Inhibition of human immunodeficiency virus type 1 reverse transcriptase by 3'-blocked oligonucleotide primers

An additional 2'-ribofuranose residue at a specific position of the DNA primer prevents Its elongation by HIV-1 reverse transcriptase

Oligodeoxynucleotides containing 2'-O-beta-D-ribofuranosyladenosine were prepared and used as modified primers in RNA-templated DNA synthesis catalyzed by HIV reverse transcriptase. It was shown that the additional 2'-ribofuranose residue in specific position of primer prevents its elongation.

HIV-1 protease inhibits its homologous reverse transcriptase by protein-protein interaction

The reading frame of the HIV-1 pol gene, encoding protease (PR) and reverse transcriptase (RT), including RNase H as well as integrase, was fused to the bacterialbeta-galactosidase gene and overexpressed in Escherichia coli cells. The resulting fusion protein was cleaved autocatalytically leading to PR, RT and integrase. Immunoprecipitations of bacterial crude extracts with anti-RT antibodies precipitated both RT and PR. Co-precipitation of PR and RT was also observed with anti-PR antibodies, strongly suggesting a physical interaction between fully processed RT and PR within the bacterial cell. Physical interactions were confirmed with purified components by means of an ELISA assay. Furthermore, purified PR inhibited the DNA synthesis activity of purified RT, while its RNase H activity remained unaffected. The type of inhibition was uncompetitive with respect to poly(rA).oligo(dT); the inhibition constant was 50-100 nM. A possible physiological significance of this type of interaction is discussed.

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.

Two step binding of HIV-1 reverse transcriptase to nucleic acid substrates

The interactions of HIV-1 reverse transcriptase (HIV-1 RT) with a synthetic 53/19-mer DNA substrate was investigated. For this template-primer HIV-1 RT displayed a Km value of 20 nM. The 53/19-mer competitively inhibited DNA synthesis performed on poly (rC).oligo(dG) with Ki value of 260 nM. This corresponded well to an equilibrium dissociation constant (Kd) of 300 nM, as determined by analytical ultracentrifugation. Since the Kd value is considerably higher than the corresponding Km value it is concluded that the enzyme--DNA complex is further stabilized by the binding of a cognate deoxynucleoside triphosphate and/or catalytic turnover. The association kinetics of HIV-1 RT with the 53/19-mer was measured by the fluorescence stopped-flow technique. RT bound the 53/19-mer with a rate constant of 2 +/- 1 x 10(8) M-1 s-1. The DNA binding step was succeeded by a concentration-independent step with a rate constant of 1.0 +/- 0.5 s-1 suggesting a conformational change of the enzyme. Template-primer binding of RT was influenced by the concentration of MgCl2, displaying a 17-fold increase in the Kd value when Mg2+ was increased from 1 mM to 30 mM. Since neither the association rate constant nor the conformational change was notably affected by changes of the Mg2+ concentration, it is concluded that the dissociation constant is increased by higher concentrations of Mg2+.