Binding of a N,N'-bisheteryl derivative of dispirotripiperazine to heparan sulfate residues on the cell surface specifically prevents infection of viruses from different families

Glycosaminoglycan lyase: A new competition between bacteria and the pacific white shrimp Litopenaeus vannamei

Horizontal gene transfer (HGT) is an important evolutionary force in the formation of prokaryotic and eukaryotic genomes. In recent years, many HGT genes horizontally transferred from prokaryotes to eukaryotes have been reported, and most of them are present in arthropods. The Pacific white shrimp Litopenaeus vannamei, an important economic species of arthropod, has close relationships with bacteria, providing a platform for horizontal gene transfer (HGT). In this study, we analyzed bacteria-derived HGT based on a high-quality genome of L. vannamei via a homology search and phylogenetic analysis, and six HGT genes were identified. Among these six horizontally transferred genes, we found one gene (LOC113799989) that contains a bacterial chondroitinase AC structural domain and encodes an unknown glycosaminoglycan (GAG) lyase in L. vannamei. The real-time quantitative PCR results showed that the mRNA expression level of LOC113799989 was highest in the hepatopancreas and heart, and after stimulation by Vibrio parahaemolyticus, its mRNA expression level was rapidly up-regulated within 12 h. Furthermore, after injecting si-RNA and stimulation by V. parahaemolyticus, we found that the experimental group had a higher cumulative mortality rate in 48 h than the control group, indicating that the bacteria-derived GAG lyase can reduce the mortality of shrimp with respect to infection by V. parahaemolyticus and might be related to the resistance of shrimp to bacterial diseases. Our findings contribute to the study of the function of GAGs and provide new insights into GAG-related microbial pathogenesis and host defense mechanisms in arthropods.

Characterization of the dispirotripiperazine derivative PDSTP as antibiotic adjuvant and antivirulence compound against Pseudomonas aeruginosa

Pseudomonas aeruginosa is a major human pathogen, able to establish difficult-to-treat infections in immunocompromised and people with cystic fibrosis (CF). The high rate of antibiotic treatment failure is due to its notorious drug resistance, often mediated by the formation of persistent biofilms. Alternative strategies, capable of overcoming P. aeruginosa resistance, include antivirulence compounds which impair bacterial pathogenesis without exerting a strong selective pressure, and the use of antimicrobial adjuvants that can resensitize drug-resistant bacteria to specific antibiotics. In this work, the dispirotripiperazine derivative PDSTP, already studied as antiviral, was characterized for its activity against P. aeruginosa adhesion to epithelial cells, its antibiotic adjuvant ability and its biofilm inhibitory potential. PDSTP was effective in impairing the adhesion of P. aeruginosa to various immortalized cell lines. Moreover, the combination of clinically relevant antibiotics with the compound led to a remarkable enhancement of the antibiotic efficacy towards multidrug-resistant CF clinical strains. PDSTP-ceftazidime combination maintained its efficacy in vivo in a Galleria mellonella infection model. Finally, the compound showed a promising biofilm inhibitory activity at low concentrations when tested both in vitro and using an ex vivo pig lung model. Altogether, these results validate PDSTP as a promising compound, combining the ability to decrease P. aeruginosa virulence by impairing its adhesion and biofilm formation, with the capability to increase antibiotic efficacy against antibiotic resistant strains.

Antiviral Evaluation of Dispirotripiperazines against Hepatitis B Virus

Hepatitis B virus (HBV) is a hepatotropic DNA virus that replicates by reverse transcription. It chronically infects >296 million people worldwide, including ∼850,000 in the USA, and kills 820,000 annually worldwide. Current nucleos(t)ide analogue (NA) or pegylated interferon α therapies do not eradicate the virus and would benefit from a complementary antiviral drug. We performed a preliminary screen of 28 dispirotripiperazines against HBV, identifying 9 hits with EC50 of 0.7-25 μM. Compound 11826096 displays the most potent activity and represents a promising lead for future optimization. While the mechanism of action is unknown, preliminary assays limit possible targets to activities involved in RNA accumulation, translation, capsid assembly, and/or capsid stability. In addition, we built machine learning models to determine if they were able to predict the activity of this series of compounds. The novelty of these molecules indicated they were outside of the applicability domain of these models.

Pentosan Polysulfate Affords Pleotropic Protection to Multiple Cells and Tissues

Pentosan polysulfate (PPS), a small semi-synthetic highly sulfated heparan sulfate (HS)-like molecule, shares many of the interactive properties of HS. The aim of this review was to outline the potential of PPS as an interventional therapeutic protective agent in physiological processes affecting pathological tissues. PPS is a multifunctional molecule with diverse therapeutic actions against many disease processes. PPS has been used for decades in the treatment of interstitial cystitis and painful bowel disease, it has tissue-protective properties as a protease inhibitor in cartilage, tendon and IVD, and it has been used as a cell-directive component in bioscaffolds in tissue engineering applications. PPS regulates complement activation, coagulation, fibrinolysis and thrombocytopenia, and it promotes the synthesis of hyaluronan. Nerve growth factor production in osteocytes is inhibited by PPS, reducing bone pain in osteoarthritis and rheumatoid arthritis (OA/RA). PPS also removes fatty compounds from lipid-engorged subchondral blood vessels in OA/RA cartilage, reducing joint pain. PPS regulates cytokine and inflammatory mediator production and is also an anti-tumor agent that promotes the proliferation and differentiation of mesenchymal stem cells and the development of progenitor cell lineages that have proven to be useful in strategies designed to effect repair of the degenerate intervertebral disc (IVD) and OA cartilage. PPS stimulates proteoglycan synthesis by chondrocytes in the presence or absence of interleukin (IL)-1, and stimulates hyaluronan production by synoviocytes. PPS is thus a multifunctional tissue-protective molecule of potential therapeutic application for a diverse range of disease processes.

