High Radiolabeling Yield Research Articles

Immuno-PET Imaging and Radioimmunotherapy of 64Cu-/177Lu-Labeled Anti-EGFR Antibody in Esophageal Squamous Cell Carcinoma Model.

Immuno-PET provides valuable information about tumor location, phenotype, susceptibility to therapy, and treatment response, especially to targeted radioimmunotherapy. In this study, we prepared antiepidermal growth factor receptor (EGFR) antibody via identical chelator, 3,6,9,15-tetraazabicyclo[9.3.1]-pentadeca-1(15),11,13-trience-3,6,9,-triacetic acid (PCTA), labeled with (64)Cu or (177)Lu to evaluate the EGFR expression levels using immuno-PET and the feasibility of radioimmunotherapy in an esophageal squamous cell carcinoma (ESCC) model. Cetuximab was conjugated with p-SCN-Bn-PCTA and radiolabeled with (64)Cu or (177)Lu. In vitro EGFR expression levels were determined and compared using flow cytometry and cell binding assay. In vivo EGFR expression levels were evaluated via immuno-PET imaging of (64)Cu-cetuximab and biodistribution analysis. Micro-SPECT/CT imaging, biodistribution, and radioimmunotherapy studies of (177)Lu-cetuximab were performed in the ESCC model. Therapeutic responses were monitored using (18)F-FDG PET and immunohistochemical staining. (64)Cu- or (177)Lu-labeled antibodies showed high radiolabeling yield (>98%), stability (>90%), and favorable immunoreactivity. In vitro EGFR status measured by cell binding assay was correlated with the flow cytometry data. Immuno-PET, micro-SPECT/CT, and biodistribution demonstrated specific uptake in ESCC tumors depending on the EGFR expression levels. Tumor accumulation of (64)Cu- and (177)Lu-cetuximab was peaked at 48 and 120 h, respectively. Radioimmunotherapy with (177)Lu-cetuximab showed significant inhibition of tumor growth (P < 0.01) and marked reduction of (18)F-FDG SUV compared with that of control (P < 0.05). Terminal deoxynucleotidyl transferase dUTP nick-end labeling positivity and Ki-67 staining indices increased and decreased, respectively, in the radioimmunotherapy group compared with other groups (P < 0.01). (64)Cu-cetuximab immuno-PET represented EGFR expression levels in ESCC tumors, and (177)Lu-cetuximab radioimmunotherapy effectively inhibited the tumor growth. The diagnostic and therapeutic convergence radiopharmaceutical (64)Cu-/(177)Lu-PCTA-cetuximab may be useful as a diagnostic tool in patient selection and a potent radioimmunotherapy agent in EGFR-positive ESCC tumors.

Trithiols and their arsenic compounds for potential use in diagnostic and therapeutic radiopharmaceuticals

IntroductionArsenic-72 (72As; 2.49MeV β+, 26h) and 77As (0.683MeV β−, 38.8h) have nuclear properties useful for positron emission tomography (PET) and radiotherapy applications, respectively. Their half-lives are sufficiently long for targeting tumors with antibodies, as well as peptides. Potential radiopharmaceuticals based on radioarsenic require development of suitable bifunctional chelates for stable conjugation of arsenic to vectors under in vivo conditions at high dilution. MethodsThe thiophilic nature of arsenic led to the synthesis and characterization of a simple trithiol ligand and its arsenic complex, and radiolabeling studies at the no carrier added (NCA) 77As level. Results1H- and 13C-NMR spectroscopy, electrospray ionization mass spectrometry (ESI-MS), and single crystal X-ray diffraction were used to characterize the trithiol ligand and its arsenic(III) complex. Radiotracer studies with no carrier added (NCA) 77As resulted in high radiolabeling yields (>96%) with high in vitro stability. ConclusionsThe high yield and stability of a single NCA 77As trithiol complex indicates that this framework is suitable for developing matched pair agents for non-invasive in vivo PET imaging and radiotherapy of tumors with 72,77As. This is the first reported chelate developed for NCA radioarsenic and studies are underway for developing a trithiol bifunctional chelate conjugated to a targeting vector, such as a peptide or monoclonal antibody.

Synthesis, Characterization, and Preclinical Evaluation of (99m)Tc-Labeled Macrobicyclic and Tricyclic Chelators as Single Photon Emission Computed Tomography Tracer.

