In vitro and in vivo characterization of newly developed iodinated 1-[2-[bis(4-fluorophenyl)methoxy]ethyl]piperazine derivatives in rats: limited value as dopamine transporter SPECT ligands

A series of 1-{2-[bis(4-fluorophenyl)methoxy]ethyl}piperazines (CYD1, 2, 3, 5) with a 4-substituent incorporating a 1-hydroxy-3-iodo-2-propenyl moiety, except CYD2 which lacks the hydroxy, was synthesized as potential in vivo imaging ligands for the dopamine transporter. For two of the piperazine derivatives (CYD3 and 5), possible stereoselectivity was considered as well (both E- and Z-form). Their in vitro potency for inhibition of [3H]dopamine uptake in rat striatal synaptosomes was 10-fold lower than that of GBR 12,909 used as a reference. The highest Ki values were 137 and 101 nM for CYD1E and CYD3E, respectively. Inhibition potency was higher for the E- than for the Z-isomers. In vivo distribution of radioactivity in rats injected with the 123I-labeled CYDs showed preferred striatal uptake for CYD1E and CYD3E as compared to the cerebellum and occipital cortex. Although the E-isomer of CYD3 showed the best in vitro and in vivo binding characteristics, its striatal uptake ratios (maximal value: 2.7 for striatum-to-cerebellum at 4 h p.i.) are too low to consider application in human Single Photon Emission Computed Tomography studies