Human adenovirus type 35 vector for gene therapy of brain cancer: improved transduction and bypass of pre-existing anti-vector immunity in cancer patients

Significance of Preexisting Vector Immunity and Activation of Innate Responses for Adenoviral Vector-Based Therapy

An adenoviral (AdV)-based vector system is a promising platform for vaccine development and gene therapy applications. Administration of an AdV vector elicits robust innate immunity, leading to the development of humoral and cellular immune responses against the vector and the transgene antigen, if applicable. The use of high doses (10¹¹-10¹³ virus particles) of an AdV vector, especially for gene therapy applications, could lead to vector toxicity due to excessive levels of innate immune responses, vector interactions with blood factors, or high levels of vector transduction in the liver and spleen. Additionally, the high prevalence of AdV infections in humans or the first inoculation with the AdV vector result in the development of vector-specific immune responses, popularly known as preexisting vector immunity. It significantly reduces the vector efficiency following the use of an AdV vector that is prone to preexisting vector immunity. Several approaches have been developed to overcome this problem. The utilization of rare human AdV types or nonhuman AdVs is the primary strategy to evade preexisting vector immunity. The use of heterologous viral vectors, capsid modification, and vector encapsulation are alternative methods to evade vector immunity. The vectors can be optimized for clinical applications with comprehensive knowledge of AdV vector immunity, toxicity, and circumvention strategies.

Brain Cancer Treatment; A Systematic Review

Context: One of the most common aggressive and primary brain tumors is glioma. The majority of diagnoses are referred to high-grade malignant glioblastoma, which carries the worst prognosis. Still, treatment of brain tumors remains a big challenge for clinicians. This study was designed to investigate the efficacy of gene therapy in the treatment of brain cancer. Methods: Studies use genes as a therapeutic agent in brain cancer treatment even alone or in combination with other treatment methods. Full-text papers, which met the inclusion criteria, were independently assessed by two reviewers. Disagreements were resolved by consultation with a third reviewer. Results: Statistical analysis showed that 50% of the papers used a virus, 36% used polymers, and 14% used cells as carriers to transfect the genes as a therapeutic agent in brain tumor models. Data showed that the estimated size of the brain tumor was reduced by using co-treatment of the gene with one of the conventional therapies. Conclusions: According to the results, co-treatment of the gene with conventional therapies could be more effective than the monotherapy methods.

Superior infectivity of the fiber chimeric oncolytic adenoviruses Ad5/35 and Ad5/3 over Ad5-delta-24-RGD in primary glioma cultures

Ad5-delta-24-RGD is currently the most clinically advanced recombinant adenovirus (rAd) for glioma therapy. We constructed a panel of fiber-modified rAds (Ad5RGD, Ad5/3, Ad5/35, Ad5/3RGD, and Ad5/35RGD, all harboring the delta-24 modification) and compared their infectivity, replication, reproduction, and cytolytic efficacy in human and rodent glioma cell lines and short-term cultures from primary gliomas. In human cells, both Ad5/35-delta-24 and Ad5/3-delta-24 displayed superior infectivity and cytolytic efficacy over Ad5-delta-24-RGD, while Ad5/3-delta-24-RGD and Ad5/35-delta-24-RGD did not show further improvements in efficacy. The expression of the adenoviral receptors/coreceptors CAR, DSG2, and CD46 and the integrins αVβ3/αVβ5 did not predict the relative cytolytic efficacy of the fiber-modified rAds. The cytotoxicity of the fiber-modified rAds in human primary normal cultures of different origins and in primary glioma cultures was comparable, indicating that the delta-24 modification did not confer tumor cell selectivity. We also revealed that CT-2A and GL261 glioma cells might be used as murine cell models for the fiber chimeric rAds in vitro and in vivo. In GL261 tumor-bearing mice, Ad5/35-delta-24, armed with the immune costimulator OX40L as the E2A/DBP-p2A-mOX40L fusion, produced long-term survivors, which were able to reject tumor cells upon rechallenge. Our data underscore the potential of local Ad5/35-delta-24-based immunovirotherapy for glioblastoma treatment.

Nonreplicating Adenoviral Vectors: Improving Tropism and Delivery of Cancer Gene Therapy

Recent preclinical and clinical studies have used viral vectors in gene therapy research, especially nonreplicating adenovirus encoding strategic therapeutic genes for cancer treatment. Adenoviruses were the first DNA viruses to go into therapeutic development, mainly due to well-known biological features: stability in vivo, ease of manufacture, and efficient gene delivery to dividing and nondividing cells. However, there are some limitations for gene therapy using adenoviral vectors, such as nonspecific transduction of normal cells and liver sequestration and neutralization by antibodies, especially when administered systemically. On the other hand, adenoviral vectors are amenable to strategies for the modification of their biological structures, including genetic manipulation of viral proteins, pseudotyping, and conjugation with polymers or biological membranes. Such modifications provide greater specificity to the target cell and better safety in systemic administration; thus, a reduction of antiviral host responses would favor the use of adenoviral vectors in cancer immunotherapy. In this review, we describe the structural and molecular features of nonreplicating adenoviral vectors, the current limitations to their use, and strategies to modify adenoviral tropism, highlighting the approaches that may allow for the systemic administration of gene therapy.