The novel tetraaza macrobicyclic chelator 3,6,9,15-tetraazabicyclo[9.3.1]pentadeca-1(15),11,13-triene-2,10-dione (TBPD) and pentaaza macrotricyclic chelator 9-oxa-3,6,12,15,21-pentaazatricyclo[15,3,2,1]trieicos-1(21),17,19-triene-2,7,11,16-tetradione (OPTT) were synthesized, characterized, and radiolabeled with (99m)Tc to produce (99m)Tc-TBPD and (99m)Tc-OPTT. These radiolabeled complexes were prepared with high radiolabeling yield, radiochemical purity, and good in vitro stability up to 24 h. The labeling efficiency of (99m)Tc-TBPD and (99m)Tc-OPTT was found 98% and 97%. In vitro serum stability of (99m)Tc-TBPD was found to be 95.2%, while that of (99m)Tc-OPTT 94.2% up to 24 h. Blood kinetics experiments of (99m)Tc-labeled complexes showed biphasic pattern of blood clearance. About 99.57 ± 0.89% activity of (99m)Tc-TBPD and 99.42 ± 0.88% activity of (9m)Tc-OPTT were cleared off blood stream at 24 h postadministration. The biological half-life of (99m) Tc-TBPD was observed: t1/2(F) 1 h 5 min and t1/2(S) 12 h and biological half-life of (99m)Tc-OPTT was observed: t1/2(F) 1 h 10 min and t1/2(S) 9 h 50 min, respectively. The biodistribution studies revealed that maximum uptake of (99m)Tc-TBPD was found in liver, concluded that excretory pathway is hepatobiliary, while that of (99m)Tc-OPTT was renal as well as hepatobiliary. The negligible activity observed in stomach confirming the stability of radiolabeled complex in biological milieu. In vitro cytotoxicity study of TBPD and OPTT did not show any considerable antiproliferative activity against cancer cells of human cervical SW756, HeLa, and glioblastoma U-87, U373 cell lines.

Development of 68Ga-labeled multivalent nitroimidazole derivatives for hypoxia imaging

Radiolabeled nitroimidazole (NI) derivatives have been extensively studied for imaging hypoxia. To increase the hypoxic tissue uptake, we developed 68Ga-labeled agents based on mono-, bis-, and trisnitroimidazole conjugates with the chelating agent 1,4,7-triazacyclononane-1,4,7-tris[methyl(2-carboxyethyl)phosphinic acid] (TRAP). All the three agents showed high radiolabeling yields (>96%) and were found to be stable up to 4h in prepared medium at room temperature and in human serum at 37°C. The trivalent agent showed a significant increase in hypoxic to normoxic uptake ratio (p <0.005) according to the in vitro cell uptake experiments. Immunohistochemical analysis confirmed the presence of hypoxia in xenografted CT26 tumor tissue. The trivalent derivative (68Ga-3: 0.17±0.04, 68Ga-4: 0.33±0.04, 68Ga-5: 0.45±0.09, and 68Ga-6: 0.47±0.05% ID/g) showed the highest uptake by tumor cells according to the biodistribution studies in CT-26 xenografted mice. All the nitroimidazole derivatives showed significantly higher uptake by tumor cells than the control agent (p <0.05) at 1h post-injection. The trivalent derivative (68Ga-3: 0.10±0.06; 68Ga-4: 0.20±0.06; 68Ga-5: 0.33±0.08; 68Ga-6: 0.59±0.09) also showed the highest standard uptake value for tumor cells at 1h post-injection in animal PET studies using CT-26 xenografted mice. In conclusion, we successfully synthesized multivalent 68Ga-labeled NI derivatives for imaging hypoxia. Among them, the trivalent agent showed the highest tumor uptake in biodistribution and animal PET studies.

