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PubMed2000

Selective in vitro and in vivo binding of [(125)I]ADAM to serotonin transporters in rat brain.

An improved iodinated tracer, ADAM (2-((2-((dimethylamino)methyl)- phenyl)thio)-5-iodophenylamine) for imaging serotonin transporters (SERT) with single photon emission computerized tomography (SPECT), was prepared and characterized. Scatchard analysis of saturation binding of [(125)I]ADAM to rat frontal cortical membrane homogenates gave a K(d) value of 0.15 +/- 0.03 nM and a B(max) value of 194 +/- 65 fmol/mg protein. Biodistribution of [(125)I]ADAM in rat brain after an iv injection showed a high specific binding in the regions of hypothalamus, cortex, striatum, and hippocampus, where SERT are concentrated and the specific binding peaked at 120-240 min postinjection [(hypothalamus-cerebellum)/cerebellum = 4.3 at 120 min post-iv injection]. Moreover, the specific hypothalamic uptake was blocked by pretreatment with SERT selective competing drugs, such as paroxetine and (+)McN5652, while other noncompeting drugs, such as ketanserin, raclopride, and methylphenidate, showed no effect. The radioactive material recovered from rat brain homogenates at 120 min after [(125)I]ADAM injection showed primarily the original compound (>90%), a good indication of in vivo stability in the brain tissues. Both male and female rats showed similar and comparable organ distribution pattern and regional brain uptakes. Ex vivo autoradiograms of rat brain sections (120 min after iv injection of [(125)I]ADAM) showed intense labeling in several regions (olfactory tubercle, lateral septal nucleus, hypothalamic and thalamic nuclei, globus pallidus, central gray, superior colliculus, substantia nigra, interpeduncular nucleus, dorsal and median raphes, and locus coerulus), which parallel known SERT density. These results strongly suggest that the novel tracer ADAM is superior to the congers (i.e., IDAM) reported previously. When labeled with I-123, ADAM will be an improved and useful SPECT imaging agent for SERT in the brain.

Animals↗
PubMed1984

Transport of [125I] IgG and [125I] ovalbumin between lymphocyte-like and macrophage-like rat spleen cells: chromatin binding.

Spleen cells from rats were incubated for 10 min in Eagle's medium containing [125I] IgG or [125I] ovalbumin. Lymphocyte-like and macrophage-like cells were separated by centrifugation in Ficoll-metrizoate solution (d = 1.095). Control spleen cells were incubated in Eagle's medium without [125I] IgG or [125I] ovalbumin and both subpopulations were separated analogically. Lymphocyte-like cells labelled with [125I] IgG or [125I] ovalbumin were incubated for 10 min with control macrophage-like cells and labelled macrophage-like cells with control lymphocyte-like cells. After the incubation time all subpopulations were separated again in Ficoll-metrizoate solution. Radioactivity of [125I] IgG or [125I] ovalbumin was found in cytoplasmic fraction, sap protein fraction (nucleoplasm) and chromatin of control lymphocyte-like and macrophage-like cells. It may be concluded that transport of these potential antigenic compounds occurs directly in lymphocyte-like and macrophage-like cells as well as transport between these two subpopulations.

Animals↗
PubMed1998

In vivo behaviour of rat band 3 cross-linked carrier erythrocytes.

Rat band 3 cross-linked carrier erythrocytes have been prepared. Iodinated carbonic anhydrase has been encapsulated into rat erythrocytes. Then, carrier erythrocytes were labeled with 51chromium. Eventually, these doubly labeled rat RBCs were treated with a band 3 cross-linking reagent, namely bis(sulfosuccinimidyl)suberate (BS3). 51Chromium labeling and 125I CA showed to have cytosolic localization in cross-linked carrier erythrocytes. Estimation of the band 3 cross-linking induced by BS3 on rat carrier erythrocytes has been done rendering values around 25% of band 3 monomer reduction. BS3-cross-linked carrier erythrocytes when injected into rats are mainly targeted to liver as shown by chromium labeling localization. Also, encapsulated CA radioactivity carried by cross-linked carrier rat erythrocytes when injected into rats is localized predominantly in liver as shown by in vivo experiments. Accordingly, cross-linked carrier erythrocytes are highly recognized by peritoneal macrophages as detected by in vitro analyses of macrophage recognition. Thus, our data revealed a targeting of carrier rat erythrocytes induced by cross-linking of band 3 protein by BS3. These results support claims in favor of this animal model as a feasible system to analyze cross-linked carrier erythrocytes survival and targeting as well as the in vivo efficacy of targeting of loaded compounds to liver.

