Iminodiacetic Acid as a Novel Metal-Binding Pharmacophore for New Delhi Metallo-β-lactamase Inhibitor Development

The fungal natural product aspergillomarasmine A (AMA) has been identified as a noncompetitive inhibitor of New Delhi metallo-β-lactamase-1 (NDM-1) that inhibits by removing ZnII from the active-site. The nonselective metal-chelating properties and difficult synthesis and derivatization of AMA have hindered the development of this scaffold into a potent and selective inhibitor of NDM-1. Iminodiacetic acid (IDA) has been identified as the metal-binding pharmacophore (MBP) core of AMA that can be leveraged for inhibitor development. Herein, we report the use of IDA for fragment-based drug discovery (FBDD) of NDM-1 inhibitors. IDA (IC50 =120 μM) was developed into inhibitor 23 f (IC50 =8.6 μM, Ki =2.6 μM), which formed a ternary complex with NDM-1, as evidenced by protein thermal-shift and native-state electrospray ionization mass spectrometry (ESI-MS) experiments. Combining mechanistic analysis with inhibitor derivatization, the use of IDA as an alternative AMA scaffold for NDM-1 inhibitor development is detailed.

Synthesis and Biocompatibility Studies of New Iminodiacetic Acid Derivatives

BACKGROUND

Iminodiacetic acid (IDA) derivatives can be used as ligands to form complexes with technetium, with potential application as hepatobiliary diagnostic agents. The aim of this study was to synthesize five novel IDA derivatives and to compare their effects on plasma haemostasis with clinically approved ligands for technetium complexation.

METHODS

The influence of synthesized IDA derivatives on plasma haemostasis was evaluated spectrophotometrically by clot formation and lysis test (CL-test), coagulation assay, Prothrombin Time and Activated Partial Tromboplastin Time. The effects of the tested compounds on erythrocytes were assessed using haemolysis assays, microscopy and flow cytometry studies.

RESULTS

Despite their significant influence on the kinetic parameters of the process of clot formation and fibrinolysis, the tested ligands, at potential diagnostic concentrations, did not alter the overall potential of clot formation and lysis (CLAUC). At potential diagnostic concentrations (0.4 μmol/mL) all the tested compounds showed no adverse effects on the membranes of RBCs (Red Blood Cells).

CONCLUSION

IDA derivatives with methoxy substituents in aromatic ring, exert multidirectional effects on plasma haemostasis and should be considered safe as their significant impacts were mostly observed at 4 μmol/mL, which is about 10-fold higher than the theoretical plasma concentrations of these compounds.

Bone selective protective effect of a novel bone-seeking estrogen on trabecular bone in ovariectomized rats

The drawbacks of estrogen restrict the clinical use of hormone replacement therapy, and it would be most helpful to explore new estrogenic substances that could prevent bone loss and be free from any adverse effects. We synthesized a new compound named bone-seeking estrogen (SE2) by combining 17β-estradiol (E2) with iminodiacetic acid through the Mannich reaction. E2 and SE2 were labeled with isotope (3)H, and the tissue distribution tests of E2-(3)H and SE2-(3)H were analyzed by the radioactivity. The specific nuclear binding of E2 and SE2 in osteoblasts was measured. SE2 exhibited significantly greater affinity for bone but lower affinity for ovary and uterus than did E2, and SE2 maintained a high affinity for the estrogen receptor alpha similar to that of E2. SE2 administration did not induce uterine hypertrophy. Body weight increase was significantly suppressed by treatment with E2 but not by SE2 after ovariectomy (OVX). SE2 decreased bone turnover as E2 after OVX detected by serum biochemical markers. Bone histology and micro-CT analysis revealed that SE2 administration, similar to E2, could improve bone mass and trabecular architecture after OVX. Biomechanical analyses showed that SE2 treatment effectively increased mechanical properties after OVX. The results suggested that SE2 was effective in preventing OVX-induced bone loss and exhibited few side effects on body weight and uterine hypertrophy, which was beneficial in reducing the adverse effects caused by E2. SE2 may be a better choice than E2 for the prevention of postmenopausal osteoporosis.

