Treatment of leukemia patients with T101 ricin A chain immunotoxins.
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Adult↗
Biomedical subjects
P Casellas
Publications and source records attributed to P Casellas.
Toxin selection and modification: utilization of the A chain of ricin.
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Amino Acids↗
T-lymphocyte killing by T101-ricin A-chain immunotoxin: pH-dependent potentiation with lysosomotropic amines.
To maximize T-lymphocyte killing with anti-pan-T-lymphocyte immunotoxin (IT), prepared by linking ricin A-chain to monoclonal antibody (MoAb) T101 (T101-RTA IT), we have established the nature and the extent of parameters that influence the sensitivity of T lymphocytes to the IT. We showed that peripheral blood T lymphocytes, which are much less susceptible than malignant T cells to the T101-RTA IT, could become highly sensitive to the IT when used in conjunction with NH4Cl. However, enhancement of the IT by NH4Cl only occurred when the pH rose above neutrality. This pH-sensitive process of IT activation by NH4Cl, which led to an all-or-nothing effect within an extremely narrow pH window of 0.7 pH unit width, is due to the fact that NH3 is the effective enhancing component of NH4Cl. We also showed that F(ab')2 or Fab containing IT were much more effective than those produced using the whole IgG counterpart. From these data, we defined a procedure for an optimal and specific elimination of T lymphocytes in vitro by treating them with (Fab)T101-RTA at 10(-8) mol/L at pH 7.8 in the presence of NH4Cl for two hours. This peripheral blood cell processing elicited an abrogation of three logs of functional T-cell response. Under the same conditions, there was no reduction in the number of marrow hematopoietic precursor granulocyte-macrophage colony-forming units (CFU-GM).
Ammonium Chloride↗
Rationale for the selection of ricin A-chain anti-T immunotoxins for mature T cell depletion.
A series of 25 different ricin A-chain immunotoxins (IT) were prepared with monoclonal antibodies reacting with several T cell antigens belonging to different clusters of differentiation (CD) to select the most appropriate immunotoxins (IT) for mature T cell depletion. Our screening procedure was performed in 2 steps. First, IT were evaluated using protein synthesis inhibition assay on clonogenic malignant cells in order to determine the most active IT for a given CD. Second, IT thus selected were evaluated for both mature T cell killing efficacy and tolerance on hematopoietic progenitor cells (HPC). This study showed that (1) different IT directed against the same CD antigen displayed a wide range of activity, suggesting the need for a large screening of IT to determine the most appropriate antibody for a given target antigen; (2) anti-CD3 and anti-CD5 ricin A-chain IT are the most active, displaying a cytoreduction of more than 2 logs on mature T cells; (3) the 3 different anti-CD2 ricin A-chain IT evaluated in this study induced poor mature T cell cytoreduction despite their relative efficacy on leukemic cells; (4) anti-CD8 ricin A-chain IT showed almost no efficacy on relevant target cells; (5) no toxicity on HPC was found for concentrations up to 10(-8) of A-chain whatever the IT used.
Antibodies, Monoclonal↗
Study of the plasma clearance of antibody--ricin-A-chain immunotoxins. Evidence for specific recognition sites on the A chain that mediate rapid clearance of the immunotoxin.
In recent years, antibody--ricin-A-chain immunotoxins have been investigated as anti-neoplastic agents. To achieve in vivo therapy it is necessary that the immunotoxin remains in circulation at a sufficiently high level for a sufficiently long time to allow binding to tumor cells to occur. Therefore, examination of the pharmacology of immunotoxins may elucidate the reasons for the poor in vivo tumoricidal effect of immunotoxin described before. In this study the plasma clearance of antibody--ricin-A-chain immunotoxins, after intravenous injection in animals of different species, has been examined. Sensitive and reproducible techniques were developed to monitor the level of immunotoxin and its constituents in the blood. It is shown that immunotoxins are rapidly eliminated from the bloodstream. Neither the properties of the antibody moiety nor the nature of the linkage binding ricin A-chain to antibody account for the disappearance of immunotoxin from the plasma. On the other hand, we found that the rapid clearance of immunotoxin is due to the mannose residues on the ricin A-chain moiety which are specifically recognized by liver cells. When immunotoxin is administrated together with yeast mannan, which enhances the level of active immunotoxin in circulation by inhibition of liver uptake, the anti-cancer efficacy of immunotoxin in vivo is drastically improved.
