Pharmacokinetics and tissue distribution of a ribozyme directed against hepatitis C virus RNA following subcutaneous or intravenous administration in mice

Therapeutic Potential of Ribozymes

Recent advances in RNA engineering during the last two decades have supported the development of RNA-based therapeutics targeting a variety of human diseases. The broad scope of these emerging drugs clearly demonstrates the versatility of RNA. Ribozymes have been seen as promising candidates in this area. However, efficient intracellular application of ribozymes remains challenging, and other strategies appear to have outperformed ribozymes as molecular drugs. Nevertheless, trans-cleaving ribozymes have been applied for specific cleavage of target mRNAs in order to inhibit undesired gene expression. Furthermore, ribozymes have been engineered to allow site-directed RNA sequence alterations, enabling the correction of genetic misinformation at the RNA level. This chapter provides an overview of ribozyme-based strategies, highlighting the promises and pitfalls for potential therapeutic applications.

Exploring Internal Ribosome Entry Sites as Therapeutic Targets

Initiation of eukaryotic mRNA translation may proceed via several different routes, each requiring a different subset of factors and relying on different and specific interactions between the mRNA and the ribosome. Two modes predominate: (i) so-called cap-dependent initiation, which requires all canonical initiation factors and is responsible for about 95–97% of all initiation events in eukaryotic cells; and (ii) cap-independent internal initiation, which requires a reduced subset of initiation factors and accounts for up to 5% of the remaining initiation events. Internal initiation relies on the presence of so-called internal ribosome entry site (IRES) elements in the 5′ UTRs of some viral and cellular mRNAs. These elements (often possessing complex secondary and tertiary structures) promote efficient interaction of the mRNA with the 40S ribosome and allow for internal ribosome entry. Internal initiation of translation of specific mRNAs may contribute to development of severe disease and pathological states, such as hepatitis C and cancer. Therefore, this cellular mechanism represents an attractive target for pharmacological modulation. The purpose of this review is to provide insight into current strategies used to target viral and cellular IRESs and discuss the physiological consequences (and potential therapeutic implications) of abrogation/modulation of IRES-mediated translation.

Enhancing the pharmacokinetic/pharmacodynamic properties of therapeutic nucleotides using lipid nanoparticle systems

Although activity has been reported in vivo, free nucleic acid-based drugs are rapidly degraded and cleared following systemic administration. To address these challenges and improve the potency and bioavailability of genetic drugs, significant efforts have been made to develop effective delivery systems of which lipid nanoparticles (LNP) represent the most advanced technology currently available. In this review, we will describe and discuss the improvements to the pharmacokinetic and pharmacodynamic properties of nucleic acid-based drugs mediated by LNP delivery. It is envisioned that the significant improvements in potency and safety, largely driven by the development of LNP encapsulated siRNA drugs, will be translatable to other types of genetic drugs and enable the rapid development of potent molecular tools and drugs.

Toxicological and pharmacokinetic properties of QPI-1007, a chemically modified synthetic siRNA targeting caspase 2 mRNA, following intravitreal injection

We report the toxicological and pharmacokinetic properties of the synthetic, small interfering RNA (siRNA), QPI-1007, following intravitreal administration. QPI-1007 is a chemically modified siRNA designed to act via the RNA interference (RNAi) pathway to temporarily inhibit expression of the caspase 2 protein and is being developed as a neuroprotectant for the treatment of nonarteritic anterior ischemic optic neuropathy and other optic neuropathies such as glaucoma that result in the death of retinal ganglion cells. The half-life of QPI-1007 in the vitreous and retina/choroid in the Dutch Belted rabbit was about 2 days, and there was no sign of accumulation after repeated administrations at either 2- or 4-week dosing intervals in the rabbit. QPI-1007 was well tolerated in Dutch Belted rabbits following single or repeated intravitreal administrations of up to 11 doses over 9 months. Test-article-related effects were limited to the eyes, with minimal to mild vitreal cellular infiltration being the major finding, which was reversible. In repeated-dose studies, a modest reduction in B-wave amplitude obtained by electroretinography was observed in animals treated with the highest dose level tested (3 mg, which is equivalent to a 12 mg/eye human dose) that was not considered to be clinically meaningful. Administration in the rat of either a single bolus intravenous (i.v.) injection of 100 mg/kg or daily bolus i.v. injections of 75 mg/kg/day for 28 days failed to elicit any macroscopic or microscopic changes, suggesting a low risk for systemic toxicity. QPI-1007 was negative in three genetic toxicity studies. Overall, the nonclinical studies support the further development of QPI-1007.