Synthesis and biodistribution of 99Tcm-Cetuximab antibody for lung tumor targeted molecular imaging

Objective To prepare and evaluate 99Tcm radiolabeled Cetuximab (C225) for imaging of EGFR specific binding. Methods Cetuximab antibody was reduced by 2-iminothiophene (2-IT). The radiolabeling of IT-Cetuximab with 99Tcm (99Tcm-IT-Cetuximab) was analyzed by HPLC, and was tested for in vitro stability and molecular integrity. The human lung cancer line (A549)-bearing nude mouse model was prepared for biodistribution and tumor targeted study. Tumor uptake was also measured by in vivo γ imaging. Results The labeling efficiency was 93.15%. The radiochemical purity was 96.46% after purification. The in vitro stability was good in 5% HSA, in which the radiochemical purity maintained above 80% at 4 ℃ for 24 h. 99Tcm-IT-Cetuximab showed good specific binding to tumor with peak uptake of (3.417±0.769) %ID/g after 4 h. The T/NT ratio of blood increased to 1.454±0.174 at 24 h. γ imaging of A549-bearing nude mice xenografts also showed high T/NT ratio. Conclusions 99Tcm-IT-Cetuximab molecular probe could be prepared with high radiolabeling yield and radiochemical purity. It has excellent in vitro and in vivo stability, and shows specific uptake in A549 tumor. Key words: Lung neoplasms; Antibodies, monoclonal; Receptors, epidemal growth factor-urogastrone; Radionuclide imaging; Mice, nude

Anti-CD20 Immunoglobulin G Radiolabeling with a 99mTc-Tricarbonyl Core: In Vitro and In Vivo Evaluations.

In recent years, the diagnostic and therapeutic uses of radioisotopes have shown significant progress. Immunoglobulin (Ig) appears to be a promising tracer, particularly due to its ability to target selected antigens. The main objective of this study is to optimize and assess an Ig radiolabeling method with Technetium 99m (99mTc), an attractive radioelement used widely for diagnostic imaging. Monoclonal anti-CD20 IgG was retained to study in vitro and in vivo radiolabeling impact. After IgG derivatization with 2-iminothiolane, IgG-SH was radiolabeled by an indirect method, using a 99mTc-tricarbonyl core. Radiolabeling stability was evaluated over 24h by thin-layer chromatography. IgG integrity was checked by sodium dodecyl sulfate—polyacrylamide gel electrophoresis coupled with Western blot and autoradiography. The radiolabeled Ig’s immunoaffinity was assessed in vitro by a radioimmunoassay method and binding experiments with cells (EL4-hCD20 and EL4-WT). Biodistribution studies were performed in normal BALB/c mice. Tumor uptake was assessed in mice bearing EL4-hCD20 and EL4-WT subcutaneous xenografts. With optimized method, high radiolabeling yields were obtained (95.9 ± 3.5%). 99mTc-IgG-SH was stable in phosphate-buffered saline (4°C and 25°C) and in serum (37°C), even if important sensitivity to transchelation was observed. IgG was not degraded by derivatization and radiolabeling, as shown by Western blot and autoradiography results. 99mTc-anti-CD20 IgG-SH immunoaffinity was estimated with Kd = 35 nM by both methods. In vivo biodistribution studies for 48h showed significant accumulation of radioactivity in plasma, liver, spleen, lungs and kidneys. Planar scintigraphy of mice bearing tumors showed a significant uptake of 99mTc-anti-CD20 IgG-SH in CD20+ tumor versus CD20- tumor. Radiolabeling of derivatized IgG with 99mTc-tricarbonyl was effective, stable and required few antibody amounts. This attractive radiolabeling method is “antibody safe” and preserves Ig affinity for antigen, as shown by both in vitro and in vivo experiments. This method could easily be used with noncommercial IgG or other antibody isotypes.

Toward realization of ‘mix-and-use’ approach in 68Ga radiopharmacy: preparation, evaluation and preliminary clinical utilization of 68Ga-labeled NODAGA-coupled RGD peptide derivative

