Biomedical subjects

I Pastan

Publications and source records attributed to I Pastan.

857 records · Page 48Linked to original sources

PubMedDate not supplied

Studies on the activity of barnase toxins in vitro and in vivo.

Pseudomonas exotoxin A (PE) is a protein toxin composed of three structural domains which are responsible for cell binding (domain Ia, amino acids 1-252), translocation into the cytosol (domain II, amino acids 253-364) and ADP-ribosylation activity (domain III, amino acids 405-613). We have previously described (Prior, T. I., FitzGerald, D. J., and Pastan, I. (1992) Biochem. 31, 3555-3559) a molecule composed of amino acids 1-412 of PE and the extracellular ribonuclease of Bacillus amyloliquefaciens, barnase (Bar), and shown that this protein (PE1-412-Bar) is toxic to cells due to its ribonuclease activity, which had been delivered to the cytosol. We have now used this model to evaluate the role played by the carboxyl end of domain II (amino acids 347-364), domain Ib, and the amino end of domain III (amino acids 405-412) in the translocation event. Toxins completely lacking domain III, termed PE1-380-Bar, or both domains Ib and III, termed PE1-364-Bar, were equally cytotoxic to a murine fibroblast cell line (L929) as was PE1-412-Bar. Extending the deletion to include part of the E-helix and all of the F-helix of domain II (amino acids 347-364) resulted in a toxin (PE1-346-Bar) that was 10-fold less toxic. Previously tested on only murine cell lines, we demonstrate that barnase toxins are cytotoxic also to a variety of human cell lines. Cytotoxicity was assessed by measuring inhibition of DNA synthesis. Surprisingly, PE1-380-Bar is not lethal when injected into mice, either intraperitoneally or intravenously, at 9 nmol, which is 2200-fold more than the amount required for killing by PE (4 pmol). In cell culture these barnase-containing toxins are 100-fold less toxic to murine fibroblast cells than PE. Barnase toxin has a greater survival time in the blood of mice than PE, with a half-life of 102 min. We conclude that domain II is sufficient to transport proteins into the cytosol. Further, since domain Ia can be replaced with other cell targeting moieties, we propose that barnase-toxins should be evaluated for utility in targeted cancer therapy.

ADP Ribose Transferases↗

PubMedDate not supplied

Characterization of RFB4-Pseudomonas exotoxin A immunotoxins targeted to CD22 on B-cell malignancies.

To develop an immunotoxin for the treatment of B-cell malignancies, we constructed several candidate conjugates with RFB4, a B-cell specific anti-CD22 IgG1, and truncated forms of Pseudomonas exotoxin (PE). The four versions of PE included PE35 and PE35KDEL, which were linked to RFB4 via a disulfide bond, and PE38 and PE38KDEL, which were linked via a thioether bond. The PE35 truncated forms, which are fully active in ADP ribosylation and lack receptor binding sequences, do not require intracellular proteolytic cleavage in order to be active. PE35KDEL has the consensus endoplasmic reticulum retention signal, KDEL, replacing the wild type PE C-terminal sequence, REDLK. The PE38 forms retain all of domain II and therefore require cleavage to be active within cells. Cytotoxicity experiments on CD22-positive cell lines revealed that the PE35 conjugates were more active than the PE38 versions and the presence of the KDEL sequence generally enhanced toxicity by 5-10-fold compared to that of REDLK. The RFB4-PE35KDEL immunotoxin was most active in cytotoxicity assays against Burkitt's lymphoma cell lines such as Daudi and CA46 (IC50 = 0.2 ng/mL) and displayed little cytotoxicity toward human vascular endothelial cells (IC50 > 20 micrograms/mL). Results of experiments conducted in nude mice showed that both RFB4-PE35KDEL and RFB4-PE35 could inhibit the development of subcutaneous CA46 tumors.

ADP Ribose Transferases↗

PubMedDate not supplied

Biodistribution and catabolism of Ga-67-labeled anti-Tac dsFv fragment.

The disulfide-linked fragment (dsFv) of the antibody to the alpha subunit of the IL2 receptor has been radiolabeled with a [Ga-67] Ga-2-(p-SCN-Bz)-NOTA derivative linked through an isothiocyanato group to either the epsilon-amino group of lysine or the alpha-amino group of the N-terminal amino acids. This low molecular weight protein (LMWP) has been proposed as a tumor diagnostic agent. However, > 60% of the injected dose localized in the mouse kidney. The major catabolites (> 95%) in the kidney were identified as the Ga-2-(p-SCN-Bz)-NOTA conjugate with either lysine or methionine, with no evidence of transchelation of Ga-67. Since different amino acids in the dsFv were radiolabeled according to this procedure, it was possible to study the relative residence times of the various catabolites. The methionine conjugate had a significantly shorter residence time than the lysine conjugate in the same kidney. Labeling the appropriate amino acid in a LMWP may lead to reduced residence times and increased diagnostic or therapeutic ratios.

