Hydroxychloroquine enhances the endocrine secretion of adenovirus-directed growth hormone from rat submandibular glands in vivo

cAMP-dependent recruitment of acidic organelles for Ca2+ signaling in the salivary gland

Autonomic neural activation of intracellular Ca²⁺ release in parotid acinar cells induces the secretion of the fluid and protein components of primary saliva critical for maintaining overall oral homeostasis. In the current study, we profiled the role of acidic organelles in shaping the Ca²⁺ signals of parotid acini using a variety of imaging and pharmacological approaches. Results demonstrate that zymogen granules predominate as an apically polarized population of acidic organelles that contributes to the initial Ca²⁺ release. Moreover, we provide evidence that indicates a role for the intracellular messenger NAADP in the release of Ca²⁺ from acidic organelles following elevation of cAMP. Our data are consistent with the "trigger" hypothesis where localized release of Ca²⁺ sensitizes canonical intracellular Ca²⁺ channels to enhance signals from the endoplasmic reticulum. Release from acidic stores may be important for initiating saliva secretion at low levels of stimulation and a potential therapeutic target to augment secretory activity in hypofunctioning salivary glands.

Advances in salivary gland gene therapy - oral and systemic implications

INTRODUCTION

Much research demonstrates the feasibility and efficacy of gene transfer to salivary glands. Recently, the first clinical trial targeting a salivary gland was completed, yielding positive safety and efficacy results.

AREAS COVERED

There are two major disorders affecting salivary glands: radiation damage following treatment for head and neck cancers and Sjögren's syndrome (SS). Salivary gland gene transfer has also been employed in preclinical studies using transgenic secretory proteins for exocrine (upper gastrointestinal tract) and endocrine (systemic) applications.

EXPERT OPINION

Salivary gland gene transfer is safe and can be beneficial in humans. Applications to treat and prevent radiation damage show considerable promise. A first-in-human clinical trial for the former was recently successfully completed. Studies on SS suffer from an inadequate understanding of its etiology. Proof of concept in animal models has been shown for exocrine and endocrine disorders. Currently, the most promising exocrine application is for the management of obesity. Endocrine applications are limited, as it is currently impossible to predict if systemically required transgenic proteins will be efficiently secreted into the bloodstream. This results from not understanding how secretory proteins are sorted. Future studies will likely employ ultrasound-assisted and pseudotyped adeno-associated viral vector-mediated gene transfer.

pH-sensitive oncolytic adenovirus hybrid targeting acidic tumor microenvironment and angiogenesis

Although oncolytic adenoviruses (Ads) are an attractive option for cancer gene therapy, the intravenous administration of naked Ad still encounters unfavorable host responses, non-specific interactions, and heterogeneity in targeted cancer cells. To overcome these obstacles and achieve specific targeting of the tumor microenvironment, Ad was coated with the pH-sensitive block copolymer, methoxy poly(ethylene glycol)-b-poly(l-histidine-co-l-phenylalanine) (PEGbPHF). The physicochemical properties of the generated nanocomplex, Ad/PEGbPHF, were assessed. At pH6.4, GFP-expressing Ad/PEGbPHF induced significantly higher GFP expression than naked Ad in both coxsackie and adenovirus receptor (CAR)-positive and -negative cells. To assess the therapeutic efficacy of the Ad/PEGbPHF complex platform, an oncolytic Ad expressing VEGF promoter-targeting transcriptional repressor (KOX) was used to form complexes. At pH6.4, KOX/PEGbPHF significantly suppressed VEGF gene expression, cancer cell migration, vessel sprouting, and cancer cell killing effect compared to naked KOX or KOX/PEGbPHF at pH7.4, demonstrating that KOX/PEGbPHF can overcome the lack of CAR that is frequently observed in tumor tissues. The antitumor activity of KOX/PEGbPHF systemically administered to a tumor xenograft model was significantly higher than that of naked KOX. Furthermore, KOX/PEGbPHF showed lower hepatic toxicity and did not induce an innate immune response against Ad. Altogether, these results demonstrate that pH-sensitive polymer-coated Ad complex significantly increases net positive charge upon exposure to hypoxic tumor microenvironment, allowing passive targeting to the tumor tissue. It may offer superior potential for systemic therapy, due to its improved tumor selectivity, increased therapeutic efficacy, and lower toxicity compared to naked KOX.

Gene therapy

Applications of gene therapy have been evaluated in virtually every oral tissue, and many of these have proved successful at least in animal models. While gene therapy will not be used routinely in the next decade, practitioners of oral medicine should be aware of the potential of this novel type of treatment that doubtless will benefit many patients with oral diseases.