Preparation of iminodiacetic acid functionalized multi-walled carbon nanotubes and its application as sorbent for separation and preconcentration of heavy metal ions

In this paper, a novel material was prepared with functionalizing multi-walled carbon nanotubes (MWCNTs) using iminodiacetic acid (IDA) and characterized by FT-IR. Isotherm and kinetics of adsorption were studied and the experimental data fitted the Langmuir model and pseudo-second-order equation very well. An on-line method for simultaneous determination of trace V (V), Cr (VI), Pb (II), Cd (II), Co (II), Cu (II) and As (III) in biological samples was developed using this material as sorbent coupled with inductively coupled plasma mass spectrometry (ICP-MS). A series of experimental parameters, including sample pH, sample flow rate and loading time, eluting solution and the effect of interfering ions have been investigated systematically. Under the optimum experimental conditions, the enrichment factors for above metal ions were ranged from 66 to 101. Detection limit (3 s) was achieved at 1.3, 1.2, 0.70, 0.40, 2.5, 3.4, 0.79 ng L(-1), respectively. At the 1.0 μg L(-1) level, the precision (RSD, %) for 11 replicate measurements was from 1.0 to 4.0. In spiked biological samples, good recoveries (n=3) were obtained in the range of 90-110%. These results had proved that the proposed method was with good accuracy and could be applied to the analysis of trace metal ions in biological samples.

Spacer-based selectivity in the binding of "two-prong" ligands to recombinant human carbonic anhydrase I

Benzenesulfonamide and iminodiacetate (IDA)-conjugated Cu(2+) independently interact at the active site and a peripheral site of carbonic anhydrases, respectively [Banerjee, A. L., Swanson, M., Roy, B. C., Jia, X., Haldar, M. K., Mallik, S., and Srivastava, D. K. (2004) J. Am. Chem. Soc. 126, 10875-10883]. By attaching IDA-bound Cu(2+) to benzenesulfonamide via different chain length spacers, we synthesized two "two-prong" ligands, L1 and L2, in which the distances between Cu(2+) and NH(2) group of sulfonamide were 29 and 22 A, respectively. We compared the binding affinities of L1 and L2, vis-a-vis their parent compound, benzenesulfonamide, for recombinant human carbonic anhydrase I (hCA-I) by performing the fluorescence titration and steady-state kinetic experiments. The experimental data revealed that whereas the binding affinity of L1 for hCA-I was similar to that of benzenesulfonamide, the binding affinity of L2 was approximately 2 orders of magnitude higher, making L2 one of the most potent ligands or inhibitors of hCA-I. Since the enhanced binding or inhibitory potency of L2 is diminished (to the level of benzenesulfonamide) either in the presence of EDTA or upon treatment of the enzyme with diethyl pyrocarbonate, it is proposed that Cu(2+) of L2 interacts with one of the surface-exposed histidine residues of the enzyme. A cumulative account of the experimental data leads to the suggestion that the differential binding of L1 versus L2 to hCA-I is encoded in the chain length of the spacer moiety.

Preparation and in-vivo evaluation of 99mTc-IOTIDA for cholescintigraphy

The synthesis, radiolabeling and in vivo evaluation of 99mTc-IOIDA(3-iodo 2,4,6-trimethylpheyl carbamoylmethyl iminodiacetic acid) for the assessment of hepatocytic function and the functional status of the cystic duct and the gallbladder are described. For a scintigraphic imaging comparison, three different 99mTc-IDA derivatives, 99mTc-DISIDA, 99mTc-mebrofenin and 99mTc-IOTIDA, were prepared and evaluated for their in vivo pharmacokinetic behavior through animal studies. Serial static image scans of rabbits injected with 99mTc-IOTIDA revealed that none of the tissues except the hepatobiliary system showed radioactivity concentrations. A scintigraphic study in a healthy volunteer showed that most of the administrated radioactivity accumulated in the liver and was rapidly excreted through the hepatobiliary system, visualizing the gallbladder within 15 min. In conclusion, 99mTc-IOTIDA is a potential hepatobiliary imaging agent for the evaluation of the functional status of hepatocytes and the patency of the biliary duct.

