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Query: UMLS:C0027651 (tumor)
 685,946 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Ricin toxin is a glycoprotein which catalytically inactivates eukaryotic ribosomes by depurination of a single adenosine residue from the 28S ribosomal RNA. The enzymatic activity is present in the A chain of the toxin molecule, whereas the B chain contains two binding sites for galactose. Since it is highly potent in inhibiting protein synthesis, the A chain is used to prepare cytotoxic conjugates effective against tumor cells. Such chimeric proteins are highly selective and have a wide range of clinical applications. Extensive preclinical studies on these conjugates require large amounts of purified A chain. Native ricin A chain is heterogeneous, since plants produce a number of isoforms of ricin toxin. Purified, native preparations often contain two types of ricin A chain which differ in the extent of glycosylation. By cloning and expressing the gene of A chain, one could obtain homogeneous toxin molecules devoid of carbohydrates. In addition, structural changes in the toxin polypeptide could be introduced by in vitro mutagenesis, which can improve the pharmacological properties and antitumor activity. Earlier methods of expression strategies using Escherichia coli have yielded only moderate levels of expression. In the present study, the coding region of ricin A chain was cloned into pET3b, a high-level expression vector under the control of the T7 promoter. Recombinant ricin A chain produced by this construct has an additional 14 amino acid residues at the NH2 terminus. Subsequently, a NdeI site was created at the 5' end of the gene by oligonucleotide-directed mutagenesis. The modified fragment was then introduced into pET3b vector to produce toxin polypeptide identical to the native sequence.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:High-level expression and simplified purification of recombinant ricin A chain. 145 52

In the present paper, the authors describe the production and testing of immunotoxins for clinical application in Hodgkin's disease. The immunotoxins were constructed by chemical coupling of deglycolysated ricin-A to monoclonal antibodies against antigens on Hodgkin's and Reed-Sternberg cells (CD25, CD30, IRac). The cytotoxic effect of the immunotoxins was investigated in vitro against Hodgkin's and Reed-Sternberg cells (H-RS) and in vivo against solid Hodgkin's tumors in nude mice and disseminated Hodgkin's tumors in SCID mice. Cross-reactivity with normal tissue and the staining behaviour observed in sections of Hodgkin's tissue of various subtypes proved important parameters for the assessment of clinical applicability. Of more than 30 evaluated MoAb's, eight immunotoxins were produced, of which six showed both, cytotoxic effects of considerable potency against Hodgkin's tumor cells and low cross-reactivity with vital human organs. The most effective immunotoxin, RFT5 gamma 1.dgA, (CD25) inhibits the growth of H-RS cells at concentrations of 7 pMol and destroys about 60% of solid Hodgkin's tumors of 0.5 cm in diameter in nude mice. This immunotoxin binds to virtually all tumor cells in more than 90% of patients with Hodgkin's disease. Sufficient quantities of RFT5 gamma 1.dgA were produced for the treatment of patients with refractory Hodgkin's disease. These patients are currently being treated in a phase I clinical trial.
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PMID:[New perspectives in oncology: is selective destruction of tumor cells with immunotoxins in Hodgkin's disease an additional therapeutic alternative?]. 146 Dec 15

A protein was purified from root tubers of Mirabilis jalapa to homogeneity by ion-exchange chromatography on CM-Sepharose CL-6B and FPLC on Mono-S column. The purified protein was confirmed to be Mirabilis antiviral protein (MAP). However, in addition to its antiviral property, the MAP was demonstrated to possess abortifacient activity in pregnant mice, inhibitory effect on cell-free protein synthesis and antiproliferative effect on tumor cells. As judged from its biological and physiochemical properties, MAP is a type I ribosome-inactivating protein.
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PMID:Characterization of Mirabilis antiviral protein--a ribosome inactivating protein from Mirabilis jalapa L. 148 97

Some patients with thyrotropin (TSH)-producing pituitary tumors are more hyperthyroid than others despite similar TSH levels in serum, suggesting that qualitatively different TSH molecules with differing bioactivities may be secreted by different tumors. We used ricin and lentil lectin-affinity chromatography to test whether the TSH oligosaccharides varied among 12 patients with TSH-producing tumors. We found that each tumor secreted heterogeneous isoforms of TSH that differed in their extents of exposed galactose (Gal) residues, and their degrees of sialylation and core fucosylation. These biochemical parameters also varied markedly for TSH secreted by different tumors. Isoforms appeared to reflect poor sialyltransferase activity in two tumors and efficient sialyltransferase in the remainder. TSH secreted by tumors was more fucosylated than TSH secreted by control euthyroid persons. There was an inverse relationship between the sialylation and fucosylation of tumor TSH. No simple relationship between TSH oligosaccharide structures and bioactivity was evident, although mixtures of isoforms having the least and most sialylated TSH seemed to be the most bioactive clinically. In three patients from whom serum and medium TSH were both available, TSH in serum was more sialylated than TSH secreted by the tumor in vitro, perhaps reflecting slow clearance of sialylated isoforms from the circulation. Core fucosylation of serum TSH was less than that of medium TSH. These data prove that human tumors secrete TSH with heterogeneous oligosaccharide structures.
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PMID:Ricin and lentil lectin-affinity chromatography reveals oligosaccharide heterogeneity of thyrotropin secreted by 12 human pituitary tumors. 151 16