Efficient antitumor effects of a novel oncolytic adenovirus fully composed of species B adenovirus serotype 35

Oncolytic adenoviruses (OAds) are among the most promising oncolytic viruses. Almost all oncolytic adenoviruses are composed of human adenovirus serotype 5 (Ad5) (OAd5). However, expression of the primary infection receptor for Ad5, coxsackievirus-adenovirus receptor (CAR), often declines on malignant tumor cells, resulting in inefficient infection in CAR-negative tumor cells. In addition, at least 80% of adults have neutralizing antibodies against Ad5. In this study, we developed a novel OAd fully composed of OAd35. OAd35 recognizes CD46, which is ubiquitously expressed on almost all human cells and is often upregulated on malignant tumor cells, as an infection receptor. Moreover, 20% or fewer adults have neutralizing antibodies against Ad35. OAd35 mediated efficient cell lysis activities at levels similar to OAd5 in CAR-positive tumor cells, while OAd35 showed higher levels of cell lysis activities than OAd5 in CAR-negative tumor cells. Anti-Ad5 serum significantly inhibited in vitro tumor cell lysis activities of OAd5, whereas OAd35 exhibited comparable levels of in vitro tumor cell lysis activities in the presence of anti-Ad5 and naive serum. OAd35 significantly suppressed growth of the subcutaneous CAR-positive and CAR-negative tumors following intratumoral administration. These results indicated that OAd35 is a promising alternative oncolytic virus for OAd5.

Immunohistochemical Characterization and Sensitivity to Human Adenovirus Serotypes 3, 5, and 11p of New Cell Lines Derived from Human Diffuse Grade II to IV Gliomas

BACKGROUND

Oncolytic adenoviruses show promise in targeting gliomas because they do not replicate in normal brain cells. However, clinical responses occur only in a subset of patients. One explanation could be the heterogenic expression level of virus receptors. Another contributing factor could be variable activity of tumor antiviral defenses in different glioma subtypes.

METHODS

We established a collection of primary low-passage cell lines from different glioma subtypes (3 glioblastomas, 3 oligoastrocytomas, and 2 oligodendrogliomas) and assessed them for receptor expression and sensitivity to human adenovirus (HAd) serotypes 3, 5, and 11p. To gauge the impact of antiviral defenses, we also compared the infectivity of the oncolytic adenoviruses in interferon (IFN)-pretreated cells with IFN-sensitive Semliki Forest virus (SFV).

RESULTS

Immunostaining revealed generally low expression of HAd5 receptor CAR in both primary tumors and derived cell lines. HAd11p receptor CD46 levels were maintained at moderate levels in both primary tumor samples and derived cell lines. HAd3 receptor DSG-2 was reduced in the cell lines compared to the tumors. Yet, at equal multiplicities of infection, the oncolytic potency of HAd5 in vitro in tumor-derived cells was comparable to HAd11p, whereas HAd3 lysed fewer cells than either of the other two HAd serotypes in 72 hours. IFN blocked replication of SFV, while HAds were rather unaffected.

CONCLUSIONS

Adenovirus receptor levels on glioma-derived cell lines did not correlate with infection efficacy and may not be a relevant indicator of clinical oncolytic potency. Adenovirus receptor analysis should be preferentially performed on biopsies obtained perioperatively.

Viruses and Virus-Like Particles in Biotechnology: Fundamentals and Applications

Although viruses are simple biological systems, they are capable of evolving highly efficient techniques for infecting cells, expressing their genomes, and generating new copies of themselves. It is possible to genetically manipulate most of the different classes of known viruses in order to produce recombinant viruses that express foreign proteins. Recombinant viruses have been used in gene therapy to deliver selected genes into higher organisms, in vaccinology and immunotherapy, and as important research tools to study the structure and function of these proteins.

Virus-like particles (VLPs) are multiprotein structures that mimic the organization and conformation of authentic native viruses but lack the viral genome. They have been applied not only as prophylactic and therapeutic vaccines but also as vehicles in drug and gene delivery and, more recently, as tools in nanobiotechnology.

In this chapter, basic and advanced features of viruses and VLPs are presented and their major applications are discussed. The different production platforms based on animal cell technology are explained, and their main challenges and future perspectives are explored. The implications of large-scale production of viruses and VLPs are discussed in the context of process control, monitoring, and optimization. The main upstream and downstream technical challenges are identified and discussed accordingly.

A vesicular stomatitis virus glycoprotein epitope-incorporated oncolytic adenovirus overcomes CAR-dependency and shows markedly enhanced cancer cell killing and suppression of tumor growth

Utility of traditional oncolytic adenovirus (Ad) has been limited due to low expression of coxsackie and adenovirus receptor (CAR) in cancer cells which results in poor infectivity of Ads. Here with an aim of improving the efficiency of Ad's entry to the cell, we generated a novel tropism-expanded oncolytic Ad which contains the epitope of vesicular stomatitis virus glycoprotein (VSVG) at the HI-loop of Ad fiber. We generated 9 variants of oncolytic Ads with varying linkers and partial deletion to the fiber. Only one VSVG epitope-incorporated variant, RdB-1L-VSVG, which contains 1 linker and no deletion to fiber, was produced efficiently. Production of 3-dimensionaly stable fiber in RdB-1L-VSVG was confirmed by immunoblot analysis. RdB-1L-VSVG shows a remarkable improvement in cytotoxicity and total viral yield in cancer cells. RdB-1L-VSVG demonstrates enhanced cytotoxicity in cancer cells with subdued CAR-expression as it can be internalized by an alternate pathway. Competition assays with a CAR-specific antibody (Ab) or VSVG receptor, phosphatidyl serine (PS), reveals that cell internalization of RdB-1L-VSVG is mediated by both CAR and PS. Furthermore, treatment with RdB-1L-VSVG significantly enhanced anti-tumor effect in vivo. These studies demonstrate that the strategy to expand oncolytic Ad tropism may significantly improve therapeutic profile for cancer treatment.

