Adenoviral vectors for gene therapy

Transforming growth factor-β gene silencing using adenovirus expressing TGF-β1 or TGF-β2 shRNA

Tumor cells secrete a variety of cytokines to outgrow and evade host immune surveillance. In this context, transforming growth factor-β1 (TGF-β1) is an extremely interesting cytokine because it has biphasic effects in cancer cells and normal cells. TGF-β1 acts as a growth inhibitor in normal cells, whereas it promotes tumor growth and progression in tumor cells. Overexpression of TGF-β1 in tumor cells also provides additional oncogenic activities by circumventing the host immune surveillance. Therefore, this study ultimately aimed to test the hypothesis that suppression of TGF-β1 in tumor cells by RNA interference can have antitumorigenic effects. However, we demonstrated here that the interrelation between TGF-β isotypes should be carefully considered for the antitumor effect in addition to the selection of target sequences with highest efficacy. The target sequences were proven to be highly specific and effective for suppressing both TGF-β1 mRNA and protein expression in cells after infection with an adenovirus expressing TGF-β1 short hairpin RNA (shRNA). A single base pair change in the shRNA sequence completely abrogated the suppressive effect on TGF-β1. Surprisingly, the suppression of TGF-β1 induced TGF-β3 upregulation, and the suppression of TGF-β2 induced another unexpected downregulation of both TGF-β1 and TGF-β3. Taken together, this information may prove useful when considering the design for a novel cancer immunogene therapy.

Inhibition of FOXM1 transcription factor suppresses cell proliferation and tumor growth of breast cancer

The forkhead box M1 (FOXM1) transcription factor regulates the expression of genes essential for cell proliferation and transformation and is implicated in tumorigenesis and tumor progression. FOXM1 has been considered as a potential target for the prevention and/or therapeutic intervention in human carcinomas. In this study, we observed a strong expression of FOXM1 in clinical tissue specimens and cell lines of human breast cancer and a correlation between FOXM1 levels and the proliferation ability in the tested MCF-7, MDA-MB-231 and ZR-75-30 cells. By using an adenovirus vector (named AdFOXM1shRNA) that expresses a short hairpin RNA (shRNA) to downregulate FOXM1 expression specifically, we found that the knockdown of FOXM1 expression diminished the proliferation and anchorage-independent growth of the breast cancer cells. The FOXM1 silencing in ZR-75-30 cells dramatically prevented the tumorigenicity of the AdFOXM1shRNA-treated cells in vitro and in vivo. Furthermore, the efficacy of AdFOXM1shRNA for tumor gene therapy was assessed with the breast cancer xenograft mouse model and the tumor growth was significantly suppressed when inoculated mice were injected with AdFOXM1shRNA in the tumors. Together, our results suggest that FOXM1 is a potential therapeutic target for breast cancer and AdFOXM1shRNA may be an additional gene therapeutic intervention for breast cancer treatment.

Alleviation of lung inflammatory responses by adeno-associated virus 2/9 vector carrying CC10 in OVA-sensitized mice

Asthma is a chronic airway inflammatory disease characterized by eosinophilic infiltration and airway hyperresponsiveness. The over-activated Th2 and lung epithelium cells express many different cytokines, and chemokines mainly contribute to the severity of lung inflammation. Clara cell 10 kD protein (CC10) is highly expressed in airway epithelium cells and exhibits anti-inflammatory and immunomodulatory effects. Adeno-associated virus (AAV) 2/9 vector, composed of AAV2 rep and AAV9 cap genes, can efficiently and specifically target lung epithelium cells. Thus, AAV2/9 vector might carry therapeutic potential gene sequences for the treatment of asthma. This study tested whether AAV2/9 vector carrying CC10 could reduce inflammatory and asthmatic responses in OVA-induced asthmatic mouse model. The results showed that AAV2/9-CC10 vector virus significantly reduced airway hyperresponsiveness, CCL11, interleukin (IL)-4, IL-5, IL-6, IL-13, and eosinophilia in the lungs of sensitized mice. CC10 level in OVA-sensitized mice was rescued with the administration of AAV2/9-CC10 vector virus. Lung tissue remodeling, including collagen deposition and goblet cell hyperplasia, was also alleviated. However, serum levels of OVA-specific IgG1 and IgE as well as Th2 cytokine levels in OVA-stimulated splenocyte culture supernatants were at the comparable levels to the sensitized control group. The results demonstrate that AAV2/9-CC10 vector virus relieved local inflammatory and asthmatic responses in lung. Therefore, we propose that AAV2/9-CC10 vector virus guaranteed sufficient CC10 expression and had an anti-inflammatory effect in asthmatic mice. It might be applied as a novel therapeutic approach for asthma.

Pseudotyped adeno-associated virus 2/9-delivered CCL11 shRNA alleviates lung inflammation in an allergen-sensitized mouse model

Airway infiltration by eosinophils is a major characteristic of chronic asthma. CCL11 (eotaxin-1) is secreted by lung epithelial cells and functions as the major chemokine for eosinophil recruitment. Pseudotyped adeno-associated virus (AAV) 2/9, composed by the AAV2 rep and AAV9 cap genes, can efficiently target lung epithelial cells and might carry gene sequences with therapeutic potential for asthma. This study aimed to determine whether pseudotyped AAV2/9 virus carrying the small hairpin RNA targeting CCL11 and expressed by CMV/U6 promoter could reduce eosinophilia and asthmatic responses in mite allergen-sensitized mice. Mice were sensitized by intraperitoneal and challenged by intratracheal injection with recombinant Dermatophagoides pteronyssinus group 2 allergen (rDp2). AAV2/9 viral vectors were intratracheally injected three days before the first challenge. AAV2/9 sh47 virus significantly reduced airway hyperresponsiveness, airway resistance, CCL11 levels, and eosinophilia in the lungs of sensitized mice. Th2 cytokines, including interleukins (IL)-4, IL-5, and IL-10, were also significantly reduced in the bronchoalveolar lavage fluid of AAV2/9 sh47 virus-treated mice. Th2 cytokine levels were also reduced in rDp2-stimulated mediastinal lymphocytes in treated mice. However, serum levels of rDp2-specific IgG1 and IgE, as well as Th2 cytokine levels in rDp2-stimulated splenocyte culture supernatants, were comparable to the sensitized control group. The results suggest that AAV2/9 sh47 virus relieved local instead of systemic inflammatory responses. Therefore, the CMV/U6 promoter with AAV2/9 viral vector, which is preferable to target lung epithelia cells, might be applied as a novel therapeutic approach for asthma.

Phoenix rising: gene therapy makes a comeback

Despite the first application of gene therapy in 1990, gene therapy has until recently failed to meet the huge expectations set forth by researchers, clinicians, and patients, thus dampening enthusiasm for an imminent cure for many life-threatening genetic diseases. Nonetheless, in recent years we have witnessed a strong comeback for gene therapy, with clinical successes in young and adult subjects suffering from inherited forms of blindness or from X-linked severe combined immunodeficiency disease. In this review, various gene therapy vectors progressing into clinical development and pivotal advances in gene therapy trials will be discussed.

