Short partially double-stranded oligodeoxynucleotide induces reverse transcriptase/RNase H-mediated cleavage of HIV RNA and contributes to abrogation of infectivity of virions

Abolishing HIV-1 infectivity using a polypurine tract-specific G-quadruplex-forming oligonucleotide

Background

HIV is primarily transmitted by sexual intercourse and predominantly infects people in Third World countries. Here an important medical need is self-protection for women, particularly in societies where condoms are not widely accepted. Therefore, availability of antiviral microbicides may significantly reduce sexual HIV transmission in such environments.

Methods

Here, we investigated structural characteristics and the antiviral activity of the polypurine tract (PPT)-specific ODN A, a 54-mer oligodeoxynucleotide (ODN) that has been previously shown to trigger the destruction of viral RNA genomes by prematurely activating the retroviral RNase H. The stability of ODN A and mutants thereof was tested at various storage conditions. Furthermore, antiviral effects of ODN A were analyzed in various tissue culture HIV-1 infection models. Finally, circular dichroism spectroscopy was employed to gain insight into the structure of ODN A.

Results

We show here that ODN A is a powerful tool to abolish HIV-1 particle infectivity, as required for a candidate compound in vaginal microbicide applications. We demonstrate that ODN A is not only capable to prematurely activate the retroviral RNase H, but also prevents HIV-1 from entering host cells. ODN A also exhibited extraordinary stability lasting several weeks. Notably, ODN A is biologically active under various storage conditions, as well as in the presence of carboxymethylcellulose CMC (K-Y Jelly), a potential carrier for application as a vaginal microbicide. ODN A’s remarkable thermostability is apparently due to its specific, guanosine-rich sequence. Interestingly, these residues can form G-quadruplexes and may lead to G-based DNA hyperstructures. Importantly, the pronounced antiviral activity of ODN A is maintained in the presence of human semen or semen-derived enhancer of virus infection (SEVI; i.e. amyloid fibrils), both known to enhance HIV infectivity and reduce the efficacy of some antiviral microbicides.

Conclusions

Since ODN A efficiently inactivates HIV-1 and also displays high stability and resistance against semen, it combines unique and promising features for its further development as a vaginal microbicide against HIV.

RNase H: specificity, mechanisms of action, and antiviral target

The Ribonuclease (RNase) H is one of the four enzymes encoded by all retroviruses, including HIV. Its main activity is the hydrolysis of the RNA moiety in RNA-DNA hybrids. The RNase H ribonuclease is essential in the retroviral life cycle, since it generates and removes primers needed by the Reverse Transcriptase (RT) for initiation of DNA synthesis. Retroviruses lacking RNase H activity are noninfectious. Despite its importance, RNase H is the only enzyme of HIV not yet targeted by antiretroviral therapy. Here, we describe functions and mechanisms of RNase H during the HIV life cycle and describe a cleavage assay, which is suitable to determine RNase H activity in samples of various kinds. In this assay, an artificial, fluorescence-labeled RNA-DNA hybrid is cleaved in vitro by an RT/RNase H enzyme. Cleavage products are analyzed by denaturing polyacrylamide gel electrophoresis (PAGE). This assay may be used to detect the RNase H, assess the effect of inhibitors, or even activators, of the RNase H, as we have described, as candidates for novel antiretroviral agents.

Premature activation of the HIV RNase H drives the virus into suicide: a novel microbicide?

