Validation of Tc-labeled “4+1” fatty acids for myocardial metabolism and flow imaging: Part 1: myocardial extraction and biodistribution

Introduction¹³C, ¹⁸F and ¹²³I fatty acids (FA) are used for myocardial imaging. Recently, our group showed that [^99mTc]-labeled “4+1” FA are extracted into the rat and guinea pig myocardium. The present study evaluates determinants of myocardial uptake and whole body biodistribution of these FA derivatives.MethodsStudies were performed with isolated perfused hearts of Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR) with a FAT/CD36 deficiency, as well as with heart type FA binding protein knockout mice (H-FABP)^?/? and H-FABP^+/+. Eight 4+1-^99mTc-FA were applied for 3 min followed by 1-min washout. A mathematical model was used to analyze FA dynamics and binding to proteins. Whole-body distribution was studied in rats with and without Tween 80. In vitro fractionation studies with [^99mTc]-FA assessed red blood cell uptake as well as association with plasma lipoproteins very low-density lipoprotein (VLDL), low-density lipoprotein (LDL) and high-density lipoprotein (HDL).ResultsMyocardial extraction was 19.0–33.0% of the infused dose in isolated WKY and 15.2–26.4% in SHR hearts. However, H-FABP^?/? showed a marked reduction of tracer extraction [2.8±0.6%ID (percent injected dose) vs. 17±2%ID P<.001]. Uptake in red blood cells (<1.2%ID) and incorporation into lipoproteins were negligible. Incubation of ^99mTc-FA with albumin reduced ventricular extraction (P<.001) into the range of established iodinated FA tracers. polyoxyethylene(20) sorbitan monooleate improved the heart-to-liver ratio in the biodistribution studies.ConclusionsMyocardial uptake of [^99mTc]-FA 4+1 derivatives is dependent on H-FABP. These substances may therefore provide a new tool to specifically assess regional myocardial changes of H-FABP.     

Stabilization of [99mTc]HMPAO—1. Ethanolic preparation

The use of [^99mTc]HMPAO for cerebral blood flow imaging has been hampered by the short useful life time of the labelled radiopharmaceutical. Preparation of [^99mTc]HMPAO in 85% ethanol was found to increase the in vitro stability (92% radiochemical purity at 90 min) in comparison to the aqueous preparation (79% at 90 min). Biological distribution studies in mice indicated similar brain uptake (4.42 ± 1.02 and 4.12 ± 0.82% per gram at 20 min) and brain:blood ratio (0.97 ± 0.27 and 1.03 ± 0.20 at 20 min) of the ethanolic (2 h after preparation) and aqueous (15 min after preparation) formulations of [^99mTc]HMPAO respectively. The improved in vitro stability of [^99mTc]HMPAO prepared in 85% ethanol may prove useful in instances where previously the 30 min time limit precluded its use.     

In vitro and in vivo evaluation of [99mTc]-labeled tricarbonyl His-annexin A5 as an imaging agent for the detection of phosphatidylserine-expressing cells

IntroductionApoptosis is one of the mechanisms behind successful chemotherapy and radiation treatment. Radiolabeled annexin A5 has been demonstrated to be a successful tool in the detection of apoptosis following chemotherapy in vivo.MethodsHis-tagged annexin A5 was labeled with [^99mTc]-tricarbonyl and evaluated as apoptosis imaging radiotracer in vitro and in vivo. The binding of the radiotracer was evaluated in Colo205 cells stimulated with 5-FU (1 mM) for 4 and 24 h, and confirmed by flow cytometry. Biodistribution and dosimetric studies were performed in healthy nude mice (n=5) via planar scintigraphy. [^99mTc]-(CO)₃ His-annexin A5 was also evaluated for in vivo imaging of spontaneous apoptosis in Colo205-bearing mice (n=12).ResultsThe labeling procedure yielded a compound with 95-99% radiochemical purity and good in vitro stability. In vitro binding experiments indicated that the radiotracer retained its PS-binding activity. [^99mTc]-(CO)₃ His-annexin A5 rapidly cleared from the blood and predominantly accumulated in the kidneys. Absorbed dose (per organ) was found to be 116±64 μGy/MBq for the kidneys and 10.38±0.50 μGy/MBq for the liver. The effective dose was 7.00±0.28 μSv/MBq. Spontaneous apoptosis in Colo205-bearing mice was visualised by [^99mTc]-(CO)₃ His-annexin A5 SPECT and correlated well with caspase-3 immunostaining (R=0.867, P<.01).Conclusion[^99mTc]-(CO)₃ His-annexin A5 may be a useful novel radioligand for the in vivo detection of cell death associated with PS expression. A simple, noninvasive way of detecting apoptosis in vivo could have many applications including a better understanding of the extent and timing of apoptosis in response to cancer therapies and assessment of early tumor response.     

