The coxsackievirus-adenovirus receptor protein can function as a cellular attachment protein for adenovirus serotypes from subgroups A, C, D, E, and F

Attachment of an adenovirus (Ad) to a cell is mediated by the capsid fiber protein. To date, only the cellular fiber receptor for subgroup C serotypes 2 and 5, the so-called coxsackievirus-adenovirus receptor (CAR) protein, has been identified and cloned. Previous data suggested that the fiber of the subgroup D serotype Ad9 also recognizes CAR, since Ad9 and Ad2 fiber knobs cross-blocked each other's cellular binding. Recombinant fiber knobs and 3H-labeled Ad virions from serotypes representing all six subgroups (A to F) were used to determine whether the knobs cross-blocked the binding of virions from different subgroups. With the exception of subgroup B, all subgroup representatives cross-competed, suggesting that they use CAR as a cellular fiber receptor as well. This result was confirmed by showing that CAR, produced in a soluble recombinant form (sCAR), bound to nitrocellulose-immobilized virions from the different subgroups except subgroup B. Similar results were found for blotted fiber knob proteins. The subgroup F virus Ad41 has both short and long fibers, but only the long fiber bound sCAR. The sCAR protein blocked the attachment of all virus serotypes that bound CAR. Moreover, CHO cells expressing human CAR, in contrast to untransformed CHO cells, all specifically bound the sCAR-binding serotypes. We conclude therefore that Ad serotypes from subgroups A, C, D, E, and F all use CAR as a cellular fiber receptor.

Identification of a cellular transcription factor involved in E1A trans-activation

We have employed a gel assay to detect a transcription factor in nuclear extracts of adenovirus-infected cells that interacts with the adenovirus E2 promoter, an E1A inducible promoter. Binding of the factor to the promoter protected sequences between -33 and -74 from DNAase cleavage in a footprint assay. This region was also protected from exonuclease III digestion. These sequences coincide with those previously shown to be essential for promoter activity and E1A stimulation. The factor could be detected in extracts of uninfected cells, although at greatly reduced levels. The increased level of factor in infected cells required a functional E1A gene. These results suggest that the E2 binding activity is a cellular transcriptional factor, the concentration or binding activity of which increases as a result of the action of the E1A gene product.

Increased in vitro and in vivo gene transfer by adenovirus vectors containing chimeric fiber proteins

Alteration of the natural tropism of adenovirus (Ad) will permit gene transfer into specific cell types and thereby greatly broaden the scope of target diseases that can be treated by using Ad. We have constructed two Ad vectors which contain modifications to the Ad fiber coat protein that redirect virus binding to either alpha(v) integrin [AdZ.F(RGD)] or heparan sulfate [AdZ.F(pK7)] cellular receptors. These vectors were constructed by a novel method involving E4 rescue of an E4-deficient Ad with a transfer vector containing both the E4 region and the modified fiber gene. AdZ.F(RGD) increased gene delivery to endothelial and smooth muscle cells expressing alpha(v) integrins. Likewise, AdZ.F(pK7) increased transduction 5- to 500-fold in multiple cell types lacking high levels of Ad fiber receptor, including macrophage, endothelial, smooth muscle, fibroblast, and T cells. In addition, AdZ.F(pK7) significantly increased gene transfer in vivo to vascular smooth muscle cells of the porcine iliac artery following balloon angioplasty. These vectors may therefore be useful in gene therapy for vascular restenosis or for targeting endothelial cells in tumors. Although binding to the fiber receptor still occurs with these vectors, they demonstrate the feasibility of tissue-specific receptor targeting in cells which express low levels of Ad fiber receptor.

Identification of a conserved receptor-binding site on the fiber proteins of CAR-recognizing adenoviridae

The human adenovirus serotype 5 (Ad5) is used widely for applications in human gene therapy. Cellular attachment of Ad5 is mediated by binding of the carboxyl-terminal knob of its fiber coat protein to the Coxsackie adenovirus receptor (CAR) protein. However, Ad5 binding to CAR hampers the development of adenovirus vectors capable of specifically targeting (diseased) tissues or organs. Through sequence analysis and mutagenesis, a conserved receptor-binding region was identified on the side of three divergent CAR-binding knobs. The feasibility of simultaneous CAR ablation and redirection of an adenovirus to a new receptor is demonstrated.

