99mTc‐labeled DTPA‐colchicine dimer with improved tumor uptake

This work reports the synthesis, radiolabeling, and biological studies of ^99mTc‐diethylene triamine pentaacetic acid (DTPA)‐colchicine dimer in tumor‐bearing mice. The novel colchicine dimer was successfully synthesized by conjugation of DTPA to 2 colchicine biomolecules. The ligand could be labeled by ^99mTc in high yield to get ^99mTc‐DTPA‐colchicine dimer, which was hydrophilic and stable at room temperature. Biodistribution and imaging studies in tumor‐bearing mice showed that ^99mTc‐DTPA‐colchicine dimer accumulated in the tumor with improved uptake and retention. The results indicate the need for synthetic modification of the parent colchicine derivative and the ^99mTc‐chelate with a view to improve the tumor‐targeting efficacy and in vivo kinetic profiles.     

Synthesis, 99mTc‐labeling,and preliminary biological evaluation of DTPA‐melphalan conjugates

Melphalan (MFL) is a typical nitrogen mustard for the treatment of many types of cancer. For the purpose to develop novel ^99mTc‐labeled tumor imaging agents with SPECT, MFL was directly labeled by ^99mTc using diethylene triamine pentacetate acid (DTPA) as bifunctional chelating agent. The novel ligands were successfully synthesized by conjugation of DTPA to MFL to get monosubstituted DTPA‐MFL and bis‐substituted DTPA‐2MFL. Radiolabeling was performed in high yield to get ^99mTc‐DTPA‐MFL and ^99mTc‐DTPA‐2MFL, respectively, which were hydrophilic and stable at room temperature. The high initial tumor uptake with retention, good tumor/muscle ratios, and satisfactory scintigraphic images suggested the potential of ^99mTc‐DTPA‐MFL and ^99mTc‐DTPA‐2MFL for tumor imaging. However, the slow normal tissue clearance would be a great obstacle. Further modification on the linker and/or ^99mTc‐chelate to improve the tumor targeting efficacy and in vivo kinetic profiles is currently in progress.     

Quality control methods for 99mTc‐labeled exogenous natural surfactant (99mTc‐ENS)

To standardize the quality control for ^99mTc‐ENS, the following methods were studied: (1) physical properties and pH, (2) radiochemical purity (chromatographic studies on Whatman‐1 paper, or instant thin‐layer chromatography and solvent extraction using different solvents and (3) rat biodistribution studies by intratracheal injection. The tolerance limits were fixed for each method. The radiopharmaceutical stability was also evaluated. The results showed that ^99mTc‐ENS was a white suspension with a pH between 4.0 and 6.0. The limit for radiochemical impurities in Whatman‐1 paper/acetone was fixed at lower than 2% and the established limit for the organic aliquot in cyclohexane extraction was greater than 2%. In the biodistribution studies, the limits for activity concentration were fixed at greater than 90% for lungs, less than 9% for the gastrointestinal system and less than 1% for the sum of the other organs studied. After a storage time of 6 h at room temperature or in a refrigerator, ^99mTc‐ENS physical properties and pH, radiochemical and biodistribution results were within the established values. In conclusion, the quality control methods for ^99mTc‐ENS are tests on physical properties and pH, radiochemical purity by Whatman‐1 paper/acetone chromatography and cyclohexane extraction and biodistribution studies in rats. The stability of this radiopharmaceutical is at least 6 h at room temperature. Copyright © 2003 John Wiley & Sons, Ltd.     