A comparison of radiopharmaceutical labelling efficiency of chromatographic generator vs MEK extraction [99mTc]pertechnetate

Technetium-99m radiopharmaceuticals prepared for routine clinical use, were labelled with [^99mTc]pertechnetate obtained from either a commercial chromatographic generator or from a Winnipeg Health Sciences Centre semi-automated self-shielded methyl ethyl ketone extraction system. The [^99mTc]pertechnetate source for each ^99mTc radiopharmaceutical was selected at random over a 16 month period of time. The routine quality control data (silica-gel thin layer chromatography) was reviewed retrospectively, as an in vitro assessment of the quality of the [^99mTc]radiopharmaceutical prepared from each [^99mTc]pertechnetate source. Bone scans ([^99mTc]pyrophosphate) and wall motion studies ([^99mTc]red blood cells) were evaluated as an in vivo assessment of the [^99mTc]pertechnetate used to label the pyrophosphate or red blood cells. The in vitro studies indicated no difference in the labelling efficiency and radiochemical purity of the ^99mTc radiopharmaceuticals prepared from either source of [^99mTc]pertechnetate and there was also no difference observed in the image quality of either bone scans or wall motion studies obtained with either source of [^99mTc]pertechnetate.     

Evaluation of the relationship between [18F]FDG and P-glycoprotein expression: an experimental study

IntroductionP-glycoprotein (P-gp) is a cell-membrane-associated protein that transports a variety of drug substrates. We sought to evaluate the relationship between 2-[¹⁸F]fluoro-2-deoxy-d-glucose ([¹⁸F]FDG) and P-gp expression using breast carcinoma Bcap37/multidrug resistant (MDR1) and Bcap37 in vitro and in vivo.MethodsThe function of P-gp expressed in Bcap37/MDR1 cells was evaluated using verapamil (VER), a classical inhibitor of P-gp. The accumulation of ^99mTc-methoxyisobutylisonitrile ([^99mTc]MIBI) in vitro was measured. In vivo imaging of severe combined immune deficiency (SCID) mice implanted with Bcap37 and Bcap37/MDR1 cells was performed by scintigraphy and micro-positron emission tomography (PET).ResultsThe uptake of [^99mTc]MIBI was 0.62%±0.05% in the Bcap37/MDR1 cells and 2.02%±0.28% in the Bcap37 cells. VER significantly increased the uptake of [^99mTc]MIBI in the Bcap37/MDR1 cells (1.90%±0.09%) but not in the Bcap37 cells (2.15%±0.27%). In vivo, neither the Bcap37 nor Bcap37/MDR1 tumors grown in the SCID mice could be detected by [^99mTc]MIBI scintigraphy. Both the Bcap37 and Bcap37/MDR1 tumors were visible by micro-PET. The mean standardized uptake value (SUV) was significantly higher in the Bcap37 tumors (1.00±0.06) than in the Bcap37/MDR1 (0.67±0.11) tumors. VER significantly increased the mean SUV in the Bcap37/MDR1 tumors (1.02±0.16) but not in the Bcap37 tumors (1.09±0.22).Conclusions[¹⁸F]FDG combined with VER may be an effective noninvasive method of determining P-gp expression in tumors.     

Synthesis and biological evaluation of a 99mTc-labelled sulfonamide conjugate for in vivo visualization of carbonic anhydrase IX expression in tumor hypoxia