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

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

MT1-MMP silencing by an shRNA-armed glioma-targeted conditionally replicative adenovirus (CRAd) improves its anti-glioma efficacy in vitro and in vivo

MMP14 (MT1-MMP) is a cell membrane-associated proteinase of the extracellular matrix, whose biological roles vary from angiogenesis to cell proliferation and survival. We recently found a direct correlation between MMP14 expression levels in brain tumors of glioma patients and the disease progression. By using gene silencing as an experimental approach we found that MMP14 knockdown decreases production of pro-angiogenic factors such as VEGF and IL8 and thereby suppresses angiogenesis in glioma tumors. Although the clinical relevance of MMP14 down-regulation and its possible implications for glioma therapy in humans remain unclear, we observed a significant improvement in animal survival upon down-regulation of MMP14 in murine intracranial glioma xenografts infected with MMP14 shRNA-expressing CRAd. We further found that down-regulation of MMP14 in gliomas by combinational treatment with CRAd-S-5/3 and Marimastat, a chemical inhibitor of metalloproteinases, augments suppression of pro-angiogenic factors, caused by the replication-competent adenovirus. We also demonstrated that delivery of MMP14-targeting shRNA by a fiber-modified adenoviral vector to the glioma cells effectively suppresses their proliferation in vitro and in vivo. Thus our data indicate that inhibition of MMP14 expression in tumors in combination with glioma virotherapy could be effectively utilized to suppress angiogenesis and neovascularization of glioma tumors by decreasing production of pro-angiogenic factors.

EXPLORING THE ANTITUMOR EFFECT OF VIRUS IN MALIGNANT GLIOMA

Malignant gliomas are the most common type of primary malignant brain tumor with no effective treatments. Current conventional therapies (surgical resection, radiation therapy, temozolomide (TMZ), and bevacizumab administration) typically fail to eradicate the tumors resulting in the recurrence of treatment-resistant tumors. Therefore, novel approaches are needed to improve therapeutic outcomes. Oncolytic viruses (OVs) are excellent candidates as a more effective therapeutic strategy for aggressive cancers like malignant gliomas since OVs have a natural preference or have been genetically engineered to selectively replicate in and kill cancer cells. OVs have been used in numerous preclinical studies in malignant glioma, and a large number of clinical trials using OVs have been completed or are underway that have demonstrated safety, as well as provided indications of effective antiglioma activity. In this review, we will focus on those OVs that have been used in clinical trials for the treatment of malignant gliomas (herpes simplex virus, adenovirus, parvovirus, reovirus, poliovirus, Newcastle disease virus, measles virus, and retrovirus) and OVs examined preclinically (vesicular stomatitis virus and myxoma virus), and describe how these agents are being used.

Changing faces in virology: the dutch shift from oncogenic to oncolytic viruses

Viruses have two opposing faces. On the one hand, they can cause harm and disease. A virus may manifest directly as a contagious disease with a clinical pathology of varying significance. A viral infection can also have delayed consequences, and in rare cases may cause cellular transformation and cancer. On the other hand, viruses may provide hope: hope for an efficacious treatment of serious disease. Examples of the latter are the use of viruses as a vaccine, as transfer vector for therapeutic genes in a gene therapy setting, or, more directly, as therapeutic anticancer agent in an oncolytic-virus therapy setting. Already there is evidence for antitumor activity of oncolytic viruses. The antitumor efficacy seems linked to their capacity to induce a tumor-directed immune response. Here, we will provide an overview on the development of oncolytic viruses and their clinical evaluation from the Dutch perspective.

A genetic fiber modification to achieve matrix-metalloprotease-activated infectivity of oncolytic adenovirus

Selective tumor targeting of oncolytic adenovirus at the level of cell entry remains a major challenge to improve efficacy and safety. Matrix metalloproteases (MMPs) are overexpressed in a variety of tumors and in particular in pancreatic cancer. In the current work, we have exploited the expression of MMPs together with the penetration capabilities of a TAT-like peptide to engineer tumor selective adenoviruses. We have generated adenoviruses containing CAR-binding ablated fibers further modified with a C-terminus TAT-like peptide linked to a blocking domain by an MMP-cleavable sequence. This linker resulted in a MMP-dependent cell transduction of the reporter MMP-activatable virus AdTATMMP and in efficient transduction of neoplastic cells and cancer-associated fibroblasts. Intravenous and intraductal administration of AdTATMMP into mice showed very low AdTATMMP activity in the normal pancreas, whereas increased transduction was observed in pancreatic tumors of transgenic Ela-myc mice. Intraductal administration of AdTATMMP into mice bearing orthotopic tumors led to a 25-fold increase in tumor targeting compared to the wild type fiber control. A replication competent adenovirus, Ad(RC)MMP, with the MMP-activatable fiber showed oncolytic efficacy and increased antitumor activity compared to Adwt in a pancreatic orthotopic model. Reduced local and distant metastases were observed in Ad(RC)MMP treated-mice. Moreover, no signs of pancreatic toxicity were detected. We conclude that MMP-activatable adenovirus may be beneficial for pancreatic cancer treatment.