Prospects for nucleic acid-based therapeutics against hepatitis C virus

In this review, we discuss recent advances in nucleic acid-based therapeutic technologies that target hepatitis C virus (HCV) infection. Because the HCV genome is present exclusively in RNA form during replication, various nucleic acid-based therapeutic approaches targeting the HCV genome, such as ribozymes, aptamers, siRNAs, and antisense oligonucleotides, have been suggested as potential tools against HCV. Nucleic acids are potentially immunogenic and typically require a delivery tool to be utilized as therapeutics. These limitations have hampered the clinical development of nucleic acid-based therapeutics. However, despite these limitations, nucleic acid-based therapeutics has clinical value due to their great specificity, easy and large-scale synthesis with chemical methods, and pharmaceutical flexibility. Moreover, nucleic acid therapeutics are expected to broaden the range of targetable molecules essential for the HCV replication cycle, and therefore they may prove to be more effective than existing therapeutics, such as interferon-α and ribavirin combination therapy. This review focuses on the current status and future prospects of ribozymes, aptamers, siRNAs, and antisense oligonucleotides as therapeutic reagents against HCV.

Hepatitis C virus translation inhibitors targeting the internal ribosomal entry site

The internal ribosome entry site (IRES) in the 5' untranslated region (UTR) of the hepatitis C virus (HCV) genome initiates translation of the viral polyprotein precursor. The unique structure and high sequence conservation of the 5' UTR render the IRES RNA a potential target for the development of selective viral translation inhibitors. Here, we provide an overview of approaches to block HCV IRES function by nucleic acid, peptide, and small molecule ligands. Emphasis will be given to the IRES subdomain IIa, which currently is the most advanced target for small molecule inhibitors of HCV translation. The subdomain IIa behaves as an RNA conformational switch. Selective ligands act as translation inhibitors by locking the conformation of the RNA switch. We review synthetic procedures for inhibitors as well as structural and functional studies of the subdomain IIa target and its ligand complexes.

Toxicological and pharmacokinetic properties of chemically modified siRNAs targeting p53 RNA following intravenous administration

We report the toxicological and pharmacokinetic properties of the synthetic, small interfering RNA I5NP following intravenous administration in rodents and nonhuman primates. I5NP is designed to act via the RNA interference (RNAi) pathway to temporarily inhibit expression of the pro-apoptotic protein p53 and is being developed to protect cells from acute ischemia/reperfusion injuries such as acute kidney injury that can occur during major cardiac surgery and delayed graft function that can occur following renal transplantation. Following intravenous administration, I5NP was very rapidly cleared from plasma was distributed predominantly to the kidney, with very low levels in liver and other tissues. Doses of 800 mg/kg I5NP in rodents, and 1,000 mg/kg I5NP in nonhuman primates, were required to elicit adverse effects, which in the monkey were isolated to direct effects on the blood that included a sub-clinical activation of complement and slightly increased clotting times. In the rat, no additional adverse effects were observed with a rat analogue of I5NP, indicating that the effects likely represent class effects of synthetic RNA duplexes rather than toxicity related to the intended pharmacologic activity of I5NP. Taken together, these data support clinical testing of intravenous administration of I5NP for the preservation of renal function following acute ischemia/reperfusion injury.

