Development of Radiohalogenated Osimertinib Derivatives as Imaging Probes for Companion Diagnostics of Osimertinib.

Osimertinib is an epidermal growth factor receptor (EGFR) tyrosine kinase inhibitor approved for treating non-small-cell lung cancer (NSCLC) with EGFR mutations. Genetic testing is required to detect the mutation for selecting patients who can use osimertinib. Here, we report an attempt to develop nuclear imaging probes that detect the EGFR mutations. We designed and synthesized I-osimertinib and Br-osimertinib with a radioactive or nonradioactive halogen atom at an indole ring in osimertinib and evaluated them. In vitro assays suggested that both I-osimertinib and Br-osimertinib exhibit a specifically high activity toward NSCLC with EGFR L858R/T790M mutations. In biodistribution experiments, the accumulation of both [125I]I-osimertinib and [77Br]Br-osimertinib in tumors with mutations was significantly higher than that in blood and muscle. However, these osimertinib derivatives showed a significantly higher accumulation in lungs than in tumors. Therefore, for detecting the mutations in lung cancer, further structural modifications of the probes are required.

Sensitive Bromine-Labeled Probe D-BPBr for Simultaneous Identification and Quantification of Chiral Amino Acids and Amino-Containing Metabolites Profiling in Human Biofluid by HPLC/MS.

A novel bromine-isotope probe named D-BPBr with stereodynamic chiral recognition characteristics was developed for the labeling, separation, and detection of trace chiral amino acids and amino-containing metabolites. Fourteen enantiomeric pairs of amino acids could be successfully separated and quantified on a reverse-phase C18 column with an HPLC-MS/MS system after D-BPBr labeling. The chromatographic resolution for d,l-amino acid enantiomers ranged from 1.14 to 8.83 with the l-amino acid derivative always eluting prior to the corresponding d-enantiomer. Meanwhile, D-BPBr showed strong chiral selectivity on d-amino acids, and the ratio of mass spectrometric response for D-BPBr labeled d-amino acids to that of l-enantiomers ranged from 1.31 to 12.87 under the same condition. The D-BPBr labeling method was also demonstrated to be highly efficient and selective in separation and quantification of chiral amino acids especially for trace-level d-amino acids in human biofluids including urine and plasma, and in total, 11 l-amino acids and 10 d-amino acids in urine and 11 l-amino acids and 6 d-amino acids in plasma were detected and quantified. Based on the characteristic 2-Da mass difference of precursor ions and the nearly 1:1 peak intensity ratio originated from79Br and 81Br natural isotopes, as well as their dissociation features, 119 amino-containing metabolites were also rapidly detected in urine and plasma samples. Our work indicated that D-BPBr may be a potentially promising tool for the detection of d-amino acid-type biomarkers in disease diagnosis.

Improved production of 76Br, 77Br and 80mBr via CoSe cyclotron targets and vertical dry distillation.

INTRODUCTION: The radioisotopes of bromine are uniquely suitable radiolabels for small molecule theranostic radiopharmaceuticals but are of limited availability due to production challenges. Significantly improved methods were developed for the production and radiochemical isolation of clinical quality 76Br, 77Br, and 80mBr. The radiochemical quality of the radiobromine produced using these methods was tested through the synthesis of a novel 77Br-labeled inhibitor of poly (ADP-ribose) polymerase-1 (PARP-1), a DNA damage response protein. METHODS: 76Br, 77Br, and 80mBr were produced in high radionuclidic purity via the proton irradiation of novel isotopically-enriched Co76Se, Co77Se, and Co80Se intermetallic targets, respectively. Radiobromine was isolated through thermal chromatographic distillation in a vertical furnace assembly. The 77Br-labeled PARP inhibitor was synthesized via copper-mediated aryl boronic ester radiobromination. RESULTS: Cyclotron production yields were 103 ±â€¯10 MBq∙µA-1∙h-1 for 76Br, 88 ±â€¯10 MBq∙µA-1∙h-1 for 80mBr at 16 MeV and 17 ±â€¯1 MBq∙µA-1∙h-1 for 77Br at 13 MeV. Radiobromide isolation yields were 76 ±â€¯11% in a small volume of aqueous solution. The synthesized 77Br-labeled PARP-1 inhibitor had a measured apparent molar activity up to 700 GBq/µmol at end of synthesis. CONCLUSIONS: A novel selenium alloy target enabled clinical-scale production of 76Br, 77Br, and 80mBr with high apparent molar activities, which was used to for the production of a new 77Br-labeled inhibitor of PARP-1. ADVANCES IN KNOWLEDGE: New methods for the cyclotron production and isolation of radiobromine improved the production capacity of 77Br by a factor of three and 76Br by a factor of six compared with previous methods. IMPLICATIONS FOR PATIENT CARE: Preclinical translational research of 77Br-based Auger electron radiotherapeutics, such as those targeting PARP-1, will require the production of GBq-scale 77Br, which necessitates next-generation, high-yielding, isotopically-enriched cyclotron targets, such as the novel intermetallic Co77Se.

