Evaluation of adenovirus vectors containing serotype 35 fibers for tumor targeting

Preclinical evaluation of the gorilla-derived HAdV-B AdV-lumc007 oncolytic adenovirus 'GoraVir' for the treatment of pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is a highly aggressive malignancy which shows unparalleled therapeutic resistance due to its genetic and cellular heterogeneity, dense stromal tissue, and immune-suppressive tumour microenvironment. Oncolytic virotherapy has emerged as a new treatment modality which uses tumour-specific viruses to eliminate cancerous cells. Non-human primate adenoviruses of the human adenovirus B (HAdV-B) species have demonstrated considerable lytic potential in human cancer cells as well as limited preexisting neutralizing immunity in humans. Previously, we have generated a new oncolytic derivative of the gorilla-derived HAdV-B AdV-lumc007 named 'GoraVir'. Here, we show that GoraVir displays oncolytic efficacy in pancreatic cancer cells and pancreatic-cancer-associated fibroblasts. Moreover, it retains its lytic potential in monoculture and co-culture spheroids. In addition, we established the ubiquitously expressed complement receptor CD46 as the main entry receptor for GoraVir. Finally, a single intratumoural dose of GoraVir was shown to delay tumour growth in a BxPC-3 xenograft model at 10 days post-treatment. Collectively, these data demonstrate that the new gorilla-derived oncolytic adenovirus is a potent oncolytic vector candidate that targets both pancreatic cancer cells and tumour-adjacent stroma.

Adenovirus as a Vector and Oncolytic Virus

Adenoviral vectors, both oncolytic viruses and gene delivery vectors, are among the earliest approved and commercialised vectors for gene therapy. Adenoviruses have high cytotoxicity and immunogenicity. Therefore, lentiviruses or adeno-associated viruses as viral vectors and herpes simplex virus as an oncolytic virus have recently drawn attention. Thus, adenoviral vectors are often considered relatively obsolete. However, their high cargo limit and transduction efficiency are significant advantages over newer viral vectors. This review provides an overview of the new-generation adenoviral vectors. In addition, we describe the modification of the fiber knob region that enhances affinity of adenoviral vectors for cancer cells and the utilisation of cancer-cell-specific promoters to suppress expression of unwanted transgenes in non-malignant tissues.

Role of Fiber Shaft Length in Tumor Targeting with Ad5/3 Vectors

Desmoglein 2 (DSG2) is overexpressed in many epithelial cancers and therefore represents a target receptor for oncolytic viruses, including Ad5/3-based viruses. For most Ad serotypes, the receptor-binding fiber is composed of tail, shaft, and knob domains. Here, we investigated the role of the fiber shaft in Ad5/3 tumor transduction in vitro and in human DSG2-transgenic mice carrying human DSG2high tumors. DSG2tg mice express DSG2 in a pattern similar to humans. We constructed Ad5/3L (with the “long” Ad5 shaft) and Ad5/3S (with the “short” Ad3 shaft) expressing GFP or luciferase. In in vitro studies we found that coagulation factor X, which is known to mediate undesired hepatocyte transduction of Ad5, enhances the transduction of Ad5/3(L), but not the transduction of Ad5/3(S). We therefore hypothesized that Ad5/3(S) would target DSG2high tumors while sparing the liver after intravenous injection. In vivo imaging studies for luciferase and analysis of luciferase activity in isolated organs, showed that Ad5/3(L) vectors efficiently transduced DSG2high tumors and liver but not normal epithelial tissues after intravenous injection. Ad5/3(S) showed minimal liver transduction, however it failed to transduce DSG2high tumors. Further modifications of the Ad5/3(S) capsid are required to compensate for the lower infectivity of Ad5/3(S) vectors.

Expression of human CD46 and trans-complementation by murine adenovirus 1 fails to allow productive infection by a group B oncolytic adenovirus in murine cancer cells

BACKGROUND

Oncolytic viruses are currently experiencing accelerated development in several laboratories worldwide, with some forty-seven clinical trials currently recruiting. Many oncolytic viruses combine targeted cytotoxicity to cancer cells with a proinflammatory cell lysis. Due to their additional potential to express immunomodulatory transgenes, they are also often known as oncolytic viral vaccines. However, several types of oncolytic viruses are human-specific and the lack of suitable immune-competent animal models complicates biologically relevant evaluation of their vaccine potential. This is a particular challenge for group B adenoviruses, which fail to infect even those immunocompetent animal model systems identified as semi-permissive for type 5 adenovirus. Here, we aim to develop a murine cell line capable of supporting replication of a group B oncolytic adenovirus, enadenotucirev (EnAd), for incorporation into a syngeneic immunocompetent animal model to explore the oncolytic vaccine potential of group B oncolytic viruses.

METHODS

Transgenic murine cell lines were infected with EnAd expressing GFP transgene under replication-independent or -dependent promoters. Virus mRNA expression, genome replication, and late protein expression were determined by qRT-PCR, qPCR, and immunoblotting, respectively. We also use Balb/c immune-competent mice to determine the tumourogenicity and infectivity of transgenic murine cell lines.

RESULTS

Our results show that a broad range of human carcinoma cells will support EnAd replication, but not murine carcinoma cells. Murine cells can be readily modified to express surface human CD46, one of the receptors for group B adenoviruses, allowing receptor-mediated uptake of EnAd particles into the murine cells and expression of CMV promoter-driven transgenes. Although the early E1A mRNA was expressed in murine cells at levels similar to human cells, adenovirus E2B and Fibre mRNA expression levels were hampered and few virus genomes were produced. Unlike previous reports on group C adenoviruses, trans-complementation of group B adenoviruses by co-infection with mouse adenovirus 1 did not rescue replication. A panel of group B adenoviruses expressing individual mouse adenovirus 1 genes were also unable to rescue EnAd replication.

