Fiber shaft extension in combination with HI loop ligands augments infectivity for CAR-negative tumor targets but does not enhance hepatotropism in vivo

Pathogenicity of a novel bovine adenovirus type 3 with a natural deletion partial fiber gene in BALB/c mice

Objective

A novel Bovine adenovirus type 3 (BAdV-3) with a natural deletion partial fiber gene was isolated in 2020 and named BO/YB24/17/CH. The objective of this study was to understand the pathogenicity of this virus.

Methods

Thiry-two 3-week-old BALB/c mice were divided into three experimental groups and a control group. Mice in the experimental groups were intranasally inoculated with virus, and mice in the control group were inoculated with MDBK cell supernatant. Mice were weighed and clinically examined daily for appearance of any clinical signs. Three infected mice and one control mouse were euthanized at 1, 3, 5, 7, 9, 11, 13, and 15 days after inoculation. Tissue samples were collected for histopathological examination, immunohistochemical staining, and detection of the replication dynamics of virus.

Results

All infected mice developed mild clinical signs such as lethargy, weight loss, loss of appetite, and a rough hair coat, and gross lesions were observed as pulmonary punctate hemorrhage, lobular atrophy and splenomegaly. Histopathological examination revealed thickening of alveolar septa and mildly dilated splenic nodules and blurred red-white medullary demarcation in the spleen. Immunohistochemical results further confirmed that the production of the above lesions was due to viral infection. Importantly, unlike previously reported BAdV-3 detection only in the lungs and trachea, this isolate could be detected in multiple organs such as the heart, liver, spleen, kidney, and even blood by virus isolation and titration and real-time PCR methods.

Clinical significance

This study provides further insight into the pathogenicity of the fiber region deletion strain BO/YB24/17/CH in BALB/c mice, which provides a reference for the prevention and control of BAdV-3 as well as the development of vaccines.

Oncolytic Adenoviruses: Strategies for Improved Targeting and Specificity

Cancer is a major health problem. Most of the treatments exhibit systemic toxicity, as they are not targeted or specific to cancerous cells and tumors. Adenoviruses are very promising gene delivery vectors and have immense potential to deliver targeted therapy. Here, we review a wide range of strategies that have been tried, tested, and demonstrated to enhance the specificity of oncolytic viruses towards specific cancer cells. A combination of these strategies and other conventional therapies may be more effective than any of those strategies alone.

Tropism and transduction of oncolytic adenovirus 5 vectors in cancer therapy: Focus on fiber chimerism and mosaicism, hexon and pIX

The cellular internalization (infection of cells) of adenovirus 5 (Ad5) is mediated by the initial attachment of the globular knob domain of the capsid fiber protein to the cell surface coxsackievirus and adenovirus receptor (CAR), then followed by the interaction of the virus penton base proteins with cellular integrins. In tumors, there is a substantial intra- and intertumoral variability in CAR expression. The CAR-negative cells generally exhibit very low infectability. Since the fiber knob is a primary mediator of Ad5 binding to the cell surface, improved infectivity of Ad5-based vectors as oncolytic agents may be achieved via genetic modifications of this domain. The strategies to modify or broaden tropism and increase transduction efficiency of Ad5-based vectors include: 1) an incorporation of a targeting peptide into the fiber knob domain (the HI loop and/or C-terminus); 2) fiber knob serotype switching, or pseudotyping, by constructing chimeric fibers consisting of the knob domain derived from an alternate serotype (e.g., Ad5/3 or Ad5/35 chimeras), which binds to receptor(s) other than CAR (e.g., desmoglein 2/DSG2 and/or CD46); 3) "fiber complex mosaicism", an approach of combining serotype chimerism with peptide ligand(s) incorporation (e.g., Ad5/3-RGD); 4) "dual fiber mosaicism" by expressing two separate fibers with distinct receptor-binding capabilities on the same viral particle (e.g., Ad5-5/3 or Ad5-5/σ1); 5) fiber xenotyping by replacing the knob and shaft domains of wild-type Ad5 fiber protein with fibritin trimerization domain of T4 bacteriophage or σ1 attachment protein of reovirus. Other genetic approaches to increase the CAR-independent transduction efficiency include insertion of a targeting peptide into the hypervariable region of the capsid protein hexon or fusion to the C-terminus of pIX. Finally, we consider a yet unsolved molecular mechanism of liver targeting by Ad5-based vectors (CAR-, integrin-, fiber shaft KKTK motif-, and hepatic heparan sulfate glycosaminoglycans-independent, but fiber-, hexon- and blood factor X-dependent).

