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R J Kreitman

Publications and source records attributed to R J Kreitman.

At least 19 recordsLinked to original sources
PubMed2002

IL-4 receptors on human medulloblastoma tumours serve as a sensitive target for a circular permuted IL-4-Pseudomonas exotoxin fusion protein.

Cytotoxins directed to interleukin-4 receptors have shown to mediate relatively selective cytotoxicity against a variety of human cancer cells in vitro and in vivo. In an ongoing Phase I clinical trial, a recombinant protein comprised of circularly permuted IL-4 fused to a mutated form of Pseudomonas exotoxin (the fusion protein termed IL-4(38-37)-PE38KDEL or cpIL4-PE) has shown antitumour activity against malignant glioma. Human medulloblastomas are neuroectodermal tumours that occur in children and have a poor prognosis. The goal of this study was to determine whether human medulloblastoma derived cell lines express interleukin-4 receptor and whether interleukin-4 receptor expression is accompanied by sensitivity to cpIL4-PE. Medulloblastoma cell lines express interleukin-4 receptor at the protein and mRNA levels as determined by binding, indirect immunofluorescence and RT--PCR studies. These cells expressed IL-4Ralpha (also known as IL-4Rbeta) and IL-13Ralpha1 (also known as IL-13Ralpha') chains, however common gamma(c), a component of the interleukin-4 receptor system in immune cells was not detected. Consistent with the expression of IL-4R, cpIL4-PE was found to be highly and specifically cytotoxic to four of five medulloblastoma cell lines. Susceptibility of medulloblastoma cell lines to cpIL4-PE seemed to correlate closely to the functional IL-4 binding sites in general as demonstrated by 125I-IL-4 binding, but did not seem to correlate with mRNA or cell surface immunoreactive receptor protein expression. The sensitivity of medulloblastoma cells to cpIL4-PE could be eliminated by concurrent incubation with IL-4 or IL-13, but not with IL-2. None of these cell lines showed any change in proliferation upon treatment with exogenous IL-4. These studies establish the interleukin-4 receptor as a medulloblastoma-associated target for possible tumour-directed cancer therapy. Further studies are warranted to investigate interleukin-4 receptor expression in primary medulloblastoma tumours and sensitivity to cpIL-4PE in vitro and in vivo.

ADP Ribose Transferases↗
PubMed2001

Efficacy of the anti-CD22 recombinant immunotoxin BL22 in chemotherapy-resistant hairy-cell leukemia.

BACKGROUND: Hairy-cell leukemia that is resistant to treatment with purine analogues, including cladribine, has a poor prognosis. We tested the safety and efficacy of an immunotoxin directed against a surface antigen that is strongly expressed by leukemic hairy cells. METHODS: RFB4(dsFv)-PE38 (BL22), a recombinant immunotoxin containing an anti-CD22 variable domain (Fv) fused to truncated pseudomonas exotoxin, was administered in a dose-escalation trial by intravenous infusion every other day for a total of three doses. RESULTS: Of 16 patients who were resistant to cladribine, 11 had a complete remission and 2 had a partial remission with BL22. The three patients who did not have a response received low doses of BL22 or had preexisting toxin-neutralizing antibodies. Of the 11 patients in complete remission, 2 had minimal residual disease in the bone marrow or blood. During a median follow-up of 16 months (range, 10 to 23), 3 of the 11 patients who had a complete response relapsed and were retreated; all of these patients had a second complete remission. In 2 of the 16 patients, a serious but completely reversible hemolytic-uremic syndrome developed during the second cycle of treatment with BL22. Common toxic effects included transient hypoalbuminemia and elevated aminotransferase levels. CONCLUSIONS: BL22 can induce complete remissions in patients with hairy-cell leukemia that is resistant to treatment with purine analogues.

Adult↗
PubMed2001

Lowering the isoelectric point of the Fv portion of recombinant immunotoxins leads to decreased nonspecific animal toxicity without affecting antitumor activity.

