Isolation and characterization of monoclonal antibodies that inhibit hepatitis C virus NS3 protease

Intracytoplasmic stable expression of IgG1 antibody targeting NS3 helicase inhibits replication of highly efficient hepatitis C Virus 2a clone

Background

Hepatitis C virus (HCV) infection is a major public health problem with more than 170 million cases of chronic infections worldwide. There is no protective vaccine currently available for HCV, therefore the development of novel strategy to prevent chronic infection is important. We reported earlier that a recombinant human antibody clone blocks viral NS3 helicase activity and inhibits replication of HCV 1b virus. This study was performed further to explore the mechanism of action of this recombinant antibody and to determine whether or not this antibody inhibits replication and infectivity of a highly efficient JFH1 HCV 2a virus clone.

Results

The antiviral effect of intracellular expressed antibody against the HCV 2a virus strain was examined using a full-length green fluorescence protein (GFP) labeled infectious cell culture system. For this purpose, a Huh-7.5 cell line stably expressing the NS3 helicase gene specific IgG1 antibody was prepared. Replication of full-length HCV-GFP chimera RNA and negative-strand RNA was strongly inhibited in Huh-7.5 cells stably expressing NS3 antibody but not in the cells expressing an unrelated control antibody. Huh-7.5 cells stably expressing NS3 helicase antibody effectively suppressed infectious virus production after natural infection and the level of HCV in the cell free supernatant remained undetectable after first passage. In contrast, Huh-7.5 cells stably expressing an control antibody against influenza virus had no effect on virus production and high-levels of infectious HCV were detected in culture supernatants over four rounds of infectivity assay. A recombinant adenovirus based expression system was used to demonstrate that Huh-7.5 replicon cell line expressing the intracellular antibody strongly inhibited the replication of HCV-GFP RNA.

Conclusion

Recombinant human anti-HCV NS3 antibody clone inhibits replication of HCV 2a virus and infectious virus production. Intracellular expression of this recombinant antibody offers a potential antiviral strategy to inhibit intracellular HCV replication and production.

Isolation of scFvs that inhibit the NS3 protease of hepatitis C virus by a combination of phage display and a bacterial genetic screen

The need for inhibitors for enzymes linked with microbial infection, specifically the NS3 protease of hepatitis C virus (HCV), inspired us to develop a unique, rapid and easy color-based method described herein. The NS3 serine protease of HCV has a role in processing viral polyprotein and it has been implicated in interactions with various cell constituents, resulting in phenotypic changes including malignant transformation. NS3 is currently regarded a prime target for antiviral drugs.We established a genetic screen that is based on coexpression of NS3, a beta-galactosidase reporter that is cleavable by NS3, and potential inhibitors within the same bacterial cell. A single-chain antibody (scFv) library was prepared from spleens of NS3-immunized mice and the screen was used to isolate a panel of protease-inhibiting scFvs. Candidate scFvs were validated for inhibitory activity using an o-nitrophenyl-beta-galactoside (ONPG) hydrolysis assay.The methods can be used more generally to isolate protease-inhibiting cytoplasmic intrabodies able to inhibit proteases or other activities that can be linked with the phenotype of Escherichia coli.

HCV-hepatocellular carcinoma: new findings and hope for effective treatment

We present here a comprehensive review of the current literature plus our own findings about in vivo and in vitro analysis of hepatitis C virus (HCV) infection, viral pathogenesis, mechanisms of interferon action, interferon resistance, and development of new therapeutics. Chronic HCV infection is a major risk factor for the development of human hepatocellular carcinoma. Standard therapy for chronic HCV infection is the combination of interferon alpha and ribavirin. A significant number of chronic HCV patients who cannot get rid of the virus infection by interferon therapy experience long-term inflammation of the liver and scarring of liver tissue. Patients who develop cirrhosis usually have increased risk of developing liver cancer. The molecular details of why some patients do not respond to standard interferon therapy are not known. Availability of HCV cell culture model has increased our understanding on the antiviral action of interferon alpha and mechanisms of interferon resistance. Interferons alpha, beta, and gamma each inhibit replication of HCV, and the antiviral action of interferon is targeted to the highly conserved 5'UTR used by the virus to translate protein by internal ribosome entry site mechanism. Studies from different laboratories including ours suggest that HCV replication in selected clones of cells can escape interferon action. Both viral and host factors appear to be involved in the mechanisms of interferon resistance against HCV. Since interferon therapy is not effective in all chronic hepatitis C patients, alternative therapeutic strategies are needed to treat chronic hepatitis C patients not responding to interferon therapy. We also reviewed the recent development of new alternative therapeutic strategies for chronic hepatitis C, which may be available in clinical use within the next decade. There is hope that these new agents along with interferon will prevent the occurrence of hepatocellular carcinoma due to chronic persistent hepatitis C virus infection. This review is not inclusive of all important scientific publications due to space limitation.