Animals↗
PubMed1983

Assessment of in vivo natural antitumor resistance and lymphocyte. Migration in mice: comparison of 125I-iododeoxyuridine with 111indium-oxine and 51chromium as cell labels.

Clearance of IV-injected tumor cells has been correlated with levels of natural killer (NK) cell activity in recipient animals. Studies of in vivo tumor cell clearance strongly suggest a relationship between levels of NK cell activity and antitumor or antimetastatic effector function. This study outlines the applicability of three radiolabels, [125I]iododeoxyuridine, ( [125I]dUrd), indium-111-oxine chelate ( [111In]Ox), and chromium-51 (51Cr), to studies of tumor cell clearance in vivo. The suitability of these labels for analysis of the in vivo migration patterns of normal lymphocytes or thymus-derived T cells cultivated in vitro (CTC) is also discussed. The results indicate that [111In]Ox and 51Cr compare favorably with the more widely used [125]dUrd as radiolabels for the assessment of IV-injected tumor cell clearance from the lungs of mice. The rates of clearance of both [111In]Ox and 51Cr, like that for [125I]dUrd, correlate closely with levels of NK-cell activity of the host. Further studies with [111In]Ox reveal that treatment of recipients with anti-asialo GM1 serum, a regimen known to suppress NK-cell activity, demonstrates the appropriate reduction in isotope clearance from the lungs after NK suppression. However, clearance data obtained by monitoring levels of radioactivity in the liver after IV injection must be viewed cautiously, since the same cells labeled with [111In]Ox and [125I]dUrd had a different pattern of clearance from the liver. The same inconsistencies in clearance were observed when [111In]Ox and [125I]dUrd were injected intrafootpad (i.f.p.). Similar effects were observed when [111In]Ox or 51Cr was applied to studies of CTC migration. Levels of [111In]Ox and 51Cr remained high in the liver after IV injection, while [125I]dUrd was rapidly cleared. Normal spleen or thymic lymphocytes exhibited the expected homing to the spleen after labeling with [111In]Ox, indicating a suitability of this label for migration studies, except possibly in the liver. These results with CTC and normal lymphocytes should be considered during the formulation of immunotherapy protocols based on cell migration data, since the choice of radiolabel can result in widely divergent levels of radioactivity accumulated in some organs, and may not provide an accurate representation of the presence of viable, intact, or functional cells.

Animals↗
PubMed1995

In vitro and in vivo studies with no-carrier added radioiodinated MIBG.

An important drawback of radioiodinated MIBG prepared by isotopic exchange (maximum specific activity: 100 Ci/mmol) is that a considerable amount of carrier is present in the "ready to use" radiopharmaceutical, thus affecting MIBG uptake in the target cells. To improve the therapeutic utility of MIBG an interesting method was developed for the no-carrier-added (n.c.a.) radioiodination of MIBG via a halodesilylation reaction using 3-trimethylsilybenzylguanidine (TMSBG) as precursor. In order to investigate its possible clinical usefulness, n.c.a. [125I]- and [131I]MIBG was prepared according this procedure. HPLC analysis of the labeling mixture showed that the labeling yield reached values greater than 98% within 20 minutes at 70 degrees C. HPLC fraction containing [131I]MIBG was then recovered and tetrahydrofurane was removed under nitrogen stream. Biodistribution studies were performed in BALB/c normal mice and compared with those obtained using [131I]MIBG prepared by isotopic exchange. Preliminary results showed that at 4 hours myocardial uptake was significantly higher than that of c.a. MIBG (20.3 +/- 0.4 %ID/g). Adrenal uptake gradually increased over time; at 24 hours adrenal uptake was almost twofold that a 1 hour. MIBG uptake was also studied in the human neuroblastoma cell line SH-SY5Y which has a specific uptake system for MIBG. The kinetic parameters for MIBG in this line are: km = 0.27 +/- 0.03 microM, Vmax = 39.5 + 1.8 pmol/10(6) cell/10 min. Preliminary data from in vitro binding studies showed that significantly higher levels of specifically incorporated radioactivity can be achieved using n.c.a. [125I]MIBG instead of c.a. [125I]MIBG.

