- Email: [email protected]
Kv7 channels as targets for anti-epileptic and psychiatric drug-development
European Journal of Pharmacology 726 (2014) 133–137
Contents lists available at ScienceDirect
European Journal of Pharmacology journal homepage: www.elsevier.com/locate/ejphar
Perspective
Kv7 channels as targets for anti-epileptic and psychiatric drug-development Morten Grunnet a, Dorte Strøbæk b, Charlotte Hougaard b, Palle Christophersen b,n a b
Lundbeck Pharma A/S, Ottiliavej 9 Valby, DK2500, Denmark Aniona Aps, Baltorpvej 154, Ballerup DK2750, Denmark
art ic l e i nf o
a b s t r a c t
Article history: Received 6 November 2013 Received in revised form 16 December 2013 Accepted 6 January 2014 Available online 20 January 2014
The Kv7 channels, a family of voltage-dependent K þ channels (Kv7.1–Kv7.5), have gained much attention in drug discovery especially because four members are genetically linked to diseases. For disorders of the CNS focus was originally on epilepsy and pain, but it is becoming increasingly evident that Kv7 channels can also be valid targets for psychiatric disorders, such as anxiety and mania. The common denominator is probably neuronal hyperexcitability in different brain areas, which can be successfully attenuated by pharmacological increment of Kv7 channel activity. This perspective attempts to review the current status and challenges for CNS drug discovery based on Kv7 channels as targets for neurological and psychiatric indications with special focus on selectivity and mode-of-actions. & 2014 Elsevier B.V. All rights reserved.
Keywords: KCNQ Kv7 Anti-manic Anti-psychotic Anti-convulsion Mode-of-action
1. Kv7 channels in health and diseases With around 150 members, ion channels constitute one of the largest groups of signaling molecules in the human genome only surpassed in numbers by G protein coupled receptors and protein kinases (Harmar et al., 2009). Basically, channels conduct ions passively across the cell membrane, in the direction dictated by the electrochemical gradient. All ion channels conduct with specified (often high) selectivity and a reductionists view might predict the need for only few types, selective for K þ , Na þ , Cl and Ca2 þ —the main physiological ions. Obviously this is not the case. Ion channels are extremely diverse with respect to activation/ inactivation properties, cellular distribution patterns, and molecular interaction partners, which is basic to their versatile and subtle influences on nearly all physiological functions. Consequently, malfunction of ion channels is associated to several pathophysiological conditions. The K þ channel family is particular numerous, with a variety of structural and functional members, constituting approximately half of all ion channels described (Wulff et al., 2009). The voltage-dependent Kv7 channels (Kv7.1–Kv7.5) have gained substantial interest due to links to diseases (Jentsch, 2000) and overall tractability as pharmacological targets. Kv7.1 is a non-neuronal
n
Corresponding author. Tel.: þ 45 30617783. E-mail address: [email protected] (P. Christophersen).
0014-2999/$ - see front matter & 2014 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.ejphar.2014.01.017
channel involved in repolarisation of cardiac action potentials and epithelial transport (Jespersen et al., 2005). Kv7.2–Kv7.5 are widely expressed and active in neuronal tissue (Brown and Passmore, 2009) with Kv7.2 (usually in assembly with Kv7.3) being exclusively neuronal, whereas Kv7.4, Kv7.5 and (less pronounced) Kv7.3 are also expressed in skeletal—and smooth muscle cells (Mackie and Byron, 2008; Ng et al., 2011). Neuronal Kv7 channels are expressed as tetramers, assempled in homomeric (Kv7.2; Kv7.4; Kv7.5) or heteromeric (Kv7.2/Kv7.3; Kv7.4/Kv7.3; Kv7.5/Kv7.3; Kv7.4/ Kv7.5) channel complexes (Bal et al., 2008). Traditionally, dysfunctional Kv7 channels have been associated to epilepsy and deafness, but the area seems to broaden and encompass also hyperactivity conditions associated to pain and psychiatric diseases. From a mechanistic and distribution perspective this makes sense: All neuronal Kv7 channels open at subthreshold depolarizations around 60 mV with quite slow activation kinetics (Fig. 2) and display only modest inactivation at prolonged depolarizations (Jensen et al., 2007). This, in combination with their subcellular localisation in the soma/axon/axon initial segment (Rasmussen et al., 2007), makes Kv7 channels ideally adapted to control neuronal resting potentials as well as transmitter generated or endogeneous plateau potentials, and thereby generation of action potentials (Shah et al., 2008). In contrast to other faster activating Kv families, Kv7 channels usually don0 t activate during individual action potentials and thus play little specific role in the repolarization of these. Thus, pharmacological activation of Kv7 channels tend to hyperpolarize neurons, counteract slow depolarizations
134
M. Grunnet et al. / European Journal of Pharmacology 726 (2014) 133–137
Fig. 1. Kv7 channel modulators affect the excitability of hippocampal CA1 neurons. Action potential firing recorded from a CA1 neuron in a rat hippocampal slice upon application of 600 ms long depolarizing current pulses. Note the slight hyperpolarization and the markedly reduced excitability in the presence of the Kv7 channel activator retigabine (10 mM), an effect that is completely reversed by compound wash-out. A slight depolarization and increased action potential frequency is observed by subsequent application of the Kv7 channel inhibitor XE991 (10 mM). The pronounced after hyperpolarization following the depolarizing current pulse is largely unaffected by the pharmacological agents, indicating that other K þ channels than Kv7 mediate this effect.
Fig. 2. Kv7 activators exert different mode-of-actions. Kv7 channels are voltage-dependent channels with a steady-state activation curve as illustrated by the black curve in all three panels. The channels start activating at or near the resting membrane potential (vertical dashed line) and become increasingly active as the membrane potential gets more positive. Kv7 channel activation/inactivation kinetics is slow and the channels therefore primarily react to prolonged physiological/pathophysiological voltage changes, such as slow synaptic potentials and endogenous plateau potentials, but not during the fast action potentials. Different pharmacological Kv7 activators may exert very different concentration-dependent effects on channel activation (the effects of two different concentrations are illustrated, the more intensely coloured curves representing the higher concentrations): Left panel: The red curves represent an example of a “clean” effect on the voltage–activation curve resulting in a left-shifting towards more negative membrane potentials (retigabine). Middle panel: The blue curves represent an example of a combined effect on the voltage–activation curve and induction of a voltage-independent component observed at more hyperpolarized potentials (BMS-204352). Right panel: The green curves represent an example of a combined left-ward shifting effect on voltage–activation curve and depression of current at more depolarized potentials resulting in a concentration dependent “cross over” profile (NS15370). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
and decrease excitability, whereas their inhibition leads to slight depolarization and increased excitability (Fig. 1). The present perspective gives an introduction to CNS-diseases associated to Kv7 channel function. In addition, their role as pharmacological targets for neurological and psychiatric diseases is discussed, together with our personal opinions on the likely characteristics of novel Kv7-based drugs in terms of selectivity and mode-of-actions. Diseases outside the CNS will not be covered.
2. Kv7 channels as targets in neurology The first direct evidence of involvement of Kv7 channels in a disease came with the association of benign familial neonatal seizures and loss-of-function mutations in the KCNQ2 and KCNQ3 genes encoding Kv7.2 and Kv7.3, respectively (Biervert et al., 1998; Charlier et al., 1998; Bellini et al., 2010). Later Kv7.4 channels were included with the notion that single nucleotide polymorphisms or loss-of-function mutations were associated to age-related hearing impairment and to autosomal dominant deafness (Kubisch et al., 1999; Van Eyken et al., 2006). Despite lack of genetic links, Kv7 channels constitutes wellvalidated targets for development of novel analgesics. Expression of Kv7 channels (Kv7.2, Kv7.3 and Kv7.5) is evident in various parts of the pain sensory pathway, such as Aδ and C-fibres in dorsal root ganglia, as well as in brain areas involved in higher pain perception, like the somatosensory cortex and thalamus (Passmore et al., 2003; Wickenden and McNaughton-Smith, 2009).
