moreover, the impact of a chemical probe on HCV genotype 2a is also documented in immune-compromised humanized transgenic mice. Our results not only expand the understanding of the biology of HCV entry and the virus-host relationship but also reveal a new target for the development of anti-HCV entry inhibitors.

Hepatitis C Virus Entry: An Intriguingly Complex and Highly Regulated Process

Hepatitis C virus (HCV) is a major cause of chronic hepatitis and liver disease worldwide. Its tissue and species tropism are largely defined by the viral entry process that is required for subsequent productive viral infection and establishment of chronic infection. This review provides an overview of the viral and host factors involved in HCV entry into hepatocytes, summarizes our understanding of the molecular mechanisms governing this process and highlights the therapeutic potential of host-targeting entry inhibitors.

Tight Junction Proteins and the Biology of Hepatobiliary Disease

Tight junctions (TJ) are intercellular adhesion complexes on epithelial cells and composed of integral membrane proteins as well as cytosolic adaptor proteins. Tight junction proteins have been recognized to play a key role in health and disease. In the liver, TJ proteins have several functions: they contribute as gatekeepers for paracellular diffusion between adherent hepatocytes or cholangiocytes to shape the blood-biliary barrier (BBIB) and maintain tissue homeostasis. At non-junctional localizations, TJ proteins are involved in key regulatory cell functions such as differentiation, proliferation, and migration by recruiting signaling proteins in response to extracellular stimuli. Moreover, TJ proteins are hepatocyte entry factors for the hepatitis C virus (HCV)—a major cause of liver disease and cancer worldwide. Perturbation of TJ protein expression has been reported in chronic HCV infection, cholestatic liver diseases as well as hepatobiliary carcinoma. Here we review the physiological function of TJ proteins in the liver and their implications in hepatobiliary diseases.

Role of Claudin Proteins in Regulating Cancer Stem Cells and Chemoresistance-Potential Implication in Disease Prognosis and Therapy

Claudins are cell–cell adhesion proteins, which are expressed in tight junctions (TJs), the most common apical cell-cell adhesion. Claudin proteins help to regulate defense and barrier functions, as well as differentiation and polarity in epithelial and endothelial cells. A series of studies have now reported dysregulation of claudin proteins in cancers. However, the precise mechanisms are still not well understood. Nonetheless, studies have clearly demonstrated a causal role of multiple claudins in the regulation of epithelial to mesenchymal transition (EMT), a key feature in the acquisition of a cancer stem cell phenotype in cancer cells. In addition, claudin proteins are known to modulate therapy resistance in cancer cells, a feature associated with cancer stem cells. In this review, we have focused primarily on highlighting the causal link between claudins, cancer stem cells, and therapy resistance. We have also contemplated the significance of claudins as novel targets in improving the efficacy of cancer therapy. Overall, this review provides a much-needed understanding of the emerging role of claudin proteins in cancer malignancy and therapeutic management.

Interferon-Induced Transmembrane Proteins Mediate Viral Evasion in Acute and Chronic Hepatitis C Virus Infection

Although adaptive immune responses against hepatitis C virus (HCV) infection have been studied in great detail, the role of innate immunity in protection against HCV infection and immune evasion is only partially understood. Interferon-induced transmembrane proteins (IFITMs) are innate effector proteins restricting host cell entry of many enveloped viruses, including HCV. However, the clinical impact of IFITMs on HCV immune escape remains to be determined. Here, we show that IFITMs promote viral escape from the neutralizing antibody (nAb) response in clinical cohorts of HCV-infected patients. Using pseudoparticles bearing HCV envelope proteins from acutely infected patients, we show that HCV variants isolated preseroconversion are more sensitive to the antiviral activity of IFITMs than variants from patients isolated during chronic infection postseroconversion. Furthermore, HCV variants escaping nAb responses during liver transplantation exhibited a significantly higher resistance to IFITMs than variants that were eliminated posttransplantation. Gain-of-function and mechanistic studies revealed that IFITMs markedly enhance the antiviral activity of nAbs and suggest a cooperative effect of human monoclonal antibodies and IFITMs for antibody-mediated neutralization driving the selection pressure in viral evasion. Perturbation studies with the IFITM antagonist amphotericin B revealed that modulation of membrane properties by IFITM proteins is responsible for the IFITM-mediated blockade of viral entry and enhancement of antibody-mediated neutralization. Conclusion: Our results indicate IFITM proteins as drivers of viral immune escape and antibody-mediated HCV neutralization in acute and chronic HCV infection. These findings are of clinical relevance for the design of urgently needed HCV B-cell vaccines and might help to increase the efficacy of future vaccine candidates.

