Adenoviral Serotype 5 Vectors Pseudotyped with Fibers from Subgroup D Show Modified TropismIn VitroandIn Vivo

Adenoviral vectors for cardiovascular gene therapy applications: a clinical and industry perspective

Abstract

Despite the development of novel pharmacological treatments, cardiovascular disease morbidity and mortality remain high indicating an unmet clinical need. Viral gene therapy enables targeted delivery of therapeutic transgenes and represents an attractive platform for tackling acquired and inherited cardiovascular diseases in the future. Current cardiovascular gene therapy trials in humans mainly focus on improving cardiac angiogenesis and function. Encouragingly, local delivery of therapeutic transgenes utilising first-generation human adenovirus serotype (HAd)-5 is safe in the short term and has shown some efficacy in drug refractory angina pectoris and heart failure with reduced ejection fraction. Despite this success, systemic delivery of therapeutic HAd-5 vectors targeting cardiovascular tissues and internal organs is limited by negligible gene transfer to target cells, elimination by the immune system, liver sequestration, off-target effects, and episomal degradation. To circumvent these barriers, cardiovascular gene therapy research has focused on determining the safety and efficacy of rare alternative serotypes and/or genetically engineered adenoviral capsid protein-modified vectors following local or systemic delivery. Pre-clinical studies have identified several vectors including HAd-11, HAd-35, and HAd-20–42-42 as promising platforms for local and systemic targeting of vascular endothelial and smooth muscle cells. In the past, clinical gene therapy trials were often restricted by limited scale-up capabilities of gene therapy medicinal products (GTMPs) and lack of regulatory guidance. However, significant improvement of industrial GTMP scale-up and purification, development of novel producer cell lines, and issuing of GTMP regulatory guidance by national regulatory health agencies have addressed many of these challenges, creating a more robust framework for future adenoviral-based cardiovascular gene therapy. In addition, this has enabled the mass roll out of adenovirus vector-based COVID-19 vaccines.

Key messages

First-generation HAd-5 vectors are widely used in cardiovascular gene therapy.

HAd-5-based gene therapy was shown to lead to cardiac angiogenesis and improved function.

Novel HAd vectors may represent promising transgene carriers for systemic delivery.

Novel methods allow industrial scale-up of rare/genetically altered Ad serotypes.

National regulatory health agencies have issued guidance on GMP for GTMPs.

Gene-modified leucoconcentrate for personalized ex vivo gene therapy in a mini pig model of moderate spinal cord injury

We previously demonstrated that gene-modified umbilical cord blood mononuclear cells overexpressing a combination of recombinant neurotrophic factors are a promising therapeutic approach for cell-mediated gene therapy for neurodegenerative diseases, neurotrauma, and stroke. In this study, using a mini pig model of spinal cord injury, we proposed for the first time the use of gene-modified leucoconcentrate prepared from peripheral blood in the plastic blood bag for personalized ex vivo gene therapy. Leucoconcentrate obtained from mini pig peripheral blood was transduced with a chimeric adenoviral vector (Ad5/35F) that carried an enhanced green fluorescent protein (EGFP) reporter gene in the plastic blood bag. The day after blood donation, the mini pigs were subjected to moderate SCI and four hours post-surgery they were intravenously autoinfused with gene-modified leucoconcentrate. A week after gene-modified leucoconcentrate therapy, fluorescent microscopy revealed EGFP-expressing leucocytes in spinal cord at the site of contusion injury. In the spleen the groups of EGFP-positive cells located in the lymphoid follicles were observed. In vitro flow cytometry and fluorescent microscopy studies of the gene-modified leucoconcentrate samples also confirmed the production of EGFP by leucocytes. Thus, the efficacy of leucocytes transduction in the plastic blood bag and their migratory potential suggest their use for temporary production of recombinant biologically active molecules to correct certain pathological conditions. This paper presents a proof-of-concept of simple, safe and effective approach for personalized ex vivo gene therapy based on gene-modified leucoconcentrate autoinfusion. The animal protocols were approved by the Kazan State Medical University Animal Care and Use Committee (approval No. 5) on May 27, 2014.