Solution-phase combinatorial synthesis of nonpeptide bradykinin antagonists

We describe the solution-phase combinatorial synthesis and pharmacological effect of fifty N,N(')-substituted-N"-1-(4-chlorobenzhydryl)piperazine iminodiacetic acid triamide derivatives as nonpeptide B2 antagonists. The synthesized compounds were tested for their antibradykinin activity by utilizing guinea-pig ileum smooth muscle. Most of the compounds showed antagonistic effects on bradykinin induced contraction. N-acetyl-N(')-(4-methylbenzyl)-N"-1-(4-chlorobenzhydryl)piperazine iminodiacetic acid triamide (A3B1C1) showed the 46% inhibition at 100nM.

Catalytic asymmetric [3+2] cycloaddition of azomethine ylides. Development of a versatile stepwise, three-component reaction for diversity-oriented synthesis

We report a new catalyst system that should enhance the use of enantioselective 1,3-dipolar cycloadditions of azomethine ylides with electronic-deficient olefins in the divergent pathways of diversity-oriented synthesis (DOS). The underlying reaction is of considerable interest in DOS because its stereospecificity enables stereochemical diversification of up to four tetrahedral centers on pyrrolidine rings. This new catalyst system extends the scope and selectivity of the azomethine ylide cycloaddition and is compatible with reagents used in a one-bead/one-stock solution technology platform for DOS.

Versatile routes to C-2- and C-6-functionalized glucose derivatives of iminodiacetic acid

A series of novel d-glucose derivatives, functionalized at the C-2 or the C-6 position with an iminodiacetic acid moiety for transition-metal complexation, has been prepared. The sugar and the metal-chelating parts are separated by either propyl or octyl chains and were introduced by the reaction of bromoalkylamine. Either N-1-Boc-3-bromopropylamine (17) or N-(8-bromooctyl)phthalimide (19) reacted with methyl 3,5,6-tri-O-benzyl-alpha-beta-d-glucofuranoside (4) (C-2 position) and 1,2:3,5-(O-methylene)-alpha-d-glucose (11) (C-6 position), respectively, in the presence of sodium hydride in DMF at room temperature, affording the desired intermediates. For aminopropyl derivatives, yields varied between 57% and 65%, and for aminooctyl derivatives, yields varied between 40% and 71%. After deprotection of the amine functionality, the metal chelate was built up by dialkylation (6a-c and 13a,b) with methyl bromoacetate in the presence of triethylamine under reflux in THF. Yields varied between 56% and 69% for the glucose modified at the C-2 position and between 58% and 62% for the one modified at the C-6 position. All compounds were characterized by 1H or 13C NMR or both, IR, and mass spectroscopy. Final products were isolated as a mixture of alpha and beta anomers.

Alpha-imino esters: versatile substrates for the catalytic, asymmetric synthesis of alpha- and beta-amino acids and beta-lactams

The catalytic asymmetric addition of organic nucleophiles to alpha-imino esters has emerged as one of the most promising and intensely investigated routes to optically enriched alpha- and beta-amino acid derivatives and beta-lactams. The importance of alpha-imino esters stems not only from the vast appeal of the potential product classes,(1) but also from their remarkable reactivity as highly electrophilic imines. With each passing year, the number of publications concerning the asymmetric alkylation of imino esters grows significantly. The asymmetric alkylation of imines(2) and N,O-acetals has been in itself a subject of intense interest.(3) In this Account, we wish to illustrate our contribution to this timely field, as well as to highlight the seminal contributions of others.