Radiobrominated benzimidazole-quinoline derivatives as Platelet-derived growth factor receptor beta (PDGFRß) imaging probes.

Platelet-derived growth factor receptor beta (PDGFRß) affects in numerous human cancers and has been recognized as a promising molecular target for cancer therapies. The overexpression of PDGFRß could be a biomarker for cancer diagnosis. Radiolabeled ligands having high affinity for the molecular target could be useful tools for the imaging of overexpressed receptors in tumors. In this study, we aimed to develop radiobrominated PDGFRß ligands and evaluate their effectiveness as PDGFRß imaging probes. The radiolabeled ligands were designed by modification of 1-{2-[5-(2-methoxyethoxy)-1H- benzo[d]imidazol-1-yl]quinolin-8-yl}piperidin-4-amine (1), which shows selective inhibition profile toward PDGFRß. The bromine atom was introduced directly into C-5 of the quinoline group of 1, or indirectly by the conjugation of 1 with the 3-bromo benzoyl group. [77Br]1-{5-Bromo-2-[5-(2-methoxyethoxy)-1H-benzo[d]imidazol-1-yl]quinoline-8-yl}piperidin-4-amine ([77Br]2) and [77Br]-N-3-bromobenzoyl-1-{2-[5-(2-methoxyethoxy)-1H-benzo[d]imidazol-1-yl]quinolin-8-yl}-piperidin-4-amine ([77Br]3) were prepared using a bromodestannylation reaction. In a cellular uptake study, [77Br]2 and [77Br]3 more highly accumulatd in BxPC3-luc cells (PDGFRß-positive) than in MCF7 cells (PDGFRß-negative), and their accumulation was significantly reduced by pretreatment with inhibitors. In biodistribution experiments, [77Br]2 accumulation was higher than [77Br]3 accumulation at 1 h postinjection. These findings suggest that [76Br]2 is more promising for positron emission tomography (PET) imaging of PDGFRß than [76Br]3.

Comparison of Radioiodine- or Radiobromine-Labeled RGD Peptides between Direct and Indirect Labeling Methods.

Radiolabeled cyclic peptides containing the (Arg-Gly-Asp) RGD sequence for use in positron emission tomography (PET) imaging, single-photon emission computed tomography (SPECT) imaging, and targeted radionuclide therapy of cancer have been reported. In this study, RGD was used as a model carrier peptide for diagnosis and therapy of cancer. To evaluate the characteristics of radiohalogen-labeled peptides, several kinds of labeled RGD peptides [125I-c(RGDyK), 77Br-c(RGDyK), [125I]SIB-c(RGDfK), [77Br]SBrB-c(RGDfK), [125I]SIB-EG2-c(RGDfK), and [77Br]SBrB-EG2-c(RGDfK)] were designed, prepared, and evaluated. In these initial studies, 77Br (t1/2=57.0 h) and 125I (t1/2=59.4 d) were used because of their longer half-lives. Precursor peptides were synthesized using a standard 9-fluorenylmethyloxycarbonyl (Fmoc)-based solid-phase methodology. Radiolabeled peptides were prepared by chloramine-T method or conjugation of RGD peptides with [125I]N-succinimidyl 3-iodobenzoate ([125I]SIB) or [77Br]N-succinimidyl 3-bromobenzoate ([77Br]SBrB). Measurement of the partition coefficients, integrin binding assay, and biodistribution experiments in tumor-bearing mice were performed. 125I and 77Br labeling were successfully performed using similar methods, and in vitro characteristics and biodistributions were similar between the 125I-labeled and corresponding 77Br-labeled peptides. [125I]SIB- and [77Br]SBrB-conjugated RGD peptides showed higher partition coefficients, lower tumor uptakes, and higher intestinal uptake than 125I-c(RGDyK) and 77Br-c(RGDyK). [125I]SIB-EG2-c(RGDfK) and [77Br]SBrB-EG2-c(RGDfK), which possess an ethylene glycol linker, decreased lipophilicity and uptake in intestine compared with [125I]SIB-c(RGDfK) and [77Br]SBrB-c(RGDfK), which possess no linker. However, the improvement in biodistribution of [125I]SIB-EG2-c(RGDfK) and [77Br]SBrB-EG2-c(RGDfK)] was insufficient. In conclusion, directly radiohalogenated c(RGDyK) peptides are potentially more useful for tumor imaging and therapy than indirectly radiohalogenated ones.

