Synthesis and Pharmacological Characterization of 2-(2,6-Dichlorophenyl)-1-((1S,3R)-5-(3-hydroxy-3-methylbutyl)-3-(hydroxymethyl)-1-methyl-3,4-dihydroisoquinolin-2(1H)-yl)ethan-1-one (LY3154207), a Potent, Subtype Selective, and Orally Available Positive Allosteric Modulator of the Human Dopamine D1 Receptor.

Clinical development of catechol-based orthosteric agonists of the dopamine D1 receptor has thus far been unsuccessful due to multiple challenges. To address these issues, we identified LY3154207 (3) as a novel, potent, and subtype selective human D1 positive allosteric modulator (PAM) with minimal allosteric agonist activity. Conformational studies showed LY3154207 adopts an unusual boat conformation, and a binding pose with the human D1 receptor was proposed based on this observation. In contrast to orthosteric agonists, LY3154207 showed a distinct pharmacological profile without a bell-shaped dose-response relationship or tachyphylaxis in preclinical models. Identification of a crystalline form of free LY3154207 from the discovery lots was not successful. Instead, a novel cocrystal form with superior solubility was discovered and determined to be suitable for development. This cocrystal form was advanced to clinical development as a potential first-in-class D1 PAM and is now in phase 2 studies for Lewy body dementia.

Active immunisation against nicotine blocks the reward facilitating effects of nicotine and partially prevents nicotine withdrawal in the rat as measured by dopamine output in the nucleus accumbens, brain reward thresholds and somatic signs.

We recently showed that active immunisation with the nicotine immunoconjugate IP18-KLH reduces the nicotine-induced increase in dopamine (DA) output in the nucleus accumbens (NAC) and prevents reinstatement of nicotine-seeking behaviour in rats. These effects are mediated by altered distribution of nicotine, resulting in reduced amounts of nicotine reaching the brain, thereby interfering with the rewarding properties of the drug. The present study was designed to explore the effect of immunisation against nicotine on mecamylamine-precipitated nicotine withdrawal as assessed by the reduction in DA output in the NAC in rats. Measuring brain reward thresholds and somatic signs of nicotine withdrawal, the effects of immunisation were also tested during chronic nicotine treatment and after its withdrawal. Finally, we examined the effect of immunisation on challenge injections of nicotine on brain reward thresholds after the increases in somatic signs and reward thresholds associated with nicotine withdrawal had dissipated. The results show that immunisation with IP18-KLH prevented the decrease in DA output in the NAC associated with mecamylamine-precipitated nicotine withdrawal. Moreover, immunisation against nicotine did not precipitate a withdrawal syndrome, as measured by brain reward thresholds and somatic signs, in rats chronically exposed to nicotine. Furthermore, the withdrawal syndrome elicited after cessation of chronic nicotine administration was attenuated in immunised rats compared to that of mock-immunised rats. Finally, the lowering in reward thresholds after nicotine challenge injections was attenuated in both naïve and previously nicotine-exposed immunised rats. In conclusion, the present results show that immunisation with IP18-KLH did not precipitate nicotine withdrawal in rats. Thus, immunisation with IP18-KLH may not elicit nicotine withdrawal in smokers either. Furthermore, since the withdrawal syndrome in rats was attenuated by immunisation, the nicotine withdrawal in smokers should not be worsened but may even be ameliorated during a quit attempt.

Novel 2-aminotetralin and 3-aminochroman derivatives as selective serotonin 5-HT7 receptor agonists and antagonists.

The understanding of the physiological role of the G-protein coupled serotonin 5-HT(7) receptor is largely rudimentary. Therefore, selective and potent pharmacological tools will add to the understanding of serotonergic effects mediated through this receptor. In this report, we describe two compound classes, chromans and tetralins, encompassing compounds with nanomolar affinity for the 5-HT(7) receptor and with good selectivity. Within theses classes, we have discovered both agonists and antagonists that can be used for further understanding of the pharmacology of the 5-HT(7) receptor.

