Retargeting of adenovirus vectors through genetic fusion of a single-chain or single-domain antibody to capsid protein IX

Redirect Tropism of Fowl Adenovirus 4 Vector by Modifying Fiber2 with Variable Domain of Heavy-Chain Antibody

The variable domain of a heavy-chain antibody (VHH) has the potential to be used to redirect the cell tropism of adenoviral vectors. Here, we attempted to establish platforms to simplify the screening of VHHs for their specific targeting function when being incorporated into the fiber of adenovirus. Both fowl adenovirus 4 (FAdV-4) and simian adenovirus 1 (SAdV-1) have two types of fiber, one of which is dispensable for virus propagation and is a proper site for VHH display. An intermediate plasmid, pMD-FAV4Fs, was constructed as the start plasmid for FAdV-4 fiber2 modification. Foldon from phage T4 fibritin, a trigger for trimerization, was employed to bridge the tail/shaft domain of fiber2 and VHHs against human CD16A, a key membrane marker of natural killer (NK) cells. Through one step of restriction-assembly, the modified fiber2 was transferred to the adenoviral plasmid, which was linearized and transfected to packaging cells. Five FAdV-4 viruses carrying the GFP gene were finally rescued and amplified, with three VHHs being displayed. One recombinant virus, FAdV4FC21-EG, could hardly transduce human 293 or Jurkat cells. In contrast, when it was used at a multiplicity of infection of 1000 viral particles per cell, the transduction efficiency reached 51% or 34% for 293 or Jurkat cells expressing exogenous CD16A. Such a strategy of fiber modification was transplanted to the SAdV-1 vector to construct SAdV1FC28H-EG, which moderately transduced primary human NK cells while the parental virus transduced none. Collectively, we reformed the strategy of integrating VHH to fiber and established novel platforms for screening VHHs to construct adenoviral vectors with a specific tropism.

Optimal delivery of RNA interference by viral vectors for cancer therapy

In recent years, there has been a surge in the innovative modification and application of the viral vector-based gene therapy field. Significant and consistent improvements in the engineering, delivery, and safety of viral vectors have set the stage for their application as RNA interference (RNAi) delivery tools. Viral vector-based delivery of RNAi has made remarkable breakthroughs in the treatment of several debilitating diseases and disorders (e.g., neurological diseases); however, their novelty has yet to be fully applied and utilized for the treatment of cancer. This review highlights the most promising and emerging viral vector delivery tools for RNAi therapeutics while discussing the variables limiting their success and suitability for cancer therapy. Specifically, we outline different integrating and non-integrating viral platforms used for gene delivery, currently employed RNAi targets for anti-cancer effect, and various strategies used to optimize the safety and efficacy of these RNAi therapeutics. Most importantly, we provide great insight into what challenges exist in their application as cancer therapeutics and how these challenges can be effectively navigated to advance the field.

Combining of Oncolytic Virotherapy and Other Immunotherapeutic Approaches in Cancer: A Powerful Functionalization Tactic

Oncolytic viruses have found a good place in the treatment of cancer. Administering oncolytic viruses directly or by applying genetic changes can be effective in cancer treatment through the lysis of tumor cells and, in some cases, by inducing immune system responses. Moreover, oncolytic viruses induce antitumor immune responses via releasing tumor antigens in the tumor microenvironment (TME) and affect tumor cell growth and metabolism. Despite the success of virotherapy in cancer therapies, there are several challenges and limitations, such as immunosuppressive TME, lack of effective penetration into tumor tissue, low efficiency in hypoxia, antiviral immune responses, and off-targeting. Evidence suggests that oncolytic viruses combined with cancer immunotherapy-based methods such as immune checkpoint inhibitors and adoptive cell therapies can effectively overcome these challenges. This review summarizes the latest data on the use of oncolytic viruses for the treatment of cancer and the challenges of this method. Additionally, the effectiveness of mono, dual, and triple therapies using oncolytic viruses and other anticancer agents has been discussed based on the latest findings.