Pharmacokinetics and Toxicity in Rats and Monkeys of coDbait: A Therapeutic Double-stranded DNA Oligonucleotide Conjugated to Cholesterol

Increased DNA repair activity in cancer cells is one of their primary mechanisms of resistance to current radio- and chemotherapies. The molecule coDbait is the first candidate in a new class of drugs that target the double-strand DNA break repair pathways with the aim of overcoming these resistances. coDbait is a 32-base pair (bp) double-stranded DNA molecule with a cholesterol moiety covalently attached to its 5′-end to facilitate its cellular uptake. We report here the preclinical pharmacokinetic and toxicology studies of subcutaneous coDbait administration in rodents and monkeys. Maximum plasma concentration occurred between 2 to 4 hours in rats and at 4 hours in monkeys. Increase in mean AUC0–24h was linear with dose reaching 0.5 mg·h/ml for the highest dose injected (32 mg) for both rats and monkeys. No sex-related differences in maximum concentration (Cmax) nor AUC0–24h were observed. We extrapolated these pharmacokinetic results to humans as the subcutaneous route has been selected for evaluation in clinical trials. Tri-weekly administration of coDbait (from 8 to 32 mg per dose) for 4 weeks was overall well tolerated in rats and monkeys as no morbidity/mortality nor changes in clinical chemistry and histopathology parameters considered to be adverse effects have been observed.

Hammerhead ribozyme-mediated knockdown of mRNA for fibrotic growth factors: transforming growth factor-beta 1 and connective tissue growth factor

Excessive scarring (fibrosis) is a major cause of pathologies in multiple tissues, including lung, liver, kidney, heart, cornea, and skin. The transforming growth factor-β (TGF-β) system has been shown to play a key role in regulating the formation of scar tissue throughout the body. Furthermore, connective tissue growth factor (CTGF) has been shown to mediate most of the fibrotic actions of TGF-β, including stimulation of synthesis of extracellular matrix and differentiation of fibroblasts into myofibroblasts. Currently, no approved drugs selectively and specifically regulate scar formation. Thus, there is a need for a drug that selectively targets the TGF-β cascade at the molecular level and has minimal off-target side effects. This chapter focuses on the design of hammerhead ribozymes, measurement of kinetic activity, and assessment of knockdown mRNAs of TGF-β and CTGF in cell cultures.

Future Therapies for Hepatitis C

Although pegylated interferon-α plus ribavirin has become the standard for treating chronic hepatitis C virus infection, a substantial number of patients do not tolerate therapy and require dose reduction or discontinuation, or do not respond to this combination therapy. Thus, new therapeutic options are needed. An increased knowledge of the hepatitis C virus and an understanding of its replication cycle, as well as advances in biotechnology, have stimulated the development of numerous new antiviral treatments for patients with hepatitis C virus infection. This review focuses on four classes of new agents: new interferons, ribavirin-like molecules, specific small-molecule hepatitis C virus inhibitors and new immune therapies, with particular emphasis on medications in the later stages of development.

Assessing evidence from clinical trials in chronic hepatitis C

Hepatitis C is a global problem with significantly associated morbidity and mortality. Although some recent therapeutic advances have shown rates of sustained virologic remission of 50% or higher, combination therapy with interferon and ribavirin is often not well tolerated and is giving rise to a growing number of nonresponders. As a result, a large number of experimental drugs for the treatment of chronic hepatitis C are in development. As the clinical trial reports are made available, physicians need to become familiar with issues related to the design of these studies and to develop strategies to interpret the evidence they yield. The articles in this supplement describe the issues in clinical trial design and the evaluation of evidence from clinical trials in patients with chronic hepatitis C.

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.

New antiviral therapies for hepatitis C

Hepatitis C affects 170 million people worldwide and is the leading indication for liver transplantation. However, despite this high prevalence and burden of disease, current treatment regimens necessitate long durations of therapy, are often poorly tolerated and have suboptimal rates of sustained virologic response. Therefore, much attention has been directed at the development of new therapeutic agents against specific viral targets. This article reviews modifications of current therapies, outlines the viral life cycle and focuses on novel therapeutic agents currently being studied.