Development of a novel radiobromine-labeled sigma-1 receptor imaging probe.

INTRODUCTION: Sigma-1 receptor is a target for tumor imaging. In a previous study, we synthesized a vesamicol analog, (+)-2-[4-(4-bromophenyl)piperidino]cyclohexanol [(+)-pBrV], with a high affinity for sigma-1 receptor, and synthesized radiobrominated (+)-pBrV. This radiobrominated (+)-pBrV showed high tumor uptake in tumor-bearing mice; however, radioactivity accumulation in normal tissues, such as the liver, was high. We assumed that the accumulation of (+)-pBrV in the non-target tissues was partially derived from its high lipophilicity; therefore, we synthesized and evaluated (+)-4-[1-(2-hydroxycyclohexyl)piperidine-4-yl]-2-bromophenol [(+)-BrV-OH], which is a more hydrophilic compound. Although we aimed to develop a PET tracer using 76Br, in these initial studies, we used 77Br because of its longer half-life. METHODS: (+)-[77Br]BrV-OH was synthesized using the chloramine-T method with a radiochemical purity of 95%. Lipophilicity and affinity for sigma-1 receptor of (+)-[77Br]BrV-OH were determined, and biodistribution experiments were performed. We also performed an in vivo blocking study by co-injecting excess amounts of the sigma-1 receptor ligand, SA4503, into mice. RESULTS: The lipophilicity and affinity for sigma-1 receptor of (+)-[77Br]BrV-OH were lower than those of (+)-[77Br]pBrV. (+)-[77Br]BrV-OH also showed high tumor uptake in biodistribution experiments in DU-145 tumor-bearing mice,. Although (+)-[77Br]pBrV was retained in most tissues, (+)-[77Br]BrV-OH was cleared from these tissues. In blocking studies, the co-injection of SA4503 significantly decreased the tumor uptake of (+)-[77Br]BrV-OH. CONCLUSION: These results indicate that (+)-[76Br]BrV-OH has potential as a PET probe for sigma-1 receptor imaging.

Evaluation of aromatic radiobromination by nucleophilic substitution using diaryliodonium salt precursors.

Radiobromine-labeled compounds can be used for positron emission tomography (PET) imaging (ie, 76 Br) and for radiation therapy (ie, 77 Br). However, the commonly used electrophilic substitution reaction using no-carrier-added radiobromide does not always afford the desired product due to the high reactivity of the brominating intermediate. A nucleophilic substitution by bromide, such as radiobromination of iodonium precursors, provides an alternative route for the synthesis of bromo-radiopharmaceuticals. The applicability of aromatic radiobromination by nucleophilic substitution using diaryliodonium salt precursors was evaluated using iodonium model compounds and [76 Br]/[77 Br]bromide. Radiobromination was observed under all conditions tested, in up to quantitative yields. A QMA cartridge treatment method and a base-free method have been developed, and no extra base is needed for either methods. The base-free conditions are mild and afford much cleaner reactions. Up to 20% water is tolerated in the reactions without reducing the radiochemical yields. No-carrier-added and carrier-added reactions afforded similar results. 4-Bromobenzaldehyde and 4-bromobenzoate have been radiosynthesized reliably and in good yields. These results indicate that this method is robust and efficient and thus will provide a route for radiobromination of electron-deficient arenes and an alternative route for the synthesis of bromo-radiopharmaceuticals for biological evaluations.

Calibration setting numbers for dose calibrators for the PET isotopes (52)Mn, (64)Cu, (76)Br, (86)Y, (89)Zr, (124)I.

