Development of probes for molecular imaging : evaluation in models of inflammation and atherosclerosis

Abstract

The imaging field is rapidly evolving and in the last two decades there have been tremendous developments in the field of multimodal imaging. Multimodal molecular imaging approaches that utilize ultrasound/magnetic resonance imaging (US/MRI), single-photon emission computed tomography/computed tomography (SPECT/CT), or positron emission tomography/MRI (PET/MRI) may provide additional detailed information at the cellular and molecular level to help identify patients with vulnerable plaques that are at risk of rupture. The search for specific biomarkers in combination with specific and optimized molecular probes may help to prevent adverse events such as myocardial infarctions or strokes. Current clinical contrast agents do not provide information on the inflammatory components of atherosclerotic plaques; thus, more specific molecular probes are needed. This thesis focuses on probe development for different molecular imaging techniques using multimodal and targeting approaches.

Several types of molecular probe were evaluated: bimodal and multimodal microbubbles, as well as chemically modified human serum albumin (HSA)-based probes (aconitylated (Aco) and maleylated (Mal)) for targeting markers of inflammation; adhesion molecules on endothelial cells or macrophages, and scavenger receptor A1 (SR-A1) on macrophages. Evaluation of these molecular probes was facilitated by their physical properties enabling assessment with fluorescence microscopy, flow cytometry, and nuclear imaging properties for in vivo molecular imaging with SPECT/CT and PET/MRI.

We found that functionalizing molecular probes with targeting moieties greatly improved the targeting specificity and avidity to the target compared to non-targeted molecular probes. Furthermore, these molecular probes were successfully radiolabeled with a detectable in vivo signal by 99mTc-anti-ICAM-1-MBs imaging of inflammation with SPETC/CT, and atherosclerosis by 89Zr-Mal-HSA with PET/MRI. Ex vivo evaluation of HSA-based probes showed significant accumulation in atherosclerotic lesions of Apoe-/- mice, as quantified by gamma counter and phosphor imaging autoradiography, compared to wild type (WT) mice. In conclusion, adhesion molecule targeting and scavenger receptor targeting with functionally modified probes in this thesis showed potential for the imaging of inflammation and atherosclerosis. Of the evaluated probes, modified HSA-based probes seem to have the greatest potential for clinical application in molecular imaging of atherosclerosis.