PDSTP Is the First Drug in Class to Treat Coronavirus Infection

The results of a comprehensive study are presented on the development and creation of an original small PDSTP molecule, able to prevent the SARS-CoV-2 coronavirus infection from binding to the host cell. The PDSTP molecule was designed to electrostatically interact with heparan sulfate proteoglycans on the cell surface, and coronaviruses, particularly SARS-CoV-2, use this mechanism as the first stage of interaction with the cell. By blocking this process, it is possible to stop the life cycle of the virus, thus leading to its death. The drug candidate PDSTP, with its unique mechanism of action, is characterized by a very low toxicity and a high safety profile and demonstrates good efficacy in animal experiments.

Broad-spectrum antiviral diazadispiroalkane core molecules block attachment and cell-to-cell spread of herpesviruses

Regarding the problems with the current available drugs many research studies deal with the class of the dispirotripiperazine (DSTP)-based compounds. These are small molecules consisting of polycyclic saturated ring systems with positively charged nitrogen atoms. These compounds can interact with negatively charged HSPGs and thus block viral attachment. In a previous paper by Adfeldt et al. (2021), we have shown that the diazadispiroalkane derivatives 11826091 and 11826236 exhibit dose-dependent antiviral activity against human cytomegalovirus (HCMV) and pseudorabies virus (PrV). In the present study, these two small molecules are evaluated against two other herpesvirus species, murine cytomegalovirus (MCMV) and herpes simplex virus type 1 (HSV-1), as well as a HCMV clinical isolate. They exhibit potent antiherpetic activity against these herpesviruses with a high selectivity index. The low cytotoxicity was underlined by the LD₅₀ determination in mice. We have shown that inhibition occurs at an early stage of infection. Interestingly, 11826091 and 11826236 reduced immediate early gene expression in HCMV and HSV-1 infected cells in a dose-dependent manner. Both small molecules probably interact electrostatically with sulfated glycosaminoglycans (GAGs) of proteoglycans on target cells resulting in blockage of adsorption sites for herpesvirus glycoprotein. Moreover, both compounds showed significant effects against the cell-associated viral spread of HSV-1 and HCMV. Overall, this study shows that 11826091 and 11826236 represent two promising candidates for a new approach of a broad antiviral therapy.

A proof-of-concept study for the efficacy of dispirotripiperazine PDSTP in a rabbit model of herpes simplex epithelial keratitis

Herpes simplex keratitis is an important infectious cause of blindness worldwide. The mainstay of antiviral therapy is treatment with long-established nucleoside analogues orally or topically. However, the emergence of resistant strains may become a major health concern in the future. Therefore, the development of backup antiherpetic medicines is urgently needed. Small molecule PDSTP is known to be active against herpes simplex type 1 strains in vitro, affecting early host-pathogen interactions. Here, we evaluated its preclinical efficacy in a rabbit model of herpes simplex epithelial keratitis. The mean course of keratitis and the corneal lesions in the 1.0% PDSTP gel group was statistically significantly less than in the negative control group and was comparable to that in the aciclovir group. These findings open up new opportunities for the development of antiherpetic drugs with an original mechanism of action.

Antiviral activities of four marine sulfated glycans against adenovirus and human cytomegalovirus

Broad-spectrum antivirals are more needed than ever to provide treatment options for novel emerging viruses and for viruses that lack therapeutic options or have developed resistance. A large number of viruses rely on charge-dependent non-specific interactions with heparan sulfate (HS), a highly sulfated glycosaminoglycan (GAG), for attachment to cell surfaces to initiate cell entry. As such, inhibitors targeting virion-HS interactions have potential to have broad-spectrum antiviral activity. Previous research has explored organic and inorganic small molecules, peptides, and GAG mimetics to disrupt virion-HS interactions. Here we report antiviral activities against both enveloped (the herpesvirus human cytomegalovirus) and non-enveloped (adenovirus) DNA viruses for four defined marine sulfated glycans: a sulfated galactan from the red alga Botryocladia occidentalis; a sulfated fucan from the sea urchin Lytechinus variegatus, and a sulfated fucan and a fucosylated chondroitin sulfate from the sea cucumber Isostichopus badionotus. As evidenced by gene expression, time of addition, and treatment/removal assays, all four novel glycans inhibited viral attachment and entry, most likely through interactions with virions. The sulfated fucans, which both lack anticoagulant activity, had similar antiviral profiles, suggesting that their activities are not only due to sulfation content or negative charge density but also due to other physicochemical factors such as the potential conformational shapes of these carbohydrates in solution and upon interaction with virion proteins. The structural and chemical properties of these marine sulfated glycans provide unique opportunities to explore relationships between glycan structure and their antiviral activities.

