Abstract 15370: The Development of LO1, a Novel IgG Monoclonal Natural Antibody, for the Near Infra-Red (NIRF) Imaging of Oxidised LDL in Atherosclerosis

Abstract

Background: The identification of inflammatory activity may help to better understand the relationship between vulnerable plaque and clinical syndromes, as well to allow for future therapeutic targeting.

Aims and objectives: We aimed to develop a near infra-red fluorescence (NIRF) antibody-targeted molecular imaging strategy for the identification of oxidised LDL within atherosclerotic lesions.

Methods and results: LO1 is a novel IgG3κ spontaneously-occurring natural monoclonal antibody isolated in our lab from an Ldlr^-/-atherosclerotic mouse. LO1 binds heavily oxidised LDL,which has been found in excess in culprit lesions. Domain swaps and peptide inhibition experiments with H3, an scFv anti-idiotype screened from a phage library, suggest that LO1 reacts with a conformational epitope on mouse and human ApoB. Immunohistochemical (IHC) staining showed that biotinylated LO1 identifies determinants in murine (Ldlr^-/-) atherosclerotic lesions and in necrotic core within culprit human carotid plaque. LO1 was directly labelled with a near infra-red (NIRF) reporter VivoTag-S MAL 750 (designated LO1-750) using the SH groups. IHC with LO1-750 showed distinct staining within aortic lesions of Ldlr^-/-mice and human necrotic core, with selective colocalisation with polyclonal anti-apoB and partial colocalisation with foam cells (CD68). En face staining of Ldlr^-/-mouse aortae demonstrated LO1-750 but not IgG3k isotype control staining of areas susceptible to atherosclerosis (lesser curvature and bifurcations). In vivo NIRF imaging of Ldlr^-/-mice using the IVIS Spectrum system showed LO1-750 but not IgG3k isotype control uptake at the aortic arch and carotid arteries as well as colocalisation to calcified lesions seen by parallel CT imaging. Wild type controls showed no specific vascular uptake.

Conclusions: LO1 shows promise as a targeting agent for in vivo NIRF imaging of atherosclerosis, as well as other molecular imaging modalities.