Advances in research on HBV inhibitors based on new targets (2): RNase H and others / 药学学报

Hepatitis B has become one of the major diseases which seriously affect people's health and social development. Hepatitis B, with high incidence and long disease course, cannot be cured by approved drugs such as the nucleoside analogues. Therefore, the discovery of safe and efficient novel HBV inhibitors is of great significance. From the point of view of medicinal chemistry, we summarized and discussed current endeavours towards the discovery and development of anti-HBV agents of RNase H and other novel target inhibitors with various scaffolds or distinct mechanisms of action, besides the existing capsid protein inhibitors.

Characterization of Echinostoma cinetorchis endoribonuclease, RNase H

Echinostoma cinetorchis is an oriental intestinal fluke causing significant pathological damage to the small intestine. The aim of this study was to determine a full-length cDNA sequence of E. cinetorchis endoribonuclease (RNase H; EcRNH) and to elucidate its molecular biological characters. EcRNH consisted of 308 amino acids and showed low similarity to endoribonucleases of other parasites (<40%). EcRNH had an active site centered on a putative DDEED motif instead of DEDD conserved in other species. A recombinant EcRNH produced as a soluble form in Escherichia coli showed enzymatic activity to cleave the 3′-O-P bond of RNA in a DNA-RNA duplex, producing 3′-hydroxyl and 5′-phosphate. These findings may contribute to develop antisense oligonucleotides which could damage echinostomes and other flukes.

Detection of stress-induced 5′tRNA halves by poly(A) tailed-RNase H digestion-RT-PCR / 军事医学

Objective To develop a simple and quick method for detection of stress-induced 5′transfer RNA( tRNA) halves.Methods Total RNA purified from stress induced cells was polyadenylated by poly( A) polymerase, and then degen-erate DNA probes were used to hybridize with 3′tRNA-halves of intact tRNAs,while RNase H specifically degraded the 3′tRNA-halves strand in tRNA-DNA probes hybrids.Using the RNase H digestion total RNA as templates, complementary DNA( cDNA) was synthesized by oligo ( dT) n-anchored primers.The primer of 5′tRNA halves and anchored-primer were used to amplify 5′tRNA halves by PCR.Results The results showed that the method of poly ( A )-tailed-RNase H digestion-RT-PCR could be successfully used to detect stress-induced 5′tRNA halves.Conclusion A simple and quick method for detection of 5′tRNA halves has been established,which is a user-friendly tool for 5′tRNA halves detection and function research.

Development of Human Antibody Inhibiting RNase H Activity of Polymerase of Hepatitis B Virus Using Phage Display Technique

BACKGROUND: To develop a novel treatment strategy for hepatitis B virus infection, a major cause of liver chirosis and cancer, we aimed to make human monoclonal antibodies inhibiting RNase H activity of P protein playing in important role in HBV replication. In this regard, phage display technology was employed and demonstrated as an efficient cloning method for human monoclonal antibody. So this study analysed the usability of human monoclonal antibody as protein based gene therapy. METHODS: RNase H of HBV was expressed as fusion protein with maltose binding protein and purified with amylose resin column. Single chain Fv (scFv) phage antibody library was constructed by PCR cloning using total RNAs of PBMC from 50 healthy volunteers. Binders to RNase H were selected with BIAcore 2000 from the constructed library, and purified as soluble antibody fragment. The affinity and sequences of selected antibody fragments were analyzed with BIAcore and ABI automatic sequencer, respectively. And finally RNase H activity inhibiting assay was carried out. RESULTS: Recombinant RNase H expressed in E. coli exhibited an proper enzyme activity. Naive library of 4.46 X 10(9) cfu was screened by BIAcore 2000. Two clones, RN41 and RN56, showed affinity of 4.5 X 10(-7) M and 1.9 X 10(-7) M, respectively. But RNase H inhibiting activity of RN41 was higher than that of RN56. CONCLUSION: We cloned human monoclonal antibodies inhibiting RNase H activity of P protein of HBV. These antibodies can be expected to be a good candidate for protein-based antiviral therapy by preventing a replication of HBV if they can be expressed intracellularly in HBV-infected hepatocytes.

Effect of cupric-isonicotinic acid hydrazide complex on avian myeloblastosis virus reverse transcriptase and its associated enzyme activities.

Cupric complex of isonicotinic acid hydrazide inhibits DNA synthesis by avian myloblastosis virus reverse transcriptase. This inhibition occurs in the presence of either ribonucleotide or deoxyribonucleotide templates. The inhibition of reverse transcriptase by cupric-INH complex is considerably reduced when stored or proteolytically cleaved enzyme was used in the reaction. The complex also inhibits the reverse transciptase-associated RNase Η activity. The cupric-isonicotinic acid hydrazide complex cleaves pBR 322 from I DNA into smaller molecules in the presence or absence of reverse transcriptase-associated endonuclease. However, in the presence of the enzyme the DNA is cleaved to a greater extent.