Tc Radiopharmaceuticals Research Articles

Speciation analysis of Tc radiopharmaceuticals by HPLC-ICP-MS and HPLC-ESI-HRMS

99mTc is commonly employed in radiotracers scintigraphy. New methods to inquire identity and to perform quantitative characterization are presented.

Internal radiation dose assessment of radiopharmaceuticals prepared with cyclotron-produced 99m Tc.

Technetium-99m (99m Tc) is the radioisotope most widely used in diagnostic nuclear medicine. It is readily available from 99 Mo/99m Tc generators as the β- decay product of the 99 Mo (T½ =66h) parent nuclide. This latter is obtained as a fission product in nuclear reactors by neutron-induced reactions on highly enriched uranium. Alternative production routes, such as direct reactions using proton beams on specific target materials [100 Mo(p,2n)99m Tc], have the potential to be both reliable and relatively cost-effective. However, results showed that the 99m Tc extracted from proton-bombarded 100 Mo-enriched targets contains small quantities of several Tc radioisotopes (93m Tc, 93 Tc, 94 Tc, 94m Tc, 95 Tc, 95m Tc, 96 Tc, and 97m Tc). The aim of this work was to estimate the dose increase (DI) due to the contribution of Tc radioisotopes generated as impurities, after the intravenous injection of four radiopharmaceuticals prepared with cyclotron-produced 99m Tc (CP-99m Tc) using 99.05% 100 Mo-enriched metallic targets. Four 99m Tc radiopharmaceuticals (pertechnetate, sestamibi (MIBI), hexamethylpropylene-amine oxime (HMPAO) and disodium etidronate (HEDP)) were considered in this study. The biokinetic models reported by the International Commission on Radiological Protection (ICRP) for each radiopharmaceutical were used to define the main source organs and to calculate the number of disintegrations per MBq that occurred in each source organ (Nsource ) for each Tc radioisotope present in the CP-99m Tc solution. Then, target organ equivalent doses and effective dose were calculated for each Tc radioisotope with the OLINDA/EXM software versions 1.1 and 2.0, using the calculated Nsource values and the adult male phantom as program inputs. Total effective dose produced by all Tc isotopes impurities present in the CP-99m Tc solution was calculated using the fraction of total activity corresponding to each radioisotope and compared with the effective dose delivered by the generator-produced 99m Tc. In all cases, the total effective DI of CP-99m Tc radiopharmaceuticals calculated with either versions of the OLINDA software was less than 10% from 6 up to 12h after EOB. 94m Tc and 93m Tc are the Tc radioisotopes with the highest concentration in the CP-99m Tc solution at EOB. However, their contribution to DI 6h after EOB is minimal, due to their short half-lives. The radioisotopes with the largest contribution to the effective DI are 96 Tc, followed by 95 Tc and 94 Tc. This is due to the types of their emissions and relatively long half-lives, although their concentration in the CP-99m Tc solution is five times lower than that of 94m Tc and 93m Tc at the EOB. The increase in the radiation dose caused by other Tc radioisotopes contained in CP-99m Tc produced as described here is quite low. Even though the concentrations of the 94 Tc and 95 Tc radioisotopes in the CP-99m Tc solution exceed the limits established by the European Pharmacopoeia, CP-99m Tc radiopharmaceuticals could be used in routine nuclear medicine diagnostic studies if administered from 6 to 12h after the EOB, thus maintaining the effective DI within the 10% limit.

Technetium-99m radiochemistry for pharmaceutical applications.

Technetium-99m (99m Tc) is a widely used radionuclide, and the development of 99m Tc imaging agents continues to be in demand. This overview discusses basic principles of 99m Tc radiopharmaceutical preparation and design and focuses on the 99m Tc radiochemistry relevant to its pharmaceutical applications. The 99m Tc complexes are described based on the most typical examples in each category, keeping up with the state-of-the-art in the field. In addition, the main current strategies to develop targeted 99m Tc radiopharmaceuticals are summarized.

