In vitro and in vivo properties of an anti-CD5-momordin immunotoxin on normal and neoplastic T lymphocytes

An anti-CD5 monoclonal antibody (mAb) was linked to the plant toxin momordin, a type-1 ribosome-inactivating protein purified from Momordica charantia. The in vitro cytotoxicity of the immunotoxin was evaluated as the inhibition of protein and/or DNA synthesis on isolated peripheral blood mononuclear cells (PBMC) and on human T cell leukemia Jurkat. The potency of the immunotoxin on PBMC was very high (IC50 = 1 - 10 pM) and was not affected by blood components. The conjugate was also very efficient in the inhibition of the proliferative response in a mixed lymphocyte reaction (IC50 = 10 pM). Moreover, the in vitro performance of the immunotoxin compared favorably with those reported for other anti-CD5-based immunoconjugates containing ricin A chain. The in vivo activity of the immunotoxin was assessed in the model of nu/nu mice bearing Jurkat leukemia. A significant inhibition of the tumour development (80%, P < 0.01) in the animals treated with immunotoxin was observed. Taken together, the in vitro and in vivo results suggest that the anti-CD5-momordin conjugate may be useful for graft-versus-host disease therapy and potentially in the treatment of CD5-positive leukemias and lymphomas.

A new 'solid phase' procedure to synthesize immunotoxins (antibody-ribosome inactivating protein conjugates)

A method to produce immunotoxins (conjugates comprising of a monoclonal antibody and toxin) using ribosome inactivating protein anchored on an affinity gel derivatized with triazinic dye is described. The adsorbed toxins were activated with 2-imino-thiolane and then conjugated to monoclonal antibody activated by SPDP. The "heterogeneous phase" system offered several advantages, reducing the usually required purification steps and opening a way to automatize the conjugation procedure.

A comparison of anti-lymphocyte immunotoxins containing different ribosome-inactivating proteins and antibodies

Immunotoxins were prepared with several single-chain ribosome-inactivating proteins (RIPs type 1) and with the A-chain of ricin linked to the F(ab')2 fragment of sheep anti-mouse IgG. The cytotoxic activity of these conjugates was tested on human lymphocytes pretreated with an anti-CD3 murine MoAb. The immunotoxins inhibited DNA synthesis in phytohaemagglutinin (PHA)-stimulated lymphocytes with IC50S (concentrations causing 50% inhibition) ranging from 8.9 x 10(-13) to 5.7 x 10(-11) M (immunotoxins containing dianthin 32, saporin, pokeweed antiviral protein from seeds (PAP-S), bryodin, momordin, momorcochin, and trichokirin), 1 x 10(-8) M (immunotoxin containing gelonin) and 5 x 10(-9) M (immunotoxin containing ricin A-chain). The immunotoxin containing saporin linked to the anti-mouse IgG F(ab')2 fragment was also highly toxic to human lymphocytes pretreated with anti-CD2, -CD3, -CD5 and -CD45 MoAbs, with IC50S less than or equal to 10(-11) M. Immunotoxins were prepared also with saporin linked to MoAbs against various CD antigens. The immunotoxin prepared with the anti-CD3 antibody had the highest specific cytotoxicity to human lymphocytes.

Recognition and killing of tumour cells expressing heat shock protein 65 kD with immunotoxins containing saporin

The expression of heat shock proteins (HSP) of the 65 kD family (groEL) has been observed by flow cytometry using murine monoclonal antibody (MoAb) anti-HSP 65 kD (ML30) on the surface of B (Daudi) or T (H9) lymphoma cells, on a monocyte cell line (U937) and also on a primary culture of a human pancreatic carcinoma (HPC). Moreover, the MoAb ML30 was coupled to Saporin 6, a ribosome-inactivating protein recovered from the seeds of Saponaria officinalis, to kill HSP-expressing cells with a specific immunotoxin. An indirect method using first MoAb ML30 and then anti-mouse IgG1 immunotoxin was also performed. With this method a human serum positive for HSP65-antibodies was tested using anti-human IgG1 or IgM immunotoxins. All cell lines were inhibited when preincubated with the specific immunotoxin directed to HSP65 (ML30 SO6), although H9 cells were susceptible to immunotoxin only after thermal stress. Daudi and HPC cells were inhibited both after long-term culture and when freshly explanted from SCID mice. Proliferation of the U937 monocytic cell line, that constitutively expresses high levels of HSP65 on the surface (as determined by flow cytometry), was completely inhibited (100% inhibition) by the ML30 SO6. However, not all tumour cells constitutively express high levels of surface HSP65, as determined by cytometric analysis. For this reason it was not always possible to obtain complete inhibition of cellular proliferation.