Small Molecules-Prospective Novel HCMV Inhibitors

Human cytomegalovirus (HCMV), a member of the betaherpesvirinae, can cause life-threatening diseases. HCMV is globally widespread, with a seroprevalence in adults varying from 50 to 100%. HCMV infection is rarely of significant consequence in immunocompetent individuals. However, although immune control is efficient, it cannot achieve the clearance of the virus. HCMV persists lifelong in the infected host and reactivates in certain circumstances. In neonates and in immunocompromised adults, HCMV is a serious pathogen that can cause fatal organ damage. Different antiviral compounds alone or in combination have been used for the treatment of HCMV diseases. In clinical use, mutations in the viral DNA polymerase or the terminase confer resistance to ganciclovir, foscarnet, cidofovir, and letermovir. There is an urgent need to find new well-tolerated compounds supporting different modes of action. The list of novel small molecules that might have anti-HCMV activity has grown in recent years. In this short review, a selection of compounds in clinical trials and novel inhibitors targeting host-cell factors or viral proteins is presented, and their modes of action, described.

Glycosaminoglycan-Protein Interactions and Their Roles in Human Disease

Glycosaminoglycans (GAGs) are a family of linear and negatively charged polysaccharides that exist ubiquitously on the human cell surface as well as in the extracellular matrix. GAGs interact with a wide range of proteins, including proteases, growth factors, cytokines, chemokines and adhesion molecules, enabling them to mediate many physiological processes, such as protein function, cellular adhesion and signaling. GAG-protein interactions participate in and intervene in a variety of human diseases, including cardiovascular disease, infectious disease, neurodegenerative diseases and tumors. The breakthrough in analytical tools and approaches during the last two decades has facilitated a greater understanding of the importance of GAG-protein interactions and their roles in human diseases. This review focuses on aspects of the molecular basis and mechanisms of GAG-protein interactions involved in human disease. The most recent advances in analytical tools, especially mass spectrometry-based GAG sequencing and binding motif characterization methods, are introduced. An update of selected families of GAG binding proteins is presented. Perspectives on development of novel therapeutics targeting specific GAG-protein interactions are also covered in this review.

Advances in Targeting HPV Infection as Potential Alternative Prophylactic Means

Infection by oncogenic human papillomavirus (HPV) is the primary cause of cervical cancer and other anogenital cancers. The majority of cervical cancer cases occur in low- and middle- income countries (LMIC). Concurrent infection with Human Immunodeficiency Virus (HIV) further increases the risk of HPV infection and exacerbates disease onset and progression. Highly effective prophylactic vaccines do exist to combat HPV infection with the most common oncogenic types, but the accessibility to these in LMIC is severely limited due to cost, difficulties in accessing the target population, cultural issues, and maintenance of a cold chain. Alternative preventive measures against HPV infection that are more accessible and affordable are therefore also needed to control cervical cancer risk. There are several efforts in identifying such alternative prophylactics which target key molecules involved in early HPV infection events. This review summarizes the current knowledge of the initial steps in HPV infection, from host cell-surface engagement to cellular trafficking of the viral genome before arrival in the nucleus. The key molecules that can be potentially targeted are highlighted, and a discussion on their applicability as alternative preventive means against HPV infection, with a focus on LMIC, is presented.

Dispirotripiperazine-core compounds, their biological activity with a focus on broad antiviral property, and perspectives in drug design (mini-review)

Viruses are obligate intracellular parasites and have evolved to enter the host cell. To gain access they come into contact with the host cell through an initial adhesion, and some viruses from different genus may use heparan sulfate proteoglycans for it. The successful inhibition of this early event of the infection by synthetic molecules has always been an attractive target for medicinal chemists. Numerous reports have yielded insights into the function of compounds based on the dispirotripiperazine scaffold. Analysis suggests that this is a structural requirement for inhibiting the interactions between viruses and cell-surface heparan sulfate proteoglycans, thus preventing virus entry and replication. This review summarizes our current knowledge about the early history of development, synthesis, structure-activity relationships and antiviral evaluation of dispirotripiperazine-based compounds and where they are going in the future.

Heparan Sulfate Proteoglycans and Viral Attachment: True Receptors or Adaptation Bias?

Heparan sulfate proteoglycans (HSPG) are composed of unbranched, negatively charged heparan sulfate (HS) polysaccharides attached to a variety of cell surface or extracellular matrix proteins. Widely expressed, they mediate many biological activities, including angiogenesis, blood coagulation, developmental processes, and cell homeostasis. HSPG are highly sulfated and broadly used by a range of pathogens, especially viruses, to attach to the cell surface.

Therapeutic strategies to target microbial protein-glycosaminoglycan interactions

Glycans are involved in a plethora of human pathologies including infectious diseases. Especially, glycosaminoglycans (GAGs), like heparan sulfate and chondroitin sulfate, have been found to be involved in different crucial stages of microbial invasion. Here, we review various therapeutic approaches, which target the interface of host GAGs and microbial proteins and discuss their limitations and challenges for drug development.

Targeting heparin and heparan sulfate protein interactions

Heparin and heparan sulfate glycosaminoglycans are long, linear polysaccharides that are made up of alternating dissacharide sequences of sulfated uronic acid and amino sugars. Unlike heparin, which is only found in mast cells, heparan sulfate is ubiquitously expressed on the cell surface and in the extracellular matrix of all animal cells. These negatively-charged glycans play essential roles in important cellular functions such as cell growth, adhesion, angiogenesis, and blood coagulation. These biomolecules are also involved in pathophysiological conditions such as pathogen infection and human disease. This review discusses past and current methods for targeting these complex biomolecules as a novel therapeutic strategy to treating disorders such as cancer, neurodegenerative diseases, and infection.

