Rosemarie Roeloffs

A-803467, a potent and selective Nav1.8 sodium channel blocker, attenuates neuropathic and inflammatory pain in the rat.

Activation of tetrodotoxin-resistant sodium channels contributes to action potential electrogenesis in neurons. Antisense oligonucleotide studies directed against Nav1.8 have shown that this channel contributes to experimental inflammatory and neuropathic pain. We report here the discovery of A-803467, a sodium channel blocker that potently blocks tetrodotoxin-resistant currents (IC50 = 140 nM) and the generation of spontaneous and electrically evoked action potentials in vitro in rat dorsal root ganglion neurons. In recombinant cell lines, A-803467 potently blocked human Nav1.8 (IC50 = 8 nM) and was >100-fold selective vs. human Nav1.2, Nav1.3, Nav1.5, and Nav1.7 (IC50 values ≥1 μM). A-803467 (20 mg/kg, i.v.) blocked mechanically evoked firing of wide dynamic range neurons in the rat spinal dorsal horn. A-803467 also dose-dependently reduced mechanical allodynia in a variety of rat pain models including: spinal nerve ligation (ED50 = 47 mg/kg, i.p.), sciatic nerve injury (ED50 = 85 mg/kg, i.p.), capsaicin-induced secondary mechanical allodynia (ED50 ≈ 100 mg/kg, i.p.), and thermal hyperalgesia after intraplantar complete Freunds adjuvant injection (ED50 = 41 mg/kg, i.p.). A-803467 was inactive against formalin-induced nociception and acute thermal and postoperative pain. These data demonstrate that acute and selective pharmacological blockade of Nav1.8 sodium channels in vivo produces significant antinociception in animal models of neuropathic and inflammatory pain.

Discovery and biological evaluation of 5-aryl-2-furfuramides, potent and selective blockers of the Nav1.8 sodium channel with efficacy in models of neuropathic and inflammatory pain.

Nav1.8 (also known as PN3) is a tetrodotoxin-resistant (TTx-r) voltage-gated sodium channel (VGSC) that is highly expressed on small diameter sensory neurons and has been implicated in the pathophysiology of inflammatory and neuropathic pain. Recent studies using an Nav1.8 antisense oligonucleotide in an animal model of chronic pain indicated that selective blockade of Nav1.8 was analgesic and could provide effective analgesia with a reduction in the adverse events associated with nonselective VGSC blocking therapeutic agents. Herein, we describe the preparation and characterization of a series of 5-substituted 2-furfuramides, which are potent, voltage-dependent blockers (IC50 < 10 nM) of the human Nav1.8 channel. Selected derivatives, such as 7 and 27, also blocked TTx-r sodium currents in rat dorsal root ganglia (DRG) neurons with comparable potency and displayed >100-fold selectivity versus human sodium (Nav1.2, Nav1.5, Nav1.7) and human ether-a-go-go (hERG) channels. Following systemic administration, compounds 7 and 27 dose-dependently reduced neuropathic and inflammatory pain in experimental rodent models.

KCNQ potassium channels: drug targets for the treatment of epilepsy and pain

Epilepsy and neuropathic pain are disorders characterised by excessive neuronal activity. These disorders are currently managed by drugs that are capable of dampening neuronal excitability, including voltage-gated sodium channel blockers, voltage-operated calcium channel modulators and modulators of inhibitory GABAergic neurotransmission. However, these drugs are rarely 100% efficacious and their use is often associated with limiting side effects. Thus, there is a clear medical need for novel agents to treat these diseases. One potential mechanism that has not yet been exploited is potassium (K+) channel opening. A significant (and growing) body of genetic, molecular, physiological and pharmacological evidence now exists to indicate that KCNQ-based currents represent particularly interesting targets for the treatment of diseases such as epilepsy and neuropathic pain. Evidence supporting these K+ channels as novel drug targets will be reviewed in the following article. Worldwide patent activity relating to KCNQ channels and KCNQ-modulating drugs and their uses will also be summarised.

In Vivo Profile of ICA-27243 [N-(6-Chloro-pyridin-3-yl)-3,4-difluoro-benzamide], a Potent and Selective KCNQ2/Q3 (Kv7.2/Kv7.3) Activator in Rodent Anticonvulsant Models

Openers or activators of neuronal KCNQ2/Q3 potassium channels decrease neuronal excitability and may provide benefit in the treatment of disorders of neuronal excitability such as epilepsy. In the present study, we evaluate the effects of ICA-27243 [N-(6-chloro-pyridin-3-yl)-3,4-difluoro-benzamide], an orally bioavailable, potent, and selective KCNQ2/Q3 opener, in a broad range of rodent seizure models. ICA-27243 was effective against maximal electroshock (MES) and pentylenetetrazole (PTZ)-induced seizures in both rats (MES, ED50 = 1.5 mg/kg p.o.; PTZ, ED50 = 2.2 mg/kg p.o.) and mice (MES, ED50 = 8.6 mg/kg p.o.; PTZ, ED50 = 3.9 mg/kg p.o.) in the rat amygdala kindling model of partial seizures (full protection from seizure at 9 mg/kg p.o.) and in the 6-Hz model of psychomotor seizures in mice (active at 10 mg/kg i.p.). Antiseizure efficacy in all models was observed at doses significantly less than those shown to effect open-field locomotor activity (rat ED50 = 40 mg/kg p.o.) or ability to remain on a Rotorod (no effect in rat at doses up to 100 mg/kg p.o.). There was no evidence of cognition impairment as measured in the Morris water maze in the rat (10 and 30 mg/kg p.o.), nor was there evidence of the development of tolerance after multiple doses of ICA-27243. Our findings suggest that selective KCNQ2/Q3 opening activity in the absence of effects on KCNQ3/Q5 or GABA-activated channels may be sufficient for broad-spectrum antiepileptic activity in rodents.

