Risperidone versus haloperidol in the treatment of acute exacerbations of chronic inpatients with schizophrenia: a randomized double-blind study

The purpose of this study was to compare the efficacy and safety of risperidone and haloperidol in treatment-resistant chronic schizophrenic patients. Subjects (n = 78) who met DSM-III criteria for schizophrenia were randomly assigned to receive 6 mg/day of risperidone or 20 mg/day of haloperidol for 12 weeks. Clinical efficacy was determined using the Positive and Negative Syndrome Scale (PANSS), and side-effects with the Treatment Emergent Symptom Scale (TESS). Risperidone produced a mean 39.8 +/- 24.1% reduction in total PANSS score compared to a mean 28.3 + 19.4% reduction in the haloperidol group (P < 0.05). Analysis of changes for the three subscores of the PANSS revealed that the general psychopathology and negative subscores were significantly improved in the risperidone group compared to the haloperidol group. As for the side-effects, the risperidone group showed a significantly lower TESS total score, as well as nervous system symptoms subscore and cardiovascular symptoms subscore, compared to the haloperidol group. Risperidone appears to be a more effective and better tolerated antipsychotic drug in treatment-refractory Chinese schizophrenia than haloperidol.

A ribonuclease H-oligo DNA conjugate that specifically cleaves hepatitis B viral messenger RNA

Ribonuclease H (RNaseH) recognizes and efficiently cleaves the RNA strand of DNA-RNA hybrids, but has no inherent sequence selectivity. However, the formation of DNA-RNA hybrids does require specific sequence recognition. On the basis of this concept, we wondered whether antisense oligonucleotides complementary to target RNA covalently linked to RNase H could be used to direct specific cleavage events mediated by RNase H. The aim of this research was to couple a DNA oligonucleotide to RNase H to confer specificity of ribonuclease activity toward hepatitis B viral (HBV) mRNA. A modified 13-base oligonucleotide that is specific for the DR1 region of HBV mRNA was conjugated to modified E. coli RNase H using a water soluble cross-linker. A 1200 base fragment of HBV RNA including the DR1 region was synthesized as a substrate using T7 RNA polymerase. Incubation of the RNase H-oligonucleotide conjugate with the RNA transcript resulted in cleavage of the HBV mRNA transcript in a concentration dependent manner. Eighty-five percent of substrate was cleaved under optimal conditions. Controls consisting of RNase H alone, oligonucleotide alone, and incubation of the conjugate with an unrelated mRNA substrate resulted in no cleavage activity. RNase H coupled to an HBV antisense oligonucleotide can specifically cleave target HBV transcripts.

Targeted polynucleotides for inhibition of hepatitis B and C viruses

AIM

To determine whether a combination of cell targeting and sequence recognition of nucleic acids can provide specificity for the inhibition of viral gene expression.

METHODS

Antisense oligonucleotides complexed to a protein-based DNA carrier system were used to target hepatocytes for the inhibition of human hepatitis viral gene expression. The DNA carrier system contained an asialoglycoprotein as a cell-targeting component, which could direct the uptake of complexed DNA specifically to asialoglycoprotein receptors present selectively on the surface of mammalian hepatocytes.

RESULTS

HBV and HCV viral gene expression were substantially and specifically inhibited by use of antisense oligonucleotides complexed to a protein-based DNA carrier system.

CONCLUSION

Targeted delivery of nucleic acids by use of receptor-mediated endocytosis can result in inhibition of viral gene expression without host toxicity.

Liver cell transplantation -- novel animal model for human hepatic viral infections

AIM

To generate a model of human hepatitis B infection (HBV) in immunocompetent rats with chimeric human liver.

METHODS AND RESULTS

Normal rats were tolerized to human hepatocytes by exposure to human hepatocytes at day 17 of gestation. We transplanted human hepatocytes and inoculated HBV into the rats after birth. Mixed lymphocytes assay, a measure for tolerance, indicated that animals fetally exposed to human hepatocytes developed tolerance to human hepatocytes. Spleen lymphocytes from tolerized animals did not proliferate when challenged with donor human hepatocytes. In contrast, control animals given saline fetally developed no tolerance to human hepatocytes. Tolerant animals with transplanted human hepatocytes were susceptible to HBV infection. Western blot analysis and immuno-histochemistry of liver sections from tolerized, HBV infected animals with transplanted human hepatocytes showed the presence of functioning human hepatocytes that synthesized human albumin, of which 30% were also positive for HB surface antigen and HBV DNA. The presence of covalent closed circular HBV DNA in the liver indicated active HBV viral replication.