Peptide-based technologies to alter adenoviral vector tropism: ways and means for systemic treatment of cancer

Due to the fundamental progress in elucidating the molecular mechanisms of human diseases and the arrival of the post-genomic era, increasing numbers of therapeutic genes and cellular targets are available for gene therapy. Meanwhile, the most important challenge is to develop gene delivery vectors with high efficiency through target cell selectivity, in particular under in situ conditions. The most widely used vector system to transduce cells is based on adenovirus (Ad). Recent endeavors in the development of selective Ad vectors that target cells or tissues of interest and spare the alteration of all others have focused on the modification of the virus broad natural tropism. A popular way of Ad targeting is achieved by directing the vector towards distinct cellular receptors. Redirecting can be accomplished by linking custom-made peptides with specific affinity to cellular surface proteins via genetic integration, chemical coupling or bridging with dual-specific adapter molecules. Ideally, targeted vectors are incapable of entering cells via their native receptors. Such altered vectors offer new opportunities to delineate functional genomics in a natural environment and may enable efficient systemic therapeutic approaches. This review provides a summary of current state-of-the-art techniques to specifically target adenovirus-based gene delivery vectors.

Circumventing antivector immunity: potential use of nonhuman adenoviral vectors

Adenoviruses are efficient gene delivery vectors based on their ability to transduce a wide variety of cell types and drive high-level transient transgene expression. While there have been advances in modifying human adenoviral (HAdV) vectors to increase their safety profile, there are still pitfalls that need to be further addressed. Preexisting humoral and cellular immunity against common HAdV serotypes limits the efficacy of gene transfer and duration of transgene expression. As an alternative, nonhuman AdV (NHAdV) vectors can circumvent neutralizing antibodies against HAdVs in immunized mice and monkeys and in human sera, suggesting that NHAdV vectors could circumvent preexisting humoral immunity against HAdVs in a clinical setting. Consequently, there has been an increased interest in developing NHAdV vectors for gene delivery in humans. In this review, we outline the recent advances and limitations of HAdV vectors for gene therapy and describe examples of NHAdV vectors focusing on their immunogenicity, tropism, and potential as effective gene therapy vehicles.

Enhanced antitumor immunotherapeutic effect of B-cell-based vaccine transduced with modified adenoviral vector containing type 35 fiber structures

For successful clinical tumor immunotherapy outcomes, strong immune responses against tumor antigens must be generated. Cell-based vaccines compromise one strategy with which to induce appropriate strong immune responses. Previously, we established a natural killer T-cell (NKT) ligand-loaded, adenoviral vector-transduced B-cell-based anticancer cellular vaccine. To enhance tumor antigen delivery to B cells, we established a modified adenoviral vector (Ad-k35) that encoded a truncated form of the breast cancer antigen Her2/neu (Ad-k35HM) in which fiber structure was substituted with adenovirus serotype 35. We observed increased tumor antigen expression with Ad-k35HM in both human and murine B cells. In addition, an Ad-k35HM-transduced B-cell vaccine elicited strong antigen-specific cellular and humoral immune responses that were further enhanced with the additional loading of soluble NKT ligand KBC009. An Ad-k35HM-transduced, KBC009-loaded B-cell vaccine efficiently suppressed the in vivo growth of established tumors in a mouse model. Moreover, the vaccine elicited human leukocyte antigen (HLA)-A2 epitope-specific cytotoxic T-cell responses in B6.Cg (CB)-Tg (HLA-A/H2-D) 2Enge/Jat mice. These findings indicated that the Ad-k35 could be appropriate for the preclinical and clinical development of B-cell-based anticancer immunotherapies.

Current status of gene therapy for brain tumors

Glioblastoma (GBM) is the most common and deadliest primary brain tumor in adults, with current treatments having limited impact on disease progression. Therefore the development of alternative treatment options is greatly needed. Gene therapy is a treatment strategy that relies on the delivery of genetic material, usually transgenes or viruses, into cells for therapeutic purposes, and has been applied to GBM with increasing promise. We have included selectively replication-competent oncolytic viruses within this strategy, although the virus acts directly as a complex biologic anti-tumor agent rather than as a classic gene delivery vehicle. GBM is a good candidate for gene therapy because tumors remain locally within the brain and only rarely metastasize to other tissues; the majority of cells in the brain are post-mitotic, which allows for specific targeting of dividing tumor cells; and tumors can often be accessed neurosurgically for administration of therapy. Delivery vehicles used for brain tumors include nonreplicating viral vectors, normal adult stem/progenitor cells, and oncolytic viruses. The therapeutic transgenes or viruses are typically cytotoxic or express prodrug activating suicide genes to kill glioma cells, immunostimulatory to induce or amplify anti-tumor immune responses, and/or modify the tumor microenvironment such as blocking angiogenesis. This review describes current preclinical and clinical gene therapy strategies for the treatment of glioma.

