Radiochemical Labeling Research Articles

Phosphonate-Based Aza-Macrocycle Ligands for Low-Temperature, Stable Chelation of Medicinally Relevant Rare Earth Radiometals and Radiofluorination.

Radioisotopes of fluorine (18F), scandium (43/44Sc, 47Sc), lutetium (177Lu), and yttrium (86Y, 90Y) have decay properties ideally suited for targeted nuclear imaging and therapy with small biologics, such as peptides and antibody fragments. However, a single-molecule strategy to introduce these radionuclides into radiopharmaceuticals under mild conditions to afford inert in vivo complexes is critically lacking. Here, we introduce H4L2 and H4L3, two small-cavity macrocyclic chelator structural isomers bearing a single phosphonate functional group. Potentiometry and spectrophotometry were employed to determine H4L2 and H4L3's ability to form a single [M(L)]- species with metals of different sizes (Sc3+, Lu3+, and Y3+) under physiologically relevant conditions. NMR spectroscopy and density functional theory (DFT) calculations suggest modulation of H4L2 and H4L3's inner-sphere hydration across the Sc3+/Lu3+/Y3+ series. Radiochemical labeling experiments with 18F, 44Sc, 177Lu, and 86Y reveal that H4L2 selectively chelates radioscandium at room temperature with high apparent molar activity (AMA, 462 mCi/μmol), while radiofluorination remains inaccessible. In contrast, H4L3 enables room temperature radiochelation 44Sc, 177Lu, and 86Y (AMA: 96-275 mCi/μmol) and incorporates 18F via the Sc-18F methodology to form [18F][ScF(L3)]2-. In vivo biodistribution analysis at 1 h postinjection confirms the broad utility of H4L3: all four radiochemical complexes clear off-target organs and remain >98% intact in urine metabolite analyses. The scope of room temperature radiochemical labeling, paired with facile 18F incorporation, to afford in vivo compatible complexes exceeds the clinical gold standard chelator DOTA and previously reported acyclic chelators, rendering H4L3 promising for prospective radiopharmaceutical applications.

Radiometallation and photo-triggered release of ready-to-inject radiopharmaceuticals from the solid phase.

The efficient, large-scale synthesis of radiometallated radiopharmaceuticals represents an emerging clinical need which, to date, is inherently limited by time consuming, sequential procedures to conduct isotope separation, radiochemical labeling and purification prior to formulation for injection into the patient. In this work, we demonstrate that a solid-phase based, concerted separation and radiosynthesis strategy followed by photochemical release of radiotracer in biocompatible solvents can be employed to prepare ready-to-inject, clinical grade radiopharmaceuticals. Optimization of resin base, resin loading, and radiochemical labeling capacity are demonstrated with 67Ga and 64Cu radioisotopes using a short model peptide sequence and further validated using two peptide-based radiopharmaceuticals with clinical relevance, targeting the gastrin-releasing peptide and the prostate specific membrane antigen. We also demonstrate that the solid-phase approach enables separation of non-radioactive carrier ions Zn2+ and Ni2+ present at 105-fold excess over 67Ga and 64Cu by taking advantage of the superior Ga3+ and Cu2+ binding affinity of the solid-phase appended, chelator-functionalized peptide. Finally, a proof of concept radiolabeling and subsequent preclinical PET-CT study with the clinically employed positron emitter 68Ga successfully exemplifies that Solid Phase Radiometallation Photorelease (SPRP) allows the streamlined preparation of radiometallated radiopharmaceuticals by concerted, selective radiometal ion capture, radiolabeling and photorelease.

Radiolabeling and in vivo evaluation of lanmodulin with biomedically relevant lanthanide isotopes.