Use of Modified Clostridium perfringens Enterotoxin Fragments for Claudin Targeting in Liver and Skin Cells

Claudins regulate paracellular permeability in different tissues. The claudin-binding domain of Clostridium perfringens enterotoxin (cCPE) is a known modulator of a claudin subset. However, it does not efficiently bind to claudin-1 (Cldn1). Cldn1 is a pharmacological target since it is (i) an essential co-receptor for hepatitis C virus (HCV) infections and (ii) a key element of the epidermal barrier limiting drug delivery. In this study, we investigated the potential of a Cldn1-binding cCPE mutant (i) to inhibit HCV entry into hepatocytes and (ii) to open the epidermal barrier. Inhibition of HCV infection by blocking of Cldn1 with cCPE variants was analyzed in the Huh7.5 hepatoma cell line. A model of reconstructed human epidermis was used to investigate modulation of the epidermal barrier by cCPE variants. In contrast to cCPEwt, the Cldn1-binding cCPE-S305P/S307R/S313H inhibited infection of Huh7.5 cells with HCV in a dose-dependent manner. In addition, TJ modulation by cCPE variant-mediated targeting of Cldn1 and Cldn4 opened the epidermal barrier in reconstructed human epidermis. cCPE variants are potent claudin modulators. They can be applied for mechanistic in vitro studies and might also be used as biologics for therapeutic claudin targeting including HCV treatment (host-targeting antivirals) and improvement of drug delivery.

Humanized Mouse Models for the Study of Hepatitis C and Host Interactions

Hepatitis C virus (HCV) infection is commonly attributed as a major cause of chronic hepatotropic diseases, such as, steatosis, cirrhosis and hepatocellular carcinoma. As HCV infects only humans and primates, its narrow host tropism hampers in vivo studies of HCV-mammalian host interactions and the development of effective therapeutics and vaccines. In this context, we will focus our discussion on humanized mice in HCV research. Here, these humanized mice are defined as animal models that encompass either only human hepatocytes or both human liver and immune cells. Aspects related to immunopathogenesis, anti-viral interventions, drug testing and perspectives of these models for future HCV research will be discussed.

Targeting claudin-4 enhances CDDP-chemosensitivity in gastric cancer

Claudins are major tight-junction proteins that mediate cellular polarity and differentiation. The present study investigated whether the 4D3 antibody to the human CLDN4 extracellular domain (that we previously established) is capable of modulating chemotherapeutic sensitivity in gastric cancer (GC). The results of the present study showed that CLDN4 was overexpressed in 137 of the 192 analyzed GC cases, and that CLDN4 expression was retained in tumors of a lower histological grade (more differentiated), and/or those that were caudal-type homeobox protein 2 (CDX2)-positive, but was reduced in more highly undifferentiated, and CDX2-negative GC cases. The study also compared the synergic effects of combining 4D3 with CDDP treatment and knocking down CLDN4 expression in MKN74 and TMK-1 human GC cells. Co-treatment with 4D3 increased anti-tumor effects of CDDP, whereas CLDN4 knockdown did not. In the TMK-1 cells, non-tight junction CLDN4 associated with integrin β1, increasing stem cell-associated proteins via FAK-c-SRC signals. The anti-tumoral effect of CDDP and 4D3 was examined in a nude mouse subcutaneous tumor model. In the two GC cell lines, concurrent treatment with 4D3 and CDDP synergistically inhibited cell proliferation and increased tumor necrosis and apoptosis to a greater degree than CDDP treatment alone. These findings suggest that 4D3 might increase chemotherapeutic sensitivity by evoking structural disintegration of tight-junction CLDN4 expressed in gastric cancer.

