Search

Abstract: Introduction: 4-[18F]Fluorobenzylamine ([18F]FBA) is an important building block for the synthesis of 18F-labeled compounds. Synthesis of [18F]FBA usually involves application of strong reducing agents like LiAlH4 which is challenging to handle in automated synthesis units (ASUs). Therefore, alternative methods for the preparation of [18F]FBA compatible with remotely-controlled syntheses in ASUs are needed. Methods: 18F]FBA was prepared in a remotely-controlled synthesis unit (GE TRACERlab™ FX) based on Ni(II)-mediated borohydride exchange resin (BER) reduction of 4-[18F]fluorobenzonitrile ([18F]FBN). [18F]FBA was used for the synthesis of novel thiol-reactive prosthetic group 4-[18F]fluorobenzyl)maleimide [18F]FBM and Hsp90 inhibitor 17-(4-[18F]fluorobenzylamino)-17-demethoxy-geldanamycin [18F] GA. Results: [18F]FBA could be prepared in high radiochemical yield greater than 80% (decay-corrected) within 60min. In a typical experiment, 7.4GBq of [18F]FBA could be obtained in high radiochemical purity of greater than 95% starting from 10GBq of cyclotron-produced n.c.a. [18F]fluoride. [18F]FBA was used for the preparation of 4-[18F]fluorobenzyl)maleimide as a novel prosthetic group for labeling of thiol groups as demonstrated with tripeptide glutathione. [18F]FBA was also used as building block for the syntheses of small molecules as exemplified by the preparation of Hsp90 inhibitor 17-(4-[18F]fluorobenzylamino)-17-demethoxy-geldanamycin. Conclusion: The described remotely-controlled synthesis of [18F]FBA will significantly improve the availability of [18F]FBA as an important and versatile building block for the development of novel 18F-labeled compounds containing a fluorobenzylamine moiety. [Copyright &y& Elsevier]

Lanthanum radiometals are well positioned to serve as theranostic PET radiometals for targeted radionuclide therapy. The positron emitters 132La and 133La show promise to serve as unique PET imaging agents for 225Ac targeted alpha-particle therapy, the 134Ce/134La pair has PET imaging potential with both 225Ac and 227Th, and 135La has potential in targeted Auger-Meitner electron therapy. With easily accessible cyclotron production routes, effective and efficient chemical separations, and robust chelation chemistry, these radionuclides are well poised for additional preclinical and clinical PET and targeted radionuclide therapy studies. This review summarizes recent advances in radiolanthanum production and preclinical applications that demonstrate the strong potential of these radionuclides in PET and targeted radionuclide therapy. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: The novel thiol-group-selective bifunctional 18F-labeling agent N-[6-(4-[18F]fluoro-benzylidene)aminooxyhexyl]maleimide ([18F]FBAM) has been developed. The bifunctional labeling precursor N-(6-aminoxyhexyl)maleimide containing a thiol-reactive maleimide group and a carbonyl-group-reactive aminooxy group was prepared in only three steps in a total chemical yield of 59%. Subsequent radiolabeling with 4-[18F]fluorobenzaldehyde gave the bifunctional 18F-labeling agent [18F]FBAM in a radiochemical yield of 29%. In a typical experiment, 3.88 GBq of [18F]fluoride could be converted into 723 MBq of [18F]FBAM within 69 min. Conjugation of [18F]FBAM with thiol groups was exemplified with the cystein-containing tripeptide glutathione and with various apolipoproteins of human low-density lipoprotein (LDL) subfractions. The latter was evaluated with respect to the uptake of [18F]FBAM-LDL subfractions in human hepatoma cells (HepG2) in vitro. In vivo biodistribution studies in rats revealed high stability for [18F]FBAM-LDL subfractions. Moreover, the metabolic fate of [18F]FBAM-LDL subfractions in vivo was delineated by dynamic positron emission tomography studies using a dedicated small animal tomograph. Data were compared to former studies that used the NH2-reactive 18F-labeling agent N-succinimidyl-4-[18F]fluorobenzoate. The compound [18F]FBAM can be considered as an excellent prosthetic group for the selective and mild 18F labeling of thiol-group-containing biomolecules suitable for subsequent investigations in vitro and in vivo. [Copyright &y& Elsevier]

