Combinatorial synergy induced by adenoviral-mediated mda-7 and Herceptin in Her-2+ breast cancer cells.

The melanoma differentiation-associated gene-7 (mda-7) is a member of the interleukin-10 cytokine family and a novel tumor suppressor gene. Adenoviral-mediated mda-7 (Ad-mda7) gene transfer has tumor-specific growth inhibitory and proapoptotic effects in a broad spectrum of cancer cells. In breast cancer cells, adenoviral-induced mda-7 expression triggers antiproliferative effects by downregulation of survival signals, such as Bcl-2 and Akt. The anti-human epidermal growth factor receptor-2 (Her-2) monoclonal antibody, Trastuzumab (Herceptin), increases the sensitivity of Her-2/neu-overexpressing breast cancer cells to chemotherapeutic agents and radiotherapy. In this study, we evaluate the effects of treatment with Ad-mda7 and Herceptin combination therapy in a panel of Her-2/neu-overexpressing cell lines, and in established tumors in nude mice. Compared to individual treatments, the combination of Ad-mda7 and Herceptin elicits supra-additive antitumor activity in Her-2/neu-overexpressing tumor cell lines: increased cell death, cell cycle block and apoptosis. The Ad-mda7 and Herceptin interaction was shown to be synergistic by isobologram analysis. Ad-mda7 does not alter cell surface Her-2/neu levels, but the combination of Ad-mda7+Herceptin results in increased expression of cell surface E-cadherin with concomitant translocation of beta-catenin from the nucleus to the cell membrane. In vivo, the combination of Ad-mda7 and Herceptin showed significantly increased antitumor activity (P<0.003) against Her-2/neu-overexpressing tumors. These data suggest that the combination of Ad-mda7 with Herceptin may be a novel therapy for breast cancer patients whose tumors overexpress Her-2/neu. The observed synergistic effect may improve treatment options for otherwise poorly responsive, Her-2-positive, breast cancer patients.

mda-7 gene transfer sensitizes breast carcinoma cells to chemotherapy, biologic therapies and radiotherapy: correlation with expression of bcl-2 family members.

Current therapies used in the treatment of breast cancer are limited by systemic toxicity, rapid drug metabolism and intrinsic and acquired drug resistance. We have previously shown that adenoviral-mediated transfer of the melanoma differentiation-associated gene-7 (mda-7) elicits growth inhibition and apoptosis in various tumor types. Here, we evaluate the effects of Ad-mda7, alone and in combination with other therapies, against a panel of nine breast tumor cell lines and their normal counterparts; we report selective Ad-mda7-mediated p53-independent growth inhibition, G2/M cell cycle arrest, and apoptosis. In vivo, Ad-mda7 induced p53-independent tumor growth inhibition (P<0.004) in multiple xenograft models. We then evaluated the combination of Ad-mda7 with agents commonly used to treat breast cancer: radiotherapy (XRT), Tamoxifen, Taxotere, Adriamycin, and Herceptin. These agents exhibit diverse modes of action, including formation of bulky adducts, inhibition of DNA replication (Adriamycin, XRT), damage to microtubules (Taxotere), nonsteroidal estrogen antagonists (Tamoxifen), or Her2/neu receptor blockade (Herceptin). Treated with conventional anticancer drugs or radiation, MDA-7-expressing cells display additive or synergistic cytotoxicity and apoptosis that correlates with decreased BCL-2 expression and BAX upregulation. In vivo, animals that received Ad-mda7 and XRT underwent significant reduction of tumor growth (P<0.002). This is the first report of the synergistic effects of Ad-mda7 combined with chemotherapy or radiotherapy on human breast carcinoma cells.

Adenovirus-mediated transfer of the PTEN gene inhibits human colorectal cancer growth in vitro and in vivo.

