Noninvasive Photoacoustic and Fluorescence Bimodality Imaging Differentiation of Vulnerable Atherosclerotic Plaques at Different Stages.

Vulnerable atherosclerotic plaques (VASPs), characterized by intense inflammation and a thin fibrous cap, pose a high risk for acute cardiovascular events. The conventional technique for their identification is angiography, but it remains challenging for angiography to differentiate VASPs at different stages. Herein, we report an activatable organic probe (RGD-IR-Dimer) for noninvasive dual-modal photoacoustic (PA) and fluorescence (FL) differentiation imaging of VASPs at different stages. This probe comprises a near-infrared chromophore, a collagenase-cleavable peptide substrate, and an αvβ3 integrin-targeting cyclic RGD moiety. For early-stage VASPs detection, after being intravenously administered, RGD-IR-Dimer selectively accumulates at atherosclerotic lesions via αvβ3-mediated targeting. High local concentration of RGD-IR-Dimer induces its self-assembly into nanofibers, turning the PA signal "on". In later VASPs, after the PA signal "on", the nanofibers are cleaved by the overexpressed matrix metalloproteinases, triggering a remarkable fluorescence "on" and a simultaneous PA "off". Thus, early-stage VASPs are characterized by an "on" PA signal, while the late-stage ones are characterized by an earlier "on" PA signal together with a later "on" FL signal. In cell models, RGD-IR-Dimer effectively discriminated between early- and late-stage VASPs. Since mouse models lack the neovascular architecture for modeling early-stage lesions, we evaluated the probe behavior in a mouse model of late-stage VASPs as a proof of concept, where it exhibited a time-dependent PA-to-FL signal transition. Our study demonstrates that RGD-IR-Dimer could be a promising probe for the noninvasive detection of high-risk plaques, potentially facilitating its early intervention.