Next-Generation Radioimmunotherapy: Characterizing Humanized and Fully Human Monoclonal Anti-CD20 Antibodies Labeled with Zirconium-89

• Published in: The Journal of nuclear medicine (1978) Vol. 58; p. 49
• Main Authors: Yoon, Jason, Longtine, Mark, Marquez-Nostra, Bernadette, Wahl, Richard
• Format: Journal Article
• Language: English
• Published: New York Society of Nuclear Medicine 01-05-2017
• Subjects: Agglomeration; Animal tissues; Assaying; B-cell lymphoma; Binding; Burkitt's lymphoma; CD20 antigen; Cells; Chromatography; Clinical trials; Computed tomography; Deferoxamine; Image acquisition; Immunodeficiency; Immunogenicity; Immunoglobulin G; Immunoreactivity; Immunotherapy; In vivo methods and tests; Liquid chromatography; Lymphocytes B; Lymphoma; Medical research; Mice; Monoclonal antibodies; Non-Hodgkin's lymphoma; Nuclear medicine; Patients; Positron emission; Proteins; Radiochemistry; Radioisotopes; Radiolabelling; Rituximab; Spleen; Targeted cancer therapy; Thin layer chromatography; Tomography; Tracers; Tumors; Xenografts; Zirconium; Zirconium isotopes
• ISSN: 0161-5505; 1535-5667

Objectives: Radioimmunotherapy (RIT) with radiolabeled anti-CD20 monoclonal antibodies (mAbs) is an effective treatment for B cell lymphomas, demonstrating better overall response rates than the respective naked (unlabeled) mAbs. Approved anti-CD20 RITs exclusively use murine or chimeric mAbs, including FDA-approved 131I-labeled murine tositumumob (Tos) or, in Australia, 131I-labeled chimeric rituximab (Rtx). The FDA recently approved two anti-CD20 mAbs for naked use, humanized obinutizumab (Obi) and fully human ofatumumab (Ofa). Compared to Tos and Rtx, both Obi and Ofa exhibit higher binding affinity to CD20 and carry less risk for immunogenicity. In addition, naked Obi has shown better overall response rates and progression-free survival than naked Rtx in phase II and III clinical trials for non-Hodgkin's lymphoma. The goal of this study is to assess Obi and Ofa as candidates for RIT clinical trials in B cell lymphoma patients. Methods: Obi, Ofa, Rtx, Tos and human IgG, as negative control, were conjugated to p-isothiocyanatobenzyl-desferrioxamine B and radiolabeled with zirconium-89 (89Zr). Instant thin-layer chromatography (iTLC) was used to assay labeling efficiency and fast protein liquid chromatography (FPLC) was used to assay antibody aggregation. The Lindmo cell-binding assay was used to determine immunoreactivity of labeled mAbs. For in vivo studies, 6-8 week old severe combined immunodeficient mice were xenografted with Raji Burkitt lymphoma cells. Mice with palpable tumors (n=5) were injected with 89Zr-Obi, 89Zr-Ofa, 89Zr-Rtx, 89Zr-Tos or 89Zr-IgG, and PET/CT images acquired at day 7 post-injection (p.i.). At day 7 p.i., mice were sacrificed and tissue samples harvested to determine tracer biodistribution using %-injected dose/gram (%ID/g). Results: For each tracer, radiolabeling yielded a specific activity of 370 MBq/mg, iTLC showed a >95% radiochemical yield and FPLC detected no antibody aggregation pre- or post-labeling. Immunoreactive fractions were 67% for Obi, 76% for Ofa, 39% for Rtx, and 79% for Tos. At day 7 p.i., standardized uptake values (SUV) for Obi (SUVmean = 3.95 + 1.28, SUVmax = 9.65 + 3.47, p<0.02), Ofa (SUVmean = 4.71 + 1.00, SUVmax = 13.36 + 2.86, p<0.002), Rtx (SUVmean = 3.77 + 0.67, SUVmax = 7.23 + 1.45, p<0.003), and Tos (SUVmean = 2.63 + 0.86, SUVmax = 7.24 + 3.93, p<0.07) were all higher than IgG control (SUVmean = 1.48 +0.16, SUVmax = 2.82 + 0.092), with Ofa significantly outperforming Tos (p<0.02) and Rtx (p<0.02, SUVmax only). Likewise, biodistribution showed higher tumor uptake for Obi (41.44 + 7.56 %ID/g, p<0.0001), Ofa (32.74 + 7.79 %ID/g, p<0.0001), Rtx (29.67 + 6.11 %ID/g, p<0.0001), and Tos (27.72 + 5.61 %ID/g, p = 0.001) than IgG control (7.65 + 0.88 %ID/g), with Obi significantly outperforming Rtx (p<0.04) and Tos (p <0.02). Tumor-to-non-tumor tissue ratios were also significantly higher for Obi, Ofa, Rtx, and Tos than for IgG control, except for Tos in tumor-to-spleen owing to Tos's high splenic uptake. Conclusion: Obi and Ofa both are strong candidates for a translational study in B cell lymphoma patients using a therapeutic radionuclide. As tracers, both performed at least as well or better than Rtx and Tos, two mAbs that have been used previously in B cell lymphoma RIT.