Mervyn Thompson

Identification and characterisation of SB-366791, a potent and selective vanilloid receptor (VR1/TRPV1) antagonist

Vanilloid receptor-1 (TRPV1) is a non-selective cation channel, predominantly expressed by peripheral sensory neurones, which is known to play a key role in the detection of noxious painful stimuli, such as capsaicin, acid and heat. To date, a number of antagonists have been used to study the physiological role of TRPV1; however, antagonists such as capsazepine are somewhat compromised by non-selective actions at other receptors and apparent modality-specific properties. SB-366791 is a novel, potent, and selective, cinnamide TRPV1 antagonist isolated via high-throughput screening of a large chemical library. In a FLIPR-based Ca(2+)-assay, SB-366791 produced a concentration-dependent inhibition of the response to capsaicin with an apparent pK(b) of 7.74 +/- 0.08. Schild analysis indicated a competitive mechanism of action with a pA2 of 7.71. In electrophysiological experiments, SB-366791 was demonstrated to be an effective antagonist of hTRPV1 when activated by different modalities, such as capsaicin, acid or noxious heat (50 degrees C). Unlike capsazepine, SB-366791 was also an effective antagonist vs. the acid-mediated activation of rTRPV1. With the aim of defining a useful tool compound, we also profiled SB-366791 in a wide range of selectivity assays. SB-366791 had a good selectivity profile exhibiting little or no effect in a panel of 47 binding assays (containing a wide range of G-protein-coupled receptors and ion channels) and a number of electrophysiological assays including hippocampal synaptic transmission and action potential firing of locus coeruleus or dorsal raphe neurones. Furthermore, unlike capsazepine, SB-366791 had no effect on either the hyperpolarisation-activated current (I(h)) or Voltage-gated Ca(2+)-channels (VGCC) in cultured rodent sensory neurones. In summary, SB-366791 is a new TRPV1 antagonist with high potency and an improved selectivity profile with respect to other commonly used TRPV1 antagonists. SB-366791 may therefore prove to be a useful tool to further study the biology of TRPV1.

Characterization of SB-705498, a Potent and Selective Vanilloid Receptor-1 (VR1/TRPV1) Antagonist That Inhibits the Capsaicin-, Acid-, and Heat-Mediated Activation of the Receptor

Vanilloid receptor-1 (TRPV1) is a nonselective cation channel, predominantly expressed by sensory neurons, which plays a key role in the detection of noxious painful stimuli such as capsaicin, acid, and heat. TRPV1 antagonists may represent novel therapeutic agents for the treatment of a range of conditions including chronic pain, migraine, and gastrointestinal disorders. Here we describe the in vitro pharmacology of N-(2-bromophenyl)-N′-[((R)-1-(5-trifluoromethyl-2-pyridyl)pyrrolidin-3-yl)]urea (SB-705498), a novel TRPV1 antagonist identified by lead optimization of N-(2-bromophenyl)-N′-{2-[ethyl(3-methylphenyl)amino]ethyl}urea (SB-452533), which has now entered clinical trials. Using a Ca2+-based fluorometric imaging plate reader (FLIPR) assay, SB-705498 was shown to be a potent competitive antagonist of the capsaicin-mediated activation of the human TRPV1 receptor (pKi = 7.6) with activity at rat (pKi = 7.5) and guinea pig (pKi = 7.3) orthologs. Whole-cell patch-clamp electrophysiology was used to confirm and extend these findings, demonstrating that SB-705498 can potently inhibit the multiple modes of receptor activation that may be relevant to the pathophysiological role of TRPV1 in vivo: SB-705498 caused rapid and reversible inhibition of the capsaicin (IC50 = 3 nM)-, acid (pH 5.3)-, or heat (50°C; IC50 = 6 nM)-mediated activation of human TRPV1 (at -70 mV). Interestingly, SB-705498 also showed a degree of voltage dependence, suggesting an effective enhancement of antagonist action at negative potentials such as those that might be encountered in neurons in vivo. The selectivity of SB-705498 was defined by broad receptor profiling and other cellular assays in which it showed little or no activity versus a wide range of ion channels, receptors, and enzymes. SB-705498 therefore represents a potent and selective multimodal TRPV1 antagonist, a pharmacological profile that has contributed to its definition as a suitable drug candidate for clinical development.

Tonabersat (SB-220453) a novel benzopyran with anticonvulsant properties attenuates trigeminal nerve-induced neurovascular reflexes.