Short-lived, radioactive lanthanides comprise an emerging class of radioisotopes attractive for biomedical imaging and therapy applications. To deliver such isotopes to target tissues, they must be appended to entities that target antigens overexpressed on the target cell's surface. However, the thermally sensitive nature of biomolecule-derived targeting vectors requires the incorporation of these isotopes without the use of denaturing temperatures or extreme pH conditions; chelating systems that can capture large radioisotopes under mild conditions are therefore highly desirable. Herein, we demonstrate the successful radiolabeling of the lanthanide-binding protein, lanmodulin (LanM), with medicinally relevant radioisotopes: 177Lu, 132/135La and 89Zr. Radiolabeling of the endogenous metal-binding sites of LanM, as well exogenous labeling of a protein-appended chelator, was successfully conducted at 25 °C and pH 7 with radiochemical yields ranging from 20-82%. The corresponding radiolabeled constructs possess good formulation stability in pH 7 MOPS buffer over 24 hours (>98%) in the presence of 2 equivalents of natLa carrier. In vivo experiments with [177Lu]-LanM, [132/135La]-LanM, and a prostate cancer targeting-vector linked conjugate, [132/135La]-LanM-PSMA, reveal that endogenously labeled constructs produce bone uptake in vivo. Exogenous, chelator-tag mediated radiolabeling to produce [89Zr]-DFO-LanM enables further study of the protein's in vivo behavior, demonstrating low bone and liver uptake, and renal clearance of the protein itself. While these results indicate that additional stabilization of LanM is required, this study establishes precedence for the radiochemical labeling of LanM with medically relevant lanthanide radioisotopes.

Comparison of three different methods in [68 Ga]Ga-PSMA11 radiolabeling.

In this study, quality control parameters such as radiochemical yield, radiochemical purity, and in vitro stability of gallium (68 Ga)-prostate-specific membrane antigen-11 ([68 Ga]Ga-PSMA11) radiopharmaceutical obtained in a research laboratory with three different synthesis algorithms were evaluated and compared. Gallium (68 Ga) chloride precursor to be used in labeling in all three methods was obtained by using ITG brand 68 Ge/68 Ga generator. The first method for the [68 Ga]Ga-PSMA11 radiopharmaceutical was performed with the automated synthesis module, which is widely used in clinical practice. Its radiochemical yield, quality assurance, and stability met expectations. Radiolabeling success, suitability of quality control parameters, and in vitro stability of [68 Ga]Ga-PSMA11 radiopharmaceutical performed with ANMI kit were examined. The final product showed success in 68 Ga-complexation kinetics. All quality control criteria performed met the expectation for clinical applications. Direct cold labeling of PSMA11 ligand with sodium bicarbonate buffer was examined. Results were similar to the ANMI kit. Considering that all three methods are successful in radiochemical labeling, labeling with NaHCO3 buffer shows the labeling preference when we choose the cheap, practical, and easy labeling option.

Homologous Structural, Chemical, and Biological Behavior of Sc and Lu Complexes of the Picaga Bifunctional Chelator: Toward Development of Matched Theranostic Pairs for Radiopharmaceutical Applications.

The radioactive isotopes scandium-44/47 and lutetium-177 are gaining relevance for radioimaging and radiotherapy, resulting in a surge of studies on their coordination chemistry and subsequent applications. Although the trivalent ions of these elements are considered close homologues, dissimilar chemical behavior is observed when they are complexed by large ligand architectures due to discrepancies between Lu(III) and Sc(III) ions with respect to size, chemical hardness, and Lewis acidity. Here, we demonstrate that Lu and Sc complexes of 1,4-bis(methoxycarbonyl)-7-[(6-carboxypyridin-2-yl)methyl]-1,4,7-triazacyclononane (H3mpatcn) and its corresponding bioconjugate picaga-DUPA can be employed to promote analogous structural features and, subsequently, biological properties for coordination complexes of these ions. The close homology was evidenced using potentiometric methods, computational modeling, variable temperature mass spectrometry, and pair distribution function analysis of X-ray scattering data. Radiochemical labeling, in vitro stability, and biodistribution studies with Sc-47 and Lu-177 indicate that the 7-coordinate ligand environment of the bifunctional picaga ligand is compatible with biological applications and the future investigation of β-emitting, picaga-chelated Sc and Lu isotopes for radiotherapy.

