Synthesis of a novel ‘smart’ bifunctional chelating agent 1-(2-[β,d-galactopyranosyloxy]ethyl)-7-(1-carboxy-3-[4-aminophenyl]propyl)-4,10-bis(carboxymethyl)-1,4,7,10-tetraazacyclododecane (Gal-PA-DO3A-NH2) and its Gd(III) complex

Synthesis and characterization of pH-sensitive, biotinylated MRI contrast agents and their conjugates with avidin

Responsive or smart contrast agents (SCAs) provide new opportunities in magnetic resonance imaging (MRI) to examine a number of physiological and pathological events. However, their application in vivo remains challenging. Therefore, much research is focused on the optimization of their properties, to enable their use in additional imaging modalities, pre-targeted delivery, or to increase the local concentration of the agent. The key feature in the SCA synthetic modification is the retention of their physicochemical properties related to the specific MR response. Here, we report the preparation and characterization of pH sensitive SCAs appended with a phosphonate pendant arm and either an aliphatic (GdL(1)) or aromatic linker (GdL(2)). The longitudinal relaxivity of GdL(1) and GdL(2) increases by 146% and 31%, respectively, while the pH decreases from 9 to 5. These two SCAs were converted to the biotinylated systems GdL(3) and GdL(4) and their interaction with avidin was investigated. The binding affinity with avidin was assessed with a fluorescence displacement assay and with MRI phantom experiments in a 3T MRI scanner. The fluorometric assay and MRI E-titrations revealed a 3 : 1 binding mode of GdL(3-4) to avidin with the binding affinity as high as that of the parent avidin-biotin complex. The high binding affinity was confirmed with MRI by a competitive assay. The avidin-GdL(3-4) complexes thus obtained exhibit changes in both r(1) and r(2) that are pH dependent. The results reveal a new pathway for the modification and improvement of SCAs to make them more suitable for in vivo application.

A new synthesis of cystamine modified Eu3+ DOTAM-Gly-Phe-OH: a conjugation ready temperature sensitive MRI contrast agent

Several approaches towards asymmetrically derivatized peptide-decorated cyclens that yield lanthanide metal chelators, in which three of the nitrogen atoms of cyclen share a common substituent and the fourth nitrogen atom is differentially substituted, have been evaluated. The most effective route consisted of selective monoalkylation followed by peralkylation with a second different electrophile. The unique substituent also possessed a masked sulfanyl group that was suitable for subsequent chemoselective conjugation chemistry.