Retargeting polymer-coated adenovirus to the FGF receptor allows productive infection and mediates efficacy in a peritoneal model of human ovarian cancer

Challenges and progress toward tumor-targeted therapy by systemic delivery of polymer-complexed oncolytic adenoviruses

Oncolytic adenovirus (oAd) elicits antitumor activity by preferential viral replication in cancer cells. However, poor systemic administrability or suboptimal intratumoral retainment of the virus remains a major challenge toward maximizing the antitumor activity of oAd in a clinical environment. To surmount these issues, a variety of non-immunogenic polymers has been used to modify the surface of oAds chemically or physically. Complexation of oAd with polymers can effectively evade the host immune response and reduces nonspecific liver sequestration. The tumor-specific delivery of these complexes can be further improved upon by inclusion of tumor-targeting moieties on the surface. Therefore, modification of the Ad surface using polymers is viewed as a potential strategy to enhance the delivery of Ad via systemic administration. This review aims to provide a comprehensive overview of polymer-complexed Ads, their progress, and future challenges in cancer treatment.

Polymer stealthing and mucin-1 retargeting for enhanced pharmacokinetics of an oncolytic vaccinia virus

Vaccinia virus (VV) is a powerful tool for cancer treatment with the potential for tumor tropism, efficient cell-to-cell spread, rapid replication in cancer cells, and stimulation of anti-tumor immunity. It has a well-defined safety profile and is being assessed in late-stage clinical trials. However, VV clinical utility is limited by rapid bloodstream neutralization and poor penetration into tumors. These factors have often restricted its route of delivery to intratumoral or intrahepatic artery injection and may impede repeat dosing. Chemical stealthing improves the pharmacokinetics of non-enveloped viruses, but it has not yet been applied to enveloped viruses such as VV. In the present study, amphiphilic polymer was used to coat VV, leading to reduced binding of a neutralizing anti-VV antibody (81.8% of polymer-coated VV [PCVV] staining positive versus 97.1% of VV [p = 0.0038]). Attachment of anti-mucin-1 (aMUC1) targeting antibody, to give aMUC1-PCVV, enabled binding of the construct to MUC1. In high MUC1 expressing CAPAN-2 cells, infection with PCVV was reduced compared to VV, while infection was restored with aMUC1-PCVV. Pharmacokinetics of aMUC1-PCVV, PCVV, and VV were evaluated. After intravenous (i.v.) injection of 1 × 108 viral genomes (VG) or 5 × 108 VG, circulation time for PCVV and aMUC1-PCVV was increased, with ~5-fold higher circulating dose at 5 min versus VV.

Methods for Modification of Therapeutic Viruses

The optimal clinical exploitation of viruses as gene therapy or oncolytic vectors will require them to be administered intravenously. Strategies must therefore be deployed to enable viruses to survive the harsh neutralizing environment of the bloodstream and achieve deposition within and throughout target tissues or tumor deposits. This chapter describes the genetic and chemical engineering approaches that are being developed to overcome these challenges.

Exploring the functions of polymers in adenovirus-mediated gene delivery: Evading immune response and redirecting tropism

Adenovirus (Ad) is a promising viral carrier in gene therapy because of its unique attribution. However, clinical applications of Ad vectors are currently restricted by their immunogenicity and broad native tropism. To address these obstacles, a variety of nonimmunogenic polymers are utilized to modify Ad vectors chemically or physically. In this review, we systemically discuss the functions of polymers in Ad-mediated gene delivery from two aspects: evading the host immune responses to Ads and redirecting Ad tropism. With polyethylene glycol (PEG) first in order, a variety of polymers have been developed to shield the surface of Ad vectors and well accomplished to evade the host immune response, block CAR-dependant cellular uptake, and reduce accumulation in the liver. In addition, shielding Ad vectors with targeted polymers (including targeting ligand-conjugated polymers and bio-responsive polymers) can also efficiently retarget Ad vectors to tumor tissues and reduce their distribution in nontargeted tissues. With its potential to evade the immune response and retarget Ad vectors, modification with polymers has been generally regarded as a promising strategy to facilitate the clinical applications of Ad vectors for virotherapy. STATEMENT OF SIGNIFICANCE: There is no doubt that Adenovirus (Ads) are attractive vectors for gene therapy, with high sophistication and effectiveness in overcoming both extra- and intracellular barriers, which cannot be exceeded by any other nonviral gene vectors. Unfortunately, their clinical applications are still restricted by some critical hurdles, including immunogenicity and native broad tropism. Therefore, a variety of elegant strategies have been developed from various angles to address these hurdles. Among these various strategies, coating Ads with nonimmunogenic polymers has attracted much attention. In this review, we systemically discuss the functions of polymers in Ad-mediated gene delivery from two aspects: evading the host immune responses to Ads and redirecting Ad tropism. In addition, the key factors in Ad modification with polymers have been highlighted and summarized to provide guiding theory for the design of more effective and safer polymer-Ad hybrid gene vectors.