CONCLUSION

Together, these results indicate that there may be major differences in the early stages of replication of group C and B adenoviruses in murine cells, and that the block to the life cycle of B adenoviruses in murine cells occurs in the early stage of virus replication, perhaps reflecting poor activity of Ad11p E1A in murine cells.

A novel fiber chimeric conditionally replicative adenovirus-Ad5/F35 for tumor therapy

Significant progress has been made in the diagnosis and treatment of cancer; however, significant challenges remain. Conditionally replicating adenoviruses (CRAds), which not only kill cancer cells, but also serve as vectors to express therapeutic genes, are a novel and effective method to treat cancer. However, most adenoviruses are Ad5, which infect cells through the coxsackie and adenovirus receptor (CAR). The transduction efficacy of Ad5 is restricted because of the absent or low expression of CAR on several cancer cells. Ad serotype 35 has a different tropism pattern to Ad5. Ad35 attaches to cells via a non-CAR receptor, CD46, which is expressed widely on most tumor cells. Thus, chimeric adenoviral vectors consisting of the knob and shaft of Ad35 combined with Ad5 have been constructed. The chimeric fiber adenoviral vectors can transduce CAR-positive and CAR-negative cell lines. In this review, we explore the application of the novel fiber chimeric conditionally replicative adenovirus-Ad5/F35 in tumor therapy in terms of safety, mechanism, transduction efficacy, and antitumor effect.

An image cytometric technique is a concise method to detect adenoviruses and host cell proteins and to monitor the infection and cellular responses induced

Background

Genetically modified adenoviruses (Ad) with preferential replications in tumor cells have been examined for a possible clinical applicability as an anti-cancer agent. A simple method to detect viral and cellular proteins is valuable to monitor the viral infections and to predict the Ad-mediated cytotoxicity.

Methods

We used type 5 Ad in which the expression of E1A gene was activated by 5′-regulatory sequences of genes that were augmented in the expression in human tumors. The Ad were further modified to have the fiber-knob region replaced with that derived from type 35 Ad. We infected human mesothelioma cells with the fiber-replaced Ad, and sequentially examined cytotoxic processes together with an expression level of the viral E1A, hexon, and cellular cleaved caspase-3 with image cytometric and Western blot analyses.

Results

The replication-competent Ad produced cytotoxicity on mesothelioma cells. The infected cells expressed E1A and hexon 24 h after the infection and then showed cleavage of caspase-3, all of which were detected with image cytometry and Western blot analysis. Image cytometry furthermore demonstrated that increased Ad doses did not enhance an expression level of E1A and hexon in an individual cell and that caspase-3-cleaved cells were found more frequently in hexon-positive cells than in E1A-positive cells. Image cytometry thus detected these molecular changes in a sensitive manner and at a single cell level. We also showed that an image cytometric technique detected expression changes of other host cell proteins, cyclin-E and phosphorylated histone H3 at a single cell level.

Conclusions

Image cytometry is a concise procedure to detect expression changes of Ad and host cell proteins at a single cell level, and is useful to analyze molecular events after the infection.

Electronic supplementary material

The online version of this article (10.1186/s12985-017-0888-0) contains supplementary material, which is available to authorized users.

In Vivo Hematopoietic Stem Cell Transduction

Current protocols for hematopoietic stem cell (HSC) gene therapy, involving the transplantation of ex vivo lentivirus vector-transduced HSCs into myeloablated recipients, are complex and not without risk for the patient. In vivo HSC gene therapy can be achieved by the direct modification of HSCs in the bone marrow after intraosseous injection of gene delivery vectors. A recently developed approach involves the mobilization of HSCs from the bone marrow into peripheral the blood circulation, intravenous vector injection, and re-engraftment of genetically modified HSCs in the bone marrow. We provide examples for in vivo HSC gene therapy and discuss advantages and disadvantages.

Cytotoxicity of replication-competent adenoviruses powered by an exogenous regulatory region is not linearly correlated with the viral infectivity/gene expression or with the E1A-activating ability but is associated with the p53 genotypes

Background

Replication-competent adenoviruses (Ad) produced cytotoxic effects on infected tumors and have been examined for the clinical applicability. A biomarkers to predict the cytotoxicity is valuable in a clinical setting.

Methods

We constructed type 5 Ad (Ad5) of which the expression of E1A gene was activated by a 5′ regulatory sequences of survivin, midkine or cyclooxygenase-2, which were highly expressed in human tumors. We also produced the same replication-competent Ad of which the fiber-knob region was replaced by that of Ad35 (AdF35). The cytotoxicity was examined by a colorimetric assay with human tumor cell lines, 4 kinds of pancreatic, 9 esophageal carcinoma and 5 mesothelioma. Ad infectivity and Ad-mediated gene expression were examined with replication-incompetent Ad5 and AdF35 which expressed the green fluorescence protein gene. Expression of cellular receptors for Ad5 and AdF35 was also examined with flow cytometry. A transcriptional activity of the regulatory sequences was investigated with a luciferase assay in the tumor cells. We then investigated a possible correlation between Ad-mediated cytotoxicity and the infectivity/gene expression, the transcriptional activity or the p53 genotype.

Results

We found that the cytotoxicity was greater with AdF35 than with Ad5 vectors, but was not correlated with the Ad infectivity/gene expression irrespective of the fiber-knob region or the E1A-activating transcriptional activity. In contrast, replication-competent Ad produced greater cytotoxicity in p53 mutated than in wild-type esophageal carcinoma cells, suggesting a possible association between the cytotoxicity and the p53 genotype.

Conclusions

Sensitivity to Ad-mediated cytotoxic activity was linked with the p53 genotype but was not lineally correlated with the infectivity/gene expression or the E1A expression.