Two drugs interacting with Kv7 channels have reached the marked for neurological indications. Flupirtine, a non-opioid, centrally acting analgesic and muscle relaxing agent, has been marketed for decades in Germany (despite no initial recognition of its Kv7 channel activation, see Szelenyi, 2013). The close analogue, retigabine (Fig. 1), has demonstrated efficacy in a number of preclinical seizure and epilepsy models including seizures induced chemically by injection of pentylenetetrazole, electrically by maximal electroshock, 6 Hz stimulation, and amygdala kindling, as well as by sound (Large et al., 2012). Retigabine (ezogabine) was finally marketed as a first-in-class, anti-epileptic drug for treatment resistant partial-onset seizures (Gunthorpe et al., 2012).
3. Kv7 channels as targets in psychiatry Genetic links between psychiatric diseases and Kv7 channels are sparse. However, a recent finding of a translocation truncation in KCNQ3 and specific loss-of-function of heterologously expressed Kv7.3/Kv7.5 channels has been associated to autism spectrum disorders (Gilling et al., 2013). Additional (primarily pharmacological) evidence exist for a broader involvement of Kv7 channels in psychiatric and cognitive disorders. The first indications dates back to before KCNQ cloning from experiments showing that increased excitability and acetylcholine release (via Kv7 channel inhibition) by linopirdine and XE991 (Fig. 1) could improve learning and memory in animals (Fontana et al., 1994; Zaczek et al., 1998). Unfortunately, the pre-clinical results did not translate into clinical efficacy (Börjesson et al., 2013) possibly related to a low therapeutic index.
M. Grunnet et al. / European Journal of Pharmacology 726 (2014) 133–137
With the emergence of the Kv7 channel activators focus have increasingly turned in the direction of disorders like mania, bipolar disorders, attention deficit hyperactivity disorder, schizophrenia, and anxiety. The efficacy of (in particular) retigabine in rodent models of these indications were increasingly associated with hyperexcitability or disturbed neuronal firing in the basal ganglia and limbic system. It was demonstrated that Kv7 channel activation reduces amphetamine þchlordiazepoxide-induced hyperactivity and attenuates induced locomotor activity administration of amphetamine (Redrobe and Nielsen, 2009; Dencker and Husum, 2010; Hansen et al., 2007; Dalby-Brown et al., 2013). The likely mechanism behind these effects was associated to reduced basal dopaminergic firing and suppression of bursting in the ventral tegmental area (Hansen et al., 2006; Sotty et al., 2009) thereby accentuating the dopaminergic component of psychosis and mania disorders. Dampening of hyperactivity of the amygdala and the dorsal raphe nucleus (DRN) have been discussed as rationales for the anxiolytic effect of Kv7 channel activators in rodent models (Korsgaard et al., 2005; Hansen et al., 2008). Interestingly, among the Kv7 channel subunits only Kv7.4 seemed to be expressed in DRN, thereby, at least from a theoretical perspective (but see below), giving the possibility for development of selective Kv7.4 activators to target anxiety conditions.
4. Modulation of Kv7 channels as a treatment principle The primary mode-of-action for retigabine (and flupirtine) is to stabilise the Kv7 open channel conformation and left-ward shift the activation curve towards more negative membrane potentials (Main et al., 2000; Schrøder et al., 2001; Tatulian and Brown, 2003), as illustrated in Fig. 2 (left panel). Retigabine acts on all neuronal Kv7 channels with limited selectivity between the subtypes (Fig. 3) and furthermore possesses significant activation of GABAA receptors (Otto et al., 2002). The relatively poor selectivity properties makes it uncertain which Kv7 subtype (or channel) exert both therapeutic and adverse effects of retigabine. Various attempts have been done to circumvent these flaws, and in the literature a number of compounds with different characteristics have appeared from Bristol-Myers Squibb, Icagen, NeuroSearch, NIH molecular libraries, Charité-Universitätsmedizin Berlin, Tel-Aviv University, and Lundbeck (Wu et al., 2004; Padilla et al., 2009; Boehlen et al., 2013; Yu et al., 2010; Peretz et al., 2012; Dalby-Brown et al., 2013). Of particular interest is the emergence of very potent Kv7 activators without effect on GABAA receptors, the delineation of new sites-of-action, and – in particular – the emerging subtype selectivity and novel mode-of-actions of several of these compounds. The overall picture suggests that Kv7.2
135
(/Kv7.3) activators with reduced Kv7.4 and/or Kv7.5 (/Kv7.3) activity (and without GABAA effect) maintain anti-epileptic and analgesic properties. It is also noteworthy that BMS-204352 (maxipost), a compound which preferentially activates Kv7.4 and Kv7.5-containing channels (Fig. 3) (but also other K þ channels), was as effective as retigabine in animal models of anxiety (Korsgaard et al., 2005) possibly exemplifying the aforementioned role of Kv7.4 in serotonergic neurons. Unfortunately, Kv7.4 and Kv7.5 channels are also principal subtypes expressed in peripheral smooth muscles, which is consistent with a potent smooth muscle relaxing effect of BMS204352 (Jepps et al., 2011). Peripheral clinical adverse reactions of retigabine, such as urinary retention (Brickel et al., 2012), may also be due to activation of these subtypes. Despite not yet systematically explored across chemical compound series and across different Kv7 subtypes, it is obvious that different Kv7 activators affects the channels very differently, which are often ignored, but may eventually translate into in vivo pharmacological significance. The “clean” concentration-dependent leftshifting of the voltage–activation curve (Fig. 2, left panel) is in our experience just one way of positive modulation encountered during drug discovery programs. As exemplified from the literature: BMS204352 induces a voltage-independent component as well as the left-shifting (Schrøder et al., 2003) (Fig. 2, middle panel), whereas the acrylamide S-2 and in particular a recently described molecule, NS15370, exerts a complex activation/inhibiting mode-of-action (Blom et al., 2009; Dalby-Brown et al., 2013) on all neuronal Kv7 subtypes: At very low concentrations (100 times more potent than retigabine) NS15370 acts as an activator at all membrane potentials and causes the conventional left-shift in the steady-state activation curve. At slightly higher concentrations, however, the compound augments current only at small depolarising steps but “crosses over” and reduces the current at larger depolarisations (Fig. 2, right panel). Intuitively such a profile might be speculated to hamper in vivo effectiveness. However, NS15370 was found to show good efficacy across a number of rodent models of psychiatric and neurological diseases (Dalby-Brown et al., 2013), which may point towards a subtle interplay between stabilizing neurons by clamping the cells at hyperpolarized potentials while allowing for activity (maybe even increased activity) under certain depolarized conditions. An inspiring finding, done by Vincent Seutin and co-workers (Drion et al., 2010), shows that Kv7 channels exert minor effect on basic pacemaker activity of dopaminergic neurons, but become important for controlling spike frequency architecture during strongly depolarized burst periods, which is thought to be important for reward based learning. Even only speculative at this stage, NS15370 may well exemplify that significantly more work needs to be done in order to link a specific electrophysiological “fingerprint” of a Kv7 channel modulator to corresponding optimal in vivo
Fig. 3. Kv7 activators exert different subtype selectivity. Comparison of the relative potencies of 4 different Kv7 channel activators (retigabine, acrylamide S-1, BMS-204352, and ICA-27243) on different monomeric and heteromeric Kv7 channels expressed in human embryonic kidney cells. Due to the very different mode-of-actions of some of these compounds (see Fig. 2) it is hard to give an accurate numeric potency measure for all combinations (a general problem in Kv7 based drug discovery). The current ranking is based on FLIPR detection of Tl þ -flux (a surrogate tracer ion for K þ ) compared with manual patch clamp analyses. Redrawn from Jørgensen et al., 2011.
136
M. Grunnet et al. / European Journal of Pharmacology 726 (2014) 133–137
efficacy. Despite lack of solid evidence we also consider the possibility that the optimal mode-of-action may differ from one indication to another.