Copper-64 (64Cu, t 1/2 = 12.7 h) is a positron emitter well suited for theranostic applications with beta-emitting 67Cu for targeted molecular imaging and radionuclide therapy. The present work aims to evaluate the radionuclidic purity and radiochemistry of 64Cu produced via the 68Zn(p,nα)64Cu nuclear reaction. Macrocyclic chelators DOTA, NOTA, TETA, and prostate-specific membrane antigen ligand PSMA I&T were radiolabeled with purified 64Cu and tested for in vitro stability. [64Cu]Cu-PSMA I&T was used to demonstrate in vivo PET imaging using 64Cu synthesized via the 68Zn(p,nα)64Cu production route and its suitability as a theranostic imaging partner alongside 67Cu therapy. 64Cu was produced on a 24 MeV TR-24 cyclotron at a beam energy of 23.5 MeV and currents up to 70 μA using 200 mg 68Zn encapsulated within an aluminum‑indium-graphite sealed solid target assembly. 64Cu semi-automated purification was performed using a NEPTIS Mosaic-LC synthesis unit employing CU, TBP, and TK201 (TrisKem) resins. Radionuclidic purity was measured by HPGe gamma spectroscopy, while ICP-OES assessed elemental purity. Radiolabeling was performed with NOTA at room temperature and DOTA, TETA, and PSMA I&T at 95 °C. 64Cu incorporation was studied by radio-TLC. 64Cu in vitro stability of [64Cu]Cu-NOTA, [64Cu]Cu-DOTA, [64Cu]Cu-TETA, and [64Cu]Cu-PSMA I&T was assessed at 37 °C from 0 to 72 h in human blood serum. Preclinical PET imaging was performed at 1, 24, and 48 h post-injection with [64Cu]Cu-PSMA I&T in LNCaP tumor-bearing mice and compared with [68Ga]Ga-PSMA I&T. Maximum purified activity of 4.9 GBq [64Cu]CuCl 2 was obtained in 5 mL of pH 2–3 solution, with 2.9 GBq 64Cu concentrated in 0.5 mL. HPGe gamma spectroscopy of purified 64Cu detected <0.3 % co-produced 67Cu at EOB with no other radionuclidic impurities. ICP-OES elemental analysis determined <1 ppm Al, Zn, In, Fe, and Cu in the [64Cu]CuCl 2 product. NOTA, DOTA, TETA, and PSMA I&T were radiolabeled with 64Cu, resulting in maximum molar activities of 164 ± 6 GBq/μmol, 155 ± 31 GBq/μmol, 266 ± 34 GBq/μmol, and 117 ± 2 GBq/μmol, respectively. PET imaging in PSMA-expressing LNCaP xenografts resulted in high tumor uptake (SUV mean = 1.65 ± 0.1) using [64Cu]Cu-PSMA I&T, while [68Ga]Ga-PSMA I&T yielded an SUV mean of 0.76 ± 0.14 after 60 min post-injection. 64Cu was purified in a small volume amenable for radiolabeling, with yields suitable for preclinical and clinical application. The 64Cu production and purification process and the favourable PET imaging properties confirm the 68Zn(p,nα)64Cu nuclear reaction as a viable 64Cu production route for facilities with access to a higher energy proton cyclotron, compared to using expensive 64Ni target material and the 64Ni(p,n)64Cu nuclear reaction. Our 64Cu production technique provides an alternative production route with the potential to improve 64Cu availability for preclinical and clinical studies alongside 67Cu therapy. [Display omitted] [ABSTRACT FROM AUTHOR]

Radiolabeled peptides play a central role in nuclear medicine as radiotheranostics for targeted imaging and therapy of cancer. We have recently proposed the use of metabolically stabilized GRPR antagonist BBN2 for radiolabeling with 18F and 68Ga and subsequent PET imaging of GRPRs in prostate cancer. The present work studied the impact of 44gSc- and 68Ga-labeled DOTA complexes attached to GRPR antagonist BBN2 on the in vitro GRPR binding affinity, and their biodistribution and tumor uptake profiles in MCF7 breast and PC3 prostate cancer models. DOTA-Ava-BBN2 was radiolabeled with radiometals 68Ga and 44gSc. Gastrin-releasing peptide receptor (GRPR) affinities of peptides were assessed in PC3 prostate cancer cells. GRPR expression profiles were studied in human breast cancer tissue samples and MCF7 breast cancer cells. PET imaging of 68Ga- and 44gSc-labeled peptides was performed in MCF7 and PC3 xenografts as breast and prostate cancer models. Radiopeptides [68Ga]Ga-DOTA-Ava-BBN2 and [44gSc]Sc-DOTA-Ava BBN2 were prepared in radiochemical yields of 70–80% (decay-corrected), respectively. High binding affinities were found for both peptides (IC 50 = 15 nM (natGa) and 5 nM (natSc)). Gene expression microarray analysis revealed high GRPR mRNA expression levels in estrogen receptor (ER)-positive breast cancer, which was further confirmed with Western blot and immunohistochemistry. However, PET imaging showed only low tumor uptake of both radiotracers in MCF7 xenografts ([68Ga]Ga-DOTA-BBN2 (SUV 60min 0.27 ± 0.06); [44gSc]Sc-DOTA-BBN2 (SUV 60min 0.20 ± 0.03)). In contrast, high tumor uptake and retention were found for both radiopeptides in PC3 tumors ([68Ga]Ga-DOTA-BBN2 (SUV 60min 0.46 ± 0.07); [44gSc]Sc-DOTA-BBN2 (SUV 60min 0.51 ± 0.11)). Comparison of 68Ga- and 44gSc-labeled DOTA-Ava-BBN2 peptides revealed slight but noticeable differences of the radiometal with an impact on the in vitro GRPR receptor binding properties in PC3 cells. No differences were found in their in vivo biodistribution profiles in MCF7 and PC3 xenografts. Radiopeptides [68Ga]Ga-DOTA-Ava-BBN2 and [44gSc]Sc-DOTA-Ava-BBN2 displayed comparable tumor uptake and retention profiles with rapid blood and renal clearance profiles in both tumor models. The favorable PET imaging performance of [44gSc]Sc-DOTA-Ava-BBN2 in prostate cancer should warrant the development of an [43Sc]Sc-DOTA-Ava-BBN2 analog for clinical translation which comes with a main γ-line of much lower energy and intensity compared to 44gSc. [ABSTRACT FROM AUTHOR]

