Hepatitis C virus (HCV) entry into host cells is a complex process requiring multiple host factors, including claudin-1 (CLDN1).Safe and effective therapeutic entry inhibitors need to be developed. We isolated a human hepatic Huh7.5.1-derived cell mutant that is nonpermissive to HCV, and comparative microarray analysis showed that the mutant was CLDN1 defective. Four hybridomas were obtained, which produced monoclonal antibodies (MAbs) that interacted with the parental Huh7.5.1 cell but not with the CLDN1-defective mutant. All MAbs produced by these hybridomas specifically bound to human CLDN1 with a very high affinity and prevented HCV infection of Huh7.5.1 cells in a dose-dependent manner, without apparent cytotoxicity. Two selected MAbs also inhibited HCV infection of human liver-chimeric mice without significant adverse effects. CLDN1 may be a potential target to prevent HCV infection in vivo. Anti-CLDN1 MAbs may hence be promising candidates as novel anti-HCV agents. IMPORTANCESafe and effective therapeutic entry inhibitors against hepatitis C virus (HCV) are very useful for combination therapies with other anti-HCV drugs, such as direct-acting antivirals. In this study, we first showed an effective strategy for developing functional monoclonal antibodies (MAbs) against extracellular domains of a multimembrane-spanning target protein, claudin-1 (CLDN1), by using parental cells expressing the intact target membrane protein and target-defective cells. The established MAbs against CLDN1, which had a very high affinity for intact CLDN1, efficiently inhibited in vitro and in vivo HCV infections. These anti-CLDN1 MAbs are promising leads for novel entry inhibitors against HCV. W orldwide, 170 million people are infected with hepatitis C virus (HCV), which is a major cause of liver cirrhosis and hepatocellular carcinoma. Thus, overcoming HCV infection is an important global health care issue (1). HCV is an enveloped, positive-sense, single-stranded RNA virus in the Flaviviridae family (2). Recent clinical research using direct-acting antivirals that target HCV enzymes, such as sofosbuvir and simeprevir, has provided new insights into combination therapy with inhibitors of multiple targets (3-5).Preventing viral entry into hepatocytes is an attractive target for anti-HCV agents, but strategies for preventing HCV entry into host cells are clinically unavailable (6). Host factors involved in initiating infection include heparan sulfate (7), low-density lipoprotein receptor (8), CD81 (9), scavenger receptor class B type I (SRBI) (10), claudin-1 (CLDN1) (11), occludin (12, 13), epidermal growth factor receptor (EGFR) (14), and Niemann-Pick C1-like 1 (15). Among these, CLDN1 is considered a potent target because it is essential for HCV entry into cells via interaction with CD81 and for cell-to-cell HCV transmission (16,17). Anti-CLDN1 antibodies (Abs) that inhibit HCV infection in vitro were reported by Baumert et al. (18,19) and Hötzel et al. (20), but a CLDN1 binder that prevents HCV infection in vivo has not...

The monoclonal antibody 6B4 has a potent antithrombotic effect in nonhuman primates by binding to the flexible loop, also known as the ␤-switch region (amino acids 230 -242), of glycoprotein Ib␣ (GPIb␣). This interaction blocks, in high shear stress conditions, the specific interaction between GPIb␣ and von Willebrand factor suppressing platelet deposition to the damaged vessel wall, a key event in the pathogenesis of arterial thrombosis. To understand the interactions between this antibody and its antigen at the amino acid level, we here report the identification of the paratope and epitope in 6B4 and GPIb␣, respectively, by using computer modeling and site-directed mutagenesis. The docking programs ZDOCK (rigid body docking) and HADDOCK (flexible docking) were used to model the interaction of 6B4 with GPIb␣ and to delineate the respective paratope and epitope. 6B4 and GPIb␣ mutants were constructed and assayed for their capacity to bind GPIb␣ and 6B4, respectively. From these data, it is found that the paratope of 6B4 is mainly formed by five residues: Tyr