For PET radionuclides, the radioactivity of a sample can be conveniently measured by a dose calibrator. These devices depend on a "calibration setting number", but many recommended settings from manuals were interpolated based on standard sources of other radionuclide(s). We conducted HPGe gamma-ray spectroscopy, resulting in a reference for determining settings in two types of vessels containing one of several PET radionuclides. Our results reiterate the notion that in-house, experimental calibrations are recommended for different radionuclides and vessels.

Synthesis and Biological Evaluation of (S)-Amino-2-methyl-4-[(76)Br]bromo-3-(E)-butenoic Acid (BrVAIB) for Brain Tumor Imaging.

The novel compound, (S)-amino-2-methyl-4-[(76)Br]bromo-3-(E)-butenoic acid (BrVAIB, [(76)Br]5), was characterized against the known system A tracer, IVAIB ([(123)I]8). [(76)Br]5 was prepared in a 51% ± 19% radiochemical yield with high radiochemical purity (≥98%). The biological properties of [(76)Br]5 were compared with those of [(123)I]8. Results showed that [(76)Br]5 undergoes mixed amino acid transport by system A and system L transport, while [(123)I]8 had less uptake by system L. [(76)Br]5 demonstrated higher uptake than [(123)I]8 in DBT tumors 1 h after injection (3.7 ± 0.4% ID/g vs 1.5 ± 0.3% ID/g) and also showed higher uptake vs [(123)I]8 in normal brain. Small animal PET studies with [(76)Br]5 demonstrated good tumor visualization of intracranial DBTs up to 24 h with clearance from normal tissues. These results indicate that [(76)Br]5 is a promising PET tracer for brain tumor imaging and lead compound for a mixed system A and system L transport substrate.

Development of a Widely Usable Amino Acid Tracer: 76Br-α-Methyl-Phenylalanine for Tumor PET Imaging.

UNLABELLED: Radiolabeled amino acids are superior PET tracers for the imaging of malignant tumors, and amino acids labeled with (76)Br, an attractive positron emitter because of its relatively long half-life (16.2 h), could potentially be a widely usable tumor imaging tracer. In this study, in consideration of its stability and tumor specificity, we designed two (76)Br-labeled amino acid derivatives, 2-(76)Br-bromo-α-methyl-l-phenylalanine (2-(76)Br-BAMP) and 4-(76)Br-bromo-α-methyl-l-phenylalanine (4-(76)Br-BAMP), and investigated their potential as tumor imaging agents. METHODS: Both (76)Br- and (77)Br-labeled amino acid derivatives were prepared. We performed in vitro and in vivo stability studies and cellular uptake studies using the LS180 colon adenocarcinoma cell line. Biodistribution studies in normal mice and in LS180 tumor-bearing mice were performed, and the tumors were imaged with a small-animal PET scanner. RESULTS: Both (77)Br-BAMPs were stable in the plasma and in the murine body. Although both (77)Br-BAMPs were taken up by LS180 cells and the uptake was inhibited by L-type amino acid transporter 1 inhibitors, 2-(77)Br-BAMP exhibited higher uptake than 4-(77)Br-BAMP. In the biodistribution studies, 2-(77)Br-BAMP showed more rapid blood clearance and lower renal accumulation than 4-(77)Br-BAMP. More than 90% of the injected radioactivity was excreted in the urine by 6 h after the injection of 2-(77)Br-BAMP. High tumor accumulation of 2-(77)Br-BAMP was observed in tumor-bearing mice, and PET imaging with 2-(76)Br-BAMP enabled clear visualization of the tumors. CONCLUSION: 2-(77)Br-BAMP exhibited preferred pharmacokinetics and high LS180 tumor accumulation, and 2-(76)Br-BAMP enabled clear visualization of the tumors by PET imaging. These findings suggest that 2-(76)Br-BAMP could constitute a potential new PET tracer for tumor imaging and may eventually enable the wider use of amino acid tracers.

The potential of o-bromo-trans-decalinvesamicol as a new PET ligand for vesicular acetylcholine transporter imaging.

