Theranostics of lymphoma with 89Zr- and 177Lu-labeled daratumumab

74 Objectives: Lymphoma is a group of highly heterogeneous malignancies that developed from lymphocytes. Accurate diagnosis and personalized treatment are urgently needed in the era of precision medicine. CD38 is highly expressed on plasma cells, especially on multiple myeloma (MM), suggesting CD38 as a suitable biomarker of MM. Daratumumab is the first anti-CD38 human monoclonal antibody. Based on its good response rate in the treatment of relapsed/refractory MM, daratumumab provides a promising candidate for CD38-targeted applications. In this study, the theranostic role of 89Zr- and 177Lu-labeled daratumumab was investigated for PET imaging and treatment of CD38-positive lymphoma. Methods: Daratumumab was conjugated with desferrioxamine (Df) for radiolabeling with 89Zr (t1/2 = 78.4 h) and it was conjugated with diethylenetriaminepentaacetic acid (DTPA) for radiolabeling with 177Lu (t1/2 = 6.65 d). Western blot (WB) was used to screen CD38 expression in lymphoma cell lines. Competitive cellular binding assay was used to measure binding affinity and cell receptor density. After lymphoma tumor-bearing mice model was established, PET imaging and biodistribution studies were performed after injection of 89Zr-Df-daratumumab. Further, four study groups were employed for the treatment study: PBS, 177Lu-only, 177Lu-DTPA-daratumumab, and 177Lu-DTPA-IgG (human non-specific). Autoradiography, tumor sizes, body weight, and biodistribution were measured within 10 days post-injection. Finally, histological analysis was performed to examine CD38 expression in tumors. Results: For daratumumab radiolabeling with 89Zr and 177Lu, labeling yields were more than 92% (n=9). Daudi cell line was found with significant overexpression of CD38 by WB. Based on competitive cell binding assay, 89Zr-Df-daratumumab showed a Kd value of 1.058 ± 0.16 nM for the Daudi cell line with a receptor density of 1.431 ×105 per cell. PET imaging of 89Zr-Df-daratumumab showed an increased tumor uptake which reached 16.2 ± 2.4 %ID/g at 120 h post-injection for Daudi tumors (n = 4). Immunofluorescent staining verified a strong CD38 expression for Daudi tumor. For the treatment group of 177Lu-DTPA-daratumumab, significant inhibition of tumor growth was observed. In comparison, PBS and 177Lu only groups exhibited continued tumor growth. 18F-FDG imaging results showed the lowest glucose metabolism of tumor in the 177Lu-DTPA-daratumumab group. In all study groups, mouse body weight did not decrease by more than 20%, indicating the safety of the radiolabeled antibody. Autoradiography showed high tumor uptake for the treatment group (i.e. 177Lu-DTPA-daratumumab) while high significant liver uptake after injection of 177Lu only. Biodistribution studies proved high uptake of 177Lu-DTPA-daratumumab at day 10 post-injection (15.2 ± 2.6 %ID/g, n = 3) but low uptake in other organs. Conclusion:89Zr- and 177Lu-labeled daratumumab displayed a significant CD38 positive tumor affinity and effective tumor therapy without significant toxicity. Therefore, 89Zr- and 177Lu-labeled daratumumab should be further investigated in the theranostic field of lymphoma and/or MM in the clinic.