Electronic supplementary material

The online version of this article (10.1186/s12885-017-3621-x) contains supplementary material, which is available to authorized users.

Preclinical Safety Studies of Enadenotucirev, a Chimeric Group B Human-Specific Oncolytic Adenovirus

Enadenotucirev is an oncolytic group B adenovirus identified by a process of bio-selection for the ability to selectively propagate in and rapidly kill carcinoma cells. It is resistant to inactivation by human blood components, potentially enabling intravenous dosing in patients with metastatic cancer. However, there are no known permissive animal models described for group B adenoviruses that could facilitate a conventional approach to preclinical safety studies. In this manuscript, we describe our tailored preclinical strategy designed to evaluate the key biological properties of enadenotucirev. As enadenotucirev does not replicate in animal cells, a panel of primary human cells was used to evaluate enadenotucirev replication selectivity in vitro, demonstrating that virus genome levels were >100-fold lower in normal cells relative to tumor cells. Acute intravenous tolerability in mice was used to assess virus particle-mediated toxicology and effects on innate immunity. These studies showed that particle toxicity could be ameliorated by dose fractionation, using an initial dose of virus to condition the host such that cytokine responses to subsequent doses were significantly attenuated. This, in turn, supported the initiation of a phase I intravenous clinical trial with a starting dose of 1 × 1010 virus particles given on days 1, 3, and 5.

Pseudotyping Serotype 5 Adenovirus with the Fiber from Other Serotypes Uncovers a Key Role of the Fiber Protein in Adenovirus 5-Induced Thrombocytopenia

Adenovirus (Ad) infection in humans is associated with inflammatory responses and thrombocytopenia. Although several studies were conducted in mice models to understand molecular and cellular mechanisms of Ad-induced inflammatory responses, only few of them turned their interest toward the mechanisms of Ad-induced thrombocytopenia. Using different depletion methods, the present study ruled out any significant role of spleen, macrophages, and vitamin K-dependent factor in Ad-induced thrombocytopenia. Interestingly, mice displaying thrombocytopenia expressed high levels of cytokines/chemokines after Ad administration. Most importantly, pseudotyping adenovirus with the fiber protein from other serotypes was associated with reduction of both cytokine/chemokine production and thrombocytopenia. Altogether, our results suggest that capsid fiber protein (and more precisely its shaft) of Ad serotype 5 triggers the cytokine production that leads to Ad-induced thrombocytopenia.

In vivo transduction of primitive mobilized hematopoietic stem cells after intravenous injection of integrating adenovirus vectors

Current protocols for hematopoietic stem/progenitor cell (HSPC) gene therapy, involving the transplantation of ex vivo genetically modified HSPCs are complex and not without risk for the patient. We developed a new approach for in vivo HSPC transduction that does not require myeloablation and transplantation. It involves subcutaneous injections of granulocyte-colony-stimulating factor/AMD3100 to mobilize HSPCs from the bone marrow (BM) into the peripheral blood stream and the IV injection of an integrating, helper-dependent adenovirus (HD-Ad5/35⁺⁺) vector system. These vectors target CD46, a receptor that is uniformly expressed on HSPCs. We demonstrated in human CD46 transgenic mice and immunodeficient mice with engrafted human CD34⁺ cells that HSPCs transduced in the periphery home back to the BM where they stably express the transgene. In hCD46 transgenic mice, we showed that our in vivo HSPC transduction approach allows for the stable transduction of primitive HSPCs. Twenty weeks after in vivo transduction, green fluorescent protein (GFP) marking in BM HSPCs (Lin^-Sca1⁺Kit^- cells) in most of the mice was in the range of 5% to 10%. The percentage of GFP-expressing primitive HSPCs capable of forming multilineage progenitor colonies (colony-forming units [CFUs]) increased from 4% of all CFUs at week 4 to 16% at week 12, indicating transduction and expansion of long-term surviving HSPCs. Our approach was well tolerated, did not result in significant transduction of nonhematopoietic tissues, and was not associated with genotoxicty. The ability to stably genetically modify HSPCs without the need of myeloablative conditioning is relevant for a broader clinical application of gene therapy.

Preclinical safety, pharmacokinetics, pharmacodynamics, and biodistribution studies with Ad35K++ protein: a novel rituximab cotherapeutic

Rituximab is a mouse/human chimeric monoclonal antibody targeted toward CD20. It is efficient as first-line therapy of CD20-positive B-cell malignancies. However, a large fraction of treated patients relapse with rituximab-resistant disease. So far, only modest progress has been made in treatment options for rituximab refractory patients. One of the mechanisms for rituximab resistance involves the upregulation of CD46, which is a key cell surface protein that blocks the activation of complement. We have recently developed a technology that depletes CD46 from the cell surface and thereby sensitizes tumor cells to complement-dependent cytotoxicity. This technology is based on a small recombinant protein, Ad35K++ that binds with high affinity to CD46. In preliminary studies using a 6 × histidinyl tagged protein, we had demonstrated that intravenous Ad35K++ injection in combination with rituximab was safe and increased rituximab-mediated killing of CD20-positive target cells in mice and nonhuman primates (NHPs). The presence of the tag, while allowing for easy purification by Ni-NTA chromatography, has the potential to increase the immunogenicity of the recombinant protein. For clinical application, we therefore developed an Ad35K++ protein without His-tag. In the present study, we performed preclinical studies in two animal species (mice and NHPs) with this protein demonstrating its safety and efficacy. These studies estimated the Ad35K++ dose range and treatment regimen to be used in patients. Furthermore, we showed that intravenous Ad35K++ injection triggers the shedding of the CD46 extracellular domain in xenograft mouse tumor models and in macaques. Shed serum CD46 can be measured in the serum and can potentially be used as a pharmacodynamic marker for monitoring Ad35K++ activity in patient undergoing treatment with this agent. These studies create the basis for an investigational new drug application for the use of Ad35K++ in combination with rituximab in the treatment of patients with B-cell malignancies.

