Cationic liposome-mediated gene transfer to rat salivary epithelial cells in vitro and in vivo

BACKGROUND

Previously we have shown that gene transfer to salivary gland epithelial cells readily occurs via recombinant adenoviruses, although the response is short-lived and results in a potent host immune response. The aim of the present study was to assess the feasibility of using cationic liposomes to mediate gene transfer to rat salivary cells in vitro and in vivo.

METHODS

Initially, for transfection in vitro, we used two cationic liposome formulations (GAP-DLRIE/DOPE and DOSPA/DOPE) complexed with plasmid encoding human growth hormone (hGH) as a reporter gene. Thereafter, using GAP-DLRIE/DOPE, plasmids were transferred to rat salivary glands in vivo, and hGH levels measured in saliva, serum and gland extracts.

RESULTS

Under optimal conditions, transfection of rat submandibular glands (SMGs) was consistently observed. Approximately 95% of the cells transfected with a plasmid encoding beta-galactosidase were acinar cells. Maximal hGH expression was obtained during the first 48 h post-transfection using a plasmid encoding the hGH cDNA and complexed with GAP-DLRIE/DOPE. hGH was detected in gland extracts and saliva, and occasionally in serum. No systemic or local gland pathology was consistently or significantly observed.

CONCLUSIONS

The levels of the reporter gene product, hGH, obtained after GAP-DLRIE/DOPE-mediated gene transfer are considerably lower (<0.5%) than those achieved with adenoviral vectors (10(8) PFU). Nonetheless, cationic liposome-mediated gene transfer to salivary glands may be useful for potential therapeutic applications.

Sodium phosphate enhances plasmid DNA expression in vivo

Intramuscular injection of plasmid DNA results in myofiber cell expression of proteins encoded by the DNA. The preferred vehicle for plasmid DNA injections has been saline (154 mM sodium chloride) or PBS (154 mM NaCl plus 10 mM sodium phosphate). Here, it is shown that injection of luciferase or beta-galactosidase encoding plasmid DNA in a 150 mM sodium phosphate vehicle into murine muscle resulted in a two- to seven-fold increase in transgene expression compared with DNA injected in saline or PBS. When the DNA encoded secreted alkaline phosphatase, preproinsulin or interferon, sodium phosphate vehicle increased their serum levels by two- to four-fold. When the DNA encoded mouse erythropoietin, sodium phosphate vehicle increased hematocrits by two-fold compared with DNA injected in saline. When the DNA encoded influenza nucleoprotein, sodium phosphate increased anti-nucleoprotein antibody titers by two-fold. The expression of luciferase from plasmid DNA instilled into lung was increased five-fold compared with that in vehicle without sodium phosphate. Incubation of plasmid DNA with muscle extract or serum showed that sodium phosphate protected the DNA from degradation. Thus, a change from sodium chloride to sodium phosphate vehicle can enhance the expression of plasmid DNA in a tissue, possibly by inhibiting DNA degradation. Gene Therapy (2000) 7, 1171-1182.