The tumor-suppressor gene PTEN encodes a multifunctional phosphatase that is mutated in a variety of human cancers. PTEN inhibits the phosphatidylinositol 3-kinase pathway and downstream functions, including activation of Akt/protein kinase B (PKB), cell survival, and cell proliferation in tumor cells carrying mutant- or deletion-type PTEN. In such tumor cells, enforced expression of PTEN decreases cell proliferation through cell-cycle arrest at G1 phase accompanied, in some cases, by induction of apoptosis. More recently, the tumor-suppressive effect of PTEN has been reported in ovarian and thyroid tumors that are wild type for PTEN. In the present study, we examined the tumor-suppressive effect of PTEN in human colorectal cancer cells that are wild type for PTEN. Adenoviral-mediated transfer of PTEN (Ad-PTEN) suppressed cell growth and induced apoptosis significantly in colorectal cancer cells (DLD-1, HT29, and SW480) carrying wtPTEN than in normal colon fibroblast cells (CCD-18Co) carrying wtPTEN. This suppression was induced through downregulation of the Akt/PKB pathway, dephosphorylation of focal adhesion kinase (FAK) and mitogen-activated protein kinase (MAPK) and cell-cycle arrest at the G2/M phase, but not the G1 phase. Furthermore, treatment of human colorectal tumor xenografts (HT-29, and SW480) with Ad-PTEN resulted in significant (P=0.01) suppression of tumor growth. These results indicate that Ad-PTEN exerts its tumor-suppressive effect on colorectal cancer cells through inhibition of cell-cycle progression and induction of cell death. Thus Ad-PTEN may be a potential therapeutic for treatment of colorectal cancers.

Intrabody-mediated phenotypic knockout of major histocompatibility complex class I expression in human and monkey cell lines and in primary human keratinocytes.

Cultured keratinocyte allografts from unrelated donors can be readily grown as sheets in large-scale cell culture and have been used as an immediate skin cover for severely burned patients. Despite the absence of passenger leukocytes and the unlimited amount of material that can be obtained for permanent skin coverage, the allografts are susceptible to rejection. Since MHC class I (MHCI) antigens serve as targets for allograft rejection, we investigated whether 'phenotypic knockout' of human MHCI could be achieved through expression of an ER-directed anti-human MHCI single-chain intrabody (sFvhMHCI) that is directed against a monomorphic, conformational epitope, expressed across species lines, on the MHCI heavy chain. Co-immunoprecipitation of both MHCI heavy chain and beta2-microglobulin occurred in transfected monkey COS-1 cells, while Jurkat T cells stably expressing the ER-directed sFvhMHCI intrabody showed that complete phenotypic knockout of MHCI cell surface expression could be achieved. Infection of several human cell lines of divergent tissue sources and different HLA haplotypes resulted in marked down-regulation of MHCI expression, even under conditions where inflammatory cytokines (eg gamma-IFN) which up-regulate MHCI expression were used. Finally, when adenovirus encoding the anti-human MHCI intrabody was used to transduce primary human keratinocytes, a marked reduction of surface MHCI expression was observed. These in vitro studies set the groundwork for in vivo studies to determine if intrabody-mediated knockout of MHCI can impair alloantigen expression and prolong the survival of keratinocyte allografts.

Genomic structure, chromosomal localization and expression profile of a novel melanoma differentiation associated (mda-7) gene with cancer specific growth suppressing and apoptosis inducing properties.