IntroductionThe present article demonstrates a ‘mix-and-use’ approach for radiolabeling RGD peptide derivative with 68Ga, which is easily adaptable in hospital radiopharmacy practice. The radiotracer thus formulated was successfully used for positron emission tomography (PET) imaging of breast cancer in human patients. MethodsThe conditions for radiolabeling NODAGA-coupled dimeric cyclic RGD peptide derivative [NODAGA-(RGD)2] with 68Ga were optimized using 68Ga obtained from a 68Ge/68Ga generator developed in-house with CeO2-PAN composite sorbent as well as from a commercial 68Ge/68Ga generator obtained from ITG, Germany. Preclinical studies were carried out in C57BL/6 mice bearing melanoma tumors. The radiotracer was prepared in a hospital radiopharmacy using 68Ga obtained from ITG generator and used for monitoring breast cancer patients by positron emission tomography (PET) imaging. Results68Ga-NODAGA-(RGD)2 could be prepared with high radiolabeling yield (>98%) and specific activity (~50GBq/μmol) within 10min at room temperature by mixing 68Ga with the solution of the peptide conjugate. In vivo biodistribution studies showed significant uptake (5.24±0.39% ID/g) in melanoma tumor at 30min post-injection, with high tumor-to-background contrast. The integrin αvβ3 specificity of the tracer was corroborated by blocking study. Preliminary clinical studies in locally advanced breast cancer (LABC) patients indicated specifically high tumor uptake (SUVmax 10–15) with good contrast. ConclusionsThis is one of the very few reports which presents preliminary clinical data on use of 68Ga-NODAGA-(RGD)2 and the developed ‘mix-and-use’ holds tremendous prospect in clinical PET imaging using 68Ga.

99mTc-Mesalamine as potential agent for diagnosis and monitoring of ulcerative colitis: labelling, characterisation and biological evaluation

Mesalamine was labelled with technetium-99m (99mTc) in high radiolabelling yield (~98.4 %), in vitro stability (~4 h) and in serum persistence (~24 h). Optimum labelling conditions were investigated. The structure of the complex was confirmed using in silico analysis. Molecular docking was performed to evaluate the complex binding to its biochemical target, the PPARγ receptor. Biodistribution and clearance studies were performed in normal and ulcerative colitis models in mice. The tracer’s localization was highest (~65.2 %) in microbial model compared to chemical model (~42.4 %) and normal mice (~22.1 %) at 60 min post injection. All data supported the usefulness of 99mTc-mesalamine as a radiotracer for ulcerative colitis.

A systematic evaluation of the potential of PCTA-NCS ligand as a bifunctional chelating agent for design of 177Lu radiopharmaceuticals

This paper explores the utility of para isothiocyanato benzyl 3,6,9,15-tetraazabicyclo [9.3.1]pentadeca-1(15),11,13-triene-3,6,9-triacetic acid (PCTA-NCS) as a bifunctional chelating agent for 177Lu in comparison to para isothiocyanato benzyl 1,4,7,10-tetra aza cyclododecane tetraacetic acid (DOTA-NCS). The 177Lu-PCTA-NCS complex could be obtained in high radiolabeling yields at ambient temperature and exhibited excellent stability in vitro. Influence of trace metal ions on the radiolabeling yields was also evaluated. Biodistribution studies revealed no significant retention of 177Lu-PCTA-NCS in any vital organ at 24 h p.i. It could be concluded from our study that PCTA-NCS could be a potential BFCA for design of 177Lu radiopharmaceuticals.

Synthesis, radioiodination and biological evaluation of a novel phthalimide derivative

Biologically active novel phthalimide derivative, N-(5-(2-hydroxyphenyl)-4,5-dihydro-1H-pyrazol-3-yl)phthalimide (HPZPHT), was synthesized in excellent yield and characterized by IR, mass and 1H NMR spectroscopy. It was radiolabeled with iodine-131 by direct electrophilic substitution reaction and radiochemical yield was determined by using different chromatographic techniques (HPLRC, paper chromatography and paper electrophoresis). 131I-HPZPHT has high radiolabeling yield (98.00 ± 2.00 %), stability, solid tumor uptake and T/NT ratio (5.17 ± 0.03 at 30 min. post-injection) compared with many new tracers which have been developed in recent years. This study encourages the possible use of this tracer as a potential imaging and/or therapeutic agent for cancer.

Highly efficient one-pot labeling of new phosphonium cations with fluorine-18 as potential PET agents for myocardial perfusion imaging.