Respiratory Syncytial Virus Aggravates Renal Injury through Cytokines and Direct Renal Injury

The purpose of this study was to investigate the relationship between renal injury and reinfection that is caused by respiratory syncytial virus (RSV) and to analyze the mechanism of renal injury. Rats were repeatedly infected with RSV on days 4, 8, 14, and 28, then sacrificed and examined on day 56 after the primary infection. Renal injury was examined by transmission electron microscopy and histopathology. The F protein of RSV was detected in the renal tissue by indirect immunofluorescence. Proteinuria and urinary glycosaminoglycans (GAGs), serum levels of albumin, urea nitrogen, and creatinine, secretion of cytokines, T lymphocyte population and subsets, and dendritic cell (DC) activation state were examined. The results showed that renal injury was more serious in the reinfection group than in the primary infection group. At a higher infection dose, 6 × 10⁶ PFU, the renal injury was more severe, accompanied by higher levels of proteinuria and urinary GAGs excretion, and lower levels of serum albumin. Podocyte foot effacement was more extensive, and hyperplasia of mesangial cells and proliferation of mesangial matrix were observed. The maturation state of DCs was specific, compared with the primary infection. There was also a decrease in the ratio of CD4⁺ to CD8⁺ T lymphocytes, due to an increase in the percentage of CD8⁺ T lymphocytes and a decrease in the percentage of CD4⁺ T lymphocytes, and a dramatic increase in the levels of IL-6 and IL-17. In terms of the different reinfection times, the day 14 reinfection group yielded the most serious renal injury and the most significant change in immune function. RSV F protein was still expressed in the glomeruli 56 days after RSV infection. Altogether, these results reveal that RSV infection could aggravate renal injury, which might be due to direct renal injury caused by RSV and the inflammatory lesions caused by the anti-virus response induced by RSV.

Glycosaminoglycans and infection

Glycosaminoglycans (GAGs) are complex linear polysaccharides expressed in intracellular compartments, at the cell surface, and in the extracellular environment where they interact with various molecules to regulate many cellular processes implicated in health and disease. Subversion of GAGs is a pathogenic strategy shared by a wide variety of microbial pathogens, including viruses, bacteria, parasites, and fungi. Pathogens use GAGs at virtually every major portals of entry to promote their attachment and invasion of host cells, movement from one cell to another, and to protect themselves from immune attack. Pathogens co-opt fundamental activities of GAGs to accomplish these tasks. This ingenious strategy to subvert essential activities of GAGs likely prevented host organisms from deleting or inactivating these mechanisms during their evolution. The goal of this review is to provide a mechanistic overview of our current understanding of how microbes subvert GAGs at major steps of pathogenesis, using select GAG-pathogen interactions as representative examples.

The BDLF3 gene product of Epstein-Barr virus, gp150, mediates non-productive binding to heparan sulfate on epithelial cells and only the binding domain of CD21 is required for infection

The cell surface molecules used by Epstein-Barr virus (EBV) to attach to epithelial cells are not well-defined, although when CD21, the B cell receptor for EBV is expressed epithelial cell infection increases disproportionately to the increase in virus bound. Many herpesviruses use low affinity charge interactions with molecules such as heparan sulfate to attach to cells. We report here that the EBV glycoprotein gp150 binds to heparan sulfate proteoglycans, but that attachment via this glycoprotein is not productive of infection. We also report that only the aminoterminal two short consensus repeats of CD21 are required for efficient infection, This supports the hypothesis that, when expressed on an epithelial cell CD21 serves primarily to cluster the major attachment protein gp350 in the virus membrane and enhance access of other important glycoproteins to the epithelial cell surface.

Small molecule antagonists of cell-surface heparan sulfate and heparin-protein interactions

Surfen, bis-2-methyl-4-amino-quinolyl-6-carbamide, was previously reported as a small molecule antagonist of heparan sulfate (HS), a key cell-surface glycosaminoglycan found on all mammalian cells. To generate structure-activity relationships, a series of rationally designed surfen analogs was synthesized, where its dimeric structure, exocyclic amines, and urea linker region were modified to probe the role of each moiety in recognizing HS. An in vitro assay monitoring inhibition of fibroblast growth factor 2 binding to wild-type CHO cells was utilized to quantify interactions with cell surface HS. The dimeric molecular structure of surfen and its aminoquinoline ring systems was essential for its interaction with HS, and certain dimeric analogs displayed higher inhibitory potency than surfen and were also shown to block downstream FGF signaling in mouse embryonic fibroblast cells. These molecules were also able to antagonize other HS-protein interactions including the binding of soluble RAGE to HS. Importantly, selected molecules were shown to neutralize heparin and other heparinoids, including the synthetic pentasaccharide fondaparinux, in a factor Xa chromogenic assay and in vivo in mice. These results suggest that small molecule antagonists of heparan sulfate and heparin can be of therapeutic potential for the treatment of disorders involving glycosaminoglycan-protein interactions.

Porcine complement regulatory protein CD46 and heparan sulfates are the major factors for classical swine fever virus attachment in vitro

Classical swine fever virus (CSFV) is the causative agent of a severe multi-systemic disease of pigs. While several aspects of virus-host-interaction are known, the early steps of infection remain unclear. For the closely related bovine viral diarrhea virus (BVDV), a cellular receptor is known: bovine complement regulatory protein CD46. Given that these two pestiviruses are closely related, porcine CD46 is also a candidate receptor for CSFV. In addition to CD46, cell-culture-adapted CSFV strains have been shown to use heparan sulfates as an additional cellular factor. In the present study, the interaction of field-type and cell-culture-adapted CSFV with a permanent porcine cell line or primary macrophages was assessed using anti-porcine CD46 monoclonal antibodies and a heparan-sulfate-blocking compound, DSTP-27. The influence of receptor blocking was assessed using virus titration and quantitative PCR. Treatment of cells with monoclonal antibodies against porcine CD46 led to a reduction of viral growth in both cell types. The effect was most pronounced with field-type CSFV. The blocking could be enhanced by addition of DSTP-27, especially for cell-culture-adapted CSFV. The combined use of both blocking agents led to a significant reduction of viral growth but was also not able to abolish infection completely. The results obtained in this study showed that both porcine CD46 and heparan sulfates play a major role in the initial steps of CSFV infection. Additional receptors might also play a role for attachment and entry; however, their impact is obviously limited in vitro in comparison to CD46 and heparan sulfates.