Radioactive Labeling of Milk-Derived Exosomes with 99mTc and In Vivo Tracking by SPECT Imaging.

Over the last decade, exosomes from diverse biological sources have been proposed as new natural platforms in drug delivery. Translation of these nanometric tools to clinical practice requires deep knowledge of their pharmacokinetic properties and biodistribution. The pharmacokinetic properties of exosomes are sometimes evaluated using biochemical and histological techniques that are considerably invasive. As an alternative, we present radiochemical labeling of milk-derived exosomes based on reduced 99mTc (IV) without modifying biological and physicochemical properties. This approach enables longitudinal tracking of natural exosomes by non-invasive single photon emission computed tomography (SPECT) imaging and the evaluation of their pharmacokinetic properties according to the route of administration.

Synthesis and characterization of boron fenbufen and its F-18 labeled homolog for boron neutron capture therapy of COX-2 overexpressed cholangiocarcinoma

Boron neutron capture therapy (BNCT) is a binary therapy that employs neutron irradiation on the boron agents to release high-energy helium and alpha particles to kill cancer cells. An optimal response to BNCT depends critically on the time point of maximal 10B accumulation and highest tumor to normal ratio (T/N) for performing the neutron irradiation. The aggressive cholangiocarcinoma (CCA) representing a liver cancer that overexpresses COX-2 enzyme is aimed to be targeted by COX-2 selective boron carrier, fenbufen boronopinacol (FBPin). Two main works were performed including: 1) chemical synthesis of FBPin as the boron carrier and 2) radiochemical labeling with F-18 to provide the radiofluoro congener, m-[18F]fluorofenbufen ester boronopinacol (m-[18F]FFBPin), to assess the binding affinity, cellular accumulation level and distribution profile in CCA rats. FBPin was prepared from bromofenbufen via 3 steps with 82% yield. The binding assay employed [18F]FFBPin to compete FBPin for binding to COX-1 (IC50=0.91±0.68μM) and COX-2 (IC50=0.33±0.24μM). [18F]FFBPin-derived 60-min dynamic PET scans predict the 10B-accumulation of 0.8–1.2ppm in liver and 1.2–1.8ppm in tumor and tumor to normal ratio=1.38±0.12. BNCT was performed 40–55min post intravenous administration of FBPin (20–30mg) in the CCA rats. CCA rats treated with BNCT display more tumor reduction than that by NCT with respect of 2-[18F]fluoro-2-deoxy glucose uptake in the tumor region of interest, 20.83±3.00% (n=12) vs. 12.83±3.79% (n=10), P=0.05. The visualizing agent [18F]FFBPin resembles FBPin to generate the time-dependent boron concentration profile. Optimal neutron irradiation period is thus determinable for BNCT. A boron-substituted agent based on COX-2-binding features has been prepared. The moderate COX-2/COX-1 selectivity index of 2.78 allows a fair tumor selectivity index of 1.38 with a mild cardiovascular effect. The therapeutic effect from FBPin with BNCT warrants a proper COX-2 targeting of boron NSAIDs.

(177) Lu-5-Fluorouracil a potential theranostic radiopharmaceutical: radiosynthesis, quality control, biodistribution, and scintigraphy.

The aim of this study is to develop (177) Lu-5-Flourouracil as a potential cancer therapeutic radiopharmaceutical. 5-Flourouracil (5-FU) is widely accepted as an anticancer drug of broad spectrum fame. The labeling of 5-FU was carried out at different set of experimental conditions using high specific activity of (177) LuCl3 . The optimum conditions for maximum radiochemical yield was set: 5-FU (5 mg), (177) LuCl3 (185 MBq), diethylenetriaminepentaacetic acid (10 µg), reaction volume (2 mL), pH (5.5), temperature (80°C), and reaction time (20 min). The radiochemical labeling was assessed with Whatman No. 2 paper, instant thin layer chromatographic, and radio-HPLC, which revealed >94% labeling results with sufficient stability up to 6 h. Serum stability study also showed (177) Lu-5-FU promising stability. Biodistribution study in normal rats and rabbits showed liver, stomach, kidney, and heart as area of increased tracer accumulation just after injection, which decreased to 1.4%, 0.4%, 0.2%, and 0.39% ID/g, respectively, after 72 h. Glomerular filtration rate and cytotoxicity study results of (177) Lu-5-FU showed it had no adverse effect on renal function and nontoxic to blood cells. The promising characteristics of (177) Lu-5-FU, that is, clever elimination from kidney and nontoxic nature toward blood cells make it the radiopharmaceutical for further testing in patients for therapeutic purposes.

