Summary of extended characterization studies of small molecule KCNQ2 channel inhibitors
Assay Implementation: Haibo Yu Ph.D., Kaiping Xu M.S., Shunyou Long M.S, Alison Neal, Owen McManus Ph.D. ..more
Source (MLPCN Center Name): Johns Hopkins Ion Channel Center (JHICC)
Center Affiliation: Johns Hopkins University, School of Medicine
Screening Center PI: Min Li, Ph.D.
Assay Provider: Min Li, Ph.D.
Network: Molecular Libraries Probe Production Centers Network (MLPCN)
Grant Proposal Number: 1 R03 DA027716-01
Grant Proposal PI: Min Li, Ph.D., Johns Hopkins University School of Medicine
Assay Implementation: Haibo Yu Ph.D., Kaiping Xu M.S., Shunyou Long M.S, Alison Neal, Owen McManus Ph.D.
Name: Summary of extended characterization studies of small molecule KCNQ2 channel inhibitors
KCNQ (Kv7.x) channels are expressed in both central nervous system and peripheral tissues, including cardiac and smooth muscle, and neurons. Unique relative to many other voltage-gated potassium channels, KCNQ channels are activated at voltages close to resting membrane potentials and tightly coupled with GPCR signaling, hence playing a critical role in regulating electrical excitability . The KCNQ family includes five members, KCNQ1 to KCNQ5. KCNQ2-5 channels are primarily expressed in brain, while KCNQ1 is abundantly expressed in cardiac tissue. Mutations in KCNQ1 lead to cardiac arrhythmias , and mutations in either KCNQ2  or KCNQ3  cause benign familial neonatal convulsion (BFNC), a rare form of epilepsy.
A high-throughput screen of the MLPCN library was performed using a thallium influx assay in order to identify inhibitors of KCNQ2 channels. SAR studies of active compounds yielded ML252, a potent (IC50 = 69 nM) inhibitor of KCNQ2 channels in electrophysiological assays . ML252 displayed more than forty-fold selectivity for blocking KCNQ2 and three-fold selectivity for KCNQ4 compared with KCNQ1 channels. ML252 has been profiled against a number of ion channels and a number of GPCRs in profiling assays and has shown excellent selectivity. SAR studies revealed a site on ML252 at which small structural changes caused a functional shift from antagonist to agonist activity, suggesting that ML252 interacted with a critical site for controlling gating of KCNQ2 channels.
However, ML252 exhibited poor metabolic stability when incubated with rat or human liver microsomes, suggesting rapid clearance after systemic exposure. Although there are several reported KCNQ2/3 inhibitors in the primary literature, ML252 is more potent and selective versus the other Kv7.X channels. In its present form, ML252 is fit for in vitro studies of the roles of KCNQ2. Therefore, an extended probe characterization was proposed to improve the metabolic stability of ML252 for in vivo studies.
Here we are reporting the results from the extended characterization studies small chemical compounds that inhibit the KCNQ2 potassium channels.
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KCNQ2, inhibitor, blocker, Concentration Response Curve, JHICC, Johns Hopkins, Molecular Libraries Probe Production Centers Network, MLPCN, extended characterization
Please see Related Bioassays for protocols performed in this probe development effort. For initial probe development in the identification of ML252, see the related summary AID 2262.