5. General conclusions and further perspectives As summarized, Kv7.2–7.5 channels show strong biological and pharmacological links to both neurological and psychiatric diseases. In that context it is surprising that, despite significant efforts in the pharmaceutical industry, only two Kv7 active drugs – both “first generation Kv7 activators” – have reached the market. Even though the registration of retigabine as a first-in-class anti-epileptic is promising, it has also revealed that the drug potential of novel Kv7 channel activators depends on the successful improvement of several clinical challenges, such as the need for a high and frequent dosing regimen as well as a relative small therapeutic index primarily defined by sedative and urinary safety adverse effects.
It is our view that future Kv7 programs should focus on the
development of subtype-selective molecules, and for CNS we give specific Kv7.2 (/Kv7.3) candidates the highest chance of success. The wide spectrum of mode-of-actions exerted by different compounds (discovered largely by serendipity) is a potential – but largely unexplored – handle to sharpen a desired therapeutic profile and mitigate adverse reactions. We think that medium to high throughput electrophysiological screening platforms are essential in order to fully exploit the versatility of drug interactions with Kv7 channels. We envision that new programs might benefit from a directed effort towards focused screening for molecules interacting with sites distinct from the retigabine site. We strongly encourage early identification of Kv7-specific radiolabeled ligands suitable for target engagement studies in vivo.
References Bal, M., Zhang, J., Zaika, O., Hernandez, C.C., Shapiro, M.S., 2008. Homomeric and heteromeric assembly of KCNQ (Kv7) K þ channels assayed by total internal reflection fluorescence/fluorescence resonance energy transfer and patch clamp analysis. J. Biol. Chem. 283 (45), 30668–30676. Bellini, G., Miceli, F., Soldovieri, M.V., Miraglia, del Giudice E., Coppola, G., Taglialatela, M., 2010. KCNQ2-related disorders. In: Pagon, R.A., Adam, M.P., Bird, T.D., Dolan, C.R., Fong, C.T., Stephens, K. (Eds.), GeneReviews™ [Internet]. Seattle (WA): University of Washington, Seattle, pp. 1993–2013 Biervert, C., Schroeder, B.C., Kubisch, C., Berkovic, S.F., Propping, P., Jentsch, T.J., Steinlein, O.K., 1998. A potassium channel mutation in neonatal human epilepsy. Science 279 (5349), 403–406. Blom, S.M., Schmitt, N., Jensen, H.S., 2009. The acrylamide (S)-2as a positive and negative modulator of Kv7 channels expressed in Xenopus laevis oocytes. PLoS One 4 (12), e8251 1–12. Boehlen, A., Schwake, M., Dost, R., Kunert, A., Fidzinski, P., Heinemann, U., Gebhardt, C., 2013. The new KCNQ2 activator 4-chlor-N-(6-chlor-pyridin-3-yl)-benzamid displays anticonvulsant potential. Br. J. Pharmacol. 168 (5), 1182–1200. Börjesson, A., Karlsson, T., Adolfsson, R., Rönnlund, M, Nilsson, L., 2013. Linopirdine (DUP 996): cholinergic treatment of older adults using successive and nonsuccessive tests. Neuropsychobiology 40 (2), 78–85. Brickel, N., Gandhi, P., VanLandingham, K., Hammond, J., DeRossett, S., 2012. The urinary safety profile and secondary renal effects of retigabine (ezogabine): a first-in-class antiepileptic drug that targets KCNQ Kv7 potassium channels. Epilepsia 53 (4), 606–612. Brown, D.A., Passmore, G.M., 2009. Neural KCNQ (Kv7) channels. Br. J. Pharmacol. 156 (8), 1185–1195. Charlier, C., Singh, N.A., Ryan, S.G., Lewis, T.B., Reus, B.E., Leach, R.J., Leppert, M., 1998. A pore mutation in a novel KQT-like potassium channel gene in an idiopathic epilepsy family. Nat. Genet. 18 (1), 53–55. Dalby-Brown, W., Jessen, C., Hougaard, C., Jensen, M.L., Jacobsen, T.A., Nielsen, K.S., Erichsen, H.K., Grunnet, M., Ahring, P.K., Christophersen, P., Strøbæk, D., Jørgensen, S., 2013. Characterization of a novel high-potency positive modulator of Kv7 channels. Eur. J. Pharmacol. 709 (1-3), 52–63. Dencker, D., Husum, H., 2010. Antimanic efficacy of retigabine in a proposed mouse model of bipolar disorder. Behav. Brain Res. 207 (1), 78–83.
Drion, G., Bonjean, M., Waroux, O., Scuvée-Moreau, J., Liégeois, J.F., Sejnowski, T.J., Sepulchre, R., Seutin, V., 2010. M-type channels selectively control bursting in rat dopaminergic neurons. Eur. J. Neurosci. 31 (5), 827–835. Van Eyken, E., Van Laer, L., Fransen, E., Topsakal, V., Lemkens, N., Laureys, W., Nelissen, N., Vandevelde, A., Wienker, T., Van De Heyning, P., Van Camp., G., 2006. KCNQ4: a gene for age-related hearing impairment? Hum. Mutat. 27 (10), 1007–1016. Fontana, D.J., Inouye, G.T., Johnson, R.M., 1994. Linopirdine (DuP 996) improves performance in several tests of learning and memory by modulation of cholinergic neurotransmission. Pharmacol. Biochem. Behav. 49 (4), 1075–1082. Gilling, M., Rasmussen, H.B., Calloe, K., Sequeira, A.F., Baretto, M., Oliveira, G., Almeida, J., Lauritsen, M.B., Ullmann, R., Boonen, S.E., Brondum-Nielsen, K., Kalscheuer, V.M., Tümer, Z., Vicente, A.M., Schmitt, N., Tommerup, N., 2013. Dysfunction of the heteromeric Kv7.3/Kv7.5 potassium channel is associated with autism spectrum disorders. Front. Genet. 4, 54. Gunthorpe, M.J., Large, C.H., Sankar, R., 2012. The mechanism of action of retigabine (ezogabine), a first-in-class K þ channel opener for the treatment of epilepsy. Epilepsia 53 (3), 412–424. Hansen, H.H., Ebbesen, C., Mathiesen, C., Weikop, P., Rønn, L.C., Waroux, O., ScuvéeMoreau, J., Seutin, V., Mikkelsen, J.D., 2006. The KCNQ channel opener retigabine inhibits the activity of mesencephalic dopaminergic systems of the rat. J. Pharmacol. Exp. Ther. 318 (3), 1006–1019. Hansen, H.H., Andreasen, J.T., Weikop, P., Mirza, N., Scheel-Krüger, J., Mikkelsen, J.D., 2007. The neuronal KCNQ channel opener retigabine inhibits locomotor activity and reduces forebrain excitatory responses to the psychostimulants cocaine, methylphenidate and phencyclidine. Eur. J. Pharmacol. 570 (1-3), 77–88. Hansen, H.H., Waroux, O., Seutin, V., Jentsch, T.J., Aznar, S., Mikkelsen, J.D., 2008. Kv7 channels: interaction with dopaminergic and serotonergic neurotransmission in the CNS. J. Physiol. 