Effect of ADRB2 polymorphisms on the efficacy of salmeterol and tiotropium in preventing COPD exacerbations: a prespecified substudy of the POET-COPD trial.

BACKGROUND
The effect of β2-adrenergic receptor (ADRB2) polymorphisms on the treatment response to longacting bronchodilators in chronic obstructive pulmonary disease (COPD) is unclear. We aimed to establish whether ADRB2 polymorphisms differentially affected COPD exacerbation outcomes in response to tiotropium versus salmeterol.


METHODS
We did a prespecified analysis of the ADRB2 polymorphisms Arg16Gly and Gln27Glu within the 1 year randomised, double-blind, double-dummy, parallel-group Prevention Of Exacerbations with Tiotropium in COPD (POET-COPD) trial, comparing the effects of treatment with tiotropium or salmeterol on exacerbations in 7376 patients with COPD. One blood sample was collected for pharmacogenetic testing from each patient who elected to participate in the substudy. Random assignment of patients to treatment groups was not stratified according to genotypes. Genomic DNA was extracted from whole-blood specimens and samples were genotyped for the two SNPs, rs1042713 (Arg16Gly) and rs1042714 (Gln27Glu). All assays were done in technical duplicates and 10% of samples that were randomly chosen were repeated as technical duplicates in a second independent genotyping process. Our primary endpoint was the risk of a first exacerbation of COPD based on time to first exacerbation data. An exacerbation of COPD was defined as the increase or new onset of more than one symptom of COPD (cough, sputum, wheezing, dyspnoea, or chest tightness), with at least one of the symptoms lasting for 3 days or more and needing treatment with antibiotics or systemic glucocorticoids (moderate exacerbations), or admission to hospital (severe exacerbations). POET-COPD is registered with ClinicalTrials.gov, number NCT00563381.


FINDINGS
5125 patients gave informed consent for genotyping. The distributions of ADRB2 genotypes were well matched among groups. Polymorphisms at aminoacid 27 did not affect exacerbation outcomes. In the salmeterol group, patients with Arg16Arg genotype had a significantly reduced exacerbation risk compared with patients with Arg16Gly (p=0·0130) and Gly16Gly (p=0·0018) genotypes (proportion of patients with at least one exacerbation was 32·3% in Arg16Arg, 39·8% in Arg16Gly, and 42·1% in Gly16Gly). By contrast, exacerbation risk was not modified by polymorphisms at aminoacid 16 in the tiotropium group. The effect of the Arg16Gly polymorphism on treatment response to salmeterol was dependent on the use of inhaled corticosteroids (ICS). In patients untreated with ICS at baseline, Arg16Gly and Arg16Arg genotypes were associated with significantly prolonged time to first exacerbation compared with Gly16Gly (vs Arg16Gly p=0·0164; Arg16Arg p=0·0316; proportion of patients with at least one exacerbation was 28·3% in Arg16Arg, 31·6% in Arg16Gly, and 39·2% in Gly16Gly), whereas in patients on ICS at baseline, only the Arg16Arg genotype was associated with significantly prolonged time to first exacerbation compared with Gly16Gly (p=0·0198; not Arg16Gly p=0·64; proportion of patients with at least one exacerbation was 35·9% in Arg16Arg, 46·7% in Arg16Gly, and 44·8% in Gly16Gly). The respiratory disorders, in particular worsening of COPD, were the most common serious adverse events.


INTERPRETATION
Patients with the Arg16Arg genotype had better exacerbation outcomes in response to salmeterol than Gly16Gly and Arg16Gly genotypes, suggesting a potential differential Arg16Gly genotype effect on treatment response to longacting β-agonists (LABAs). However, the use of ADRB2 polymorphisms for predicting LABA treatment response is still limited and further prospective validation will be needed to advance the mechanistic understanding of β-adrenergic polymorphisms and their association with clinical features of COPD.


FUNDING
Boehringer Ingelheim and Pfizer.