Reversal of impaired wound repair in iNOS-deficient mice by topical adenoviral-mediated iNOS gene transfer

Most evidence indicates that nitric oxide plays a role in normal wound repair; however, involvement of inducible nitric oxide synthase (iNOS) has not been established. Experiments were carried out to determine the requirement for iNOS in closing excisional wounds. Wound closure was delayed by 31% in iNOS knockout mice compared with wild-type animals. An identical delay in wound closure was observed in wild-type mice given a continuous infusion of the partially selective iNOS inhibitor N6-(iminoethyl)-L-lysine. Delayed wound healing in iNOS-deficient mice was completely reversed by a single application of an adenoviral vector containing human iNOS cDNA (AdiNOS) at the time of wounding. Reverse transcription PCR identified iNOS mRNA expression in wild-type mice peaking 4-6 d after wounding, and confirmed expression of human iNOS in the adenoviral vector containing human iNOS cDNA-treated animals. These results establish the key role of iNOS in wound closure, and suggest a gene therapy strategy to improve wound healing in iNOS-deficient states such as diabetes, and during steroid treatment.

Adenovirus targeted to heparan-containing receptors increases its gene delivery efficiency to multiple cell types

Adenovirus (Ad) is used as a vector for gene delivery in therapies involving genetic disease, vascular disease, and cancer. The first step for efficient gene transfer is effective virus binding to the target cells. We have found that Ad-mediated gene delivery to multiple cell types is much less efficient compared to epithelial-derived cells. Low gene delivery to nonepithelial cell types was directly correlated to a deficiency of the cellular receptor which mediates Ad binding. To overcome this inefficiency we constructed a new virus, AdPK, that contains a heparin-binding domain that targets the virus to broadly expressed, heparan-containing cellular receptors. AdPK delivers genes to multiple cell types at markedly higher efficiencies than unmodified Ad. Viruses with enhanced attachment characteristics significantly improve gene transfer efficiency and may expand the tissues amenable to efficient Ad-mediated gene therapy.

Targeted adenovirus gene transfer to endothelial and smooth muscle cells by using bispecific antibodies

A major hurdle to adenovirus (Ad)-mediated gene transfer is that the target issue lacks sufficient levels of receptors to mediate vector attachment via its fiber coat protein. Endothelial and smooth muscle cells are primary targets in gene therapy approaches to prevent restenosis following angioplasty or to promote or inhibit angiogenesis. However, Ad poorly binds and transduces these cells because of their low or undetectable levels of functional Ad fiber receptor. The Ad-binding deficiency of these cells was overcome by targeting Ad binding to alpha v integrin receptors that are sufficiently expressed by these cells. In order to target alpha v integrins, a bispecific antibody (bsAb) that comprised a monoclonal Ab to the FLAG peptide epitope, DYKDDDDK, and a monoclonal Ab to alpha v integrins was constructed. In conjunction with the bsAb, a new vector, AdFLAG, which incorporated the FLAG peptide epitope into its penton base protein was constructed. Complexing AdFLAG with the bsAb increased the beta-glucuronidase transduction of human venule endothelial cells and human intestinal smooth muscle cells by seven- to ninefold compared with transduction by AdFLAG alone. The increased transduction efficiency was shown to occur through the specific interaction of the complex with alpha v integrins. These results demonstrate that bsAbs can be successfully used to target Ad to a specific cellular receptor and thereby increase the efficiency of gene transfer.

Biologic bypass with the use of adenovirus-mediated gene transfer of the complementary deoxyribonucleic acid for vascular endothelial growth factor 121 improves myocardial perfusion and function in the ischemic porcine heart

OBJECTIVES

Vascular endothelial growth factor (VEGF), a potent angiogenic mediator, can be delivered to targeted tissues by means of a replication-deficient adenovirus (Ad) vector. We hypothesized that direct administration of Ad vector expressing the VEGF121 complementary deoxyribonucleic acid (AdGVVEGF121.10) into regions of ischemic myocardium would enhance collateral vessel formation and improve regional perfusion and function.

METHODS

Yorkshire swine underwent thoracotomy and placement of an Ameroid constrictor (Research Instruments & MFG, Corvallis, Ore.) on the circumflex coronary artery. Three weeks later, myocardial perfusion and function were assessed by single photon emission computed tomography imaging (SPECT) with 99mTc-labeled sestamibi and by echocardiography during rest and stress. AdGVVEGF121.10 (n = 7) or the control vector, AdNull (n = 8), was administered directly into the myocardium at 10 sites in the circumflex distribution (10(8) pfu/site). Four weeks later, these studies were repeated and ex vivo angiography was performed.