Physical, chemical, and synthetic virology: Reprogramming viruses as controllable nanodevices

The fields of physical, chemical, and synthetic virology work in partnership to reprogram viruses as controllable nanodevices. Physical virology provides the fundamental biophysical understanding of how virus capsids assemble, disassemble, display metastability, and assume various configurations. Chemical virology considers the virus capsid as a chemically addressable structure, providing chemical pathways to modify the capsid exterior, interior, and subunit interfaces. Synthetic virology takes an engineering approach, modifying the virus capsid through rational, combinatorial, and bioinformatics-driven design strategies. Advances in these three subfields of virology aim to develop virus-based materials and tools that can be applied to solve critical problems in biomedicine and biotechnology, including applications in gene therapy and drug delivery, diagnostics, and immunotherapy. Examples discussed include mammalian viruses, such as adeno-associated virus (AAV), plant viruses, such as cowpea mosaic virus (CPMV), and bacterial viruses, such as Qβ bacteriophage. Importantly, research efforts in physical, chemical, and synthetic virology have further unraveled the design principles foundational to the form and function of viruses. This article is categorized under: Diagnostic Tools > Diagnostic Nanodevices Biology-Inspired Nanomaterials > Protein and Virus-Based Structures.

Strategies in regulating glioblastoma signaling pathways and anti-invasion therapy

Glioblastoma multiforme is one of the most invasive type of glial tumors, which rapidly grows and commonly spreads into nearby brain tissue. It is a devastating brain cancer that often results in death within approximately 12 to 15 months after diagnosis. In this work, optimal control theory was applied to regulate intracellular signaling pathways of miR-451–AMPK–mTOR–cell cycle dynamics via glucose and drug intravenous administration infusions. Glucose level is controlled to activate miR-451 in the up-stream pathway of the model. A potential drug blocking the inhibitory pathway of mTOR by AMPK complex is incorporated to explore regulation of the down-stream pathway to the cell cycle. Both miR-451 and mTOR levels are up-regulated inducing cell proliferation and reducing invasion in the neighboring tissues. Concomitant and alternating glucose and drug infusions are explored under various circumstances to predict best clinical outcomes with least administration costs.

Virus oncolíticos: un arma contra el cáncer

Introducción. Los virus oncolíticos son virus atenuados, mutados o que por naturaleza se dirigen y matan específicamente células tumorales, sin afectar a las células normales. La administración intratumoral del virus ofrece la oportunidad de tratar el tumor primario pero no focos metastásicos, los cuales pueden ser alcanzados mediante la administración intravenosa. Sin embargo, su eficiencia puede disminuir por la presencia de una respuesta inmunológica preexistente en los sujetos tratados.Objetivo. Exponer las técnicas utilizadas para envolver y transportar los virus con el fin de eludir el sistema inmunológico antes de que el virus llegue al tumor.Materiales y métodos. Se realizó una búsqueda narrativa de la literatura original y de revisión en las bases de datos PubMed, JSTOR y EBSCO sobre métodos o técnicas utilizadas para el tratamiento del cáncer mediante el uso de virus oncolíticos.Resultados. La formación de nanocomplejos entre los virus oncolíticos y biopolímeros —ya sea mediante la unión química o mediante la unión a través de interacciones electrostáticas o el uso de micropartículas, células transportadoras, liposomas, ultrasonido o terapias combinadas– es eficaz para evitar la respuesta inmunológica del huésped contra el virus.Conclusión. Para evitar la respuesta inmunológica del huésped contra los virus oncolíticos se han desarrollo diversos métodos que permiten la liberación controlada y especifica de los mismos. Sin embargo, debido a la diversidad de los virus, se debe tener en cuenta que la eficacia de los métodos de protección y transporte depende de las características bioquímicas tanto del biomaterial como del virus.