Insulin delivery with plasmid DNA

Success in controlling hyperglycemia in type I diabetics will require a restoration of basal insulin. To this end, three plasmid DNAs (pDNA) encoding preproinsulin were compared for constitutive expression and processing to insulin in nonendocrine cells in vitro. The pDNAs were designed to express rat proinsulin I (VR-3501), rat proinsulin I with the B10 aspartic acid point mutation (VR-3502), and a derivative of VR-3502 with a furin cleavage site added at the B-chain and C-peptide junction (VR-3503). Cells transfected with VR-3501 or VR-3502 were able to secrete only proinsulin, whereas transfection with VR-3503 yielded 30-70% mature insulin, which could be increased to >99% by cotransfection with a furin expression plasmid (VR-3505). The insulin produced was biologically active. The bilateral injection of 100 microg of VR-3502 plasmid into the tibialis anterior muscles of mice on two consecutive days yielded, on average, several hundred picograms of heterologous proinsulin per milliliter of serum. In BALB/c mice, serum proinsulin peaked 7-14 days postinjection and declined to preinjection levels by days 21-28. In athymic nude mice, serum proinsulin was sustained for at least 6 weeks. The therapeutic efficacy of delivering insulin via muscle injection of pDNA was evaluated in athymic nude mice made diabetic with the beta cell toxin streptozotocin (STZ). All animals given control DNA died within 1 week of receiving STZ while 40% of the mice coinjected with plasmids VR-3503 and VR-3505 lived through the duration of the 4-week experiment. Muscles of the surviving animals contained 17-100 ng of immune-reactive insulin (IRI), 86-94% of which was mature insulin. The results suggest that heterologous insulin made in muscle increased the survival rate. We propose that insulin plasmid expression in skeletal muscle may be a valid approach to basal insulin delivery. The feasibility of plasmid DNA-based delivery of basal insulin was investigated. An expression system consisting of pDNAs encoding a selectively mutated rat preproinsulin and mouse furin was developed and characterized in vitro and in vivo. When injected with preproinsulin pDNA, the mouse tibialis anterior muscle expressed and released proinsulin into serum at levels comparable to normal basal insulin in rodents. These heterologous proinsulin levels were sustained for several weeks in immune-compromised nondiabetic mice. Mouse muscle coinjected with a pDNA encoding the endopeptidase furin and a pDNA encoding a pre-proinsulin modified to contain two furin cleavage sites produced fully processed insulin. This muscle-made insulin appears to have contributed to the survival of mice treated with a highly diabetogenic dose of streptozotocin, a beta cell toxin. The results demonstrate that skeletal muscle is able to express and deliver therapeutic insulin from plasmid DNA.

Antitumor effects of interferon-omega: in vivo therapy of human tumor xenografts in nude mice

The antitumor effect of the type I IFN, IFN-omega, was evaluated in both in vitro and in vivo studies of human cancer. For these studies, the cDNA for human IFN-omega was cloned into a eukaryotic expression plasmid DNA (pDNA) driven by the cytomegalovirus promoter. Supernatants from UM449 cells transfected in vitro with IFN-omega pDNA had antiproliferative effects on 11 of 13 human tumor cell lines. For in vivo studies, nude mice were implanted s.c. with one of the following human tumors: NIH: OVCAR-3 ovarian carcinoma, A375 melanoma, or A431 epidermoid carcinoma. Direct intratumoral injection of 100 microg of a IFN-omega pDNA DMRIE/DOPE complex (1:1 DNA:DMRIE mass ratio) for 6 consecutive days resulted in a significant reduction in the tumor volume of NIH: OVCAR-3 ovarian carcinoma or A375 melanoma (P = 0.02). IFN-omega pDNA delivered by i.m. injection also had an antitumor effect. Nude mice bearing s.c. A431 epidermoid carcinoma and injected i.m. with 100 microg of IFN-omega pDNA, twice per week for 3 weeks, had a significant reduction in tumor volume (P = 0.009). These results demonstrate for the first time that IFN-omega can have in vivo antitumor effects in several models of human cancer.

A gene therapy for cancer using intramuscular injection of plasmid DNA encoding interferon alpha

A cancer treatment is described in which i.m. injection of plasmid DNA (pDNA) encoding murine interferon alpha (mIFN-alpha) leads to potent antitumor effects on primary and metastatic tumors in mice. Mice bearing s.c. B16F10 melanoma, Cloudman melanoma, or glioma 261 tumors were injected i.m. with mIFN-alpha pDNA. In all three tumor models, a significant reduction in tumor volume and enhancement of survival was found after IFN pDNA therapy. The mIFN-alpha pDNA could be injected as infrequently as once every other week and still produce a significant antitumor effect, and, in a metastatic tumor model, the therapy markedly reduced the number of lung tumor metastases. Depletion of immune cell subsets indicated that CD8(+) T cells were required for the antitumor response. These studies demonstrate that primary and metastatic tumors can be treated systemically by i.m. injection of a plasmid encoding a cytokine gene.