Gene therapy research for kidney diseases

A resurgence in the development of newer gene therapy systems has led to recent successes in the treatment of B cell cancers, retinal degeneration and neuromuscular atrophy. Gene therapy offers the ability to treat the patient at the root cause of their malady by restoring normal gene function and arresting the pathological progression of their genetic disease. The current standard of care for most genetic diseases is based upon the symptomatic treatment with polypharmacy while minimizing any potential adverse effects attributed to the off-target and drug-drug interactions on the target or other organs. In the kidney, however, the development of gene therapy modifications to specific renal cells has lagged far behind those in other organ systems. Some positive strides in the past few years provide continued enthusiasm to invest the time and effort in the development of new gene therapy vectors for medical intervention to treat kidney diseases. This mini-review will systematically describe the pros and cons of the most commonly tested gene therapy vector systems derived from adenovirus, retrovirus, and adeno-associated virus and provide insight about their potential utility as a therapy for various types of genetic diseases in the kidney.

Oncolytic Adenovirus: Strategies and Insights for Vector Design and Immuno-Oncolytic Applications

Adenoviruses (Ad) are commonly used both experimentally and clinically, including oncolytic virotherapy applications. In the clinical area, efficacy is frequently hampered by the high rates of neutralizing immunity, estimated as high as 90% in some populations that promote vector clearance and limit bioavailability for tumor targeting following systemic delivery. Active tumor targeting is also hampered by the ubiquitous nature of the Ad5 receptor, hCAR, as well as the lack of highly tumor-selective targeting ligands and suitable targeting strategies. Furthermore, significant off-target interactions between the viral vector and cellular and proteinaceous components of the bloodstream have been documented that promote uptake into non-target cells and determine dose-limiting toxicities. Novel strategies are therefore needed to overcome the obstacles that prevent efficacious Ad deployment for wider clinical applications. The use of less seroprevalent Ad serotypes, non-human serotypes, capsid pseudotyping, chemical shielding and genetic masking by heterologous peptide incorporation are all potential strategies to achieve efficient vector escape from humoral immune recognition. Conversely, selective vector arming with immunostimulatory agents can be utilized to enhance their oncolytic potential by activation of cancer-specific immune responses against the malignant tissues. This review presents recent advantages and pitfalls occurring in the field of adenoviral oncolytic therapies.

Noncovalently associated cell-penetrating peptides for gene delivery applications

The use of various cell-penetrating peptides (CPPs) to deliver genetic material for gene therapy applications has been a topic of interest for more than 20 years. The delivery of genetic material by using CPPs can be divided into two categories: covalently bound and electrostatically bound. Complexity of the synthesis procedure can be a significant barrier to translation when using a strategy requiring covalent binding of CPPs. In contrast, electrostatically complexing CPPs with genetic material or with a viral vector is relatively simple and has been demonstrated to improve gene delivery in both in vitro and in vivo studies. This review highlights gene therapy applications of complexes formed noncovalently between CPPs and genetic material or viruses.

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.

Adenovirus receptors: implications for targeting of viral vectors

Cancer, cardiovascular disease, and infectious diseases are all global health threats. To combat these diseases with gene therapies, adenovirus-based vectors have been developed. Although certain clinical trials appear successful, there is an obvious need to improve the efficacy of most adenovirus-based vectors. For the most commonly used vector (based on type 5; Ad5), a main problem is its accumulation in the liver, which can be attributed to interactions with specific host factors. The diverse tropism for types other than Ad5 implies that vectors based on alternative types could have advantages. The numerous interactions of different adenoviruses with host molecules - such as the recently identified desmoglein-2 receptor - may cause novel and unexpected obstacles, but also may provide possibilities for vectors based on alternative types. This review provides an update of new and previously known molecules that mediate cellular attachment of human adenoviruses and discusses how these may influence the targeting of adenovirus-based vectors.

Vector systems for prenatal gene therapy: principles of adenovirus design and production

Adenoviruses have many attributes, which have made them one of the most widely investigated vectors for gene therapy applications. These include ease of genetic manipulation to produce replication-deficient vectors, ability to readily generate high titer stocks, efficiency of gene delivery into many cell types, and ability to encode large genetic inserts. Recent advances in adenoviral vector engineering have included the ability to genetically manipulate the tropism of the vector by engineering of the major capsid proteins, particularly fiber and hexon. Furthermore, simple replication-deficient adenoviral vectors deleted for expression of a single gene have been complemented by the development of systems in which the majority of adenoviral genes are deleted, generating sophisticated Ad vectors which can mediate sustained transgene expression following a single delivery. This chapter outlines methods for developing simple transgene over expressing Ad vectors and detailed strategies to engineer mutations into the major capsid proteins.

