Identification of [4-[4-(methylsulfonyl)phenyl]-6-(trifluoromethyl)-2-pyrimidinyl] amines and ethers as potent and selective cyclooxygenase-2 inhibitors.

A novel series of [4-[4-(methylsulfonyl)phenyl]-6-(trifluoromethyl)-2-pyrimidine-based cyclooxygenase-2 (COX-2) inhibitors, which have a different arrangement of substituents compared to the more common 1,2-diarylheterocycle based molecules, have been discovered. For example, 2-(butyloxy)-4-[4-(methylsulfonyl)phenyl]-6-(trifluoromethyl)pyrimidine (47), a member of the 2-pyrimidinyl ether series, has been shown to be a potent and selective inhibitor with a favourable pharmacokinetic profile, high brain penetration and good efficacy in rat models of hypersensitivity.

The discovery of biaryl carboxamides as novel small molecule agonists of the motilin receptor.

Optimisation of urea (5), identified from high throughput screening and subsequent array chemistry, has resulted in the identification of pyridine carboxamide (33) which is a potent motilin receptor agonist possessing favourable physicochemical and ADME profiles. Compound (33) has demonstrated prokinetic-like activity both in vitro and in vivo in the rabbit and therefore represents a promising novel small molecule motilin receptor agonist for further evaluation as a gastroprokinetic agent.

In vivo pharmacological effects of JZP-4, a novel anticonvulsant, in models for anticonvulsant, antimania and antidepressant activity.

JZP-4 is a potent calcium and sodium channel blocker, which is currently being evaluated in patients as an anticonvulsant and mood stabilizer. In the current studies, JZP-4 was evaluated in a variety of animal models for anticonvulsant, antimania and antidepressant activity. In the mouse and rat maximal electroshock models, JZP-4 was slightly more potent than LTG. In the mouse pentylenetetrazole induced seizures model, JZP-4 was approximately twice as potent as lamotrigine in prolonging the time to clonus. In the mouse 6-Hz model for drug resistant or refractory epilepsy, JZP-4 had potent anticonvulsant activity at all current intensities, whereas LTG was active at only the lowest current intensity. In the mouse amphetamine-chlordiazepoxide model for antimanic effects, JZP-4, but not LTG, produced dose-related and significant effects at 3 and 10 mg/kg i.p. In the rat forced swim model of antidepressant activity, JZP-4 (30 mg/kg i.p.) produced a significant reduction in immobility and an increase in climbing behavior. LTG (30 mg/kg i.p.) produced similar effects but these effects did not achieve statistical significance. The specificity of this antidepressant response was confirmed in the rat locomotor test. In this test, JZP-4 produced dose-related and significant reductions in locomotor activity, indicating that it was not a CNS stimulant. LTG produced no significant effects in the rat locomotor test. The studies have demonstrated that JZP-4 has greater potency and efficacy than LTG in models of refractory epilepsy, antidepressant activity and antimania activity. The variance between the effects of LTG and JZP-4 may be related to the greater potency at sodium channels or the additional pharmacological actions of JZP-4 on calcium channels.

Anticonvulsant mechanisms for today and tomorrow.

Epilepsy is perhaps the most common of all the serious neurological disorders, with 50-100 million people worldwide exhibiting clinically recognized epilepsy. However, there has been relatively little improvement in anticonvulsant drug efficacy since the introduction of, for example, phenobarbital and phenytoin in 1912 and 1930. Epilepsy can be broadly subdivided into partial, generalized and unclassified seizures, and seizure type is used to guide the selection of the anticonvulsant drug to be used. If monotherapy with one anticonvulsant class fails, then an agent from a different class is attempted. If patients still prove to be refractory, combination therapy is considered. Despite side effects, approximately 60% of patients experience long-term remission of their symptoms following drug therapy, while 40% remain refractory to drug treatment, emphasizing the need to develop novel anticonvulsant mechanisms with enhanced efficacy.

Effect of lamotrigine on the activities of monoamine oxidases A and B in vitro and on monoamine disposition in vivo.

