Similarities and differences in 111In- and 90Y-labeled 1B4M-DTPA antiTac monoclonal antibody distribution.
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Monoclonal antibodies (MoAb) labeled with 90Y are being used for radioimmunotherapy. Because 90Y is a beta emitter, quantitative information from imaging is suboptimal. With the concept of a "matched pair" of isotopes, 111In is used as a surrogate markerfor90Y. We evaluated the differences in biodistribution between 111In- and 90Y-labeled murine antiTac MoAb directed against the IL-2Ralpha receptor. METHODS: The antiTac was conjugated to the 2-(4-isothiocyanatobenzyl)-6-methyl-diethylenetriamine pentaacetic acid (1B4M-DTPA, also known as MX-DTPA). Nine patients with adult T-cell leukemia were treated. Patients received approximately 185 MBq (5 mCi) 111In-labeled antiTac for imaging and 185-555 MBq (5-15 mCi) 90Y-labeled antiTac for therapy. The immunoreactivity of 111In-labeled antiTac was 90%+/-6%, whereas for 90Y-labeled antiTac, it was 74%+/-12%. RESULTS: The differences in blood and plasma kinetics of the two isotopes were small. The area undemeath the blood radioactivity curve was 1.91 percentage+/-0.58 percentage injected dose (%ID) x h/mL for 111In and 1.86%+/-0.64 %ID x h/mL for 90Y. Urinary excretion of 90Y was significantly greater than that of 111In in the first 24 h (P = 0.001), but later, the excretion of 111In was significantly greater (P = 0.001 to P = 0.04). Core biopsies of bone marrow showed a mean of 0.0029+/-0.0012 %ID/g for 111In, whereas the 90Y concentration was 0.0049+/-0.0021 %ID/g. Analyses of activity bound to circulating cells showed concentrations of 500-30,000 molecules of antiTac per cell. When cell-bound activity was corrected for immunoreactive fraction, the ratio of 111In to 90Y in circulating cells was 1.11+/-0.17. Three biopsies of tumor-involved skin showed ratios of 111In to 90Y of 0.7, 0.9 and 1.1. CONCLUSION: This study shows that differences typically ranging from 10% to 15% exist in the biodistribution between 111In- and 90Y-labeled antiTac. Thus, it appears that 111In can be used as a surrogate marker for 90Y when labeling antiTac with the 1 B4M chelate, although underestimates of the bone marrow radiation dose should be anticipated. (+info)
Segmental colonic transit after oral 67Ga-citrate in healthy subjects and those with chronic idiopathic constipation.
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Measurement of segmental colonic transit is important in the assessment of patients with severe constipation. 111In-diethylenetriamine pentaacetic acid (DTPA) has been established as the tracer of choice for these studies, but it is expensive and not readily available. 67Ga-citrate is an inexpensive tracer and when given orally is not absorbed from the bowel. It was compared with 111In-DTPA in colonic transit studies in nonconstipated control subjects and then in patients with idiopathic constipation. METHODS: Studies were performed after oral administration of 3 MBq (81 microCi) 67Ga-citrate or 4 MBq (108 microCi) 111In-DTPA in solution. Serial abdominal images were performed up to 96 h postinjection, and computer data were generated from geometric mean images of segmental retention of tracer, mean activity profiles and a colonic tracer half-clearance time. RESULTS: There were no differences in segmental retention of either tracer or in mean activity profiles between control subjects and constipated patients. Results in constipated subjects were significantly different from those in controls. The mean half-clearance times of tracer for control subjects were 28.8 h for 67Ga-citrate and 29.9 h for 111In-DTPA in control subjects and 75.0 h for 67Ga-citrate and 70.8 h for 111In-DTPA in constipated patients. CONCLUSION: Oral 67Ga-citrate can be used as a safe alternative to 111In-DTPA for accurate measurement of segmental colonic transit. (+info)
Kinetics of oxidation of aliphatic and aromatic thiols by myeloperoxidase compounds I and II.