Optimizing adenoviral transduction of endothelial cells under flow conditions

PURPOSE

To target adenoviral vectors to cells of the vasculature and shielding vectors from inactivation by the immune system.

METHODS

Complexes of reporter gene expressing adenoviral vectors with positively charged magnetic nanoparticles were formed by electrostatic interaction in presence or absence of additional negatively charged poly(ethylene glycol)-based polymer. Transduction of HUVEC was analyzed in vitro under flow. Protection from inactivation by the immune system was analyzed by pre-incubation of AdV and complexes with neutralizing antibodies and subsequent reporter protein analysis of infected cells.

RESULTS

Physical association of AdV with MNP and polymers was demonstrated by radioactive labelling of components and co-sedimentation in a magnetic field. Ad-MNP+/-polymer resulted in efficient transduction of HUVEC, depending on MOI and flow rate in presence of magnetic field, whereas no transduction was observed without complex formation with MNP or in absence of magnetic field. Association with MNP did result in protection from neutralizing antibodies, with slightly increased protection provided by the polymer.

CONCLUSIONS

Complex formation of AdV with MNP is a viable means for targeting of vectors to areas of magnetic field gradient. Additional coating with polymer might proof useful in protection from inactivation by the immune system.

Tropism-modification strategies for targeted gene delivery using adenoviral vectors

Achieving high efficiency, targeted gene delivery with adenoviral vectors is a long-standing goal in the field of clinical gene therapy. To achieve this, platform vectors must combine efficient retargeting strategies with detargeting modifications to ablate native receptor binding (i.e. CAR/integrins/heparan sulfate proteoglycans) and “bridging” interactions. “Bridging” interactions refer to coagulation factor binding, namely coagulation factor X (FX), which bridges hepatocyte transduction in vivo through engagement with surface expressed heparan sulfate proteoglycans (HSPGs). These interactions can contribute to the off-target sequestration of Ad5 in the liver and its characteristic dose-limiting hepatotoxicity, thereby significantly limiting the in vivo targeting efficiency and clinical potential of Ad5-based therapeutics. To date, various approaches to retargeting adenoviruses (Ad) have been described. These include genetic modification strategies to incorporate peptide ligands (within fiber knob domain, fiber shaft, penton base, pIX or hexon), pseudotyping of capsid proteins to include whole fiber substitutions or fiber knob chimeras, pseudotyping with non-human Ad species or with capsid proteins derived from other viral families, hexon hypervariable region (HVR) substitutions and adapter-based conjugation/crosslinking of scFv, growth factors or monoclonal antibodies directed against surface-expressed target antigens. In order to maximize retargeting, strategies which permit detargeting from undesirable interactions between the Ad capsid and components of the circulatory system (e.g. coagulation factors, erythrocytes, pre-existing neutralizing antibodies), can be employed simultaneously. Detargeting can be achieved by genetic ablation of native receptor-binding determinants, ablation of “bridging interactions” such as those which occur between the hexon of Ad5 and coagulation factor X (FX), or alternatively, through the use of polymer-coated “stealth” vectors which avoid these interactions. Simultaneous retargeting and detargeting can be achieved by combining multiple genetic and/or chemical modifications.

Serotype chimeric human adenoviruses for cancer gene therapy

Cancer gene therapy consists of numerous approaches where the common denominator is utilization of vectors for achieving therapeutic effect. A particularly potent embodiment of the approach is virotherapy, in which the replication potential of an oncolytic virus is directed towards tumor cells to cause lysis, while normal cells are spared. Importantly, the therapeutic effect of the initial viral load is amplified through viral replication cycles and production of progeny virions. All cancer gene therapy approaches rely on a sufficient level of delivery of the anticancer agent into target cells. Thus, enhancement of delivery to target cells, and reduction of delivery to non-target cells, in an approach called transductional targeting, is attractive. Both genetic and non-genetic retargeting strategies have been utilized. However, in the context of oncolytic viruses, it is beneficial to have the specific modification included in progeny virions and hence genetic modification may be preferable. Serotype chimerism utilizes serotype specific differences in receptor usage, liver tropism and seroprevalence in order to gain enhanced infection of target tissue. This review will focus on serotype chimeric adenoviruses for cancer gene therapy applications.

Development of viral vectors for use in cardiovascular gene therapy

Cardiovascular disease represents the most common cause of mortality in the developed world but, despite two decades of promising pre-clinical research and numerous clinical trials, cardiovascular gene transfer has so far failed to demonstrate convincing benefits in the clinical setting. In this review we discuss the various targets which may be suitable for cardiovascular gene therapy and the viral vectors which have to date shown the most potential for clinical use. We conclude with a summary of the current state of clinical cardiovascular gene therapy and the key trials which are ongoing.