Lipophilic cations such as phosphonium salts can accumulate in mitochondria of heart in response to the negative inner-transmembrane potentials. Two phosphonium salts [(18)F]FMBTP and [(18)F]mFMBTP were prepared and evaluated as potential myocardial perfusion imaging (MPI) agents in this study. The cations were radiolabeled via a simplified one-pot method starting from [(18)F]fluoride and followed by physicochemical property tests, in vitro cellular uptake assay, ex vivo mouse biodistribution, and in vivo rat microPET imaging. The total radiosynthesis time was less than 60 min including HPLC purification. The [(18)F] labeled compounds were obtained in high radiolabeling yield (∼50%) and good radiochemical purity (>99%). Both compounds were electropositive, and their log P values at pH 7.4 were 1.16 ± 0.003 (n = 3) and 1.05 ± 0.01 (n = 3), respectively. Both [(18)F]FMBTP and [(18)F]mFMBTP had high heart uptake (25.24 ± 2.97% ID/g and 31.02 ± 0.33% ID/g at 5 min postinjection (p.i.)) in mice with good retention (28.99 ± 3.54% ID/g and 26.82 ± 3.46% ID/g at 120 min p.i.). From the PET images in rats, the cations exhibited high myocardium uptake and fast clearance from liver and small intestine to give high-contrast images across all time points. These phosphonium cations were radiosynthesized via a highly efficient one-pot procedure for potential MPI offering high heart accumulation and rapid nontarget clearance.

Synthesis and biological evaluation of 99mTc-ECF: a new ethionamide derivative for tuberculosis diagnosis

In this work we propose a technetium-99m-labeled derivative from Ethionamide (ETH), further referred to as 99mTc-ECF for tuberculosis diagnosis. The biological features of this radioactive agent have been studied. The 2-ethylpyridine-4-carbothioamide-ferrocene (ECF) was chemically synthesized and then labeled with technetium-99m. It has been confirmed through this work that 99mTc-ECF is obtained with high radiolabelling yield (>90 %). Radiochemical analysis of 99mTc-ECF revealed that the molecule was efficiently labeled with a little free remaining pertechnetate. Only 1–2 % of the tracer was leached out from the complex at 24 h when incubated in serum at 37 °C which confirmed its high stability. The sensitivity test of ECF showed that the group of grafted ferrocenyl does not seem to have largely altered the active site of the molecule. In-vitro investigations were conducted using BCG (Bacille Calmette-Guerin) as analogue of Mycobacterium Tuberculosis and Listeria Monocytogenes as negative control. It was proved that for BCG, ECF has kept the bacteriostatic properties of the parent compound (ETH). In physiological conditions, the measured up-take of the tracer with live bacteria was about 24.1 and 7.1 % for BCG and Listeria Monocytogenese, respectively. The comparison of the 99mTc-ECF accumulation at sites of BCG infected animals, which is expressed as target-to-non-target ratio (found to be equal to 2.15) with other radiotracers was discussed. This allowed us to consider that 99mTc-ECF could be a reasonable radiotracer for mycobacterial infections. Obtained results were good and encourage to undergo a similar labeling for the Mycobacterium tuberculosis as perspective of this work.

Comparative in vitro stability and scintigraphic imaging for trafficking and tumor targeting of a directly and a novel 99mTc(I)(CO)3 labeled liposome

Liposomes radiolabelling with diagnostic radionuclides is an excellent tool for studying pharmacokinetics with the view of developing liposome-based drug delivery agents. The aim of the present study is to evaluate the in vitro and in vivo behavior of a (99m)Tc-labeled liposome by applying either a direct labeling strategy via a carboxyl group, LP-COOH, or a surface chelating method via pyridyl ethyl cysteine compound (with the intermediate [⁹⁹mTc(I)(CO)₃(H₂O)(3)](+)), LP-PEC. ⁹⁹mTc-LP-COOH was obtained in high radiolabelling yield and radiochemical purity, while ⁹⁹mTc(I)(CO)₃-LP-PEC was initially purified before being in vitro and in vivo evaluated. ⁹⁹mTc-LP-COOH was less stable in the presence of competitive for ⁹⁹mTc ligands than ⁹⁹mTc(I)(CO)₃-LP-PEC. According to DLS measurements, the presence of serum as well as the applied radiolabelling conditions did not affect the liposomes' size. The different radiolabelling methods seemed to exert an influence on the biodistribution pattern of the liposomes with the ⁹⁹mTc(I)(CO)₃-LP-PEC showing slow blood clearance, which was also confirmed by in vivo scintigraphic imaging. Nevertheless, passive tumor targeting was attained at a similar extent no matter which radiolabelling technique was followed.

