Efficient photodynamic therapy against drug-resistant prostate cancer using replication-deficient virus particles and talaporfin sodium.

To enhance the potency of photosensitizer, we developed a novel photosensitizer, Laserphyrin®-HVJ-E (L-HVJ-E), by incorporating talaporfin sodium (Laserphyrin®, Meiji Seika Pharma) into hemagglutinating virus of Japan envelope (HVJ-E). In this study, we examined the optimal Laserphyrin® concentration for preparation of Laserphyrin®-HVJ-E which had photocytotoxicity and maintained direct cytotoxicity derived from HVJ-E. Then, potency of Laserphyrin®-HVJ-E and Laserphyrin® were compared in vitro using castration-resistant prostate cancer cell line (PC-3). A laser diode (L660P120, Thorlabs, USA) with a wavelength of 664 nm was used for light activation of Laserphyrin®, which corresponds to an absorption peak of Laserphyrin® and provides a high therapeutic efficiency. The photocytotoxicity and direct cytotoxicity of Laserphyrin®-HVJ-E prepared using various Laserphyrin® concentrations were evaluated using PC-3 cell in vitro. We categorized the treatment groups as Group 1: 50 µL of D-MEM treatment group, Group 2: HVJ-E treatment group, Group 3: Laserphyrin®-HVJ-E treatment group, and Group 4: Laserphyrin® treatment group. Group 3 was subjected to different concentrations of Laserphyrin®-HVJ-E suspension, and all groups were subjected to different incubation periods (24, 48 h), (30 min, 1 h, or 3 h,) respectively, without and after PDT. Laserphyrin®-HVJ-E prepared using 15 mM Laserphyrin® had high photocytotoxicity and maintained HVJ-E's ability to induce direct cytotoxicity. Therapeutic effect of Laserphyrin®-HVJ-E was substantially equivalent to that of Laserphyrin® alone even at half Laserphyrin® concentration. By utilizing Laserphyrin®-HVJ-E, PDT could be performed with lower Laserphyrin® concentration. In addition, Laserphyrin®-HVJ-E showed higher potency than Laserphyrin® by combining cytotoxicities of HVJ-E and PDT.

Immune Modulation to Improve Survival of Viral Pneumonia in Mice.

Viral pneumonias remain global health threats, as exemplified in the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic, requiring novel treatment strategies both early and late in the disease process. We have reported that mice treated before or soon after infection with a combination of inhaled Toll-like receptor (TLR) 2/6 and 9 agonists (Pam2-ODN) are broadly protected against microbial pathogens including respiratory viruses, but the mechanisms remain incompletely understood. The objective of this study was to validate strategies for immune modulation in a preclinical model of viral pneumonia and determine their mechanisms. Mice were challenged with the Sendai paramyxovirus in the presence or absence of Pam2-ODN treatment. Virus burden and host immune responses were assessed to elucidate Pam2-ODN mechanisms of action and to identify additional opportunities for therapeutic intervention. Enhanced survival of Sendai virus pneumonia with Pam2-ODN treatment was associated with reductions in lung virus burden and with virus inactivation before internalization. We noted that mortality in sham-treated mice corresponded with CD8+ T-cell lung inflammation on days 11-12 after virus challenge, after the viral burden had declined. Pam2-ODN blocked this injurious inflammation by minimizing virus burden. As an alternative intervention, depleting CD8+ T cells 8 days after viral challenge also decreased mortality. Stimulation of local innate immunity within the lungs by TLR agonists early in disease or suppression of adaptive immunity by systemic CD8+ T-cell depletion late in disease improves outcomes of viral pneumonia in mice. These data reveal opportunities for targeted immunomodulation to protect susceptible human subjects.

C6orf106 is a novel inhibitor of the interferon-regulatory factor 3-dependent innate antiviral response.

Host recognition of intracellular viral RNA and subsequent induction of cytokine signaling are tightly regulated at the cellular level and are a target for manipulation by viruses and therapeutics alike. Here, we characterize chromosome 6 ORF 106 (C6orf106) as an evolutionarily conserved inhibitor of the innate antiviral response. C6orf106 suppresses the synthesis of interferon (IFN)-α/ß and proinflammatory tumor necrosis factor (TNF) α in response to the dsRNA mimic poly(I:C) and to Sendai virus infection. Unlike canonical inhibitors of antiviral signaling, C6orf106 blocks interferon-regulatory factor 3 (IRF3) and, to a lesser extent, NF-κB activity without modulating their activation, nuclear translocation, cellular expression, or degradation. Instead, C6orf106 interacts with IRF3 and inhibits IRF3 recruitment to type I IFN promoter sequences while also reducing the nuclear levels of the coactivator proteins p300 and CREB-binding protein (CBP). In summary, we have defined C6orf106 as a negative regulator of antiviral immunity that blocks IRF3-dependent cytokine production via a noncanonical and poorly defined mechanism. This work presents intriguing implications for antiviral immunity, autoimmune disorders, and cancer.