Oncolytic Virotherapy in Peritoneal Metastasis Gastric Cancer: The Challenges and Achievements

Gastric cancer (GC) is the fourth most common cancer and the second leading cause of cancer death globally. Although the mortality rate in some parts of the world, such as East Asia, is still high, new treatments and lifestyle changes have effectively reduced deaths from this type of cancer. One of the main challenges of this type of cancer is its late diagnosis and poor prognosis. GC patients are usually diagnosed in the advanced stages of the disease, which is often associated with peritoneal metastasis (PM) and significantly reduces survival. This type of metastasis in patients with GC poses a serious challenge due to limitations in common therapies such as surgery and tumor resection, as well as failure to respond to systemic chemotherapy. To solve this problem, researchers have used virotherapy such as reovirus-based anticancer therapy in patients with GC along with PM who are resistant to current chemotherapies because this therapeutic approach is able to overcome immune suppression by activating dendritic cells (DCs) and eventually lead to the intrinsic activity of antitumor effector T cells. This review summarizes the immunopathogenesis of peritoneal metastasis of gastric cancer (PMGC) and the details for using virotherapy as an effective anticancer treatment approach, as well as its challenges and opportunities.

A comprehensive comparison between camelid nanobodies and single chain variable fragments

By the emergence of recombinant DNA technology, many antibody fragments have been developed devoid of undesired properties of natural immunoglobulins. Among them, camelid heavy-chain variable domains (VHHs) and single-chain variable fragments (scFvs) are the most favored ones. While scFv is used widely in various applications, camelid antibodies (VHHs) can serve as an alternative because of their superior chemical and physical properties such as higher solubility, stability, smaller size, and lower production cost. Here, these two counterparts are compared in structure and properties to identify which one is more suitable for each of their various therapeutic, diagnosis, and research applications.

The genome position of a therapeutic transgene strongly influences the level of expression in an armed oncolytic human adenovirus vector

Efficacy of oncolytic, conditionally-replicating adenovirus (CRAd) vectors can be enhanced by "arming" the vector with therapeutic transgenes. We examined whether inclusion of an intact early region 3 (E3) and the reptilian reovirus fusogenic p14 fusion-associated small transmembrane (FAST) protein enhanced vector efficacy. The p14 FAST transgene was cloned between the fiber gene and E4 region, with an upstream splice acceptor for replication-dependent expression from the major late promoter. In A549 cells, this vector expressed p14 FAST protein at very low levels, and showed a poor ability to mediate cell-cell fusion, relative to a similar vector encoding p14 FAST within the E3 deletion. Although expression of E3 proteins from the CRAd increased plaque size, poor expression of p14 FAST protein compromised the fusogenic capacity of the vector. Thus, location of a therapeutic transgene within a CRAd can significantly impact expression of the transgene and is an important consideration in vector design.

Fusion of Large Polypeptides to Human Adenovirus Type 5 Capsid Protein IX Can Compromise Virion Stability and DNA Packaging Capacity

The human adenovirus (HAdV) protein IX (pIX) is a minor component of the capsid that acts in part to stabilize the hexon-hexon interactions within the mature capsid. Virions lacking pIX have a reduced DNA packaging capacity and exhibit thermal instability. More recently, pIX has been developed as a platform for presentation of large polypeptides, such as fluorescent proteins or large targeting ligands, on the viral capsid. It is not known whether such modifications affect the natural ability of pIX to stabilize the HAdV virion. In this study, we show that addition of large polypeptides to pIX does not alter the natural stability of virions containing sub-wild-type-sized genomes. However, similar virions containing wild-type-sized genomes tend to genetically rearrange, likely due to selective pressure caused by virion instability as a result of compromised pIX function.IMPORTANCE Human adenovirus capsid protein IX (pIX) is involved in stabilizing the virion but has also been developed as a platform for presentation of various polypeptides on the surface of the virion. Whether such modifications affect the ability of pIX to stabilize the virion is unknown. We show that addition of large polypeptides to pIX can reduce both the DNA packaging capacity and the heat stability of the virion, which provides important guidance for the design of pIX-modified vectors.

