Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0023418 (leukemia)
 93,477 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

An immunoconjugate was prepared containing a disulfide linker between a murine monoclonal antibody (5E9), which recognized the human transferrin receptor, and the ribosome-inactivating protein gelonin. This immunoconjugate was found to consist of two major species, 5E9-gelonin2 and 5E9-gelonin1, and a minor species of 5E9-gelonin3 and less than 10% of either free antibody or gelonin. 5E9-gelonin was extremely toxic in vitro to human tumor cell lines expressing the 5E9 antigen, including a Burkitt's lymphoma, an adult T-cell acute lymphocytic leukemia, an acute myelogenous leukemia, a promyelocytic leukemia, and a cervical carcinoma line. A 24-hour exposure to 10(-9) M immunoconjugate killed 90-99.9% of tumor cells, depending on the cell line. A 5E9-negative murine leukemia was not sensitive to this conjugate. Pharmacokinetic analysis of the disappearance of this immunoconjugate from the murine circulation revealed that it had a biphasic clearance, with an initial rapid phase with a half-life (t1/2) of 3 hours and a later, slower phase with a t1/2 of about 1 day. Analysis of blood samples by sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis revealed that a substantial degree of disulfide-linker breakdown occurred in vivo and that the 5E9-gelonin2 species was cleared more rapidly than the 5E9-gelonin1. With use of the same clonogenic assays used to measure in vitro toxicity, biologically active immunoconjugate could be detected in murine plasma for up to 24 hours after iv administration, but the concentration of immunoconjugate by this measure was considerably less than that predicted by SDS-gel electrophoresis. The ability to deliver immunoconjugate to tumor cells in vivo was studied with use of the Burkitt's lymphoma Namalwa as a xenograft in nude mice. It was possible to deliver substantial amounts of immunoconjugate to Namalwa cells in xenografted ascites with direct ip inoculation; lower but significant amounts of immunoconjugate could be delivered to this xenograft after systemic iv administration, provided the tumor burden was low. The 5E9-gelonin conjugate, when administered iv at the time of ip tumor inoculation, prolonged survival of nude mice bearing Namalwa or other human tumors as ascites xenografts and delayed or prevented the growth of subcutaneous nodules of Namalwa in an antigen-specific fashion after a single iv injection. Direct intratumoral administration also inhibited the growth of visible subcutaneous nodules of Namalwa. This immunoconjugate may be useful in the treatment of human cancer.
 ...
PMID:An immunotoxin composed of a monoclonal antitransferrin receptor antibody linked by a disulfide bond to the ribosome-inactivating protein gelonin: potent in vitro and in vivo effects against human tumors. 350 Mar 56

Effective autologous bone marrow transplantation for leukemia and lymphoma is likely to depend upon the selective removal in vitro of malignant cells from normal human bone marrow precursors. Highly specific cytotoxic conjugates formed by coupling ricin A chain to monoclonal antibodies might prove useful for the selective elimination of malignant cells. Consequently, ricin A chain conjugates have been prepared with several different murine monoclonal antibodies and tested for their ability to eliminate clonogenic Burkitt's lymphoma cells from an excess of human bone marrow. The most active reagents included an antibody:A chain conjugate which bound to the nonpolymorphic chain of the la molecule and another which reacted with the mu heavy chain of cell surface immunoglobulin. Conjugates formed with anti-common acute lymphoblastic leukemia antigen, anti-Mr 26,000 glycoprotein, and anti-B1 were much less active on these Burkitt's cells, contrasting with results of complement-dependent tumor cell lysis. Tumor cell kill was partially inhibited by the addition of greater than 2 X 10(6) human bone marrow cells/ml but could be potentiated by increasing the concentration of conjugate or by the addition of 10 mM ammonium chloride. In the presence of ammonium chloride, at least 4 logs of clonogenic tumor cells could be eliminated within 24 h from a 20-fold excess of bone marrow using 10(-7) M ricin A chain linked to one or two different antibodies. Similar treatment of normal human bone marrow temporarily inhibited granulocyte-macrophage colony-forming units (cell) formation but did not compromise establishment of continuous bone marrow cultures. The degree of selective elimination of tumor cells with A chain antibody conjugates was comparable to that achieved with 4-hydroperoxycyclophosphamide or with multiple monoclonal antibodies and complement.
 ...
PMID:Elimination of clonogenic tumor cells from human bone marrow using a combination of monoclonal antibody:ricin A chain conjugates. 351 Jul 20

