Convergent synthesis of ribonuclease L-active 2',5'-oligoadenylate-peptide nucleic acids

3'-Modification stabilizes mRNA and increases translation in cells

Successful implementation of mRNA gene therapy is facing many hurdles, for example poor expression levels of the exogenously delivered mRNA transcripts. Herein we describe the synthesis of various 3'-modified RNA oligonucleotides, and we show that 3'-modification drastically stabilizes these oligonucleotides in cell extracts. Modification of the 3'-terminus of gaussia luciferase mRNA results in 3-fold increased and extended (>48 h) translation of the mRNA. Our findings suggest 3'-modification of RNA-transcripts as a valid approach to increase expression levels for application in mRNA gene therapy.

Probing the activation site of ribonuclease L with new N6-substituted 2',5'-adenylate trimers

2-5A trimer [5'-monophosphoryladenylyl(2'-5')adenylyl(2'-5')adenosine] activates RNase L. While the 5'-terminal and 2'-terminal adenosine N(6)-amino groups play a key role in binding to and activation of RNase L, the exocyclic amino function of the second adenylate (from the 5'-terminus) plays a relatively minor role in 2-5A's biological activity. To probe the available space proximal to the amino function of the central adenylate of 2-5A trimer during binding to RNase L, a variety of substituents were placed at that position. To accomplish this, the convertible building block 5'-O-dimethoxytrityl-3'-O-(tert-butyldimethylsilyl)-6-(2,4-dinitrophenyl)thioinosine 2'-(2-cyanoethylN,N-diisopropylphosphoramidite) was prepared as a synthon to introduce 6-(2,4-dinitrophenyl)thioinosine into the middle position of the 2-5A trimer during automated synthesis. Post-synthetic treatment with aqueous amines transformed the (2,4-dinitrophenyl)thioinosine into N(6)-substituted adenosines. Assays of these modified trimers for their ability to bind and activate RNase L showed that activation activity could be retained, albeit with some sacrifice compared to unmodified p5'A2'p5'A2'p5'A. Thus, the spatial domain about this N(6)-amino function could be available for modifications to enhance the biological potency of 2-5A analogues and to ligate 2-5A to targeting vehicles such as antisense molecules.

The quest for an efficacious antiviral for respiratory syncytial virus

Respiratory syncytial virus (RSV) continues as an emerging infectious disease not only among infants and children, but also for the immune-suppressed, hospitalized and the elderly. To date, ribavirin (Virazole) remains the only therapeutic agent approved for the treatment of RSV. The prophylactic administration of palivizumab is problematic and costly. The quest for an efficacious RSV antiviral has produced a greater understanding of the viral fusion process, a new hypothesis for the mechanism of action of ribavirin, and a promising antisense strategy combining the 2'-5' oligoadenylate antisense (2-5A-antisense) approach and RSV genomics.