Abstract
[(177)Lu]-Lu-DOTA-Trastuzumab is currently under clinical evaluation for radioimmunotherapy (RIT) for HER2-positive breast cancer. This study aimed to enhance its internalization by modifying Trastuzumab with a nuclear localization signal (NLS: PKKKRKV). The NLS, bearing a terminal azide group, was synthesized via solid-phase peptide synthesis. DOTA, a chelator for (177)Lu, was incorporated at the α-amino group of lysine at the NLS's proline end, allowing UV-vis-based drug-to-antibody ratio (DAR) estimation. Both DOTA-Trastuzumab and DOTA-NLS-Trastuzumab, along with their [(177)Lu]-Lu-labeled counterparts, were synthesized. In vitro studies in HER2-positive SK-OV-3 and SK-BR-3 cells showed an enhanced internalization of the NLS-modified conjugate. However, ex vivo and in vivo evaluation in SCID mice revealed lower tumor and nontarget organ accumulation for [(177)Lu]-Lu-DOTA-NLS-Trastuzumab compared to [(177)Lu]-Lu-DOTA-Trastuzumab, indicating altered biodistribution despite improved cellular uptake.