Tamoxifen improves cytopathic effect of oncolytic adenovirus in primary glioblastoma cells mediated through autophagy

Oncolytic gene therapy using viral vectors may provide an attractive therapeutic option for malignant gliomas. These viral vectors are designed in a way to selectively target tumor cells and spare healthy cells. To determine the translational impact, it is imperative to assess the factors that interfere with the anti-glioma effects of the oncolytic adenoviral vectors. In the current study, we evaluated the efficacy of survivin-driven oncolytic adenoviruses pseudotyping with adenoviral fiber knob belonging to the adenoviral serotype 3, 11 and 35 in their ability to kill glioblastoma (GBM) cells selectively without affecting normal cells. Our results indicate that all recombinant vectors used in the study can effectively target GBM in vitro with high specificity, especially the 3 knob-modified vector. Using intracranial U87 and U251 GBM xenograft models we have also demonstrated that treatment with Conditionally Replicative Adenovirus (CRAd-S-5/3) vectors can effectively regress tumor. However, in several patient-derived GBM cell lines, cells exhibited resistance to the CRAd infection as evident from the diminishing effects of autophagy. To improve therapeutic response, tumor cells were pretreated with tamoxifen. Our preliminary data suggest that tamoxifen sensitizes glioblastoma cells towards oncolytic treatment with CRAd-S-5/3, which may prove useful for GBM in future experimental therapy.

Immunochemistry of adenoviruses: limitations and new horizons of gene therapy

Adenoviruses have increasingly been recognized as significant viral pathogens causing high morbidity and mortality especially among immunocompromised individuals such as transplant recipients and AIDS patients. Through the infection process, after the adenovirus fiber and penton are bonded to cell surface receptors through special amino acid moieties, secondary messengers activate protein kinases, pro-inflammatory cytokines and chemokines. Serotype and species specific antibodies also are induced. Recombinant human adenoviruses have been pivotal in the development of gene therapy strategies and have shown a great promise for the treatment of genetic disorders and malignancies. Recent studies have enlightened their harmful immunological effects dependent on fiber and hexon polypeptide structure and receptor binding. Pre-existing antibodies or those elicited by vectors neutralize input recombinant adenovirus particles rendering them ineffective. Mediators induce serious even lethal side effects and cytotoxic reactions which extinguish transgene expression. To overcome these difficulties new strategies are required in the application of recombinant adenoviruses to redirect vector entry from the natural receptors to alternative binding sites or using rare human or animal adenovirus fiber molecules to modify the native fiber structure by altering amino acid structure and creating chimeric fibers. This requires searching for, isolating and characterizing new serotypes, mutants or variants for new generation vectors. Human adenovirus 1 feline isolate (feline adenovirus) might fulfil these criteria.

Enhanced antitumor efficacy of fiber-modified, midkine promoter-regulated oncolytic adenovirus in human malignant mesothelioma

Oncolytic virotherapy using adenoviruses has potential for therapeutic benefits in malignant mesothelioma. However, the downregulation of coxsackie virus/adenovirus receptor (CAR) expression is frequently a critical rate-limiting factor that impedes the effectiveness of adenovirus serotype 5 (Ad5)-based vectors in many cancer types. We evaluated CAR (Ad5 receptor) and CD46 (adenovirus serotype 35 [Ad35] receptor) expression in six human malignant mesothelioma cell lines. Very low CAR expression was observed in MSTO-211H and NCI-H2052 cells, whereas the other cell lines showed strong expression. In contrast, CD46 was highly expressed in all mesothelioma cell lines. On this basis, we replaced the CAR binding sequence of Ad5 with the CD46 binding sequence of Ad35 in the replication-defective adenoviruses and the tumor-specific midkine promoter-regulated oncolytic adenoviruses. By this fiber modification, the infectivity, virus progeny production, and in vitro cytocidal effects of the adenoviruses were significantly enhanced in low CAR-expressing MSTO-211H and NCI-H2052 cells, also resulting in similar or even higher levels in high CAR-expressing mesothelioma cell lines. In MSTO-211H xenograft models, the fiber-modified oncolytic adenovirus significantly enhanced antitumor effect compared to its equivalent Ad5-based vector. Our data demonstrate that Ad35 fiber modification of binding tropism in a midkine promoter-regulated oncolytic Ad5 vector confers transductional targeting to oncolytic adenoviruses, thereby facilitating more effective treatment of malignant mesothelioma.

Transient removal of CD46 is safe and increases B-cell depletion by rituximab in CD46 transgenic mice and macaques

We have developed a technology that depletes the complement regulatory protein (CRP) CD46 from the cell surface, and thereby sensitizes tumor cells to complement-dependent cytotoxicity triggered by therapeutic monoclonal antibodies (mAbs). This technology is based on a small recombinant protein, Ad35K++, which induces the internalization and subsequent degradation of CD46. In preliminary studies, we had demonstrated the utility of the combination of Ad35K++ and several commercially available mAbs such as rituximab, alemtuzumab, and trastuzumab in enhancing cell killing in vitro as well as in vivo in murine xenograft and syngeneic tumor models. We have completed scaled manufacturing of Ad35K++ protein in Escherichia coli for studies in nonhuman primates (NHPs). In macaques, we first defined a dose of the CD20-targeting mAb rituximab that did not deplete CD20-positive peripheral blood cells. Using this dose of rituximab, we then demonstrated that pretreatment with Ad35K++ reconstituted near complete elimination of B cells. Further studies demonstrated that the treatment was well tolerated and safe. These findings in a relevant large animal model provide the rationale for moving this therapy forward into clinical trials in patients with CD20-positive B-cell malignancies.