Abnormalities in cellular differentiation are frequent occurrences in human cancers. Treatment of human melanoma cells with recombinant fibroblast interferon (IFN-beta) and the protein kinase C activator mezerein (MEZ) results in an irreversible loss in growth potential, suppression of tumorigenic properties and induction of terminal cell differentiation. Subtraction hybridization identified melanoma differentiation associated gene-7 (mda-7), as a gene induced during these physiological changes in human melanoma cells. Ectopic expression of mda-7 by means of a replication defective adenovirus results in growth suppression and induction of apoptosis in a broad spectrum of additional cancers, including melanoma, glioblastoma multiforme, osteosarcoma and carcinomas of the breast, cervix, colon, lung, nasopharynx and prostate. In contrast, no apparent harmful effects occur when mda-7 is expressed in normal epithelial or fibroblast cells. Human clones of mda-7 were isolated and its organization resolved in terms of intron/exon structure and chromosomal localization. Hu-mda-7 encompasses seven exons and six introns and encodes a protein with a predicted size of 23.8 kDa, consisting of 206 amino acids. Hu-mda-7 mRNA is stably expressed in the thymus, spleen and peripheral blood leukocytes. De novo mda-7 mRNA expression is also detected in human melanocytes and expression is inducible in cells of melanocyte/melanoma lineage and in certain normal and cancer cell types following treatment with a combination of IFN-beta plus MEZ. Mda-7 expression is also induced during megakaryocyte differentiation induced in human hematopoietic cells by treatment with TPA (12-O-tetradecanoyl phorbol-13-acetate). In contrast, de novo expression of mda-7 is not detected nor is it inducible by IFN-beta+MEZ in a spectrum of additional normal and cancer cells. No correlation was observed between induction of mda-7 mRNA expression and growth suppression following treatment with IFN-beta+MEZ and induction of endogenous mda-7 mRNA by combination treatment did not result in significant intracellular MDA-7 protein. Radiation hybrid mapping assigned the mda-7 gene to human chromosome 1q, at 1q 32.2 to 1q41, an area containing a cluster of genes associated with the IL-10 family of cytokines. Mda-7 represents a differentiation, growth and apoptosis associated gene with potential utility for the gene-based therapy of diverse human cancers.

Down-regulated melanoma differentiation associated gene (mda-7) expression in human melanomas.

The melanoma differentiation associated gene-7 (mda-7) has a potential inhibitory role in melanoma progression, although the mechanisms underlying this effect are still unknown. mda-7 mRNA has been found to be present at higher levels in cultured normal melanocytes compared with metastatic melanoma cell lines. Furthermore, levels of mda-7 message have shown an inverse correlation with melanoma progression in human tumor samples, suggesting that mda-7 may be a novel tumor suppressor gene. We have designed this study to investigate MDA-7 protein expression in different stages of melanoma progression and to examine its antiproliferative effects in vitro. Our data demonstrate that MDA-7 protein can be found in normal melanocytes and early stage melanomas. It is also observed in smooth muscle cells in the skin. However, in keeping with a possible role as a tumor suppressor, MDA-7 expression is decreased in more advanced melanomas, with nearly undetectable levels in metastatic disease. We also investigated antitumor effects of overexpressed MDA-7 on human melanoma cells in vitro. Our results demonstrate that Ad-mda-7 induces apoptosis and G2/M cell cycle arrest in melanoma cells, but not in normal human melanocytes.

Melanoma differentiation associated gene-7 (mda-7): a novel anti-tumor gene for cancer gene therapy.

BACKGROUND: The mda-7 gene (melanoma differentiation associated gene-7) is a novel tumor suppressor gene. The anti-proliferative activity of MDA-7 has been previously reported. In this report, we analyze the anti-tumor efficacy of Ad-mda7 in a broad spectrum of cancer lines. MATERIALS AND METHODS: Ad-mda7-transduced cancer or normal cell lines were assayed for cell proliferation (tritiated thymidine incorporation assay, Alamar blue assay, and trypan-blue exclusion assay), apoptosis (TUNEL, and Annexin V staining visualized by fluorescent microscopy or FACs analysis), and cell cycle regulation (Propidium Iodide staining and FACs analysis). RESULTS: Ad-mda7 treatment of tumor cells resulted in growth inhibition and apoptosis in a temporal and dose-dependent manner. The anti-tumor effects were independent of the genomic status of p53, RB, p16, ras, bax, and caspase 3 in these cells. In addition, normal cell lines did not show inhibition of proliferation or apoptotic response to Ad-mda7. Moreover, Ad-mda7-transduced cancer cells secreted a soluble form of MDA-7 protein. Thus, Ad-mda7 may represent a novel gene-therapeutic agent for the treatment of a variety of cancers. CONCLUSIONS: The potent and selective killing activity of Ad-mda7 in cancer cells but not in normal cells makes this vector a potential candidate for cancer gene therapy.