Serotype chimeric and fiber-mutated adenovirus Ad5/19p-HIT for targeting renal cancer and untargeting the liver

Despite some advances, patients with advanced renal cell carcinoma (RCC) cannot usually be cured. Alteration of the natural tropism of adenoviruses may permit more specific gene transfer to target tissues. The aim of this study was to use novel targeting moieties for adenoviral gene therapy of RCC. Previous work in rats suggested that use of Ad5/19p (Ad5 capsid with Ad19p fiber) with kidney vascular targeting moieties HTTHREP (HTT), HITSLLS (HIT), and APASLYN (APA) placed into the fiber knob might be useful for targeting kidney vasculature. Therefore, we sought to investigate the utility of Ad5/19p variants for gene delivery to human RCC cell lines, clinical samples, and orthotopic murine models of metastatic RCC. Six different human RCC cell lines were infected but only Ad5/19p-HIT showed increased transduction, and only in one cell line. Thus, we analyzed human normal and cancerous kidney specimens fresh from patients, which might better mimic the three-dimensional architecture of clinical tumors and found that Ad5/19p-HIT showed transduction levels similar to Ad5. In mice, we found that intraperitoneal and intravenous Ad5/19p-HIT transduced tumors at levels comparable to Ad5, and that intratumoral Ad5/19p-HIT was superior to Ad5. Liver tropism was significantly reduced in comparison with Ad5. Improvements in tumor-to-liver transduction ratios suggested that Ad5/19p-HIT may be promising for systemic gene delivery to kidney tumors.

Adenovirus receptors: implications for tropism, treatment and targeting

Adenoviruses (Ads) are the most frequently used viral vectors in gene therapy and cancer therapy. Obstacles to successful clinical application include accumulation of vector and transduction in liver cells, coupled with poor transduction of target cells and tissues such as tumours. Many host molecules, including coagulation factor X, have been identified and suggested to serve as mediators of Ad liver tropism. This review summarises current knowledge concerning these molecules and the mechanisms used by Ads to bind to target cells, and considers the prospects of designing vectors that have been detargeted from the liver and retargeted to cells and tissues of interest in the context of gene therapy and cancer therapy.

Use of in vivo phage display to engineer novel adenoviruses for targeted delivery to the cardiac vasculature

We performed in vivo phage display in the stroke prone spontaneously hypertensive rat, a cardiovascular disease model, and the normotensive Wistar Kyoto rat to identify cardiac targeting peptides, and then assessed each in the context of viral gene delivery. We identified both common and strain-selective peptides, potentially indicating ubiquitous markers and those found selectively in dysfunctional microvasculature of the heart. We show the utility of the peptide, DDTRHWG, for targeted gene delivery in human cells and rats in vivo when cloned into the fiber protein of subgroup D adenovirus 19p. This study therefore identifies cardiac targeting peptides by in vivo phage display and the potential of a candidate peptide for vector targeting strategies.

Mouse adenovirus type 1 and human adenovirus type 5 differ in endothelial cell tropism and liver targeting

BACKGROUND

For adenovirus vectors derived from human serotype 5 (Ad5), the efficiency and safety after intravascular delivery is hindered by their sequestration in nontarget tissues, predominantly the liver. The latter is largely dictated by adenovirus binding to blood coagulation zymogens. In addition, several target cells, such as endothelial and smooth muscle cells, are difficult to transduce by Ad5 due to the low expression of the primary coxsackie-adenovirus receptor (CAR). Therefore, alternative adenovirus serotypes are being explored.

METHODS

In the present study, we assessed the tropism of mouse adenovirus type 1 (MAV-1), a nonhuman adenovirus for which cellular attachment is CAR-independent.

RESULTS

The typical replication of MAV-1 in endothelial cells as observed in vivo was not reflected in elevated attachment to primary and continuous endothelial cells in cell culture. Remarkably, MAV-1 displayed a higher affinity for primary human smooth muscle cells than recombinant Ad5 (rAd5). Attachment of MAV-1 to human and mouse cells of hepatocyte origin was not altered by physiological concentrations of human coagulation factor XI (FXI) or the vitamin K-dependent FIX, FX and FVII. By contrast, attachment of Ad5-derived vectors was enhanced at least eight-fold by FX. Using surface plasmon resonance, MAV-1 was shown to directly associate with human FX and murine FX and FIX but, opposite to rAd5, this interaction did not lead to enhanced cellular attachment. In intravenously injected severe combined immunodeficiency mice, distribution of MAV-1 to the liver was markedly lower than that observed with rAd5.

