Dual Labelling of low density Lipoproteins to Image and Characterize Atherosclerosis and cell Types with Elevated LDL uptake – DLLICATE

Atherosclerosis is a leading cause of death worldwide. This complex disease is the subject of intensive research to improve detection/diagnosis and consequently therapeutic approaches. The exploration of atherosclerotic disease requires different imaging techniques such as echography, X rays, magnetic resonance and scintigraphy. However, while some techniques lack specificity, some other are dedicated to only one aspect of the diagnosis and only give specific information on either structural, metabolic or cellular characteristics of the aortic sections of interest. Therefore, gathering enough information in order to choose the most adequate therapeutic strategy often requires the use of multiple imaging techniques.
A key feature of atherosclerosis is altered metabolism of LDL (Low Density Lipoproteins), natural particles that carry cholesterol in the bloodstream. Indeed, high LDL plasma levels are a critical risk factor for atherosclerosis, and abnormal LDL uptake occurs in atherosclerotic plaques. The use of LDL as imaging tracers should therefore constitute a new versatile tool to complement the former imaging techniques in order to detect, diagnose and increase our understanding of the mechanisms involved in this silent disease.
The DLLICATE project aims at generating bimodal (radioactive and fluorescent) imaging probes that will be bound to LDL in order to determine the fate of these particles by analyzing simultaneously whole body distribution (non-invasive scintigraphy), and tissue and cell distribution (in situ imaging and fluorescence microscopy). Two generations of dually-labelled LDL or oxidized LDL will be synthesized and characterized in order to define a labelling protocol that does not alter their natural biological features. The imaging efficacy of the most promising conjugates will be tested in models of atherosclerosis with different levels of progression and inflammatory status.
On the short term, this project will establish the preclinical proof of concept of the approach and validate our labelling techniques for the production of dual-labelled LDL. Efficient bimodal labelling of LDL will enable to determine the metabolic fate of LDL in vivo by the visualization of arterial sections and cell types showing high LDL uptake in pathological conditions, such as immune cells in atheromatous plaques. Whole body imaging (radioactive mode) will allow exhaustive localization of atherosclerotic plaques. Then, the use of a near-infrared fluorescent probe will allow direct visualization the LDL uptake pattern in arterial sections exposed on the surgical field. Finally, the analysis of plaque biopsies obtained from our pre-clinical models will help to establish the possible link between localization, type and inflammatory status of immune cell subtypes which take up LDL as markers of plaque stability. In this way, our technique will help to provide new risk markers of plaque rupture and infarction.
On the long term, our concept based on the use of endogenous, well-tolerated particles as imaging agents will allow a possible translation in the context of human atherosclerosis. Our LDL conjugates could constitute new clinical diagnostic tools for the exhaustive detection and precise localization of atheroma plaques in subjects at high cardiovascular risk. In addition, the use of NIR fluorescent probes might also be helpful for intravascular imaging and fluorescence-assisted surgery. Finally, ex vivo fluorescence microscopy on tissues biopsies will allow a better understanding of the disease (plaque stability, immune cell profiling) and thus will help in selecting the best therapies to be implemented.