Chronic hepatitis C and no response to antiviral therapy: potential current and future therapeutic options

A significant proportion of chronic hepatitis C patients fails to achieve sustained virologic response even after treatment with the current, more potent, combination of pegylated interferon-alpha (IFNa) plus ribavirin. Such patients represent a rather heterogeneous group and may be divided initially into relapsers and nonresponders. Both the type of previous therapy and of previous response are very important factors for the indication and the type of re-treatment. The combination of pegylated IFNa and ribavirin seems to be a rational approach for patients who failed to respond to IFNa monotherapy. Pegylated IFNa-based regimens appear to induce sustained responses in 40-68% of relapsers but in only 11% of nonresponders to previous therapy with standard IFNa plus ribavirin. Thus, new therapeutic approaches are needed for the latter subgroup of patients as well as those who fail to respond to pegylated IFNa-based regimens. Such new approaches currently under evaluation include the triple combination of pegylated IFNa, ribavirin, and amantadine, alternative types of IFN, use of agents with ribavirin like activity but lesser degrees of side-effects, inhibitors of hepatitis C virus (HCV) replication, mainly inhibitors of NS3 protease or helicase, antisense oligonucleotides, and ribozymes, and several immunomodulators. Moreover, maintenance antifibrotic therapy, mostly with low doses of pegylated IFNa, are under evaluation in patients with advanced fibrosis. Thus, even in the current era of the potent pegylated IFNa-based regimens, the management of these difficult-to-treat patients represents an increasingly frequent problem and perhaps the most challenging therapeutic task in chronic hepatitis C.

Future trends in managing hepatitis C

Despite recent improvements in the treatment of patients who have chronic hepatitis C, a large proportion of patients do not achieve viral clearance. Treatment regimens are also costly, associated with significant morbidity, require substantial patient commitment, and are not appropriate for all patients. Therefore, it is important to maximize and enhance current therapeutic approaches and to investigate new approaches and therapies. Because the ability to maintain adherence to current treatment is associated with higher sustained virologic response rates (particularly in patients infected with genotype 1), strategies directed at patients and support staff to promote treatment adherence are important. Other strategies to enhance current therapy include alternative interferons (IFNs)/cytokines and new IFN delivery systems. Current therapy may also be enhanced by new ribavirin (RBV) analogs with an improved safety profile or by the addition of other immunomodulatory agents such as inosine 5'-monophosphate dehydrogenase inhibitors, histamine dihydrochloride, thymosin alfa 1, and amantadine. Some of these agents have demonstrated promising results, although further evaluation is required. Greater knowledge of the molecular biology of the hepatitis C virus (HCV) holds promise for the development of targeted therapies such as specific inhibitors of HCV polymerase, protease, or helicase, as well as therapeutic vaccines. Other potential molecular-based therapies include antisense oligonucleotides, ribozymes, and short interfering ribonucleic acid (RNA) molecules. Therapies aimed at reducing or preventing the development of fibrosis are also under investigation. Multiple-drug regimens will likely be required to enhance viral clearance and reduce viral resistance, while providing greater tolerability.

Engineered catalytic RNA and DNA : new biochemical tools for drug discovery and design

Since the fundamental discovery that RNA catalyzes critical biological reactions, the conceptual and practical utility of nucleic acid catalysts as molecular therapeutic and diagnostic agents continually develops. RNA and DNA catalysts are particularly attractive tools for drug discovery and design due to their relative ease of synthesis and tractable rational design features. Such catalysts can intervene in cellular or viral gene expression by effectively destroying virtually any target RNA, repairing messenger RNAs derived from mutant genes, or directly disrupting target genes. Consequently, catalytic nucleic acids are apt tools for dissecting gene function and for effecting gene pharmacogenomic strategies. It is in this capacity that RNA and DNA catalysts have been most widely utilized to affect gene expression of medically relevant targets associated with various disease states, where a number of such catalysts are presently being evaluated in clinical trials. Additionally, biotechnological prospects for catalytic nucleic acids are seemingly unlimited. Controllable nucleic acid catalysts, termed allosteric ribozymes or deoxyribozymes, form the basis of effector or ligand-dependent molecular switches and sensors. Allosteric nucleic acid catalysts promise to be useful tools for detecting and scrutinizing the function of specified components of the metabolome, proteome, transcriptome, and genome. The remarkable versatility of nucleic acid catalysis is thus the fountainhead for wide-ranging applications of ribozymes and deoxyribozymes in biomedical and biotechnological research.

Hepatitis C: a review

Hepatitis C virus is an RNA virus in the Flavivirus family that was identified in 1989. Since then, blood donor screening has reduced the incidence of acute infections; however, because this virus frequently leads to asymptomatic chronic infection, the prevalence of infection remains high. Chronic infection leads to increased risks of cirrhosis and hepatocellular carcinoma, as well as extrahepatic manifestations. Guidelines for widespread screening continue to evolve, and early diagnosis is likely to become more important with the development of more effective treatments. Current recommendations regarding screening are reviewed.

