Information prepared by Eisai Europe Ltd Mode of Action of Perampanel: a selective non-competitive AMPA receptor antagonist Information prepared by Eisai Europe Ltd

Contents Mode of Action (MOA) of existing anti-epileptic drugs (AEDs) Glutamate mediated Post Synaptic Excitation MOA of Perampanel, a selective, non-competitive AMPA receptor antagonist AMPA: α-amino-3-hydroxy-5-methyl-4-isoxazole-proprionic acid

Understanding key transmitter systems is important in understanding seizures and AED actions The CNS uses a large number of ion channels, neurotransmitters, and receptors to communicate Several of these systems are important in understanding epilepsy The biological mechanisms underlying seizure activity The mechanism of action of antiepileptic drugs (AEDs) The following slides provide information on some of these key ion channels and neurotransmitter systems, arranged in 3 conceptual groups: Pre-synaptic excitability and transmitter release GABA inhibitory systems Post-synaptic glutamate receptors

Understanding key transmitter systems is important in understanding seizures and AED actions The CNS uses a large number of ion channels, neurotransmitters, and receptors to communicate Several of these systems are important in understanding epilepsy The biological mechanisms underlying seizure activity The mechanism of action of antiepileptic drugs (AEDs) The following slides provide information on some of these key ion channels and neurotransmitter systems, arranged in 3 conceptual groups: Pre-synaptic excitability and transmitter release GABA inhibitory systems Post-synaptic glutamate receptors

1. Pre-synaptic excitability and neurotransmitter release and transmitter release Pre-synaptic neuron Voltage-gated Na+ channel Voltage-gated K+ channel Voltage-gated Ca2+ channel Many AEDs target the voltage-gated ion channels that control pre-synaptic excitability and neurotransmitter release. Reference Rogawski MA, Löscher W. The neurobiology of antiepileptic drugs. Nat Rev Neurosci 2004;5:553–564. Inhibitory interneuron Post-synaptic neuron Redrawn and adapted from: Rogawski MA, Löscher W. Nat Rev Neurosci 2004;5:553–564; Rogawski MA. Epilepsy Currents 2011;11:56–63.

2. GABA inhibitory systems Pre-synaptic neuron GABAA receptor GABA transaminase GABA transporter Other AEDs act to increase inhibitory controls, by targeting aspects of the GABA inhibitory system. Reference Rogawski MA, Löscher W. The neurobiology of antiepileptic drugs. Nat Rev Neurosci 2004;5:553–564. Inhibitory interneuron Post-synaptic neuron Redrawn and adapted from : Rogawski MA, Löscher W. Nat Rev Neurosci 2004;5:553–564; Rogawski MA. Epilepsy Currents 2011;11:56–63.

3. Post-synaptic excitability Not targeted selectively by any approved AEDs prior to perampanel Pre-synaptic neuron Felbamate has weak affinity for NMDA receptors and topiramate binds both AMPA and kainate receptors... ...but the primary MOA of these AEDs is inhibition of voltage-gated Na+ channels AMPA receptor Glutamate NMDA receptor The final common pathway in synaptic neurotransmission – post-synaptic glutamate receptors – is not targeted selectively by any AEDs prior to perampanel receiving a licence in the European Union.1,2 References Rogawski MA, Löscher W. The neurobiology of antiepileptic drugs. Nat Rev Neurosci 2004;5:553–564. Rogawski MA. Revisiting AMPA receptors as an antiepileptic drug target. Epilepsy Currents 2011;11:56–63. Inhibitory interneuron Post-synaptic neuron Redrawn and adapted from: Rogawski MA, Löscher W. Nat Rev Neurosci 2004;5:553–564; Rogawski MA. Epilepsy Currents 2011;11:56–63.