Role of extracellular matrix and microenvironment in regulation of tumor growth and LAR-mediated invasion in glioblastoma

The cellular dispersion and therapeutic control of glioblastoma, the most aggressive type of primary brain cancer, depends critically on the migration patterns after surgery and intracellular responses of the individual cancer cells in response to external biochemical cues in the microenvironment. Recent studies have shown that miR-451 regulates downstream molecules including AMPK/CAB39/MARK and mTOR to determine the balance between rapid proliferation and invasion in response to metabolic stress in the harsh tumor microenvironment. Surgical removal of the main tumor is inevitably followed by recurrence of the tumor due to inaccessibility of dispersed tumor cells in normal brain tissue. In order to address this complex process of cell proliferation and invasion and its response to conventional treatment, we propose a mathematical model that analyzes the intracellular dynamics of the miR-451-AMPK- mTOR-cell cycle signaling pathway within a cell. The model identifies a key mechanism underlying the molecular switches between proliferative phase and migratory phase in response to metabolic stress in response to fluctuating glucose levels. We show how up- or down-regulation of components in these pathways affects the key cellular decision to infiltrate or proliferate in a complex microenvironment in the absence and presence of time delays and stochastic noise. Glycosylated chondroitin sulfate proteoglycans (CSPGs), a major component of the extracellular matrix (ECM) in the brain, contribute to the physical structure of the local brain microenvironment but also induce or inhibit glioma invasion by regulating the dynamics of the CSPG receptor LAR as well as the spatiotemporal activation status of resident astrocytes and tumor-associated microglia. Using a multi-scale mathematical model, we investigate a CSPG-induced switch between invasive and non-invasive tumors through the coordination of ECM-cell adhesion and dynamic changes in stromal cells. We show that the CSPG-rich microenvironment is associated with non-invasive tumor lesions through LAR-CSGAG binding while the absence of glycosylated CSPGs induce the critical glioma invasion. We illustrate how high molecular weight CSPGs can regulate the exodus of local reactive astrocytes from the main tumor lesion, leading to encapsulation of non-invasive tumor and inhibition of tumor invasion. These different CSPG conditions also change the spatial profiles of ramified and activated microglia. The complex distribution of CSPGs in the tumor microenvironment can determine the nonlinear invasion behaviors of glioma cells, which suggests the need for careful therapeutic strategies.

pH-sensitive oncolytic adenovirus hybrid targeting acidic tumor microenvironment and angiogenesis

Although oncolytic adenoviruses (Ads) are an attractive option for cancer gene therapy, the intravenous administration of naked Ad still encounters unfavorable host responses, non-specific interactions, and heterogeneity in targeted cancer cells. To overcome these obstacles and achieve specific targeting of the tumor microenvironment, Ad was coated with the pH-sensitive block copolymer, methoxy poly(ethylene glycol)-b-poly(l-histidine-co-l-phenylalanine) (PEGbPHF). The physicochemical properties of the generated nanocomplex, Ad/PEGbPHF, were assessed. At pH6.4, GFP-expressing Ad/PEGbPHF induced significantly higher GFP expression than naked Ad in both coxsackie and adenovirus receptor (CAR)-positive and -negative cells. To assess the therapeutic efficacy of the Ad/PEGbPHF complex platform, an oncolytic Ad expressing VEGF promoter-targeting transcriptional repressor (KOX) was used to form complexes. At pH6.4, KOX/PEGbPHF significantly suppressed VEGF gene expression, cancer cell migration, vessel sprouting, and cancer cell killing effect compared to naked KOX or KOX/PEGbPHF at pH7.4, demonstrating that KOX/PEGbPHF can overcome the lack of CAR that is frequently observed in tumor tissues. The antitumor activity of KOX/PEGbPHF systemically administered to a tumor xenograft model was significantly higher than that of naked KOX. Furthermore, KOX/PEGbPHF showed lower hepatic toxicity and did not induce an innate immune response against Ad. Altogether, these results demonstrate that pH-sensitive polymer-coated Ad complex significantly increases net positive charge upon exposure to hypoxic tumor microenvironment, allowing passive targeting to the tumor tissue. It may offer superior potential for systemic therapy, due to its improved tumor selectivity, increased therapeutic efficacy, and lower toxicity compared to naked KOX.

Choindroitinase ABC I-mediated enhancement of oncolytic virus spread and anti tumor efficacy: a mathematical model