Histone Deacetylase Inhibitor Suberoylanilide Hydroxamic Acid Suppresses Human Adenovirus Gene Expression and Replication

Human adenovirus (HAdV) causes minor illnesses in most patients but can lead to severe disease and death in pediatric, geriatric, and immunocompromised individuals. No approved antiviral therapy currently exists for the treatment of these severe HAdV-induced diseases. In this study, we show that the pan-histone deacetylase (HDAC) inhibitor SAHA reduces HAdV-5 gene expression and DNA replication in tissue culture, ultimately decreasing virus yield from infected cells. Importantly, SAHA also reduced gene expression from more virulent and clinically relevant serotypes, including HAdV-4 and HAdV-7. In addition to SAHA, several other HDAC inhibitors (e.g., trichostatin A, apicidin, and panobinostat) also affected HAdV gene expression. We determined that loss of class I HDAC activity, mainly HDAC2, impairs efficient expression of viral genes, and that E1A physically interacts with HDAC2. Our results suggest that HDAC activity is necessary for HAdV replication, which may represent a novel pharmacological target in HAdV-induced disease.IMPORTANCE Although human adenovirus (HAdV) can cause severe diseases that can be fatal in some populations, there are no effective treatments to combat HAdV infection. In this study, we determined that the pan-histone deacetylase (HDAC) inhibitor SAHA has inhibitory activity against several clinically relevant serotypes of HAdV. This U.S. Food and Drug Administration-approved compound affects various stages of the virus lifecycle and reduces virus yield even at low concentrations. We further report that class I HDAC activity, particularly HDAC2, is required for efficient expression of viral genes during lytic infection. Investigation of the mechanism underlying SAHA-mediated suppression of HAdV gene expression and replication will enhance current knowledge of virus-cell interaction and may aid in the development of more effective antivirals with lower toxicity for the treatment of HAdV infections.

An Oncolytic Adenovirus Vector Expressing p14 FAST Protein Induces Widespread Syncytium Formation and Reduces Tumor Growth Rate In Vivo

Intratumoral injection of oncolytic viruses provides a direct means of tumor cell destruction for inoperable tumors. Unfortunately, oncolytic vectors based on human adenovirus (HAdV) typically do not spread efficiently throughout the tumor mass, reducing the efficacy of treatment. In this study, we explore the efficacy of a conditionally replicating HAdV vector expressing the p14 Fusion-Associated Small Transmembrane (FAST) protein (CRAdFAST) in both immunocompetent and immunodeficient mouse models of cancer. The p14 FAST protein mediates cell-cell fusion, which may enhance spread of the virus-mediated, tumor cell-killing effect. In the murine 4T1 model of cancer, treatment with CRAdFAST resulted in enhanced cell death compared to vector lacking the p14 FAST gene, but it did not reduce the tumor growth rate in vivo. In the human A549 lung adenocarcinoma model of cancer, CRAdFAST showed significantly improved oncolytic efficacy in vitro and in vivo. In an A549 xenograft tumor model in vivo, CRAdFAST induced tumor cell fusion, which led to the formation of large acellular regions within the tumor and significantly reduced the tumor growth rate compared to control vector. Our results indicate that expression of p14 FAST from an oncolytic HAdV can improve vector efficacy for the treatment of cancer.

Designer Oncolytic Adenovirus: Coming of Age

The licensing of talimogene laherparepvec (T-Vec) represented a landmark moment for oncolytic virotherapy, since it provided unequivocal evidence for the long-touted potential of genetically modified replicating viruses as anti-cancer agents. Whilst T-Vec is promising as a locally delivered virotherapy, especially in combination with immune-checkpoint inhibitors, the quest continues for a virus capable of specific tumour cell killing via systemic administration. One candidate is oncolytic adenovirus (Ad); it’s double stranded DNA genome is easily manipulated and a wide range of strategies and technologies have been employed to empower the vector with improved pharmacokinetics and tumour targeting ability. As well characterised clinical and experimental agents, we have detailed knowledge of adenoviruses’ mechanisms of pathogenicity, supported by detailed virological studies and in vivo interactions. In this review we highlight the strides made in the engineering of bespoke adenoviral vectors to specifically infect, replicate within, and destroy tumour cells. We discuss how mutations in genes regulating adenoviral replication after cell entry can be used to restrict replication to the tumour, and summarise how detailed knowledge of viral capsid interactions enable rational modification to eliminate native tropisms, and simultaneously promote active uptake by cancerous tissues. We argue that these designer-viruses, exploiting the viruses natural mechanisms and regulated at every level of replication, represent the ideal platforms for local overexpression of therapeutic transgenes such as immunomodulatory agents. Where T-Vec has paved the way, Ad-based vectors now follow. The era of designer oncolytic virotherapies looks decidedly as though it will soon become a reality.

