Adenovirus-induced release of epidermal growth factor and pseudomonas toxin into the cytosol of KB cells during receptor-mediated endocytosis.
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ADP Ribose Transferases↗
Biomedical subjects
D J FitzGerald
Publications and source records attributed to D J FitzGerald.
Enhancement of toxicity of antitransferrin receptor antibody-Pseudomonas exotoxin conjugates by adenovirus.
Cytotoxic conjugates were constructed by chemically coupling Pseudomonas exotoxin to antitransferrin receptor antibodies. Toxicity of these conjugates, due to entry via the transferrin receptor, was enhanced 100- to 300-fold in the presence of adenovirus. By electron microscopy and immunofluorescence it was determined that antitransferrin receptor antibodies and the conjugates derived from them entered cells from coated pits into receptosomes. We believe that the enhanced toxicity resulted when adenovirus and the toxin conjugates were internalized into the same receptosomes. In the process of infection, adenovirus enters cells and brings about a virus-mediated disruption of receptosomes; and this disruption can liberate many more toxin molecules into the cytosol than is possible in the absence of virus.
ADP Ribose Transferases↗
Rational design of a chimeric toxin: an intramolecular location for the insertion of transforming growth factor alpha within Pseudomonas exotoxin as a targeting ligand.
To investigate the potential utility of Pseudomonas exotoxin (PE) in forming rationally designed chemotherapeutic agents, we inserted a cDNA encoding transforming growth factor alpha (TGF alpha) at several locations in a gene encoding a mutant full-length PE (PE4E) which does not bind to the PE receptor. After expression in Escherichia coli, we purified the chimeric toxins to near homogeneity and showed that they were specifically cytotoxic to human epidermoid, ovarian, colon, and hepatocellular carcinoma lines. Like the previously reported TGF alpha-PE40, one of the new molecules (TGF alpha-PE4E) contains the ligand at the amino terminus. Two additional chimeras (PE4E-TGF alpha and PE4E-TGF alpha-598-613) each contain TGF alpha inserted near the carboxyl terminus of PE. We show that preservation of the correct PE carboxyl-terminal amino acid sequence, REDLK, allows the toxins containing TGF alpha carboxyl inserts to retain significant cytotoxicity against target cells, since another molecule (PE4E-TGF alpha-ILK) containing a nonfunctional carboxyl-terminal sequence was over 100-fold less active. The chimeric toxins with TGF alpha had the same binding affinity for the EGF receptor whether the ligand occupied the amino or carboxyl position. Molecules with TGF alpha near the carboxyl position were consistently less active against target cells but also less toxic to mice than those with TGF alpha at the amino terminus, indicating both types of molecules might be therapeutically effective. Our results establish that a ligand can be placed near the carboxyl terminus of PE, within the portion of the toxin that translocates to the cytosol. The amino-terminal position in such molecules is then available for the placement of other targeting ligands.
Amino Acid Sequence↗
Properties of chimeric toxins with two recognition domains: interleukin 6 and transforming growth factor alpha at different locations in Pseudomonas exotoxin.
Pseudomonas exotoxin (PE) is a potent cytotoxic agent that is composed of 613 amino acids arranged into three major domains. We have previously identified two positions where ligands can successfully be placed in PE to direct it to cells with specific surface receptors. One site is at the amino terminus and the other is close to but not at the C-terminus. To examine the possibility of constructing oncotoxins with two different recognition elements that will bind to two different receptors, we have placed cDNAs encoding either transforming growth factor alpha (TGF alpha) or interleukin 6 (IL6) at the 5' end of a PE gene and also inserted a cDNA encoding TGF alpha near the 3' end of the PE gene. The plasmids encoding these chimeric toxins were expressed in Escherichia coli and the chimeric proteins purified to near homogeneity. In all the new toxins, the TGF alpha near the C-terminus was inserted after amino acid 607 of PE and followed by amino acids 604-613 so that the correct PE C-terminus (REDLK) was preserved. For each chimera, the toxin portion was either PE4E, in which the cell binding domain (domain Ia) is mutated, PE40, in which domain Ia is deleted, or PE38, in which domain Ia and part of domain Ib are deleted. These derivatives of PE do not bind to the PE receptor and allow 607, 355, or 339 amino acids, respectively, between the two ligands.(ABSTRACT TRUNCATED AT 250 WORDS)
ADP Ribose Transferases↗
Single-chain immunotoxin fusions between anti-Tac and Pseudomonas exotoxin: relative importance of the two toxin disulfide bonds.
