Biomedical subjects

A M Mhashilkar

Publications and source records attributed to A M Mhashilkar.

12 recordsLinked to original sources

PubMed2002

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.

Amino Acid Sequence↗

PubMed2001

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.

Apoptosis↗

PubMed2001

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.

Adenoviridae↗

PubMed1999

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.

Amino Acid Sequence↗

PubMed1999

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.

Biotechnology↗

PubMed1998

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.

Anti-HIV Agents↗

PubMed1997

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.

Anti-HIV Agents↗

PubMed1997

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.

Animals↗

PubMed1995

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.

Amino Acid Sequence↗

PubMed1993

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.

Amino Acid Sequence↗

PubMed1989

Involvement of protein kinase C in activation of human granulocytes and peritoneal macrophages by type 1 fimbriated (mannose specific) Escherichia coli.

Specific binding of bacteria to phagocytic cells mediated by antibody and complement (opsonins) or by lectin-carbohydrate interactions is required for their efficient uptake and killing by opsonophagocytosis or lectinophagocytosis, respectively (Ofek and Sharon, Infect. Immun. 56, 539, 1988). An early step in these processes is activation of the phagocytes by the bound bacteria, as evidenced by appearance of an oxidative burst. Previous work has shown that protein kinase C (PKC) is involved in activation of human granulocytes by opsonized Escherichia coli. In the present study, we used three inhibitors of PKC to examine the possible involvement of the enzyme in activation of human granulocytes and peritoneal macrophages by type 1 fimbriated (mannose-specific) Escherichia coli in the absence of opsonins. Activation, as measured by chemiluminescence, was completely inhibited by sphingosine (50 microM) and only partially (50%) by 100 microM H-7 [1-(5-isoquinolinesulfonyl)-2-methylpiperazine]; in both cases it was fully reversible. The third inhibitor, K252a, also inhibited almost completely the activation at 1 microM. The inhibitors acted similarly on activation of the phagocytic cells by opsonized bacteria or by phorbol-12-myristate-13-acetate (0.1 microM). Down regulation of the kinase, by pretreatment of the human granulocytes or macrophages with a high concentration (1.6 microM) of phorbol myristate acetate, abolished their ability to respond to stimulation by the bacteria. Our findings provide evidence for the involvement of PKC in the activation of phagocytic cells by type 1 fimbriated bacteria.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗

PubMed1989

Lectin-mediated, nonopsonic phagocytosis of type 1 Escherichia coli by human peritoneal macrophages of uremic patients treated by peritoneal dialysis.

Human peritoneal macrophages isolated from uremic patients undergoing peritoneal dialysis bind type 1 fimbriated Escherichia coli in the absence of opsonins. The number of bacteria bound per macrophage was 6.9, as determined by microscopic examination. Methyl alpha-mannoside (0.1 mM) and p-nitrophenyl alpha-mannoside (0.01 mM) inhibited this binding by about 66%. The ability of peritoneal macrophages to bind E. coli in a mannose-specific manner was confirmed in further experiments using an enzyme-linked immunosorbent assay (ELISA) with an antibacterial antibody, radiolabelled E. coli, and counts of colony-forming units (CFU). The number of bacteria bound per macrophage was 7 to 12 in the ELISA and 5.5-8.5 in the CFU assay. Methyl alpha-mannoside caused 70% inhibition of binding in the ELISA and 84% in the CFU assay, whereas p-nitrophenyl alpha-mannoside showed inhibition of 79% and 90%, respectively. Most bound bacteria (76-80%) were subsequently killed. Nonfimbriated E. coli 827 bound poorly to the macrophages (approximately 22%) as compared to that of the fimbriated bacteria. Although this binding was not inhibited by methyl alpha-D-mannoside or p-nitrophenyl alpha-mannoside, the percentage of bacteria killed was similar to that of the fimbriated phenotype. The peritoneal macrophage is thus able to phagocytose E. coli in the absence of opsonins. This may explain the relative rarity of E. coli as an etiologic agent of peritoneal infections in the dialysed patient.

Adult↗