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Myeloperoxidase (MPO) is the most abundant protein in neutrophils and plays a central role in microbial killing and inflammatory tissue damage. Because most of the non-steroidal anti-inflammatory drugs and other drugs contain a thiol group, it is necessary to understand how these substrates are oxidized by MPO. We have performed transient kinetic measurements to study the oxidation of 14 aliphatic and aromatic mono- and dithiols by the MPO intermediates, Compound I (k3) and Compound II (k4), using sequential mixing stopped-flow techniques. The one-electron reduction of Compound I by aromatic thiols (e.g. methimidazole, 2-mercaptopurine and 6-mercaptopurine) varied by less than a factor of seven (between 1.39 +/- 0.12 x 10(5) M(-1) s(-1) and 9.16 +/- 1.63 x 10(5) M(-1) s(-1)), whereas reduction by aliphatic thiols was demonstrated to depend on their overall net charge and hydrophobic character and not on the percentage of thiol deprotonation or redox potential. Cysteamine, cysteine methyl ester, cysteine ethyl ester and alpha-lipoic acid showed k3 values comparable to aromatic thiols, whereas a free carboxy group (e.g. cysteine, N-acetylcysteine, glutathione) diminished k3 dramatically. The one-electron reduction of Compound II was far more constrained by the nature of the substrate. Reduction by methimidazole, 2-mercaptopurine and 6-mercaptopurine showed second-order rate constants (k4) of 1.33 +/- 0.08 x 10(5) M(-1) s(-1), 5.25 +/- 0.07 x 10(5) M(-1) s(-1) and 3.03 +/- 0.07 x 10(3) M(-1) s(-1). Even at high concentrations cysteine, penicillamine and glutathione could not reduce Compound II, whereas cysteamine (4.27 +/- 0.05 x 10(3) M(-1) s(-1)), cysteine methyl ester (8.14 +/- 0.08 x 10(3) M(-1) s(-1)), cysteine ethyl ester (3.76 +/- 0.17 x 10(3) M(-1) s(-1)) and alpha-lipoic acid (4.78 +/- 0.07 x 10(4) M(-1) s(-1)) were demonstrated to reduce Compound II and thus could be expected to be oxidized by MPO without co-substrates. (+info)
In vivo localization of [(111)In]-DTPA-D-Phe1-octreotide to human ovarian tumor xenografts induced to express the somatostatin receptor subtype 2 using an adenoviral vector.
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Adenoviral vectors, encoding genes for cell surface antigens or receptors, have been used to induce their high level expression on tumor cells in vitro and in vivo. These induced antigens and receptors can then be targeted with radiolabeled antibodies or peptides for potential radiotherapeutic applications. The purpose of this study was to determine a dosing schema of an adenoviral vector encoding the human somatostatin receptor subtype 2 (AdCMVhSSTr2) for achieving the highest tumor localization of [(111)In]-DTPA-D-Phe1-octreotide, which binds to this receptor, in a human ovarian cancer model as a prelude to future therapy studies. AdCMVhSSTr2 was produced and used to induce hSSTr2 on A427 human nonsmall cell lung cancer cells and on SKOV3.ipl human ovarian cancer cells in vitro, as demonstrated by competitive binding assays using [125I]-Tyr1-somatostatin and [(111)In]-DTPA-D-Phe1-octreotide. Mice bearing i.p. SKOV3.ip1 tumors administered 1 x 10(9) plaque-forming units of AdCMVhSSTr2 i.p. 5 days after tumor cell inoculation, followed by an i.p. injection of [(111)In]-DTPA-D-Phe1-octreotide 2 days later, showed a range of 15.3-60.4% median injected dose/gram (ID/g) in tumor at 4 h after injection compared with 3.5% ID/g when [125I]-Tyr1-somatostatin was administered and 0.3% ID/g when the negative control peptide [125I]-mIP-bombesin was administered. Mice administered a control adenoviral vector encoding the gastrin-releasing peptide receptor did not have tumor localization of [(111)In]-DTPA-D-Phe1-octreotide (<1.6% ID/g), demonstrating specificity of [(111)In]-DTPA-D-Phe1-octreotide for the AdCMVhSSTr2 induced tumor cells. In another set of experiments, the tumor localization of [(111)In]-DTPA-D-Phe1-octreotide was not different 1, 2, or 4 days after AdCMVhSSTr2 injection (31.8, 37.7, and 40.7% ID/g, respectively; P = 0.88), indicating that multiple injections of radiolabeled peptide can be administered with equivalent uptake over a 4-day period. [(111)In]-DTPA-D-Phe1-octreotide tumor localization in animals administered AdCMVhSSTr2 on consecutive days or 2 days apart was 22.4% ID/g and 53.2% ID/g, respectively (P = 0.009) when [(111)In]-DTPA-D-Phe1-octreotide was given 1 day after the second AdCMVhSSTr2 injection. There was no difference in [(111)In]-DTPA-D-Phe1-octreotide localization after a single AdCMVhSSTr2 injection (40.7% ID/g) or two injections of AdCMVhSSTr2 given 1 (45.9% ID/g) or 2 (53.2% ID/g) days apart, where [(111)In]-DTPA-D-Phe1-octreotide was given in each case 4 days after the first AdCMVhSSTr2 injection (P = 0.65). Therefore, two AdCMVhSSTr2 injections did not increase [(111)In]-DTPA-D-Phe1-octreotide tumor localization compared with one injection, which eliminates concerns about an immune response to a second dose of AdCMVhSSTr2. This will be the basis for a therapeutic protocol with multiple administrations of an octreotide analogue labeled with a therapeutic radioisotope. (+info)
Ferritin mutants of Escherichia coli are iron deficient and growth impaired, and fur mutants are iron deficient.
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Escherichia coli contains at least two iron storage proteins, a ferritin (FtnA) and a bacterioferritin (Bfr). To investigate their specific functions, the corresponding genes (ftnA and bfr) were inactivated by replacing the chromosomal ftnA and bfr genes with disrupted derivatives containing antibiotic resistance cassettes in place of internal segments of the corresponding coding regions. Single mutants (ftnA::spc and bfr::kan) and a double mutant (ftnA::spc bfr::kan) were generated and confirmed by Western and Southern blot analyses. The iron contents of the parental strain (W3110) and the bfr mutant increased by 1.5- to 2-fold during the transition from logarithmic to stationary phase in iron-rich media, whereas the iron contents of the ftnA and ftnA bfr mutants remained unchanged. The ftnA and ftnA bfr mutants were growth impaired in iron-deficient media, but this was apparent only after the mutant and parental strains had been precultured in iron-rich media. Surprisingly, ferric iron uptake regulation (fur) mutants also had very low iron contents (2.5-fold less iron than Fur+ strains) despite constitutive expression of the iron acquisition systems. The iron deficiencies of the ftnA and fur mutants were confirmed by Mossbauer spectroscopy, which further showed that the low iron contents of ftnA mutants are due to a lack of magnetically ordered ferric iron clusters likely to correspond to FtnA iron cores. In combination with the fur mutation, ftnA and bfr mutations produced an enhanced sensitivity to hydroperoxides, presumably due to an increase in production of "reactive ferrous iron." It is concluded that FtnA acts as an iron store accommodating up to 50% of the cellular iron during postexponential growth in iron-rich media and providing a source of iron that partially compensates for iron deficiency during iron-restricted growth. In addition to repressing the iron acquisition systems, Fur appears to regulate the demand for iron, probably by controlling the expression of iron-containing proteins. The role of Bfr remains unclear. (+info)
Core RNA polymerase from E. coli induces a major change in the domain arrangement of the sigma 70 subunit.
