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Biomedical subjects

J E Leonard

Publications and source records attributed to J E Leonard.

At least 19 recordsLinked to original sources
PubMed1999

Preclinical evaluation of 90Y-labeled anti-CD20 monoclonal antibody for treatment of non-Hodgkin's lymphoma.

A high-affinity IgG1 kappa murine monoclonal anti-CD20 antibody (IDEC-2B8) was developed for radioimmunotherapy of non-Hodgkin's B-cell lymphoma. A stable immunoconjugate (Zevalintrade mark) was prepared by reacting IDEC-2B8 with a derivative of diethylenetriaminepentaacetic acid, designated MX-DTPA, a chelator exhibiting high affinity and retention for 90Y. Zevalin exhibited antigen specificity, human tissue reactivity, and preclinical safety profile comparable to the native antibody. The conjugate radiolabeled with 90Y (90Y-Zevalin) or 111In (111In-Zevalin) exhibited excellent retention of immunoreactivity with radioincorporations >95%. The radiolabeled conjugates formulated in PBS containing human serum albumin were stable in vitro at 4 degrees C for 48 h as indicated by negligible loss of radioisotope and retention of binding to CD20+ cells. In vitro human serum stability studies at 37 degrees C with 90Y-Zevalin indicated that loss of 90Y from the conjugate was minimal, averaging 1% per day. Biodistribution studies in BALB/c mice confirmed the in vitro stability of 90Y-Zevalin and 111In-Zevalin. In particular, excellent in vivo retention of 90Y by the conjugate was demonstrated by minimal bone accumulation (</=3% of the injected dose over three days). Radiation dose estimates to normal organs calculated from mouse biodistribution studies with 90Y-Zevalin were comparable to those determined in a phase I/II clinical trial and below generally accepted safe radiation levels. Studies in athymic mice bearing CD20+ tumors demonstrated that 111In-Zevalin accumulated in the tumors preferentially compared with normal organs. 90Y-Zevalin is currently being evaluated in phase III clinical trials for treatment of relapsed or refractory low-grade, follicular or transformed B-cell non-Hodgkin's lymphoma.

Animals↗
PubMed1996

Apical and coronal seal of roots obturated with a dentine bonding agent and resin.

The efficacy of sealing root canal systems with a dentine bonding agent and resin cement was compared with that of a glass ionomer sealer. Scanning electron microscopic examination of the bonding agent-dentine interface was also performed. The root canals of 50 single rooted teeth with mature apices were prepared chemomechanically and the smear layer removed with 17% REDTA and 5.25% NaOCl. Specimens were divided into two groups of 24 teeth each. One group had the dentine conditioned with a 10:3 citric acid-ferric chloride solution and obturated with the dentine bonding agent and resin, radiopaque C & B Metabond. The other group was obturated with the glass ionomer sealer, Ketac-Endo and a single cone of gutta-percha. After immersion in Indian ink for 90 h, the teeth were cleared and the quality of the apical and coronal seal was assessed using India ink dye penetration. There was a significantly better seal in both the apical and coronal directions when using the dentine bonding agent and resin obturation material. Scanning electron microscopic examination of the demineralized dentine and the C & B Metabond interface revealed the presence of the characteristic hybrid layer along with microtags of resin penetrating deep into the dentine tubules.

Boron Compounds↗
PubMed1995

Multidisciplinary aspects of root resection failure: a case report.

Creative approaches to tooth maintenance often include tooth resection and retention of one or more of the roots. Although this procedure is reasonably successful, failure of supportive endodontic, periodontic, and restorative management of the retained roots can jeopardize a successful outcome. The following is a case report evaluating multiple aetiologies contributing to root resection failure.

Dental Leakage↗
PubMed1995

Problem solving in endodontic working-length determination.

The success of nonsurgical endodontic treatment is influenced significantly by accurate working-length determination. A variety of guidelines and techniques are available to clinicians in mastering working-length analysis with routine success achieved when multiple methods are used. This article stresses a cognitive, problem-solving approach in the management of clinical variations in working-length determination and interpretation.

Dental Pulp Cavity↗
PubMed1994

Depletion of B cells in vivo by a chimeric mouse human monoclonal antibody to CD20.

