Adenovirus-mediated generation of cAMP-stimulated Cl- transport in cystic fibrosis airway epithelia in vitro: effect of promoter and administration method

Cystic fibrosis (CF) is a common autosomal recesses disease in which loss of CFTR-Cl- channel function of defective cAMP-stimulated Cl- transport transfer across airway epithelia. Recombinant adenoviruses have shown progress as vectors with which to transfer CFTR cDNA to CF airway epithelia. Here we investigated variables involved in adenovirus-mediated transfer of CFTR by measuring cAMP- stimulated Cl- transport in CF airway epithelia grown as monolayers on permeable filter supports. When we compared the effects of different promoters, we found that persistent correction of Cl- transport was obtained when the vector contained the E1a promoter, or to a lesser extent the PGK promoter. Vector containing the CMV promoter produced a greater initial cAMP-stimulated Cl- current, but the duration of correction was shorter and the infection procedure itself increased CFTR expression, suggesting that high input doses of virus stimulate expression. We compared the level of expression, measured with a beta-galactosidase reporter of CFTR mRNA, with CFTR-mediated Cl- transport. Even low levels of expression generated significant Cl- current and marked increases in expression produced only modest increments in Cl- current. Correction of the CF Cl- transport defect was also improved when the concentration of adenovirus vector was high and when the duration of contact with the epithelium was prolonged. These findings may help optimize the ability of adenovirus vectors encoding CFTR to correct the CF Cl- transport defect.

Humoral and cellular immune responses of nonhuman primates to long-term repeated lung exposure to Ad2/CFTR-2

To evaluate the host immune response to long-term repeat administration of adenovirus vector, rhesus monkeys were treated at intervals of approximately 3 weeks with up to 18 instillations of Ad2/CFTR-2, a second generation vector encoding the cystic fibrosis transmembrane conductance regulator (CFTR). All monkeys instilled with Ad2/CFTR-2 developed a significant humoral immune response against adenovirus but not CFTR. Antibodies with virus neutralizing activity were detected in the serum and bronchoalveolar lavage (BAL) of all vector-treated monkeys and included both IgG and secretory IgA. Virus-specific T cells capable of proliferating in response to stimulation with adenovirus antigen were detected in all vector-treated monkeys. No CFTR-specific proliferation of peripheral blood lymphocytes was detected. An increase in the proportion of CD8+ T cells was noted in the BAL of virus-treated monkeys but cells from the BAL displayed little or no cytolytic activity against infected autologous fibroblasts when tested under a variety of culture conditions. However, MHC-restricted cytolytic activity was detected in the tracheobronchial lymph nodes and spleen of one of three virus-treated monkeys tested. MHC-unrestricted killing of infected fibroblasts was also observed with spleen cells from all animals tested. From these results, it appears that both the humoral and cell-mediated arms of the immune response were stimulated by repeated administration of high doses of Ad2/CFTR-2 suggesting that effective, long-term adenovirus gene therapy may require modification of the vector or treatment of the host to allow the virus to evade host immune defenses.

Biological response of nonhuman primates to long-term repeated lung exposure to Ad2/CFTR-2

We have assessed the safety and efficacy of repeated adenovirus vector administration by exposing the left caudal lung lobe of rhesus monkeys to as many as 17 exposures of Ad2/CFTR-2. After nine doses of either 3 x 10(9) or 3 x 10(10) infectious units, the monkeys were free of adverse effects as assessed by thoracic radiographs, CBCs, clinical chemistries, arterial blood gases, and physical and clinical signs. In some animals elevated protein levels and increased numbers of cells were recovered in bronchoalveolar lavage (BAL), and in all animals there were increased proportions of lymphocytes in the BAL. After 11 doses, two animals were killed. In the lower dose animal (3 x 10(9) IU), there was little histopathology evident. In the higher dose animal (3 x 10(10) IU), histopathology was largely confined to a focal fibrotic lesion that may have been associated with treatment. At the tenth exposure, the dose was increased to 6 x 10(10) or 3 x 10(11) IU. There was evidence of lung injury by thoracic radiographs after two additional exposures and an increase in protein and number of cells in the BAL. The animals were still free of evidence of adverse effects by other parameters, but histopathologic changes were noted upon death. After 15 or 17 doses, three animals were instilled with Ad2/beta gal-2 and killed 3 days later. These animals had greatly reduced levels of transgene expression when compared with controls.