Sexual transmission of HIV is the major cause of spread of HIV in Africa and the Third World and is an unmet medical need. Recently, microbicides have attracted attention because they allow females to protect themselves and their offspring. We are exploiting one of the four retroviral enzymes, the ribonuclease H, RNase H, as a novel approach for a microbicide. It is the only enzyme of HIV not yet targeted by antiretroviral therapy. The enzyme is linked to the reverse transcriptase (RT) and hydrolyzes the RNA moiety of RNA-DNA hybrids. The RNase H is located inside virus particles and normally functions during viral replication inside cells. Here we show that activating the RNase H prematurely inside the virus particles destroys the viral genome and abrogates viral infectivity. The antiviral compound consists of a synthetic oligodeoxynucleotide (ODN), which creates an artificial RNA-DNA hybrid substrate for the RNase H inside the particle. The compound was analyzed in mouse models including humanized SCID mice and the vagina of mice. Infection was reduced up to 1000-fold or could be completely prevented. The compound is suitable as microbicide or to prevent mother-to-child transmission.

Targeting the retroviral ribonuclease H by rational drug design

Ribonucleases H or RNases H are conserved and exist in almost every organism. They generate and remove RNA primers, which are required for DNA replication. RNases H hydrolyze RNA in RNA-DNA hybrids. RNases H and related enzymes contribute to reduction of gene expression in antisense and small-interfering RNA mechanisms for gene silencing. Retroviruses code for RNases H, which are required for DNA provirus synthesis. Their RNase H is fused to the reverse transcriptase and essential for virus replication inside the cell. Retroviruses code for four enzymes, three of which have been targeted by antiretroviral therapies. A drug against the fourth one, the retroviral RNase H, does not yet exist. The viral but not cellular RNases H should be targeted by drug design. Some details will be discussed here. Furthermore, a compound is described, which enables the RNase H to kill cell-free HIV particles by driving the virus into suicide - with potential use as a microbicide.

Short hairpin-looped oligodeoxynucleotides reduce hepatitis C virus replication

Background

Persistent infection with hepatitis C virus (HCV) is a leading cause of chronic hepatitis, liver cirrhosis, and hepatocellular carcinoma. Standard therapy consists of a combination of interferon-alpha and ribavirin, but many patients respond poorly, especially those infected with HCV genotypes 1 and 4. Furthermore, standard therapy is associated with severe side-effects. Thus, alternative therapeutic approaches against HCV are needed.

Findings

Here, we studied the effect of a new class of antiviral agents against HCV, short, partially double-stranded oligodeoxynucleotides (ODNs), on viral replication. We targeted the 5’ nontranslated region (5’ NTR) of the HCV genome that has previously been shown as effective target for small interfering RNAs (siRNAs) in vitro. One of the investigated ODNs, ODN 320, significantly and efficiently reduced replication of HCV replicons in a sequence-, time- and dose-dependent manner. ODN 320 targets a genomic region highly conserved among different HCV genotypes and might thus be able to inhibit a broad range of genotypes and subtypes.

Conclusions

ODNs provide an additional approach for inhibition of HCV, might be superior to siRNAs in terms of stability and cellular delivery, and suitable against HCV resistant to standard therapy. This study underlines the potential of partially double-stranded ODNs as antiviral agents.

A short hairpin loop-structured oligodeoxynucleotide targeting the virion-associated RNase H of HIV inhibits HIV production in cell culture and in huPBL-SCID mice

BACKGROUND

We have recently demonstrated that an oligodeoxynucleotide (ODN) can enter HIV particles and form a local hybrid at the highly conserved polypurine tract (PPT), the target site of the ODN. This hybrid is recognized by the retrovirus-specific RNase H, which is a virion-associated enzyme. It cleaves the RNA at local hybrids and thereby destroys viral infectivity. This mechanism has been described previously in a mouse model using an oncogenic retrovirus and was commented as driving HIV into suicide. The RNase H is one of four retrovirus-specific enzymes and not yet targeted by antiviral drugs.

AIMS

We wanted to analyze the tendency of ODNs to induce mutations in cell culture and its efficacy to inhibit HIV in humanized SCID mice.

METHOD

We used cultures of CD4+ T cells infected with HIV-1 after serial passage in the presence of ODNs in the supernatant for up to 3 months, using Foscarnet as positive control, and treated HIV-infected huPBL-SCID mice repeatedly with ODN.