Novel KCNQ2/Q3 Agonists as Potential Therapeutics for Epilepsy and Neuropathic Pain

Current drugs for the treatment of seizure disorders, although effective in many patients, still suffer from a number of failures and are not effective in some forms of resistant epilepsies. Historically, many of these drugs have multiple mechanisms of action including calcium and sodium channel blockade as well as GABAergic activity and thus a number of associated side effects. Modulation of the M-current through opening of KCNQ channels has been proposed as a way to attenuate neuroexcitability and have a therapeutic benefit for the treatment of seizure disorders. Therefore, as part of our program to identify new treatments for epilepsy, we set out to identify agonists of KCNQ channels. High throughput screening of our corporate collection led to the identification of 1, adamantane-1-carboxylic acid (3-methyl-3H-benzothiazol-2-ylidine) hydrazide, a potent KCNQ2/Q3 agonist. Herein, we describe the syntheses and structure-activity relationships of analogues of 1 as well as their in vivo activity in animal models of epilepsy and neuropathic pain.

A novel selective and orally bioavailable Nav1.8 channel blocker, PF‐01247324, attenuates nociception and sensory neuron excitability

NaV1.8 ion channels have been highlighted as important molecular targets for the design of low MW blockers for the treatment of chronic pain. Here, we describe the effects of PF‐01247324, a new generation, selective, orally bioavailable Nav1.8 channel blocker of novel chemotype.

N-Pyridyl and Pyrimidine Benzamides as KCNQ2/Q3 Potassium Channel Openers for the Treatment of Epilepsy

A series of N-pyridyl benzamide KCNQ2/Q3 potassium channel openers were identified and found to be active in animal models of epilepsy and pain. The best compound 12 [ICA-027243, N-(6-chloro-pyridin-3-yl)-3,4-difluoro-benzamide] has an EC50 of 0.38 μM and is selective for KCNQ2/Q3 channels. This compound was active in several rodent models of epilepsy and pain but upon repeated dosing had a number of unacceptable toxicities that prevented further development. On the basis of the structure-activity relationships developed around 12, a second compound, 51, [N-(2-chloro-pyrimidin-5-yl)-3,4-difluoro-benzamide, ICA-069673], was prepared and advanced into a phase 1 clinical study. Herein, we describe the structure-activity relationships that led to the identification of compound 12 and to the corresponding pyrimidine 51.

Subtype-selective Nav1.8 sodium channel blockers: Identification of potent, orally active nicotinamide derivatives

A series of aryl-substituted nicotinamide derivatives with selective inhibitory activity against the Na(v)1.8 sodium channel is reported. Replacement of the furan nucleus and homologation of the anilide linker in subtype-selective blocker A-803467 (1) provided potent, selective derivatives with improved aqueous solubility and oral bioavailability. Representative compounds from this series displayed efficacy in rat models of inflammatory and neuropathic pain.

Discovery of potent furan piperazine sodium channel blockers for treatment of neuropathic pain

The synthesis and pharmacological characterization of a novel furan-based class of voltage-gated sodium channel blockers is reported. Compounds were evaluated for their ability to block the tetrodotoxin-resistant sodium channel Na(v)1.8 (PN3) as well as the Na(v)1.2 and Na(v)1.5 subtypes. Benchmark compounds from this series possessed enhanced potency, oral bioavailability, and robust efficacy in a rodent model of neuropathic pain, together with improved CNS and cardiovascular safety profiles compared to the clinically used sodium channel blockers mexiletine and lamotrigine.

The effect of kappa-opioid receptor agonists on tetrodotoxin-resistant sodium channels in primary sensory neurons.

BACKGROUND: A non-opioid receptor-mediated inhibition of sodium channels in dorsal root ganglia (DRGs) by &kgr;-opioid receptor agonists (&kgr;-ORAs) has been reported to contribute to the antinociceptive actions in animals and humans. In this study, we examined structurally diverse &kgr;-ORAs for their abilities to inhibit tetrodotoxin-resistant (TTX-r) sodium channels in adult rat DRGs. METHODS: Whole-cell recordings of TTX-r sodium currents were performed on cultured adult rat DRGs. Structurally diverse &kgr;-ORAs were studied for their abilities to inhibit TTX-r sodium channels. RESULTS: The racemic &kgr;-ORA, (±)U50,488, inhibited TTX-r sodium currents in a voltage-dependent manner, yielding IC50 values of 49 and 8 &mgr;M, at prepulse potentials of −100 and −40 mV, respectively. Furthermore, we found that both the &kgr;-ORA U50,488 active enantiomer 1S,2S U50,488 and the inactive enantiomer 1R,2R U50,488 were equally potent inhibitors of TTX-r sodium currents. Structurally related &kgr;-ORAs, such as BRL 52537 and ICI 199,441 also inhibited TTX-r sodium currents. However, sodium channel inhibition and &kgr;-opioid receptor agonism have a distinct structure-activity relationship because another &kgr;-ORA (ICI 204,488) was inactive versus TTX-r sodium channels. We further investigated the sodium channel block of this class of compounds by studying (±)U50,488. (±)U50,488 was found to preferentially interact with the slow inactivated state of TTX-r sodium channels and to retard recovery from inactivation. CONCLUSION: Our results suggest that TTX-r sodium channels can be inhibited by many &kgr;-ORAs via an opioid receptor-independent mechanism. Although the potency for sodium channel inhibition is typically much less than apparent affinity for opioid receptors, sodium channel block may still contribute to the antinociceptive effects of this class of compounds.