Antiviral activities of extremophilic actinomycetes extracts from Kazakhstan's unique ecosystems against influenza viruses and paramyxoviruses.

BACKGROUND: Commercially available antiviral drugs, when used in the treatment of viral infections, do not always result in success. This is an urgent problem currently that needs to be addressed because several viruses including influenza and paramyxoviruses are acquiring multi-drug resistance. A potential solution for this emerging issue is to create new antiviral drugs from available compounds of natural products. It is known that the majority of drugs have been developed using compounds derived from actinomycetes, which are naturally occurring gram-positive bacteria. The purpose of this study was to investigate the antiviral properties of extremophilic actinomycetes extracts from strains that were isolated from extreme environments in Kazakhstan. METHODS: Five strains of extremophilic actinomycetes isolated from the unique ecosystems of Kazakhstan were extracted and tested for antiviral activity against influenza viruses (strains H7N1, H5N3, H1N1 and H3N2) and paramyxoviruses (Sendai Virus and Newcastle Disease Virus). The antiviral activity of these selected extracts was tested by checking their effect on hemagglutination and neuraminidase activities of the studied viruses. Additionally, actinomycetes extracts were compared with commercially available antiviral drugs and some plant preparations that have been shown to exhibit antiviral properties. RESULTS: The main findings show that extracts from strains K-192, K-340, K-362, K-522 and K525 showed antiviral activities when tested using influenza viruses, Sendai Virus, and Newcastle Disease Virus. These activities were comparable to those shown by Rimantadine and Tamiflu drugs, and "Virospan" and "Flavovir" plant preparations. CONCLUSIONS: We identified several extracts with antiviral activities against several strains of influenza viruses and paramyxoviruses. Our research findings can be applied towards characterization and development of new antiviral drugs from the active actinomycetes extracts.

Sialylneolacto-N-tetraose c (LSTc)-bearing liposomal decoys capture influenza A virus.

Influenza is a severe disease in humans and animals with few effective therapies available. All strains of influenza virus are prone to developing drug resistance due to the high mutation rate in the viral genome. A therapeutic agent that targets a highly conserved region of the virus could bypass resistance and also be effective against multiple strains of influenza. Influenza uses many individually weak ligand binding interactions for a high avidity multivalent attachment to sialic acid-bearing cells. Polymerized sialic acid analogs can form multivalent interactions with influenza but are not ideal therapeutics due to solubility and toxicity issues. We used liposomes as a novel means for delivery of the glycan sialylneolacto-N-tetraose c (LSTc). LSTc-bearing decoy liposomes form multivalent, polymer-like interactions with influenza virus. Decoy liposomes competitively bind influenza virus in hemagglutination inhibition assays and inhibit infection of target cells in a dose-dependent manner. Inhibition is specific for influenza virus, as inhibition of Sendai virus and respiratory syncytial virus is not observed. In contrast, monovalent LSTc does not bind influenza virus or inhibit infectivity. LSTc decoy liposomes prevent the spread of influenza virus during multiple rounds of replication in vitro and extend survival of mice challenged with a lethal dose of virus. LSTc decoy liposomes co-localize with fluorescently tagged influenza virus, whereas control liposomes do not. Considering the conservation of the hemagglutinin binding pocket and the ability of decoy liposomes to form high avidity interactions with influenza hemagglutinin, our decoy liposomes have potential as a new therapeutic agent against emerging influenza strains.

Rapid and Highly Sensitive Method for Evaluating Surface Coatings against an Enveloped RNA Virus.

