Fiber Knob Research Articles

Expression and Purification of a Recombinant Adenovirus Fiber Knob in a Baculovirus System

Objectives: To construct a recombinant baculovirus expressing the fiber knob domain of human adenovirus type 2 modified by the insertion of a foreign peptide, purify this protein after its production in insect cells, and to test its properties. Methods: Recombinant baculoviruses expressing the fiber knob were produced in Sf9 cells. The recombinant fiber knob was recovered from culture supernatants of infected cells and purified by a combination of Ni-NTA and ion-exchange chromatography. Results: Fiber knob was recovered from the culture media as a soluble protein. In the system used, the fiber knob is expressed fused with the V5 epitope and a histidine tag, which allowed purification by Ni-NTA chromatography. The protein was further purified by ion-exchange chromatography. We show that the recombinant fiber knob produced, with 31 extra amino acids in the C-terminus, can oligomerize and bind to the adenovirus receptor CAR, as it can block the infection of a recombinant type 5 adenovirus. Conclusions: The modified form of the fiber knob, produced in insect cells and purified by Ni-NTA and ion-exchange chromatography, retains the properties of oligomerization and binding to the fiber natural receptor, CAR. This construct has the potential to be a new adjuvant.

Thiamine diphosphate binds to intermediates in the assembly of adenovirus fiber knob trimers in Escherichia coli

Assembly of the adenovirus (Ad) homotrimeric fiber protein is nucleated by its C-terminal knob domain, which itself can trimerize when expressed as a recombinant protein fragment. The non-interlocked, globular structure of subunits in the knob trimer implies that trimers assemble from prefolded monomers through a dimer intermediate, but these intermediates have not been observed and the mechanism of assembly therefore remains uncharacterized. Here we report that expression of the Ad serotype 2 (Ad2) knob was toxic for thi- strains of Escherichia coli, which are defective in de novo synthesis of thiamine (vitamin B1). Ad2 knob trimers isolated from a thi+ strain copurified through multiple chromatography steps with a small molecule of mass equivalent to that of thiamine diphosphate (ThDP). Mutant analysis did not implicate any specific site for ThDP binding. Our results suggest that ThDP may associate with assembly intermediates and become trapped in assembled trimers, possibly within one of several large cavities that are partially solvent-accessible or buried completely within the trimer interior.

An Oncolytic Adenovirus Redirected with a Tumor-Specific T-Cell Receptor

To improve safety and specificity of oncolytic adenoviruses, we introduced T-cell receptors (TCR) specific for a unique class of truly tumor-specific antigens into the adenoviral fiber protein. The adenoviral fiber knob responsible for attachment to the coxsackie-adenoviral receptor (CAR) on target cells was replaced by a single-chain TCR (scTCR) molecule with specificity for the melanoma-associated cancer-testis antigen MAGE-A1, presented by HLA-A1, and an extrinsic trimerization motif in a replicating Ad5 vector (Ad5.R1-scTCR). The production of the recombinant virus was initiated in a novel producer cell line that expressed an antibody-based hexon-specific receptor (293T-AdR) in the cell membrane. This new production system allowed CAR-independent and target antigen-independent propagation of Ad5.R1-scTCR. Infection with adenovirus bearing the scTCR-based fiber resulted in an efficient killing of target tumor cells. The infection was cell type specific because only HLA-A1(+)/MAGE-A1(+) melanoma cells were killed, and thus, this retargeting strategy provides a versatile tool for future clinical application.

Species B adenovirus serotypes 3, 7, 11 and 35 share similar binding sites on the membrane cofactor protein CD46 receptor