Abstract 1814: Effective auger electron radioimmunotherapy using modified anti-HER2 antibody with nuclear localizing signal

Abstract Objective: Radioimmunotherapy has an advantage in treating tumors scattered in the body. Auger electrons have high cell killing effect because of its high LET, and the short range can prevent damages to normal tissue. However, to achieve higher therapeutic effect, it is desirable to deliver Auger electrons into nucleus and locate close to DNA. The use of nuclear localizing signal (NLS) has been proposed to transport Auger electron emitters into nucleus. To evaluate the cytotoxicity of nuclear localized Auger electron emitter, we performed in-vitro assay using 111In-labeled anti-HER2 antibody attached with NLS peptides to human breast cancer cell lines overexpressing HER2. Material and methods: Trastuzumab, a monoclonal antibody to HER2, was conjugated with CHX-A”-DTPA (DTPA) and derivatized with sulfosuccinimdyl-4-(N-maleimidomethyl) cyclohexane-1carboxylate (sulfo-SMCC) for reaction with synthetic 13-mer NLS peptides (CGYGPKKKRKVGG). 111In was labeled with either trastuzumab-DTPA or NLS-trastuzumab-DTPA, NLS-trastuzumab-DTPA-S carried approximately 4 NLS peptides per antibody and NLS-trastuzumab-DTPA-L carried 10. The radiochemical labeling of 111In-NLS-trastuzumab and 111In-trastuzumab was determined by HPLC. Human mammary epithelial cells HMEpC and two types of human breast cancer cells with low and high HER2 expression, MCF-7 and SKBR3, respectively, were employed for in-vitro study. Nuclear accumulation of 111In was measured in SKBR3 cells by subcellular fraction. Cell viability was evaluated with dye-based cell viability assays in all cell lines. DNA damages were examined with γ-H2AX immunohistochemistry in SKBR3 cells. Results: Nuclear uptake of 111In was 1.3-1.5-fold higher in SKBR3 cells treated with 111In-NLS-trastuzumab than 111In-trastuzumab and increased depending on the number of NLS peptides. Cell viability was significantly reduced with 111In-NLS-trastuzumab comparing 111In-trastuzumab in SKBR3 cells. Both of 111In-NLS-trastuzumab had little or no cytotoxicity on MCF-7 cells and HMEpC cells. SKBR3 cells treated with 111In-NLS-trastuzumab-L showed more γ-H2AX foci than 111In-trastuzumab. Conclusions: The cytotoxicity of 111In-NLS-trastuzumab was higher than that of 111In-trastuzumab by inducing more DNA damages in HER2-overexpressing human breast cancer cells. These data demonstrate that delivery of 111In into cell nucleus by anti-HER2 antibody harboring NLS is an effective strategy for targeted cell killing of the human cancer cells overexpressing HER2. Citation Format: Huizi Li, Sumitaka Hasegawa, Tadashi Kamada, Tsuneo Saga. Effective auger electron radioimmunotherapy using modified anti-HER2 antibody with nuclear localizing signal. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1814. doi:10.1158/1538-7445.AM2015-1814

Fluorine-18 radiochemistry, labeling strategies and synthetic routes.