586 (7), 1823–1832. Harmar, A.J., Hills, R.A., Rosser, E.M., Jones, M., Buneman, O.P., Dunbar, D.R., Greenhill, S.D., Hale, V.A., Sharman, J.L., Bonner, T.I., Catterall, W.A., Davenport, A.P., Delagrange, P., Dollery, C.T., Foord, S.M., Gutman, G.A., Laudet, V., Neubig, R.R., Ohlstein, E.H., Olsen, R.W., Peters, J., Pin, J.P., Ruffolo, R.R., Searls, D.B., Wright, M.W., Spedding, M., 2009. IUPHAR-DB: the IUPHAR database of G protein-coupled receptors and ion channels. Nucleic Acids Res. (Database issue), D680–D685 Jensen, H.S., Grunnet, M., Olesen, S.P., 2007. Inactivation as a new regulatory mechanism for neuronal Kv7 channels. Biophys. J. 92 (8), 2747–2756. Jentsch, T.J., 2000. Neuronal KCNQ potassium channels: physiology and role in disease. Nat. Rev. Neurosci. 2000 (1), 21–30. Jepps, T.A., Chadha, P.S., Davis, A.J., Harhun, M.I., Cockerill, G.W., Olesen, S.P., Hansen, R.S., Greenwood, I.A., 2011. Downregulation of Kv7.4 channel activity in primary and secondary hypertension. Circulation 124 (5), 602–611. Jespersen, T., Grunnet, M., Olesen, S.P., 2005. The KCNQ1 potassium channel: from gene to physiological function. Physiology (Bethesda) 20, 408–416. Jørgensen, S., Jensen, M.L., Hougaard, C. Dyhring, T. Christophersen, P., Strøbæk D., 2011. Subtype-dependent potencies and mode-of-actions for the Kv7 positive modulators retigabine, ICA-27243, BMS-204352 and (S)-1. Society for Neuroscience Meeting. P139.01. Kubisch, C., Schroede,r, B.C., Friedrich, T., Lütjohann, B., El-Amraoui, A., Marlin, S., Petit, C., Jentsch, T.J., 1999. KCNQ4, a novel potassium channel expressed in sensory outer hair cells, is mutated in dominant deafness. Cell 96 (3), 437–446. Korsgaard, M.P., Hartz, B.P., Brown, W.D., Ahring, P.K., Strøbaek, D., Mirza, N.R., 2005. Anxiolytic effects of Maxipost (BMS-204352) and retigabine via activation of neuronal Kv7 channels. J. Pharmacol. Exp. Ther. 314 (1), 282–292. Large, C.H., Sokal, D.M., Nehlig, A., Gunthorpe, M.J., Sankar, R., Crean, C.S., Vanlandingham, K.E., White, H.S., 2012. The spectrum of anticonvulsant efficacy of retigabine (ezogabine) in animal models: implications for clinical use. Epilepsia 53 (3), 425–436. Mackie, A.R., Byron, K.L., 2008. Cardiovascular KCNQ (Kv7) potassium channels: physiological regulators and new targets for therapeutic intervention. Mol. Pharmacol. 74 (5), 1171–1179. Main, M.J., Cryan, J.E., Dupere, J.R., Cox, B., Clare, J.J., Burbidge, S.A., 2000. Modulation of KCNQ2/3 potassium channels by the novel anticonvulsant retigabine. Mol. Pharmacol. 58 (2), 253–262. Ng, F.L., Davis, A.J., Jepps, T.A., Harhun, M.I., Yeung, S.Y., Wan, A., Reddy, M., Melville, D., Nardi, A., Khong, T.K., Greenwood, I.A., 2011. Expression and function of the K þ channel KCNQ genes in human arteries. Br. J. Pharmacol. 162 (1), 42–53. Otto, J.F., Kimball, M.M., Wilcox, K.S., 2002. Effects of the anticonvulsant retigabine on cultured cortical neurons: changes in electroresponsive properties and synaptic transmission. Mol. Pharmacol. 61 (4), 921–927. Padilla, K., Wickenden, A.D., Gerlach, A.C., McCormack, K., 2009. The KCNQ2/3 selective channel opener ICA-27243 binds to a novel voltage-sensor domain site. Neurosci. Lett. 465 (2), 138–142. Passmore, G.M., Selyanko, A.A., Mistry, M., Al-Qatari, M., Marsh, S.J., Matthews, E.A., Dickenson, A.H., Brown, T.A., Burbidge, S.A., Main, M., Brown, D.A., 2003. KCNQ/ M currents in sensory neurons: significance for pain therapy. J. Neurosci. 23 (18), 7227–7236. Peretz, A., Pell, L., Gofman, Y., Haitin, Y., Shamgar, L., Patrich, E., Kornilov, P., GourgyHacohen, O., Ben-Tal, N., Attali, B., 2012. Targeting the voltage sensor of Kv7.2 voltage-gated K þ channels with a new gating-modifier. Proc. Nat. Acad. Sci. U.S.A. 107 (35), 15637–15642. Rasmussen, H.B., Frøkjaer-Jensen, C., Jensen, C.S., Jensen, H.S., Jørgensen, N.K., Misonou, H, Trimmer, J.S., Olesen, S.P., Schmitt, N., 2007. Requirement of
M. Grunnet et al. / European Journal of Pharmacology 726 (2014) 133–137
subunit co-assembly and ankyrin-G for M-channel localization at the axon initial segment. J. Cell. Sci. 120 (Pt 6), 953–963. Redrobe, J.P., Nielsen, A.N., 2009. Effects of neuronal Kv7 potassium channel activators on hyperactivity in a rodent model of mania. Behav. Brain Res. 198 (2), 481–485. Schrøder, R.L., Jespersen, T., Christophersen, P., Strøbæk, D., Jensen, B.S., Olesen, S.P., 2001. KCNQ4 channel activation by BMS-204352 and retigabine. Neuropharmacology 40 (7), 888–898. Schrøder, R.L., Strøbæk, D., Olesen, S.P., Christophersen, P., 2003. Voltageindependent KCNQ4 currents induced by ( þ / )BMS-204352. Pflugers Arch. 446 (5), 607–616. Shah, M.M., Migliore, M., Valencia, I., Cooper, E.C., Brown, D.A., 2008. Functional significance of axonal Kv7 channels in hippocampal pyramidal neurons. Proc. Nat. Acad. Sci. U.S.A. 2008 105 (22), 7869–7874. Sotty, F., Damgaard, T., Montezinho, L.P., Mørk, A., Olsen, C.K., Bundgaard, C., Husum, H., 2009. Antipsychotic-like effect of retigabine [N-(2-amino-4-(fluorobenzylamino)-phenyl)carbamic acid ester], a KCNQ potassium channel opener, via modulation of mesolimbic dopaminergic neurotransmission. J. Pharmacol. Exp. Ther. 328 (3), 951–962. Szelenyi, I., 2013. Flupirtine, a re-discovered drug, revisited. Inflamm. Res. 62 (3), 251–258. Tatulian, L., Brown, D.A., 2003. Effect of the KCNQ potassium channel opener retigabine on single KCNQ2/3 channels expressed in CHO cells. J. Physiol. 549 (Pt 1), 57–63.
137
Wickenden, A.D., McNaughton-Smith, G., 2009. Kv7 channels as targets for the treatment of pain. Curr. Pharm. Des. 15 (15), 1773–1798. Wu, Y.J., Boissard, C.G., Chen, J., Fitzpatrick, W., Gao, Q., Gribkoff, V.K., Harden, D.G., He, H., Knox, R.J., Natale, J., Pieschl, R.L., Starrett , J.E., Sun, L.Q., Thompson, M., Weaver, D., Wu, D., Dworetzky, S.I., 2004. (S)-N-[1-(4-cyclopropylmethyl-3,4-dihydro-2H-benzo [1,4]oxazin-6-yl)-ethyl]-3-(2-fluoro-phenyl)-acrylamide is a potent and efficacious KCNQ2 opener which inhibits induced hyperexcitability of rat hippocampal neurons. Bioorg. Med. Chem. Lett. 14 (8), 1991–1995. Wulff, H., Castle, N.A., Pardo, L.A., 2009. Voltage-gated potassium channels as therapeutic targets. Nat. Rev. Drug Discovery 12, 982–1001. Yu, H., Wu, M., Hopkins, C., Engers, J., Townsend, S., Lindsley, C., McManus, O.B., Li, M., 2010. A Small Molecule Activator of KCNQ2 and KCNQ4 Channels. Probe Reports from the NIH Molecular Libraries Program [Internet]. Bethesda (MD): National Center for Biotechnology Information (US); 2010-2011 Mar 29 [updated 2013 Feb 28]. Zaczek, R., Chorvat, R.J., Saye, J.A., Pierdomenico, M.E., Maciag, C.M., Logue, A.R., Fisher, B.N., Rominger, D.H., Earl, R.A., 1998. Two new potent neurotransmitter release enhancers, 10,10-bis(4-pyridinylmethyl)-9(10H)-anthracenone and 10,10-bis(2-fluoro-4-pyridinylmethyl)-9(10H)-anthracenone: comparison to linopirdine. J. Pharmacol. Exp. Ther. 285 (2), 724–730.