IntroductionCarbonic anhydrase (CA) IX is a transmembrane protein overexpressed in many frequently occurring tumors associated with tumor hypoxia. Sulfonamides and their bioisosteres are known to inhibit CA IX activity. In this study, 4-(2-aminoethyl)benzenesulfonamide was conjugated to a tridentate ligand, N-2-picolyl-N-acetic acid and labeled with a ^99mTc(I)-tricarbonyl moiety resulting in [^99mTc(CO)₃ (L)] (L=N-(pyridin-2-yl-methyl)-N[2-(4-sulfamoylphenyl)-ethyl]aminoethyl acetate) complex, [^99mTc]-5. Similarly the corresponding rhenium congener (Re-4) was synthesized. The in vitro CA IX affinity and inhibitory activity of Re-4 were determined and [^99mTc]-5 was evaluated as a tracer for in vivo visualisation of CA IX expression.MethodsEvaluation of the in vitro affinity (inhibition constant, K_i) of Re-4 for CA isozymes I, II, IX and XII was carried out by assaying the CA catalyzed CO₂ hydration activity and efficacy studies were performed in HT 29 cell lines expressing CA IX under normoxia or hypoxia. Biodistribution studies of [^99mTc]-5 were performed in xenograft mice bearing CA IX expressing tumors.ResultsThe in vitro affinity of Re-4 for CA IX was 58 nM and CA IX induced acidification of extracellular medium was efficiently reduced (P<.05) in the presence of 1 mM Re-4. Biodistribution studies indicated a maximal tumor uptake of [^99mTc]-5 of 0.1% ID/g at 30 min post injection.Conclusion[^99mTc]-5 and its rhenium congener were synthesized and characterized. In vitro studies showed that the rhenium compound has a high affinity for CA IX and effectively inhibits CA IX activity. In vivo studies revealed a limited tracer accumulation in a CA IX expressing tumor but with increasing tumor-to-blood activity ratios as a function of time.     

[<Superscript>99m</Superscript>Tc]Demotensin 5 and 6 in the NTS1-R-targeted imaging of tumours: synthesis and preclinical results

Purpose The aim of this study was to evaluate the applicability of [^99mTc]Demotensin 5 and 6 in the targeted diagnostic imaging of neurotensin subtype 1 receptor (NTS1-R)-expressing tumours. Methods Labelling of Demotensin 5 and 6 with ^99mTc was conducted by brief incubation with ^99mTcO₄ ⁻, SnCl₂ and citrate anions in alkaline medium at ambient temperature. Affinities of conjugates for the NTS1-R were determined by competition binding experiments in WiDr cell membranes using [¹²⁵I-Tyr³]NT as the radioligand. Saturation binding assays were conducted for [^99mTc/^99gTc]Demotensin 6 in WiDr cell membranes. Internalisation of [^99mTc]Demotensin 5 and 6 was studied at 37°C in WiDr cells. Biodistribution of [^99mTc]Demotensin 5 and 6 was performed in female Swiss nu/nu mice bearing human WiDr xenografts. Results Unlabelled conjugates showed a high affinity for the human NTS1-R (Demotensin 5 IC₅₀=0.03±0.01 nM; Demotensin 6 IC₅₀=0.08±0.02 nM), while high affinity was also exhibited by (radio)metallated [^99mTc/^99gTc]Demotensin 6 (K _d=0.13±0.01 nM). [^99mTc]Demotensin 5 and 6 internalised rapidly and specifically in WiDr cells. After injection in WiDr tumour-bearing mice, radiopeptides, and especially the doubly stabilised [^99mTc]Demotensin 6, showed NTS1-R-mediated uptake in the intestines and in the implanted tumour (4.30±0.45%ID/g at 1 h post injection) and rapid renal excretion from non-target tissues into the urine. Conclusion [^99mTc]Demotensin 6 shows a favourable preclinical profile and further testing in patients is warranted to monitor its eventual applicability as a radiotracer in the diagnostic imaging of NTS1-R-positive tumours.     

Is [99mTc]glucarate uptake mediated by fructose transporter GLUT-5?

PurposeThere is growing interest in the ability of [^99mTc]Glucarate ([^99mTc]GLA) to accumulate in viable tumor cells. Recent vivo studies suggest that [^99mTc]Glucarate could be helpful for tumor detection. Fructose transport is thought to be implicated. It is clearly established that facilitated fructose transport in tumor cells is related to the GLUT-5 transporter. This study therefore investigated whether [^99mTc]GLA uptake is mediated by GLUT-5 transporter.MethodsDifferent tumor cell lines were used. Modulation of GLUT-5 expression was assessed with and without antisense oligonucleotides directed against GLUT-5. GLUT-5 expression was assessed by indirect cell ELISA. To correlate GLUT-5 expression with tracer accumulation, [^99mTc]GLA uptake was determined after antisense treatment. A competition with fructose was also monitored.ResultsInhibition of GLUT-5 expression by antisense oligonucleotides directed against GLUT-5 was effective after 24 h. An optimal of 10 μM antisense oligonucleotides directed against GLUT-5 produced a 30%–40% decrease in protein expression. Modulation of [^99mTc]GLA uptake was monitored either by use of specific antisense oligonucleotides or by competition with fructose. Both of them produced a significant decrease of [^99mTc]GLA accumulation in all tested cell lines.ConclusionOur results clearly demonstrate that [^99mTc]GLA uptake is related to GLUT-5 transporter expression and transport. In tumor imaging, [^99mTc]GLA may be a useful tool for non-invasive detection of malignant tumors expressing high levels of GLUT-5 transporter as, for example, breast cancers.     