A novel capsid-modified oncolytic recombinant adenovirus type 5 for tumor-targeting gene therapy by intravenous route

Oncolytic adenovirus (Ad)-vectored gene therapy is a promising strategy for cancer treatment. However, the lack of cancer cell selectivity or tumor tissue specificity of Ads limits their clinical application by intravenous (IV) injection. In this paper, a novel recombinant Ad5 vector was constructed carrying the capsid protein IX modified by the tumor necrosis factor related apoptosis-inducing ligand (TRAIL), which targets tumor cells bearing high levels of its receptor far above those of normal cells. Specific association of the Ad virion with TRAIL was achieved using synthetic leucine zipper-like dimerization domains (zippers). Analysis of the chemical properties of the modified recombinant Ad (rAd5pz-zTRAIL-RFP) showed that the TRAIL protein was present on the surface of purified virus particles, and it could induce apoptosis of infected cancer cells prior to expression of foreign genes. We also constructed a novel modified recombinant oncolytic Ad (rAd5pz-zTRAIL-RFP-SΔ24E1a) which showed significantly enhanced anti-tumor effects both in vitro and in vivo by linkage of TRAIL to the viral capsid. Moreover, rAd5pz-zTRAIL-RFP-SΔ24E1a showed significantly improved tumor tissue targeting and reduced liver tropism when IV injected in vivo. Thus, we successfully obtained new oncolytic Ad5 gene therapy vectors with enhanced targeting and efficacy, providing a platform for further clinical application of Ad vectors for cancer treatment.

Development of an adenovirus vector vaccine platform for targeting dendritic cells

Adenoviral (Ad) vector vaccines represent one of the most promising modern vaccine platforms, and Ad vector vaccines are currently being investigated in human clinical trials for infectious disease and cancer. Our studies have shown that specific targeting of adenovirus to dendritic cells dramatically enhanced vaccine efficacy. However, this was achieved using a molecular adapter, thereby necessitating a two component vector approach. To address the mandates of clinical translation of our strategy, we here sought to accomplish the goal of DC targeting with a single-component adenovirus vector approach. To redirect the specificity of Ad vector vaccines, we replaced the Ad fiber knob with fiber-fibritin chimeras fused to DC1.8, a single-domain antibody (sdAb) specific for murine immature DC. We engineered a fiber-fibritin-sdAb chimeric molecule using the coding sequence for DC1.8, and then replaced the native Ad5 fiber knob sequence by homologous recombination. The resulting Ad5 virus, Ad5FF1.8, expresses the chimeric fiber-fibritin sdAb chimera. Infection with Ad5FF1.8 dramatically enhances transgene expression in DC2.4 dendritic cells compared with infection with native Ad5. Ad5FF1.8 infection of bone marrow-derived DC demonstrates that Ad5FF1.8 selectively infects immature DC consistent with the known specificity of DC1.8. Thus, sdAb can be used to selectively redirect the tropism of Ad5 vector vaccines, providing the opportunity to engineer Ad vector vaccines that are specifically targeted to DC, or specific DC subsets.

Assessment of Specificity of an Adenovirus Targeted to HER3/4

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

Adenoviral Vectors Armed with Cell Fusion-Inducing Proteins as Anti-Cancer Agents

Cancer is a devastating disease that affects millions of patients every year, and causes an enormous economic burden on the health care system and emotional burden on affected families. The first line of defense against solid tumors is usually extraction of the tumor, when possible, by surgical methods. In cases where solid tumors can not be safely removed, chemotherapy is often the first line of treatment. As metastatic cancers often become vigorously resistant to treatments, the development of novel, more potent and selective anti-cancer strategies is of great importance. Adenovirus (Ad) is the most commonly used virus in cancer clinical trials, however, regardless of the nature of the Ad-based therapeutic, complete responses to treatment remain rare. A number of pre-clinical studies have shown that, for all vector systems, viral spread throughout the tumor mass can be a major limiting factor for complete tumor elimination. By expressing exogenous cell-fusion proteins, many groups have shown improved spread of Ad-based vectors. This review summarizes the research done to examine the potency of Ad vectors expressing fusogenic proteins as anti-cancer therapeutics.