B-B10 (anti-CD25)-saporin immunotoxin--a possible tool in graft-versus-host disease treatment

An immunotoxin containing the B-B10 MoAb, directed against the CD25 determinant, and the ribosome-inactivating protein saporin, inhibits 3H-TdR incorporation in phytohemagglutin, allogeneic-stimulated lymphocytes (primary and secondary mixed-lymphocyte reaction), and in an alloreactive T cell clone. A lower degree of inhibition was obtained with the B-B10 MoAb, which is known to inhibit IL-2 activity, as well as with the unconjugated compounds. These results suggest that the in vivo administration of the conjugate might be a more effective tool in the treatment of patients affected by graft-versus-host disease than B-B10 alone, by inducing an efficient killing of allogeneic-reacting T lymphocytes.

Ber-H2 (anti-CD30)-saporin immunotoxin: a new tool for the treatment of Hodgkin's disease and CD30+ lymphoma: in vitro evaluation

An immunotoxin containing an anti-CD30 monoclonal antibody (Ber-H2) and saporin, a ribosome-inactivating protein type 1, is described. It specifically inhibits protein synthesis by Hodgkin derived target cell lines with a very high efficiency (IC50 ranging from 5 x 10(-12) M to 5 x 10(-14) M, as saporin), while irrelevant immunotoxins do not. Present results suggest that this immunotoxin could be used for in vivo therapy as well as for ex vivo bone marrow purging in Hodgkin's disease and CD30+ lymphomas.

Response of refractory Hodgkin's disease to monoclonal anti-CD30 immunotoxin

In Hodgkin's disease, Hodgkin and Reed-Sternberg cells consistently express the antigen CD30. We investigated the possible therapeutic role of an immunotoxin prepared by covalent linking of an anti-CD30 monoclonal antibody (Ber-H2) to saporin (SO6), a type-1 ribosome-inactivating protein. The immunotoxin (0.8 mg/kg in one or two doses) was given to four patients with advanced refractory Hodgkin's disease. In three, there was rapid and substantial reduction in tumour mass (50% to greater than 75%). Clinical responses were transient (6-10 weeks). In-vivo binding of the immunotoxin to tumour cells was shown by immunohistology in two patients. Antibodies to both parts of the immunotoxin developed in all patients.

T lymphocyte killing by a xanthine-oxidase-containing immunotoxin

We report on the preparation of an immunotoxin consisting of xanthine oxidase, a free-radical-producing enzyme, covalently linked to an anti-CD3 monoclonal antibody. The immunotoxin retained both enzymic and immunological properties and its toxicity to target cells (a) was greater than that of the free enzyme, (b) was proportional to the enzyme concentration, and (c) was reduced either in the absence of hypoxanthine or by an excess of free anti-CD3 monoclonal antibody. The cytotoxicity and selectivity of the hypoxanthine/conjugated xanthine oxidase system were potentiated by the addition of chelated iron and by washing away the unbound immunotoxin prior to the addition of substrate. The same system was not toxic to bone marrow progenitor cells. A possible use of this immunotoxin for the ex vivo purging of organs to be transplanted from T lymphocytes, to avoid the graft-versus-host reaction, is suggested.