Human parathyroid hormone is secreted primarily into the bloodstream after rat parotid gland gene transfer

Hypoparathyroidism is a hormone deficiency syndrome that leads to low blood calcium levels and for which current replacement therapy is inadequate. Gene transfer to salivary glands leads to safe and abundant secretion of therapeutic protein into either saliva or the bloodstream. We previously reported the successful transduction of rat submandibular glands with an adenoviral vector encoding human parathyroid hormone (Ad.hPTH), but unfortunately most of the hPTH was secreted into saliva. Because submandibular and parotid glands are morphologically and functionally different, we hypothesized that hPTH sorting might be different in parotid glands. After 2 days, the pattern of hPTH secretion from transduced parotid glands of intact rats was reversed from that of transduced submandibular glands, that is, most transgenic hPTH was detected in serum (5 × 10(10) viral particles per gland; the saliva-to-serum ratio of total hPTH secreted was 0.04). Vector copies were localized to the targeted parotid glands, with none detected in liver or spleen. Ad.hPTH next was administered to parotid glands of parathyroidectomized rats. Two days after delivery no hPTH was detectable in saliva, but high levels were found in serum, leading to normalization of serum calcium and a significant increase in the urinary phosphorus-to-creatinine ratio. This study demonstrates for the first time differential sorting of transgenic hPTH between submandibular and parotid glands, suggesting that hPTH may be a valuable model protein for understanding the molecular basis of transgenic secretory protein sorting in these exocrine glands. We also show the clinical potential of salivary gland hPTH gene therapy for patients with hypoparathyroidism.

Production and sorting of transgenic, modified human parathyroid hormone in vivo in rat salivary glands

Polarized salivary epithelial cells can sort secretory proteins towards either the basolateral or apical pole. Transgenic human parathyroid hormone (hPTH) exclusively sorts apically in rat submandibular glands. To help understand this specific process we modified the hPTH cDNA sequence and delivered the cDNAs to glands in vivo using adenoviral (Ad) vectors. The Ad vectors encoded: (1) the native form of hPTH (Ad.pre-pro-hPTH1-84), (2) the native sequence, but with the pro-segment deleted (Ad.pre-hPTH1-84), and (3) a sequence containing the pre-segment followed by the first 34 amino acids of hPTH (Ad.pre-hPTH1-34). hPTH production and sorting were studied after two days. All constructs were effectively transcribed in targeted glands. However, the pre-hPTH1-84 modification led to reduced hPTH secretion and production, while no immunoreactive hPTH resulted from pre-hPTH1-34 cDNA infusion. The pre-hPTH1-84 modification had no effect on apical sorting. These in vivo results show that the signal responsible for hPTH's apical sorting does not reside in the pro-segment and that deleting both the pro-segment and the carboxyl-terminal region severely impairs post-translational processing of hPTH.

Sorting of transgenic secretory proteins in rhesus macaque parotid glands after adenovirus-mediated gene transfer

We have previously used viral vectors encoding either human growth hormone (hGH) or erythropoietin (hEPO) to study the sorting of transgenic proteins in mouse and minipig salivary glands. Whereas hGH (a regulated secretory pathway [RSP] protein) is secreted predominantly into saliva in both species, hEPO (a constitutive secretory pathway [CSP] protein) is found primarily in the bloodstream with mice, but overwhelmingly in saliva with minipigs. In view of the hEPO sorting difference, we have conducted a similar study in nonhuman primates. Specifically, we examined hGH and hEPO sorting after adenoviral (Ad) vector-mediated gene transfer to parotid glands of rhesus macaques, another large and important animal model. Two groups (n = 2 per dose group; total n = 8) of male macaques received either 10(10) particles per gland (low-dose group) or 10(11) particles per gland (high-dose group) of adenoviral (Ad) vectors encoding either hGH (AdhGH) or hEPO (Ad-hEPO) via intraoral cannulation of both parotid glands. All macaques tolerated administration of Ad vectors well, with no clinically significant changes observed in any hematological and serum chemistry parameters. In AdhGH-treated animals, hGH was secreted exclusively into saliva. In contrast, after AdhEPO delivery, hEPO was secreted both in serum and saliva, at levels intermediate between mice and minipigs. We conclude that RSP proteins are faithfully secreted into saliva in all model species tested, whereas patterns of CSP protein secretion are variable.

In vivo secretion of the mouse immunoglobulin G Fc fragment from rat submandibular glands

BACKGROUND

Salivary glands have been proposed as target organs for gene therapy. They secrete endogenous, as well as transgenic proteins, in a polarized manner. Transgene-encoded regulated pathway proteins primarily follow the regulated pathway in rat salivary glands and are secreted into saliva in an exocrine manner. Conversely, constitutive pathway proteins generally are secreted more basolaterally and thus follow the endocrine route. In the present study, we studied in vivo the sorting of the mouse immunoglobulin G2b Fc fragment, which is physiologically secreted via the constitutive pathway.

METHODS

Adenoviral vectors encoding the Fc fragment and human growth hormone were delivered into rat and mouse submandibular glands in vivo to compare their serum-to-saliva distribution. We also compared the intracellular localization of the Fc fragment and growth hormone by confocal microscopy.