N/A

N/A

Advances in the Development of Ribozymes and Antisense Oligodeoxynucleotides as Antiviral Agents for Human Papillomaviruses

Urogenital human papillomavirus (HPV) infections are the most common viral sexually transmitted disease in women. On a worldwide basis cervical cancer is the second most prevalent cancer of women. Although HPV infection is not sufficient to induce cancer, the causal relation between high-risk HPV infection and cervical cancer is well established. Over 99% of cervical cancers are positive for high-risk HPV. Therefore, there is a need for newer approaches to treat HPV infection. Two novel approaches for inactivating gene expression involve ribozymes and oligonucleotides. Methods for identification of target genes involved in neoplastic transformation and tumour growth have been established, and these will lead to therapeutic approaches without any damage to normal cellular RNA molecules, which is often associated with conventional therapeutics. Ribozymes and oligonucleotides represent rational antiviral approaches for inhibiting the growth of cervical lesions and carcinomas by interfering with E6/E7 RNA production. The E6 and E7 genes of high-risk HPVs cooperate to immortalize primary epithelial cells and because they are found in cervical cancer are considered the hallmark of cervical cancer. The use and modification of ribozymes and antisense oligodeoxynucleotides can inhibit the growth of HPV-16 and HPV-18 immortalized cells, and tumour cells by eliminating E6/E7 transcript. Hammerhead and hairpin ribozymes have been widely studied because of their potential use for gene therapy and their place as therapeutic tools for cervical cancer is being evaluated. Although antiviral ribozymes and anti-sense molecules have been effective as in vitro or in vivo inhibitors of high-risk HPV-positive cells, none is currently in clinical trial. There are, however, a number of other antisense therapies in Phase I–III clinical trial for several oncogenes.

RNA as a target for developing antivirals

The base of knowledge concerning RNA structure and function has been expanding rapidly in recent years. Simultaneously, an increasing awareness of the pivotal role RNA plays in viral diseases has prompted many researchers to apply new technologies in high-throughput screening and molecular modelling to the design of antiviral drugs that target RNA. While the two RNA viruses with the greatest unmet medical need, HIV and HCV, have been most actively pursued, the approaches discussed in this review are relevant to all virus infections. Both traditional small-molecule and large-molecule therapeutics, such as antisense, ribozymes and interfering dsRNAs have been described, and several molecules are under development for commercialization. The purpose of this review is to summarize the current state of the art in this field and to postulate new directions in the future.

Intracellular immunization by hammerhead ribozyme against HCV

AIM: To evaluate the effect of hammerhead ribozyme 213 (Rz 213) against hepatitis C virus (HCV) infection.

METHODS: Rz213 cleaving 5'oncoding region (5'CR) of HCV was beforehand transfected in a human hepatic carcinoma cell (HHCC) line and selected for G418 resistance. Cells stably expressing Rz213 were retransfected with pCMVNCRluc containing 5扤CR-luc fusion genes by lipofectAMINE; luciferase activity in lysate of transfactant was measured in scintillation counter.

RESULTS: HHCC cells stably expressing Rz213 exhibited significant resistance to retransfection of targeting gene.

CONCLUSION: Stably transfected cells with Rz213 were selected and expressed in HHCC, and thus exerted the intracellular immunity against infection of HCV.

N/A

N/A

New therapies on the horizon for hepatitis C: are we close?

A myriad of new therapies for treating hepatitis C are in various stages of preclinical and clinical development. As reviewed here, these include nucleic acid-based approaches (antisense and ribozymes), small molecule inhibitors of essential hepatitis C virus (HCV)-encoded enzymes (protease, helicase, and polymerase), immune modulation, and immunotherapy. As more details of the HCV lifecycle are elucidated, new targets and approaches will be discovered. Drug development is difficult, expensive, and always agonizingly slow for patients in need and their physicians. Nonetheless, a broad effort has been mounted for HCV, and substantial progress has been achieved. The prospects for new HCV treatments are bright.