Gene therapy. Therapeutic approaches and implications.

The present article is an overview of gene therapy with an emphasis on different approaches and its implications in the clinic. Genetic interventions have been applied to the diagnosis of and therapy for an array of human diseases. The initial concept of gene therapy was focused on the treatment of genetic diseases. Subsequently, the field of gene therapy has been expanded, with a major focus on cancer. Although the results of early gene therapy-based clinical trials have been encouraging, there is a need for gene delivery vectors that feature reduced immunogenicity and improved targeting ability. The results of phases I/II clinical trials have suggested the important role of gene therapy as a versatile and powerful treatment tool, especially for human cancers. One reasonable expectation is that performing gene therapy at an earlier stage in the disease process or for minimal residual disease may be more advantageous.

Upregulation of the apoptosis-associated protein Grb3-3 in HIV-1-infected human CD4(+) lymphocytes.

The mechanism(s) by which HIV-1 infection contributes to depletion of CD4(+) T cell is not well understood. In this report, we investigated whether a recently identified isoform of growth factor receptor bound protein (Grb2), named Grb3-3, a signaling molecule that is associated with the MAP kinase pathway and with apoptosis could be involved. We find that Grb3-3 is markedly up-regulated following HIV-1 infection of CD4(+) peripheral blood mononuclear cells undergoing apoptosis. Although IL-2 deprived CD4(+) cells also undergo apoptosis to a similar extent, Grb3-3 upregulation is not detected under these experimental conditions. Transient overexpression of Grb3-3 in Jurkat T-cells also causes apoptosis. Upon staurosporine stimulation, Grb3-3 predisposes Sup-T1 cell to apoptosis. Finally, analysis of the HIV-1 genes responsible for Grb3-3 expression demonstrates that Tat and Nef can independently induces its expression, suggesting these two earliest viral gene products of HIV-1 may share some common pathway(s) in up-regulating Grb3-3 expression.

Grb3-3 is up-regulated in HIV-1-infected T-cells and can potentiate cell activation through NFATc.

The MAPK pathway is required for T-cell activation; however, its role in modulating T-cell function following human immunodeficiency virus type 1 (HIV-1) infection is poorly understood. In this report, we investigated whether Grb3-3, an isoform of the Grb2 (growth factor receptor-bound protein-2) adaptor molecule that is associated with the MAPK pathway, could be involved. We found that Grb3-3, but not its isoform Grb2, is markedly up-regulated in CD4(+) peripheral blood mononuclear cells derived from either in vitro HIV-1-infected cultures or HIV-1-infected human subjects. Analysis of HIV-1 gene products indicated that Tat and Nef, both of which have been implicated in modulating T-cell function, can independently induce expression of Grb3-3. By using NFAT/AP-1, AP-1, or NFAT reporter assays, we found that Grb3-3 can potentiate NFAT (but not AP-1) promoter activity in Jurkat T-cells upon engagement of the T-cell receptor and CD28 co-receptor. In addition, potentiation of NFAT by Grb3-3 is substantially suppressed by MEKK1, a kinase that may play an important role in retaining NFAT in the cytoplasm, and by cyclosporin A. Finally, we also found that Grb3-3 potentiates HIV-1 long terminal (LTR) repeat promoter activity following T-cell receptor stimulation, an effect that can be largely suppressed by cyclosporin A. Taken together, this study indicates that Grb3-3 is a cellular factor that can be up-regulated by HIV-1. In addition, Grb3-3 can also function as a positive factor for T-cell activation and, in doing so, may aid in establishing an intracellular environment that can optimally support HIV-1 replication.