Animals↗
Reconstitution of hematopoiesis after bone marrow purging with ricin A chain immunotoxin.
Bone marrow cells from healthy individuals were treated with an antihuman T cell immunotoxin (IT101). The treated marrow cells were cultured for multilineage hematopoietic colonies (CFU-GEMMT) containing various myeloid cell lineages and T lymphocytes, erythroid colonies (BFU-E), and granulocytic colonies (CFU-C). Optimal conditions were defined for the elimination of clonogenic human T leukemic cells artificially admixed with bone marrow cells. Marrow purging with IT101 led to the restoration of hematopoietic colony formation which was abolished in the presence of T leukemic cells. Mixed colonies grown from bone marrow treated with IT101 contained cells that reacted with monoclonal anti-T-cell antibodies. This suggests that pluripotent stem cells are not affected by marrow IT101 purging and may be able to regenerate lymphoid as well as myeloid lineages.
Antibodies, Monoclonal↗
Effects of therapy with T101 ricin A-chain immunotoxin in two leukemia patients.
Two leukemia patients, refractory to chemotherapy, were treated with T101-ricin A-chain immunotoxin (T101 IT). Patient 1 (T-ALL) received a single 13.5 mg dose of T101 IT IV (12-hour infusion). Patient 2 (B-CLL) was treated with a daily 25 mg dose of T101 IT IV (two-hour infusion) over three consecutive days. Patient 2 also received 300 mg of chloroquine IM on days two and three as enhancer. In vivo binding of T101 IT was demonstrated by FACS analysis using either an antimouse Ig-FITC or anti-A-chain-FITC antibodies. Following IT therapy, the expression of T65 antigen on target cells dropped to 50% and 20% of pretreatment levels, respectively. In patient 1, circulating blast cells remained unsaturated during therapy while in patient 2, cells were fully saturated for four to six hours following each infusion. Pharmacokinetic studies showed a rapid clearance of T101 IT after IV administration. Antimouse and anti-A-chain antibodies could not be detected. There were no treatment-related adverse effects. In patient 1 a rapid but transient decrease of target cells was observed, possibly related to the administration of the antibody part of T101 IT. In contrast, patient 2 showed a 40% reduction of the lymphocyte count, which remained stable over a period of 2 weeks. Such a clinical benefit following IT therapy in patient 2 could be ascribed to the absence of circulating free antigen and the complete saturation of target cells.
Adult↗
Determination of sensitivity of fresh leukemia cells to immunotoxins.
In clinical practice, sensitivity of malignant cells to a given immunotoxin remains hypothetical, since standard test systems such as the protein synthesis inhibition assay or the cloning assay are not appropriate. This study evaluated the feasibility of a semi-routine procedure based on dye exclusion assay enumerating the percentage of living cells after fluorescein diacetate-propidium iodide staining. The validity of the method was evaluated using five different subclones derived from the CEM cell line, which expressed a wide range of sensitivity to T101 A-chain immunotoxin. The comparison between dye exclusion assay and standard test systems suggested that this method might allow an easy and reproducible semi-quantitative evaluation of the sensitivity of leukemia cells. In a series of 21 patients suffering from various blood diseases in which the malignant cells expressed the T65 antigen, dye exclusion assay could detect clear T101 immunotoxin cell sensitivity in about 50% of the cases. The mean density of T65 antigen on malignant cells was found to influence dramatically the sensitivity of target cells to T101 immunotoxin.
Antibodies, Monoclonal↗
Studies on components of immunotoxins: purification of ricin and its subunits and influence of unreacted antibodies.
Two ricins were purified from the seeds of Ricinus communis by a simple method based on affinity chromatography allowing large-scale preparations. Separation of these 2 ricins was achieved by ion-exchange chromatography and studies of purified subunits demonstrated that the 2 forms of ricin differed only in their B-chains which showed widely differing isoelectric points. The A-chains isolated from both ricins showed similar biological properties and contained 2 variants, A1 and A2, differing in their molecular weights and carbohydrate contents. These variants could be separated by affinity chromatography on Con-A-Sepharose which bound the A2 variant more tightly than A1. This property allowed us to obtain immunotoxin preparations devoid of free antibodies and to study the in vitro influence of free antibody on immunotoxin activity.
Animals↗
Endocytosis of an antibody ricin A-chain conjugate (immuno-A-toxin) adsorbed on colloidal gold. Effects of ammonium chloride and monensin.
