S‐Gal®, A novel 1H MRI reporter for β‐galactosidase

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Abstract
Reporter genes and associated enzyme activity are becoming increasingly significant for research in vivo. The lacZ gene and β‐galactosidase (β‐gal) expression have long been exploited as reporters of biologic manipulation at the molecular level, and a noninvasive detection strategy based on proton MRI is particularly attractive. 3,4‐Cyclohexenoesculetin β‐D‐galactopyranoside (S‐Gal®) is a commercial histologic stain, which forms a black precipitate in the presence of β‐gal and ferric ions, suggesting potential detectability by MRI. Generation of the precipitate is now shown to cause strong T2* relaxation, revealing β‐gal activity. A series of tests with the enzyme in vitro and with tumor cells shows that this approach can be used as an assay for β‐gal activity. Proof of principle is shown in human breast tumor xenografts in mice. Upon direct injection of a mixture of 3,4‐cyclohexenoesculetin β‐D‐galactopyranoside and ferric ammonium citrate, intense contrast was observed immediately in MCF7‐lacZ tumors, but not in wild‐type tumors. 3,4‐Cyclohexenoesculetin β‐D‐galactopyranoside activation in combination with ferric ions introduces a novel approach for assaying enzyme activity by MRI in vivo. Magn Reson Med, 2010.

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