RESULTS

SPECT imaging 4 weeks after vector administration demonstrated significant reduction in the ischemic area at stress in AdGVVEFG121.10-treated animals compared with AdNull control animals (p = 0.005). Stress echocardiography at the same time demonstrated improved segmental wall thickening in AdGVVEGF121.10 animals compared with AdNull control animals (p = 0.03), with AdGVVEGF121.10 animals showing nearly normalized function in the circumflex distribution. Collateral vessel development assessed by angiography was also significantly greater in AdGVVEGF121.10 animals than in AdNull control animals (p = 0.04), with almost complete reconstitution of circumflex filling in AdGVVEGF121.10 animals.

CONCLUSIONS

An Ad vector expressing the VEGF121 cDNA induces collateral vessel development in ischemic myocardium and results in significant improvement in both myocardial perfusion and function. Such a strategy may be useful in patients with ischemic heart disease in whom complete revascularization is not possible.

Role of an adenovirus E2 promoter binding factor in E1A-mediated coordinate gene control

A product of the adenovirus gene E1A is responsible for the stimulation of transcription from six viral promoters as well as at least two cellular promoters. We have detected a HeLa cell factor, termed E2 promoter binding factor (E2F), that appears to mediate the transcriptional stimulation of the viral E2 promoter. Competition experiments revealed that E2F did not recognize and bind to the E1B, E3, E4, or major late promoter sequences. Furthermore, three additional promoters stimulated by E1A, heat shock protein 70, beta-globin, and early simian virus 40, do not bind E2F. In contrast, the factor does recognize sequences in the E1A enhancer, and within the E1A enhancer are duplicated binding sites for E2F. Finally, a single E2F binding site from the E1A enhancer can confer increased transcription to a mouse beta-globin promoter, dependent on the action of the E1A gene product. This stimulation requires binding of E2F since methylation of the binding site, which blocks binding in vitro, reduces transcription stimulation in vivo. We, therefore, conclude that E2F is likely to be responsible for the E1A-mediated stimulation of the E1A gene as well as the E2 gene but is not involved in the activation of the other E1A-inducible promoters.

Selectivity of a replication-competent adenovirus for human breast carcinoma cells expressing the MUC1 antigen

The DF3/MUC1 gene is aberrantly overexpressed in human breast and other carcinomas. Previous studies have demonstrated that the DF3/MUC1 promoter/enhancer confers selective expression of diverse transgenes in MUC1-positive breast cancer cells. In this study, we show that an adenoviral vector (Ad.DF3-E1) in which the DF3/MUC1 promoter drives expression of E1A selectively replicates in MUC1-positive breast cancer cells. We also show that Ad.DF3-E1 infection of human breast tumor xenografts in nude mice is associated with inhibition of tumor growth. In contrast to a replication-incompetent adenoviral vector that infects along the injection track, Ad.DF3-E1 infection was detectable throughout the tumor xenografts. To generate an Ad.DF3-E1 vector with the capacity for incorporating therapeutic products, we inserted the cytomegalovirus (CMV) promoter upstream of the TNF cDNA. Infection with Ad.DF3-E1/CMV-TNF was associated with selective replication and production of TNF in cells that express MUC1. Moreover, treatment of MUC1-positive, but not MUC1-negative, xenografts with a single injection of Ad.DF3-E1/CMV-TNF was effective in inducing stable tumor regression. These findings demonstrate that the DF3/MUC1 promoter confers competence for selective replication of Ad.DF3-E1 in MUC1-positive breast tumor cells, and that the antitumor activity of this vector is potentiated by integration of the TNF cDNA.

Inducible nitric oxide synthase suppresses the development of allograft arteriosclerosis

