Jotham Wadsworth Coe

Pharmacological profile of the α4β2 nicotinic acetylcholine receptor partial agonist varenicline, an effective smoking cessation aid

The preclinical pharmacology of the α4β2 nicotinic acetylcholine receptor (nAChR) partial agonist varenicline, a novel smoking cessation agent is described. Varenicline binds with subnanomolar affinity only to α4β2 nAChRs and in vitro functional patch clamp studies in HEK cells expressing nAChRs show that varenicline is a partial agonist with 45% of nicotines maximal efficacy at α4β2 nAChRs. In neurochemical models varenicline has significantly lower (40–60%) efficacy than nicotine in stimulating [3H]-dopamine release from rat brain slices in vitro and in increasing dopamine release from rat nucleus accumbens in vivo, while it is more potent than nicotine. In addition, when combined with nicotine, varenicline effectively attenuates the nicotine-induced dopamine release to the level of the effect of varenicline alone, consistent with partial agonism. Finally, varenicline reduces nicotine self-administration in rats and supports lower self-administration break points than nicotine. These data suggest that varenicline can reproduce to some extent the subjective effects of smoking by partially activating α4β2 nAChRs, while preventing full activation of these receptors by nicotine. Based on these findings, varenicline was advanced into clinical development and recently shown to be an effective and safe aid for smoking cessation treatment.

METABOLISM AND DISPOSITION OF VARENICLINE, A SELECTIVE α4β2 ACETYLCHOLINE RECEPTOR PARTIAL AGONIST, IN VIVO AND IN VITRO

The metabolism and disposition of varenicline (7,8,9,10-tetrahydro-6,10-methano-6H-pyrazino[2,3-h][3]benzazepine), a partial agonist of the nicotinic acetylcholine receptor for the treatment of tobacco addiction, was examined in rats, mice, monkeys, and humans after oral administration of [14C]varenicline. In the circulation of all species, the majority of drug-related material was composed of unchanged varenicline. In all four species, drug-related material was primarily excreted in the urine. A large percentage was excreted as unchanged parent drug (90, 84, 75, and 81% of the dose in mouse, rat, monkey, and human, respectively). Metabolites observed in excreta arose via N-carbamoyl glucuronidation and oxidation. These metabolites were also observed in the circulation, in addition to metabolites that arose via N-formylation and formation of a novel hexose conjugate. Experiments were conducted using in vitro systems to gain an understanding of the enzymes involved in the formation of the N-carbamoylglucuronide metabolite in humans. N-Carbamoyl glucuronidation was catalyzed by UGT2B7 in human liver microsomes when incubations were conducted under a CO2 atmosphere. The straightforward dispositional profile of varenicline should simplify its use in the clinic as an aid in smoking cessation.

Pre-clinical properties of the α4β2 nicotinic acetylcholine receptor partial agonists varenicline, cytisine and dianicline translate to clinical efficacy for nicotine dependence

Background and purpose:  Smoking cessation trials with three high‐affinity partial agonists of α4β2 neuronal nicotinic acetylcholine receptors (nAChRs) have demonstrated differences in their clinical efficacy. This work examines the origin of the differences by taking into account brain exposure and pharmacological effects at human α4β2 nAChRs.

Partial agonists of the α3β4* neuronal nicotinic acetylcholine receptor reduce ethanol consumption and seeking in rats.

Alcohol use disorders (AUDs) impact millions of individuals and there remain few effective treatment strategies. Despite evidence that neuronal nicotinic acetylcholine receptors (nAChRs) have a role in AUDs, it has not been established which subtypes of the nAChR are involved. Recent human genetic association studies have implicated the gene cluster CHRNA3–CHRNA5–CHRNB4 encoding the α3, α5, and β4 subunits of the nAChR in susceptibility to develop nicotine and alcohol dependence; however, their role in ethanol-mediated behaviors is unknown due to the lack of suitable and selective research tools. To determine the role of the α3, and β4 subunits of the nAChR in ethanol self-administration, we developed and characterized high-affinity partial agonists at α3β4 nAChRs, CP-601932, and PF-4575180. Both CP-601932 and PF-4575180 selectively decrease ethanol but not sucrose consumption and operant self-administration following long-term exposure. We show that the functional potencies of CP-601932 and PF-4575180 at α3β4 nAChRs correlate with their unbound rat brain concentrations, suggesting that the effects on ethanol self-administration are mediated via interaction with α3β4 nAChRs. Also varenicline, an approved smoking cessation aid previously shown to decrease ethanol consumption and seeking in rats and mice, reduces ethanol intake at unbound brain concentrations that allow functional interactions with α3β4 nAChRs. Furthermore, the selective α4β2* nAChR antagonist, DHβE, did not reduce ethanol intake. Together, these data provide further support for the human genetic association studies, implicating CHRNA3 and CHRNB4 genes in ethanol-mediated behaviors. CP-601932 has been shown to be safe in humans and may represent a potential novel treatment for AUDs.

Varenicline has antidepressant-like activity in the forced swim test and augments sertraline's effect.