Biodistribution imaging of a paclitaxel-hyaluronan bioconjugate

IntroductionGamma-ray detectors represent sensitive and noninvasive instruments to evaluate in vivo the metabolic trapping of radiopharmaceuticals. This study aimed to assess the imaging biodistribution of a [^99mTc]-radiolabelled new prototype bioconjugate composed of paclitaxel linked to hyaluronan (ONCOFID-P).MethodsA small gamma camera providing high-resolution images was employed. Imaging of biodistribution following intravenous, intraperitoneal, intravesical and oral administration was carried out for a 2-h period in anesthetized mice receiving [^99mTc]ONCOFID-P. At the end of the observation time, radioactivity in organs was directly measured. As a control, groups of mice were treated with free [³H]paclitaxel given according to the same administration routes, and organ biodistribution of the drug was assessed after 2 h.ResultsIntravenous inoculation of [^99mTc]ONCOFID-P was followed by a rapid and strong liver uptake. In fact, almost 80% of the imaging signal was detected in this organ 10 min after injection and such value remained constant thereafter, thus indicating that the bioconjugate given through the intravenous route could be well suited to targeting primary or metastatic liver neoplasias. Imaging of the bladder, abdomen and gastrointestinal tract after local administration disclosed that the radiolabelled compound remained confined to the cavities, suggesting a potential regional application for transitional bladder cell carcinomas, ovarian cancers and gastric tumors, respectively. Free [³H]paclitaxel biodistribution profoundly differed from that of [^99mTc]ONCOFID-P.ConclusionsConjugation of drugs with polymers results in new chemical entities characterized by a modified biodistribution pattern. Therefore, preclinical studies based on imaging analysis of such new compounds can suggest novel therapeutic applications.     

<Superscript>18</Superscript>F-labelled annexin V: a PET tracer for apoptosis imaging

Annexin V can be used to detect apoptotic cells in vitro and in vivo, based on its ability to identify extracellular phosphatidylserine, which arises during apoptosis. In the present study, we examined the synthesis of fluorine-18 labelled annexin V as a positron emission tomography tracer for apoptosis imaging. The distribution of [¹⁸F]annexin V and technetium-99m labelled annexin V, a well-characterised SPET tracer for apoptosis imaging, was compared. [¹⁸F]annexin V was synthesised using N-succinimidyl 4-[¹⁸F]fluorobenzoate as an ¹⁸F labelling reagent. Synthesised and purified [¹⁸F]annexin V was confirmed by SDS-PAGE. In an ex vivo imaging experiment, [¹⁸F]annexin V was intravenously injected into rats 24 h after the induction of myocardial ischaemia, and accumulation in the left ventricle was examined. [¹⁸F]annexin V accumulated in the infarct area of the left ventricle, where apoptotic cells were observed. In separate experiments, [¹⁸F]annexin V or [^99mTc]annexin V was intravenously injected into ischaemic or normal animals, and the distribution of the tracers was compared. In ischaemic animals, accumulation of [¹⁸F]annexin V and [^99mTc]annexin V in the infarct area was about threefold higher than in the non-infarct area. Furthermore, the ratio of accumulation in the normal heart to the blood radioactivity was not significantly different between the tracers. In normal animals, however, the uptake of [¹⁸F]annexin V in the liver, spleen and kidney was much lower than that of [^99mTc]annexin V. The low uptake of [¹⁸F]annexin V in these organs might represent an advantage over [^99mTc]annexin V.     