Tumor-reactive antibodies coupled to ricin or its A-chain (immunotoxins) have been used in rodents and humans to treat a variety of neoplastic diseases. Side-effects of such treatment include hepatotoxicity, vascular leak syndrome, myalgia and low grade fever. At high doses, severe toxicities include liver damage, pulmonary edema, aphasia, rhabdomyolysis and kidney failure. There have been a limited number of toxicologic studies on uncoupled ricin or its A-chain and none on deglycosylated A-chain. Since the latter has been utilized in "second generation" immunotoxins, the current studies were carried out to evaluate the toxicities induced by deglycosylated ricin A-chain (dgA) in mice. The administration of dgA to normal BALB/c mice causes early (24 h) weight loss and late (10 day) accumulation of ascites. These effects could be partially altered by changing the route of injection of dgA from i.v. to i.p. Thus, i.p. administration caused weight loss but not ascites, whereas i.v. administration caused both. Weight loss was associated with reduced fluid intake by the treated mice, and was not associated with increased levels of serum TNF-alpha. SCID mice injected with the same dose of dgA as normal BALB/c mice developed ascites, but it was of lesser severity, suggesting that a functional immune system, differences in microbial flora, or strain differences may be involved in the development of ascites.
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PMID:The toxicity of chemically deglycosylated ricin A-chain in mice. 162 27

The streptavidin-biotin system has been used to immunotarget whole ricin to tumor cells in a system that overcomes ricin-nonspecific cytotoxicity. Biotin was linked to ricin via a disulfide-containing reagent, sulfosuccinimidyl-2-(biotinamido)ethyl-1,3'-dithiopropionate. The product, biotinyl-S,S-ricin (b-ricin), retained most of its in vitro cytotoxic activity against human epidermoid carcinoma (KB) cells. Complexing b-ricin to streptavidin resulted in greater than 99% loss of its cellular toxicity which is associated with loss of cell-binding activity. The streptavidin-b-ricin complex could, however, be targeted to KB cells via the biotinylated monoclonal antibody 108 which is specific to the epidermal growth factor receptor overexpressed on KB cells. The complex did not regain its activity if the specific antibody was not biotinylated or if the biotinylated antibody was of a different specificity. Streptavidin is thus used to block b-ricin, presumably due to a steric restraint of the streptavidin on the ricin B-chain, and to bridge it to biotinyl antibody recognizing the target cell. Avidin could not replace streptavidin in this system since a complex between b-ricin and avidin retained a major part (60%) of ricin cytotoxic activity. This is attributed to the nonspecific binding of avidin to cells in vitro, including the KB cells. It is suggested that b-ricin is blocked by both streptavidin and avidin, but once the complex gains access to the cell surface, its cytotoxic activity is specifically retrieved.
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PMID:Cytotoxicity of streptavidin-blocked biotinyl-ricin is retrieved by in vitro immunotargeting via biotinyl monoclonal antibody. 164 36

Two monoclonal antibodies, designated BR64 (IgG1) and BR96 (IgG3), were generated that, according to immunohistology, bind selectively to carcinomas of the colon, breast, ovary, and lung. They have no or very low reactivity with normal human tissues, except for the fact that BR64 strains capillaries in the hearts from certain normal donors and that both monoclonal antibodies stain some epithelial cells from the gastrointestinal system, including stomach. Preliminary studies indicate that at least a portion of the epitope recognized by BR64 and BR96 is a Le(y) carbohydrate chain. Both monoclonal antibodies can be "internalized" by antigen-positive tumor cells, since immunoconjugates with ricin A-chain are cytotoxic. BR96 has the additional properties of being cytotoxic by itself, and it can mediate antibody-dependent cellular cytotoxicity and complement dependent cytotoxicity.
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PMID:Highly tumor-reactive, internalizing, mouse monoclonal antibodies to Le(y)-related cell surface antigens. 169 May 95

The tumor localization of various anti-CD5 immunotoxins (ITs) was studied in vivo in BALB/c nude mice bearing human ascitic Ichikawa tumor cells. Plasma and ascitic clearance of IT as well as the number of intact IT molecules taken up per tumor cell was measured with a highly sensitive immunoenzymometric assay. This assay allowed the quantification of as few as 400 molecules per cell, either bound to cell surface antigens or internalized. Tumor cell localization of an i.v.-administered IT composed of a whole IgG linked by a disulfide bond to native ricin A chain (RTA) was extremely small. The highest binding level of this IT to ascitic cells did not exceed 1,600 molecules per cell, whereas up to 25,000 molecules per cell were quantified after i.p. injection. To improve IT localization after i.v. injection, both the size of the monoclonal antibody moiety and glycosylation of the ricin A chain were examined. Two major additive improvements were obtained by (a) Fc removal and (b) partial deglycosylation of RTA. The localization of F(ab')2-deglycosylated RTA IT was 5.5 times greater than that of IgG-RTA IT, resulting from reduced plasma clearance and better extravasation of the conjugate. However, the IT targeting observed in vivo after i.v. administration was unexpectedly lower than the theoretical number of bound IT molecules, calculated from the concentration of soluble IT molecules in the ascitic fluid. This discrepancy was found to be related to a dramatic decrease in the antigen binding capacity of the antibody moiety in ascitic fluid.
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PMID:Parameters affecting tumor-specific delivery of anti-CD5 antibody-ricin A chain immunotoxins in vivo. 169 50