We recently characterized the domains of the human cofactor protein CD46 involved in binding species B2 adenovirus (Ad) serotype 35. Here, the CD46 binding determinants are mapped for the species B1 Ad serotypes 3 and 7 and for the species B2 Ad11. Ad3, 7 and 11 bound and transduced CD46-positive rodent BHK cells at levels similar to Ad35. By using antibody-blocking experiments, hybrid CD46-CD4 receptor constructs and CD46 single point mutants, it is shown that Ad3, 7 and 11 share many of the Ad35-binding features on CD46. Both CD46 short consensus repeat domains SCR I and SCR II were necessary and sufficient for optimal binding and transgene expression, provided that they were positioned at an appropriate distance from the cell membrane. Similar to Ad35, most of the putative binding residues of Ad3, 7 and 11 were located on the same glycan-free, solvent-exposed face of the SCR I or SCR II domains, largely overlapping with the binding surface of the recently solved fiber knob Ad11-SCR I-II three-dimensional structure. Differences between species B1 and B2 Ads were documented with competition experiments based on anti-CD46 antibodies directed against epitopes flanking the putative Ad-binding sites, and with competition experiments based on soluble CD46 protein. It is concluded that the B1 and B2 species of Ad engage CD46 through similar binding surfaces.

Experimental treatment of ovarian cancers by adenovirus vectors combining receptor targeting and selective expression of tumor necrosis factor

Ovarian cancer is the fourth most common cancer among women and existing treatment is not routinely curative. One new strategy for cancer therapy is the selective delivery of TNFalpha to tumors via adenovirus vectors. We have tested the combination of two modifications to adenovirus vectors designed to limit delivery to tumors, capsid modification and expression control. To target alpha(v)beta(3/5) integrin receptors that are highly expressed in tumor and sparsely expressed in the epithelial layer of peritoneum, we modified the capsid fiber and penton base to remove native receptor binding and incorporated an RGD-4C motif in the fiber knob (Ad.PB*F*RGD). This vector exhibits effective gene transfer in all of the alpha(v)beta(3/5)-positive ovarian cancer cells tested in vitro and in vivo. Importantly, the Ad.PB*F*RGD vector is able to transduce ovarian tumor nodules and avoid infecting the normal mesothelial cells that line the intraperitoneal space following intraperitoneal administration. To further increase selectivity, different promoters were incorporated into the capsid-modified vector to confer the expression of the hTNFalpha therapeutic gene. We analyzed both constitutive (CMV or RSV) and potentially tumor selective promoters (MUC-1, E2F or hTERT) in terms of efficacy, selectivity and safety. TNF-expressing Ad.PB*F*RGD vectors containing the MUC-1 promoter showed anti-tumor activity in two ovarian cancer xenograft models (Caov3 and Igr-ov1) with little evidence of toxicity or systemic TNF. The data indicate that combination of capsid modification and transcriptional regulation of expression is a promising strategy for development of a new ovarian cancer treatment.

Identification of CD46 binding sites within the adenovirus serotype 35 fiber knob.

Species B human adenoviruses (Ads) are often associated with fatal illnesses in immunocompromised individuals. Recently, species B Ads, most of which use the ubiquitously expressed complement regulatory protein CD46 as a primary attachment receptor, have gained interest for use as gene therapy vectors. In this study, we focused on species B Ad serotype 35 (Ad35), whose trimeric fiber knob domain binds to three CD46 molecules with a KD (equilibrium dissociation constant) of 15.5 nM. To study the Ad35 knob-CD46 interaction, we generated an expression library of Ad35 knobs with random mutations and screened it for CD46 binding. We identified four critical residues (Phe242, Arg279, Ser282, and Glu302) which, when mutated, ablated Ad35 knob binding to CD46 without affecting knob trimerization. The functional importance of the identified residues was validated in surface plasmon resonance and competition binding studies. To model the Ad35 knob-CD46 interaction, we resolved the Ad35 knob structure at 2-A resolution by X-ray crystallography and overlaid it onto the existing structure for Ad11-CD46 interaction. According to our model, all identified Ad35 residues are in regions that interact with CD46, whereby one CD46 molecule binds between two knob monomers. This mode of interaction might have potential consequences for CD46 signaling and intracellular trafficking of Ad35. Our findings are also fundamental for better characterization of species B Ads and design of antiviral drugs, as well as for application of species B Ads as in vivo and in vitro gene transfer vectors.

