Efficient Inhibition of Hepatitis B Virus Replication and cccDNA Formation by HBV Ribonuclease H Inhibitors During Infection

The Hepatitis B Virus (HBV) ribonuclease H (RNase H) is an attractive but unexploited drug target. Here, we addressed three limitations to the current state of RNase H inhibitor development: i) Efficacy has been assessed only in transfected cell lines; ii) Cytotoxicity data are from transformed cell lines rather than primary cells; and iii) It is unknown how the compounds work against nucleos(t)ide analog resistant HBV strains. Three RNase H inhibitors from different chemotypes, 110 (α-hydroxytropolone), 1133 (N-hydroxypyridinedione), and 1073 (N-hydroxynapthyridinone), were tested in HBV-infected HepG2-NTCP cells for inhibition of cccDNA accumulation and HBV product formation. 50% effective concentrations (EC 50 s) were 0.049-0.078 μM in the infection studies compared to 0.29-1.6 μM in transfected cells. All compounds suppressed cccDNA formation by >98% at 5 μM when added shortly after infection. HBV RNA, intracellular and extracellular DNA, and HBsAg secretion were all robustly suppressed. The greater efficacy of the inhibitors when added shortly after infection is presumably due to blocking amplification of the HBV cccDNA, which suppresses events downstream of cccDNA formation. The compounds had 50% cytotoxic concentrations (CC 50 s) of 16-100 μM in HepG2-derived cell lines but were non-toxic in primary human hepatocytes, possibly due to the quiescent state of the hepatocytes. The compounds had similar EC 50 s against replication of wild-type, Lamivudine-resistant and Adefovir/Lamivudine-resistant HBV, as expected because the RNase H inhibitors do not target the viral reverse transcriptase active site. These studies expand confidence in inhibiting the HBV RNase H as a drug strategy and support inclusion of RNase H inhibitors in novel curative drug combinations for HBV.

Hepatitis B virus polymerase restricts LINE-1 retrotransposition

Long interspersed element-1 (LINE-1, L1) retrotransposon composes about 17% of the human genome. However, genetic and biochemical interactions between L1 and hepatitis B virus (HBV) remain poorly understood. In this study, we found that HBV restricts L1 mobility without inhibiting the L1 promoter activity. Notably, HBV polymerase (Pol) strongly inhibited L1 retrotransposition in a reverse transcriptase (RT)-independent manner. Indeed, the ribonuclease H (RNase H) domain was essential for inhibition of L1 retrotransposition. L1 ORF1p RNA-binding protein predominantly localized into cytoplasmic RNA granule termed P-body. However, HBV Pol sequestered L1 ORF1p from P-body and colocalized with L1 ORF1p in cytoplasm, when both proteins were co-expressed. Altogether, HBV Pol seems to restrict L1 mobility through a sequestration of L1 ORF1p from P-body. Thus, these results suggest a novel function or activity of HBV Pol in regulation of L1 retrotransposition.

Small-molecule Inhibitors of HIV-1 Reverse Transcriptase-Associated Ribonuclease H function: Challenges and Recent Developments.

: Multiple combination of antiretroviral drugs has remarkably improved the treatment of HIV-1 infection. However, life-long treatments and drug resistance are a still open issue that requires continuous efforts for identification of novel antiviral drugs. Background: the reverse transcriptase-associated ribonuclease H (RNase H) hydrolyzes the HIV genome to allow synthesizing viral DNA. Currently, no RNase H inhibitors (RHIs) have reached the clinical phase. Therefore, RNase H can be defined as an attractive target for drug design. Objective: despite the wealth of information available for RNase H domain, the development of RHIs with high specificity and low cellular toxicity has been disappointing. However, it is now becoming increasingly evident that reverse transcriptase is a highly versatile enzyme, undergoing major structural alterations to complete its catalysis, and that exists a close spatial and temporal interplay between reverse transcriptase polymerase and RNase H domains. This review sums up the present dares in targeting RNase H encompassing the challenges in selectively inhibiting RNase H vs polymerase and/or HIV-1 integrase and the weak antiviral activity of active site inhibitors, probably for a substrate barrier that impedes small molecules to reach the targeted site. Moreover, focus is given on the most recent progresses in the field of medicinal chemistry that have led to the identification of several small molecules as RHIs in the last few years. Conclusion: RHIs could be a new class of drugs with novel mechanism of action highly precious for the treatment of resistant HIV strains.