Oncolytic viruses are genetically engineered viruses that are designed to kill cancer cells while doing minimal damage to normal healthy tissue. After being injected into a tumor, they infect cancer cells, multiply inside them, and when a cancer cell is killed they move on to spread and infect other cancer cells. Chondroitinase ABC (Chase-ABC) is a bacterial enzyme that can remove a major glioma ECM component, chondroitin sulfate glycosoamino glycans from proteoglycans without any deleterious effects in vivo. It has been shown that Chase-ABC treatment is able to promote the spread of the viruses, increasing the efficacy of the viral treatment. In this paper we develop a mathematical model to investigate the effect of the Chase-ABC on the treatment of glioma by oncolytic viruses (OV). We show that the model's predictions agree with experimental results for a spherical glioma. We then use the model to test various treatment options in the heterogeneous microenvironment of the brain. The model predicts that separate injections of OV, one into the center of the tumor and another outside the tumor will result in better outcome than if the total injection is outside the tumor. In particular, the injection of the ECM-degrading enzyme (Chase-ABC) on the periphery of the main tumor core need to be administered in an optimal strategy in order to infect and eradicate the infiltrating glioma cells outside the tumor core in addition to proliferative cells in the bulk of tumor core. The model also predicts that the size of tumor satellites and distance between the primary tumor and multifocal/satellite lesions may be an important factor for the efficacy of the viral therapy with Chase treatment.

The targeted transduction of MMP-overexpressing tumor cells by ACPP-HPMA copolymer-coated adenovirus conjugates

We have designed and tested a new way to selectively deliver HPMA polymer-coated adenovirus type 5 (Ad5) particles into matrix metalloproteinase (MMP)-overexpressing tumor cells. An activatable cell penetrating peptide (ACPP) was designed and attached to the reactive 4-nitrophenoxy groups of HPMA polymers by the C-terminal amino acid (asparagine, N). ACPPs are activatable cell penetrating peptides (CPPs) with a linker between polycationic and polyanionic domains, and MMP-mediated cleavage releases the CPP portion and its attached cargo to enable cell entry. Our data indicate that the transport of these HPMA polymer conjugates by a single ACPP molecule to the cytoplasm occurs via a nonendocytotic and concentration-independent process. The uptake was observed to finish within 20 minutes by inverted fluorescence microscopy. In contrast, HPMA polymer-coated Ad5 without ACPPs was internalized solely by endocytosis. The optimal formulation was not affected by the presence of Ad5 neutralizing antibodies during transduction, and ACPP/polymer-coated Ad5 also retained high targeting capability to several MMP-overexpressing tumor cell types. For the first time, ACPP-mediated cytoplasmic delivery of polymer-bound Ad5 to MMP-overexpressing tumor cells was demonstrated. These findings are significant, as they demonstrate the use of a polymer-based system for the targeted delivery into MMP-overexpressing solid tumors and highlight how to overcome major cellular obstacles to achieve intracellular macromolecular delivery.

The evolution of adenoviral vectors through genetic and chemical surface modifications

A long time has passed since the first clinical trial with adenoviral (Ad) vectors. Despite being very promising, Ad vectors soon revealed their limitations in human clinical trials. The pre-existing immunity, the marked liver tropism and the high toxicity of first generation Ad (FG-Ad) vectors have been the main challenges for the development of new approaches. Significant effort toward the development of genetically and chemically modified adenoviral vectors has enabled researchers to create more sophisticated vectors for gene therapy, with an improved safety profile and a higher transduction ability of different tissues. In this review, we will describe the latest findings in the high-speed, evolving field of genetic and chemical modifications of adenoviral vectors, a field in which different disciplines, such as biomaterial research, virology and immunology, co-operate synergistically to create better gene therapy tools for modern challenges.

Arming viruses in multi-mechanistic oncolytic viral therapy: current research and future developments, with emphasis on poxviruses

The field of oncolytic virology has made great strides in recent years. However, one key finding has been that the use of viral agents that replicate selectively in tumors is usually insufficient to achieve anything beyond small and transient responses. Instead, like most cancer therapies, oncolytic viruses are most effective in combination with other therapies, which is where they have proven therapeutic effects in clinical and preclinical studies. In cases of some of the smaller RNA viruses, effects can only be achieved through combination regimens with chemotherapy, radiotherapy, or targeted conventional therapies. However, larger DNA viruses are able to express one or more transgenes; thus, therapeutic mechanisms can be built into the viral vector itself. The incorporated approaches into arming oncolytic viruses through transgene expression will be the main focus of this review, including use of immune activators, prodrug converting enzymes, anti-angiogenic factors, and targeting of the stroma. This will focus on poxviruses as model systems with large cloning capacities, which have routinely been used as transgene expression vectors in different settings, including vaccine and oncolytic viral therapy.