An automated module for the separation and purification of cyclotron-produced 99mTcO4-

IntroductionThe shortage of reactor-produced molybdenum-99 (⁹⁹Mo, t_½=66 h) has renewed interest in alternative production methods of its daughter isotope, technetium-99m (^99mTc, t_½=6.02 h). While adsorption chromatography serves as a mechanism for selective elution of sodium pertechnetate from technetium generators, this method of purification is not sufficient for many alternative production methods. Several ion-separation/solid phase extraction chromatography methods are known, yet none have been demonstrated on cyclotron-produced [^99mTc]TcO₄^?. Herein we describe the design, manufacture and optimization of a remotely operated module for the purification of sodium pertechnetate from a bulk solution of molybdate.MethodsThe automated purification module was designed to separate [^99mTc]TcO₄^? using either Dowex 1x8 or an Aqueous Biphasic Extraction Chromatography (ABEC) resin. ¹⁰⁰Mo composite targets were irradiated with 18.5 MeV protons for 10 μA·h using an ASCI TR19 cyclotron. Once purified, the radiopharmaceutical quality of ^99mTcO₄^? isolated from each process (Dowex and/or ABEC) was established by assaying for molybdate breakthrough, alumina levels and, in the case of the Dowex approach, residual organics.ResultsThe separation processes are efficient (75% for Dowex, 90% for ABEC) and complete in less than 30 min. Overall, up to 2.1 GBq of ^99mTc was produced using the ¹⁰⁰Mo(p,2n)^99mTc transformation, processed using the separation module and subjected to a detailed chemical and radionuclidic analysis. Due to its expense and limited availability, ¹⁰⁰MoO₄^2? was recovered in >90% yield using a precipitation/filtration/lyophilization approach.ConclusionsNa[^99mTc]TcO₄ was produced using a medical cyclotron, recovered using an automated purification module and found to exceed all established quality control parameters.     

Sentinel lymph node accumulation of Lymphoseek and Tc-99m-sulfur colloid using a “2-day” protocol

Lymphoseek is a receptor-binding radiopharmaceutical specifically designed for sentinel lymph node (SLN) mapping. We conducted a clinical trial which measured the injection site clearance and sentinel lymph node accumulation after a single intradermal injection of Lymphoseek or unfiltered [^99mTc]sulfur colloid (TcSC) using a “2-day” protocol for SLN mapping of breast cancer. Eleven patients with breast cancer participated in this study. Five patients received an intradermal administration of 1.0 nmol of ^99mTc-labeled Lymphoseek; SLN mapping was performed on four subjects within 19 to 27 h. Six subjects received an intradermal administration of TcSC; SLN mapping was performed on five subjects within 18 to 26 h. Lymphoseek exhibited a significantly (P<.001) faster injection site clearance than TcSC. The mean Lymphoseek clearance half-time was 2.18±1.09 h compared to 57.4±92.8 h for TcSC. The mean sentinel lymph node uptake of Lymphoseek (1.5±1.7%) and TcSC (3.5±3.1%) was statistically equivalent (P=.213). When an intradermal injection is employed, Lymphoseek demonstrated faster injection site clearance than unfiltered [^99mTc]sulfur colloid and persistent SLN accumulation for at least 24 h.     

Insights into the failure of the potential, neutral myocardial imaging agent TcN-NOET: physicochemical identification of by-products and degradation species

IntroductionThe neutral complex [^99mTc(N)(NOEt)₂], often referred to as TcN-NOET [NOEt=N-ethoxy,N-ethyldithiocarbamate(1?)], was proposed several years ago as a myocardial imaging agent. Despite some favorable clinical properties evidenced during phase I and phase II studies, the overall results of the European and American phase III clinical studies have been judged insufficient for a successful approval process by the regulatory agencies.MethodsNon-carrier-added and carrier-added experiments using short-lived ^99mTc and long-lived ^99gTc have been utilized to prepare a series of bis-substituted [Tc(N)(DTC)₂] complexes [DTC=dithiocarbamate(1?)]. They have been purified by means of chromatographic techniques (high-performance liquid chromatography and thin-layer chromatography) and identified via double detection (UV-vis and radiometry) by comparison with authenticated samples of ^99gTc compounds prepared by conventional coordination chemistry procedures.ResultsThe molecular structure of the lipophilic, neutral complex cis-[Tc(N)(NOEt)₂] has been assigned by comparison with similar nitrido-Tc(V) complexes already reported in the literature. Novel bis-substituted nitrido-Tc complexes containing hydrolyzed portions of coordinated NOEt, namely, N-ethyldithiocarbamate [NHEt(1?)] and N-hydroxy, N-ethyldithiocarbamate [NOHEt(1?)], have been prepared and characterized by means of multinuclear nuclear magnetic resonance spectroscopy and mass spectrometry.ConclusionsDespite the identification of these “hydrolyzed” species, it is still unclear whether the failure to reach the clinical goal of the perfusion tracer [^99mTc(N)(NOEt)₂] is related to the degradation processes evidenced in this study or is the result of the mediocre imaging properties of the tracer.     

