Production and purification of 43Sc and 47Sc from enriched [46Ti]TiO2 and [50Ti]TiO2 targets.

The radioscandium isotopes, 43Sc and 47Sc, compose a promising elementally matched theranostic pair that can be used for the development of imaging and therapeutic radiopharmaceuticals with identical structures. This study aimed to investigate the production of high radionuclidic purity 43Sc from enriched [46Ti]TiO2 targets and 47Sc from enriched [50Ti]TiO2 targets and establish a target recycling technique. Enriched [46Ti]TiO2 targets were irradiated with 18 MeV protons, and enriched [50Ti]TiO2 targets were bombarded with 24 MeV protons. 43Sc and 47Sc were purified using ion chromatography attaining recovery yields of 91.7 ± 7.4% and 89.9 ± 3.9%, respectively. The average radionuclidic purity for 43Sc was 98.8 ± 0.3% and for 47Sc 91.5 ± 0.6%, while the average recovery of enriched titanium target material was 96 ± 4.0%. The highest apparent molar activity for [43Sc]Sc-DOTA was 23.2 GBq/µmol and 3.39 GBq/µmol for [47Sc]Sc-DOTA. This work demonstrates the feasibility of using enriched recycled [46Ti]TiO2 and [50Ti]TiO2 targets to produce high purity 43Sc and 47Sc as an elementally matched theranostic isotope pair.

Optimized Methods for the Production of High-Purity 203Pb Using Electroplated Thallium Targets.

203Pb is a surrogate imaging match for 212Pb. This elementally matched pair is emerging as a suitable pair for imaging and targeted radionuclide therapy in cancer care. Because of the half-life (51.9 h) and low-energy γ-rays emitted, 203Pb is suitable for the development of diagnostic radiopharmaceuticals. The aim of this work was to optimize the production and separation of high-specific-activity 203Pb using electroplated thallium targets. We further investigated the radiochemistry optimization using a suitable chelator, tetraazacyclododecane-1,4,7-triacetic acid (DO3A), and targeting vector, VMT-α-NET (lead-specific chelator conjugated to tyr3-octreotide via a polyethylene glycol linker). Methods: Targets were prepared by electroplating of natural or enriched (205Tl) thallium metal. Scanning electron microscopy was performed to determine the structure and elemental composition of electroplated targets. Targets were irradiated with 24-MeV protons with varying current and beam time to investigate target durability. 203Pb was purified from the thallium target material using an extraction resin (lead resin) column followed by a second column using a weak cation-exchange resin to elute the lead isotope as [203Pb]PbCl2 Inductively coupled plasma mass spectrometry studies were used to further characterize the separation for trace metal contaminants. Radiolabeling efficiency was also investigated for DO3A chelator and VMT-α-NET (a peptide-based targeting conjugate). Results: Electroplated targets were prepared at a high plating density of 76-114 mg/cm2 using a plating time of 5 h. A reproducible separation method was established with a final elution in HCl (400 µL, 1 M) suitable for radiolabeling. Greater than 90% recovery yields were achieved, with an average specific activity of 37.7 ± 5.4 GBq/µmol (1.1 ± 0.1 Ci/µmol). Conclusion: An efficient electroplating method was developed to prepare thallium targets suitable for cyclotron irradiation. A simple and fast separation method was developed for routine 203Pb production with high recovery yields and purity.

In vivo Assessment of the Impact of Molecular Weight on Constructs of 68Ga-DOTA-Manocept in a Syngeneic Mouse Tumor Model.