An immunotoxin (IT) formed by a specific antibody coupled to the ricin A chain was adsorbed on colloidal gold particles (IT-Au). Binding and internalization of IT-Au in human lymphoblastic CEM cells were studied using electron microscopy. IT-Au showed specific cytotoxic activity toward the target cells. After 1 h at 4 degrees C, IT-Au were linked diffusely to the plasma membrane with 45% of the particles regrouped in clusters. Upon transfer to 37 degrees C, the particles carrying the ligand were regrouped more frequently and internalized into the cell by endocytosis through smooth microinvaginations or coated pits of the plasma membrane. After 15 min, IT-Au was observed in endocytic vacuoles, or receptosomes, in tubular structure near the Golgi apparatus and in lysosomes. Entry of IT-Au into lysosomes was rapid (around 50% of intracellular IT-Au particles after 30 min). NH4Cl or monensin, well-known potentiators of immunotoxin activity, when present in incubation medium, altered neither the processes nor the rate of IT-Au endocytosis. In the presence of either of these substances, IT-Au accumulated in the normal or often enlarged endocytic vacuoles, and entry into the lysosomes was slowed down (50% of particles after 2 h 15 min). We conclude that this intense slowing-down in the speed of IT-Au transportation into lysosomes and the functional modifications of these organelles help to explain the increased efficacy of immunotoxins in the presence of potentiators.
Adsorption↗
Optimal elimination of leukemic T cells from human bone marrow with T101-ricin A-chain immunotoxin.
In view of bone marrow purging before autologous transplantation in T cell malignancies, an anti-human T cell immunotoxin (IT) has been prepared by coupling ricin A-chain to the monoclonal antibody T101 that binds the T1 differentiation antigen expressed by T lymphocytes as well as by T cell-derived hematologic malignancies. Using a sensitive and reliable clonogenic assay, optimal conditions were defined for the elimination of clonogenic human T leukemic cells among bone marrow cells. Maximal cytoreduction was obtained with IT at a dose of 2 micrograms/mL in the presence of 10 mmol/L NH4Cl. This treatment led to the reduction of more than six orders of magnitude of T101-positive clonogenic leukemic cells, with no harm to T101-negative cells. Moreover, we observed no toxicity of IT to human hematopoietic stem cells (CFU-GEMMT) derived from bone marrow of healthy volunteers. Thus, pretreatment of bone marrow samples with IT plus NH4Cl offers a safe, simple, reliable, and highly efficient means to eliminate undesirable leukemic T cells from the graft.
Ammonium Chloride↗
Evidence for absence of toxicity of T101 immunotoxin on human hematopoietic progenitor cells prior to bone marrow transplantation.
T101-ricin A-chain immunotoxin is a hybrid molecule made up of the T101 monoclonal antibody bound to the A-chain of ricin. It specifically destroys cells expressing the cell surface T65 antigen. We have designed a preclinical study to evaluate its possible use for the in vitro treatment of T-cell hematological cancers prior to autologous bone marrow transplantation. The data presented here show that conditions previously defined to produce high tumor cell killing, i.e., a 20-hr incubation at 37 degrees in the presence of T101-ricin A-chain immunotoxin up to 10(-7) M in a 10 mM ammonium chloride solution, do not affect the in vitro proliferative capacity of human hematopoietic stem cells studied by means of semisolid medium cultures (granulocyte-macrophage progenitors, burst-forming units-erythrocyte) and continuous liquid cultures (pre-granulocyte-macrophage progenitors). Therefore, autologous bone marrow transplantation with T101-ricin A-chain immunotoxin-treated graft should be feasible.
Antibodies, Monoclonal↗
Kinetics of cytotoxicity induced by immunotoxins. Enhancement by lysosomotropic amines and carboxylic ionophores.