Direct selection of targeted adenovirus vectors by random peptide display on the fiber knob

Targeting of gene transfer at the level of cell entry is one of the most attractive challenges in vector development. However, attempts to redirect adenovirus vectors to alternative receptors by engineering the capsid-coding region have shown limited success because proper targeting ligand-receptor systems on the cells of interest are generally unknown. Systematic approaches to generate adenovirus vectors targeting any given cell type need to be developed to achieve this goal. Here, we constructed an adenovirus library that was generated by a Cre-lox-mediated in vitro recombination between an adenoviral fiber-modified plasmid library and genomic DNA to display random peptides on a fiber knob. As proof of concept, we screened the adenovirus display library on a glioma cell line and observed selection of several particular peptide sequences. The targeted vector carrying the most frequently isolated peptide significantly enhanced gene transduction in the glioma cell line but not in many other cell lines. Because the insertion of a pre-selected peptide into a fiber knob often fails to generate an adenovirus vector, the selection of targeting peptides is highly useful in the context of the adenoviral capsid. This vector-screening system can facilitate the development of a targeted adenovirus vector for a variety of applications in medicine.

Targeted Delivery of CX3CL1 to Multiple Lung Tumors by Mesenchymal Stem Cells

MSCs are nonhematopoietic stem cells capable of differentiating into various mesoderm-type cells. MSCs have been considered to be a potential vehicle for cell-based gene therapy because MSCs are relatively easily expanded in vitro and have the propensity to migrate to and proliferate in the tumor tissue after systemic administration. Here, we demonstrated the tropism of mouse MSCs to tumor cells in vitro and multiple tumor tissues in the lung after i.v. injection of green fluorescent protein-positive MSCs in vivo. We transduced CX3CL1 (fractalkine), an immunostimulatory chemokine, to the mouse MSCs ex vivo using an adenoviral vector with the Arg-Gly-Asp-4C peptide in the fiber knob. Intravenous injection of CX3CL1-expressing MSCs to the mice bearing lung metastases of C26 and B16F10 cells strongly inhibited the development of lung metastases and thus prolonged the survival of these tumor-bearing mice. This antitumor effect depended on both innate and adaptive immunity. These results suggest that MSCs can be used as a vehicle for introducing biological agents into multiple lung tumor tissues. Disclosure of potential conflicts of interest is found at the end of this article.

Gene delivery into malignant glioma by infectivity-enhanced adenovirus: In vivo versus in vitro models

Adenoviral (Ad) vectors demonstrate several attributes of potential utility for glioma gene therapy. Although Ad infection is limited in vitro by low expression levels of the coxsackie-adenoviral receptor (CAR), in vivo studies have shown the efficacy of Ad vectors as gene delivery vectors. To evaluate the in vivo utility of CAR-independent, infectivity-enhanced Ad vectors, we employed genetically modified Ad vectors in several experimental models of human gliomas. We used three capsid-modified Ad vectors: (1) a chimeric Ad vector with a human Ad backbone and a fiber knob of a canine Ad, (2) an Ad vector with a polylysine motif incorporated into the fiber gene, and (3) a double-modified Ad vector incorporating both an RGD4C peptide and the polylysine motif. These three modified Ad vectors target, respectively, the putative membrane receptor(s) of the canine Ad vector, heparan sulfate proteoglycans (HSPGs), and both integrins and HSPGs. Our in vitro studies indicated that these retargeting strategies all enhanced CAR-independent infectivity in both established and primary low-passage glioma cells. Enhancement of in vitro gene delivery by the capsid-modified vectors correlated inversely with the levels of cellular CAR expression. However, in vivo in orthotopic human glioma xenografts, the unmodified Ad vector was not inferior relative to the capsid-modified Ad vector. Although genetic strategies to circumvent CAR deficiency in glioma cells could reproducibly expand the cellular entry mechanisms of Ad vectors in cultured and primary glioma cells, these approaches were insufficient to confer in vivo significant infectivity enhancement over unmodified Ad vectors. Other factors, probably the extracellular matrix, stromal cells, and the three-dimensional tumor architecture, clearly play important roles in vivo and interfere with Ad-based gene delivery into glioma tumors.