Ribonucleoside analogue that blocks replication of bovine viral diarrhea and hepatitis C viruses in culture

A base-modified nucleoside analogue, beta-D-N(4)-hydroxycytidine (NHC), was found to have antipestivirus and antihepacivirus activities. This compound inhibited the production of cytopathic bovine viral diarrhea virus (BVDV) RNA in a dose-dependant manner with a 90% effective concentration (EC(90)) of 5.4 microM, an observation that was confirmed by virus yield assays (EC(90) = 2 microM). When tested for hepatitis C virus (HCV) replicon RNA reduction in Huh7 cells, NHC had an EC(90) of 5 microM on day 4. The HCV RNA reduction was incubation time and nucleoside concentration dependent. The in vitro antiviral effect of NHC was additive with recombinant alpha interferon-2a and could be prevented by the addition of exogenous cytidine and uridine but not of other natural ribo- or 2'-deoxynucleosides. When HCV RNA replicon cells were cultured in the presence of increasing concentrations of NHC (up to 40 micro M) for up to 45 cell passages, no resistant replicon was selected. Similarly, resistant BVDV could not be selected after 20 passages. NHC was phosphorylated to the triphosphate form in Huh7 cells, but in cell-free HCV NS5B assays, synthetic NHC-triphosphate (NHC-TP) did not inhibit the polymerization reaction. Instead, NHC-TP appeared to serve as a weak alternative substrate for the viral polymerase, thereby changing the mobility of the product in polyacrylamide electrophoresis gels. We speculate that incorporated nucleoside analogues with the capacity of changing the thermodynamics of regulatory secondary structures (with or without introducing mutations) may represent an important class of new antiviral agents for the treatment of RNA virus infections, especially HCV.

Mechanisms of drug resistance and novel approaches to therapy for chronic hepatitis C

Hepatitis C virus (HCV) is now the major cause of transfusion-associated and parenterally transmitted viral hepatitis and accounts for a significant proportion of hepatitis cases worldwide. The majority of infections become persistent and approximately 20% of chronically infected individuals develop cirrhosis, which is strongly associated with progression to hepatocellular carcinoma. Molecular biological investigations into the structure and function of HCV and its genes has led to the identification of a number of potential targets for selective antiviral intervention. The present review summarizes current research activity into these novel drug targets and addresses the basis for clinical non-response in the current interferon-alpha-based therapies. Future therapeutic strategies that utilize HCV-specific antiviral agents should prove effective in controlling active viral replication, but the risk of emergence of drug-resistance will need to be addressed due to the quasispecies feature of HCV replication.

Characterization of nuclease-resistant ribozymes directed against hepatitis B virus RNA

Hepatitis B virus (HBV) is responsible for > 350 million cases of chronic hepatitis B worldwide and 1.2 million deaths each year. To explore the use of ribozymes as a novel therapy for HBV infection, nuclease-resistant ribozymes that target highly conserved regions of HBV RNA were screened in cell culture. These synthetic ribozymes have the potential to cleave all four major HBV RNA transcripts and to block the HBV lifecycle by cleavage of the pregenomic RNA. A number of the screened ribozymes demonstrate activity in cell culture systems, as measured by decreased levels of HBV surface antigen, HBV e antigen and HBV DNA. In addition, a lead anti-HBV ribozyme maintains activity against a lamivudine-resistant HBV variant in cell culture. Treatment of HBV transgenic mice with lead anti-HBV ribozymes significantly reduced viraemia compared with saline-treated animals and was as effective as treatment with lamivudine. In conclusion, the therapeutic use of a ribozyme alone or in combination with current therapies (lamivudine or interferons) may lead to improved HBV therapy.

