Development of a Gd(III)-Based Receptor-Induced Magnetization Enhancement (RIME) Contrast Agent for β‑Glucuronidase Activity Profiling

• Published in: Inorganic chemistry 2012-11, Vol.51 (22), p.12426-12435
• Main Authors: Chen, Shih-Hsien, Kuo, Yu-Ting, Singh, Gyan, Cheng, Tian-Lu, Su, Yu-Zheng, Wang, Tzu-Pin, Chiu, Yen-Yu, Lai, Jui-Jen, Chang, Chih-Ching, Jaw, Twei-Shiun, Tzou, Shey-Cherng, Liu, Gin-Chung, Wang, Yun-Ming
• Format: Article
• Language: English
• Subjects: Animals; Antineoplastic Agents - chemical synthesis; Antineoplastic Agents - chemistry; Antineoplastic Agents - pharmacology; Cell Line, Tumor; Cell Survival - drug effects; Contrast Media - chemical synthesis; Contrast Media - chemistry; Contrast Media - pharmacology; Dose-Response Relationship, Drug; Enzyme Activation; Gadolinium - chemistry; Glucuronidase - metabolism; Ligands; Magnetic Resonance Imaging; Mice; Mice, Inbred BALB C; Neoplasms, Experimental - drug therapy; Neoplasms, Experimental - enzymology; Neoplasms, Experimental - pathology; Organometallic Compounds - chemical synthesis; Organometallic Compounds - chemistry; Organometallic Compounds - pharmacology; Structure-Activity Relationship; Xenograft Model Antitumor Assays
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/ic301827p

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 (K A) of [Gd­(DOTA-FPβGu)] is 7.42 × 102, which is significantly lower than that of a commercially available MS-325 (K A = 3.0 × 104) RIME contrast agent. The low K A 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 K m = 1.38 mM, k cat = 3.76 × 103, and k cat/K m = 2.72 × 103 M–1 s–1. The low K m value indicates high affinity of β-glucuronidase for [Gd­(DOTA-FPβGu)] at physiological pH. Relaxometric studies revealed that T 1 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.