RESULTS

Treatment with ODN did not induce mutations of the PPT or the reverse transcriptase polymerase domain in vitro, whereas Foscarnet did. We furthermore demonstrate that ODNs inhibit HIV-1 replication in humanized HIV-infected SCID mice.

The development of antiretroviral therapy and its impact on the HIV-1/AIDS pandemic

In the last 25 years, HIV-1, the retrovirus responsible for the acquired immunodeficiency syndrome (AIDS), has gone from being an "inherently untreatable" infectious agent to one eminently susceptible to a range of approved therapies. During a five-year period, starting in the mid-1980s, my group at the National Cancer Institute played a role in the discovery and development of the first generation of antiretroviral agents, starting in 1985 with Retrovir (zidovudine, AZT) in a collaboration with scientists at the Burroughs-Wellcome Company (now GlaxoSmithKline). We focused on AZT and related congeners in the dideoxynucleoside family of nucleoside reverse transcriptase inhibitors (NRTIs), taking them from the laboratory to the clinic in response to the pandemic of AIDS, then a terrifying and lethal disease. These drugs proved, above all else, that HIV-1 infection is treatable, and such proof provided momentum for new therapies from many sources, directed at a range of viral targets, at a pace that has rarely if ever been matched in modern drug development. Antiretroviral therapy has brought about a substantial decrease in the death rate due to HIV-1 infection, changing it from a rapidly lethal disease into a chronic manageable condition, compatible with very long survival. This has special implications within the classic boundaries of public health around the world, but at the same time in certain regions may also affect a cycle of economic and civil instability in which HIV-1/AIDS is both cause and consequence. Many challenges remain, including (1) the life-long duration of therapy; (2) the ultimate role of pre-exposure prophylaxis (PrEP); (3) the cardiometabolic side-effects or other toxicities of long-term therapy; (4) the emergence of drug-resistance and viral genetic diversity (non-B subtypes); (5) the specter of new cross-species transmissions from established retroviral reservoirs in apes and Old World monkeys; and (6) the continued pace of new HIV-1 infections in many parts of the world. All of these factors make refining current therapies and developing new therapeutic paradigms essential priorities, topics covered in articles within this special issue of Antiviral Research. Fortunately, there are exciting new insights into the biology of HIV-1, its interaction with cellular resistance factors, and novel points of attack for future therapies. Moreover, it is a short journey from basic research to public health benefit around the world. The current science will lead to new therapeutic strategies with far-reaching implications in the HIV-1/AIDS pandemic. This article forms part of a special issue of Antiviral Research marking the 25th anniversary of antiretroviral drug discovery and development, Vol. 85, issue 1, 2010.

A short hairpin DNA analogous to miR-125b inhibits C-Raf expression, proliferation, and survival of breast cancer cells

The noncoding RNA miR-125b has been described to reduce ErbB2 protein expression as well as proliferation and migration of cancer cell lines. As additional target of miR-125b, we identified the c-raf-1 mRNA by sequence analysis. We designed a short hairpin-looped oligodeoxynucleotide (ODN) targeted to the same 3' untranslated region of c-raf-1 mRNA as miR-125b. The fully complementary ODN antisense strand is linked to a second strand constituting a partially double-stranded structure of the ODN. Transfection of the c-raf-1-specific ODN (ODN-Raf) in a breast cancer cell line reduced the protein levels of C-Raf, ErbB2, and their downstream effector cyclin D1 similar to miR-125b. MiR-125b as well as ODN-Raf showed no effect on the c-raf-1 mRNA level in contrast to small interfering RNA. Unlike miR-125b, ODN-Raf induced a cytopathic effect. This may be explained by the structural properties of ODN-Raf, which can form G-tetrads. Thus, the short hairpin-looped ODN-Raf, targeting the same region of c-raf-1 as miR-125b, is a multifunctional molecule reducing the expression of oncoproteins and stimulating cell death. Both features may be useful to interfere with tumor growth.