Recombinant adeno-associated virus: clinical application and development as a gene-therapy vector

Gene therapy is gaining momentum as a method of treating human disease. Initially conceived as a strategy to complement defective genes in monogenic disorders, the scope of gene therapy has expanded to encompass a variety of applications. Likewise, the molecular tools for gene delivery have evolved and diversified to meet these various therapeutic needs. Recombinant adeno-associated virus (rAAV) has made significant strides toward clinical application with an excellent safety profile and successes in several clinical trials. This review covers the basic biology of rAAV as a gene therapy vector as well as its advantages compared with other methods of gene delivery. The status of clinical trials utilizing rAAV is also discussed in detail. In conclusion, methods of engineering the vector to overcome challenges identified from these trials are covered, with emphasis on modification of the viral capsid to increase the tissue/cell-specific targeting and transduction efficiency.

Investigation of siRNA-loaded polyethylenimine-coated human serum albumin nanoparticle complexes for the treatment of breast cancer

Small interfering RNA (siRNA) molecules have great potential for developing into a future therapy for breast cancer. To overcome the issues related to rapid degradation and low transfection of naked siRNA, polyethylenimine (PEI)-coated human serum albumin (HSA) nanoparticles have been characterized and studied here for efficient siRNA delivery to the MCF-7 breast cancer cell line. The optimized nanoparticles were ~90 nm in size, carrying a surface charge of +26 mV and a polydispersity index (PDI) less than 0.25. The shape and morphology of the particles was studied using electron microscopy. A cytotoxicity assessment of the nanoparticles showed no correlation of cytotoxicity with HSA concentration, while using high molecular weight PEI (MW of 70 against 25 kDa) showed higher cytotoxicity. The optimal transfection achieved of fluorescin-tagged siRNA loaded into PEI-coated HSA nanoparticles was 61.66 ± 6.8%, prepared with 6.25 μg of PEI (25 kDa) added per mg of HSA and 20 mg/ml HSA, indicating that this nonviral vector may serve as a promising gene delivery system.

Excision of HIV-1 proviral DNA by recombinant cell permeable tre-recombinase

Over the previous years, comprehensive studies on antiretroviral drugs resulted in the successful introduction of highly active antiretroviral therapy (HAART) into clinical practice for treatment of HIV/AIDS. However, there is still need for new therapeutic approaches, since HAART cannot eradicate HIV-1 from the infected organism and, unfortunately, can be associated with long-term toxicity and the development of drug resistance. In contrast, novel gene therapy strategies may have the potential to reverse the infection by eradicating HIV-1. For example, expression of long terminal repeat (LTR)-specific recombinase (Tre-recombinase) has been shown to result in chromosomal excision of proviral DNA and, in consequence, in the eradication of HIV-1 from infected cell cultures. However, the delivery of Tre-recombinase currently depends on the genetic manipulation of target cells, a process that is complicating such therapeutic approaches and, thus, might be undesirable in a clinical setting. In this report we demonstrate that E.coli expressed Tre-recombinases, tagged either with the protein transduction domain (PTD) from the HIV-1 Tat trans-activator or the translocation motif (TLM) of the Hepatitis B virus PreS2 protein, were able to translocate efficiently into cells and showed significant recombination activity on HIV-1 LTR sequences. Tre activity was observed using episomal and stable integrated reporter constructs in transfected HeLa cells. Furthermore, the TLM-tagged enzyme was able to excise the full-length proviral DNA from chromosomal integration sites of HIV-1-infected HeLa and CEM-SS cells. The presented data confirm Tre-recombinase activity on integrated HIV-1 and provide the basis for the non-genetic transient application of engineered recombinases, which may be a valuable component of future HIV eradication strategies.

Gene therapy for lung neoplasms

Both advanced-stage lung cancer and malignant pleural mesothelioma are associated with a poor prognosis. Advances in treatment regimens for both diseases have had only a modest effect on their progressive course. Gene therapy for thoracic malignancies represents a novel therapeutic approach and has been evaluated in several clinical trials. Strategies have included induction of apoptosis, tumor suppressor gene replacement, suicide gene expression, cytokine-based therapy, various vaccination approaches, and adoptive transfer of modified immune cells. This review considers the clinical results, limitations, and future directions of gene therapy trials for thoracic malignancies.

Process optimization and scale-up for production of rabies vaccine live adenovirus vector (AdRG1.3)

Rabies virus is an important causative agent of disease resulting in an acute infection of the nervous system and death. Although curable if treated in a timely manner, rabies remains a serious public health issue in developing countries, and the indigenous threat of rabies continues in developed countries because of wildlife reservoirs. Control of rabies in wildlife is still an important challenge for governmental authorities. There are a number of rabies vaccines commercially available for control of wildlife rabies infection. However, the vaccines currently distributed to wildlife do not effectively immunize all at-risk species, particularly skunks. A replication competent recombinant adenovirus expressing rabies glycoprotein (AdRG1.3) has shown the most promising results in laboratory trials. The adenovirus vectored vaccine is manufactured using HEK 293 cells. This study describes the successful scale-up of AdRG1.3 adenovirus production from 1 to 500 L and the manufacturing of large quantities of bulk material required for field trials to demonstrate efficacy of this new candidate vaccine. The production process was streamlined by eliminating a medium replacement step prior to infection and the culture titer was increased by over 2 fold through optimization of cell culture medium. These improvements produced a more robust and cost-effective process that facilitates industrialization and commercialization. Over 17,000 L of AdRG1.3 adenovirus cultures were manufactured to support extensive field trials. AdRG1.3 adenovirus is formulated and packaged into baits by Artemis Technologies Inc. using proprietary technology. Field trials of AdRG1.3 rabies vaccine baits have been conducted in several Canadian provinces including Ontario, Quebec and New Brunswick. The results from field trials over the period 2006-2009 demonstrated superiority of the new vaccine over other licensed vaccines in immunizing wild animals that were previously difficult to vaccinate.