Recent clinical evidence indicates that the broad spectrum anticonvulsant drug lamotrigine is effective against the depressive phase of bipolar illness and the difficult to treat rapid cycling form of the disorder. However, the molecular mechanism underlying this therapeutic action remains uncertain. Given that inhibition of the A-type of monoamine oxidase (MAO) is a proven antidepressant mechanism, we investigated the effects of lamotrigine on MAO activities in vitro and on monoamine disposition in vivo. In vitro, lamotrigine inhibited rat brain MAO activities with Ki values (MAO-A, 15 microM; MAO-B, 18 microM) potentially within the therapeutic range for this drug. The effects of lamotrigine on the MAO-A activities of rat brain and human liver preparations were almost identical suggesting minimal species or tissue variation. In contrast, there was no (MAO-A) or minimal (MAO-B) reduction in brain MAO activities when assayed ex vivo following the administration of lamotrigine to rats. In vivo brain microdialysis failed to detect meaningful alterations in extracellular hippocampal or frontal cortex monoamine concentrations. Furthermore, lamotrigine did not modulate oral tyramine-induced hypertension in rats or 5-hydroxytryptophan-induced head shaking in mice, providing strong evidence that the drug does not perturb monoamine metabolism in vivo. The absence of observable effects of lamotrigine on monoamine disposition in vivo may be explained by the competitive and highly reversible nature of the interaction of lamotrigine with MAO isoforms. Thus, altered monoamine metabolism in vivo is unlikely to account for the antidepressant action of the drug in bipolar depression.

LABORAS: Initial pharmacological validation of a system allowing continuous monitoring of laboratory rodent behaviour.

A newly developed apparatus for automated behavioural analysis, Laboratory Animal Behaviour Observation, Registration and Analysis System (LABORAS), has been further validated with respect to the ability of the system to detect the pharmacodynamic effects of standard pharmacological tools. Data were obtained from rats administered with mCPP (reversal with SB242084), 8-OH-DPAT (reversal with WAY100635), amphetamine (reversal with haloperidol) and angiotensin, with the focus on locomotor activity, feeding and drinking behaviours. The data captured and analysed by LABORAS, suggests that the automated system is able to detect pharmacologically induced changes in behaviour, reliably and efficiently, with a significant reduction in the number of animals required, and reduced operator input.

Effect of lamotrigine treatment on epileptogenesis: an experimental study in rat.

Prevention of epileptogenesis in patients with acute brain damaging insults like status epilepticus (SE) is a major challenge. We investigated whether lamotrigine (LTG) treatment started during SE is antiepileptogenic or disease-modifying. To mimic a clinical study design, LTG treatment (20 mg/kg) was started 2 h after the beginning of electrically induced SE in 14 rats and continued for 11 weeks (20 mg/kg per day for 2 weeks followed by 10 mg/kg per day for 9 weeks). One group of rats (n = 14) was treated with vehicle. Nine non-stimulated rats with vehicle treatment served as controls. Outcome measures were occurrence of epilepsy, severity of epilepsy, and histology (neuronal loss, mossy fiber sprouting). Clinical occurrence of seizures was assessed with 1-week continuous video-electroencephalography monitoring during the 11th (i.e. during treatment) and 14th week (i.e. after drug wash-out) after SE. LTG reduced the number of electrographic seizures during SE to 43% of that in the vehicle group (P < 0.05). In the vehicle group, 93% (13/14), and in the LTG group, 100% (14/14) of the animals, developed epilepsy. In both groups, 64% of the rats had severe epilepsy (seizure frequency >1 per day). The mean frequency of spontaneous seizures, seizure duration, or behavioral severity of seizures did not differ between groups. The severity of hippocampal neuronal damage and density of mossy fiber sprouting were similar. In LTG-treated rats with severe epilepsy, however, the duration of seizures was shorter (34 versus 54s, P < 0.05) and the behavioral seizure score was milder (1.4 versus 3.4, P < 0.05) during LTG treatment than after drug wash-out. LTG treatment started during SE and continued for 11 weeks was not antiepileptogenic but did not worsen the outcome. These data, together with earlier studies of other antiepileptic drugs, suggest that strategies other than Na(+)-channel blockade should be explored to modulate the molecular cascades leading to epileptogenesis after SE.

Effects of lamotrigine and levetiracetam on seizure development in a rat amygdala kindling model.

