Oligonucleotide antiviral therapeutics: antisense and RNA interference for highly pathogenic RNA viruses

Abstract

RNA viruses are a significant source of morbidity and mortality in humans every year. Additionally, the potential use of these viruses in acts of bioterrorism poses a threat to national security. Given the paucity of vaccines or postexposure therapeutics for many highly pathogenic RNA viruses, novel treatments are badly needed. Sequence-based drug design, under development for almost 20 years, is proving effective in animal models and has moved into clinical trials. Important advances in the field include the characterization of RNA interference in mammalian cells and chemical modifications that can dramatically increase the in vivo stability of therapeutic oligonucleotides. Antisense strategies utilize single-stranded DNA oligonucleotides that inhibit protein production by mediating the catalytic degradation of target mRNA, or by binding to sites on mRNA essential for translation. Double-stranded RNA oligonucleotides, known as short-interfering RNAs (siRNAs), also mediate the catalytic degradation of complementary mRNAs. As RNA virus infection is predicated on the delivery, replication, and translation of viral RNA, these pathogens present an obvious target for the rapidly advancing field of sequence-specific therapeutics. Antisense oligonucleotides or siRNAs can be designed to target the viral RNA genome or viral transcripts. This article reviews current knowledge on therapeutic applications of antisense and RNA interference for highly pathogenic RNA viral infections.

Fig. 1

Mechanism of action of antisense and RNA interference-based therapeutics. The formation of an ASO:RNA hybrid directs the RNase H-mediated cleavage of the target RNA molecule. PMO:RNA hybrids are not substrates of RNase H-mediated cleavage. Rather, when targeted near the AUG start codon, PMOs inhibit translation by preventing ribosome entry. Introduced synthetic siRNAs are incorporated into the multiprotein RISC complex where they direct the cleavage of complementary target RNA molecules.

Fig. 2

RNase H-dependent, modified ASO therapeutic design. A trinucleotide portion of an ASO is shown with phosphorothioate internucleotide linkages (A). The 3′-most nucleotide is 2′-O-(2-methoxy)ethyl (2′MOE) modified (B). Both modifications can be found in “gapmer” ASOs which feature a phosphorothioate core (gap) flanked by 2′-modified nucleotides (2′MOE wings).

Fig. 3

Phosphorodiamidate Morpholino Oligomer (PMO). A trinucleotide PMO is shown. PMO compounds are designed with uncharged phosphorodiamidate internucleotide linkages (A). Additionally, the ribose ring of the nucleic acid is replaced with a morpholine ring (B).