Reactivation of p53 mutants by prima-1 [corrected] in thyroid cancer cells

Most undifferentiated thyroid carcinomas express p53 mutants and thereafter, are very resistant to chemotherapy. p53 reactivation and induction of massive apoptosis (Prima-1) is a compound restoring the tumor-suppressor activity of p53 mutants. We tested the effect of Prima-1 in thyroid cancer cells harboring p53 mutations. Increasing doses of Prima-1 reduced viability of thyroid cancer cells at a variable extent (range 20-80%). Prima-1 up-regulated p53 target genes (p21(WAF1) , BCL2-associated X protein (Bax), and murine double minute 2 (MDM2)), in BC-PAP and Hth-74 cells (expressing D259Y/K286E and K286E p53 mutants) but had no effect in SW1736 (p53 null) and TPC-1 (expressing wild-type p53) thyroid cancer cells. Prima-1 also increased the cytotoxic effects of either doxorubicin or cisplatin in thyroid cancer cells, including the chemo-resistant 8305C, Hth-74 and BC-PAP cells. Moreover, real-time PCR and Western blot indicated that Prima-1 increases the mRNA of thyroid-specific differentiation markers in thyroid cancer cells. Fluorescence-activated cell sorting analysis revealed that Prima-1 effect on thyroid cancer cells occurs via the enhancement of both cell cycle arrest and apoptosis. Small interfering RNA experiments indicated that Prima-1 effect is mediated by p53 mutants but not by the p53 paralog p73. Moreover, in C-643 thyroid cancer cells, forced to ectopically express wild-type p53, Prima-1 prevented the dominant negative effect of double K248Q/K286E p53 mutant. Finally, co-IP experiments indicated that in Hth-74 cells Prima-1 prevents the ability of p53 mutants to sequestrate the p53 paralog TAp73. These in vitro studies imply that p53 mutant reactivation by small compounds may become a novel anticancer therapy in undifferentiated thyroid carcinomas.

Gene therapy for mesothelioma

Mesothelioma represents an especially good target for gene therapy since few effective therapies exist, the disease remained relatively localized until late in its course, the tumor can be accessed relatively easily through the chest wall, and the thin layer of mesothelial cells offers a large surface area for efficient, rapid, and diffuse gene transfer. Gene therapy trials in mesothelioma have shown safety, and some limited evidence of efficacy. We present a review of clinical trials that have been performed in mesothelioma and describe several new approaches currently being pursued.

Generation of a replication-deficient recombinant human adenovirus type 35 vector using bacteria-mediated homologous recombination

The use of adenovirus type 35 (Ad35) as a vector in vaccine and gene therapy studies is promising due to its broad cell tropism and low seroprevalence in humans. However, to date, a simple and effective system for producing recombinant Ad35 (rAd35) has not been well developed. This report describes a two-plasmid Ad35-Easy system to facilitate the production of recombinant Ad35 (rAd35). The system employed the pAd35-shuttle vector for foreign gene transfer and the pAd35-backbone vector to provide the Ad35 genomic backbone. A 293-Ad35E1B cell line was used to trans-complement rAd35 replication. rAd35 plasmids were obtained through homologous recombination following co-transformation of E. coli BJ5183 cells with recombinant pAd35-shuttle vectors harboring foreign genes. rAd35 viruses were obtained directly by transfecting 293-Ad35E1B cells with foreign gene-containing rAd35 plasmids and the pAd35-backbone vector. The production of E1 deficient rAd35 was evaluated by transfecting the 293-Ad35E1B cells with the rAd35 plasmid containing the enhanced green fluorescent protein (EGFP) gene. The virus grew effectively at a yield comparable to that of wild type Ad35 in HEp2 cells, indicating that the Ad35-Easy system is an efficient method for rapid production of rAd35 in sufficient quantities for vaccine development or gene therapy.

miRNA cassettes in viral vectors: problems and solutions

The discovery of RNA interference (RNAi), an evolutionary conserved gene silencing mechanism that is triggered by double stranded RNA, has led to tremendous efforts to use this technology for basic research and new RNA therapeutics. RNAi can be induced via transfection of synthetic small interfering RNAs (siRNAs), which results in a transient knockdown of the targeted mRNA. For stable gene silencing, short hairpin RNA (shRNA) or microRNA (miRNA) constructs have been developed. In mammals and humans, the natural RNAi pathway is triggered via endogenously expressed miRNAs. The use of modified miRNA expression cassettes to elucidate fundamental biological questions or to develop therapeutic strategies has received much attention. Viral vectors are particularly useful for the delivery of miRNA genes to specific target cells. To date, many viral vectors have been developed, each with distinct characteristics that make one vector more suitable for a certain purpose than others. This review covers the recent progress in miRNA-based gene-silencing approaches that use viral vectors, with a focus on their unique properties, respective limitations and possible solutions. Furthermore, we discuss a related topic that involves the insertion of miRNA-target sequences in viral vector systems to restrict their cellular range of gene expression. This article is part of a Special Issue entitled: MicroRNAs in viral gene regulation.

Short communication: enhancement of immunogenicity of replication-defective adenovirus-based human immunodeficiency virus vaccines in rhesus monkeys

Adenovirus (Ad) is still under extensive investigation as a vector for HIV vaccination; however, one possible explanation for the failure of Merck's STEP trial is the relatively weak immunogenicity of replication-defective Ad vectors. In this study, a novel strategy to enhance the immunogenicity of replication-defective Ad-based HIV vaccines was developed. First, a recombinant plasmid expressing adenoviral E1 protein (pVAX-E1) was constructed to complement the E1-deleted replication-defective Ad vectors in trans. Then, the immunogenicity of the vaccine regimen of Ad5-HIV gag plus pVAX-E1 plasmid was assessed in rhesus macaques. Compared with traditional administration of Ad-based vectors alone, the results showed that our strategy elicited a more sustained and robust HIV gag-specific cellular response and enhanced long-term proliferation of CD4(+) and CD8(+) T lymphocytes. This strategy represents a proof-of-concept that enhances the immunogenicity of replication-defective Ad-based vectors, and it exemplifies the useful implications for Ad-based HIV vaccines and other vaccines.

Effects of adeno-associated virus-2-mediated human BMP-7 gene transfection on the phenotype of nucleus pulposus cells

Bone morphogenetic protein-7 (BMP-7) was found to stimulate the synthesis of proteoglycans (PGs) and collagen type II. To increase the biological function of the nucleus pulposus (NP) cells, the Ad-hBMP-7 vector was also successfully constructed and transfected NP cells. However, the disadvantages of adenovirus limit the usefulness of the Ad-hBMP7 vector for clinical application. The rAAV2 vector has empirical advantages, especially for clinical use, to transfer exogenous genes into cells. The purpose of this study was to first determine whether a rAAV2-hBMP-7 vector could be used to transfect canine NP cells and effect on the biological functions of canine NP cells. The canine NP cells transfected by the rAAV-BMP7 were assessed semi-quantitatively for BMP-7 expression with real-time PCR and westernbloting. Aggrecan and collagens type I and II secreted by the NP cells were qualitatively assessed at 4, 7, and 14 days post-transfection in the transfection and control groups. We found that rAAV2 can successfully transfer the hBMP-7 gene into canine NP cells. NP cells transfected by the rAAV-hBMP-7 vector express hBMP-7 for at least 14 days. At 7 and 14 days, the expressed hBMP-7 promotes a remarkable and significant accumulation of both proteoglycans (42% and 77% higher than non-transfected cells) (p<0.05) and collagen type II (63% and 94% higher than non-transfected cells) (p<0.05). Thus, we could speculate that the rAAV-based gene delivery technique promotes the expression of proteoglycans and collagen type II of nucleus pulposus cells. Moreover, this technique may be applicable for the future treatment of degenerative disc disease.

