Comparison of MRI properties between derivatized DTPA and DOTA gadolinium–dendrimer conjugates

In this report we directly compare the in vivo and in vitro MRI properties of gadolinium–dendrimer conjugates of derivatized acyclic diethylenetriamine-N,N′,N′,N″,N″-pentaacetic acid (1B4M-DTPA) and macrocyclic 1,4,7,10-tetraazacyclododecane-N,N′,N″,N‴-tetraacetic acid (C-DOTA). The metal–ligand chelates were pre-formed in alcohol prior to conjugation to the generation 4 PAMAM dendrimer (G4D), and the dendrimer-based agents were purified by Sephadex® G-25 column. The analysis and SE-HPLC data indicated chelate to dendrimer ratios of 30:1 and 28:1, respectively. Molar relaxivity measured at pH 7.4, 22 °C, and 3T are comparable (29.5 vs 26.9 mM−1 s−1), and both conjugates are equally viable as MRI contrast agents based on the images obtained. The macrocyclic agent however exhibits a faster rate of clearance in vivo (t1/2 = 16 vs 29 min). Our conclusion is that the macrocyclic-based agent is the more suitable agent for in vivo use for these reasons combined with kinetic inertness associated with the Gd(III) DOTA complex stability properties.

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