Beyond Gene Delivery: Strategies to Engineer the Surfaces of Viral Vectors

Viral vectors have been extensively studied due to their great transduction efficiency compared to non-viral vectors. These vectors have been used extensively in gene therapy, enabling the comprehension of, not only the advantages of these vectors, but also the limitations, such as the activation of the immune system after vector administration. Moreover, the need to control the target of the vector has led to the development of chemical and non-chemical modifications of the vector surface, allowing researchers to modify the tropism and biodistribution profile of the vector, leading to the production of viral vectors able to target different tissues and organs. This review describes recent non-genetic modifications of the surfaces of viral vectors to decrease immune system activation and to control tissue targeting. The developments described herein provide opportunities for applications of gene therapy to treat acquired disorders and genetic diseases and to become useful tools in regenerative medicine.

EGFR-Targeted Adenovirus Dendrimer Coating for Improved Systemic Delivery of the Theranostic NIS Gene

We recently demonstrated tumor-selective iodide uptake and therapeutic efficacy of combined radiovirotherapy after systemic delivery of the theranostic sodium iodide symporter (NIS) gene using a dendrimer-coated adenovirus. To further improve shielding and targeting we physically coated replication-selective adenoviruses carrying the hNIS gene with a conjugate consisting of cationic poly(amidoamine) (PAMAM) dendrimer linked to the peptidic, epidermal growth factor receptor (EGFR)-specific ligand GE11. In vitro experiments demonstrated coxsackie-adenovirus receptor-independent but EGFR-specific transduction efficiency. Systemic injection of the uncoated adenovirus in a liver cancer xenograft mouse model led to high levels of NIS expression in the liver due to hepatic sequestration, which were significantly reduced after coating as demonstrated by ¹²³I-scintigraphy. Reduction of adenovirus liver pooling resulted in decreased hepatotoxicity and increased transduction efficiency in peripheral xenograft tumors. ¹²⁴I-PET-imaging confirmed EGFR-specificity by significantly lower tumoral radioiodine accumulation after pretreatment with the EGFR-specific antibody cetuximab. A significantly enhanced oncolytic effect was observed following systemic application of dendrimer-coated adenovirus that was further increased by additional treatment with a therapeutic dose of ¹³¹I. These results demonstrate restricted virus tropism and tumor-selective retargeting after systemic application of coated, EGFR-targeted adenoviruses therefore representing a promising strategy for improved systemic adenoviral NIS gene therapy.

Evolution of oncolytic adenovirus for cancer treatment

Oncolytic adenovirus (Ad) has been used in cancer gene therapy largely due to its ability to selectively infect and replicate in tumor cells. However, because the oncolytic antitumor activity is insufficient to effectively eliminate tumors, various strategies have been devised to improve the therapeutic efficacy. Single-vector Ads "armed" with short hairpin RNA, cytokines, or matrix-modulating proteins have been developed. Two clear advantages are viral amplification of the therapeutic gene, and the additive effects of oncolytic and therapeutic gene-mediated antitumor activities. To develop systemically injectable Ad carriers, strategies to modify the Ad surface with polymers, liposomes, or nanoparticles have been shown to extend circulation time, reduce immunogenicity, and result in increased antitumor effect as well as lower accumulation and toxicity in liver. Specific targeting platforms for tumor-selective oncolytic therapies against both primary and metastatic cancers have been developed. This review will focus on updated strategies to develop potent oncolytic Ads for use in cancer treatment.

Polymer coatings for delivery of nucleic acid therapeutics

Gene delivery remains the greatest challenge in applying nucleic acid therapeutic for a broad range of diseases. Combining stability during the delivery phase with activation and transgene expression following arrival at the target site requires sophisticated vectors that can discriminate between cell types and respond to target-associated conditions to trigger expression. Efficient intravenous delivery is the greatest single hurdle, with synthetic vectors frequently found to be unstable in the harsh conditions of the bloodstream, and viral vectors often recognized avidly by both the innate and the adaptive immune system. Both types of vectors benefit from coating with hydrophilic polymers. Self-assembling polyelectrolyte non-viral vectors can achieve both steric and lateral stabilization following surface coating, endowing them with much improved systemic circulation properties and better access to disseminated targets; similarly viral vectors can be 'stealthed' and their physical properties modulated by surface coating. Both types of vectors may also have their tropism changed following chemical linkage of novel ligands to the polymer coating. These families of vectors go some way towards realizing the goal of efficient systemic delivery of genes and should find a range of important uses in bringing this still-emerging field to fruition.