Targeted gene therapy for the treatment of heart failure

Chronic heart failure is one of the leading causes of morbidity and mortality in Western countries and is a major financial burden to the health care system. Pharmacologic treatment and implanting devices are the predominant therapeutic approaches. They improve survival and have offered significant improvement in patient quality of life, but they fall short of producing an authentic remedy. Cardiac gene therapy, the introduction of genetic material to the heart, offers great promise in filling this void. In-depth knowledge of the underlying mechanisms of heart failure is, obviously, a prerequisite to achieve this aim. Extensive research in the past decades, supported by numerous methodological breakthroughs, such as transgenic animal model development, has led to a better understanding of the cardiovascular diseases and, inadvertently, to the identification of several candidate genes. Of the genes that can be targeted for gene transfer, calcium cycling proteins are prominent, as abnormalities in calcium handling are key determinants of heart failure. A major impediment, however, has been the development of a safe, yet efficient, delivery system. Nonviral vectors have been used extensively in clinical trials, but they fail to produce significant gene expression. Viral vectors, especially adenoviral, on the other hand, can produce high levels of expression, at the expense of safety. Adeno-associated viral vectors have emerged in recent years as promising myocardial gene delivery vehicles. They can sustain gene expression at a therapeutic level and maintain it over extended periods of time, even for years, and, most important, without a safety risk.

Epidemiology of adenovirus type 5 neutralizing antibodies in healthy people and AIDS patients in Guangzhou, southern China

Recombinant adenovirus serotype 5 (Ad5) viruses have been extensively explored as vectors for vaccination or gene therapy. However, one major obstacle to their clinical application is the high prevalence of preexisting anti-Ad5 immunity resulting from natural infection. It has been reported that there are geographic variations in the prevalence of natural adenovirus infection. In the present study, we investigated the seroprevalence of Ad5 in Guangzhou, southern China by measuring the Ad5 neutralizing antibodies in blood samples collected from several sites. The seroprevalence was 77.34% in the general healthy population. The seroprevalence and antibody titers increased with age, with the older population (41-72 years old) having the highest seropositivity (84.8%) and percentage (54.4%) of high Ad5 neutralizing antibody titers (>1000). The dynamics of Ad5 neutralizing antibodies were stable and persistent over the course of eight months. Furthermore, the seroprevalence of Ad5 in the HIV-infected AIDS patients was investigated and there was no significant difference from the general healthy population. Our survey provides useful insights for the future development of Ad5-based vaccination and gene therapy.

Electrotransfer of the full-length dog dystrophin into mouse and dystrophic dog muscles

Duchenne muscular dystrophy (DMD) is an X-linked genetic disease characterized by the absence of dystrophin (427 kDa). An approach to eventually restore this protein in patients with DMD is to introduce into their muscles a plasmid encoding dystrophin cDNA. Because the phenotype of the dystrophic dog is closer to the human phenotype than is the mdx mouse phenotype, we have studied the electrotransfer of a plasmid carrying the full-length dog dystrophin (FLDYS(dog)) in dystrophic dog muscle. To achieve this nonviral delivery, the FLDYS(dog) cDNA was cloned in two plasmids containing either a cytomegalovirus or a muscle creatine kinase promoter. In both cases, our results showed that the electrotransfer of these large plasmids (∼17 kb) into mouse muscle allowed FLDYS(dog) expression in the treated muscle. The electrotransfer of pCMV.FLDYS(dog) in a dystrophic dog muscle also led to the expression of dystrophin. In conclusion, introduction of the full-length dog dystrophin cDNA by electrotransfer into dystrophic dog muscle is a potential approach to restore dystrophin in patients with DMD. However, the electrotransfer procedure should be improved before applying it to humans.

Delivery route, MyD88 signaling and cross-priming events determine the anti-tumor efficacy of an adenovirus based melanoma vaccine

Adenovirus (Ad)-based vaccines are considered for cancer immunotherapy, yet, detailed knowledge on their mechanism of action and optimal delivery route for anti-tumor efficacy is lacking. Here, we compared the anti-tumor efficacy of an Ad-based melanoma vaccine after intradermal, intravenous, intranasal or intraperitoneal delivery in the B16F10 melanoma model. The intradermal route induced superior systemic anti-melanoma immunity which was MyD88 signaling-dependent. Predominant transduction of non-professional antigen-presenting cells at the dermal vaccination sites and draining lymph nodes, suggested a role for cross-presentation, which was confirmed in vitro. We conclude that the dermis provides an optimal route of entry for Ad-based vaccines for high-efficacy systemic anti-tumor immunization and that this immunization likely involves cross-priming events in the draining lymph nodes.

Introduction to viral vectors

Viral vector is the most effective means of gene transfer to modify specific cell type or tissue and can be manipulated to express therapeutic genes. Several virus types are currently being investigated for use to deliver genes to cells to provide either transient or permanent transgene expression. These include adenoviruses (Ads), retroviruses (γ-retroviruses and lentiviruses), poxviruses, adeno-associated viruses, baculoviruses, and herpes simplex viruses. The choice of virus for routine clinical use will depend on the efficiency of transgene expression, ease of production, safety, toxicity, and stability. This chapter provides an introductory overview of the general characteristics of viral vectors commonly used in gene transfer and their advantages and disadvantages for gene therapy use.

In vitro and in vivo studies of adenovirus-mediated human norepinephrine transporter gene transduction to hepatocellular carcinoma

The clinical value of (131)I-MIBG for targeted imaging and targeted radiotherapy is limited to neural crest-derived tumors expressing human norepinephrine transporters (hNET) protein. To extend (131)I-MIBG-targeted therapy to other nonexpressed hNET tumors, this study investigated the hNET expression in vitro and in vivo in HepG2 hepatoma mediated by recombinant adenovirus encoding the hNET gene (Ad-hNET). For this purpose, the HepG2 cells showed a 4.87-fold increase in (125)I-MIBG uptake after infection with Ad-hNET, and the uptake of (125)I-MIBG could be specifically inhibited by maprotiline. Immunohistological analysis, in vivo biological study and (131)I-MIBG scintigraphic imaging also revealed the high expression of hNET protein in hepatoma. This in vitro and in vivo studies demonstrate the feasibility of hNET gene transfer, meditated by adenovirus vector, could extend to tumors other than those derived from the neural crest, which provides a sound foundation for further investigation of hepatocellular carcinoma-targeted radiotherapy mediated by adenovirus transfection with hNET gene.

Concise review: Nanoparticles and cellular carriers-allies in cancer imaging and cellular gene therapy?