Antitumor activity of small double-stranded oligodeoxynucleotides targeting telomerase RNA in malignant melanoma cells

Human telomerase RNA (hTR) is an intrinsic component of telomerase enzyme. Small interfering RNAs (siRNAs) and single-stranded antisense oligonucleotides have been used previously for silencing of the hTR. The objective of this study was to investigate the effect of partially double-stranded oligodeoxynucleotides (ODNs), in vitro and in vivo in comparison to single-stranded antisense ODNs and siRNAs. ODNs were designed on the basis of structural properties of an ODN from previous studies on HIV, to target the hTR in the human cervical carcinoma HeLa cell line and mouse telomerase RNA (mTR) in the murine metastatic melanoma B16-F10 cell line, respectively. Our results indicate that ODNs were able to inhibit the hTR by 68% and the mTR by 81% in the respective cell lines. This correlated with ODN-mediated rapid inhibition of cell proliferation and induction of apoptosis excluding slow effects on telomerase function. The inhibition of the hTR was decreased by knock-down of the cellular RNases H suggesting their contribution. Furthermore, we showed a reduction in numbers of metastases by 70% after intravenous administration of ODN-transfected B16-F10 cells in C57BL/6 mice. Our study demonstrates the potential utility of these hairpin-loop-structured ODNs as a different group of nucleic acids for telomerase-based antiproliferative strategies.

Reduction of gene expression by a hairpin-loop structured oligodeoxynucleotide: alternative to siRNA and antisense

BACKGROUND

We previously described the inhibition of HIV-1 replication by a 54-mer hairpin-loop structured oligodeoxynucleotide (ODN) A, which binds the polypurine tract (PPT) on HIV-1 RNA. ODN A was shown to lead to reduced viral RNA in virions or early during infection.

METHODS AND RESULTS

Here we demonstrated that ODN A was able to cause hydrolysis of viral RNA not only by retroviral RT-associated RNase H but also cellular RNase H1 and RNase H2 in vitro. Furthermore, ODN A reduced gene expression in a dose-dependent manner in a cell-based reporter assay where a PPT sequence was inserted in the 5' untranslated region of the reporter gene. The efficacy of ODN A was higher than that of its siRNA and antisense counterparts. By knocking down cellular RNases H, we showed that RNase H1 contributed to the gene silencing by ODN A but the possibility of a partial contribution of RNase H-independent mechanisms could not be ruled out.

GENERAL SIGNIFICANCE

Our findings highlight the potential application of hairpin-loop structured ODNs for reduction of gene expression in mammalian cells and underscore the possibility of using ODN A to trigger the hydrolysis of HIV RNA in infected cells by cellular RNases H.

Short hairpin-loop-structured oligodeoxynucleotides reduce HSV-1 replication

The Herpes simplex virus (HSV) is known as an infectious agent and widespread in the human population. The symptoms of HSV infections can range from mild to life threatening, especially in immune-compromised individuals. HSV infections are commonly treated with the guanosine analogue Aciclovir, but reports of resistance are increasing. Efforts are made to establish single-stranded antisense oligodeoxynucleotides (as) and small interfering ribonucleic acids (siRNAs) for antiviral treatment. Recently, another class of short interfering nucleic acids, partially double-stranded hairpin loop-structured 54 mer oligodeoxynucleotides (ODNs), was shown to allow hydrolysis of HIV RNA by binding to the viral RNA. This leads to a substrate for the viral RNase H. To assess the potential of such ODNs for inhibition of HSV-1 replication, five partially double-stranded ODNs were designed based on the sequences of known siRNAs against HSV-1 with antiviral activity. Three of them are directed against early and two against leaky late genes. Primary human lung fibroblasts, MRC-5, and African green monkey kidney cells, Vero, were transfected with ODNs and subsequently infected. The effect on HSV-1 replication was determined by analyzing the virus titer in cell culture supernatants by quantitative PCR and plaque assays. An inhibitory effect was observed with all five selected ODNs, with two cases showing statistical significance in both cell types. The observed effect was sequence-specific and dose dependent. In one case the ODN was more efficient than a previously described siRNA directed against the same target site in the mRNA of UL5, a component of the helicase/primase complex. HSV-1 virions and ODNs can be applied simultaneously without transfection reagent, but at a 50-fold higher concentration to Vero cells with similar efficiencies. The results underline the potential of partially double-stranded hairpin loop-structured ODNs as antiviral agents.