CONCLUSION

Tolerized rats with chimeric human livers can be infected with HBV and used as an animal model for HBV infection. Tolerized rats with chimeric human livers can also be used for generating models of other human hepatic viral diseases.

Transplantation of human hepatocytes into tolerized genetically immunocompetent rats

AIM: To determine whether normal genetically immunocompetent rodent hosts could be manipulated to accept human hepatocyte transplants with long term survival without immunosuppression.

METHODS: Tolerance towards human hepatocytes was established by injection of primary human hepatocytes or Huh7 human hepatoma cells into the peritoneal cavities of fetal rats. Corresponding cells were subsequently transplanted into newborn rats via intrasplenic injection within 24 h after birth.

RESULTS: Mixed lymphocyte assays showed that spleen cells from non-tolerized rats were stimulated to proliferate when exposed to human hepatocytes, while cells from tolerized rats were not. Injections made between 15 d and 17 d of gestation produced optimal tolerizaton. Transplanted human hepatocytes in rat livers were visualized by immunohistochemical staining of human albumin. By dot blotting of genomic DNA in livers of tolerized rats 16 weeks after hepatocyte transplantation, it was found that approximately 2.5 × 10⁵ human hepatocytes survived per rat liver. Human albumin mRNA was detected in rat livers by RT-PCR for 15 wk, and human albumin protein was also detectable in rat serum.

CONCLUSION: Tolerization of an immunocompetent rat can permit transplantation, and survival of functional human hepatocytes.

The scaffold protein, Homer1b/c, regulates axon pathfinding in the central nervous system in vivo

Homer proteins are a family of multidomain cytosolic proteins that have been postulated to serve as scaffold proteins that affect responses to extracellular signals by regulating protein-protein interactions. We tested whether Homer proteins are involved in axon pathfinding in vivo, by expressing both wild-type and mutant isoforms of Homer in Xenopus optic tectal neurons. Time-lapse imaging demonstrated that interfering with the ability of endogenous Homer to form protein-protein interactions resulted in axon pathfinding errors at stereotypical choice points. These data demonstrate a function for scaffold proteins such as Homer in axon guidance. Homer may facilitate signal transduction from cell-surface receptors to intracellular proteins that govern the establishment of axon trajectories.

Crystallographic structures of the ligand-binding domains of the androgen receptor and its T877A mutant complexed with the natural agonist dihydrotestosterone

The structures of the ligand-binding domains (LBD) of the wild-type androgen receptor (AR) and the T877A mutant corresponding to that in LNCaP cells, both bound to dihydrotestosterone, have been refined at 2.0 A resolution. In contrast to the homodimer seen in the retinoid-X receptor and estrogen receptor LBD structures, the AR LBD is monomeric, possibly because of the extended C terminus of AR, which lies in a groove at the dimerization interface. Binding of the natural ligand dihydrotestosterone by the mutant LBD involves interactions with the same residues as in the wild-type receptor, with the exception of the side chain of threonine 877, which is an alanine residue in the mutant. This structural difference in the binding pocket can explain the ability of the mutant AR found in LNCaP cells (T877A) to accommodate progesterone and other ligands that the wild-type receptor cannot.

AACR/NHRI Joint Conference: hepatitis and hepatocellular carcinoma: novel approaches

This international meeting, co-sponsored by the National Health Research Institutes of Taiwan (NHRI) and the AmericanAssociation for Cancer Research (AACR), was dedicated to two pioneering scientists, Juei-Low Sung (Koo Foundation, Sun Yat-Sen Cancer Center, Taipei, Taiwan) and Kwang-Juei Lo (Taipei Veterans General Hospital, Taipei, Taiwan). The meeting focused on various aspects of viral hepatitis and hepatocellular carcinoma (HCC), and the relation between the two. Topics ranged from epidemiological studies, identification of environmental and genetic risk factors, mechanisms of pathogenesis, and research presentations on standard and novel treatment modalities. Highlights included discussions on adefovir dipivoxil (Gilead Sciences), emtricitabine (FTC; Triangle Pharmaceuticals), clevudine (L-FMAU; Triangle Pharmaceuticals/Abbott/Bukwang Pharmaceutical Industries), entecavir (Bristol-Myers Squibb), and especially L-isomer nucleoside analogs, for use in hepatitis B virus (HBV) therapy. Mention was also made of the potential roles of histamine and mycophenolic acid in the treatment of hepatitis C virus (HCV) infections, and of polyphenols and thalidomide for HCC.

