Broad-spectrum antiviral therapeutics

Currently there are relatively few antiviral therapeutics, and most which do exist are highly pathogen-specific or have other disadvantages. We have developed a new broad-spectrum antiviral approach, dubbed Double-stranded RNA (dsRNA) Activated Caspase Oligomerizer (DRACO) that selectively induces apoptosis in cells containing viral dsRNA, rapidly killing infected cells without harming uninfected cells. We have created DRACOs and shown that they are nontoxic in 11 mammalian cell types and effective against 15 different viruses, including dengue flavivirus, Amapari and Tacaribe arenaviruses, Guama bunyavirus, and H1N1 influenza. We have also demonstrated that DRACOs can rescue mice challenged with H1N1 influenza. DRACOs have the potential to be effective therapeutics or prophylactics for numerous clinical and priority viruses, due to the broad-spectrum sensitivity of the dsRNA detection domain, the potent activity of the apoptosis induction domain, and the novel direct linkage between the two which viruses have never encountered.     

Pokeweed antiviral protein inactivates pokeweed ribosomes; implications for the antiviral mechanism

Pokeweed antiviral protein (PAP) and other ribosome-inactivating proteins (RIPs) had previously been thought to be incapable of attacking conspecific ribosomes, thus having no effect on endogenous processes. This assertion conflicts with a model for PAP's in vivo antiviral mechanism in which PAP (a cell wall protein) selectively enters virus-infected cells and disrupts protein synthesis, thus causing local suicide and preventing virus replication. We show here that pokeweed ( Phytolacca americana ) ribosomes, as well as endod ( Phytolacca dodecandra ) ribosomes, are indeed highly sensitive to inactivation by conspecific RIPs. Ribosomes isolated from RIP-free pokeweed and endod suspension culture cells were found to be highly active in vitro , as measured by poly(U)-directed polyphenylalanine synthesis. Phytolacca ribosomes challenged with conspecific RIPs generated doseresponse curves (IC₅₀ of 1 nM PAP or dodecandrin) very similar to those from wheat germ ribosomes. To determine if Phytolacca cells produce a cytosolic 'anti-RIP' protective element, ribosomes were combined with Phytolacca postribosomal supernatant factors from culture cells, then challenged with conspecific RIPs. Resulting IC₅₀ values of 3–7 nM PAP, PAP-II, PAP-S or dodecandrin indicate that supernatants from these Phytolacca cells lack a ribosomal protective element. This research demonstrates that PAP inactivates pokeweed ribosomes (and is therefore potentially toxic to pokeweed cells) and supports the local suicide model for PAP's in vivo antiviral mechanism. The importance of spatial separation between PAP and ribosomes of cells producing this RIP is emphasized, particularly if crop plants are transformed with the PAP gene to confer antiviral protection.     

Cytokines and antiviral immuniy

In the review of modern literature and results of own research about role of immunoregulation cytokines imbalance system in pathogen of deep-rooted virus infections are analyzed. The question on molecular mechanisms of cytokine chain deregulation at persistent virus infections is discussed.     

Antivirals and antiviral strategies

In recent years, the demand for new antiviral strategies has increased markedly. There are many contributing factors to this increased demand, including the ever-increasing prevalence of chronic viral infections such as HIV and hepatitis B and C, and the emergence of new viruses such as the SARS coronavirus. The potential danger of haemorrhagic fever viruses and eradicated viruses such as variola virus being used as bioterrorist weapons has also increased the profile of antiviral drug discovery. Here, the virus infections for which antiviral therapy is needed and the compounds that are available, or are being developed, for the treatment of these infections are described.     

Ribonucleases as antiviral agents

Many ribonucleases (RNases) are able to inhibit the reproduction of viruses in infected cell cultures and laboratory animals, but the molecular mechanisms of their antiviral activity remain unclear. The review discusses the well-known RNases that possess established antiviral effects, including both intracellular RNases (RNase L, MCPIP1 protein, and eosinophil-associated RNases) and exogenous RNases (RNase A, BS-RNase, onconase, binase, and synthetic RNases). Attention is paid to two important, but not always obligatory, aspects of molecules of RNases that have antiviral properties, i.e., catalytic activity and ability to dimerize. The hypothetic scheme of virus elimination by exogenous RNases that reflects possible types of interaction of viruses and RNases with a cell is proposed. The evidence for RNases as classical components of immune defense and thus perspective agents for the development of new antiviral therapeutics is proposed.     

