Date of Award
11-19-2021
Degree Name
Doctor of Philosophy (PhD)
Degree Type
Dissertation
Abstract
Multiple myeloma (MM) is a debilitating hematologic malignancy of terminally differentiated plasma cells in the bone marrow (BM). Daratumumab (DARA) is an FDA-approved high-affinity monoclonal antibody targeting CD38 that has shown promising therapeutic efficacy in relapsed and refractory MM. Despite the well-established clinical efficacy of DARA, not all heavily pretreated patients respond to DARA monotherapy, and the majority of patients who initially respond eventually progress. This may be due to upregulation of pathways that inhibit DARA-mediated tumor killing. Antibody drug conjugates (ADCs) combine the highly targeted tumor antigen recognition of antibodies with cell killing properties of chemotherapy for effective internalization and processing of the drug. Here, we evaluated the antitumor efficacy of DARA conjugated to the maytansine derivative, mertansine (DM1), linked via a non-cleavable bifunctional linker (DARA-DM1). The near-infrared (NIR) fluorophore, IRDye800, was conjugated to DARA (DARA-IR) and DARA-DM1 (DARA-DM1-IR) to evaluate the mechanisms of action and biodistribution of the antibody constructs through two specific aims: The first aim was focused on performing functional imaging of CD38 expression using bioconjugates of DARA in preclinical MM models. Conjugation of IRDye800 did not affect the stability or affinity of DARA in vitro and in vivo. Additionally, uptake of DARA-IR was significantly reduced in DARA-treated mice bearing intramedullary tumors, indicating a reduction in the expression of CD38. These observations are concordant with the known downregulation of CD38 in patients who do and do not respond to DARA therapy. Our results demonstrated the viability of using IRDye800 for sensitive, longitudinal assessment of the DARA antibody. DARA-IR can additionally be used as its own NIR contrast agent for monitoring CD38 expression in vivo in relation to DARA and other anti-CD38 therapies. The second aim assessed the efficacy and mechanisms of DARA-DM1. Conjugation of DM1 improved antitumor efficacy of DARA in vitro and in vivo. Flow cytometry and fluorescence microscopy demonstrated similar binding and internalization of DARA-DM1-IR to DARA-IR in MM cells. Clearance of the DARA conjugates was primarily observed through the liver with no significant difference observed in tumoral uptake in vivo. Our observations validated that 1) DARA-DM1, compared to DARA, showed enhanced therapeutic efficacy and 2) the conjugation of IRDye800 does not affect the biologic activity or tumor targeting ability of the ADC. In summary, these studies demonstrated the addition of a drug payload could enhance the therapeutic window of the native antibody. Fluorophore labelling allowed for evaluation of the different antibody constructs on a whole-body and cellular level in preclinical MM models. With the advent of other classes of anti-CD38 immunoconjugates for use in MM, we reasoned that such imaging techniques can be utilized to evaluate the tumor distribution and mechanism of action of promising conjugates in preclinical MM models. Future studies would adapt this approach into different cell lines and humanized, immunocompetent tumor models.
Language
English (en)
Chair
Monica Shokeen