CONCLUSIONS

Our data on the tropism of MAV-1 suggest that this virus may find utility in the field of gene therapy.

The development of gene therapy: from monogenic recessive disorders to complex diseases such as cancer

During the last 4 decades, gene therapy has moved from preclinical to clinical studies for many diseases ranging from monogenic recessive disorders such as hemophilia to more complex diseases such as cancer, cardiovascular disorders, and human immunodeficiency virus (HIV). To date, more than 1,340 gene therapy clinical trials have been completed, are ongoing, or have been approved in 28 countries, using more than 100 genes. Most of those clinical trials (66.5%) were aimed at the treatment of cancer. Early hype, failures, and tragic events have now largely been replaced by the necessary stepwise progress needed to realize clinical benefits. We now understand better the strengths and weaknesses of various gene transfer vectors; this facilitates the choice of appropriate vectors for individual diseases. Continuous advances in our understanding of tumor biology have allowed the development of elegant, more efficient, and less toxic treatment strategies. In this introductory chapter, we review the history of gene therapy since the early 1960s and present in detail two major recurring themes in gene therapy: (1) the development of vector and delivery systems and (2) the design of strategies to fight or cure particular diseases. The field of cancer gene therapy experienced an "awkward adolescence." Although this field has certainly not yet reached maturity, it still holds the potential of alleviating the suffering of many individuals with cancer.

Enhanced Gene Delivery to Human Primary Endothelial Cells Using Tropism-Modified Adenovirus Vectors

Endothelial cells have been noted to have relatively low expression of the native receptor for adenovirus serotype 5 (Ad5), coxsackie and adenovirus receptor (CAR), and are thus refractory to Ad5 infection. In this study, we hypothesize that increases in the infectivity of Ad5 in primary human pulmonary artery (HPAEC), coronary artery (HCAEC) and umbilical vein endothelial cells (HUVEC) can be achieved through genetic capsid modification of Ad5 to bypass CAR-dependent infection. The modifications tested in this study include incorporation of an integrin-binding RGD peptide motif (Ad5.RGD), a poly-lysine motif (Ad5.pK7), a combination of both of these peptide domains (Ad5.RGD.pK7), an adenovirus serotype 3 knob domain (Ad5/3Luc1) and canine adenovirus serotype 1 or 2 knob domains (Ad5Luc1-CK1 and Ad5Luc1-CK2). In HPAEC and HCAEC, the greatest infectivity enhancements were achieved using Ad5/3Luc1 (26-fold and 30-fold respectively). HUVEC was most readily infected by Ad5Luc1-CK1 (213-fold). These results demonstrate that gains in Ad5 infectivity in endothelial cells can be accomplished with genetic capsid modifications.

Novel vectors forin vivogene delivery to vascular tissue

Although some success has been achieved with gene delivery in animal models of vascular disorders, the results from some clinical trials have been less promising, possibly due, in part, to the use of suboptimal vectors for in vivo gene transfer. Non-viral vectors have a very low transfection efficiency so are largely unsuitable for most in vivo applications, and the relatively broad tropism of many of the commonly used viral vectors can limit efficient gene delivery specifically to target vascular tissues. However, characterisation of novel virus serotypes and advances in techniques that enable vectors to be targeted to the required tissue have led to progress in the development of novel vectors that could be utilised for gene delivery for vascular disorders.

Development of renal-targeted vectors through combined in vivo phage display and capsid engineering of adenoviral fibers from serotype 19p

The potential efficacy of gene delivery is dictated by the infectivity profile of existing vectors, which is often restrictive. In order to target cells and organs for which no efficient vector is currently available, a promising approach would be to engineer vectors with novel transduction profiles. Applications that involve injecting adenovirus (Ad) vectors into the bloodstream require that native tropism for the liver be removed, and that targeting moieties be engineered into the capsid. We previously reported that pseudotyping the Ad serotype 5 fiber for that of Ad19p results in reduced hepatic transduction. In this study we show that this may be caused, at least in part, by a reduction in the capacity of the Ad19p-based virus to bind blood coagulation factors. It is therefore a potential candidate for vector retargeting, focusing on the kidney as a therapeutic target. We used in vivo phage display in rats, and identified peptides HTTHREP and HITSLLS that homed to the kidneys following intravenous injection. We engineered the HI loop of Ad19p to accommodate peptide insertions and clones. Intravenous delivery of each peptide-modified virus resulted in selective renal targeting, with HTTHREP and HITSLLS-targeted viruses selectively transducing tubular epithelium and glomeruli, respectively. Our study has important implications for the use of genetic engineering of Ad fibers to produce targeted gene delivery vectors.