Vaccination of mice with DNA plasmids coding for the Chlamydia trachomatis major outer membrane protein elicits an immune response but fails to protect against a genital challenge

A DNA plasmid encoding the gene of the major outer membrane protein (MOMP) of the Chlamydia trachomatis mouse pneumonitis (MoPn) serovar and three plasmids containing the variable domains (VD) of the MOMP were constructed. Female mice were inoculated with the plasmids and 60 days later were challenged in the genital tract with C. trachomatis. Six weeks after challenge female mice were caged with male mice and the course of the mating followed. Mice immunized with the MOMP plasmids mounted weak humoral and cell mediated immune responses. However, following the genital challenge no significant differences in vaginal shedding were observed between the groups immunized with the MOMP and control plasmids. In addition, the fertility rates were similar in the experimental and negative control groups. In conclusion, vaccination with DNA plasmids encoding the MOMP elicited a modest immune response but did not protect against infection or disease.

CpG motifs as immune adjuvants

Bacterial DNA contains immunostimulatory motifs that trigger an innate immune response characterized by the production of predominantly Th1-type cytokines. These motifs consist of an unmethylated CpG dinucleotide flanked by two 5' purines and two 3' pyrimidines. We examined whether synthetic oligodeoxynucleotides (oligos) expressing these motifs would act as adjuvants to boost the immune response to DNA- and protein-based immunogens. In vivo experiments demonstrate that CpG-containing oligos augment antigen-specific serum antibody levels by up to tenfold, and IFNgamma production by up to sixfold. These effects were optimized by physically linking the CpG-containing motifs to the immunogen.

Enhancer and promoter chimeras in plasmids designed for intramuscular injection: a comparative in vivo and in vitro study

Enhancers and promoters from various muscle-specific genes were substituted for or combined with the enhancer/promoter of the human cytomegalovirus (CMV) IE gene in a luciferase reporter gene plasmid in an effort to identify new promoter chimeras with increased expression activity after direct intramuscular injection. The regulatory sequence substitutions or additions varied in content, location, and orientation relative to the CMV regulatory sequences. The expression activities of the derivative and parent plasmids were compared quantitatively in vivo using a standard mouse intramuscular injection assay, and in vitro by transfection of differentiated C2C12 mouse myoblasts and BHK hamster kidney cells, to test whether cultured cell transfection could substitute for at least some animal experimentation. In vivo, 1 of 19 of the enhancer/promoter chimeras increased expression levels. In vitro, some chimeras showed significant expression augmentation in C2C12 cells, but not in BHK cells. We conclude that because of differences in plasmid expression profiles, these cell culture systems cannot readily substitute for in vivo testing of new plasmid constructs.

Immunotherapy of established tumors in mice by intratumoral injection of interleukin-2 plasmid DNA: induction of CD8+ T-cell immunity

Intratumoral (i.t.) injection of a plasmid DNA vector encoding the murine interleukin-2 (IL-2) gene was used to treat established renal cell carcinoma (Renca) tumors in BALB/c mice. Tumor regression was observed in 60-90% of mice that were injected i.t. for 4 days with IL-2 plasmid DNA complexed with the cationic lipid DMRIE/DOPE ((+/-)-N-(2-hydroxyethyl)-N,N-dimethyl-2,3-bis(tetradecyloxy)-1-propa naminium bromide/dioleoylphosphatidylethanolamine). The mice remained tumor-free until the conclusion of the study, which was 4 months after tumor challenge. In a rechallenge experiment, mice that were rendered tumor-free for 6 months by IL-2 plasmid DNA treatment rejected a subsequent challenge of Renca cells but could not reject a challenge with the unrelated, syngeneic CT-26 tumor. Spleen cells from cured mice contained Renca-specific cytotoxic T lymphocytes, and adoptive transfer of mixed lymphocyte cultures into naive mice at 2 days after challenge with Renca cells prevented tumor growth. In vivo depletion of T-cell subsets at the time of i.t. injection with IL-2 plasmid DNA demonstrated that CD8+ T cells, but not CD4+ T cells, were the primary effectors of the antitumor response.

