SYNTHESIS, CHARACTERIZATION AND RELAXIVITY OF POLYMERIC GADOLINIUM CHELATES AS POTENTIAL MRI CONTRAST AGENTS

Two polymeric carbohydrate-containing Gd (III) chelates were synthesized and studied as potential Magnetic Resonance Imaging (MRI) contrast agents.Poly[Gd(DTPA-TD)] and poly[Gd(DTPA-β Cd)] were synthesized via copolymerization of DTPA-BA (DTPA-BA = diethylenetriamine-N,N,N',N'',N'''-pentaacetate-bis anhydride) with 6,6'-diamino-6,6'-dideoxy-D-trehalose (TD), and 6A,6D-dideoxy-6A,6D-diamino β-cyclodextrin (β-Cd) respectively, followed by the complexation with Gd(III).In addition, poly[Gd(DTPA-HD)] [1] and poly[Gd(DTPA-CHD)] (HD = hexamethylenediamine, CHD = trans 1,4 diaminocyclohexane) [1] were also synthesized in a similar fashion to serve as a model for comparison with our novel agents.The longitudinal relaxation time (T 1 ) of these agents and of GdDTPA (Magnevist) were measured and plotted as 1/T 1 versus concentration.From these plots, relaxivity (R 1 ) was deduced.The R 1 for these agents were 5.22mM -1 s -1 poly[Gd(DTPA-TD)], 4.46mM - 1 s -1 poly[Gd(DTPA-β Cd)], and 6.25mM -1 s -1 poly[Gd(DTPA-HD)], 5.68mM -1 s -1 poly[Gd(DTPA-CHD)], and 4.60mM -1 s -1 for Magnevist respectively.The efficiency of these agents to enhance the relaxation rate of water protons are; poly[Gd(DTPA-HD)] > poly[Gd(DTPA-CHD)] >poly[Gd(DTPA-TD)]> Magnevist > poly[Gd(DTPA-βCd)].