Enhancing the therapeutic efficacy of adenovirus in combination with biomaterials

With the reason that systemically administered adenovirus (Ad) is rapidly extinguished by innate/adaptive immune responses and accumulation in liver, in vivo application of the Ad vector is strictly restricted. For achieving to develop successful Ad vector systems for cancer therapy, the chemical or physical modification of Ad vectors with polymers has been generally used as a promising strategy to overcome the obstacles. With polyethylene glycol (PEG) first in order, a variety of polymers have been developed to shield the surface of therapeutic Ad vectors and well accomplished to extend circulation time in blood and reduce liver toxicity. However, although polymer-coated Ads can successfully evacuate from a series of guarding systems in vivo and locate within tumors by enhanced permeability and retention (EPR) effect, the possibility to entering into the target cell is few and far between. To endow targeting moiety to polymer-coated Ad vectors, a diversity of ligands such as tumor-homing peptides, growth factors or antibodies, have been introduced with avoiding unwanted transduction and enhancing therapeutic efficacy. Here, we will describe and classify the characteristics of the published polymers with respect to Ad vectors. Furthermore, we will also compare the properties of variable targeting ligands, which are being utilized for addressing polymer-coated Ad vectors actively.

Retargeting of viruses to generate oncolytic agents

Oncolytic virus therapy is based on the ability of viruses to effectively infect and kill tumor cells without destroying the normal tissues. While some viruses seem to have a natural preference for tumor cells, most viruses require the modification of their tropism to specifically enter and replicate in such cells. This review aims to describe the transductional targeting strategies currently employed to specifically redirect viruses towards surface receptors on tumor cells. Three major strategies can be distinguished; they involve (i) the incorporation of new targeting specificity into a viral surface protein, (ii) the incorporation of a scaffold into a viral surface protein to allow the attachment of targeting moieties, and (iii) the use of bispecific adapters to mediate targeting of a virus to a specified moiety on a tumor cell. Of each strategy key features, advantages and limitations are discussed and examples are given. Because of their potential to cause sustained, multiround infection—a desirable characteristic for eradicating tumors—particular attention is given to viruses engineered to become self-targeted by the genomic expression of a bispecific adapter protein.

Enhancing the Clinical Potential of AAV Vectors by Capsid Engineering to Evade Pre-Existing Immunity

Vectors based on adeno-associated viruses (AAV) have shown considerable promise in both preclinical models and increasingly in clinical trials. However, one formidable challenge is pre-existing immunity due to widespread exposure to numerous AAV variants and serotypes within the human population, which affect efficacy of clinical trials due to the accompanying high levels of anti-capsid neutralizing antibodies. Transient immunosuppression has promise in mitigating cellular and humoral responses induced by vector application in naïve hosts, but cannot overcome the problem that pre-existing neutralizing antibodies pose toward the goal of safe and efficient gene delivery. Shielding of AAV from antibodies, however, may be possible by covalent attachment of polymers to the viral capsid or by encapsulation of vectors inside biomaterials. In addition, there has been considerable progress in using rational mutagenesis, combinatorial libraries, and directed evolution approaches to engineer capsid variants that are not recognized by anti-AAV antibodies generally present in the human population. While additional progress must be made, such strategies, alone or in combination with immunosuppression to avoid de novo induction of antibodies, have strong potential to significantly enhance the clinical efficacy of AAV vectors.

Engineering biomaterial systems to enhance viral vector gene delivery

Integrating viral gene delivery with engineered biomaterials is a promising strategy to overcome a number of challenges associated with virus-mediated gene delivery, including inefficient delivery to specific cell types, limited tropism, spread of vectors to distant sites, and immune responses. Viral vectors can be combined with biomaterials either through encapsulation within the material or immobilization onto a material surface. Subsequent biomaterial-based delivery can increase the vector's residence time within the target site, thereby potentially providing localized delivery, enhancing transduction, and extending the duration of gene expression. Alternatively, physical or chemical modification of viral vectors with biomaterials can be employed to modulate the tropism of viruses or reduce inflammatory and immune responses, both of which may benefit transduction. This review describes strategies to promote viral gene delivery technologies using biomaterials, potentially providing opportunities for numerous applications of gene therapy to inherited or acquired disorders, infectious disease, and regenerative medicine.

Current advances in adenovirus nanocomplexes: more specificity and less immunogenicity

An often overlooked issue in the field of adenovirus (Ad)-mediated cancer gene therapy is its limited capacity for effective systemic delivery. Although primary tumors can be treated effectively with intralesional injection of conventional Ad vectors, systemic metastasis is difficult to cure. Systemic administration of conventional naked Ads leads to acute accumulation of Ad particles in the liver, induction of neutralizing antibody, short blood circulation half-life, non-specific biodistribution in undesired organs, and low selective accumulation in the target disease site. Versatile strategies involving the modification of viral surfaces with polymers and nanomaterials have been designed for the purpose of maximizing Ad anti-tumor activity and specificity by systemic administration. Integration of viral and non-viral nanomaterials will substantially advance both fields, creating new concepts in gene therapeutics. This review focuses on current advances in the development of smart Ad hybrid nanocomplexes based on various design-based strategies for optimal Ad systemic administration.

