Nicotine abstinence genotyping: assessing the impact on smoking cessation clinical trials

A preliminary exploration of college smokers' reactions to nicotine dependence genetic susceptibility feedback

INTRODUCTION

Many young smokers underestimate their risk for becoming addicted to cigarettes. We explored whether informing light college smokers (i.e., fewer than 5 cigarettes/day) of their genetic predisposition to nicotine dependence influenced their perceived risks and worry about becoming addicted, their ability to quit (i.e., self-efficacy), their desire to quit, and smoking cessation.

METHODS

College smokers (n = 142) received educational materials on mechanisms and consequences of nicotine addiction and were offered genetic susceptibility testing for nicotine dependence. Participants who accepted testing were randomized to receive feedback or no feedback (i.e., control). Tested participants learned they were above or not above average genetic risk for nicotine dependence. All participants responded to questions about perceived risks and worry about becoming addicted, efficacy to quit, and desire to quit. Cessation was assessed during a 1-month follow-up.

RESULTS

Efficacy beliefs, worry about becoming addicted, and desire to quit did not differ by study condition or feedback. Perceived risk for becoming addicted was highest among tested participants informed they were above average risk for nicotine dependence. Overall, self-reported 30- but not 7-day quit rate was higher among participants who underwent genetic testing compared with control participants.

CONCLUSIONS

This pilot study is the first to show that among light college smokers, receipt of genetic susceptibility feedback to nicotine dependence potentially curbs smoking without producing detrimental effects.

Smoking quit success genotype score predicts quit success and distinct patterns of developmental involvement with common addictive substances

Genotype scores that predict relevant clinical outcomes may detect other disease features and help direct prevention efforts. We report data that validate a previously established v1.0 smoking cessation quit success genotype score and describe striking differences in the score in individuals who display differing developmental trajectories of use of common addictive substances. In a cessation study, v1.0 genotype scores predicted ability to quit with P=0.00056 and area under receiver-operating characteristic curve 0.66. About 43% vs 13% quit in the upper vs lower genotype score terciles. Latent class growth analyses of a developmentally assessed sample identified three latent classes based on substance use. Higher v1.0 scores were associated with (a) higher probabilities of participant membership in a latent class that displayed low use of common addictive substances during adolescence (P=0.0004) and (b) lower probabilities of membership in a class that reported escalating use (P=0.001). These results indicate that: (a) we have identified genetic predictors of smoking cessation success, (b) genetic influences on quit success overlap with those that influence the rate at which addictive substance use is taken up during adolescence and (c) individuals at genetic risk for both escalating use of addictive substances and poor abilities to quit may provide especially urgent focus for prevention efforts.

Implications of genome wide association studies for addiction: are our a priori assumptions all wrong?

Substantial genetic contributions to addiction vulnerability are supported by data from twin studies, linkage studies, candidate gene association studies and, more recently, Genome Wide Association Studies (GWAS). Parallel to this work, animal studies have attempted to identify the genes that may contribute to responses to addictive drugs and addiction liability, initially focusing upon genes for the targets of the major drugs of abuse. These studies identified genes/proteins that affect responses to drugs of abuse; however, this does not necessarily mean that variation in these genes contributes to the genetic component of addiction liability. One of the major problems with initial linkage and candidate gene studies was an a priori focus on the genes thought to be involved in addiction based upon the known contributions of those proteins to drug actions, making the identification of novel genes unlikely. The GWAS approach is systematic and agnostic to such a priori assumptions. From the numerous GWAS now completed several conclusions may be drawn: (1) addiction is highly polygenic; each allelic variant contributing in a small, additive fashion to addiction vulnerability; (2) unexpected, compared to our a priori assumptions, classes of genes are most important in explaining addiction vulnerability; (3) although substantial genetic heterogeneity exists, there is substantial convergence of GWAS signals on particular genes. This review traces the history of this research; from initial transgenic mouse models based upon candidate gene and linkage studies, through the progression of GWAS for addiction and nicotine cessation, to the current human and transgenic mouse studies post-GWAS.

Biomarkers for smoking cessation

One way to enhance therapeutic development is through the identification and development of evaluative tools such as biomarkers. This review focuses on putative diagnostic, pharmacodynamic, and predictive biomarkers for smoking cessation. These types of biomarkers may be used to more accurately diagnose a disease, personalize treatment, identify novel targets for drug discovery, and enhance the efficiency of drug development. Promising biomarkers are presented across a range of approaches including metabolism, genetics, and neuroimaging. A preclinical viewpoint is also offered, as are analytical considerations and a regulatory perspective summarizing a pathway toward biomarker qualification.

Pharmacogenetic smoking cessation intervention in a health care setting: a pilot feasibility study

INTRODUCTION

There is increasing evidence that response to pharmacological treatment for nicotine dependence may be moderated by genetic polymorphisms. However, the feasibility, acceptability, and impact of genetically tailoring treatment in real-world clinical settings are unknown.

METHODS

We conducted a multiphased, mixed-methods feasibility study with current smokers to develop and evaluate a patient-centered, theoretically grounded personalized medicine treatment protocol. The initial research phase included formative work to develop intervention materials. The second phase included a randomized pilot trial to evaluate the intervention. Trial participants (n = 36) were genotyped for ANKK1 rs1800497 and were randomized to receive genetic feedback (GF) plus standard behavioral counseling (BC) for smoking cessation or BC without GF. All participants received genetically tailored pharmacotherapy (nicotine patch or bupropion).

