Radiolabeled Angiopep‐2 Peptide Vector as a Preclinical Platform for Blood–Brain Barrier Targeting: Synthesis, Radiolabeling, and Preliminary In Vivo Biodistribution in Mice

ABSTRACT Brain tumor therapy remains limited by the blood–brain barrier (BBB), which restricts drug access. BBB‐penetrating peptides offer a promising strategy for delivering therapeutic and diagnostic payloads. Angiopep‐2 is a well‐established vector, yet novel radioconjugates based on this vector remain of interest. We report the synthesis and evaluation of DOTA‐Angiopep‐2 for radiolabeling with Lutetium‐177 ( 177 Lu) and Terbium‐161 ( 161 Tb). Notably, 177 Lu serves as a β‐ and γ‐emitter, whereas 161 Tb is an Auger and β‐emitter; both are utilized in therapy and SPECT imaging. Peptides were synthesized via solid‐phase peptide synthesis. Cytotoxicity assays in T98 glioblastoma cells showed that Angiopep‐2 is well‐tolerated, maintaining ~100% viability at 20 μM and a moderate decline up to 100 μM. Radiolabeling achieved yields > 95% with excellent radiochemical stability at room temperature for up to 10 days and moderate stability in the presence of human serum. Biodistribution in healthy CFW mice showed a brain‐associated radioactivity of 0.24% ± 0.05% IA/g at 5 min p.i. and a 12‐fold increase in the brain‐to‐blood ratio (0.028–0.339) by 60 min p.i. These results support DOTA‐Angiopep‐2 as a versatile platform for radionuclide delivery and a potential candidate for future glioma‐targeted studies. Further studies in tumor‐bearing models are ongoing to evaluate therapeutic efficacy and translational potential.