Targeting adenovirus gene delivery to activated tumour-associated vasculature via endothelial selectins

Clinical experience with adenovirus vectors has highlighted the need for improved delivery and targeting. Tumour-associated endothelium offers an additional mechanism for enhanced viral uptake into tumours which is accessible for systemic gene delivery. Building on expertise in using polymer ‘stealthed’ viruses for targeting in vivo, adenovirus expressing luciferase (Adluc) was coated with an amino-reactive polymer based on poly [N-(2-hydroxypropyl) methacrylamide] to ablate normal infection pathways. Direct linkage of a monoclonal antibody against E-selectin (MHES) demonstrated E-selectin-specific transduction of tumour necrosis factor-α (TNF-α)-activated endothelial cells. A two-component targeting system using protein G was developed, to provide optimal antibody orientation. We report an enhancement in transduction of TNF-α-activated endothelium in vitro and ex vivo in a human umbilical vein cord model using the MHES antibody. Similarly a virus retargeted using a chimeric P-selectin Glycoprotein Ligand-1-Fc fusion (PSGL-1) protein showed better circulation kinetics and significant uptake into HepG2 xenografts following systemic administration in mice, with 36-fold higher genome copies, compared with non-modified virus. Immunohistochemistry staining of tumour sections from mice treated with PSGL-1-retargeted virus showed a co-localisation of firefly luciferase with CD31 suggesting selective endothelial targeting. Employment of optimal viral modification using protein G will enable exploration and comparison of alternative targeting ligands targeting tumour-associated endothelium.

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.

Advances with the use of bio-inspired vectors towards creation of artificial viruses

IMPORTANCE OF THE FIELD

In recent years, there has been a great deal of interest in the development of recombinant vectors based on biological motifs with potential applications in gene therapy. Several such vectors have been genetically engineered, resulting in biomacromolecules with new properties that are not present in nature.

AREAS COVERED IN THIS REVIEW

This review briefly discusses the advantages and disadvantages of the current state-of-the-art gene delivery systems (viral and non-viral) and then provides an overview on the application of various biological motifs in vector development for gene delivery. Finally, it highlights some of the most advanced bio-inspired vectors that are designed to perform several self-guided functions.

WHAT THE READER WILL GAIN

This review helps the readers get a better understanding about the history and evolution of bio-inspired fusion vectors with the potential to merge the strengths of both viral and non-viral vectors in order to create efficient, safe and cost-effective gene delivery systems.

TAKE HOME MESSAGE

With the emergence of new technologies such as recombinant bio-inspired vectors, it may not take long before non-viral vectors are observed that are not just safe and tissue-specific, but even more efficient than viral vectors.

Bio and nanotechnological strategies for tumor-targeted gene therapy

Gene therapy is a new medical approach for the treatment of tumors. For safe and efficient gene therapy, therapeutic genes need to be delivered efficiently into the target tumor cells. Development of gene delivery systems to specifically recognize and target tumor cells and to distinguish them from normal cells, especially in the same tissue or organ, is one of the most important issues regarding the present gene delivery methodologies. The enhanced permeability and retention (EPR) effect using the characteristics of angiogenic tumor blood vessels, as well as gene delivery systems recognizing hyperactivated receptors or intracellular signals, is broadly applied to tumor-targeted gene therapy. In addition, bacterial vectors can be a useful means for targeting hypoxic or anoxic regions of a tumor.

Strategies to overcome host immunity to adenovirus vectors in vaccine development

The first clinical evaluations of adenovirus (Ad)-based vectors for gene therapy were initiated in the mid-1990s and led to great anticipation for future utility. However, excitement surrounding gene therapy, particularly Ad-based therapy, was diminished upon the death of Jesse Gelsinger, and recent discouraging results from the HIV vaccine STEP trial have brought efficacy and safety issues to the forefront again. Even so, Ad vectors are still considered among the safest and most effective vaccine vectors. Innate and pre-existing immunity to Ad mediate much of the acute toxicities and reduced therapeutic efficacies observed following vaccination with this vector. Thus, innovative strategies must continue to be developed to reduce Ad-specific antigenicity and immune recognition. This review provides an overview and critique of the most promising strategies, including results from preclinical trials in mice and nonhuman primates, which aim to revive the future of Ad-based vaccines.