[Analysis of the results of 264 cases of small breast carcinoma treated with conservative surgery and radiotherapy]

From January 1981 to December 1987, 264 patients affected with small breast cancers were treated with quadrantectomy plus axillary dissection and radiation therapy on the breast remnant (QUART). Mean age of the patients was 53 years; 124 of them were less than or equal to 50 years old (46.9%); 85 had axillary nodal metastases (32.2%), and 58 presented a primary tumor with pathologic size (greater than 2 cm) (22.9%). Overall actuarial survival at 3 and 7 years, according to the Kaplan and Meyer method, was 95.5% and 85.3%, respectively; NED survival was 85.9% and 77.4%. Twenty patients died (19 of cancer). Local relapses were 6 (2.3% on the whole and 13.3% on the whole of recurrences observed at follow-up). Local relapses were central in the quadrantectomy scar in 4/6 patients. Histology and site of the primary lesion were not correlated with a major risk of local failure. Isolated recurrences in the breast did not worsen survival. Nodal failures were 5 (1.9% on the whole of cases; 11.1% on the whole of failures). Our study confirms the role of QUART as an effective and reliable method in the treatment of small breast carcinomas.

Intra-thecal treatment of leptomeningeal lymphoma with immunotoxin

An animal model has been established to investigate the effect of intra-thecal (i.t.) immunotoxins in the treatment of leptomeningeal metastases of acute lymphoblastic leukaemia (ALL). Direct inoculation of L2C lymphoma cells into the cisterna magna of guinea-pigs gives rise to a leptomeningeal pattern of growth, similar to that of human ALL, and to a systemic leukaemia which develops in approximately 14 days. In our model the systemic disease could be controlled with cyclophosphamide while the meningeal disease progressed and provided a target for i.t. immunotoxin. The immunotoxin used consisted of an anti-idiotypic antibody disulphide-bonded to the ribosome-inactivating protein saporin. It was highly cytotoxic to L2C cells in vitro, being around 30,000 times more potent than a control immunotoxin at inhibiting protein synthesis. In vivo, the maximum tolerated dose of i.t. immunotoxin was 10 micrograms. From the rate at which radiolabelled immunotoxins appeared in the plasma following i.t. injection, we were able to estimate that its half-life in the cerebrospinal fluid (CSF) was between 1 1/2 and 2 hr. Intrathecal treatment of guinea-pigs with immunotoxin 1 day after inoculation of L2C cells into the cisterna magna had a remarkable therapeutic effect. All guinea-pigs treated with 0.5 or 5 micrograms of immunotoxin survived, and remained tumour-free for more than 100 days after treatment, while control animals given cyclophosphamide alone or an irrelevant immunotoxin had a mean survival time of 28 days. Provided concerns over toxicity can be overcome, these results indicate that i.t. immunotoxins offer an alternative, highly specific form of treatment in leptomeningeal neoplasia.

Systemic preoperative chemotherapy with cisplatin, methotrexate and vinblastine for locally advanced bladder cancer: local tumor response and early followup results

A total of 44 patients with infiltrating, locally advanced bladder cancer (stages T 3a-b, T 4a-b and N+/N0) were treated with the systemic chemotherapy regimen of cisplatin, methotrexate and vinblastine (CMV) in the neoadjuvant setting, of whom 39 were evaluable for response. After planned radical cystectomy and 2 to 3 cycles of chemotherapy no tumor was found on the pathological specimen of 4 patients (10%), the tumor was downstaged in 19 (49%) and no change was observed in 16 (41%). Toxicity included leukopenia in 29 patients (66%), 1 of whom died of granulocytopenic sepsis, nausea and vomiting in 39 (89%) and mild to moderate mucositis in 18 (41%). Median followup is 12 months with a range of 6 to 39 months. Of 32 patients followed for longer than 6 months 6 (19%) experienced progression or recurrence of disease. We conclude that preoperative CMV chemotherapy is effective in inducing downstaging of the tumor, although systemic toxicity limits its use to cautiously selected patients.

