Targeted Alpha Therapy is a research field of highest interest in specialized radionuclide therapy. Over the last decades, several alpha-emitting radionuclides have entered and left research topics towards their clinical translation. Especially,
225Ac provides all necessary physical and chemical properties for a
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Targeted Alpha Therapy is a research field of highest interest in specialized radionuclide therapy. Over the last decades, several alpha-emitting radionuclides have entered and left research topics towards their clinical translation. Especially,
225Ac provides all necessary physical and chemical properties for a successful clinical application, which has already been shown by [
225Ac]Ac-PSMA-617. While PSMA-617 carries the DOTA moiety as the complexing agent, the chelator macropa as a macrocyclic alternative provides even more beneficial properties regarding labeling and complex stability in vivo. Lanthanum-133 is an excellent positron-emitting diagnostic lanthanide to radiolabel macropa-functionalized therapeutics since
133La forms a perfectly matched theranostic pair of radionuclides with the therapeutic radionuclide
225Ac, which itself can optimally be complexed by macropa as well.
133La was thus produced by cyclotron-based proton irradiation of an enriched
134Ba target. The target (30 mg of [
134Ba]BaCO
3) was irradiated for 60 min at 22 MeV and 10–15 µA beam current. Irradiation side products in the raw target solution were identified and quantified:
135La (0.4%),
135mBa (0.03%),
133mBa (0.01%), and
133Ba (0.0004%). The subsequent workup and anion-exchange-based product purification process took approx. 30 min and led to a total amount of (1.2–1.8) GBq (decay-corrected to end of bombardment) of
133La, formulated as [
133La]LaCl
3. After the complete decay of
133La, a remainder of ca. 4 kBq of long-lived
133Ba per 100 MBq of
133La was detected and rated as uncritical regarding personal dose and waste management. Subsequent radiolabeling was successfully performed with previously published macropa-derived PSMA inhibitors at a micromolar range (quantitative labeling at 1 µM) and evaluated by radio-TLC and radio-HPLC analyses. The scale-up to radioactivity amounts that are needed for clinical application purposes would be easy to achieve by increasing target mass, beam current, and irradiation time to produce
133La of high radionuclide purity (>99.5%) regarding labeling properties and side products.
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