Active immunization against nicotine alters the distribution of nicotine but not the metabolism to cotinine in the rat.

We have previously shown that active immunization with the nicotine immunoconjugate IP18-KLH attenuates the reinforcing effects of nicotine, i.e., suppresses the nicotine-induced brain dopamine release and prevents reinstatement of the nicotine-seeking behavior in rats. These effects are thought to be due to an alteration of the kinetics of nicotine distribution by the antibodies, resulting in an attenuated nicotine distribution to the brain. In this study, the distribution of nicotine administered at doses corresponding to those used in our previous studies, was investigated in immunized rats and controls. Male Wistar rats received two immunizations with IP18-KLH in Freund's incomplete adjuvant, 21 days apart, and experiments were performed 7-11 days post-immunization under chloral hydrate anesthesia. Blood samples were collected to determine antibody titer and nicotine selectivity using enzyme-linked immunosorbent assay (ELISA) techniques. The animals received an intravenous nicotine dose and were sacrificed either 3 min or 60 min after nicotine administration. Trunk blood was collected and the brains were removed for analysis of nicotine content. The results showed that immunization against nicotine increases the nicotine concentration in blood and significantly decreases the amount of nicotine that reaches the brain. The present findings thus demonstrate an altered distribution of nicotine after immunization with IP18-KLH. Despite the sustained nicotine binding by the antibodies, the active immunization did not alter the metabolism of nicotine to cotinine, the major nicotine metabolite. In conclusion, the attenuation of the reinforcing effect of nicotine after immunization with IP18-KLH, shown previously, is indeed associated with an altered distribution of nicotine.

Discovery of a potent, dual serotonin and norepinephrine reuptake inhibitor.

The objective of the described research effort was to identify a novel serotonin and norepinephrine reuptake inhibitor (SNRI) with improved norepinephrine transporter activity and acceptable metabolic stability and exhibiting minimal drug-drug interaction. We describe herein the discovery of a series of 3-substituted pyrrolidines, exemplified by compound 1. Compound 1 is a selective SNRI in vitro and in vivo, has favorable ADME properties, and retains inhibitory activity in the formalin model of pain behavior. Compound 1 thus represents a potential new probe to explore utility of SNRIs in central nervous system disorders, including chronic pain conditions.

Effects of the dopamine stabilizers (S)-(-)-OSU6162 and ACR16 on prolactin secretion in drug-naive and monoamine-depleted rats.

Dopaminergic stabilizers may be conceptualized as drugs with normalizing effects on dopamine-mediated behaviours and neurochemical events. (S)-(-)-OSU6162 (OSU6162) and ACR16 are two structurally related compounds ascribed such properties, principally because of their stabilizing effects on motor activity in rodents. Reports in the literature indicate possible partial D2 receptor agonist effects using various in vitro systems. This study aimed to measure D2 receptor antagonist and agonist effects of OSU6162 and ACR16 in vivo. To address this, we have studied the effects of both compounds on prolactin secretion in drug-naive and dopamine-depleted rats; dopamine depletion was induced by pretreatment with reserpine plus α-methyl-DL: -p-tyrosine. We find that OSU6162 and ACR16 both stimulate prolactin secretion in drug-naive rats with OSU6162 being considerably more potent and efficacious. Both compounds show a non-significant trend towards reversal of the increased secretion caused by dopamine depletion, whereas the D2 receptor antagonist haloperidol further increased prolactin secretion. Thus, this study suggests that OSU6162 and ACR16 act as D2 receptor antagonists under normal conditions in vivo, possibly with minor agonist effects in a state of dopamine depletion.

Analysis of the actions of the novel dopamine receptor-directed compounds (S)-OSU6162 and ACR16 at the D2 dopamine receptor.