We investigated the characteristics of the regional rat brain distribution of radio-brominated o-bromo-decalinvesamicol (OBDV) in vivo to evaluate its potential as a PET ligand for vesicular acetylcholine transporter (VAChT). In in vivo biodistribution study, the specific brain regional accumulation of [(77) Br]OBDV was revealed 30 min after intravenous injection. The specific brain regional accumulation of [(77) Br]OBDV was significantly inhibited by co-injection of (+/-)-vesamicol. In contrast, no significant inhibition of the uptake of [(77) Br]OBDV in all brain regions was observed with co-injection of (+)-pentazocine (selective σ-1 receptor agonist) and (+)-3-(3-hydroxyphenyl)-N-propylpiperidine, [(+)-3-PPP] (σ-1 and σ-2 receptor agonist) with [(77) Br]OBDV. [(77) Br]OBDV accumulation in VAChT-rich brain regions was observed in ex vivo autoradiography. These results showed that [(77) Br]OBDV selectively bound to VAChT with high affinity in rat brain in vivo. Hence, OVBDV radiolabelled with more suitable (76) Br was suggested to be a potent VAChT ligand for PET.

Development and evaluation of a radiobromine-labeled sigma ligand for tumor imaging.

INTRODUCTION: Sigma receptors are appropriate targets for tumor imaging because they are highly expressed in a variety of human tumors. Previously, we synthesized a vesamicol analog, (+)-2-[4-(4-iodophenyl)piperidino]cyclohexanol ((+)-pIV), with high affinity for sigma receptors, and prepared radioiodinated (+)-pIV. In this study, to develop a radiobromine-labeled vesamicol analog as a sigma receptor imaging agent for PET, nonradioactive and radiobromine-labeled (+)-2-[4-(4-bromophenyl)piperidino]cyclohexanol ((+)-pBrV) was prepared and evaluated in vitro and in vivo. In these initial studies, (77)Br was used because of its longer half-life. METHODS: (+)-[(77)Br]pBrV was prepared by a bromodestannylation reaction with radiochemical purity of 98.8% after HPLC purification. The partition coefficient of (+)-[(77)Br]pBrV was measured. In vitro binding characteristics of (+)-pBrV to sigma receptors were assayed. Biodistribution experiments were performed by intravenous administration of a mixed solution of (+)-[(77)Br]pBrV and (+)-[(125)I]pIV into DU-145 tumor-bearing mice. RESULTS: The lipophilicity of (+)-[(77)Br]pBrV was lower than that of (+)-[(125)I]pIV. As a result of in vitro binding assay to sigma receptors, the affinities of (+)-pBrV to sigma receptors were competitive to those of (+)-pIV. In biodistribution experiments, (+)-[(77)Br]pBrV and (+)-[(125)I]pIV showed high uptake in tumor via sigma receptors. The biodistributions of both radiotracers showed similar patterns. However, the accumulation of radioactivity in liver after injection of (+)-[(77)Br]pBrV was significantly lower compared to that of (+)-[(125)I]pIV. CONCLUSION: These results indicate that radiobromine-labeled pBrV possesses great potential as a sigma receptor imaging agent for PET.

Immuno-PET of the hepatocyte growth factor receptor Met using the 1-armed antibody onartuzumab.