Antigen-specific tumor vaccines. Development and characterization of recombinant adenoviruses encoding MART1 or gp100 for cancer therapy

The human melanoma tumor Ags, MART1 and gp100, are specifically recognized by HLA-A2-restricted CD8+ CTLs derived from melanoma patients and appear to be involved in tumor regression. In order to develop immunizing vectors for the treatment of patients with metastatic melanoma, replication-defective recombinant adenoviruses, Ad2CMV-MART1 and Ad2CMV-gp100, which encode these tumor Ags, have been generated. Infection of non-Ag expressing HLA-A2+ cell lines A375 and MDA-231 with the vectors resulted in recognition by Ag-specific CTLs as demonstrated by specific target cell lysis and release of cytokines, including IFN-gamma, TNF-alpha, and granulocyte-macrophage-CSF. Sodium butyrate and TNF-alpha can further augment adenovirus-mediated transgene expression and increase recognition by specific CTLs. Although adenovirus-infected cells expressed the E3/19K protein at detectable levels, significant reduction of surface MHC class I expression was observed in only 3 of 10 tumor cell lines infected with either Ad2CMV-MART1 or Ad2CMV-gp100. Because of the suspected homology between the human MART1 and gp100 genes and their murine counterparts, we immunized C57BL/6 mice with these recombinant adenoviruses and demonstrated that immunization with Ad2CMV-gp100 could protect mice from murine melanoma B16 challenge administered intradermally. Depletion of CD8+ but not CD4+ T cells in vivo from Ad2CMV-gp100-vaccinated mice eliminated the protective effect. The anti-gp100 T cells induced by Ad2CMV-gp100 vaccinated appeared to be responsible for the protection. Thus, these recombinant adenoviruses encoding tumor Ags may be useful as vaccines to induce specific T cell immunity for cancer therapy.

Antigen-specific tumor vaccines. Development and characterization of recombinant adenoviruses encoding MART1 or gp100 for cancer therapy

The human melanoma tumor Ags, MART1 and gp100, are specifically recognized by HLA-A2-restricted CD8+ CTLs derived from melanoma patients and appear to be involved in tumor regression. In order to develop immunizing vectors for the treatment of patients with metastatic melanoma, replication-defective recombinant adenoviruses, Ad2CMV-MART1 and Ad2CMV-gp100, which encode these tumor Ags, have been generated. Infection of non-Ag expressing HLA-A2+ cell lines A375 and MDA-231 with the vectors resulted in recognition by Ag-specific CTLs as demonstrated by specific target cell lysis and release of cytokines, including IFN-gamma, TNF-alpha, and granulocyte-macrophage-CSF. Sodium butyrate and TNF-alpha can further augment adenovirus-mediated transgene expression and increase recognition by specific CTLs. Although adenovirus-infected cells expressed the E3/19K protein at detectable levels, significant reduction of surface MHC class I expression was observed in only 3 of 10 tumor cell lines infected with either Ad2CMV-MART1 or Ad2CMV-gp100. Because of the suspected homology between the human MART1 and gp100 genes and their murine counterparts, we immunized C57BL/6 mice with these recombinant adenoviruses and demonstrated that immunization with Ad2CMV-gp100 could protect mice from murine melanoma B16 challenge administered intradermally. Depletion of CD8+ but not CD4+ T cells in vivo from Ad2CMV-gp100-vaccinated mice eliminated the protective effect. The anti-gp100 T cells induced by Ad2CMV-gp100 vaccinated appeared to be responsible for the protection. Thus, these recombinant adenoviruses encoding tumor Ags may be useful as vaccines to induce specific T cell immunity for cancer therapy.