3-Iodobenzylguanidine↗
PubMed1987

A new experimental model for studies of drug actions on myocardial metabolism. Application to a study of the influence of POCA.

In order to study myocardial metabolism by external detection, quantitative information on the metabolism of a gamma-emitting iodinated fatty acid (IHA) was obtained from time-activity curves of radioactivity in different compartments. A 4-compartment mathematical model was then developed; compartments 0, 1, 2, and 3 correspond respectively to vascular IHA, intracellular IHA, esterified forms, and iodide resulting from mitochondrial oxidation of IHA. We applied this model to a study of the influence of an inhibitor of fatty acid oxidation, POCA (2-[5(4 chlorophenyl) pentyl]-oxirane-2-carboxylate). Isolated rat hearts were perfused for 20 min with Krebs liquid containing increasing concentrations of POCA. IHA was then injected as a bolus at the entrance of the coronary network. The level of cardiac radioactivity was recorded for 30 min and the division into the 4 compartments was simulated at different concentrations of POCA. The drug appeared to increase the myocardial retention of IHA and slow down the speed of degradation and storage; the variations were dose-dependent. These results correspond to those obtained by intracellular analysis. The proposed method, which is reliable and sensitive, is an interesting experiment for pharmacological studies of cardiac metabolism.

Animals↗
PubMed1997

SIMS microscopy: methodology, problems and perspectives in mapping drugs and nuclear medicine compounds.

Secondary ion mass spectrometry (SIMS) microscopy, a mass spectrometry method designed in the 1960s, offers new analytical capabilities, high sensitivity (ppm to ppb region), high specificity and improved lateral resolution, thus facilitating insight into many physiological and biomedical questions. Apart from the sample preparation and the physical characteristics of the detection, the biological model must also be considered. SIMS analysis of diffusible ions and molecules requires strict cryogenic procedures which always begin by a flash-freeze fixation. Cellular integrity can be checked by mapping the major element distributions since intra and extracellular ions are redistributed only in damaged cells. Cryofixing may be followed either by a freeze-fracture methodology or by cryoembedding and dry-cutting. Chemical sample preparation is only used for ions or molecules bound to fixed cell structures. The use of scanning procedures ameliorates the lateral resolution and chromosome imaging has been reported with probe size of below 50 nm. Absolute quantification can be derived for embedded specimen by using internal references included in tissue equivalent resins. The sensitivity is limited by the ionization yield of the tag element and may be further impaired when working at high mass resolution (> or = 5000) to eliminate interfering cluster ions. SIMS drug mapping is usually performed after in vitro administration of a molecule to cell culture systems. Drug detection is accomplished indirectly by detecting a tag isotope naturally present or introduced by labelling, mainly with halogens, 15N and 14C. Molecular imaging with TOF-SIMS is an appealing alternative especially for heavier compounds. We stress some biological problems through a critical review of published SIMS drug studies. SIMS proved useful in assessing the targeting specificity of nuclear medicine pharmaceutics, even after in vivo administration. The first microscopic evidence of a thionamide induced follicular blockade of the iodine organification process is presented in a human sample.

Animals↗
PubMed1997

Cysteine-specific radioiodination of proteins with fluorescein maleimide.

A protocol is described for coupling of carrier-free iodine to protein sulfhydryl groups via fluorescein maleimide. 125I is first coupled to fluorescein maleimide in the presence of chloramine T. Iodination is stopped with sodium thiosulfate, and the iodine-substituted fluorescein maleimide is reacted with free cysteines of the protein. Excess label is then removed by gel-permeation chromatography. The procedure avoids exposition of the protein to oxidative conditions and does not require purification of the labeled carrier reagent. Suitability of the method for a given protein can be evaluated spectrophotometrically without employing radioactivity. It can be applied under denaturing conditions and may be particularly useful with mutant proteins carrying engineered single cysteine residues at sites that are not functionally critical.