The specific cytotoxic activity of anti-human T cell leukaemia immunotoxins (IT) was investigated for their effects on in vitro colony formation of leukaemic cells and normal haematopoietic progenitors, i.e., CFU-GM, CFU-E and CFU-GEMM. These IT were prepared by conjugating ricin A chain with the monoclonal antibodies SN1 and SN2. These antibodies define two unique human T cell leukaemia antigens. This study reveals that while these IT are only marginally cytotoxic to normal haematopoietic progenitors, they strongly suppress colony formation of human T leukaemia cells. The latter suppression is augmented by the presence of 10 mM NH4Cl which results in total suppression. The present results indicate the therapeutic usefulness of these IT for in vitro eradication of leukemia cells in the bone marrow of patients with T cell leukaemia. Potentially, such a purged bone marrow can be used in autologous transplantation in leukaemia patients.
 ...
PMID:Effect of specific anti-human leukaemia immunotoxins on the colony formation by human haematopoietic progenitors and by human leukaemia cells. 387 27

Ricin-resistant variants of the SH9 T-cell line were selected after growth of this line in medium containing toxic amounts of ricin, a lectin derived from Ricinus communis. The ricin-resistant SH9 lines, SH9.R0 and SH9.R1, were demonstrated to be deficient in cell surface ricin-binding sites, but otherwise had the cellular phenotype of SH9 cells. Ricin-resistant T-cell hybridomas were prepared by fusion of SH9.R0 and SH9.R1 with activated T-lymphocytes. The presence of ricin in the selection medium rapidly killed unfused T-lymphocytes and prevented cell transformation by human T-cell leukaemia virus type 1 (HTLV-1) which is shed by the SH9.R0 and SH9.R1 cells. This ensured that the cells growing out were indeed hybridomas. Ricin-resistant T-cell hybridomas were characterised and also shown to lack cell surface receptors for ricin. Analysis of T-cell surface markers indicated that the T-cell hybridomas could be the result of fusions between SH9.R1 cells and T-helper lymphocytes or T-suppressor lymphocytes. All of the T-cell hybridomas prepared in this study spontaneously produced interferon gamma (IFN gamma).
 ...
PMID:Ricin-resistant human T-cell hybridomas producing interferon gamma. 392 Mar 24

We have studied the potential use of immunotoxins (ITs) for therapeutic treatment of human tumors in an experimental model of human neoplasia. We tested intact ricin IT for its antitumor activity against established tumors. CEM, a human T-cell leukemia line expressing an Mr 67,000 cell surface antigen, and Daudi, a human B-cell lymphoma line which does not express the antigen, were found to be consistently tumorigenic in nude mice. ITs were synthesized using T101, a high-affinity monoclonal antibody reacting with the Mr 67,000 protein determinant and intact ricin. We have shown for the first time that established CEM solid tumors in nude mice will regress following intratumoral injection of T101-ricin IT, while Daudi tumors will not. Selective activity of T101-ricin is dependent on systemic i.v. administration of lactose and local intratumoral injection of the T101-ricin IT with lactose. Intact ricin ITs require the presence of lactose to block native ricin binding and render them antigen specific when linked to monoclonal antibody. Killing of target was cell specific since (a) nonspecific (irrelevant) ITs did not cause the regression of CEM tumors, and (b) injection of large amounts of free T101 antibody prior to T101-ricin IT blocked antitumor activity. Selectivity was not absolute, since regression occurred in one of six animals given irrelevant IT, and blocking was observed in two of four mice. Intratumoral IT treatment with 1 or 2 micrograms of T101-ricin IT plus lactose was not harmful to mice in contrast to intratumoral ricin treatment, which killed all treated tumor-bearing mice at a dose of 0.3 micrograms. Without i.v. injection of lactose, intratumoral injection of T101-ricin IT was also effective in eliminating established tumors. However, this treatment did not result in the selective elimination of tumor, since Daudi tumors also regressed following T101-ricin IT treatment. IT, made with ricin A chain only (T101-A chain IT), was also tested against established CEM tumors. We found that high dosages of T101-A chain IT did not destroy CEM tumors when injected intratumorally, even in the presence of activating agents such as NH4Cl or the carboxylic ionophore X-537 A. In contrast, in vitro experiments demonstrated that T101-A chain IT plus activating agents had potent and selective cytotoxic effect against CEM cells. We conclude that ITs are specifically toxic to established tumors. Although selectivity is not absolute, ITs exhibit potential as a new class of antitumor reagents.
 ...
PMID:Cytotoxic effect of anti-Mr 67,000 protein immunotoxins on human tumors in a nude mouse model. 397 76

