Lipophilic nalmefene prodrugs to achieve a one-month sustained release.

Nalmefene is an opioid antagonist which as a once-a-day tablet formulation has recently been approved for reducing ethanol intake in alcoholic subjects. In order to address the compliance issue in this patient population, a number of potential nalmefene prodrugs were synthesized with the aim of providing a formulation that could provide plasma drug concentrations in the region of 0.5-1.0ng/mL for a one-month period when dosed intramuscular to dogs or minipigs. In an initial series of studies, three different lipophilic nalmefene derivatives were evaluated: the palmitate (C16), the octadecyl glutarate diester (C18-C5) and the decyl carbamate (CB10). They were administered intramuscularly to dogs in a sesame oil solution at a dose of 1mg-eq. nalmefene/kg. The decyl carbamate was released relatively quickly from the oil depot and its carbamate bond was too stable to be used as a prodrug. The other two derivatives delivered a fairly constant level of 0.2-0.3ng nalmefene/mL plasma for one month and since there was no significant difference between these two, the less complex palmitate monoester was chosen to demonstrate that dog plasma nalmefene concentrations were dose-dependent at 1, 5 and 20mg-eq. nalmefene/kg. In a second set of experiments, the effect of the chain length of the fatty acid monoester promoieties was examined. The increasingly lipophilic octanoate (C8), decanoate (C10) and dodecanoate (C12) derivatives were evaluated in dogs and in minipigs, at a dose of 5mg-eq. nalmefene/kg and plasma nalmefene concentrations were measured over a four-week period. The pharmacokinetic profiles were very similar in both species with Cmax decreasing and Tmax increasing with increasing fatty acid chain length and the target plasma concentrations (0.5-1.0ng/mL over a month-long period) were achieved with the dodecanoate (C12) prodrug. These data therefore demonstrate that sustained plasma nalmefene concentrations can be achieved in both dog and minipig using nalmefene prodrugs and that the pharmacokinetic profile of nalmefene can be tuned by varying the length of the alkyl group.

PDE10A inhibitors stimulate or suppress motor behavior dependent on the relative activation state of the direct and indirect striatal output pathways.

The enzyme phosphodiesterase 10A (PDE10A) regulates the activity of striatal, medium spiny neurons (MSNs), which are divided into a behaviorally stimulating, Gs-coupled D1 receptor-expressing "direct" pathway and a behaviorally suppressant, Gi-coupled D2 receptor-expressing "indirect" pathway. Activating both pathways, PDE10A inhibitors (PDE10AIs) combine functional characteristics of D2 antagonists and D1 agonists. While the effects of PDE10AIs on spontaneous and stimulated behavior have been extensively reported, the present study investigates their effects on suppressed behavior under various conditions of reduced dopaminergic neurotransmission: blockade of D1 receptors with SCH-23390, blockade of D2 receptors with haloperidol, or depletion of dopamine with RO-4-1284 or reserpine. In rats, PDE10AIs displayed relatively low cataleptic activity per se. After blocking D1 receptors, however, they induced pronounced catalepsy at low doses close to those required for inhibition of apomorphine-induced behavior; slightly higher doses resulted in behavioral stimulant effects, counteracting the catalepsy. PDE10AIs also counteracted catalepsy and related behaviors induced by D2 receptor blockade or dopamine depletion; catalepsy was replaced by behavioral stimulant effects under the latter but not the former condition. Similar interactions were observed at the level of locomotion in mice. At doses close to those inhibiting d-amphetamine-induced hyperlocomotion, PDE10AIs reversed hypolocomotion induced by D1 receptor blockade or dopamine depletion but not hypolocomotion induced by D2 receptor blockade. It is concluded that PDE10AIs stimulate or inhibit motor behavior dependent on the relative activation state of the direct and indirect striatal output pathways.

JNJ-40255293, a novel adenosine A2A/A1 antagonist with efficacy in preclinical models of Parkinson's disease.

