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To enhance targeting efficacy in the radioimmunotherapy of disseminated cancer, several pretargeting strategies have been developed. In pretargeted radioimmunotherapy, the tumor is pretargeted with a modified monoclonal antibody that has an affinity for both tumor antigens and radiolabeled carriers. In this work, we aimed to synthesize and evaluate poly-L-lysine-based effector molecules for pretargeting applications based on the tetrazine and trans-cyclooctene reaction using 211At for targeted alpha therapy and 125I as a surrogate for the imaging radionuclides 123, 124I. Poly-L-lysine in two sizes was functionalized with a prosthetic group, for the attachment of both radiohalogens, and tetrazine, to allow binding to the trans-cyclooctene-modified pretargeting agent, maintaining the structural integrity of the polymer. Radiolabeling resulted in a radiochemical yield of over 80% for astatinated poly-L-lysines and a range of 66–91% for iodinated poly-L-lysines. High specific astatine activity was achieved without affecting the stability of the radiopharmaceutical or the binding between tetrazine and transcyclooctene. Two sizes of poly-L-lysine were evaluated, which displayed similar blood clearance profiles in a pilot in vivo study. This work is a first step toward creating a pretargeting system optimized for targeted alpha therapy with 211At. [ABSTRACT FROM AUTHOR]

A set of 211At-astatoarenes were synthesized from corresponding trimethylgermyl arenes with radiochemical conversions (RCCs) of up to 90%. Both electron rich and electron poor substrates were successfully radiolabeled at room temperature (RT) using relatively low precursor amounts (0.15 µmol/ 0.02 mL solvent (7.5 mM)). Ready access to ortho-, para- and meta- astatinated arenes was achievable. Optimized reaction conditions were successfully applied to label a poly (ADP-ribose) polymerase (PARP) inhibitor with a RCC of approx. 50%. We believe that trimethylgermanyl derivatives are a viable addition to the astatination precursor toolbox and facilitate astatination of arenes. The developed labeling method should easily be applicable for productions under good manufacturing practice (GMP)., (© 2024 Wiley‐VCH GmbH.)

The application of prostate-specific membrane antigen (PSMA)-targeted α-therapy is a promising alternative to β - -particle-based treatments. 211 At is among the potential α-emitters that are favorable for this concept. Herein, 211 At-based PSMA radiopharmaceuticals were designed, developed, and evaluated. Methods: To identify a 211 At-labeled lead, a surrogate strategy was applied. Because astatine does not exist as a stable nuclide, it is commonly replaced with iodine to mimic the pharmacokinetic behavior of the corresponding 211 At-labeled compounds. To facilitate the process of structural design, iodine-based candidates were radiolabeled with the PET radionuclide 68 Ga to study their preliminary in vitro and in vivo properties before the desired 211 At-labeled lead compound was formed. The most promising candidate from this evaluation was chosen to be 211 At-labeled and tested in biodistribution studies. Results: All 68 Ga-labeled surrogates displayed affinities in the nanomolar range and specific internalization in PSMA-positive LNCaP cells. PET imaging of these compounds identified [ 68 Ga]PSGa- 3 as the lead compound. Subsequently, [ 211 At]PSAt- 3 -Ga was synthesized in a radiochemical yield of 35% and showed tumor uptake of 19 ± 8 percentage injected dose per gram of tissue (%ID/g) at 1 h after injection and 7.6 ± 2.9 %ID/g after 24 h. Uptake in off-target tissues such as the thyroid (2.0 ± 1.1 %ID/g), spleen (3.0 ± 0.6 %ID/g), or stomach (2.0 ± 0.4 %ID/g) was low, indicating low in vivo deastatination of [ 211 At]PSAt- 3 -Ga. Conclusion: The reported findings support the use of iodine-based and 68 Ga-labeled variants as a convenient strategy for developing astatinated compounds and confirm [ 211 At]PSAt- 3 as a promising radiopharmaceutical for targeted α-therapy., (© 2024 by the Society of Nuclear Medicine and Molecular Imaging.)