RESULTS

We found that the Fc fragment was secreted almost entirely into the bloodstream from rat and mouse submandibular glands via a constitutive or constitutive-like pathway. This sorting behaviour is clearly different from that of transgenic human growth hormone, which is secreted in a regulated pathway, both in neuroendocrine cells and as a transgenic protein from salivary gland cells. We also found that simultaneously expressed human growth hormone and the mouse Fc fragment do not appear to influence each other's sorting behaviour. The Fc fragment showed a primarily basal localization, whereas growth hormone showed an apical localization, in rat submandibular gland acinar cells.

CONCLUSIONS

The results obtained in the present study indicate that the mouse Fc fragment is a useful model protein for examining the basolateral versus apical secretory pathways employed by transgenic secretory proteins in salivary glands.

Differential sorting of human parathyroid hormone after transduction of mouse and rat salivary glands

Gene transfer to salivary glands leads to abundant secretion of transgenic protein into either saliva or the bloodstream. This indicates significant clinical potential, depending on the route of sorting. The aim of this study was to probe the sorting characteristics of human parathyroid hormone (hPTH) in two animal models for salivary gland gene transfer. PTH is a key hormone regulating calcium levels in the blood. A recombinant serotype 5 adenoviral vector carrying the hPTH cDNA was administered to the submandibular glands of mice and rats. Two days after delivery, high levels of hPTH were found in the serum of mice, leading to elevated serum calcium levels. Only low amounts of hPTH were found in the saliva. Two days after vector infusion into rats, a massive secretion of hPTH was measured in saliva, with little secretion into serum. Confocal microscopy showed hPTH in the glands, localized basolaterally in mice and apically in rats. Submandibular gland transduction was effective and the produced hPTH was biologically active in vivo. Whereas hPTH sorted toward the basolateral side in mice, in rats hPTH was secreted mainly at the apical side. These results indicate that the interaction between hPTH and the cell sorting machinery is different between mouse and rat salivary glands. Detailed studies in these two species should result in a better understanding of cellular control of transgenic secretory protein sorting in this tissue.

Sorting behavior of a transgenic erythropoietin-growth hormone fusion protein in murine salivary glands

Salivary glands are useful gene transfer target sites for the production of therapeutic proteins, and can secrete proteins into both saliva and the bloodstream. The mechanisms involved in this differential protein sorting are not well understood, although it is believed, at least in part, to be based on the amino acid sequence of the encoded protein. We hypothesized that a transgenic protein, human erythropoietin (hEpo), normally sorted from murine salivary glands into the bloodstream, could be redirected into saliva by fusing it with human growth hormone (hGH). After transfection, the hEpo-hGH fusion protein was expressed and glycosylated in both HEK 293 and A5 cells. When packaged in an adenovirus serotype 5 vector and delivered to murine submandibular cells in vivo via retroductal cannulation, the hEpo-hGH fusion protein was also expressed, albeit at approximately 26% of the levels of hEpo expression. Importantly, in multiple experiments with different cohorts of mice, the hEpo-hGH fusion protein was sorted more frequently into saliva, versus the bloodstream, than was the hEpo protein (p < 0.001). These studies show it is possible to redirect the secretion of a transgenic constitutive pathway protein from salivary gland cells after gene transfer in vivo, a finding that may facilitate developing novel treatments for certain upper gastrointestinal tract disorders.

Sorting of growth hormone-erythropoietin fusion proteins in rat salivary glands

Neuroendocrine and exocrine cells secrete proteins in either a constitutive manner or via the regulated secretory pathway (RSP), but the specific sorting mechanisms involved are not fully understood. After gene transfer to rat salivary glands, the transgenic model proteins human growth hormone (hGH) and erythropoietin (hEpo) are secreted primarily into saliva (RSP; exocrine) and serum (constitutive; endocrine), respectively. We hypothesized that fusion of hGH at either the C-terminus or the N-terminus of hEpo would re-direct hEpo from the bloodstream into saliva. We constructed and expressed two fusion proteins, hEpo-hGH and hGH-hEpo, using serotype 5-adenoviral vectors, and delivered them to rat submandibular glands in vivo via retroductal cannulation. Both the hEpo-hGH and hGH-hEpo fusion proteins, but not hEpo alone, were secreted primarily into saliva (p<0.0001 and p=0.0083, respectively). These in vivo studies demonstrate for the first time that hGH, in an N- as well as C-terminal position, influences the secretion of a constitutive pathway protein.

Secretory cargo composition affects polarized secretion in MDCK epithelial cells

Polarized epithelial cells secrete proteins at either the apical or basolateral cell surface. A number of non-epithelial secretory proteins also exhibit polarized secretion when they are expressed in polarized epithelial cells but it is difficult to predict where foreign proteins will be secreted in epithelial cells. The question is of interest since secretory epithelia are considered as target tissues for gene therapy protocols that aim to express therapeutic secretory proteins. In the parathyroid gland, parathyroid hormone is processed by furin and co-stored with chromogranin A in secretory granules. To test the secretion of these proteins in epithelial cells, they were expressed in MDCK cells. Chromogranin A and a secreted form of furin were secreted apically while parathyroid hormone was secreted 60% basolaterally. However, in the presence of chromogranin A, the secretion of parathyroid hormone was 65% apical, suggesting that chromogranin can act as a "sorting escort" (sorting chaperone) for parathyroid hormone. Conversely, apically secreted furin did not affect the sorting of parathyroid hormone. The apical secretion of chromogranin A was dependent on cholesterol, suggesting that this protein uses an established cellular sorting mechanism for apical secretion. However, this sorting does not involve the N-terminal membrane-binding domain of chromogranin A. These results suggest that foreign secretory proteins can be used as "sorting escorts" to direct secretory proteins to the apical secretory pathway without altering the primary structure of the secreted protein. Such a system may be of use in the targeted expression of secretory proteins from epithelial cells.

