Analysis of the interaction between RGD-expressing adenovirus type 5 fiber knob domains and alphavbeta3 integrin reveals distinct binding profiles and intracellular trafficking

Adenovirus and the Cornea: More Than Meets the Eye

Human adenoviruses cause disease at multiple mucosal sites, including the respiratory, gastrointestinal, and genitourinary tracts, and are common agents of conjunctivitis. One site of infection that has received sparse attention is the cornea, a transparent tissue and the window of the eye. While most adenovirus infections are self-limited, corneal inflammation (keratitis) due to adenovirus can persist or recur for months to years after infection, leading to reduced vision, discomfort, and light sensitivity. Topical corticosteroids effectively suppress late adenovirus keratitis but are associated with vision-threatening side effects. In this short review, we summarize current knowledge on infection of the cornea by adenoviruses, including corneal epithelial cell receptors and determinants of corneal tropism. We briefly discuss mechanisms of stromal keratitis due to adenovirus infection, and review an emerging therapy to mitigate adenovirus corneal infections based on evolving knowledge of corneal epithelial receptor usage.

HIV-1 Tat Protein Enters Dysfunctional Endothelial Cells via Integrins and Renders Them Permissive to Virus Replication

Previous work has shown that the Tat protein of Human Immunodeficiency Virus (HIV)-1 is released by acutely infected cells in a biologically active form and enters dendritic cells upon the binding of its arginine-glycine-aspartic acid (RGD) domain to the α5β1, αvβ3, and αvβ5 integrins. The up-regulation/activation of these integrins occurs in endothelial cells exposed to inflammatory cytokines that are increased in HIV-infected individuals, leading to endothelial cell dysfunction. Here, we show that inflammatory cytokine-activated endothelial cells selectively bind and rapidly take up nano-micromolar concentrations of Tat, as determined by flow cytometry. Protein oxidation and low temperatures reduce Tat entry, suggesting a conformation- and energy-dependent process. Consistently, Tat entry is competed out by RGD-Tat peptides or integrin natural ligands, and it is blocked by anti-α5β1, -αvβ3, and -αvβ5 antibodies. Moreover, modelling–docking calculations identify a low-energy Tat-αvβ3 integrin complex in which Tat makes contacts with both the αv and β3 chains. It is noteworthy that internalized Tat induces HIV replication in inflammatory cytokine-treated, but not untreated, endothelial cells. Thus, endothelial cell dysfunction driven by inflammatory cytokines renders the vascular system a target of Tat, which makes endothelial cells permissive to HIV replication, adding a further layer of complexity to functionally cure and/or eradicate HIV infection.

Factors Which Contribute to the Immunogenicity of Non-replicating Adenoviral Vectored Vaccines

Adenoviral vectors are a safe and potently immunogenic vaccine delivery platform. Non-replicating Ad vectors possess several attributes which make them attractive vaccines for infectious disease, including their capacity for high titer growth, ease of manipulation, safety, and immunogenicity in clinical studies, as well as their compatibility with clinical manufacturing and thermo-stabilization procedures. In general, Ad vectors are immunogenic vaccines, which elicit robust transgene antigen-specific cellular (namely CD8+ T cells) and/or humoral immune responses. A large number of adenoviruses isolated from humans and non-human primates, which have low seroprevalence in humans, have been vectorized and tested as vaccines in animal models and humans. However, a distinct hierarchy of immunological potency has been identified between diverse Ad vectors, which unfortunately limits the potential use of many vectors which have otherwise desirable manufacturing characteristics. The precise mechanistic factors which underlie the profound disparities in immunogenicity are not clearly defined and are the subject of ongoing, detailed investigation. It has been suggested that a combination of factors contribute to the potent immunogenicity of particular Ad vectors, including the magnitude and duration of vaccine antigen expression following immunization. Furthermore, the excessive induction of Type I interferons by some Ad vectors has been suggested to impair transgene expression levels, dampening subsequent immune responses. Therefore, the induction of balanced, but not excessive stimulation of innate signaling is optimal. Entry factor binding or receptor usage of distinct Ad vectors can also affect their in vivo tropism following administration by different routes. The abundance and accessibility of innate immune cells and/or antigen-presenting cells at the site of injection contributes to early innate immune responses to Ad vaccination, affecting the outcome of the adaptive immune response. Although a significant amount of information exists regarding the tropism determinants of the common human adenovirus type-5 vector, very little is known about the receptor usage and tropism of rare species or non-human Ad vectors. Increased understanding of how different facets of the host response to Ad vectors contribute to their immunological potency will be essential for the development of optimized and customized Ad vaccine platforms for specific diseases.