Biosynthetic and growth abnormalities are associated with high-level expression of CFTR in heterologous cells

An inducible gene amplification system was utilized to study the effects of overexpression of cystic fibrosis transmembrane conductance regulator (CFTR) in vitro. BTS, a monkey kidney cell line expressing a temperature-sensitive simian virus 40 (SV-40) large T antigen was stably transfected at the nonpermissive temperature with a plasmid containing an SV-40 origin of replication and the cDNA for either the wild-type CFTR or the mutant G551D-CFTR. Shift of the isolated cell lines to the permissive temperature resulted in induction and accumulation to high levels of the CFTR plasmid, mRNA, and protein. However, high-level expression of CFTR was transient in both BTS-CFTR and BTS-G551D cells due to a decrease in their respective levels of CFTR mRNA. Because G551D-CFTR only exhibits residual Cl channel activity, this suggests that the observed downregulation with BTS-G551D cells may have been induced by either the physical presence of high amounts of CFTR or some low threshold level of Cl- channel activity. Examination of cell growth properties revealed a correlation between high-level expression of wild-type CFTR and growth arrest of the cells at the G2/M phase. However, similar induction of the G551D-CFTR mutant showed only a slight growth inhibition and little enrichment of cells at the G2/M phase. Cytofluorographic analysis further revealed that BTS-CFTR cells were significantly larger than parental BTS or BTS-G551D cells at all stages of the cell cycle. These results indicate that CFTR overexpression is capable of inducing its own downregulation and that high levels of Cl- channel activity can result in increased cell volume and subsequent cell growth abnormalities.

Analysis of 2,2,2-trifluoroethyl derivatives of carboxylic acid herbicides by gas chromatography with mass-selective and electron capture detection

A method for derivatizing carboxylic acid herbicides with 2,2,2-trifluoroethanol (TFE) in preparation for gas chromatographic (GC) analysis was developed. Esterification efficiency was determined by GC with electron capture detection (ECD), and esters were identified by GC with mass-selective detection (MSD). On the basis of reaction temperature for optimum esterification efficiency, 13 common carboxylic acid herbicides were separated into 2 groups before reaction with TFE. TFE derivatization was optimized for simultaneous analyses by altering reaction temperature, re action time, and concentration of sulfuric acid in reaction solutions. The method is simple, safe, and economical, and it gives good resolution without a laborious cleanup. Recovery of 13 analytes from water, taken from a pesticide residue well, was greater than 80% for all except 2 analytes. The well-water was fortified with analytes at the lower microgram-per-liter concentrations required for detection of pesticide residues in potable water systems. The method can simultaneously determine multiple herbicide residues in water samples with a high degree of accuracy and precision.

Viral vectors in gene therapy

The use of DNA as a drug is both appealing and simple in concept. Indeed in many instances the feasibility of such an approach has been established using model systems. In practical terms, however, the delivery of DNA to human tissues presents a wide variety of problems that differ with each potential therapeutic application. In this review, the design, production, and application of viral vectors for human gene therapy are considered. Although viral vectors are an obvious starting point because viruses have evolved efficient mechanisms to introduce and express their nucleic acid into recipient cells, by the same token the viral hosts have evolved sophisticated mechanisms to rid themselves of such pathogens. The challenge for the therapeutic use of viral vectors is to achieve efficient and often extended expression of the exogenous gene while evading the host defenses. Methodology used and progress towards that goal are reviewed.