Recombinant immunotoxins are genetically engineered proteins in which the Fv portion of an antibody is fused to a toxin. Our laboratory uses a 38-kDa form of Pseudomonas exotoxin A termed PE38 for this purpose. Clinical studies with immunotoxins targeting CD25 and CD22 have shown that dose-limiting side effects are attributable to liver damage and other inflammatory toxicities. We recently showed that mutating exposed surface neutral residues to acidic residues in the framework region of the Fv portion of an immunotoxin targeting CD25 [anti-Tac(scFv)-PE38] lowered its isoelectric point (pI) and decreased its toxicity in mice without impairing its cytotoxic or antitumor activities. We have now extended these studies and made mutations that change basic residues to neutral or acidic residues. Initially the pI of the mutant Fv (M1) of anti-Tac(scFv)-PE38 was decreased further. Subsequently, mutations were made in two other immunotoxins, SS1(dsFv)-PE38 targeting ovarian cancer and B3(dsFv)-PE38 targeting colon and breast cancers. We have found that all these mutant molecules fully retained specific target cell cytotoxicity and antitumor activity but were considerably less toxic to mice. Therefore, lowering the pI of the Fv may be a general approach to diminish the nonspecific toxicity of recombinant immunotoxins and other Fv fusion proteins without losing antitumor activity.

ADP Ribose Transferases↗
PubMed2001

Isolation of new anti-CD30 scFvs from DNA-immunized mice by phage display and biologic activity of recombinant immunotoxins produced by fusion with truncated pseudomonas exotoxin.

To target CD30 on Hodgkin's disease and anaplastic large-cell lymphoma, anti-CD30 single-chain antibodies were obtained by DNA immunization of mice with the complete human CD30 cDNA. Spleens were isolated from mice with high anti-CD30 titer, and the RNA was used for the production of an scFv-displaying phage library. Specific phages were enriched by 3 rounds of panning on soluble CD30 or CD30+ K562 cells. Recombinant immunotoxins (rITs) were made from 3 ELISA-positive scFv phages by fusion to a 38 kDa truncated mutant of Pseudomonas exotoxin (PE38) with or without a KDEL mutant sequence at the C terminus. In vitro cytotoxicity of purified anti-CD30 rITs was measured on CD30-transfected A431 cells. IC50 values ranged from 3 to 7 ng/ml (50-110 pM) for PE38 rITs and 0.1 ng/ml (2 pM) for the PE38-KDEL IT on A431-CD30 cells. The parental A431 cells were resistant, indicating that the cytotoxicity was specific and CD30-mediated. rITs were tested for anti-tumor activity in a nude mouse model. A431-CD30 cells were injected s.c. on day 0; then, mice bearing measurable tumors were treated beginning on day 4 with 3 alternate daily doses i.v. Anti-tumor activity was dose-dependent and not found when irrelevant ITs were administered or when CD30- tumors were treated. Our data show that DNA immunization and antibody phage display may be useful in producing new rITs against hematologic malignancies. Published 2001 Wiley-Liss, Inc.

ADP Ribose Transferases↗
PubMed2001

Antibody response to DT-GM, a novel fusion toxin consisting of a truncated diphtheria toxin (DT) linked to human granulocyte-macrophage colony stimulating factor (GM), during a phase I trial of patients with relapsed or refractory acute myeloid leukemia.

We are conducting a Phase I trial of a fusion toxin (DT-GM) for the treatment of relapsed or refractory acute myeloid leukemia (AML). The fusion toxin consists of a truncated diphtheria toxin (DT) linked to human granulocyte-macrophage colony stimulating factor (GM). Prior to beginning the Phase I trial, our first goal was to determine whether healthy controls and adult AML patients had preexisting antibodies able to inhibit DT-GM. Sera from 5 of the 9 controls completely neutralized DT-GM by an in vitro bioassay to assess the inhibition of DT-GM. Sera from 43 patients with AML were tested by bioassay and a specific enzymoimmunoassay (EIA) for anti-DT-GM antibodies. Forty-two of 43 samples were positive by EIA, and 5 patients (11.6%) showed complete neutralization of DT-GM in the bioassay. Anti-DT-GM concentrations were significantly higher in samples demonstrating neutralization than in samples demonstrating no neutralization (P = 0.003). In the Phase I trial of DT-GM prior to therapy, none of 28 patients exhibited neutralization by bioassay, but 89% were positive by EIA. After the first course of DT-GM, 23% developed neutralizing antibodies by the bioassay, and 64% of patients exhibited an increase in their anti-DT-GM antibody concentrations by EIA. Further studies are needed to determine the clinical impact of the anti-DT-GM antibodies and whether the neutralization bioassay can be replaced by our EIA.

