Pharmacogenetic clinical trial of sustained-release bupropion for smoking cessation

Abstract

This randomized, double-blinded, placebo-controlled trial examined genetic influences on treatment response to sustained-release bupropion for smoking cessation. Smokers of European ancestry (N = 291), who were randomized to receive bupropion or placebo (12 weeks) plus counseling, were genotyped for the dopamine D2 receptor (DRD2-Taq1A), dopamine transporter (SLC6A3 3' VNTR), and cytochrome P450 2B6 (CYP2B6 1459 CT) polymorphisms. Main outcome measures were cotinine-verified point prevalence of abstinence at end of treatment and at 2-, 6-, and 12-month follow-ups post quit date. Using generalized estimating equations, we found that bupropion, compared with placebo, was associated with significantly greater odds of abstinence at all time points (all p values<.01). We found a significant DRD2 x bupropion interaction (B = 1.49, SE = 0.59, p = .012) [corrected] and a three-way DRD2 x bupropion x craving interaction on 6-month smoking cessation outcomes (B = -0.45, SE = 0.22, p = .038), such that smokers with the A2/A2 genotype demonstrated the greatest craving reduction and the highest abstinence rates with bupropion. Furthermore, there was a significant DRD2 x CYP2B6 interaction (B = 1.43, SE = 0.56, p = .01), such that individuals with the DRD2-Taq1 A2/A2 genotype demonstrated a higher odds of abstinence only if they possessed the CYP2B6 1459 T/T or C/T genotype. Because the sample size of this study was modest for pharmacogenetic investigations, the results should be interpreted with caution. Although these results require replication, the data suggest preliminarily that the DRD2-Taq1A polymorphism may influence treatment response to bupropion for smoking cessation and, further, that exploration of gene x gene and gene x craving interactions in future, larger studies may provide mechanistic insights into the complex pharmacodynamics of bupropion.

Figure 1

Smoking cessation outcomes by treatment assignment and genotype. Biochemically verified 7-day point prevalence of abstinence at end of treatment (EOT) and at 2, 6, and 12 months are presented for participants randomized to bupropion or placebo according to genotype for (a) SLC6A3 3′ VNTR, (b) DRD2 Taq1A1/A2, and (c) CYP2B6 1459 C→T genotypes.

Figure 2

DRD2 × CYP2B6 interaction on 6-month abstinence. Biochemically verified 7-day point prevalence of abstinence at 6 months for subjects with CYP2B6 1459 C/C, T/T, or C/T alleles according to DRD2-Taq1A A1/A1 or A1/A2 and A2/A2 alleles.