Adenosine A2A antagonists are believed to have therapeutic potential in the treatment of Parkinson's disease (PD). We have characterized the dual adenosine A2A/A1 receptor antagonist JNJ-40255293 (2-amino-8-[2-(4-morpholinyl)ethoxy]-4-phenyl-5H-indeno[1,2-d]pyrimidin-5-one). JNJ-40255293 was a high-affinity (7.5 nM) antagonist at the human A2A receptor with 7-fold in vitro selectivity versus the human A1 receptor. A similar A2A:A1 selectivity was seen in vivo (ED50's of 0.21 and 2.1 mg/kg p.o. for occupancy of rat brain A2A and A1 receptors, respectively). The plasma EC50 for occupancy of rat brain A2A receptors was 13 ng/mL. In sleep-wake encephalographic (EEG) studies, JNJ-40255293 dose-dependently enhanced a consolidated waking associated with a subsequent delayed compensatory sleep (minimum effective dose: 0.63 mg/kg p.o.). As measured by microdialysis, JNJ-40255293 did not affect dopamine and noradrenaline release in the prefrontal cortex and the striatum. However, it was able to reverse effects (catalepsy, hypolocomotion, and conditioned avoidance impairment in rats; hypolocomotion in mice) produced by the dopamine D2 antagonist haloperidol. The compound also potentiated the agitation induced by the dopamine agonist apomorphine. JNJ-40255293 also reversed hypolocomotion produced by the dopamine-depleting agent reserpine and potentiated the effects of l-dihydroxyphenylalanine (L-DOPA) in rats with unilateral 6-hydroxydopamine-induced lesions of the nigro-striatal pathway, an animal model of Parkinson's disease. Extrapolating from the rat receptor occupancy dose-response curve, the occupancy required to produce these various effects in rats was generally in the range of 60-90%. The findings support the continued research and development of A2A antagonists as potential treatments for PD.

mGlu(2) receptor-mediated modulation of conditioned avoidance behavior in rats.

Inhibition of conditioned avoidance behavior in rats is generally considered predictive for antipsychotic activity in man. The present study investigated the mGlu2-mediated modulation of conditioned avoidance and compared mGlu2 agonists with available antipsychotics for their relative effects on conditioned avoidance behavior and locomotion. The mGlu2/3 orthosteric agonist 4-amino-2-thiabicyclo[3.1.0]hexane-4,6-dicarboxylic acid 2,2-dioxide (LY-404039) and mGlu2 positive allosteric modulator (PAM) 3-(cyclopropylmethyl)-7-(4-phenylpiperidin-1-yl)-8-(trifluoromethyl)[1,2,4]triazolo[4,3-a]pyridine (JNJ-42153605) inhibited avoidance and blocked escape behavior. The mGlu2/3 negative allosteric modulators (NAMs) 7-(dimethylamino)-4-(3-pyridin-3-ylphenyl)-8-(trifluoromethyl)-1,3-dihydro-2 H-1,5-benzodiazepin-2-one (JNJ-42112265) and 4-[3-(2,6-dimethylpyridin-4-yl)phenyl]-7-methyl-8-(trifluoromethyl)-1,3-dihydro-2H-1,5-benzodiazepin-2-one (RO-4491533) reversed the LY-404039-induced impairment of avoidance and escape. JNJ-42112265 also reversed the impairment of avoidance and escape induced by the mGlu2-specific PAM JNJ-42153605, suggesting that the effects on conditioned avoidance are specifically mGlu2-mediated. The mGlu2/3 antagonist (2-(2-carboxycyclopropyl)-3-(9H-xanthen-9-yl)-d-alanine (LY-341495; s.c.) reversed the LY-404039-induced escape impairment but failed to restore avoidance, suggesting interfering side effects. Like the tested antipsychotics, mGlu2/3 orthosteric and allosteric agonists inhibited avoidance behavior and locomotion at similar doses. Hence no clear-cut differences between mGlu2 modulators and currently available antipsychotics in the way they interfere with avoidance behavior in relation to inhibition of locomotion could be established.

Pharmacology of JNJ-42314415, a centrally active phosphodiesterase 10A (PDE10A) inhibitor: a comparison of PDE10A inhibitors with D2 receptor blockers as potential antipsychotic drugs.