In cardiac transplantation, chronic rejection takes the form of an occlusive vasculopathy. The mechanism underlying this disorder remains unclear. The purpose of this study was to investigate the role nitric oxide (NO) may play in the development of allograft arteriosclerosis. Rat aortic allografts from ACI donors to Wistar Furth recipients with a strong genetic disparity in both major and minor histocompatibility antigens were used for transplantation. Allografts collected at 28 d were found to have significant increases in both inducible NO synthase (iNOS) mRNA and protein as well as in intimal thickness when compared with isografts. Inhibiting NO production with an iNOS inhibitor increased the intimal thickening by 57.2%, indicating that NO suppresses the development of allograft arteriosclerosis. Next, we evaluated the effect of cyclosporine (CsA) on iNOS expression and allograft arteriosclerosis. CsA (10 mg/kg/d) suppressed the expression of iNOS in response to balloon-induced aortic injury. Similarly, CsA inhibited iNOS expression in the aortic allografts, associated with a 65% increase in intimal thickening. Finally, we investigated the effect of adenoviral-mediated iNOS gene transfer on allograft arteriosclerosis. Transduction with iNOS using an adenoviral vector suppressed completely the development of allograft arteriosclerosis in both untreated recipients and recipients treated with CsA. These results suggest that the early immune-mediated upregulation in iNOS expression partially protects aortic allografts from the development of allograft arteriosclerosis, and that iNOS gene transfer strategies may prove useful in preventing the development of this otherwise untreatable disease process.

Airway epithelial CFTR mRNA expression in cystic fibrosis patients after repetitive administration of a recombinant adenovirus

We sought to evaluate the ability of an E1(-), E3(-) adenovirus (Ad) vector (Ad(GV)CFTR.10) to transfer the normal human cystic fibrosis transmembrane conductance regulator (CFTR) cDNA to the airway epithelium of individuals with cystic fibrosis (CF). We administered Ad(GV)CFTR.10 at doses of 3 x 10(6) to 2 x 10(9) plaque-forming units over 9 months by endobronchial spray to 7 pairs of individuals with CF. Each 3-month cycle, we measured vector-derived versus endogenous CFTR mRNA in airway epithelial cells prior to therapy, as well as 3 and 30 days after therapy. The data demonstrate that (a) this strategy appears to be safe; (b) after the first administration, vector-derived CFTR cDNA expression in the CF airway epithelium is dose-dependent, with greater than 5% endogenous CFTR mRNA levels at the higher vector doses; (c) expression is transient, lasting less than 30 days; (d) expression can be achieved with a second administration, but only at intermediate doses, and no expression is observed with the third administration; and (e) the progressive lack of expression with repetitive administration does not closely correlate with induction of systemic anti-Ad neutralizing antibodies. The major advantage of an Ad vector is that it can deliver sufficient levels of CFTR cDNA to the airway epithelium so that CFTR expression protects the lungs from the respiratory manifestations of CF. However, this impressive level of expression is linked to the challenging fact that expression is limited in time. Although this can be initially overcome by repetitive administration, unknown mechanisms eventually limit this strategy, and further repetitive administration does not lead to repetitive expression.

Adenovirus infection stimulates the Raf/MAPK signaling pathway and induces interleukin-8 expression

Previous studies have shown that airway administration of adenovirus or adenovirus vectors results in a dose-dependent inflammatory response which limits the duration of transgene expression. We explored the possibility that adenovirus infection triggers signal transduction pathways that induce the synthesis of cytokines and thus contribute to the early inflammatory response. Since stimulation of the Raf/mitogen-activated protein kinase (MAPK) pathway activates transcription factors that control the expression of inflammatory cytokines, we examined the activation of this pathway following adenovirus infection. Adenovirus infection induced the rapid activation of Raf-1 and a transient increase in the tyrosine phosphorylation and activation of p42mapk at early times postinfection. Activation of the Raf/MAPK pathway by adenovirus is likely triggered by the infection process, since it occurred rapidly and with various mutant adenoviruses and adenovirus vectors. Moreover, interleukin-8 (IL-8) mRNA accumulation was evident at 20 min postinfection and was induced even in the presence of cycloheximide. Both MAPK activation and IL-8 production were inhibited by forskolin, a potent inhibitor of Raf-1. These results suggest that adenovirus-induced Raf/MAPK activation contributes to IL-8 production. Adenovirus-induced activation of the Raf/MAPK signaling pathway and IL-8 production may play critical roles in the inflammation observed following in vivo administration of adenovirus vectors for gene therapy.

