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Molecular actions of smoking cessation drugs at ?4?2 nicotinic receptors defined in crystal structures of a homologous binding protein.

ABSTRACT: Partial agonists of the ?4?2 nicotinic acetylcholine receptor (nAChR), such as varenicline, are therapeutically used in smoking cessation treatment. These drugs derive their therapeutic effect from fundamental molecular actions, which are to desensitize ?4?2 nAChRs and induce channel opening with higher affinity, but lower efficacy than a full agonist at equal receptor occupancy. Here, we report X-ray crystal structures of a unique acetylcholine binding protein (AChBP) from the annelid Capitella teleta, Ct-AChBP, in complex with varenicline or lobeline, which are both partial agonists. These structures highlight the architecture for molecular recognition of these ligands, indicating the contact residues that potentially mediate their molecular actions in ?4?2 nAChRs. We then used structure-guided mutagenesis and electrophysiological recordings to pinpoint crucial interactions of varenicline with residues on the complementary face of the binding site in ?4?2 nAChRs. We observe that residues in loops D and E are molecular determinants of desensitization and channel opening with limited efficacy by the partial agonist varenicline. Together, this study analyzes molecular recognition of smoking cessation drugs by nAChRs in a structural context.

SUBMITTER: Billen B

PROVIDER: S-EPMC3384148 | biostudies-literature | 2012 Jun

REPOSITORIES: biostudies-literature

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Molecular actions of smoking cessation drugs at α4β2 nicotinic receptors defined in crystal structures of a homologous binding protein.

Billen Bert B Spurny Radovan R Brams Marijke M van Elk René R Valera-Kummer Soledad S Yakel Jerrel L JL Voets Thomas T Bertrand Daniel D Smit August B AB Ulens Chris C

Proceedings of the National Academy of Sciences of the United States of America 20120522 23

Partial agonists of the α4β2 nicotinic acetylcholine receptor (nAChR), such as varenicline, are therapeutically used in smoking cessation treatment. These drugs derive their therapeutic effect from fundamental molecular actions, which are to desensitize α4β2 nAChRs and induce channel opening with higher affinity, but lower efficacy than a full agonist at equal receptor occupancy. Here, we report X-ray crystal structures of a unique acetylcholine binding protein (AChBP) from the annelid Capitella ...[more]

PMID: 22619328

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Project description:ImportanceCigarette smoking leads to upregulation of nicotinic acetylcholine receptors (nAChRs) in the human brain, including the common α4β2* nAChR subtype. While subjective aspects of tobacco dependence have been extensively examined as predictors of quitting smoking with treatment, no studies to our knowledge have yet reported the relationship between the extent of pretreatment upregulation of nAChRs and smoking cessation.ObjectiveTo determine whether the degree of nAChR upregulation in smokers predicts quitting with a standard course of treatment.Design, setting, and participantsEighty-one tobacco-dependent cigarette smokers (volunteer sample) underwent positron emission tomographic (PET) scanning of the brain with the radiotracer 2-FA followed by 10 weeks of double-blind, placebo-controlled treatment with nicotine patch (random assignment). Pretreatment specific binding volume of distribution (VS/fP) on PET images (a value that is proportional to α4β2* nAChR availability) was determined for 8 brain regions of interest, and participant-reported ratings of nicotine dependence, craving, and self-efficacy were collected. Relationships between these pretreatment measures, treatment type, and outcome were then determined. The study took place at academic PET and clinical research centers.Main outcomes and measuresPosttreatment quit status after treatment, defined as a participant report of 7 or more days of continuous abstinence and an exhaled carbon monoxide level of 3 ppm or less.ResultsSmokers with lower pretreatment VS/fP values (a potential marker of less severe nAChR upregulation) across all brain regions studied were more likely to quit smoking (multivariate analysis of covariance, F8,69 = 4.5; P < .001), regardless of treatment group assignment. Furthermore, pretreatment average VS/fP values provided additional predictive power for likelihood of quitting beyond the self-report measures (stepwise binary logistic regression, likelihood ratio χ21 = 19.8; P < .001).Conclusions and relevanceSmokers with less upregulation of available α4β2* nAChRs have a greater likelihood of quitting with treatment than smokers with more upregulation. In addition, the biological marker studied here provided additional predictive power beyond subjectively rated measures known to be associated with smoking cessation outcome. While the costly, time-consuming PET procedure used here is not likely to be used clinically, simpler methods for examining α4β2* nAChR upregulation could be tested and applied in the future to help determine which smokers need more intensive and/or lengthier treatment.Trial registrationclinicaltrials.gov Identifier: NCT01526005.

Project description:BACKGROUND:The identification of variants in the nicotinic acetylcholine receptor (nAChR) subunit genes associated with smoking phenotypes are increasingly important for prevention and treatment of nicotine dependence. In the context of personalized medicine, the aims of this study were to evaluate whether cholinergic receptor nicotinic alpha 2 (CHRNA2), cholinergic receptor nicotinic alpha 3 (CHRNA3), cholinergic receptor nicotinic alpha 5 (CHRNA5) and cholinergic receptor nicotinic beta 3 (CHRNB3) polymorphisms were associated with nicotine dependence severity, and to investigate possible pharmacogenetics markers of smoking cessation treatment. METHODS:This study cohort enrolled 1049 smoking patients who received pharmacological treatment (varenicline, varenicline plus bupropion, bupropion plus/or nicotine replacement therapy). Smoking cessation success was considered for patients who completed 6 months of continuous abstinence. Fagerström test for nicotine dependence (FTND) and Issa situational smoking scores (Issa score) were analyzed for nicotine dependence. CHRNA2 (rs2472553), CHRNA3 (rs1051730), CHRNA5 (rs16969968 and rs2036527) and CHRNB3 (rs6474413) polymorphisms were genotyped by high resolution melting analysis. RESULTS:Females with GA and AA genotypes for CHRNA5 rs16969968 and rs2036527 polymorphisms had higher success rate in smoking cessation treatment: 44.0% and 56.3% (rs16969968), 41.5% and 56.5% (rs2036527), respectively, compared with carriers of the GG genotypes: 35.7% (rs16969968), 34.8% (rs2036527), (P?=?0.03, n?=?389; P?=?0.01, n?=?391). The GA or AA genotypes for the rs16969968 and rs2036527 were associated with higher odds ratio for success in women (OR?=?1.63; 95% CI?=?1.04 to 2.54; P?=?0.03 and OR?=?1.59, 95% CI?=?1.02 to 2.48; P?=?0.04; respectively). We did not find association of these polymorphisms with nicotine dependence related scores. Polymorphisms in the CHRNA2, CHRNA3 and CHRNB3 genes were not associated with the phenotypes studied. CONCLUSION:CHRNA5 rs16969968 and rs2036527 were associated with higher success rate in the smoking cessation treatment in women. These findings might contribute to advances in personalized medicine.

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Molecular actions of smoking cessation drugs at ?4?2 nicotinic receptors defined in crystal structures of a homologous binding protein.

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Molecular actions of smoking cessation drugs at α4β2 nicotinic receptors defined in crystal structures of a homologous binding protein.

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