Murine monoclonal antibody 2B8 specifically recognizes the CD20 phosphoprotein expressed on the surface of normal B lymphocytes and B-cell lymphomas. The light- and heavy-chain variable regions of 2B8 were cloned, after amplification by the polymerase chain reaction, into a cDNA expression vector that contained human IgG1 heavy chain and human kappa-light chain constant regions. High-level expression of chimeric-2B8 antibody (C2B8) was obtained in Chinese hamster ovary cells. Purified C2B8 exhibited antigen binding affinity and human-tissue reactivity similar to the native murine antibody. In vitro studies showed the ability of C2B8 to bind human C1q, mediate complement-dependent cell lysis of human B-lymphoid cell lines, and lyse human target cells through antibody-dependent cellular cytotoxicity. Infusion of macaque cynomolgus monkeys with doses ranging from 1.6 mg/kg to 6.4 mg/kg resulted in greater than 98% depletion of peripheral blood (PB) B cells and 40% to 70% depletion of lymph node B cells. Recovery of PB B cells usually started at 2 weeks after treatment and required 60 to greater than 90 days to reach normal levels. As much as 95% depletion of B cells in peripheral lymph nodes and bone marrow was observed following weekly injections of 16.8 mg/kg antibody. No toxicity was observed in any of the animals. These results offer the possibility of using an "immunologically active" chimeric anti-CD20 antibody as an alternative approach in the treatment of B-cell lymphoma.

Amino Acid Sequence↗
PubMed1993

Music therapy: fertile ground for application of research in practice.

When participating in research studies in the clinical setting it is important to remember the goals of the interventions under study. Frequently the parameters and design of the research, while necessary to validate findings, are not written in stone for future application. It is possible to consider other situations in which the intervention might be applied that lie outside the current research protocols. To fully utilize research findings, apply them to your own unique practice and then set up your own study using the original work as a starting place.

Female↗
PubMed1991

Assessment of ligand effects in intracellular trafficking of ricin A chain using anti-ricin hybridomas.

Intracellular ricin and immunotoxin trafficking has been difficult to study as only one to two cytosolic ricin A chain (RTA) molecules are sufficient to cause cell death. Previous studies (R.J. Youle and M. Colombatti, J. Biol. Chem., 262: 4676-4882, 1987) using anti-ricin hybridomas identified the secretory pre-Golgi as a critical site for RTA intoxication. We used ricin and RTA immunotoxins constructed with transferrin (TF) or anti-murine TF receptor antibody (RI7/217) to compare patterns of cytotoxicity and intracellular trafficking in anti-ricin hybridomas. Anti-RTA and anti-ricin B chain (RTB) hybridomas bound similar amounts of ricin and secreted comparable amounts of anti-ricin immunoglobulin. Anti-RTA hybridomas were 50- to 500-fold more resistant to ricin than nonsecretory and anti-RTB hybridomas, defining a ricin-resistant phenotype. All hybridomas expressed similar levels of surface TF receptors. RTA immunotoxins were constructed using human TF or RI7/217 and a disulfide linker. In protein synthesis inhibition assays, ricin-resistant hybridomas were manyfold more resistant to RI7/217-RTA than were ricin-sensitive hybridomas. In contrast, all hybridomas were equally sensitive to TF-RTA. Monensin increased ricin cytotoxicity minimally against all hybridomas, but dramatically increased RI7/217-RTA cytotoxicity in ricin-resistant and ricin-sensitive hybridomas in a way that abrogated the ricin-resistant phenotype. In contrast, monensin increased TF-RTA cytotoxicity equally in all hybridomas. Ammonium chloride had little effect on ricin or RI7/217-RTA cytotoxicity, but increased TF-RTA cytotoxicity against all hybridomas. Taken together, these results suggest that RTA molecules mediating cytotoxicity pass through an anti-RTA antibody-containing pre-Golgi compartment when bound to RTB or RI7/217, but not when bound to TF. Monensin abrogates the ricin-resistant phenotype when RTA is linked to RI7/217, but not RTB. This suggests that monensin alters RI7/217-RTA processing proximal to the pre-Golgi and that passage through the pre-Golgi may not be necessary for translocation of RTA to the cytoplasm. Ammonium chloride alters toxin cytotoxicity only when RTA is linked to TF, suggesting that only TF trafficks RTA through an acid-sensitive compartment prior to cytoplasmic translocation. With the addition of potentiating agents, each toxin studied showed a unique cytotoxicity profile against the anti-ricin hybridomas, demonstrating a dominant role of the cell binding ligand in intracellular toxin trafficking.

Ammonium Chloride↗
PubMed1988

Inhibition of human T-cell tumor growth by T101-ricin A-chain in an athymic mouse model.