Lipid- and adenoviral-mediated gene transfer into AIDS-Kaposi's sarcoma cell lines

Kaposi's sarcoma (KS) is the most frequent malignancy occurring in HIV-positive individuals. AIDS-KS is a more aggressive disease than the classical form, frequently having a rapid clinical course with numerous serious complications. Current systemic treatments for KS, such as chemotherapy and the administration of biological modifiers, are complicated by both the drug resistance of the tumor and the dose-limiting toxicity of the reagents. The relative accessibility of many KS lesions makes the disease a particularly attractive candidate for in vivo gene therapy protocols. In this regard, we are interested in delivering conditionally toxic suicide and/or antiangiogenic vectors to accomplish targeted cell death selectively in AIDS-KS cells. To this end, we examined both cationic lipid- and adenoviral-mediated DNA transfection methods. Using the firefly luciferase reporter gene, we optimized numerous variables known to be important in lipid-mediated DNA transfection, including lipid formulation, the amount of lipid and DNA, lipid/DNA ratio, and cell concentration. Under optimal transfection conditions, approximately 5-25% of KS cells expressed the introduced DNA sequences. Adenoviral-mediated DNA delivery was more efficient than lipid delivery in 4 of 5 primary KS cell lines. Two of the lines (RW248 and RW376) were transduced by adenovirus at frequencies approaching 100%; two cell lines (CVU-1 and RW80) gave efficiencies of 20-35%. Two immortalized KS cell lines (KS Y-1 and KS SLK) were poorly infected, giving a transduction efficiency of <5%. These findings demonstrate that gene transfer into AIDS-KS cells is feasible, and suggest that vector strategies may be permissive for translating gene therapy approaches for the disease.

The orphan nuclear receptor, steroidogenic factor-1, regulates the glycoprotein hormone alpha-subunit gene in pituitary gonadotropes

Tissue-specific expression of the glycoprotein hormone alpha-subunit gene in pituitary gonadotropes relies on a gonadotrope-specific element (GSE), which binds an approximately 54-kilodalton protein termed GSE-binding protein 1 (GSEB1). We report here that GSEB1 is the orphan nuclear receptor steroidogenic factor-1 (SF-1), which has been shown to be a primary regulator of steroidogenic enzymes in the adrenal gland and gonadal tissues. GSEB1 from alpha T3-1 pituitary gonadotrope cells and SF-1 from Y1 adrenocortical cells and R2C testicular Leydig cells display identical binding properties with both the GSE and SF-1 elements. Antiserum specific to the SF-1 DNA-binding domain abolishes the binding of both GSEB1 and SF-1 to both elements. SF-1 mRNA is found in the mouse pituitary and in the alpha T3-1 cell line but not in other pituitary cell lines, consistent with the pattern of GSEB 1-binding activity. The GSE element specifically enhances transcription in SF-1-containing cells. The discovery that an orphan nuclear receptor regulates the expression of both the gonadotropin hormones in the pituitary and the steroidogenic enzymes in the gonad provides a potential molecular mechanism for coordinate control in reproductive function, perhaps through an as yet unidentified endocrine ligand for SF-1.

The sequence of a murine cDNA encoding Ear-2, a nuclear orphan receptor

A 1643-bp cDNA that encodes the mouse Ear-2 orphan nuclear receptor has been isolated from a pituitary cell library. The predicted 389-aa mouse Ear-2 protein bears significant homology to the known human Ear-2 protein especially in the DNA-binding domain.

Helix-loop-helix proteins are present and differentially expressed in different cell lines from the anterior pituitary

The basic-helix-loop-helix (bHLH) class of transcriptional activators, important in the establishment of many different cell lineages, share two important properties: the ability to heterodimerize with other members of this family and to bind DNA containing the loose consensus sequence CANNTG. This study takes advantage of these shared characteristics to begin to address whether or not bHLH proteins are present in pituitary cells. Gel-shift and Southwestern assays using an oligonucleotide containing a bHLH binding consensus sequence demonstrate that pituitary-specific proteins are present in extracts from adult pituitary tissue and pituitary cell lines and bind specifically to this sequence. Pituitary extracts were also found to contain several factors which interact with Id protein, a negative regulator of bHLH activity, in Far-Western assays of protein-protein interactions. Finally, messenger RNA for Id is present in pituitary cell lines but is absent in adult pituitary tissue. Together, these studies indicate that bHLH proteins are present in pituitary cells and their levels are differentially regulated in the separate cell types.

