title: ML418: The First Selective, Sub-Micromolar Pore Blocker of Kir7.1 Potassium Channels.
abstract: The inward rectifier potassium (Kir) channel Kir7.1 (KCNJ13) has recently emerged as a key regulator of melanocortin signaling in the brain, electrolyte homeostasis in the eye, and uterine muscle contractility during pregnancy. The pharmacological tools available for exploring the physiology and therapeutic potential of Kir7.1 have been limited to relatively weak and nonselective small-molecule inhibitors. Here, we report the discovery in a fluorescence-based high-throughput screen of a novel Kir7.1 channel inhibitor, VU714. Site-directed mutagenesis of pore-lining amino acid residues identified glutamate 149 and alanine 150 as essential determinants of VU714 activity. Lead optimization with medicinal chemistry generated ML418, which exhibits sub-micromolar activity (IC50 = 310 nM) and superior selectivity over other Kir channels (at least 17-fold selective over Kir1.1, Kir2.1, Kir2.2, Kir2.3, Kir3.1/3.2, and Kir4.1) except for Kir6.2/SUR1 (equally potent). Evaluation in the EuroFins Lead Profiling panel of 64 GPCRs, ion-channels, and transporters for off-target activity of ML418 revealed a relatively clean ancillary pharmacology. While ML418 exhibited low CLHEP in human microsomes which could be modulated with lipophilicity adjustments, it showed high CLHEP in rat microsomes regardless of lipophilicity. A subsequent in vivo PK study of ML418 by intraperitoneal (IP) administration (30 mg/kg dosage) revealed a suitable PK profile (Cmax = 0.20 μM and Tmax = 3 h) and favorable CNS distribution (mouse brain/plasma Kp of 10.9 to support in vivo studies. ML418, which represents the current state-of-the-art in Kir7.1 inhibitors, should be useful for exploring the physiology of Kir7.1 in vitro and in vivo.
authors.forename: Daniel R
authors.initials: DR
authors.lastname: Swale
authors.forename: Haruto
authors.initials: H
authors.lastname: Kurata
authors.forename: Sujay V
authors.initials: SV
authors.lastname: Kharade
authors.affiliation: Department of Chemistry, Vanderbilt University , Nashville, Tennessee 37232, United States.
authors.forename: Jonathan
authors.initials: J
authors.lastname: Sheehan
authors.forename: Rene
authors.initials: R
authors.lastname: Raphemot
authors.forename: Karl R
authors.initials: KR
authors.lastname: Voigtritter
authors.forename: Eric E
authors.initials: EE
authors.lastname: Figueroa
authors.affiliation: Department of Chemistry, Vanderbilt University , Nashville, Tennessee 37232, United States.
authors.forename: Jens
authors.initials: J
authors.lastname: Meiler
authors.forename: Anna L
authors.initials: AL
authors.lastname: Blobaum
authors.forename: Craig W
authors.initials: CW
authors.lastname: Lindsley
authors.forename: Corey R
authors.initials: CR
authors.lastname: Hopkins
authors.forename: Jerod S
authors.initials: JS
authors.lastname: Denton
mesh_terms: D000818:Animals; D004305:Dose-Response Relationship, Drug; D057809:HEK293 Cells; D006801:Humans; D008564:Membrane Potentials / Q000187:drug effects / Q000235:genetics; D008958:Models, Molecular; D016297:Mutagenesis, Site-Directed; D009154:Mutation / Q000235:genetics; D018408:Patch-Clamp Techniques; D011188:Potassium / Q000378:metabolism; D026902:Potassium Channel Blockers / Q000737:chemistry* / Q000494:pharmacology*; D024661:Potassium Channels, Inwardly Rectifying / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D013329:Structure-Activity Relationship; D013997:Time Factors; D014162:Transfection
chemical_list: C489477:Kir7.1 channel; D026902:Potassium Channel Blockers; D024661:Potassium Channels, Inwardly Rectifying; D011188:Potassium
keywords: KCNJ13; comparative modeling; electrophysiology; melanocortin signaling; myometrium; thallium flux