An immunotoxin prepared with the pan-T-cell, anti-CD5, antibody T101, and purified ricin A-chain (RTA) was selectively cytotoxic in vitro, inactivating protein synthesis in the human T-cell line MOLT-4 but not in the human B-cell line 8392. Modulation studies showed that the immunoconjugate was more rapidly cleared from the cell surface than unconjugated T101. Preclinical evaluation of T101-RTA was conducted in a human T-cell, athymic mouse model (Dillman et al., Cancer Res., 45:5632-5336, 1985). Tumor-bearing mice received single i.p. injections of saline, T101, UPC-10 (irrelevant IgG2a), unconjugated RTA, an irrelevant conjugate, UPC-10-RTA, a mixture of T101 plus RTA, or T101-RTA. T101-RTA was the most effective reagent. Thirty animals given injections of 33 micrograms of T101 showed reductions in tumor growth (compared to tumor growth in animals receiving phosphate-buffered saline) but no complete regressions. No decrease in tumor growth was observed with UPC-10. Animals given 12 micrograms of free RTA exhibited reduced tumor growth but only one complete regression was observed; similar results were obtained with mice given 45 micrograms of UPC-10-RTA or a mixture of 33 micrograms of T101 plus 12 micrograms of RTA. Eleven complete regressions and 18 partial regressions were produced in the 46 animals given injections of 45 micrograms of T101-RTA and tumor growth was almost completely blocked. No toxicity was observed in any experimental arm. These results suggest that T101-RTA may be administered safely and with significant antitumor effect.

Animals↗
PubMed1988

Ricin binding and protein synthesis inhibition in human hematopoietic cell lines.

Previous studies showed that human blood cells exhibited varying sensitivities to ricin. To investigate the basis for these differences, ricin binding to human hematopoietic cell lines was assessed and correlated with in vitro ricin sensitivities. Resistant mutants were also isolated and characterized. Ricin binding to CEM cells was rapid, time-dependent, and blocked by unlabeled ricin, but not albumin; ricin binding approached saturation at 3 mumol/L. Scatchard analyses showed multiple classes of binding sites, with maximum and minimum Kd values estimated at 1.5 x 10(-8) mol/L and 2.5 x 10(-7) mol/L. At 4 degrees C, membrane-bound ricin dissociated slowly from the cell surface in the presence of unlabeled ricin, but greater than 95% of the surface-bound ricin was removed with 0.1 mol/L lactose. At 37 degrees C, ricin dissociated from the cell surface with biphasic kinetics. Ricin uptake at 37 degrees C increased linearly for 15 to 30 minutes and plateaued at levels representing 12% to 29% of the amount of ricin bound at 4 degrees C, depending on the cell line. Ricin binding at 4 degrees C varied two- to fivefold among hematopoietic cell lines and was reduced approximately tenfold by incubation with lactose. When compared with parent CEM cells, ricin-resistant CEM variants showed a greater than 95% reduction in ricin binding and showed no detectable binding with lactose added. However, these cells were as sensitive as parent CEM cells to an anti-T-cell ricin immunoconjugate. For all cells examined, there was a close correlation (r = +.9) between ricin bound per cell and in vitro ricin sensitivity. Human hematopoietic cells show widely varying ricin binding, indicating major differences in the carbohydrate content or structure of surface glycoproteins and glycolipids. These variations are probably the major determinant of nonspecific toxicity of ricin immunoconjugates.

Cell Line↗
PubMed1987

Establishment of a human B-cell tumor in athymic mice.

Human B-cell tumors have been established in athymic, BALB/c mice using the EBV-positive Burkitt lymphoma cell line Namalwa. One-hundred-one of 104 animals (97%) developed tumors 10-14 days following s.c. injection of a mixture of 20 x 10(6) Namalwa and 5 X 10(6) irradiated human fibrosarcoma (HT-1080) cells. Tumors developed at the site of injection and reached approximately 300 mm2 (product of cross-sectional diameters) after 21 days; no metastases were found. Histological analysis showed that tumors consisted solely of lymphoid cells. Immunofluorescence assays demonstrated that while 85% of the tumor cells retained reactivity with the monoclonal B-cell antibody BA-1, 96% retained reactivity with antibody BA-2 and 43% with BA-3. A similar reactivity profile was observed with cultured Namalwa cells. Tumors were passaged serially 10 times without significant change in BA-1, BA-2, or BA-3 reactivity. Indirect immunofluorescence demonstrated that antibody BA-2 reached tumor cells within 2 h following i.p. injection; antigen modulation was not observed. These results demonstrate the suitability of this B-cell model for testing the in vivo efficacy and stability of anti-B-cell immunoconjugates.

Animals↗
PubMed1987

Monoclonal antibodies to purified ricin A-chain: production and properties.