Contents lists available at ScienceDirect
European Journal of Pharmacology journal homepage: www.elsevier.com/locate/ejphar
Perspective
Kv7 channels as targets for anti-epileptic and psychiatric drug-development Morten Grunnet a, Dorte Strøbæk b, Charlotte Hougaard b, Palle Christophersen b,n a b
Lundbeck Pharma A/S, Ottiliavej 9 Valby, DK2500, Denmark Aniona Aps, Baltorpvej 154, Ballerup DK2750, Denmark
art ic l e i nf o
a b s t r a c t
Article history: Received 6 November 2013 Received in revised form 16 December 2013 Accepted 6 January 2014 Available online 20 January 2014
The Kv7 channels, a family of voltage-dependent K þ channels (Kv7.1–Kv7.5), have gained much attention in drug discovery especially because four members are genetically linked to diseases. For disorders of the CNS focus was originally on epilepsy and pain, but it is becoming increasingly evident that Kv7 channels can also be valid targets for psychiatric disorders, such as anxiety and mania. The common denominator is probably neuronal hyperexcitability in different brain areas, which can be successfully attenuated by pharmacological increment of Kv7 channel activity. This perspective attempts to review the current status and challenges for CNS drug discovery based on Kv7 channels as targets for neurological and psychiatric indications with special focus on selectivity and mode-of-actions. & 2014 Elsevier B.V. All rights reserved.
Keywords: KCNQ Kv7 Anti-manic Anti-psychotic Anti-convulsion Mode-of-action
1. Kv7 channels in health and diseases With around 150 members, ion channels constitute one of the largest groups of signaling molecules in the human genome only surpassed in numbers by G protein coupled receptors and protein kinases (Harmar et al., 2009). Basically, channels conduct ions passively across the cell membrane, in the direction dictated by the electrochemical gradient. All ion channels conduct with specified (often high) selectivity and a reductionists view might predict the need for only few types, selective for K þ , Na þ , Cl and Ca2 þ —the main physiological ions. Obviously this is not the case. Ion channels are extremely diverse with respect to activation/ inactivation properties, cellular distribution patterns, and molecular interaction partners, which is basic to their versatile and subtle influences on nearly all physiological functions. Consequently, malfunction of ion channels is associated to several pathophysiological conditions. The K þ channel family is particular numerous, with a variety of structural and functional members, constituting approximately half of all ion channels described (Wulff et al., 2009). The voltage-dependent Kv7 channels (Kv7.1–Kv7.5) have gained substantial interest due to links to diseases (Jentsch, 2000) and overall tractability as pharmacological targets. Kv7.1 is a non-neuronal
n
Corresponding author. Tel.: þ 45 30617783. E-mail address: [email protected] (P. Christophersen).
0014-2999/$ - see front matter & 2014 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.ejphar.2014.01.017
channel involved in repolarisation of cardiac action potentials and epithelial transport (Jespersen et al., 2005). Kv7.2–Kv7.5 are widely expressed and active in neuronal tissue (Brown and Passmore, 2009) with Kv7.2 (usually in assembly with Kv7.3) being exclusively neuronal, whereas Kv7.4, Kv7.5 and (less pronounced) Kv7.3 are also expressed in skeletal—and smooth muscle cells (Mackie and Byron, 2008; Ng et al., 2011). Neuronal Kv7 channels are expressed as tetramers, assempled in homomeric (Kv7.2; Kv7.4; Kv7.5) or heteromeric (Kv7.2/Kv7.3; Kv7.4/Kv7.3; Kv7.5/Kv7.3; Kv7.4/ Kv7.5) channel complexes (Bal et al., 2008). Traditionally, dysfunctional Kv7 channels have been associated to epilepsy and deafness, but the area seems to broaden and encompass also hyperactivity conditions associated to pain and psychiatric diseases. From a mechanistic and distribution perspective this makes sense: All neuronal Kv7 channels open at subthreshold depolarizations around 60 mV with quite slow activation kinetics (Fig. 2) and display only modest inactivation at prolonged depolarizations (Jensen et al., 2007). This, in combination with their subcellular localisation in the soma/axon/axon initial segment (Rasmussen et al., 2007), makes Kv7 channels ideally adapted to control neuronal resting potentials as well as transmitter generated or endogeneous plateau potentials, and thereby generation of action potentials (Shah et al., 2008). In contrast to other faster activating Kv families, Kv7 channels usually don0 t activate during individual action potentials and thus play little specific role in the repolarization of these. Thus, pharmacological activation of Kv7 channels tend to hyperpolarize neurons, counteract slow depolarizations
134
M. Grunnet et al. / European Journal of Pharmacology 726 (2014) 133–137
Fig. 1. Kv7 channel modulators affect the excitability of hippocampal CA1 neurons. Action potential firing recorded from a CA1 neuron in a rat hippocampal slice upon application of 600 ms long depolarizing current pulses. Note the slight hyperpolarization and the markedly reduced excitability in the presence of the Kv7 channel activator retigabine (10 mM), an effect that is completely reversed by compound wash-out. A slight depolarization and increased action potential frequency is observed by subsequent application of the Kv7 channel inhibitor XE991 (10 mM). The pronounced after hyperpolarization following the depolarizing current pulse is largely unaffected by the pharmacological agents, indicating that other K þ channels than Kv7 mediate this effect.
Fig. 2. Kv7 activators exert different mode-of-actions. Kv7 channels are voltage-dependent channels with a steady-state activation curve as illustrated by the black curve in all three panels. The channels start activating at or near the resting membrane potential (vertical dashed line) and become increasingly active as the membrane potential gets more positive. Kv7 channel activation/inactivation kinetics is slow and the channels therefore primarily react to prolonged physiological/pathophysiological voltage changes, such as slow synaptic potentials and endogenous plateau potentials, but not during the fast action potentials. Different pharmacological Kv7 activators may exert very different concentration-dependent effects on channel activation (the effects of two different concentrations are illustrated, the more intensely coloured curves representing the higher concentrations): Left panel: The red curves represent an example of a “clean” effect on the voltage–activation curve resulting in a left-shifting towards more negative membrane potentials (retigabine). Middle panel: The blue curves represent an example of a combined effect on the voltage–activation curve and induction of a voltage-independent component observed at more hyperpolarized potentials (BMS-204352). Right panel: The green curves represent an example of a combined left-ward shifting effect on voltage–activation curve and depression of current at more depolarized potentials resulting in a concentration dependent “cross over” profile (NS15370). (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
and decrease excitability, whereas their inhibition leads to slight depolarization and increased excitability (Fig. 1). The present perspective gives an introduction to CNS-diseases associated to Kv7 channel function. In addition, their role as pharmacological targets for neurological and psychiatric diseases is discussed, together with our personal opinions on the likely characteristics of novel Kv7-based drugs in terms of selectivity and mode-of-actions. Diseases outside the CNS will not be covered.
2. Kv7 channels as targets in neurology The first direct evidence of involvement of Kv7 channels in a disease came with the association of benign familial neonatal seizures and loss-of-function mutations in the KCNQ2 and KCNQ3 genes encoding Kv7.2 and Kv7.3, respectively (Biervert et al., 1998; Charlier et al., 1998; Bellini et al., 2010). Later Kv7.4 channels were included with the notion that single nucleotide polymorphisms or loss-of-function mutations were associated to age-related hearing impairment and to autosomal dominant deafness (Kubisch et al., 1999; Van Eyken et al., 2006). Despite lack of genetic links, Kv7 channels constitutes wellvalidated targets for development of novel analgesics. Expression of Kv7 channels (Kv7.2, Kv7.3 and Kv7.5) is evident in various parts of the pain sensory pathway, such as Aδ and C-fibres in dorsal root ganglia, as well as in brain areas involved in higher pain perception, like the somatosensory cortex and thalamus (Passmore et al., 2003; Wickenden and McNaughton-Smith, 2009).