Synthesis, characterization, conformational analysis of a cyclic conjugated octreotate peptide and biological evaluation of 99mTc-HYNIC-His3-Octreotate as novel tracer for the imaging of somatostatin receptor-positive tumors

Peptides are attracting increasing interest in nuclear oncology for targeted tumor diagnosis and therapy. We therefore synthesized new cyclic octapeptides conjugated with HYNIC by Fmoc solid-phase peptide synthesis. These were purified and analyzed by RP-HPLC, MALDI mass, (1)H NMR, (13)C NMR, HSQC, HMBC, COSY and IR spectroscopy. Conformational analysis of the peptides was performed by circular dichroism spectroscopy, in pure water and trifluoroethanol-water (1:1), revealed the presence of strong secondary structural features like β-sheet and random coils. Labeling was performed with (99m)Tc using Tricine and EDDA as coligands by SnCl(2) method to get products with excellent radiochemical purity >99.5 %. Metabolic stability analysis did not show any evidence of breaking of the labeled compounds and formation of free (99m)Tc. Internalization studies were done and IC(50) values were determined in somatostatin receptor-expressing C6 glioma cell line and rat brain cortex membrane, and the results compared with HYNIC-TOC as standard. The IC(50) values of (99m)Tc-HYNIC-His(3)-Octreotate (21 ± 0.93 nM) and (99m)Tc-HYNIC-TOC (2.87 ± 0.41 nM) proved to be comparable. Biodistribution and image study on normal rat under gamma camera showed very high uptake in kidney and urine, indicating kidney as primary organ for metabolism and route of excretion. Biodistribution and image study on rats bearing C6 glioma tumor found high uptake in tumor (1.27 ± 0.15) and pancreas (1.71 ± 0.03). Using these findings, new derivatives can be prepared to develop (99m)Tc radiopharmaceuticals for imaging somatostatin receptor-positive tumors.

Effect of 99Tc on the radiochemical purity of 99mTc radiopharmaceuticals

The longer the time between elutions of a technetium-99m (Tc) generator, the greater the Tc : Tc ratio in the eluate. Information is limited on how this affects the radiochemical purity (RCP) of Tc radiopharmaceuticals. The aim was to determine whether the RCPs of Tc radiopharmaceuticals are affected when prepared using Tc-pertechnetate from a generator that remained uneluted for 7 days. Eight Tc radiopharmaceuticals were investigated: albumin nanocolloid, macrosalb, medronate, mertiatide, pentetate, sestamibi, succimer and tetrofosmin. Five samples of each were prepared with eluate from a generator that had been previously eluted within 24 h (control). These were compared with five samples adulterated with Tc to replicate the Tc : Tc ratio present in eluate from a generator that has remained uneluted for 7 days (test). The RCP of each sample was measured 1 h after preparation and at the product's expiry. Significant differences (P<0.05) were found between the RCPs of control and test samples of albumin nanocolloid, mertiatide and sestamibi 1 h after preparation. In each, the test sample had lower RCP, but was satisfactory. Similar results were found for macrosalb with added Tc, but the RCPs of the test samples were unsatisfactory at 83.9±4.2%. The RCPs of all control and test samples were satisfactory at expiry. Seven of the eight radiopharmaceuticals tested can safely be prepared using eluate from a generator that has remained uneluted for 7 days. Under these conditions, care must be taken when preparing Tc-macrosalb, as its RCP remains unsatisfactory up to 2 h after preparation.

Novel 99m Tc radiopharmaceuticals with bifunctional chelating agents

Today the main radionuclide used for preparing radiopharmaceuticals throughout the world is 99m Tc, thanks to its optimal nuclear-physical characteristics and ready availability. Several approaches are used for tethering this radionuclide to biomolecules (peptides, antibodies, etc.); one of them involves the use of so-called bifunctional chelating agents (BCAs). These compounds are capable both of binding 99m Tc and of linking to biomolecules. Today the most frequently used BCAs are DTPA, MAG3, and HYNIC. These BCAs are described and compared. The peptides that are most frequently used in combination with these agents are described and compared. Published data on the choice of a coligand for use in combination with HYNIC are discussed.