UNLABELLED: The overexpression and overactivation of hepatocyte growth factor receptor (Met) in various cancers has been linked to increased proliferation, progression to metastatic disease, and drug resistance. Developing a PET agent to assess Met expression would aid in the diagnosis and monitoring of responses to Met-targeted therapies. In these studies, onartuzumab, the experimental therapeutic 1-armed monoclonal antibody, was radiolabeled with (76)Br or (89)Zr and evaluated as an imaging agent in Met-expressing cell lines and mouse xenografts. METHODS: (89)Zr-desferrioxamine (df)-onartuzumab was synthesized using a df-conjugate; (76)Br-onartuzumab was labeled directly. Met-binding studies were performed using the human tumor-derived cell lines MKN-45, SNU-16, and U87-MG, which have relatively high, moderate, and low levels of Met, respectively. Biodistribution and small-animal PET studies were performed in MKN-45 and U87-MG xenografts. RESULTS: (76)Br-onartuzumab and (89)Zr-df-onartuzumab exhibited specific, high-affinity Met binding (in the nanomolar range) that was concordant with established Met expression levels. In MKN-45 (gastric carcinoma) xenografts, both tracers cleared slowly from nontarget tissues, with the highest uptake in tumor, blood, kidneys, and lungs. (76)Br-onartuzumab MKN-45 tumor uptake remained relatively constant from 18 h (5 percentage injected dose per gram of tissue [%ID/g]) to 48 h (3 %ID/g) and exhibited tumor-to-muscle ratios ranging from 4:1 to 6:1. In contrast, (89)Zr-df-onartuzumab MKN-45 tumor uptake continued to accumulate from 18 h (10 %ID/g) to 120 h (23 %ID/g), attaining tumor-to-muscle ratios ranging from 20:1 to 27:1. MKN-45 tumors were easily visualized in imaging studies with both tracers at 18 h, but after 48 h (89)Zr-df-onartuzumab image quality improved, with at least 2-fold-greater tumor uptake than nontarget tissues. MKN-45 tumor uptake for both tracers correlated significantly with tumor mass and Met expression and was not affected by the presence of plasma shed Met. CONCLUSION: (89)Zr-df-onartuzumab and (76)Br-onartuzumab specifically targeted Met in vitro and in vivo; (89)Zr-df-onartuzumab achieved higher tumor uptake and tumor-to-muscle ratios than (76)Br-onartuzumab at later times, suggesting that (89)Zr-df-onartuzumab would be better suited to image Met for diagnostic and prognostic purposes.

Radiobromine-labelled tracers for positron emission tomography: possibilities and pitfalls.

The use of positron emission tomography (PET) for radionuclide imaging provides better sensitivity, better spatial and temporal resolution and better quantification accuracy in comparison with single photon emission computed tomography (SPECT). One limitation of PET is the predominant use of short-lived (with half-life up to 2 h) radionuclides. Extension of PET utility might be achieved by the use of more long-lived, "non-conventional" positron emitters. Two positron-emitting isotopes of bromine, 75Br (T1/2 = 96.7 min) and 76Br (T1/2 = 16.2 h), can be considered as labels for targeting proteins and peptides, and for small molecules, which have an optimal imaging time outside the time frame provided by conventional biogenic positron emitters. Variety of tracers might be labelled by electrophilic bromination of activated phenolic rings, electrophilic bromodestannylation and halogen exchange. A major problem is that in vivo metabolism of tracers might lead to formation of radiobromide as a main radiocatabolite. Radiobromide is very slowly excreted, and is distributed in the extracellular space creating high background. Careful tracer design optimisation is required to avoid this obstacle in the introduction of bromine isotopes into PET practice.

Evaluation of excitation functions of proton, ³He- and α-particle induced reactions for production of the medically interesting positron-emitter bromine-76.

Cross section data for production of the medically interesting radionuclide 76Br (T(½)=16.2 h) via the proton induced reactions on 76Se, 77Se, 78Se and 79Br, and ³He- and α-particle induced reactions on 75As were evaluated. The nuclear model codes STAPRE, EMPIRE and TALYS were used to check the consistency in the experimental data and a statistical procedure was applied to derive the recommended excitation functions. A comparison of various production routes of 76Br (and of 75Br) is presented.

An experimental approach to study the biosynthesis of brominated metabolites by the red algal genus Laurencia.

The production of labeled brominated metabolites with radioactive (82)Br in Laurencia species was investigated as part of a study of the biosynthesis of halogenated metabolites from species belonging to the red algal genus Laurencia (Rhodomelaceae, Ceramiales). Radiobromide [(82)Br], thin-layer chromatography (TLC), and TLC-autoradioluminography (ARLG) were used. When cultured in artificial seawater medium (ASP(12)NTA including Na(82)Br) under 16:8 h light:dark (LD) illumination cycles for 24 h, each of the strains of Laurencia, Laurencia japonensis Abe et Masuda, Laurencia nipponica Yamada (laurencin-producing race and laureatin-producing race), and Laurencia okamurae Yamada, produced species- (or race-) specific (82)Br-containing metabolites. In the case of the laurencin-producing race of L. nipponica, laurencin and deacetyllaurencin were found to be produced in approximately 1:1 ratio, though laurencin is the major metabolite in the wild sample. Furthermore, when cultured in the dark, the production rates of brominated metabolites in Laurencia spp. were found to be diminished. The present study strongly indicates that the use of radiobromine [(82)Br] in combination with the TLC-ARLG method is an effective approach for investigating the biosynthesis of brominated metabolites in Laurencia.

