title: S-Gal, a novel 1H MRI reporter for beta-galactosidase.
abstract: Reporter genes and associated enzyme activity are becoming increasingly significant for research in vivo. The lacZ gene and beta-galactosidase (beta-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 beta-D-galactopyranoside (S-Gal) is a commercial histologic stain, which forms a black precipitate in the presence of beta-gal and ferric ions, suggesting potential detectability by MRI. Generation of the precipitate is now shown to cause strong T(2)* relaxation, revealing beta-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 beta-gal activity. Proof of principle is shown in human breast tumor xenografts in mice. Upon direct injection of a mixture of 3,4-cyclohexenoesculetin beta-D-galactopyranoside and ferric ammonium citrate, intense contrast was observed immediately in MCF7-lacZ tumors, but not in wild-type tumors. 3,4-Cyclohexenoesculetin beta-D-galactopyranoside activation in combination with ferric ions introduces a novel approach for assaying enzyme activity by MRI in vivo.
authors.affiliation: Department of Radiology, The University of Texas Southwestern Medical Center, Dallas, Texas 75390-9058, USA.
authors.forename: Weina
authors.initials: W
authors.lastname: Cui
authors.forename: Li
authors.initials: L
authors.lastname: Liu
authors.forename: Vikram D
authors.initials: VD
authors.lastname: Kodibagkar
authors.forename: Ralph P
authors.initials: RP
authors.lastname: Mason
mesh_terms: D000818:Animals; D015153:Blotting, Western; D001943:Breast Neoplasms / Q000175:diagnosis* / Q000000981:diagnostic imaging; D045744:Cell Line, Tumor; D003287:Contrast Media / Q000737:chemistry; D005260:Female; D005697:Galactosides / Q000737:chemistry*; D017930:Genes, Reporter; D006801:Humans; D008279:Magnetic Resonance Imaging; D051379:Mice; D015394:Molecular Structure; D011859:Radiography; D014468:Umbelliferones / Q000737:chemistry*; D001616:beta-Galactosidase / Q000737:chemistry*
chemical_list: D003287:Contrast Media; D005697:Galactosides; D014468:Umbelliferones; C101993:cyclohexenoesculetin-beta-galactoside; D001616:beta-Galactosidase