Two drugs interacting with Kv7 channels have reached the marked for neurological indications. Flupirtine, a non-opioid, centrally acting analgesic and muscle relaxing agent, has been marketed for decades in Germany (despite no initial recognition of its Kv7 channel activation, see Szelenyi, 2013). The close analogue, retigabine (Fig. 1), has demonstrated efficacy in a number of preclinical seizure and epilepsy models including seizures induced chemically by injection of pentylenetetrazole, electrically by maximal electroshock, 6 Hz stimulation, and amygdala kindling, as well as by sound (Large et al., 2012). Retigabine (ezogabine) was finally marketed as a first-in-class, anti-epileptic drug for treatment resistant partial-onset seizures (Gunthorpe et al., 2012).
3. Kv7 channels as targets in psychiatry Genetic links between psychiatric diseases and Kv7 channels are sparse. However, a recent finding of a translocation truncation in KCNQ3 and specific loss-of-function of heterologously expressed Kv7.3/Kv7.5 channels has been associated to autism spectrum disorders (Gilling et al., 2013). Additional (primarily pharmacological) evidence exist for a broader involvement of Kv7 channels in psychiatric and cognitive disorders. The first indications dates back to before KCNQ cloning from experiments showing that increased excitability and acetylcholine release (via Kv7 channel inhibition) by linopirdine and XE991 (Fig. 1) could improve learning and memory in animals (Fontana et al., 1994; Zaczek et al., 1998). Unfortunately, the pre-clinical results did not translate into clinical efficacy (Börjesson et al., 2013) possibly related to a low therapeutic index.
M. Grunnet et al. / European Journal of Pharmacology 726 (2014) 133–137
With the emergence of the Kv7 channel activators focus have increasingly turned in the direction of disorders like mania, bipolar disorders, attention deficit hyperactivity disorder, schizophrenia, and anxiety. The efficacy of (in particular) retigabine in rodent models of these indications were increasingly associated with hyperexcitability or disturbed neuronal firing in the basal ganglia and limbic system. It was demonstrated that Kv7 channel activation reduces amphetamine þchlordiazepoxide-induced hyperactivity and attenuates induced locomotor activity administration of amphetamine (Redrobe and Nielsen, 2009; Dencker and Husum, 2010; Hansen et al., 2007; Dalby-Brown et al., 2013). The likely mechanism behind these effects was associated to reduced basal dopaminergic firing and suppression of bursting in the ventral tegmental area (Hansen et al., 2006; Sotty et al., 2009) thereby accentuating the dopaminergic component of psychosis and mania disorders. Dampening of hyperactivity of the amygdala and the dorsal raphe nucleus (DRN) have been discussed as rationales for the anxiolytic effect of Kv7 channel activators in rodent models (Korsgaard et al., 2005; Hansen et al., 2008). Interestingly, among the Kv7 channel subunits only Kv7.4 seemed to be expressed in DRN, thereby, at least from a theoretical perspective (but see below), giving the possibility for development of selective Kv7.4 activators to target anxiety conditions.
4. Modulation of Kv7 channels as a treatment principle The primary mode-of-action for retigabine (and flupirtine) is to stabilise the Kv7 open channel conformation and left-ward shift the activation curve towards more negative membrane potentials (Main et al., 2000; Schrøder et al., 2001; Tatulian and Brown, 2003), as illustrated in Fig. 2 (left panel). Retigabine acts on all neuronal Kv7 channels with limited selectivity between the subtypes (Fig. 3) and furthermore possesses significant activation of GABAA receptors (Otto et al., 2002). The relatively poor selectivity properties makes it uncertain which Kv7 subtype (or channel) exert both therapeutic and adverse effects of retigabine. Various attempts have been done to circumvent these flaws, and in the literature a number of compounds with different characteristics have appeared from Bristol-Myers Squibb, Icagen, NeuroSearch, NIH molecular libraries, Charité-Universitätsmedizin Berlin, Tel-Aviv University, and Lundbeck (Wu et al., 2004; Padilla et al., 2009; Boehlen et al., 2013; Yu et al., 2010; Peretz et al., 2012; Dalby-Brown et al., 2013). Of particular interest is the emergence of very potent Kv7 activators without effect on GABAA receptors, the delineation of new sites-of-action, and – in particular – the emerging subtype selectivity and novel mode-of-actions of several of these compounds. The overall picture suggests that Kv7.2
135
(/Kv7.3) activators with reduced Kv7.4 and/or Kv7.5 (/Kv7.3) activity (and without GABAA effect) maintain anti-epileptic and analgesic properties. It is also noteworthy that BMS-204352 (maxipost), a compound which preferentially activates Kv7.4 and Kv7.5-containing channels (Fig. 3) (but also other K þ channels), was as effective as retigabine in animal models of anxiety (Korsgaard et al., 2005) possibly exemplifying the aforementioned role of Kv7.4 in serotonergic neurons. Unfortunately, Kv7.4 and Kv7.5 channels are also principal subtypes expressed in peripheral smooth muscles, which is consistent with a potent smooth muscle relaxing effect of BMS204352 (Jepps et al., 2011). Peripheral clinical adverse reactions of retigabine, such as urinary retention (Brickel et al., 2012), may also be due to activation of these subtypes. Despite not yet systematically explored across chemical compound series and across different Kv7 subtypes, it is obvious that different Kv7 activators affects the channels very differently, which are often ignored, but may eventually translate into in vivo pharmacological significance. The “clean” concentration-dependent leftshifting of the voltage–activation curve (Fig. 2, left panel) is in our experience just one way of positive modulation encountered during drug discovery programs. As exemplified from the literature: BMS204352 induces a voltage-independent component as well as the left-shifting (Schrøder et al., 2003) (Fig. 2, middle panel), whereas the acrylamide S-2 and in particular a recently described molecule, NS15370, exerts a complex activation/inhibiting mode-of-action (Blom et al., 2009; Dalby-Brown et al., 2013) on all neuronal Kv7 subtypes: At very low concentrations (100 times more potent than retigabine) NS15370 acts as an activator at all membrane potentials and causes the conventional left-shift in the steady-state activation curve. At slightly higher concentrations, however, the compound augments current only at small depolarising steps but “crosses over” and reduces the current at larger depolarisations (Fig. 2, right panel). Intuitively such a profile might be speculated to hamper in vivo effectiveness. However, NS15370 was found to show good efficacy across a number of rodent models of psychiatric and neurological diseases (Dalby-Brown et al., 2013), which may point towards a subtle interplay between stabilizing neurons by clamping the cells at hyperpolarized potentials while allowing for activity (maybe even increased activity) under certain depolarized conditions. An inspiring finding, done by Vincent Seutin and co-workers (Drion et al., 2010), shows that Kv7 channels exert minor effect on basic pacemaker activity of dopaminergic neurons, but become important for controlling spike frequency architecture during strongly depolarized burst periods, which is thought to be important for reward based learning. Even only speculative at this stage, NS15370 may well exemplify that significantly more work needs to be done in order to link a specific electrophysiological “fingerprint” of a Kv7 channel modulator to corresponding optimal in vivo
Fig. 3. Kv7 activators exert different subtype selectivity. Comparison of the relative potencies of 4 different Kv7 channel activators (retigabine, acrylamide S-1, BMS-204352, and ICA-27243) on different monomeric and heteromeric Kv7 channels expressed in human embryonic kidney cells. Due to the very different mode-of-actions of some of these compounds (see Fig. 2) it is hard to give an accurate numeric potency measure for all combinations (a general problem in Kv7 based drug discovery). The current ranking is based on FLIPR detection of Tl þ -flux (a surrogate tracer ion for K þ ) compared with manual patch clamp analyses. Redrawn from Jørgensen et al., 2011.
136
M. Grunnet et al. / European Journal of Pharmacology 726 (2014) 133–137
efficacy. Despite lack of solid evidence we also consider the possibility that the optimal mode-of-action may differ from one indication to another.