Tight junctions (TJs) are complex biochemical structures that seal the intercellular space and prevent the free movement of solutes across epithelial cell sheets. Modulating the TJ seal is a promising option for increasing the transdermal absorption of drugs. Within TJs, the binding of the claudin (CLDN) family of tetratransmembrane proteins through cis-and trans-interactions is an integral part of seal formation. Because epidermal TJs contain CLDN-1 and CLDN-4, a binder for these CLDNs may be a useful modulator of the permeability of the epidermal barrier. Here, we investigated whether m19, which can bind to CLDN-1/-4 (also CLDN-2/-5), modulates the integrity of epidermal TJs and the permeability of cell sheets to solutes. Treatment of normal human epidermal keratinocytes (NHEKs) with the CLDN binder reduced the integrity of TJs. A CLDN-1-specific binder (a monoclonal antibody, clone 7A5) also weakened the TJ seal in NHEKs. Although m19 attenuated the TJ barrier in human intestinal epithelial cells (Caco-2), 7A5 did not. Treatment of NHEKs with 7A5 enhanced permeation of a paracellular permeation marker. These findings indicate that CLDN-1 is a potential target for modulating the permeability of the epidermis, and that our CLDN-1 binder is a promising candidate molecule for development as a dermal absorption enhancer.

Claudin-1 (CLDN1), a known host factor for hepatitis C virus (HCV) entry and cell-to-cell transmission, is a target molecule for inhibiting HCV infection. We previously developed four clones of mouse anti-CLDN1 monoclonal antibody (mAb) that prevented HCV infection in vitro. Two of these mAbs showed the highest antiviral activity. Here, we optimized the anti-CLDN1 mAbs as candidates for therapeutics by protein engineering. Although Fab fragments of the mAbs prevented in vitro HCV infection, their inhibitory effects were much weaker than those of the whole mAbs. In contrast, human chimeric IgG1 mAbs generated by grafting the variable domains of the mouse mAb light and heavy chains inhibited in vitro HCV infection as efficiently as the parental mouse mAbs. However, the chimeric IgG1 mAbs activated Fcg receptor, suggesting that cytotoxicity against mAb-bound CLDN1-expressing cells occurred through the induction of antibodydependent cellular cytotoxicity (ADCC). To avoid ADCC-induced side effects, we prepared human chimeric IgG4 mAbs. The chimeric IgG4 mAbs did not activate Fcg receptor or induce ADCC, but they prevented in vitro HCV infection as efficiently as did the parental mouse mAbs. These findings indicate that the IgG4 form of human chimeric anti-CLDN1 mAb may be a candidate molecule for clinically applicable HCV therapy.

Silica nanoparticles were synthesized via a sol-gel method in which tetraethyl orthosilicate was hydrolyzed by the alkaline core of the nitroxide radical-containing nanoparticle (RNP). The silica nanoparticles were successively captured in the RNP core to obtain silica/RNP nanocomposite (siRNP). Alternatively, siRNP was prepared using commercially available silica nanoparticles. The amount of elemental Si present in the siRNPs was controlled from 3 wt% to 12 wt%. Notably, the obtained siRNPs were stable in acidic media, whereas the starting RNP disintegrated immediately. Crosslinking of the RNP by the entrapped silica might improve stability of the siRNPs under such acidic conditions. Rebamipide was found to be stably encapsulated in the cores of the prepared siRNPs even under acidic conditions, probably due to the both basic environment of the cores and absorption tendencies of the entrapped silica. Under neutral to alkaline conditions, release of the rebamipide is accelerated, which is probably due to the repulsion between the anionic silica surface and the anionic rebamipide. Rebamipide-loaded siRNPs (rebamipide@siRNP) were orally administered to mice, and the plasma level of rebamipide was checked at predetermined time intervals, showing a significantly higher uptake of rebamipide in the plasma when compared to orally-administered free rebamipide. Because siRNP possesses nitroxide radicals in the core, it is confirmed that dextran sodium sulfate-induced colon inflammation was effectively suppressed by the oral administration of rebamipide@siRNP in mice.

