225AcAc/89ZrZr-labeled N4MU01 radioimmunoconjugates as theranostics against nectin-4 positive triple negative breast cancer

Abstract Purpose Nectin-4 is an overexpressed biomarker in 60-70% of triple-negative breast cancer (TNBC), and an ideal target for radiotherapy and PET imaging. In this study, we have developed theranostic radioimmunoconjugates (RICs) based on a fully-human anti-nectin-4 antibody, N4MU01. We characterized and evaluated the efficacy of these RICs for applications in molecular imaging and radiotherapy of aggressive TNBC models. Methods An anti-nectin-4 antibody (N4MU01) was radiolabeled with 89 Zr and 225 Ac, for imaging and radiotherapy, respectively, using TNBC xenograft and syngeneic models. Biodistribution & PET imaging of 89 ZrZr-DFO-N4MU01 RIC was studied in mice bearing nectin-4 positive xenografts. Dosimetry of 225 AcAc-Macropa-N4MU01 was studied in healthy mice, and therapeutic efficacy was evaluated in mice bearing human TNBC MDA-MB-468 xenograft and in a syngeneic xenograft model using murine 4T1 breast cancer cells transfected with human nectin-4 (4T1. nectin-4 ). Mice received 2 doses of 13 kBq or 18.6 kBq 10 days apart. Results The pharmacokinetic profile of 89 ZrZr-DFO-N4MU01 RIC showed biphasic distribution with a moderate elimination half-life of 63 h. PET imaging and biodistribution of 89 ZrZr-DFO-N4MU01 in mice bearing MDA-MB-468 xenograft showed high tumor uptake of 13.2 ± 1.12 %IA/g at 120 h. 225 AcAc-Macropa-N4MU01 was effectively internalized in MDA-MB-468 and was cytotoxic to the cells with IC 50 of 1.2 kBq/mL. Mice bearing MDA-MB-468 xenograft treated with 225 AcAc-Macropa-N4MU01 (13 kBq or 18.6 kBq) had a remarkable tumor growth inhibition that was dose dependent. For the syngeneic 4T1. nectin-4 model, treatment with 225 AcAc-Macropa-N4MU01 (13 kBq) led to complete tumor remission in 83.3% (5/6) of mice. Conclusion The specific tumor uptake and remarkable effectiveness at shrinking aggressive TNBC tumors is very promising towards clinical development of N4MU01 RICs as theranostics against TNBC.