Three monoclonal antibodies which strongly bind to Hodgkin and Reed-Sternberg cells and two corresponding Fab' fragments were linked to deglycosylated ricin A chain (dg A) to evaluate their potential as immunotoxins for the treatment of Hodgkin's disease. Two of the antibodies, Ber-H2 and HRS-3, were shown to bind to the same epitope on the CD30 antigen, whereas the third antibody, IRac, bound to a different antigen. None of the antibodies significantly cross-reacted with normal human tissues as judged by indirect immunofluorescence and immunoperoxidase analyses on frozen sections from 28 normal tissues. All three antibodies formed potent and specific immunotoxins. They inhibited protein synthesis of the L540 Hodgkin's disease cell line in vitro by 50% at concentrations of 1 x 10(-11) M for IRac.dgA, 9 x 10(-11) M for HRS-3.dgA, and 2 x 10(-10) M for Ber-H2.dgA. HRS-3 Fab' and IRac Fab' immunotoxins were 7.8- and 60-fold less cytotoxic, respectively, than their intact counterparts in vitro. In vivo, a single i.v. injection of a dose of Ber-H2.dgA, HRS-3.dgA, or IRac.dgA corresponding to 40% of the LD50 induced lasting complete remissions in 38, 44, and 50%, respectively, of mice with solid s.c. L540 tumors of 60 to 80 mm3 size (0.5-cm diameter). At equivalent dosage (40% of the LD50), the HRS-3 Fab'.dgA and the IRac Fab'.dgA both induced lasting complete remissions in 25% of the mice, although the HRS-3 Fab'.dgA was significantly superior to IRac Fab'.dgA at retarding tumor growth in the remaining animals. The effectiveness of the immunotoxins depended on the size of the tumor at the time of injection, since IRac.dgA treatment induced complete remissions in 100% of mice with small tumors (10 to 20 mm3, approximately 0.3 cm in diameter) but only 13% of mice with larger tumors of 400 to 600 mm3 (approximately 1 cm in diameter). Tumors which regrew after IRac.dgA treatment mainly consisted of antigen-deficient mutants having reduced sensitivity to IRac.dgA but normal sensitivity to HRS-3.dgA. It is concluded that HRS-3.dgA, HRS-3 Fab'.dgA, and IRac.dgA are candidates for the treatment of Hodgkin's disease in humans.
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PMID:Antitumor effects of ricin A chain immunotoxins prepared from intact antibodies and Fab' fragments on solid human Hodgkin's disease tumors in mice. 169 51

The monoclonal antibody L6 recognizes a determinant that is expressed on lung, breast, colon, and ovarian carcinomas and is present only at trace levels in normal tissues. L6 was covalently linked to intact ricin by a thioether bond to produce an immunotoxin (IT). Gel analysis revealed that this IT was heterogeneous, but mostly one monoclonal antibody molecule linked to one ricin molecule. The L6-ricin IT selectively bound and was selectively toxic to L6-positive H2981-T3 adenocarcinoma cells in protein synthesis inhibition assays in which lactose was added to block the native ricin binding site. Clonogenic studies showed that 1 microgram/ml L6-ricin could inhibit about 99.99% of H2981-T3 growth in a limiting dilution assay, even in the presence of a 20-fold excess of human bone marrow cells. Treatment of bone marrow cells with the same dose of L6-ricin resulted in the growth of ample numbers of bone marrow progenitor cells (colony-forming units-mixed, colony-forming units granulocyte/macrophage, and blast-forming units erythroid) after 14 days. We also evaluated the antitumor effect of L6-ricin administered intratumorally with lactose against established H2981-T3 tumors in a nude mouse model. Thirty % of the tumor-bearing animals responded completely to single-dose treatment, while 60% gave partial responses. The in vivo effects were not absolutely specific, since irrelevant anti-CD5 IT also induced tumor regression in this model (10% responded completely, while 30% gave partial responses). However, irrelevant IT gave higher systemic toxicity (50% mortality) than L6-ricin (23% mortality). The nonspecific activity of IT was possibly due to Fc binding, which was demonstrated in vitro, or due to ricin B-chain binding. Ricin alone was too toxic for sustained tumor protection. Unconjugated L6 had no antitumor effect. The data suggest that L6-ricin may be useful for in vitro purging of autologous bone marrow from patients with solid tumors and marrow involvement and for in vivo regional therapy of L6-positive carcinomas.
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PMID:Antitumor activity of L6-ricin immunotoxin against the H2981-T3 lung adenocarcinoma cell line in vitro and in vivo. 169 58


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