Adenovirus serotype 5 vectors with Tat-PTD modified hexon and serotype 35 fiber show greatly enhanced transduction capacity of primary cell cultures

Recombinant adenovirus serotype 5 (Ad5) vectors represent one of the most efficient gene delivery vectors in life sciences. However, Ad5 is dependent on expression of the coxsackievirus-adenovirus-receptor (CAR) on the surface of target cell for efficient transduction, which limits it’s utility for certain cell types. Herein we present a new vector, Ad5PTDf35, which is an Ad5 vector having serotype 35 fiber-specificity and Tat-PTD hexon-modification. This vector shows dramatically increased transduction capacity of primary human cell cultures including T cells, monocytes, macrophages, dendritic cells, pancreatic islets and exocrine cells, mesenchymal stem cells and tumor initiating cells. Biodistribution in mice following systemic administration (tail-vein injection) show significantly reduced uptake in the liver and spleen of Ad5PTDf35 compared to unmodified Ad5. Therefore, replication-competent viruses with these modifications may be further developed as oncolytic agents for cancer therapy. User-friendly backbone plasmids containing these modifications were developed for compatibility to the AdEasy-system to facilitate the development of surface-modified adenoviruses for gene delivery to difficult-to-transduce cells in basic, pre-clinical and clinical research.

A novel Ad5/11 chimeric oncolytic adenovirus for improved glioma therapy

Effective therapies are needed for malignant glioma patients because of the poor prognosis. Gene therapy combined with virotherapy could be the strategy of choice. In this study, we constructed a modified conditionally replicating adenoviral vector CRAd5/11-Sp-eGFP. The novel vector has the following features: i) the transduction efficiency of CRAd5 was increased using a chimeric fiber 5/11 consisting of an Ad5 tail and an Ad11 shaft and knob; ii) the tumor-specific replication of the vector was improved by utilizing the human survivin promoter to control E1 expression and a poly-A signal inserted right after the inverted terminal repeat (ITR) to stop the non-specific transcriptional activity of the ITR; iii) an expression cassette was inserted into the region between the fiber and E4 region for expressing eGFP. In vitro assays demonstrated that the novel vector could efficiently replicate and kill human glioma cells. Furthermore, CRAd5/11‑Sp-eGFP exhibited significantly increased antitumor effects compared with the control adenoviruses in a xenograft model of glioma. Our results indicate that CRAd5/11-Sp-eGFP represents a promising candidate drug in the treatment of malignant gliomas.

Chapter six--Adenovirus-based immunotherapy of cancer: promises to keep

Progress in vector design and an increased knowledge of mechanisms underlying tumor-induced immune suppression have led to a new and promising generation of Adenovirus (Ad)-based immunotherapies, which are discussed in this review. As vaccine vehicles Ad vectors (AdVs) have been clinically evaluated and proven safe, but a major limitation of the commonly used Ad5 serotype is neutralization by preexistent or rapidly induced immune responses. Genetic modifications in the Ad capsid can reduce intrinsic immunogenicity and facilitate escape from antibody-mediated neutralization. Further modification of the Ad hexon and fiber allows for liver and scavenger detargeting and selective targeting of, for example, dendritic cells. These next-generation Ad vaccines with enhanced efficacy are now becoming available for testing as tumor vaccines. In addition, AdVs encoding immune-modulating products may be used to convert the tumor microenvironment from immune-suppressive and proinvasive to proinflammatory, thus facilitating cell-mediated effector functions that can keep tumor growth and invasion in check. Oncolytic AdVs, that selectively replicate in tumor cells and induce an immunogenic form of cell death, can also be armed with immune-activating transgenes to amplify primed antitumor immune responses. These novel immunotherapy strategies, employing highly efficacious AdVs in optimized configurations, show great promise and warrant clinical exploration.

Truncating the i-leader open reading frame enhances release of human adenovirus type 5 in glioma cells

Background

The survival of glioma patients with the current treatments is poor. Early clinical trails with replicating adenoviruses demonstrated the feasibility and safety of the use of adenoviruses as oncolytic agents. Antitumor efficacy has been moderate due to inefficient virus replication and spread. Previous studies have shown that truncation of the adenovirus i-leader open reading frame enhanced cytopathic activity of HAdV-5 in several tumor cell lines. Here we report the effect of an i-leader mutation on the cytopathic activity in glioma cell lines and in primary high-grade glioma cell cultures.

Results

A mutation truncating the i-leader open reading frame was created in a molecular clone of replication-competent wild-type HAdV-5 by site-directed mutagenesis. We analyzed the cytopathic activity of this RL-07 mutant virus. A cell-viability assay showed increased cytopathic activity of the RL-07 mutant virus on U251 and SNB19 glioma cell lines. The plaque sizes of RL-07 on U251 monolayers were seven times larger than those of isogenic control viruses. Similarly, the cytopathic activity of the RL-07 viruses was strongly increased in six primary high-grade glioma cell cultures. In glioma cell lines the RL-07 virus was found to be released earlier into the culture medium. This was not due to enhanced viral protein synthesis, as was evident from equivalent E1A, Fiber and Adenovirus Death Protein amounts, nor to higher virus yields.