A Portable Test System for Determination of Bacterial Endotoxins in 18F-FDG, 99mTc, and Lyophilized Reagents for Labeling with 99mTc

A rapid quantitative kinetic chromogenic test in an automated portable test system has been developed for in-process and end-product determination of bacterial endotoxins in water using the Limulus amebocyte lysate. The aim of this work was to validate the method for (18)F-FDG, (99m)Tc, and the lyophilized reagents methylene diphosphonic acid (MDP) and pyrophosphate for labeling with (99m)Tc radiopharmaceuticals with no interfering factors. Experiments were performed on 3 consecutive batches of (18)F-FDG, (99m)Tc, MDP, and pyrophosphate produced at the Nuclear Energy and Research Institute of São Paulo, Brazil, using a portable test system. The maximum valid dilution (=500) was calculated to establish the extent of dilution to avoid interfering test conditions. Better results were obtained above a 1:5 dilution factor for (18)F-FDG and (99m)Tc, 1:20 for MDP, and 1:100 for pyrophosphate. The requirements of the test were satisfied (R ≤ 0.980, recovery of product positive control between 50% and 200%, and coefficient variation of samples < 25%), and the endotoxin concentration was lower than the lowest concentration of the standard curve (0.05 endotoxin unit mL(-1)) and therefore less than the established limit in pharmacopoeias. The portable test system is a rapid, simple, and accurate technique using the quantitative kinetic chromogenic method for bacterial endotoxin determination. For this reason, the test is practical for radiopharmaceutical uses and tends to be the method of choice for the pyrogen test. For (18)F-FDG, (99m)Tc, MDP, and pyrophosphate, the validation was successfully performed.

Radiolabeling of fab and f(ab′)2 antibody fragments with 99mTc(I) tricarbonyl core using a new bifunctional tridentate ligand

The objective of this study was to design and evaluate a new histidine-modified tridentate chelator for labeling antimesothelin fab and f(ab')2 antibody fragments with the Tc(I) tricarbonyl ([Tc(CO)3]) core. N-(ortho-phenol)-histidine chelator was synthesized by modifying the single amino acid L-histidine, a natural amino acid, with an additional phenol group to obtain the bifunctional tridentate ligand after reductive amination. Bioconjugation was based on the carbodiimide activation of the carboxylate of chelator and on further reaction with the amine groups present on the antibody fragments. Radiolabeling was accomplished by replacing the three aqua ligands of the complex precursor [Tc(CO)3(H2O)3] with the tridentate chelator. The antibody fragments radiolabeled with [Tc(CO)3] core were tested for stability by the cysteine challenge test. The immunoreactivity and binding affinity of the radiolabeled fragments were studied using in-vitro cell-binding assays. Radiochemical yields achieved for [Tc(CO)3] core labeling of fab and f(ab')2 were 91.6±9.1% and 80.7±8.5%, respectively. Stability studies of radiolabeled antibody fragments showed that the Tc label was stable to transchelation by cysteine. Both Tc-fab and Tc-f(ab')2 retained their reactivity and affinity to the mesothelin antigen. From our studies, it can be concluded that the newly synthesized N-(ortho-phenol)-histidine chelator is a promising candidate for [Tc(CO)3] labeling of biomolecules and for developing other novel Tc radiopharmaceuticals.

