Expression of antisense RNA fails to inhibit influenza virus replication

Towards Gene-Inhibition Therapy: A Review of Progress and Prospects in the Field of Antiviral Antisense Nucleic Acids and Ribozymes

Antisense RNA and its derivatives may provide the basis for highly selective gene inhibition therapies of virus infections. In this review, I concentrate on advances made in the study of antisense RNA and ribozymes during the last five years and their implications for the development of such therapies. It appears that antisense RNAs synthesized at realistic levels within the cell can be much more effective inhibitors than originally supposed. Looking at those experiments that enable comparisons to be made, it seems that inhibitory antisense RNAs are not those that are complementary to particular sites within mRNAs but those that are able to make stable duplexes with their targets, perhaps by virtue of their secondary structure and length. The inclusion of ribozyme sequences within antisense RNAs confers RNA-cleaving activity upon them in vitro and possibly in cells, thereby offering the possibility of markedly increasing their therapeutic potential. The varieties of natural ribozyme and their adaptation as artificial catalysts are reviewed. The implications of these developments for antiviral therapy are discussed.

Novel retroviral vectors to facilitate expression screens in mammalian cells

As tools for functional genomics, expression profiling and proteomics provide correlative data, while expression cloning screens can link genes directly to biological function. However, technical limitations of gene transfer, expression, and recovery of candidate genes have limited wider application of genome-wide expression screens. Here we describe the pEYK retroviral vectors, which maintain high titers and robust gene expression while addressing the major bottleneck of expression cloning--efficient candidate gene recovery. By exploiting schemes for enhanced PCR rescue or strategies for direct isolation of proviral DNA as plasmids in bacterial hosts, the pEYK vectors facilitate cDNA isolation from selected cells and enable rapid iteration of screens and genetic reversion analyses to validate gene candidates. These vectors have proven useful to identify genes linked to cell proliferation, senescence and apoptosis.

Loss-of-function genetics in mammalian cells: the p53 tumor suppressor model

Using an improved system for the functional identification of active antisense fragments, we have isolated antisense fragments which inactivate the p53 tumour suppressor gene. These antisense fragments map in two small regions between nt 350 and 700 and nt 800 and 950 of the coding sequence. These antisense fragments appear to act by inhibition of p53 mRNA translation both in vivo and in vitro. Expression of these antisense fragments overcame the p53-induced growth arrest in a cell line which expresses a thermolabile mutant of p53 and extended the in vitro lifespan of primary mouse embryonic fibroblasts. Continued expression of the p53 antisense fragment contributed to immortalisation of primary mouse fibroblasts. Subsequent elimination of the antisense fragment in these immortalised cells led to restoration of p53 expression and growth arrest, indicating that immortal cells continuously require inactivation of p53. Expression of MDM2 or SV40 large T antigen, but not E7 nor oncogenic ras, overcomes the arrest induced by restoration of p53 expression. Functional inactivation of both p21 and bax (by overexpression of Bcl2), but not either alone, allowed some bypass of p53-induced growth arrest, indicating that multiple transcriptional targets of p53 may mediate its antiproliferative action. The ability to conditionally inactivate and subsequently restore normal gene function may be extremely valuable for genetic analysis of genes for which loss-of-function is involved in specific phenotypes.

Inhibition of influenza A virus reproduction by a ribozyme targeted against PB1 mRNA

A ribozyme gene directed at a specific cleavage of mRNA coding for PB1 protein, a component of RNA-dependent RNA-polymerase of influenza A virus, was constructed. The avian adenovirus CELO virus-associated RNA (VA RNA CELO) promoter and human cytomegalovirus (CMV) promoter were used for the permanent expression of the ribozyme in cell lines. The cells were infected with influenza A virus strains A/Singapore/1/57 and A/WSN/33, and the suppression of the virus reproduction and virus-specific protein synthesis was measured. The maximal level of the inhibition of virus reproduction as compared to the reproduction in non-transformed cells was 93.5%. Defective recombinant adenoviruses were constructed carrying the genes of functional and non-functional ribozymes under the control of human cytomegalovirus (CMV) promoter. The reproduction of A/WSN/33 virus in CV-1 cells preinfected with recombinant adenoviruses was shown to be suppressed.

Antisense inhibition of virus infections

This chapter summarizes the new approaches to identify novel antiviral drug targets and to develop novel antiviral strategies. The chapter also reviews genetic pharmacology as it relates to antiviral antisense research and drug development. Antisense oligonucleotides are selective compounds by virtue of their interaction with specific segments of RNA. For potential antivirals, identification of appropriate target RNA sequences for antisense oligonucleotides is performed at two levels: the optimal gene within the virus, and the optimal sequence within the RNA. The importance of these oligonucleotide modifications in designing effective drugs is just now being evaluated, both in animal model systems and in the clinic. The first generation of widely used antisense oligonucleotides has been the phosphorothioate (PS) compounds and a body of data on biodistribution, pharmacokinetics, and metabolism in animals and in humans is now available. Since the identification and sequencing of human immunodeficiency virus (HIV), there has been a strong interest in identifying a potent oligonucleotide inhibitor that would have the potential for development as a therapy for acquired immunodeficiency syndrome (AIDS). Numerous phosphorothioate oligonucleotides, with no apparent antisense sequence specificity, can have an anti-herpes simplex virus (HSV) effect. Oligonucleotides can be effective anti-influenza agents in cell culture assays. Hepatitis B virus (HBV) X protein that is a transactivator has been also reported to be targeted successfully by antisense oligonucleotides in vivo. Several of picornaviruses have been targets for antisense oligonucleotide inhibition, and the studies demonstrate the versatility of the antisense approach. However, the fact that oligonucleotides may contribute numerous mechanisms toward the antiviral activity, in addition to the antisense mechanism, may in some cases be an asset in the pursuit of clinically useful antiviral drugs.