Expression of the fusogenic p14 FAST protein from a replication-defective adenovirus vector does not provide a therapeutic benefit in an immunocompetent mouse model of cancer

When injected directly into a tumor mass, adenovirus (Ad) vectors only transduce cells immediately along the injection tract. Expression of fusogenic proteins from the Ad vector can lead to syncytium formation, which efficiently spreads the therapeutic effect. Fusogenic proteins can also cause cancer cell death directly, and enhance the release of exosome-like particles containing tumor-associated antigens, which boosts the anti-tumor immune response. In this study, we have examined whether delivery of an early region 1 (E1)-deleted, replication-defective Ad vector encoding the reptilian reovirus p14 fusion-associated small transmembrane (FAST) protein can provide therapeutic efficacy in an immunocompetent mouse tumor model. A high multiplicity of infection of AdFAST is required to induce cell fusion in mouse mammary carcinoma 4T1 cells in vitro, and FAST protein expression caused a modest reduction in cell membrane integrity and metabolic activity compared with cells infected with a control vector. Cells expressing FAST protein released significantly higher quantities of exosomes. In immunocompetent Balb/C mice harboring subcutaneous 4T1 tumors, AdFAST did not induce detectable cancer cell fusion, promote tumor regression or prolong mouse survival compared with untreated mice. This study suggests that in the context of the 4T1 model, Ad-mediated FAST protein expression did not elicit a therapeutic effect.

Adenovirus-Mediated Expression of the p14 Fusion-Associated Small Transmembrane Protein Promotes Cancer Cell Fusion and Apoptosis In Vitro but Does Not Provide Therapeutic Efficacy in a Xenograft Mouse Model of Cancer

Adenoviruses (Ads) are used in numerous preclinical and clinical studies for delivery of anti-cancer therapeutic genes. Unfortunately, Ad has a poor ability to distribute throughout a tumor mass after intratumoral injection, and infects cells primarily within the immediate area of the injection tract. Thus, Ad-encoded transgene expression is typically limited to only a small percentage of cells within the tumor. One method to increase the proportion of the tumor impacted by Ad is through expression of fusogenic proteins. Infection of a single cell with an Ad vector encoding a fusogenic protein should lead to syncytium formation with adjacent cells, effectively spreading the effect of Ad and Ad-encoded therapeutic transgenes to a greater percentage of the tumor mass. Moreover, syncytium formation can be cytotoxic, suggesting that such proteins may be effective sole therapeutics. We show that an early region 1 (E1)-deleted Ad expressing reptilian reovirus p14 fusion-associated small transmembrane (FAST) protein caused extensive cell fusion in the replication-permissive 293 cell line and at high multiplicity of infection in non-permissive human lung adenocarcinoma A549 cells in vitro. FAST protein expression in the A549 cancer cell line led to a loss of cellular metabolic activity and membrane integrity, which correlated with induction of apoptosis. However, in an A549 xenograft CD-1 nude mouse cancer model, Ad-mediated FAST gene delivery did not induce detectable cell fusion, reduce tumor burden nor enhance mouse survival compared to controls. Taken together, our results show that, although AdFAST can enhance cancer cell killing in vitro, it is not effective as a sole therapeutic in the A549 tumor model in vivo.

Synthetic virology: engineering viruses for gene delivery

The success of gene therapy relies heavily on the performance of vectors that can effectively deliver transgenes to desired cell populations. As viruses have evolved to deliver genetic material into cells, a prolific area of research has emerged over the last several decades to leverage the innate properties of viruses as well as to engineer new features into them. Specifically, the field of synthetic virology aims to capitalize on knowledge accrued from fundamental virology research in order to design functionally enhanced gene delivery vectors. The enhanced viral vectors, or 'bionic' viruses, feature engineered components, or 'parts', that are natural (intrinsic to viruses or from other organisms) and synthetic (such as man-made polymers or inorganic nanoparticles). Various design strategies--rational, combinatorial, and pseudo-rational--have been pursued to create the hybrid viruses. The gene delivery vectors of the future will likely criss-cross the boundaries between natural and synthetic domains to harness the unique strengths afforded by the various functional parts that can be grafted onto virus capsids. Such research endeavors will further expand and enable enhanced control over the functional capacity of these nanoscale devices for biomedicine.

