In vivo and in vitro evaluation of Cu-64-ENOTA and PNOTA complexes as potential bifunctional chelators for radiopharmaceuticals

Objectives Investigated ENOTA (4,7,4',7'-tetraacetic acid-bis-1,1',1,4,7-triazacyclononylethane) and PNOTA (4,7,4',7'-tetraacetic acid-bis-1,1',1,4,7-triazacyclononylpropane) as potential chelating agents for ⁶⁴Cu (t_½ = 12.7 h).

Methods The ENOTA and PNOTA ligands were reacted with ⁶⁴Cu and the % yield was confirmed by TLC. The in vitro stability was tested in rat serum at 37°C and monitoring the % intact complex by TLC out to 66 hr. The in vivo stability was tested in CF-1 normal mice.

Results Both complexes exhibited high in vitro stability with only 3.5 – 4.5 % decomposition out to 66 hr. The complexes in vivo exhibited low blood uptake and rapid clearance through the urine. The urine contained 57.8 % of the injected dose of ⁶⁴Cu-ENOTA and 65.8 % of ⁶⁴Cu-PNOTA at 15 min after injection. The urine excretion increased to > 95 % at 2 hr for both complexes. The % ID in the blood was 5.7% for ⁶⁴Cu-ENOTA and 6.0% for ⁶⁴Cu-PNOTA at 15 min. This rapidly decreased to less than 0.8 % ID at 2 hr. The highest liver uptake for ⁶⁴Cu-ENOTA was detected at 15 min with 1.7 % ID that dropped to 0.6 % ID at 1 hr. The liver uptake decreased to 0.4 % ID at 4 hr and remained constant out to 48 hr. The ⁶⁴Cu-PNOTA had the highest liver uptake 2.6 % ID at 15 min. The liver uptake decreased to 0.5 % ID at 48 hr.

Conclusions Both Cu-64 complexes exhibited promising in vitro and in vivo results and are being further investigated.

Research Support DOE De-FG07-03ID14531