Molecular Assembly of Multifunctional 99mTc Radiopharmaceuticals Using “Clickable” Amino Acid Derivatives

Synthetic strategies that enable the efficient and selective combination of different biologically active entities hold great promise for the development of multifunctional hybrid conjugates useful for biochemical and medical applications. Starting from side-chain-functionalized N(α)-propargyl lysine derivatives, conjugates containing a ⁹⁹(m)Tc-based imaging probe for SPECT and two different moieties (e.g., tumor-targeting vectors, pharmacological modifiers, affinity tags, or second imaging probes) can be assembled using the Cu(I)-catalyzed alkyne-azide cycloaddition in efficient one-pot protocols. This strategy was successfully applied to the preparation of a ⁹⁹(m)Tc-labeled conjugate comprising a tumor-targeting peptide sequence (bombesin(7-14)) and a low-molecular-weight albumin binder, a pharmacological modifier that prolongs the blood circulation time of the conjugate. Evaluation of the conjugate in vitro and in vivo provided promising results for its use as an imaging agent for the visualization of tumors positive for the gastrin-releasing peptide receptor. The methodology presented herein provides an attractive synthetic tool for the preparation of multifunctional ⁹⁹(m)Tc-based radiopharmaceuticals with significant potential for a multitude of applications.

Coordination modes of multidentate ligands in fac-[Re(CO)(3)(polyaminocarboxylate)] analogues of (99m)Tc radiopharmaceuticals. dependence on aqueous solution reaction conditions.

We study Re analogues of (99m)Tc renal agents to interpret previous results at the (99m)Tc tracer level. The relative propensities of amine donors versus carboxylate oxygen donors of four L = polyaminocarboxylate ligands to coordinate in fac-[Re(I)(CO)(3)L](n) complexes were assessed by examining the reaction of fac-[Re(I)(CO)(3)(H(2)O)(3)](+) under conditions differing in acidity and temperature. All four L [N,N-bis-(2-aminoethyl)glycine (DTGH), N,N-ethylenediaminediacetic acid, diethylenetriamine-N-malonic acid, and diethylenetriamine-N-acetic acid] can coordinate as tridentate ligands while creating a dangling chain terminated in a carboxyl group. Dangling carboxyl groups facilitate renal clearance in fac-[(99m)Tc(I)(CO)(3)L](n) agents. Under neutral conditions, the four ligands each gave two fac-[Re(I)(CO)(3)L](n) products with HPLC traces correlating well with known traces of the fac-[(99m)Tc(I)(CO)(3)L](n) mixtures. Such mixtures are common in renal agents because the needed dangling carboxyl group can compete for a coordination site. However, the HPLC separations needed to assess the biodistribution of a single tracer are impractical in a clinical setting. One goal in investigating this Re chemistry is to identify conditions for avoiding this problem of mixtures in preparations of fac-[(99m)Tc(I)(CO)(3)L](n) renal tracers. After separation and isolation of the fac-[Re(I)(CO)(3)L](n) products, NMR analysis of all products and single crystal X-ray crystallographic analysis of both DTGH products, as well as one product each from the other L, allowed us to establish coordination mode unambiguously. The product favored in acidic conditions has a dangling amine chain and more bound oxygen. The product favored in basic conditions has a dangling carboxyl chain and more bound nitrogen. At the elevated temperatures used for simulating tracer preparation, equilibration was facile (ca. 1 h or less), allowing selective formation of one product by utilizing acidic or basic conditions. The results of this fundamental study offer protocols and guidance useful for the design and preparation of fac-[(99m)Tc(I)(CO)(3)L](n) agents consisting of a single tracer.

Several Novel N-Donor Tridentate Ligands Formed in Chemical Studies of Newfac-Re(CO)3Complexes Relevant tofac-99mTc(CO)3Radiopharmaceuticals: Attack of a Terminal Amine on Coordinated Acetonitrile

