[O-methyl-11C]N-(4-(4-(3-Chloro-2-methoxyphenyl)-piperazin-1-yl)butyl)-1H-indole-2-carboxamide ([11C]BAK4-51) Is an Efflux Transporter Substrate and Ineffective for PET Imaging of Brain D₃ Receptors in Rodents and Monkey

Synthesis and biological evaluation of 18F-labelled dopamine D3 receptor selective ligands

The dopamine D₃ receptor (D₃R) is highly expressed in the limbic regions of the brain and closely related to a variety of neurological disorders including Parkinson's disease, schizophrenia and drug-seeking behavior. In vivo imaging of D₃R with radio-labelled tracers and positron emission tomography (PET) has become a powerful technique in related disorders. In this study, we synthesized three novel aromatically ¹⁸F-labelled phenylpiperazine-like D₃R selective radioactive ligands ([¹⁸F]5b, [¹⁸F]8b and [¹⁸F]11b) and developed a simple, rapid and efficient ¹⁸F-labelling method by condition optimization. Radiosynthesis of [¹⁸F]5b, [¹⁸F]8b and [¹⁸F]11b was achieved by ¹⁸F-fluorination from nitroarene precursors. Final radiochemical purities of [¹⁸F]5b, [¹⁸F]8b and [¹⁸F]11b solution were > 99% and remained good stability (> 98% for up to 6 h) in PBS and FBS. PET imaging and cellular binding studies revealed that [¹⁸F]8b had a higher D₃R affinity than [¹⁸F]5b and [¹⁸F]11b. Autoradiography and biodistribution studies of the brain showed that [¹⁸F]8b had medium intensity specific accumulation in the striatum and cortex. Meanwhile, the low skeletal uptake of [¹⁸F]8b revealed a good in vivo stability with negligible defluorination. These results indicated that [¹⁸F]8b might be a potential ¹⁸F-labelled D₃R PET imaging agent.

2016 Philip S. Portoghese Medicinal Chemistry Lectureship: Designing Bivalent or Bitopic Molecules for G-Protein Coupled Receptors. The Whole Is Greater Than the Sum of Its Parts

The genesis of designing bivalent or bitopic molecules that engender unique pharmacological properties began with Portoghese's work directed toward opioid receptors, in the early 1980s. This strategy has evolved as an attractive way to engineer highly selective compounds for targeted G-protein coupled receptors (GPCRs) with optimized efficacies and/or signaling bias. The emergence of X-ray crystal structures of many GPCRs and the identification of both orthosteric and allosteric binding sites have provided further guidance to ligand drug design that includes a primary pharmacophore (PP), a secondary pharmacophore (SP), and a linker between them. It is critical to note the synergistic relationship among all three of these components as they contribute to the overall interaction of these molecules with their receptor proteins and that strategically designed combinations have and will continue to provide the GPCR molecular tools of the future.