Synthesis and DNA binding properties of iminodiacetic acid-linked polyamides: characterization of cooperative extended 2:1 side-by-side parallel binding

A series of iminodiacetic acid (IDA)-linked polyamides (DpPyPyPy-IDA-PyPyPyDp) were prepared and constitute polyamides joined head-to-head by a functionalizable five-atom linker. It was found that the IDA linker exerts a unique influence over the DNA binding conformation differing from both the beta-alanine (extended) or gamma-aminobutyric acid (hairpin) linkers, resulting in cooperative parallel side-by-side 2:1 binding in an extended conformation most likely with a staggered versus stacked alignment. A generalized variant of a fluorescent intercalator displacement (FID) assay conducted on a series of hairpin deoxyoligonucleotides containing a systematically varied A/T-rich binding-site size was used to distinguish between the binding modes of the IDA-linked polyamides.

Application of MCR: Facile one-pot diastereoselective syntheses of novel chiral {α,α'-iminodiacetic acid analogues

Several pairs of enantiomeric alpha,alpha'-iminodiacetic acid analogues (2 and 4) were prepared separately by highly diastereoselective 3CR, which involves a reaction of an isocyanide, an aldehyde, and an enantiomerically pure amino acid in methanol. Synthesis of each of the enantiomers was controlled by the configuration of the amino acid; L-amino acid produces one enantiomer and D-amino acid generates the other. The diastereoselectivity of the 3CR is very sensitive to the substituent size of both aldehyde and enantiomerically pure amino acid.

Technetium-99m complex of N-(2-pyridylmethyl)iminodiacetic acid as a new renal radiopharmaceutical

A tetradentate chelating agent constituting of an iminodiacetic acid group and a nitrogen atom of pyridine, N-(2-pyridylmethyl)iminodiacetic acid (PMIDA), was coordinated with 99mTc and evaluated as a renal functional agent. The complex of PMIDA with 99mTc was prepared by using a stannous chloride solution as a reducing agent. The chelating efficiency was analyzed by thin layer chromatography and electrophoresis. Chelation with 99mTc resulted in a single radiochemical product. Biological studies were performed in mice and rats. 99mTc-PMIDA was removed from the circulation solely by the kidneys. Clearance of 99mTc-PMIDA from the blood and the kidneys was as rapid as that of 99mTc-diethylenetriaminepentaacetic acid. The rate of blood clearance was unaffected by the administration of probenecid (a test for tubular secretion by the weak-acid mechanism), so that the glomerular filtration rate could be estimated by measuring its clearance from the blood. The results in animals with myohemoglobinuric acute renal failure suggested that 99mTc-PMIDA might be a useful renal function radiopharmaceutical.

Higher order iminodiacetic acid libraries for probing protein-protein interactions

Higher order iminodiacetic acid diamide trimer (560 compounds) and tetramer libraries (1260 compounds) are described and were assembled in a convergent multistep solution-phase synthesis for use in studying protein-protein interactions.

Higher order iminodiacetic acid libraries for probing protein-protein interactions

Full details of the preparation of iminodiacetic acid diamide dimer (2040 compounds), trimer (560 compounds), and tetramer (1596 compounds) libraries by multistep convergent solution-phase synthesis for studying protein-protein interactions are provided. The libraries were assembled in a format providing small 8-10 compound mixtures and the deconvolution of many of the small mixtures to identify screening leads by resynthesis of the individual components have been conducted for 320 of the individual compounds to date. A representative example of the subsequent exploration of the structure-activity relationships for an identified receptor binding antagonist (200 additional individual compounds) and steps taken for potential elaboration to a receptor dimerization agonist are defined with preparation of representative linked dimers (70 compounds).

An approach towards surface imprinting using the enzyme ribonuclease A

An adsorbent showing enhanced selectivity for the enzyme RNase A was prepared by a surface imprinting procedure based on metal coordination. A metal chelating monomer, N-(4-vinyl)-benzyl iminodiacetic acid, was polymerized onto methacrylate-derivatized silica particles in the presence of RNase A and metal ions. Lysozyme and RNase A were separated on the adsorbent used as stationary phase in high-performance liquid chromatography.