The COVID-19 pandemic has increased public health vigilance worldwide. The coronavirus (SARS-CoV-2) can spread via aerosols, and droplet-borne viruses remain viable on nonliving surfaces for long duration. Hence, effective antiviral coatings are highly useful in eliminating viral persistence on nonliving surfaces. Although innovative antiviral coatings have been designed, conventional procedures for antiviral assays are generally laborious, time-consuming, and have a high limit of detection. In the present study, we report a rapid and highly sensitive method for evaluating antiviral coatings by measuring the luciferase activity derived from recombinant Sendai virus (SeV). The physicochemical characteristics of SeV, which has a single-stranded RNA genome encapsulated within a lipid envelope, allow us to exploit it as an indicator of the physicochemical potential of coating materials against enveloped RNA viruses in general. We demonstrate that SeV-based assay systems allow for the rapid and quantitative evaluation of the surface coatings composed of iodine solubilized in polyvinyl acetate. Additionally, we have investigated the effect of mucins, the dominant protein component of saliva, on the antiviral activity of surface coatings. The presence of mucins in the SeV suspension considerably rescues luciferase activity at the viral-surface interface, presumably due to mucin-mediated viral protection. Our findings provide insights into a procedure capable of the rapid evaluation and optimization of surface coatings, and suggest an important role of the mucin in the valid evaluation of antiviral agents.

Effects of baicalein on Sendai virus in vivo are linked to serum baicalin and its inhibition of hemagglutinin-neuraminidase.

Parainfluenza viruses are significant respiratory-tract pathogens that are notorious for infecting children. However, there are no clinical drugs to control the infection caused by these viruses. Sendai virus (SeV) belongs to the family Paramyxoviridae and causes fatal pneumonia in mice, its natural host. Baicalein is a flavonoid derived from the root of Scutellaria baicalensis, which is a traditional Chinese medicine that has been used for hundreds of years and has demonstrated a variety of biological activities. Our findings reveal that oral administration of baicalein to mice infected with Sendai virus results in a significant reduction in virus titers in the lungs and protection from death. The in vivo inhibitory effects of baicalein on Sendai virus are determined by baicalin in the serum. The mean IC(50) of baicalin was 0.71 µg/ml in an HA inhibition assay and 3.22 µg/ml in an NA inhibition assay. The mean IC(50) of baicalin in a CPE assay was measured to be 0.70 µg/ml, and significant inhibition was observed in a plaque assay at a concentration of 1.6 µg/ml baicalin in overlay medium, which suggests that baicalein is a potential anti-parainfluenzaviral agent in vivo.

iPSC screening for drug repurposing identifies anti-RNA virus agents modulating host cell susceptibility.

Human pathogenic RNA viruses are threats to public health because they are prone to escaping the human immune system through mutations of genomic RNA, thereby causing local outbreaks and global pandemics of emerging or re-emerging viral diseases. While specific therapeutics and vaccines are being developed, a broad-spectrum therapeutic agent for RNA viruses would be beneficial for targeting newly emerging and mutated RNA viruses. In this study, we conducted a screen of repurposed drugs using Sendai virus (an RNA virus of the family Paramyxoviridae), with human-induced pluripotent stem cells (iPSCs) to explore existing drugs that may present anti-RNA viral activity. Selected hit compounds were evaluated for their efficacy against two important human pathogens: Ebola virus (EBOV) using Huh7 cells and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) using Vero E6 cells. Selective estrogen receptor modulators (SERMs), including raloxifene, exhibited antiviral activities against EBOV and SARS-CoV-2. Pioglitazone, a PPARγ agonist, also exhibited antiviral activities against SARS-CoV-2, and both raloxifene and pioglitazone presented a synergistic antiviral effect. Finally, we demonstrated that SERMs blocked entry steps of SARS-CoV-2 into host cells. These findings suggest that the identified FDA-approved drugs can modulate host cell susceptibility against RNA viruses.

Understanding inhibition of viral proteins on type I IFN signaling pathways with modeling and optimization.

The interferon system provides a powerful and universal intracellular defense mechanism against viruses. As one part of their survival strategies, many viruses have evolved mechanisms to counteract the host type I interferon (IFN-alpha/beta) responses. In this study, we attempt to investigate virus- and double-strand RNA (dsRNA)-triggered type I IFN signaling pathways and understand the inhibition of IFN-alpha/beta induction by viral proteins using mathematical modeling and quantitative analysis. Based on available literature and our experimental data, we develop a mathematical model of virus- and dsRNA-triggered signaling pathways leading to type I IFN gene expression during the primary response, and use the genetic algorithm to optimize all rate constants in the model. The consistency between numerical simulation results and biological experimental data demonstrates that our model is reasonable. Further, we use the model to predict the following phenomena: (1) the dose-dependent inhibition by classical swine fever virus (CSFV) N(pro) or E(rns) protein is observed at a low dose and can reach a saturation above a certain dose, not an increase; (2) E(rns) and N(pro) have no synergic inhibitory effects on IFN-beta induction; (3) the different characters in an important transcription factor, phosphorylated IRF3 (IRF3p), are exhibited because N(pro) or E(rns) counteracted dsRNA- and virus-triggered IFN-beta induction by targeting the different molecules in the signaling pathways and (4) N(pro) inhibits the IFN-beta expression not only by interacting with IFR3 but also by affecting its complex with MITA. Our approaches help to gain insight into system properties and rational therapy design, as well as to generate hypotheses for further research.