Purification and properties of new ribosome-inactivating proteins with RNA N-glycosidase activity

Ribosome-inactivating proteins (RIPs) similar to those already known (Stirpe & Barbieri (1986) FEBS Lett. 195, 1-8) were purified from the seeds of Asparagus officinalis (two proteins, asparin 1 and 2), of Citrullus colocynthis (two proteins, colocin 1 and 2), of Lychnis chalcedonica (lychnin) and of Manihot palmata (mapalmin), from the roots of Phytolacca americana (pokeweed antiviral protein from roots, PAP-R) and from the leaves of Bryonia dioica (bryodin-L). The two latter proteins can be considered as isoforms, respectively, of previously purified PAP, from the leaves of P. americana, and of bryodin-R, from the roots of B. dioica. All proteins have an Mr at approx, 30,000, and an alkaline isoelectric point. Bryodin-L, colocins, lychnin and mapalmin are glycoproteins. All RIPs inhibit protein synthesis by a rabbit reticulocyte lysate and phenylalanine polymerization by isolated ribosomes and alter rRNA in a similar manner as the A-chain of ricin and related toxins (Endo et al. (1987) J. Biol. Chem. 262, 5908-5912).

Purification and properties of a new ribosome-inactivating protein with RNA N-glycosidase activity suitable for immunotoxin preparation from the seeds of Momordica cochinchinensis

A ribosome-inactivating protein similar to those already known (Stirpe and Barbieri (1986) FEBS Lett. 195, 1-8) was purified from the seeds of Momordica cochinchinensis. This protein, for which the name of momorcochin-S is proposed, is a glycoprotein, has an Mr of approx. 30,000, and an alkaline isoelectric point and can be considered as an iso-form of the previously purified momorcochin from the roots of M. cochinchinensis. Momorcochin-S inhibits protein synthesis by a rabbit-reticulocyte lysate and phenylalanine polymerization by isolated ribosomes, and alters rRNA in a similar manner as the A-chain of ricin and related toxins (Endo et al. (1987) J. Biol. Chem. 262, 5908-5912). Momorcochin-S was linked to a monoclonal antibody (8A) against human plasma cells, and the resulting immunotoxin was selectively toxic to target cells.

An immunotoxin containing momordin suitable for bone marrow purging in multiple myeloma patients

Attempts have been made by a number of methods to eliminate minimal residual disease from bone marrow to be reinfused in autologous transplantation. In this paper we describe a conjugate containing a monoclonal antibody, named 8A, recognising a plasma cell-associated antigen, and momordin, a ribosome-inactivating protein similar to the ricin A-chain. This immunotoxin is active on target cell lines and on neoplastic plasma cells, while myeloid progenitors are fairly resistant. The conjugate is shown to be acceptable for ex vivo purging in autologous bone marrow transplantation in multiple myeloma patients.

Selective killing of CD4+ and CD8+ cells with immunotoxins containing saporin

Saporin, a ribosome-inactivating protein from the seeds of Saponaria officinalis, was covalently linked to an anti-CD4 monoclonal antibody. The resulting immunotoxin at 10(-9)M concentration was toxic to CD4+ lymphocytes without affecting other cells. Selective elimination of CD4+ and CD8+ cells was also obtained with murine monoclonal anti-CD4 and anti-CD8 antibodies and an immunotoxin consisting of saporin linked to an anti-mouse IgG antibody.

Purification and partial characterization of a lectin from the seeds of Trichosanthes kirilowii Maximowicz

A lectin was purified from the seeds of Trichosanthes kirilowii, belonging to the family Cucurbitaceae, growing in China. The lectin is a glycoprotein of 57 kDa, consists of two subunits with apparent molecular masses of 37 and 25 kDa, is specific for galactose, and is not mitogenic for human lymphocytes.

Ribosome-inactivating proteins from plant cells in culture

1. Ribosome-inactivating proteins were found in high amounts in one line of cells of Phytolacca americana (pokeweed) cultured in vitro and, in less quantity, in lines of Saponaria officinalis (soapwort) and of Zea mays (corn) cells. 2. The main ribosome-inactivating protein from pokeweed cells was purified to homogeneity. It is a protein with Mr 29,000 and basic pI, similar to the 'pokeweed antiviral protein' (PAP), a ribosome-inactivating protein from pokeweed leaves. We propose to call the pokeweed antiviral protein isolated from pokeweed cells PAP-C. 3. PAP-C inactivates ribosomes in a less-than-equimolar ratio, thus inhibiting protein synthesis by a rabbit reticulocyte lysate with an IC50 (concentration causing 50% inhibition) of 0.067 nM (2 ng/ml), and modifies rRNA in a manner apparently identical to that of ricin and other ribosome-inactivating proteins. It inhibits protein synthesis by intact cells with an IC50 of 0.7-3.4 microM, and is toxic to mice with an LD50 of 0.95 mg/kg.

