Investigations on the Ga(III) Complex of EOB-DTPA and Its 68Ga Radiolabeled Analogue.

We demonstrate a method for the isolation of EOB-DTPA (3,6,9-triaza-3,6,9-tris(carboxymethyl)-4-(ethoxybenzyl)-undecanedioic acid) from its Gd(III) complex and protocols for the preparation of its novel non-radioactive, i.e., natural Ga(III) as well as radioactive (68)Ga complex. The ligand as well as the Ga(III) complex were characterized by nuclear magnetic resonance (NMR) spectroscopy, mass spectrometry and elemental analysis. (68)Ga was obtained by a standard elution method from a (68)Ge/(68)Ga generator. Experiments to evaluate the (68)Ga-labeling efficiency of EOB-DTPA at pH 3.8-4.0 were performed. Established analysis techniques radio TLC (thin layer chromatography) and radio HPLC (high performance liquid chromatography) were used to determine the radiochemical purity of the tracer. As a first investigation of the (68)Ga tracers' lipophilicity the n-octanol/water distribution coefficient of (68)Ga species present in a pH 7.4 solution was determined by an extraction method. In vitro stability measurements of the tracer in various media at physiological pH were performed, revealing different rates of decomposition.