Fluorine-18 is the most frequently used radioisotope in positron emission tomography (PET) radiopharmaceuticals in both clinical and preclinical research. Its physical and nuclear characteristics (97% β+ decay, 109.7 min half-life, 635 keV positron energy), along with high specific activity and ease of large scale production, make it an attractive nuclide for radiochemical labeling and molecular imaging. Versatile chemistry including nucleophilic and electrophilic substitutions allows direct or indirect introduction of 18F into molecules of interest. The significant increase in 18F radiotracers for PET imaging accentuates the need for simple and efficient 18F-labeling procedures. In this review, we will describe the current radiosynthesis routes and strategies for 18F labeling of small molecules and biomolecules.

Determination ofIn VivoBehavior of Mitomycin C-Loaded O/W Soybean Oil Microemulsion and Mitomycin C Solution Via Gamma Camera Imaging

In this study, a microemulsion system was evaluated for delivery of mitomycin C (MMC). To track the distribution of the formulated drug after intravenous administration, radiochemical labeling and gamma scintigraphy imaging were used. The aim was to evaluate a microemulsion system for intravenous delivery of MMC and to compare its in vivo behavior with that of the MMC solution. For microemulsion formulation, soybean oil was used as the oil phase. Lecithin and Tween 80 were surfactants and ethanol was the cosurfactant. To understand the whole body localization of MMC-loaded microemulsion, MMC was labeled with radioactive technetium and gamma scintigraphy was applied for visualization of drug distribution. Radioactivity in the bladder 30 minutes after injection of the MMC solution was observed, according to static gamma camera images. This shows that urinary excretion of the latter starts very soon. On the other hand, no radioactivity appeared in the urinary bladder during the 90 minutes following the administration of MMC-loaded microemulsion. The unabated radioactivity in the liver during the experiment shows that the localization of microemulsion formulation in the liver is stable. In the light of the foregoing, it is suggested that this microemulsion formulation may be an appropriate carrier system for anticancer agents by intravenous delivery in hepatic cancer chemotherapy.

HPLC ANALYSIS OF RADIOGALLIUM LABELED PROTEINS USING A TWO-SOLVENT SYSTEM

A two-solvent system was used in high-performance liquid chromatography (HPLC) analysis of radiolabeled pharmaceutically active proteins. The proteins were successively labeled with [67Ga]-gallium chloride separately after conjugation with diethylenetriaminepentaacetic acid dianhydride (ccDTPA). The radiolabelded proteins were purified using size exclusion chromatography and/or solid-phase purification. A two-solvent system consisting sodium acetate/citrate buffer was used for the determination of radiochemical purity (90–98%), specific activity (22–23 TeBq/mM), and labeling efficiency (70–82%) at optimized conditions in each case. The retention times for insulin, β-HCG, gonadotropin, erythropoietin, glucagon, (1-24-corticotrophin, rituximab, oxytocine, and streptokinase were 17.2, 14.8, 18.31, 12.77, 20.0, 21.97, 15.2, and 17.2 min, respectively, while for 67Ga3+ cation and/or 67Ga-DTPA were at the range of 2.70–2.90 min. This is a simple and inexpensive HPLC method for the analysis of radiolabeled peptides and proteins using reverse-phase columns.

Activity of Lambda-Exonuclease on Surface-Attached Oligonucleotide Detected by Acoustic Wave Device and Radiochemical Labeling

Single-strand 25-mer oligonucleotides have been attached to the surface of a 9-MHz acoustic wave sensor incorporated into a flow-through configuration. This was achieved by an online interaction of the biotinylated probe with chemisorbed neutravidin. Duplex formation with complementary 25-mer was monitored by acoustic wave detection in real time. Regeneration of the probe-modified surface was achieved using online introduction of λ-exonuclease, an enzyme that digests a single strand of double-stranded DNA beginning with the 5′ end, cleaving single nucleotides as it progresses. Thus, with the 5′ end of the probe strand remaining inaccessible because of the biotin-neutravidin linkage, the target strand was successfully removed by enzymatic digestion. The results of the acoustic wave work are correlated with analogous experiments involving oligonucleotides labeled with 32P.