The Strecker synthesis as a source of amino acids in carbonaceous chondrites: deuterium retention during synthesis

Deuterium-enriched amino acids occur in the Murchison carbonaceous chondrite. Synthesis from D-enriched interstellar precursors by Strecker reactions during aqueous alteration of the parent body has been proposed. To test this hypothesis, we have measured the retention of deuterium in amino acids produced from HCN, NH3, and formaldehyde-D2, acetaldehyde-D4, and acetone-D6 in H2O. The isotopic label is 50% to 98% retained, with variations in retentivity depending on the amino acid and the reaction conditions. If amino acids, once formed on the parent body by the Strecker synthesis, lose no deuterium by subsequent exchange with water or H-bearing minerals, then the observed deuterium isotopic composition of Murchison amino acids represents as much as 50% or more of the enrichments inherited from their interstellar precursors. Imino diacids are prominent side products of the Strecker synthesis which have not been reported in carbonaceous chondrites. Under the conditions of the Strecker reaction using deuterium labeled aldehydes and ketones, unlabeled amino acids are also formed by an HCN polymerization route indicating multiple pathways for the synthesis of amino acids in meteorites.

Ligandin binding phthalein complexone complex of technetium for hepatic function studies

In our pursuit for liver functional diagnosis, development of bifunctional radiopharmaceutical containing iminodiacetic acid (IDA), as the technetium chelating site along with phthalein or fluorescein structure, the skeleton of BSP and Rose Bengal, long used for the assessment of liver function is considered. Among the various PC, PPC, TPC and calcein IDA derivatives commercially available, 99mTc-PC (PC: 3,3'-bis(N, N-dicarboxymethylaminomethyl)o-cresolphthalein) showed the highest hepatobiliary excretion. The functionality of the various technetium labeled phthalein and fluorescein IDA derivatives was evaluated by competitive BSP binding studies and by comparative binding with the hepatocyte specific protein, ligandin.

99mTc-labelled trimethylmonoiodo-IDA: a new radiopharmaceutical for hepatobiliary imaging

A new radiopharmaceutical, 99mTc-3-iodo-2,4,6-trimethylphenylcarbamoylmethyl iminodiacetic acid (99mTc-trimethylmonoiodo-IDA) was prepared and evaluated for hepatobiliary scintigraphy. The new agent has less plasma protein binding capacity and greater lipophilicity as compared to that of di-isopropyl-IDA. Hepatobiliary specificity, a short transit time and a high gall bladder-to-liver ratio of the new agent were evident from tissue distribution data in mice. Blood tmax and clearance t1/2 of the radiopharmaceutical were observed at 2 and 3.5 min respectively. The hepatic peak-time tmax (5 min) and release time t1/2 (12.75 min) and release t1/2 (25.00 min) suggest the suitability of this agent for hepatobiliary imaging. Results of hepatobiliary scintigraphy in rabbits have further confirmed the above view.

Synthesis and quality control of 99mTc-p-butyl IDA

A procedure is described for synthesis of p-butyl IDA and for identification of the product by i.r. and NMR spectroscopy and by chemical analysis. A method for preparing this compound by "instant" technique and for its labelling with 99mTc is also given, as well as a procedure for control of the chemical and biological properties of the radiopharmaceutical. Radiochemical study shows a high labelling yield of 95%. Investigation of the biodistribution proves that this preparation is a good hepatobiliary reagent, suitable for use in investigation of the liver functions and for quantitative visualization of the hepatobiliary system.

Preparation and biokinetic studies of 99mTc-p-butyl-IDA for hepatobiliary scintigraphy

A freeze-dried powder of tin-p-butyl-IDA to be labelled with 99mTc for hepatobiliary scintigraphy has been developed. Gel chromatography column scanning has been applied for evaluating the labeling efficiency of the complex under different conditions. The results of organ distribution studies in mice and of clinical investigations in human beings showed the stability of the radiopharmaceutical. The preparative 99mTc-p-butyl-IDA concentrates moderately well in the bile with a rapid blood clearance into hepatocytes, very low excretion in the urine and slow clearance into the bile.