Ascertainment of variations in the biological half-lives of bromide and sodium ions in the rat by in vivo gamma-ray measurement of 82Br and 24Na radionuclides.

With the aid of in vivo whole-body counting of the rats (administered simultaneously with the radionuclides (82)Br and (24)Na) by high-resolution gamma-ray spectrometry, we extended the applicability of our experimentally proved hypothesis that the biological half-life of bromide depends on the magnitude of sodium intake rather than on the intake of chloride, as was generally assumed. Variations in the biological half-life of bromide, as a substitute for sodium, were investigated in animals situated in very different physiological states, as regards their metabolic activity.

Bromination from the macroscopic level to the tracer radiochemical level: (76)Br radiolabeling of aromatic compounds via electrophilic substitution.

No-carrier-added (NCA) (76)Br labeling of 4-(5-acetoxy-7-bromobenzoxazol-2-yl)phenyl acetate, a diacetate-protected estrogen-receptor beta (ERbeta) selective ligand, was carried out successfully using [(76)Br]bromide ion. The labeling was achieved via oxidative electrophilic destannylation of an organotin precursor molecule by modification of the leaving group (from Bu(3)Sn to Me(3)Sn) and the addition of methanol to the reaction mixture. The differences between the oxidative bromination reaction under small-scale macroscopic vs tracer level radiochemical conditions were explored in terms of effective brominating agents, which depend greatly on the nature of the solvent during the radiochemical bromination, and the potential interference by trace levels of highly reactive impurities in the reaction that compete for the desired bromination at the NCA level. Our observations, and our development of experimental protocols for successful radiobromination at the tracer NCA-scale, should be applicable to the synthesis of other radiobromine-labeled organic compounds of potential interest as PET radiopharmaceuticals and radiotherapy agents.

Determination of dispersion coefficients using radioisotope data in river environment.

A field tracer experiment using radioisotope (82)Br was performed to estimate the dispersion characteristics of pollutants in river environment. The dispersion coefficients in the longitudinal and transverse directions were determined by using the measured concentration of a radioisotope. Numerical models were applied to calculate the flow and concentration fields at the experimental site. Several numerical simulations were performed to investigate the effects of the numerical results according to variations of the dispersion coefficients. The calculated results for several runs were compared with the measured ones by using statistical methods. The calculated concentrations agreed well with the measured ones.

Synthesis and characterization of [76Br]-labeled high-affinity A3 adenosine receptor ligands for positron emission tomography.

INTRODUCTION: Bromine-76-radiolabeled analogues of previously reported high-affinity A(3) adenosine receptor (A(3)AR) nucleoside ligands have been prepared as potential radiotracers for positron emission tomography. METHODS: The radiosyntheses were accomplished by oxidative radiobromination on the N(6)-benzyl moiety of trimethyltin precursors. Biodistribution studies of the kinetics of uptake were conducted in awake rats. RESULTS: We prepared an agonist ligand {[(76)Br](1'S,2'R,3'S,4'R,5'S)-4'-{2-chloro-6-[(3-bromophenylmethyl)amino]purin-9-yl}-1'-(methylaminocarbonyl)bicyclo[3.1.0]hexane-2',3'-diol (MRS3581)} in 59% radiochemical yield with a specific activity of 19.5 GBq/micromol and an antagonist ligand {[(76)Br](1'R,2'R,3'S,4'R,5'S)-4'-(6-(3-bromobenzylamino)-2-chloro-9H-purin-9-yl)bicyclo[3.1.0]hexane-2',3'-diol (MRS5147)} in 65% radiochemical yield with a specific activity of 22 GBq/micromol. The resultant products exhibited the expected high affinity (K(i) approximately 0.6 nM) and specific binding at the human A(3)AR in vitro. Biodistribution studies in the rat showed uptake in the organs of excretion and metabolism. The antagonist MRS5147 exhibited increasing uptake in testes, an organ that contains significant quantities of A(3)AR, over a 2-h time course, which suggests the presence of a specific A(3)AR retention mechanism. CONCLUSION: We were able to compare uptake of the [(76)Br]-labeled antagonist MRS5147 to [(76)Br]agonist MRS3581. The antagonist MRS5147 shows increasing uptake in the testes, an A(3)AR-rich tissue, suggesting that this ligand may have promise as a molecular imaging agent.