Synthesis and Evaluation of Technetium-99m-Labeled Bioreductive Pharmacophores Conjugated with Amino Acids and Peptides for Tumor Imaging

Development of molecular imaging agents to target tumor has become a major trend in nuclear medicine. With the aim to develop new potential ^99mTc-radiopharmaceuticals for targeting tumor, we have synthesized 5-nitroimidazolyl amino acids and RGD-coupled 2-nitroimidazoles. Technetium-99m radiolabeling with high radiochemical purity (>90%) was achieved for all the compounds. The radiolabeled complexes exhibited substantial in vitro stability in saline, serum, and histidine solution (10⁻² m ). Cell binding studies in EAC and B16F10 cell lines also revealed rapid and comparatively high cellular internalization. Among all the compounds studied, the binding of ^99mTc(CO)₃- 5 to B16F10 cells was moderately inhibited by the competitive peptide c[RGDfV], suggesting specificity of the radioligand toward α_vβ₃ receptor. However, no significant displacement of bound radioligand was observed when the binding of the ^99mTc-labeled complexes to above cells was challenged with excess competitive peptide. Fluorescent microscopy study provided direct evidence of intracellular localization of 5(6)-carboxyfluorescein-labeled 2-nitroimidazolyl-RGD-peptide in α_vβ₃-positive B16F10 mouse melanoma cell line. The ligands caused only 8–13% of hemolysis toward rat erythrocytes at concentrations as high as 100 μm . Imaging and biodistribution studies were performed in Swiss albino mice bearing induced tumor. ^99mTc- 1 and ^99mTc(CO)₃- 5 demonstrated a very favorable in vivo profile. Selective uptake and retention in tumor with encouraging tumor/muscle and tumor/blood ratio and significant cellular uptake of fluorescence-labeled-2-nitroimidazolyl RGD indicate the great potentiality of the pharmacophore for further evaluation as potential molecular imaging agent in cancer diagnosis.     

Initial evaluation of 99mTc‐tricarbonyl‐cyclopentadienyl fatty acids derivatives as SPECT tracers for myocardium

Fatty acids are myocardial metabolic agent for detecting myocardial ischemia and infraction. However, no ^99mTc‐labeled fatty acids had potential use in clinical practice. In this study, ^99mTc‐CpTT‐10‐oxo‐para‐PPA ( 1d ), ^99mTc‐CpTT‐11‐oxo‐para‐PPA ( 2d ), ^99mTc‐CpTT‐12‐oxo‐para‐PPA ( 3d ), ^99mTc‐CpTT‐11‐oxo‐ortho‐PPA ( 4d ), and ^99mTc‐CpTT‐11‐oxo‐meta‐PPA ( 5d ) were synthesized by a double ligand transfer reaction, and their biological behaviors were investigated. Compound 2d achieved good heart to blood ratio (3.39 at 5 min after intravenous), and 2d showed high‐heart uptake of 6.20% ID/g at 5 minutes after injection. Compound 3d displayed a prolonged retention in the myocardium (1.43% ID/g at 60 min after injection). Radioactivity accumulation in the lungs, spleen, and blood was eliminated rapidly. In vivo, metabolite analysis presented that compound 6d may be metabolite of 2d through β‐oxidation in tissue. Unfortunately, the biodistribution studies of 1d , 2d , 3d , 4d , and 5d showed fast heart clearance and poor heart to liver ratios, which suggested that the 5 ^99mTc‐labeled fatty acid analogues cannot be used for diagnosis.     

Design of 99mTc‐DTPA‐CLP and Preliminary Evaluation in Rats

Radiopharmaceuticals are localized in (malignant) tumor tissues by different mechanisms. One of these mechanisms, gelatinase enzyme activity, is associated with poor prognosis in cancer patients and potential targets for tumor imaging. There are some gelatinases to be associated with metastatic potential for tumor imaging to possibly predict metastases. In this study, a cyclic decapeptide conjugate, DTPA‐CLP (DTPA‐Cys‐Leu‐Pro‐Gly‐His‐Trp‐Gly‐Phe‐Pro‐Ser‐Cys), was selected as a peptide conjugate because of its selective inhibitory activity toward gelatinases. Peptide‐conjugated DTPA‐CLP was labeled with ^99mTc with a radiolabeling efficiency of 97.0 ± 2.8%. After determining optimization conditions for radiolabeling, a biodistribution study of radiolabeled peptide in albino Wistar rats was performed. According to biodistribution data, ^99mTc‐DTPA‐CLP showed high uptake in the lung, liver, uterus, and spleen. These results show that ^99mTc‐DTPA‐CLP may be used for the imaging of gelatinase activity in metastatic tumors.     