A reduction in the human adenovirus virion size through use of a shortened fibre protein does not enhance muscle transduction following systemic or localised delivery in mice

We have investigated whether reducing the overall size of adenovirus (Ad), through use of a vector containing a shortened fibre, leads to enhanced distribution and dissemination of the vector. Intravenous or intraperitoneal injection of Ad5SlacZ (12 nm fibre versus the normal Ad5 37 nm fibre) or Ad5SpKlacZ (shortened fibre with polylysine motif in the H-I loop of fibre knob domain) led to similar levels of lacZ expression compared to Ad5LlacZ (native Ad5 fibre) in the liver of treated animals, but did not enhance extravasation into the tibialis anterior muscle. Direct injection of the short-fibre vectors into the tibialis anterior muscle did not result in enhanced spread of the vector through muscle tissue, and led to only sporadic transgene expression in the spinal cord, suggesting that modifying the fibre length or redirecting viral infection to a more common cell surface receptor does not enhance motor neuron uptake or retrograde transport.

Adenoviral targeting using genetically incorporated camelid single variable domains

The unique ability of human adenovirus serotype 5 (Ad5) to accomplish efficient transduction has allowed the use of Ad5-based vectors for a range of gene therapy applications. Several strategies have been developed to alter tropism of Ad vectors to achieve a cell-specific gene delivery by using fiber modifications via genetic incorporation of targeting motifs. In this study, we have explored the utility of novel anti-human carcinoembryonic antigen (hCEA) single variable domains derived from heavy chain (VHH) camelid family of antibodies to achieve targeted gene transfer. To obtain anti-CEA VHHs, we produced a VHH-display library from peripheral blood lymphocytes RNA of alpacas at the peak of immune response to the hCEA antigen (Ag). We genetically incorporated an anti-hCEA VHH into a de-knobbed Ad5 fiber-fibritin chimera and demonstrated selective targeting to the cognate epitope expressed on the membrane surface of target cells. We report that the anti-hCEA VHH used in this study retains Ag recognition functionality and provides specificity for gene transfer of capsid-modified Ad5 vectors. These studies clearly demonstrated the feasibility of retargeting of Ad5-based gene transfer using VHHs.

New viruses for cancer therapy: meeting clinical needs

Early-stage clinical trials of oncolytic virotherapy have reported the safety of several virus platforms, and viruses from three families have progressed to advanced efficacy trials. In addition, preclinical studies have established proof-of-principle for many new genetic engineering strategies. Thus, the virotherapy field now has available a diverse collection of viruses that are equipped to address unmet clinical needs owing to improved systemic administration, greater tumour specificity and enhanced oncolytic efficacy. The current key challenge for the field is to develop viruses that replicate with greater efficiency within tumours while achieving therapeutic synergy with currently available treatments.

Supraphysiological expression of survival motor neuron protein from an adenovirus vector does not adversely affect cell function

Spinal muscular atrophy (SMA) is the most common inherited neurodegenerative disease that leads to infant mortality. It is caused by mutations in the survival motor neuron (SMN) protein resulting in death of alpha motor neurons. Increasing evidence suggests that several other tissues are also affected in SMA, including skeletal and cardiac muscle, liver, and pancreas, indicating that systemic delivery of therapeutics may be necessary for true disease correction. Due to the natural biodistribution of therapeutics, a level of SMN several-fold above physiological levels can be achieved in some tissues. In this study, we address whether supraphysiological levels of SMN adversely affects cell function. Infection of a variety of cell types with an adenovirus (Ad) vector encoding SMN leads to very high expression, but the resulting protein correctly localizes within the cell, and associates with normal cellular partners. Although SMN affects transcription of certain target genes and can alter the splicing pattern of others, we did not observe any difference in select target gene splicing or expression in cells overexpressing SMN. However, normal human fibroblasts treated with Ad-SMN showed a slight reduction in growth rate, suggesting that certain cell types may be differently impacted by high levels of SMN.