PURPOSE: Manocept™ constructs are mannosylated amine dextrans (MADs) that bind with high affinity to the mannose receptor, CD206. Tumor-associated macrophages (TAMs) are the most numerous immune cells in the tumor microenvironment and a recognized target for tumor imaging and cancer immunotherapies. Most TAMs express CD206, suggesting utility of MADs to deliver imaging moieties or therapeutics to TAMs. The liver Kupffer cells also express CD206, making them an off-target localization site when targeting CD206 on TAMs. We evaluated TAM targeting strategies using two novel MADs differing in molecular weight in a syngeneic mouse tumor model to determine how varying MAD molecular weights would impact tumor localization. Increased mass dose of the non-labeled construct or a higher molecular weight (HMW) construct were also used to block liver localization and enhance tumor to liver ratios. PROCEDURES: Two MADs, 8.7 kDa and 22.6 kDa modified with DOTA chelators, were synthesized and radiolabeled with 68Ga. A HMW MAD (300 kDa) was also synthesized as a competitive blocking agent for Kupffer cell localization. Balb/c mice, with and without CT26 tumors, underwent dynamic PET imaging for 90 min followed by biodistribution analyses in selected tissues. RESULTS: The new constructs were readily synthesized and labeled with 68Ga with ≥ 95% radiochemical purity in 15 min at 65 °C. When injected at doses of 0.57 nmol, the 8.7 kDa MAD provided 7-fold higher 68Ga tumor uptake compared to the 22.6 kDa MAD (2.87 ± 0.73%ID/g vs. 0.41 ± 0.02%ID/g). Studies with increased mass of unlabeled competitors showed reduced liver localization of the [68Ga]MAD-8.7 to varying degrees without significant reductions in tumor localization, resulting in enhanced tumor to liver signal ratios. CONCLUSION: Novel [68Ga]Manocept constructs were synthesized and studied in in vivo applications, showing that the smaller MAD localized to CT26 tumors more effectively than the larger MAD and that the unlabeled HMW construct could selectively block liver binding of [68Ga]MAD-8.7 without diminishing the localization to tumors. Promising results using the [68Ga]MAD-8.7 show a potential path to clinical applications.

Production of 52Mn using a semi-automated module.

This work focused on the production and purification of the positron emitter 52Mn (t1/2 = 5.6 d) via the natCr(p,n)52Mn reaction, using a TR24 cyclotron and a semi-automated system for the purification of 52Mn. Based on two-column and three-column systems, the recovery of 52Mn was 79.7 ± 6.2% (n = 3) and 70.8 ± 3.3% (n = 3), with processing times of 6.9 ± 0.5 h and 8.2 ± 0.6 h, respectively.

Production of [89 Zr]Oxinate4 and cell radiolabeling for human use.

[89 Zr]Oxinate4 is a Positron Emission Tomography (PET) tracer for cell radiolabeling that can enable imaging techniques to help better understand cell trafficking in various diseases. Although several groups have synthetized this compound for use in preclinical studies, there is no available data regarding the production of [89 Zr]Oxinate4 for human use. In this report, we describe the detailed production of [89 Zr]Oxinate4 under USP <823> and autologous leukocyte radiolabeling under USP <797>. The final product presented high radiochemical purity and stability at 24 h post synthesis (>99%) and passed in all quality control assays required for clinical use. [89 Zr]Oxinate4 did not compromise the white blood cells viability and did not show considerable cellular efflux up to 3 h post labeling. The translation of this technique into human use can provide insight into several disease mechanisms since [89 Zr]Oxinate4 has the potential to label any cell subset of interest.

Novel multimodal molecular imaging of Vitamin H (Biotin) transporter activity in the murine placenta.

Vitamin H (biotin) is delivered to the fetus transplacentally by an active biotin-transport mechanism and is critical for fetal development. Our objective was to develop a comprehensive MRI technique for mapping biotin transporter activity in the murine placenta. Visualization of transporter activity can employ MRI's unique T2*-dependent signal 'off-switch', which is triggered by transporter mediated aggregation of biotinylated contrast agent (b-BSA-Gd-DTPA). MRI data were collected from pregnant mice after administration of b-BSA-Gd-DTPA and analyzed using a new sub-voxel biophysical signal model. Validation experiments included competition with native biotin, comparative tests using PET, histology, and ICPMS. MRI signal was governed by binding, aggregation, and clearance of biotin (confirmed by histology). Signal dynamics reflected the placenta's perfusion pattern modulated by biotin transporter activity and trophoblast mediated retention, and were in congruence with a three-compartment sub-voxel model. Pre-saturation of the transporters with free biotin suppressed b-BSA-Gd-DTPA uptake. The results were confirmed by PET, histology and ICPMS. The presented MRI-based platform allows to track activity of essential molecular transporters in the placenta, reflecting a transporter-mediated uptake, followed by retention and aggregation, and recycling associated with the large b-BSA-Gd-DTPA conjugate. The presented DCE-MRI technique can furthermore be used to map and characterize microstructural compartmentation and transporter activity without exposing the fetus to contrast media.

Improved production of 76Br, 77Br and 80mBr via CoSe cyclotron targets and vertical dry distillation.