Glutamate mediated Post-synaptic excitability

Glutamate mediates most fast excitatory neurotransmission in the CNS Glutamate is the principal excitatory neurotransmitter in the CNS1 Effects mediated via ionotropic receptors (ion channels) and metabotropic receptors1,2 Ionotropic receptors mediate glutamate’s fast excitatory neurotransmission at synapses2,3 Three types, all activated by glutamate but named after the synthetic agonists used to characterise the receptors: AMPA: -amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid NMDA: N-methyl-D-aspartate Kainate: Kainic acid Glutamate is the principal excitatory neurotransmitter in the CNS, and acts via ionotropic and metabotropic groups of receptors.1,2 ,3 Metabotropic receptors are ‘G-protein-coupled receptors’. Rather than directly affecting the excitability of the neuron, they initiate biochemical cascades that lead to the modification of other proteins – which may include ion channels.4 In contrast, when glutamate binds to one of its ionotropic receptors, it directly affects neuronal excitability through activating the integral ion channel in the receptor, to allow flux of ions into and out of the neuron.3,4 There are three types of ionotropic glutamate receptor: AMPA, NMDA, and kainate receptors. They were named after the synthetic agonists that bind to the respective receptor types and selectively open the associated ion channels. The three types of ionotropic glutamate receptor are pharmacologically distinct but are all activated by glutamate.4 References Rogawski MA. Revisiting AMPA receptors as an antiepileptic drug target. Epilepsy Currents 2011;11:56–63. Meldrum BS. Glutamate as a neurotransmitter in the brain: review of physiology and pathology. J Nutr 2000;130:1007S–1015S. Meldrum BS, Rogawski MA. Molecular targets for antiepileptic drug development. Neurotherapeutics 2007;4:18–61. Wilcox KS et al. Chapter 22: Excitatory synaptic transmission. In: Epilepsy: a comprehensive textbook. Engel J Jr, Pedley TA (Eds). 2nd Edition. Wolters Kluwer Health, Lippincott Williams & Wilkins. 2008. AMPA receptor Kainate receptor NMDA receptor 1Rogawski MA. Epilepsy Currents 2011;11:56–63; 2Meldrum BS. J Nutr 2000;130:1007S–1015S; 3Meldrum BS, Rogawski MA. Neurotherapeutics 2007;4:18–61.

AMPA receptors mediate glutamate fast signalling AMPA receptors are the most abundant ionotropic glutamate receptors in the mammalian brain They are localised at excitatory synapses, post-synaptically AMPA receptors mediate the fast response to glutamate Generate the fast component of the excitatory post synaptic potential (EPSP) If sufficient EPSPs result, these summate and result in firing of an action potential AMPA receptors mediate the majority of glutamate transmission; situated in the post- synaptic membrane, they generate EPSPs in response to activation by glutamate. With sufficient glutamate present, AMPA-receptor-generated EPSPs will summate to trigger action potentials. Reference Rogawski MA. Revisiting AMPA receptors as an antiepileptic drug target. Epilepsy Currents 2011;11:56–63. Action potentials EPSP Rogawski MA. Epilepsy Currents; 2011;11:56–63.

Glutamate mediates most fast excitatory neurotransmission in the CNS AMPA is the main receptor mediating rapid effects of glutamate1 Underlies fast component of EPSP1,2 NMDA receptor does not normally contribute to fast neurotransmission1,2 Underlies slow component of the EPSP1,2 Involved in plasticity e.g. learning and memory1,3 EPSP Fast Glutamate, via the AMPA receptor, mediates most fast excitatory neurotransmission in the CNS,1 and underlies the fast component of the EPSP.1,2 NMDA receptors do not contribute to synaptic transmission immediately; they need to be activated by depolarisation, as well as glutamate binding, so they contribute to the EPSP with a later and slower component.1,2 NMDA receptors are involved in the synaptic plasticity that underlies, for example, learning and memory.1,3 NMDA receptor antagonists include ketamine and phencyclidine (PCP), which have been used as drugs of abuse with psychoactive properties.1 AMPA receptors are not known to be targeted by any drugs of abuse and are not expected to cause psychomimetic effects in man.1,3 The role of the kainate receptor is unclear, and this receptor is not known to be targeted selectively by any currently available drugs. References Rogawski MA. Revisiting AMPA receptors as an antiepileptic drug target. Epilepsy Currents 2011;11:56–63. Meldrum BS. Glutamate as a neurotransmitter in the brain: review of physiology and pathology. J Nutr 2000;130:1007S–1015S. Meldrum BS, Rogawski MA. Molecular targets for antiepileptic drug development. Neurotherapeutics 2007;4:18–61. Slow 1Rogawski MA. Epilepsy Currents; 2011;11:56–63; 2Meldrum BS. J Nutr 2000;130:1007S–1015S; 3Meldrum BS, Rogawski MA. Neurotherapeutics 2007;4:18–61. 11