Tissue-specific gene expression in the pituitary: the glycoprotein hormone alpha-subunit gene is regulated by a gonadotrope-specific protein

The molecular mechanisms for the development of multiple distinct endocrine cell types in the anterior pituitary have been an area of intensive investigation. Though the homeodomain protein Pit-1/GHF-1 is known to be involved in differentiation of the somatotrope and lactotrope lineages, which produce growth hormone and prolactin, respectively, little is known of the transcriptional regulators important for the gonadotrope cell lineage, which produces the glycoprotein hormones luteinizing hormone and follicle-stimulating hormone. Using transgenic mice and transfection into a novel gonadotrope lineage cell line, we have identified a regulatory element that confers gonadotrope-specific expression to the glycoprotein hormone alpha-subunit gene. A tissue-specific factor that binds to this element is purified and characterized as a 54-kDa protein which is present uniquely in cells of the gonadotrope lineage and is not Pit-1/GHF-1. The human and equine alpha-subunit genes are also expressed in placental cells. However, the previously characterized placental transcription factors designated TSEB and alpha-ACT are not found in the pituitary gonadotrope cells, indicating that independent mechanisms confer expression of these genes in the two different tissues.

Promoter elements and erythroid cell nuclear factors that regulate alpha-globin gene transcription in vitro

We have previously purified four factors (alpha-IRP, alpha-CP1, alpha-CP2, and NF-E1) that interact with the promoter of the alpha-globin gene. One of these (NF-E1) is a tissue-restricted factor that has recently been cloned. The binding sites of these factors identify DNA sequence elements that might mediate the tissue-specific and inducible transcription of the alpha-globin gene. This possibility was tested in a series of in vitro transcription experiments. An examination of 5' truncated templates and synthetic promoters constituted from individual factor-binding sites apposed to the alpha-TATAA box showed that the binding elements of three factors (alpha-CP1, alpha-IRP, and NF-E1) mediate four- to sixfold activation of transcription in vitro. In contrast, one element (alpha-CP2) stimulated transcription less than twofold. The 5- to 10-fold stimulation of these latter templates upon addition of a DNA sequence affinity-purified factor suggests that alpha-CP2 is functionally limiting in nuclear extracts. Additional experiments further tested the effect of supplementing extracts with factors purified from erythroid cell nuclear extracts or, in the case of NF-E1, enriched from a bacterial cDNA expression system. Each factor tested stimulated transcription in vitro in a binding-site-dependent manner. Our results provide a comprehensive functional view of the murine alpha-globin promoter and suggest possible mechanisms for activation of alpha-globin gene transcription during induced differentiation of murine erythroleukemia cells.

Purification and characterization of an erythroid cell-specific factor that binds the murine alpha- and beta-globin genes

An erythroid cell-specific nuclear factor that binds tightly to a sequence motif (5'-GATAAGGA-3') shared by many erythroid cell-specific promoters was purified to homogeneity by DNA sequence affinity chromatography. Visualization of the purified factor, which we term EF-1, showed a simple pattern comprising a polypeptide doublet with Mrs of 18,000 and 19,000. We confirmed that these species account for EF-1-binding activity by eluting the polypeptides from sodium dodecyl sulfate-polyacrylamide gels and renaturing the appropriate binding activity. Using the purified polypeptides, we mapped seven factor-binding sites that are dispersed across the murine alpha- and beta-globin genes. The murine alpha-globin gene is flanked by at least two EF-1-binding sites. One site is centered at nucleotide (nt) -180 (with respect to the alpha-globin cap site). A fivefold-weaker site is located downstream of the alpha-globin poly(A) addition site, at nt +1049. We mapped five EF-1-binding sites near the murine beta-globin gene. The strongest site was centered at nt -210. Four additional sites were centered at nt -266 (adjacent to the binding site of a factor present in both murine erythroleukemia and Raji cells), -75 (overlapping the beta-globin CCAAT box), +543 (within the second intervening sequence), and -111.

