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

Stable expression of antisense RNAs targeted to the 5' non-coding region confers heterotypic inhibition to foot-and-mouth disease virus infection

The antiviral potential of transcripts targeted to the non-coding regions (NCRs) of foot-and-mouth disease virus (FMDV) RNA have been studied during transient and constitutive expression in susceptible BHK-21 cells. Transient expression of antisense transcripts corresponding to the 5' and 3'NCRs, alone or in combination, confers specific inhibition of homologous (serotype C) virus infection in BHK-21 cells. Constitutive expression of antisense 5'NCR transcripts (5'AS) exerted higher levels of inhibition to homologous and heterologous (serotypes O, A, Asia, SAT 1, SAT 2 and SAT 3) FMDV infection, as estimated by a 10-fold reduction in virus titre in the supernatants from infected clones and by a plaque reduction assay. These inhibitions were also observed, albeit to a lesser extent, in clones stably expressing antisense 3'NCR transcripts. The antiviral response was specific for FMDV, as the picornavirus encephalomyocarditis virus was not inhibited in any of the transformed cell lines. In all cases, a correlation was found between the level of transcript expression and the extent of virus inhibition. The potential to efficiently inhibit FMDV, including isolates representing the seven serotypes, by expressing interfering 5'AS transcripts opens the possibility of developing transgenic animals with a reduced susceptibility to FMDV.

Heterotypic inhibition of foot-and-mouth disease virus infection by combinations of RNA transcripts corresponding to the 5' and 3' regions

Strategies to inhibit RNA virus multiplication based on the use of interfering nucleic acids have to consider the high genetic polymorphism exhibited by this group of viruses. Here, we report high levels of heterotypic inhibition of foot-and-mouth disease virus (FMDV) infective particle formation in cotransfection experiments of susceptible cell lines with infections viral RNA and combinations of viral transcripts. The interfering molecules used include the following regions on type C FMDV RNA: (i) sequences from the 5' region, spanning the proximal part of the internal ribosome entry site element and the two functional initiator AUGs; and (ii) the 3' terminal region including the 3' end of 3D gene and the complete 3' non-coding region. Combination of 5' antisense RNA molecules with either sense or antisense RNA molecules from the 3' region resulted in inhibition of up to 90% of the infectivity of homologous type C FMDV RNA. The inhibition was dose-dependent and specific, as no reduction was observed in the plaque-forming units recovered from RNA of swine vesicular disease virus, a related picornavirus. Interestingly, high levels-of intertypic inhibition, about 60% or higher, were observed when viral RNAs of serotypes O and A were analysed. These levels of inhibition are consistent with the levels of nucleotide homology exhibited by the viruses analysed in the target sequences. Inhibition of virus yield was also observed in FMDV-infected cells transiently expressing the interfering RNAs. Thus, transcripts of the FMDV RNA corresponding to the 5' and 3' regions specifically inhibit FMDV particle formation in a serotype-independent manner.

Ribozymes and the anti-gene therapy: how a catalytic RNA can be used to inhibit gene function

Ribozymes are RNA molecules that possess the dual properties of RNA sequence-specific recognition and site-specific cleavage of other RNA molecules. These properties provide powerful tools for studies requiring gene inhibition, when the DNA sequence is known. The use of these molecules goes beyond basic research, with a potential impact in therapeutical practice in medicine in the near future. In this review, we briefly describe the progress towards developing this class of molecules and its applications for the control of gene expression.

Antiviral ribozymes. New jobs for ancient molecules

Catalytic RNAs are a genetic property not only of some particular viroids or viruses, but also are more common naturally among eukaryotes and even prokaryotes than earlier expected. However, the major interest in ribozymes results from their potential for development of "tailor-made" cDNA constructions designed to be transcribed into catalytic RNAs that will recognize by hybridization and destroy by specific cleavage their cellular or viral RNA targets. The efficiency of an antiviral ribozyme is determined by both the accessibility and sequence conservation of the target region, as well as the design of the ribozyme: its type, size, and composition of flanking sequences; expression rates; and cellular compartment localization. Until now the most frequently selected viral target is the human immunodeficiency virus, where an up to a 10(4)-fold inhibition in its progeny production has been achieved. Although the first generation ribozymes focused on improvements in basic design and expression rates, more recently the efficiency of antiviral catalytic activity has been increased by employing polyribozymes and/or multitarget ribozymes, as well as special constructions to enhance the cellular co-compartmentation of the ribozyme with its viral RNA target.

Recent status of the antisense oligonucleotide approaches in oncology

Antisense oligonucleotides designed to complement a region of a particular messenger RNA may inhibit gene expression potentially through sequence-specific hybridization. Their inhibiting effect has been shown in a variety of in vitro and in vivo models in oncology, whereas much rarer clinical trials have been carried out. Rigorous demonstration of in vitro and in vivo specific effects upon their targets is mandatory before their use as drugs in cancer therapy.

RNA enzymes as tools for gene ablation

Ribozymes have the potential to ablate the expression of any gene in a sequence-specific manner and, therefore, may be useful as therapeutic molecules or as tools for the analysis of gene function. Although a number of reports have described ribozymes that are effective in inhibiting gene expression, few studies have attempted, systematically, to analyze the features of ribozymes that affect their potency within cells. Experimental observations suggest that emerging rules governing ribozyme potency in cells can be understood in terms of the competitive interactions between RNA-binding proteins, complementary RNAs and their internal secondary structure.