Gadoxane – A Novel Degradable Silsesquioxane Based Macromolecular MRI Contrast Agent

Introduction Since their discovery polyhedral oligosilsesquioxanes (POSS) have found an ever increasing number of applications in material science, catalysis, as building blocks for dendrimers and only recently biomedical use (e.g. as drug carrier systems) were reported as well. In the last two years studies of silsesquioxane based contrast agents (CA) for MRI were published [1,2] in which the silsesquioxane acts as a core dendrimer for MRI reporters like gadolinium chelates. The resulting compact globular macromolecular contrast agents show significantly enhanced relaxivities due to their increased size. Although it is known that POSS can be hydrolysed in aqueous media no studies on the stability of the core structure under physiological conditions are reported so far. Here we are presenting a new silsesquioxane based macromolecular CA (Gadoxane, Fig. 1). Its stability towards hydrolysis was studied by nuclear magnetic resonance (NMR) spectroscopy, mass spectrometry and relaxivity measurements.