Genomic analysis of a large set of currently-and historically-important human adenovirus pathogens

Human adenoviruses (HAdVs) are uniquely important “model organisms” as they have been used to elucidate fundamental biological processes, are recognized as complex pathogens, and are used as remedies for human health. As pathogens, HAdVs may effect asymptomatic or mild and severe symptomatic disease upon their infection of respiratory, ocular, gastrointestinal, and genitourinary systems. High-resolution genomic data have enhanced the understanding of HAdV epidemiology, with recombination recognized as an important and major pathway in the molecular evolution and genesis of emergent HAdV pathogens. To support this view and to actualize an algorithm for identifying, characterizing, and typing novel HAdVs, we determined the DNA sequence of 95 isolates from archives containing historically important pathogens and collections housing currently circulating strains to be sequenced. Of the 85 samples that were completely sequenced, 18 novel recombinants within species HAdV-B and D were identified. Two HAdV-D genomes were found to contain novel penton base and fiber genes with significant divergence from known molecular types. In this data set, we found additional isolates of HAdV-D53 and HAdV-D58, two novel genotypes recognized recently using genomics. This supports the thesis that novel HAdV genotypes are not limited to “one-time” appearances of the prototype but are of importance in HAdV epidemiology. These data underscore the significance of lateral genomic transfer in HAdV evolution and reinforce the potential public health impact of novel genotypes of HAdVs emerging in the population.

Pseudotyped αvβ6 integrin-targeted adenovirus vectors for ovarian cancer therapies

Encouraging results from recent clinical trials are revitalizing the field of oncolytic virotherapies. Human adenovirus type 5 (HAdV-C5/Ad5) is a common vector for its ease of manipulation, high production titers and capacity to transduce multiple cell types. However, effective clinical applications are hindered by poor tumor-selectivity and vector neutralization. We generated Ad5/kn48 by pseudotyping Ad5 with the fiber knob domain from the less seroprevalent HAdV-D48 (Ad48). The vector was shown to utilize coxsackie and adenovirus receptor (CAR) but not CD46 for cell entry. A 20-amino acid peptide NAVPNLRGDLQVLAQKVART (A20) was inserted into the Ad5. Luc HI loop (Ad5.HI.A20) and Ad5/kn48 DG loop (Ad5/kn48.DG.A20) to target a prognostic cancer cell marker, αvβ6 integrin. Relative to the Ad5.Luc parent vector, Ad5.HI.A20, Ad5.KO1.HI.A20 (KO1, ablated CAR-binding) and Ad5/kn48.DG.A20 showed ~ 160-, 270- and 180-fold increased transduction in BT-20 breast carcinoma cells (αvβ6high). Primary human epithelial ovarian cancer (EOC) cultures derived from clinical ascites provided a useful ex vivo model for intraperitoneal virotherapy. Ad5.HI.A20, Ad5.KO1.HI.A20 and Ad5/kn48.DG.A20 transduction was ~ 70-, 60- and 16-fold increased relative to Ad5.Luc in EOC cells (αvβ6high), respectively. A20 vectors transduced EOC cells at up to ~ 950-fold higher efficiency in the presence of neutralizing ovarian ascites, as compared to Ad5.Luc. Efficient transduction and enhanced cancer-selectivity via a non-native αvβ6-mediated route was demonstrated, even in the presence of pre-existing anti-Ad5 immunity. Consequently, αvβ6-targeted Ad vectors may represent a promising platform for local intraperitoneal treatment of ovarian cancer metastases.