A new human DSG2-transgenic mouse model for studying the tropism and pathology of human adenoviruses

We have recently reported that a group of human adenoviruses (HAdVs) uses desmoglein 2 (DSG2) as a receptor for infection. Among these are the widely distributed serotypes HAdV-B3 and HAdV-B7, as well as a newly emerged strain derived from HAdV-B14. These serotypes do not infect rodent cells and could not up until now be studied in small-animal models. We therefore generated transgenic mice containing the human DSG2 locus. These mice expressed human DSG2 (hDSG2) at a level and in a pattern similar to those found for humans and nonhuman primates. As an initial application of hDSG2-transgenic mice, we used a green fluorescent protein (GFP)-expressing HAdV-B3 vector (Ad3-GFP) and studied GFP transgene expression by quantitative reverse transcription-PCR (qRT-PCR) and immunohistochemistry subsequent to intranasal and intravenous virus application. After intranasal application, we found efficient transduction of bronchial and alveolar epithelial cells in hDSG2-transgenic mice. Intravenous Ad3-GFP injection into hDSG2-transgenic mice resulted in hDSG2-dependent transduction of epithelial cells in the intestinal and colon mucosa. Our findings give an explanation for clinical symptoms associated with infection by DSG2-interacting HAdVs and provide a rationale for using Ad3-derived vectors in gene therapy.

Virus chimeras for gene therapy, vaccination, and oncolysis: adenoviruses and beyond

Several challenges need to be addressed when developing viruses for clinical applications in gene therapy, vaccination, or viral oncolysis, including specific and efficient target cell transduction, virus delivery via the blood stream, and evasion of pre-existing immunity. With rising frequency, these goals are tackled by generating chimeric viruses containing nucleic acid fragments or proteins from two or more different viruses, thus combining different beneficial features of the parental viruses. These chimeras have boosted the development of virus-based treatment regimens for major inherited and acquired diseases, including cancer. Using adenoviruses as the paradigm and prominent examples from other virus families, we review the technological and functional advances in therapeutic virus chimera development and recent successful applications that can pave the way for future therapies.

Multimerization of adenovirus serotype 3 fiber knob domains is required for efficient binding of virus to desmoglein 2 and subsequent opening of epithelial junctions

Recently, we identified desmoglein 2 (DSG2) as the main receptor for a group of species B adenoviruses (Ads), including Ad3, a serotype that is widely distributed in the human population (H. Wang et al., Nat. Med. 17:96-104, 2011). In this study, we have attempted to delineate structural details of the Ad3 interaction with DSG2. For CAR- and CD46-interacting Ad serotypes, attachment to cells can be completely blocked by an excess of recombinant fiber knob protein, while soluble Ad3 fiber knob only inefficiently blocks Ad3 infection. We found that the DSG2-interacting domain(s) within Ad3 is formed by several fiber knob domains that have to be in the spatial constellation that is present in viral particles. Based on this finding, we generated a small recombinant, self-dimerizing protein containing the Ad3 fiber knob (Ad3-K/S/Kn). Ad3-K/S/Kn bound to DSG2 with high affinity and blocked Ad3 infection. We demonstrated by confocal immunofluorescence and transmission electron microscopy analyses that Ad3-K/S/Kn, through its binding to DSG2, triggered the transient opening of intercellular junctions in epithelial cells. The pretreatment of epithelial cells with Ad3-K/S/Kn resulted in increased access to receptors that are localized in or masked by epithelial junctions, e.g., CAR or Her2/neu. Ad3-K/S/Kn treatment released CAR from tight junctions and thus increased the transduction of epithelial cells by a serotype Ad5-based vector. Furthermore, the pretreatment of Her2/neu-positive breast cancer cells with Ad3-K/S/Kn increased the killing of cancer cells by the Her2/neu-targeting monoclonal antibody trastuzumab (Herceptin). This study widens our understanding of how Ads achieve high avidity to their receptors and the infection of epithelial tissue. The small recombinant protein Ad3-K/S/Kn has practical implications for the therapy of epithelial cancer and gene/drug delivery to normal epithelial tissues.

Improving gene transfer in human renal carcinoma cells: Utilization of adenovirus vectors containing chimeric type 5 and type 35 fiber proteins

The transduction efficacy of adenovirus serotype 5 (Ad5) vector in human renal carcinoma cells is generally low due to the down-regulated expression of Coxsackie and adenovirus receptor (CAR) in target cells. By contrast, the infectivity of adenovirus serotype 35 vectors depends on the binding rate to CD46 receptor, independent of CAR. In this study, we examined whether an adenovirus vector containing chimeric type 5 and type 35 fiber proteins (Ad5/F35) increases transduction efficiency compared to Ad5 vector in human renal carcinoma cells in vitro. The expression of CAR was much lower in the human renal carcinoma cells than in control HEK293 cells. By contrast, the expression of CD46 was similar and perhaps at a higher level in the human renal carcinoma cells than in the HEK293 cells. The transduction efficacy of Ad5/F35 vector was dramatically higher compared to that of Ad5 in human renal carcinoma cells, and was correlated to the expression of CD46. Thus, Ad5/35 vector may be useful for the development of novel gene therapy approaches to renal cell carcinoma.

The influence of innate and pre-existing immunity on adenovirus therapy

Recombinant adenovirus serotype 5 (Ad5) vectors have been studied extensively in preclinical gene therapy models and in a range of clinical trials. However, innate immune responses to adenovirus vectors limit effectiveness of Ad5 based therapies. Moreover, extensive pre-existing Ad5 immunity in human populations will likely limit the clinical utility of adenovirus vectors, unless methods to circumvent neutralizing antibodies that bind virus and block target cell transduction can be developed. Furthermore, memory T cell and humoral responses to Ad5 are associated with increased toxicity, raising safety concerns for therapeutic adenovirus vectors in immunized hosts. Most preclinical studies have been performed in naïve animals; although pre-existing immunity is among the greatest hurdles for adenovirus therapies, it is also one of the most neglected experimentally. Here we summarize findings using adenovirus vectors in naïve animals, in Ad-immunized animals and in clinical trials, and review strategies proposed to overcome innate immune responses and pre-existing immunity.

