PT - JOURNAL ARTICLE AU - Selwyn S. Jayakar AU - Xiaojuan Zhou AU - David C. Chiara AU - Carlos Jarava-Barrera AU - Pavel Y. Savechenkov AU - Karol S. Bruzik AU - Mariola Tortosa AU - Keith W. Miller AU - Jonathan B. Cohen TI - Identifying drugs that bind selectively to intersubunit general anesthetic sites in the α1β3γ2 GABA<sub>A</sub>R transmembrane domain AID - 10.1124/mol.118.114975 DP - 2019 Jan 01 TA - Molecular Pharmacology PG - mol.118.114975 4099 - http://molpharm.aspetjournals.org/content/early/2019/04/05/mol.118.114975.short 4100 - http://molpharm.aspetjournals.org/content/early/2019/04/05/mol.118.114975.full AB - GABAA receptors (GABAARs) are targets for important classes of clinical agents (e.g. anxiolytics, anticonvulsants and general anesthetics) that act as positive allosteric modulators (PAMs). Previously, using photoreactive analogs of etomidate ([3H]azietomidate) and mephobarbital ([3H]R-mTFD-MPAB), we identified two homologous but pharmacologically distinct classes of general anesthetic binding sites in the α1β3γ2 GABAAR transmembrane domain at β+-α- (β+-sites) and α+-β-/γ+-β- (β--sites) subunit interfaces. We now use competition photolabeling with [3H]azietomidate and [3H]R-mTFD-MPAB to identify para-substituted propofol analogs and other drugs that bind selectively to intersubunit anesthetic sites. Propofol and 4-chloro-propofol bind with 5-fold selectivity to β+, while derivatives with bulkier lipophilic substitutions [4-(tert-butyl)-propofol and 4-(hydroxyl(phenyl)methyl)-propofol] bind with ~10-fold higher affinity to β- sites. Similar to R-mTFD-MPAB and propofol, these drugs bind in the presence of GABA with similar affinity to the α+-β- and γ+-β- sites. However, we discovered four compounds that bind with different affinities to the two β- interface sites. Two of these bind with higher affinity to one of the β- sites than to the β+ sites. We deduce that 4-benzoyl-propofol binds with &gt;100- fold higher affinity to the γ+-β- site than to the α+-β- or β+–α- sites, whereas loreclezole, an anticonvulsant, binds with 5- and 100- fold higher affinity to the α+-β- site than to the β+ and γ+-β- sites. These studies provide a first identification of PAMs that bind selectively to a single intersubunit site in the GABAAR transmembrane domain, a property that may facilitate the development of subtype selective GABAAR PAMs.