Conclusion

The cytopathic activity of replicating adenovirus in glioblastoma cells is increased by truncating the i-leader open reading frame. Such mutations may help enhancing the antitumor cytopathic efficacy of oncolytic adenoviruses in the treatment of glioblastoma.

Transduction and oncolytic profile of a potent replication-competent adenovirus 11p vector (RCAd11pGFP) in colon carcinoma cells

Replication-competent adenovirus type 5 (Ad5) vectors promise to be more efficient gene delivery vehicles than their replication-deficient counterparts, and chimeric Ad5 vectors that are capable of targeting CD46 are more effective than Ad5 vectors with native fibers. Although several strategies have been used to improve gene transduction and oncolysis, either by modifying their tropism or enhancing their replication capacity, some tumor cells are still relatively refractory to infection by chimeric Ad5. The oncolytic effects of the vectors are apparent in certain tumors but not in others. Here, we report the biological and oncolytic profiles of a replication-competent adenovirus 11p vector (RCAd11pGFP) in colon carcinoma cells. CD46 was abundantly expressed in all cells studied; however, the transduction efficiency of RCAd11pGFP varied. RCAd11pGFP efficiently transduced HT-29, HCT-8, and LS174T cells, but it transduced T84 cells, derived from a colon cancer metastasis in the lung, less efficiently. Interestingly, RCAd11p replicated more rapidly in the T84 cells than in HCT-8 and LS174T cells and as rapidly as in HT-29 cells. Cell toxicity and proliferation assays indicated that RCAd11pGFP had the highest cell-killing activities in HT29 and T84 cells, the latter of which also expressed the highest levels of glycoproteins of the carcinoma embryonic antigen (CEA) family. In vivo experiments showed significant growth inhibition of T84 and HT-29 tumors in xenograft mice treated with either RCAd11pGFP or Ad11pwt compared to untreated controls. Thus, RCAd11pGFP has a potent cytotoxic effect on colon carcinoma cells.

5/35 fiber-modified conditionally replicative adenovirus armed with p53 shows increased tumor-suppressing capacity to breast cancer cells

Conditionally replicative adenoviruses (CRAds) are widely used for cancer biotherapy and show a significant growth-suppressing effect on many types of cancer. However, it was reported that breast cancer was highly resistant to the infection of traditionally used adenovirus of serotype 5 (Ad5)-based CRAds. Although partial substitution of the fiber protein of replication-deficient Ad5 with that of adenovirus of serotype 35 (Ad35) facilitated infection of breast cancer cells by adenoviral vectors, it is still unknown whether this modification can improve CRAds in their tumor-eliminating capacity. We generated a 5/35 fiber-modified CRAd with a p53 cDNA construct and investigated whether this alteration in fiber region can make CRAds suppress the growth of breast cancer more effectively. Our data reinforced the proposal that 5/35-modified fiber conferred higher adenovirus infectivity for breast cancer cells than natural Ad5 fiber. Interestingly, 5/35 fiber-modified CRAd replicated more efficiently in breast cancer cells than Ad5-based CRAd. We also found 5/35 fiber-modified CRAd mediated higher expression of p53 in breast cancer cells. In vitro, 5/35 fiber-modified CRAd eliminated breast cancer cells more efficiently. Growth of xenograft tumors in nude mice was also significantly retarded by 5/35 fiber-modified CRAd. The 5/35 fiber-modified CRAd suppressed the growth of breast cancer cells more effectively than Ad5-based CRAd, both in vitro and in vivo. Thus CRAd with 5/35 hybrid fiber may be a promising vector for breast cancer treatment.

Viruses and Virus-Like Particles in Biotechnology

Although viruses are simple biological systems, they are capable of evolving highly efficient techniques for infecting cells, expressing their genomes, and generating new copies of themselves. It is possible to genetically manipulate most of the different classes of known viruses in order to produce recombinant viruses that express foreign proteins. Recombinant viruses have been used in gene therapy to deliver selected genes into higher organisms, in vaccinology and immunotherapy, and as important research tools to study the structure and function of these proteins.

Virus-like particles (VLPs) are multiprotein structures that mimic the organization and conformation of authentic native viruses but lack the viral genome. They have been applied not only as prophylactic and therapeutic vaccines but also as vehicles in drug and gene delivery and, more recently, as tools in nanobiotechnology.

In this article, basic and advanced features of viruses and VLPs are presented and their major applications are discussed. The different production platforms based on animal cell technology are explained, and their main challenges and future perspectives are explored. The implications of large-scale production of viruses and VLPs are discussed in the context of process control, monitorization, and optimization. The main upstream and downstream technical challenges are identified and discussed accordingly.

Serotype chimeric human adenoviruses for cancer gene therapy

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

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

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

Viruses, gene therapy and stem cells for the treatment of human glioma

Cancer gene therapy is based on the transfer of genetic material to cancer cells to modify a normal or abnormal cellular function, or to induce cell death. Modified viruses or stem cells have been used as carriers to transfer the genetic material to cancer cells avoiding trafficking through normal cells. However, although the current vectors have been successful in delivering genes in vitro and in vivo, little has been achieved with human cerebral gliomas. Poor transduction efficiency of viruses in human glioma cells and limited spread and distribution to the tumor limits our current expectations for successful gene therapy of central nervous system cancer until and if effective transfer vehicles are available. Nevertheless, continuing research in better vector development may overcome these limitations and offer a therapeutic advantage over the standard therapies for glioma.