CYCLIC CHOLECYSTOKININ ANALOGUES EXHIBIT HIGH BLOOD STABILITY AND BINDING AFFINITY WITH CHOLECYSTOKININ RECEPTOR

Recently, incidence of Cholecystokinin (CCK) receptor is recognized as a factor that determines the aggressive phenotype of pancreatic cancer. In this study, a novel Cholecystokinin (CCK) analogues; DOTA-Nle-cyclo (Glu-Trp-Met-Asp-Phe-Lys-NH2) (DOTA-cCCK) and DOTA-Nle-cyclo (Glu-Trp-Nle-Asp-Phe-Lys-NH2) (DOTA-[Nle]-cCCK) were synthesized and radiolabeled and the targeting abilities on the CCK receptor were evaluated for new CCK receptor targeting agents searching. Peptides were prepared through a solid phase synthesis method and their purity was over 98%. DOTA is the chelating agent for 68Ga-labelling, which the peptides were radiolabeled with 68Ga by a high radiolabeling yield (>98%). Peptides were stable over 98% by incubation in mouse blood at 37°C for 2 h. A competitive displacement of 125I-CCK8 on the AR42J human pancreatic carcinoma cells revealed that 50% inhibitory concentration value (IC50) were 12.31 nM of DOTA-cCCK and 1.69 nM of DOTA-[Nle]-cCCK. Stable in the blood of both DOTA-cCCK and DOTA-[Nle]-cCCK, but the binding rate with the CCK receptor on AR42J cells, DOTA-[Nle]-cCCK confirmed better than DOTA-cCCK. Therefore, it is concluded that 68Ga-DOTA-[Nle]-cCCK can be potential candidate as a targeting modality for the CCK receptor over-expressing tumors and further studies to evaluate their biological characteristics are needed.

Radioiodinated and astatinated NHC rhodium complexes: Synthesis

IntroductionThe clinical development of radioimmunotherapy with astatine-211 is limited by the lack of a stable radiolabeling method for antibody fragments. An astatinated N-heterocyclic carbene (NHC) Rhodium complex was assessed for the improvement of radiolabeling methodologies with astatine. MethodsWet harvested astatine-211 in diisopropyl ether was used. Astatine was first reduced with cysteine then was reacted with a chlorinated Rh-NHC precursor to allow the formation of the astatinated analogue. Reaction conditions have been optimized. Astatine and iodine reactivity were also compared. Serum stability of the astatinated complex has been evaluated. ResultsQuantitative formation of astatide was observed when cysteine amounts higher than 46.2 nmol/μl of astatine solution were added. Nucleophilic substitution kinetics showed that high radiolabeling yields were obtained within 15 min at 60°C (88%) or within 5 min at 100°C (95%). Chromatographic characteristics of this new astatinated compound have been correlated with the cold iodinated analog ones. The radioiodinated complex was also synthesized from the same precursor (5 min. at 100°C, up to 85%) using [125I]NaI as a radiotracer. In vitro stability of the astatinated complex was controlled after 15 h incubation in human serum at 4°C and 37°C. No degradation was observed, indicating the good chemical and enzymatic stability. ConclusionThe astatinated complex was obtained in good yield and exhibited good chemical and enzymatic stability. These preliminary results demonstrate the interest of this new radiolabeling methodology, and further functionalizations should open new possibilities in astatine chemistry. Advances in knowledge and implications for patient careAlthough there are many steps and pitfalls before clinical use for a new prosthetic group from the family of NHC complexes, this work may open a new path for astatine-211 targeting.

Reactor production and electrochemical purification of 169Er: A potential step forward for its utilization in in vivo therapeutic applications