Retroviral self-inactivation in the mouse vagina induced by short DNA

Human immunodeficiency virus (HIV) has been shown to undergo self-destruction upon treatment of cell-free virions with partially double-stranded oligodeoxynucleotides targeting the polypurine tract (PPT) of the viral RNA in the virus particle. The ODN forms a local hybrid with the PPT activating the viral RNase H to prematurely cleave the genomic RNA. Here we are describing the self-destruction of a recombinant lentivirus harboring the PPT of HIV in a mouse vagina model. We showed a decrease in viral RNA levels in cell-free virus particles and a reduction reverse transcribed complementary DNA (cDNA) in virus-infected human and primary murine cells by incubation with ODNs. In the vagina simultaneous, prophylactic or therapeutic ODN treatments led to a significant reduction in viral RNA levels. Our finding may have some relevance for the design of other viral self-destruction approaches. It may lead to a microbicide for reduction of sexual and mother-to-child transmission.

Oligonucleotide-mediated retroviral RNase H activation leads to reduced HIV-1 titer in patient-derived plasma

BACKGROUND

The retroviral RNase H is essential for viral replication. This component has not yet been extensively studied for antiviral therapy. It can be activated by an oligodeoxynucleotide (ODN) resulting in self-destruction of the virions.

OBJECTIVE

To examine antiviral potential of ODN in clinical samples using plasma of HIV-1-infected patients.

DESIGN

Plasma of 19 HIV-1-infected patients from Zurich and 10 HIV-1 isolates from Africa and drug-resistant strains were processed for ex-vivo treatment.

METHODS

Cell-free virions were treated with ODN in the plasma and HIV RNA was measured by quantitative reverse transcription polymerase chain reaction (qRT-PCR). Furthermore, infectivity of the treated virions was tested on primary human peripheral blood mononuclear cells.

RESULTS

Cell-free virions in plasma contained significantly less intact HIV RNA upon treatment with ODN (P = 0.0004), and their infectivity was decreased 52-fold (P = 0.0004). In 39% of the Zurich samples, infectivity was reduced more than 10-fold, in 33% more than 100-fold, and in 28% more than 1000-fold. Also, the isolates from Africa exhibited a 63-fold reduction in infectivity (P = 0.0069) with 80% of the isolates responding more than 10-fold, 40% more than 100-fold, and 10% more than 1000-fold.

CONCLUSION

Significant reduction of plasma HIV RNA levels and infectivity of treated virions was achieved on the basis of induced self-destruction of HIV observed with clinical samples. Reduction of viral load ex vivo was designed as model for potential effects in vivo. Premature activation rather than inhibition of a viral enzyme could be a model strategy for future antiretroviral control.

Inhibition of influenza A virus replication by short double-stranded oligodeoxynucleotides

Influenza A virus causes prevalent respiratory tract infections in humans. Small interfering RNA (siRNA) and antisense oligonucleotides (asODNs) have been used previously for silencing the RNA genome of influenza virus. Here, we explored the use of partially double-stranded oligodeoxynucleotides (dsODNs) to suppress the production of influenza A virus in cell cultures and animal models. We were able to inhibit influenza A virus replication in cultured human lung cells as well as in the lungs of infected C57BL/6 mice by treatment with dsODN 3-h post-infection. In about 20% of the cases (15/77) the titer was reduced by 10- to 100-fold and in 10% up to 1,000-fold. The antiviral effects of dsODNs were dose-dependent, sequence-dependent and comparable to those of its antisense and siRNA analogues. Thus, dsODNs may be developed as an additional class of nucleic acids for the inhibition of influenza virus replication.