Characterization of an adenovirus gene transfer vector containing an E4 deletion

We describe the construction and characterization of an adenovirus type 2 vector, Ad2E4ORF6, which has been modified in the E4 region to contain only open reading frame 6. When assayed in cultured cells, Ad2E4ORF6 virus replication is slightly delayed but viral DNA synthesis, host-cell protein synthesis shut-off, and virus yield are indistinguishable from wild type. Late protein synthesis is normal with the exception of fiber synthesis, which is reduced approximately 10-fold. Despite the reduced fiber synthesis, Ad2E4ORF6 viral particles appear to contain a full complement of fiber protein. Virus replication in cotton rats indicates that Ad2E4ORF6 is replication defective in vivo. This may have safety implications for the development adenovirus vectors in that virus arising by recombination in the E1 region of an Ad2E4ORF6-based vector would be defective for growth in vivo. The deletion of E4 open reading frames that are not required for virus growth in vitro increases the cloning capacity of adenovirus vectors by 1.9 kb and may be generally useful for the construction of adenovirus vectors containing large cDNA inserts and/or regulatory elements. We describe the inclusion of the A2E4ORF6 modification in a recombinant adenovirus vector, Ad2/CFTR-2, for gene transfer of the human cystic fibrosis transmembrane regulator (CFTR).

Delivery of purified, functional CFTR to epithelial cells in vitro using influenza hemagglutinin

To assess the feasibility of protein replacement as a potential therapy for cystic fibrosis, we have evaluated the ability of influenza hemagglutinin (HA) to mediate the delivery of purified cystic fibrosis transmembrane conductance regulator (CFTR) to recipient cells in vitro. CFTR was purified from both CHO cells and Sf9 cells and reconstituted into two different types of vesicular delivery vehicles. In one, CFTR and HA were co-reconstituted into the same lipid vesicle. After binding to the cell surface, delivery of CFTR to the recipient cell was achieved by a transient, low-pH activation of the fusion activity of HA. A second delivery strategy used HA virosomes together with purified CFTR that had been reconstituted into vesicles containing gangliosides, a receptor for HA. After binding of the HA virosomes and CFTR-containing vesicles to the recipient cells, delivery to the plasma membrane again was achieved by a transient pH drop. Delivery of functional CFTR was assessed using the SPQ fluorescence assay. Functional CFTR was detected in a fraction (> 20%) of the recipient cells using this assay. Quantitative binding and fusion assays using radiolabeled virosomes and lipid vesicles showed that on the order of 1,000 of the added CFTR-containing vesicles bound to each C127 cell under the conditions of our delivery protocols. However, only a fraction of these vesicles fused and delivered CFTR to the cell plasma membrane. The two delivery strategies were found to be approximately equivalent in their ability to deliver active CFTR, and there were no significant differences between deliveries using purified CFTR from either cell source. These feasibility studies suggest that purified CFTR can be delivered to a recipient cell in a functional form and therefore represent a significant step in establishing the concept of protein replacement as a therapy for cystic fibrosis.

Sequence homologies between nucleotide binding regions of CFTR and G-proteins suggest structural and functional similarities

Sequence homology between the alpha-subunits of G-proteins and other GTP-binding proteins and certain regions within the nucleotide binding domains (NBDs) of cystic fibrosis transmembrane conductance regulator (CFTR) indicates that these protein structures may be similar. A sequence alignment of the NBDs of CFTR and NBDs from other membrane transporters, forms the basis of a structural model. This model predicts that one of the conserved sequences GGQR, within which a number of CF mutations occur, forms part of the nucleotide binding pocket and serves as an ON/OFF conformational switch as observed in GTP binding proteins. Furthermore, based on subtle sequence differences between the first and second NBDs of CFTR and from structure-activity data, we suggest that the nucleotide binding site environments of the two NBDs are different.

