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

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 × 10(2), which is significantly lower than that of a commercially available MS-325 (K(A) = 3.0 × 10(4)) 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 × 10(3), and k(cat)/K(m) = 2.72 × 10(3) 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.

Citation

Shih-Hsien Chen, Yu-Ting Kuo, Gyan Singh, Tian-Lu Cheng, Yu-Zheng Su, Tzu-Pin Wang, Yen-Yu Chiu, Jui-Jen Lai, Chih-Ching Chang, Twei-Shiun Jaw, Shey-Cherng Tzou, Gin-Chung Liu, Yun-Ming Wang. Development of a Gd(III)-Based Receptor-Induced Magnetization Enhancement (RIME) Contrast Agent for β-Glucuronidase Activity Profiling. Inorganic chemistry. 2012 Nov 1

PMID: 23116118

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