Animals↗

PubMedDate not supplied

Comparison of recombinant immunotoxins against LeY antigen expressing tumor cells: influence of affinity, size, and stability.

Monoclonal antibody B3 (MAb B3) reacts with many epithelial cancers. It recognizes a carbohydrate antigen (Ley) which is expressed in a variety of solid tumors including breast and colon. We have used the Fab portion of MAb B3 and a portion of the constant domain of human IgG1 to make recombinant immunotoxins of different compositions. The toxin component employed is a truncated form of Pseudomonas exotoxin (PE38). The light chain or Fd of the antibody was cloned from hybridoma RNA and fused to PE38. Immunotoxin (IT) was then expressed in Escherichia coli as a fusion protein and refolded with either the Fd or the light chain. We have also made B3(Fab) immunotoxins of different sizes ranging 85-140 kDa, by introducing different portions of the constant domain of human IgG1 at the junction of Fd and PE38 fusion site. We compared the properties of the resulting immunotoxins with existing anti-Ley immunotoxins side by side. All recombinant Fab-immunotoxins made in this study were cytotoxic to antigen-positive cancer cell lines. However, in contrast to the B3(scFv) immunotoxin, the B3(Fab) immunotoxins are very stable, retaining 90% of their activity after 24 h of incubation in human serum albumin at 37 degreesC. A pharmacokinetics study with these immunotoxin molecules showed a longer survival in the circulation of mice compared to the smaller Fv immunotoxins. The smaller size of the Fab immunotoxins compared to B3Lys-PE38 and the increased T1/2 value compared to B3(scFv)-PE38 and B3(dsFv)-PE38 make these recombinant immunotoxins alternative therapeutic agents to treat Ley antigen positive cancers.

Animals↗

PubMedDate not supplied

Chemical modification to reduce renal uptake of disulfide-bonded variable region fragment of anti-Tac monoclonal antibody labeled with 99mTc.

The anti-Tac disulfide-bonded variable region fragment (dsFv) is a genetically engineered, 25 kDa, murine monoclonal antibody fragment that recognizes the alpha subunit of the interleukin-2 receptor (IL-2Ralpha). The dsFv radiolabeled with the tetrafluorophenyl ester (TFP) of [99mTc]mercaptoacetyltriglycine ([99mTc]MAG3-TFP) showed rapid tumor uptake and fast blood clearance in mice, resulting in high tumor-to-nontumor background ratios. However, its high renal uptake was a problem. In this study, we tested the effect of lowering the isoelectric point (pI) of dsFv to <9.3 on renal and tumor uptake. To lower the pI, dsFv was acylated simultaneously with both [99mTc]MAG3-TFP and TFP-glycolate. The acylation of dsFv decreased its pI and its immunoreactivity inversely proportional to the molar ratio of TFP-glycolate to dsFv, whereas the conjugation of [99mTc]MAG3-TFP alone did not. When biodistribution studies were performed in nude mice, the effect of the lowered pI was reflected primarily in decreased kidney uptake and whole-body retention, with its highest effect seen at the earliest time point (15 min) after injection. In tumor-bearing nude mice, glycolated [99mTc]MAG3-dsFv with a pI range of 4.9 to 6.5 accumulated selectively into IL-2 receptor-positive SP2/Tac tumor similar to that of the control [125I]dsFv labeled by the Iodo-Gen method, whereas its renal uptake was 25% of [125I]dsFv at 15 min. At 90 min, the ratios of tumor to receptor-negative SP2/0 tumor, liver, kidney, stomach, and blood had peaked at 10.9, 8.5, 0.3, 5.0, and 6.2, respectively, for the glycolated [99mTc]MAG3-dsFv. The corresponding ratios for [125I]dsFv were 3.7, 5.0, 0.1, 1.5, and 2.1, respectively.

Animals↗

PubMedDate not supplied

Human epidermal growth factor receptor cDNA is homologous to a variety of RNAs overproduced in A431 carcinoma cells.