AMPA receptors may trigger seizure activity via the PDS (Paroxysmal Depolarising Shift) AMPA receptors drive EPSPs at individual synapses and across networks Synchronised EPSPs across neuronal networks are thought to drive the PDS1,2 The AMPA receptor is thought to mediate the initial component of the PDS EPSP PDS Initial component mediated by AMPA receptors A measurable pattern of neuronal activity, the PDS, might be involved in generating seizure activity. This is considered a cellular correlate of interictal spikes measured on an EEG, and it is thought to result when multiple EPSPs co-occur, generating giant EPSPs synchronised across a network of neurons. The resulting PDS has a rapid AMPA-receptor-mediated component and a delayed, NMDA-receptor-mediated component.1–3 References Rogawski MA. Revisiting AMPA receptors as an antiepileptic drug target. Epilepsy Currents 2011;11:56–63. Acharya JN. Recent advances in epileptogenesis. Curr Sci 2002;82:679–688. Chapman AG. Glutamate and epilepsy. J Nutr 2000;130:1043S–1045S. Later component mediated by NMDA receptors 1Acharya JN. Curr Sci 2002;82:679–688; 2Chapman AG. J Nutr 2000;130:1043S–1045S.

Neuronal hyperexcitability results, somehow, in seizures Individual neurons within an area may be hyperexcitable1 These neurons occasionally have sudden (paroxysmal), synchronous depolarisations, and fire bursts of action potential bursts1 Paroxysmal depolarisation shift (PDS)2 Although our understanding of seizures has advanced, the fundamental mechanisms are still not clear. In the development of partial-onset seizures, it appears that individual neurons within epileptic areas are hyperexcitable, and occasionally depolarise in sync, firing bursts of action potentials.1 This electrical activity has been recorded from neurons experimentally, and is referred to as the paroxysmal depolarisation shift (PDS).2 References Dichter MA. Chapter 20: Overview: The neurobiology of epilepsy. In: Epilepsy: a comprehensive textbook. Engel J Jr, Pedley TA (Eds). 2nd Edition. Wolters Kluwer Health, Lippincott Williams & Wilkins. 2008. Rang HP et al. Chapter 30: Antiepileptic drugs and centrally acting muscle relaxants. In: Pharmacology. 3rd Edition. Churchill Livingstone. 1995. PDS 1Dichter MA. In: Epilepsy. A comprehensive textbook. 2008; 2Rang HP et al. In: Pharmacology. 1995.

Glutamate and the AMPA receptor play an important role in seizure activity Glutamate and the AMPA receptor are important in seizure activity1–4 Glutamate is implicated in acute and chronic neurodegeneration How do we know glutamate is important in seizures? Glutamate levels increase before and during seizures in humans1 Suggests that elevated glutamate levels can trigger and maintain seizures AMPA receptor agonists initiate seizures in animal models3 AMPA receptor antagonists have anti-seizure activity in animal models3 Suggests AMPA receptors are involved in seizure initiation and spread2–4 How are AMPA receptors involved in seizures? AMPA receptors are known to drive EPSPs at excitatory synapses (normal neuronal activity) It is thought that AMPA receptors are involved in the PDS (Paroxysmal Depolarising Shift)5,6 Glutamate and the AMPA receptor are thought to be important in seizure activity, in both initiation and spread of seizures.1–4 Glutamate levels have been shown to increase during seizures in humans.1 During and Spencer showed that in 6 patients with complex partial epilepsy, concentrations of glutamate increased in the epileptogenic hippocampus before seizures started. During seizures, there was a sustained increase in extracellular glutamate to potentially neurotoxic concentrations. This suggests that elevated levels of glutamate can trigger initiation of seizures, as well as maintenance. AMPA receptor agonists have been shown to trigger seizures in animal models, and AMPA receptor antagonists can protect against seizures in animal seizure models.2–4 How AMPA receptors drive seizures is unclear, but a specific, measurable pattern of neuronal activity, the PSD, might be involved in generating seizure activity. This is a pattern of activity that correlates with interictal spikes measured on an electroencephalograph (EEG), and it is thought to result when multiple EPSPs co- occur, generating giant EPSPs synchronised across a network of neurons.5,6 References During MJ, Spencer DD. Extracellular hippocampal glutamate and spontaneous seizure in the conscious human brain. Lancet 1993;341:1607–1610. Meldrum BS, Rogawski MA. Molecular targets for antiepileptic drug development. Neurotherapeutics 2007;4:18–61. Meldrum BS. Glutamate as a neurotransmitter in the brain: review of physiology and pathology. J Nutr 2000;130:1007S–1015S. Rogawski MA, Donevan SD. AMPA receptors in epilepsy and as targets for antiepileptic drugs. Adv Neurol 1999;79:947–963. Acharya JN. Recent advances in epileptogenesis. Curr Sci 2002;82:679–688. Chapman AG. Glutamate and epilepsy. J Nutr 2000;130:1043S–1045S. 1During MJ, Spencer DD. Lancet 1993;341:1607–1610; 2Meldrum BS, Rogawski MA. Neurotherapeutics 2007;4:18–61; 3Meldrum BS. J Nutr 2000;130:1007S–1015S; 4Rogawski MA, Donevan SD. Adv Neurol 1999;79:947–63; 5Acharya JN. Curr Sci 2002;82:679–688; 6Chapman AG. J Nutr 2000;130:1043S–1045S.