Tumor-suppressive effects by adenovirus-mediated mda-7 gene transfer in non-small cell lung cancer cell in vitro.

The melanoma differentiation-associated gene-7 (mda-7), cloned from a human melanoma cell line H0-1, is known to induce tumor cell-selective growth inhibition in breast cancer cells in vitro and loss of tumorigenicity ex vivo. Yet, the mechanisms underlying these effects are still unknown. Therefore, we investigated these mechanisms on the molecular level in human non-small cell lung carcinoma (NSCLC) cells in vitro. Overexpression of mda-7 protein by Ad-mda-7 significantly suppressed proliferation and induced G2/M cell cycle arrest in wild-type p53 (A549, H460), and p53-null (H1299) non-small cell lung cancer cell lines, but not in normal human lung fibroblast (NHLF) cells. p53, Bax, and Bak protein expression was up-regulated in wild-type p53 tumor cell lines, but not in p53-null cells, suggesting that an intact p53 pathway was required for Bax and Bak induction. However, in all three cancer cell lines tested, activation of the caspase cascade and cleavage of poly(ADP-ribose) polymerase (PARP) appeared to be independent of the p53 mutational status. Together, these results suggest that apoptosis may be induced via multiple pathways by Ad-mda-7 in lung cancer cells and that Ad-mda-7 has the potential to become a novel therapeutic for clinical cancer gene therapy. Gene Therapy (2000) 7, 2051-2057.

Inhibition of human immunodeficiency virus type 1 replication in vitro in acutely and persistently infected human CD4+ mononuclear cells expressing murine and humanized anti-human immunodeficiency virus type 1 Tat single-chain variable fragment intrabodies.

We have previously reported that a murine anti-Tat sFv intrabody, termed sFvtat1Ck, directed against the proline-rich N-terminal activation domain of HIV-1, is a potent inhibitor of HIV-1 replication [Mhashilkar, A. M., et al. (1995). EMBO J. 14, 1542-1551]. In this study, the protective effect of sFvtat1Ck expression on HIV-1 replication in both acutely infected and persistently infected CD4+ cells was examined. Stably transfected CD4+ SupT1 cells were resistant to HIV-1 infection at high MOI with both the laboratory isolate HxB2 and six syncytium-inducing (SI) primary isolates. Persistently infected U1 cells, which can be induced to increase HIV-1 mRNA synthesis on addition of PMA or TNF-alpha, showed decreased production of HIV-1 in the presence of sFvtat1Ck. In transduced CD4+-selected, CD8+-depleted, and total PMBCs, the sFvtat1Ck-expressing cells showed marked inhibition of HIV-1 replication. The anti-Tat sFv was subsequently humanized by substituting compatible human framework regions that were chosen from a large database of human V(H) and V(L) sequences on the basis of high overall framework matching, similar CDR length, and minimal mismatching of canonical and V(H)/V(L) contact residues. One humanized anti-Tat sFv intrabody, termed sFvhutat2, demonstrated a level of anti-HIV-1 activity that was comparable to the parental murine sFv when transduced PBMCs expressing the murine or humanized sFv intrabodies were challenged with HxB2 and two SI primary isolates. Because Tat is likely to have both direct and indirect effects in the pathogenesis of AIDS through its multiple roles in the HIV-1 life cycle and through its effects on the immune system, the strategy of genetically blocking Tat protein function with a humanized anti-Tat sFv intrabody may prove useful for the treatment of HIV-1 infection and AIDS, particularly when used as an adjuvant gene therapy together with highly active antiretroviral therapies that are currently available.

Technology evaluation: StealthVector (HIV) Enzo.