Phylogenetic Analysis and Structural Predictions of Human Adenovirus Penton Proteins as a Basis for Tissue-Specific Adenovirus Vector Design

The penton base is a major capsid protein of human adenoviruses (HAdV) which forms the vertices of the capsid and interacts with hexon and fiber protein. Two hypervariable loops of the penton are exposed on the capsid surface. Sequences of these and 300 adjacent amino acid residues of all 51 HAdV and closely related simian adenoviruses were studied. Adjacent sequences and predicted overall secondary structure were conserved. Phylogenetic analysis revealed clustering corresponding to the HAdV species and recombination events in the origin of HAdV prototypes. All HAdV except serotypes 40 and 41 of species F exhibited an integrin binding RGD motif in the second loop. The lengths of the loops (HVR1 and RGD loops) varied significantly between HAdV species with the longest RGD loop observed in species C and the longest HVR1 in species B. Long loops may permit the insertion of motifs that modify tissue tropism. Genetic analysis of HAdV prime strain p17'H30, a neutralization variant of HAdV-D17, indicated the significance of nonhexon neutralization epitopes for HAdV immune escape. Fourteen highly conserved motifs of the penton base were analyzed by site-directed mutagenesis of HAdV-D8 and tested for sustained induction of early cytopathic effects. Thus, three new motifs essential for penton base function were identified additionally to the RGD site, which interacts with a secondary cellular receptor responsible for internalization. Therefore, our penton primary structure data and secondary structure modeling in combination with the recently published fiber knob sequences may permit the rational design of tissue-specific adenoviral vectors.

Fiber-modified adenovirus vectors containing the TAT peptide derived from HIV-1 in the fiber knob have efficient gene transfer activity

The interaction between viral capsid proteins and specific molecules exposed on the plasma membrane of the cells is involved in the viral tropism. A human adenovirus (Ad) belonging to subgroups A, C, D, E and F infects cells via the interaction between the fiber knob and the primary receptor, the coxsackievirus and adenovirus receptor (CAR). Conventional human adenovirus type 5 (hAd5) vectors show efficient transduction in CAR-positive cells; in contrast, hAd5 vector application is limited by poor transduction into cells lacking CAR expression. In the present study, to broaden the tropism of hAd5 vectors, we generated hAd5 vectors containing the TAT peptide, which is a protein transduction domain derived from human immunodeficiency virus, in the HI loop of the fiber knob (Ad-TAT(HI)-L2) or the C-terminus of the fiber knob (Ad-TAT(C)-L2). In CAR-negative adherent cells, Ad-TAT(HI)-L2 and Ad-TAT(C)-L2 showed approximately 50- to 500-fold higher gene expression than the conventional hAd5 vector (Ad-L2). Ad-TAT(HI)-L2 was also more efficient than Ad-L2 in blood cell lines and in two types of primary cultured human vascular smooth muscle cells, which are almost refractory to Ad-L2. Furthermore, Ad-TAT(HI)-L2 was more efficient than other types of fiber-modified Ad vectors, which harbor an RGD (Arg-Gly-Asp) or a poly-lysine (KKKKKKK;K7) peptide in the HI loop or the C-terminus of the fiber knob, respectively. Ad-TAT(HI)-L2 efficiently transduced the organs in levels and patterns that were roughly similar to those of Ad-L2 after being systemically injected into mice. To the best of our knowledge, this study is the first report showing that hAd5 vectors containing the TAT peptide in the fiber knob could efficiently transduce cells independently of CAR. These Ad vectors should be useful for gene functional analysis and gene therapy.