Vibrational Analysis and Molecular Docking Studies on some Ribonuclease-H HIV Inhibitors

Ribonuclease-H (RNase-H) enzyme of the human immunodeficiency virus (HIV) reverse transcriptase (RT) shows inhibitory activity with novel galloyl derivatives having enzymatic assays of IC50 S at sub to low micromolar concentration. The computational analysis of these stated galloyl derivatives was carried out in order to extract information and performance with the target proteins. The compounds N-hydroxylisoquinolinediones (HID), β-thujaplicinol, diketoacid, diketoacid ester, pyrimidinol carboxylic acids, naphthyridinones, 3hydroxypyrimidine-2,4-dione (HPD), and hydroxypyridonecarboxylic acids are the selected galloyl derivatives of human immunodeficiency virus-I (HIV-I) RNase-H active site inhibitors that were optimized using Turbomole software. Further evaluation of their NMR shielding of the stated compounds was performed using B3-LYP hybrid functional, and the def-SV basis set was carried out from the same software. These optimized compounds were then docked to targets (PDB Id: 5EGA and 3K2P) using AutoDock 4 software. After analyzing the docking result, Hydroxylisoquinoline and Naphthyridinones give better binding results with both the targets.

Inhibition of off-target cleavage by RNase H using an artificial cationic oligosaccharide

Sequence-dependent off-target effects are a serious problem of antisense oligonucleotide-based drugs. Some of these side effects are induced by ribonuclease H (RNase H)-mediated cleavage of non-target RNAs with similar base...

Improvement of Moloney murine leukemia virus reverse transcriptase thermostability by introducing a disulfide bridge in the ribonuclease H region

Moloney murine leukemia virus (MMLV) reverse transcriptase (RT) is widely used in research and clinical diagnosis. Improvement of MMLV RT thermostability has been an important topic of research for increasing the efficiency of cDNA synthesis. In this study, we attempted to increase MMLV RT thermostability by introducing a disulfide bridge in its RNase H region using site-directed mutagenesis. Five variants were designed, focusing on the distance between the two residues to be mutated into cysteine. The variants were expressed in Escherichia coli and purified. A551C/T662C was determined to be the most thermostable variant.

A Sister Lineage of Sampled Retroviruses Corroborates the Complex Evolution of Retroviruses

The origin and deep history of retroviruses remain mysterious and contentious, largely because the diversity of retroviruses is incompletely understood. Here, we report the discovery of lokiretroviruses, a novel major lineage of retroviruses, within the genomes of a wide range of vertebrates (at least 137 species), including lampreys, ray-finned fishes, lobe-finned fishes, amphibians, and reptiles. Lokiretroviruses share a similar genome architecture with known retroviruses, but display some unique features. Interestingly, lokiretrovirus Env proteins share detectable similarity with fusion glycoproteins of viruses within the Mononegavirales order, blurring the boundary between retroviruses and negative sense single-stranded RNA viruses. Phylogenetic analyses based on reverse transcriptase demonstrate that lokiretroviruses are sister to all the retroviruses sampled to date, providing a crucial nexus for studying the deep history of retroviruses. Comparing congruence between host and virus phylogenies suggests lokiretroviruses mainly underwent cross-species transmission. Moreover, we find that retroviruses replaced their ribonuclease H and integrase domains multiple times during their evolutionary course, revealing the importance of domain shuffling in the evolution of retroviruses. Overall, our findings greatly expand our views of the diversity of retroviruses, and provide novel insights into the origin and complex evolutionary history of retroviruses.