Targeting murine heart and brain: visualisation conditions for multi-pinhole SPECT with <Superscript>99m</Superscript>Tc- and <Superscript>123</Superscript>I-labelled probes

Purpose  The study serves to optimise conditions for multi-pinhole SPECT small animal imaging of ¹²³I- and ^99mTc-labelled radiopharmaceuticals with different distributions in murine heart and brain and to investigate detection and dose range thresholds for verification of differences in tracer uptake. Methods  A Triad 88/Trionix system with three 6-pinhole collimators was used for investigation of dose requirements for imaging of the dopamine D₂ receptor ligand [¹²³I]IBZM and the cerebral perfusion tracer [^99mTc]HMPAO (1.2–0.4 MBq/g body weight) in healthy mice. The fatty acid [¹²³I]IPPA (0.94 ± 0.05 MBq/g body weight) and the perfusion tracer [^99mTc]sestamibi (3.8 ± 0.45 MBq/g body weight) were applied to cardiomyopathic mice overexpressing the prostaglandin EP₃ receptor. Results  In vivo imaging and in vitro data revealed 45 kBq total cerebral uptake and 201 kBq cardiac uptake as thresholds for visualisation of striatal [¹²³I]IBZM and of cardiac [^99mTc]sestamibi using 100 and 150 s acquisition time, respectively. Alterations of maximal cerebral uptake of [¹²³I]IBZM by >20% (116 kBq) were verified with the prerequisite of 50% striatal of total uptake. The labelling with [^99mTc]sestamibi revealed a 30% lower uptake in cardiomyopathic hearts compared to wild types. [¹²³I]IPPA uptake could be visualised at activity doses of 0.8 MBq/g body weight. Conclusion  Multi-pinhole SPECT enables detection of alterations of the cerebral uptake of ¹²³I- and ^99mTc-labelled tracers in an appropriate dose range in murine models targeting physiological processes in brain and heart. The thresholds of detection for differences in the tracer uptake determined under the conditions of our experiments well reflect distinctions in molar activity and uptake characteristics of the tracers. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Visualizing inflammation activity in rheumatoid arthritis with Tc-99 m Anti-CD4-mAb fragment scintigraphy

PurposeT-cell-located CD4 antigen represents one of the therapeutic targets in rheumatoid arthritis (RA). However, up to now there is no established imaging tool to visualize this target in vivo. The aim of our study was to assess the safety and tolerability of a technetium-99 m labelled murine anti-human CD4 IgG1-Fab fragment ([^99mTc]-anti-CD4-Fab, [^99mTc]-EP1645) in patients with active synovitis due to RA, and to evaluate its potential as a marker of disease activity.MethodsIn the present phase I proof of principle study five patients with RA were examined. Planar scans of the whole body, hands, and feet were taken 30 min up to 24 h after application of 550 ± 150 MBq [^99mTc]-anti-CD4-Fab, followed by visual analyses, comparison with clinical data in 68 joints per patient and semiquantitative analysis of hand and wrist joints.ResultsNeither infusion related adverse events nor adverse events during follow up were observed. No increase in human anti-murine antibody titres was seen. All patients had positive scans in almost 70% of clinically affected joints. Positive scans were also found in 8% of joints without evidence of swelling or tenderness.ConclusionScintigraphy with [^99mTc]-anti-CD4-Fab is a promising technique for evaluation of inflammatory activity in patients with RA, pre-therapeutical evaluation of CD4 status and therapy control. Tracer uptake in clinically inconspicuous joints strongly indicates diagnostic potential of [^99mTc]-anti-CD4-Fab. Whether this technique is eligible as a prognostic factor in RA needs to be analysed in further studies as well as the pathophysiological background of clinically affected joints lacking tracer uptake.     