A recombinant adenovirus type 35 fiber knob protein sensitizes lymphoma cells to rituximab therapy

Many tumors, including lymphomas, up-regulate expression of CD46 to escape destruction by complement. Tumor cells are therefore relatively resistant to therapy by monoclonal antibodies, which act through complement-dependent cytotoxicity (CDC). From an Escherichia coli expression library of adenovirus type 35 fiber knob mutants, we selected a variant (Ad35K(++)) that had a higher affinity to CD46 than did the natural Ad35 fiber knob. We demonstrated that incubation of lymphoma cells with recombinant Ad35K(++) protein resulted in transient removal of CD46 from the cell surface. Preincubation of lymphoma cells with Ad35K(++) sensitized cells to CDC, triggered by the CD20-specific monoclonal antibody rituximab. In xenograft models with human lymphoma cells, preinjection of Ad35K(++) dramatically increased the therapeutic effect of rituximab. Blood cell counts and organ histology were normal after intravenous injection of Ad35K(++) into mice that express human CD46. The presence of polyclonal anti-Ad35K(++) antibodies did not affect the ability of Ad35K(++) to enhance rituximab-mediated CDC in in vitro assays. The Ad35K(++)-based approach has potential implications in monoclonal antibody therapy of malignancies beyond the combination with rituximab.

Transduction of liver metastases after intravenous injection of Ad5/35 or Ad35 vectors with and without factor X-binding protein pretreatment

Inefficient tumor transduction with targeted adenoviral vectors is largely due to unspecific virus sequestration by blood components, including coagulation factor X, and Kupffer cell scavenging. In this study, we show that preinjection of snake venom factor X-binding protein (X-bp) reduces hepatocyte transduction and increases the circulation time in blood of an intravenously injected, fiber-chimeric Ad5/35 vector. X-bp pretreatment resulted in improved Ad5/35 transduction of liver metastases and increased the antitumor efficacy of an Ad5/35-based oncolytic adenovirus. Furthermore, we demonstrate that a vector based on adenoviral serotype 35, which is less sequestered by factor X, is efficient in tumor targeting. This gives a rationale for using Ad35-based vectors in virotherapy of cancer.

New insights on adenovirus as vaccine vectors

Adenovirus (Ad) vectors were initially developed for treatment of genetic diseases. Their usefulness for permanent gene replacement was limited by their high immunogenicity, which resulted in rapid elimination of transduced cells through induction of T and B cells to antigens of Ad and the transgene product. The very trait that excluded their use for sustained treatment of genetic diseases made them highly attractive as vaccine carriers. Recently though results showed that Ad vectors based on common human serotypes, such as serotype 5, may not be ideal as vaccine carriers. A recently conducted phase 2b trial, termed STEP trial, with an AdHu5-based vaccine expressing antigens of human immunodeficiency virus 1 (HIV-1) not only showed lack of efficacy in spite of the vaccine's immunogenicity, but also suggested an increased trend for HIV acquisition in individuals that had circulating AdHu5 neutralizing antibodies prior to vaccination. Alternative serotypes from humans or nonhuman primates (NHPs), to which most humans lack pre-existing immunity, have been vectored and may circumvent the problems encountered with the use of AdHu5 vectors in humans. In summary, although Ad vectors have seen their share of setbacks in recent years, they remain viable tools for prevention or treatment of a multitude of diseases.

Influence of coagulation factor x on in vitro and in vivo gene delivery by adenovirus (Ad) 5, Ad35, and chimeric Ad5/Ad35 vectors

The binding of coagulation factor X (FX) to the hexon of adenovirus (Ad) 5 is pivotal for hepatocyte transduction. However, vectors based on Ad35, a subspecies B Ad, are in development for cancer gene therapy, as Ad35 utilizes CD46 (which is upregulated in many cancers) for transduction. We investigated whether interaction of Ad35 with FX influenced vector tropism using Ad5, Ad35, and Ad5/Ad35 chimeras: Ad5/fiber(f)35, Ad5/penton(p)35/f35, and Ad35/f5. Surface plasmon resonance (SPR) revealed that Ad35 and Ad35/f5 bound FX with approximately tenfold lower affinities than Ad5 hexon-containing viruses, and electron cryomicroscopy (cryo-EM) demonstrated a direct Ad35 hexon:FX interaction. The presence of physiological levels of FX significantly inhibited transduction of vectors containing Ad35 fibers (Ad5/f35, Ad5/p35/f35, and Ad35) in CD46-positive cells. Vectors were intravenously administered to CD46 transgenic mice in the presence and absence of FX-binding protein (X-bp), resulting in reduced liver accumulation for all vectors. Moreover, Ad5/f35 and Ad5/p35/f35 efficiently accumulated in the lung, whereas Ad5 demonstrated poor lung targeting. Additionally, X-bp significantly reduced lung genome accumulation for Ad5/f35 and Ad5/p35/f35, whereas Ad35 was significantly enhanced. In summary, vectors based on the full Ad35 serotype will be useful vectors for selective gene transfer via CD46 due to a weaker FX interaction compared to Ad5.

