Synthesis and biodistribution of lipophilic and monocationic gallium radiopharmaceuticals derived from N, N′- bis(3-aminopropyl)- N, N′-dimethylethylenediamine: potential agents for PET myocardial imaging with 68Ga

In locations that lack nearby cyclotron facilities for radionuclide production, generator-based 68Ga radiopharmaceuticals might have clinical utility for positron emission tomography (PET) studies of myocardial perfusion and other physiological processes. The lipophilic and monocationic 67Ga-labeled gallium chelates of five novel hexadentate bis(salicylaldimine) ligands the bis(salicylaldimine), bis(3-methoxysalicylaldimine), bis(4-methoxysalicylaldimine), bis(6-meth,oxysalicylaldimine), and bis(4,6-dimethoxysalicylaldimine) of N, N′- bis(3-aminopropyl) -N, N′ -dimethylethylenediamine (BAPDMEN), were prepared. The structure of the unlabeled [Ga(4-MeOsal) 2BAPDMEN] +PF 6 − salt was determined by X-ray crystallography, and the biodistribution of each of the 67Ga-labeled gallium chelates was determined in rats following intravenous administration and compared with the biodistribution of [ 86Rb]rubidium chloride. The [Ga(4-MeOsal) 2BAPDMEN] +PF 6 − complex exhibited the expected pseudo-octahedral N 4O 2 2− coordination sphere about the Ga 3+ center with a trans disposition of the phenolate oxygen atoms. All five 67Ga radiopharmaceuticals were found to afford the desired myocardial retention of the radiogallium. The [ 67/68Ga][Ga(3-MeOsal) 2BAPDMEN] 1+ radiopharmaceutical appears to have the best properties for myocardial imaging, exhibiting 2% of the injected dose in the heart 1 min and 2 h postinjection and very high heart/nontarget ratios (heart/blood ratios of 7.6±1.0 and 54±10 at 1 and 120 min, respectively; heart/liver ratios of 1.8±0.4 and 39±3 at 1 and 120 min, respectively). Most of these new agents, particularly [ 67/68Ga][Ga(3-MeOsal) 2BAPDMEN] 1+, would appear superior to previously reported bis(salicylaldimine) ligands of N, N′- bis(3-aminopropyl)ethylenediamine as candidates for PET imaging of the heart with 68Ga.