Ricin A chain and pokeweed antiviral protein (PAP), two enzymes that inhibit the action of eukaryotic ribosomes, were coupled by cleavable, N-succinimidyl-3-(2-pyridyldithio)propionate, and noncleavable m-maleimidobenzoyl-N-hydroxysuccinimide ester, cross-linking reagents to monoclonal antibodies directed against Thy 1.1 antigen. Leukemia cells that contained Thy 1.1 antigen were selectively killed compared to Thy 1.2-containing cells. The composition of the conjugates was determined by radioimmunoassay, and most of the immunotoxins contained about equal molar quantities of antibody and ribosomal inhibitor. Ricin A chain linked to antibody by a noncleavable m-maleimidobenzoyl-N-hydroxysuccinimide ester cross-link was not cytotoxic, but PAP coupled to the same antibody was. Both immunotoxins linked by a cleavable disulfide bond were cytotoxic. Disulfide-linked F(ab')2-PAP was cytotoxic, but it was about 45 times less efficient than disulfide-linked IgG-PAP. There was only a 3.2-fold difference in their ability to inhibit ribosomes in vitro. The relative difference between in vitro action and cytotoxicity could be accounted for by differences in the affinity of the immunotoxins to the cell surface. Neither PAP or ricin A chain disulfide linked to a monoclonal antibody against Mr 15,000 envelope protein, a murine leukemia virus coat protein, were not cytotoxic, although both conjugates bound to the cell surface. Because of its stability, ease of purification, and lack of an analogue of ricin B chain, PAP may be more useful than ricin A for immunotoxin synthesis.
 ...
PMID:Comparison of the selective cytotoxic effects of immunotoxins containing ricin A chain or pokeweed antiviral protein and anti-Thy 1.1 monoclonal antibodies. 614 77

Pokeweed antiviral protein (PAP) and ricin A chain are potent inhibitors of protein synthesis that inactivate eukaryotic 60S ribosomal subunits. Immunotoxins were prepared by linking monoclonal anti-Thy 1.1 antibodies to PAP and ricin A chain through a disulfide bond. Both the conjugates were shown earlier to specifically inhibit protein synthesis of Thy 1.1-positive target leukemic cells (AKR SL3). In the present study, the efficacy of the immunotoxins to prevent the growth of AKR SL3 cell-induced tumor was checked in vivo in a model system. Injection of AKR SL3 cells s.c. into AKR/Cum (Thy 1.2-positive) mice developed into a solid tumor which was fatal. Administration of 31-E6:PAP and 31-E6:ricin A chain suppressed tumor growth. Suppression was specific, as similar treatment could not prevent the growth of a nontarget Thy 1.2-positive leukemia cell line (AKR SL1) derived from a congenic mouse. Unconjugated anti-Thy 1.1 immunoglobulin antibodies also showed significant tumor protection; however, administration of F(ab')2 fragment could not prevent the tumor growth. Injection of F(ab')2:PAP efficiently protected mice from AKR SL3-induced tumor. All the conjugate-treated mice showed antibody response against the toxin polypeptide. Anti-toxin antibody response was found as early as 26 days after the initiation of therapy and lasted as long as 179 days of observation. Further studies indicate that the presence of anti-toxin antibodies blocked completely the inhibitory ability of the respective immunotoxin in vitro. Anti-ricin antibodies neutralized the activity of 31-E6:ricin A chain conjugate but not OX-7:PAP immunotoxin, and similarly, anti-PAP antibodies inhibited the activity of the latter and not the activity of 31-E6:ricin A chain conjugate. These observations indicate that the use of alternate immunotoxins having an immunologically distinct toxin polypeptide may be necessary for tumor therapy during relapse, as exposure to the conjugates results in the formation of specific neutralizing anti-toxin antibodies. The anti-toxin antibodies did not prevent the binding of immunotoxin to target cells. Nevertheless, preincubation of conjugate with anti-toxin antibodies specifically blocked the respective conjugate-induced inhibition of polyuridylic acid translation in a cell-free assay system.
 ...
PMID:Prevention of growth of leukemia cells in mice by monoclonal antibodies directed against Thy 1.1 antigen disulfide linked to two ribosomal inhibitors:pokeweed antiviral protein or ricin A chain. 614 65

