Abstract 14212: P22 Protein Cage Nanoparticles targeted With RGD Enhance Detection of Vascular Inflammation

Introduction: The 60-nm protein cage of the bacteriophage P22 has promising properties for molecular/cellular imaging when loaded with imaging agents and targeting ligands. We evaluated RGD-conjugated P22 for macrophage imaging in vitro and in murine carotid arteries. Methods: 1) In vitro : Mouse macrophage cells (RAW 264.7) were incubated for both 4 and 24 hours with P22 loaded with Gadolinium (Gd , 0.1mM) plus the RGD peptide bound through a decorating (Dec) protein (P22-RGD-Dec-Gd). The same conditions were used for two controls: P22-wtDec-Gd (w/o RGD) and P22-Gd (w/o RGD or wtDec). After washing in PBS, cells were scanned with 3T MRI using spin echo sequence (TR/TE=400ms/11ms, slice thickness=1mm, FOV=12cm, matrix=256x256). 2) In vivo : FVB mice (N=18) underwent induction of diabetes and hyperlipidemia, followed by carotid ligation to develop macrophage-rich atherosclerotic lesions. Two weeks post carotid ligation, mice were injected with RGD-targeted (P22-RGD-Dec-Cy5.5) or non-targeted control (P22-wtDec-Cy5.5) via tail vein (4 nmol/mouse) and scanned by in-vivo fluorescence imaging for up to 48 hours (FMT, Visen, Bedford, MA). After in vivo imaging, carotid arteries were harvested and scanned ex vivo (Maestro, Cri, Woburn MA). Results: In vitro MRI (Fig 1) showed higher signal to noise ratio in cells incubated with RGD-targeted P22 compared to cells with non-targeted P22 (4 hour; 1.3x, 24 hour; 1.1x). In vivo fluorescence molecular tomography showed the accumulation of both targeted and non-targeted P22 in carotid arteries. Ex vivo fluorescence imaging (Fig 2) demonstrated significant 75% signal enhancement in atherosclerotic lesions of RGD-targeted P22 compared to non-targeted control (0.021 ± 0.003 vs. 0.012 ± 0.002 counts/second, p Conclusions: Both in vitro and in vivo studies show RGD enhances P22 molecular/cellular imaging of macrophages. P22 with RGD-targeting can detect high-risk biological activity in vascular inflammation.