Anti-Tac(Fv)-PE40 is a recombinant single-chain immunotoxin in which the variable heavy and light domains of the anti-IL2 receptor antibody, anti-Tac, are connected to each other by a peptide linker and then fused to PE40, a truncated form of Pseudomonas exotoxin (PE). This fusion protein has four disulfide bonds: one in each of the two variables domains, one in domain II (Cys 265-287), and one in domain Ib (Cys 372-379) of PE. To study the importance of the disulfide bonds of the toxin to the activity of single-chain immunotoxins, we constructed mutants in which either the cysteines in the toxin were changed to alanines or the amino acids 365-380 of PE were deleted. We began this study with anti-Tac(Fv)-PE40 and a more active variant, anti-Tac(Fv)-PE40KDEL, in which the carbonyl terminus is changed from REDLK to KDEL. From these proteins we made anti-Tac(Fv)-PE40(4)A and anti-Tac(Fv)-PE40KDEL4A, respectively, by converting cysteins at amino acids 265, 287, 372, and 379 of PE to alanines. This change resulted in a 20-100-fold loss of activity toward human target cells, but no significant change in binding affinity to p55. To determine the importance of the second toxin disulfide bond, we removed amino acids 365-380 from anti-Tac(Fv)-PE40, anti-Tac(Fv)-PE40KDEL, and anti-Tac(Fv)-PE40KDEL4A, resulting in anti-Tac(Fv)-PE38, anti-Tac(Fv)-PE38KDEL, and anti-Tac(Fv)-PE38KDEL2A, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)
ADP Ribose Transferases↗
Generation of a potent chimeric toxin by replacement of domain III of Pseudomonas exotoxin with ricin A chain KDEL.
Following cellular uptake, Pseudomonas exotoxin (PE) is cleaved by cellular protease which generates an enzymatically active C-terminal fragment (amino acids 280-613). This 37 kD fragment translocates to the cell cytosol where it ADP-ribosylates elongation factor 2 and inhibits protein synthesis. A recombinant hybrid toxin (designated PE-RTA) in which the ADP-ribosylation domain (domain 111) was replaced by the RNA N-glycosidase domain of ricin (the A chain or RTA) has been produced in E. coli. The hybrid toxin effectively and specifically depurinated 28S ribosomal RNA, indicating that the ricin A moiety folded into its native conformation. The cytotoxicity of PE-RTA for L929 cells was approximately 100-fold less than either native PE or whole ricin. However, the addition of the tetrapeptide KDEL to the C-terminus of PE-RTA (producing PE-RTA KDEL) increased cytotoxicity to the level of the native toxins. By analogy to PE, both PE-RTA and PE-RTA KDEL would be proteolytically cleaved within PE domain II during cell entry. A single amino acid substitution, believed to disrupt an essential step in the transport of the catalytically active PE fragment to the cell cytosol (Trp281 to Ala: Zdanovsky, A.G., Chiron, M., Pastan, I., and FitzGerald, D. J. (1993) J. Biol. Chem. 268, 21791-21799), reduced the cytotoxicities of both PE and PE-RTA KDEL by approximately 100-fold. Taken together, these data show that the ricin A chain component of the hybrid toxin requires essential PE-derived sequences at both the N- and C-termini of the translocating fragment. Clearly, in the context of this fusion protein, ricin A chain cannot effect its own transfer to the cytosol.
ADP Ribose Transferases↗
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↗
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↗