Future therapy of hepatitis C

Currently available therapies for the treatment of chronic hepatitis C are effective in half of patients, but are expensive, often poorly tolerated, and unsuitable for certain patient populations. The ideal therapy would be highly effective, orally bioavailable, have minimal side effects, be cost effective, and suitable for the majority of patients with hepatitis C. Recent advances in understanding the replication cycle of hepatitis C virus (HCV) and structural, crystallographic definitions of components of the viral polyprotein have improved the prospects for development of novel therapies. The lack of a small animal model of HCV infection continues to hamper progress in the preclinical evaluation of new antivirals and vaccines. Strategies to enhance response to current therapies include the development of novel interferons and delivery systems, nucleoside analogues that have reduced hemolysis compared with ribavirin, inosine 5' monophosphate dehydrogenase inhibitors, and other immunomodulators that are being evaluated as adjunctive therapy to interferon-based regimens. Compounds in preclinical or early phase human trials include small molecules that inhibit virus specific enzymes (such as the serine proteases, RNA polymerase and helicase), or those that prevent translation initiation (such as antisense molecules and ribozymes). Antifibrotic agents are also being developed in an attempt to prevent disease progression in patients in whom HCV RNA cannot be eradicated. While the advent of these newer compounds represent an exciting phase in the treatment of HCV, their safety and efficacy need to be established. Most of these newer therapies are unlikely to be available for routine clinical use in the next 3 to 5 years.

DNA-based immunotherapy: potential for treatment of chronic viral hepatitis?

Persistent HBV and HCV infection represent major causes of chronic liver disease with a high risk of progression to liver cirrhosis and hepatocellular carcinoma (HCC). Conventional protein-based vaccines are highly efficacious in preventing HBV infection; whereas in therapeutic settings with chronically infected patients, results have been disappointing. Prophylactic vaccination against HCV infection has not yet been achieved due to many impediments including frequent spontaneous mutations of the virus with escape from immune system control. Using animal models it has been demonstrated that DNA-based immunisation strategies may overcome this problem because of their potential to induce immunity against multiple viral epitopes. DNA-based vaccines mimic the effect of live attenuated viral vaccines, eliciting cell mediated immunity in addition to inducing humoral responses. Efficacy may further be improved by addition of DNA encoding immunomodulatory cytokines and more recently, direct genetic modulation of antigen-presenting cells, such as dendritic cells (DC), has been shown to increase antigen-specific immune responses. This review focuses on immunological aspects of chronic HBV and HCV infection and on the potential of DNA- and DC-based vaccines for the treatment of chronic viral hepatitis.

The development of a monoclonal antibody specific for a 2(')-C-allyl modification of uridine, and its use in the localization of ribozymes in vivo

Ribozymes are catalytically active RNA molecules that cleave other RNA molecules in a sequence-specific fashion, with significant turnover. The successful design and synthesis of ribozymes with modifications to increase their stability in biological fluids, while maintaining catalytic activity, has been instrumental in moving this technology from the laboratory into clinical trials. With the entry of ribozymes into the clinical setting, the need has arisen for reagents and/or assays to detect these drugs in tissues. We have developed a monoclonal antibody to the 2(')-deoxy-2(')-C-allyl uridine modification present in our synthetic hammerhead ribozymes. The monoclonal antibody, termed CA1USR, is a murine IgG1(k), whose epitope appears to involve both the 2(')-C-allyl modification, and the uridine base. Use of CA1USR for immunohistochemical detection of ribozymes in the tissues of mice which were administered two structurally different ribozymes has demonstrated its utility as a reagent for in vivo localization of ribozymes containing the 2(')-C-allyl uridine modification.

Advances in hepatitis C: what is coming in the next 5 years?

Hepatitis C virus (HCV) is a leading cause of chronic hepatitis, liver cirrhosis and hepatocellular carcinoma. Numerous advances have been made in the understanding of HCV replication, including detailed molecular characterization of its viral proteins and genomic RNA. The inability to grow HCV in cell culture had impeded the development of antiviral agents against this virus. To overcome this obstacle, a number of unique tools have been prepared, such as molecular clones that are infectious in the chimpanzee animal model of infection, and the development of a subgenomic replicon system in Huh7 cells. In addition, the major non-structural proteins have been crystallized, thus enabling rational drug design directed to these targets. Current developments in antiviral agents are reviewed in the context of these potential new viral targets for the future treatment of HCV in chronically infected individuals.

