DOPAMINE TRANSPORTER OCCUPANCY BY NOVEL PYROVALERONE ANALOGS, A PET STUDY

Harvard Medical School, Boston MA

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Abstract

This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. AIMS: Compounds that affect dopamine transporter (DAT) function have therapeutic potential to treat cocaine addiction, and other CNS disorders. They also have abuse potential, depending on structure, potency, dose, pharmacokinetic properties and route of administration. The stimulant pyrovalerone is a relatively high affinity DAT inhibitor with limited therapeutic use because of abuse liability. To develop medications with reduced abuse liability, we designed pyrovalerone analogs and assessed in vitro potencies at monoamine transporters (dopamine, serotonin, norepinephrine) and in vivo occupancy of the DAT. METHODS: DAT affinity was determined in HEK-293 cells transfected with the human DAT. DAT occupancy (reduction in binding potential) was measured with PET imaging of the DAT probe (11C)CFT ((11C)WIN 35,428) and anesthetized rhesus monkeys. After acquisition of baseline DAT levels, the test compound was administered and PET imaging performed with a second injection of (11C)CFT one hour later. RESULTS: Novel pyrovalerone analogs exhibited high to moderate DAT potency (3.1 - 216 nM) and moderate to high DAT:SERT selectivity. All compounds (1 mg/kg) occupied 59 percent or more of DAT sites in the striatum. Several compounds with high affinity for the DAT in vitro showed lower DAT occupancy than lower affinity compounds, within the time frame of the PET session. DAT occupancy correlated with lipophilicity (logP values) and not with DAT affinity. CONCLUSIONS: For pyrovalerone analogs, lipophilicity, but not in vitro affinity, predicts in vivo DAT occupancy, Several compounds displayed rapid DAT onset, findings relevant both for therapeutic potential or abuse liability.