Abstract
Biomedical imaging techniques such as skeletal survey and 18F-fluorodeoxyglucose (FDG)/Positron Emission Tomography (PET) are frequently used to diagnose and stage multiple myeloma (MM) patients. However, skeletal survey has limited sensitivity as it can detect osteolytic lesions only after 30–50% cortical bone destruction, and FDG is a marker of cell metabolism that has limited sensitivity for intramedullary lesions in MM. Targeted, and non-invasive novel probes are needed to sensitively and selectively image the unique molecular signatures and cellular processes associated with MM. Very late antigen-4 (VLA-4; also called α4β1 integrin) is over-expressed on MM cells, and is one of the key mediators of myeloma cell adhesion to the bone marrow (BM) that promotes MM cell trafficking and drug resistance. Here we describe a proof-of-principle, novel molecular imaging strategy for MM tumors using a VLA-4 targeted PET radiopharmaceutical, 64Cu-CB-TE1A1P-LLP2A. Cell uptake studies in a VLA-4-positive murine MM cell line, 5TGM1, demonstrated receptor specific uptake (P<0.0001, block vs. non-block). Tissue biodistribution at 2 h of 64Cu-CB-TE1A1P-LLP2A in 5TGM1 tumor bearing syngeneic KaLwRij mice demonstrated high radiotracer uptake in the tumor (12±4.5%ID/g), and in the VLA-4 rich organs, spleen (8.8±1.0%ID/g) and marrow (11.6±2.0%ID/g). Small animal PET/CT imaging with 64Cu-CB-TE1A1P-LLP2A demonstrated high uptake in the 5TGM1 tumors (SUV 6.6±1.1). There was a 3-fold reduction in the in vivo tumor uptake in the presence of blocking agent (2.3±0.4). Additionally, 64Cu-CB-TE1A1P-LLP2A demonstrated high binding to the human MM cell line RPMI-8226 that was significantly reduced in the presence of the cold targeting agent. These results provide pre-clinical evidence that VLA-4-targeted imaging using 64Cu-CB-TE1A1P-LLP2A is a novel approach to imaging MM tumors.
Highlights
Multiple myeloma (MM) is the second most commonly diagnosed hematologic cancer characterized by immunoglobulin secreting malignant plasma B-cells [1]
Very late antigen-4 (VLA-4) has been implicated in promoting the activity of bone-resorbing osteoclasts in MM by up-regulating secretion of osteoclast activating factors such as macrophage inflammatory protein (MIP)-1a and MIP-1b [10]. These findings suggest that VLA-4 is a MM marker that is associated with myeloma cell trafficking
The in vitro binding affinity of 64Cu-CB-TE1A1P-LLP2A was investigated by determining the equilibrium dissociation constant (Kd) and the maximum specific binding (Bmax) of the radiolabeled conjugate to 5TGM1 cells in saturation binding assays
Summary
Multiple myeloma (MM) is the second most commonly diagnosed hematologic cancer characterized by immunoglobulin secreting malignant plasma B-cells [1]. Myeloma arises from postgerminal center B-cells and its pathogenesis involves both acquired intrinsic genetic abnormalities as well as changes to the bone marrow (BM) microenvironment [1,3]. Interactions between myeloma cells and BM stroma enhance tumor survival [4]. Clinical and pre-clinical data have demonstrated that changes in the expression of adhesion molecules facilitate the dissemination of plasma cells out of the BM, leading to malignant transformation, tumor spreading and immortalization [5]. MM cells thrive on strong cell-receptor mediated interactions with the BM microenvironment [3]_ENREF_10. Therapeutics targeting tumor-microenvironment interactions are currently being evaluated clinically and pre-clinically [6,7]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