5. General conclusions and further perspectives As summarized, Kv7.2–7.5 channels show strong biological and pharmacological links to both neurological and psychiatric diseases. In that context it is surprising that, despite significant efforts in the pharmaceutical industry, only two Kv7 active drugs – both “first generation Kv7 activators” – have reached the market. Even though the registration of retigabine as a first-in-class anti-epileptic is promising, it has also revealed that the drug potential of novel Kv7 channel activators depends on the successful improvement of several clinical challenges, such as the need for a high and frequent dosing regimen as well as a relative small therapeutic index primarily defined by sedative and urinary safety adverse effects.
It is our view that future Kv7 programs should focus on the
development of subtype-selective molecules, and for CNS we give specific Kv7.2 (/Kv7.3) candidates the highest chance of success. The wide spectrum of mode-of-actions exerted by different compounds (discovered largely by serendipity) is a potential – but largely unexplored – handle to sharpen a desired therapeutic profile and mitigate adverse reactions. We think that medium to high throughput electrophysiological screening platforms are essential in order to fully exploit the versatility of drug interactions with Kv7 channels. We envision that new programs might benefit from a directed effort towards focused screening for molecules interacting with sites distinct from the retigabine site. We strongly encourage early identification of Kv7-specific radiolabeled ligands suitable for target engagement studies in vivo.
References Bal, M., Zhang, J., Zaika, O., Hernandez, C.C., Shapiro, M.S., 2008. Homomeric and heteromeric assembly of KCNQ (Kv7) K þ channels assayed by total internal reflection fluorescence/fluorescence resonance energy transfer and patch clamp analysis. J. Biol. Chem. 283 (45), 30668–30676. Bellini, G., Miceli, F., Soldovieri, M.V., Miraglia, del Giudice E., Coppola, G., Taglialatela, M., 2010. KCNQ2-related disorders. In: Pagon, R.A., Adam, M.P., Bird, T.D., Dolan, C.R., Fong, C.T., Stephens, K. (Eds.), GeneReviews™ [Internet]. Seattle (WA): University of Washington, Seattle, pp. 1993–2013 Biervert, C., Schroeder, B.C., Kubisch, C., Berkovic, S.F., Propping, P., Jentsch, T.J., Steinlein, O.K., 1998. A potassium channel mutation in neonatal human epilepsy. Science 279 (5349), 403–406. Blom, S.M., Schmitt, N., Jensen, H.S., 2009. The acrylamide (S)-2as a positive and negative modulator of Kv7 channels expressed in Xenopus laevis oocytes. PLoS One 4 (12), e8251 1–12. Boehlen, A., Schwake, M., Dost, R., Kunert, A., Fidzinski, P., Heinemann, U., Gebhardt, C., 2013. The new KCNQ2 activator 4-chlor-N-(6-chlor-pyridin-3-yl)-benzamid displays anticonvulsant potential. Br. J. Pharmacol. 168 (5), 1182–1200. Börjesson, A., Karlsson, T., Adolfsson, R., Rönnlund, M, Nilsson, L., 2013. Linopirdine (DUP 996): cholinergic treatment of older adults using successive and nonsuccessive tests. Neuropsychobiology 40 (2), 78–85. Brickel, N., Gandhi, P., VanLandingham, K., Hammond, J., DeRossett, S., 2012. The urinary safety profile and secondary renal effects of retigabine (ezogabine): a first-in-class antiepileptic drug that targets KCNQ Kv7 potassium channels. Epilepsia 53 (4), 606–612. Brown, D.A., Passmore, G.M., 2009. Neural KCNQ (Kv7) channels. Br. J. Pharmacol. 156 (8), 1185–1195. Charlier, C., Singh, N.A., Ryan, S.G., Lewis, T.B., Reus, B.E., Leach, R.J., Leppert, M., 1998. A pore mutation in a novel KQT-like potassium channel gene in an idiopathic epilepsy family. Nat. Genet. 18 (1), 53–55. Dalby-Brown, W., Jessen, C., Hougaard, C., Jensen, M.L., Jacobsen, T.A., Nielsen, K.S., Erichsen, H.K., Grunnet, M., Ahring, P.K., Christophersen, P., Strøbæk, D., Jørgensen, S., 2013. Characterization of a novel high-potency positive modulator of Kv7 channels. Eur. J. Pharmacol. 709 (1-3), 52–63. Dencker, D., Husum, H., 2010. Antimanic efficacy of retigabine in a proposed mouse model of bipolar disorder. Behav. Brain Res. 207 (1), 78–83.
Drion, G., Bonjean, M., Waroux, O., Scuvée-Moreau, J., Liégeois, J.F., Sejnowski, T.J., Sepulchre, R., Seutin, V., 2010. M-type channels selectively control bursting in rat dopaminergic neurons. Eur. J. Neurosci. 31 (5), 827–835. Van Eyken, E., Van Laer, L., Fransen, E., Topsakal, V., Lemkens, N., Laureys, W., Nelissen, N., Vandevelde, A., Wienker, T., Van De Heyning, P., Van Camp., G., 2006. KCNQ4: a gene for age-related hearing impairment? Hum. Mutat. 27 (10), 1007–1016. Fontana, D.J., Inouye, G.T., Johnson, R.M., 1994. Linopirdine (DuP 996) improves performance in several tests of learning and memory by modulation of cholinergic neurotransmission. Pharmacol. Biochem. Behav. 49 (4), 1075–1082. Gilling, M., Rasmussen, H.B., Calloe, K., Sequeira, A.F., Baretto, M., Oliveira, G., Almeida, J., Lauritsen, M.B., Ullmann, R., Boonen, S.E., Brondum-Nielsen, K., Kalscheuer, V.M., Tümer, Z., Vicente, A.M., Schmitt, N., Tommerup, N., 2013. Dysfunction of the heteromeric Kv7.3/Kv7.5 potassium channel is associated with autism spectrum disorders. Front. Genet. 4, 54. Gunthorpe, M.J., Large, C.H., Sankar, R., 2012. The mechanism of action of retigabine (ezogabine), a first-in-class K þ channel opener for the treatment of epilepsy. Epilepsia 53 (3), 412–424. Hansen, H.H., Ebbesen, C., Mathiesen, C., Weikop, P., Rønn, L.C., Waroux, O., ScuvéeMoreau, J., Seutin, V., Mikkelsen, J.D., 2006. The KCNQ channel opener retigabine inhibits the activity of mesencephalic dopaminergic systems of the rat. J. Pharmacol. Exp. Ther. 318 (3), 1006–1019. Hansen, H.H., Andreasen, J.T., Weikop, P., Mirza, N., Scheel-Krüger, J., Mikkelsen, J.D., 2007. The neuronal KCNQ channel opener retigabine inhibits locomotor activity and reduces forebrain excitatory responses to the psychostimulants cocaine, methylphenidate and phencyclidine. Eur. J. Pharmacol. 570 (1-3), 77–88. Hansen, H.H., Waroux, O., Seutin, V., Jentsch, T.J., Aznar, S., Mikkelsen, J.D., 2008. Kv7 channels: interaction with dopaminergic and serotonergic neurotransmission in the CNS. J. Physiol. 