To evaluate syntheses of fac-[Re(CO)(3)L](+) complexes in organic solvents, we treated fac-[Re(CO)(3)(CH(3)CN)(3)]PF(6)/BF(4) in acetonitrile with triamine ligands (L). When L had two primary or two tertiary terminal amine groups, the expected fac-[Re(CO)(3)L](+) complexes formed. In contrast, N,N-dimethyldiethylenetriamine (N,N-Me(2)dien) formed an unusual compound, fac-[Re(CO)(3)(DAE)]BF(4) {DAE = (Z)-N'-(2-(2-(dimethylamino)ethylamino)ethyl)acetimidamide = (Me(2)NCH(2)CH(2))NH(CH(2)CH(2)N=C(NH(2))Me)}. DAE is formed by addition of acetonitrile to the N,N-Me(2)dien terminal primary amine, converting this sp(3) nitrogen to an sp(2) nitrogen with a double bond to the original acetonitrile sp carbon. The three Ns bound to Re derive from N,N-Me(2)dien. The pathway to fac-[Re(CO)(3)(DAE)]BF(4) is suggested by a second unusual compound, fac-[Re(CO)(3)(MAE)]PF(6) {MAE = N-methyl-N-(2-(methyl-(2-(methylamino)ethyl)amino)ethyl)acetimidamide = MeN(H)-CH(2)CH(2)-N(Me)-CH(2)CH(2)-N(Me)-C(Me)=NH}, isolated after treating fac-[Re(CO)(3)(CH(3)CN)(3)]PF(6) with N,N',N''-trimethyldiethylenetriamine (N,N',N''-Me(3)dien). MAE chelates via a terminal and a central sp(3) N from N,N',N''-Me(3)dien and via one sp(2) NH in a C(Me)=NH group. This group is derived from acetonitrile by addition of the other N,N',N''-Me(3)dien terminal amine to the nitrile carbon. This addition creates an endocyclic NMe group within a seven-membered chelate ring. The structure and other properties of fac-[Re(CO)(3)(MAE)]PF(6) allow us to propose a reaction scheme for the formation of the unprecedented DAE ligand. The new compounds advance our understanding of the spectral and structural properties of Re analogues of (99m)Tc radiopharmaceuticals.

An evaluation of GMCP‐SA as a replacement for ITLC‐SG when measuring the levels of radiochemical impurities in 99mTc radiopharmaceuticals by thin‐layer chromatography

AbstractBackground: The European Pharmacopoeia and radiopharmaceutical manufacturers specify Instant Thin‐Layer Chromatography Silica Gel impregnated glass fibre (ITLC‐SG) as the stationary phase for measuring the radiochemical purity (RCP) of most technetium‐99m (99mTc) radiopharmaceuticals. During 2008, The Pall Corporation stopped manufacturing ITLC‐SG. A replacement is required. Aim: To evaluate Varian's Glass Microfibre Chromatography Paper impregnated with salicic acid (GMCP‐SA) as a replacement. Experimental: Samples of six 99mTc radiopharmaceuticals (albumin nanocolloid, colloidal tin, exametazime, medronate, pentetate and succimer) were prepared containing levels of radiochemical impurities between 0 and 10%. Samples were tested using ITLC‐SG and GMCP‐SA with the mobile phase specified in the pharmacopoeia or by the manufacturer. Analysis was performed by thin‐layer radiochromatogram scanning. Results: For measuring the RCP of albumin nanocolloid, colloidal tin, exametazime and succimer, GMCP‐SA is a suitable replacement for ITLC‐SG. For medronate, GMCP‐SA is suitable for measuring colloidal 99mTc impurity despite producing slightly higher values than ITLC‐SG, but unsuitable for measuring 99mTc pertechnetate impurity due to significant over‐estimation. For pentetate, GMCP‐SA is suitable for measuring colloidal 99mTc impurity but gives slightly higher values for 99mTc pertechnetate impurity than ITLC‐SG. Conclusion: GMCP‐SA is a suitable alternative to ITLC‐SG for analysing some 99mTc radiopharmaceuticals but is not a universal replacement. Copyright © 2009 John Wiley &amp; Sons, Ltd.

