title: Photodynamic therapy using a protease-mediated theranostic agent reduces cathepsin-B activity in mouse atheromata in vivo.
abstract: OBJECTIVE
  To investigate whether an intravenously injected cathepsin-B activatable theranostic agent (L-SR15) would be cleaved in and release a fluorescent agent (chlorin-e6) in mouse atheromata, allowing both the diagnostic visualization and therapeutic application of these fluorophores as photosensitizers during photodynamic therapy to attenuate plaque-destabilizing cathepsin-B activity by selectively eliminating macrophages.
  
  
  RESULTS
  Thirty-week-old apolipoprotein E knock-out mice (n=15) received intravenous injection of L-SR15 theranostic agent, control agent D-SR16, or saline 3× (D0, D7, D14). Twenty-four hours after each injection, the bilateral carotid arteries were exposed, and Cy5.5 near-infrared fluorescent imaging was performed. Fluorescent signal progressively accumulated in the 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, photodynamic therapy was applied with a continuous-wave diode-laser. Additional near-infrared fluorescent imaging at a longer wavelength (Cy7) with a cathepsin-B-sensing activatable molecular imaging agent showed attenuation of cathepsin-B-related signal in the L-SR15 group. Histological studies demonstrated that L-SR15-based photodynamic therapy decreased macrophage infiltration by inducing apoptosis without significantly affecting plaque size or smooth muscle cell numbers. Toxicity studies (n=24) showed that marked erythematous skin lesion was generated in C57/BL6 mice at 24 hours after intravenous injection of free chlorin-e6 and ultraviolet light irradiation; however, L-SR15 or saline did not cause cutaneous phototoxicity beyond that expected of ultraviolet irradiation alone, neither did we observe systemic toxicity or neurobehavioral changes.
  
  
  CONCLUSIONS
  This is the first study showing that macrophage-secreted cathepsin-B activity in atheromata could be attenuated by photodynamic therapy using a protease-mediated theranostic agent.
authors.affiliation: Molecular Imaging and Neurovascular Research Laboratory, Dongguk University Ilsan Hospital, Goyang, Republic of Korea.
authors.forename: Soo-Min
authors.initials: SM
authors.lastname: Shon
authors.forename: Yongdoo
authors.initials: Y
authors.lastname: Choi
authors.forename: Jeong-Yeon
authors.initials: JY
authors.lastname: Kim
authors.forename: Dong Kun
authors.initials: DK
authors.lastname: Lee
authors.forename: Jin-Yong
authors.initials: JY
authors.lastname: Park
authors.forename: Dawid
authors.initials: D
authors.lastname: Schellingerhout
authors.forename: Dong-Eog
authors.initials: DE
authors.lastname: Kim
mesh_terms: D000818:Animals; D001057:Apolipoproteins E / Q000172:deficiency; D002339:Carotid Arteries / Q000187:drug effects / Q000473:pathology; D002401:Cathepsin B / Q000037:antagonists & inhibitors* / Q000378:metabolism*; D002735:Chlorophyllides; D004195:Disease Models, Animal; D003875:Drug Eruptions / Q000209:etiology; D004890:Erythema / Q000139:chemically induced; D007275:Injections, Intravenous; D051379:Mice; D018345:Mice, Knockout; D010778:Photochemotherapy / Q000379:methods*; D017319:Photosensitizing Agents / Q000008:administration & dosage* / Q000633:toxicity; D058226:Plaque, Atherosclerotic / Q000188:drug therapy* / Q000473:pathology; D011166:Porphyrins / Q000494:pharmacology; D011897:Random Allocation; D012016:Reference Values
chemical_list: D001057:Apolipoproteins E; D002735:Chlorophyllides; D017319:Photosensitizing Agents; D011166:Porphyrins; C062985:phytochlorin; D002401:Cathepsin B
keywords: atherosclerosis; cathepsin-B; molecular imaging; photodynamic therapy; photosensitizer; protease-mediated theranostic agent