99mTc‐anti‐epidermal growth factor receptor nanobody for tumor imaging

Nanobodies are important biomolecules for tumor targeting. In this study, we synthesized and labeled anti‐epidermal growth factor receptor (EGFR) nanobody OA‐cb6 with ^99mTc(CO)₃⁺ and evaluated its characteristics for targeting the EGFR in the A431 human epidermal carcinoma cell line. Nanobody radiolabeling was achieved with high yield and radiochemical purity, and the radioconjugate was stable. Biodistribution results in nude mice exhibited a favorable tumor‐to‐muscle ratio at 4‐hr postinjection, and tumor location was visualized at 4 hr after injection of radiolabeled nanobody. Our result showed that the OA‐cb6‐^99mTc‐tricarbonyl radiolabeled nanobody is a promising radiolabeled biomolecule for tumor imaging in cancers with high EGFR overexpression.     

Preparation and comparative evaluation of 99mTc‐HYNIC‐cNGR and 99mTc‐HYNIC‐PEG2‐cNGR as tumor‐targeting molecular imaging probes

The tripeptide sequence asparagine‐glycine‐arginine (NGR) specifically recognizes aminopeptidase N (APN or CD13) receptors highly expressed on tumor cells and vasculature. Thus, NGR peptides can precisely deliver therapeutic and diagnostic compounds to CD13 expressing cancer sites. In this regard, 2 NGR peptide ligands, HYNIC‐c(NGR) and HYNIC‐PEG₂‐c(NGR), were synthesized, radiolabeled with ^99mTc, and evaluated in CD13‐positive human fibrosarcoma HT‐1080 tumor xenografts. The radiotracers, ^99mTc‐HYNIC‐c(NGR) and ^99mTc‐HYNIC‐PEG₂‐c(NGR), could be prepared in approximately 95% radiochemical purity and exhibited excellent in vitro and in vivo stability. The radiotracers were hydrophilic in nature with log P values being ?2.33 ± 0.05 and ?2.61 ± 0.08. The uptake of 2 radiotracers ^99mTc‐HYNIC‐c(NGR) and ^99mTc‐HYNIC‐PEG₂‐c(NGR) was similar in nude mice bearing human fibrosarcoma HT‐1080 tumor xenografts, which was significantly reduced (P < .05) during blocking studies. The 2 radiotracers being hydrophilic cleared rapidly from blood, liver, and intestine and were excreted through renal pathway. The pharmacokinetics of ^99mTc‐labeled HYNIC peptide could not be modulated through introduction of PEG₂ unit, thus posing a challenge for studies with other linkers towards enhanced tumor uptake and retention.     

Synthesis and preliminary evaluation of a 99mTc‐labeled folate‐PAMAM dendrimer for FR imaging

Folate receptor is an ideal target for tumor‐specific diagnostic and therapeutic. The aim of this study was to synthesize ^99mTc‐labeled folate‐polyamidoamine dendrimer modified with 2‐hydrazinonicotinic acid (^99mTc‐HP ₃FA ) for FR imaging. The ^99mTc‐HP ₃FA conjugate was prepared using N‐tris‐(hydroxymethyl)‐methylglycine and trisodium triphenylphosphine‐3,3′,3″‐trisulfonate as coligands. Physicochemical properties, in vitro cell uptake study, and in vivo micro‐single‐photon emission computed tomography/CT imaging were performed. The radiolabeled ^99mTc‐HP ₃FA conjugate was prepared with high radiolabeling yield, good stability, and water solubility (logP  = ?1.70 ± 0.21). In cell uptake study, the radiolabeled conjugate showed high uptakes in the FR ‐abundant KB cells and could be blocked significantly by excess folic acid. The 7721 cells which served as control group substantially had no uptakes. The results of micro‐single‐photon emission computed tomography/CT imaging exhibited that high accumulation of activity was found in FR ‐overexpressed KB tumor, and the tumor‐to‐muscle ratio was approximately 25.78, while, using free FA as inhibitor, the uptakes of ^99mTc‐HP ₃FA in KB tumor and kidney were obviously inhibited. In summary, a new radiocompound was synthesized successfully with specific FR targeting ability. The feasibility of ^99mTc‐HP ₃FA for early diagnosis of FR ‐positive tumors with non‐invasive single‐photon emission computed tomography imaging was demonstrated and the possibility of imaging‐guided drug delivery based on multifunctional polyamidoamine will be studied in the future.     