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

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

Genomic and bioinformatics analyses of HAdV-14p, reference strain of a re-emerging respiratory pathogen and analysis of B1/B2

Unlike other human adenovirus (HAdV) species, B is divided into subspecies B1 and B2. Originally this was partly based on restriction enzyme (RE) analysis. B1 members, except HAdV-50, are commonly associated with respiratory diseases while B2 members are rarely associated with reported respiratory diseases. Recently two members of B2 have been identified in outbreaks of acute respiratory disease (ARD). One, HAdV-14, has re-emerged after an apparent 52-year absence. Genomic analysis and bioinformatics data are reported for HAdV-14 prototype for use as a reference and to understand and counter its re-emergence. The data complement and extend the original criteria for subspecies designation, unique amongst the adenoviruses, and highlight differences between B1 and B2, representing the first comprehensive analysis of this division. These data also provide finer granularity into the pathoepidemiology of the HAdVs. Whole genome analysis uncovers heterogeneous identity structures of the hexon and fiber genes amongst the HAdV-14 and the B1/B2 subspecies, which may be important in prescient vaccine development. Analysis of cell surface proteins provides insight into HAdV-14 tropism, accounting for its role as a respiratory pathogen. This HAdV-14 prototype genome is also a reference for applications of B2 adenoviruses as vectors for vaccine development and gene therapy.

Neural stem cells target intracranial glioma to deliver an oncolytic adenovirus in vivo

Adenoviral oncolytic virotherapy represents an attractive treatment modality for central nervous system (CNS) neoplasms. However, successful application of virotherapy in clinical trials has been hampered by inadequate distribution of oncolytic vectors. Neural stem cells (NSCs) have been shown as suitable vehicles for gene delivery because they track tumor foci. In this study, we evaluated the capability of NSCs to deliver a conditionally replicating adenovirus (CRAd) to glioma. We examined NSC specificity with respect to viral transduction, migration and capacity to deliver a CRAd to tumor cells. Fluorescence-activated cell sorter (FACS) analysis of NSC shows that these cells express a variety of surface receptors that make them amenable to entry by recombinant adenoviruses. Luciferase assays with replication-deficient vectors possessing a variety of transductional modifications targeted to these receptors confirm these results. Real-time PCR analysis of the replication profiles of different CRAds in NSCs and a representative glioma cell line, U87MG, identified the CRAd-Survivin (S)-pk7 virus as optimal vector for further delivery studies. Using in vitro and in vivo migration studies, we show that NSCs infected with CRAd-S-pk7 virus migrate and preferentially deliver CRAd to U87MG glioma. These results suggest that NSCs mediate an enhanced intratumoral distribution of an oncolytic vector in malignant glioma when compared with virus injection alone.

Development and evaluation of a novel gene delivery vehicle composed of adenovirus serotype 35

The capacity of gene delivery vehicles is considered to be a critical factor determining the success of gene therapy. To date, various types of gene delivery vehicle have been developed. Among them, recombinant adeno-virus (Ad) vectors have potential that has favored their worldwide use in vitro and in vivo. Conventional Ad vectors are composed of subgroup C Ad serotype 5 (Ad5), although it has been clarified that the drawbacks of Ad5 vectors are a high seroprevalence of Ad5 in adults and low transduction efficiencies in cells lacking the primary receptor for Ad5, coxsackievirus and adenovirus receptor. To overcome these problems, we developed a novel Ad vector fully composed of Ad serotype 35 (Ad35). Ad35 vectors show a wide tropism for human cells because Ad35 binds to human CD46, which is ubiquitously expressed on almost all human cells, as a primary receptor. In addition, anti-Ad5 antibodies do not inhibit Ad35 vector-mediated transduction and the seroprevalence of Ad35 in adults is lower than that of Ad5. This paper reviews our studies on the development and evaluation of Ad35 vectors. Ad vectors derived from other Ad serotypes different from Ad5, including Ad35, are expected to be gene delivery vehicles alternative to conventional Ad5 vectors.

Vector therapies for malignant glioma: shifting the clinical paradigm

BACKGROUND

Malignant glioma represents one of the most aggressive and devastating forms of human cancer. At present, there exists no successful treatment for this disease. Gene therapy, or vector therapy, has emerged as a viable experimental treatment method for intracranial malignancies.

OBJECTIVE

Vector therapy paradigms that have entered the clinical arena have shown adequate safety; however, the majority of the studies failed to observe significant clinical benefits. As such, researchers have refocused their efforts on developing novel vectors as well as new delivery methods to enhance the therapeutic effect of a particular vector. In this review, we discuss common vector therapy approaches used in clinical trials, their drawbacks and potential ways of overcoming these challenges.

METHODS

We focus on the experimental evaluation of cell-based vector therapies and adenoviral and herpes simplex virus type 1 vectors in the treatment of malignant glioma.