Influence of coagulation factor zymogens on the infectivity of adenoviruses pseudotyped with fibers from subgroup D

Recent evidence supports a role for vitamin K-dependent coagulation zymogens in adenovirus serotype 5 (Ad5, subgroup C) infection of hepatocytes. Here, we assessed the effect of virus-zymogen interaction on cellular transduction using a panel of fiber (f)-pseudotyped viruses derived from subgroup D (f47, f33, f24, f45, f17, f30). Each virus directly bound factor X (FX) as determined by surface plasmon resonance, resulting in enhanced cell surface binding. Infection of HepG2 cells was promoted by FX but not by FVII or FIX, while transduction of CHO cells was blocked in heparan sulfate proteoglycan-deficient cells. This suggests a broad role for FX in adenovirus infectivity.

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.

Structural and Mutational Analysis of Human Ad37 and Canine Adenovirus 2 Fiber Heads in Complex with the D1 Domain of Coxsackie and Adenovirus Receptor

Adenovirus fibers from most serotypes bind the D1 domain of coxsackie and adenovirus receptor (CAR), although the binding residues are not strictly conserved. To understand this further, we determined the crystal structures of canine adenovirus serotype 2 (CAV-2) and the human adenovirus serotype 37 (HAd37) in complex with human CAR D1 at 2.3 and 1.5A resolution, respectively. Structure comparison with the HAd12 fiber head-CAR D1 complex showed that the overall topology of the interaction is conserved but that the interfaces differ in number and identity of interacting residues, shape complementarity, and degree of conformational adaptation. Using surface plasmon resonance, we characterized the binding affinity to CAR D1 of wild type and mutant CAV-2 and HAd37 fiber heads. We found that CAV-2 has the highest affinity but fewest direct interactions, with the reverse being true for HAd37. Moreover, we found that conserved interactions can have a minor contribution, whereas serotype-specific interactions can be essential. These results are discussed in the light of virus evolution and design of adenovirus vectors for gene transfer.

Efficient gene transfer into hematopoietic cells by a retargeting adenoviral vector system with a chimeric fiber of adenovirus serotype 5 and 11p

OBJECTIVE

Adenoviral vectors (Ad) were widely used in gene therapy and study of gene function, but the commonly used serotype 5 adenovirus-based vectors (Ad5) could poorly transduce hematopoietic cells because of low expression of viral receptors on these cells. To overcome this limitation, we developed a retargeting adenovector with a chimeric fiber of Ad5 and Ad11p (Ad5F11p) and evaluated its gene transfer ability in hematopoietic cells.

MATERIALS AND METHODS

An Ad11p fiber pseudotyped Ad5 vector was generated by modifying the fiber gene of pAdEasy-1 backbone plasmid. Ad5F11p-GFP encoding enhanced green fluorescence protein (GFP) gene was transferred into human leukemic cell lines, primary leukemic cells, and CD34(+) hematopoietic cells. The gene transduction efficiency was determined by fluorescence-activated cell sorting assay.

RESULTS

More than 90% of U937 or K562 cells could be infected by Ad5F11p-GFP at a moderate multiplicity of infection (MOI). Ad5F11p-GFP is also significantly more effective than control Ad5-GFP in infection of primary myeloid leukemic cells. At 200 MOI, GFP-positive percentages of Ad5F11p-GFP transduced myeloid leukemic cells range from 10.58% to 92.63% with a median of 28.65%. Ad5F11p-GFP could transduce about 50% human hematopoietic stem/progenitor (CD34(+)) cells, while Ad5-GFP could transduce <15% at 200 MOI. CD46 was reported to be the receptor of Ad11p. Our data suggest that CD46 participates in the process of Ad5F11p-GFP infection but is not the unique molecule determining its gene transfer efficiency of host cells.

CONCLUSION

We established a retargeting adenovector system, which could infect hematopoietic cells effectively and would benefit research work on Ad tropism.