Ineffective treatment and poor patient management continue to plague the arena of clinical oncology. The crucial issues include inadequate treatment efficacy due to ineffective targeting of cancer deposits, systemic toxicities, suboptimal cancer detection and disease monitoring. This has led to the quest for clinically relevant, innovative multifaceted solutions such as development of targeted and traceable therapies. Mesenchymal stem cells (MSCs) have the intrinsic ability to "home" to growing tumors and are hypoimmunogenic. Therefore, these can be used as (a) "Trojan Horses" to deliver gene therapy directly into the tumors and (b) carriers of nanoparticles to allow cell tracking and simultaneous cancer detection. The camouflage of MSC carriers can potentially tackle the issues of safety, vector, and/or transgene immunogenicity as well as nanoparticle clearance and toxicity. The versatility of the nanotechnology platform could allow cellular tracking using single or multimodal imaging modalities. Toward that end, noninvasive magnetic resonance imaging (MRI) is fast becoming a clinical favorite, though there is scope for improvement in its accuracy and sensitivity. In that, use of superparamagnetic iron-oxide nanoparticles (SPION) as MRI contrast enhancers may be the best option for tracking therapeutic MSC. The prospects and consequences of synergistic approaches using MSC carriers, gene therapy, and SPION in developing cancer diagnostics and therapeutics are discussed.

AAV's anatomy: roadmap for optimizing vectors for translational success

Adeno-Associated Virus based vectors (rAAV) are advantageous for human gene therapy due to low inflammatory responses, lack of toxicity, natural persistence, and ability to transencapsidate the genome allowing large variations in vector biology and tropism. Over sixty clinical trials have been conducted using rAAV serotype 2 for gene delivery with a number demonstrating success in immunoprivileged sites, including the retina and the CNS. Furthermore, an increasing number of trials have been initiated utilizing other serotypes of AAV to exploit vector tropism, trafficking, and expression efficiency. While these trials have demonstrated success in safety with emerging success in clinical outcomes, one benefit has been identification of issues associated with vector administration in humans (e.g. the role of pre-existing antibody responses, loss of transgene expression in non-immunoprivileged sites, and low transgene expression levels). For these reasons, several strategies are being used to optimize rAAV vectors, ranging from addition of exogenous agents for immune evasion to optimization of the transgene cassette for enhanced therapeutic output. By far, the vast majority of approaches have focused on genetic manipulation of the viral capsid. These methods include rational mutagenesis, engineering of targeting peptides, generation of chimeric particles, library and directed evolution approaches, as well as immune evasion modifications. Overall, these modifications have created a new repertoire of AAV vectors with improved targeting, transgene expression, and immune evasion. Continued work in these areas should synergize strategies to improve capsids and transgene cassettes that will eventually lead to optimized vectors ideally suited for translational success.

Gene therapy for bone healing

Clinical problems in bone healing include large segmental defects, spinal fusions, and the nonunion and delayed union of fractures. Gene-transfer technologies have the potential to aid healing by permitting the local delivery and sustained expression of osteogenic gene products within osseous lesions. Key questions for such an approach include the choice of transgene, vector and gene-transfer strategy. Most experimental data have been obtained using cDNAs encoding osteogenic growth factors such as bone morphogenetic protein-2 (BMP-2), BMP-4 and BMP-7, in conjunction with both nonviral and viral vectors using in vivo and ex vivo delivery strategies. Proof of principle has been convincingly demonstrated in small-animal models. Relatively few studies have used large animals, but the results so far are encouraging. Once a reliable method has been developed, it will be necessary to perform detailed pharmacological and toxicological studies, as well as satisfy other demands of the regulatory bodies, before human clinical trials can be initiated. Such studies are very expensive and often protracted. Thus, progress in developing a clinically useful gene therapy for bone healing is determined not only by scientific considerations, but also by financial constraints and the ambient regulatory environment.

Suppression of tumor growth in xenograft model mice by programmed cell death 4 gene delivery using folate-PEG-baculovirus

Cancer gene therapy using tumor suppressor genes is considered to be an attractive approach for arresting cell growth and inducing apoptosis. Programmed cell death 4 (Pdcd4) is a tumor suppressor gene, which prevents tumorigenesis and tumor progression. To address the issue of whether expression of PDCD4 protein induces apoptosis in cancerous cells, the Pdcd4 gene was delivered using folate-PEG-baculovirus. Folate-PEG-baculovirus containing Pdcd4 gene (F-P-Bac-Pdcd4) was constructed by attachment of F-PEG to the baculovirus surface using chemical modification. The F-P-Bac-Pdcd4 showed enhanced transduction efficiency, efficiently expressed PDCD4 protein, and induced apoptosis in human epidermal carcinoma (KB) cells as compared with an unmodified baculovirus. In a tumor xenograft study, injection of F-P-Bac-Pdcd4 into tumors established from the KB cell line by subcutaneous implantation significantly suppressed tumor growth and induced apoptosis. Thus, this study shows a new baculovirus-mediated tumor suppressor gene delivery system for cancer therapy.

Ex vivo transfer of the Hoxc-8-interacting domain of Smad1 by a tropism-modified adenoviral vector results in efficient bone formation in a rabbit model of spinal fusion

STUDY DESIGN

Ex vivo gene transfer for spinal fusion.

OBJECTIVE

This study aimed to evaluate ex vivo transfer of the nuclear-localized Hoxc-8-interacting domain of Smad1 (termed Smad1C) to rabbit bone marrow stromal cells (BMSCs) by a tropism-modified human adenovirus serotype 5 (Ad5) vector as a novel therapeutic approach for spinal fusion.

SUMMARY OF BACKGROUND DATA

Novel approaches are needed to improve the success of bone union after spinal fusion. One such approach is the ex vivo transfer of a gene encoding an osteoinductive factor to BMSCs which are subsequently reimplanted into the host. We have previously shown that heterologous expression of the Hoxc-8-interacting domain of Smad1 in the nuclei of osteoblast precursor cells is able to stimulate the expression of genes related to osteoblast differentiation and induce osteogenesis in vivo. Gene delivery vehicles based on human Ad5 are well suited for gene transfer for spinal fusion because they can mediate high-level, short-term gene expression. However, Ad5-based vectors with native tropism poorly transduce BMSCs, necessitating the use of vectors with modified tropism to achieve efficient gene transfer.

METHODS

The gene encoding Smad1C was transferred to rabbit BMSCs by an Ad5 vector with native tropism or a vector retargeted to alphav integrins, which are abundantly expressed on rabbit BMSCs. Transduced BMSCs were maintained in osteoblastic differentiation medium for 30 days. Alkaline phosphatase activity was determined and cells stained for calcium deposition. As positive controls for osteogenesis, we used Ad5 vectors expressing bone morphogenetic protein 2. As negative controls, BMSCs were mock-transduced or transduced with an Ad5 vector expressing beta-galactosidase. In an immunocompetent rabbit model of spinal fusion, transduced BMSCs were coated onto absorbable gelatin sponge and implanted between decorticated transverse processes L6 and L7 of 8-week-old female New Zealand white rabbits. Animals were killed 4 weeks after implantation of the sponges, the fusion masses harvested and the area of new bone quantified using image analysis software.

