Data from <sup>89</sup>Zr-ImmunoPET Shows Therapeutic Efficacy of Anti-CD20-IFNα Fusion Protein in a Murine B-cell Lymphoma Model

Abstract

<div>Abstract<p>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 B-cell 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.</p><p>Here, we used immunoPET to study the <i>in vivo</i> biodistribution and tumor targeting of the anti-CD20 rituximab-murine IFNα1 fusion protein (Rit-mIFNα) and compared it with the parental mAb (rituximab, Rit). Rit-mIFNα and Rit were radiolabeled with zirconium-89 (<sup>89</sup>Zr, <i>t</i><sub>1/2</sub> 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. <i>Ex vivo</i> biodistribution was performed after the final scan.</p><p>Both <sup>89</sup>Zr-Rit-mIFNα and <sup>89</sup>Zr-Rit specifically target hCD20-expressing B-cell lymphoma <i>in vivo</i>. <sup>89</sup>Zr-Rit-mIFNα showed specific uptake in tumors (7.6 ± 1.0 %ID/g at 75 hours p.i.), which was significantly lower than <sup>89</sup>Zr-Rit (38.4 ± 9.9 %ID/g, <i>P</i> < 0.0001). ImmunoPET studies also revealed differences in the biodistribution, <sup>89</sup>Zr-Rit-mIFNα showed rapid blood clearance and high accumulation in the liver compared with <sup>89</sup>Zr-Rit. Importantly, immunoPET clearly revealed a therapeutic effect of the single <sup>89</sup>Zr-Rit-mIFNα dose, resulting in smaller tumors and fewer lymph node metastases compared with mice receiving <sup>89</sup>Zr-Rit. Mice receiving <sup>89</sup>Zr-Rit-mIFNα had enlarged spleens, suggesting that systemic immune activation contributes to therapeutic efficacy in addition to the direct antitumoral activity of IFNα.</p><p>In conclusion, immunoPET allows the noninvasive tracking and quantification of the antibody-cytokine fusion protein and helps understand the <i>in vivo</i> behavior and therapeutic efficacy.</p></div>