Novel S-Gal® analogs as 1H MRI reporters for in vivo detection of β-galactosidase

Abstract

The quantitative assessment of gene expression and related enzyme activity in vivo could be important for the characterization of gene altering diseases and therapy. The development of imaging techniques, based on specific reporter molecules may enable routine non-invasive assessment of enzyme activity and gene expression in vivo. We recently reported the use of commercially available S-Gal® as a β-galactosidase reporter for 1HMRI, and the synthesis of several S-Gal® analogs with enhanced response to β-galactosidase activity. We have now compared these analogs in vitro and have identified the optimal analog, C3-GD, based on strong T1 and T2 response to enzyme presence (ΔR1 and ΔR2 ∼ 1.8 times S-Gal®). Moreover, application is demonstrated in vivo in human breast tumor xenografts. MRI studies in MCF7-lacZ tumors implanted subcutaneously in athymic nude mice (n = 6), showed significant reduction in T1 and T2 values (each ∼ 13%) 2 h after intratumoral injection of C3-GD, whereas the MCF7 (wild type) tumors showed slight increase. Thus, C3-GD successfully detects β-galactosidase activity in vivo and shows promise as a lacZ gene 1HMR reporter molecule.

Cellular magnetic resonance imaging contrast generated by the ferritin heavy chain genetic reporter under the control of a Tet-On switch

“…Several genetic MRI reporting systems have been investigated, including divalent metal transporters [ 24 , 25 ], β-galactosidase [ 26 ], tyrosinase [ 27 ], transferrin receptor [ 28 ], magA [ 29 , 30 ] and ferritin [ 31 , 32 ]. Among these candidates, ferritin, which displays a high transverse relaxation rate by inducing the expression of the transferrin receptor and increasing iron uptake, has been widely used as a reproducible and functional MRI reporter in extensive molecular imaging studies [ 2 , 33 ].…”

Magnetic Resonance Microscopy (MRM) of Single Mammalian Myofibers and Myonuclei

“…In our experience the extrapolation to in vivo studies is not limited by the promoter but by the substrate availability of S-gal and the iron. Whereas we have shown in the past this reporter system can be used in mice39 and others have demonstrated its use in a in vivo tumor model it relied on highly tissue permeability in vivo 30. Human represents further challenges due to the need to introduce a marker gene without clinical benefit, the off-label use of iron supplementation, and the approval to use S-gal in humans.…”

“…Due to the increased induced magnetic field inhomogeneities this has been used to detect single cells in vitro 26 and in vivo 27. It can also be used to assess transgene expression using the beta-galactosidase reporter system in translational research studies22282930 as well as cancer clinical trials3132. Other commonly employed cellular contrast agents include gadolinium-loaded nanoparticles, which increase T 1 relaxation rates of neighboring water molecules3334.…”

Nanoparticles for Bioimaging

“…Some MRI contrast agents are specifically designed to alter their relaxation behavior based on environmental conditions, such as temperature [27], pH [28], oxygenation [29], ion concentration [30,31], or enzyme activity [32,33]. These effects are often achieved by developing an agent that alters its chemical structure based on the local conditions.…”