Abstract 1649: Development of a near-infrared daratumumab-based contrast agent for preclinical imaging of CD38 expression in multiple myeloma
Authors: Cho Nicholas , Ko Sooah , Shokeen Monica 
Published: September 2020

Abstract
Multiple myeloma (MM) is a cancer of terminally differentiated plasma B cells that originates in the bone marrow and accounts for 15% of all hematologic malignancies. CD38 is a type II transmembrane glycoprotein over-expressed in MM cells. Daratumumab (DARA) is a FDA approved, high-affinity monoclonal antibody targeting CD38 that has shown promising therapeutic efficacy in double refractory MM patients. However, heterogeneity in CD38 expression and therapy response remains a major challenge; thus necessitating stratification strategies to minimize off-target toxicities and improve quality of life.
DARA conjugated to the near-infrared (NIR) fluorescent dye, IRDye800CW (Li Cor), (DARA-IRDye800) will allow for long-term in vivo and ex vivo spatial localization of CD38+ MM tumors preclinically. We hypothesize that the enhanced specific expression of CD38 glycoprotein on malignant plasma cells will favor increased DARA-IRDye800 uptake and allow for impactful NIR fluorescence imaging for therapeutic planning as a companion diagnostic.
After conjugation and purification, spectrophotometric analysis showed a degree of labelling of 1.2 with a 3:1 molar dye to antibody ratio. High specificity of DARA-IRDye800 to CD38+ luciferase-expressing MM.1S (MM.1S-GFP-luc) human myeloma cells was observed with a dissociation constant (Kd) of 3.5 ± 0.05 nM. In vivo fluorescence imaging was performed with DARA-IRDye800 in Fox Chase severe combined immunodeficient (SCID) beige mice that were injected intravenously with MM.1S-GFP-luc cells. At 7 days post administration of 100µg of DARA-IRDye800, multifocal fluorescent lesions were pronounced in the tumor-infiltrated axial skeleton (skull, spine, tibia and femur). Ex vivo biodistribution at 7 days showed clearance primarily through liver. Flow cytometric analysis of viable malignant plasma cells obtained from tibial and femoral bone marrow flush showed significantly high specificity of DARA-IRDye800 (relative to IgG-IRDye800) to MM cells (P&lt; 0.001).
Further, to noninvasively monitor CD38 expression during DARA treatment, Fox Chase SCID beige mice subcutaneously injected with MM.1S-GFP-luc cells were treated with DARA at a clinical dose of 16mg/kg weekly for 3 weeks when tumors reached ~100 mm3. Following therapy, in vivo and ex vivo imaging with 100µg of DARA-IRDye800 administered in untreated and treated mice showed reduced tissue-to-muscle ratio in tumors of treated mice compared to those of untreated mice (P &lt; 0.01). Weekly bioluminescence imaging also demonstrated a concurrent decrease in mean photon flux in tumor-bearing regions of treated mice compared to those of untreated mice (P &lt; 0.01). Our results demonstrate the potential of a DARA-based NIR imaging agent for long-term in vivo and ex vivo fluorescence imaging of CD38+ focal lesions for diagnosis and therapeutic monitoring in clinically relevant preclinical models.
Citation Format: Nicholas Cho, Sooah Ko, Monica Shokeen. Development of a near-infrared daratumumab-based contrast agent for preclinical imaging of CD38 expression in multiple myeloma [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr 1649.