Varenicline, an alpha4beta2 nicotinic acetylcholine receptor partial agonist developed as a smoking cessation aid, showed antidepressant-like activity in the forced swim test in two mouse strains. In addition, a low varenicline dose significantly enhanced the effects of moderately active doses of the selective serotonin reuptake inhibitor sertraline. These findings are consistent with the notion that reducing alpha4beta2 nicotinic acetylcholine receptor activity either by antagonists or by partial agonists that can partially activate or desensitize acetylcholine receptors is associated with antidepressant-like properties. These data suggest that varenicline may have antidepressant potential and can, when combined, augment antidepressant responses of selective serotonin reuptake inhibitors.

Discovery of 4-(5-Methyloxazolo[4,5-b]pyridin-2-yl)-1,4-diazabicyclo[3.2.2]nonane (CP-810,123), a Novel α7 Nicotinic Acetylcholine Receptor Agonist for the Treatment of Cognitive Disorders in Schizophrenia: Synthesis, SAR Development, and in Vivo Efficacy in Cognition Models

A novel alpha 7 nAChR agonist, 4-(5-methyloxazolo[4,5-b]pyridin-2-yl)-1,4-diazabicyclo[3.2.2]nonane (24, CP-810,123), has been identified as a potential treatment for cognitive deficits associated with psychiatric or neurological conditions including schizophrenia and Alzheimers disease. Compound 24 is a potent and selective compound with excellent pharmaceutical properties. In rodent, the compound displays high oral bioavailability and excellent brain penetration affording high levels of receptor occupancy and in vivo efficacy in auditory sensory gating and novel object recognition. The structural diversity of this compound and its preclinical in vitro and in vivo package support the hypothesis that alpha 7 nAChR agonists may have potential as a pharmacotherapy for the treatment of cognitive deficits in schizophrenia.

A mild method for the conversion of activated aryl methyl groups to carboxaldehydes via the uncatalyzed periodate cleavage of enamines

Abstract A mild procedure for the oxidative cleavage of aryl enamines to aryl aldehydes by periodate without the need for transition metal catalysis is presented.

Selection of a Novel Anti-Nicotine Vaccine: Influence of Antigen Design on Antibody Function in Mice

Anti-nicotine vaccines may aid smoking cessation via the induction of anti-nicotine antibodies (Ab) which reduce nicotine entering the brain, and hence the associated reward. Ab function depends on both the quantity (titer) and the quality (affinity) of the Ab. Anti-nicotine vaccines tested previously in clinical studies had poor efficacy despite high Ab titer, and this may be due to inadequate function if Ab of low affinity were induced. In this study, we designed and synthesized a series of novel nicotine-like haptens which were all linked to diphtheria toxoid (DT) as carrier, but which differed in the site of attachment of linker to nicotine, the nature of linker used, and the handle used to attach the hapten to DT. The resulting hapten conjugates were evaluated in a mouse model, using CpG (a TLR9 agonist) and aluminum hydroxide (Al(OH)3) as adjuvants, whereby Ab titers, affinity and function were evaluated using a radiolabeled nicotine challenge model. A series of additional linkers varying in length, rigidity and polarity were used with a single hapten to generate additional DT-conjugates, which were also tested in mice. Conjugates made with different haptens resulted in various titers of anti-nicotine Ab. Several haptens gave similarly high Ab titers, but among these, Ab affinity and hence function varied considerably. Linker also influenced Ab titer, affinity and function. These results demonstrate that immune responses induced in mice by nicotine-conjugate antigens are greatly influenced by hapten design including site of attachment of linker to nicotine, the nature of linker used, and the handle used to attach the hapten to DT. While both Ab titer and affinity contributed to function, affinity was more sensitive to antigen differences.

α4β2 nicotinic acetylcholine receptor partial agonists with low intrinsic efficacy have antidepressant-like properties.

Previous studies have suggested that treatment with antagonists or partial agonists of nicotinic acetylcholine receptors containing the &bgr;2-subunit (&bgr;2* nAChRs) results in antidepressant-like effects. In this study, we tested three novel compounds with different affinity and functional efficacy at &agr;4&bgr;2* nAChRs, which were synthesized as part of nAChR discovery projects at Pfizer, in the tail-suspension, forced-swim, and novelty-suppressed feeding tests of antidepressant efficacy. All compounds tested reduced immobility in the forced-swim test and one of the compounds also reduced immobility in the tail-suspension test. All the compounds appeared to affect food intake on their own, with two compounds reducing feeding significantly in the home cage, precluding a clear interpretation of the results in the novelty-suppressed feeding test. None of the compounds altered locomotor activity at the doses and time points used here. Therefore, a subset of these compounds has pharmacological and behavioral properties that demonstrate the potential of nicotinic compounds as a treatment of mood disorders. Further development of nicotinic-based antidepressants should focus on increasing nAChR subtype selectivity to obtain consistent antidepressant properties with an acceptable side-effect profile.

Convenient preparation of N-substituted indoles by modified Leimgruber-Batcho indole synthesis

A modified reductive alkylation of pre-indole 3, prepared from readily available Leimgruber-Batcho indole synthesis derived intermediates, followed by acidic methanolysis generates 6-carbomethoxy-N-substituted indoles. The three step preparation of pre-indole 3 from substituted 2-nitrotoluene 1 in 66% yield and conversion to a variety of N-substituted indoles is presented.