Evolutionary Differences in Glycosaminoglycan Fine Structure Detected by Quantitative Glycan Reductive Isotope Labeling

To facilitate qualitative and quantitative analysis of glycosaminoglycans, we tagged the reducing end of lyase-generated disaccharides with aniline-containing stable isotopes (12C6 and 13C6). Because different isotope tags have no effect on chromatographic retention times but can be discriminated by a mass detector, differentially isotope-tagged samples can be compared simultaneously by liquid chromatography/mass spectrometry and quantified by admixture with known amounts of standards. The technique is adaptable to all types of glycosaminoglycans, and its sensitivity is only limited by the type of mass spectrometer available. We validated the method using commercial heparin and keratan sulfate as well as heparan sulfate isolated from mutant and wild-type Chinese hamster ovary cells, and select tissues from mutant and wild-type mice. This new method provides more robust, reliable, and sensitive means of quantitative evaluation of glycosaminoglycan disaccharide compositions than existing techniques allowing us to compare the chondroitin and heparan sulfate compositions of Hydra vulgaris, Drosophila melanogaster, Caenorhabditis elegans, and mammalian cells. Our results demonstrate significant differences in glycosaminoglycan structure among these organisms that might represent evolutionarily distinct functional motifs.

Direct Procedure for the Production of211At-Labeled Antibodies with an ε-Lysyl-3-(Trimethylstannyl)Benzamide Immunoconjugate

(211)At-labeled tumor-specific antibodies have long been considered for the treatment of disseminated cancer. However, the limited availability of the nuclide and the poor efficacy of labeling procedures at clinical activity levels present major obstacles to their use. This study evaluated a procedure for the direct astatination of antibodies for the production of clinical activity levels. The monoclonal antibody trastuzumab was conjugated with the reagent N-succinimidyl-3-(trimethylstannyl)benzoate, and the immunoconjugate was labeled with astatine. Before astatination of the conjugated antibody, the nuclide was activated with N-iodosuccinimide. The labeling reaction was evaluated in terms of reaction time, volume of reaction solvent, immunoconjugate concentration, and applied activity. The quality of the astatinated antibodies was determined by in vitro analysis and biodistribution studies in nude mice. The reaction proceeded almost instantaneously, and the results indicated a low dependence on immunoconjugate concentration and applied activity. Radiochemical labeling yields were in the range of 68%-81%, and a specific radioactivity of up to 1 GBq/mg could be achieved. Stability and radiochemical purity were equal to or better than those attained with a conventional 2-step procedure. Dissociation constants for directly astatinated, conventionally astatinated, and radioiodinated trastuzumab were 1.0+/-0.06 (mean+/-SD), 0.44+/-0.06, and 0.29+/-0.02 nM, respectively. The tissue distribution in non-tumor-bearing nude mice revealed only minor differences in organ uptake relative to that obtained with the conventional method. The direct astatination procedure enables the high-yield production of astatinated antibodies with radioactivity in the amounts required for clinical applications.

Synthesis, biological evaluation and radiochemical labeling of a dansylhydrazone derivative as a potential imaging agent for apoptosis

To develop a small molecule-based tracer for in vivo apoptosis imaging, dansylhydrazone (DFNSH) was synthesized in 93% yield in less than 30 min. The biological evaluation showed that DFNSH selectively binds to paclitaxel-induced apoptotic cancer cells. The high magnification fluorescent images demonstrate that DFNSH is localized within the cytoplasm of cells that bound Alexa ® 488 labeled annexin V on the plasma membrane. [ 18F]-DFNSH ([ 18F]- 3) was synthesized and isolated in 50–60% radiochemical yields, based on [K/K 222] 18F, with a synthesis time of 50 min (EOB). The straightforward preparation of fluorine-18 labeled 3 makes it a promising tracer for PET imaging of apoptosis.