Efficient inhibition of human immunodeficiency virus-1 (HIV-1) replication with intracellularly expressed antiviral genes would be an important step toward clinical gene therapy for HIV-1 disease. Enzo Biochem is investigating and developing antisense genes as a potential gene therapy approach against a variety of conditions including acquired immunodeficiency syndrome (AIDS), cancer and hepatitis. The subsidiary of Enzo Biochem, Enzo Therapeutics, utilized its StealthVector technology and initiated phase I trials in July 1998 [291511,307156]. StealthVector, which is comprised of independent antisense sequences directed against two functional HIV-1 regions, is involved in regulation of gene expression soon after HIV infection, transactivation response (TAR) and tat/rev. StealthVector localizes primarily in the cell nucleus, where it could be most effective in inhibiting viral growth.

Inhibition of HIV-1 replication by combination of a novel inhibitor of TNF-alpha with AZT.

The small molecule S9a was derived from an established tumor necrosis factor-alpha (TNF-alpha) inhibitor (Canventol) by replacement of the isopropylidine group with a phenyl ring. S9a at 10 to 100 nM inhibited HIV production as potently as 3'-azido-3'-deoxythymidine (AZT), an inhibitor of viral reverse transcriptase. Furthermore, S9a and AZT in combination, at noncytoxic concentrations strongly inhibited HIV-1 replication that was more than additive and substantially prolonged the appearance of virus both in acutely infected CD4+ lymphocytes (SupT) in culture and in peripheral blood mononuclear cells (PBMCs) infected with a primary HIV-1 isolate. S9a inhibited TNF-alpha promoter-driven reporter gene activity. It was proposed that the mechanism of antiviral action of S9a was on the host cell, by blocking TNF-alpha transcription via a Tat-induced tar-independent loop, which decreases downstream NF-kappaB activation of HIV-1 long terminal repeat (LTR). S9a was superior to the first generation compound Canventol, which was superior to the natural compound sarcophytol A, demonstrating that further structure-based enhancement of potency of these compounds is feasible. This study suggests a therapeutic approach against AIDS by application of two drugs, one against a cellular and the other a viral target, which may provide an approach to the problem of frequent emergence of resistant variants to combinations of drugs that target only HIV genes.

Inhibition of human immunodeficiency virus replication and growth advantage of CD4+ T cells from HIV-infected individuals that express intracellular antibodies against HIV-1 gp120 or Tat.

Current clinical gene therapy protocols for the treatment of human immunodeficiency virus type 1 (HIV-1) infection often involve the ex vivo transduction and expansion of CD4+ T cells derived from HIV-positive patients at a late stage in their disease (CD4 count <400). These protocols involve the transduction of T cells by murine leukemia virus (MLV)-based vectors encoding antiviral constructs such as the rev m10 dominant negative mutant or a ribozyme directed against the CAP site of HIV-1 RNA. We examined the efficiency and stability of transduction of CD4+ T cells derived from HIV-infected patients at different stages in the progression of their disease, from seroconversion to AIDS. CD4+ T cells from HIV-positive patients and uninfected donors were transduced with MLV-based vectors encoding beta-galactosidase and an intracellular antibody directed against gp120 (sFv 105) or Tat. (sFvtat1-Ckappa). The expression of marker genes and the effects of the antiviral constructs were monitored in vitro in unselected transduced CD4+ T cells. Efficiency and stability of transduction varied during the course of HIV infection; CD4+ T cells derived from asymptomatic patients were transducible at higher efficiencies and stabilities than CD4+ T cells from patients with acquired immunodeficiency syndrome (AIDS). Expression of the anti-tat intracellular antibody was more effective at stably inhibiting HIV-1 replication in transduced cells from HIV-infected individuals than was sFv 105. The results of this study have important implications for the development of a clinically relevant gene therapy for the treatment of HIV-1 infection.

Localization of HIV-1 co-receptors CCR5 and CXCR4 in the brain of children with AIDS.