Anti-tumor effect of adenovirus-mediated gene transfer of pigment epithelium-derived factor on mouse B16-F10 melanoma

Background

Angiogenesis plays an important role in tumor growth, invasion, and eventually metastasis. Antiangiogenic strategies have been proven to be a promising approach for clinical therapy for a variety of tumors. As a potent inhibitor of tumor angiogenesis, pigment epithelium-derived factor (PEDF) has recently been studied and used as an anticancer agent in several tumor models.

Methods

A recombined adenovirus carrying PEDF gene (Ad-PEDF) was prepared, and its expression by infected cells and in treated animals was confirmed with Western blotting and ELISA, respectively. Its activity for inhibiting human umbilical vein endothelial cell (HUVEC) proliferation was tested using the MTT assay. C57BL/6 mice bearing B16-F10 melanoma were treated with i.v. administration of 5 × 10⁸ IU/mouse Ad-PEDF, or 5 × 10⁸ IU/mouse Ad-Null, or normal saline (NS), every 3 days for a total of 4 times. Tumor volume and survival time were recorded. TUNEL, CD31 and H&E stainings of tumor tissue were conducted to examine apoptosis, microvessel density and histological morphology changes. Antiangiogenesis was determined by the alginate-encapsulated tumor cell assay.

Results

The recombinant PEDF adenovirus is able to transfer the PEDF gene to infected cells and successfully produce secretory PEDF protein, which exhibits potent inhibitory effects on HUVEC proliferation. Through inhibiting angiogenesis, reducing MVD and increasing apoptosis, Ad-PEDF treatment reduced tumor volume and prolonged survival times of mouse bearing B16-F10 melanoma.

Conclusion

Our data indicate that Ad-PEDF may provide an effective approach to inhibit mouse B16-F10 melanoma growth.

Cetuximab retargeting of adenovirus via the epidermal growth factor receptor for treatment of intraperitoneal ovarian cancer

Gene and virotherapy of ovarian cancer, using type 5 adenovirus (Ad5), has demonstrated good activity in preclinical animal studies, particularly after intraperitoneal administration of virus; however, success in clinical trials has been limited by poor infectivity of ovarian cancer cells and inflammatory responses to Ad5. We previously demonstrated that covalent modification of Ad5 with reactive copolymers on the basis of poly(hydroxypropylmethacrylamide) can shield the virus, offering protection from neutralizing antibodies and enabling retargeting to cancer-upregulated receptors with peptide ligands (basic fibroblast growth factor [bFGF] and murine epidermal growth factor [EGF]). These ligands may be less than ideal for clinical use, however, because they are potential mitogens. Accordingly, in this study we investigated the use of an anti-EGF receptor (EGFR) antibody, cetuximab, to retarget adenoviral transduction of EGFR-positives in vitro and in vivo. Cetuximab retargeting altered the physicochemical characteristics of Ad5, although it did not cause particle aggregation. Although cetuximab stimulated internalization of EGFR, similarly to EGF, it inhibited EGFR phosphorylation. Adenoviral transduction was inhibited after polymer coating, but was rescued in EGFR-positive cells (and not in EGFR-negative cells) by cetuximab retargeting. Cetuximab retargeting of wild-type adenovirus serotype 5 (Ad5WT) prolonged survival in an animal model of human ovarian cancer, similar to unmodified Ad5WT, but polymer coating ameliorated stimulation of adhesion formation. We conclude that polymer coating and covalent attachment of cetuximab successfully retargeted adenovirus to EGFR-positive cells, retained in vivo efficacy of an oncolytic adenovirus, and ameliorated side effects caused by unmodified adenovirus.

Oncolytic adenoviral gene therapy in ovarian cancer: why we are not wasting our time

Preclinical gene-therapy studies in the past 15 years have repeatedly raised hopes that we were about to enter a brave new era. However, many clinical trials have disappointed. For tumor types with poor response rates to first-line conventional cytotoxic chemotherapy and/or high rates of chemorefractory disease, there remain very few treatment options. In this article we review gene therapy within the context of ovarian cancer. We examine why clinical data have been discouraging and discuss how the lessons learned from earlier trials are being applied to current research.

Targeted and armed oncolytic poxviruses: a novel multi-mechanistic therapeutic class for cancer

Viruses have been engineered for cancer therapy in a variety of ways. Approaches include non-replicating gene therapy vectors, cancer vaccines and oncolytic viruses, but the clinical efficacy of these approaches has been limited by multiple factors. However, a new therapeutic class of oncolytic poxviruses has recently been developed that combines targeted and armed approaches for treating cancer. Initial preclinical and clinical results show that products from this therapeutic class can systemically target cancers in a highly selective and potent fashion using a multi-pronged mechanism of action.