Adult↗
PubMed2001

Toxin-labeled monoclonal antibodies.

To arm monoclonal antibodies (MAbs) with the power to kill malignant cells, they have been connected to toxins to create chimeric proteins called immunotoxins. Conventional immunotoxins contain a MAb chemically conjugated to a toxin which is mutated or chemically modified to minimize binding to normal cells. Examples include anti-B4-blocked ricin, targeting CD5, and RFB4-deglycosylated ricin A chain, targeting CD22. Conventional immunotoxins are capable of inducing responses in patients with hematologic malignancies, with dose-limiting toxicities being vascular leak syndrome, thrombocytopenia, and hepatic damage. Newer immunotoxins contain a recombinant ligand, either the variable domains (Fv) of a MAb, or a growth factor, fused to a truncated bacterial toxin. Bacterial toxins commonly used for this purpose include diphtheria toxin and Pseudomonas exotoxin. DAB389lL2 (Ontak) is a recently approved growth factor fusion toxin containing human interleukin-2 and diphtheria toxin and is effective in chemotherapy-resistant cutaneous T-cell lymphoma. Anti-Tac(Fv)-PE38 (LMB-2) and RFB4(dsFv)-PE38 (BL22) are two recombinant immunotoxins, targeting CD25 and CD22, respectively, in which Fvs of MAbs targeting these antigens are fused to truncated Pseudomonas exotoxin. Both LMB-2 and BL22 have exhibited clinical activity in patients with hematologic malignancies, with less vascular leak syndrome and probably less immunogenicity than the larger conventional immunotoxin conjugates. New recombinant immunotoxins are currently being engineered and developed to target other hematologic and solid tumor antigens.

Animals↗
PubMed2001

Chimeric fusion proteins--Pseudomonas exotoxin-based.

Recombinant fusion toxins have several potential advantages over conventional immunotoxin chemical conjugates, including (i) a defined toxin-ligand junction; (ii) efficient and relatively inexpensive production in large scale from bacteria; (iii) shorter plasma half-lives which might avoid diffuse endothelial damage which leads to vascular leak syndrome (VLS); and (iv) ability to genetically engineer mutations in the recombinant toxin to increase its potency or lower its non-specific toxicity. Two major varieties of recombinant fusion toxins include growth factor fusion toxins, containing a growth factor fused to truncated toxin, and recombinant immunotoxins, containing the variable fragments of an antibody fused to truncated toxin. In either case the ligand is used to bind selectively to tumor cells while the toxin kills the target cell following internalization. The bacterial toxins Pseudomonas exotoxin and diphtheria toxin are most often used for making recombinant fusion toxins. This review will focus on several agents containing truncated Pseudomonas exotoxin, which are undergoing preclinical and clinical development.

Animals↗
PubMed2000

Inhibition of TNF-alpha produced by Kupffer cells protects against the nonspecific liver toxicity of immunotoxin anti-Tac(Fv)-PE38, LMB-2.

LMB-2 (anti-Tac(Fv)-PE38) is a recombinant immunotoxin composed of the Fv fragment of the anti-Tac Ab fused to a 38-kDa form of Pseudomonas: exotoxin A. Recent clinical trials showed that LMB-2 is a promising agent for the treatment of patients with Tac-positive leukemia or lymphoma. One major side effect that needs to be overcome is nonspecific liver toxicity. In the current study, we have analyzed the mechanism of this toxicity using a mouse model. Mice that were injected with a lethal dose of LMB-2 showed severe hepatic necrosis. Immunohistochemistry revealed that LMB-2 accumulated in Kupffer cells in the liver, suggesting that the damage to the hepatocytes was indirect. When we examined the effects of LMB-2 on peritoneal macrophages, cells in the same lineage as Kupffer cells, we found that LMB-2 induced the production of TNF-alpha by these cells. Following LMB-2 administration to mice, the levels of TNF-alpha in the liver increased to very high levels, whereas the rise in serum levels was modest. In addition, the LMB-2-induced liver toxicity was blocked by a specific TNF binding protein (TNFsRp55). Liver toxicity was also blocked by indomethacin, which also blocked the rise of TNF-alpha in the liver. Both TNFsRp55 and indomethacin treatment protected mice against a lethal dose of LMB-2. These data indicate that TNF-alpha produced in the liver by Kupffer cells has an important causal role in the nonspecific liver toxicity of LMB-2. These findings have important clinical implications for the use of immunotoxins in the therapy of patients with cancer.