History. Development of new radiopharmaceuticals based on N-substitution of iminodiacetic acid. By Michael D. Loberg, Malcolm Cooper, Elizabeth Harvey, Patrick Callery, and William Faith. 1976

A new approach to radiopharmaceutical design is demonstrated, in which small chelating groups capable of binding gamma-emitting radiometals are attached to biologically active molecules, thus producing radiopharmaceuticals based on bifunctional drug and biochemical analogs. The chelating group iminodiacetic acid has been evaluated for this role by examining two N-substituted iminodiacetic acids: methyliminodiacetic acid (MIDA) and N-(2,6-dimethylphenylcarbamoylmethyl)iminodiacetic acid (HIDA). Radiochemical and biologic studies showed that both agents were obtained in high radiochemical purity, were stable in vitro and in vivo, and possessed biologic distributions governed almost exclusively by the N-substituted group. These characteristics of 99mTc-labled N-substituted iminodiacetic acids, prepared using an "instant kit" method, provide the basis for a valuable new class of radiopharmaceuticals based on bifunctional drug and biochemical analogs.

The investigation of radiopharmaceutical components by fast atom bombardment mass spectrometry: the identification of Tc-HIDA and the epimers of Tc-CO2DADS

The nature of two technetium-labeled radiopharmaceutical components has been established by means of fast-atom-bombardment mass spectrometry (FABMS) in combination with carrier-added (CA) and no-carrier-added (NCA) reversed-phase high-pressure liquid chromatography (HPLC). Negative-ion FABMS was used to determine that the epimers of Tc-CO2DADS are the oxo[N,N'-(1-carboxyethylene)-bis-(2-mercaptoacetimido)]technetate(V) ions; positive-ion FABMS showed that Tc-HIDA is bis[N-(2,6-dimethylphenyl-carbamoylmethyliminodiaceto]technetate(III).

Evaluation of 99mTc-labeled iminodiacetic acid derivatives of substituted 2-aminopyrroles as hepatobiliary imaging agents in rats II

The synthesis and biodistribution properties of 99mTc-labeled 5-substituted N-(3-cyano-4-methyl-2-pyrrylcarbamoylmethyl)iminodiacetic acids and a similar series of N1-methyl analogs are described. These compounds were compared with 99mTc-labeled N-(2,6-dimethylphenylcarbamoylmethyl)iminodiacetic acid for hepatobiliary activity in the rat. The effects of structural modifications on biological activity are also reported.

Time dependence of iprofenin-labeling with technetium Tc 99m

The incubation time required to attain 90% labeling efficiency (90% radiochemical purity) for technetium Tc 99m labeling of iprofenin (PIPIDA, Diagnostic Isotopes, Inc.), was investigated. Thirty iprofenin vials were prepared according to the manufacturer's instructions. Aliquots were withdrawn from 12 vials at times 0.5, 1, 2, 3, 5, 7, 10, 12, 15, 20, 30, 45, and 60 minutes after mixing. Aliquots were withdrawn from 18 vials at 1, 2, 3, 5, 7, and 10 minutes. Free pertechnetate and reduced/hydrolyzed technetium were isolated from aliquots with instant thin-layer chromatography and quantified with a scintillation well counter. Based on the 30 vials, a mean (+/- S.E.M.) of 5.83 +/- 4.32 minutes was required to attain 90% labeling efficiency. Using tolerance limits calculations, the incubation time required to be assured that 95% of vials have achieved 90% labeling is 16.8 minutes. It is concluded that 99mTc iprofenin vials should be incubated 17 minutes to be assured of 90% labeling efficiency.