Bacterial Proteins↗
PubMedDate not supplied

Metabolism of urographic contrast media.

The metabolism of ionic and nonionic contrast agents was examined in the rabbit and in humans by specific measurement of iodide present in urine at different time intervals after injection of high contrast medium doses. Interest was focused on the experimental model compound C-29, which was investigated using a 125I-labeled compound, permitting a study of iodide release and the appearance of other metabolites in serum, bile, and urine from rabbits. Large, quantitative, individual variations were found, but in most cases th urine collected from both rabbits and humans contained more iodide than had been injected. A mean of 0.07% of total injected iodine was found within three days after injection of the ionic contrast medium metrizoate. The results with rabbits indicated that this figure may increase to 1% using the nonionic media tested. Direct evidence of metabolism of C-29 was found in bile, where up to 35% of the total radioactivity present in the bile 4-6 hours after injection was identified as a metabolite.

Animals↗
PubMed1996

Targeting disseminated melanoma with radiolabelled methylene blue: Comparative bio-distribution studies in man and animals.

Targeted radiotherapy for pigmented melanoma with 3,7-(dimethylamino) phenazathionium chloride [methylene blue (MTB)] labelled with Astatine-211 (211At; alpha-particle emitter) proved to be very effective in animal model systems. Since the results justified an introduction of the treatment to the clinic, the aim of the bio-distribution studies using [123I]-MTB and [131I]-MTB in patients was to confirm selectiveness of radiolabelled MTB uptake in melanoma lesions. The investigations were carried out using planar and SPECT (single photon emission computed tomography) gamma-cameras. A stable uptake of radioiodinated MTB was found in pigmented melanomas in man, with tumour/surrounding tissue and tumour/blood ratios amounting to 9 at 19 h after a single i.v. injection. A time-dependent kinetics of radioiodinated MTB distribution was similar to that observed in human melanoma-bearing athymic mice. Blood radioactivity decreased by about 90% during the first 2.5 min after i.v. injection of the compound (T1/2biol = 0.58 min). Its retention time in various organs was either the same or very similar to that characteristic of the blood. A rapid uptake of radioiodinated MTB in the liver and kidneys confirmed the importance of these organs in excreting the compound: 25-30% of the radioactivity administered was expelled with urine over the first 24 h after the injection. There was no obvious retention of radioiodinated MTB in the brain over the observation period and in the eyes for at least the first 14 h.

Adult↗
PubMed1982

Purification of retrovirus genomic RNA suitable for chemical radioiodination.

An efficient method for the purification of genomic RNA from the retrovirus, caprine arthritis-encephalitis virus, is described. The method utilizes proteinase K, extraction with sodium perchlorate and chromatography on oligo(dT)-cellulose and results in highly purified RNA capable of being chemically iodinated with Na125 I to high specific radioactivity. The iodinated RNA exhibits 80-90% precipitability in 5% trichloroacetic acid and is greater than or equal to 99% sensitive to hydrolysis by ribonuclease. Several alternative methods which are effective for the preparation of eukaryotic ribosomal RNA are unreliable for purification of retrovirus RNA suitable for radioiodination.

Chromatography↗
PubMedDate not supplied

99mTc-labeled MIBG derivatives: novel 99mTc complexes as myocardial imaging agents for sympathetic neurons.