Gallium-68 is an important radionuclide for positron emission tomography (PET) with steadily increasing applications of 68Ga-based radiopharmaceuticals for clinical use. Current 68Ga sources are primarily 68Ge/68Ga-generators, along with successful attempts of 68Ga production using a cyclotron. This study evaluated cyclotron 68Ga production and automated separation using expeditiously manufactured solid targets, demonstrates an order of magnitude improvement in yield compared to 68Ge/68Ga generators, and presents a convenient alternative to existing cyclotron production processes. A comparison of radiolabeling and preclinical PET imaging was performed with both cyclotron and generator produced 68Ga. 100 mg enriched 68Zn (99.3% 68Zn, 0.48% 67Zn, 0.1% 66Zn) pellets pressed on silver discs were bombarded for 20–75 min using 12.5 MeV proton beam energies and 10–30 μA currents. 68Ga was separated using an automated TRASIS AllinOne synthesizer employing AG 50W-X8 and UTEVA resins. Post-separation recovery of the 68Zn by electrolysis yielded 76.7 ± 4.3%. Radionuclidic purity of cyclotron-produced 68Ga was investigated with gamma spectroscopy using a HPGe-detector. Radiolabeling was investigated using the macrocyclic chelator DOTA and the bombesin-derived peptide NOTA-BBN2. PET imaging was performed using [68Ga]Ga-NOTA-BBN2 in a PC3 xenograft model. 600 μA·min fresh and recycled quadruplet 68Zn target irradiations (n = 8) at 12.5 MeV and 30 μA yielded 13.9 ± 1.0 GBq 68Ga; 2200 μA·min irradiations (n = 3) yielded 37.5 ± 1.9 GBq 68Ga. HPGe analysis showed EOB 0.0074% and 0.0084% of total activity of 66Ga and 67Ga, respectively. Metal impurities were 0.06 ± 0.03 μg/GBq Zn, 0.13 ± 0.007 μg/GBq Fe, and 0.02 ± 0.01 μg/GBq Al for cyclotron 68Ga. Cyclotron and 68Ge/68Ga generator 68Ga respective DOTA and NOTA-BBN2 labeling incorporations were 99.4 ± 0.0% and 99.3 ± 0.2%, and 90.4 ± 1.5% and 93.0 ± 3.6% determined by radio-thin layer chromatography (radio-TLC). Preclinical PET imaging comparison between generator and cyclotron produced 68Ga showed identical radiotracer tumor uptake and biodistribution profiles in PC3 tumor bearing mice. Cyclotron 68Ga production provides highly scalable production with equivalent or superior quality 68Ga to a 68Ge/68Ga generator, while providing identical biodistribution and tumor uptake profiles. Our described targetry is simpler and more cost-effective than existing liquid and solid targetry, enabling a turnkey production system for multi-facility distribution of cyclotron produced 68Ga. The manufacturing simplicity described has potential applications for producing other radiometals such as 44Sc. Our cost-effective method of solid target 68Ga production can enhance 68Ga production capabilities to meet the high demand for 68Ga-radiopharmaceuticals for research and clinical use. [ABSTRACT FROM AUTHOR]

Tumour hypoxia is associated with increased metastasis, invasion, poor therapy response and prognosis. Most PET radiotracers developed and used for clinical hypoxia imaging belong to the 2-nitroimidazole family. Recently we have developed novel 2-nitroimidazole-derived PET radiotracer [18F]FBNA (N -(4-[18F]fluoro-benzyl)-2-(2-nitro-1 H -imidazol-1-yl)-acet-amide), an 18F-labeled analogue of antiparasitic drug benznidazole. The present study aimed to analyze its radio-pharmacological properties and systematically compare its PET imaging profiles with [18F]FMISO and [18F]FAZA in preclinical triple-negative (MDA-MB231) and estrogen receptor-positive (MCF-7) breast cancer models. In vitro cellular uptake experiments were carried out in MDA-MB321 and MCF-7 cells under normoxic and hypoxic conditions. Metabolic stability in vivo was determined in BALB/c mice using radio-TLC analysis. Dynamic PET experiments over 3 h post-injection were performed in MDA-MB231 and MCF-7 tumour-bearing mice. Those PET data were used for kinetic modelling analysis utilizing the reversible two-tissue-compartment model. Autoradiography was carried out in tumour tissue slices and compared to HIF-1α immunohistochemistry. Detailed ex vivo biodistribution was accomplished in BALB/c mice, and this biodistribution data were used for dosimetry calculation. Under hypoxic conditions in vitro cellular uptake was elevated in both cell lines, MCF-7 and MDA-MB231, for all three radiotracers. After intravenous injection, [18F]FBNA formed two radiometabolites, resulting in a final fraction of 65 ± 9 % intact [18F]FBNA after 60 min p.i. After 3 h p.i., [18F]FBNA tumour uptake reached SUV values of 0.78 ± 0.01 in MCF-7 and 0.61 ± 0.04 in MDA-MB231 tumours (both n = 3), representing tumour-to-muscle ratios of 2.19 ± 0.04 and 1.98 ± 0.15, respectively. [18F]FMISO resulted in higher tumour uptakes (SUV 1.36 ± 0.04 in MCF-7 and 1.23 ± 0.08 in MDA-MB231 (both n = 4; p < 0.05) than [18F]FAZA (0.66 ± 0.11 in MCF-7 and 0.63 ± 0.14 in MDA-MB231 (both n = 4; n.s.)), representing tumour-to-muscle ratios of 3.24 ± 0.30 and 3.32 ± 0.50 for [18F]FMISO, and 2.92 ± 0.74 and 3.00 ± 0.42 for [18F]FAZA, respectively. While the fraction per time of radiotracer entering the second compartment (k3) was similar within uncertainties for all three radiotracers in MDA-MB231 tumours, it was different in MCF-7 tumours. The ratios k3/(k3 + k2) and K1*k3/(k3 + k2) in MCF-7 tumours were also significantly different, indicating dissimilar fractions of radiotracer bound and trapped intracellularly: K1*k3/(k2 + k3) [18F]FMISO (0.0088 ± 0.001)/min, n = 4; p < 0.001) > [18F]FAZA (0.0052 ± 0.002)/min, n = 4; p < 0.01) > [18F]FBNA (0.003 ± 0.001)/min, n = 3). In contrast, in MDA-MB231 tumours, only K1 was significantly elevated for [18F]FMISO. However, this did not result in significant differences for K1*k3/(k2 + k3) for all three 2-nitroimidazoles in MDA-MB231 tumours. Novel 2-nitroimidazole PET radiotracer [18F]FBNA showed uptake into hypoxic breast cancer cells and tumour tissue presumably associated with elevated HIF1-α expression. Systematic comparison of PET imaging performance with [18F]FMISO and [18F]FAZA in different types of preclinical breast cancer models revealed a similar tumour uptake profile for [18F]FBNA with [18F]FAZA and, despite its higher lipophilicity, still a slightly higher muscle tissue clearance compared to [18F]FMISO. [Display omitted] [ABSTRACT FROM AUTHOR]