In kindling models of epilepsy, the period during which repeated stimulation evokes intensifying seizures is attributed to an underlying epileptogenic process, and the point at which class 5 kindled seizures occur is considered the established epileptic state. Previous studies have indicated that a separation can occur between drug effects on these two components. For example, carbamazepine and phenytoin inhibit kindled seizures but have no effect on seizure development, whereas levetiracetam inhibits both components. We have investigated the profile of lamotrigine in the amygdala kindling model, including levetiracetam for comparison. As expected, both treatments dose-dependently inhibited class 5 kindled seizures. In a separate study, daily administration of either lamotrigine (20mgkg(-1) i.p.) or levetiracetam (50mgkg(-1) i.p.) demonstrated antiepileptogenic-like effects by blocking seizure development during the treatment period. Following cessation of drug treatment, further daily stimulation resulted in kindled seizure development, though there was a significant increase with both treatment groups, relative to the control group, in the total number of stimulations required to produce classes 3 and 5 seizures. In addition, prior levetiracetam treatment appeared to delay or prevent the expected increase in after-discharge duration (ADD). These results suggest that lamotrigine, like levetiracetam, possesses the ability to counteract kindling acquisition, which differentiates it from other drugs with sodium channel blocking activity.

Broad spectrum anticonvulsant activity of BW534U87: possible role of an adenosine-dependent mechanism.

The novel putative anticonvulsant drug 1-[2,6-difluorophenyl)-methyl]-1H-1,2,3-triazolo[4,5-c]) pyridine-4-amine monohydrochloride (BW534U87) effectively reduced seizures induced in rodents by threshold maximal and supramaximal electroshock, electrical kindling, pentylenetetrazole (PTZ) infusion and by vestibular stimulation in the genetically seizure-prone epilepsy-like (EL) mouse. The range of animal seizure models in which BW534U87 was effective is consistent with a broad spectrum anticonvulsant profile. In the EL mouse, the activity of BW534U87 was partially reversed by predosing with the selective adenosine A1 receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX), suggesting that an adenosine-dependent mechanism contributed to the antiseizure activity of the drug. BW534U87 inhibited rat brain homogenate adenosine deaminase activity, thus, raising the possibility that, by blocking the metabolism of endogenous adenosine by this route, BW534U87 limited seizure activity by promoting the inhibitory tone mediated by endogenous adenosine in the brain. The seizure protection conferred by the selective adenosine deaminase inhibitor erythro-9-(2-hydroxy-3-nonyl)adenine (EHNA) in EL mice and mice infused with PTZ confirms that inhibition of adenosine metabolism by deamination is an effective antiseizure strategy in these models.

The cyclooxygenase-2 inhibitor GW406381X [2-(4-ethoxyphenyl)-3-[4-(methylsulfonyl)phenyl]-pyrazolo[1,5-b]pyridazine] is effective in animal models of neuropathic pain and central sensitization.

The pathogenic form of the cyclooxygenase (COX) enzyme, COX-2, is also constitutively present in the spinal cord and has been implicated in chronic pain states in rat and man. A number of COX-2 inhibitors, including celecoxib and rofecoxib, are already used in man for the treatment of inflammatory pain. Preclinically, the dual-acting COX-2 inhibitor, GW406381X [2-(4-ethoxyphenyl)-3-[4-(methylsulfonyl)phenyl]-pyrazolo[1,5-b]pyridazine, where X denotes the free base], is as effective as rofecoxib and celecoxib in the rat established Freund's Complete Adjuvant model with an ED(50) of 1.5 mg/kg p.o. compared with 1.0 mg/kg p.o. for rofecoxib and 6.6 mg/kg p.o. for celecoxib. However, in contrast to celecoxib (5 mg/kg p.o. b.i.d.) and rofecoxib (5 mg/kg p.o. b.i.d.), which were without significant effect, GW406381X (5 mg/kg p.o. b.i.d.) fully reversed mechanical allodynia in the chronic constriction injury model and reversed thermal hyperalgesia in the mouse partial ligation model, both models of neuropathic pain. GW406381X, was also effective in a rat model of capsaicin-induced central sensitization, when given intrathecally (ED(50) = 0.07 mug) and after chronic but not acute oral dosing. Celecoxib and rofecoxib had no effect in this model. Several hypotheses have been proposed to try to explain these differences in efficacy, including central nervous system penetration, enzyme kinetics, and potency. The novel finding of effectiveness of GW406381X in these models of neuropathic pain/central sensitization, in addition to activity in inflammatory pain models and together with its central efficacy, suggests dual activity of GW406381X compared with celecoxib and rofecoxib, which may translate into greater efficacy in a broader spectrum of pain states in the clinic.

The design of 8,8-dimethyl[1,6]naphthyridines as potential anticonvulsant agents.

Starting from a series of 7-linked tetrahydroisoquinoline derivatives, as exemplified by SB-270664, a new series of 8,8-dimethylnaphthyridine compounds has been identified. SAR studies around these attractive leads have provided compounds such as 12 which display excellent anticonvulsant activity and an encouraging pharmacokinetic profile in vivo.