Human hepatocytes transplanted into genetically immunocompetent rats are susceptible to infection by hepatitis B virus in situ

Immune tolerance of human cells without generalized immunosuppression was created in groups of normal fetal rats at 17 days of gestation by inoculation ip with primary human hepatocytes in utero. One day after birth, suspensions of human hepatocytes were transplanted via intrasplenic injection and one week later groups of rats were inoculated with hepatitis B virus (HBV). Tolerized rats that were transplanted with human hepatocytes and subsequently infected with HBV produced hepatitis B surface antigen (HBsAg) in serum beginning on day 3. Levels rose fivefold and remained stable at 0.75 pg/ml through at least 60 days. Of cells that stained positive for human serum albumin, approximately 30% were found to be also positive for HBsAg by immunohistochemistry. Serum HBV DNA was detectable from 1 to 15 weeks postinfection. Finally, covalently closed circular DNA, reflecting HBV replication, was found in liver and serum. Controls that were tolerized and not transplanted, but inoculated with HBV, as well as untreated controls, had no evidence of HBV gene expression or replication under identical conditions. The data support the conclusion that primary human hepatocytes transplanted into genetically immunocompetent rodent hosts, survive and maintain sufficient differentiation to produce human serum albumin and be infected by HBV.

Activity-dependent CREB phosphorylation: convergence of a fast, sensitive calmodulin kinase pathway and a slow, less sensitive mitogen-activated protein kinase pathway

The cAMP-responsive element binding protein (CREB), a key regulator of gene expression, is activated by phosphorylation on Ser-133. Several different protein kinases possess the capability of driving this phosphorylation, making it a point of potential convergence for multiple intracellular signaling cascades. Previous work in neurons has indicated that physiologic synaptic stimulation recruits a fast calmodulin kinase IV (CaMKIV)-dependent pathway that dominates early signaling to CREB. Here we show in hippocampal neurons that the fast, CaMK-dependent pathway can be followed by a slower pathway that depends on Ras/mitogen-activated protein kinase (MAPK), along with CaMK. This pathway was blocked by dominant-negative Ras and was specifically recruited by depolarizations that produced strong intracellular Ca(2+) transients. When both pathways were recruited, phosphorylated CREB (pCREB) formation was overwhelmingly dominated by the CaMK pathway between 0 and 10 min, and by the MAPK pathway at 60 min, whereas the two pathways acted in concert at 30 min. The Ca(2+) signals that produced only rapid CaMK signaling to pCREB or both rapid CaMK and slow MAPK signaling deviated significantly for only approximately 1 min, yet their differential impact on pCREB extended over a much longer period, between 20 and 60 min and beyond, which is of likely significance for gene expression. The CaMK-dependent MAPK pathway may inform the nucleus about stimulus amplitude. In contrast, the CaMKIV pathway may be well suited to conveying information on the precise timing of localized synaptic stimuli, befitting its greater speed and sensitivity, whereas the previously described calcineurin pathway may carry information about stimulus duration.

Spaced stimuli stabilize MAPK pathway activation and its effects on dendritic morphology

Memory storage in mammalian neurons probably depends on both biochemical events and morphological alterations in dendrites. Here we report an activity-dependent stabilization of the MAP kinase (MAPK) pathway, prominent in hippocampal dendrites. The longevity of the signal in these dendrites was increased to hours when multiple spaced stimuli were used. Likewise, spaced stimuli and MAPK activation were critical for protrusion of new dendritic filopodia that also remained stable for hours. Our experiments define a new role for stimulus-specific responses of MAPK signaling in activity-dependent neuronal plasticity. The local biochemical signaling in dendrites complements MAPK signaling in gene expression. Together, these processes may support long-lasting behavioral changes.