HCV NS3 serine protease-neutralizing single-chain antibodies isolated by a novel genetic screen

Hepatitis C virus (HCV) infection is a major world-wide health problem causing chronic hepatitis, liver cirrhosis and primary liver cancer. The high frequency of treatment failure points to the need for more specific, less toxic and more active antiviral therapies for HCV. The HCV NS3 is currently regarded as a prime target for anti-viral drugs, thus specific inhibitors of its activity are of utmost importance. Here, we report the development of a novel bacterial genetic screen for inhibitors of NS3 catalysis and its application for the isolation of single-chain antibody-inhibitors. Our screen is based on the concerted co-expression of a reporter gene, of recombinant NS3 protease and of fusion-stabilized single-chain antibodies (scFvs) in Escherichia coli. The reporter system had been constructed by inserting a short peptide corresponding to the NS5A/B cleavage site of NS3 into a permissive site of the enzyme beta-galactosidase. The resulting engineered lacZ gene, coding for an NS3-cleavable beta-galactosidase, is carried on a low copy plasmid that also carried the NS3 protease-coding sequence. The resultant beta-galactosidase enzyme is active, conferring a Lac+ phenotype (blue colonies on indicator 5-bromo-4-chloro-3-indolyl beta-D-galactoside (X-gal) plates), while induction of NS3 expression results in loss of beta-galactosidase activity (transparent colonies on X-gal plates). The identification of inhibitors, as shown here by isolating NS3-inhibiting single-chain antibodies, expressed from a compatible high copy number plasmid, is based on the appearance of blue colonies (NS3 inhibited) on the background of colorless colonies (NS3 active). Our source of inhibitory scFvs was an scFv library that we prepared from spleens of NS3-immunized mice and subjected to limited affinity selection. Once isolated, the inhibitors were validated as genuine and specific NS3 binders by an enzyme-linked immunosorbent assay and as bone fide NS3 serine protease inhibitors by an in vitro catalysis assay. We further show that upon expression as cytoplasmic intracellular antibodies (intrabodies) in NS3-expressing mammalian cells, three of the scFvs inhibit NS3-mediated cell proliferation. Although applied here for the isolation of antibody-based inhibitors, our genetic screen should be applicable for the identification of candidate inhibitors from other sources.

Emerging therapies for hepatitis C virus infection

Hepatitis C virus (HCV) has infected millions of people worldwide and has emerged as a global health crisis. The currently available therapy is interferon (IFN) either alone or in combination with ribavirin. However, the disappointing efficacy of IFN has led to the considerable need for improved treatments and a number of new therapies are under evaluation in clinical trials. These include pegylated IFNs, which have altered physiochemical characteristics allowing once-weekly dosing. Combination of pegylated IFN with ribavirin should further improve sustained response rates. However, not all patients are successfully treated with IFNs, particularly those infected with genotype 1 of the virus, and it is likely that potent, specific drugs will be required. The majority of new approaches currently trying to combat this viral disease are aimed at inhibition of viral targets. Most effort has been directed towards inhibition of the NS3 serine protease, and potent inhibitors have now been described. However, a clinical candidate is yet to emerge against this difficult target. Considerable work by leading researchers has provided crystal structures of the key replicative enzymes, NS3 protease, NS3 helicase, NS5B polymerase and full-length NS3 protease-helicase, and there is much hope that such structural information will bear fruit. More recently, inhibition of host targets, particularly inosine monophosphate dehydrogenase (IMPDH), has become of interest and there are on-going clinical trials with such inhibitors. Research aimed at novel treatments for HCV disease is gathering pace and very recent developments in cell-based assay systems can only hasten the discovery of improved therapies.