AMPA receptor structure (closed, inactive state) AMPA receptor (open, active state) Glutamate-binding sites (also ligand-binding sites or domains) Na+ ions Glutamate The AMPA receptor is a ligand-gated ion channel, and the channel is closed in its resting state.1 Each functional receptor has 2 glutamate-binding sites (or ligand-binding sites/domains), to which glutamate (endogenous agonist) binds.2 Non-competitive antagonists bind at a different site, and this (or these) has not yet been characterised. References Wilcox KS et al. Chapter 22: Excitatory synaptic transmission. In: Epilepsy: a comprehensive textbook. Engel J Jr, Pedley TA (Eds). 2nd Edition. Wolters Kluwer Health, Lippincott Williams & Wilkins. 2008. Clements JD et al. Activation kinetics of AMPA receptor channels reveal the number of functional agonist binding sites. J Neurosci 1998;18:119–127. Non-competitive binding sites The receptor’s ion channel allows influx of Na+ ions (and sometimes Ca2+ ions) into the neuron 1Wilcox KS et al. In: Epilepsy: a comprehensive textbook. 2008; 2Clements JD et al. J Neurosci 1998;18:119–121.

Glutamate opens the AMPA receptor to allow Na+ influx Normal situation 1. Glutamate binds and activates the receptor 2. Na+ enters through the open channel 3. Channel returns to closed state when glutamate dissociates Upon binding of glutamate (or any agonist, such as AMPA), to the AMPA receptor, the receptor is activated and the ion channel opens. Na+ ions flow in through the channel (and K+ ions flow out), and this current causes the neuron to depolarise and become more excitable. Some AMPA receptors (those lacking the GluR2 subunit) are also permeable to Ca2+, which flows in through the open ion channel with the Na+ ions. When glutamate dissociates, the channel returns to its resting, or inactive, state. Reference Wilcox KS et al. Chapter 22: Excitatory synaptic transmission. In: Epilepsy: a comprehensive textbook. Engel J Jr, Pedley TA (Eds). 2nd Edition. Wolters Kluwer Health, Lippincott Williams & Wilkins. 2008. Na+ ions Glutamate Wilcox KS et al. In: Epilepsy: a comprehensive textbook. 2008.

Competitive antagonists may be displaced by high levels of glutamate In the presence of a competitive antagonist 1. Glutamate cannot bind so cannot activate the receptor BUT when glutamate levels are high... 2. Glutamate displaces the antagonist... 3. ...binds to the receptor and activates it, opening the channel and allowing Na+ influx Antagonists bind to receptors, but do not provoke a biological response; instead, they block or attenuate agonist-mediated activity. Competitive antagonists bind to the receptor at the same binding site as the endogenous ligand (in this case glutamate) but do not activate the receptor. The antagonist therefore competes with glutamate for receptor binding sites. Once bound, a competitive antagonist will block glutamate from binding, so it cannot activate the receptor. When the concentration of the endogenous ligand (glutamate) is high, it can displace (or out-compete) the antagonist from the glutamate-binding sites, surmounting the antagonism. Glutamate can then bind to the receptor and activate it. In reality, it is not quite so black-and-white, but this simplification helps to describe what is happening. Reference Rang HP et al. Chapter 1: How drugs act: general principles. In: Pharmacology. Rang HP, Dale MM, Ritter JM (Eds). 3rd Edition. Churchill Livingstone. 1995. Na+ ions Glutamate Competitive antagonist Rang HP et al. In: Pharmacology. 1995.