Progress toward a synthetic virus : a multicomponent system for liver-directed DNA delivery

Vectors for gene transfer can be categorized as viral and nonviral. The advantages of nonviral carriers are their ease of preparation and scale-up, flexibility regarding the size of DNA to be transferred, and safety in vivo. Despite these advantages, nonviral vectors need to be further optimized for their efficiency is generally low. Thus, the future of non-viral vectors will be dependent on the possibility of creating synthetic efficient systems. A possible and reasonable approach is to develop artificial nucleic acid carriers that incorporate functional elements mimicking viruses.

Transfection and expression of HCV-NS5B gene in Huh-7 cells

OBJECTIVE

To study the mechanism of hepatitis C virus (HCV) replication and to test gene therapy for hepatitis C, a human liver cell line expressed HCV RNA polymerase has been established.

METHODS

NS5B gene has been transfected into Huh-7 cells by lipofectamine. The results of transfection were confirmed by PCR and Southern blot analysis, and the level of the non-structural protein 5B (NS5B) in Huh-7 cells was detected by Western blot analysis.

RESULTS

There were NS5B gene fragments and the expression of NS5B protein in Huh-7c cells transfected with pTeT-NS5B or pcDNA-NS5B plasmid.

CONCLUSIONS

We have established a HCV RNA polymerase expression system in Huh-7 cells which can be further used to analyze the mechanism of HCV replication and provide a cell model for gene therapy in vitro.

Gene therapy applications in gastroenterology and hepatology

Advantages and disadvantages of viral vectors and nonviral vectors for gene delivery to digestive organs are reviewed. Advances in systems for the introduction of new gene expression are described, including self-deleting retroviral transfer vectors, chimeric viruses and chimeric oligonucleotides. Systems for inhibition of gene expression are discussed, including antisense oligonucleotides, ribozymes and dominant-negative genes.

Multicomponent DNA carrier with a vesicular stomatitis virus G-peptide greatly enhances liver-targeted gene expression in mice

Genes can be targeted to hepatocytes in vitro and in vivo by the use of asialoorosomucoid-polylysine conjugates. After systemic application, this nonviral vector is recognized by highly selective asialoglycoprotein (AsGP) receptors on the sinusoidal liver cell membrane and is taken up via receptor-mediated endocytosis. As most of the DNA is rapidly transferred to lysosomes where it is degraded, transfection efficiency is low and gene expression transient. To address this problem, we incorporated a pH-dependent synthetic hemolytic peptide derived of the G-protein of Vesicular Stomatitis Virus (VSV) into the gene transfer system, to increase endosomal escape of internalized DNA. The multicomponent carrier binds DNA in a nondamaging way, is still recognized by the AsGP receptor, and is targeted to the liver in vivo. Injection of DNA complexes containing a luciferase marker gene resulted in luciferase expression of 29 000 pg/g liver which corresponded to an increase of a factor of 10(3) overexpression after injection of DNA complexes without endosomolytic peptide. Furthermore, the amount of intact transgene within isolated liver cell nuclei was increased by a factor of 10(1)-10(2) by the use of the multicomponent carriers. These results demonstrate that incorporation of a hemolytic peptide into a nonviral vector can greatly increase gene expression while retaining cell type targetability in vivo.

Inhibition of hepatitis C virus-directed gene expression by a DNA ribonuclease

BACKGROUND/AIMS

The aim of this study was to determine whether DNA analogs of ribozymes could be prepared to inhibit hepatitis C virus (HCV) gene expression.

METHODS

Two DNA ribonucleases, Dz2 and Dz4, were designed with varying arm lengths, to cleave at the 5'-noncoding region (NCR) just upstream from the translation start site, and core region of HCV genome, respectively. A reporter vector was prepared to contain target HCV regulatory sequences controlling a downstream luciferase gene. DNA ribonucleases with normal phosphodiester, as well as with terminal phosphorothioate linkages, were administered to Huh7 cells, and luciferase activity was measured.

RESULTS

DNA ribonucleases were highly active in cleaving HCV RNA targets. Enzymes with longer arms had consistently higher cleavage activity compared to enzymes with shorter arms under cell-free conditions. Furthermore, in Huh7 cells, terminal phosphorothioate derivatives, Dz2 and Dz4, significantly suppressed HCV-luciferase fusion gene expression up to 45% and 67% of controls, respectively. Interestingly, phosphorothioate-modified DNA ribonucleases had greater inhibitory effects on target gene expression than their unmodified counterparts. In contrast, DNA ribonucleases with point mutations in the catalytic domain had significantly lower inhibitory effects compared to wild-type DNA ribonucleases. However, activity was not eliminated, suggesting that some antisense contribution was present.