Concomitant use of Ad5/35 chimeric oncolytic adenovirus with TRAIL gene and taxol produces synergistic cytotoxicity in gastric cancer cells

Chimeric adenoviral vectors possessing fiber derived from human adenovirus subgroup B (Ad35) have been developed for their high infection efficiency in cell types which are refractory to adenovirus serotype 5 (Subgroup C). The present study constructed an E1B-deleted chimeric oncolytic adenovirus, SG235-TRAIL, which carries a human TRAIL gene expression cassette and whose fiber shaft and knob domains are from serotype Ad35. It was found that SG235-TRAIL preferentially replicated in gastric cancer cell lines, SGC-7901 and BGC-823 compared to in normal human fibroblast BJ cells. Also, when compared with a replication-deficient chimeric vector Ad5/35-TRAIL, SG235-TRAIL mediated a higher level of the transgene expression via viral replication in the cancer cells. Further, because of the more efficient cell-entry and infection, SG235-TRAIL induced stronger cell apoptosis than the Ad5 CRAD vector, ZD55-TRAIL. In addition, SG235-TRAIL in combination with the chemotherapeutic drug, taxol, produced a synergistic cytotoxic effect in cancer cells in vitro without causing significant toxicity to normal cells. In the gastric tumor xenograft mouse model, intratumoral SG235-TRAIL injection produced a significant antitumor effect 14 days after treatment. Pathological examination demonstrated TRAIL expression and associated apoptosis in majority of SG235-TRAIL-treated tumor cells. These results suggest that SG235-TRAIL is a potential novel, efficient anti-cancer agent, and in combination with taxol, it would be even more useful with considerably low toxic side effects.

Adenoviral vector-based strategies for cancer therapy

Definitive treatment of cancer has eluded scientists for decades. Current therapeutic modalities like surgery, chemotherapy, radiotherapy and receptor-targeted antibodies have varied degree of success and generally have moderate to severe side effects. Gene therapy is one of the novel and promising approaches for therapeutic intervention of cancer. Viral vectors in general and adenoviral (Ad) vectors in particular are efficient natural gene delivery systems and are one of the obvious choices for cancer gene therapy. Clinical and preclinical findings with a wide variety of approaches like tumor suppressor and suicide gene therapy, oncolysis, immunotherapy, anti-angiogenesis and RNA interference using Ad vectors have been quite promising, but there are still many hurdles to overcome. Shortcomings like increased immunogenicity, prevalence of preexisting anti-Ad immunity in human population and lack of specific targeting limit the clinical usefulness of Ad vectors. In recent years, extensive research efforts have been made to overcome these limitations through a variety of approaches including the use of conditionally-replicating Ad and specific targeting of tumor cells. In this review, we discuss the potential strengths and limitations of Ad vectors for cancer therapy.

Adenovirus receptors and their implications in gene delivery

Adenoviruses (Ads) have gained popularity as gene delivery vectors for therapeutic and prophylactic applications. Ad entry into host cells involves specific interactions between cell surface receptors and viral capsid proteins. Several cell surface molecules have been identified as receptors for Ad attachment and entry. Tissue tropism of Ad vectors is greatly influenced by their receptor usage. A variety of strategies have been investigated to modify Ad vector tropism by manipulating the receptor-interacting moieties. Many such strategies are aimed at targeting and/or detargeting of Ad vectors. In this review, we discuss the various cell surface molecules that are implicated as receptors for virus attachment and internalization. Special emphasis is given to Ad types that are utilized as gene delivery vectors. Various strategies to modify Ad tropism using the knowledge of Ad receptors are also discussed.

In vitro and in vivo properties of adenovirus vectors with increased affinity to CD46

Gene transfer vectors containing adenovirus (Ad) serotype 35 (Ad35) fibers have shown promise for cancer and stem cell gene therapy. In this study, we attempted to improve the in vitro and in vivo infection properties of these vectors by increasing their affinity to the Ad35 fiber receptor CD46. We constructed Ad vectors containing either the wild-type Ad35 fiber knob (Ad5/35) or Ad35 knob mutants with 4-fold- and 60-fold-higher affinity to CD46 (Ad5/35+ and Ad5/35++, respectively). In in vitro studies with cell lines, the higher affinities of Ad5/35+ and Ad5/35++ to CD46 did not translate into correspondingly higher transduction efficiencies, regardless of the CD46 receptor density present on cells. However, in vivo, in a mouse model with preestablished CD46(high) liver metastases, intravenous injection of Ad5/35++ resulted in more-efficient tumor cell transduction. We conclude that Ad5/35 vectors with increased affinity to CD46 have an advantage in competing with non-CD46-mediated sequestration of vector particles after intravenous injection.

Changing the adenovirus fiber for retaining gene delivery efficacy in the presence of neutralizing antibodies

Prior infection has primed most adult humans for a rapid neutralizing antibody (NAb) response when re-exposed to adenovirus. NAb induction can severely limit the efficacy of systemic re-administration of adenoviral gene therapy. We hypothesized that changing the fiber knob could overcome NAb. Immune-competent mice were exposed to serotype 5 adenovirus (Ad5)(GL), Ad5/3luc1, Ad5lucRGD or Ad5pK7(GL). Mice immunized with Ad5(GL) featured reduced intravenous Ad5(GL) gene transfer to most organs, including the liver, lung and spleen. Ad5(GL) gene transfer was affected much less by exposure to capsid-modified viruses. Anti-Ad5(GL) NAb blocked intravenous Ad5(GL) gene transfer to orthotopic lung cancer xenografts, whereas capsid-modified viruses were not affected. When gene transfer to fresh cancer and normal lung explants was analyzed, we found that capsid-modified viruses allowed effective gene delivery to tumors in the presence of anti-Ad5(GL) NAb, whereas Ad5(GL) was blocked. In contrast, crossblocking by NAbs induced by different viruses affected gene delivery to normal human lung explants, suggesting the importance of non-fiber-knob-mediated infection mechanisms. We conclude that changing the adenovirus fiber knob is sufficient to allow a relative degree of escape from preexisting NAb. If confirmed in trials, this approach might improve the efficacy of re-administration of adenoviral gene therapy to humans.