Synthesis and preliminary biological evaluation of a 99mTc‐chlorambucil derivative as a potential tumor imaging agent

Technetium‐99m‐based radiopharmaceuticals have been used widely as diagnostic agents in the nuclear medicine. Chlorambucil (CLB) as one typical alkylating drug exhibits excellent inhibition effects against many human malignancies. To develop and explore a novel potential imaging agent for early diagnosis of tumors, tricarbonyl technetium‐99m and rhenium complexes on the basis of the tridentate ligand dipicolylamine (DPA) bound to the chlorambucil pharmacophore were designed and synthesized: ^99mTc‐DPA‐CLB ( 3 ) and Re‐DPA‐CLB ( 4 ). The high performance liquid chromatography analyses showed that the retention time of 3 and 4 was 13.5 and 13.6 minutes, respectively. Radiolabeling efficiency of the ^99mTc‐DPA‐CLB tracer was 97%, and the radiochemical purity was larger than 95% after 6 hours stored in phosphate buffered saline or human serum as observed by thin layer chromatography and high performance liquid chromatography. Biodistribution studies in a mouse model of breast cancer showed ^99mTc‐DPA‐CLB exhibited a favorable tumor affinity. The radiotracer cleared quickly in the first hour via hepatobiliary and renal routes of excretion, resulted in a very low background at 4 hours post injection (p.i.). It had moderate uptake ratios of tumor to blood and tumor to muscle. These results suggested ^99mTc‐DPA‐CLB might be a promising SPECT imaging agent for tumor diagnosis.     

Biodistribution of 99mTc‐sunitinib as a potential radiotracer for tumor hypoxia imaging

Tyrosine kinases are groups of enzymes, which are over‐expressed in solid tumor cells, representing good targets for different drugs such as sunitinib (N‐[2‐(diethylamino)ethyl]‐5‐{[(3Z)‐5‐fluoro‐2‐oxo‐2,3‐dihydro‐1H‐indol‐3‐ylidene]methyl}‐2,4‐dimethyl‐1H‐pyrrole‐3‐carboxamide). The aim of this work was to design and synthesize ^99mTc‐sunitinib radiotracer and to study its tumor binding specificity as a novel selective radiopharmaceutical for tumor hypoxia imaging. The in vivo biodistribution of ^99mTc‐sunitinib in tumor bearing mice showed high target/non‐target (T/NT) ratio (T/NT ~ 3 at 60 min post injection). This preclinical high biological accumulation in tumor cells suggests that ^99mTc‐sunitinib is ready to go through the clinical trials as a potential selective radiotracer able to image tumor hypoxia.     