Adenoviral-mediated gene transfer to fetal pulmonary epithelia in vitro and in vivo

Vector-mediated gene transfer offers a direct method of correcting genetic pulmonary diseases and might also be used to correct temporary abnormalities associated with acquired, nongenetic disorders. Because the fetus or newborn may be a more immune tolerant host for gene transfer using viral vectors, we used replication defective recombinant adenoviral vectors to test the feasibility of gene transfer to the fetal pulmonary epithelium in vitro and in vivo. Both proximal and distal epithelial cells in cultured fetal lung tissues from rodents and humans diffusely expressed the lacZ transgene 3 d after viral infection. In vivo gene delivery experiments were performed in fetal mice and lambs. Delivery of Ad2/CMV-beta Gal to the amniotic fluid in mice produced intense transgene expression in the fetal epidermis and amniotic membranes, some gastrointestinal expression, but no significant airway epithelial expression. When we introduced the adenoviral vector directly into the trachea of fetal lambs, the lacZ gene was expressed in the tracheal, bronchial, and distal pulmonary epithelial cells 3 d after viral infection. Unexpectedly, reactive hyperplasia and squamous metaplasia were noted in epithelia expressing lacZ in the trachea, but not in the distal lung of fetal lambs. 1 wk after infection, adenovirus-treated fetuses developed inflammatory cell infiltrates in the lung tissue with CD4, CD8, IgM, and granulocyte/macrophage positive immune effector cells. Transgene expression faded coincident with inflammation and serologic evidence of antiadenoviral antibody production. While these studies document the feasibility of viral-mediated gene transfer in the prenatal lung, they indicate that immunologic responses to E1-deleted recombinant adenoviruses limit the duration of transgene expression.

Specific competitive inhibitor of secreted phospholipase A2 from berries of Schinus terebinthifolius

Two structurally related triterpenoids 1 and 2 from pink peppercorn (berries of Schinus terebinthifolius) are identified and characterized as active site-directed specific competitive inhibitors of the three classes of secreted 14 kDa phospholipase A2. The inhibitors not only protect the active site histidine from alkylation but also inhibit the action of secreted phospholipase A2 from pig pancreas, human synovial fluid, and bee venom. Detailed X-ray crystallographic results on the structures of the inhibitors are provided. By physical methods and X-ray crystallography the triterpenoids were identified as masticadienoic acid and masticadienolic acid (schinol). Several other triterpenoids were ineffective as inhibitors of phospholipase A2; however certain ganoderic acid derivatives showed noticeable inhibition. Results show that the side chain of these acidic tetracyclic terpenoids can access the catalytic-site region of phospholipase A2, whereas the acyclic nucleus is at the interfacial recognition region. The selectivity of the assay protocol used here is demonstrated by the fact that the original screen of ethyl acetate extracts of 60 commercially available spices and herbs was carried out with phospholipase A2 from pig pancreas, and only one extract showed inhibitory action on the hydrolytic activity in the scooting mode. Under such assay conditions the enzyme remains tightly bound to the surface of the substrate vesicles. In this way, nonspecific effects of additives that promote desorption of the enzyme from the substrate vesicle surface, under conditions in which the binding of the enzyme to the vesicle is weak, are avoided. The assay protocol is useful for the kinetic characterization of the inhibitors of phospholipase A2, and it does not give false positive results with amphiphilic and hydrophobic compounds, as is the case with virtually all assay systems in use.

The ability of predicted internal dose measures to reconcile tumor bioassay data for chloroform

PBPK models are developed in the hope that they will improve our ability to extrapolate from one species to another and from one exposure regime to another. Evidence that a dose measure was successful at reconciling the available animal bioassay data would be encouraging. It would give us some confidence that the dose measure (as evaluated by a PBPK model) might yield reasonable predictions for yet other species (e.g., humans) and other dose routes. We have investigated the ability of a modified version of the Corley et al. (R. A. Corley, A. L. Mendrala, F. A. Smith, D. A. Staats, M. L. Gargas, R. B. Conolly, M. E. Andersen, and R. H. Reitz, 1990, Toxicol. Appl. Pharmacol. 103, 512-527) PBPK model for chloroform to reconcile the available bioassay data. Two rate-dependent dose measures, maximal rate of metabolism in the liver, and percentage of hepatocytes killed per day performed well at reconciling the rodent liver bioassay data, while all rate-independent dose measures performed less well. In contrast, none of the PBPK dose measures were capable of reconciling the rat and mouse kidney tumor response data. Here, administered dose scaled to body surface area performed the best.