Assessment of Specificity of an Adenovirus Targeted to HER3/4

Gene therapy with viral vectors, such as adenovirus (Ad), targeted to the human epidermal growth factor receptors 3 and 4 (HER3/4) are potentially useful for cancer therapy. Testing the expression of a reporter gene from these viruses in target cells is essential to determine functionality of the targeted virus. A competition assay with a relevant ligand (heregulin, HRG) can provide convincing evidence that blocking binding to the HER3/4 receptor results in decreased reporter gene expression. Labeling individual viruses with a fluorescent molecule allows examination of the targeted virus in specific steps in the infection. Virus internalization into cell lines can be determined using antibody-labeled receptors, and the virus colocalization with receptors can also be visualized. Characterization of a targeted virus in this fashion is important to demonstrate that the targeting of the virus functions in an expected manner, and provides support for larger-scale testing of the virus. Information acquired in these experiments may also be useful to inform and improve on the design of future targeted viruses.

Targeted drug delivery of Sunitinib Malate to tumor blood vessels by cRGD-chiotosan-gold nanoparticles

The unique characteristics of tumor vasculature represent an attractive strategy for targeted delivery of antitumor and antiangiogenic agents to the tumor. The purpose of this study was to prepare c(RGDfK) labeled chitosan capped gold nanoparticles [cRGD(CS-Au) NPs] as a carrier for selective intracellular delivery of Sunitinib Malate (STB) to the tumor vasculature. cRGD(CS-Au) NPs was formed by electrostatic interaction between cationic CS and anionic AuNPs. cRGD modified CS-Au NPs had a spherical shape with a narrow size distribution. The entrapment efficiency of sunitinib molecule was found to be 45.2%±2.05. Confocal microscopy showed enhanced and selective uptake of cRGD(CS-Au) NPs into MCF-7 and HUVEC cells compared with non-targeted CS-Au NPs. Our results suggest that it may be possible to use cRGD(CS-Au) NPs as a carrier for delivery of anticancer drugs, genes and biomolecules for inhibiting tumor vasculature.

Selection Pressure in the Human Adenovirus Fiber Knob Drives Cell Specificity in Epidemic Keratoconjunctivitis

Human adenoviruses (HAdVs) contain seven species (HAdV-A to -G), each associated with specific disease conditions. Among these, HAdV-D includes those viruses associated with epidemic keratoconjunctivitis (EKC), a severe ocular surface infection. The reasons for corneal tropism for some but not all HAdV-Ds are not known. The fiber protein is a major capsid protein; its C-terminal "knob" mediates binding with host cell receptors to facilitate subsequent viral entry. In a comprehensive phylogenetic analysis of HAdV-D capsid genes, fiber knob gene sequences of HAdV-D types associated with EKC formed a unique clade. By proteotyping analysis, EKC virus-associated fiber knobs were uniquely shared. Comparative structural modeling showed no distinct variations in fiber knobs of EKC types but did show variation among HAdV-Ds in a region overlapping with the known CD46 binding site in HAdV-B. We also found signature amino acid positions that distinguish EKC from non-EKC types, and by in vitro studies we showed that corneal epithelial cell tropism can be predicted by the presence of a lysine or alanine at residue 240. This same amino acid residue in EKC viruses shows evidence for positive selection, suggesting that evolutionary pressure enhances fitness in corneal infection, and may be a molecular determinant in EKC pathogenesis.

IMPORTANCE

Viruses adapt various survival strategies to gain entry into target host cells. Human adenovirus (HAdV) types are associated with distinct disease conditions, yet evidence for connections between genotype and cellular tropism is generally lacking. Here, we provide a structural and evolutionary basis for the association between specific genotypes within HAdV species D and epidemic keratoconjunctivitis, a severe ocular surface infection. We find that HAdV-D fiber genes of major EKC pathogens, specifically the fiber knob gene region, share a distinct phylogenetic clade. Deeper analysis of the fiber gene revealed that evolutionary pressure at crucial amino acid sites has a significant impact on its structural conformation, which is likely important in host cell binding and entry. Specific amino acids in hot spot residues provide a link to ocular cell tropism and possibly to corneal pathogenesis.