Animals↗
PubMed2000

Synaptic integration mediated by striatal cholinergic interneurons in basal ganglia function.

The physiological role of striatal cholinergic interneurons was investigated with immunotoxin-mediated cell targeting (IMCT). Unilateral cholinergic cell ablation caused an acute abnormal turning behavior. These mice showed gradual recovery but displayed abnormal turning by both excess stimulation and inhibition of dopamine actions. In the acute phase, basal ganglia function was shifted to a hyperactive state by stimulation and suppression of striatonigral and striatopallidal neurons, respectively. D1 and D2 dopamine receptors were then down-regulated, relieving dopamine-predominant synaptic perturbation but leaving a defect in controlling dopamine responses. The acetylcholine-dopamine interaction is concertedly and adaptively regulated for basal ganglia synaptic integration.

Acetylcholine↗
PubMed2000

Site-specific chemical modification with polyethylene glycol of recombinant immunotoxin anti-Tac(Fv)-PE38 (LMB-2) improves antitumor activity and reduces animal toxicity and immunogenicity.

Chemical modification of proteins with polyethylene glycol (PEGylation) can increase plasma half-lives, stability, and therapeutic potency. To make a PEGylated recombinant immunotoxin with improved therapeutic properties, we prepared a mutant of anti-Tac(Fv)-PE38 (LMB-2), a recombinant immunotoxin composed of a single-chain Fv fragment of the anti-human Tac monoclonal antibody to the IL-2 receptor alpha subunit fused to a 38-kDa fragment of Pseudomonas exotoxin. For site-specific PEGylation of LMB-2, one cysteine residue was introduced into the peptide connector (ASGCGPE) between the Fv and the toxin. This mutant LMB-2 (cys1-LMB-2), which retained full cytotoxic activity, was then site-specifically conjugated with 5 or 20 kDa of polyethylene glycol-maleimide. When compared with unmodified LMB-2, both PEGylated immunotoxins showed similar cytotoxic activities in vitro but superior stability at 37 degrees C in mouse serum, a 5- to 8-fold increase in plasma half-lives in mice, and a 3- to 4-fold increase in antitumor activity. This was accompanied by a substantial decrease in animal toxicity and immunogenicity. Site-specific PEGylation of recombinant immunotoxins may increase their therapeutic potency in humans.

Animals↗
PubMed2000

Apoptosis induced by immunotoxins used in the treatment of hematologic malignancies.

The recombinant immunotoxins anti-Tac(Fv)-PE38 (LMB-2), targeting the interleukin-2 receptor alpha subunit (IL-2Ralpha, Tac or CD25), and RFB4(dsFv)-PE38 (BL22), targeting CD22, are being evaluated in clinical trials as treatment for hematologic malignancies. The toxin moiety Pseudomonas exotoxin A (PE) of these recombinant molecules leads to the arrest of protein synthesis due to inactivation of elongation factor 2. Here, we provide evidence that cell lines derived from patients with hematologic malignancies react to immunotoxins not only with inhibition of protein synthesis but also with characteristic hallmarks of apoptosis such as caspase activation, cleavage of the "death substrate poly(ADP)-ribose polymerase and DNA laddering. Anti-Tac(Fv)-PE38 leads to a 10-fold increase in the cleavage of the fluorescent substrate DEVD-AFC, suggesting that a caspase-3-like enzyme is involved. This was verified by cleavage of caspase-3 (CPP32). MT1 cells exhibited DNA laddering after treatment with immunotoxin, which was reversed by pre-treatment with the protease inhibitor zVAD-fmk. This caspase inhibitor led to an at least 5-fold improvement in cell viability without altering inhibition of protein synthesis. Interestingly, HUT-102 cells did not undergo programmed cell death after exposure to immunotoxins that kill these cells. We conclude that immunotoxins may be valuable in the treatment of cancers that are resistant toward apoptosis because their targeted killing is often facilitated by, but not completely dependent on, programmed cell death. Int. J. Cancer 87:86-94, 2000. Published 2000 Wiley-Liss, Inc.

