Antisense treatment of viral infection

Experimental and emerging therapies for chronic hepatitis C virus infection

Hepatitis C virus infection is prevalent throughout the world and is associated with substantial morbidity, mortality and health economic burden. No effective preventative measure, including vaccination, is currently available. Incremental and substantial progress in the rate of viral eradication using interferon-based therapies has been made over the past decade. The most recent advance has been related to the development of a pegylated form of IFN-alpha by two independent pharmaceutical companies. Pegylation of IFN-alpha appears to prolong its half-life, allowing for less frequent dosing. Reports have suggested that pegylated interferons are also associated with better efficacy for viral eradication in patients with hepatitis C virus. Slower progress also has been made in developing non-interferon-based therapeutic agents against hepatitis C virus, including protease inhibitors, helicase inhibitors, ribozymes, antisense therapies, cytokine-based therapies and T-cell-based therapeutic vaccines.

Inhibiting effect of antisense oligonucleotides phosphorthioate on gene expression of TIMP-1 in rat liver fibrosis

AIM

To observe the inhibition of antisense oligonucleotides (asON) phosphorthioate to the tissue inhibitors metalloproteinase-1 (TIMP-1) gene and protein expression in the liver tissue of immunologically induced hepatic fibrosis rats. The possibility of reversing hepatic fibrosis through gene therapy was observed.

METHODS

Human serum albumin (HSA) was used to attack rats, as hepatic fibrosis model, in which asONs were used to block the gene and protein expressing TIMP-1. According to the analysis of modulator, structure protein, coding series of TIMP-1 genome, we designed four different asONs. These asONs were injected into the hepatic fibrosis models through coccygeal vein. The results was observed by RT-PCR for measuring TIMP-1 mRNA expression, immunohistochemistry and in situ hybridization for collagen I, II, special staining of collagen fiber, and electron microscopic examination.

RESULTS

Hepatic fibrosis could last within 363 days in our modified model. The expressing level of TIMP-1 was high during hepatic fibrosis process. It has been proved by the immunohistochemical and the electron microscopic examination that the asON phosphorthioate of TIMP-1 could exactly express in vivo. The effect of colchicine was demonstrated to inhibit the expressing level of mRNA and the content of collagen I, III in the liver of experimental hepatic fibrosis rats. However, the electron microscopy research and the pathologic grading of hepatic fibrosis showed that there was no significant difference between the treatment group and the model group (P> 0.05).

CONCLUSION

The experimental rat model of hepatic fibrosis is one of the preferable models to estimate the curative effect of anti-hepatic fibrosis drugs. The asON phosphorthioate of TIMP-1 could block the gene and protein expression of TIMP-1 in the liver of experimental hepatic fibrosis rats at the mRNA level. It is possible to reverse hepatic fibrosis, and it is expected to study a new drug of antihepatic fibrosis on the genetic level. Colchicine has very limited therapeutic effect on hepatic fibrosis, furthermore, its toxicity and side effects are obvious.

Antisense RNA complementary to hepatitis B virus specifically inhibits viral replication

BACKGROUND & AIMS

Chronic infection with the hepatitis B virus (HBV) is a major public health problem, and currently available therapies have limited efficacy. Gene therapy strategies for HBV infection are under active investigation. We evaluated the potential of antisense RNA transcribed from antisense genes to interfere with HBV replication.

METHODS

Subgenomic fragments of the HBV genome were studied with respect to the property of inhibiting HBV replication when intracellularly expressed in the antisense orientation.

RESULTS

Antisense RNAs derived from the HBV genome specifically inhibited HBV replication and antigen expression in human hepatocellular carcinoma cells by 60%-75%. DNA sequences corresponding to the identified RNAs had no effect on HBV replication, indicating that inhibitory effects are mediated by RNA. Transcripts corresponding to the inhibitory subgenomic fragments were present at high levels. One antisense RNA was found to reduce the amount of pregenomic RNA encapsidated into core particles as a molecular mechanism of antiviral effects.

CONCLUSIONS

Certain antisense RNA molecules will have substantial antiviral effects against HBV. Antisense RNAs derived from the HBV genome are promising candidates as antiviral agents and may serve as novel tools to identify functionally important regions of HBV transcripts.

