89Zr-ImmunoPET Shows Therapeutic Efficacy of Anti-CD20-IFNα Fusion Protein in a Murine B-cell Lymphoma Model

Abstract

Antibody-mediated tumor delivery of cytokines can overcome limitations of systemic administration (toxicity, short half-lives). Previous work showed improved antitumor potency of anti- CD20-IFNα. fusion proteins in preclinical mouse models of Bcell lymphoma. Although tumor targeting is mediated by the antibody part of the fusion protein, the cytokine component might strongly influence biodistribution and pharmacokinetics, as a result of its affinity, size, valency, and receptor distribution. Here, we used immunoPET to study the in vivo biodistribution and tumor targeting of the anti-CD20 rituximab-murine IFNa1 fusion protein (Rit-mIFNα.) and compared it with the parental mAb (rituximab, Rit). Rit-mIFNα. and Rit were radiolabeled with zirconium-89 (89Zr, t1/2 78.4 hours) and injected into C3H mice bearing syngeneic B-cell lymphomas (38C13-hCD20). Dynamic [(2 hours post injection (p.i.)] and static (4, 24, and 72 hours) PET scans were acquired. Ex vivo biodistribution was performed after the final scan. Both 89Zr-Rit-mIFNa and 89Zr-Rit specifically target hCD20- expressing B-cell lymphoma in vivo. 89Zr-Rit-mIFNa showed specific uptake in tumors (7.6 ± 1.0 %ID/g at 75 hours p.i.), which was significantly lower than 89Zr-Rit (38.4 ± 9.9 %ID/g, P < 0.0001). ImmunoPET studies also revealed differences in the biodistribution, 89Zr-Rit-mIFNa showed rapid blood clearance and high accumulation in the liver compared with 89Zr-Rit. Importantly, immunoPET clearly revealed a therapeutic effect of the single 89Zr-Rit-mIFNa dose, resulting in smaller tumors and fewer lymph node metastases compared with mice receiving 89Zr-Rit. Mice receiving 89Zr-Rit-mIFNα. had enlarged spleens, suggesting that systemic immune activation contributes to therapeutic efficacy in addition to the direct antitumoral activity of IFNα. In conclusion, immunoPET allows the noninvasive tracking and quantification of the antibody-cytokine fusion protein and helps understand the in vivo behavior and therapeutic efficacy.