Tight junction proteins in gastrointestinal and liver disease

Over the past two decades a growing body of evidence has demonstrated an important role of tight junction (TJ) proteins in the physiology and disease biology of GI and liver disease. On one side, TJ proteins exert their functional role as integral proteins of TJs in forming barriers in the gut and the liver. Furthermore, TJ proteins can also be expressed outside TJs where they play important functional roles in signalling, trafficking and regulation of gene expression. A hallmark of TJ proteins in disease biology is their functional role in epithelial-to-mesenchymal transition. A causative role of TJ proteins has been established in the pathogenesis of colorectal cancer and gastric cancer. Among the best characterised roles of TJ proteins in liver disease biology is their function as cell entry receptors for HCV-one of the most common causes of hepatocellular carcinoma. At the same time TJ proteins are emerging as targets for novel therapeutic approaches for GI and liver disease. Here we review our current knowledge of the role of TJ proteins in the pathogenesis of GI and liver disease biology and discuss their potential as therapeutic targets.

In vivo combination of human anti-envelope glycoprotein E2 and -Claudin-1 monoclonal antibodies for prevention of hepatitis C virus infection

Despite the development of direct-acting antivirals (DAAs), hepatitis C virus (HCV) infection remains a major cause for liver disease and cancer worldwide. Entry inhibitors block virus host cell entry and, therefore, prevent establishment of chronic infection and liver disease. Due to their unique mechanism of action, entry inhibitors provide an attractive antiviral strategy in organ transplantation. In this study, we developed an innovative approach in preventing HCV infection using a synergistic combination of a broadly neutralizing human monoclonal antibody (HMAb) targeting the HCV E2 protein and a host-targeting anti-claudin 1 (CLDN1) humanized monoclonal antibody. An in vivo proof-of-concept study in human liver-chimeric FRG-NOD mice proved the efficacy of the combination therapy at preventing infection by an HCV genotype 1b infectious serum. While administration of individual antibodies at lower doses only showed a delay in HCV infection, the combination therapy was highly protective. Furthermore, the combination proved to be effective in preventing infection of primary human hepatocytes by neutralization-resistant HCV escape variants selected during liver transplantation, suggesting that a combination therapy is suited for the neutralization of difficult-to-treat variants. In conclusion, our findings suggest that the combination of two HMAbs targeting different steps of virus entry improves treatment efficacy while simultaneously reducing treatment duration and costs. Our approach not only provides a clinical perspective to employ HMAb combination therapies to prevent graft re-infection and its associated liver disease but may also help to alleviate the urgent demand for organ transplants by allowing the transplantation of organs from HCV-positive donors.

Introducing fluorescence guided surgery into orthopedic oncology: A systematic review of candidate protein targets for Ewing sarcoma

Ewing sarcoma (ES), an aggressive bone and soft‐tissue tumor, is treated with chemotherapy, radiotherapy, and surgery. Intra‐operative distinction between healthy and tumorous tissue is of paramount importance but challenging, especially after chemotherapy and at complex anatomical locations. Near infrared (NIR) fluorescence‐guided surgery (FGS) is able to facilitate the determination of tumor boundaries intra‐operatively, improving complete resection and therefore survival. This review evaluates potential ES‐specific proteins from the literature as targets for NIR FGS.

Mapping Determinants of Virus Neutralization and Viral Escape for Rational Design of a Hepatitis C Virus Vaccine

Hepatitis C virus (HCV) continues to spread worldwide with an annual increase of 1.75 million new infections. The number of HCV cases in the U.S. is now greater than the number of HIV cases and is increasing in young adults because of the opioid epidemic sweeping the country. HCV-related liver disease is the leading indication of liver transplantation. An effective vaccine is of paramount importance to control and prevent HCV infection. While this vaccine will need to induce both cellular and humoral immunity, this review is focused on the required antibody responses. For highly variable viruses, such as HCV, isolation and characterization of monoclonal antibodies mediating broad virus neutralization are an important guide for vaccine design. The viral envelope glycoproteins, E1 and E2, are the main targets of these antibodies. Epitopes on the E2 protein have been studied more extensively than epitopes on E1, due to higher antibody targeting that reflects these epitopes having higher degrees of immunogenicity. E2 epitopes are overall organized in discrete clusters of overlapping epitopes that ranged from high conservation to high variability. Other epitopes on E1 and E1E2 also are targets of neutralizing antibodies. Taken together, these regions are important for vaccine design. Another element in vaccine design is based on information on how the virus escapes from broadly neutralizing antibodies. Escape mutations can occur within the epitopes that are involved in antibody binding and in regions that are not involved in their epitopes, but nonetheless reduce the efficiency of neutralizing antibodies. An understanding on the specificities of a protective B cell response, the molecular locations of these epitopes on E1, E2, and E1E2, and the mechanisms, which enable the virus to negatively modulate neutralizing antibody responses to these regions will provide the necessary guidance for vaccine design.