871. Characterization of Coagulation Factor IX Interactions with Human Adenovirus Fiber Knob Domains Using Tandem Mass Spectrometry and Surface Plasmon Resonance

871. Characterization of Coagulation Factor IX Interactions with Human Adenovirus Fiber Knob Domains Using Tandem Mass Spectrometry and Surface Plasmon Resonance

Adenovirus 5 Fibers Mutated at the Putative HSPG-binding Site Show Restricted Retargeting with Targeting Peptides in the HI Loop

Adenoviral vectors are commonly used for liver-directed gene therapy following systemic administration owing to their strong propensity for hepatocyte transduction. However, many disease applications would benefit from the delivery of adenoviruses to alternate tissues via this route. Research has thus focused on stripping the virus of native hepatic tropism in conjunction with modifying virus capsid proteins to incorporate novel tropism. Recently, the KO1S* adenovirus serotype 5 fiber mutant, devoid of both coxsackie and adenovirus receptor binding in the fiber knob domain and mutated at the putative heparan sulphate proteoglycan binding site in the fiber shaft, was shown to possess strikingly poor hepatic tropism in mice, rats, and non-human primates. Thus, it is an ideal candidate for retargeting strategies. We therefore assessed the ability of peptide-modified KO1S* fibers to retarget adenovirus. Peptide insertions were well tolerated and virions produced to high titers. However, expected retargeting at the level of transduction was not observed, despite cell-binding studies showing enhanced vector targeting at the cell surface. Cy3 labeling studies showed retarded trafficking of S*-containing fibers. Taken together, our data demonstrates that KO1S* mutant fibers are ineffective for cell retargeting strategies.

Downregulation of human CD46 by adenovirus serotype 35 vectors

Human CD46 (membrane cofactor protein), which serves as a receptor for a variety of pathogens, including strains of measles virus, human herpesvirus type 6 and Neisseria, is rapidly downregulated from the cell surface following infection by these pathogens. Here, we report that replication-incompetent adenovirus (Ad) serotype 35 (Ad35) vectors, which belong to subgroup B and recognize human CD46 as a receptor, downregulate CD46 following infection. A decline in the surface expression of CD46 in human peripheral blood mononuclear cells was detectable 6 h after infection, and reached maximum (72%) 12 h after infection. Ad35 vector-induced downregulation of surface CD46 levels gradually recovered after the removal of Ad35 vectors, however, complete recovery of CD46 expression was not observed even at 96 h after removal. The surface expression of CD46 was also reduced after incubation with fiber-substituted Ad serotype 5 (Ad5) vectors bearing Ad35 fiber proteins, ultraviolet-irradiated Ad35, vectors and recombinant Ad35 fiber knob proteins; in contrast, conventional Ad5 vectors did not induce surface CD46 downregulation, suggesting that the fiber knob protein of Ad35 plays a crucial role in the downregulation of surface CD46 density. These results have important implications for gene therapy using CD46-utilizing Ad vectors and for the pathogenesis of Ads that interact with CD46.

Enhancement of Gene Transfer to Human Myeloid Cells by Adenovirus–Fiber Complexes

Adenoviral (Ad) vectors are currently being developed for immunotherapy and vaccine delivery, particularly for cancer and antiviral treatment (e.g., human immunodeficiency virus vaccine). However, the inefficient transduction of antigen-presenting cells of myeloid lineage such as dendritic cells (DCs) by conventional Ad5-based vectors limits these applications. DCs lack the coxsackie and adenovirus receptor but express CD46, a member of the family of complement regulatory proteins, as well as sialic acid glycoconjugates, a situation that allows infection by Ad type 37 as well as most subgroup B Ads. In this study, we generated recombinant Ad fiber knobs (FKs) to probe Ad37 receptor usage on immune cells. Remarkably, treatment of human myeloid cells with Ad37 FK (37FK) enhanced, rather than inhibited transduction by Ad5 or Ad37 pseudotyped virions. The enhanced gene transfer was dose dependent, involved association with alpha(2,6)-linked sialic acid residues, and was limited to blood cells of myeloid lineage, including immature and mature DCs. We also provide evidence that 37FK binds directly to Ad5 virus particles, likely acting as a bridge to facilitate greater virus-cell interaction.

