A Theranostic Study of ¹⁷⁷ Lu-Labeled Anti-ADAM9 Antibody for the Treatment of Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) is highly aggressive with limited diagnostic and therapeutic options. ADAM9 is overexpressed in TNBC and may serve as a theranostic target. Therefore, this study aims to develop [177Lu]Lu-DOTA-48HZ810, an ADAM9-targeted probe, and evaluate its targeting specificity, imaging capability, efficacy, and safety in TNBC models. ADAM9 expression in TNBC cells was assessed by flow cytometry, and the probe was constructed by conjugating 177Lu to the ADAM9-specific antibody 48HZ810 via DOTA, after which binding specificity, affinity, and internalization were evaluated using radioligand binding, immunoreactive fraction, and internalization assays. In vivo targeting and pharmacokinetics were further analyzed by SPECT/CT imaging and biodistribution studies, while efficacy, safety, and mechanisms were assessed via tumor growth, body weight, survival, hematology, histopathology, and immunofluorescence. High ADAM9 expression was confirmed in BT-549 cells, and [177Lu]Lu-DOTA-48HZ810 showed >99% radiochemical purity and stability, high affinity (Kd: 3.75 ± 0.72 nmol/L), and specificity (Bmax: 422.5 ± 17.85 nmol). The tumor was clearly visualized at 72 h, with peak uptake at 96 h (8.56 ± 0.69%ID/g), and the probe significantly inhibited tumor growth (TGI: 46.04% vs antibody: 18.14%) and improved survival (70% vs antibody: 50% vs control: 0%), with no significant toxicity observed. The antitumor activity was mediated by DNA damage, apoptosis induction, and proliferation suppression. Overall, the first ADAM9-targeted theranostic probe, [177Lu]Lu-DOTA-48HZ810, was successfully developed, demonstrating excellent tumor targeting, antitumor efficacy, and safety in TNBC models, and validating ADAM9 as a viable theranostic target.