Estradiol-tethered micropatterned surfaces for the study of estrogenic non-genomic pathways

Besides its well-known hormonal effects initiated in the nucleus, estradiol (E2) also activates non-nuclear pathways through interactions with receptors located on the cell plasma membrane. Micropatterned substrates consisting of gold dots bearing tethered E2 distributed on a cell-adhesive substrate were prepared and shown to trigger specifically E2 non-genomic effects in cells grown on the substrates.

Human Parechovirus 1 Infection Occurs via αVβ1 Integrin

Human parechovirus 1 (HPeV-1) (family Picornaviridae) is a global cause of pediatric respiratory and CNS infections for which there is no treatment. Although biochemical and in vitro studies have suggested that HPeV-1 binds to αVβ1, αVβ3 and αVβ6 integrin receptor(s), the actual cellular receptors required for infectious entry of HPeV-1 remain unknown. In this paper we analyzed the expression profiles of αVβ1, αVβ3, αVβ6 and α5β1 in susceptible cell lines (A549, HeLa and SW480) to identify which integrin receptors support HPeV-1 internalization and/or replication cycle. We demonstrate by antibody blocking assay, immunofluorescence microscopy and RT-qPCR that HPeV-1 internalizes and replicates in cell lines that express αVβ1 integrin but not αVβ3 or αVβ6 integrins. To further study the role of β1 integrin, we used a mouse cell line, GE11-KO, which is deficient in β1 expression, and its derivate GE11-β1 in which human integrin β1 subunit is overexpressed. HPeV-1 (Harris strain) and three clinical HPeV-1 isolates did not internalize into GE11-KO whereas GE11-β1 supported the internalization process. An integrin β1-activating antibody, TS2/16, enhanced HPeV-1 infectivity, but infection occurred in the absence of visible receptor clustering. HPeV-1 also co-localized with β1 integrin on the cell surface, and HPeV-1 and β1 integrin co-endocytosed into the cells. In conclusion, our results demonstrate that in some cell lines the cellular entry of HPeV-1 is primarily mediated by the active form of αVβ1 integrin without visible receptor clustering.

Retargeting adenovirus serotype 48 fiber knob domain by peptide incorporation

Adenovirus type 5 (Ad5) is a commonly used vector for gene therapy, but its efficacy is limited by high seroprevalence and off-target hepatic and splenic sequestration. In order to circumvent these limitations, the use of vectors derived from rare species adenoviruses is appealing. The opportunity to retarget rare species vectors to defined cell types through the incorporation of peptide ligands would be advantageous, particularly in targeting tumors and disseminated metastases. We used predictive structural modeling to assess the CD, DG, HI, and IJ loops of the Ad48 fiber knob and identify optimal incorporation locales for the 20-mer peptide, A20FMDV2 (A20). A20FMDV2 targets ανβ6 integrin, which is overexpressed in human carcinomas. Recombinant Ad48 fiber knob proteins Knob48, Knob48-CD-A20, Knob48-DG-A20, Knob48-HI-A20, and Knob48-IJ-A20 were engineered and purified after expression in Escherichia coli. We confirmed that Knob48, Knob48-CD-A20, and Knob48-IJ-A20 formed stable homotrimers. However, Knob48-DG-A20 and Knob-HI-A20 failed to form a trimer. All A20-modified knob proteins blocked the transduction of Ad5-EGFPA20 via ανβ6, demonstrating that the inserted A20 peptide was functional. In conclusion, we show that the CD and IJ loops of Ad48 represent suitable sites for targeting peptide incorporation. Interestingly, in vitro gene transfer mediated by the non-factor-X-binding Ad48 vector was not sensitive to immunoglobulins and complement when incubated in the presence of mouse serum, unlike Ad5. These data support the future generation of the corresponding Ad48 viral vectors, Ad48-CD-A20 and Ad48-IJ-A20, which may offer favorable characteristics for targeted delivery in vivo.