Amino Acid Chloromethyl Ketones↗
PubMed2000

Recombinant toxins that bind to the urokinase receptor are cytotoxic without requiring binding to the alpha(2)-macroglobulin receptor.

The alpha(2-)macroglobulin receptor (alpha(2)MR) has been reported to mediate the internalization of the urokinase plasminogen activator receptor (uPAR) via ligand binding to both receptors. To target malignant uPAR-expressing cells and to determine whether uPAR can internalize without ligand binding to alpha(2)MR, we engineered two recombinant toxins, ATF-PE38 and ATF-PE38KDEL. Each consists of the amino-terminal fragment (ATF) of human urokinase and a truncated form of Pseudomonas exotoxin (PE) devoid of domain Ia, which binds alpha(2)MR. ATF-PE38 and ATF-PE38KDEL were cytotoxic toward malignant uPAR-bearing cells, with IC(50) values as low as 0.02 ng/ml (0.3 pM). Cytotoxicity could be blocked using either recombinant urokinase or free ATF, indicating that the cytotoxicity of the recombinant toxins was specific. Radiolabeled ATF-PE38 had high affinity for uPAR (K(d) = 0.4-8 nM) on a variety of different malignant cell types and internalized at a rate similar to that of ATF. The cytotoxicity was not diminished by receptor-associated protein, which binds and shields the alpha(2)MR from other proteins, or by incubation with phorbol myristate acetate, which is known to decrease the number of alpha(2)MRs in U937 cells or by antibodies to alpha(2)MR. Therefore, these recombinant toxins appear to internalize via uPAR without association with the alpha(2)MR.

ADP Ribose Transferases↗
PubMed2000

Diphtheria toxin fused to human interleukin-3 is toxic to blasts from patients with myeloid leukemias.

Leukemic blasts from patients with acute phase chronic myeloid leukemic and refractory acute myeloid leukemia are highly resistant to a number of cytotoxic drugs. To overcome multi-drug resistance, we engineered a diphtheria fusion protein by fusing human interleukin-3 (IL3) to a truncated form of diphtheria toxin (DT) with a (G4S)2 linker (L), expressed and purified the recombinant protein, and tested the cytotoxicity of the DTLIL3 molecule on human leukemias and normal progenitors. The DTLIL3 construct was more cytotoxic to interleukin-3 receptor (IL3R) bearing human myeloid leukemia cell lines than receptor-negative cell lines based on assays of cytotoxicity using thymidine incorporation, growth in semi-solid medium and induction of apoptosis. Exposure of mononuclear cells to 680 pM DTLIL3 for 48 h in culture reduced the number of cells capable of forming colonies in semi-solid medium (colony-forming units leukemia) > or =10-fold in 4/11 (36%) patients with myeloid acute phase chronic myeloid leukemia (CML) and 3/9 (33%) patients with acute myeloid leukemia (AML). Normal myeloid progenitors (colony-forming unit granulocyte-macrophage) from five different donors treated and assayed under identical conditions showed intermediate sensitivity with three- to five-fold reductions in colonies. The sensitivity to DTLIL3 of leukemic progenitors from a number of acute phase CML patients suggests that this agent could have therapeutic potential for some patients with this disease.

DNA Replication↗
PubMed2000

Phase I trial of recombinant immunotoxin anti-Tac(Fv)-PE38 (LMB-2) in patients with hematologic malignancies.