RESULTS

The Smad1C-expressing tropism-modified Ad5 vector mediated a significantly higher level of alkaline phosphatase activity and calcium deposition in transduced rabbit BMSCs than all other vectors. The rabbit BMSCs transduced ex vivo with the Smad1C-expressing tropism-modified Ad5 vector mediated a greater amount of new bone formation than BMSCs transduced with any other vector.

CONCLUSIONS

Delivery of the Smad1C gene construct to BMSCs by an alphav integrin-targeted Ad5 vector shows promise for spinal fusion and other applications requiring the formation of new bone in vivo.

Expression of dog microdystrophin in mouse and dog muscles by gene therapy

Duchenne muscular dystrophy (DMD) is characterized by the absence of dystrophin. Several previous studies demonstrated the feasibility of delivering microdystrophin complementary DNA (cDNA) into mouse and normal nonhuman primate muscles by ex vivo gene therapy. However, these animal models do not reproduce completely the human DMD phenotype, while the dystrophic dog model does. To progress toward the use of the best animal model of DMD, a dog microdystrophin was transduced into human and dystrophic dog muscle precursor cells (MPCs) with a lentivirus before their transplantation into mouse muscles. One month following MPC transplantation, myofibers expressing the dog microdystrophin were observed. We also used another approach to introduce this transgene into myofibers, i.e., the electrotransfer of a plasmid coding for the dog microdystrophin. The plasmid was injected into mouse and dog muscles, and brief electric pulses were applied in the region of injection. Two weeks later, the transgene was detected in both animals. Therefore, ex vivo gene therapy and electrotransfer are two possible methods to introduce a truncated version of dystrophin into myofibers of animal models and eventually into myofibers of DMD patients.

Gene therapy for mesothelioma and lung cancer

Both malignant pleural mesothelioma and advanced stage lung cancer are associated with a poor prognosis. Unfortunately, current treatment regimens have had only a modest effect on their progressive course. Gene therapy for thoracic malignancies represents a novel therapeutic approach and has been evaluated in a number of clinical trials over the last two decades. Using viral vectors or anti-sense RNA, strategies have included induction of apoptosis, tumor suppressor gene replacement, suicide gene expression, cytokine-based therapy, various vaccination approaches, and adoptive transfer of modified immune cells. This review will consider the clinical results, limitations, and future directions of gene therapy trials for thoracic malignancies.

The non-essential left end region of the fowl adenovirus 9 genome is suitable for foreign gene insertion/replacement

The goals of this study were to demonstrate that a non-essential region at the left end of the fowl adenovirus 9 (FAdV-9) genome could be used to generate recombinant viruses, examine their in vitro growth characteristics and determine their ability to transduce non-avian cells. Three FAdV-9 vectors (rFAdV-9s) were generated carrying the enhanced-green fluorescent protein (EGFP) gene: FAdV-9inEGFP, FAdV-9 Delta 1-EGFP and FAdV-9 Delta 4-EGFP. FAdV-9inEGFP carried the EGFP cassette inserted into the non-essential region without deletion resulting in an increase of the genome size to 103.7% of the wild-type. FAdV-9 Delta 1-EGFP and FAdV-9 Delta 4-EGFP (rFAdV-9 Delta s) carried the EGFP cassette replacing the non-essential sequences at nucleotides 1194-2342 and 491-2782, respectively. All rFAdV-9s had wild-type growth kinetics and plaque morphology. The rFAdV-9 Delta s replicated in CH-SAH cells with the same titers as the wild-type virus. The FAdV-9inEGFP titers were approximately 1 log lower than those of rFAdV-9 Delta s and wt FAdV-9 at 36 and 48 h post-infection (h.p.i.). EGFP was expressed in avian and mammalian cells infected with rFAdV-9s. EGFP expression, based on spectrofluorometry, was significantly higher in chicken hepatoma cells infected with FAdV-9inEGFP than in those with rFAdV-9 Delta s at 18 and 24h.p.i, suggesting a functional role of some or all non-essential ORFs on foreign gene expression. This study demonstrated the suitability of the non-essential region as an insertion/replacement site for foreign genes to generate FAdV-9-based vectors that can be applied as recombinant vaccines for poultry or gene delivery vehicles for mammalian systems.

PEGylated Adenoviruses: From Mice to Monkeys

Covalent modification with polyethylene glycol (PEG), a non-toxic polymer used in food, cosmetic and pharmaceutical preparations for over 60 years, can profoundly influence the pharmacokinetic, pharmacologic and toxciologic profile of protein and peptide-based therapeutics. This review summarizes the history of PEGylation and PEG chemistry and highlights the value of this technology in the context of the design and development of recombinant viruses for gene transfer, vaccination and diagnostic purposes. Specific emphasis is placed on the application of this technology to the adenovirus, the most potent viral vector with the most highly characterized toxicity profile to date, in several animal models.

Targeted systemic gene therapy and molecular imaging of cancer contribution of the vascular-targeted AAVP vector

Gene therapy and molecular-genetic imaging have faced a major problem: the lack of an efficient systemic gene delivery vector. Unquestionably, eukaryotic viruses have been the vectors of choice for gene delivery to mammalian cells; however, they have had limited success in systemic gene therapy. This is mainly due to undesired uptake by the liver and reticuloendothelial system, broad tropism for mammalian cells causing toxicity, and their immunogenicity. On the other hand, prokaryotic viruses such as bacteriophage (phage) have no tropism for mammalian cells, but can be engineered to deliver genes to these cells. However, phage-based vectors have inherently been considered poor vectors for mammalian cells. We have reported a new generation of vascular-targeted systemic hybrid prokaryotic-eukaryotic vectors as chimeras between an adeno-associated virus (AAV) and targeted bacteriophage (termed AAV/phage; AAVP). In this hybrid vector, the targeted bacteriophage serves as a shuttle to deliver the AAV transgene cassette inserted in an intergenomic region of the phage DNA genome. As a proof of concept, we assessed the in vivo efficacy of vector in animal models of cancer by displaying on the phage capsid the cyclic Arg-Gly-Asp (RGD-4C) ligand that binds to alphav integrin receptors specifically expressed on the angiogenic blood vessels of tumors. The ligand-directed vector was able to specifically deliver imaging and therapeutic transgenes to tumors in mice, rats, and dogs while sparing the normal organs. This chapter reviews some gene transfer strategies and the potential of the vascular-targeted AAVP vector for enhancing the effectiveness of existing systemic gene delivery and genetic-imaging technologies.

Long-term virus-induced alterations of CYP3A-mediated drug metabolism: a look at the virology, immunology and molecular biology of a multi-faceted problem

Virus infections are on the rise. Although the first description of CYP expression during virus infection was recorded 50 years ago, mechanistic studies of this phenomenon only began to appear in the last decade due to breakthroughs in molecular biology, genomic and transgenic technology. This review describes the relationship(s) among CYP-mediated drug metabolism, virus infection and the immune response and evaluates in vitro and in vivo models for mechanistic studies. The first studies that assessed CYP expression during infection focused on inflammatory mediators and the innate immune response at early time points. Recent studies assessing virus infection and its effect on hepatic CYP expression noted more long-term effects. An obvious approach toward understanding how viruses affect hepatic CYP3A expression and function would be to assess key regulators of CYP during infection. Improvements in techniques to identify post-translational modifications of CYP and systems that focus on virus-receptor interactions which allow subtraction and addition of immunological and regulatory elements that drive CYP will demonstrate that long-term changes in drug metabolism start from the time the virus enters the circulation, are reinforced by virus binding to cellular targets and further solidified by changes in cellular processes long after the virus is cleared.