CAR-dependent and CAR-independent pathways of adenovirus vector-mediated gene transfer and expression in human fibroblasts

Primary fibroblasts are not efficiently transduced by subgroup C adenovirus (Ad) vectors because they express low levels of the high-affinity Coxsackie virus and adenovirus receptor (CAR). In the present study, we have used primary human dermal fibroblasts as a model to explore strategies by which Ad vectors can be designed to enter cells deficient in CAR. Using an Ad vector expressing the human CAR cDNA (AdCAR) at high multiplicity of infection, primary fibroblasts were converted from being CAR deficient to CAR sufficient. Efficiency of subsequent gene transfer by standard Ad5-based vectors and Ad5-based vectors with alterations in penton and fiber was evaluated. Marked enhancement of binding and transgene expression by standard Ad5 vectors was achieved in CAR-sufficient fibroblasts. Expression by AdDeltaRGDbetagal, an Ad5-based vector lacking the arginine-glycine-aspartate (RGD) alphaV integrin recognition site from its penton base, was achieved in CAR-sufficient, but not CAR-deficient, cells. Fiber-altered Ad5-based vectors, including (a) AdF(pK7)betagal (bearing seven lysines on the end of fiber) (b) AdF(RGD)betagal (bearing a high-affinity RGD sequence on the end of fiber), and (c) AdF9sK betagal (bearing a short fiber and Ad9 knob), demonstrated enhanced gene transfer in CAR-deficient fibroblasts, with no further enhancement in CAR-sufficient fibroblasts. Together, these observations demonstrate that CAR deficiency on Ad targets can be circumvented either by supplying CAR or by modifying the Ad fiber to bind to other cell-surface receptors.

Reducing the native tropism of adenovirus vectors requires removal of both CAR and integrin interactions

The development of tissue-selective virus-based vectors requires a better understanding of the role of receptors in gene transfer in vivo, both to rid the vectors of their native tropism and to introduce new specificity. CAR and alphav integrins have been identified as the primary cell surface components that interact with adenovirus type 5 (Ad5)-based vectors during in vitro transduction. We have constructed a set of four vectors, which individually retain the wild-type cell interactions, lack CAR binding, lack alphav integrin binding, or lack both CAR and alphav integrin binding. These vectors have been used to examine the roles of CAR and alphav integrin in determining the tropism of Ad vectors in a mouse model following intrajugular or intramuscular injection. CAR was found to play a significant role in liver transduction. The absence of CAR binding alone, however, had little effect on the low level of expression from Ad in other tissues. Binding of alphav integrins appeared to have more influence than did binding of CAR in promoting the expression in these tissues and was also found to be important in liver transduction by Ad vectors. An effect of the penton base modification was a reduction in the number of vector genomes that could be detected in several tissues. In the liver, where CAR binding is important, combining defects in CAR and alphav integrin binding was essential to effectively reduce the high level of expression from Ad vectors. While there may be differences in Ad vector tropism among species, our results indicate that both CAR and alphav integrins can impact vector distribution in vivo. Disruption of both CAR and alphav integrin interactions may be critical for effectively reducing native tropism and enhancing the efficacy of specific targeting ligands in redirecting Ad vectors to target tissues.

"Sero-switch" adenovirus-mediated in vivo gene transfer: circumvention of anti-adenovirus humoral immune defenses against repeat adenovirus vector administration by changing the adenovirus serotype

Recombinant, replication-deficient adenovirus (Ad) vectors have been successfully used to transfer and express the normal human cystic fibrosis transmembrane conductance regulator (CFTR) cDNA in vivo in the respiratory epithelium of experimental animals and humans with cystic fibrosis (CF). Since Ad-directed gene expression wanes over time, repeat administration is necessary to achieve an effective treatment for CF. A major hurdle to such a strategy is the possibility that anti-Ad humoral immunity may prevent gene expression in individuals with pre-existing anti-Ad immunity or following repeat administration. One strategy to circumvent such a problem would be alternating the use of Ad vectors belonging to different subgroups. Neutralizing antibodies developed with the administration of one Ad serotype do not cross-react with an Ad belonging to a second serotype in a manner that blocks infection and gene expression. To test this hypothesis, an immunizing dose of wild-type Ad5 (subgroup C), Ad4 (subgroup E), or Ad30 (subgroup D) was administered intratracheally to experimental animals, followed by an intratracheal administration of a replication-deficient subgroup C-derived vector coding for marker genes (chloramphenicol acetyl transferase or beta-galactosidase) or for the normal human CFTR cDNA. As expected, studies with vectors coding for marker genes or for CFTR cDNA demonstrated that airway administration of a vector does not yield efficient gene transfer, if there has been prior recent airway administration of the same Ad subgroup. In contrast, effective expression from the second administration can be achieved with an adenovirus vector belonging to a subgroup different from the first adenovirus administered. These data support the paradigm of alternating Ad vectors derived from different subgroups as strategy to circumvent anti-Ad humoral immunity, thus permitting the use of Ad vectors as a means to treat the respiratory manifestations of CF.