The recently discovered similarity between the human epidermal growth factor (EGF) receptor and the avian erythroblastosis virus v-erb-B protein supports the hypothesis that viral oncogenes share a common evolutionary origin with genes encoding growth-regulating cell-surface receptors. To elucidate the relationship between receptors and malignant transformation, we have now used a fragment of v-erb-B as a probe to screen a cDNA library of mRNA from A431 human carcinoma cells, which possess a large number of EGF receptors. Of the six clones isolated, the largest (pE7) contains an insert of 2.4 kilobase pairs (kbp) whose deduced amino acid sequence is homologous to the v-erb-B protein and identical to reported EGF receptor peptide sequences. This pE7 cDNA hybridized to three prominent RNAs of approximately 10, 5.6 and 2.9 kilobases (kb), and to three minor species of 6.3, 4.6 and 3.3 kb. All were present in elevated levels in A431 cells. The prominent 2.9-kb RNA was homologous only to the 5' portion of the pE7 insert. This result raises the possibility that differential RNA processing is used by A431 cells to generate a variety of RNAs.

Amino Acid Sequence↗

PubMedDate not supplied

Use of Pseudomonas aeruginosa toxin A in the construction of conjugate vaccines and immunotoxins.

Pseudomonas aeruginosa toxin A was used to construct conjugate vaccines and potent cytotoxic immunotoxins. Nontoxic, serologically active O polysaccharide derived from P. aeruginosa lipopolysaccharide (LPS) was covalently coupled to toxin A via reductive amination. The conjugate was nontoxic, nonpyrogenic, and had a molecular size of 2 X 10(6). The conjugate vaccine was safe when administered to human volunteers and was capable of evoking an immune response to both LPS and toxin A. Native toxin A was coupled to monoclonal antibodies to the human transferrin receptor and the human interleukin 2 receptor to produce immunotoxins active against receptor-bearing cell lines. Antitumor activity was demonstrated when the immunotoxin directed against the transferrin receptor was administered to nude mice bearing human ovarian tumors.

ADP Ribose Transferases↗

PubMedDate not supplied

Anti-tumor activity of K1-LysPE38QQR, an immunotoxin targeting mesothelin, a cell-surface antigen overexpressed in ovarian cancer and malignant mesothelioma.

Mesothelin, a differentiation antigen, is a 40-kD glycosylphosphatidylinositol-linked cell-surface glycoprotein, that is present on the surface of normal mesothelium and is overexpressed in many patients with epithelial ovarian cancer and malignant mesotheliomas. Monoclonal antibody K1 is a murine immunoglobulin G1 that recognizes mesothelin. LysPE38QQR is a truncated form of Pseudomonas exotoxin that lacks the cell-binding domain, but retains the translocation and adenosine diphosphate-ribosylation domains. It has a single lysine residue near the amino terminus that is available for conjugation to antibodies. To prevent chemical conjugation of the antibody to lysine residues at the C-terminus of Pseudomonas exotoxin, the two lysine residues at positions 590 and 606 were mutated to glutamine, and the lysine residue at position 613 was mutated to arginine. Monoclonal antibody K1 was chemically conjugated with LysPE38QQR, by modifying the antibody with sulfosuccinimidyl-4-(N-maleimidomethyl)cyclohexane-1-carboxylate and coupling it with SPDP N-succinimidyl 3-(2-pyridyldithio)propionate-modified LysPE38QQR. The resulting immunotoxin K1-LysPE38QQR was highly toxic to A431-K5 cells (a human epidermoid carcinoma cell line transfected with a mesothelin expression plasmid) with a half-maximal inhibitory concentration of 3-6 ng/mL. The immunotoxin had negligible activity against A431 cells, which do not express mesothelin (median inhibitory concentration > 100 ng/mL). This immunotoxin also caused complete regression of tumors in nude mice that received xenografts of mesothelin-positive human carcinomas. These results show that immunotoxins directed against mesothelin are a therapeutic option that merits further investigation for the treatment of ovarian cancer and malignant mesotheliomas.

ADP Ribose Transferases↗

PubMedDate not supplied

Cytotoxicity of antiosteosarcoma recombinant immunotoxins composed of TP-3 Fv fragments and a truncated Pseudomonas exotoxin A.