Characterization of the interferon regulatory factor 3-mediated antiviral response in a cell line deficient for IFN production.

The innate cellular response to virus particle entry in non-immune cells requires the transcriptional activity of interferon regulatory factor 3 (IRF-3), but not production of type I interferon (IFN). Here, we characterize the IFN-independent innate cellular response to virus-derived stimuli in Vero cells, a monkey kidney epithelial cell line deficient for IFN production. We provide evidence that Vero cells are deficient in their ability to mount an IRF-3-dependent, IFN-independent antiviral response against either incoming virus particles or polyinosinic:polycytidylic acid (pIC), a dsRNA mimetic. We further demonstrate that abundance of IRF-3 protein is a determinant in the pIC-mediated antiviral signalling pathway. These observations further characterize the permissive nature of Vero cells to viral infection, and highlight the crucial involvement of IRF-3 in the innate antiviral response.

Effect of hemagglutinin-neuraminidase inhibitors BCX 2798 and BCX 2855 on growth and pathogenicity of Sendai/human parainfluenza type 3 chimera virus in mice.

Human parainfluenza virus type 3 (hPIV-3) is a major respiratory tract pathogen that affects young children, but no vaccines or antiviral drugs against it have yet been developed. We developed a mouse model to evaluate the efficacies of the novel parainfluenza virus hemagglutinin-neuraminidase (HN) inhibitors BCX 2798 and BCX 2855 against a recombinant Sendai virus (rSeV) in which the fusion (F) and HN surface glycoproteins (FHN) were replaced by those of hPIV-3 [rSeV(hPIV-3FHN)]. In the prophylaxis model, 129X1/SvJ mice were infected with a 90% or 20% lethal dose of the virus and were treated intranasally for 5 days with 10 mg/kg of body weight/day of either compound starting 4 h before infection. Prophylactic treatment of the mice with either compound did not prevent their death in a 90% lethality model of rSeV(hPIV-3FHN) infection. However, it significantly reduced the lung virus titers, the amount of weight lost, and the rate of mortality in mice infected with a 20% lethal virus dose. In the therapy model, mice were infected with a nonlethal dose of the virus (100 PFU/mouse) and were treated intranasally with 1 or 10 mg/kg/day of either compound for 5 days starting at 24 or 48 h postinfection. Treatment of the mice with either compound significantly reduced the virus titer in the lungs, subsequently causing a reduction in the number of immune cells and the levels of cytokines in the bronchoalveolar lavage fluid and histopathologic changes in the airways. Our results indicate that BCX 2798 and BCX 2855 are effective inhibitors of hPIV-3 HN in our mouse model and may be promising candidates for the prophylaxis and treatment of hPIV-3 infection in humans.

2-Substituted-4,5-dihydroxypyrimidine-6-carboxamide antiviral targeted libraries.

To identify novel potentially broad spectrum antiviral compounds against RNA viruses, we have developed the parallel synthesis of a structurally interesting class of 2-substituted-4,5-dihydroxypyrimidine-6-carboxamides. Variously 2-substituted-4,5-dihydroxypyrimidine-6-carboxylate methyl esters were initially prepared and were then diversified via a facile amidation reaction. This strategy affords libraries of thousands of diverse drug-like compounds for screening. Biological evaluation of a set of these compounds, via a small initial screen, identified antiviral compounds against a representative RNA virus (Sendai virus, a paramyxovirus). We provide details on the synthetic protocols and the in vitro antiviral activity studies, as part of our initial investigation of the resulting targeted libraries.

Butyroyl-arginine as a potent virus inactivation agent.