Human papillomavirus species-specific interaction with the basement membrane-resident non-heparan sulfate receptor

Using a cell culture model where virus is bound to the extracellular matrix (ECM) prior to cell surface binding, we determined that human papillomavirus type 16 (HPV16) utilizes ECM resident laminin (LN) 332 as an attachment receptor for infectious entry. In presence of LN332, soluble heparin can function as ligand activator rather than competitive inhibitor of HPV16 infection. We also show that the ability to use LN332 binding as a productive attachment step for infectious entry is not conserved amongst HPV types. In the alpha genus, species 9 members (HPV16) attach to ECM via LN332, while members of species 7 (HPV18) are completely inhibited by heparin pre-incubation due to an inability to use LN332. Since HPV species 7 and 9 are preferentially associated with adenocarcinoma and squamous cell carcinoma of the cervix, respectively, our data provide first evidence that pre-entry events may contribute to the anatomical-site preference of HPV species.

DSTP-27 prevents entry of human cytomegalovirus

Human cytomegalovirus (HCMV) can cause life-threatening diseases in neonates and immunocompromised patients. Due to multiple problems caused by the current available drugs, development of new antiviral compounds is urgently needed. In this study, we characterize the anti-HCMV spectrum and mechanism of action of the N-N'-(bis-5 nitropyrimidyl)dispirotripiperazine derivate 27 (DSTP-27). DSTP-27 exhibited strong antiviral activity against two laboratory HCMV strains with different cell tropism as well as ganciclovir (GCV)-sensitive and GCV-resistant clinical isolates in plaque reduction assays and viral growth kinetics experiments. Interestingly, neither infectious nor noninfectious viral particles were observed by electron microscopy. Pretreatment of cell-free virus with DSTP-27 prevented virus infection. The results from time of addition assays, in which DTSP-27 was added to cells (i) before infection, (ii) during virus adsorption, or (iii) after adsorption, demonstrated an inhibitory effect on early steps of the HCMV replication cycle. This observation was confirmed by immunofluorescence as well as Western blot analysis, whereby reduced levels of the immediate early protein IE1, the processivity factor pUL44, and the tegument protein pp28 were detected. Results from attachment and penetration analyses of prechilled human embryonic lung fibroblasts revealed that virus attachment is not blocked. In addition, DSTP-27 inactivated HCMV by stable binding. Taken together, these results demonstrate that DSTP-27 (i) blocks viral penetration by interacting with the host cell and (ii) inactivates HCMV by interacting with the virus.

Multiple heparan sulfate binding site engagements are required for the infectious entry of human papillomavirus type 16

Human papillomavirus (HPV) entry is accompanied by multiple receptor-induced conformational changes (CCs) affecting both the major and minor capsid proteins, L1 and L2. Interaction of heparan sulfate (HS) with L1 is essential for successful HPV16 entry. Recently, cocrystallization of HPV16 with heparin revealed four distinct binding sites. Here we characterize mutant HPV16 to delineate the role of engagement with HS binding sites during infectious internalization. Site 1 (Lys278, Lys361), which mediates primary binding, is sufficient to trigger an L2 CC, exposing the amino terminus. Site 2 (Lys54, Lys356) and site 3 (Asn57, Lys59, Lys442, Lys443) are engaged following primary attachment and are required for infectious entry. Site 2 mutant particles are efficiently internalized but fail to undergo an L1 CC on the cell surface and subsequent uncoating in the endocytic compartment. After initial attachment to the cell, site 3 mutants undergo L1 and L2 CCs and then accumulate on the extracellular matrix (ECM). We conclude that the induction of CCs following site 1 and site 2 interactions results in reduced affinity for the primary HS binding site(s) on the cell surface, which allows engagement with site 3. Taken together, our findings suggest that HS binding site engagement induces CCs that prepare the virus for downstream events, such as the exposure of secondary binding sites, CCs, transfer to the uptake receptor, and uncoating.

Pathophysiology of heparan sulphate: many diseases, few drugs

Heparan sulphate (HS) polysaccharides are covalently attached to the core proteins of various proteoglycans at cell surfaces and in the extracellular matrix. They are composed of alternating units of hexuronic acid and glucosamine, with sulphate substituents in complex and variable yet cell-specific patterns. Whereas HS is produced by virtually all cells in the body, heparin, a highly sulphated HS variant, is confined to connective-tissue-type mast cells. The polysaccharides interact with a multitude of proteins, mainly through ionic binding, and thereby control key processes in development and homoeostasis. Similar interactions also implicate HS in various pathophysiological settings, including cancer, amyloid diseases, infectious diseases, inflammatory conditions and some developmental disorders. Prospects for the development of HS-based drugs, which are still largely unrealized, are discussed.