Redirecting adenovirus tropism by genetic, chemical, and mechanical modification of the adenovirus surface for cancer gene therapy

INTRODUCTION

Despite remarkable advancements, clinical evaluations of adenovirus (Ad)-mediated cancer gene therapies have highlighted the need for improved delivery and targeting.

AREA COVERED

Genetic modification of Ad capsid proteins has been extensively attempted. Although genetic modification enhances the therapeutic potential of Ad, it is difficult to successfully incorporate extraneous moieties into the capsid and the engineering process is laborious. Recently, chemical modification of the Ad surface with nanomaterials and targeting moieties has been found to enhance Ad internalization into the target by both passive and active mechanisms. Alternatively, external stimulus-mediated targeting can result in selective accumulation of Ad in the tumor and prevent dissemination of Ad into surrounding nontarget tissues. In the present review, we discuss various genetic, chemical, and mechanical engineering strategies for overcoming the challenges that hinder the therapeutic efficacy of Ad-based approaches.

EXPERT OPINION

Surface modification of Ad by genetic, chemical, or mechanical engineering strategies enables Ad to overcome the shortcomings of conventional Ad and enhances delivery efficiency through distinct and unique mechanisms that unmodified Ad cannot mimic. However, although the therapeutic potential of Ad-mediated gene therapy has been enhanced by various surface modification strategies, each strategy still possesses innate limitations that must be addressed, requiring innovative ideas and designs.

Quantum dot labelling of adenovirus allows highly sensitive single cell flow and imaging cytometry

A quantum dot method for highly efficient labelling of single adenoviral particles is developed. The technique has no impact on viral fitness and allows the imaging and tracking of virus binding and internalisation events using a variety of techniques including imaging cytometry and confocal microscopy. The method is applied to characterise the tropism of different adenoviral vectors.

Expression of osteoprotegerin from a replicating adenovirus inhibits the progression of prostate cancer bone metastases in a murine model

Metastatic involvement of the skeleton is a frequent consequence of advanced prostate cancer. These skeletal metastases cause a number of debilitating complications and are refractory to current treatments. New therapeutic options are being explored, including conditionally replicating adenoviruses (CRAds). CRAds are engineered to selectively replicate in and destroy tumor cells and can be 'armed' with exogenous transgenes for enhanced potency. We hypothesized that a CRAd armed with osteoprotegerin (OPG), an inhibitor of osteoclastogenesis, would inhibit the progression of prostate cancer bone metastases by directly lysing tumor cells and by reducing osteoclast activity. Although prostate cancer bone metastases are predominantly osteoblastic in nature, increased osteoclast activity is critical for the growth of these lesions. Ad5-Δ24-sOPG-Fc-RGD is a CRAd that carries a fusion of the ligand-binding domains of OPG and the Fc region of human IgG1 in place of the viral E3B genes. To circumvent low tumor cell expression of the native adenoviral receptor, an arginine-glycine-aspartic acid (RGD) peptide insertion within the viral fiber knob allows infection of cells expressing α(v) integrins. A 24-base pair deletion (Δ24) within viral E1A limits replication to cells with aberrant retinoblastoma cell cycle regulator/tumor suppressor expression. We have confirmed that Ad5-Δ24-sOPG-Fc-RGD replicates within and destroys prostate cancer cells and, in both murine and human coculture models, that infection of prostate cancer cells inhibits osteoclastogenesis in vitro. In a murine model, progression of advanced prostate cancer bone metastases was inhibited by treatment with Ad5-Δ24-sOPG-Fc-RGD but not by an unarmed control CRAd.

Virus chimeras for gene therapy, vaccination, and oncolysis: adenoviruses and beyond

Several challenges need to be addressed when developing viruses for clinical applications in gene therapy, vaccination, or viral oncolysis, including specific and efficient target cell transduction, virus delivery via the blood stream, and evasion of pre-existing immunity. With rising frequency, these goals are tackled by generating chimeric viruses containing nucleic acid fragments or proteins from two or more different viruses, thus combining different beneficial features of the parental viruses. These chimeras have boosted the development of virus-based treatment regimens for major inherited and acquired diseases, including cancer. Using adenoviruses as the paradigm and prominent examples from other virus families, we review the technological and functional advances in therapeutic virus chimera development and recent successful applications that can pave the way for future therapies.