The effects of tonabersat (SB‐220453) were evaluated on trigeminal nerve ganglion stimulation‐induced sensory‐autonomic neurovascular reflexes in the anaesthetized cat. Comparisons were made to intravenous administration of carabersat (SB‐204269), and to valproate, gabapentin and lamotrigine following intraduodenal administration. There were no effects on resting blood pressure, heart rate, carotid blood flow or carotid vascular resistance for any compound evaluated. Trigeminal nerve ganglion stimulation increased carotid blood flow by 65% and reduced vascular resistance by 41% with minimal effect on blood pressure (<10%) and no effect on heart rate. Intravenous infusion of tonabersat or carabersat (both 3.4 μmol h−1) produced time related reductions in stimulation‐induced responses with a maximal inhibition (relative to control) of 30±7% (n=4), at 240 min for tonabersat and 33±4% (n=3) at 180 min for carabersat. Tonabersat (11.5 μmol h−1) produced a similar inhibitory effect (32±9%, n=4) after 120 min of infusion. Following intraduodenal administration of tonabersat, the maximal inhibition of nerve stimulation‐induced responses was 55±4% at 120 min (n=4) for tonabersat 10 mg kg−1, and 24±2% after 180 min for 1 mg kg−1 (n=4). Intraduodenal administration of sodium valproate (10 or 100 mg kg−1 n=4/group) had no effect on neurovascular reflexes. Maximal inhibition of nerve ganglion‐stimulated reductions in carotid vascular resistance were observed at 150 min for lamotrigine (50 mg kg−1, 52±12%, n=4) and gabapentin (100 mg kg−1, 17±13%, n=3). Lamotrigine 10 mg kg−1 produced 22±11% (n=3) inhibition after 180 min. These data demonstrate blockade of trigeminal parasympathetic reflexes with tonabersat, carabersat and other anticonvulsants. These agents may therefore have therapeutic benefit in conditions where this type of reflex is evident.

Identification of (-)-cis-6-acetyl-4S-(3-chloro-4-fluoro-benzoylamino)- 3,4-dihydro-2,2-dimethyl-2H-benzo[b]pyran-3S-ol as a potential antimigraine agent.

Optimisation of novel cis- and trans-4-(substituted-amido)benzopyran-3-ol derivatives has led to the identification of SB-220453 20 with an in vivo pre-clinical CNS profile predictive of potential antimigraine activity.

Profile of SB-204269, a mechanistically novel anticonvulsant drug, in rat models of focal and generalized epileptic seizures

1 Earlier optimization of structure‐activity relationships in a novel series of 4‐(benzoylamino)‐benzopyrans, led to the discovery of SB‐204269 (trans‐(+)‐6‐acetyl‐4S‐(4‐fluorobenzoylamino)‐3,4‐dihydro‐2,2‐dimethyl‐2H‐benzo[b]pyran‐3R‐ol, hemihydrate), a potent orally‐active anticonvulsant in the mouse maximal electroshock seizure threshold (MEST) test. 2 Studies have now been undertaken to determine the effects of SB‐204269 in a range of seizure models and tests of neurological deficits in rats. In addition, the compound has been evaluated in a series of in vitro mechanistic assays. 3 SB‐204269 proved to be an orally‐effective anticonvulsant agent, at doses (0.1–30 mg kg−1) devoid of overt behavioural depressant properties, in models of both electrically (MEST and maximal electroshock (MES)) and chemically (i.v. pentylenetetrazol (PTZ) infusion)‐evoked tonic extension seizures. However, the compound did not inhibit PTZ‐induced myoclonic seizures at doses up to 30 mg kg−1, p.o. 4 SB‐204269 also selectively reduced focal electrographic seizure activity in an in vitro elevated K+ rat hippocampal slice model at concentrations (0.1–10 μM) that had no effect on normal synaptic activity and neuronal excitability. 5 In all of these seizure models, SB‐204269 was equivalent or better than the clinically established antiepileptic drugs carbamazepine and lamotrigine, in terms of anticonvulsant potency and efficacy. 6 Unlike SB‐204269, the corresponding trans 3S,4R enantiomer, SB‐204268, did not produce marked anticonvulsant effects, an observation in accord with previous findings for other related pairs of trans enantiomers in the benzopyran series. 7 In the rat accelerating rotarod test, a sensitive paradigm for the detection of neurological deficits such as sedation and motor incoordination, SB‐204269 was inactive even at doses as high as 200 mg kg−1, p.o. This was reflected in the excellent therapeutic index (minimum significantly effective dose in the rotarod test/ED50 in the MES test) for SB‐204269 of >31, as compared to equivalent values of only 7 and 13 for carbamazepine and lamotrigine, respectively. 8 At concentrations (10 μM) well above those required to produce anticonvulsant activity in vivo (i.e. 0.1 μM in brain), SB‐204269 did not interact with many of the well known mechanistic targets for established antiepileptic drugs (e.g. Na+ channels or GABAergic neurotransmission). Subsequent studies have shown that the anticonvulsant properties of SB‐204269 are likely to be mediated by a novel stereospecific binding site present in the CNS. 9 The overall efficacy profile in rodent seizure models, together with a minimal liability for inducing neurological impairment and an apparently unique mechanism of action, highlight the therapeutic potential of SB‐204269 for the treatment of refractory partial and generalized tonic‐clonic seizures.