Multiple vitamin K-dependent coagulation zymogens promote adenovirus-mediated gene delivery to hepatocytes

Upon local delivery, adenovirus (Ad) serotype 5 viruses use the coxsackie and Ad receptor (CAR) for cell binding and alpha(v) integrins for internalization. When administered systemically, however, their role in liver tropism is limited because CAR-permissive and mutated viruses show similar biodistribution, a finding recently attributed to blood coagulation factor (F) IX or complement protein C4BP binding to the adenovirus fiber and "bridging" to either low-density lipoprotein receptor-related protein or heparan sulfate proteoglycans. Here, we show that hepatocyte transduction in vitro can be enhanced by the vitamin K-dependent factors FX, protein C, and FVII in addition to FIX but not by prothrombin (FII), FXI, and FXII. This phenomenon was not dependent on proteolytic activation or cell signaling activity and for FX was mediated by direct virus-factor binding. Human FX substantially enhanced hepatocyte transduction by CAR-permissive and mutated viruses in an ex vivo liver perfusion model. In vivo, global down-regulation of vitamin K-dependent zymogens by warfarin significantly diminished liver uptake of CAR-deleted Ads; however, this phenomenon was fully rescued by acute infusion of human FX. Our results indicate a common and pivotal role for distinct vitamin K-dependent coagulation factors in mediating hepatocyte transduction by adenoviruses in vitro and in vivo.

Late expression of nitroreductase in an oncolytic adenovirus sensitizes colon cancer cells to the prodrug CB1954

We have constructed an oncolytic adenovirus expressing the Escherichia coli nitroreductase gene nfsB from an internal ribosome entry site (IRES) in the adenovirus L5 major late transcript. The virus (Tcf-NTR) has Tcf transcription factor-binding sites in the E1A, E1B, and E4 promoters, which restrict viral replication to cells that have activation of the Wnt signaling pathway. This virus was compared with an E1B-55K-deleted virus expressing nitroreductase (NTR) from a cytomegalovirus (CMV) promoter in the E1B-55K region [CRAd-NTR(PS1217H6)]. Both viruses express NTR in colorectal cancer cell lines and show increased cytopathic effect in the presence of the prodrug CB1954. Unlike the Tcf-NTR virus, the CMV-NTR virus expresses NTR in human lung fibroblasts and sensitizes these normal cells to CB1954. The in vivo activity of the viruses was tested in SW620 xenografts in nude mice by intravenous injection of 1,011 particles of virus followed 1 week later by intraperitoneal injections of CB1954. The CMV-NTR virus produced minimal effects in this model. The median time to form 1,000-mm(3) tumors in mice treated with the Tcf-NTR virus plus CB1954 was increased from 14 to 26 days (p=0.003), but this was due mainly to the direct oncolytic effect of the virus. Combination therapy with 3 x 10(11) particles of Tcf-NTR virus (given intravenously) and the mammalian target of rapamycin (mTOR) inhibitor RAD001 (everolimus) (given orally) significantly improved survival (median, >50 days), and addition of CB1954 to this regimen further delayed tumor growth. These results show that the Tcf-NTR virus is more tumor selective and active than the CMV-NTR virus. At the level of transduction that can be achieved currently with oncolytic viruses given intravenously, drugs such as RAD001, which do not require activation by the virus, produce greater increases in efficacy than prodrugs such as CB1954.

Adenoviral vectors--how to use them in cancer gene therapy?

Gene therapy is most often described as a technique for introducing the foreign genetic material into cells with a correction of a dysfunctional gene as its final goal. Today, it is well known that cancer is one of the leading causes of mortality in the world. Besides classical methods for cancer treatment new strategies against cancer are needed. Although originally being designed as a treatment for monogenetic illness, soon after, gene therapy appeared as a potential new strategy in cancer therapy. One of the widely used vectors for cancer gene therapy is adenovirus. In this review we have described molecular biology of adenoviruses and basis for construction of adenoviral vectors. We have also described concepts for cancer gene therapy including their in vitro and in vivo application. Special attention is drawn toward retargeting of adenovirus as a new approach in vector design for cancer gene therapy, in order to restrict transgene expression in tumor tissue. This approach uses biophysical as well as genetic characteristics of tumor itself and its supporting tissue, allowing new "bypass" in cancer gene therapy.

