Evaluation of salivary gland acinar and ductal cell-specific promoters in vivo with recombinant adenoviral vectors

Retrograde ductal administration of the adenovirus-mediated NDRG2 gene leads to improved sialaden hypofunction in estrogen-deficient rats

One of the most common oral manifestations of menopause is xerostomia. Oral dryness can profoundly affect quality of life and interfere with basic daily functions, such as chewing, deglutition, and speaking. Although the feeling of oral dryness can be ameliorated after estrogen supplementation, the side effects of estrogen greatly restrict its application. We previously found that N-myc downstream-regulated gene 2 (NDRG2) is involved in estrogen-mediated ion and fluid transport in a cell-based model. In the present study, we used an ovariectomized rat model to mimic xerostomia in menopausal women and constructed two adenovirus vectors bearing NDRG2 to validate their therapeutic potential. Ovariectomized rats exhibited severe sialaden hypofunction, including decreased saliva secretion and ion reabsorption as well as increased water intake. Immunohistochemistry revealed that the expression of NDRG2 and Na(+) reabsorption-related Na(+)/K(+)-ATPase and epithelial sodium channels (EnaC) decreased in ovariectomized rat salivary glands. We further showed that the localized delivery of NDRG2 improved the dysfunction of Na(+) and Cl(-) reabsorption. In addition, the saliva flow rate and water drinking recovered to normal. This study elucidates the mechanism of estrogen deficiency-mediated xerostomia or sialaden hypofunction and provides a promising strategy for therapeutic intervention.

Gene delivery in salivary glands: from the bench to the clinic

In vivo gene delivery has long been seen as providing opportunities for the development of novel treatments for disorders refractory to existing therapies. Over the last two decades, salivary glands have proven to be a useful, if somewhat unconventional, target tissue for studying several potential clinical applications of therapeutic gene delivery. Herein, we follow the progress, address some problems and assess the outlook for clinical applications of salivary gland gene delivery. Our experience with these tissues provides a roadmap for the process of moving an idea from the laboratory bench to patients.

Sensitivity of salivary glands to radiation: from animal models to therapies

Radiation therapy for head and neck cancer causes significant secondary side-effects in normal salivary glands, resulting in diminished quality of life for these individuals. Salivary glands are exquisitely sensitive to radiation and display acute and chronic responses to radiotherapy. This review will discuss clinical implications of radiosensitivity in normal salivary glands, compare animal models used to investigate radiation-induced salivary gland damage, address therapeutic advances, and project future directions in the field.

Evaluation of promoters for use in tissue-specific gene delivery

Vectors used in gene therapy require an expression cassette. The expression cassette consists of three important components: promoter, therapeutic gene and polyadenylation signal. The promoter is essential to control expression of the therapeutic gene. A tissue-specific promoter is a promoter that has activity in only certain cell types. Use of a tissue-specific promoter in the expression cassette can restrict unwanted transgene expression as well as facilitate persistent transgene expression. Therefore, choosing the correct promoter, especially a tissue-specific promoter, is a major step toward achieving successful therapeutic transgene expression. Ideally, the elements of the natural promoter region, necessary for obtaining the required level of the gene expression while retaining tissue-specificity, should be known. Also, it is important to understand whether interactions occur between the promoter region and the rest of the vector genome that could affect promoter activity and specificity. To assess this, it is helpful to select a suitable vector system that will be used in further gene therapy studies. Second, have one or several candidate tissue-specific promoters available for use. Third, ideally have an in vitro cell model suitable to evaluate tissue-specificity. Fourth, have a convenient in vivo animal model to use. Fifth, select a good reporter gene system. Next, using conventional recombinant DNA techniques create different promoter constructs with the selected vector system. Lastly, have a suitable transfection method to test the plasmid constructs in both the in vitro and the in vivo models.

Dental caries

Dental caries, otherwise known as tooth decay, is one of the most prevalent chronic diseases of people worldwide; individuals are susceptible to this disease throughout their lifetime. Dental caries forms through a complex interaction over time between acid-producing bacteria and fermentable carbohydrate, and many host factors including teeth and saliva. The disease develops in both the crowns and roots of teeth, and it can arise in early childhood as an aggressive tooth decay that affects the primary teeth of infants and toddlers. Risk for caries includes physical, biological, environmental, behavioural, and lifestyle-related factors such as high numbers of cariogenic bacteria, inadequate salivary flow, insufficient fluoride exposure, poor oral hygiene, inappropriate methods of feeding infants, and poverty. The approach to primary prevention should be based on common risk factors. Secondary prevention and treatment should focus on management of the caries process over time for individual patients, with a minimally invasive, tissue-preserving approach.