Design and synthesis of 6-phenylnicotinamide derivatives as antagonists of TRPV1

6-Phenylnicotinamide (2) was previously identified as a potent TRPV1 antagonist with activity in an in vivo model of inflammatory pain. Optimization of this lead through modification of both the biaryl and heteroaryl components has resulted in the discovery of 6-(4-fluorophenyl)-2-methyl-N-(2-methylbenzothiazol-5-yl)nicotinamide (32; SB-782443) which possesses an excellent overall profile and has been progressed into pre-clinical development.

Characterization of the binding of [3H]‐SB‐204269, a radiolabelled form of the new anticonvulsant SB‐204269, to a novel binding site in rat brain membranes

1 SB‐204269 (trans‐(+)‐6‐acetyl‐4S‐(4‐fluorobenzoylamino)‐3,4‐dihydro‐2,2‐dimethyl‐2H‐benzol[b]pyran‐3R‐ol, hemihydrate) shows potent anticonvulsant activity in a range of animal seizure models, with a lack of neurological or cardiovascular side‐effects. The profile of the compound suggests that it may have a novel mechanism of action. This study describes the characteristics of a binding site for [3H]‐SB‐204269 in rat forebrain membranes. 2 Specific [3H]‐SB‐204269 binding was saturable and analysis indicated binding to a homogenoeous population of non‐interacting binding sites with a dissociation constant (KD) of 32±1 nM and a maximum binding capacity (Bmax) of 253±18 fmol mg−1 protein. Kinetic studies indicated monophasic association and dissociation. Binding was similar in HEPES or Tris‐HCl buffers and was unaffected by Na+, K+, Ca2+ or Mg2+ ions. Specific binding was widely distributed in brain, but was minimal in a range of peripheral tissues. 3 Specific [3H]‐SB‐204269 binding was highly stereoselective, with a 1000 fold difference between the affinities of SB‐204269 and its enantiomer SB‐204268 for the binding site. The affinities of analogues of SB‐204269 for binding can be related to their activities in the mouse maximal electroshock seizure threshold (MEST) test of anticonvulsant action. 4 None of the standard anticonvulsant drugs, phenobarbitone, phenytoin, sodium valproate, carbamazepine, diazepam and ethosuximide, or the newer anticonvulsants, lamotrigine, vigabatrin, gabapentin and levetiracetam, showed any affinity for the [3H]‐SB‐204269 binding site. A wide range of drugs active at amino acid receptors, Na+ or K+ channels or various other receptors did not demonstrate any affinity for the binding site. 5 These studies indicate that SB‐204269 possesses a specific CNS binding site which may mediate its anticonvulsant activity. This binding site does not appear to be directly related to the sites of action of other known anticonvulsant agents, but may have an important role in regulating neuronal excitability.

Discovery of N-(3-Fluorophenyl)-1-[(4-([(3S)-3-methyl-1-piperazinyl]methyl)phenyl)acetyl]-4-piperidinamine (GSK962040), the First Small Molecule Motilin Receptor Agonist Clinical Candidate

N-(3-fluorophenyl)-1-[(4-([(3S)-3-methyl-1-piperazinyl]methyl)phenyl)acetyl]-4-piperidinamine 12 (GSK962040) is a novel small molecule motilin receptor agonist. It possesses excellent activity at the recombinant human motilin receptor and also at the native rabbit motilin receptor where its agonist activity results in potentiation of the amplitude of neuronal-mediated contractions of isolated gastric antrum tissue. Compound 12 also possesses highly promising pharmacokinetic profiles in both rat and dog, and these results, in combination with further profiling in human native tissue and an in vivo model of gastrointestinal transit in the rabbit, have led to its selection as a candidate for further development.

Synthesis and potential anxiolytic activity of 4-amino-pyrido[2,3-b]indoles

Abstract A novel series of 4-amino-pyrido[2,3-b]indoles is presented as GABAA modulators with good potential as therapeutic agents for the treatment of anxiety disorders.

A simplified template approach towards the synthesis of a potent beta-3 adrenoceptor agonist at the human receptor

Abstract A simplified template approach was used to delineate the structural requirements for high potency and intrinsic activity of aryloxypropanolamines as agonists at the human beta-3 adrenoceptor. The information generated was used to prepare selective beta-3 adrenoceptor agonists.