The aim of the present study was to develop and demonstrate a viable method for the reactor production of (169)Er with acceptable specific activity using moderate flux reactor and its purification from (169)Yb following electrochemical pathway based on mercury-pool cathode to avail (169)Er in radionuclidically pure form essential for its therapeutic use. Erbium-169 was produced in reactor by neutron bombardment of isotopically enriched (98.2% in (168)Er) erbium target at a thermal neutron flux of ~8×10(13) n.cm(-2).s(-1) for 21 d. A thorough optimization of irradiation parameters including neutron flux, irradiation time and target cooling time was carried out. The influence of different experimental parameters for the quantitative removal (169)Yb from (169)Er was investigated, optimized and based on the results; a two-cycle electrochemical separation procedure was adopted. The suitablility of purified (169)Er for application in radiation synovectomy and bone pain palliation was ascertained by carrying out radiolabeling studies with hydroxypaptite (HA) particles and 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraaminomethylene phosphonic acid (DOTMP), respectively. Thermal neutron irradiation of 10mg of isotopically enriched (98.2% in (168)Er) erbium target at a flux of ~8×10(13) n.cm(-2).s(-1) for 21 d followed by a two-step electrochemical separation of (169)Yb impurity yielded ~3.7GBq (100mCi) of (169)Er with a specific activity of ~370MBq/mg (10mCi/mg) and radionuclidic purity of >99.99%. The reliability of this approach was amply demonstrated by performing several production batches, where the performance of each batch remained consistent. The utility of the purified (169)Er was demonstrated in the radiolabeling studies with HA particles and DOTMP, wherein both the radiolabeled products were obtained with high radiolabeling yield (>99%). A viable strategy for the batch production and purification of (169)Er, suitable for therapeutic applications, has been developed and demonstrated.

99mTc-labeled butyl-substituted zoledronic acid as a novel potential SPECT imaging agent: preparation and preclinical pharmacology study

Zoledronic acid (ZL) is the most potent among the tested diphosphonates. To develop a superior bone imaging agent that could improve the efficiency of bone scanning, an optimized radiotracer was designed from ZL and prepared successfully, 99mTc-BIDP [BIDP, 1-hydroxy-2-(2-butyl-1H-imidazole-1-yl) ethylidene-1,1-diphosphonic acid]. It possesses high radiolabeling yield, radiochemical purity, and stability. The biodistribution in mice shows that 99mTc-BIDP has high specificity in the skeleton with the maximum uptake of 24.6 ± 1.65 % ID g−1 at 120 min post injection. It can be quickly absorbed and rapidly eliminated from the blood judged from the short distribution half-life (t 1/2α = 1.65 min) and elimination half-life (t 1/2β = 30.91 min). The bone imaging of the rabbit showed that 99mTc-BIDP has highly selective uptake in the skeletal system and rapid clearance from the soft tissues. An excellent scintigraphic image can be obtained at 1 h with clear visualization of the skeleton.

Facile Method To Radiolabel Glycol Chitosan Nanoparticles with 64Cu via Copper-Free Click Chemistry for MicroPET Imaging

An efficient and straightforward method for radiolabeling nanoparticles is urgently needed to understand the in vivo biodistribution of nanoparticles. Herein, we investigated a facile and highly efficient strategy to prepare radiolabeled glycol chitosan nanoparticles with (64)Cu via a strain-promoted azide-alkyne cycloaddition strategy, which is often referred to as click chemistry. First, the azide (N3) group, which allows for the preparation of radiolabeled nanoparticles by copper-free click chemistry, was incorporated to glycol chitosan nanoparticles (CNPs). Second, the strained cyclooctyne derivative, dibenzyl cyclooctyne (DBCO) conjugated with a 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (DOTA) chelator, was synthesized for preparing the preradiolabeled alkyne complex with (64)Cu radionuclide. Following incubation with the (64)Cu-radiolabeled DBCO complex (DBCO-PEG4-Lys-DOTA-(64)Cu with high specific activity, 18.5 GBq/μmol), the azide-functionalized CNPs were radiolabeled successfully with (64)Cu, with a high radiolabeling efficiency and a high radiolabeling yield (>98%). Importantly, the radiolabeling of CNPs by copper-free click chemistry was accomplished within 30 min, with great efficiency in aqueous conditions. In addition, we found that the (64)Cu-radiolabeled CNPs ((64)Cu-CNPs) did not show any significant effect on the physicochemical properties, such as size, zeta potential, or spherical morphology. After (64)Cu-CNPs were intravenously administered to tumor-bearing mice, the real-time, in vivo biodistribution and tumor-targeting ability of (64)Cu-CNPs were quantitatively evaluated by microPET images of tumor-bearing mice. These results demonstrate the benefit of copper-free click chemistry as a facile, preradiolabeling approach to conveniently radiolabel nanoparticles for evaluating the real-time in vivo biodistribution of nanoparticles.