Introduction Non-invasive imaging of COX-2 in cancer represents a powerful tool for assessing COX-2-mediated effects on chemoprevention and radiosensitization using potent and selective COX-2 inhibitors as an emerging class of anticancer drugs. Careful assessment of the pharmacokinetic profile of radiolabeled COX-2 inhibitors is of crucial importance for the development of suitable radiotracers for COX-2 imaging in vivo . The delicate balance between the selection of typical COX-2 pharmacophores and the resulting physicochemical characteristics of the COX-2 inhibitor represents a formidable challenge for the search of radiolabeled COX-2 imaging agents. Several pyrimidine-based COX-2 inhibitors demonstrated favorable in vitro and in vivo COX-2 imaging properties in various COX-2 expressing cancer cell lines. Here, we describe a comparative radiopharmacological study of three 18 F-labeled COX-2 inhibitors based on a pyrimidine scaffold. The objective of this study was to investigate how subtle structural alterations influence the pharmacokinetic profile of lead compound [ 18 F ] 1a ([ 18 F]Pyricoxib) to afford 18 F-labeled pyrimidine-based COX-2 inhibitors with improved COX-2 imaging properties in vivo . Methods Radiosynthesis of radiotracers was accomplished through reaction with 4-[ 18 F]fluorobenzyl amine on a methyl-sulfone labeling precursor ([ 18 F ] 1a and [ 18 F] 2a ) or late-stage radiofluorination using a iodyl-containing labeling precursor ([ 18 F ] 3a ). Radiopharmacological profile of 18 F-labeled pyrimidine-based COX-2 inhibitors [ 18 F ] 1a , [ 18 F ] 2a and [ 18 F ] 3a was studied in COX-2-expressing human HCA-7 colorectal cancer cell line, including cellular uptake studies in HCA-7 cells and dynamic PET imaging studies in HCA-7 xenografts. Results Cellular uptake of radiotracers [ 18 F ] 2a and [ 18 F ] 3a in HCA-7 cells was 450% and 300% radioactivity/mg protein, respectively, after 90 min incubation, compared to 600% radioactivity/mg protein for radiotracer [ 18 F ] 1a . Dynamic PET imaging studies revealed a tumor SUV of 0.53 ([ 18 F ] 2a ) and 0.54 ([ 18 F ] 3a ) after 60 min p.i. with a tumor-to-muscle ratio of ~1. Tumor SUV for [ 18 F ] 1a (60 min p.i.) was 0.76 and a tumor-to-muscle ratio of ~1.5. Pyricoxib analogues [ 18 F ] 2a and [ 18 F ] 3a showed distinct pharmacokinetic profiles in comparison to lead compound [ 18 F ] 1a with a significantly improved lung clearance pattern. Replacing the 4-[ 18 F]fluorobenzyl amine motif in radiotracer [ 18 F ] 1a with a 4-[ 18 F]fluorobenzyl alcohol motif in radiotracer [ 18 F ] 3a resulted in re-routing of the metabolic pathway as demonstrated by a more rapid liver clearance and higher initial kidney uptake and more rapid kidney clearance compared to radiotracers [ 18 F ] 1a and [ 18 F ] 2a . Moreover, radiotracer [ 18 F ] 3a displayed favorable rapid brain uptake and retention. Conclusion The radiopharmacological profile of three 18 F-labeled COX-2 inhibitors based on a pyrimidine scaffold were evaluated in COX-2 expressing human colorectal cancer cell line HCA-7 and HCA-7 xenografts in mice. Despite the overall structural similarity and comparable COX-2 inhibitory potency of all three radiotracers, subtle structural alterations led to significantly different in vitro and in vivo metabolic profiles. Advances in knowledge Among all tested pyrimidine-based 18 F-labeled COX-2 inhibitors, lead compound [ 18 F ] 1a remains the most suitable radiotracer for assessing COX-2 expression in vivo . Radiotracer [ 18 F ] 3a showed significantly improved first pass pulmonary passage in comparison to radiotracer [ 18 F ] 1a and might represents a promising lead compound for the development of radiotracers for PET imaging of COX-2 in neuroinflammation. [ABSTRACT FROM AUTHOR]

