Clopidogrel pharmacogenomics: next steps: a clinical algorithm, gene-gene interactions, and an elusive outcomes trial

Clopidogrel pharmacogenomics has received significant attention since a black box warning was announced by the Food and Drug Administration in March. This has left clinicians in a difficult situation where many questions remain unanswered. In this brief viewpoint article, we ask some pointed questions of our own and outline the pathway that needs to be taken for clinical translation to occur.

Longitudinal study of a 9p21.3 SNP using a national electronic healthcare database

AIMS

Genome-wide association studies have identified a number of SNPs associated with complex disease. The longitudinal significance of these variants is uncertain and clinical genomic studies are required to elucidate what clinical value these variants have. Linking DNA to clinical health information databases is a powerful and potentially low-cost means of performing such research. Here, we describe a proof-of-principle study demonstrating the potential of this method.

MATERIALS & METHODS

A total of 376 individuals presenting to a hospital with severe coronary artery disease were enrolled into a prospective cohort study. DNA, demographic data, ethnicity and other clinical information was collected in an electronic database. Genotyping for SNPs rs2383207 and rs10757278 was performed using Sequenom^® (CA, USA) matrix-assisted laser desorption/ionisation-time of flight mass spectrometry. Health outcomes were tracked from when patients were discharged from the hospital using the New Zealand Health Information Service (Wellington, New Zealand).

RESULTS

A total of 253 (67%) patients were of New Zealand European descent, 47 (13%) patients were of Maori descent and 21 (6%) were of Pacific Island ancestry. The Maori and Pacific Island group were younger at presentation (63 ± 11 vs 70 ± 9 years of age; p < 0.0001) and had a higher prevalence of cardiovascular risk factors. The frequency of the at-risk rs2383207 G allele in the Maori and Pacific group was 70%, compared with 54% in Europeans (p = 0.002). Similarly, the rs10757278 G allele was also present at a higher frequency (68 vs 52%; p = 0.003). No association was seen between the rs10757278 SNP and cardiovascular risk factors or markers of disease severity. GA and GG individuals had a higher rate of cardiovascular (p = 0.04) and all-cause death (p = 0.02).

CONCLUSION

The linking of genetic data to electronic medical databases is an effective tool to assess the longitudinal effect of gene variants on health outcomes and will aid in the implementation of personalized medicine. Larger sample sizes with longer study duration may yield clinically useful information that aids preventative healthcare.

A simulation of warfarin maintenance dose requirement using a pharmacogenetic algorithm in an ethnically diverse cohort

AIMS

Patient demographics and variant alleles in the CYP2C9 and VKORC1 genes account for 50% of the population variability in warfarin maintenance doses. These variant alleles occur in varying frequencies between racial groups and contribute to differences in mean dose requirements between these groups. We used a pharmacogenetic simulation to estimate warfarin maintenance doses in an ethnically diverse cohort.

MATERIALS & METHODS

In total, 366 individuals with coronary disease, of mixed South Pacific and European ethnicity, were genotyped for the CYP2C9*2 (rs1799853), *3 (rs1057910) and the VKORC1*2 haplotype, -1639 G>A, (rs9923231). The cohort contained New Zealand Europeans (n = 287), Mãori (n = 49), Pacific Islanders (n = 21) and Chinese subjects (n = 9). SNPs were genotyped using the Sequenom (CA, USA) mass spectrometer. Body surface area, age, smoking status and genotype were entered into a modified pharmacogenetic algorithm with a target international normalized ratio of 2.5. Bootstrap analysis using the @RISK software v5.0, (Palisade Co., NY, USA) was performed to simulate a population of 1000 for each ethnic group.

RESULTS

Simulated warfarin doses were lower in Chinese subjects than New Zealand Europeans (Δ1.39 mg; 95% CI: 0.4-2.4; p = 0.006) owing to the high prevalence of the VKORC1*2 haplotype in Chinese subjects. Doses were higher in Pacific Islanders compared with New Zealand Europeans (Δ1.26 mg; 95% CI: 0.6-1.9; p = 0.0002) owing to the near absence of the CYP2C9 variant alleles. Simulated warfarin doses in Mãori patients were similar to those in European patients.

CONCLUSION

This simulation study demonstrated differences in mean warfarin maintenance doses between ethnic groups in this cohort. Individualizing treatment regimens, using pharmacogenetics, may reduce ethnic disparities in treatment outcomes, particularly if differences can be appreciated at the genomic level.

Prasugrel, Māori, and personalised medicine in New Zealand

The response to thienopyridine antiplatelet therapy is heterogeneous and is in part explained by clinical and genetic factors. A recent meta-analysis has demonstrated the clinical significance of a genetic polymorphism in the cytochrome P450 2C19 gene. Carriers of this polymorphism have a higher incidence of stent thrombosis and cardiovascular death, whilst on the thienopyridine clopidogrel. The polymorphism and rarer variants display higher carrier frequencies in ethnic groups with disproportionate cardiovascular mortality, such as Māori. Knowledge of an individual's genetic status may assist in optimising antiplatelet therapy, thereby reducing the cost of adverse events, expenditure on new medicines, and the ethnic disparities seen in healthcare outcomes. A demonstration of the cost-effectiveness of genetic testing, on a population basis, and a proven alternative, personalised strategy is required before the adoption of this technology can be advocated.