Polyethylenimine is a strong inhibitor of human papillomavirus and cytomegalovirus infection

Polyethylenimines are cationic polymers with potential as delivery vectors in gene therapy and with proven antimicrobial activity. However, the antiviral activity of polyethylenimines has not been addressed in detail thus far. We have studied the inhibitory effects of a linear 25-kDa polyethylenimine on infections with human papillomaviruses and human cytomegaloviruses. Preincubation of cells with polyethylenimine blocked primary attachment of both viruses to cells, resulting in a significant reduction of infection. In addition, the dissemination of human cytomegalovirus in culture cells was efficiently reduced by recurrent administration of polyethylenimine. Polyethylenimine concentrations required for inhibition of human papillomavirus and cytomegalovirus did not cause any cytotoxic effects. Polyethylenimines and their derivatives may thus be attractive molecules for the development of antiviral microbicides.

Propagation of classical swine fever virus in vitro circumventing heparan sulfate-adaptation

Amplification of natural virus isolates in permanent cell lines can result in adaptation, in particular enhanced binding to heparan sulfate (HS)-containing glycosaminoglycans present on most vertebrate cells. This has been reported for several viruses, including the pestivirus classical swine fever virus (CSFV), the causative agent of a highly contagious hemorrhagic disease in pigs. Propagation of CSFV in cell culture is essential in virus diagnostics and research. Adaptation of CSFV to HS-binding has been related to amino acid changes in the viral E(rns) glycoprotein, resulting in viruses with altered replication characteristics in vitro and in vivo. Consequently, a compound blocking the HS-containing structures on cell surfaces was employed to monitor conversion from HS-independency to HS-dependency. It was shown that the porcine PEDSV.15 cell line permitted propagation of CSFV within a limited number of passages without adaptation to HS-binding. The selection of HS-dependent CSFV mutants was also prevented by propagation of the virus in the presence of DSTP 27. The importance of these findings can be seen from the altered ratio of cell-associated to secreted virus upon acquisition of enhanced HS-binding affinity, a phenotype proposed previously to be related to virulence in the natural host.

Sulfated derivatives of Escherichia coli K5 capsular polysaccharide are potent inhibitors of human cytomegalovirus

To date, there are few drugs licensed for the treatment of human cytomegalovirus (HCMV) infections, most of which target the viral DNA polymerase and suffer from many drawbacks. Thus, there is still a strong need for new anti-HCMV compounds with novel mechanisms of action. In this study, we investigated the anti-HCMV activity of chemically sulfated derivatives of Escherichia coli K5 capsular polysaccharide. These compounds are structurally related to cellular heparan sulfate and have been previously shown to be effective against some enveloped and nonenveloped viruses. We demonstrated that two derivatives, i.e., K5-N,OS(H) and K5-N,OS(L), are able to prevent cell infection by different strains of HCMV at concentrations in the nanomolar range while having no significant cytotoxicity. Studies performed to elucidate the mechanism of action of their anti-HCMV activity revealed that these compounds do not interact with either the host cell or the viral particle but need a virus-cell interaction to exert antiviral effects. Furthermore, these K5 derivatives were able to inhibit the attachment step of HCMV infection, as well as the viral cell-to-cell spread. Since the mode of inhibition of these compounds appears to differ from that of the available anti-HCMV drugs, sulfated K5 derivatives could represent the basis for the development of a novel class of potent anti-HCMV compounds. Interestingly, our studies highlight that small variations of the K5 derivatives structure can modulate the selectivity and potency of their activities against different viruses, including viruses belonging to the same family.

Proteoglycans in host-pathogen interactions: molecular mechanisms and therapeutic implications

Many microbial pathogens subvert proteoglycans for their adhesion to host tissues, invasion of host cells, infection of neighbouring cells, dissemination into the systemic circulation, and evasion of host defence mechanisms. Where studied, specific virulence factors mediate these proteoglycan-pathogen interactions, which are thus thought to affect the onset, progression and outcome of infection. Proteoglycans are composites of glycosaminoglycan (GAG) chains attached covalently to specific core proteins. Proteoglycans are expressed ubiquitously on the cell surface, in intracellular compartments, and in the extracellular matrix. GAGs mediate the majority of ligand-binding activities of proteoglycans, and many microbial pathogens elaborate cell-surface and secreted factors that interact with GAGs. Some pathogens also modulate the expression and function of proteoglycans through known virulence factors. Several GAG-binding pathogens can no longer attach to and invade host cells whose GAG expression has been reduced by mutagenesis or enzymatic treatment. Furthermore, GAG antagonists have been shown to inhibit microbial attachment and host cell entry in vitro and reduce virulence in vivo. Together, these observations underscore the biological significance of proteoglycan-pathogen interactions in infectious diseases.

Diverse functions of glycosaminoglycans in infectious diseases

Glycosaminoglycans (GAGs) are complex carbohydrates that are expressed ubiquitously and abundantly on the cell surface and in the extracellular matrix (ECM). The extraordinary structural diversity of GAGs enables them to interact with a wide variety of biological molecules. Through these interactions, GAGs modulate various biological processes, such as cell adhesion, proliferation and migration, ECM assembly, tissue repair, coagulation, and immune responses, among many others. Studies during the last several decades have indicated that GAGs also interact with microbial pathogens. GAG-pathogen interactions affect most, if not all, the key steps of microbial pathogenesis, including host cell attachment and invasion, cell-cell transmission, systemic dissemination and infection of secondary organs, and evasion of host defense mechanisms. These observations indicate that GAG-pathogen interactions serve diverse functions that affect the pathogenesis of infectious diseases.