Interchromosomal huddle kickstarts antiviral defense

Genomic instability in ataxia telangiectasia-like disorder and Nijmegen breakage syndrome is due to disruption of the Mre11-Rad50-Nbs1 complex. Buis et al. (2008) and Williams et al. (2008) now reveal the importance of the nuclease activity of Mre11 for mammalian genome maintenance and present a molecular view of its active site.     

Approaches to antiviral drug development

At present, only a few drugs have been approved by the FDA for therapy of viral infections in humans. There is a great need for antiviral drugs with increased potency and decreased toxicity, as well as drugs to treat viral diseases for which no drug or vaccine is currently available. Two approaches for development of antiviral drugs are described--an empirical strategy and a rational strategy--with several examples of each. Although many compounds have potent antiviral activity in cell culture, only a small fraction of these will go on to become antiviral drugs for use in humans. At this time, only seven synthetic compounds and alpha interferon have been approved by the FDA for therapy of viral infections in humans. None of these approved drugs are without toxicities, however, and hence there is a great need for antiviral drugs with increased potency and decreased toxicity, as well as for drugs to treat viral diseases for which no drug or vaccine is currently available. Two approaches for the development of antiviral drugs--the empirical and the rational strategies--and their applications and future directions are discussed.     

Autophagy in antiviral innate immunity

Several autonomous arms of innate immunity help cells to combat viral infections. One of these is autophagy, a central cytosolic lysosomal‐dependent catabolic process constitutively competent to destroy infectious viruses as well as essential viral components that links virus detection to antiviral innate immune signals. Ongoing autophagy can be upregulated upon virus detection by pathogen receptors, including membrane bound and cytosolic pattern recognition receptors, and may further facilitate pattern recognition receptor‐dependent signalling. Autophagy or autophagy proteins also contribute to the synthesis of antiviral innate type I interferon cytokines as well as to antiviral interferon γ signalling. Additionally, autophagy may play a crucial role during viral infections in containing an excessive cellular response by regulating the intensity of the inflammatory response. As a consequence, viruses have evolved strategies to counteract antiviral innate immunity through manipulation of autophagy. This review highlights recent findings on the cross‐talk between autophagy and innate immunity during viral infections.     

抗病毒免疫研究进展

抗病毒免疫的机制极其复杂,宿主的免疫系统需要经过抗原肽的加工提纯、淋巴细胞活化、抗体和细胞因子的产生等一系列步骤才能最终清除病毒的感染。从蛋白酶体在病毒肽抗原加工中的作用、免疫支配效应的意义、CTL杀伤病毒感染细胞的机制、细胞因子的作用和免疫逃逸机制等方面阐述了抗病毒免疫机制,对于病毒的防治将是十分重要的。     

Mitochondria and antiviral innate immunity

Mitochondria, dynamic organelles that undergo continuous cycles of fusion and fission, are the powerhouses of eukaryotic cells. Recent research indicates that mitochondria also act as platforms for antiviral immunity in vertebrates. Mitochondrial-mediated antiviral immunity depends on activation of the retinoic acid-inducible gene I (RIG-I)-like receptors signal transduction pathway and the participation of the mitochondrial outer membrane adaptor protein “mitochondrial antiviral signaling (MAVS)”. Here we discuss recent findings that suggest how mitochondria contribute to antiviral innate immunity.     

Cytotoxicity of pokeweed antiviral protein

Pokeweed antiviral protein, a plant protein which inactivates eukaryotic ribosomes, was found to be cytotoxic to both HeLa and Vero cells. Cellular protein synthesis was inhibited by exposure of the cells to microM concentrations of the antiviral protein for 24 h periods or longer. The extent of the inhibition of cellular protein synthesis was dependent upon the time of exposure to pokeweed antiviral protein and was partially reversed by washing the cells at various times prior to the measurement of protein synthesis. The antiviral protein was also observed to bind nonspecifically to cells at both 4 degrees and 34 degrees C. The data indicate that the pokeweed antiviral protein is capable of slowly entering mammalian cells which results in the inhibition cellular protein synthesis.     

The antiviral action of interferon

On interferon treatment cells develop an antiviral state. This requires time and RNA and protein synthesis. At least six polypeptides and two enzymes have been reported to be synthesized in increased amounts in response to interferon and a multiplicity of effects have been attributed to it. Interferon has been reported to inhibit virus growth at the level of the uncoating of the virus, virus RNA and protein synthesis and virus maturation. This has led to the acceptance of a multisite model for interferon action. The evidence for this and for the role of two known interferon-mediated enzymes, the 2-5A synthetase and protein kinase, are reviewed.