Enhanced antiviral effect in cell culture of type 1 interferon and ribozymes targeting HCV RNA

We have recently shown that the replication of an HCV-poliovirus (PV) chimera that is dependent upon the hepatitis C virus (HCV) 5' untranslated region (UTR) can be inhibited by treatment with ribozymes targeting HCV RNA. To determine the antiviral effects of anti-HCV ribozyme treatment in combination with type 1 interferon (IFN), we analysed the replication of this HCV-PV chimera in HeLa cells treated with anti-HCV ribozyme and/or IFN-alpha2a, IFN-alpha2b, or consensus IFN. The anti-HCV ribozyme, or any of the IFNs alone have significant inhibitory effects on HCV-PV replication compared to control treatment (> or = 85%, P < 0.01). The maximal inhibition due to IFN treatment (94%, P < 0.01) was achieved with > or = 50 U/ml for either IFN-alpha2a or IFN-alpha2b compared to control treatment. A similar level of inhibition in viral replication could be achieved with a 5-fold lower dose of IFN if ribozyme targeting the HCV 5' UTR was given in combination. For consensus IFN, the dose could be reduced by > 12.5-fold if ribozyme targeting the HCV 5' UTR was given in combination. Conversely, the dose of ribozyme could be reduced 3-fold if given in combination with any of the IFN preparations. Moreover, treatment with low doses (1-25 U/mL) of IFN-alpha2a, IFN-alpha2b, or consensus IFN in combination with anti-HCV ribozyme resulted in > 98% inhibition of HCV-PV replication compared to control treatment (P < 0.01). These results demonstrate that IFN and ribozyme each have a beneficial antiviral effect that is augmented when given in combination.

Treatment of chronic viral hepatitis

Significant advances have been made in the treatment of both hepatitis B and C. Cure for the majority is becoming reality. Combination regimens are now established therapy in hepatitis C and the near future will see the adoption of a similar approach to hepatitis B. Interferon alpha therapy remains important, with the development of more efficacious pegylated forms. In this article we review current therapy and discuss future strategies of the therapy for chronic viral hepatitis.

Ribozyme gene therapy: applications for molecular medicine

RNA enzymes--ribozymes--are being developed as treatments for a variety of diseases ranging from inborn metabolic disorders to viral infections and acquired diseases such as cancer. Ribozymes can be used both to downregulate and to repair pathogenic genes. In some instances, short-term exogenous delivery of stabilized RNA is desirable, but many treatments will require viral-mediated delivery to provide long-term expression of the therapeutic catalyst. Current gene therapy applications employ variations on naturally occurring ribozymes, but in vitro selection has provided new RNA and DNA catalysts, and research on trans-splicing and RNase P has suggested ways to harness the endogenous ribozymes of the cell for therapeutic purposes.

Viral hepatitis

Viral hepatitis constitutes the most common entity seen in hepatology practice. Hepatitis A vaccination is recommended for patients with chronic hepatitis. Both lamivudine and interferon are established therapies against chronic hepatitis B, with other treatments not equally effective. Adefovir dipivoxil is a promising new treatment for lamivudine-resistant hepatitis B mutants. Lamivudine and hepatitis B immunoglobulin are effective in preventing recurrence of hepatitis B after transplantation. The combination of interferon and ribavirin has been shown to be effective for treatment of hepatitis C. Studies support the antiviral, antifibrotic, and antineoplastic effect of interferon therapy. Recurrence of hepatitis C after transplantation has been associated with more rapid progression to cirrhosis. Other major advances in the field of viral hepatitis during the past year are highlighted.

Current and future therapies of hepatitis C

With recent advances in the treatment of chronic hepatitis C, patients with elevated aminotransferase levels, detectable HCV RNA in the serum, and chronic inflammation are candidates for therapy. The best initial therapy is interferon plus ribavirin, achieving a sustained response rate in 40% of patients. The duration of therapy should be based on HCV genotype (48 weeks for genotype 1; 24 weeks for other genotypes). Serum HCV RNA should be measured at week 24 to assess response and guide further therapy in patients with genotype 1 infection. Patients unsuitable for combination therapy can be treated with interferon monotherapy. Side effects, dose modification and discontinuation are generally more frequent with interferon plus ribavirin, but can be managed with close follow-up and careful monitoring. With rapid developments in treatment, new therapies will require careful prospective evaluation according to HCV genotype and viral-load characteristics. Recommendations for therapy will probably change every few years, and novel approaches may provide effective therapy for most patients with hepatitis C.