RESULTS

The intervention was feasible to implement and was acceptable to participants based on satisfaction ratings and objective measures of participation. There was no evidence that the GF resulted in adverse psychological outcomes (e.g., depression, fatalism, reduced perceived control over quitting, differential motivation for quitting) based on quantitative or qualitative outcomes.

CONCLUSIONS

Study results suggest that it is feasible to offer treatment within a health care setting that includes genetically tailored pharmacotherapy and doing so had no apparent adverse psychological impacts. Further evaluation of pharmacogenetically tailored smoking cessation interventions appears warranted.

Impact of genetic notification on smoking cessation: systematic review and pooled-analysis

Objectives

This study aimed to evaluate the impact of genetic notification of smoking-related disease risk on smoking cessation in the general population. Secondary objectives were to assess the impact of genetic notification on intention-to-quit smoking and on emotional outcomes as well as the understanding and the recall of this notification.

Methods

A systematic review of articles from inception to August 2011 without language restriction was realized using PubMed, Embase, Scopus, Web of Science, PsycINFO and Toxnet. Other publications were identified using hand search. The pooled-analysis included only randomized trials. Comparison groups were (i) high and low genetic risk versus control, and (ii) high versus low genetic risk. For the pooled-analysis random effect models were applied and sensitivity analyses were conducted.

Results

Eight papers from seven different studies met the inclusion criteria of the review. High genetic risk notification was associated with short-term increased depression and anxiety. Four randomized studies were included in the pooled-analysis, which revealed a significant impact of genetic notification on smoking cessation in comparison to controls (clinical risk notification or no intervention) in short term follow-up less than 6 months (RR = 1.55, 95% CI 1.09–2.21).

Conclusions

In short term follow-up, genetic notification increased smoking cessation in comparison to control interventions. However, there is no evidence of long term effect (up to 12 month) on smoking cessation. Further research is needed to assess more in depth how genetic notification of smoking-related disease could contribute to smoking cessation.

Mouse models for studying genetic influences on factors determining smoking cessation success in humans

Humans differ in their ability to quit using addictive substances, including nicotine, the major psychoactive ingredient in tobacco. For tobacco smoking, a substantial body of evidence, largely derived from twin studies, indicates that approximately half of these individual differences in ability to quit are heritable genetic influences that likely overlap with those for other addictive substances. Both twin and molecular genetic studies support overlapping influences on nicotine addiction vulnerability and smoking cessation success, although there is little formal analysis of the twin data that support this important point. None of the current datasets provides clarity concerning which heritable factors might provide robust dimensions around which individuals differ in ability to quit smoking. One approach to this problem is to test mice with genetic variations in genes that contain human variants that alter quit success. This review considers which features of quit success should be included in a comprehensive approach to elucidate the genetics of quit success, and how those features may be modeled in mice.

Genetics of dopamine receptors and drug addiction

Dopamine plays a key role in reward behavior, yet the association of drug dependence as a chronic, relapsing disorder with the genes encoding the various dopaminergic receptor subtypes remains difficult to delineate. In the context of subsequent genome-wide association (GWAS) research and post-GWAS investigations, we summarize the novel data that link genes encoding molecules involved in the dopaminergic system (dopamine receptors, transporter and enzymes in charge of its metabolism) to drug addiction. Recent reports indicate that the heritability of drug addiction should be high enough to allow a significant role for a specific set of genes, and the available genetic studies, which might not be already conclusive because of the heterogeneity of designs, methods and recruited samples, should support the idea of a significant role of at least one gene related to dopaminergic system. Evolutionary changes in primates and non-primate animals of genes coding for molecules involved in dopaminergic system highlight why addictive disorders are mainly limited to humans. Restricting the analyses to more specific intermediate phenotypes (or endophenotypes) such as attention allocation, stress reactivity, novelty seeking, behavioral disinhibition and impulsivity, instead of the broad addictive disorder concept can be instrumental to identify novel genes associated with these traits in the context of genome-wide studies.

Personalized smoking cessation: interactions between nicotine dose, dependence and quit-success genotype score

Improving and targeting nicotine replacement therapy (NRT) are cost-effective strategies for reducing adverse health consequences for smokers. Treatment studies document the efficacy of precessation NRT and support important roles for level of nicotine dependence and precessation smoking reduction in successful quitting. However, prior work has not identified the optimal precessation dose or means for personalizing NRT. Genome-wide association has identified groups of genomic markers associated with successful quitting, allowing us to develop a v1.0 "quit-success" genotype score. We now report influences of v1.0 quit-success genotype score, level of dependence and precessation smoking reduction in a smoking cessation trial that examined effects of 21 versus 42 mg/24 h precessation NRT. Four hundred seventy-nine smokers were randomized to 21 or 42 mg NRT, initiated 2 wks prior to target quit dates. We monitored self-reported abstinence and end-expired air carbon monoxide (CO). Genotyping used Affymetrix arrays (Santa Clara, CA, USA). The primary outcome was 10-wk continuous smoking abstinence. NRT dose, level of nicotine dependence and genotype scores displayed significant interactive effects on successful quitting. Successful abstinence also was predicted by CO reductions during precessation NRT. These results document ways in which smoking cessation strategies can be personalized based on levels of nicotine dependence, genotype scores and CO monitoring. These assessments, taken together, can help match most smokers with optimal NRT doses and help rapidly identify some who may be better treated using other methods.