Abstract 501: Noninvasive Photodynamic Therapy of Murine Atherosclerosis Using Macrophage-Targeted Nanoparticles

Abstract

Objectives: Cerebrovascular disease leading to stroke remains a leading cause of death and disability worldwide. Photodynamic therapy (PDT) of atherosclerotic plaque macrophages may be a promising approach to stabilize rupture-prone carotid lesions, but a noninvasive PDT method for carotid atherosclerosis is lacking. Here we developed a near-infrared (NIR) absorbing macrophage-targeted photosensitizing nanoparticle to determine whether plaque macrophages can be successfully ablated using noninvasive PDT. Methods: CLIO-CyAm7-Chlorin is a dextran-based nanoparticle that contains a NIR photosensitizer (Chlorin, abs 650nm) for PDT, and a discrete NIR fluorochrome (CyAm7, ex/em 750/767nm) for fluorescence imaging of nanoparticle distribution. Noninvasive PDT optimization was performed in vivo via a PDT ablation study of hepatic macrophages in C57BL6 mice (n=65). Varying doses, exposure times, and laser power were explored. A separate group of ApoE-/- mice (n=16, 8wk HCD) injected with CLIO-Chlorin-CyAm7 or control CLIO-CyAm7 (10mgFe/kg) received noninvasive PDT of aortic root atheroma. Mice were sacrificed 1 day post-PDT for histology. Computational simulations of noninvasive PDT for human plaques were studied at multiple PDT wavelengths and light fluence. Results: Noninvasive PDT optimization showed that increasing doses of CLIO-CyAm7-Chlorin and laser exposure time had strong linear correlations with increasing liver injury (r2=0.88 and 0.65, respectively). Mice injected with control CLIO-CyAm7 showed no damage of the liver by tunel or H&E, independent of dose or time of PDT. In ApoE-/- mice, CLIO-CyAm7-Chlorin and CLIO-CyAm7 localized to inflamed aortic root plaques, and was confirmed to be macrophage localized on fluorescence imaging. CLIO-CyAm7-Chlorin/PDT showed a 6-fold increase in tunel (+) cells in aortic root plaques compared to control CLIO-CyAm7/PDT treated animals (p<0.01). Computational simulations revealed that further NIR-shifting of the photosensitizer would enable noninvasive PDT up to 1-2 cm deep, potentially enabling noninvasive PDT of human carotid plaques. Conclusions: CLIO-CyAm7-Chlorin is a multifunctional NIR nanoparticle that allows noninvasive macrophage-targeted PDT of atherosclerosis.