Novel strategies in tailoring human adenoviruses into therapeutic cancer gene therapy vectors

Gene therapy is a novel approach for the treatment of cancer that has so far not been realized. The scope of this review is to try to define the remaining barriers to the successful use of adenovirus vectors for gene and viral therapy of human tumors and to suggest solutions whereby these barriers can be bypassed. It is the conviction of the authors that too many studies have been performed in animal models that are not sufficiently comprehensive to allow conclusions to be drawn for application in humans. For example, in the case of the murine experimental model, in which most studies have been performed, mice are devoid of circulating antibodies to adenovirus type 5 and adenovirus cannot replicate in mouse cells. While the problems are real enough, as witnessed by the quite limited success in human trials, some of the solutions that will be suggested here are hypothetical and have not as yet been tried, even in animals. The review has no ambition to be exhaustive but is intended as a contribution in order to forward the field of gene therapy vectors for systemic clinical application.

Gene therapy of gynaecological diseases

Gene therapy represents a potentially useful approach for the treatment of diseases refractory to conventional therapies. Various preclinical and clinical strategies have been explored for treatment of gynaecological diseases. Given the most severe unmet clinical need, much of the work has been performed with gynaecological cancers and ovarian cancer in particular. Although the safety of many treatment strategies has been demonstrated in early phase clinical trials, efficacy has been mostly limited heretofore. Major challenges include improving the vectors used with the aim of more effective and selective delivery. In addition, effective penetration into and spreading within advanced and complex tumour masses and metastases remains challenging. This review focuses on existing and developmental gene transfer applications for gynaecological diseases.

Comparison of adenoviruses from species B, C, E, and F after intravenous delivery

Recent attempts to circumvent the limitations of adenovirus (Ad) vectors derived from species C serotype Ad5 have focused on the use of alternative human serotypes. These new serotypes have multiple benefits including a low prevalence of neutralizing antibodies in humans and alternate tropisms. To investigate the characteristics of alternatives to Ad5 vectors, we compared the biodistribution and safety of Ads from species B (Ad3, 11p, 35), C (Ad5), E (Ad4), and F (Ad41), or chimeric Ad5 viruses containing the Ad11 or Ad35 fibers (Ad5/11 and Ad5/35), after intravenous (IV) delivery into hCD46 transgenic mice. Our data suggest that (i) mechanisms of cell and tissue sequestration differ; (ii) levels of sequestration to lung, liver, or spleen do not correlate with toxicity; (iii) delivery of all serotypes causes activation of coagulation, possibly through platelet interaction; (iv) despite binding to the same receptor in vitro, Ad serotypes act differently in vivo; and (v) platelet depletion affects blood clearance, organ sequestration and chemokine/cytokine release of some, but not all Ad serotypes. Overall, our data indicate that Ad5-based vectors are relatively safe as compared to other serotypes. This data should be taken into consideration in future studies about the clinical use of Ad vectors.

Targeted gene-delivery strategies for angiostatic cancer treatment

Gene therapy is one of the promising strategies in cancer treatment. Recent studies identified molecular targets on angiogenically activated endothelial cells that can be used to deliver gene-transfer vehicles to the tumor site specifically. Furthermore, non-viral vehicles are emerging as an alternative for traditional viral gene-therapy approaches. Here, we describe how viral and non-viral gene-transfer vehicles have been and can be modified to target tumor endothelial cells for anti-angiogenesis gene therapy. Improving the specificity and safety of existing gene-therapy vehicles will make angiogenesis-targeted cancer gene therapy a valuable tool in the clinical setting.

Adenoviral serotypes in gene therapy for esophageal carcinoma

PURPOSE

Adenoviral gene therapy could potentially play a role in the treatment of esophageal cancer and Barrett's esophagus. The adenoviruses can be categorized in different serotypes. The goal of the present study was to investigate the transduction efficacy of different adenoviral serotypes in different models of esophageal cancer and Barrett's esophagus.

METHODS

Chimeras of the adenoviral serotype 5 backbone and fibers of serotypes 5, 16, 35, 40, and 50 were constructed with PCR technology. For esophageal cancer, cell lines were used originating from with adenocarcinoma and squamous cell carcinoma, respectively. Differentiating Caco-2 cells were used as an in vitro model for Barrett's esophagus. GFP was used as a reporter gene and transduction efficacy was assessed by flow cytometry.

RESULTS

Overall transduction was rather efficient in the cancer cell lines. Especially serotype 16 and 50 exhibited an improved transduction compared with the other serotypes. In the Caco-2 cell lines, we observed a decreased transduction upon differentiation of the cells. All serotypes had a very limited transduction and no serotype had an additional value in this setting.

CONCLUSIONS

Some serotypes could have an additional value in the development of gene therapy for esophageal cancer. Especially serotype 16 and 50 exhibited an improved transduction in esophageal cancer cells compared with the native serotype 5. In the setting of Barrett's esophagus, none of the serotypes had an improved potency as in differentiated intestinal cells all serotypes had a very limited transduction.

Adenovirus-platelet interaction in blood causes virus sequestration to the reticuloendothelial system of the liver

Intravenous (i.v.) delivery of recombinant adenovirus serotype 5 (Ad5) vectors for gene therapy is hindered by safety and efficacy problems. We have discovered a new pathway involved in unspecific Ad5 sequestration and degradation. After i.v. administration, Ad5 rapidly binds to circulating platelets, which causes their activation/aggregation and subsequent entrapment in liver sinusoids. Virus-platelet aggregates are taken up by Kupffer cells and degraded. Ad sequestration in organs can be reduced by platelet depletion prior to vector injection. Identification of this new sequestration mechanism and construction of vectors that avoid it could improve levels of target cell transduction at lower vector doses.