Evaluation of 99mTc‐immunoglobulins for imaging infection in the rat

Three immunoglobulin molecules were evaluated as infection imaging agents in a rat model of S. aureas infection: ^99mTc‐infliximab, ^99mTc‐human immunoglobulin (HIG) and ^99mTc‐rat immunoglobulin (RIG). Infliximab is a chimeric monoclonal antibody specific for human tumour necrosis factor alpha (TNFα). ^99mTc‐HIG was chosen as an exogenous protein and ^99mTc‐RIG as an endogenous marker. Each immunoglobulin was treated with 2‐mercaptoethanol and the reduced antibody was isolated by size exclusion chromatography. In combination with Sn^II‐methylenediphosphonic acid, cold kit formulations were prepared. Native and reduced infliximab were tested for rat TNFα binding ability in vitro. A focal intramuscular infection of S. aureus (1 × 10⁸ colony forming units) was induced in the left thigh muscle of rats, that developed for 24 h. In separate experiments each tracer was administered by intravenous injection, then whole body scintigraphic imaging and biodistribution studies were performed at 1 and 4 h later. ^99mTc‐infliximab, ^99mTc‐HIG and ^99mTc‐RIG were prepared with ?95% radiochemical purity from stable cold kits. Results from the organ assay gave infected (target) to non‐infected (control) muscle ratios for ^99mTc‐infliximab as 5.7±0.8, 7.1±1.2, ^99mTc‐HIG gave 3.1±1.1, 7.8±1.2, and ^99mTc‐RIG 7.9±0.3, 12.5±1.5 at 1 and 4 h, respectively. Infliximab and Sn^II‐infliximab did not bind to rat TNFα by the in vitro assay. Although lacking specific affinity for TNFα, ^99mTc‐infliximab accumulated at infectious sites in vivo. ^99mTc‐infliximab gave similar infection uptake ratios to ^99mTc‐HIG at 1 and 4 h, but these proteins were inferior in comparison to ^99mTc‐RIG, and is likely to be due to increased clearance associated with the foreign protein structure. Copyright © 2006 John Wiley & Sons, Ltd.     

Development of a novel 99mTc‐labeled small molecular antagonist for CXCR4 positive tumor imaging

The chemokine receptor 4 (CXCR4) has been an attractive molecular target for tumor imaging, because it is overexpressed in many tumor types and involved in tumor progression and metastasis. The purpose of this study is to examine the CXCR4 targeting properties of ^99mTc‐labeled AMD3465, a small molecule antagonist of CXCR4. ^99mTc‐AMD3465 was prepared in high yield (>95%) and stable in mice serum at least for 4 hours. In vitro cell binding experiments were performed with Chinese hamster ovary (CHO), MCF‐7 (breast cancer), and CHO‐CXCR4 (CHO stably transfected to express CXCR4) cell lines. Small animal single photon emission computed tomography/computed tomography imaging studies in nude mice bearing MCF‐7 and CHO xenografts showed that the uptakes of the radiotracer in MCF‐7 tumors were significantly higher than those in the CXCR4‐negative CHO tumors (P < 0.05), and the MCF‐7 tumors uptake could be blocked with an excess of unlabeled AMD3465 (P < 0.05). These results suggested that ^99mTc‐AMD3465 could be a potential single photon emission computed tomography radiotracer for CXCR4 imaging.     

Labeling and evaluation of 99mTc‐tricarbonyl‐meloxicam as a preferential COX‐2 inhibitor for inflammation imaging

Imaging of inflammation has an important role in dissolving problems in diagnosis and therapy of patients with inflammatory disorders. In this study meloxican as a nonsteroidal anti‐inflammatory drug (NSAID) has been labeled with thechnetium‐99m‐tricarbonyl core ([^99mTc (CO)₃ (H₂O)₃]⁺) in order to evaluate its feasibility as an inflammation imaging agent for in vivo use. ^99mTc‐tricabonyl labeling of meloxicam was performed by its incubation with prepared precursor ^99mTc‐tricabonyl and heating in a boiling water bath for 30 min while various range of pH (1–9) was adjusted. The stability of ^99mTc‐tricarbonyl‐Meloxicam was checked in human serum at 37 °C, and biodistribution was studied in mice. Labeling yield of 98.1 ± 0.4% was obtained corresponding to a specific activity of 0.14 GBq/µmol. The radioconjugate showed good stability in human serum. Our main achievement was high accumulation of ^99mTc‐tricarbonyl‐Meloxicam in the inflammated muscle in mice (T/NT = 3.90 at 4 h post injection) which may diagnostically be beneficial for distinguish sites of inflammation.     