Circumvention of anti-adenovirus neutralizing immunity by administration of an adenoviral vector of an alternate serotype

Effective gene transfer and expression following repetitive administration of adenoviral (Ad) vectors in experimental animals is limited by anti-Ad neutralizing antibodies. Knowing that anti-Ad humoral immunity is serotype-specific, we hypothesized that anti-Ad neutralizing immunity could be circumvented using Ad vectors of different serotypes (Ad2, Ad5) within the same subgroup (C) to transfer and express beta-glucuronidase (beta glu) in the lung. Sprague-Dawley rats received an intratracheal administration of either Ad2 beta glu or Ad5 beta glu, and, 14 days later, repeat administration of either the same vector or a vector of a different serotype. Analysis of serum and bronchoalveolar lavage fluid following initial vector administration demonstrated systemic and local serotype-specific neutralizing antibodies. For both the Ad2 and Ad5 vectors, beta glu expression 24 hr following the second administration of the same serotype was < 30% of that of naive animals. In contrast, beta glu expression 24 hr following second administration of a different serotype Ad vector was similar to expression at 24 hr of naive animals receiving a single administration (Ad5 beta glu followed by Ad2 beta glu, as well as Ad2 beta glu followed by Ad5 beta glu; p > 0.2 both comparisons). Although the alternative serotype bypassed anti-Ad neutralizing immunity, persistence of expression was reduced compared to that following administration to naive animals. Compatible with this observation, systemic administration of the same vectors to C57B1/6 mice demonstrated induction of cytotoxic T lymphocytes directed against the beta glu transgene, as well as products of the Ad genome. Interestingly, intratracheal administration of vectors with different serotypes and different transgenes to rats resulted in longer expression (but still not normalized) compared to that achieved with vectors of different serotypes but the same transgene. These observations demonstrate that alternate use of Ad vectors from different serotypes within the same subgroup can circumvent anti-Ad humoral immunity to permit effective gene transfer after repeat administration, although the chronicity of expression is limited, likely by cellular immune process directed against both the transgene and viral gene products expressed by the vector.

Efficient inhibition of intimal hyperplasia by adenovirus-mediated inducible nitric oxide synthase gene transfer to rats and pigs in vivo

BACKGROUND

Inadequate nitric oxide (NO) availability may underlie vascular smooth muscle overgrowth that contributes to vascular occlusive diseases including atherosclerosis and restenosis. NO possesses a number of properties that should inhibit this hyperplastic healing response, such as promoting reendothelialization, preventing platelet and leukocyte adherence, and inhibiting cellular proliferation.

STUDY DESIGN

We proposed that shortterm but sustained increases in NO synthesis achieved with inducible NO synthase (iNOS) gene transfer at sites of vascular injury would prevent intimal hyperplasia. We constructed an adenoviral vector, AdiNOS, carrying the human iNOS cDNA and used it to express iNOS at sites of arterial injury in vivo.

RESULTS

AdiNOS-treated cultured vascular smooth muscle cells produced up to 100-fold more NO than control cells. In vivo iNOS gene transfer, using low concentrations of AdiNOS (2 x 10(6) plaque forming units [PFU]/rat) to injured rat carotid arteries, resulted in a near complete (>95%) reduction in neointima formation even when followed longterm out to 6 weeks post-injury. This protective effect was reversed by the continuous administration of an iNOS selective inhibitor L-N6-(1-iminoethyl)-lysine. However, iNOS gene transfer did not lead to regression of preestablished neointimal lesions. In an animal model more relevant to human vascular healing, iNOS gene transfer (5 x 10(8) PFU/pig) to injured porcine iliac arteries in vivo was also efficacious, reducing intimal hyperplasia by 51.8%.

CONCLUSIONS

These results indicate that shortterm overexpression of the iNOS gene initiated at the time of vascular injury is an effective method of locally increasing NO levels to prevent intimal hyperplasia.