The toxic A chain of ricin was linked to human transferrin via a disulfide bond and the resulting conjugate was shown to bind to cell membrane transferrin receptors. Surface-localized transferrin A chain (TF-A chain) gained access to the cytoplasm and inactivated ribosomes as witnessed by a rapid curtailment of cellular protein synthesis (t1/2 = 6 h) and subsequent cytolysis. The intact conjugate produced potent cytotoxic effects on human leukemia CEM cells, (ID50 = 3 X 10(-11) M), while a 10,000-fold higher concentration of uncoupled transferrin plus A chain was required for comparable action. TF-A chain cytotoxicity was totally blocked by native transferrin or by antibodies directed against ricin A chain and human transferrin. CEM cells gradually acclimated to grow in the presence of TF-A chain displayed 1000-fold resistance to the conjugate while their sensitivity to whole ricin was undiminished. The level of transferrin receptor expressed by these cells was 1/20 the amount present on the parent line and their capacity to bind human transferrin was below the limits of detectability using fluorescent probes. This receptor-deficient cell line was unresponsive to the low levels of transferrin which stimulated proliferation of control CEM cells, but their growth was supported by greatly elevated concentrations of ligand. Receptor variant CEM cells, together with the specific TF-A chain toxin, will be useful for studying the mechanisms for transmembrane delivery of both Fe3+ and ricin A chain into cells and will aid in understanding the growth regulatory functions of the receptor-ligand interaction.
 ...
PMID:A highly cytotoxic human transferrin-ricin A chain conjugate used to select receptor-modified cells. 631 79

Clinical trials in autologous BMT to date have indicated that significant salvage and potential cures can be obtained in patients with high grade non-Hodgkin's lymphoma (NHL) who have failed primary therapy and are treated with high dose chemoradiotherapy and autologous marrow rescue. The major need in NHL is to better define those patients who might benefit by autologous BMT and to reduce the relapse rate by improved pre- or post-transplant therapy. Similar results to those in NHL could be obtained in acute leukemia if occult tumor cells could be eliminated from autologous marrow. Animal model experiments have shown that it is feasible to eliminate low level contamination with tumor cells by in vitro immunologic or pharmacologic treatment. While it is too early to accurately assess the efficacy of ongoing clinical trials using those marrow purging techniques, a few patients have exhibited encouraging durations of CCR. Should these approaches prove to be effective in only a fraction of cases, combination in vitro treatment or the use of more efficient effector mechanisms for cell killing (e.g., ricin conjugated antibody) may very well clear occult tumor from the marrow of most patients. The encouraging results with autologous BMT in leukemia and lymphoma stand in sharp contrast to the disappointing results so far achieved with the non-hematologic solid tumors. It is, however, possible that those cancers have not been subjected to the most rigorous test for successful autologous BMT and that the search for newer agents which can produce operationally irreversible aplasia may provide a fairer test of this approach. It is to be hoped that future research will settle this point.
 ...
PMID:Autologous bone marrow transplantation (ABMT) in the treatment of cancer. 632 87

Two anti-Mr 65,000 protein (p65) murine monoclonal antibodies, T101 and VIII-1, were conjugated to intact ricin. Toxicity of the resulting immunotoxins (IT) was measured against leukemic cell lines treated alone and in the presence of excess bone marrow using a highly sensitive colony inhibition assay. Cells were pretreated with IT in the presence of lactose to block the native binding of ricin. The IT proved to be potent cytotoxins for the p65-positive cell lines, CEM and MOLT-4. Treatment with T101-ricin (1000 ng/ml) inhibited clonogenic activity of these lines by more than 5.1 logs. Less than 1 log of the inhibition at this dose was due to nonspecific killing by IT. Notably, the presence of excess bone marrow did not reduce IT toxicity against the leukemic populations. Comparison of IT concentrations which inhibited 50% of clonogenic activity showed that T101-ricin was 140- to 540-fold and VIII-1-ricin was 12- to 192-fold more toxic to p65-positive than to p65-negative cell lines. Neither unconjugated anti-p65 nor IT prepared with an irrelevant antibody inhibited clonogenic activity. Blocking of IT toxicity by unconjugated antibody further demonstrated that the antibody moiety of the IT directed the selective toxicity. We found that T101-ricin was more toxic for CEM cells than was VIII-1-ricin, even though blocking studies indicated that the two antibodies bind to proximal or identical epitopes. This report is unique in that an IT was shown to specifically eliminate greater than 99.99% of leukemic cells from human bone marrow. These findings indicate the utility of T101-ricin as an in vitro reagent for autologous bone marrow transplantation in treatment of T-cell leukemia.
 ...
PMID:Elimination of clonogenic T-leukemic cells from human bone marrow using anti-Mr 65,000 protein immunotoxins. 637 99


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>