Expression of an antisense hla fragment in Staphylococcus aureus reduces alpha-toxin production in vitro and attenuates lethal activity in a murine model

Isogeneic bacterial strains that differ only in the production of a single microbial factor have been invaluable in studying the pathogenesis of bacterial infections. The targeted, intentional inactivation of a gene encoding a potential virulence determinant generally requires homologous recombination to replace the gene with an inactivated allele. To determine whether the insertion and expression of a fragment of a bacterial gene in an antisense orientation could be used as a rapid alternative to allelic inactivation for producing paired isogeneic isolates, we inverted a 600-bp fragment of the Staphylococcus aureus gene encoding alpha-toxin, hla, behind its native promoter on an Escherichia coli-S. aureus shuttle vector. A transformant of an S. aureus strain carrying the antisense hla fragment produced antisense hla RNA and made 16-fold less alpha-toxin than either its parent or an isogeneic transformant containing vector DNA without hla. Also, intraperitoneal injection of 1.5 x 10(9) CFU of the antisense hla-containing transformant was significantly less lethal in a murine model than that of the parent (1 of 10 versus 7 of 10 mice expired [P < 0.02]) or the transformant without hla (1 of 10 versus 7 of 7 mice expired [P < 0.001]). We conclude that the expression of a fragment of hla in an antisense orientation in S. aureus on a plasmid vector reduces alpha-toxin production and the lethal activity of the strain in a murine model. The antisense strategy for creating isogeneic strains of bacteria may facilitate molecular investigations into the pathogenesis of infection. It also may be useful in creating novel live-attenuated strains of bacteria for use as vaccine candidates.

Comparison of the antiviral efficacy of ribozymes and antisense RNA directed against bovine leukemia virus rex/tax

Despite the theoretical attraction of ribozymes, which cleave their target RNA, as compared with antisense RNA, which only blocks translation, few studies have assessed the relative efficacy of ribozymes and antisense RNA directed against the identical target sequence. Previously, we described the efficacy of a hammerhead ribozyme targeted against rex/tax, a regulatory gene of bovine leukemia virus (BLV). In this study, we asked whether antisense RNA targeted against the same site would also be efficacious. BLV-infected bat lung cells were transfected with an antisense RNA-encoding plasmid under the control of sarcoma virus (RSV) promoter, and stable cell lines were selected. No inhibition of viral p24 expression was demonstrated in seven cell lines transfected with the antisense RNA targeted at the same site as the ribozyme or in three cell lines transfected with an antisense sequence targeted against the tax 5' initiation codon. Although in previous experiments antisense DNA oligonucleotides inhibited Tax expression in vitro, stably transfected plasmids encoding antisense RNA of the same sequence did not inhibit viral expression in BLV-infected cells in this study. These results suggest that in persistently infected cells producing high levels of BLV, the ribozyme is more effective than antisense RNA directed at rex/tax transcripts.

"Hairpin" and "hammerhead" ribozymes directed towards the mumps virus nucleocapsid RNA: specific cleavage of a small synthetic RNA substrate and full-length mRNA

In an attempt to develop efficient antiviral agents against Mumps virus, we designed ribozymes targeting the nucleocapsid (NP) mRNA. Transacting catalytic RNAs of the hammerhead and hairpin types were synthesized; they contained specific motifs, shared similar flanking regions and were directed against a 5'GUC3' target immediately downstream to the initiation codon of NP mRNA. Both ribozymes were first assayed on a synthetic 16 bases target RNA and found to catalytically and efficiently cleave the substrate in a sequence specific way. No cleavage, however, occurred when mutated forms of the ribozymes were used. In addition, both ribozyme types, when tested on the full length NP mRNA, were also able to cleave the substrate although turnover could not be demonstrated. As a rule, the hammerhead ribozyme proved more efficient than its hairpin counterpart, as well on the synthetic RNA substrate as on the full length NP mRNA target.

Efficient hammerhead ribozyme-mediated cleavage of the structured hepatitis B virus encapsidation signal in vitro and in cell extracts, but not in intact cells

Hepatitis B virus (HBV), the causative agent of B-type hepatitis in man, is a small enveloped DNA virus that replicates through reverse transcription of an RNA intermediate, the terminally redundant RNA pregenome. An essential highly conserved cis-element present twice on this RNA is the encapsidation signal epsilon, a stem-loop structure that is critical for pregenome packaging and reverse transcription. Epsilon is hence an attractive target for antiviral therapy. Its structure, however, is a potential obstacle to antivirals whose action depends on hybridization, e.g. ribozymes. Here we demonstrate effective in vitro cleavage inside epsilon by hammerhead ribozymes containing flanking sequences complementary to an adjacent less structured region. Upon co-transfection with a HBV expression construct corresponding ribozymes embedded in a U6 snRNA context led to a significant, though modest, reduction in the steady-state level of HBV pregenomes. Inactive ribozyme mutants revealed that antisense effects contributed substantially to this reduction, however, efficient epsilon cleavage by the intracellularly expressed ribozymes was observed in Mg(2+)-supplemented cell lysates. Artificial HBV pregenomes carrying the ribozymes in cis and model RNAs lacking all HBV sequences except epsilon exhibited essentially the same behaviour. Hence, neither the absence of co-localization of ribozyme and target nor a viral component, but rather a cellular factor(s), is responsible for the strikingly different ribozyme activities inside cells and in cellular extracts.