Monoclonal Antibodies against Occludin Completely Prevented Hepatitis C Virus Infection in a Mouse Model

Hepatitis C virus (HCV) entry into host cells is a multistep process requiring various host factors, including the tight junction protein occludin (OCLN), which has been shown to be essential for HCV infection in in vitro cell culture systems. However, it remains unclear whether OCLN is an effective and safe target for HCV therapy, owing to the lack of binders that can recognize the intact extracellular loop domains of OCLN and prevent HCV infection. In this study, we successfully generated four rat anti-OCLN monoclonal antibodies (MAbs) by the genetic immunization method and unique cell differential screening. These four MAbs bound to human OCLN with a very high affinity (antibody dissociation constant of <1 nM). One MAb recognized the second loop of human and mouse OCLN, whereas the three other MAbs recognized the first loop of human OCLN. All MAbs inhibited HCV infection in Huh7.5.1-8 cells in a dose-dependent manner without apparent cytotoxicity. Additionally, the anti-OCLN MAbs prevented both cell-free HCV infection and cell-to-cell HCV transmission. Kinetic studies with anti-OCLN and anti-claudin-1 (CLDN1) MAbs demonstrated that OCLN interacts with HCV after CLDN1 in the internalization step. Two selected MAbs completely inhibited HCV infection in human liver chimeric mice without apparent adverse effects. Therefore, OCLN would be an appropriate host target for anti-HCV entry inhibitors, and anti-OCLN MAbs may be promising candidates for novel anti-HCV agents, particularly in combination with direct-acting HCV antiviral agents.IMPORTANCE HCV entry into host cells is thought to be a very complex process involving various host entry factors, such as the tight junction proteins claudin-1 and OCLN. In this study, we developed novel functional MAbs that recognize intact extracellular domains of OCLN, which is essential for HCV entry into host cells. The established MAbs against OCLN, which had very high affinity and selectivity for intact OCLN, strongly inhibited HCV infection both in vitro and in vivo Using these anti-OCLN MAbs, we found that OCLN is necessary for the later stages of HCV entry. These anti-OCLN MAbs are likely to be very useful for understanding the OCLN-mediated HCV entry mechanism and might be promising candidates for novel HCV entry inhibitors.

Host-targeting therapies for hepatitis C virus infection: current developments and future applications

Chronic hepatitis C virus (HCV) infection is a leading cause of chronic liver diseases and hepatocellular carcinoma (HCC) worldwide. In the past few years, anti-HCV therapies have undergone a revolution with the approval of multiple direct-acting antivirals (DAAs), which enable interferon-free treatments with considerable improvement of sustained virologic response in patients. Today, DAAs have become the standard of care for HCV therapy. However, several limitations remain, which include access to therapy, treatment failure in a subset of patients and persistent risk of HCC development following cure in patients with advanced fibrosis. By targeting conserved host proteins involved in the HCV life cycle, host-targeting agents (HTAs) offer opportunities for pan-genotypic antiviral approaches with a high barrier to drug resistance. Moreover, when applied in combination with DAAs, HTAs could improve the management of difficult-to-treat patients by acting through a complementary mechanism of action. In this review, we summarize the different HTAs evaluated in preclinical and clinical development and discuss their potential role for anti-HCV therapies.

Entry Inhibitors: A Perspective for Prevention of Hepatitis C Virus Infection in Organ Transplantation

Entry inhibitors are emerging as an attractive class of therapeutics for hepatitis C virus (HCV) infection. Entry inhibitors target either virion-associated factors or cellular factors necessary for infection. By blocking entry into cells, entry inhibitors prevent both the establishment of persistent reservoirs and the emergence of resistant variants during viral replication. Furthermore, entry inhibitors protect naïve cells from virus-induced alterations. Combining entry inhibitors with direct-acting antivirals (DAAs) may therefore improve treatment outcomes, particularly in the context of organ transplantation. The role of DAAs in transplantation, while still under clinical investigation, carries the risk of recipient infection and HCV-induced disease, since DAAs act only after infection is established. Thus, entry inhibitors provide a perspective to improve patient outcomes during organ transplantation. Applying this approach for transplant of organs from HCV-positive donors to HCV-negative recipients may also contribute to alleviate the medical burden of organ shortage.