The chemokine receptors CCR5 and CXCR4 are co-receptors together with CD4 for human immunodeficiency virus (HIV)-1 entry into target cells. Macrophage-tropic HIV-1 viruses use CCR5 as a co-receptor, whereas T-cell-line tropic viruses use CXCR4. HIV-1 infects the brain and causes a progressive encephalopathy in 20 to 30% of infected children and adults. Most of the HIV-1-infected cells in the brain are macrophages and microglia. We examined expression of CCR5 and CXCR4 in brain tissue from 20 pediatric acquired immune deficiency syndrome (AIDS) patients in relation to neuropathological consequences of HIV-1 infection. The overall frequency of CCR5-positive perivascular mononuclear cells and macrophages was increased in the brains of children with severe HIV-1 encephalitis (HIVE) compared with children with mild HIVE or non-AIDS controls, whereas the frequency of CXCR4-positive perivascular cells did not correlate with disease severity. CCR5- and CXCR4-positive macrophages and microglia were detected in inflammatory lesions in the brain of children with severe HIVE. In addition, CXCR4 was detected in a subpopulation of neurons in autopsy brain tissue and primary human brain cultures. Similar findings were demonstrated in the brain of adult AIDS patients and controls. These findings suggest that CCR5-positive mononuclear cells, macrophages, and microglia contribute to disease progression in the central nervous system of children and adults with AIDS by serving as targets for virus replication.

Inhibition of human immunodeficiency virus type 1 replication in vitro by a novel combination of anti-Tat single-chain intrabodies and NF-kappa B antagonists.

Human immunodeficiency virus type 1 (HIV-1) Tat, an early regulatory protein that is critical for viral gene expression and replication, transactivates the HIV-1 long terminal repeat (LTR) via its binding to the transactivation response element (TAR) and, along with other cellular factors, increases viral transcription initiation and elongation. Tat also superactivates the HIV-1 promoter through a TAR-independent mechanism, including tumor necrosis factor alpha-induced and protein kinase C (PKC)-dependent activation of NF-kappa B, and inhibitors of Tat and NF-kappa B cooperatively down-regulate this Tat-mediated LTR superactivation. In this study, a combined pharmacologic and genetic strategy using two PKC (NF-kappa B) inhibitors, pentoxifylline (PTX) and Gö-6976, and a stably expressed anti-Tat single-chain intracellular antibody (sFv intrabody) was employed to obtain cooperative inhibition of both HIV-1 LTR-driven gene expression and HIV-1 replication. Treatment of cells with PTX and Gö-6976 resulted in cooperative inhibition of both HIV-1 LTR-driven gene expression and HIV-1 replication. In addition, the combined use of anti-Tat sFv intrabodies and the two NF-kappa B inhibitors retained the virus in the latent state for as long as 45 days. The combined treatment resulted in more durable inhibition of HIV-1 replication than was seen with the NF-kappa B inhibitors alone or the anti-Tat sFv intrabodies alone. Together, these results suggest that in future clinical gene therapy trials, a combined pharmacologic and genetic strategy like the one reported here may improve the survival of transduced cells and prolong clinical benefit.

Inhibition of early and late events of the HIV-1 replication cycle by cytoplasmic Fab intrabodies against the matrix protein, p17.

BACKGROUND: The HIV-1 matrix (MA) protein, p17, contains two subcellular localization signals that facilitate both nuclear import of the viral preintegration complex early during infection and virus particle assembly late in infection. The dual role of MA in both the afferent and efferent arms of the HIV-1 life cycle makes it an important target for intracellular immunization-based gene therapy strategies. MATERIALS AND METHODS: Here we report, using a new bicistronic vector, that an intracellular Fab antibody, or Fab intrabody, directed against a carboxy-terminal epitope of MA from the Clade B HIV-1 genotype, can inhibit HIV-1 infection when expressed in the cytoplasm of actively dividing CD4+ T cells. RESULTS: Marked inhibition of proviral gene expression occurred when single-round HIV-1 CAT virus was used for infections. In challenge experiments using both laboratory strains and syncytium-inducing primary isolates of HIV-1, a substantial reduction in the infectivity of virions released from the cells was also observed. CONCLUSIONS: This novel strategy of simultaneously blocking early and late events of the HIV-1 life cycle may prove useful in clinical gene therapy approaches for the treatment of HIV-1 infection and AIDS, particularly when combined with genetic or pharmacologic-based strategies that inhibit other HIV-1 target molecules simultaneously.