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Luminescence resonance energy transfer measurements were used to show that binding of E. coli core RNA polymerase induced major changes in interdomain distances in the sigma 70 subunit. The simplest model describing core-induced changes in sigma 70 involves a movement of the conserved region 1 by approximately 20 A and the conserved region 4.2 by approximately 15 A with respect to conserved region 2. The core-induced movement of region 1 (autoinhibition domain) and region 4.2 (DNA-binding domain) provides structural rationale for allosteric regulation of sigma 70 DNA binding properties by the core and suggests that this regulation may not only involve directly the autoinhibition domain of sigma 70 but also could involve a modulation of spacing between DNA-binding domains of sigma 70 induced by binding of core RNAP. (+info)
Transient and steady-state kinetics of the oxidation of substituted benzoic acid hydrazides by myeloperoxidase.
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Myeloperoxidase is the most abundant protein in neutrophils and catalyzes the production of hypochlorous acid. This potent oxidant plays a central role in microbial killing and inflammatory tissue damage. 4-Aminobenzoic acid hydrazide (ABAH) is a mechanism-based inhibitor of myeloperoxidase that is oxidized to radical intermediates that cause enzyme inactivation. We have investigated the mechanism by which benzoic acid hydrazides (BAH) are oxidized by myeloperoxidase, and we have determined the features that enable them to inactivate the enzyme. BAHs readily reduced compound I of myeloperoxidase. The rate constants for these reactions ranged from 1 to 3 x 10(6) M-1 s-1 (15 degrees C, pH 7.0) and were relatively insensitive to the substituents on the aromatic ring. Rate constants for reduction of compound II varied between 6.5 x 10(5) M-1 s-1 for ABAH and 1.3 x 10(3) M-1 s-1 for 4-nitrobenzoic acid hydrazide (15 degrees C, pH 7.0). Reduction of both compound I and compound II by BAHs adhered to the Hammett rule, and there were significant correlations with Brown-Okamoto substituent constants. This indicates that the rates of these reactions were simply determined by the ease of oxidation of the substrates and that the incipient free radical carried a positive charge. ABAH was oxidized by myeloperoxidase without added hydrogen peroxide because it underwent auto-oxidation. Although BAHs generally reacted rapidly with compound II, they should be poor peroxidase substrates because the free radicals formed during peroxidation converted myeloperoxidase to compound III. We found that the reduction of ferric myeloperoxidase by BAH radicals was strongly influenced by Hansch's hydrophobicity constants. BAHs containing more hydrophilic substituents were more effective at converting the enzyme to compound III. This implies that BAH radicals must hydrogen bond to residues in the distal heme pocket before they can reduce the ferric enzyme. Inactivation of myeloperoxidase by BAHs was related to how readily they were oxidized, but there was no correlation with their rate constants for reduction of compounds I or II. We propose that BAHs destroy the heme prosthetic groups of the enzyme by reducing a ferrous myeloperoxidase-hydrogen peroxide complex. (+info)
Expression of somatostatin receptors in oncocytic (Hurthle cell) neoplasia of the thyroid.
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Ten consecutive patients with Hurthle cell lesions of the thyroid (nodule/adenoma/carcinoma) were studied by (111)In-DTPA-D-Phe1-octreotide scintigraphy. Octreotide scintigraphy localized the primary Hurthle cell tumour in eight patients as distinct areas of increased uptake of radionuclide. Two patients with Hurthle cell carcinoma, previously thyroidectomized, had their metastases visualized by octreotide scintigraphy. Northern analyses showed expression of multiple somatostain receptor subtypes. Visualization of the Hurthle cell tumour may be due to a higher expression of somatostatin receptors in the lesions than in surrounding normal thyroid tissue. The tissue/blood (111)In concentration ratios for tumour samples from five patients showed clearly higher values than observed for normal connective tissue, muscle or lymph nodes. A relatively high uptake of (111)In was also observed in goiter tissue, which may lead to misinterpretations. The main indication for octreotide scintigraphy in patients with Hurthle cell carcinoma is suspicion of metastatic disease. (+info)