Ability of low-molecular-weight heparin to alleviate proteinuria by inhibiting respiratory syncytial virus infection

AIM

Low-molecular-weight heparin (LMWH) is a negatively charged glycoprotein and has a very similar structure to that of cell surface heparin sulfate (HS). Thus, LMWH, an analog of HS, may inhibit positively charged respiratory syncytial virus (RSV) infection through cooperative electrostatic association.

METHODS

In this study, rats were respectively treated with 400 IU/kg LMWH before, during or after being inoculated with 6 x 10(6) plaque-forming unit (PFU) RSV. RSV and normal control groups were respectively inoculated by RSV and virus-free Dulbecco's modified Eagle's medium (DMEM). HeLa cells in vitro were pretreated with LMWH, elastase (ELA), heparinase (HpaIII) and protamine before being inoculated with 6 x 10(1) PFU RSV. RSV infectivity was determined by in situ hybridization and plaque assay.

RESULTS

After inoculation, the urinary protein excretion and serum parameters in LMWH-treated rats were significantly lower than those in the RSV group. No abnormalities of glomerular structure were observed in LMWH-treated groups whereas swelling and slight hypercellularity in minority glomeruli and foot process effacement were observed in the RSV group. RSV RNA of LMWH-treated rats had weaker expression than that of the RSV group. In vitro, RSV infection in RSV + LMWH, HpaIII + ELAI, protamine + ELAI, ELAI, HpaIII and protamine treatment cells were significantly lower than that of the RSV control, and that in RSV + LMWH was the least. There were no significant differences in RSV infection between ELAI + LMWH and RSV control.

CONCLUSION

Our study confirmed that there is a correlation between RSV and proteinuria in rats. LMWH can alleviate proteinuria in rats through inhibiting RSV from binding with HS which plays an important role in the onset of RSV infection.

Dendritic cell internalization of foot-and-mouth disease virus: influence of heparan sulfate binding on virus uptake and induction of the immune response

Dendritic cells (DC), which are essential for inducing and regulating immune defenses and responses, represent the critical target for vaccines against pathogens such as foot-and-mouth disease virus (FMDV). Although it is clear that FMDV enters epithelial cells via integrins, little is known about FMDV interaction with DC. Accordingly, DC internalization of FMDV antigen was analyzed by comparing vaccine virus dominated by heparan sulfate (HS)-binding variants with FMDV lacking HS-binding capacity. The internalization was most efficient with the HS-binding virus, employing diverse endocytic pathways. Moreover, internalization relied primarily on HS binding. Uptake of non-HS-binding virus by DC was considerably less efficient, so much so that it was often difficult to detect virus interacting with the DC. The HS-binding FMDV replicated in DC, albeit transiently, which was demonstrable by its sensitivity to cycloheximide treatment and the short duration of infectious virus production. There was no evidence that the non-HS-binding virus replicated in the DC. These observations on virus replication may be explained by the activities of viral RNA in the DC. When DC were transfected with infectious RNA, only 1% of the translated viral proteins were detected. Nevertheless, the transfected cells, and DC which had internalized live virus, did present antigen to lymphocytes, inducing an FMDV-specific immunoglobulin G response. These results demonstrate that DC internalization of FMDV is most efficient for vaccine virus with HS-binding capacity, but HS binding is not an exclusive requirement. Both non-HS-binding virus and infectious RNA interacting with DC induce specific immune responses, albeit less efficiently than HS-binding virus.

Inhibition of transfer to secondary receptors by heparan sulfate-binding drug or antibody induces noninfectious uptake of human papillomavirus

Infection with various human papillomaviruses (HPVs) induces cervical cancers. Cell surface heparan sulfates (HS) have been shown to serve as primary attachment receptors, and molecules with structural similarity to cell surface HS, like heparin, function as competitive inhibitors of HPV infection. Here we demonstrate that the N,N'-bisheteryl derivative of dispirotripiperazine, DSTP27, efficiently blocks papillomavirus infection by binding to HS moieties, with 50% inhibitory doses of up to 0.4 mug/ml. In contrast to short-term inhibitory effects of heparin, pretreatment of cells with DSTP27 significantly reduced HPV infection for more than 30 h. Using DSTP27 and heparinase, we furthermore demonstrate that HS moieties, rather than laminin 5, present in the extracellular matrix (ECM) secreted by keratinocytes are essential for infectious transfer of ECM-bound virions to cells. Prior binding to ECM components, especially HS, partially alleviated the requirement for cell surface HS. DSTP27 blocks infection by cell-bound virions by feeding into a noninfectious entry pathway. Under these conditions, virus colocalized with HS moieties in endocytic vesicles. Similarly, postattachment treatment of cells with heparinase, cytochalasin D, or neutralizing antibodies resulted in uptake of virions without infection, indicating that deviation into a noninfectious entry pathway is a major mode of postattachment neutralization. In untreated cells, initial colocalization of virions with HS on the cell surface and in endocytic vesicles was lost with time. Our data suggest that initial attachment of HPV to HS proteoglycans (HSPGs) must be followed by secondary interaction with additional HS side chains and transfer to a non-HSPG receptor for successful infection.

Identification of individual structural fragments of N,N'-(bis-5-nitropyrimidyl)dispirotripiperazine derivatives for cytotoxicity and antiherpetic activity allows the prediction of new highly active compounds

OBJECTIVES

The objectives of this study were (i) to apply computer-based technologies to evaluate the structure of 48 N,N'-(bis-5-nitropyrimidyl)dispirotripiperazines which belong to a new class of highly active antiviral compounds binding to cell surface heparan sulphates, (ii) to understand the chemical- biological interactions governing their activities, and (iii) to design new compounds with strong antiviral activity.