Virus inactivation is a critical step in the manufacturing of recombinant therapeutic proteins, in particular antibodies, using mammalian expression systems. We have shown in the previous paper that arginine is effective in inactivation of herpes simplex virus type 1 (HSV-1) and influenza virus at low temperature under mildly acidic pH, i.e., above pH 4.0; above this pH, conformational changes of most antibodies are negligible. We have here extended virus inactivation study of arginine to other enveloped viruses, such as Sendai virus and Newcastle Disease Virus (NDV), and observed that arginine was ineffective against both viruses under the similar conditions, i.e., on ice and above pH 4.0. However, an arginine derivative, butyroyl-arginine, showed a strong virucidal potency against Sendai virus, leading to a 4log reduction in virus yield at pH 4.0, but not against NDV. In addition, although arginine and butyroyl-arginine were equally effective against influenza virus having a cleaved form of hemagglutinin spike proteins, only butyroyl-arginine was significantly effective against the same virus, but having an uncleaved hemagglutinin spike proteins. Furthermore, butyroyl-arginine was more effective than arginine against HSV-1 at pH 4.5; i.e., it has a broader pH spectrum than does arginine.

PPM1A silences cytosolic RNA sensing and antiviral defense through direct dephosphorylation of MAVS and TBK1.

Cytosolic RNA sensing is a prerequisite for initiation of innate immune response against RNA viral pathogens. Signaling through RIG-I (retinoic acid-inducible gene I)-like receptors (RLRs) to TBK1 (Tank-binding kinase 1)/IKKε (IκB kinase ε) kinases is transduced by mitochondria-associated MAVS (mitochondrial antiviral signaling protein). However, the precise mechanism of how MAVS-mediated TBK1/IKKε activation is strictly controlled still remains obscure. We reported that protein phosphatase magnesium-dependent 1A (PPM1A; also known as PP2Cα), depending on its catalytic ability, dampened the RLR-IRF3 (interferon regulatory factor 3) axis to silence cytosolic RNA sensing signaling. We demonstrated that PPM1A was an inherent partner of the TBK1/IKKε complex, targeted both MAVS and TBK1/IKKε for dephosphorylation, and thus disrupted MAVS-driven formation of signaling complex. Conversely, a high level of MAVS can dissociate the TBK1/PPM1A complex to override PPM1A-mediated inhibition. Loss of PPM1A through gene ablation in human embryonic kidney 293 cells and mouse primary macrophages enabled robustly enhanced antiviral responses. Consequently, Ppm1a(-/-) mice resisted to RNA virus attack, and transgenic zebrafish expressing PPM1A displayed profoundly increased RNA virus vulnerability. These findings identify PPM1A as the first known phosphatase of MAVS and elucidate the physiological function of PPM1A in antiviral immunity on whole animals.

High throughput screening assay for negative single stranded RNA virus polymerase inhibitors.

The Paramyxoviridae form a large family of viruses containing many human and veterinary pathogens for which a need for antiviral treatment is emphasized, particularly following the recent emergence of new viruses. The viral RNA-dependent RNA polymerase constitutes an obvious target for antiviral compounds. An in vitro assay was developed that allows high throughput screening of compounds potentially inhibiting the Sendai virus RNA-dependent RNA polymerase. Screening relies on the detection of the Photinus pyralis luciferase produced in a transcription/translation coupled assay using a mini-replicon virus. It contains an internal control for possible adverse effects of the tested compounds on translation or on luciferase activity. It is estimated that the mini-replicon template produced in one fertilized egg is sufficient to run 5000-10,000 reactions. This assay constitutes a simple, sensitive and easily automated method to perform high throughput screening of Paramyxoviridae RNA-dependent RNA polymerase inhibitors.

Stucturally Diverse Sesquiterpenes Produced by a Chinese Tibet Fungus Stereum hirsutum and Their Cytotoxic and Immunosuppressant Activities.

Two new heterodimeric sesquiterpenes, sterhirsutins C (1) and D (2), along with eight new sesquiterpenoid derivatives, sterhirsutins E--L (3-10), were isolated from the culture of Stereum hirsutum. The absolute configuration of 1 was assigned by a single-crystal X-ray diffraction experiment. Compounds 1 and 2 possessed an unprecedented chemical skeleton with a 5/5/5/6/9/4 fused ring system. Compound 10 is the first sesquiterpene coupled with a xanthine moiety. Compounds 1-10 showed cytotoxicity against K562 and HCT116 cell lines. Compound 9 induced autophagy in HeLa cells. Compound 5 inhibited the activation of IFNß promoter in Sendai virus infected cells.

Breaking resistance of pancreatic cancer cells to an attenuated vesicular stomatitis virus through a novel activity of IKK inhibitor TPCA-1.