INTRODUCTION: The radioisotopes of bromine are uniquely suitable radiolabels for small molecule theranostic radiopharmaceuticals but are of limited availability due to production challenges. Significantly improved methods were developed for the production and radiochemical isolation of clinical quality 76Br, 77Br, and 80mBr. The radiochemical quality of the radiobromine produced using these methods was tested through the synthesis of a novel 77Br-labeled inhibitor of poly (ADP-ribose) polymerase-1 (PARP-1), a DNA damage response protein. METHODS: 76Br, 77Br, and 80mBr were produced in high radionuclidic purity via the proton irradiation of novel isotopically-enriched Co76Se, Co77Se, and Co80Se intermetallic targets, respectively. Radiobromine was isolated through thermal chromatographic distillation in a vertical furnace assembly. The 77Br-labeled PARP inhibitor was synthesized via copper-mediated aryl boronic ester radiobromination. RESULTS: Cyclotron production yields were 103 ±â€¯10 MBq∙µA-1∙h-1 for 76Br, 88 ±â€¯10 MBq∙µA-1∙h-1 for 80mBr at 16 MeV and 17 ±â€¯1 MBq∙µA-1∙h-1 for 77Br at 13 MeV. Radiobromide isolation yields were 76 ±â€¯11% in a small volume of aqueous solution. The synthesized 77Br-labeled PARP-1 inhibitor had a measured apparent molar activity up to 700 GBq/µmol at end of synthesis. CONCLUSIONS: A novel selenium alloy target enabled clinical-scale production of 76Br, 77Br, and 80mBr with high apparent molar activities, which was used to for the production of a new 77Br-labeled inhibitor of PARP-1. ADVANCES IN KNOWLEDGE: New methods for the cyclotron production and isolation of radiobromine improved the production capacity of 77Br by a factor of three and 76Br by a factor of six compared with previous methods. IMPLICATIONS FOR PATIENT CARE: Preclinical translational research of 77Br-based Auger electron radiotherapeutics, such as those targeting PARP-1, will require the production of GBq-scale 77Br, which necessitates next-generation, high-yielding, isotopically-enriched cyclotron targets, such as the novel intermetallic Co77Se.

Synthesis and Biological Evaluation of (S)-Amino-2-methyl-4-[(76)Br]bromo-3-(E)-butenoic Acid (BrVAIB) for Brain Tumor Imaging.

The novel compound, (S)-amino-2-methyl-4-[(76)Br]bromo-3-(E)-butenoic acid (BrVAIB, [(76)Br]5), was characterized against the known system A tracer, IVAIB ([(123)I]8). [(76)Br]5 was prepared in a 51% ± 19% radiochemical yield with high radiochemical purity (≥98%). The biological properties of [(76)Br]5 were compared with those of [(123)I]8. Results showed that [(76)Br]5 undergoes mixed amino acid transport by system A and system L transport, while [(123)I]8 had less uptake by system L. [(76)Br]5 demonstrated higher uptake than [(123)I]8 in DBT tumors 1 h after injection (3.7 ± 0.4% ID/g vs 1.5 ± 0.3% ID/g) and also showed higher uptake vs [(123)I]8 in normal brain. Small animal PET studies with [(76)Br]5 demonstrated good tumor visualization of intracranial DBTs up to 24 h with clearance from normal tissues. These results indicate that [(76)Br]5 is a promising PET tracer for brain tumor imaging and lead compound for a mixed system A and system L transport substrate.

Site-selective chemistry and the attachment of peptides to the surface of a microelectrode array.

Peptides have been site-selectively placed on microelectrode arrays with the use of both thiol-based conjugate additions and Cu(I)-coupling reactions between thiols and aryl halides. The conjugate addition reactions used both acrylate and maleimide Michael acceptors. Of the two methods, the Cu(I)-coupling reactions proved far superior because of their irreversibility. Surfaces constructed with the conjugate addition chemistry were not stable at neutral pHs, especially the surface using the maleimide acceptor. Once a peptide was placed onto the array, it could be monitored in "real-time" for its interactions with a biological receptor.

A new porous reaction layer for developing addressable molecular libraries.

A new diblock copolymer-derived porous reaction layer for microelectrode arrays has been tested for its stability and its compatibility with both site-selective synthesis and electrochemical signaling experiments. The diblock copolymer consisted of a cinnamoyl-substituted polymethacrylate block for attachment to the surface of the array and a bromo-substituted polystyrene block for selective functionalization of the surface proximal to microelectrodes in the array. Site-selective Suzuki, Heck, and Cu(I)-coupling reactions were all performed on the new reaction layer along with electrochemical impedance studies.

Building addressable libraries: a site-selective click-reaction strategy for rapidly assembling mass spectrometry cleavable linkers.

A click-reaction was site-selectively carried out on 1000 and 12,000 microelectrode arrays and characterized using TOF-SIMS.