Evaluation of 99mTc(CO)5I as a potential lung perfusion agent

IntroductionThe use of ^99mTc-macroggregated albumin for lung perfusion imaging is well established in nuclear medicine. However, there have been safety concerns over the use of blood-derived products because of potential contamination by infective agents, for example, Variant Creutzfeldt Jakob Disease. Preliminary work has indicated that Tc(CO)₅I is primarily taken up in the lungs following intravenous administration. The aim of this study was to evaluate the biodistribution and pharmacokinetics of ^99mTc(CO)₅I and its potential as a lung perfusion agent.Methods^99mTc(CO)₅I was synthesized by carbonylation of ^99mTcO_4? at 160 atm of CO at 170°C in the presence of HI for 40 min. Radiochemical purity was determined by HPLC using ⁹⁹Tc(CO)₅I as a reference. ^99mTc(CO)₅I was administered by ear-vein injection to three chinchilla rabbits, and dynamic images were acquired using a gamma camera (Siemens E-cam) over 20 min. Imaging studies were also performed with ^99mTc-labeled macroaggregated albumin (^99mTc-MAA) and ^99mTcO_4? for comparison. ^99mTc(CO)₅I was administered intravenously to Sprague–Dawley rats, and tissue distribution studies were obtained at 15 min and 1 h postinjection. Comparative studies were performed using ^99mTc-MAA.ResultsRadiochemical purity, assessed by HPLC, was 98%. The retention time was similar to that of ⁹⁹Tc(CO)₅I. The dynamic images showed that 70% of ^99mTc(CO)₅I appeared promptly in the lungs and remained constant for at least 20 min. In contrast, ^99mTcO_4? rapidly washed out of the lungs after administration. As expected ^99mTc-MAA showed 90% lung accumulation. The percentage of injected dose per gram of organ ±S.D. at 1 h for ^99mTc(CO)₅I was as follows: blood, 0.22±0.02; lung, 12.8±2.87; liver, 0.8±0.15; heart, 0.15±0.01; kidney, 0.47±0.08. The percentage of injected dose per organ ±S.D. at 1 h was as follows: lung, 22.47±2.31; liver, 10.53±1.8; heart, 0.18±0.01; kidney, 1.2±0.17. Tissue distribution studies with ^99mTc-MAA showed 100% lung uptake.Conclusion^99mTc(CO)₅I was synthesized with a high radiochemical purity and showed a high accumulation in the lungs. Further work on the mechanism and optimization of lung uptake of ^99mTc-pentacarbonyl complexes is warranted.     

Dual-isotope single-photon emission computed tomography for dopamine and serotonin transporters in normal and parkinsonian monkey brains

IntroductionParkinson's disease (PD) affects both dopaminergic and serotonergic systems. In this study, we simultaneously evaluated dopamine and serotonin transporters in primates using dual-isotope single-photon emission computed tomography (SPECT) imaging and compared the results with traditional single-isotope imaging.MethodsFour healthy and one 6-OHDA-induced PD monkeys were used for this study. SPECT was performed over 4 h after individual or simultaneous injection of [^99mTc]TRODAT-1 (a dopamine transporter imaging agent) and [¹²³I]ADAM (a serotonin transporter imaging agent).ResultsThe results showed that the image quality and uptake ratios in different brain regions were comparable between single- and dual-isotope studies. The striatal [^99mTc]TRODAT-1 uptake in the PD monkey was markedly lower than that in normal monkeys. The uptake of [¹²³I]ADAM in the midbrain of the PD monkey was comparable to that in the normal monkeys, but there were decreased uptakes in the thalamus and striatum of the PD monkey.ConclusionsOur results suggest that dual-isotope SPECT using [^99mTc]TRODAT-1 and [¹²³I]ADAM can simultaneously evaluate changes in dopaminergic and serotonergic systems in a PD model.     