Radioactive-iodine-labeled meta-iodobenzylguanidine (MIBG) is currently being used as an in vivo imaging agent to evaluate neuroendocrine tumors as well as the myocardial sympathetic nervous system in patients with myocardial infarct and cardiomyopathy. It is generally accepted that MIBG is an analogue of norepinephrine and its uptake in the heart corresponds to the distribution of norepinephrine and the density of sympathetic neurons. A series of MIBG derivatives containing suitable chelating functional groups N2S2 for the formation of [TcvO]3+N2S2 complex was successfully synthesized, and the 99mTc-labeled complexes were prepared and tested in rats. One of the compounds, [99mTc]2, tested showed significant, albeit lower, heart uptakes post iv injection in rats (0.21% dose/g at 4 h) as compared to [125I]MIBG (1.7% dose/g at 4 h). The heart uptake of the 99mTc-labeled complex appears to be specific and can be reduced by co-injection with nonradioactive MIBG or by pretreatment with desipramine, a selective norepinephrine transporter inhibitor. Further evaluation of the in vitro uptake of [99mTc]2 in cultured neuroblastoma cells displayed consistently lower, but measurable uptake (approximately 10% of that for [125I]MIBG). These preliminary results suggested that the mechanisms of heart uptake of [99mTc]2 may be related to those for [125I]MIBG uptake. If suitable 99mTc-labeled MIBG derivatives can be further developed, the prevalent availability of 99mTc in nuclear medicine clinics will allow them to be readily available for widespread application.

3-Iodobenzylguanidine↗
PubMed1993

A potential imaging agent for the GABAA receptor: 4-t-butyl-1-(4-[123I]iodophenyl)-2,6,7-trioxabicyclo-[2.2.2]octane.

Based upon the known high toxicity and high antagonist activity of t-butylorthobenzoates towards the GABA receptor complex, 4-t-butyl-1-(4-iodophenyl)-2,6,7-trioxabicyclo[2.2.2]octane 5 and its radioiodo analogues ([123I]-5 and [131I]-5 were prepared as potential markers for the gated chloride channel of GABAA receptors. Mice showed rapid clearance of [131I]-5 from all organs including the brain. The radioactivity was found to proceed into the urine in spite of the high lipophilicity of 5, the high binding affinity of 5 for plasma protein and the apparent chemical stability of 5 in plasma.

Animals↗
PubMedDate not supplied

Assessment of radiochemical design of antibodies using an ester bond as the metabolizable linkage: evaluation of maleimidoethyl 3-(tri-n-butylstannyl)hippurate as a radioiodination reagent of antibodies for diagnostic and therapeutic applications.

Reduction of radioactivity levels in nontarget tissues such as the liver and kidney constitutes a problem to be resolved in diagnostic and therapeutic applications of radiolabeled monoclonal antibodies (mAbs). A new radioiodination reagent with an ester bond to liberate m-iodohippuric acid from covalently conjugated proteins, maleimidoethyl 3-(tri-n-butylstannyl)hippurate (MIH), was recently developed. MIH liberated m-iodohippuric acid from galactosylneoglycoalbumin in murine liver, and the radiometabolite was rapidly eliminated from the liver into urine as an intact structure. In this study, intact IgG and Fab fragment of a mAb against osteogenic sarcoma were radioiodinated with MIH to further assess the applicability of MIH to radioimmunoimaging and therapy. For comparison, a mAb radioiodinated with N-succinimidyl iodobenzoate (SIB) and indium-111 (111In)-labeled mAbs with diethylenetriaminepentaacetic dianhydride (cDTPA) or 1-[4-[(5-maleimidopentyl)amino]benzyl]-ethylenediaminetetraacetic acid (EMCS-Bz-EDTA) were used. Size-exclusion HPLC analysis and cell binding assays indicated the preservation of both structure and antigen binding affinity of radioiodinated MIH-OST7 (IgG). In biodistribution studies in mice, [125I]MIH-OST7 (IgG) showed faster systemic clearance of radioactivity after 24 h postinjection than did [131I]SIB- and [111In]EMCS-Bz-EDTA-OST7 (IgG). [125I]MIH-OST7 (IgG) also exhibited much lower radioactivity levels in nontarget tissues such as the liver and kidney, with higher radioactivity levels in the blood up to 72 h postinjection when compared with [111In]cDTPA-OST7 (IgG). Radioactivity excreted from the mice was found in the urine as m-iodohippuric acid, following administration of [125I]MIH-OST7 (IgG). In athymic mice bearing osteogenic sarcoma, [131I]MIH-OST7 (IgG) indicated higher tumor-to-nontarget ratios of radioactivity at both 24 and 48 h postinjection than [125I]SIB-OST7 (IgG). Although both radioiodinated OST7s showed similar radioactivity levels in the target at 24 h postinjection, a small but significant decrease in the target radioactivity level was observed with [131I]MIH-OST7 (IgG) at 48 h postinjection. In addition, [131I]MIH-OST7 (Fab) showed very rapid cleavage of the ester bond both in vivo and in vitro. These findings indicated that while MIH may be a useful reagent for radioimmunoimaging using IgG, mAb, its application to smaller molecular weight mAbs and radioimmunotherapy would be hindered due to the labile characteristics of the ester bond in plasma. Thus, while the present study reinforced the usefulness of metabolizable linkages for reducing nontarget radioactivity levels, a development of plasma-stable metabolizable linkages is also warranted for radioimmunotherapy and for smaller molecular weight polypeptides.