Growth factor delivery for oral and periodontal tissue engineering

The treatment of oral and periodontal diseases and associated anomalies accounts for a significant proportion of the healthcare burden, with the manifestations of these conditions being functionally and psychologically debilitating. Growth factors are critical to the development, maturation, maintenance and repair of craniofacial tissues, as they establish an extracellular environment that is conducive to cell and tissue growth. Tissue-engineering principles aim to exploit these properties in the development of biomimetic materials that can provide an appropriate microenvironment for tissue development. These materials have been constructed into devices that can be used as vehicles for delivery of cells, growth factors and DNA. In this review, different mechanisms of drug delivery are addressed in the context of novel approaches to reconstruct and engineer oral- and tooth-supporting structures, namely the periodontium and alveolar bone.

Prolonged transgene expression in murine salivary glands following non-primate lentiviral vector transduction

Salivary glands are an accessible organ for gene therapy, enabling expression of recombinant proteins for both exocrine and endocrine secretion. Lentivirus-based vectors have many advantages for gene therapy, including their ability to infect nondividing cells and to stably integrate into the host genome, enabling long-term transgene expression without eliciting an inflammatory immune response. In the present study, murine salivary glands were inoculated with feline immunodeficiency virus (FIV)-based lentiviral vectors expressing various reporter genes. Luciferase expression was observed as early as 24 h posttransduction, peaked at 17-21 days, and remained stable for more than 80 days. Staining with X-gal suggested that mucous acinar cells were effectively transduced. FIV vector transduction with the secreted alkaline phosphatase gene increased serum levels in treated animals for up to 45 days, and the FIV vector harboring the interferon-gamma (IFN-gamma) expression cassette induced an increase in IFN-gamma serum levels as well as in the supernatant of salivary gland explant cultures. These results demonstrate that the transduction of salivary glands with nonprimate lentiviral vectors may provide a novel and highly effective vehicle for long-term endocrine transgene expression.

An adenoviral vector for probing promoter activity in primary immune cells

Functional analysis of the DNA regulatory regions that control gene expression has largely been performed through transient transfection of promoter-reporter constructs into transformed cells. However, transformed cells are often poor models of primary cells. To directly analyze DNA regulatory regions in primary cells, we generated a novel adenoviral luciferase reporter vector, pShuttle-luciferase-GFP (pSLUG) that contains a promoterless luciferase cassette (with an upstream cloning site) for probing promoter activity, and a GFP expression cassette that allows for the identification of transduced cells. Recombinant adenoviruses generated from this vector can transduce a wide range of primary immune cells with high efficiency, including human macrophages, dendritic cells and T cells; and mouse T cells transgenic for the coxsackie and adenoviral receptor (CAR). In primary T cells, we show inducible nuclear factor of activated T cells (NF-AT) activity using a recombinant pSLUG adenovirus containing a consensus NF-AT promoter. We further show inducible IL-12/23 p40 promoter activity in primary macrophages and dendritic cells using a recombinant pSLUG adenovirus containing the proximal human IL-12/23 p40 promoter. The pSLUG system promises to be a powerful tool for the analysis of DNA regulatory regions in diverse types of primary immune cells.

Gene therapy as a therapeutic approach for the treatment of rheumatoid arthritis: innovative vectors and therapeutic genes

In recent years, significant progress has been made in the treatment of rheumatoid arthritis (RA). In addition to conventional therapy, novel biologicals targeting tumour necrosis factor-alpha have successfully entered the clinic. However, the majority of the patients still has some actively inflamed joints and some patients suffer from side-effects associated with the high systemic dosages needed to achieve therapeutic levels in the joints. In addition, due to of the short half-life of these proteins there is a need for continuous, multiple injections of the recombinant protein. An alternative approach might be the use of gene transfer to deliver therapeutic genes locally at the site of inflammation. Several viral and non-viral vectors are being used in animal models of RA. The first gene therapy trials for RA have already entered the clinic. New vectors inducing long-term and regulated gene expression in specific tissue are under development, resulting in more efficient gene transfer, for example by using distinct serotypes of viral vectors such as adeno-associated virus. This review gives an overview of some promising vectors used in RA research. Furthermore, several therapeutic genes are discussed that could be used for gene therapy in RA patients.