More than 170 million people worldwide are infected with hepatitis C virus (HCV). Despite concerted research efforts, anti‐HCV agents resistant to the high mutability of the HCV RNA genome have not yet been produced. Claudin 1 (CLDN1) is a co‐receptor for HCV entry into hepatocytes and is an attractive potential target for HCV therapy, because such host factors are genetically stable. Here, we investigated the effects of 4 previously generated mouse anti‐CLDN1 antibodies on HCV infection. All 4 clones attenuated the infection of Huh7 cells by HCV (genotype 2a) and HCV pseudoviral particles (HCVpp, genotypes 1b and 2a). Two of 4 clones also prevented HCV (genotype 1b) infection of human‐liver‐chimeric mice. Injection of mouse anti‐CLDN1 antibodies did not adversely affect serum human albumin levels, apparent character, and motility. For future clinical application, we prepared human‐mouse chimeric anti‐CLDN1 antibodies. The chimeric antibodies prevented HCV and HCVpp infection of Huh7 cells as effectively as did the mouse antibodies. Our findings suggest that mouse and mouse‐human chimeric anti‐CLDN1 antibodies prevent HCV infection and may therefore be promising candidate anti‐HCV agents. Grant Funding Source: supported by the Ministry of Health, Labor, and Welfare of Japan

Claudins (CLs) are a family of tetratransmembrane proteins consisting of 27 members and are potential targets for enhancing mucosal drug absorption, treating cancer, and mucosal vaccination using the C‐terminal fragment of Clostridium perfringens enterotoxin (C‐CPE), a CL‐3/‐4 binder. The development of efficient CL binders is important for their future clinical application. We previously developed a broadly specific CL binder by using C‐CPE as a prototype; however, we did not successfully generate a CL subtype‐specific binder. Here, we focused on developing a CL subtype‐specific antibody. Because of the low antigenicity of CLs, we performed three different immunization procedures. BXSB mice with an autoimmune disorder were immunized with CL‐1‐displayed budded baculovirus, CL‐1‐expressing cells, or plasmid DNA encoding CL‐1. The DNA‐based immunization showed the highest production of serum anti‐CL‐1 antibodies. Therefore, B cells were isolated from the DNA‐immunized mice, and the B cells were fused with myeloma cells to form hybridomas. Hybridomas were screened for the production of the anti‐CL‐1 antibody. The antibodies bound to CL‐1‐expressing cells, but not to CL‐2, ‐4 or ‐5‐expressing cells. These results indicate that immunization of BXSB mice with CL DNA is a potentially useful method for the development of specific CL ligands.

Epithelium plays pivotal roles in barriers that separate the inside of the body from the outside environment. Passage across epithelial barriers is the first step in drug absorption. Epidermal absorption is an ideal route for drug administration because it is non‐invasive and easily controlled. Claudin‐1 (CLDN1) seals tight junctions in the stratum granulosum, but whether modulation of CLDN1 enhances epidermal permeability is unclear. We investigated the effect of an anti‐CLDN1 antibody on the epidermal epithelial barrier by using human epidermal keratinocytes (NHEK), a popular in vitro model of human epithelial cell sheets. Immunoblot and FACS analyses showed that CLDN1 was expressed on NHEK cell membranes. Treatment of NHEK monolayers with anti‐CLDN1 antibody decreased the integrity of tight junctions between adjacent cells and enhanced the permeation of solutes across the cell sheets. Furthermore, treatment of Caco‐2 cell monolayers, a popular model of the human intestinal barrier that expresses CLDN1 and CLDN4, with anti‐CLDN4, but not treatment with anti‐CLDN1, decreased the integrity of tight junctions. These findings suggest that CLND1 may be a target for specific modulation of epidermal barrier. Grant Funding Source: supported by the Ministry of Health, Labor, and Welfare of Japan