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 [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.

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

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

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 ± 10 MBq∙μA^-1∙h^-1 for ⁷⁶Br, 88 ± 10 MBq∙μA^-1∙h^-1 for ^80mBr at 16 MeV and 17 ± 1 MBq∙μA^-1∙h^-1 for ⁷⁷Br at 13 MeV. Radiobromide isolation yields were 76 ± 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.

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.

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.

Multiple Hox/HOM-class homeoboxes in Platyhelminthes

The importance of the Hox/HOM class of homeobox genes in early anterior-posterior pattern formation and the conserved genomic organization of this gene family provides an interesting study in genome evolution. The Platyhelminthes (flatworms) are a basal metazoan group with a simple bilateral body plan. We used the polymerase chain reaction (PCR) to detect Hox/HOM-class homeobox genes from species representing two classes of flatworms. Seven planarian and five trematode Hox/HOM-class homeoboxes were found. The sequences of the genes are consistent with the presence of one Hox/HOM-type cluster in the flatworms. Further analysis of this putative cluster may be expected to provide outgroup information for studying the evolution of the Hox/HOM clusters in the higher metazoa.

Increased assembly of clathrin occurs in response to mitogenic activation of murine lymphocytes

The unassembled (soluble) and assembled (particulate) pools of clathrin in murine lymphocytes have been separated by centrifugation, and specifically quantified by immunoblotting of cellular extracts with an anticlathrin heavy chain monoclonal antibody. In resting spleen lymphocytes only 25-30% of the total cellular clathrin was found to be present in an assembled form. Upon activation of lymphocytes with B or T cell mitogens (lipopolysaccharide or concanavalin A), the levels of assembled clathrin increased to 60% of the total. These changes in the levels of assembled clathrin were not due to an increase in total cellular clathrin concentration following lymphocyte activation, but rather to changes in the steady state ratio of assembled to unassembled clathrin. The increase in assembled clathrin preceded the expression of transferrin receptors, as measured by the cell surface binding of an antitransferrin receptor monoclonal antibody, and maximal DNA synthesis, indicating that clathrin assembly occurs early after lymphocyte activation and precedes cell division. Immunofluorescence analysis of activated lymphocytes with an anti-clathrin heavy chain monoclonal antibody revealed a punctuate staining pattern characteristic of coated pits and vesicles. Activated B lymphocytes displayed particularly prominent staining in the perinuclear region compared to T cells, suggesting that clathrin assembly may be important for B cell functions such as immunoglobulin synthesis or secretion. These results suggest that in lymphocytes, clathrin assembly is a dynamic process that is triggered by mitogenic stimuli.