Targeting of adenovirus vectors carrying a tumor cell-specific peptide: in vitro and in vivo studies

Previously, we have identified a tumor cell-specific peptide, HEW, by panning of phage display libraries on the human colorectal cancer cell line WiDr. In this report we demonstrate that this peptide can modify the infection properties of adenovirus vectors. Increased infectivity of replication-deficient adenovirus 5 vectors in WiDr cells was observed upon genetic insertion of the HEW peptide in the HI loop of the fiber knob. Moreover, whereas the coxsackie and adenovirus receptor (CAR)-ablating fiber mutation S408E abolished apparent infection in CAR-positive WiDr cells, the insertion of HEW completely restored infectivity toward these cells in vitro. To assess whether the de- and re-targeted infection profile was maintained in vivo, the fiber-modified adenovirus vectors were injected intratumorally or intravenously in WiDr tumor-bearing Swiss nu/nu mice. No significant differences in efficiency of infection could be observed suggesting alternative viral uptake mechanisms in vivo. Next, we have included the fiber shaft mutation S(*) in our studies, which was described to confer a de-targeted phenotype in vivo. Reduced gene transfer due to the S(*) mutation both in vitro and in vivo could be confirmed. Insertion of HEW in the HI knob loop of shaft-mutated fiber, however, did not rescue infectivity in target cells neither in vitro nor in vivo. We demonstrate the efficient ligand-mediated re-targeting of adenoviral vector infection to the human cancer cell line WiDr. The lack of apparent re-targeting in the in vivo situation is described.

Fiber-Modified Adenovirus Vectors Decrease Liver Toxicity through Reduced IL-6 Production

Adenovirus (Ad) vectors are one of the most commonly used viral vectors in gene therapy clinical trials. However, they elicit a robust innate immune response and inflammatory responses. Improvement of the therapeutic index of Ad vector gene therapy requires elucidation of the mechanism of Ad vector-induced inflammation and cytokine/chemokine production as well as development of the safer vector. In the present study, we found that the fiber-modified Ad vector containing poly-lysine peptides in the fiber knob showed much lower serum IL-6 and aspartate aminotransferase levels (as a maker of liver toxicity) than the conventional Ad vector after i.v. administration, although the modified Ad vector showed higher transgene production in the liver than the conventional Ad vector. RT-PCR analysis showed that spleen, not liver, is the major site of cytokine, chemokine, and IFN expression. Splenic CD11c(+) cells were found to secret cytokines. The tissue distribution of Ad vector DNA showed that spleen distribution was much reduced in this modified Ad vector, reflecting reduced IL-6 levels in serum. Liver toxicity by the conventional Ad vector was reduced by anti-IL-6R Ab, suggesting that IL-6 signaling is involved in liver toxicity and that decreased liver toxicity of the modified Ad vector was due in part to the reduced IL-6 production. This study contributes to an understanding of the biological mechanism in innate immune host responses and liver toxicity toward systemically administered Ad vectors and will help in designing safer gene therapy methods that can reduce robust innate immunity and inflammatory responses.

Contrasting Effects of Human, Canine, and Hybrid Adenovirus Vectors on the Phenotypical and Functional Maturation of Human Dendritic Cells: Implications for Clinical Efficacy

Antipathogen immune responses create a balance between immunity, tolerance, and immune evasion. However, during gene therapy most viral vectors are delivered in substantial doses and are incapable of expressing gene products that reduce the host's ability to detect transduced cells. Gene transfer efficacy is also modified by the in vivo transduction of dendritic cells (DC), which notably increases the immunogenicity of virions and vector-encoded genes. In this study, we evaluated parameters that are relevant to the use of canine adenovirus serotype 2 (CAV-2) vectors in the clinical setting by assaying their effect on human monocyte-derived DC (hMoDC). We compared CAV-2 to human adenovirus (HAd) vectors containing the wild-type virion, functional deletions in the penton base RGD motif, and the CAV-2 fiber knob. In contrast to the HAd type 5 (HAd5)-based vectors, CAV-2 poorly transduced hMoDC, provoked minimal upregulation of major histocompatibility complex class I/II and costimulatory molecules (CD40, CD80, and CD86), and induced negligible morphological changes indicative of DC maturation. Functional maturation assay results (e.g., reduced antigen uptake; tumor necrosis factor alpha, interleukin-1beta [IL-1beta], gamma interferon [IFN-gamma], IL-10, IL-12, and IFN-alpha/beta secretion; and stimulation of heterologous T-cell proliferation) were also significantly lower for CAV-2. Our data suggested that this was due, in part, to the use of an alternative receptor and a block in vesicular escape. Additionally, HAd5 vector-induced hMoDC maturation was independent of the aforementioned cytokines. Paradoxically, an HAd5/CAV-2 hybrid vector induced the greatest phenotypical and functional maturation of hMoDC. Our data suggest that CAV-2 and the HAd5/CAV-2 vector may be the antithesis of Adenoviridae immunogenicity and that each may have specific clinical advantages.