Expedient Multi-Step Synthesis of Organometallic Complexes of Tc and Re in High Effective Specific Activity. A New Platform for the Production of Molecular Imaging and Therapy Agents

For over thirty years, instant labeling kits which involve no purification steps have been the only method used to prepare (99m)Tc radiopharmaceuticals for clinical studies. To address the limitations imposed by instant kits, which is hindering the development of molecularly targeted Tc- and Re-based imaging and therapy agents, a new strategy for the rapid multistep synthesis and purification of organometallic technetium-based molecular probes and corresponding rhenium-based therapeutic analogues was developed. Beginning with MO4(-) (M = (99m)Tc, (186/188)Re), the carbonyl precursor [M(CO)3(H2O)3](+) was synthesized in 3 min in quantitative yield in a microwave reactor. A dipicolyl ligand was added and the chelate complex was formed in high yield in 2 min using microwave heating at 150 degrees C. This was followed by a new purification strategy to remove unlabeled ligand which entailed using a copper resin/C18 solid phase extraction protocol giving the desired product in greater than 78% decay corrected yield (dcy). Conversion to the corresponding succinimidyl active ester was achieved following a 5 min microwave irradiation at 120 degrees C and C18 solid phase extraction purification in 60% dcy. A series of amides were prepared subsequently by microwave heating at 120 degrees C for 5 min producing the desired targets in greater than 86% dcy. The reported method represents a move away from traditional instant kits toward more versatile platform synthesis and purification technologies that are better suited for producing modern molecular imaging and therapy agents.

Assessment of Macrocyclic Triamine Ligands As Synthons for Organometallic 99mTc Radiopharmaceuticals

In a search of coordination molecules suitable to the fac-{(99m)Tc(CO)3}(+) core as a synthon for (99m)Tc-radiopharmaceuticals, nonradioactive rhenium complexes of two macrocyclic triamine compounds with different chelate ring structures, 1,4,7-triazacyclononane (9N3) and 1,5,9-triazacyclododecane (12N3), were synthesized and characterized. (99m)Tc-labeled 9N3 and 12N3 compounds were also prepared using [(99m)Tc(OH 2)3(CO)3](+) and were characterized by both in vitro and in vivo studies. 9N3 produced a single rhenium complex, whereas 12N3 generated two major complexes. The crystallographic data and infrared absorption wavenumber assigned to the C-O stretch suggested that the coordination geometry of 9N3 would be more suitable to fac-{Re(CO)3}(+) than that of 12N3. In contrast, both 9N3 and 12N3 provided a single (99m)Tc-labeled compound. However (99m)Tc-labeled 9N3 exhibited higher stability than (99m)Tc-labeled 12N3 in rat plasma and in the presence of histidine at an elevated temperature. In biodistribution studies, both (99m)Tc-labeled compounds did not show any specific accumulation of radioactivity in any organs except for the excretory organs such as the liver and kidney. These findings showed that 9N3 would constitute a macrocyclic chelating molecule of choice to prepare (99m)Tc radiopharmaceuticals using a fac-{(99m)Tc(CO)3}(+) core.

Two novel procedures of preparation for [Tc(CO)2(NO)]2+labeled by EHIDA and its biodistribution

To develop potential new Tc radiopharmaceuticals, a novel compound [99mTc(CO)2(NO)(EHIDA)]0 (EHIDA: 2,6-diethylphenylcarbamoylmethyliminodiacetic acid) has been prepared by reacting [99mTc(CO)3)(EHIDA)]− with NOBF4 both in water and acetonitrile. The conversion of [99mTc(CO)3)(EHIDA)]− to [99mTc(CO)2(NO)(EHIDA)]0 was supported by TLC, HPLC and eletrophoresis. The radiochemical purity (more than 99%) was proved by TLC and HPLC. The biodistribution in mice demonstrated that [Tc(CO)2(NO)(EHIDA)]0 showed higher uptake in blood, kidney and lung (15 min, blood: 19.24±2.95; kidney: 13.61±3.49; lung: 10.81±1.09.) but a lower uptake in liver (15 min, 5.73±0.74). The slower clearances (120 min, blood: 12.75±1.34; kidney: 13.61±3.49) from blood and kidney were also found. This research describes two methods for the conversion of [99mTc(CO)3]+ into [99mTc(CO)2)(NO)]2+ by using NOBF4 as the source of NO+ both in organic solvent and water. The latter method offers the possibility to introduce the NO-group in high yield in water.