UNLABELLED: BACKGROUND AND PURPOSE; The two phenylpiperidines, OSU6162 and ACR16, have been proposed as novel drugs for the treatment of brain disorders, including schizophrenia and Huntington's disease, because of their putative dopamine stabilizing effects. Here we evaluated the activities of these compounds in a range of assays for the D(2) dopamine receptor in vitro. EXPERIMENTAL APPROACH: The affinities of these compounds for the D(2) dopamine receptor were evaluated in competition with [(3) H]spiperone and [(3) H]NPA. Agonist activity of these compounds was evaluated in terms of their ability to stimulate [(35) S]GTPγS binding. KEY RESULTS: Both compounds had low affinities for inhibition of [(3) H]spiperone binding (pK(i) vs. [(3) H]spiperone, ACR16: <5, OSU6162: 5.36). Neither compound was able to stimulate [(35) S]GTPγS binding when assayed in the presence of Na(+) ions, but if the Na(+) ions were removed, both compounds were low-affinity, partial agonists (E(max) relative to dopamine: ACR16: 10.2%, OSU6162:54.3%). Schild analysis of the effects of OSU6162 to inhibit dopamine-stimulated [(35) S]GTPγS binding indicated Schild slopes of ∼0.9, suggesting little deviation from competitive inhibition. OSU6162 was, however, able to accelerate [(3) H]NPA dissociation from D(2) dopamine receptors, indicating some allosteric effects of this compound. CONCLUSIONS AND IMPLICATIONS: The two phenylpiperidines were low-affinity, low-efficacy partial agonists at the D(2) dopamine receptor in vitro, possibly exhibiting some allosteric effects. Comparing their in vitro and in vivo effects, the in vitro affinities were a reasonable guide to potencies in vivo. However, the lack of in vitro-in vivo correlation for agonist efficacy needs to be further addressed. LINKED ARTICLES: This article is part of a themed section on Analytical Receptor Pharmacology in Drug Discovery. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2010.161.issue-6.

Nicotine hapten structure, antibody selectivity and effect relationships: results from a nicotine vaccine screening procedure.

The aim of the present study was to synthesise and screen a set of novel nicotine hapten immunogens used for the treatment of nicotine dependence. In the screening process we studied the amount of antibodies generated and their selectivity, using ELISA techniques, and their effects on nicotine-induced dopamine release in the NAC(shell) of the rat, assessed by in vivo voltammetry. We conclude that even small changes such as the linker attachment on the nicotine molecule as well as the structure of the linker may greatly influence the selectivity of the antibodies and the central neurobiological effects of nicotine that are considered critical for its dependence producing properties.

Effects of (-)-OSU6162 and ACR16 on motor activity in rats, indicating a unique mechanism of dopaminergic stabilization.

Dopaminergic stabilizers can be defined as drugs that stimulate or inhibit dopaminergic signalling depending on the dopaminergic tone. (-)-OSU6162 and ACR16 appear to possess such a profile. They have been proposed to act as partial dopamine receptor agonists or as antagonists with preferential action on dopaminergic autoreceptors. Previous studies have shown either stimulation or inhibition of behaviour in response to (-)-OSU6162 and ACR16, which has been suggested to reflect their dual effects on dopaminergic signalling. The aims of the present work are to (1) examine the relation between behavioural response to these drugs and activity baseline, and (2) test the suggested mechanisms of action by means of close comparisons with the known partial D2-receptor agonists (-)-3-PPP and aripiprazole, and the D2 autoreceptor preferring antagonist amisulpride with respect to effects on behaviour. From the results of these experiments it can be concluded that: (1) The direction of the response to (-)-OSU6162 and ACR16 is dependent on activity baseline, which in turn, under physiological conditions, is determined primarily by test arena size of and degree of habituation to the environment. (2) The effects of (-)-OSU6162 and ACR16 cannot be explained on the basis of either partial dopamine receptor agonism or preferential dopamine autoreceptor antagonism. Nevertheless, the current data suggest at least two different D2-receptor-associated targets which mediate opposite effects on activity. This result fits in with a mechanism proposed from a recent in vitro study, according to which (-)-OSU6162 has a dual action on dopamine D2 receptors, (a) an allosteric effect causing an enhanced response to dopamine, and (b) the previously proposed orthosteric effect antagonizing the action of dopamine.

