Development and preclinical evaluation of novel fluorinated ammonium salts for PET myocardial perfusion imaging

We previously presented the radiolabeled ammonium salt [¹¹C]-dimethyl diphenylammonium trifluoromethanesulfonate ([¹¹C]DMDPA) as a potential novel PET-MPI agent. The current study aimed to increase the clinical applicability of PET-MPI by designing and synthesizing fluorinated ammonium salt derivatives. Four fluorinated DMDPA derivatives and two quinolinium salt analogs were radiolabeled. The dynamic distribution in vivo, following injection of each derivative into male SD rats, was evaluated using small-animal dedicated PET/CT. Organ uptake after injection of [¹⁸F]fluoroethylquinolinium acetate ([¹⁸F]FEtQ) was examined ex vivo. Four fluorinated DMDPA derivatives were synthesized, two were labeled with fluorine-18: [¹⁸F]fluoroethyl-methyldiphenylammonium trifluoromethanesulfonate ([¹⁸F]FEMDPA) and [¹⁸F]fluorobuthyl-methyldiphenylammonium trifluoromethanesulfonate ([¹⁸F]FBMDPA). The other two were labeled using carbon-11: [¹¹C]methyl-(3-fluorophenyl)-methylphenylammonium trifluoromethanesulfonate ([¹¹C]3-F-DMDPA) and [¹¹C]methyl-(4-fluorophenyl)-methylphenylammonium trifluoromethanesulfonate ([¹¹C]4-F-DMDPA). All four DMDPA derivatives exhibited significantly lower heart/liver radioactivity uptake ratios (0.6, 0.4, 0.7 and 0.6, respectively) compared to that of [¹¹C]DMDPA (1.2). Conversely, the two radiolabeled quinolinium salt derivatives, [¹¹C]methylquinolinium iodide ([¹¹C]MeQ) and [¹⁸F]FEtQ demonstrated improved heart/liver ratios (2.0 and 1.3, respectively) with clear visualization of the left ventricle myocardium. Renal clearance was the major route of elimination. Among the fluorinated quaternary ammonium salts tested, [¹⁸F]FEtQ yielded the best images. Further studies are in progress to elucidate the underlying mechanism of its cardiac uptake.