Introduction Receptor tyrosine kinase (RTK) platelet-derived growth factor receptor-alpha (PDGFRα) was recently identified as a molecular switch for dedifferentiation in thyroid cancer that predicts resistance to therapy as well as recurrence of disease in papillary thyroid cancer. Here we describe the radiolabeling and functional characterization of an imaging probe based on a PDGFRα-specific monoclonal antibody (mAb) for immuno-PET imaging of PDGFRα in papillary thyroid cancer. Methods Antibody D13C6 (Cell Signaling) was decorated with chelator NOTA using bioconjugation reaction with 2-( p -NCS-Bz)-NOTA. Radiolabeling was carried out using 40 μg of antibody-NOTA conjugate with 143–223 MBq of [ 64 Cu]CuCl 2 in 0.25 M NaOAc (pH 5.5) at 30 °C for 1 h. The reaction mixture was purified with size-exclusion chromatography (PD-10 column). PDGFRα and mock transfected B-CPAP thyroid cancer cells lines for validation of 64 Cu-labeled immuno-conjugates were generated using LVX-Tet-On technology. PET imaging was performed in NSG mice bearing bilaterally-induced PDGFRα (+/−) B-CPAP tumors. Results Bioconjugation of NOTA chelator to monoclonal antibody D13C6 resulted in 2.8 ± 1.3 chelator molecules per antibody as determined by radiometric titration with 64 Cu. [ 64 Cu]Cu-NOTA-D13C6 was isolated in high radiochemical purity (>98%) and good radiochemical yields (19–61%). The specific activity was 0.9–5.1 MBq/μg. Cellular uptake studies revealed a specific radiotracer uptake in PDGFRα expressing cells compared to control cells. PET imaging resulted in SUV mean values of ~5.5 for PDGFRα (+) and ~2 for PDGFRα (−) tumors, after 48 h p.i.. After 1 h, radiotracer uptake was also observed in the bone marrow (SUV mean ~5) and spleen (SUV mean ~8.5). Conclusion Radiolabeled antibody [ 64 Cu]Cu-NOTA-D13C6 represents a novel and promising radiotracer for immuno-PET imaging of PDGFRα in metastatic papillary thyroid cancer. Advances in knowledge and implications for patient care The presented work has the potential to allow physicians to identify papillary thyroid cancer patients at risk of metastases by using the novel immuno-PET imaging assay based on PDGFRα-targeting antibody [ 64 Cu]Cu-NOTA-D13C6. [ABSTRACT FROM AUTHOR]

203Pb (t 1/2 = 51.9 h, 279 keV (81 %)) is a diagnostic SPECT imaging radionuclide ideally suited for theranostic applications in combination with 212Pb for targeted alpha particle therapy. Our objectives were to develop a high-yield solid target 203Pb cyclotron production route using isotopically enriched 205Tl target material and the 205Tl(p,3n)203Pb reaction as an alternative to lower energy production via the 203Tl(p,n)203Pb reaction. 250 mg 205Tl metal (99.9 % isotopic enrichment) was pressed using a hardened stainless steel die. Aluminum target discs were machined with a central depression and annulus groove. The flattened 205Tl pellet was placed into the central depression of the Al disc and a circle of indium wire was laid in the machined annulus surrounding the pellet. An aluminum foil cover was then pressed onto the target disc to create an airtight bond. Targets were irradiated at 23.3 MeV for up to 516 min on a TR-24 cyclotron at currents up to 60 μA to produce 203Pb via the 205Tl(p,3n)203Pb nuclear reaction. Following a cool-down period of >12 h, the target was removed and 205Tl dissolved in 4 M HNO 3. A NEPTIS Mosaic-LC synthesis unit performed automated separation using Eichrom Pb resin, and 203Pb was eluted using 8 M HCl or 1 M NH 4 OAc. 205Tl was diverted to a vial for recovery in an electrolytic cell. 203Pb product radionuclidic purity was assessed by HPGe gamma spectroscopy, while elemental purity was assessed by ICP-OES. Radiolabeling and stability studies were performed with PSC, TCMC, and DOTA chelators, and 203Pb incorporation was verified by radio-TLC analysis. Cyclotron irradiations performed at 60 μA proton beam current and 23.3 MeV (205Tl incident energy) had a 203Pb saturated yield of 4658 ± 62 MBq/μA (n = 3). Automated NEPTIS separation took <4 h from the start of target dissolution to product elution, yielding >85 % decay-corrected [203Pb]PbCl 2 with a radionuclidic purity of >99.9 %. Purified [203Pb]PbCl 2 yields of up to 12 GBq 203Pb were attained (15.8 GBq at EOB). The [203Pb]PbCl 2 and [203Pb]Pb(OAc) 2 products contained no detectable radionuclidic impurities besides 201Pb (<0.1 %), and <0.4 ppm stable Pb. 205Tl metal was recovered with a 92 % batch yield. Aliquots of 100 μL [203Pb]Pb(OAc) 2 were used for radiolabeling PSC-Bn-NCS, TCMC-NCS, and DOTA-NCS chelators at pH 4.5 and 22 °C for 30 min, with maximum respective molar activities of 461 ± 30 GBq/μmol, 195 ± 37 GBq/μmol, and 83 ± 12 GBq/μmol. PSC, TCMC, and DOTA chelators exhibited >99.9 % incorporation after a 120-hour incubation in human serum at 37 °C. Nuclear medicine centers with access to higher energy cyclotrons can produce large 203Pb activities sufficient for clinical applications, with a convenient separation technique producing highly pure [203Pb]PbCl 2 or [203Pb]Pb(OAc) 2 for direct radiolabeling. This represents an attractive route to produce 203Pb for diagnostic SPECT imaging alongside 212Pb targeted alpha particle therapy. Our high-yield 203Pb production technique significantly enhances 203Pb production capabilities to meet the growing preclinical and clinical demand for 203Pb radiopharmaceuticals alongside 212Pb target alpha particle therapy. [Display omitted] [ABSTRACT FROM AUTHOR]

