title: Activatable iRGD-based peptide monolith: Targeting, internalization, and fluorescence activation for precise tumor imaging.
abstract: A disulfide-bridged cyclic RGD peptide, named iRGD (internalizing RGD, c(CRGDK/RGPD/EC)), is known to facilitate tumor targeting as well as tissue penetration. After the RGD motif-induced targeting on αv integrins expressed near tumor tissue, iRGD encounters proteolytic cleavage to expose the CendR motif that promotes penetration into cancer cells via the interaction with neuropilin-1. Based on these proteolytic cleavage and internalization mechanism, we designed an iRGD-based monolithic imaging probe that integrates multiple functions (cancer-specific targeting, internalization and fluorescence activation) within a small peptide framework. To provide the capability of activatable fluorescence signaling, we conjugated a fluorescent dye to the N-terminal of iRGD, which was linked to the internalizing sequence (CendR motif), and a quencher to the opposite C-terminal. It turned out that fluorescence activation of the dye/quencher-conjugated monolithic peptide probe requires dual (reductive and proteolytic) cleavages on both disulfide and amide bond of iRGD peptide. Furthermore, the cleavage of the iRGD peptide leading to fluorescence recovery was indeed operative depending on the tumor-related angiogenic receptors (αvβ3 integrin and neuropilin-1) in vitro as well as in vivo. Compared to an 'always fluorescent' iRGD control probe without quencher conjugation, the dye/quencher-conjugated activatable monolithic peptide probe visualized tumor regions more precisely with lower background noise after intravenous injection, owing to the multifunctional responses specific to tumor microenvironment. All these results, along with minimal in vitro and in vivo toxicity profiles, suggest potential of the iRGD-based activatable monolithic peptide probe as a promising imaging agent for precise tumor diagnosis.
authors.affiliation: Center for Theragnosis, Korea Institute of Science and Technology, 39-1 Hawolgok-dong, Seongbuk-gu, Seoul 136-791, Republic of Korea.
authors.forename: Hong-Jun
authors.initials: HJ
authors.lastname: Cho
authors.affiliation: Radiopharmaceutical Laboratory, Nuclear Medicine Division, Radiology and Imaging Sciences, Clinical Center, NIH, Bethesda, MD, USA.
authors.forename: Sung-Jin
authors.initials: SJ
authors.lastname: Lee
authors.affiliation: Center for Theragnosis, Korea Institute of Science and Technology, 39-1 Hawolgok-dong, Seongbuk-gu, Seoul 136-791, Republic of Korea; School of Chemical and Biological Engineering, Seoul National University, Seoul 151-744, Republic of Korea.
authors.forename: Sung-Jun
authors.initials: SJ
authors.lastname: Park
authors.affiliation: Radiopharmaceutical Laboratory, Nuclear Medicine Division, Radiology and Imaging Sciences, Clinical Center, NIH, Bethesda, MD, USA.
authors.forename: Chang H
authors.initials: CH
authors.lastname: Paik
authors.affiliation: Department of Chemical Engineering, Kangwon National University, Kangwon-Do 200-701, Republic of Korea. Electronic address: sangmyung@kangwon.ac.kr.
authors.forename: Sang-Myung
authors.initials: SM
authors.lastname: Lee
authors.affiliation: Center for Theragnosis, Korea Institute of Science and Technology, 39-1 Hawolgok-dong, Seongbuk-gu, Seoul 136-791, Republic of Korea. Electronic address: sehoonkim@kist.re.kr.
authors.forename: Sehoon
authors.initials: S
authors.lastname: Kim
authors.affiliation: School of Chemical and Biological Engineering, Seoul National University, Seoul 151-744, Republic of Korea. Electronic address: yslee@snu.ac.kr.
authors.forename: Yoon-Sik
authors.initials: YS
authors.lastname: Lee
mesh_terms: D000818:Animals; D045744:Cell Line, Tumor; D016503:Drug Delivery Systems; D005453:Fluorescence; D005456:Fluorescent Dyes / Q000032:analysis / Q000378:metabolism*; D006801:Humans; D039302:Integrin alphaVbeta3 / Q000378:metabolism*; D051379:Mice; D009369:Neoplasms / Q000000981:diagnostic imaging* / Q000378:metabolism; D039942:Neuropilin-1 / Q000378:metabolism*; D009842:Oligopeptides / Q000032:analysis / Q000378:metabolism*; D061848:Optical Imaging / Q000379:methods*
chemical_list: D005456:Fluorescent Dyes; D039302:Integrin alphaVbeta3; C569656:N-end cysteine peptide tumor-homing peptide; D009842:Oligopeptides; D039942:Neuropilin-1
keywords: Activatable probe; Internalizing RGD (iRGD); Peptide monolith; Tumor imaging