Gallium-68 Complexes Conjugated to Pittsburgh Compound B: Radiolabeling and Biological Evaluation

The aim of this work is to develop an efficient and fully automated radiosynthesis of three derivatives of the Pittsburgh compound B labeled with gallium-68 for the detection of amyloid plaques. The radiolabeling of the precursors and purification of the radiolabeled agents by high pressure liquid chromatography has been studied prior to their in vitro and in vivo evaluations. The complete process led, in 50 min, to pure Ga-68 products in a 12-38 % yield and with appreciable specific radioactivity (SRA, 85-168 GBq/mu mol) which enabled us to demonstrate a considerable in vivo stability of the products. Unfortunately, this result was associated with a poor blood-brain barrier (BBB) permeability and a limited uptake of our compounds by amyloid deposits was observed by in vitro autoradiography. Although we have not yet identified a compound able to significantly mark cerebral amyloidosis, this present investigation will likely contribute to the development of more successful Ga-68 radiotracers.