CONCLUSION

Vector therapy remains a promising treatment strategy for malignant glioma. Although significant questions remain to be answered, early clinical data suggest safety of this approach and future studies will likely address the efficacy of the proposed therapy.

Targeting malignant gliomas with a glial fibrillary acidic protein (GFAP)-selective oncolytic adenovirus

Glial fibrillary acidic protein (GFAP) is an intermediate filament protein abundantly expressed in malignant gliomas. We have constructed a novel oncolytic adenovirus, Ad5-gfa2(B)3-E1, for treatment of these tumors. In this construct, the E1 region is under control of the tissue-specific GFAP promoter (gfa2) with three additional copies of the glial specific 'B' enhancer. Infection of a GFAP-positive cell line with Ad5-gfa2(B)3-E1 resulted in E1A and E1B expression at 75% and 30% of the levels obtained after wtAd5 infection. Q-PCR showed that Ad5-gfa2(B)3-E1 replicated 4.5 times more efficiently in the GFAP-positive than in the GFAP-negative cell lines. Cell viability assays showed efficient elimination of GFAP-positive cells by Ad5-gfa2(B)3-E1, in some cell lines as efficiently as wtAd5, while the elimination was attenuated in GFAP-negative cell lines. When tested in human tumor xenografts in nude mice, Ad5-gfa2(B)3-E1 effectively suppressed the growth of GFAP-positive SNB-19 glial tumors but not of GFAP-negative A549 lung tumors. In Ad5-gfa2(B)3-E1, the E3 region was deleted to create space for future insertion of heterologous therapeutic genes. Experiments with dl7001, an E3-deleted variant of wtAd5, confirmed that the specificity of Ad5-gfa2(B)3-E1 replication was based on the promoter driving E1 and not on the E3 deletion. Strategies to further improve the efficacy of Ad5-gfa2(B)3-E1 for the treatment of malignant gliomas include the insertion of therapeutic genes in E3 or retargeting to receptors that are more abundantly expressed on primary glioma cells than CAR.

Improved glioblastoma treatment with Ad5/35 fiber chimeric conditionally replicating adenoviruses

Adenovirus type 5 (Ad5)-based vectors have been used in clinical trials for glioblastoma treatment, but the capacity of Ad5 to infect human glioma cells was questioned. Seeking to improve the adenovirus transduction, we tested four Ad5-based vectors differing only in their fiber gene on permanent and short-term cultures of glioblastoma cells. A wild-type fiber Ad5 vector (Ad5.Luc) was compared to an RGD integrin-binding motif-containing fiber adenovirus (AdlucRGD) and the two fiber chimeras Ad5/3 and Ad5/35, with vector binding redirected to the Ad3 or Ad35 receptor, respectively. Compared to Ad5, the transduction of the tested short-term glioblastoma cultures with the vector Ad5/35.Luc, AdlucRGD and Ad5/3.Luc was enhanced by approximately 72%, approximately 13% and approximately 2%, respectively. To limit adenovirus spread, we aimed to develop conditionally replicative Ad5/35 vectors by targeting the expression of the essential E1 and E4 genes; in addition, some vectors had the E1Delta24 deletion. We analyzed eleven promoters for their activity in glioblastoma cells and determined the specificity of eight replicative adenovirus vectors in vitro. We evaluated the most promising vectors with E1/E4 under the control of the GFAP/Ki67 or E2F-1/COX-2 promoters, and the native Ad5 or the chimeric Ad5/35 fiber for their antineoplastic activity in a subcutaneous and intracranial glioblastoma xenograft model. Animals treated with the Ad5/35-based vectors showed significantly smaller tumors and longer survival than those treated with the homologous Ad5 vectors; no significant toxicity was observed in the intracranial model. Our data suggest that Ad5/35-based vectors are promising tools for glioblastoma treatment.

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

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

Retrograde infection of precerebellar nuclei neurons by injection of a recombinant adenovirus into the cerebellar cortex of normal and reeler mice

The reeler mouse is an autosomal recessive mutant mouse caused by mutation of the reelin gene and characterized by cerebellar ataxia. To determine whether the distribution pattern of precerebellar nuclei neurons in the brainstem of the reeler mouse changes, we injected a small volume of a replication-defective recombinant adenovirus carrying E. coli beta-galactosidase (lacZ) into the cerebellar cortex of normal and reeler mice. Five days later, the mice were transcardially perfused by a fixative solution. X-gal staining of coronal or sagittal sections of the brainstem revealed that many origins for reticulocerebellar, cuneocerebellar, trigeminocerebellar, and pontocerebellar projections were retrogradely labeled, but only a few olivocerebellar neurons were labeled. Retrogradely labeled neurons in the lateral reticular nucleus tended to locate more laterally and be more condensed into a small compartment in the reeler compared with their normal counterparts. Retrogradely labeled neurons in the external cuneate nucleus were more dorsally shifted in the reeler mice compared with their normal counterparts. We could not find any differences between the normal and reeler mice in the distribution patterns of their trigeminocerebellar projection neurons. Retrogradely labeled pontocerebellar neurons in the basilar pons of the reeler mouse were reduced in number compared with their normal counterparts in addition to being more ventrally and laterally shifted. These findings strongly suggest that the migration of some precerebellar nuclei neurons from the rhombic lip to their final loci may be obstructed in the reeler mice.