放射性药物99mTc-HL91在大鼠脑缺血模型的初步研究

目的 探讨国内首次合成的放射性药物＾９９ｍＴｃ－ＨＬ９１在脑血管疾病诊断中的应用的可能性。方法 对＾９９ｍＴｃ－ＨＬ９１进行一般性质、标记率、体外稳定性、异常毒性和正常小鼠体内生物分布等实验。建立１５只大鼠脑缺血模型,并在该模型上进行＾９９ｍＴｃ－ＨＬ９１体内分布和乏氧显像研究。结果（１）ＨＬ９１药盒标记简便,安全稳定,（２）正常小鼠静脉注射＾９９ｍＴｃ－ＨＬ－９１后血中放射性迅速下降,肝、肾和胃     

Left ventricular dysfunction in coronary artery disease: Comparison between rest-redistribution thallium 201 and resting technetium 99m methoxyisobutyl isonitrile cardiac imaging

Background

We compared rest-redistribution thallium 201 and resting technetium 99m methoxyisobutyl isonitrile (MIBI) cardiac imaging in 29 men with angiographically proven coronary artery disease and regional ventricular dysfunction. Left ventricular ejection fraction at radionuclide angiography was 35%±9%.

Methods and Results

Regional left ventricular wall motion was assessed on gated^99mTc MIBI images according to a 3-point scale (0=normal, 1=hypokinetic, 2=akinetic or dyskinetic).²⁰¹Tl and^99mTc MIBI uptake values were analyzed quantitatively. A total of 435 myocardial segments were classified on the basis of wall motion analysis into three groups: group 1 (normal wall motion;n=201), group 2 (hypokinetic;n=132), and group 3 (akinetic or dyskinetic;n=102).²⁰¹Tl and^99mTc MIBI uptake values were significantly higher in groups 1 and 2 compared with group 3 (p<0.05) and in group 1 compared with group 2 (p<0.05). When²⁰¹Tl and^99mTc MIBI uptake values were directly compared, no significant differences in groups 1 and 2 were observed. In group 3,^99mTc MIBI uptake (67%±14%) was significantly lower (p<0.001) than initial (72%±11%) and delayed²⁰¹Tl uptake (73%±12%).

Conclusion

Thus rest-redistribution²⁰¹Tl and resting^99mTc MIBI cardiac imaging reflect the severity of left ventricular dysfunction in coronary artery disease. However, in segments with severely impaired regional ventricular function,²⁰¹Tl uptake is significantly higher than^99mTc MIBI uptake.     

In vivo imaging of serotonin transporters with [99mTc]TRODAT-1 in nonhuman primates

[^99mTc]TRODAT-1 was the first ^99mTc-labeled imaging agent to show specific binding to dopamine transporters (DAT) in the striatum (STR) of human brain. Additionally, in vitro binding and autoradiographic experiments demonstrated that this tracer also binds to serotonin transporters (SERT) in the midbrain/hypothalamus (MB) area. In this study, [^99mTc]TRODAT-1 was investigated as a potentially useful ligand to image SERT in the MB of living brain. A total of eight single-photon emission tomography (SPET) scans were performed in two baboons (Papio anubis) after intravenous (i.v.) injection of 740 MBq (20 mCi) of [^99mTc]TRODAT-1 using a triple-head gamma camera equipped with ultra-high-resolution fan-beam collimators (scan time: 0–210 min). In four blocking studies, baboons were pretreated with (+)McN5652 (1 mg/kg, i.v.) or methylphenidate (1 mg/kg, i.v.) to specifically block SERT or DAT, respectively. After co-registration with magnetic resonance images of the same baboon, a region of interest analysis was performed using predefined templates to calculate specific uptake in the midbrain area and the striatum, with the cerebellum as the background region [(MB–CB)/CB, (STR–CB)/CB]. Additionally, two PET scans of the same baboons were performed after i.v. injections of 74–111 MBq (2–3 mCi) of [¹¹C](+)McN5652 to identify the SERT sites. In [^99mTc]TRODAT-1/SPET scans, the SERT sites in the MB region were clearly visualized. Semiquantitative analysis revealed a specific uptake in MB ([MB–CB]/CB) of 0.30±0.02, which was decreased to 0.040±0.005 after pretreatment with nonradioactive (+)McN5652, a selective SERT ligand. Pretreatment with methylphenidate reduced the specific binding of [^99mTc]TRODAT-1 to DAT sites [(STR-CB)/CB] from 2.45±0.13 to 0.32±0.04 without any effect on its binding to SERT sites [(MB–CB)/CB], which was confirmed by the co-registration of the [¹¹C](+)McN5652/PET scans. This preliminary study suggests that specific binding of [^99mTc]TRODAT-1 to SERT sites can be detected by in vivo SPET imaging despite the low target to background ratio. These findings provide impetus for further development of similar compounds with improved binding affinity and selectivity to SERT sites. Received 15 September and in revised form 15 November 1998