Feasibility of ⁶⁴Cu-DOTA-AE105 for arterial wall in vivo PET of the urokinase-plasminogen-activator-receptor (uPAR).

Objectives The urokinase-plasminogen-activator-receptor (uPAR) is a component of the plasminogen activation system of the coagulation system and responsible for tissue fibrin degradation and tissue remodeling. uPAR is tethered to cell membranes and associated with macrophages in atherosclerotic lesions, which can be targeted using molecular imaging. We hypothesize that uPAR expression can be assessed non-invasively with the novel tracer ⁶⁴Cu-DOTA-AE105 using positron-emission tomography/computed tomography (PET/CT).

Methods Patients with cancer of the prostate (n=4), bladder (n=3) and breast (n=3) evaluated for uPAR activity in a clinical Phase I trial, were retrospectively evaluated for atherosclerosis by combined whole-body PET/CT performed a median of 180 minutes (range 67-183 minutes) post injection, with 200 MBq (range 197-219 MBq) of ⁶⁴Cu-DOTA-AE105. Regions of interest were drawn guided by CT to include vessel wall and lumen of; A. carotis communis, aorta ascendens, aorta descendens, aorta abdominalis and A. iliaca communis. Mean and maximum standardized-uptake values (SUVs) were calculated for the arterial segments and subsequently blood-pool corrected activity was calculated, yielding target-to-background ratios (mean TBR_mean; mean TBR_max). Vessel wall tracer uptake was compared to flowcytometric analyses of uPAR activity in activated macrophages from healthy donors: Peripheral blood mononuclear cells (PBMCs) were isolated with CD14 microbeads and kept in cell suspension with macrophage colony stimulating factor (M-CSF) for four days. PBMCs were activated by adding lipopolysaccharide (LPS) and IFN-γ followed by 24-hours incubation and subsequently harvested at day five. For FACS analysis the cells were stained with viability dye (fixable viability dye®/efluor780) followed by FC-block and HLA-DR/PE, Mertk/PE-Cy™7, uPAR/APC staining.

Results Ten patients (6 male) with a median age of 67 (range: 47-75) were included. PET/CT were feasible in all patients. Mean ⁶⁴Cu-DOTA-AE105 uptake values were calculated for all arterial beds and patients: A. carotis communis TBRmean = 0.95 and TBRmax = 1.69 (range: TBR_mean 0.36 - 1.88; TBR_max: 0.69 - 1.69), aorta ascendens TBR_mean = 0.97 and TBR_max = 2.50 (range: TBR_mean 0.68 - 1.47; TBR_max: 1.32 - 5.18), aorta descendens TBR_mean = 0.93 and TBR_max = 2.23 (range: TBR_mean 0.54 - 1.63; TBR_max: 1.21 - 4.17), aorta abdominalis TBR_mean = 1.03 and TBR_max = 2.75 (range: TBR_mean 0.45 - 2.12; TBR_max: 1.09 - 5.58) and A. iliaca communis TBR_mean = 0.90 and TBR_max = 2.24 (range: TBR_mean 0.48 - 1.74; TBR_max: 0.69 - 5.28). FACS analysis showed uPAR expression in PBMCs and an elevated expression in activated macrophages (Mφ).

Conclusions Non-invasive targeting of the uPAR system with PET/CT is feasible and allow for assessment of tissue fibrin degradation and remodeling in the arterial system. In vitro analysis of monocytes in an atherogenic milieu stimulates concomitant uPAR expression and macrophage differentiation. We infer that uPAR PET allow for evaluation of arterial tissue remodeling, in part, driven by macrophage activity and state of activation. Potentially this could improve identification of vulnerable atherosclerotic plaques using molecular imaging. $$graphic_C816A32D-2895-4978-8FA1-75FF967AD6B4$$ $$graphic_F57CAE56-3F25-4B25-8EEE-B47FF3B84642$$