<sup>225</sup> Ac/ <sup>89</sup> Zr-Labeled N4MU01 Radioimmunoconjugates as Theranostics Against Nectin-4–Positive Triple-Negative Breast Cancer
Hanan Babeker, Fabrice Ngoh Njotu, Jessica Pougoue Ketchemen, Alissar Monzer, Anjong Florence Tikum, Alireza Doroudi, Emmanuel Nwangele, Maruti Uppalapati, Humphrey Fonge
Abstract
Nectin-4 is an overexpressed biomarker in 60%–70% of triple-negative breast cancer (TNBC) cases and an ideal target for radiotherapy and PET imaging. In this study, theranostic radioimmunoconjugates were developed using a fully human anti–nectin-4 antibody (N4MU01). The imaging properties and therapeutic effectiveness of the radioimmunoconjugates were evaluated using TNBC models. <b>Methods:</b> N4MU01 was radiolabeled with <sup>89</sup>Zr and <sup>225</sup>Ac for imaging and radiotherapy, respectively, using TNBC xenograft and syngeneic models. Biodistribution and PET imaging of the [<sup>89</sup>Zr]Zr-deferoxamine (DFO)-N4MU01 radioimmunoconjugate was studied in mice bearing nectin-4–positive xenografts. Dosimetry and toxicity of [<sup>225</sup>Ac]Ac-Macropa-N4MU01 were studied in naïve BALB/c mice, and the therapeutic efficacy was evaluated with two doses of 13 or two doses of 18.6 kBq, administered 10 d apart in athymic BALB/c nude mice bearing either a human TNBC MDA-MB-468 xenograft or a human nectin-4–transfected 4T1 (4T1.<sub>nectin-4</sub>) syngeneic allograft. <b>Results:</b> The pharmacokinetic profile of the [<sup>89</sup>Zr]Zr-DFO-N4MU01 radioimmunoconjugate showed biphasic distribution with a moderate elimination half-life of 63 h. PET imaging and biodistribution of [<sup>89</sup>Zr]Zr-DFO-N4MU01 in mice bearing the MDA-MB-468 xenograft showed high tumor uptake of 13.2 ± 1.12 percent injected activity per gram at 120 h. [<sup>225</sup>Ac]Ac-Macropa-N4MU01 was effectively internalized in MDA-MB-468 and was cytotoxic to the cells with a 50% inhibition concentration of 1.2 kBq/mL. Toxicity studies revealed that 15 kBq of [<sup>225</sup>Ac]Ac-Macropa-N4MU01 was generally well tolerated, as indicated by hematologic, blood chemistry, and histopathologic analysis. Mice bearing MDA-MB-468 and 4T1.<sub>nectin-4</sub> xenografts treated with 13 kBq of [<sup>225</sup>Ac]Ac-Macropa-N4MU01 had 100% (6/6) and 83.3% (5/6) complete tumor remissions, respectively. <b>Conclusion:</b> The specific tumor uptake and remarkable effectiveness against aggressive TNBC tumors are very promising and warrant the clinical development of N4MU01 radioimmunoconjugates.