title: Development of a Gd(III)-based receptor-induced magnetization enhancement (RIME) contrast agent for β-glucuronidase activity profiling.
abstract: β-Glucuronidase is a key lysosomal enzyme and is often overexpressed in necrotic tumor masses. We report here the synthesis of a pro receptor-induced magnetization enhancement (pro-RIME) magnetic resonance imaging (MRI) contrast agent ([Gd(DOTA-FPβGu)]) for molecular imaging of β-glucuronidase activity in tumor tissues. The contrast agent consists of two parts, a gadolinium complex and a β-glucuronidase substrate (β-d-glucopyranuronic acid). The binding association constant (KA) of [Gd(DOTA-FPβGu)] is 7.42 × 10(2), which is significantly lower than that of a commercially available MS-325 (KA = 3.0 × 10(4)) RIME contrast agent. The low KA value of [Gd(DOTA-FPβGu)] is due to the pendant β-d-glucopyranuronic acid moiety. Therefore, [Gd(DOTA-FPβGu)] can be used for detection of β-glucuronidase through RIME modulation. The detail mechanism of enzymatic activation of [Gd(DOTA-FPβGu)] was elucidated by LC-MS. The kinetics of β-glucuronidase catalyzed hydrolysis of [Eu(DOTA-FPβGu)] at pH 7.4 best fit the Miechalis-Menten kinetic mode with Km = 1.38 mM, kcat = 3.76 × 10(3), and kcat/Km = 2.72 × 10(3) M(-1) s(-1). The low Km value indicates high affinity of β-glucuronidase for [Gd(DOTA-FPβGu)] at physiological pH. Relaxometric studies revealed that T1 relaxivity of [Gd(DOTA-FPβGu)] changes in response to the concentration of β-glucuronidase. Consistent with the relaxometric studies, [Gd(DOTA-FPβGu)] showed significant change in MR image signal in the presence of β-glucuronidase and HSA. In vitro and in vivo MR images demonstrated appreciable differences in signal enhancement in the cell lines and tumor xenografts in accordance to their expression levels of β-glucuronidase.
authors.affiliation: Graduate Institute of Medicine, College of Medicine, Kaohsiung Medical University , 100 Shih-Chuan first Road, Kaohsiung 807, Taiwan.
authors.forename: Shih-Hsien
authors.initials: SH
authors.lastname: Chen
authors.forename: Yu-Ting
authors.initials: YT
authors.lastname: Kuo
authors.forename: Gyan
authors.initials: G
authors.lastname: Singh
authors.forename: Tian-Lu
authors.initials: TL
authors.lastname: Cheng
authors.forename: Yu-Zheng
authors.initials: YZ
authors.lastname: Su
authors.forename: Tzu-Pin
authors.initials: TP
authors.lastname: Wang
authors.forename: Yen-Yu
authors.initials: YY
authors.lastname: Chiu
authors.forename: Jui-Jen
authors.initials: JJ
authors.lastname: Lai
authors.forename: Chih-Ching
authors.initials: CC
authors.lastname: Chang
authors.forename: Twei-Shiun
authors.initials: TS
authors.lastname: Jaw
authors.forename: Shey-Cherng
authors.initials: SC
authors.lastname: Tzou
authors.forename: Gin-Chung
authors.initials: GC
authors.lastname: Liu
authors.forename: Yun-Ming
authors.initials: YM
authors.lastname: Wang
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000138:chemical synthesis / Q000737:chemistry / Q000494:pharmacology*; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects; D003287:Contrast Media / Q000138:chemical synthesis / Q000737:chemistry / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D004789:Enzyme Activation; D005682:Gadolinium / Q000737:chemistry; D005966:Glucuronidase / Q000378:metabolism*; D008024:Ligands; D008279:Magnetic Resonance Imaging; D051379:Mice; D008807:Mice, Inbred BALB C; D009374:Neoplasms, Experimental / Q000188:drug therapy* / Q000201:enzymology / Q000473:pathology; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry / Q000494:pharmacology*; D013329:Structure-Activity Relationship; D023041:Xenograft Model Antitumor Assays
chemical_list: D000970:Antineoplastic Agents; D003287:Contrast Media; D008024:Ligands; D009942:Organometallic Compounds; D005682:Gadolinium; D005966:Glucuronidase