Bridging the past and the future of virology: surface plasmon resonance as a powerful tool to investigate virus/host interactions

Despite decades of antiviral drug research and development, viruses still remain a top global healthcare problem. Compared to eukaryotic cells, viruses are composed by a limited numbers of proteins that, nevertheless, set up multiple interactions with cellular components, allowing the virus to take control of the infected cell. Each virus/host interaction can be considered as a therapeutical target for new antiviral drugs but, unfortunately, the systematic study of a so huge number of interactions is time-consuming and expensive, calling for models overcoming these drawbacks. Surface plasmon resonance (SPR) is a label-free optical technique to study biomolecular interactions in real time by detecting reflected light from a prism-gold film interface. Launched 20 years ago, SPR has become a nearly irreplaceable technology for the study of biomolecular interactions. Accordingly, SPR is increasingly used in the field of virology, spanning from the study of biological interactions to the identification of putative antiviral drugs. From the literature available, SPR emerges as an ideal link between conventional biological experimentation and system biology studies functional to the identification of highly connected viral or host proteins that act as nodal points in virus life cycle and thus considerable as therapeutical targets for the development of innovative antiviral strategies.

The disulfide bond of an RGD4C motif inserted within the Hi loop of the adenovirus type 5 fiber protein is critical for retargeting to αv -integrins

BACKGROUND

The α(v) -integrin binding motif RGD4C (CDCRGDCFC) has been used extensively to circumvent inefficient adenovirus type 5 (Ad5) transduction of cells expressing low levels of the coxsackie and adenovirus receptor. However, until now, it has been unclear whether disulfide bonds in the RGD4C motif influence the retargeting potential of RGD4C-modified Ad5.

METHODS

Replication deficient Ad5 bearing wild-type fiber (Ad5wt) or RGD4G, RGD4C and RGD2C2G insertions within the HI loop of the fiber protein (Ad5RGD4G, Ad5RGD4C and Ad5RGD2C2G, respectively) were used to transduce a panel of cancer cell lines, with or without previous treatment of these Ad5s with the reducing agent dithiothreitol (DTT). In parallel, native and DTT-treated fiber proteins isolated from purified Ad5RGD4C were compared by mass spectrometry.

RESULTS

Ad5RGD4C transduced all studied cell lines much more efficiently than Ad5wt, whereas Ad5RGD4G transduced cells only slightly more efficiently than Ad5wt. DTT treatment had no effect on cell transduction by wild-type Ad5wt and Ad5RGD4G but abolished the increased transduction efficacy of Ad5RGD4C in a dose-dependent manner. The mass spectra of native and DTT-reduced tryptic digests of the Ad5RGD4C fiber protein are consistent with the presence of a C(547) -C(549) linkage in the C(547) DC(549) RGDC(553) FC(555) motif. Finally, the high transduction efficacy of Ad5RGD4C is conserved in Ad5RGD2C2G.

CONCLUSIONS

We provide genetic and biochemical data strongly suggesting that cysteines C(547) and C(549) from the C(547) DC(549) RGDC(553) FC(555) motif inserted in the HI loop of the Ad5 fiber form a single disulfide bond, with this disulfide bond being crucial for Ad5RGD4C retargeting to av-integrins.

