The design of antiviral agents based on strategic sequences in viral RNA and antiviral effects of single stranded polynucleotides

Potential targets for antiviral chemotherapy

Serendipity and random screening have been successful in producing effective antiviral agents. The increase in our knowledge of the basic biochemistry of viral replication and of virus-host interrelationships has revealed not only an understanding of the targets upon which existing antiviral agents exert their inhibitory effect, but also has uncovered new potential targets. The hope is that such molecular understanding will afford the synthesis of compounds with selective antiviral activity. A review of various viral targets which are potentially susceptible to attack, and a few approaches for development of antiviral agents are presented.

Selectivity of antitemplates as inhibitors of deoxyribonucleic acid polymerases

DNA polymerase alpha from calf thymus was relatively insensitive to the action of partially thiolated polycytidylic acid (MPC) which had been shown previously to be a potent inhibitor of the corresponding enzyme from regenerating rat liver, competitive with the activated DNA template. In contrast, partially thiolated polyuridylic acid (MPU) strongly inhibited the calf thymus enzyme as well, but showed non-competitive kinetics with respect to the activated DNA template. The much more potent inhibitory activity of MPU compared to MPC was attributed to the less rigid conformation of the former. Methyl substitution on the 5-mercapto groups of MPU substantially decreased but did not abolish its inhibitory activity. MPU was also a potent inhibitor of the herpes virus (HSV-1) induced DNA polymerase which, too, showed little sensitivity toward MPC; in this case, the inhibition by MPU was uncompetitive with respect to the DNA template. In preliminary experiments, MPU showed significant (61%) inhibition of the replication of HSV-1, while MPC was inactive. The results demonstrate that the inhibitory activity of partially thiolated synthetic polynucleotides toward certain DNA polymerases is dependent on the base composition.

Studies on the mode of action of single-stranded polynucleotides which are antiviral against encephalomyocarditis virus infection of mice

Poly(dI) and poly(dC) administered separately or sequentially show no antiviral effects against EMC virus infection of mice, whereas poly(rI) and poly(rC) are antiviral in such treatment regimens without evidence of interferon induction. The antiviral effects of poly(rI) and poly(rC) appear to depend on single-strandedness because their antiviral effects are decreased by annealing to poly(dC) and poly(dI) respectively. This decrease in antiviral effect would not seem to be due to an adverse effect of polydeoxyribonucleotides on EMC virus infection because the polydeoxyribonucleotides have no effect on the antiviral activity of another single-stranded RNA, E. coli tRNA.