PDGF-B gene therapy accelerates bone engineering and oral implant osseointegration

Platelet-derived growth factor-BB (PDGF-BB) stimulates repair of healing-impaired chronic wounds such as diabetic ulcers and periodontal lesions. However, limitations in predictability of tissue regeneration occur due in part to transient growth factor bioavailability in vivo. Here, we report that gene delivery of PDGF-B stimulates repair of oral implant extraction socket defects. Alveolar ridge defects were created in rats and were treated at the time of titanium implant installation with a collagen matrix containing an adenoviral (Ad) vector encoding PDGF-B (5.5×10⁸ or 5.5×10⁹ pfu/ml), Ad encoding luciferase (Ad-Luc; 5.5×10⁹ pfu/ml; control) or recombinant human PDGF-BB protein (rhPDGF-BB, 0.3 mg/ml). Bone repair and osseointegration were measured via backscattered SEM, histomorphometry, microcomputed tomography, and biomechanical assessments. Further, a panel of local and systemic safety assessments was performed. Results demonstrated bone repair was accelerated by Ad-PDGF-B and rhPDGF-BB delivery compared to Ad-Luc, with the high dose of Ad-PDGF-B more effective than the low dose. No significant dissemination of the vector construct or alteration of systemic parameters was noted. In summary, gene delivery of Ad-PDGF-B demonstrates regenerative and safety capabilities for bone tissue engineering and osseointegration in alveolar bone defects comparable to rhPDGF-BB protein delivery in vivo.

Safety studies on an adenovirus recombinant vaccine for rabies (AdRG1.3-ONRAB) in target and non-target species

A replication-competent human adenovirus vector in which the rabies virus glycoprotein gene was inserted (AdRG1.3-ONRAB) was given by direct instillation into the oral cavity to representatives of three wildlife vector species of concern in Ontario (red fox, raccoon and striped skunk) and to a variety of non-target wildlife species, domestic and laboratory species. Despite use of a relatively high dose of vaccine, no untoward clinical signs were observed. Subsequent to vaccine exposure, detection of vaccine virus in lung, spleen, intestine, liver, kidney and brain of each animal was attempted using an ONRAB-specific assay combining PCR with Southern blotting (PCR-SB). Of the 1280 tissue samples obtained from vaccinates or contact animals, 18 (1.4%) were found to be PCR-SB positive. Virus isolation attempts were performed utilizing cell culture for all PCR-SB positive tissues and a selection of PCR-SB negative tissues. Histological examination performed on all PCR-SB positive tissues failed to identify lesions attributed to the vaccine. A quantitative real-time PCR was used to determine the excretion of the vaccine in feces and in the oral cavity with 0.8% of oral swabs and 6.8% of fecal specimens found to be positive. The low rates of recovery of vaccine virus from tissues, feces and the oral cavity suggest that the likelihood of ONRAB causing a negative impact on wildlife species is unlikely.

Gene- and viral-based therapies for brain tumors

Advances in understanding and controlling genes and their expression have set the stage to alter genetic material to fight or prevent disease with brain tumors being among one of the first human malignancies to be targeted by gene therapy. All proteins are coded for by DNA and most neoplastic diseases ultimately result from the expression or lack thereof with one or more proteins (e.g., coded by oncogenes or tumor suppressor genes, respectively). In theory, therefore, diseases could be treated by expression of the appropriate protein in the affected cells. Gene therapy is an experimental treatment that involves introducing genetic material (DNA or RNA) into cells, and it has made important advances in the past decade. Within this short time span, it has moved from the conceptual laboratory research stage to clinical translational trials for brain tumors. The most efficient approaches for gene delivery are based on viral vectors, which have been proven relatively safe in the CNS, despite occasional cases of morbidity and death in non-neurosurgical trials. However, the human response to various viral vectors can not be predicted in a reliable manner from animal experimentation, nor can size, consistency, and extent of experimental brain tumors in mouse models reflect the large, necrotic, infiltrative nature of malignant gliomas. Furthermore, the problem of delivering genetic vectors into solid brain tumors and the efficiency in situ gene transfer remains one of the most significant hurdles in gene therapy.

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.

Recombinant Sendai Virus-Mediated Gene Transfer to Mouse Pancreatic Stem Cells

Efficient gene transfer into stem cells is essential for the basic research and for therapeutic applications in gene-modified regenerative medicine. Adenovirus (AdV) vectors, one of the most commonly used types of vectors, can mediate high, albeit transient, levels of expression of the transgene in pancreatic stem/progenitor cells. However, high multiplicity of infection (MOI) with AdV vectors can result in cellular toxicity. Therefore, AdV vectors have been of limited usefulness in clinical applications. In this study, we investigated the in vitro gene transfer efficiency of Sendai virus (SeV) vectors, a paramyxovirus vector that can efficiently introduce foreign genes without toxicity into several cell types, including pancreatic stem cells. The dose-dependent GFP expression of pancreatic stem cells transfected with SeV vectors after 48 h of culture at 37°C was observed. The transfection of pancreatic stem cells with SeV vectors and AdV vectors results in equal expression of the transgene (GFP expression) in the cells after 48 h of culture at 37°C. Although the transfection of pancreatic stem cells with AdV vectors at high MOIs was cytotoxic, transfection with SeV vectors at high MOIs was rarely cytotoxic. In addition, pancreatic stem cells transfected with SeV maintained their differentiation ability. These data suggest that SeV could provide advantages with respect to safety issues in gene-modified regenerative medicine.

Adenoviral vector-based strategies for cancer therapy

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

Hybrid of baculovirus and galactosylated PEI for efficient gene carrier

Baculovirus, containing an appropriate eukaryotic promoter, is considered an attractive approach for an efficient and safe gene delivery vehicle. However, the drawbacks of baculovirus, such as the lack of specificity and the inactivation of baculovirus by the complement system in human serum, negatively affect efficient gene delivery. Therefore, a hybrid system utilizing the positive aspects of both viral and non-viral vector systems would be useful to overcome the obstacles of either system alone. In this study, we constructed a hybrid system composed of baculovirus (B) and galactosylated polyethylenimine (GP)/DNA complexes through electrostatic interaction. The resulting GP/B hybrid had suitable physicochemical properties and low cytotoxicity for use in gene therapy. Furthermore, the GP/B significantly enhanced transduction efficiency and showed good cell-specificity compared to either viral or non-viral vector systems. These results suggest that the GP/B hybrid system can be used in gene therapy to enhance transduction efficiency and hepatocyte specificity.