99mTc‐tricarbonyl labeling of paclitaxel as an antimicrotubule agent and its evaluation in B16‐F10 melanoma tumor‐bearing mice

In the present study paclitaxel (taxol) was labeled with [^99mTc(CO)₃(H₂O)₃]⁺ core. Labeling was optimized, and radiochemical analysis was determined by thin layer chromatography and high performance liquid chromatography. Radiocomplex was evaluated and verified further as a tumor characterization agent in B16‐F10 melanoma tumor‐bearing mice. The [^99mTc(CO)₃(H₂O)₃]⁺‐paclitaxel complex with high specific activity (0.77 GBq/μmol) and labeling yield (96.8 ± 1.3) was obtained. No decrease in labeling was observed up to 6 hours, and the stability of the radiocomplex was found adequate. Our main achievement was high accumulation of radiolabeled paclitaxel in tumor (4.51 ± 0.65 percentage injected dose per gram [%ID/g] at 2‐h postinjection) followed by significant reduction (1.86 ± 0.27%ID/g) at 4‐hour postinjection. Because paclitaxel is a substrate for multidrug resistance, ^99mTc‐tricarbonyl‐paclitaxel imaging would be useful for tumor characterization rather than tumor detection.     

Evaluation of a 99mTc‐labelled meso‐bisphenylporphyrin as a tumour image agent

Porphyrins are excellent agents for photodynamic treatment of various types of cancer and also good metal chelators that form highly stable metallo‐complexes with different radionuclides. Therefore, radiolabelled porphyrins could also be potentially used as tumour imaging agents. In this context, the aim of this work was the radiolabelling of meso‐bis[3,4‐bis(carboxymethyleneoxy)phenyl]porphyrin, 2CPP, with Technetium‐99 m (^99mTc) and the evaluation of its radiochemical and biological properties in vitro and in vivo. The labelling procedure was optimized resulting in an efficiency of 92.52 ± 0.48%. The complex ^99mTC‐2CPP remained stable for more than 4 h. The biodistribution showed that ^99mTc‐2CPP is eliminated by gastrointestinal and urinary pathways. The tumour/muscle ratio increases over time, being 3.33 ± 1.22 and 3.55 ± 1.29 in WiDr‐bearing tumours mice and in H1299‐bearing tumours mice, respectively, 6 h post‐injection, showing the tumour specificity of the ^99mTc‐2CPP complex. The favourable tumour/muscle ratio of ^99mTc‐2CPP shows that this complex could potentially be used as tumour imaging agent. Moreover, it could be used to follow the progression or regression of tumours before, during and after the radiotherapy, chemotherapy and photodynamic therapy. Copyright © 2014 John Wiley & Sons, Ltd.     

Synthesis,Biological Evaluation and Molecular Docking Studies of High‐Affinity Bone Targeting N,N'‐Bis (alendronate) Diethylenetriamene‐N,N'‐Triacetic Acid: A Bifunctional Bone Scintigraphy Agent

A bisphosphonate derivative DTPA‐bis(alendronate) conjugate has been synthesized and evaluated as potential radiopharmaceutical for bone imaging. The compound was synthesized by the covalent coupling of DTPA‐bis(anhydride) with alendronate and was char‐acterized on the basis of IR, NMR and mass spectroscopy. It was labelled with ^99mTc with 96% efficacy and was found stable for about 24 h under physiological conditions. Blood kinetic studies of ^99mTc DTPA‐bis(alendronate) showed a biexponential pattern as well as quick washout from the blood circulation. The biological t_1/2(F) and t_1/2(S) were found to be 50 min ± 0.001 and 6 h 30 min ± 0.005, respectively. Imaging and biodistribution studies showed a significant accumulation of ^99mTc DTPA‐bis(alendronate) conjugate at bone site. Bone‐to‐muscles ratios were 12.08 ± 0.001 at 1 h, 45.33 ± 0.001 at 4 h and 35.83 ± 0.001 at 24 h after post‐injection, respectively. The receptor binding of the ^99mTc‐DTPA‐bis (alendronate) was established on human bone cell line (Soas‐2) revealed K_D = 0.86 nm . The preliminary result of the ^99mTc‐DTPA‐bis(alendronate) is encouraging to carrying out further in vivo experiment for targeted bone imaging because of good‐bone‐to‐normal‐organ contrast. Further docking analysis with molecular targets, farnesyl diphosphate synthase, geranylgeranyl pyrophosphate and osteocalcin revealed the high affinity of ?17.419 and thus represents strong potential of bone‐imaging agent.     