Purification of multiple erythroid cell proteins that bind the promoter of the alpha-globin gene

Three erythroid cell factors that bind the murine alpha-globin promoter were enriched more than 1,000-fold by conventional and DNA sequence affinity chromatography. Visualization of enriched polypeptides revealed simple patterns suggesting that each binding activity was purified. Two of the purified proteins, alpha-CP1 and alpha-CP2, have been shown previously to interact with distinct binding sites that overlap in the alpha-globin CCAAT box. Affinity purification of alpha-CP1 revealed seven polypeptides with Mrs raging from 27,000 to 38,000. In contrast, purified alpha-CP2 was made up of a polypeptide doublet with Mrs of 64,000 and 66,000. The third purified binding activity, alpha-IRP, interacted with sequences that formed an inverted repeat (IR) between the alpha-globin CCAAT and TATAA boxes. Affinity-purified alpha-IRP was made up of a single polypeptide with an Mr of 85,000. We confirmed that the purified polypeptides corresponded to alpha-CP1-, alpha-CP2-, and alpha-IRP-binding activities by UV cross-linking experiments (alpha-CP2 and alpha-IRP) or by renaturation of binding activity after elution of polypeptides from sodium dodecyl sulfate-polyacrylamide gels (alpha-CP1 and alpha-CP2). The apparent complexity of the polypeptides accounting for alpha-CP1 binding activity prompted a further physical characterization of this factor. Sedimentation of affinity-purified alpha-CP1 in glycerol gradients containing 100 mM KCl showed that all seven polypeptides migrated as a complex that cosedimented with alpha-CP1-binding activity. In contrast, when sedimented in glycerol gradients containing 500 mM KCl, alpha-CP1 dissociated into at least two components. Under these conditions, alpha-CP1-binding activity was reduced or lost. Activity was reconstituted, however, by combining fractions that were enriched in the two components. These results were confirmed by experiments in which we showed that alpha-CP1-binding activity can be recovered only by combining distinct sets of polypeptides that were isolated and renatured from sodium dodecyl sulfate-polyacrylamide gels. Our results suggest that the seven polypeptides visualized after affinity purification of alpha-CP1 interact to form a heterotypic complex (or set of complexes) required for alpha-CP1-binding activity.

Identification and characterization of multiple erythroid cell proteins that interact with the promoter of the murine alpha-globin gene

The proteins responsible for erythroid-specific footprints extending to -180 on the mouse alpha-globin gene were identified, enriched, and characterized from extracts of murine erythroleukemia (MEL) cells. Three proteins accounted for most aspects of the footprints. The binding sites of two proteins, termed alpha-CP1 and alpha-CP2, overlapped in the CCAAT box. Further characterization of these two CCAAT binding proteins showed that neither interacted with the adenovirus origin of replication, a strong CCAAT transcription factor-nuclear factor 1 binding site. A third protein, termed alpha-IRP, interacted with two sequences that formed an inverted repeat (IR) between the CCAAT and TATAA boxes. Interestingly, the binding domain of one of the CCAAT factors, alpha-CP1, overlapped one alpha-IRP binding site. alpha-CP1 thus overlapped the binding domains of both alpha-CP2 and alpha-IRP. The IRs included GC-rich sequences reminiscent of SP1-binding sites. Indeed, alpha-IRP bound as well to the alpha-promoter as it did to SP1 sites in the simian virus 40 early promoter. These results suggest that alpha-IRP may be related to the transcription factor Sp1. We determined the level of each alpha-globin-binding activity before and after induced erythroid differentiation of MEL cells. We found that differentiation caused alpha-CP1 activity to drop three- to fivefold, while alpha-IRP activity decreased slightly and alpha-CP2 activity increased two- to threefold.

Cisplatin as an initiating agent in two-stage mouse skin carcinogenesis

Single i.p. injections of cisplatin followed by 12-O-tetradecanoylphorbol-13-acetate TPA promotion led to the formation of skin tumors in mice, as did topical applications of urethane with TPA promotion. This is the first example of the use of cisplatin in a single treatment as an initiating agent in the standard initiation-promotion regime. Treatment of the skin with TPA 24 h before initiation increased tumor yield, both in terms of the percentage of mice with tumors and the average number of tumors per mouse.