The kinetics of cytotoxicity induced by ricin and a series of immunotoxins consisting of ricin A-chain coupled to antibodies against cell-surface antigens has been studied. The inhibition of protein synthesis in cells treated with immunotoxins or ricin occurs after a lag period. The rate of protein synthesis decreases according to a mono-exponential function, indicating a first-order process. With increasing concentration of immunotoxin, a maximal rate of inhibition is reached. The inactivation rate induced by immunotoxins was much slower than that achieved with ricin, even when products were compared on a basis of an identical number of molecules bound per cell, demonstrating the real higher efficacy of ricin. The time required to reduce protein synthesis by 90%, denoted T10, was 1.4-1.6 h with ricin, 60 h with anti-T65 immunotoxin on CEM human T leukemia cells (T65 positive), 65 h with anti-p97 immunotoxin on SK-MEL 28 human melanoma cells (p97 positive), and 20 h with an IgM anti-Thy 1.2 immunotoxin on WEHI-7 mouse T leukemia cells (Thy 1.2 positive). In this latter case, when the IgM antibody was replaced by an IgG anti-Thy 1.2, a 5-fold increase in the inactivation rate was obtained, demonstrating the importance of the binding moiety for the immunotoxins. Lysosomotropic amines such as ammonium chloride, chloroquine, and methylamine and carboxylic ionophores such as monensin, which are known to interfere with the uptake of certain macromolecules, strongly increased the rate of protein synthesis inhibition by all immunotoxins tested and increased 4-50,000-fold the sensitivity of cells to the immunotoxin. Enhancement in the inactivation rate was as much as 7-10-fold when either of these compounds was added, generating T10 values comparable to those of ricin.
Amines↗
Present potential of immunotoxins.
Immuno-a-toxins (I-a-T) are hybrid molecules designed for a more selective therapy of cancer, which combine an antibody preferentially directed against tumour cells and the A-chain of the toxin ricin. Although a majority of them are highly and selectively cytotoxic to their target cells in vitro, only some of them gave rise to a therapeutic effect in animal models. In vitro kinetics studies suggested the importance of a rapid mode of action for in vivo efficacy, which is not the property of all I-a-T. Ways of accelerating and potentiating such conjugates are proposed, such as the use of lysosomotropic amines like ammonium chloride. Whereas the in vivo use of these activators is still under research, their in vitro use gives rise to a 99.99% cytoreduction of leukemic cells and thus is directly applicable to clinical situations such as bone marrow transplantations.
Animals↗
[Immunotoxins].
Immunotoxins are conjugates between antibodies especially directed against cancer cells and a subunit of a powerful toxin. We used the A-chain of ricin. These conjugates are specifically cytotoxic when used at very low concentrations in vitro and can destroy more than 99.99% of clonogenic cells. The efficacy of immunotoxins was also demonstrated in vivo but is inferior to its in vitro potency. For this reason the first use of immunotoxins in man can be the cleaning up of bone marrow from leukemic cells in the near future.
Animals↗
Human melanoma cells can be killed in vitro by an immunotoxin specific for melanoma-associated antigen p97.
Conjugates (immunotoxins) comprising ricin A-chain and monoclonal antibody 96.5, which is specific for human melanoma-associated antigen p97, inhibited protein synthesis and colony formation of cultured human melanoma cells that expressed more than 80,000 molecules of p97 per cell. Cells expressing fewer than 5,000 molecules of p97 were not killed. The presence of 10 mM ammonium chloride significantly increased the efficiency of the immunotoxin, tumor cells expressing high levels of p97 being killed at immunotoxin concentrations as low as 10(-10) M.
Antibodies, Neoplasm↗
Immunotoxins: hybrid molecules combining high specificity and potent cytotoxicity.
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Animals↗
Immunotoxins: hybrid molecules of monoclonal antibodies and a toxin subunit specifically kill tumour cells.
Several attempts to attack tumours in experimental systems have been made using conjugates of chemotherapeutic agents or potent toxins with antibodies (immunotoxins). In vitro studies have been highly successful, showing target specificity of a high order in some cases. However, so far, such conjugates have been inadequate in vivo, probably for two main reasons. First, conventional heteroclonal antibodies are perhaps inappropriate, because purification by biochemical methods leaves a large amount of non-antibody gamma-globulins. The use of monoclonal antibodies may overcome this problem. Second, when whole toxins have been conjugated to antibodies there has been a strong residual nonspecific cytotoxicity due to the binding capacity of a subunit, the B-piece of the toxin. (Diphtheria toxin or ricin consist of two polypeptide subunits. The A-piece is responsible for inhibition of protein synthesis on ribosomes, and the B-piece binds to galactose residues on the cell membrane and facilitates the transmembrane passage of the A-piece.) In the present work the problem of nonspecific binding by the B-piece has been circumvented by using the A-piece only as the toxin component of immunotoxins; these immunotoxins are active both in vitro and in vivo.
Animals↗