Antisense RNA-mediated inhibition of mouse hepatitis virus replication in L2 cells

We have successfully used antisense RNA to inhibit replication of the mouse hepatitis virus (MHV) in a cell culture system. MHV is a single-stranded RNA virus of positive polarity. Mouse L2 cells were stably transfected with an antisense construct that targets regions of genes 5 and 6 of the virus. High levels of expression from this construct, which is under control of the human elongation factor 1 alpha promoter, were found. After infection of the antisense cell lines with MHV, replication of the virus was significantly reduced compared with control cells. In a viral plaque assay, smaller plaques were found in the antisense cell lines. In addition, up to a 92% inhibition in the number of viral particles produced in one antisense cell line could be seen. This inhibitory effect decreased at longer (> 16 hour) infection times. It was possible to both increase the amount of inhibition and prolong the inhibitory effect by reducing the multiplicity of infection. Our results suggest that antisense RNA may be an effective tool to slow down progression of MHV infection in mice.

Intracellular immunization of mosquito cells to LaCrosse virus using a recombinant Sindbis virus vector

A cDNA of the small RNA genome segment of La Crosse (LAC) virus was inserted, in an antisense orientation, into a double subgenomic Sindbis (dsSIN) virus expression vector generating pTE/3'2J/ANTI-S (15,000bp). In vitro transcription of the pTE/3'2J/ANTI-S template generated genomic RNA that was electrotransfected into BHK-21 cells to produce virus. Northern blot analysis of RNA isolated from infected Aedes albopictus (C6/36) cells showed that the TE/3'2J/ANTI-S virus produced a subgenomic mRNA of the appropriate size, indicating transcription of the LAC cDNA segment. C6/36 cells were infected with either TE/3'2J/ANTI-S, TE/3'2J (a dsSIN virus with no LAC insert), or wild type Sindbis (SIN, strain AR339) viruses and subsequently challenged with LAC virus. LAC virus titers were determined using a capture antibody ELISA. Mosquito cells infected with TE/3'2J/ANTI-S virus yielded at least 4 log10 TCID50/ml less LAC virus than cells infected with either TE/3'2J or AR339 SIN viruses. The use of the infectious SIN virus expression vectors provides a novel approach for high level cytoplasmic expression of genes or sequences of interest in arthropod cells, and for evaluating strategies for intracellular immunization against arboviruses.

Antisense treatment of viral infection

In this chapter I have attempted to outline the rationale that underlies the antisense approach to treatment of virus infection, to catalog the effector molecules that are currently available, and to estimate the relative worth of each. In so doing I have tried to describe the criteria that might be employed in their design and the factors that may determine their efficacy in tissue culture and, perhaps, in vivo. Finally, I have described the few examples presently available that indicate that antisense approaches may one day be therapeutically useful in treatment of disease of viral or nonviral origin.

Inhibition of mouse hepatitis virus multiplication by antisense oligonucleotide, antisense RNA, sense RNA and ribozyme

Antisense nucleic acids against specific sequences of mouse hepatitis virus (MHV)-RNAs were tested for their inhibitory effects on viral multiplication in mouse DBT cells. An antisense oligonucleotide containing a sequence complementary to leader RNA was synthesized and shown to induce a significant inhibitory effect on the multiplication of MHV-JHM. A vector which expressed the antisense or sense mRNA7 of MHV was transfected into DBT cells. A decreased multiplication of MHV was observed in both cell lines. The transfected cell line which expressed ribozyme against the 5'-end of the MHV genome was established. The rate of inhibition of MHV-multiplication and the quantity of synthesized virus-specific mRNAs in this transfected cell line were the same for both antisense and sense RNA. These results show that antisense nucleic acids might be eligible for use as antiviral agents against MHV multiplication.

Constitutive synthesis of polyoma antisense RNA renders cells immune to virus infection

Mouse fibroblasts were stably transfected with expression plasmids in which sequences of the early region of polyomavirus were inserted both in sense and antisense orientation. The cell lines that synthesize in the antisense orientation, a 1195-bp viral genome fragment covering the Ori, Cap, ATG, and all of the early mRNA splicing sites acquire resistance to viral infection. Smaller fragments covering Ori, Cap, and ATG sites or the splicing sites, as well as fragments cloned in sense orientation, failed to confer cell immunity to polyoma infection. The resistance proved to be directly dependent upon the specific antisense RNA and to be inversely proportional to the multiplicity of infecting polyoma.

Isolation of dominant negative mutants and inhibitory antisense RNA sequences by expression selection of random DNA fragments

Selective inhibition of specific genes can be accomplished using genetic suppressor elements (GSEs) that encode antisense RNA, dominant negative mutant proteins, or other regulatory products. GSEs may correspond to partial sequences of target genes, usually identified by trial and error. We have used bacteriophage lambda as a model system to test a concept that biologically active GSEs may be generated by random DNA fragmentation and identified by expression selection. Fragments from eleven different regions of lambda genome, encoding specific peptides or antisense RNA sequences, rendered E. coli resistant to the phage. Analysis of these GSEs revealed some previously unknown functions of phage lambda, including suppression of the cellular lambda receptor by an 'accessory' gene of the phage. The random fragment selection strategy provides a general approach to the generation of efficient GSEs and elucidation of novel gene functions.

Influenza: status and prospects for its prevention, therapy, and control

This article describes current knowledge of the molecular properties of orthomyxoviruses, their epidemiology, and approaches to the control of influenza. The host's response to infection, approaches to prevent infection through vaccination, and the use of antiviral agents to treat or prevent this important infection are covered.