Reengineering salivary gland cells to enhance protein secretion for use in developing artificial salivary gland device

Salivary glands (SGs) are considered exocrine glands, which mainly secrete water into the oral cavity. Nevertheless, they also exhibit a smaller endocrine secretory pathway toward the bloodstream. The concept of an artificial SG device for exocrine fluid secretion into the oral region in xerostomic patients has been previously studied. The purpose of the current study was to examine the potential of such a device for enhancing bioactive protein secretion. We engineered a plasmid encoding a SG-specific signal peptide sequence adjacent to a normally nonsecreted encoded reporter gene creating a chimera protein, and examined if this construct can enhance secretion from salivary epithelial cells. An N-terminal encoding epidermal growth factor (EGF) sequence was synthesized and inserted into a pGL3 control vector 5' of a firefly luciferase gene, creating a pGL3-EGF signal peptide (pGL3-EGFSP) fused vector. This vector was cotransfected with a pRL-CMV vector containing a Renilla luciferase gene, in 293 cells (serving as controls), and human submandibular gland ductal epithelial (HSG), rat submandibular gland acinar epithelial (SMIE), and rat submandibular gland ductal epithelial (A5) salivary cell lines. The transfected 293, SMIE, and HSG cells showed 8-, 18-, and 40-fold higher luciferase activity, respectively. These observations lead to the concept of an envisioned secretory device, which can serve as a potential biological pump for bioactive proteins.

Isoproterenol increases sorting of parotid gland cargo proteins to the basolateral pathway

Exocrine cells have an essential function of sorting secreted proteins into the correct secretory pathway. A clear understanding of sorting in salivary glands would contribute to the correct targeting of therapeutic transgenes. The present work investigated whether there is a change in the relative proportions of basic proline-rich protein (PRP) and acidic PRPs in secretory granules in response to chronic isoproterenol treatment, and whether this alters the sorting of endogenous cargo proteins. Immunoblot analysis of secretory granules from rat parotids found a large increase of basic PRP over acidic PRPs in response to chronic isoproterenol treatment. Pulse chase experiments demonstrated that isoproterenol also decreased regulated secretion of newly synthesized secretory proteins, including PRPs, amylase and parotid secretory protein. This decreased efficiency of the apical regulated pathway may be mediated by alkalization of the secretory granules since it was reversed by treatment with mild acid. We also investigated changes in secretion through the basolateral (endocrine) pathways. A significant increase in parotid secretory protein and salivary amylase was detected in sera of isoproterenol-treated animals, suggesting increased routing of the regulated secretory proteins to the basolateral pathway. These studies demonstrate that shifts of endogenous proteins can modulate regulated secretion and sorting of cargo proteins.

Adeno-associated virus serotype 2-mediated gene transfer to the parotid glands of nonhuman primates

Salivary glands (SGs) are promising gene transfer targets with potential clinical applicability. Previous experiments in rodents using recombinant serotype 2 adeno-associated viral (rAAV2) vectors have demonstrated relatively stable transgene-encoded protein levels after SG gene transfer. In the present study, we examine direct SG administration of rAAV2 vectors encoding rhesus macaque erythropoietin (RhEPO) to the parotid glands of nonhuman primates using two different doses (n = 3 per group; 1 x 10(10) or 3 x 10(11) particles/gland, respectively). Gene transfer had no negative effects on general macaque physiology (e.g., weight, complete blood count, and serum chemistry). Macaques were euthanized 6 months after vector administration and complete necropsy and pathology assessments were performed, revealing no vector-related pathological lesions in any of the examined organs. In the high-dose group, RhEPO expression increased quickly (i.e., by week 1) and levels remained relatively stable both in serum and saliva until the end of the study. Serum-to-saliva ratios of RhEPO revealed secretion of the transgene product into the bloodstream, but not to the extent previously observed in mice. Furthermore, the kinetic results were not predicted by those observed in murine SGs. With respect to viral biodistribution, at necropsy vector was found overwhelmingly in the targeted parotid gland ( approximately 100 times more than levels in other tissues, most of which were similar to tissue levels in nontreated animals). We conclude that administration of modest doses of rAAV2 vectors to SGs for therapeutic purposes can be accomplished without significant or permanent injury to the targeted gland or to distant organs of nonhuman primates.

