Development and Characterization of the [ ¹⁷⁷ Lu]Lu-Labeled Anti-CDH17 Nanobody Derivative for Radioimmunotherapy in the Gastric Cancer Xenograft Model

Cadherin 17 (CDH17) is highly expressed in digestive system cancers, and the potential of nanobodies targeting CDH17 as imaging probes and delivery vehicles for radioactive β-particles warrants exploration for their theranostic potential in CDH17-overexpressing gastric cancer (GC). In this study, we screened an anti-CDH17 nanobody library and constructed two antibodies: anti-CDH17 VHH (recombinant nanobody fused with a polyhistidine tag) and anti-CDH17 VHH-ABD (recombinant nanobody fused with an albumin-binding domain). VHH targeting CDH17 and its derivative VHH-ABD were conjugated with DOTA and labeled with radionuclide ¹⁷⁷Lu. The pharmacokinetics and theranostic efficacy of these agents were evaluated in the GC xenograft models. [¹⁷⁷Lu]Lu-VHH and [¹⁷⁷Lu]Lu-VHH-ABD exhibited high radiochemical purity (>99%, <i>n</i> = 3) and successfully delineated CDH17-positive gastric cancer tissues on SPECT/CT imaging. Compared with the rapid renal clearance of [¹⁷⁷Lu]Lu-VHH, [¹⁷⁷Lu]Lu-VHH-ABD demonstrated prolonged circulation times with increased and sustained tumor accumulation. Survival experiments in the MKN-45 tumor model revealed that two doses of [¹⁷⁷Lu]Lu-VHH-ABD effectively suppressed tumor growth, with limited systemic biotoxicity. Histological analysis using hematoxylin and eosin (H&E) staining and Ki67 immunohistochemistry confirmed structural disruption and low tumor cell proliferative activity in the tumor tissue. In preclinical studies, [¹⁷⁷Lu]Lu-anti-CDH17 VHH-ABD demonstrated substantial antitumor efficacy with manageable toxicity, offering promising clinical potential as a viable therapeutic option for CDH17-overexpressing GC.