Synthesis and evaluation of a 99mTc‐labeled tubulin‐binding agent for tumor imaging

Cholchicine and its derivatives are very potent tubulin‐binding compounds and can be used as a potential tumor targeting agents. In this study, colchicine was labeled with ^99mTc via hydrazinonicotinic acid (HYNIC) and was investigated further. HYNIC/cholchicine was synthesized and labeling with ^99mTc was performed at 95 °C for 15 min and radiochemical analysis included HPLC method. The stability of radiconjugate was checked in the presence of human serum at 37 °C up to 24 h. Biodistribution was studied in breast tumor‐bearing mice. Labeling yield of 95.8 ± 0.54% was obtained corresponding to a specific activity of 54 MBq/µmol. Radioconjugate showed good stability in the presence of human serum. Biodistribution studies in tumor‐bearing mice showed that ^99mTc/HYNIC/colchicine conjugate accumulated in tumor with good uptake (3.17 ± 0.14% g/g at 1 h post‐injection). The radioconjugate was cleared fast from normal organs and showed clearance through urinary and hepatobiliary systems with accumulation of activity in kidneys and intestine. This radioconjugate may be useful to assess the presence of tumor by imaging.     

Synthesis,separation and biodistribution of 99mTc‐CO‐MIBI complex

^99mTc‐CO‐MIBI was prepared by a two‐step procedure involving the convenient preparation of the [^99mTc(CO)₃(OH₂)₃]⁺ precursor and followed by the substitution of the water molecules by the MIBI (2‐methoxyisobutylisonitrile) ligands. In a second step, the reaction solution was adjusted to different pH values, and then the product, ^99mTc‐CO‐MIBI, was confirmed to be a mixture of two complexes: complex A and complex B, whose labeling yields could be over 90%. The ratio of complex B to the sum of A and B could increase gradually from 0 to 1 when pH was shifted from 3.0 to 9.0. These changes were monitored by thin layer chromatography (TLC) and high performance liquid chromatography (HPLC). The two complexes were stable within 8 h at room temperature in vitro. The partition coefficient of the two complexes indicated that there was distinct difference between them. Biodistribution in mice demonstrated that complex B showed better myocardial imaging properties than that of complex A. The heart/liver ratios of complex A, the mixture, and complex B were 1.57, 1.93, and 2.33, respectively, for 30 min post‐injection. The discovery of chemical and biological properties of ^99mTc‐CO‐MIBI would certainly promote the research on a new promising myocardial perfusion‐imaging agent. Copyright © 2004 John Wiley & Sons, Ltd.     

99mTc‐labeled rHuEpo for imaging of the erythropoietin receptor in tumors

To analyze erythropoietin receptor (EpoR) status in tumors, recombinant human erythropoietin (rHuEpo) was labeled with ^99mTc by ^99mTc‐centered 1‐pot synthesis, resulting in high radiochemical purity, stability, and biological activity. Both in vitro cell culture experiments and biodistribution studies of normal rats demonstrated successful EpoR targeting. The biodistribution of labeled rHuEpo in a NCI‐H1975 xenograft model showed tumor accumulation (tumor‐to‐muscle ratio, 4.27 ± 1.77), confirming the expression of active EpoR in tumors. Thus, as a novel single positron emission computerized tomography tracer for the imaging of EpoR expression in vivo, ^99mTc‐rHuEpo is effective for exploring the role of EpoR in cancer growth, metastasis and angiogenesis.