With an aim of developing a bacteria-specific molecular imaging agent,
ciprofloxacin has been modified with a propylamine spacer and linked to two common bifunctional
chelators, p-SCN-Bz-
DOTA and p-SCN-Bz-
NOTA. The two
ciprofloxacin conjugates, CP-PA-SCN-Bz-
DOTA (1) and CP-PA-SCN-Bz-
NOTA (2), were radiolabeled with (68)Ga in >90% radiochemical yield and were moderately stable in vitro for 4 h. The efficacy of (68)Ga-1 and (68)Ga-2 has been investigated in vitro in Staphylococcus aureus cells where bacterial binding of the radiotracers (0.9-1.0% for (68)
Ga-1 and 1.6-2.3% for (68)Ga-2) could not be blocked in the presence of excess amount of unlabeled
ciprofloxacin. However, uptake of radiotracers in live bacterial cells was significantly higher (p < 0.01) than that in non-viable bacterial cells.
Bacterial infection targeting efficacy of (68)Ga-1 and (68)Ga-2 was tested in vivo in rats where the infected muscle-to-inflamed muscle ((68)
Ga-1: 2 ± 0.2, (68)Ga-2: 3 ± 0.5) and infected muscle-to-normal muscle ratios ((68)
Ga-1: 3 ± 0.4, (68)Ga-2: 6.6 ± 0.8) were found to improve at 120 min p.i. Fast blood clearance and renal excretion was observed for both the radiotracers. The two (68)Ga-labeled
infection targeting radiotracers could discriminate between
bacterial infection and
inflammation in vivo and are worthy of further detailed investigation as
infection imaging agents at the clinical level.