Animals↗
PubMed1976

Synthesis and purification of radioactive 6beta-iodomethyl-19-norcholest-5(10)-en-3beta-ol.

A method for the synthesis and purification of 6beta-iodomethyl-19-norcholest-5(10)-ene-3beta-ol-131I of greater than 98 mole% chemical purity and greater than 99% radiochemical purity is presented. Carbon-13 and proton NMR were used to establish the identity and purity. Discrepancies in the characterization of this compound, previously published by two other research groups, are discussed.

Cholestenes↗
PubMed1977

Topography of the external surface of the human red blood cell membrane studied with a nonpenetrating label, [125I]diazodiiodosulfanilic acid.

The topography of the external surface of the human red cell membrane has been studied using an impermeant radioactive probe, [125I]diazodiiodosulfanilic acid, which binds covalently to protein groups of the membrane following reaction with intact cells. The pattern of labeling was assessed by sodium dodecyl sulfate-polyacrylamide disc gel electrophoresis followed by sequential analysis of single gels for carbohydrates (by staining with the periodic acid-Schiff (PAS) reagent), for proteins (by staining with Coomassie blue), and for radioactivity (by counting gels sliced in 2-mm segments). The radioactive probe bound to membrane polypeptides with apparent molecular weights of 94,200, 58,100, and 46,500 (Peaks A, B, and C, respectively). Peak A co-migrated with a small periodic acid-Schiff-positive band and protein Band 3 (nomenclature of Steck) (Steck, T.L. (1974)J. Cell Biol. 62: 1-19). Peak B migrated with protein Band(s) 4.5 slightly ahead of the major membrane glycoprotein (PAS-1). Peak C migrated like glycoprotein PAS-2 and protein Band 5, the actin-like, water-soluble membrane protein. In contrast to lactoperoxidase iodination and a number of other probes, [125I]diazodiiodosulfanilic acid reacted minimally with the major membrane glycoprotein, glycophorin. When it was reacted with isolated ghosts, all molecular weight classes of polypeptides were labeled. Treatment of labeled cells with neuraminidase or trypsin altered the glycoprotein staining pattern, but not the radioactive peaks. On the other hand, Pronase eliminated the Mr=94,200 radioactive peak, diminished the other two radioactive peaks, and profoundly changed the glycoprotein and protein staining patterns. Treatment of the membranes of labeled cells in a low ionic strength alkaline medium did not alter radioactive peaks and demonstrated that Peak C differed from the actin-like membrane protein. A nonionic detergent, Triton X-100, solubilized all radioactive components. The studies have defined the binding of [125I]diazodiiodosulfanilic acid to external proteins of the human red cell membrane. Its pattern of reaction differs quantitatively and qualitatively from other commonly used reagents, and it provides a useful additional vectorial probe for the study of membrane topography. Its reactions provide further evidence of the organizational complexity of the red cell membrane and emphasize the fact that interpretation of information derived from the use of membrane probes must take into account the differences resulting from the properties of the probing reagents themselves.

Azo Compounds↗
PubMed1985

Protein S4 is near the elongation factor G binding site in the ribosome.

Using a mild iodination method for protein radioactive labeling, it has been shown that elongation factor G, when bound to the ribosome as EFG-GDP-fusidic acid complex, protects protein S4 from labeling. The results indicate that protein S4 is probably near the ribosomal EFG binding site.

Chloramines↗