Identification of contact residues and definition of the CAR-binding site of adenovirus type 5 fiber protein

The binding of adenovirus (Ad) fiber knob to its cellular receptor, the coxsackievirus and Ad receptor (CAR), promotes virus attachment to cells and is a major determinant of Ad tropism. Analysis of the kinetics of binding of Ad type 5 (Ad5) fiber knob to the soluble extracellular domains of CAR together (sCAR) and each immunoglobulin (Ig) domain (IgV and IgC2) independently by surface plasmon resonance demonstrated that the IgV domain is necessary and sufficient for binding, and no additional membrane components are required to confer high-affinity binding to Ad5 fiber knob. Four Ad5 fiber knob mutations, Ser408Glu and Pro409Lys in the AB loop, Tyr477Ala in the DG loop, and Leu485Lys in beta strand F, effectively abolished high-affinity binding to CAR, while Ala406Lys and Arg412Asp in the AB loop and Arg481Glu in beta strand E significantly reduced the level of binding. Circular dichroism spectroscopy showed that these mutations do not disorder the secondary structure of the protein, implicating Ser408, Pro409, Tyr477, and Leu485 as contact residues, with Ala406, Arg412, and Arg481 being peripherally or indirectly involved in CAR binding. The critical residues have exposed side chains that form a patch on the surface, which thus defines the high-affinity interface for CAR. Additional site-directed mutagenesis of Ad5 fiber knob suggests that the binding site does not extend to the adjacent subunit or toward the edge of the R sheet. These findings have implications for our understanding of the biology of Ad infection, the development of novel Ad vectors for targeted gene therapy, and the construction of peptide inhibitors of Ad infection.

A gene transfer vector-cell line system for complete functional complementation of adenovirus early regions E1 and E4

The improvements to adenovirus necessary for an optimal gene transfer vector include the removal of virus gene expression in transduced cells, increased transgene capacity, complete replication incompetence, and elimination of replication-competent virus that can be produced during the growth of first-generation adenovirus vectors. To achieve these aims, we have developed a vector-cell line system for complete functional complementation of both adenovirus early region 1 (E1) and E4. A library of cell lines that efficiently complement both E1 and E4 was constructed by transforming 293 cells with an inducible E4-ORF6 expression cassette. These 293-ORF6 cell lines were used to construct and propagate viruses with E1 and E4 deleted. While the construction and propagation of AdRSV beta gal.11 (an E1-/E4- vector engineered to contain a deletion of the entire E4 coding region) were possible in 293-ORF6 cells, the yield of purified virus was depressed approximately 30-fold compared with that of E1- vectors. The debilitation in AdRSV beta gal.11 vector growth was found to correlate with reduced fiber protein and mRNA accumulation. AdCFTR.11A, a modified E1-/E4- vector with a spacer sequence placed between late region 5 and the right inverted terminal repeat, efficiently expressed fiber and grew with the same kinetic profile and virus yield as did E1- vectors. Moreover, purified AdCFTR.11A yields were equivalent to E1- vector levels. Since no overlapping sequences exist in the E4 regions of E1-/E4- vectors and 293-ORF6 cell lines, replication-competent virus cannot be generated by homologous recombination. In addition, these second-generation E1-/E4- vectors have increased transgene capacity and have been rendered virus replication incompetent outside of the new complementing cell lines.

Adenoviral vectors for gene transfer

Adenoviruses began to be developed into highly effective gene expression vectors in the early 1980s. Recently, the increased interest in utilizing this transfer system in vivo has posed new problems for heterologous gene-transfer, spurring a renewed effort in the field of vector development toward solving the structural, immunological and targeting problems posed by gene therapy applications.

Regional suppression of tumor growth by in vivo transfer of a cDNA encoding a secreted form of the extracellular domain of the flt-1 vascular endothelial growth factor receptor

Vascular endothelial growth factor (VEGF), a potent angiogenic mediator, is overexpressed in most solid tumors. On the basis of the knowledge that solid tumor growth beyond a small volume is critically dependent on angiogenesis, and that adenovirus (Ad) vectors can mediate efficient in vivo gene transfer and expression, we hypothesized that Ad-mediated transfer of a secreted form of the extracellular domain of the flt-1 VEGF receptor (Adsflt) would suppress tumor growth on a regional basis. To evaluate this concept, three tumor models were examined using a murine colon carcinoma cell line and syngeneic BALB/c mice. First, mice with preestablished splenic CT26.CL25 tumors and liver metastases were given Adsflt on AdNull intravenously and, after 15 days, spleens and livers were harvested to quantify tumor burden. Adslft-treated animals had minimal residual splenic tumors and liver metastases; in contrast, control animals had bulky splenic tumors and extensive liver metastases (p < 0.003). Second, mice with preestablished lung metastases showed a significant reduction in pulmonary metastases with regionally administered Adslft (intratracheal, p < 0.02) but not when the vector was systemically administered (intravenous, p > 0.9). Finally, mice with primary subcutaneous tumors treated with intratumoral administration of Adslft showed significant tumor suppression (p < 0.05) not observed in AdNull-treated mice or mice given Adslft intravenously (p > 0.3). We conclude that Ad-mediated in vivo regional delivery of a secreted form of the extracellular domain of the flt-1 VEGF receptor can effectively inhibit regional tumor growth, a strategy that may provide a means to control tumor growth within the treated organ without the risk of systemic antiangiogenesis.