Sorting of transgenic secretory proteins in miniature pig parotid glands following adenoviral-mediated gene transfer

BACKGROUND

Gene transfer to salivary glands for use in treating both systemic and upper gastrointestinal tract diseases shows considerable potential. Numerous studies in rodents demonstrate that salivary glands can secrete transgenic secretory proteins either into saliva, primarily via the regulated secretory pathway (RSP), or into the bloodstream, primarily by the constitutive secretory pathway (CSP). The purpose of the present study was to assess the sorting characteristics of human growth hormone (hGH), a RSP protein, and human erythropoietin (hEpo), a CSP protein, in a large animal model of salivary gland gene transfer, the miniature pig.

METHODS

Recombinant serotype 5 adenoviral (Ad5; 10(11) particles/gland) vectors encoding either hGH (AdCMVhGH) or hEpo (AdCMVhEpo) were administered to both parotid glands of male miniature pigs by intraductal cannulation. The secretion of hGH or hEpo was measured in both saliva and serum on days 3, 7 and 14 following administration. Detailed serum chemistry and hematological analyses were performed, and the presence of serum antibodies to hGH and hEpo was measured. For AdCMVhEpo-treated minipigs vector distribution in multiple tissues was determined by quantitative polymerase chain reaction (QPCR).

RESULTS

The RSP protein hGH was secreted entirely into saliva, while the CSP protein hEpo was secreted into both saliva and serum. Most hEpo was found in saliva, but serum hEpo levels were sufficient to significantly increase hematocrit levels in treated animals by approximately 10%. Expression of both transgenes was maximal on day 3 and declined to near background by day 14. The amount of vector found in the targeted glands was 100 x more than in other tissues.

CONCLUSIONS

Secretion of transgenic hGH from minipig parotid glands occurred principally into saliva via the RSP, as seen in rodents, while hEpo was secreted into both saliva and serum, the latter presumably via the CSP. Even though hEpo secretion into the bloodstream was not to the extent previously observed in rodents, serum hEpo levels were considerable and the hEpo was biologically active. Ad5 vector distribution was highly restricted to the parotid glands with little vector detected elsewhere. While the results in this large animal model support the established notion that salivary gland gene transfer can be used for treating systemic single protein deficiency disorders, they also highlight differences in transgenic CSP protein sorting between rodents and miniature pigs.

The transduction of rat submandibular glands by an adenoviral vector carrying the human growth hormone gene is associated with limited and reversible changes at the infusion site

Adenoviral vectors have been shown to efficiently deliver exogenous genes to salivary glands and have therefore been investigated as tools for the treatment of human disease. The purpose of this study was to evaluate the response of F344 rats to intraductal infusion of the right submandibular salivary gland with an adenoviral vector encoding the gene for human growth hormone (AdCMVhGH). Co-administration of hydroxychloroquine (HCQ) was used to redirect the secretion of human growth hormone (hGH) from saliva into serum. This paper documents the findings of the pathology evaluation of this National Toxicology Program study. The right submandibular salivary gland (infusion site) was the primary target organ, with microscopic lesions characteristic of a mild to moderate insult observed at 3 days post infusion in vector exposed animals. These lesions were characterized by variable degrees of acute glandular inflammation, degeneration and necrosis, with more severe lesions in the higher dose groups. Rats at 28 days post infusion had milder inflammation, degeneration and necrosis compared to day 3 rats, with variable degrees of regeneration. In conclusion, the effects on the salivary glands are reversible as indicated by the milder inflammation and degeneration in the day 28 rats concomitant with mild to moderate regeneration. Therefore, the vector appears relatively innocuous with limited tissue toxicity. [The supplemental data referenced in this paper is not printed in this issue of Toxicologic Pathology. It is available as a downloadable file in the online edition of Toxicologic Pathology, 34(4). In order to access the full article online, you must have either an individual subscription or a member subscription accessed through www.toxpath.org.].

Salivary gland gene therapy

Salivary glands have proven to be unusual but valuable target sites for multiple clinical gene transfer applications. Access to salivary glands for gene transfer is easy. Multiple studies in animal models have yielded proofs of concept for novel treatments for damaged salivary glands following therapeutic irraditation, in Sjögren's syndrome, and for gene therapeutics systemically by way of the blood-stream and locally in the oral cavity and upper gastrointestinal tract.

Toxicity and biodistribution of a first-generation recombinant adenoviral vector, in the presence of hydroxychloroquine, following retroductal delivery to a single rat submandibular gland

OBJECTIVE

We examined the toxicity and biodistribution associated with a single administration of a first-generation, serotype 5, adenoviral vector encoding human growth hormone (hGH; AdCMVhGH) to a single rat submandibular gland in the presence of hydroxychloroquine (HCQ). Previously, we showed that hGH is primarily secreted into saliva (approximately ninefold serum level) when expressed as a transgene in salivary glands (e.g. Baum et al, 1999), but administration of HCQ substantially increases the hGH levels secreted into the bloodstream (Hoque et al, 2001). A potential application of this observation is for patients with adult hGH deficiency.

METHODS

Six groups of male and female adult rats (n = 12 each) were studied, with zero to 1.5 x 10(11) particles of AdCMVhGH, +/-HCQ, administered retroductally. Multiple clinical and pathological parameters, as well as vector tissue distribution, were assessed.