Inhibition of HIV-1 Tat-mediated LTR transactivation and HIV-1 infection by anti-Tat single chain intrabodies.

Genes encoding the rearranged immunoglobulin heavy and light chain variable regions of anti-HIV-1 Tat, exon 1 or exon 2 specific monoclonal antibodies have been used to construct single chain intracellular antibodies 'intrabodies' for expression in the cytoplasm of mammalian cells. These anti-Tat single chain intrabodies (anti-Tat sFvs) are additionally modified with a C-terminal human C kappa domain to increase cytoplasmic stability and/or the C-terminal SV40 nuclear localization signal to direct the nascent intrabody to the nuclear compartment, respectively. The anti-Tat sFvs with specific binding activity against the N-terminal activation domain of Tat, block Tat-mediated transactivation of HIV-1 LTR as well as intracellular trafficking of Tat in mammalian cells. As a result, the transformed lymphocytes expressing anti-Tat sFvs are resistant to HIV-1 infection. Thus, these studies demonstrate that stably expressed single chain intrabodies and their modified forms can effectively target molecules in the cytoplasm and nuclear compartments of eukaryotic cells. Furthermore, these studies suggest that anti-Tat sFvs used either alone or in combination with other genetically based strategies may be useful for the gene therapy of HIV-1 infection and AIDS.

Breaching the conformational integrity of the catalytic triad of the serine protease plasmin: localized disruption of a side chain of His-603 strongly inhibits the amidolytic activity of human plasmin.

Site-directed mutagenesis has been used to construct a cDNA that encodes a recombinant variant human plasminogen (hPg) containing a Pro-611-->Ile mutation (MrhPg). The mutein was expressed in recombinant baculovirus-infected Spodoptera frugiperda cells (IPLB-SF-21AE), and purified. After activation of this zymogen to its corresponding form of the serine protease plasmin (MrhPm), this latter enzyme was essentially inactive toward an amide plasmin substrate, most likely from alteration of the spatial relationships of the active-site His-603 to its partners of the catalytic triad, Asp-646 and Ser-741. Partial amidolytic activity of MrhPm was restored as a consequence of imidazole addition to the assay medium, due to an increase in the catalytic constant kcat of the enzyme. The serine protease inhibitor, diisopropylphosphofluoridate, when preincubated with MrhPm, did not inhibit restoration of its amidolytic activity with imidazole, whereas diisopropylphosphofluoridate did inhibit the amidolytic activity of MrhPm in the presence of imidazole. This result implies that His-603 directly influences the nucleophilic character of Ser-741. When imidazole as pretreated with alpha-N-tosyl-L-lysine chloromethyl ketone, the ability of this imidazole solution to restore amidolytic activity to MrhPm was eliminated, suggesting that N alpha-(p-tosyl)lysine chloromethyl ketone directs into the binding pocket a derivatized form of imidazole, which is ineffective as an His-603 substitute. These results indicate that the conformational reorientation of His-603 results in a malfunctional catalytic triad in the serine protease MrhPm, thus leading to an inactive enzyme despite the presence of all three essential amino acids of the catalytic triad. Addition of extramolecular imidazole restores a portion of the amidolytic activity of this mutant enzyme. These data also argue for an enzyme mechanism in which the active-center His-603 residue directly influences the nucleophilicity of the active-site Ser 741 residue.