CONCLUSIONS

DNA ribonucleases directed against the HCV genome can specifically cleave target HCV RNA. Modifications of the extreme 3'- and 5'-termini protect against nuclease degradation without appreciable reduction in inhibitory activity against viral gene expression under intracellular conditions.

Dual actions of isthmic input to tectal neurons in a reptile, Gekko gekko

We analyzed postsynaptic potentials and dye-labeled morphology of tectal neurons responding to electrical stimulation of the optic nerve and of the nucleus isthmi in a reptile, Gekko gekko, in order to compare with previously reported interactions between the optic tectum and the nucleus isthmi in amphibians and birds. The results indicate that isthmic stimulation exerts inhibitory and excitatory actions on tectal cells, similar to dual isthmotectal actions in amphibians. It appears that dual actions of the isthmotectal pathway in amphibians and reptiles are shared by two subdivisions of the nucleus isthmi in birds. The morphology of tectal cells responding to isthmic stimulation is generally similar to that of tectoisthmic projecting neurons, but they differ particularly in that some tectoisthmic cells bear numerous varicosities whereas cells receiving isthmic afferents do not. Thus, it is likely that at least some tectoisthmic cells may not be in the population of tectal cells that can be affected by isthmic stimulation. Forty-four percent of injections resulted in dye-coupled labeling, suggesting extensive electrical connections between tectal cells in reptiles.

Hepatocyte-directed gene delivery by receptor-mediated endocytosis

The application of gene therapy to liver disease is contingent on the development of an effective gene delivery vehicle. Receptor-mediated endocytosis can be exploited as a means of selective and efficient targeting of gene therapy vectors to hepatocytes. DNA-binding conjugates have been directed to the liver by the attachment of asialoglycoproteins or other ligands for receptors expressed on hepatocytes. Recent studies suggest refinements in this approach through which high transduction rates in vitro may be reproduced in vivo. The intrinsic liver tropism of viral vectors and liposomes can be augmented by the addition of targeting features, as demonstrated in animal models. With further modification, such as the incorporation of hepatotropic elements of the hepatitis viruses or lipoproteins, the next generation of delivery systems may achieve efficient, persistent expression of therapeutic genes in a safe and cell type-specific manner.

Dendritic dynamics in vivo change during neuronal maturation

In vivo imaging of optic tectal neurons in the intact Xenopus tadpole permits direct observation of the structural dynamics that occur during dendritic arbor formation. Based on images of single DiI-labeled neurons collected at daily intervals over a period of 6 d, we divided tectal cell development into three phases according to the total length of the dendritic arbor. During phase 1, the cell differentiates from a neuroepithelial cell type and extends an axon out of the tectum. The total dendritic branch length (TDBL) is <100 micrometers. During phase 2, when TDBL is 100-400 micrometers, the dendritic arbor grows rapidly. During phase 3, when TDBL is >400 micrometers, the dendritic arbor grows slowly and appears stable. Neurons at different positions along the rostrocaudal developmental axis of the tectum were imaged at 2 hr intervals over 6 hr and at 24 hr intervals over several days. Images collected at 2 hr intervals were analyzed to determine rates of branch additions and retractions. Morphologically complex, phase 3 neurons show half the rate of branch additions and retractions as phase 2 neurons. Therefore, rapidly growing neurons have dynamic dendritic arbors, and slower-growing neurons are structurally stable. The change in growth rate and dendritic arbor dynamics from phase 2 to phase 3 correlates with the developmental increase in synaptic strength in neurons located along the rostrocaudal tectal axis. The data are consistent with the idea that strong synaptic inputs stabilize dendritic arbor structures and that weaker synaptic inputs are permissive for a greater degree of dynamic rearrangements and a faster growth rate in the dendritic arbor.

A method for purification of listeriolysin O from a hypersecretor strain of Listeria monocytogenes

A simple and convenient method for the purification of the hemolytic toxin listeriolysin O (LLO) from Listeria monocytogenes is described. Supernatants from bacteria cultures were purified by application to a CH2 spiral cartridge concentrator (Amicon) and ion exchange chromatography. A critical step is removal of contaminating RNA. The purified proteins had characteristics described for bacterial thiol-activated hemolysins: activation by a reducing agent (DTT) and inactivation by cholesterol. In addition, the molecular weight of 58, 000 and pH-dependent hemolytic activity of this purified protein are consistent with the previously published characteristics of LLO.