Adenovirus Vectors Based on Human Adenovirus Type 19a Have High Potential for Human Muscle-Directed Gene Therapy

Until recently, adenovirus-based gene therapy has been almost exclusively based on human adenovirus serotype 5 (Ad5). The aim of this study was to systematically compare the efficiency of transduction of primary muscle cells from various species by two adenoviral vectors from subgroups C and D. Transduction of a panel of myoblasts demonstrated a striking specificity of an Ad19a-based replication-defective E1-deleted vector (Ad19aEGFP) for human cells, whereas the Ad5-based vector had high affinity for nonhuman primate myoblasts. Transgene expression correlated well with cell-associated vector genomes. Up to 6.59% of the initially applied Ad19aEGFP vector particles were taken up by human myoblasts, as compared with 0.1% of the corresponding Ad5 vector. Remarkably, Ad19aEGFP but not Ad5EGFP efficiently transduced differentiated human myotubes, an in vitro model for skeletal muscle transduction. Uptake of Ad19aEGFP vector particles in human myotubes was 12-fold more efficient than that of Ad5EGFP. Moreover, both vectors demonstrated an early block at the level of vector uptake in mouse myoblasts and rat L6 cells. Investigation of the underlying mechanism for binding and uptake of the two vectors by human myoblasts showed high susceptibility for Ad19a to neuraminidase and wheat germ agglutinin (WGA) lectin, whereas Ad5-mediated transduction was dependent on binding to the coxsackie-adenovirus receptor (CAR) and sensitive to soluble RGD peptide and heparin. Our study offers insights into species-dependent factors that determine Ad tropism and, moreover, provides a basis for application of the novel Ad19a-based vector for gene transfer into human skeletal muscle.

Gene therapy for gastric cancer: Is it promising?

Gastric cancer is one of the most common tumors worldwide. The therapeutic outcome of conventional therapies is inefficient. Thus, new therapeutic strategies are urgently needed. Gene therapy is a promising molecular alternative in the treatment of gastric cancer, including the replacement of defective tumor suppressor genes, the inactivation of oncogenes, the introduction of suicide genes, genetic immunotherapy, anti-angiogenetic gene therapy, and virotherapy. Improved molecular biological techniques and a better understanding of gastric carcinogenesis have allowed us to validate a variety of genes as molecular targets for gene therapy. This review provides an update of the new developments in cancer gene therapy, new principles, techniques, strategies and vector systems, and shows how they may be applied in the treatment of gastric cancer.

Oncolytic adenoviruses - selective retargeting to tumor cells

Virotherapy is an approach for the treatment of cancer, in which the replicating virus itself is the anticancer agent. Virotherapy exploits the lytic property of virus replication to kill tumor cells. As this approach relies on viral replication, the virus can self-amplify and spread in the tumor from an initial infection of only a few cells. The success of this approach is fundamentally based on the ability to deliver the replication-competent viral genome to target cells with a requisite level of efficiency. With virotherapy, while a number of transcriptional retargeting strategies have been utilized to restrict viral replication to tumor cells, this review will focus primarily on transductional retargeting strategies, whereby oncolytic viruses can be designed to selectively infect tumor cells. Using the adenoviral vector paradigm, there are three broad strategies useful for viral retargeting. One strategy uses heterologous retargeting ligands that are bispecific in that they bind both to the viral vector as well as to a cell surface target. A second strategy uses genetically modified viral vectors in which a cellular retargeting ligand is incorporated. A third strategy involves the construction of chimeric recombinant vectors, in which a capsid protein from one virus is exchanged for that of another. These transductional retargeting strategies have the potential for reducing deleterious side effects, and increasing the therapeutic index of virotherapeutic agents.

The influence of adenovirus fiber structure and function on vector development for gene therapy

The collective attributes of adenoviruses (Ads), including ease of accomplishing replication deficiency, readily achievable high titers, encoding of large expression cassettes, efficiency of gene delivery to most cell types, and well-characterized biology, have made Ads, particularly Ad serotype 5 (Ad 5), some of the most utilized vectors for gene delivery. In recent years, however, it has become apparent that additional aspects of basic Ad virology must be uncovered for this vector system to succeed in the clinic. While local gene delivery is generally efficient, the broad tropism of Ad 5 and its tendency to home to the liver after systemic administration have proved to be limitations for other therapeutic applications, such as the treatment of disseminated cancers and cardiovascular disease. This has refocused research into the biology of Ad capsid components, particularly the main tropism determinant, the fiber/penton base complex, and their influence on transduction of selected cell types in vivo.