Primary and secondary prevention services in clinical practice. Twenty years' experience in development, implementation, and evaluation

This article reviews lessons from 20 years of experience in development and provision of clinical preventive services at Group Health Cooperative of Puget Sound, a large health maintenance organization. Critical factors for enhancing service include the use of a population-based epidemiologic viewpoint coupled with specific evidence-based criteria to examine issues; involvement of practitioners in the process; a systems approach to implementation focused on predisposing factors of the practitioners and enabling factors in the practice, organizational, and community environments; feedback of program outcomes; and the use of automated clinical information systems. Outcome results from our clinical prevention efforts include a 32% decrease in late-stage breast cancer (1989 to 1990); 89% of 2-year-old children with complete immunizations (1994); decrease in adult smokers from 25% to 17% (1985 to 1994); and an increase in bicycle safety helmet use among children from 4% to 48% along with a 67% decrease in bicycle-related head injuries (1987 to 1992). Systematic population-based approaches to the development and provision of clinical preventive services targeting the one-to-one level of primary care and multiple infrastructure levels of care are forging a synthesis of clinical medicine and public health approaches. This approach will become pervasive as clinical information systems improve, risk information is captured routinely, and practitioners gain skills in the art of patient risk behavior change and population-based care.

Uncertainty in fitted estimates of apparent in vivo metabolic constants for chloroform

It has become common practice to rely on fitted estimates of apparent in vivo metabolic constants (e.g., Vmax and KM) in the parameterization of PBPK models. Yet, quantitative estimates of precision in these fitted parameters are not routinely reported. Such information is needed to assess the reliability of model predictions. The purpose of this study was to assess the precision in estimates of Vmax and KM for chloroform, accounting for both the statistical uncertainties in parameter estimates from individual data sets and any additional uncertainty due to differences in the parameter estimates derived from various experiments. Joint confidence regions for Vmax and KM from each experiment, generated using maximum likelihood techniques, were used to evaluate these questions. Three previously published data sets were considered. Estimates of Vmax and KM obtained from these data sets differed more than could be explained as a consequence of a limited number of observations, measurement error, or stochastic error. Issues associated with the use of maximum likelihood techniques to estimate joint confidence regions, the estimation of metabolic constants from individual experiments within a gas uptake study versus the full data set, the degree of overlap in the joint confidence regions for metabolic constants obtained from separate data sets, and the implications for risk assessment are discussed.

Functional activation of the cystic fibrosis trafficking mutant delta F508-CFTR by overexpression

The most common mutation in the gene associated with cystic fibrosis (CF) causes deletion of phenylalanine at residue 508 (delta F508) of the gene product called CFTR. This mutation results in the synthesis of a variant CFTR protein that is defective in its ability to traffic to the plasma membrane. Because earlier studies showed delta F508-CFTR retains significant phosphorylation-regulated chloride (Cl-) channel activity, processes capable of restoring the mislocalized delta F508-CFTR to the correct cellular destination may have therapeutic benefit. Here we report one such process that involves overexpression of the mutant protein and appears to result in the escape of a small amount of delta F508-CFTR to the plasma membrane. In recombinant cells where expression of delta F508-CFTR is controlled by the metallothionein promoter, this effect can be brought about by treatment with sodium butyrate. Although cAMP-activated Cl- channel activity could also be detected in immortalized human airway epithelial cells homozygous for the delta F508 mutation at the single cell level, treatment with butyrate did not generate a measurable cAMP-stimulated Cl- current in polarized monolayers of primary CF airway epithelia. However, the observation that overexpression can effect the presence of recombinant delta F508-CFTR at the plasma membrane suggests that perhaps other butyrate-like compounds that are more potent and more specific for the promoter of the CF gene may be efficacious in alleviating the Cl- channel defect associated with CF.