Target-specific copper hybrid T7 phage particles

Target-specific nanoparticles have attracted significant attention recently, and have greatly impacted life and physical sciences as new agents for imaging, diagnosis, and therapy, as well as building blocks for the assembly of novel complex materials. While most of these particles are synthesized by chemical conjugation of an affinity reagent to polymer or inorganic nanoparticles, we are promoting the use of phage particles as a carrier to host organic or inorganic functional components, as well as to display the affinity reagent on the phage surface, taking advantage of the fact that some phages host well-established vectors for protein expression. An affinity reagent can be structured in a desired geometry on the surface of phage particles, and more importantly, the number of the affinity reagent molecules per phage particle can be precisely controlled. We previously have reported the use of the T7 phage capsid as a template for synthesizing target-specific metal nanoparticles. In this study herein, we reported the synthesis of nanoparticles using an intact T7 phage as a scaffold from which to extend 415 copies of a peptide that contains a hexahistidine (6His) motif for capture of copper ions and staging the conversion of copper ions to copper metal, and a cyclic Arginine-Glycine-Aspartic Acid (RGD4C) motif for targeting integrin and cancer cells. We demonstrated that the recombinant phage could load copper ions under low bulk copper concentrations without interfering with its target specificity. Further reduction of copper ions to copper metal rendered a very stable copper hybrid T7 phage, which prevents the detachment of copper from phage particles and maintains the phage structural integrity even under harsh conditions. Cancer cells (MCF-7) can selectively uptake copper hybrid T7 phage particles through ligand-mediated transmembrane transportation, whereas normal control cells (MCF-12F) uptake 1000-fold less. We further demonstrated that copper hybrid T7 phage could be endocytosed by cancer cells in culture.

Guiding plant virus particles to integrin-displaying cells

Viral nanoparticles (VNPs) are structurally regular, highly stable, tunable nanomaterials that can be conveniently produced in high yields. Unmodified VNPs from plants and bacteria generally do not show tissue specificity or high selectivity in binding to or entry into mammalian cells. They are, however, malleable by both genetic and chemical means, making them useful scaffolds for the display of large numbers of cell- and tissue-targeting ligands, imaging moieties, and/or therapeutic agents in a well-defined manner. Capitalizing on this attribute, we modified the genetic sequence of the Cowpea mosaic virus (CPMV) coat protein to display an RGD oligopeptide sequence derived from human adenovirus type 2 (HAdV-2). Concurrently, wild-type CPMV was modified via NHS acylation and Cu(I)-catalyzed azide-alkyne cycloaddition (CuAAC) chemistry to attach an integrin-binding cyclic RGD peptide. Both types of particles showed strong and selective affinity for several different cancer cell lines that express RGD-binding integrin receptors.

In vivo retargeting of adenovirus type 5 to alphavbeta6 integrin results in reduced hepatotoxicity and improved tumor uptake following systemic delivery

A key impediment to successful cancer therapy with adenoviral vectors is the inefficient transduction of malignant tissue in vivo. Compounding this problem is the lack of cancer-specific targets, coupled with a shortage of corresponding high-efficiency ligands, permitting selective retargeting. The epithelial cell-specific integrin alphavbeta6 represents an attractive target for directed therapy since it is generally not expressed on normal epithelium but is upregulated in numerous carcinomas, where it plays a role in tumor progression. We previously have characterized a high-affinity, alphavbeta6-selective peptide (A20FMDV2) derived from VP1 of foot-and-mouth disease virus. We generated recombinant adenovirus type 5 (Ad5) fiber knob, incorporating A20FMDV2 in the HI loop, for which we validated the selectivity of binding and functional inhibition of alphavbeta6. The corresponding alphavbeta6-retargeted virus Ad5-EGFP(A20) exhibited up to 50-fold increases in coxsackievirus- and-adenovirus-receptor-independent transduction and up to 480-fold-increased cytotoxicity on a panel of alphavbeta6-positive human carcinoma lines compared with Ad5-EGFP(WT). Using an alphavbeta6-positive (DX3-beta6) xenograft model, we observed a approximately 2-fold enhancement in tumor uptake over Ad5-EGFP(WT) following systemic delivery. Furthermore, approximately 5-fold-fewer Ad5-EGFP(A20) genomes were detected in the liver (P = 0.0002), correlating with reduced serum transaminase levels and E1A expression. Warfarin pretreatment, to deplete coagulation factors, did not improve tumor uptake significantly with either virus but did significantly reduce liver sequestration and hepatic toxicity. The ability of Ad5-EGFP(A20) to improve delivery to alphavbeta6, combined with its reduced hepatic tropism and toxicity, highlights its potential as a prototype virus for future clinical investigation.