Noninvasive PET imaging of CD38 expression using 89Zr-labeled daratumumab in lymphoma

462 Objectives: Lymphomas are a highly heterogeneous group of malignancies of the lymphatic system. Although 18F-fluorodeoxyglucose (18F-FDG) PET imaging is now widely used for the detection and follow-up of lymphoma, it lacks specificity to make a differentiation malignancy and inflammation. CD38 has shown strong links with several kinds of lymphoma and leukemia. In vivo evaluation of CD38 expression may provide useful information about lesion detection and prognosis of treatment in multiple myeloma (MM). In this study, immunoPET imaging with 89Zr-labeled daratumumab was used for differentiation of CD38 expression in murine lymphoma models to provide a potential noninvasive method for monitoring CD38 for the future clinical application. Methods: After Daratumumab was conjugated with desferrioxamine (Df), it could be radiolabeled with 89Zr (t1/2 = 78.4 h) at room temperature. Western blot (WB) was used to screen CD38 expression in lymphoma cell lines. Flow cytometry and cellular binding assays were performed to measure the binding ability in vitro. PET imaging and biodistribution studies were performed to after injection of 89Zr-Df-daratumumab or 89Zr-Df-IgG (non-specific IgG) in some lymphoma murine model. Finally, histological analysis was performed to verify the CD38 expression in tumors. Results: Ramos cells were found to express the highest level of CD38 by WB while HBL-1 cells showed the lowest expression. Shown by flow cytometry, Df-conjugated or non-conjugated daratumumab displayed similarly high binding affinity in Ramos cells. 89Zr-Df-daratumumab had a Ka value of 1.3 ± 0.4 nM. Ramos cells had a receptor density at approximately (1.43 ± 0.16) ×105 per cell by cell binding assay. PET imaging of 89Zr-Df-daratumumab showed a high tumor uptake of up to 26.6 ± 8.0 %ID/g for Ramos at 120 h post-injection, and only up to 6.6 ± 2.9 %ID/g for HBL-1 (n = 4). Additionally, 89Zr-Df-IgG demonstrated a low tumor uptake in the Ramos model (only 4.3 ± 0.8 %ID/g at 120 h post-injection). Ex vivo biodistribution studies verified these imaging results. Immunofluorescent staining of tumor tissues displayed strong CD38 expression in the tumor of Ramos while HBL-1 tumor showed rare expression of CD38. Conclusion: This study showed that 89Zr-Df-daratumumab could be a promising imaging agent for specific displaying CD38 positive lesions in vivo. It might be further applied for noninvasive diagnosis of multiple myeloma in the clinic.