Ricin A-chain was purified from native ricin using lactosyl-Sepharose. It was non-toxic to whole cells at a concentration of 1 microM yet nearly as effective as an equimolar concentration of ricin in blocking in vitro protein synthesis. Hybridomas secreting monoclonal antibodies to ricin A-chain were produced using the murine myeloma cell line NS-1. These anti-ricin A-chain antibodies cross-reacted with whole ricin but exhibited little cross-reactivity with purified ricin B-chain. Antibodies 2F2 and 2F5 both immunoprecipitated ricin A-chain. Both antibodies also precipitated ricin B-chain, as did the irrelevant control antibodies MOPC-21 and MPC-11. Pre-incubation of B-chain with 0.1 M galactose eliminated greater than 90% of precipitation by 2F2, MOPC-21 and MPC-11 but effected minimally precipitation by 2F5. Enzyme-linked immunosorbent assays using antibodies 2F2 and 2F5 to detect ricin A-chain in murine or human serum were linear between 40 and 800 ng ricin A-chain per ml. Anti-ricin A-chain antibodies 2F2 and 2F5 produced some inhibition of in vitro A-chain catalytic activity. Specific monoclonal antibodies to A-chain hemitoxin will be useful for characterization of functional hemitoxin domains, in in vitro assays for the stability of A-chain immunotoxins, and in characterizing the cellular internalization and processing of conjugates containing ricin or ricin A-chain.

Animals↗
PubMed1985

Identification of the phosphocarrier protein enzyme IIIgut: essential component of the glucitol phosphotransferase system in Salmonella typhimurium.

The phosphoenolpyruvate-dependent phosphorylation of glucitol has been shown to require four distinct proteins in Salmonella typhimurium: two general energy-coupling proteins, enzyme I and HPr, and two glucitol-specific proteins, enzyme IIgut and enzyme IIIgut. The enzyme IIgut was solubilized from the membrane and purified about 100-fold, free of the other protein constituents of the phosphotransferase system. Enzyme IIIgut was found in both the soluble and the membrane fractions. The soluble enzyme IIIgut was purified to near homogeneity by gel filtration, hydroxylapatite chromatography, and hydrophobic chromatography on butylagarose. It was sensitive to parital inactivation by trypsin and N-ethylmaleimide, but was stable at 80 degrees C. The protein had an approximate molecular weight of 15,000. It was phosphorylated in the presence of phosphoenolpyruvate, enzyme I, and HPr, and this phosphoprotein was dephosphorylated in the presence of enzyme IIgut and glucitol. Antibodies were raised against enzyme IIIgut. Enzyme IIIglc and enzyme IIIgut exhibited no enzymatic or immunological cross-reactivity. Enzyme IIgut, enzyme IIIgut, and glucitol phosphate dehydrogenase activities were specifically induced by growth in the presence of glucitol. These results serve to characterize the glucitol-specific proteins of the phosphotransferase system in S. typhimurium.

Escherichia coli Proteins↗
PubMed1985

Kinetics of protein synthesis inactivation in human T-lymphocytes by selective monoclonal antibody-ricin conjugates.

Immunotoxins synthesized with the pan-T-cell monoclonal antibody T101 and ricin, acetylricin, or ricin A-chain have been compared. Native ricin was acetylated with N-acetylimidazole to block the galactose-binding site of the toxin B (binding)-chain. In the presence of lactose, both whole-ricin-containing immunotoxins were selectively cytotoxic but the ricin A-chain conjugate was less effective in blocking cellular protein synthesis. Immunotoxin-treated cells cultured in fresh growth medium exhibited no growth, declining viabilities, and no protein synthesis activity. Lymphocytes treated with T101:ricin or ricin did not form clusters or colonies when plated in 0.3% Bacto-agar. Ammonium chloride markedly enhanced the efficacy of T101:ricin and T101:ricin A-chain. Our results suggest that: (a) all immunotoxins were selectively cytotoxic; (b) in the presence of ammonium chloride the effectiveness of the T101:ricin A-chain conjugate approached that of T101:ricin; and (c) the toxin B-chain may facilitate conjugate internalization and/or processing.

Acetylation↗
PubMed1985

Preclinical studies on the use of selective antibody-ricin conjugates in autologous bone marrow transplantation.

