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 (68)Ga radiopharmaceuticals might have clinical utility for positron emission tomography (PET) studies of myocardial perfusion and other physiological processes. The lipophilic and monocationic (67)Ga-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)(2)BAPDMEN](+)PF(6)(-) salt was determined by X-ray crystallography, and the biodistribution of each of the (67)Ga-labeled gallium chelates was determined in rats following intravenous administration and compared with the biodistribution of [(86)Rb]rubidium chloride. The [Ga(4-MeOsal)(2)BAPDMEN](+)PF(6)(-) complex exhibited the expected pseudo-octahedral N(4)O(2)(2-) coordination sphere about the Ga(3+) center with a trans disposition of the phenolate oxygen atoms. All five (67)Ga radiopharmaceuticals were found to afford the desired myocardial retention of the radiogallium. The [(67/68)Ga][Ga(3-MeOsal)(2)BAPDMEN](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 [(67/68)Ga][Ga(3-MeOsal)(2)BAPDMEN](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 (68)Ga.