Adenovirus receptors and their implications in gene delivery

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

Novel markers for enterochromaffin cells and gastrointestinal neuroendocrine carcinomas

The gene expression profile of metastasizing serotonin-producing neuroendocrine carcinomas, which arise from enterochromaffin cells in the jejunum and ileum, is still largely unknown. The aim of this study was to identify genes and proteins, which are preferentially expressed by neuroendocrine carcinoma and enterochromaffin cells and therefore potential novel biomarkers and/or therapeutic targets. Six carcinoma specimens and six normal ileal mucosas were profiled by Affymetrix microarrays. Advanced bioinformatics identified differentially and specifically expressed genes, which were validated by quantitative real-time-PCR on tumor cells extracted by laser capture microdissection and normal enterochromaffin cells extracted by immunolaser capture microdissection. We identified six novel marker genes for neuroendocrine carcinoma cells: paraneoplastic antigen Ma2 (PNMA2), testican-1 precursor (SPOCK1), serpin A10 (SERPINA10), glutamate receptor ionotropic AMPA 2 (GRIA2), G protein-coupled receptor 112 (GPR112) and olfactory receptor family 51 subfamily E member 1 (OR51E1). GRIA2 is specifically expressed by neuroendocrine carcinoma cells whereas the others are also expressed by normal enterochromaffin cells. GPR112 and OR51E1 encode proteins associated with the plasma membrane and may therefore become targets for antibody-based diagnosis and therapy. Hierarchical clustering shows high similarity between primary lesions and liver metastases. However, chemokine C-X-C motif ligand 14 (CXCL14) and NK2 transcription factor related locus 3 Drosophila (NKX2-3) are expressed to a lower level in liver metastases than in primary tumors and normal enterochromaffin cells, which implies a role in neuroendocrine carcinoma differentiation. In conclusion, this study provides a list of genes, which possess relatively specific expression to enterochromaffin and neuroendocrine carcinoma cells and genes with differential expression between primary tumors and metastases. We verified six novel marker genes that may be developed as biomarkers and/or therapeutic targets.

Gene transfer into guinea pig cochlea using adeno-associated virus vectors

BACKGROUND

Several genes are candidates for treating inner ear diseases. For clinical applications, minimally invasive approaches to the inner ear are desirable along with minimal side-effects.

METHODS

Adeno-associated virus (AAV) was used as a vector into the guinea pig inner ear. Six AAV-cytomegalovirus hybrids (AAV-2/1, -2/2, -2/5, -2/7, -2/8 and -2/9) were infused into perilymph of the cochlea basal turn, an approach that could be used in cochlear implant surgery. At 7 days after injection, distribution of gene expression, hearing and morphology were evaluated. Adenoviral vector was also used to compare distributions of gene expression. Moreover, distribution of cell surface receptors of AAV in the cochlea was examined using immunohistochemistry.

RESULTS

Using the perilymphatic approach, adenovirus could be transferred to mesothelial cells lining the perilymph, but not sensory cells. Conversely, all AAV serotypes displayed tissue tropism to inner hair cells, with AAV-2/2 showing particularly efficient transfer to sensory cells. This tissue tropism of AAV could not be explained by the distribution of AAV receptors. Hearing and morphology were largely unaffected.

CONCLUSIONS

Our results indicate that AAV vector can be safely applied to the inner ear and AAV-2/2 offers a good tool for transferring transgenes into sensory cells of the inner ear efficiently without toxicity.

Molecular and macromolecular alterations of recombinant adenoviral vectors do not resolve changes in hepatic drug metabolism during infection

In this report we test the hypothesis that long-term virus-induced alterations in CYP occur from changes initiated by the virus that may not be related to the immune response. Enzyme activity, protein expression and mRNA of CYP3A2, a correlate of human CYP3A4, and CYP2C11, responsive to inflammatory mediators, were assessed 0.25, 1, 4, and 14 days after administration of several different recombinant adenoviruses at a dose of 5.7 × 10¹² virus particles (vp)/kg to male Sprague Dawley rats. Wild type adenovirus, containing all viral genes, suppressed CYP3A2 and 2C11 activity by 37% and 39%, respectively within six hours. Levels fell to 67% (CYP3A2) and 79% (CYP2C11) of control by 14 days (p ≤ 0.01). Helper-dependent adenovirus, with all viral genes removed, suppressed CYP3A2 (43%) and CYP2C11 (55%) within six hours. CYP3A2 remained significantly suppressed (47%, 14 days, p ≤ 0.01) while CYP2C11 returned to baseline at this time. CYP3A2 and 2C11 were reduced by 45 and 42% respectively 6 hours after treatment with PEGylated adenovirus, which has a low immunological profile (p ≤ 0.05). CYP3A2 remained suppressed (34%, p ≤ 0.05) for 14 days while CYP2C11 recovered. Inactivated virus suppressed CYP3A2 activity by 25–50% for 14 days (p ≤ 0.05). CYP2C11 was affected similar manner but recovered by day 14. Microarray and in vitro studies suggest that changes in cellular signaling pathways initiated early in virus infection contribute to changes in CYP.

Cryoelectron microscopy map of Atadenovirus reveals cross-genus structural differences from human adenovirus

A three-dimensional (3D) cryoelectron microscopy reconstruction of the prototype Atadenovirus (OAdV [an ovine adenovirus isolate]) showing information at a 10.6-A resolution (0.5 Fourier shell correlation) was derived by single-particle analysis. This is the first 3D structure solved for any adenovirus that is not a Mastadenovirus, allowing cross-genus comparisons between structures and the assignment of genus-specific capsid proteins. Viable OAdV mutants that lacked the genus-specific LH3 and p32k proteins in purified virions were also generated. Negatively stained 3D reconstructions of these mutants were used to identify the location of protein LH3 and infer that of p32k within the capsid. The key finding was that LH3 is a critical protein that holds the outer capsid of the virus together. In its absence, the outer viral capsid is unstable. LH3 is located in the same position among the hexon subunits as its protein IX equivalent from mastadenoviruses but sits on top of the hexon trimers, forming prominent "knobs" on the virion surface that visually distinguish OAdV from other known AdVs. Electron density was also assigned to hexon and penton subunits and to proteins IIIa and VIII. There was good correspondence between OAdV density and human AdV hexon structures, which also validated the significant differences that were observed between the penton base protein structures.

New therapies for Duchenne muscular dystrophy: challenges, prospects and clinical trials

Muscular dystrophies primarily affect skeletal muscle. Mutations in a large number of genes, mainly encoding cytoskeletal proteins, cause different forms of dystrophy that compromise patient mobility and quality of life, and in the most severe cases lead to complete paralysis and premature death. Although muscular dystrophies still lack an effective therapy, several novel strategies are entering or are ready to enter clinical trials. Here we review the main experimental strategies, namely drug, gene and cell therapies, outlining their goals and limitations. We also provide an update of ongoing or planned clinical trials based on these strategies.