Novel Fe ³⁺-Based ¹H MRI β-galactosidase reporter molecules

There is increasing interest in the development of reporter agents to reveal enzyme activity in vivo using imaging in small animals. We have previously demonstrated the feasibility of detecting lacZ gene activity using the commercially available 3,4-cyclohexenoesculetin-β-D-galactopyranoside (S-Gal) as a 1H MRI reporter. Specifically, β-galactosidase (β-gal) releases the aglycone, which forms a magnetic resonance contrast-inducing paramagnetic precipitate in the presence of Fe ³⁺. Contrast was primarily T ₂-weighted signal loss, but T ₁ effects were also observed. Since T ₁-contrast generally provides signal enhancement as opposed to loss, it appeared attractive to explore whether analogues could be generated with enhanced characteristics. We now report the design and synthesis of novel analogues together with characterization of 1H MRI contrast based on both T ₁ and T ₂ response to β-gal activity in vitro for the lead agent.