Human portal serum stimulates cell proliferation in immature Schistosoma mansoni

Schistosomula of Schistosoma mansoni were incubated in RPMI 1640 medium containing 10% fetal calf serum, 10% human portal venous or 10% human peripheral venous sera in the presence of bromodeoxyuridine (BrdU) in order to measure differences in cell proliferation. The rates of cell proliferation as expressed by BrdU labelling indices (BLI) were determined as a function of time of incubation by immunohistochemistry using monoclonal antibody to BrdU. Compared to schistosomula cultured in the presence of RPMI plus 10% fetal calf serum, BLIs were increased by 60% in the presence of human portal, but not in peripheral serum. This stimulatory effect was substantially reproduced by a fraction of portal serum with a molecular weight range between 1 and 50 kDa. However, in the presence of human peripheral venous serum, either whole or fractionated, schistosomula showed no significant difference compared to RPMI plus 10% fetal calf serum alone. Furthermore, human portal serum fractions of molecular weight greater than 50 kDa also revealed no significant difference relative to control. The results indicate that portal venous serum component(s) of a molecular weight range higher than most simple nutrients can greatly stimulate the rate of cell proliferation of Schistosoma mansoni schistosomula.

Promotion of dendritic growth by CPG15, an activity-induced signaling molecule

Activity-independent and activity-dependent mechanisms work in concert to regulate neuronal growth, ensuring the formation of accurate synaptic connections. CPG15, a protein regulated by synaptic activity, functions as a cell-surface growth-promoting molecule in vivo. In Xenopus laevis, CPG15 enhanced dendritic arbor growth in projection neurons, with no effect on interneurons. CPG15 controlled growth of neighboring neurons through an intercellular signaling mechanism that requires its glycosylphosphatidylinositol link. CPG15 may represent a new class of activity-regulated, membrane-bound, growth-promoting proteins that permit exquisite spatial and temporal control of neuronal structure.

Recent advances in gene therapy of GI and liver diseases

Gene therapy toward the digestive organs has made substantial progress. The strategies applied include ex vivo and in vivo delivery. The ex vivo pathway does not require a tissue-specific vector while the in vivo pathway is advantageous for tissues not obtainable or hard to culture. The specific vectors of gene delivery for the liver and gastrointestinal tract include (1) viral vectors: retrovirus, adenovirus, and adeno-associated virus are the three most common currently used. (2) liposomes: when cationic substances are incorporated, DNA can be coated on the surface and carried into cells. (3) receptor-mediated gene therapy: natural and physiological and tissue-specific ligands were incorporated and modified to carry foreign DNA into the cells. They are tissue-specific and relatively nontoxic. The innovations focus on the prolongation of gene expression and a more efficient gene delivery.

DNA ribonucleases that are active against intracellular hepatitis B viral RNA targets

DNA ribonucleases directed against direct repeat 1 (DR1) and polyadenylation signal regions of hepatitis B virus (HBV) messages were prepared with phosphorothioate modifications and varying arm lengths. DNA ribonucleases modified throughout the entire molecule and in the target binding arms were completely protected from degradation after incubation with serum. DNA ribonuclease modified only at the 5' and 3' termini remained 92.9% intact after incubation. Molecules with no modification were degraded to 67.6% under the same conditions. However, modification of the entire molecule and in the recognition arms resulted in 99.8% and 98.4% inactivation of cleavage activity, respectively. Modification of only the termini resulted in retention of 20% to 40% of original activity. Lengthening each terminally modified arm from 9 to 11 nucleotides increased cleavage efficiency almost 10-fold. In Huh 7 cells, DR1-directed DNA ribonucleases with terminal modifications significantly suppressed HBV-luciferase fusion gene expression up to 48% of control. In contrast, DNA ribonucleases had no effect on a control construct lacking any HBV target sequences. Moreover, inactivated mutant and HCV-directed DNA ribonucleases had no significant effects on the HBV target. We conclude that resistance of DNA ribonucleases to degradation can be enhanced through phosphorothioate modification. Cleavage activity can be retained by limiting modification to the termini and lengthening the recognition arms. Such DNA ribonucleases can be made to specifically cleave target HBV RNA and substantially inhibit intracellular viral gene expression.