The prevalence of a raised aldosterone–renin ratio (ARR) among new referrals to a hypertension clinic

The wider application of the plasma aldosterone to renin activity ratio (ARR) test has led independent groups to report a 10-fold or higher prevalence in the detection and prevalence of primary aldosteronism than previously suggested, although such figures have been contested. We determined the prevalence of a raised ARR in an unselected group of patients who were referred to the hypertension clinic at Aberdeen Royal Infirmary. Over a 4-month period, all newly referred patients had an ARR, urea and electrolytes, and 24-h ambulatory blood pressure monitoring (ABPM) performed in addition to a detailed clinical examination. One hundred and twenty-two patients (mean age 51 +/- 16 years) were examined over the study period; 57 (47%) were receiving no anti-hypertensive medication, 32(26% of total) had a normal 24-h ABPM of which 15 patients were receiving antihypertensive medication ("controlled" hypertensives) and 17(14%) were receiving no anti-hypertensive medication ("white-coat hypertensives). Twenty patients (mean age 58 +/- 11 years) were found to have a raised ARR (> 750), of which 10 patients were receiving beta-blocker therapy as part of their anti-hypertensive regimen. Patients with a raised ARR were more likely (odds ratio 3.6, 95% confidence interval 1.2-13.2, p < 0.05) to be classified as a "non-dipper" compared with those whose blood pressure fell at night. The proportion of newly referred hypertensive patients with a raised ARR is still significant and confirms that of previous studies The ratio appears to be significantly driven by a suppressed renin value and further investigation is required to clarify the status of those patients receiving anti-hypertensive medications, particularly beta-blockers.

Optimal use of taxanes in metastatic breast cancer

The role of taxanes in the treatment of breast cancer is becoming increasingly important. In clinical practice, the taxanes are now standard therapy in both early-stage and metastatic breast cancer. Since the 1990s, multiple randomized clinical trials have been evaluating the efficacy of taxanes in the treatment of metastatic breast cancer. These trials have included treatment with taxanes alone or in combination with other chemotherapeutic agents. Pre-existing published guidelines for the use of taxanes in the management of metastatic breast cancer are available. The mandate of the Alberta Cancer Board Provincial Breast Tumour Group Guideline Panel was to consider and adapt the recommendations of the existing guidelines and to develop de novo guidelines to account for current evidence. For this task, the panel used the ADAPTE process, which is a systematic process of guideline adaptation developed by the ADAPTE Collaboration.The recommendations formulated by the panel included the identification of taxane regimens that could be offered in anthracycline-naïve patients, anthracycline-pretreated or -resistant patients, and patients overexpressing the human epidermal growth factor receptor 2. Potential toxicities and benefits in terms of time to progression, progression-free survival, overall survival, and quality of life were also considered.

A bioabsorbable everolimus-eluting coronary stent system (ABSORB): 2-year outcomes and results from multiple imaging methods

BACKGROUND

Drug-eluting metallic coronary stents predispose to late stent thrombosis, prevent late lumen vessel enlargement, hinder surgical revascularisation, and impair imaging with multislice CT. We assessed the safety of the bioabsorbable everolimus-eluting stent (BVS).

METHODS

30 patients with a single de-novo coronary artery lesion were followed up for 2 years clinically and with multiple imaging methods: multislice CT, angiography, intravascular ultrasound, derived morphology parameters (virtual histology, palpography, and echogenicity), and optical coherence tomography (OCT).

FINDINGS

Clinical data were obtained from 29 of 30 patients. At 2 years, the device was safe with no cardiac deaths, ischaemia-driven target lesion revascularisations, or stent thromboses recorded, and only one myocardial infarction (non-Q wave). 18-month multislice CT (assessed in 25 patients) showed a mean diameter stenosis of 19% (SD 9). At 2-year angiography, the in-stent late loss of 0.48 mm (SD 0.28) and the diameter stenosis of 27% (11) did not differ from the findings at 6 months. The luminal area enlargement on OCT and intravascular ultrasound between 6 months and 2 years was due to a decrease in plaque size without change in vessel size. At 2 years, 34.5% of strut locations presented no discernible features by OCT, confirming decreases in echogenicity and in radiofrequency backscattering; the remaining apparent struts were fully apposed. Additionally, vasomotion occurred at the stented site and adjacent coronary artery in response to vasoactive agents.

INTERPRETATION

At 2 years after implantation the stent was bioabsorbed, had vasomotion restored and restenosis prevented, and was clinically safe, suggesting freedom from late thrombosis. Late luminal enlargement due to plaque reduction without vessel remodelling needs confirmation.

Antiplatelet drug nonresponsiveness

The response to most medication, including antiplatelet drugs, is highly variable between individuals. Observational studies have shown that nonresponders to antiplatelet agents appear to have an increased incidence of vascular events. This review article reviews the background, mechanisms, and evidence in support of the clinical significance of this phenomenon.