RNase H activity: structure, specificity, and function in reverse transcription

This review compares the well-studied RNase H activities of human immunodeficiency virus, type 1 (HIV-1) and Moloney murine leukemia virus (MoMLV) reverse transcriptases. The RNase H domains of HIV-1 and MoMLV are structurally very similar, with functions assigned to conserved subregions like the RNase H primer grip and the connection subdomain, as well as to distinct features like the C-helix and loop in MoMLV RNase H. Like cellular RNases H, catalysis by the retroviral enzymes appears to involve a two-metal ion mechanism. Unlike cellular RNases H, the retroviral RNases H display three different modes of cleavage: internal, DNA 3' end-directed, and RNA 5' end-directed. All three modes of cleavage appear to have roles in reverse transcription. Nucleotide sequence is an important determinant of cleavage specificity with both enzymes exhibiting a preference for specific nucleotides at discrete positions flanking an internal cleavage site as well as during tRNA primer removal and plus-strand primer generation. RNA 5' end-directed and DNA 3' end-directed cleavages show similar sequence preferences at the positions closest to a cleavage site. A model for how RNase H selects cleavage sites is presented that incorporates both sequence preferences and the concept of a defined window for allowable cleavage from a recessed end. Finally, the RNase H activity of HIV-1 is considered as a target for anti-virals as well as a participant in drug resistance.

Relationship between retroviral replication and RNA interference machineries

Small interfering RNAs (siRNAs) associated with gene silencing are cellular defense mechanisms against invading viruses. The viruses fight back by suppressors or escape mechanisms. The retroviruses developed a unique escape mechanism by disguising as DNA proviruses. An evolutionary relationship between the siRNA machinery and the replication machinery of retroviruses is likely. The RNA cleavage enzymes PIWI and RNase H proteins are structurally related. This relationship can be extended from structure to function, since the retroviral reverse transcriptase (RT)/RNase H can also cause silencing of viral RNA by siRNA. Thus, both enzymes can cleave RNA-DNA hybrids and double-stranded RNA (dsRNA) with various efficiencies shown previously and here, demonstrating that their specificities are not absolute. Other similarities may exist, for example between PAZ and the RT and between RNA-binding proteins and the viral nucleocapsid protein. Dicer has some similarities with the viral integrase, since both specifically generate dinucleotide 3'-overhanging ends. We described previously the destruction of the human immunodeficiency virus (HIV) RNA by a DNA oligonucleotide ODN (oligodeoxynucleotide). Variants of the ODN indicated high length and sequence specificities, which is reminiscent of siRNA and designated here as "siDNA." Cleavage of the viral RNA in the presence of the ODN is caused by the retroviral RT/RNase H and cellular RNase H activities. Several siRNA-mediated antiviral defense mechanisms resemble the interferon system.

RNase H-mediated retrovirus destruction in vivo triggered by oligodeoxynucleotides

The HIV-1 RNase H can be prematurely activated by oligodeoxynucleotides targeting the highly conserved polypurine tract required for second strand DNA synthesis. This inhibits retroviral replication in cell-free HIV particles and newly infected cells. Here we extend these studies to an in vivo model of retroviral replication. Mice that are chronically infected with the spleen focus-forming virus and treated with oligodeoxynucleotides that target the polypurine tract, exhibit either transient or long-term reductions in plasma virus titer, depending on the therapeutic regimen. Treatment prior to, during or shortly after infection can delay disease progression, increase survival rates and prevent viral infection. This strategy destroys viral RNA template in virus particles in serum as well as early retroviral replication intermediates in infected cells. As it targets events common to the replication cycle of all retroviruses, this approach may be broadly applicable to retroviruses of medical and agricultural importance.