PURPOSE: To evaluate the toxicity, pharmacokinetics, immunogenicity, and antitumor activity of anti-Tac(Fv)-PE38 (LMB-2), an anti-CD25 recombinant immunotoxin that contains an antibody Fv fragment fused to truncated Pseudomonas exotoxin. PATIENTS AND METHODS: Patients with CD25(+) hematologic malignancies for whom standard and salvage therapies failed were treated with LMB-2 at dose levels that ranged from 2 to 63 microg/kg administered intravenously over 30 minutes on alternate days for three doses (QOD x 3). RESULTS: LMB-2 was administered to 35 patients for a total of 59 cycles. Dose-limiting toxicity at the 63 microg/kg level was reversible and included transaminase elevations in one patient and diarrhea and cardiomyopathy in another. LMB-2 was well tolerated in nine patients at the maximum-tolerated dose (40 microg/kg QOD x 3); toxicity was transient and most commonly included transaminase elevations (eight patients) and fever (seven patients). Only six of 35 patients developed significant neutralizing antibodies after the first cycle. The median half-life was 4 hours. One hairy cell leukemia (HCL) patient achieved a complete remission, which is ongoing at 20 months. Seven partial responses were observed in cutaneous T-cell lymphoma (one patient), HCL (three patients), chronic lymphocytic leukemia (one patient), Hodgkin's disease (one patient), and adult T-cell leukemia (one patient). Responding patients had 2 to 5 log reductions of circulating malignant cells, improvement in skin lesions, and regression of lymphomatous masses and splenomegaly. All four patients with HCL responded to treatment. CONCLUSION: LMB-2 has clinical activity in CD25(+) hematologic malignancies and is relatively nonimmunogenic. It is the first recombinant immunotoxin to induce major responses in cancer. LMB-2 and similar agents that target other cancer antigens merit further clinical development.

Adult↗
PubMed2000

Immunotoxins.

Immunotoxins are molecules which contain a protein toxin connected to a targeting antibody. The goal of therapy is for the molecule to bind selectively to cancer cells, or to cells mediating autoimmune disease, internalise and then for the toxin to kill the cell. Several immunotoxins meeting this definition are in preclinical and clinical development, but none are approved yet for use in general practice. One close relative of immunotoxins is the growth factor fusion toxin, wherein the targeting antibody is replaced with a growth factor that selectively binds and this ligand is fused in a recombinant fashion to a protein toxin. One such molecule, containing human interleukin-2 (IL-2) fused to truncated diphtheria toxin (DT), has recently been approved under the name Ontak, and others are under development. A newer class of immunotoxins, termed recombinant immunotoxins, contain the variable or antigen binding domains of an antibody fused in recombinant fashion to a toxin. Recombinant immunotoxins, like growth factor fusion toxins, can be produced efficiently from bacteria and have a defined structure with respect to the linkage between the toxin and the ligand. However, they can, like conventional immunotoxins, be directed to antigens other than growth factor receptors, including receptor subunits. Several recombinant immunotoxins are under clinical testing and major responses have been reported, particularly in haematological malignancies. Some of these molecules may enter clinical practice in the future as targeted therapy, which is a modality distinct from those of chemotherapy, surgery and radiation therapy.

Animals↗
PubMed2000

Development of lymphoproliferative disorder of granular lymphocytes in association with hairy cell leukemia.

Lymphoproliferative disorder of granular lymphocytes (LDGL) is a low grade T-cell disease characterized by clonal expansion of large granular lymphocytes of either T cell or natural killer (NK) cell lineage that express the cytotoxic T-cell/NK cell antigens CD16, CD56 and/or CD57. LDGL has been described in association with other malignancies, leading to theories of a common abnormal stem cell as well as development of the LDGL as an immune response to a primary tumor. We have studied 32 patients with hairy cell leukemia (HCL). In 15 patients (47%) we detected an increase in cells expressing cytotoxic T-cell/NK cell antigens. In 10(31%) patients these cells were of T cell lineage, while 5 patients (16%) had increased NK-cells. T cell clonality was detected by PCR in all cases with increased cytotoxic T-cells in which adequate DNA was obtained from peripheral blood. Since in 2 patients the LDGL was not present at diagnosis but developed during follow up, our data suggests that clonal LDGL may develop in response to the HCL. The significance of LDGL in the setting of HCL and flow cytometric evaluation of HCL versus LDGL will be discussed.

Adult↗
PubMed2000

Targeted toxins.

Targeted toxins, consisting of tumor-selective ligands coupled to polypeptide toxins, represent a new class of cancer therapeutics that kills malignant cells by inactivating cytosolic protein synthesis and inducing apoptosis. A number of these molecules have been produced under good manufacturing practice conditions and given systemically to patients with a variety of neoplasms. The promising results to date and the remaining pharmacological hurdles are discussed.

Antineoplastic Agents↗