Re(CO)3 Complexes Synthesized via an Improved Preparation of Aqueous fac-[Re(CO)3(H2O)3]+ as an Aid in Assessing 99mTc Imaging Agents. Structural Characterization and Solution Behavior of Complexes with Thioether-Bearing Amino Acids as Tridentate Ligands

Parallel studies of the preparation of Re and (99m)Tc agents aid in interpreting the nature of tracer (99m)Tc radiopharmaceuticals. Aqueous solutions of the fac-[(99m)Tc(CO)(3)(H(2)O)(3)](+) cation are gaining wide use and are readily prepared, but such solutions of the fac-[Re(CO)(3)(H(2)O)(3)](+) cation (1) are not so easily accessible. Herein we describe a new, reliable, and straightforward preparation of aqueous solutions of 1, characterized by HPLC and ESI-MS. Treatment of solutions of 1 with thioether-bearing amino acids, AAH = S-methyl-l-cysteine (MECYSH), S-propyl-l-cysteine (PRCYSH), and methionine (METH), gave high yields of fac-Re(CO)(3)AA complexes. X-ray crystallographic and NMR analyses indicated that MECYS(-), PRCYS(-), and MET(-) were bound in fac-Re(CO)(3)AA complexes as tridentate monoanionic ligands through amino, thioether, and alpha-carboxyl groups. In CD(3)OD, (1)H NMR spectra have broad signals but have two sets of signals at -10 degrees C, consistent with two isomers with different configurations at the pyramidal sulfur; these interconvert slowly on the NMR time scale at low temperatures. Indeed, the crystal structure of the fac-Re(CO)(3)(PRCYS) reveals a mixture of the two possible diastereoisomers. S-(Carboxymethyl)-l-cysteine (CCMH(2)) and 1 gave two products, 5A (kinetically favored) and 5B (thermodynamically favored). X-ray crystallographic analyses of a crystal of 5B and of a 1:1 cocrystal of 5A and 5B showed that 5A and 5B are diastereoisomers with the CCMH(-) alpha-carboxyl group dangling. In addition to the amino and thioether groups, the S-(carboxymethyl) carboxyl group is coordinated, a feature that slows interconversion of diastereoisomers relative to the other fac-Re(CO)(3)AA complexes because interconversion can now occur only after the rupture of Re-ligand bonds. These N, O, and S tridentate adducts are quite stable, and the grouping has promise in (99m)Tc(CO)(3) tracer development.

Production of high purity 94mTc for positron emission tomography studies

The radioisotope 94mTc (T 1/2 = 52.5 min; I β+ = 72%; E β+ = 2.47 MeV) is of considerable interest for quantitative biodistribution studies of Tc radiopharmaceuticals using positron emission tomography. The nuclear processes 94Mo(p,n), 93Nb( 3He,2n), 92Mo(α,pn), and 92Mo(α,2n) 94Ru → 94mTc are of potential interest for the production of 94mTc. Detailed cross section and yield measurements showed that the 94Mo(p,n)-reaction over the energy range E p = 13 → 7 MeV is most suitable: The yield of 94mTc is high (2 GBq/μAh), the impurity level is low (provided highly-enriched 94Mo is used as target material), and a small-sized cyclotron is adequate. Using conventional targetry, sufficient quantities of the radioisotope can be produced. The chemical processing methods employed include both solvent extraction and thermochromatography. The quality of the final product is discussed.

Radio-LC-MS for the characterization of 99mTc-labeled bioconjugates.