586 (7), 1823–1832. Harmar, A.J., Hills, R.A., Rosser, E.M., Jones, M., Buneman, O.P., Dunbar, D.R., Greenhill, S.D., Hale, V.A., Sharman, J.L., Bonner, T.I., Catterall, W.A., Davenport, A.P., Delagrange, P., Dollery, C.T., Foord, S.M., Gutman, G.A., Laudet, V., Neubig, R.R., Ohlstein, E.H., Olsen, R.W., Peters, J., Pin, J.P., Ruffolo, R.R., Searls, D.B., Wright, M.W., Spedding, M., 2009. IUPHAR-DB: the IUPHAR database of G protein-coupled receptors and ion channels. Nucleic Acids Res. (Database issue), D680–D685 Jensen, H.S., Grunnet, M., Olesen, S.P., 2007. Inactivation as a new regulatory mechanism for neuronal Kv7 channels. Biophys. J. 92 (8), 2747–2756. Jentsch, T.J., 2000. Neuronal KCNQ potassium channels: physiology and role in disease. Nat. Rev. Neurosci. 2000 (1), 21–30. Jepps, T.A., Chadha, P.S., Davis, A.J., Harhun, M.I., Cockerill, G.W., Olesen, S.P., Hansen, R.S., Greenwood, I.A., 2011. Downregulation of Kv7.4 channel activity in primary and secondary hypertension. Circulation 124 (5), 602–611. Jespersen, T., Grunnet, M., Olesen, S.P., 2005. The KCNQ1 potassium channel: from gene to physiological function. Physiology (Bethesda) 20, 408–416. Jørgensen, S., Jensen, M.L., Hougaard, C. Dyhring, T. Christophersen, P., Strøbæk D., 2011. Subtype-dependent potencies and mode-of-actions for the Kv7 positive modulators retigabine, ICA-27243, BMS-204352 and (S)-1. Society for Neuroscience Meeting. P139.01. Kubisch, C., Schroede,r, B.C., Friedrich, T., Lütjohann, B., El-Amraoui, A., Marlin, S., Petit, C., Jentsch, T.J., 1999. KCNQ4, a novel potassium channel expressed in sensory outer hair cells, is mutated in dominant deafness. Cell 96 (3), 437–446. Korsgaard, M.P., Hartz, B.P., Brown, W.D., Ahring, P.K., Strøbaek, D., Mirza, N.R., 2005. Anxiolytic effects of Maxipost (BMS-204352) and retigabine via activation of neuronal Kv7 channels. J. Pharmacol. Exp. Ther. 314 (1), 282–292. Large, C.H., Sokal, D.M., Nehlig, A., Gunthorpe, M.J., Sankar, R., Crean, C.S., Vanlandingham, K.E., White, H.S., 2012. The spectrum of anticonvulsant efficacy of retigabine (ezogabine) in animal models: implications for clinical use. Epilepsia 53 (3), 425–436. Mackie, A.R., Byron, K.L., 2008. Cardiovascular KCNQ (Kv7) potassium channels: physiological regulators and new targets for therapeutic intervention. Mol. Pharmacol. 74 (5), 1171–1179. Main, M.J., Cryan, J.E., Dupere, J.R., Cox, B., Clare, J.J., Burbidge, S.A., 2000. Modulation of KCNQ2/3 potassium channels by the novel anticonvulsant retigabine. Mol. Pharmacol. 58 (2), 253–262. Ng, F.L., Davis, A.J., Jepps, T.A., Harhun, M.I., Yeung, S.Y., Wan, A., Reddy, M., Melville, D., Nardi, A., Khong, T.K., Greenwood, I.A., 2011. Expression and function of the K þ channel KCNQ genes in human arteries. Br. J. Pharmacol. 162 (1), 42–53. Otto, J.F., Kimball, M.M., Wilcox, K.S., 2002. Effects of the anticonvulsant retigabine on cultured cortical neurons: changes in electroresponsive properties and synaptic transmission. Mol. Pharmacol. 61 (4), 921–927. Padilla, K., Wickenden, A.D., Gerlach, A.C., McCormack, K., 2009. The KCNQ2/3 selective channel opener ICA-27243 binds to a novel voltage-sensor domain site. Neurosci. Lett. 465 (2), 138–142. Passmore, G.M., Selyanko, A.A., Mistry, M., Al-Qatari, M., Marsh, S.J., Matthews, E.A., Dickenson, A.H., Brown, T.A., Burbidge, S.A., Main, M., Brown, D.A., 2003. KCNQ/ M currents in sensory neurons: significance for pain therapy. J. Neurosci. 23 (18), 7227–7236. Peretz, A., Pell, L., Gofman, Y., Haitin, Y., Shamgar, L., Patrich, E., Kornilov, P., GourgyHacohen, O., Ben-Tal, N., Attali, B., 2012. Targeting the voltage sensor of Kv7.2 voltage-gated K þ channels with a new gating-modifier. Proc. Nat. Acad. Sci. U.S.A. 107 (35), 15637–15642. Rasmussen, H.B., Frøkjaer-Jensen, C., Jensen, C.S., Jensen, H.S., Jørgensen, N.K., Misonou, H, Trimmer, J.S., Olesen, S.P., Schmitt, N., 2007. Requirement of
M. Grunnet et al. / European Journal of Pharmacology 726 (2014) 133–137
subunit co-assembly and ankyrin-G for M-channel localization at the axon initial segment. J. Cell. Sci. 120 (Pt 6), 953–963. Redrobe, J.P., Nielsen, A.N., 2009. Effects of neuronal Kv7 potassium channel activators on hyperactivity in a rodent model of mania. Behav. Brain Res. 198 (2), 481–485. Schrøder, R.L., Jespersen, T., Christophersen, P., Strøbæk, D., Jensen, B.S., Olesen, S.P., 2001. KCNQ4 channel activation by BMS-204352 and retigabine. Neuropharmacology 40 (7), 888–898. Schrøder, R.L., Strøbæk, D., Olesen, S.P., Christophersen, P., 2003. Voltageindependent KCNQ4 currents induced by ( þ / )BMS-204352. Pflugers Arch. 446 (5), 607–616. Shah, M.M., Migliore, M., Valencia, I., Cooper, E.C., Brown, D.A., 2008. Functional significance of axonal Kv7 channels in hippocampal pyramidal neurons. Proc. Nat. Acad. Sci. U.S.A. 2008 105 (22), 7869–7874. Sotty, F., Damgaard, T., Montezinho, L.P., Mørk, A., Olsen, C.K., Bundgaard, C., Husum, H., 2009. Antipsychotic-like effect of retigabine [N-(2-amino-4-(fluorobenzylamino)-phenyl)carbamic acid ester], a KCNQ potassium channel opener, via modulation of mesolimbic dopaminergic neurotransmission. J. Pharmacol. Exp. Ther. 328 (3), 951–962. Szelenyi, I., 2013. Flupirtine, a re-discovered drug, revisited. Inflamm. Res. 62 (3), 251–258. Tatulian, L., Brown, D.A., 2003. Effect of the KCNQ potassium channel opener retigabine on single KCNQ2/3 channels expressed in CHO cells. J. Physiol. 549 (Pt 1), 57–63.
137
Wickenden, A.D., McNaughton-Smith, G., 2009. Kv7 channels as targets for the treatment of pain. Curr. Pharm. Des. 15 (15), 1773–1798. Wu, Y.J., Boissard, C.G., Chen, J., Fitzpatrick, W., Gao, Q., Gribkoff, V.K., Harden, D.G., He, H., Knox, R.J., Natale, J., Pieschl, R.L., Starrett , J.E., Sun, L.Q., Thompson, M., Weaver, D., Wu, D., Dworetzky, S.I., 2004. (S)-N-[1-(4-cyclopropylmethyl-3,4-dihydro-2H-benzo [1,4]oxazin-6-yl)-ethyl]-3-(2-fluoro-phenyl)-acrylamide is a potent and efficacious KCNQ2 opener which inhibits induced hyperexcitability of rat hippocampal neurons. Bioorg. Med. Chem. Lett. 14 (8), 1991–1995. Wulff, H., Castle, N.A., Pardo, L.A., 2009. Voltage-gated potassium channels as therapeutic targets. Nat. Rev. Drug Discovery 12, 982–1001. Yu, H., Wu, M., Hopkins, C., Engers, J., Townsend, S., Lindsley, C., McManus, O.B., Li, M., 2010. A Small Molecule Activator of KCNQ2 and KCNQ4 Channels. Probe Reports from the NIH Molecular Libraries Program [Internet]. Bethesda (MD): National Center for Biotechnology Information (US); 2010-2011 Mar 29 [updated 2013 Feb 28]. Zaczek, R., Chorvat, R.J., Saye, J.A., Pierdomenico, M.E., Maciag, C.M., Logue, A.R., Fisher, B.N., Rominger, D.H., Earl, R.A., 1998. Two new potent neurotransmitter release enhancers, 10,10-bis(4-pyridinylmethyl)-9(10H)-anthracenone and 10,10-bis(2-fluoro-4-pyridinylmethyl)-9(10H)-anthracenone: comparison to linopirdine. J. Pharmacol. Exp. Ther. 285 (2), 724–730.