Intravascular detection of inflamed atherosclerotic plaques using a fluorescent photosensitizer targeted to the scavenger receptor

Abstract

Inflammation plays an important role in the pathophysiology of atherosclerotic disease. We have previously shown that the targeted photosensitizer chlorin (e(6)) conjugated with maleylated albumin (MA-ce6) is taken up by macrophages via the scavenger receptor with high selectivity. In a rabbit model of inflamed plaque in New Zealand white rabbits via balloon injury of the aorto-iliac arteries and high cholesterol diet we showed that the targeted conjugate showed specificity towards plaques compared to free ce6. We now show that an intravascular fiber-based spectrofluorimeter advanced along the -iliac vessel through blood detects 24-fold higher fluorescence in atherosclerotic vessels compared to control rabbits (p < 0.001 ANOVA). Within the same animals, signal derived from the injured iliac artery was 16-fold higher than the contralateral uninjured iliac (p < 0.001). Arteries were removed and selective accumulation of MA-ce6 in plaques was confirmed using: (1) surface spectrofluorimetry, (2) fluorescence extraction of ce6 from aortic segments, and (3) confocal microscopy. Immunohistochemical analysis of the specimens showed a significant correlation between MA-ce6 uptake and RAM-11 macrophage staining (R = 0.83, p < 0.001) and an inverse correlation between MA-ce6 uptake and smooth muscle cell staining (R = -0.74, p < 0.001). MA-ce6 may function as a molecular imaging agent to detect and/or photodynamically treat inflamed plaques.

Imaging and Photodynamic Therapy: Mechanisms, Monitoring, and Optimization

“…A confocal laser scanning fluorescence microscope is used to monitor the subcellular localization of the PS with high spatial resolution, fluorescence from the mitochondrial markers is shown in false color as green and BPD is shown in false color as red; 139 ( B ) confocal microscopy shows that TPC conjugated to a membrane-penetrating arginine oligopeptide (R7) enters MDA-MB-468 (human breast carcinoma) cells efficiently where red represents fluorescence signal from TPC; 142 ( C ) monitoring fluorescence signal distribution after intravenous injection of 100 nmol of Pyro-GDEVDGSGK-Folate conjugate to double tumor-bearing mice (with a FR positive tumor on the right side and negative one on the left side), indicates preferential accumulation of construct in the receptor positive tumor, establishing NIR imaging ability of the targeted PS construct; 143 ( D ) fluorescence from aortic segments 24 hr post injection of Ce6-maleylated albumin conjugate indicates the constructs ability to detect and/or photodynamically treat inflamed plaques. Red represents Ce6 and yellow is tissue autofluorescence from the elastic fibers; 146 ( E ) post-PDT changes in VEGF expression are monitored with the molecular imaging strategy, where an Avastin-Alexa Fluor construct was imaged in PDT-treated subcutaneous PC-3 (prostate cancer) tumors, 6 h following laser irradiation and fluorescence image of tumor labeling is pseudocolored in gold; 147 and ( F ) T2-weighted magnetic resonance images at day 8 after PDT treatment from F3-targeted Photofrin-containing nanoparticles in a 9L brain tumor showing imaging and monitoring of therapeutic efficacy post treatment 22. (Figures reproduced with permission from: (A) ref 139.…”

“…Copyright 2006, Wiley; (C) ref 143. Copyright 2007, American Chemical Society; (D) ref 146. Copyright 2008, The Royal Society of Chemistry and Owner Societies; (E) ref 147.…”

Optical molecular imaging in atherosclerosis

“…Accordingly, the probe was shown to be potentially useful for measurement of plaque inflammation. 24,25 a v b 3 integrins which are receptors which help in cell-cell and cell-matrix binding and important part of cell signaling cascade. These receptors are highly expressed by macrophages in plaque lesions and play a key role on pathogenesis of atherosclerosis.…”

The impact of macrophage-cancer cell interaction on the efficacy of photodynamic therapy

“…46 The strategy of macrophage-targeting by scavenger-receptor targeted conjugates was later utilized to localize photosensitizers to vulnerable atherosclerotic plaques in rabbits, allowing fluorescence diagnosis and PDT; these lesions are particularly rich in macrophages. 47,48 Macrophage-targeted photosensitizer delivery for both diagnostic and therapeutic purposes can be facilitated by the nanoparticles technology. The nanoformulations explored for such approach include: biodegradable polymer poly(DL-lactide-co-glycolide) containing photosensitizer bacteriochlorophyll- a 49 , theranostic nanoparticles prepared by conjugating photosensitizer chlorin e6 to hyaluronic acid 50 , and positively charged nanoparticles consisting of a calcium phosphate core with shells of carboxymethyl cellulose and poly(ethyleneimine) loaded with photosensitizer 5,10,15,20-tetrakis(3-hydroxyphenyl)-porphyrin (mTHPP) 51 .…”