Transfer of the AQP1 cDNA for the correction of radiation-induced salivary hypofunction

The treatment of most patients with head and neck cancer includes ionizing radiation (IR). Salivary glands in the IR field suffer significant and irreversible damage, leading to considerable morbidity. Previously, we reported that adenoviral (Ad)-mediated transfer of the human aquaporin-1 (hAQP1) cDNA to rat [C. Delporte, B.C. O'Connell, X. He, H.E. Lancaster, A.C. O'Connell, P. Agre, B.J. Baum, Increased fluid secretion after adenoviral-mediated transfer of the aquaporin-1 cDNA to irradiated rat salivary glands. Proc. Natl. Acad. Sci. U S A. 94 (1997) 3268-3273] and miniature pig [Z. Shan, J. Li, C. Zheng, X. Liu, Z. Fan, C. Zhang, C.M. Goldsmith, R.B. Wellner, B.J Baum, S. Wang. Increased fluid secretion after adenoviral-mediated transfer of the human aquaporin-1 cDNA to irradiated miniature pig parotid glands. Mol. Ther. 11 (2005) 444-451] salivary glands approximately 16 weeks following IR resulted in a dose-dependent increase in salivary flow to > or =80% control levels on day 3. A control Ad vector was without any significant effect on salivary flow. Additionally, after administration of Ad vectors to salivary glands, no significant lasting effects were observed in multiple measured clinical chemistry and hematology values. Taken together, the findings show that localized delivery of AdhAQP1 to IR-damaged salivary glands is useful in transiently increasing salivary secretion in both small and large animal models, without significant general adverse events. Based on these results, we are developing a clinical trial to test if the hAQP1 cDNA transfer strategy will be clinically effective in restoring salivary flow in patients with IR-induced parotid hypofunction.

Evaluation of viral and mammalian promoters for use in gene delivery to salivary glands

To optimize vectors for salivary gland gene transfer, we screened viral [cytomegalovirus (CMV; human immediate early), Rous sarcoma virus (RSV), simian virus 40, and Moloney murine leukemia virus long terminal repeat] and mammalian [elongation factor 1alpha (EF1alpha), cytokeratin 18 (K18), cytokeratin 19 (K19), kallikrein (Kall), and amylase (AMY), all human, and rat aquaporin-5 (rAQP5), and derivative elements] promoters driving luciferase activity in vitro and in vivo. In adenoviral vectors, the CMV promoter showed highest activity, with the EF1alpha and RSV promoters slightly less powerful, in rat submandibular glands (SMGs). The K18 2.5-kb, K19 3.0-kb, and rAQP5 0.4-kb and Kall promoters had intermediate activity, while the AMY promoter exhibited lowest activity. To localize transgene expression, enhanced green fluorescence protein was used. The CMV, RSV, EF1alpha, K18 2.5-kb, K19 3.0-kb, rAQP5 0.4-kb, and AMY promoters were not cell-type specific in SMGs; however, the Kall promoter was primarily active in ductal cells. These data will facilitate optimal expression cassette design for salivary gland gene transfer.

Increased fluid secretion after adenoviral-mediated transfer of the human aquaporin-1 cDNA to irradiated miniature pig parotid glands

The treatment of most head and neck cancer patients includes ionizing radiation (IR). Salivary glands in the IR field suffer irreversible damage. Previously, we reported that adenoviral (Ad)-mediated transfer of the human aquaporin-1 (hAQP1) cDNA to rat submandibular glands following IR restored salivary flow to near normal levels. It is unclear if this strategy is useful in larger animals. Herein, we evaluated AdhAQP1-mediated gene transfer after parotid gland IR (20 Gy) in the miniature pig. Sixteen weeks following IR, salivation from the targeted gland was decreased by >80%. AdhAQP1 administration resulted in a dose-dependent increase in parotid salivary flow to approximately 80% of pre-IR levels on day 3. A control Ad vector was without significant effect. The effective AdhAQP1 dose was 2.5 x 10(5) pfu/microl infusate, a dose that leads to comparable transgene expression in murine and minipig salivary glands. Three days after Ad vector administration little change was observed in clinical chemistry and hematology values. These findings demonstrate that localized delivery of AdhAQP1 to IR-damaged salivary glands increases salivary secretion, without significant general adverse events, in a large animal model.

Reengineered salivary glands are stable endogenous bioreactors for systemic gene therapeutics

The use of critical-for-life organs (e.g., liver or lung) for systemic gene therapeutics can lead to serious safety concerns. To circumvent such issues, we have considered salivary glands (SGs) as an alternative gene therapeutics target tissue. Given the high secretory abilities of SGs, we hypothesized that administration of low doses of recombinant adeno-associated virus (AAV) vectors would allow for therapeutic levels of transgene-encoded secretory proteins in the bloodstream. We administered 10(9) particles of an AAV vector encoding human erythropoietin (hEPO) directly to individual mouse submandibular SGs. Serum hEPO reached maximum levels 8-12 weeks after gene delivery and remained relatively stable for 54 weeks (longest time studied). Hematocrit levels were similarly increased. Moreover, these effects proved to be vector dose-dependent, and even a dosage as low as 10(8) particles per animal led to significant increases in hEPO and hematocrit levels. Vector DNA was detected only within the targeted SGs, and levels of AAV copies within SGs were highly correlated with serum hEPO levels (r = 0.98). These results show that SGs appear to be promising targets with potential clinical applicability for systemic gene therapeutics.