Whole-ricin immunoconjugates were synthesized with the pan-T cell antibodies T101 and 3A1 and assayed in the presence of 0.1 mol/L lactose. Their toxicity for cell lines, peripheral blood T lymphocytes, and normal bone marrow progenitors was compared with that of whole ricin. In the presence of 0.1 mol/L lactose, normal cells and cell lines exhibited the following sensitivities to ricin: 8392 (human malignant B cell line) less than E rosette-positive lymphocytes less than bone marrow progenitors less than 8402 (human T ALL) less than CEM (human T ALL). Ricin sensitivities correlated with ricin binding as determined by immunofluorescence. In the presence of lactose, peripheral blood T cells were resistant to 0.1 nmol/L ricin, but a similar concentration of T101-ricin inhibited normal and malignant T colony formation by greater than 98%. 3A1-ricin was slightly less effective. At a conjugate concentration of 0.1 nmol/L, bone marrow progenitor colony formation was inhibited by 30% or less; T101-positive cells were at least tenfold more sensitive than normal progenitors. When mixtures of 10% CEM cells and marrow cells were incubated with T101-ricin, 95% of CEM colonies were killed, and 96% of marrow granulocyte/ macrophage progenitors survived. Some free ricin was released from immunotoxin-treated cells, producing minimal inhibition of protein synthesis or cell growth. We conclude that (a) normal blood cells and malignant cell lines exhibit varying degrees of ricin sensitivity in the presence of lactose; (b) T101-ricin is at least tenfold more toxic to T lymphocytes than to bone marrow progenitor cells and is effective in mixtures of normal and malignant cells; and (c) treatment of infiltrated marrow with anti-T cell immunotoxins should safely remove target T cells without excessively damaging normal progenitors or producing excessive free ricin. Anti-T cell, whole-ricin immunotoxins merit trials for autologous transplantation.

Antibodies, Monoclonal↗
PubMed1985

Athymic mouse model of a human T-cell tumor.

Because of the large number of different immunoconjugates which can be produced from monoclonal antibody-directed anti-cancer therapy, it would be useful to have in vivo tumor models to compare such preparations. Although historically human leukemias-lymphomas have been difficult to establish in athymic mice we have succeeded in establishing human T-cell tumors from primary MOLT-4 cultures in 290 of 353 animals and have successfully transferred tumors in 42 of 45 animals during ten serial passages. The potential utility of this model for testing immunoconjugates of murine monoclonal antibody T101 have been confirmed by: (a) in all 148 tumors sampled including all passaged tumors the human T-cell antigen, T65, was expressed in a manner identical to that of cultured cells; (b) 111In-T101 was concentrated preferentially in the tumor; and (c) T101 injected by both the i.p. and i.v. routes bound to tumor and induced antigenic modulation to the same extent as that observed previously in vitro and in human studies.

Animals↗
PubMed1984

Carbon dioxide laser blepharoplasty.

An experience utilizing the carbon dioxide laser for blepharoplasty in a series of 40 patients with an average follow-up of 16 months is reported. The advantages of this method include improved control of intraoperative hemorrhage which occurs because the laser cauterizes small vessels as it cuts tissues. Postoperative ecchymosis and edema are minimal and early rehabilitation occurs. Complications and technical disadvantages are discussed, concluding that the carbon dioxide laser offers a safe alternative with some distinct intraoperative and postoperative advantages to conventional blepharoplasty surgery.

Blepharoptosis↗
PubMed1983

Mannitol-specific enzyme II of the bacterial phosphotransferase system. I. Properties of the purified permease.

The integral membrane protein responsible for the transport and phosphorylation of D-mannitol in Escherichia coli, the mannitol-specific Enzyme II of the phosphotransferase system (Mr = 60,000), has been purified to apparent homogeneity using a modification of a previously published procedure (Jacobson, G. R., Lee, C. A., and Saier, M. H., Jr. (1979) J. Biol. Chem. 254, 249-252). The purified enzyme was dependent on Lubrol PX and phospholipid for maximal activity. It catalyzed both the phosphoenolpyruvate- and the mannitol 1-phosphate-dependent phosphorylation of D-mannitol with high specificity for the accepting sugar and the phosphoryl donor. Both mannitol and mannitol 1-phosphate gave strong substrate inhibition at neutral pH in the transphosphorylation reaction catalyzed by the purified mannitol Enzyme II, while no substrate inhibition by mannitol was observed for the phosphoenolpyruvate-dependent reaction. The purified enzyme did not catalyze hydrolysis of mannitol 1-phosphate, a product of both reactions. Antibody directed against the mannitol Enzyme II inhibited the phosphoenolpyruvate-dependent activity to a greater extent than the transphosphorylation activity. Limited proteolysis with trypsin rapidly inactivated both purified and membrane-bound mannitol Enzyme II, and the purified protein was concomitantly cleaved into fragments with apparent molecular weights of about 29,000. These results show that although the mannitol Enzyme II is an integral membrane protein, a considerable portion of its polypeptide chain must also extend into a hydrophilic environment, presumably the cytoplasm.

Cross Reactions↗