Introduction Radiolabeled phosphatidylserine (PS)-binding peptides represent an innovative strategy for molecular imaging of apoptosis with positron emission tomography (PET). The goal of this study was the radiopharmacological evaluation of radiolabeled peptides for their binding to PS on apoptotic cancer cells, involving metabolic stability, cellular uptake, biodistribution, and dynamic PET imaging experiments. Methods Binding of peptides LIKKPF, PGDLSR, FBz-LIKKPF, FBz-PGDLSR, FBAM-CLIKKPF and FBAM-CPGDLSR to PS was analyzed in a newly developed radiometric binding assay using 64 Cu-labeled wild-type annexin-V as radiotracer. Radiolabeling of most potent peptides with fluorine-18 was carried out with thiol-selective prosthetic group [ 18 F]FBAM to give [ 18 F]FBAM-CLIKKPF and [ 18 F]FBAM-CPGDLSR. [ 18 F]FBAM-labeled peptides were studied in camptothecin-induced apoptotic human T lymphocyte Jurkat cells, and in a murine EL4 tumor model of apoptosis using dynamic PET imaging and biodistribution. Results Peptides LIKKPF and PGDLSR inhibited binding of 64 Cu-labeled annexin-V to immobilized PS in the millimolar range (IC 50 10–15 mM) compared to annexin-V (45 nM). Introduction of FBAM prosthetic group slightly increased inhibitory potencies (FBAM-CLIKKPF: IC 50 = 1 mM; FBAM-CPGDLSR: IC 50 = 6 mM). Radiolabeling succeeded in good radiochemical yields of 50–54% using a chemoselective alkylation reaction of peptides CLIKKPF and CPGDLSR with [ 18 F]FBAM. In vivo metabolic stability studies in mice revealed 40–60% of intact peptides at 5 min p.i. decreasing to 25% for [ 18 F]FBAM-CLIKKPF and less than 5% for [ 18 F]FBAM-CPGDLSR at 15 min p.i.. Cell binding of [ 18 F]FBAM-CLIKKPF in drug-treated Jurkat cells was significantly higher compared to untreated cells, but this was not observed for [ 18 F]FBAM-CPGDLSR. Dynamic PET imaging experiments showed that baseline uptake of [ 18 F]FBAM-CLIKKPF in EL4 tumors was higher (SUV 5min 0.46, SUV 60min 0.13) compared to [ 18 F]FBAM-CPGDLSR (SUV 5min 0.16, SUV 60min 0.10). Drug-treated EL4 tumors did not show an increased uptake for both [ 18 F]FBAM-labeled peptides. Conclusion Although both 18 F-labeled peptides [ 18 F]FBAM-CLIKKPF and [ 18 F]FBAM-CPGDLSR showed higher binding to apoptotic Jurkat cells in vitro , their in vivo uptake profiles were not different in apoptotic EL4 tumors. This may explained by the relatively low potency of both compounds to compete with binding of 64 Cu-labeled annexin-V to PS. Overall the novel competitive radiometric PS-binding assay with 64 Cu-labeled annexin-V represents a versatile and very robust screening platform to analyze potential PS-binding compounds in vitro . Further studies will be necessary to evaluate alternative peptide structures toward their use as PET radiotracers imaging apoptosis in vivo . Advances in knowledge and implications for patient care Development of peptide-based radiotracers for imaging apoptosis in vivo remains a significant challenge. [ABSTRACT FROM AUTHOR]

Introduction 18 F-labeled amino acids are important PET radiotracers for molecular imaging of cancer. This study describes synthesis and radiopharmacological evaluation of 2-amino-5-(4-[ 18 F]fluorophenyl)pent-4-ynoic acid ([ 18 F]FPhPA) as a novel amino acid radiotracer for oncologic imaging. Methods 18 F]FPhPA was prepared using Pd-mediated S onogashira cross-coupling reaction between 4-[ 18 F]fluoroiodobenzene ([ 18 F]FIB) and propargylglycine. The radiopharmacological profile of [ 18 F]FPhPA was evaluated in comparison with O -(2-[ 18 F]fluoroethyl)-L-tyrosine ([ 18 F]FET) using the murine breast cancer cell line EMT6 involving cellular uptake studies, radiotracer uptake competitive inhibition experiments and small animal PET imaging. Results 18 F]FPhPA was prepared in 42 ± 10% decay-corrected radiochemical yield with high radiochemical purity >95% after semi-preparative HPLC purification. Cellular uptake of L-[ 18 F]FPhPA reached a maximum of 58 ± 14 % radioactivity/mg protein at 90 min. Lower uptake was observed for racemic and D-[ 18 F]FPhPA. Radiotracer uptake inhibition studies by synthetic and naturally occurring amino acids suggested that Na + -dependent system ASC, especially ASCT2, and Na + -independent system L are important amino acid transporters for [ 18 F]FPhPA uptake into EMT6 cells. Small animal PET studies demonstrated similar high tumor uptake of [ 18 F]FPhPA in EMT6 tumor-bearing mice compared to [ 18 F]FET reaching a maximum standardized uptake value (SUV) of 1.35 after 60 min p.i.. Muscle uptake of [ 18 F]FPhPA was higher (SUV 30min = 0.65) compared to [ 18 F]FET (SUV 30min = 0.40), whereas [ 18 F]FPhPA showed a more rapid uptake and clearance from the brain compared to [ 18 F]FET. Conclusion L-[ 18 F]FPhPA is the first 18 F-labeled amino acid prepared through Pd-mediated cross-coupling reaction. Advances in Knowledge and Implications for patient Care L-[ 18 F]FPhPA displayed promising properties as a novel amino acid radiotracer for molecular imaging of system ASC and system L amino acid transporters in cancer. [ABSTRACT FROM AUTHOR]