Non-competitive antagonists should maintain activity even when glutamate levels are high In the presence of perampanel1 1. Glutamate binds but cannot activate the receptor1 AND when glutamate levels are high... 2. ...non-competitive antagonist is not displaced by glutamate2 In the presence of perampanel, a non-competitive antagonist, glutamate can bind to the receptor (at the glutamate-binding sites) but cannot activate the receptor.1 One major implication of this non-competitive antagonism is that the effect should be insurmountable:2,3 Because the antagonist binds to a different site than glutamate binds (i.e. there is no competition between agonist and antagonist for binding sites). Even when glutamate concentrations are very high (as might occur in seizure), the antagonism is maintained, as the glutamate cannot displace the antagonist and overcome the antagonism.2,3 References Hanada T et al. Perampanel: A novel, orally active, non-competitive AMPA-receptor antagonist that reduces seizure activity in rodent models of epilepsy. Epilepsia 2011;52:1331–1340. Kenakin T. Allosteric modulators: The new generation of receptor antagonists. Molecular Interventions 2004;4:222–229. Kenakin T. A pharmacology primer. Theory, applications, and methods. 2nd Edition. Academic Press. 2006. 3. Receptor antagonism is maintained and the channel remains closed Na+ ions Glutamate Perampanel 1Hanada T et al. Epilepsia 2011;52:1331–1340; 2Kenakin T. Molecular Interventions 2004;4:222–229.

AMPA receptor antagonism and seizure activity AMPA receptors: Important role in seizure initiation and spread Important and promising target for epilepsy therapy AMPA receptor antagonists: Anti-seizure activity in a broad range of animal models The AMPA receptor is the main receptor mediating the excitatory effects of glutamate and is implicated in the initiation and spread of seizures. As such, AMPA receptors are an important and promising target for epilepsy therapy. Several AMPA receptor antagonists have demonstrated anti-seizure activity in a broad range of animal seizure models, and perampanel, a non-competitive AMPA receptor antagonist, has completed Phase III clinical trials in patients with refractory partial-onset epilepsy. Reference Rogawski MA. Revisiting AMPA receptors as an antiepileptic drug target. Epilepsy Currents 2011;11:56–63. Perampanel: A non-competitive AMPA receptor antagonist Studied in Phase III clinical trials in patients with refractory partial-onset seizures Rogawski MA. Epilepsy Currents 2011;11:56–63.

Perampanel is selective for AMPA receptors Confidential Perampanel is selective for AMPA receptors In ligand-binding studies1,2 Perampanel has minimal affinity for receptors other than the AMPA receptor In receptor function studies1 Perampanel inhibits function of AMPA receptors at concentrations that have no effect on NMDA receptor function Effect on AMPA receptor function Effect on NMDA receptor function 50% inhibition at 93 nMa 18% inhibition at 30 μMa Ligand-binding studies:1,2 Perampanel was tested in a series of binding assays to evaluate potential activity at other physiologically important target molecules, such as receptors, voltage-gated channels, and enzymes. At relatively high concentrations (10 μM), perampanel did not reach 50% displacement of any of the 86 ligands tested, suggesting that perampanel selectively binds at the AMPA receptor. Examples of the ligands assessed were: angiotensin, adenosine, histamine, dopamine, endothelin, and glycine. Receptor function studies:2 In an assay that assesses receptor function in vitro, perampanel inhibits function of AMPA receptors at concentrations that have no effect on NMDA receptor function. The IC50 of perampanel (concentration required to achieve 50% inhibition of AMPA- induced Ca2+ influx) was 93 nM. In the same assay (NMDA-induced Ca2+ influx), perampanel could only achieve 18% inhibition of the response at a concentration of 30 μM (meaning that a 300-times higher concentration was required to achieve a smaller inhibition). References Hanada T et al. Perampanel: A novel, orally active, noncompetitive AMPA-receptor antagonist that reduces seizure activity in rodent models of epilepsy. Epilepsia 2011;52(7):1331–1340. Tokuhara N et al. Pharmacologic profile of perampanel: A novel, noncompetitive, selective, AMPA receptor antagonist. Poster presented at AAN 2008. a300-times higher concentration required to achieve a smaller inhibitory effect 1Hanada T et al. Epilepsia 2011;52(7):1331–1340; 2Tokuhara N et al. Poster presented at AAN 2008.