Replacement of native adenovirus receptor-binding sites with a new attachment moiety diminishes hepatic tropism and enhances bioavailability in mice

The in vivo efficacy of adenoviral vectors (AdVs) in gene delivery strategies is hampered by the broad tissue tropism of the virus and its efficient binding to human erythrocytes. To circumvent these limitations, we developed a prototype AdV lacking native binding sites. We replaced the adenoviral fiber with a chimeric molecule consisting of the fiber tail domain, the reovirus sigma1 oligomerization domain, and a polyhistidine tag as model targeting moiety. We also abolished the integrin-binding motif in the penton base protein. The chimeric attachment molecule was efficiently incorporated onto AdV capsids, allowed efficient propagation of AdV without requirement for complementing fiber and conferred highly specific tropism to the AdV. Importantly, the targeted AdV exhibited markedly reduced tropism for liver cells. In comparison with control AdV with native tropism, the targeted AdV showed 1000-fold reduced transduction of HepG2 cells and 10,000-fold reduced transduction of mouse liver cells in freshly isolated liver slices. After intravenous inoculation of C57BL/6 mice, the targeted AdV exhibited delayed clearance in comparison with the native AdV, leaving approximately 10-fold greater levels in the blood 2 hr after inoculation. For all tissues analyzed, the targeted AdV displayed significantly reduced in vivo transduction in comparison with the native vector. Furthermore, in contrast to the native AdV, the targeted AdV did not bind human erythrocytes. Together, our findings suggest that the targeted AdV design described here provides a promising platform for systemic in vivo gene delivery.

Survivin-driven and fiber-modified oncolytic adenovirus exhibits potent antitumor activity in established intracranial glioma

The poor prognosis of patients with malignant gliomas necessitates the development of novel therapies. Virotherapy, using genetically engineered adenovectors that selectively replicate in and kill neoplastic cells, represents one such strategy. In this study, we examined several oncolytic vectors with modified transcriptional and transductional control of viral replication. First, we incorporated the survivin promoter (S) to drive E1A gene expression. We then modified the adenovirus serotype 5 (Ad5) fiber protein via genetic knob switching or incorporation of peptide ligands to target the following glioma-associated receptors: the Ad3 attachment protein, or CD46, alpha(v) beta(3)/alpha(v)beta(5) integrins, or heparan sulfate proteoglycans. The three conditionally replicative adenoviruses, CRAd-S-5/3, CRAd-S-RGD, and CRAd-S-pk7, were then examined in vitro with respect to transduction efficiency and tissue specificity. The most promising virus was then tested in vivo for evidence of tumor growth inhibition. CRAd-S-pk7 provided the highest level of viral replication and tumor oncolysis in glioma cell lines. At the same time, we observed minimal viral replication and toxicity in normal human brain. Injection of CRAd-S-pk7 inhibited xenograft tumor growth by more than 300% (p < 0.001). Sixty-seven percent of treated mice with intracranial tumors were long-term survivors (>110 days; p < 0.005). Analysis of tumor tissue indicated increased adenoviral infectivity, decreased mitotic activity, and enhanced tumor apoptosis. These findings demonstrate the effectiveness of CRAd-S-pk7 and provide the rationale for further development of this novel oncolytic virus for glioma gene therapy.

Genetic incorporation of the protein transduction domain of Tat into Ad5 fiber enhances gene transfer efficacy

Background

Human adenovirus serotype 5 (Ad5) has been widely explored as a gene delivery vector for a variety of diseases. Many target cells, however, express low levels of Ad5 native receptor, the Coxsackie-Adenovirus Receptor (CAR), and thus are resistant to Ad5 infection. The Protein Transduction Domain of the HIV Tat protein, namely PTD_tat, has been shown to mediate protein transduction in a wide range of cells. We hypothesize that re-targeting Ad5 vector via the PTD_tat motif would improve the efficacy of Ad5-mediated gene delivery.