RESULTS

All animals survived until the scheduled day of sacrifice, and essentially no untoward events were observed clinically or at gross necropsy. We observed no vector-related effects on clinical hematology evaluations and a single, transient significant change on clinical chemistry evaluations (increased serum globulin levels). Three days after AdCMVhGH administration, the vector distributed to all tissues analyzed with the exception of gonads and heart. By day 29, most organs, other than the targeted and contralateral submandibular glands, were negative for the presence of vector. On day 3, none of the animals tested positive for the presence of replication competent adenovirus in either their blood or saliva.

CONCLUSION

Salivary gland delivery of AdCMVhGH +/-HCQ appears associated with limited toxicity in rats.

Partial redirection of transgenic human growth hormone secretion from rat salivary glands

Regulated secretory pathway proteins, when delivered as transgenes to salivary glands, are secreted predominantly into saliva. This is not useful for those proteins whose therapeutic function is required systemically, for example, human growth hormone (hGH). One strategy to improve the efficiency of hGH secretion into the bloodstream involves manipulation of existing sorting signals. The C terminus of hGH is highly conserved and contains a domain similar to the regulated pathway sorting domain of pro-opiomelanocortin (POMC). We hypothesized that, similar to POMC, mutation of this domain would divert hGH secretion from the regulated to the constitutive pathway, which in salivary glands leads to the bloodstream. Several mutations were made in the C terminus of the hGH cDNA and tested in vitro. One biologically active mutant containing E174A and E186A substitutions, and with an included C-terminal extension, was studied in greater detail. Compared with wild-type hGH, we found that this mutant hGH accumulated in the Golgi/trans-Golgi network and showed increased basal secretion in AtT20 cells, a model endocrine cell line. Importantly, in vivo, the mutant hGH displayed a relative increase in the proportion of constitutive pathway secretion seen from rat salivary glands, with a significantly lower saliva-versus-serum secretion ratio (p=0.03). Although this mutant is unlikely to be therapeutically beneficial, these results suggest that the final destination of a transgenic secretory protein may be controlled by reengineering its sorting determinants.

Effect of human vasoactive intestinal peptide gene transfer in a murine model of Sjogren's syndrome

BACKGROUND

Sjögren's syndrome (SS), an autoimmune exocrinopathy mainly affecting lachrymal and salivary glands, results in ocular and oral dryness (keratoconjunctivitis sicca and xerostomia). The aetiology and pathogenesis are largely unknown; currently, only palliative treatment is available.

OBJECTIVE

To determine whether gene transfer of vasoactive intestinal peptide (VIP), based on its immunomodulatory properties, might be useful in the management of SS.

METHODS

A recombinant serotype 2 adeno-associated virus encoding the human VIP transgene (rAAV2hVIP) was constructed and its efficacy tested in the female non-obese diabetic (NOD) mouse model for SS after retrograde instillation in submandibular glands (SMGs). 10(10) particles/gland of rAAV2hVIP or rAAV2LacZ (encoding beta-galactosidase; control vector) were administered at 8 weeks of age (before sialadenitis onset). Salivary flow rates were determined before vector delivery and at time of death (16 weeks). After death, saliva, serum, and SMGs were harvested. Salivary output, inflammatory infiltrates (focus scores), VIP protein expression, cytokine profile, and serum anti-VIP antibodies were analysed.

RESULTS

rAAV2hVIP significantly improved the salivary flow, increased SMG and serum expression of VIP, and reduced SMG cytokines interleukin (IL) 2, IL10, IL12 (p70), and tumour necrosis factor alpha, and serum RANTES, compared with the control vector. No difference in focus scores or apoptotic rates was found; neutralising antibodies were not detected.

CONCLUSIONS

Local delivery of rAAV2hVIP can have disease modifying and immunosuppressive effects in SMGs of the NOD mouse model of SS. The new strategy of employing VIP prophylactically may be useful for both understanding and managing the salivary component of SS.

Parotid secretory granules: crossroads of secretory pathways and protein storage

Saliva plays an important role in digestion, host defense, and lubrication. The parotid gland contributes a variety of secretory proteins-including amylase, proline-rich proteins, and parotid secretory protein (PSP)-to these functions. The regulated secretion of salivary proteins ensures the availability of the correct mix of salivary proteins when needed. In addition, the major salivary glands are targets for gene therapy protocols aimed at targeting therapeutic proteins either to the oral cavity or to circulation. To be successful, such protocols must be based on a solid understanding of protein trafficking in salivary gland cells. In this paper, model systems available to study the secretion of salivary proteins are reviewed. Parotid secretory proteins are stored in large dense-core secretory granules that undergo stimulated secretion in response to extracellular stimulation. Secretory proteins that are not stored in large secretory granules are secreted by either the minor regulated secretory pathway, constitutive secretory pathways (apical or basolateral), or the constitutive-like secretory pathway. It is proposed that the maturing secretory granules act as a distribution center for secretory proteins in salivary acinar cells. Protein distribution or sorting is thought to involve their selective retention during secretory granule maturation. Unlike regulated secretory proteins in other cell types, salivary proteins do not exhibit calcium-induced aggregation. Instead, sulfated proteoglycans play a role in the storage of secretory proteins in parotid acinar cells. This work suggests that unique sorting and retention mechanisms are responsible for the distribution of secretory proteins to different secretory pathways from the maturing secretory granules in parotid acinar cells.