Perampanel is a non-competitive antagonist Confidential Perampanel is a non-competitive antagonist Radiolabelled binding studies demonstrate perampanel binds at a non- competitive site In these studies, perampanel was radioactively labelled, and its binding to neuronal membranes in vitro was measured Radiolabelled perampanel binds with high affinity This shows that perampanel binds to a specific target site in the brain Adding AMPA or glutamate does not reduce binding of radio-labelled perampanel This shows that perampanel does NOT bind to the glutamate-binding site of the AMPA receptor; if it did, glutamate and AMPA would displace its binding Adding known non-competitive AMPA receptor antagonists does reduce binding of radio-labelled perampanel This shows that perampanel DOES bind to a non-competitive site In these studies, perampanel was radioactively labelled, referred to as [3H]perampanel, and its binding to neuronal membranes in vitro was measured (rat forebrain membrane cultures). [3H]perampanel binds with high affinity to the membranes (with a Kd of 60 nM). This shows that perampanel binds to a specific target site in the brain. Adding AMPA or glutamate does not reduce binding of [3H]perampanel. This shows that perampanel does NOT bind to the glutamate-binding site of the AMPA receptor; if it did, glutamate and AMPA would displace its binding Adding a known non-competitive AMPA receptor antagonists DOES reduce binding of radiolabelled perampanel. In the presence of CP-465022 and GYKI 52466, binding of [3H]perampanel is reduced. This indicates that perampanel binds at the same site as these non-competitive antagonists, suggesting that perampanel is itself a non- competitive antagonist. Reference Hanada T et al. Perampanel: A novel, orally active, noncompetitive AMPA-receptor antagonist that reduces seizure activity in rodent models of epilepsy. Epilepsia 2011;52(7):1331–1340. Hanada T et al. Epilepsia 2011;52(7):1331–1340.

Perampanel is a selective, non-competitive, AMPA receptor antagonist Confidential Perampanel is a selective, non-competitive, AMPA receptor antagonist What does this mean? Explanation1–3 AMPA receptor antagonist1 Reduces the ability of glutamate (or any other AMPA receptor agonist) to activate the AMPA receptor Selective1 Selectively binds to AMPA receptors Doesn’t have significant affinity for other glutamate receptors or other receptors or transporters Non-competitive1 Binds to the AMPA receptor at a non-competitive site Does not DIRECTLY block glutamate from binding to the receptor at the glutamate-binding site Does INDIRECTLY (or non-competitively) inhibit the ability of glutamate to activate the receptor, by binding to the AMPA receptor at a non-competitive site In describing the properties of perampanel in more detail, it makes most sense to discuss antagonism first, then the selectivity of this interaction, then the non-competitive nature of the antagonism. Antagonist: Perampanel is an AMPA receptor antagonist.1 This means that it reduces the ability of glutamate, or any other AMPA receptor agonist (e.g. the chemical -amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid) to activate the glutamate AMPA receptor.1 Selective: The affinity of perampanel is selective for AMPA receptors over other glutamate receptors, and over other receptors and transporters.1 In other words, at a concentration that allows perampanel to bind to AMPA receptors, it does not bind to other glutamate receptors (e.g. the NMDA receptor, kainate receptor, or metabotropic receptors), or to other non-glutamate receptors or transporters.1,2 Non-competitive: An antagonist that binds to a receptor but does not compete with the agonist for the agonist-binding site is referred to as a non-competitive antagonist (or allosteric antagonist).3 It doesn’t act like a competitive antagonist, which binds to the receptor at the SAME binding site as the endogenous ligand, DIRECTLY blocking the ligand (glutamate) from binding to the receptor (at the glutamate-binding site).3, 4 Instead, it binds at a DIFFERENT binding site (the non-competitive site, or allosteric site) and causes a change in the receptor which means that the ligand (glutamate) can still bind but cannot activate the receptor.3, 4 References Hanada T et al. Perampanel: A novel, orally active, noncompetitive AMPA-receptor antagonist that reduces seizure activity in rodent models of epilepsy. Epilepsia 2011;52(7):1331–1340. Rang HP et al. Chapter 1. How drugs act: general principles. In: Pharmacology. Rang HP, Dale MM, Ritter JM (Eds). 3rd Edition. Churchill Livingstone. 1995. Kenakin T. Allosteric modulators: The new generation of receptor antagonists. Molecular Interventions 2004;4:222–229. Kenakin T. A Pharmacology Primer. Theory, Applications, and Methods. 2nd Edition. Academic Press. 2006. 1Hanada T et al. Epilepsia 2011;52(7):1331–1340; 2Rang HP et al. In: Pharmacology. 1995; 3Kenakin T. Molecular Interventions 2004;4:222–229.

