title: Structure-activity-relationship study of N-acyl-N-phenylpiperazines as potential inhibitors of the Excitatory Amino Acid Transporters (EAATs): improving the potency of a micromolar screening Hit is not truism.
abstract: The excitatory amino acid transporters (EAATs) are transmembrane proteins responsible for the uptake of (S)-glutamate from the synaptic cleft. To date, five subtypes EAAT1-5 have been identified for which selective inhibitors have been discovered for EAAT1 and EAAT2. By screening of a commercially available compound library consisting of 4,000 compounds, N-acyl-N-phenylpiperazine analog (±)- exo -1 was identified to be a non-selective inhibitor at EAAT1-3 displaying IC50 values in the mid-micromolar range (10 μM, 40 μM and 30 μM at EAAT1, 2 and 3, respectively). Subsequently, we designed and synthesized a series of analogs to explore the structure-activity-relationship of this scaffold in the search for analogs characterized by increased inhibitory potency and/or EAAT subtype selectivity. Despite extensive efforts, all analogs of (±)- exo -1 proved to be either inactive or to have least 3-fold lower inhibitory potency than the lead, and furthermore none of the active analogs displayed selectivity for a particular subtype amongst the EAAT1-3. On the basis of our findings, we speculate that (±)- exo -1 binds to a recess (deepening) on the EAAT proteins than a well-defined pocket.
authors.affiliation: Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Universitetsparken 2, Copenhagen, OE 2100 Denmark.
authors.forename: Tri Hv
authors.initials: TH
authors.lastname: Huynh
authors.affiliation: Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Universitetsparken 2, Copenhagen, OE 2100 Denmark.
authors.forename: Charles S
authors.initials: CS
authors.lastname: Demmer
authors.affiliation: Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Universitetsparken 2, Copenhagen, OE 2100 Denmark.
authors.forename: Bjarke
authors.initials: B
authors.lastname: Abrahamsen
authors.affiliation: Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Universitetsparken 2, Copenhagen, OE 2100 Denmark.
authors.forename: Emil
authors.initials: E
authors.lastname: Marcher
authors.affiliation: Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Universitetsparken 2, Copenhagen, OE 2100 Denmark.
authors.forename: Mikael
authors.initials: M
authors.lastname: Frykman
authors.affiliation: Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Universitetsparken 2, Copenhagen, OE 2100 Denmark.
authors.forename: Anders A
authors.initials: AA
authors.lastname: Jensen
authors.affiliation: Department of Drug Design and Pharmacology, Faculty of Health and Medical Sciences, University of Copenhagen, Universitetsparken 2, Copenhagen, OE 2100 Denmark.
authors.forename: Lennart
authors.initials: L
authors.lastname: Bunch
keywords: EAATs; Excitatory amino acid transporters; Medicinal chemistry; Rational ligand design