Salivary glands: novel target sites for gene therapeutics

Directing the local or systemic expression of therapeutic proteins is a potentially important clinical application of gene transfer technology. Gene-based therapeutics theoretically offer many advantages over protein therapeutics. Numerous tissues have been evaluated for this purpose in animal models, most commonly the liver and skeletal muscle. Based on pre-clinical studies, we suggest that salivary glands are a valuable, yet under-appreciated, target tissue for both systemic and upper gastrointestinal tract gene therapeutic applications.

Local adeno-associated virus-mediated interleukin 10 gene transfer has disease-modifying effects in a murine model of Sjögren's syndrome

Female nonobese diabetic (NOD) mice develop spontaneous autoimmune sialadenitis and loss of salivary flow, and are a widely used model of Sjögren's syndrome. We examined the feasibility of local salivary gland immunomodulatory gene delivery to alter these sequelae in NOD mice. We constructed recombinant adeno-associated virus (rAAV) vectors encoding either human interleukin 10 (rAAVhIL-10) or beta-galactosidase (rAAVLacZ, control vector). Mice received rAAVhIL-10 or rAAVLacZ by retrograde submandibular ductal instillation either at age 8 weeks (early, before onset of sialadenitis), or at 16 weeks (late, after onset of sialadenitis). As a systemic treatment control, separate mice received intramuscular delivery of rAAVhIL-10 at each time point. Both submandibular and intramuscular delivery of vector led to low circulating levels of hIL-10. After submandibular administration of rAAVhIL-10, salivary flow rates at 20 weeks for both the early and late treatment groups were significantly higher than for both rAAVLacZ-administered and untreated mice. Systemic delivery of rAAVhIL-10 led to improved salivary flow in the late treatment group. Inflammatory infiltrates in submandibular glands, however, were significantly reduced only in mice receiving rAAVhIL-10 locally in the salivary gland compared with mice receiving this vector intramuscularly, or rAAVLacZ or no treatment. In addition, after submandibular rAAVhIL-10 delivery, NOD mice exhibited significantly lower blood glucose, and higher serum insulin, levels than all other groups, indicating some systemic benefit of this treatment. These studies show that expression of hIL-10 by rAAV vectors can have disease-modifying effects in the salivary glands of NOD mice, and suggest that local immunomodulatory gene transfer may be useful for managing the salivary gland pathology in Sjögren's syndrome.

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.

Enhanced systemic transgene expression after nonviral salivary gland transfection using a novel endonuclease inhibitor/DNA formulation

Gene transfer to the major salivary glands is an attractive method for the systemic delivery of therapeutic proteins. To date, nonviral gene transfer to these glands has resulted in inadequate systemic protein concentrations. We believe that identification of the barriers responsible for this inefficient transfection will enable the development of enhanced nonviral gene transfer in salivary glands and other tissues. One potential barrier is the degradation of plasmid DNA by endonucleases. To test this hypothesis, we coadministered two endonuclease inhibitors ((zinc and aurintricarboxylic acid (ATA)) with plasmid DNA, containing the secreted alkaline phosphatase gene (SEAP), to the submandibular glands of rats. The effect of zinc and ATA on SEAP expression, tissue accumulation of plasmid DNA, and plasmid DNA stability was then characterized. We observed that mixtures containing zinc/DNA, ATA/DNA, and zinc/ATA/DNA significantly enhanced both systemic transgene expression and the amount of plasmid DNA associated with treated tissues. The relative endonuclease inhibitory activity of zinc, ATA, and zinc/ATA correlated with the observed effects on transfection efficacy. The use of zinc/ATA enhanced the efficacy of salivary gland transfection by at least 1000-fold versus DNA alone. Importantly, this improved performance resulted in robust systemic secretion of an exogenous protein (SEAP), thus demonstrating the potential this nonviral gene transfer technology has as a method to treat systemic protein deficiencies.

Rapamycin control of exocrine protein levels in saliva after adenoviral vector-mediated gene transfer