The new phosphodiesterase 10A inhibitor (PDE10AI) JNJ-42314415 [3-[6-(2-methoxyethyl)pyridin-3-yl]-2-methyl-8-morpholin-4-ylimidazo[1,2-a]pyrazine] was compared with three reference PDE10AIs and eight dopamine 2 (D(2)) receptor blockers. Despite displaying relatively low PDE10A activity in vitro, JNJ-42314415 was found to be a relatively potent and specific PDE10AI in vivo. The compound was devoid of effects on prolactin release and of receptor interactions associated with other commonly observed adverse effects of available antipsychotics. Similar to D(2) receptor blockers, the tested PDE10AIs antagonized stimulant-induced behavior and inhibited conditioned avoidance behavior; these effects were observed at doses close to the ED(50) for striatal PDE10A occupancy. Relative to the ED(50) for inhibition of apomorphine-induced stereotypy, PDE10AIs blocked conditioned avoidance behavior and behaviors induced by nondopaminergic stimulants (phencyclidine, scopolamine) more efficiently than did D(2) receptor blockers; however, they blocked behaviors induced by dopaminergic stimulants (apomorphine, d-amphetamine) less efficiently. PDE10AIs also induced less pronounced catalepsy than D(2) receptor blockers. The effects of PDE10A inhibition against dopaminergic stimulants and on catalepsy were potentiated by the D(1) antagonist SCH-23390 (8-chloro-3-methyl-5-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepin-7-ol), suggesting that enhancement of D(1) receptor-mediated neurotransmission contributes to the behavioral profile of PDE10AIs. By reducing dopamine D(2) and concomitantly potentiating dopamine D(1) receptor-mediated neurotransmission, PDE10AIs may show antipsychotic activity with an improved side-effect profile relative to D(2) receptor blockers. However, the clinical implications of this dual mechanism must be further explored.

Differential interaction of neuroleptics with apomorphine-induced behavior in rats as a function of changing levels of dopamine receptor stimulation.

Twenty-two neuroleptic drugs were studied for interaction with the behavior induced by intravenous injection of apomorphine in rats. All compounds dose-dependently shortened the duration of the apomorphine-induced agitation and-with the exception of clozapine-shortened the onset of the de-arousal grooming that typically occurs immediately after the agitation phase has been terminated. Progressively higher doses were required to antagonize higher levels of apomorphine at earlier time intervals after the intravenous injection. The compounds also decreased palpebral opening, and most of them suppressed grooming behavior at higher doses. Compounds differed considerably in dose increments required for: 1) suppression of grooming, from 0.33 for clozapine to >600 for remoxipride, raclopride, and droperidol; 2) blockade of agitation at 5 minutes after apomorphine, from 2.6 for pimozide to 165 for chlorprothixene and 254 for remoxipride; 3) mild decrease of palpebral opening, from 0.21 for sertindole to 191 for remoxipride; and 4) pronounced decrease of palpebral opening, from 10 for melperone to >820 for raclopride. Only four compounds were able to advance grooming to 15 minutes postapomorphine, but again dose increments varied considerably: droperidol (3.4), pimozide (9.1), raclopride (42), and remoxipride (383). Based on these results obtained in a single animal model, compounds were differentiated in terms of behavioral specificity, incisiveness (the power to counteract the effects of progressively higher apomorphine concentrations), and sedative side-effect liability. Possible explanations for the observed differences and clinical relevance are discussed.

Does phenylethylamine act as an endogenous amphetamine in some patients?

In brain capillary endothelium and catecholaminergic terminals a single decarboxylation step effected by aromatic amino-acid decarboxylase converts phenylalanine to phenylethylamine, at a rate comparable to that of the central synthesis of dopamine. Phenylethylamine, however, is not stored in intra-neuronal vesicles and is rapidly degraded by monoamine oxidase-B. Despite its short half-life, phenylethylamine attracts attention as an endogenous amphetamine since it can potentiate catecholaminergic neurotransmission and induce striatal hyperreactivity. Subnormal phenylethylamine levels have been linked to disorders such as attention deficit and depression; the use of selegiline (Deprenyl) in Parkinson's disease may conceivably favour recovery from deficient dopaminergic neurotransmission by a monoamine oxidase-B inhibitory action that increases central phenylethylamine. Excess phenylethylamine has been invoked particularly in paranoid schizophrenia, in which it is thought to act as an endogenous amphetamine and, therefore, would be antagonized by neuroleptics. The importance of phenylethylamine in mental disorders is far from fully elucidated but the evolution of phenylethylamine concentrations in relation to symptoms remains a worthwhile investigation for individual psychotic patients.