Inhibition of hepatitis C virus nonstructural protein, helicase activity, and viral replication by a recombinant human antibody clone

Hepatitis C virus (HCV) nonstructural protein 3 (NS3), with its protease, helicase, and NTPase enzymatic activities, plays a crucial role in viral replication, and therefore represents an ideal target for the development of anti-viral agents. We have developed a recombinant human antibody (Fab) that reacts with the helicase domain of HCV NS3. The affinity-purified Fab antibody completely inhibited the helicase activity of HCV NS3 at equimolar concentration. To evaluate the effect of the Fab on HCV replication, the clone encoding the Fab gene was put into an expression vector, which converts Fab into a complete IgG1 antibody. Using a DNA-based transfection model, we demonstrated that intracellular expression of this antibody resulted in significant reduction of HCV-negative strand RNA synthesis. Intracellular expression of this antibody into either a stable cell line replicating subgenomic RNA, or a transient full-length HCV replication model, reduced both HCV RNA and viral protein expression. These results support the use of recombinant antibody fragments to inhibit NS3 enzyme as a novel, feasible, and effective approach for inhibiting HCV replication.

Inhibition of hepatitis C virus NS3 protease by peptides derived from complementarity-determining regions (CDRs) of the monoclonal antibody 8D4: tolerance of a CDR peptide to conformational changes of a target

We have synthesized and characterized peptides derived from complementarity-determining regions (CDRs) of 8D4, a mouse monoclonal antibody against NS3 protease domain of hepatitis C virus. 8D4 inhibits enzymatic activity without its cofactor, NS4A peptide. One of the synthetic peptides derived from CDRs, CDR1 of the heavy-chain (CDR-H1) peptide strongly inhibited NS3 protease activity competitively in the absence of NS4A and non-competitively in the presence of NS4A. Moreover, cyclic CDR-H1 peptides bridged by disulfide inhibited NS3 protease more potently. The chain length of the CDR-H1 peptide is critical for strong inhibition, even when the peptide is circularized. This finding suggests the importance of peptide conformation. In contrast to a cognate antibody molecule, CDR-derived peptides may provide good ligands for target molecules by having a tolerance to conformational changes of the targets caused by cofactor binding or mutation.

Selection of human antibody fragments on the basis of stabilization of the variable domain in the presence of target antigens

Here we report a novel method for selecting human antibody fragments from nonimmunized variable domain libraries. The antibody fragments are selected on the basis of stabilization of the variable domain fragment (F(v)) in the presence of target antigens ("open sandwich selection"). One variable domain is displayed on phages and another is prepared as soluble molecules. These two reagents are mixed with the biotinylated target molecule and ternary complexes are captured by using streptavidin-conjugated magnet beads. After extensive washing, enriched clones are eluted by using target antigen. Some of the clones selected after 3 rounds are prepared as soluble domains, which then undergo another selection process. We obtained several human antibody fragments specific for human soluble erythropoietin receptor by using this method. Our method minimizes several of the disadvantages associated with human antibody selection through a phage-display system, such as construction of a large-scale library, deletion of genes during selection, and nonspecific binding.

Survey of the year 2000 commercial optical biosensor literature

We have compiled a comprehensive list of the articles published in the year 2000 that describe work employing commercial optical biosensors. Selected reviews of interest for the general biosensor user are highlighted. Emerging applications in areas of drug discovery, clinical support, food and environment monitoring, and cell membrane biology are emphasized. In addition, the experimental design and data processing steps necessary to achieve high-quality biosensor data are described and examples of well-performed kinetic analysis are provided.

Inhibition of the hepatitis C virus NS3 protease activity by Fv fragment of antibody 8D4

An antibody variable domain fragment (Fv) is a candidate for a specific inhibitor of the hepatitis C virus (HCV) NS3 protease. Here we report the functional characterization of the Fv of antibody 8D4, which is specific for the active site of the HCV NS3 protease domain. The variable fragments of 8D4 in the forms of Fv and scFv (VH-(G(4)S)(3)-VL) were expressed as insoluble fractions in the periplasm of Escherichia coli, and were subsequently solubilized, purified under denaturing conditions, and refolded. The Fv had an inhibition profile almost identical to that of the parent IgG, with an IC(50) of 71.3 nM, whereas the scFv had a greatly decreased affinity to NS3 and was the same as the isolated VH fragment. To date, this is the first report of an antibody Fv fragment specific for the HCV NS3 protease domain, aimed at designing potent protease inhibitors and antiviral drugs.