Preclinical Theranostic Study of ⁶⁸Ga/¹⁷⁷Lu/²²⁵Ac-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, HEK293_nectin4) 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.