Perampanel is a selective, non-competitive, AMPA receptor antagonist Confidential Perampanel is a selective, non-competitive, AMPA receptor antagonist What are the theoretical implications? Implications1–4 AMPA receptor antagonist1 Reduces activation of AMPA receptors by glutamate, reducing excitability of neurons expressing these receptors Selective1 Perampanel is unlikely to have effects on non-AMPA glutamate receptors low potential for phencyclidine-likea effects as no significant NMDA receptor binding Unlikely to have effects on other receptors or transporters Non-competitive1 Activity of a non-competitive antagonist is maintained even when levels of the agonist (e.g. glutamate) are high In contrast, a competitive antagonist is displaced (out- competed) when agonist concentrations are high, allowing glutamate to bind and activate the receptor aPhencyclidine also known as ‘angel dust’ or PCP The mechanism of action of perampanel has a number of implications. Antagonism: Perampanel is an AMPA receptor antagonist.1 As with any other antagonist, it will act to reduce ability of the ligand (glutamate) to activate the receptor (the AMPA receptor). Because the AMPA receptor is the main receptor mediating the rapid effects of glutamate, the major excitatory neurotransmitter2 the result of this antagonism would logically be a reduction in the excitability of neurons expressing this receptor, in response to glutamate. Selective: The selectivity of perampanel suggests that it is unlikely to have effects on non-AMPA glutamate receptors, or on other receptors or transporters, when used at concentrations that are sufficient to cause antagonism of AMPA receptors.1 Importantly, perampanel does not have significant affinity for the NMDA receptor for glutamate1, and thus should avoid effects like those caused by phencyclidine (PCP or angel dust) or ketamine, drugs which inhibit the NMDA receptor. Non-competitive: One major implication of a non-competitive mechanism of antagonism is that the effect should be insurmountable.3 Because the antagonist binds to a different site than glutamate binds (i.e. there is no competition for sites), when glutamate concentrations are very high (as might occur in pathological conditions like severe seizure or status epilepticus), then the glutamate cannot overcome the antagonism.3 In contrast, a competitive antagonist is “surmountable”4 and can be displaced from the binding site by high glutamate concentrations, thus limiting the effect of the antagonist at high glutamate levels. References Hanada T et al. Perampanel: A novel, orally active, noncompetitive AMPA-receptor antagonist that reduces seizure activity in rodent models of epilepsy. Epilepsia 2011;52(7):1331–1340. Rogawski MA. Revisiting AMPA receptors as an antiepileptic drug target. Epilepsy Currents 2011;11(2):56–63. Kenakin T. A Pharmacology Primer. Theory, Applications, and Methods. 2nd Edition. Academic Press. 2006. Rang HP et al. Chapter 1. How drugs act: general principles. In: Pharmacology. Rang HP, Dale MM, Ritter JM (Eds).3rd Edition. Churchill Livingstone. 1995 1Hanada T et al. Epilepsia 2011;52(7):1331–1340; 2Rogawski MA. Epilepsy Currents 2011;11:56–63; 3Kenakin T. In: A Pharmacology Primer. 2006; 4Rang HP et al. In: Pharmacology. 1995.