Preclinical Theranostic Study of ⁶⁸ Ga/ ¹⁷⁷ Lu/ ²²⁵ Ac-Labeled Bicyclic Peptides Targeting Nectin-4 in Lung Cancer

Nectin-4, a cell adhesion molecule frequently overexpressed in non-small cell lung cancer (NSCLC), has emerged as a promising target for theranostic applications due to its involvement in tumor progression and association with poor prognosis. This study aimed to develop radiolabeled agents based on bicyclic peptides for both imaging and targeted therapy for Nectin-4 positive tumors. We designed and synthesized 68Ga-labeled probes ([68Ga]Ga-3 and [68Ga]Ga-5) for PET imaging and 177Lu-labeled agents ([177Lu]Lu-6) for targeted radionuclide therapy. Radiochemical yields and purity were optimized, and the agents were evaluated for cellular uptake, internalization, and biodistribution in Nectin-4-expressing cell lines (H1975, ABC-1, HEK293nectin4) and xenograft models. Target specificity was confirmed through blocking studies with the Nectin-4 specific inhibitor peptide N188. The 68Ga-labeled probes exhibited high radiochemical yields (78–81%) and purity (>95%), with specific uptake observed in Nectin-4-positive cells (e.g., 69.20 ± 2.31%ID/106 cells for [68Ga]Ga-3 at 120 min) and tumors. Blocking studies resulted in significant reductions in uptake, with 39-fold and 22-fold decreases for [68Ga]Ga-3 and [68Ga]Ga-5, respectively, confirming Nectin-4 specificity. [177Lu]Lu-6 showed superior tumor retention (13% uptake) and internalization (3.5%) compared to [177Lu]Lu-FAP-2286/N188, with sustained tumor growth suppression in xenograft models. PET/SPECT imaging revealed high tumor-to-background ratios and favorable pharmacokinetics, highlighting the potential of these agents for clinical application.