Biological Evaluation of ¹⁸F-FHTP as a Potential Dopamine D₄ Receptor PET Imaging Agent

3-(4-¹⁸Ffluorobenzyl)-8-hydroxy-1, 2, 3, 4-tetrahydrochromeno3, 4-c pyridin-5-one (¹⁸F-FHTP) was in vitroand in vivoevaluated as a potential dopamine D₄ receptor PET imaging agent. Through receptor binding assay, the Kiof FHTP were determined to be 2.9 nmol/L for D_4.2 receptor, and to be greater than 3 000 and 5 800 nmol/L for D₃ and D₂ receptor, respectively. The lgP was measured to be 1.11 through octanol experiment. The regional biodistribution studies in rats were carried out through biological distribution and blocking biodistribution experiments. The biodistributions studies show that ¹⁸F-FHTP can penetrate through bloodbrain barrier and selectively accumulate in striatum, hypothalamus, frontal cortex, hippocampus, cerebellum, where the D₄ receptor is reportedly located, and among organs, lung and kidney have higher uptakes than the others. Conclusively, in vitro and in vivo biological studies demonstrate that ¹⁸F-FHTP is a potential dopamine D₄ receptor imaging agent.