Trichokirin, a ribosome-inactivating protein from the seeds of Trichosanthes kirilowii Maximowicz. Purification, partial characterization and use for preparation of immunotoxins

A protein, here named trichokirin, was extracted from the seeds of Trichosanthes kirilowii and purified by ion-exchange and gel-filtration chromatography. Trichokirin is a basic glycoprotein of apparent relative molecular mass of 27,000 with a strong ribosome-inactivating activity. Alignment of the trichokirin, trichosanthin and momordin N-terminal sequences shows a substantial degree of homology. Trichokirin was conjugated to a monoclonal antibody directed against the Thy 1.2 antigen with the cleavable dimethyl 3,3'-dithiobispropionimidate cross-linking reagent. This immunotoxin selectively killed leukemia cells expressing the Thy 1.2 antigen. The addition of ammonium chloride, which increases the cytotoxicity of ricin A-chain immunotoxins, blocks that of the trichokirin immunotoxin, suggesting that they enter cells by different mechanisms. In vivo studies showed that the pharmacokinetic properties of the trichokirin immunotoxin could be more advantageous than those of the ricin A-chain immunotoxins for in vivo applications.

Ribosome-inactivating proteins from plants inhibit ribosome activity of Trypanosoma and Leishmania

Ribosomes from Trypanosoma brucei rhodesiense and from Leishmania infantum were isolated and optimal conditions for in vitro translation were established. The effect of ribosome-inactivating proteins extracted from several plants was then assessed in order to identify those suitable for the preparation of immunotoxins against these organisms. Ribosomes from both species were inactivated by some ribosome-inactivating proteins (dianthins, saporins, pokeweed antiviral proteins, and the ribosome-inactivating chain of abrin). The similarity of the effects on the ribosomes from the two species examined indicates that ribosome-inactivating proteins should also be effective in a similar way on ribosomes from other species of Trypanosoma and Leishmania.

Effect of ribosome-inactivating proteins on ribosomes from Tetrahymena pyriformis and Acanthamoeba castellanii

The effect of ribosome-inactivating proteins type 1 (single-chain) and type 2 (two-chain, toxins) on polyphenylalanine polymerization by Tetrahymena pyriformis and Acanthamoeba castellanii ribosomes has been studied. The reaction catalysed by tetrahymena ribosomes was inhibited by two ribosome-inactivating proteins type 1 (dianthin 32 and, less effectively, momordin) whereas the reaction catalysed by amoeba ribosomes was inhibited, in a decreasing order of activity, by three ribosome-inactivating proteins type 1 (dianthin 32, saporin 6 and bryodin) and by two toxins (abrin and volkensin).

Recycling of the asialoglycoprotein receptor and the effect of lysosomotropic amines in hepatoma cells

Receptor-mediated uptake and degradation of 125I-asialoorosomucoid (ASOR) in human hepatoma HepG2 cells is inhibited by the lysosomotropic amines chloroquine and primaquine. In the absence of added ligand at 37 degrees C, these amines induce a rapid (t1/2 5.5-6 min) and reversible loss of cell surface 125I-ASOR binding sites as well as a rapid decrease in 125I-ASOR uptake and degradation. There is no effect of these amines on the binding of 125I-ASOR to the cell surface at 4 degrees C or on the rate of internalization of prebound 125I-ASOR. The loss of 125I-ASOR surface binding at 37 degrees C is not attributable to altered affinity of ligand-receptor binding. In the presence of added ligand at 37 degrees C, there is a more rapid (t1/2 2.5-3 min) loss of hepatoma cell surface receptors. In addition, the amines inhibit the rapid return of the internalized receptor to the cell surface. We examined the nature of this loss of 125I-ASOR surface binding sites by following the fate of receptor molecules after biosynthetic labeling and after cell surface iodination. At 37 degrees C, chloroquine and primaquine induce a loss of asialoglycoprotein receptor molecules from the hepatoma cell surface to an internal pool.