Semisynthetic cephalosporins with alpha-oximino acid side chains. The preparation and coupling of 4-acylamino-alpha-oximinobenzeneacetic acids and 1,2-dihydro-6-methyl-alpha-oximino-2-oxo-3-pyridineacetic acid to 7-aminocephalosporanic acid

A series of 4-acylamino-alpha-oximinobenzeneacetic acids, and 1,2-dihydro-6-methyl-alpha-oximino-2-oxo-3-pyridineacetic acid were prepared and coupled to 7-aminocephalosporanic acid and its 3'-(1-methyltetrazol-5-yl)thiolo analogue. Several coupling methods and oxime protecting groups were thoroughly examined. The best coupling procedure employed dimethylchloroformiminium chloride, and the tetrahydropyranyl (THP) group was selected for oxime protection. The cephalosporins prepared were tested and compared to cefuroxime and cefotaxime. The corresponding alpha-keto acids, and O-methyl oximes were also examined.

Determination of radiochemical purity and stability of 99mTc-diethyl HIDA

Several chromatographic methods have been used for determining the radiochemical purity of 99m Tc-diethyl HIDA (Solco HIDA). Good separation of 99mTc-HIDA from 99mTc-hydrolyzate and nonreduced 99mTcO4- was obtained in a short time using Gelman ITLC (SA) and 2N NaC1 as the mobile phase. In vitro stability was followed by the same method. It was found that the presence of oxygen from air enhances the percentage of 99mTcO4- in the preparation. Formation of a chelate of 99mTc-HIDA with a high stability constant was established by using Sephadex G-25 filtration. The degree of binding of 99mTc-diethyl HIDA to blood plasma proteins, examined by the same method. In vivo stability was examined by analyzing bile and urine, which were found to contain 99mTc-HIDA chelate. Biodistribution of the preparation was also investigated in experimental animals.

Synthesis of five new 99mTc-HIDA isomers and comparison with 99mTc-HIDA

Five new HIDA-compounds were synthesized, labelled with 99mTc and compared with 99mTc-(2,6-dimethyl)HIDA viz. (N-2,6-dimethylphenylcarbamoylmethyl)iminodiacetic acid by means of TLC and biodistribution studies on rabbits. The computerized method used by Britton and Brown during renal studies was successfully adapted to study the biodistribution of these agents.

A clinical comparison of 99mTc-diethyl-iminodiacetic acid, 99mTc-pyridoxylideneglutamate, and 131I-rose bengal in liver transplant patients

The relative merits of three radiopharmaceuticals for evaluating liver transplant patients were determined in paired studies. In 86% of studies both 131I-RB and 99mTc-PG gave similar information for differentiation of hepatocellular disease and billary tract obstruction. 99mTc-PG probably demonstrates the biliary tract and small intestine better early after injection (8%); 131I-RB is probably better in showing the colon at 24 hours when intestinal activity is not seen by 1 hour (6%). 99mTc-diethyl-IDA is superior in all respects when compared to 99mTc-PG. The blood retention method (20 min./5 min.) showed that none of the radiopharmaceuticals was a reliable indicator of hepatocyte function when compared to total serum bilirubin.

Development of new radiopharmaceuticals based on N-substitution of iminodiacetic acid

A new approach to radiopharmaceutical design is demonstrated, in which small chelating groups capable of binding gamma-emitting radiometals are attached to biologically active molecules, thus producing radiopharmaceuticals based on bifunctional drug and biochemical analogs. The chelating group iminodiacetic acid has been evaluated for this role by examining two N-substituted iminodiacetic acids: methyliminodiacetic acid (MIDA) and N-(2,6-dimethylphenylcarbamoylmethyl)iminodiacetic acid (HIDA). Radiochemical and biologic studies showed that both agents were obtained in high radiochemical purity, were stable in vitro and in vivo, and possessed biologic distributions governed almost exclusively by the N-substituted group. These characteristics of 99mTc-labeled N-substituted iminodiacetic acids, prepared using an "instant kit" method, provide the basis for a valuable new class of radiopharmaceuticals based on bifunctional drug and biochemical analogs.