A targeted adenovirus vector displaying a human fibronectin type III domain-based monobody in a fiber protein

A major drawback of adenovirus (Ad) vectors is their nonspecific transduction into various types of cells or tissue after in vivo application, which might lead to unexpected toxicity and tissue damage. To overcome this problem, we developed a fiber-mutant Ad vector displaying a monobody specific for epidermal growth factor receptor (EGFR) or vascular endothelial growth factor receptor 2 (VEGFR2) in the C-terminus of the knobless fiber protein derived from T4 phage fibritin. A monobody, which is a single domain antibody mimic based on the tenth human fibronectin type III domain scaffold with a structure similar to the variable domains of antibodies, would be suitable as a targeting molecule for display on the Ad capsid proteins because of its highly stable structure even under reducing conditions and low molecular weight (approximately 10 kDa). Surface plasmon resonance (SPR) analysis revealed that the monobody-displaying Ad vector specifically bound to the targeted molecules, leading to significant increases in cellular binding and transduction efficiencies in the targeted cells. Transduction with the monobody-displaying Ad vectors was significantly inhibited in the presence of the Fc-chimera protein of EGFR and VEGFR2. This monobody-displaying Ad vector would be a crucial resource for targeted gene therapy.

Chapter two--Adenovirus strategies for tissue-specific targeting

Cancer gene therapy approaches have benefited greatly from the utilization of molecular-based therapeutics. Of these, adenovirus-based interventions hold much promise as a platform for targeted therapeutic delivery to tumors. However, a barrier to this progression is the lack of native adenovirus receptor expression on a variety of cancer types. As such, any adenovirus-based cancer therapy must take into consideration retargeting the vector to nonnative cellular surface receptors. Predicated upon the knowledge gained in native adenovirus biology, several strategies to transductionally retarget adenovirus have emerged. Herein, we describe the biological hurdles as well as strategies utilized in adenovirus transductional targeting, covering the progress of both adapter-based and genetic manipulation-based targeting. Additionally, we discuss recent translation of these targeting strategies into a clinical setting.

HER3 targeting of adenovirus by fiber modification increases infection of breast cancer cells in vitro, but not following intratumoral injection in mice

Despite the tremendous potential of adenovirus (Ad) as a delivery vector for cancer gene therapy, its use in clinical settings has been limited, mainly as a result of the limited infectivity in many tumors and the wide tissue tropism associated with Ad. To modify the tropism of the virus, we have inserted the epidermal growth factor-like domain of the human heregulin-α (HRG) into the HI loop of Ad5 fiber. This insertion had no adverse effect on fiber trimerization nor did it affect incorporation of the modified fiber into infectious viral particles. Virions bearing modified fiber displayed growth characteristics and viral yields indistinguishable from those of wild-type (wt) virus. Most importantly, HRG-tagged virions showed enhanced infection of cells expressing the cognate receptors HER3/ErbB3 and HER4/ErbB4. This was significantly reduced in the presence of soluble HRG. Furthermore, HER3-expressing Chinese hamster ovary (CHO) cells were transduced by the HRG-modified virus, but not by wt virus. In contrast, CHO cells expressing the coxsackie-Ad receptor were transduced with both viruses. However, infection of an in vivo breast cancer xenograft model after intratumoral injection was similar with both viruses, suggesting that the tumor microenvironment and/or the route of delivery have important roles in infection of target cells with fiber-modified Ads.

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.

Use of microRNA Let-7 to control the replication specificity of oncolytic adenovirus in hepatocellular carcinoma cells

Highly selective therapy for hepatocellular carcinoma (HCC) remains an unmet medical need. In present study, we found that the tumor suppressor microRNA, let-7 was significantly downregulated in a proportion of primary HCC tissues (12 of 33, 36.4%) and HCC cell lines. In line with this finding, we have engineered a chimeric Ad5/11 fiber oncolytic adenovirus, SG7011^let7T, by introducing eight copies of let-7 target sites (let7T) into the 3′ untranslated region of E1A, a key gene associated with adenoviral replication. The results showed that the E1A expression (both RNA and protein levels) of the SG7011^let7T was tightly regulated according to the endogenous expression level of the let-7. As contrasted with the wild-type adenovirus and the control virus, the replication of SG7011^let7T was distinctly inhibited in normal liver cells lines (i.e. L-02 and WRL-68) expressing high level of let-7 (>300 folds), whereas was almost not impaired in HCC cells (i.e. Hep3B and PLC/PRF/5) with low level of let-7. Consequently, the cytotoxicity of SG7011^let7T to normal liver cells was successfully decreased while was almost not attenuated in HCC cells in vitro. The antitumor ability of SG7011^let7Tin vivo was maintained in mice with Hep3B xenograft tumor, whereas was greatly decreased against the SMMC-7721 xenograft tumor expressing a high level of let-7 similar with L-02 when compared to the wild-type adenovirus. These results suggested that SG7011^let7T may be a promising anticancer agent or vector to mediate the expression of therapeutic gene, broadly applicable in the treatment for HCC and other cancers where the let-7 gene is downregulated.