Introduction: Bombesin (BBN) and BBN analogues have attracted much attention as high-affinity ligands for selective targeting of the gastrin-releasing peptide (GRP) receptor. GRP receptors are overexpressed in a variety of human cancers including prostate cancer. Radiolabeled BBN derivatives are promising diagnostic probes for molecular imaging of GRP receptor-expressing prostate cancer. This study describes the synthesis and radiopharmacological evaluation of various metabolically stabilized fluorobenzoylated bombesin analogues (BBN-1, BBN-2, BBN-3). Methods: Three fluorobenzoylated BBN analogues containing an aminovaleric (BBN-1, BBN-2), or an aminooctanoic acid linker (BBN-3) were tested in a competitive binding assay against 125I-[Tyr4]-BBN for their binding potency to the GRP receptor. Intracellular calcium release in human prostate cancer cells (PC3) was measured to determine agonistic or antagonistic profiles of fluorobenzoylated BBN derivatives. Bombesin derivative BBN-2 displayed the highest inhibitory potency toward GRP receptor (IC50 =8.7±2.2nM) and was subsequently selected for radiolabeling with fluorine-18 (18F) through acylation with N-succinimidyl-4-[18F]fluorobenzoate ([18F]SFB). The radiopharmacological profile of 18F-labeled bombesin [18F]BBN-2 was evaluated in PC3 tumor-bearing NMRI nude mice involving metabolic stability studies, biodistribution experiments and dynamic small-animal PET studies. Results: All fluorobenzoylated BBN derivatives displayed high inhibitory potency toward the GRP receptor (IC50 =8.7–16.7nM), and all compounds exhibited antagonistic profiles as determined in an intracellular calcium release assay. The 18F-labeled BBN analogue [18F]BBN-2 was obtained in 30% decay-corrected radiochemical yield with high radiochemical purity >95% after semi-preparative HPLC purification. [18F]BBN-2 showed high metabolic stability in vivo with 65% of the radiolabeled peptide remaining intact after 60min p.i. in mouse plasma. Biodistribution experiments and dynamic small-animal PET studies demonstrated high tumor uptake of [18F]BBN-2 in PC3 xenografts (2.75±1.82 %ID/g after 5min and 2.45±1.25 %ID/g after 60min p.i.). Specificity of radiotracer uptake in PC3 tumors was confirmed by blocking experiments. Conclusion: The present study demonstrates that 18F-labeled BBN analogue [18F]BBN-2 is a suitable PET radiotracer with favorable metabolic stability in vivo for molecular imaging of GRP receptor-positive prostate cancer. [ABSTRACT FROM AUTHOR]

Abstract: Introduction: Phosphopeptides represent interesting compounds to study and elucidate cellular protein phosphorylation/dephosphorylation processes underlying various signal transduction pathways. However, studies of phosphopeptide action in cells are severely constrained by the negatively charged phosphate moiety of the phosphopeptide resulting in poor transport through the cell membrane. The following study describes the synthesis and radiopharmacological evaluation of two 18F-labeled phosphopeptide-cell-penetrating peptide dimers. The polo-like kinase-1-binding hexaphosphopeptide H-Met-Gln-Ser-pThr-Pro-Leu-OH was coupled to cell-penetrating peptides (CPPs), either sC18, a cathelicidin-derived peptide, or the human calcitonin derivative hCT(18-32)-k7. Methods: Radiolabeling was accomplished with the prosthetic group N-succinimidyl 4-[18F]fluorobenzoate ([18F]SFB) using both, conventional and microfluidic-based bioconjugation of [18F]SFB to N-terminal end of phosphopeptide part of the peptide dimers. Cellular uptake studies in human cancer cell lines HT-29 and FaDu cells at 4 °C and 37 °C and small animal PET in BALB/c mice were utilized for radiopharmacological characterization. Results: Isolated radiochemical yields ranged from 2% to 4% for conventional bioconjugation with [18F]SFB. Significantly improved isolated radiochemical yields of up to 26% were achieved using microfluidic technology. Cellular uptake studies of radiolabeled phosphopeptide and phosphopeptide-CPP dimers indicate enhanced internalization of 50% ID/mg protein after 2 h for both phosphopeptide dimers compared to the phosphopeptide alone (<1% ID/mg protein). In vivo biodistribution of 18F-labeled peptide dimers was determined with small animal PET revealing a superior biodistribution pattern of sC18-containing peptide dimer MQSpTPL-sC18 [18F]4. Conclusion: [18F]SFB labeling of the phosphopeptide-CPP dimers using a microfluidic system leads to an improved chemoselectivity towards the N-terminal NH2 group compared to the conventional labeling approach. Cell-penetrating peptide sC18 can be considered as an ideal molecular shuttle for intracellular delivery of the Plk1-PBD-binding hexaphosphopeptide as demonstrated by its favourable radiopharmacological profile. [Copyright &y& Elsevier]

