Abstract WP441: Photodynamic Therapy Using Protease-Mediated Theranostic Photodynamic Agent Reduces Cathepsin-B Activity in Mouse Carotid Atheromata In Vivo

Abstract

Background Carotid atherosclerosis is a major cause of ischemic stroke. Nanotechology-based theranostics for atherosclerosis and stroke is still in its infancy. Objective —To investigate if an intravenously-injected cathepsin-B activatable theranostic agent (L-SR15) would be cleaved in and release a fluorescent agent (chlorine-e6) in mouse carotid atheromata, allowing both the diagnostic visualization and therapeutic application of these fluorophores as photosensitizers during photodynamic therapy (PDT) to attenuate plaque-destabilizing cathepsin-B activity by selectively eliminating macrophages. Methods and Results Thirty-week-old Apolipoprotein-E knock-out mice received intravenous injection of L-SR15 theranostic agent (n=5), control agent D-SR16 (n=5), or PBS (n=5) three times at days 0, 7, and 14. Twenty-four hours after each injection, the bilateral carotid arteries were exposed and Cy5.5 near-infrared fluorescent (NIRF) imaging was performed. Fluorescent signal progressively accumulated in atheromata of the L-SR15 group animals only, indicating that photosensitizers had been released from the theranostic agent, and were accumulating in the plaque. After each imaging session, PDT was applied with a continuous-wave diode-laser. Additional Cy7 near infrared imaging with a CatB-sensing activatable NIRF imaging agent reduced CatB-realated signal only in the L-SR15, with activity at day 22 significantly lower than at baseline. Histological studies demonstrated that L-SR15-based PDT eliminated macrophages by inducing apoptosis without affecting plaque size or smooth muscle cell numbers. Conclusion This is the first study showing that macrophage-secreted cathepsin-B activity could be attenuated by PDT using a protease-mediated theranostic agent.