The dopamine stabilizers (S)-(-)-(3-methanesulfonyl-phenyl)-1-propyl-piperidine [(-)-OSU6162] and 4-(3-methanesulfonylphenyl)-1-propyl-piperidine (ACR16) show high in vivo D2 receptor occupancy, antipsychotic-like efficacy, and low potential for motor side effects in the rat.

"Dopamine stabilizers" are a new class of compounds that have the ability to reverse both hypo- as well as hyperdopaminergia in vivo. This class, exemplified by the phenylpiperidines (S)-(-)-3-(3-methanesulfonyl-phenyl)-1-propyl-piperidine [(-)-OSU6162] and 4-(3-methanesulfonyl-phenyl)-1-propyl)-piperidine [ACR16] although lacking high in vitro binding affinity for dopamine D2 receptor [(-)-OSU6162, Ki = 447 nM; ACR16, Ki > 1 microM], shows functional actions, suggestive of their interaction. Hence, we evaluated in vivo D2 occupancy of these agents in rats and correlated it to observed effects in a series of behavioral, neurochemical, and endocrine models relevant to the dopamine system and antipsychotic effect. Both (-)-OSU6162 and ACR16 showed robust dose-dependent striatal D2 occupancy with ED50 values of 5.27 and 18.99 mg/kg s.c., respectively, and functional assays showed no partial agonism. Over an occupancy range of 37 to 87% (3-60 mg/kg) for (-)-OSU6162 and 35 to 74% (10-60 mg/kg) for ACR16, we observed both inhibitory (amphetamine-induced locomotor activity) and stimulatory effects (in habituated rats). Haloperidol, over a similar occupancy range (33-78%), potently inhibited psychostimulant activity and induced catalepsy, but it failed to activate habituated animals. In the conditioned avoidance response assay, ACR16 was clearly more efficacious than (-)-OSU6162. In addition, both these compounds demonstrated significant preferential Fos induction in the nucleus accumbens compared with the dorsolateral striatum, a strong predictor of atypical antipsychotic efficacy. The results suggest that dopamine stabilizers exhibit locomotor stabilizing as well as antipsychotic-like effects, with low motor side effect liability, in a dose range that corresponds to high D2 in vivo occupancy.

Novel 3-aminochromans as potential pharmacological tools for the serotonin 5-HT(7) receptor.

The synthesis of novel C6-aryl substituted derivatives of 3-(dimethylamino)chroman is described. The novel derivatives display 5-HT(7) receptor affinities that varies from nM to muM, indicating that this small set of derivatives constitute a novel and interesting starting point for further structure-serotonin 5-HT(7) activity relationship (SAR) studies.

Mechanisms of ligand binding and efficacy at the human D2(short) dopamine receptor.

Mechanisms of ligand binding and receptor activation for the human D2(short) dopamine receptor have been probed using two homologous series of monohydroxylated and dihydroxylated agonists (phenylethylamines and 2-dipropylaminotetralins). In ligand binding studies, the majority of compounds exhibited competition curves versus [3H]spiperone that were best fitted using a two site binding model. The compounds had different abilities (potencies and maximal effects) to stimulate [35S]GTPgammaS binding and to inhibit forskolin-stimulated cAMP accumulation. From the data it can be concluded that: (i) the ability of an agonist to stabilize receptor/G protein coupling can be used to predict agonist efficacy for some groups of compounds (2-dipropylaminotetralins) but not for others (phenylethylamines); (ii) the receptor may be activated by unhydroxylated compounds; (iii) single hydroxyl groups or pairs of hydroxyl groups on the agonist may contribute to binding affinity, potency and efficacy; and (iv) for the 2-dipropylaminotetralin series two modes of agonist/receptor interaction have been identified associated with different relative efficacy.