Abstract: Introduction: Several clinical studies have shown low or no expression of GLUT1 in breast cancer patients, which may account for the low clinical specificity and sensitivity of 2-deoxy-2-[18F]fluoro-d-glucose ([18F]FDG) used in positron emission tomography (PET). Therefore, it has been proposed that other tumor characteristics such as the high expression of GLUT2 and GLUT5 in many breast tumors could be used to develop alternative strategies to detect breast cancer. Here we have studied the in vitro and in vivo radiopharmacological profile of 6-deoxy-6-[18F]fluoro-d-fructose (6-[18F]FDF) as a potential PET radiotracer to image GLUT5 expression in breast cancers. Methods: Uptake of 6-[18F]FDF was studied in murine EMT-6 and human MCF-7 breast cancer cells over 60 min and compared to [18F]FDG. Biodistribution of 6-[18F]FDF was determined in BALB/c mice. Tumor uptake was studied with dynamic small animal PET in EMT-6 tumor-bearing BALB/c mice and human xenograft MCF-7 tumor-bearing NIH-III mice in comparison to [18F]FDG. 6-[18F]FDF metabolism was investigated in mouse blood and urine. Results: 6-[18F]FDF is taken up by EMT-6 and MCF-7 breast tumor cells independent of extracellular glucose levels but dependent on the extracellular concentration of fructose. After 60 min, 30±4% (n=9) and 12±1% (n=7) ID/mg protein 6-[18F]FDF was found in EMT-6 and MCF-7 cells, respectively. 6-deoxy-6-fluoro-d-fructose had a 10-fold higher potency than fructose to inhibit 6-[18F]FDF uptake into EMT-6 cells. Biodistribution in normal mice revealed radioactivity uptake in bone and brain. Radioactivity was accumulated in EMT-6 tumors reaching 3.65±0.30% ID/g (n=3) at 5 min post injection and decreasing to 1.75±0.03% ID/g (n=3) at 120 min post injection. Dynamic small animal PET showed significantly lower radioactivity uptake after 15 min post injection in MCF-7 tumors [standard uptake value (SUV)=0.76±0.05; n=3] compared to EMT-6 tumors (SUV=1.23±0.09; n=3). Interestingly, [18F]FDG uptake was significantly different in MCF-7 tumors (SUV15 min 0.74±0.12 to SUV120 min 0.80±0.15; n=3) versus EMT-6 tumors (SUV 15 min 1.01±0.33 to SUV 120 min 1.80±0.25; n=3). 6-[18F]FDF was shown to be a substrate for recombinant human ketohexokinase, and it was metabolized rapidly in vivo. Conclusion: Based on the GLUT5 specific transport and phosphorylation by ketohexokinase, 6-[18F]FDF may represent a novel radiotracer for PET imaging of GLUT5 and ketohexokinase-expressing tumors. [Copyright &y& Elsevier]

Abstract: Introduction: Microfluidic technology allows fast reactions in a simple experimental setup, while using very low volumes and amounts of starting material. Consequently, microfluidic technology is an ideal tool for radiolabeling reactions involving short-lived positron emitters. Optimization of the complex array of different reaction conditions requires knowledge of the different reaction parameters linked to the microfluidic system as well as their influence on the radiochemical yields. 1-(5-Deoxy-5-fluoro-α-d-arabinofuranosyl)-2-nitroimidazole ([18F]FAZA) is a frequently used radiotracer for PET imaging of tumor hypoxia. The present study describes the radiosynthesis of [18F]FAZA by means of microfluidic technology and subsequent small animal PET imaging in EMT-6 tumor-bearing mice. Methods: Radiosyntheses were performed using the NanoTek Microfluidic Synthesis System (Advion BioSciences, Inc.). Optimal reaction conditions were studied through screening different reaction parameters like temperature, flow rate, residency time, concentration of the labeling precursor (1-(2,3-di-O-acetyl-5-O-tosyl-α-d-arabinofuranosyl)-2-nitroimidazole) and the applied volume ratio between the labeling precursor and [18F]fluoride. Results: Optimized reaction conditions at low radioactivity levels (1 to 50 MBq) afforded 63% (decay-corrected) of HPLC-purified [18F]FAZA within 25 min. Higher radioactivity levels (0.4 to 2.1 GBq) gave HPLC-purified [18F]FAZA in radiochemical yields of 40% (decay-corrected) within 60 min at a specific activity in the range of 70 to 150 GBq/μmol. Small animal PET studies in EMT-6 tumor-bearing mice showed radioactivity accumulation in the tumor (SUV20min 0.74 ± 0.08) resulting in an increasing tumor-to-muscle ratio over time. Conclusions: Microfluidic technology is an ideal method for the rapid and efficient radiosynthesis of [18F]FAZA for preclinical radiopharmacological studies. Careful analysis of various reaction parameters is an important requirement for the understanding of the influence of different reaction parameters on the radiochemical yield using microfluidic technology. Exploration of microfluidic technology for the radiosynthesis of other PET radiotracers in clinically relevant radioactivity levels is currently in progress. [Copyright &y& Elsevier]

Abstract: This work involves the production, processing and imaging of the short-lived, rarely used positron emission tomography (PET) radionuclide technetium-94m (94mTc). Our procedures are an extension of methods reported in the literature and are detailed within. A key modification was the development of a single step that combines purification and concentration of an aqueous 94mTc-pertechnetate solution, which both reduces processing time and increases the final concentration of the solution. Additionally, a convenient method for the direct recovery of 94mTc into an organic solvent was developed, eliminating the solvent transfer step needed for organic syntheses using 94mTc. Each of these advances potentially extends the scope of syntheses possible with this short-lived radionuclide. To explore the imaging potential of 94mTc, we carried out phantom imaging studies on small-scale high-resolution PET scanners to estimate the limitations of detection associated with 94mTc and PET. Preliminary studies demonstrate that useful images can be obtained with modern image reconstruction algorithms when using a correction for the cascade gamma ray contamination. [Copyright &y& Elsevier]

Abstract: Oxidative modification of low-density lipoprotein (LDL) is regarded as a crucial event in atherogenesis. Assessing the metabolic fate of oxidized LDL (oxLDL) in vivo with radiotracer techniques is hindered by the lack of suitable sensitive and specific radiolabeling methods. We evaluated an improved methodology based on the radiolabeling of native LDL (nLDL) and oxLDL with the positron emitter fluorine-18 (18F) by conjugation with N-succinimidyl-4-[18F]fluorobenzoate ([18F]SFB). We investigated whether radiolabeling of LDL induces adverse structural modifications. Results suggest that radiolabeling of both nLDL and oxLDL using [18F]SFB causes neither additional oxidative structural modifications of LDL lipids and proteins nor alteration of their biological activity and functionality, respectively. Thus, radiolabeling of LDL using [18F]SFB could prove to be a promising approach for studying the kinetics of oxLDL in vivo. [Copyright &y& Elsevier]