Transgene-encoded therapeutic secretory proteins can be efficiently secreted from salivary glands into saliva or the bloodstream after adenoviral (Ad)-mediated gene transfer. Since transgene expression from conventional vectors is typically unregulated, we evaluated the rapamycin-based dimerizer regulation system for control of transgene expression in, and consequent exocrine protein secreted from, rat salivary glands. We used human growth hormone (hGH) as a surrogate exocrine secretory protein. Two Ad vectors, Ad C4ZF3, encoding activation and DNA binding domain fusion polypeptides, and Ad Z12-I-GH-2, encoding hGH, were constructed and shown useful in vitro. Thereafter, both vectors were delivered into submandibular glands by retroductal infusion. After 24 h, rapamycin (0, 1, 3 or 10 mg/kg) was administered, and 20 h later hGH levels in saliva were determined. Salivary hGH levels were rapamycin concentration dependent. At a rapamycin dose of 10 mg/kg, total salivary hGH was 693+/-197 ng and the hGH concentration in saliva was 4.6+/-1.3 microg/ml. Over a 16-day experimental period, three separate administrations of rapamycin (3 mg/kg) induced distinct elevations of salivary hGH (approximately 100-200 ng total hGH) that were entirely rapamycin dependent. This study demonstrates for the first time pharmacological control of transgenic exocrine protein production and presence in saliva after salivary gland gene transfer, and the potential for its application to the management of oral, oropharyngeal and upper gastrointestinal tract disorders.

Utilizing endocrine secretory pathways in salivary glands for systemic gene therapeutics

Mammalian salivary glands are commonly used models of exocrine secretion. However, there is substantial experimental evidence showing the physiological existence of endocrine secretory pathways in these tissues. The use of gene transfer technology in vivo has allowed the unambiguous demonstration of these endocrine pathways. We and others have exploited such findings and evaluated salivary glands as possible target tissues for systemic applications of gene therapeutics. Salivary glands present numerous advantages for this purpose, including being well encapsulated, which limits extra-glandular vector dissemination, and having the luminal membranes of almost all parenchymal cells accessible via intraoral delivery of vectors through the main excretory ducts. Existing studies suggest that clinical benefits will result from salivary gland targeted 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.

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.

Using salivary glands as a tissue target for gene therapeutics

Gene transfer offers a potential way to correct local and systemic protein deficiency disorders by using genes as drugs, so called gene therapeutics. Salivary glands present an interesting target site for gene therapeutic applications. Herein, we review proofs of concept achieved for salivary glands with in vivo animal models. In that context we discuss problems (general and salivary tissue-specific) that limit immediate clinical use for this application of gene transfer. Ongoing efforts, however, suggest that salivary glands may be suitable as gene therapeutic target sites for drug delivery in the near future.

Recombinant adeno-associated virus serotype 2 vectors mediate stable interleukin 10 secretion from salivary glands into the bloodstream

We have constructed a recombinant adeno-associated virus serotype 2 vector encoding human interleukin 10 (rAAVhIL10). IL-10 is a potent antiinflammatory/immune cytokine, which has received growing attention for its therapeutic potential. Human IL-10 (hIL-10) production was virus dose dependent after in vitro infection of HSG cells, a human submandibular gland cell line. The vector-derived hIL-10 produced was biologically active, as the medium from rAAVhIL10-infected HSG cells caused a dose-dependent blockade of IL-12 secretion from spleen cells of IL-10 knockout mice challenged with heat-killed Brucella abortus. Administration of rAAVhIL10 (10(10) genomes per gland) to both mouse submandibular glands led to hIL-10 secretion into the bloodstream (approximately 1-5 pg/ml), that is, in an endocrine manner, which was stable for approximately 2 months. Salivary gland administration of rAAVhIL10 under experimental conditions was more efficacious than intravenous administration (approximately 0.5-0.7 pg/ml). Also, hIL-10 was readily secreted in vitro from organ cultures of minced submandibular glands infected with rAAVhIL10, 6 or 8 weeks earlier. Consistent with these results, hIL-10 mRNA was detected by reverse transcription-polymerase chain reaction in submandibular glands of mice infected with rAAVhIL10 but not from control mice. At these doses, little to no hIL-10 was detected in mouse saliva. Using a rAAV serotype 2 vector encoding beta-galactosidase, we observed that the primary parenchymal target cells were ductal. These findings represent the first report of rAAV use to target exocrine glands for systemic secretion of a therapeutic protein, and support the notion that rAAV serotype 2 vectors may be useful in salivary glands for local (periglandular) and systemic gene-based protein therapeutics.

The impact of gene therapy on dentistry: a revisiting after six years

BACKGROUND

Gene therapy is an emerging field of biomedicine that has commanded considerable scientific and popular attention. The procedure involves the transfer of genes to patients for clinical benefit. Transferred genes can b e used for either reparative or pharmacological purposes.

OVERVIEW

In 1995, the first author and a colleague described the potential impact of gene therapy on dentistry, on the basis of initial studies of gene transfer applications to salivary glands, keratinocytes and cancer cells. Their conclusion was that gene therapy would have a significant impact on the nature of dental practice within 20 years. In this article, the authors consider research progress since 1995 and reexamine the earlier conclusion.

PRACTICE IMPLICATIONS

In the past six years, remarkable progress has been made in the field of gene therapy, including seven areas relevant to dental practice: bone repair, salivary glands, autoimmune disease, pain, DNA vaccinations, keratinocytes and cancer. While considerable problems remain, thus impeding the routine clinical use of gene transfer, gene therapy will have a pervasive and significant impact on areas of dental practice that are based in biological science. By 2015, this will translate into practitioners' having a wide range of novel biological treatment options for their patients.