Total synthesis and evaluation of [18F]MHMZ

Radiochemical labeling of MDL 105725 using the secondary labeling precursor 2-[(18)F]fluoroethyltosylate ([(18)F]FETos) was carried out in yields of approximately 90% synthesizing [(18)F]MHMZ in a specific activity of approximately 50MBq/nmol with a starting activity of approximately 3GBq. Overall radiochemical yield including [(18)F]FETos synthon synthesis, [(18)F]fluoroalkylation and preparing the injectable [(18)F]MHMZ solution was 42% within a synthesis time of approximately 100 min. The novel compound showed excellent specific binding to the 5-HT(2A) receptor (K(i)=9.0 nM) in vitro and promising in vivo characteristics.

마이크로파를 이용한 간담도계 영상 방사성의약품99mTc-Mebrofenin의 합성

Tc-Labeled N-(3-bromo-2,4,6-trimethylacetanilido)-iminodiacetic acid (Tc-mebrofenin) has been used to assess the functional integrity of the hepatobiliary system. A fast and convenient procedure was established for the synthesis of mebrofenin and radiochemical labeling with Tc. 3-Bromo-2,4,6-trimethylacetanilide was synthesized in large scale under microwave irradiation (300 W, 5 min) by acylation (60% yield) and bromination (96% yield). And it was treated with the disodium salt of iminodiacetic acid under microwave irradiation (300 W, 20 min) to afford mebrofenin in 86% yield. The attractive feature in this procedure involves microwave irradiation that results in shorter reaction times, higher yields, cleaner reaction products and an easier work-up than classical heating. The synthesis time of 2,4,6trimethylacetanilide was reduced from 1 h to 5 min; the synthesis time of 3-bromo-2,4,6-trimethylacetanilide was reduced from 24 h to 5 min; the synthesis time of mebrofenin was reduced from 48 h to 20 min, when compared with that of the conventional method. Iminodiacetic acid of mebrofenin is a metal complexing moiety that strongly binds Tc. Tc-Mebrofenin between the reduced technetium, prepared by a stannous reduction of the pertechnetate ion, and mebrofenin was formed under microwave irradiation (300 W, 1 min). The synthesis time of Tc-mebrofenin was reduced from 30 min to 1 min, when compared with that of the conventional method. 99.5% of Labeling efficiency (LE) of Tc-mebrofenin was determined by using radio-TLC.

Synthesis and Radiochemical Labeling of N‐(2,6‐Diisopropylacetanilido)‐Iminodiacetic Acid and Its Analogues under Microwave Irradiation: A Hepatobiliary Imaging Agent

AbstractThis paper describes a fast and convenient procedure for the synthesis of 2,6‐diisopropylacetanilidoiminodiacetic acid and its analogues and radiochemical labeling with 99mTc. They were synthesized in large scale under microwave irradiation in very short reaction times. A microwave reactor offers a rapid and efficient methodology for the formation of a considerable range of IDA derivatives. The method is expected to be applicable to the preparation of radiopharmaceuticals.

High surface density immobilization of oligonucleotide on silicon.

Oligonucleotide (11-mer) molecules are immobilized on silicon in high surface population using either a permanent thioether bond or a chemo-selectively reversible disulfide bond to the surface thiol functionality. Substrate hydroxy groups are first silanized with an 11 carbon trichlorosilane containing a terminal, protected thiol moiety. Oligonucleotide modified with a tether possessing a terminal thiol group is further derivatized with a water-soluble, halobenzylic bifunctional reagent, which allows the complete conjugate to be attached to the surface through a permanent thioether bond. Alternatively, the oligonucleotide-tether complex can be combined with a pyridyldisulfide compound, which, in turn, facilitates the formation of a reversible disulfide bond with surface thiol. The amount of immobilized oligonucleotide was determined by radiochemical labeling with 32P. Additional verification of surface amounts was obtained from X-ray photoelectron spectroscopic analysis of substrates. The results of the immobilization protocols are compared with the oligonucleotide surface population achieved through the conventional silanizing agent, mercaptopropyltrimethoxysilane. Finally, a preliminary confirmation of duplex formation of a TTU-attached 25-mer with its complementary strand is outlined.