Vesicular stomatitis virus (VSV) is an effective oncolytic virus against most human pancreatic ductal adenocarcinoma (PDAC) cell lines. However, some PDAC cell lines are highly resistant to oncolytic VSV-ΔM51 infection. To better understand the mechanism of resistance, we tested a panel of 16 small molecule inhibitors of different cellular signaling pathways, and identified TPCA-1 (IKK-ß inhibitor) and ruxolitinib (JAK1/2 inhibitor), as strong enhancers of VSV-ΔM51 replication and virus-mediated oncolysis in all VSV-resistant PDAC cell lines. Both TPCA-1 and ruxolitinib similarly inhibited STAT1 and STAT2 phosphorylation and decreased expression of antiviral genes MxA and OAS. Moreover, an in situ kinase assay provided biochemical evidence that TPCA-1 directly inhibits JAK1 kinase activity. Together, our data demonstrate that TPCA-1 is a unique dual inhibitor of IKK-ß and JAK1 kinase, and provide a new evidence that upregulated type I interferon signaling plays a major role in resistance of pancreatic cancer cells to oncolytic viruses.

Synthesis, biological evaluation, and pharmacophore generation of uracil, 4(3H)-pyrimidinone, and uridine derivatives as potent and selective inhibitors of parainfluenza 1 (Sendai) virus.

Several new 6-oxiranyl-, 6-oxiranylmethyluracils, and pyrimidinone derivatives, synthesized by lithiation-alkylation sequence of 1,3,6-trimethyluracil, 1,3-dimethyl-6-chloromethyluracil, and 2-alkoxy-6-methyl-4(3H)-pyrimidinones, showed a potent and selective antiviral activity against Sendai virus (SV) replication. To gain insight into the structural features required for SV inhibition activity, the new compounds were submitted to a pharmacophore generation procedure using the program Catalyst. The resulting pharmacophore model showed high correlation and predictive power. It also rationalized the relationships between structural properties and biological data of these inhibitors of SV replication.

New synthetic glutathione derivatives with increased antiviral activities.

A series of glutathione (GSH) derivatives with aliphatic chains of different lengths, coupled by peptides bound to the alpha-NH2 group of Glu, were synthesized. When added to several cell lines, the C6 (n-hexanoyl), C8 (n-octanoyl) and C12 (n-dodecanoyl) derivatives were toxic while the C2 (nethanoyl) and C4 (n-butanoyl) derivatives were not. Preliminary experiments were performed to investigate the potential antiviral activity of the C2 and C4 derivatives compared to GSH. The C4 derivative was the most potent and fully characterized. GSH-C4 is a poor substrate of GSH metabolizing enzymes; once oxidized by disulphide-bound formation, C4 is slowly reduced by GSH-reductase. GSH-C4 completely abrogated Sendai virus replication at 7.5 mM with an EC50 of 3.6 mM, compared to 7.5 mM for GSH. GSH-C4 completely inhibited herpes simplex virus (HSV-1) virus production in Vero cells at 10 mM, while the same dose of GSH caused only a 2.5 log10 reduction. Furthermore, the GSH-C4 treatment (7.5 mM) was able to markedly reduce the cytopathic effect of HSV-1 in Vero cells. Thus, GSH derivatives with increased hydrophobic properties are more effective antiviral agents against Sendai and HSV-1 viruses than GSH, suggesting their usefulness in antiviral therapy.

Fusion and infection of influenza and Sendai viruses as modulated by dextran sulfate: a comparative study.

We have directly compared the effect of two types of dextran sulfate with distinct molecular weights (500 kDa and 5 kDa) on the fusion activity and infectivity of both Sendai and influenza viruses, two lipid-enveloped viruses that differ in their routes of entry into target cells. To correlate membrane merging and infectivity MDCK cells were used as targets for the viruses in both approaches. In either case pronounced inhibition of virus-cell interactions by dextran sulfate was only observed at low pH, even though Sendai virus fuses maximally at pH 7.4. Although membrane merging could not be fully abolished, the inhibitory effect was always greater when the higher molecular weight dextran sulfate was used. The presence of this residual fusion activity, that could not be reduced even with high concentrations of agent, suggests that a limited number of binding sites for dextran sulfate may exist on the viral envelopes. The compounds also inhibited fusion of bound virions, and all results could be reproduced using erythrocyte ghosts as target membranes in the fusion assay, instead of MDCK cells. In agreement with these observations only the infectivity of influenza virus (which requires a low pH-dependent step to enter target cells) was affected by dextran sulfate, again the higher molecular weight compound showing a more pronounced inhibitory effect.