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Purpose: Abnormal CD38 expression in some hematologic malignancies, including lymphoma, has made it a biomarker for targeted therapies. Daratumumab (Dara) is the first FDA-approved CD38-specific monoclonal antibody, enabling successfully immunoPET imaging over the past years. Radiolabeled Dara however has a long blood circulation and delayed tumor uptake which can limit its applications. The focus of this study is to develop 64Cu-labeled Dara-F(ab′)2 for the visualization of CD38 in lymphoma models. Methods: F(ab′)2 fragment was prepared from Dara using an IdeS enzyme and purified with Protein A beads. Western blotting, flow cytometry, and surface plasmon resonance (SPR) were performed for in vitro assay. Probes were labeled with 64Cu after the chelation of 1,4,7-triazacyclononane-1,4,7-triacetic acid (NOTA). Small animal PET imaging and quantitative analysis were performed after injection of 64Cu-labeled Dara-F(ab′)2, IgG-F(ab′)2, and Dara for evaluation in lymphoma models. Results: Flow cytometry and SPR assay proved the specific binding ability of Dara-F(ab′)2 and NOTA-Dara-F(ab′)2 in vitro. Radiolabeling yield of [64Cu]Cu-NOTA-Dara-F(ab′)2 was over 90% and with a specific activity of 4.0 ± 0.6 × 103 MBq/μmol (n = 5). PET imaging showed [64Cu]Cu-NOTA-Dara-F(ab′)2 had a rapid and high tumor uptake as early as 2 h (6.9 ± 1.2%ID/g) and peaked (9.5 ± 0.7%ID/g) at 12 h, whereas [64Cu]Cu-NOTA-Dara reached its tumor uptake peaked at 48 h (8.3 ± 1.4%ID/g, n = 4). In comparison, IgG-F(ab′)2 and HBL-1 control groups found no noticeable tumor uptake. [64Cu]Cu-NOTA-Dara-F(ab′)2 had significantly lower uptake in blood pool, bone, and muscle than [64Cu]Cu-NOTA-Dara and its tumor-to-blood and tumor-to-muscle ratios were significantly higher than controls. Conclusions: [64Cu]Cu-NOTA-Dara-F(ab′)2 showed a rapid and high tumor uptake in CD38-positive lymphoma models with favorable imaging contrast, showing its promise as a potential PET imaging agent for future clinical applications. [ABSTRACT FROM AUTHOR]

Purpose: CD38 is considered a potential biomarker for multiple myeloma (MM) and has shown a strong link with chronic lymphocytic leukemia due to high and uniform expression on plasma cells. In vivo evaluation of CD38 expression may provide useful information about lesion detection and prognosis of treatment in 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 non-invasive method for monitoring CD38 in the clinic.Methods: Daratumumab was radiolabeled with 89Zr (t1/2 = 78.4 h) via conjugation with desferrioxamine (Df). After Western blot (WB) was used to screen CD38 expression in five lymphoma cell lines, flow cytometry and cellular binding assays were performed to test the binding ability of labeled or conjugated daratumumab with CD38 in vitro. PET imaging and biodistribution studies were performed to evaluate CD38 expression after injection of 89Zr-Df-daratumumab. 89Zr-Df-IgG was also evaluated as a non-specific control group in the Ramos model. Finally, CD38 expression in tumor tissues was verified by histological analysis.Results: Using WB screening, the Ramos cell line was found to express the highest level of CD38 while the HBL-1 cell line had the lowest expression. Df-conjugated and 89Zr-labeled daratumumab displayed similar high binding affinities with Ramos cells. 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 showed similar trends with imaging results. Immunofluorescence staining of tumor tissues verified higher CD38 expression of Ramos than that of HBL-1.Conclusions: The role of 89Zr-Df-daratumumab was investigated for evaluating CD38 expression in lymphoma models non-invasively and was found to be to a promising imaging agent of CD38-positive hematological diseases such as MM in future clinical applications. [ABSTRACT FROM AUTHOR]