This report describes the first example of using radio-LC-MS for determining the composition of (99m)Tc radiopharmaceuticals at the tracer level. The in-line radiometric detector is a useful addition to a standard LC-MS and provides direct correlation between the MS data and the radioactive species in a radiopharmaceutical kit. Complexes [(99m)Tc(HYNICtide)(tricine)(L)] (RP444, L = TPPTS; RP445, L = TPPDS; and RP446, L = TPPMS) were prepared using a decayed generator eluant. All the ternary ligand (99m)Tc complexes show the expected monoprotonated molecular ions, (M + 1)(+), and diprotonated molecular ions, (M + 2)(2+). The LC-MS spectral data support the proposed structure and are consistent with those obtained for their corresponding (99)Tc analogues. Ternary ligand complexes [(99m)Tc(HYNICtide)(tricine)(L)] (L = ISONIC-HE and ISONIC-Sorb) are neutral, and the molecular weights are also lower than that of RP444. Using a fresh generator eluant (24 h prior elution), only 1-2 mCi of (99m)Tc [(7 x 10(-)(12))-(1.5 x 10(-)(11)) mol of technetium complex] are required to obtain a reasonably clean mass spectrum. Radio-LC-MS is a quick and accurate analytical tool for characterization of (99m)Tc radiopharmaceuticals at the tracer level.

Convenient preparation of no-carrier-added technetium-99m radiopharmaceuticals using solid-phase technology.

A solid-phase technetium chelation chemistry was developed as a means of preparing (99m)Tc radiopharmaceuticals at high effective specific activity (HSA). Three peptidic N(3)S (99m)Tc ligands [mercaptoacetyl-Gly-Gly-Gly (MAG3), picolinyl-Ser-Cys-Gly-Thr-Lys-Pro-Pro-Arg (RP063), and dimethyl-Gly-Ser-Cys-Gly-Thr-Lys-Pro-Pro-Arg (RP128)] were used. The free thiol of Cys in each was attached to a series of commercially available amine-functionalized supports in a two-step process. The amine groups on the solid supports were converted to maleimide groups followed by the attachment of the (99m)Tc chelators through a thiol ether linkage with Cys. The optimized loading of the supports ranged 6-122 micromol/g support as determined by amino acid analysis. Each of the peptide-loaded supports (50-100 mg) was placed in either glass syringe vessels or disposable chromatography columns. Labeling with [(99m)Tc]pertechnetate (200-800 MBq) in the presence of stannous gluconate was achieved at room temperature for 30-60 min or in a 100 degrees C water bath for 10 min. Up to 80% of the activity was eluted from the column with saline to give products with purity up to 99.8% as determined by HPLC. Amino acid analysis indicated as little as 100 pmol of peptide present in the (99m)Tc products, demonstrating that extremely high effective specific activity can be achieved without the need for purification.

Relative biological effectiveness of 99m Tc radiopharmaceuticals

The radiotoxicity of three 99mTc-labeled compounds is investigated using spermatogenesis in mouse testis as the experimental model, and spermatogonial cell survival as the biological end point. The radiopharmaceuticals studied are pertechnetate (99mTcO4-), pyrophosphate (99mTc-PYP), and hydroxyethylene diphosphate (99mTc-HDP). The mean lethal doses at 37% survival (D37) are 0.70 +/- 0.06, 0.84 +/- 0.13, and 0.59 +/- 0.08 Gy for 99mTcO4-, 99mTc-PYP, and 99mTc-HDP, respectively. When these results are compared with the D37 value obtained with external x rays or internal gamma rays, the relative biological effectiveness (RBE) of these compounds are 0.94 +/- 0.09, 0.79 +/- 0.13, and 1.1 +/- 0.16, respectively. These results show that the radiotoxicity of 99mTc in mouse testis is essentially similar to that of low-LET radiations (i.e., RBE approximately 1). To understand these results, the distribution of these radiocompounds in the testis is determined and correlated with the observed RBE values. The expected range of RBE values for 99mTc radiopharmaceuticals in organs is 0.95 to 1.5, depending on the fraction of organ activity that is bound to DNA. This suggests that the Auger electrons emitted in the decay of 99mTc are not capable of causing extreme toxicity in vivo. These results provide further support for 99mTc as the radionuclide of choice for imaging in nuclear medicine.