Expression of the E2F1 transcription factor overcomes type beta transforming growth factor-mediated growth suppression

Inhibition of cell growth by type beta transforming growth factor (TGF-beta) occurs in mid-G1 and is associated with decreased G1 cyclin-dependent kinase activity and maintenance of the retinoblastoma tumor suppressor protein Rb in an underphosphorylated, growth-suppressive state. A variety of recent experiments suggest that a functional target of Rb is the E2F transcription factor. In addition, the growth-suppressive effects of TGF-beta can be overcome by expression of viral oncogene products that dissociate E2F from Rb and Rb-related polypeptides. These results suggest the possibility that control of E2F may be a downstream event of TGF-beta action. Consistent with that possibility is the observation that E2F1 RNA levels are drastically reduced in TGF-beta-treated cells. We have also used a recombinant adenovirus containing the human E2F1 gene to overexpress the E2F1 product in mink lung epithelial cells that were growth arrested with TGF-beta. We find that overexpression of E2F1 can overcome the TGF-beta-mediated effect as measured by the activation of cellular DNA synthesis. These results suggest that a likely downstream target for the cyclin-dependent kinases, which are controlled by TGF-beta, is the activation of E2F.

Adenoviral transfer of the inducible nitric oxide synthase gene blocks endothelial cell apoptosis

BACKGROUND

We have previously reported that vascular inducible nitric oxide synthase (iNOS) gene transfer inhibits injury-induced intimal hyperplasia in vitro and in vivo. One mechanism by which NO may prevent intimal hyperplasia is by preserving the endothelium or promoting its regeneration. To study this possibility we examined the effect of iNOS gene transfer on endothelial cell (EC) proliferation and viability.

METHODS

An adenoviral vector (AdiNOS) containing the human iNOS cDNA was constructed and used to infect cultured sheep arterial ECs. NO production was measured, and the effects of continuous NO exposure on EC proliferation, viability, and apoptosis were evaluated.

RESULTS

AdiNOS-infected ECs produced 25- to 100-fold more NO than control (AdlacZ) infected cells as measured by nitrite accumulation. This increased NO synthesis did not inhibit EC proliferation as reflected by tritiated thymidine incorporation. Chromium 51 release assay revealed that EC viability was also unaffected by AdiNOS infection and NO synthesis. In addition, prolonged exposure to NO synthesis did not induce EC apoptosis. Instead, NO inhibited lipopolysaccharide-induced apoptosis in these cells by reducing caspase-3-like protease activity.

CONCLUSIONS

Vascular iNOS gene transfer, while inhibiting smooth muscle cell proliferation, does not impair EC mitogenesis or viability. Augmented NO synthesis may also protect ECs against apogenic stimuli such as lipopolysaccharide. Therefore iNOS gene transfer may promote endothelial regeneration and can perhaps accelerate vascular healing.

Protection from reoxygenation injury by inhibition of rac1

We demonstrate that adenoviral-mediated gene transfer of a dominant negative rac1 gene product (N17rac1) inhibits the intracellular burst of reactive oxygen species (ROS) that occurs after reoxygenation of vascular smooth muscle cells. In contrast, expression of a dominant negative ras gene (N17ras) had no effect. Challenge of control cells and cells expressing N17rac1 with a direct oxidant stress produced an equivalent increase in intracellular ROS levels and subsequent cell death. This suggests that N17rac1 expression appears to block production of harmful oxygen radicals and does not act directly or indirectly to scavenge ROS generated during reoxygenation. Expression of N17rac1 results in protection from hypoxia/reoxygenation-induced cell death in a variety of cell types including vascular smooth muscle cells, fibroblasts, endothelial cells, and ventricular myocytes. These results suggest that reoxygenation injury requires the activation of rac proteins, and that inhibition of rac-dependent pathways may be a useful strategy for the prevention of reperfusion injury in ischemic tissues.