Results

In this study, we genetically incorporated the PTD_tat motif into the knob domain of Ad5 fiber, and rescued the resultant viral vector, Ad5.PTD_tat. Our data showed the modification did not interfere with Ad5 binding to its native receptor CAR, suggesting Ad5 infection via the CAR pathway is retained. In addition, we found that Ad5.PTD_tat exhibited enhanced gene transfer efficacy in all of the cell lines that we have tested, which included both low-CAR and high-CAR decorated cells. Competitive inhibition assays suggested the enhanced infectivity of Ad5.PTD_tat was mediated by binding of the positively charged PTD_tat peptide to the negatively charged epitopes on the cells' surface. Furthermore, we investigated in vivo gene delivery efficacy of Ad5.PTD_tat using subcutaneous tumor models established with U118MG glioma cells, and found that Ad5.PTD_tat exhibited enhanced gene transfer efficacy compared to unmodified Ad5 vector as analyzed by a non-invasive fluorescence imaging technique.

Conclusion

Genetic incorporation of the PTD_tat motif into Ad5 fiber allowed Ad5 vectors to infect cells via an alternative PTD_tat targeting motif while retaining the native CAR-mediated infection pathway. The enhanced infectivity was demonstrated in both cultured cells and in in vivo tumor models. Taken together, our study identifies a novel tropism expanded Ad5 vector that may be useful for clinical gene therapy applications.

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

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

Comparison of the efficiency of transduction of leukemic cells by fiber-modified adenoviruses

Efficient gene transfer with adenoviral type 5 (Ad5) vectors depends on the initial attachment of their fiber, which binds the coxsackie-adenovirus receptor (CAR), and their subsequent internalization, mediated by the interaction of viral penton base with target cell alphav integrins. We previously demonstrated that human leukemic cells lack these receptors and are therefore resistant to Ad5 transduction, limiting efforts to genetically modify these cells. Human leukemic blasts are, however, susceptible to transduction with an adenovector made CAR independent by substitution of a chimeric Ad5/35 fiber [Yotnda et al. (2001). Gene Ther. 8, 930-937]. Other receptors can also be targeted with recombinant ligand moieties incorporated into adenovirus fiber. We have determined which of these fiber-modified adenovectors is most effective at modifying human primary leukemia cells, and lines. We used a replication-incompetent Ad5-beta-gal vector, in which the Ad5 fiber was replaced with fiber from various adenovirus serotypes (Ad35 and Ad11), or modified either with variable length polylysine (K4, K7, K21) or RGD-4C peptide. All the modified fiber vectors transduced primary leukemia cells and cell lines more efficiently than Ad5. Polylysine-substituted Ad5F/K21 and peptide-modified Ad5F/RGD vectors were most effective overall (up to 100% efficiency), whereas Ad5F/RGD was the most effective at transducing B cell acute lymphoblastic leukemia cells (90% efficiency). Ad5F/K21 and Ad5F/RGD should be of value for the genetic modification of human primary leukemia cells.

Identification of sites in adenovirus hexon for foreign peptide incorporation

Adenovirus type 5 (Ad5) is one of the most promising vectors for gene therapy applications. Genetic engineering of Ad5 capsid proteins has been employed to redirect vector tropism, to enhance infectivity, or to circumvent preexisting host immunity. As the most abundant capsid protein, hexon modification is particularly attractive. However, genetic modification of hexon often results in failure of rescuing viable viruses. Since hypervariable regions (HVRs) are nonconserved among hexons of different serotypes, we investigated whether the HVRs could be used for genetic modification of hexon by incorporating oligonucleotides encoding six histidine residues (His6) into different HVRs in the Ad5 genome. The modified viruses were successfully rescued, and the yields of viral production were similar to that of unmodified Ad5. A thermostability assay suggested the modified viruses were stable. The His6 epitopes were expressed in all modified hexon proteins as assessed by Western blotting assay, although the intensity of the reactive bands varied. In addition, we examined the binding activity of anti-His tag antibody to the intact virions with the enzyme-linked immunosorbent assay and found the His6 epitopes incorporated in HVR2 and HVR5 could bind to anti-His tag antibody. This suggested the His6 epitopes in HVR2 and HVR5 were exposed on virion surfaces. Finally, we examined the infectivities of the modified Ad vectors. The His6 epitopes did not affect the native infectivity of Ad5 vectors. In addition, the His6 epitopes did not appear to mediate His6-dependent viral infection, as assessed in two His6 artificial receptor systems. Our study provided valuable information for studies involving hexon modification.