Synthesis and application of a novel cysteine-based DTPA-NCS for targeted radioimmunotherapy

For the development of safe and effective protein-based radiolabeled complexes such as radioimmunotherapy (RIT), the selection of the radionuclides and the chelating agents used for the radiolabeling of tumor-targeting molecules is a critical factor. We aim to synthesize a novel bifunctional chelating agent containing the isothiocyanate group for easy conjugation with antibodies having the characteristics of high stable chelation with therapeutic radionuclides. We have synthesized the DTPA analogue retaining L-cysteine as a core ligand of the thiol group. The chelating power of cysteine-based DTPA-NCS (cys-DTPA-NCS) was compared with that of commercial ρ-SCN-Bn-DTPA. In an application, the cetuximab was radioimmunoconjugated with (177)Lu using cys-DTPA-NCS. The affinity was tested in a cell line overexpressing EGFR. A therapy study was conducted in nude mice with subcutaneous HT-29 xenografts. The cys-DTPA-NCS presents an excellent ability to chelate as compared to the ρ-SCN-Bn-DTPA. For mean ratio chemical labeling yields of 95%, the result was 0.97. (177)Lu-cys-DTPA-NCS-cetuximab was prepared under ambient condition with a high radiolabeling yield and the radiochemical purity was sustained for at least 6days. The IC50 value of the (177)Lu-labeled cetuximab was 10nM (95% confidence). The stability and therapeutic efficacy of the candidate radiopharmaceutical were verified. The new DTPA derivative, cys-DTPA-NCS, is a good bifunctional chelating agent that can be used for protein-based radiopharmaceutical using lanthanides such as (177)Lu and (90)Y. The prepared (177)Lu-cys-DTPA-NCS-cetuximab can be used for the diagnosis and treatment of human colorectal tumor.

Experimental study of labeling and biodistribution of 68Ga-NOTA-Duramycin

Objective To synthesize 68Ga-1,4,7-triazacyclononane-1,4,7-triacetic acid-Duramycin （NOTA-Duramycin） and evaluate its biodistribution and kinetics in mice and a myocardial ischemia and reperfusion injury porcine model. Methods NOTA-Duramycin was synthesized by the solid phase method and labeled with 6SGa at room temperature. Radiochemical purity and radiolabeling yield were analyzed by HPLC. Stability in vitro and biodistribntion of 68Ga-NOTA-Duramycin in normal mice were studied. Myocardial ischemia and repeffusion injury in porcine models （n =6） was induced with balloon angioplasty. 68Ga-NOTA-Duramycin （37.0 MBq） was injected intravenously and PET/CT images were acquired at 1 h post injection. Myocardial tis- sues were analyzed to confirm the presence of cell death. Results 68Ga-NOTA-Duramycin was easily prepared at room temperature with high radiolabeling yield （92.5 ± 2.1 ）% and radiochemical purity （ 〉 90% ）, and its stability in vitro was satisfactory. The biodistribution of 68 Ga-NOTA-Duramycin in the blood, heart, liver, spleen, lung and kidney was （23.50±15.38） %ID/g, （8.53 ±4.52） %ID/g, （8.26±2.24） %ID/g, （2.12±O. 28 ） % ID/g, （5.02 ± 1.46） % ID/g, （50.62 ± 54.24） % ID/g at 5 min post-injection and （1.83±0.31） %ID/g, （1.05 ±0.31） %ID/g, （0.97 ±0.28） %ID/g, （0.68 ±0.27） %ID/g, （2. 15 ±0.90） % ID/g, （8.12 ±2.74） %ID/g at 60 rain postinjection, respectively. The compound washed out quickly from the circulation via urine excretion. PET/CT showed increased uptake of 68Ga-NOTA-Duramycin by lesions with ischemia and reperfusion injury in porcine models, which was histologically confirmed. Conclusions 68Ga-NOTA-Duramycin can he easily synthesized at room temperature and can detect ischemia and reperfusion injury in porcine models effectively. It may serve as a potential radiotracer for the detection of apoptosis. Key words: NOTA-Duramycin ; Gallium radioisotopes ; Pharmacokinetics ; Cell apoptosis ; Animals, laberatory ; Mice ; Swine