Regrowth of drug-resistant tumor cells is responsible for approximately half of an unselected osteosarcoma population still dying of the disease despite aggressive combination therapy. Two monoclonal antibodies, TP-1 (immunoglobulin 2a) and TP-3 (immunoglobulin 2b) are available, which specifically recognize an antigen on osteosarcoma cells. In this work, we have fused the variable (V) genes of TP-3 to a truncated fragment of Pseudomonas exotoxin A, referred to as PE38. Two immunotoxins were made that differed in the Fv portion: TP-3(scFv)-PE38, which contains a peptide linker, and TP-3(dsFv)-PE38, which contains a disulfide bond for stabilization of the association between the V domains. Recombinant TP-3 immunotoxins were expressed in Escherichia coli and purified from inclusion bodies. We describe the design and expression of these immunotoxins, and their properties with regard to antigen binding, stability, and cytotoxicity. Toxicity studies were done in mice. We found that the immunotoxins exhibited very similar in vitro properties, whereas in vivo TP-3(dsFv)-PE38 was much better tolerated than TP-3(scFv)-PE38.

ADP Ribose Transferases↗

PubMedDate not supplied

Coexpression of a multidrug resistance gene (MDR1) and herpes simplex virus thymidine kinase gene in a bicistronic retroviral vector Ha-MDR-IRES-TK allows selective killing of MDR1-transduced human tumors transplanted in nude mice.

Ha-MDR-IRES-TK is a bicistronic vector that coexpresses the MDR1 gene and the herpes simplex virus thymidine kinase (HSV-TK) gene. In the present study we examined the effect of ganciclovir on MDR1-positive tumors that have been transduced with Ha-MDR-IRES-TK. To establish a human tumor xenograft model of MDR1-transduced recurrent tumors, human KB-3-1 carcinoma cells were transduced with HaMDR or Ha-MDR-IRES-TK, and one each of representative clones, termed KB/MDR and KB/MDR-TK, respectively, were isolated. KB/MDR and KB/MDR-TK showed similar levels of multidrug resistance in vitro. Vinblastine strongly inhibited the growth of the parental KB-3-1 tumors in nude mice but showed little or no effect against KB/MDR-TK tumors. Ganciclovir inhibited the in vivo growth of KB/MDR-TK tumors almost completely under conditions that did not affect the growth of KB-3-1 tumors. Coadministration of vinblastine and ganciclovir inhibited the in vivo growth of KB/MDR-TK premixed with KB-3-1 at any ratio. Long-term, high-level expression of human P-glycoprotein was observed in peripheral blood cells of mice transplanted with Ha-MDR-IRES-TK-transduced bone marrow cells. Ganciclovir eliminated the P-glycoprotein-positive normal blood cells. However, no systemic toxicity was observed. These results clearly demonstrate that it is possible to use ganciclovir to treat MDR1-positive tumors that have been unintentionally transduced with Ha-MDR-IRES-TK. This safety-modified vector should be useful for introducing the MDR1 gene into bone marrow cells to protect normal cells from the toxic effects of cancer chemotherapy.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMedDate not supplied

Construction and characterization of bicistronic retroviral vectors encoding the multidrug transporter and beta-galactosidase or green fluorescent protein.

Multidrug resistance (MDR) can be conferred by overexpression of the adenosine triphosphate-driven multidrug transporter P-glycoprotein (Pgp) known as MDR1. Thus, two potential applications of the MDR1 gene that may be useful in gene therapy are the protection of bone marrow cells from the cytotoxic effects of chemotherapy regimens in cancer patients and its possible use as an in vivo selectable gene when linked to a therapeutic gene. In this study, we have designed two retroviral bicistronic expression vectors by linking the MDR1 gene to the reporters known as beta-galactosidase and the red-shifted green fluorescent protein (GFP). We report the creation of stable producer cell lines that synthesize virus particles carrying the MDR-internal ribosomal entry site (IRES)-lacZ and the MDR-IRES-GFP transgenes. These transcriptional fusions allow coordinate expression of Pgp and the reporter gene product to easily mark the MDR phenotype. Using the MDR-IRES-lacZ retrovirus, we demonstrate that periodic pulses of cytotoxic drug selection with a Pgp substrate enable sustained, long-term expression of the reporter beta-galactosidase in otherwise unstable transductants. We have also incorporated the improved features of GFP as a reporter gene into our MDR-IRES-GFP retrovirus. This vector allows rapid and specific identification of MDR1 gene transfer and expression in living cells either by fluorescence microscopy or by fluorescence-activated cell sorter analysis. These two MDR/reporter gene systems should be useful for in vivo studies, the evaluation of the potential of the MDR1 gene in gene therapy applications, and as a monitor of the selective efficacy of its MDR phenotype.

3T3 Cells↗