Tropism Modification of Adenovirus Vectors by Peptide Ligand Insertion into Various Positions of the Adenovirus Serotype 41 Short-Fiber Knob Domain

Recombinant adenoviruses have emerged as promising agents in therapeutic gene transfer, genetic vaccination, and viral oncolysis. Therapeutic applications of adenoviruses, however, would benefit substantially from targeted virus cell entry, for example, into cancer or immune cells, as opposed to the broad tropism that adenoviruses naturally possess. Such tropism modification of adenoviruses requires the deletion of their natural cell binding properties and the incorporation of cell binding ligands. The short fibers of subgroup F adenoviruses have recently been suggested as a tool for genetic adenovirus detargeting based on the reduced infectivity of corresponding adenovectors with chimeric fibers in vitro and in vivo. The goal of our study was to determine functional insertion sites for peptide ligands in the adenovirus serotype 41 (Ad41) short fiber knob. With a model peptide, CDCRGDCFC, we could demonstrate that ligand incorporation into three of five analyzed loops of the knob, namely, EG, HI, and IJ, is feasible without a loss of fiber trimerization. The resulting adenovectors showed enhanced infectivity for various cell types, which was superior to that of viruses with the same peptide fused to the fiber C terminus. Strategies to further augment gene transfer efficacy by extension of the fiber shaft, insertion of tandem copies of the ligand peptide, or extension of the ligand-flanking linkers failed, indicating that precise ligand positioning is pivotal. Our study establishes that internal ligand incorporation into a short-shafted adenovirus fiber is feasible and suggests the Ad41 short fiber with ligand insertion into the top (IJ loop) or side (EG and HI loops) of the knob domain as a novel platform for genetic targeting of therapeutic adenoviruses.

Evaluation of Twenty Human Adenoviral Types and One Infectivity-Enhanced Adenovirus for the Therapy of Soft Tissue Sarcoma

The clinical course of sarcoma warrants the development of new therapeutic options, such as gene therapy. However, the lack of coxsackievirus-adenovirus receptor (CAR) on sarcoma cells limits the efficacy of adenovirus type 5 (Ad5)-based gene therapy. In this study we evaluated 20 different adenoviral types and 1 Ad5 vector with RGD-containing fiber for their internalization efficiency in sarcoma cells. We demonstrated that adenovirus types 35, 3, 7, 11, 9, and 22 and Ad5lucRGD virions (ranked in descending order) have significantly higher internalization efficiency in the tested sarcoma cells when compared with Ad5. On the basis of these results we developed a conditionally replication-competent adenoviral vector, Ad5Delta24.Ki.COX, and compared its oncolytic efficacy with that of Ad5/35Delta24.Ki.COX, an Ad5-based vector with the Ad35 fiber shaft and knob domains. Because both vectors differed only in the fiber, we were able to assess whether the adenoviral type with the most efficient internalization resulted also in enhanced treatment efficacy. We evaluated the antineoplastic activity of the oncolytic adenoviral vectors alone or in combination with the expression of measles virus fusogenic membrane glycoproteins and/or ifosfamide. The findings of our xenograft model were as follows: animals that received Ad5/35-based therapy had significantly smaller tumors than animals treated with the homologous Ad5-based vectors. In addition, we demonstrated that the combination of virotherapy, intratumoral expression of fusogenic membrane glycoproteins, and ifosfamide was clearly superior compared with treatment with individual components alone or as combinations of two components. In conclusion, Ad35-based vectors are promising for the treatment of sarcoma.