Gene therapy for the treatment of heart failure--calcium signaling

The knowledge of molecular mechanisms indicated in cardiac dysfunction has increased dramatically over the last decade and yields considerable potential for new treatment options in heart failure. Alterations in intracellular calcium signaling play a crucial role in the pathophysiology of heart failure, and in recent years, somatic gene transfer has been identified as an important tool to help understand the relative contribution of specific calcium-handling proteins in heart failure. This article reviews recent advances in gene delivery techniques aimed at global myocardial transfection and discusses molecular therapeutic targets identified within intracellular calcium signaling pathways in heart failure.

An adenoviral vector containing an arg-gly-asp (RGD) motif in the fiber knob enhances protein product levels from transgenes refractory to expression

Genetic manipulation of the adenovirus type 5 represents one strategy to modify viral transduction properties in vitro and in vivo. In the majority of studies to date, reporter gene activity has been monitored to assess transduction efficiency. BRCA1 is a gene whose protein product is clinically important, biologically toxic, difficult to overexpress, and difficult to detect as an untagged protein species. Thus, it represents an attractive candidate from which to evaluate the efficacy of a gene delivery system. In the present study, transgene expression was assessed employing otherwise isogenic viruses, which differed only in the presence or absence of an RGD integrin-binding motif in the HI loop of the Ad fiber knob. We utilized a combination of BRCA1 expression level comparisons among several human BRCA1/mutant BRCA1/murine Brca1 constructs and reporter gene activity following transduction of a panel of human breast and ovarian tumor cell lines representative of both sporadic and hereditary cases. A general overall concordance in efficiency was observed, whether the biological readout measured was reporter gene activity or steady-state level of ectopic BRCA1 protein produced. Importantly, the expression of full-length wild-type BRCA1 protein, clinically relevant mutant BRCA1 proteins or murine Brca1 was superior when the gene was delivered via the RGD-modified Ad. The ectopic BRCA1 stabilized endogenous BARD1 and this functional effect was evident at lower input viral doses when BRCA1 was delivered via the RGD-modified Ad. Quantitative, noninvasive, real-time image analysis of reporter gene function in nude mice harboring human ovarian tumor xenographs demonstrated a similar enhancement of expression in vivo by the RGD fiber modification, with low levels of transduction of normal mouse mesothelium. These results provide additional evidence supporting the concept that rational modification of viral vectors can result in the delivery of functionally active therapeutic proteins such as BRCA1 that present with technical difficulties with regard to their expression.

Construction and characterization of adenovirus serotype 5 packaged by serotype 3 hexon

Adenovirus serotype 5 (Ad5) has great potential for gene therapy applications. A major limitation, however, is the host immune response against Ad5 infection that often prevents the readministration of Ad5 vectors. In this regard, the most abundant capsid protein, hexon, has been implicated as the major target for neutralizing antibodies. In this study, we sought to escape the host neutralization response against Ad5 via hexon replacement. We constructed a chimeric adenovirus vector, Ad5/H3, by replacing the Ad5 hexon gene with the hexon gene of Ad3. The chimeric viruses were successfully rescued in 293 cells. Compared to that for the control Ad5/H5, the growth rate of Ad5/H3 was significantly slower and the final yield was about 1 log order less. These data indicate that the Ad3 hexon can encapsidate the Ad5 genome, but with less efficiency than the Ad5 hexon. The gene transfer efficacy of Ad5/H3 in HeLa cells was also lower than that of Ad5/H5. Furthermore, we tested the host neutralization responses against the two viruses by using C57BL/6 mice. The neutralizing antibodies against Ad5/H3 and Ad5/H5 generated by the immunized mice did not cross-neutralize each other in the context of in vitro infection of HeLa cells. Preimmunization of C57BL/6 mice with one of the two types of viruses also did not prevent subsequent infection of the other type. These data suggest that replacing the Ad5 hexon with the Ad3 hexon can circumvent the host neutralization response to Ad5. This strategy may therefore be used to achieve the repeated administration of Ad5 in gene therapy applications.