Use of localised gene transfer to develop new treatment strategies for the salivary component of Sjögren's syndrome

Effective treatment for Sjögren's syndrome (SS) might be developed locally by introducing genes encoding cytokines, which are potentially anti-inflammatory, or by introducing a cDNA encoding a soluble form of a key cytokine receptor, which can act as an antagonist and decrease the availability of certain cytokines, such as soluble tumour necrosis factor alpha receptors. Currently, the preferred choice of viral vector for immunomodulatory gene transfer is recombinant adeno-associated virus. The use of gene transfer to help determine the pathophysiology and to alter the course of the SS-like disease in the NOD mouse model can ultimately lead to the development of new treatments for managing the salivary component in patients with SS.

Advances in vector-mediated gene transfer

Clinical applications of gene transfer technology initially targeted the treatment of inherited monogenetic disorders and cancers refractory to conventional therapies. Today, gene transfer approaches are being developed for most tissues and for multiple disorders including those affecting quality of life. The focus herein is eventual application of gene transfer technology for the management of organ-directed autoimmunity. A specific example is presented: Sjögren's syndrome and localized salivary gland gene transfer. The status of relevant pre-clinical gene transfer studies is reviewed, with an emphasis on use of adenoviral and adeno-associated viral vectors. Current limitations of effective organ-directed gene transfer are also discussed.

Distribution and toxicity resulting from adenoviral vector administration to a single salivary gland in adult rats

BACKGROUND

We examined the distribution and toxicity associated with a single salivary gland administration of a recombinant adenoviral vector, AdCMVH3, encoding human histatin 3.

METHODS

Adult rats received different doses of AdCMVH3 (0, 106, 3 x 107, and 109 pfu; 50 microl) via the right submandibular gland and were followed for 15 days. Food consumption, weight gain, clinical appearance, and serum chemistry were monitored, and a necropsy was performed. Vector distribution was examined by polymerase chain reaction, and selected saliva samples were tested for replication-competent adenovirus (RCA).

RESULTS

All animals survived to sacrifice (days 2, 8, and 15), and appeared normal clinically. There were no differences in food consumption, weight gain, and serum chemistry. The only consistent necropsy findings were lymphoid infiltrates and necrosis in the target submandibular glands of high-dosage animals. AdCMVH3 detection was virus dose dependent, decreased with time, and at low dose preferentially observed in the targeted gland. No RCA was detected.

CONCLUSIONS

Salivary gland administration of 109 pfu AdCMVH3 elicits an initial focal pathologic response and wide tissue distribution. There is no associated systemic toxicity up to 15 days, and lower doses are primarily found in glands.

Vectors for the treatment of autoimmune disease

Gene therapy has been applied in a variety of experimental models of autoimmunity with some success. In this article, we outline recent developments in gene therapy vectors, discuss advantages and disadvantages of each, and highlight their recent applications in autoimmune models. We also consider progress in vector targeting and components for regulating transgene expression, which will both improve gene therapy safety and empower gene therapy to fullfil its potential as a therapeutic modality. In conclusion, we consider candidate vectors that satisfy requirements for application in the principal therapeutic strategies in which gene therapy will be applied to autoimmune conditions.

Integration efficiency of a hybrid adenoretroviral vector

The frequency with which the hybrid vector AdLTR-luc mediates genomic integration [Nat. Biotech. 18 (2000) 176-180] is unknown. To address this, we constructed AdLTR-red, using the AdLTR-luc backbone and the enhanced red fluorescence protein cDNA. Kinetic studies showed that AdLTR-red and a conventional adenoviral vector, AdCMV-red, entered and transduced epithelial cells comparably. AdLTR-red integration frequency in vitro, i.e., the percentage of red clones after 10-12 doubling times from limiting dilutions, was 8.0% (36/450; at 67 particles/cell). With AdCMV-red, 0/549 clones were integration-positive. Seven days after AdLTR-luc or AdCMV-luc (10(11) particles) femoral vein administration to adult rats splenocytes were prepared, stimulated with concanavalin A, and examined by FISH. AdLTR-luc integration occurred in 5-11% of mitotic rat splenocytes, while no unequivocal integration was found with AdCMV-luc. These data provide the first quantitative evidence of the frequency for genomic integration with this hybrid vector.