METHODS

The logarithm of 50% cytotoxic concentration (CC(50)) in GMK cells, of 50% inhibitory concentration (IC(50)) against herpes simplex virus type 1, and of selectivity index (SI = CC(50)/IC(50)) was used to develop quantitative structure-activity relationships (QSARs) based on simplex representation of molecular structure. The QSAR model was applied to design new compounds. Two of these compounds were synthesized, physico-chemically characterized and tested for cytotoxicity and antiviral activity.

RESULTS

Statistic characteristics for partial least squares models allow the prediction of CC(50), IC(50) and SI values. The QSAR results demonstrate a high impact of individual structural fragments for antiviral activity. Molecular fragments that promote and interfere with antiviral activity were defined on the basis of the obtained models. Electrostatic factors (38%) and hydrophobicity (34%) were the most important determinants of antiherpetic activity. Using the established method, new potential dispirotripiperazine derivatives were computationally designed. Two of these computationally designed compounds were synthesized. The biological test results confirm the computationally predicted values of these compounds.

CONCLUSIONS

The established QSAR model is suitable for the design of new antiherpetic compounds and prediction of their activity.

Detection of multiple human herpes viruses by DNA microarray technology

BACKGROUND

The detailed characterization of virus DNA is a challenge, and the genotyping that has been achieved to date has only been possible because researchers have sent a great deal of time and effort to do so. Instead of the simultaneous detection of hundreds of viruses on a single high-density DNA-chip at very high costs per chip, we present here an alternative approach using a well-designed and tailored microarray which can establish whether or not a handful of viral genes are present in a clinical sample.

METHODS

In this study we applied a new concept of microarray-based, optimized and robust biochemistry for molecular diagnostics of the herpesviruses. For comparison, all samples were genotyped using standard procedures.

RESULTS

The biochemical procedure of a knowledge-based, low-density microarray was established based on the molecular diagnostics of human herpes viruses: herpes simplex virus (HSV) HSV-1, HSV-2, varicella zoster virus (VZV), Epstein-Barr virus (EBV), cytomegalovirus (CMV), and HHV-6. The study attempted to optimize parameters of microarray design, surface chemistry, oligonucleotide probe spotting, sample labeling and DNA hybridization to the developed DNA microarray. The results of 12 900 hybridization reactions on about 150 configured herpes virus microarrays showed that the established microarray-based typing procedure was reproducible, virus-specific and sufficiently sensitive with a lower limit of 100 viral copies per mL sample.

CONCLUSIONS

The developed method utilizes low-fluorescence background coverslips, epoxy surface chemistry, standardized oligonucleotide probe spotting, PCR-labeling with Cy3 of isolated DNA, array hybridization, and detecting of specific spot fluorescence by an automatic microarray reader. We expect the configured microarray approach to be the method for high-throughput associated studies on human herpes viruses.

Evolutionary rates in the adaptive radiation of beetles on plants

Herbivorous insects and other small consumers are often specialized both in use of particular host taxa and in use of particular host tissues. Such consumers also often seem to show consistent differences in the rates of evolution of these two dimensions of host use, implying common processes, but this has been little studied. Here we quantify these rates of change in host use evolution in a major radiation of herbivorous insects, the Chrysomeloidea, whose diversity has been attributed to their use of flowering plants. We find a significant difference in the rates of evolutionary change in these two dimensions of host use, with host taxon associations most labile. There are apparently similar differences in rates of host use evolution in other parasite groups, suggesting the generality of this pattern. Divergences in parasite form associated with use of different host tissues may facilitate resource partitioning among successive adaptive radiations on particular host taxa.

Heparan sulfates and coxsackievirus-adenovirus receptor: each one mediates coxsackievirus B3 PD infection

Amino acid exchanges in the virus capsid protein VP1 allow the coxsackievirus B3 variant PD (CVB3 PD) to replicate in decay accelerating factor (DAF)-negative and coxsackievirus-adenovirus receptor (CAR)-negative cells. This suggests that molecules other than DAF and CAR are involved in attachment of this CVB3 variant to cell surfaces. The observation that productive infection associated with cytopathic effect occurred in Chinese hamster ovary (CHO-K1) cells, whereas heparinase-treated CHO-K1 cells, glucosaminoglycan-negative pgsA-745, heparan sulfate (HS)-negative pgsD-677, and pgsE-606 cells with significantly reduced N-sulfate expression resist CVB3 PD infection, indicates a critical role of highly sulfated HS. 2-O-sulfate-lacking pgsF-17 cells represented the cell line with minimum HS modifications susceptible for CVB3 PD. Inhibition of virus replication in CHO-K1 cells by polycationic compounds, pentosan polysulfate, lung heparin, and several intestinal but not kidney HS supported the hypothesis that CVB3 PD uses specific modified HS for entry. In addition, recombinant human hepatocyte growth factor blocked CVB3 PD infection. However, CAR also mediates CVB3 PD infection, because this CVB3 variant replicates in HS-lacking but CAR-bearing Raji cells, infection could be prevented by pretreatment of cells with CAR antibody, and HS-negative pgsD-677 cells transfected with CAR became susceptible for CVB3 PD. These results demonstrate that the amino acid substitutions in the viral capsid protein VP1 enable CVB3 PD to use specific modified HS as an entry receptor in addition to CAR.