Enhanced in vivo gene transfer into the placenta using RGD fiber-mutant adenovirus vector

Among viral vectors, the fiber-mutant adenovirus vector carrying the Arg-Gly-Asp (RGD) peptide sequence (Ad-RGD) seems to have potential for both clinical gene therapy and basic research. As a part of a thorough evaluation of Ad-RGD in preclinical studies, we designed an experiment to investigate in detail the distribution of Ad-RGD compared with conventional adenovirus vector (WT-Ad) in pregnant mice. Surprisingly, Ad-RGD had substantial placental tropism, at 10-100 times that of WT-Ad. Transgene expression was sustained for at least 7 days, and Ad-RGD expressing firefly luciferase or red fluorescent protein has so far caused no placental dysfunction leading to fetal death. Ad-RGD showed high levels of transduction efficiency in in vitro-differentiated trophoblast stem cells, in which higher expression of αvβ3 integrin than in undifferentiated cells was observed. Our results suggest that the use of Ad-RGD or another RGD-mediated targeting strategy holds promise for drug delivery to the placenta.

Rational design of murine secreted alkaline phosphatase for enhanced performance as a reporter gene in mouse gene therapy preclinical studies

Many preclinical gene therapy studies use a reporter gene to evaluate vector design and performance in mouse models of human disease. Unfortunately, most commonly used reporter genes are immunogenic in mice, which confounds accurate evaluation of vector function. In previous studies, we showed that the murine secreted alkaline phosphatase (mSEAP) gene functions well as a simple and sensitive reporter gene in mice. In this study, we have used rational design to enhance mSEAP performance. The majority of native mSEAP remains attached to the outer surface of the cell through glycan phosphatidylinositol linkage; removal of the carboxy-terminal tail of mSEAP resulted in a dramatic enhancement of release of the protein into cell culture medium and into mouse plasma in whole animal experiments. We increased the heat stability of mSEAP through mutation of a key residue in the crown domain of the protein (H451E), thus allowing us to reduce endogenous, background AP activity through heat inactivation for enhanced sensitivity. We show that these alterations in mSEAP result in enhanced performance in tissue culture and mouse studies. Taken together, these data illustrate that mSEAP is a sensitive, nonimmunogenic reporter for preclinical mouse studies.

Assembly of helper-dependent adenovirus DNA into chromatin promotes efficient gene expression

Helper-dependent adenovirus (hdAd) vectors have shown tremendous potential in animal models of human disease in numerous preclinical studies. Expression of a therapeutic transgene can be maintained for several years after a single administration of the hdAd vector. However, despite the long-term persistence of hdAd DNA in the transduced cell, little is known of the fate and structure of hdAd DNA within the host nucleus. In this study, we have characterized the assembly of hdAd DNA into chromatin in tissue culture. Eviction of the Ad DNA-packaging protein VII, histone deposition, and vector-associated gene expression all began within 2 to 6 h of host cell transduction. Inhibition of transcription elongation through the vector DNA template had no effect on the loss of VII, suggesting that transcription was not necessary for removal of the majority of protein VII. Vector DNA assembled into physiologically spaced nucleosomes within 6 h. hdAd vectors incorporated the histone H3 variant H3.3, which was dependent on the histone chaperone HIRA. Knockdown of HIRA reduced hdAd association with histones and reduced expression of the vector-carried transgene by 2- to 3-fold. Our study elucidates an essential role for hdAd DNA chromatinization for optimal vector gene expression.