Pharmacogenomic polygenic response score predicts ischaemic events and cardiovascular mortality in clopidogrel-treated patients

AIMS

Clopidogrel is prescribed for the prevention of atherothrombotic events. While investigations have identified genetic determinants of inter-individual variability in on-treatment platelet inhibition (e.g. CYP2C19*2), evidence that these variants have clinical utility to predict major adverse cardiovascular events (CVEs) remains controversial.

METHODS AND RESULTS

We assessed the impact of 31 candidate gene polymorphisms on adenosine diphosphate (ADP)-stimulated platelet reactivity in 3391 clopidogrel-treated coronary artery disease patients of the International Clopidogrel Pharmacogenomics Consortium (ICPC). The influence of these polymorphisms on CVEs was tested in 2134 ICPC patients (N = 129 events) in whom clinical event data were available. Several variants were associated with on-treatment ADP-stimulated platelet reactivity (CYP2C19*2, P = 8.8 × 10-54; CES1 G143E, P = 1.3 × 10-16; CYP2C19*17, P = 9.5 × 10-10; CYP2B6 1294 + 53 C > T, P = 3.0 × 10-4; CYP2B6 516 G > T, P = 1.0 × 10-3; CYP2C9*2, P = 1.2 × 10-3; and CYP2C9*3, P = 1.5 × 10-3). While no individual variant was associated with CVEs, generation of a pharmacogenomic polygenic response score (PgxRS) revealed that patients who carried a greater number of alleles that associated with increased on-treatment platelet reactivity were more likely to experience CVEs (β = 0.17, SE 0.06, P = 0.01) and cardiovascular-related death (β = 0.43, SE 0.16, P = 0.007). Patients who carried eight or more risk alleles were significantly more likely to experience CVEs [odds ratio (OR) = 1.78, 95% confidence interval (CI) 1.14-2.76, P = 0.01] and cardiovascular death (OR = 4.39, 95% CI 1.35-14.27, P = 0.01) compared to patients who carried six or fewer of these alleles.

CONCLUSION

Several polymorphisms impact clopidogrel response and PgxRS is a predictor of cardiovascular outcomes. Additional investigations that identify novel determinants of clopidogrel response and validating polygenic models may facilitate future precision medicine strategies.

Genomewide Association Study of Platelet Reactivity and Cardiovascular Response in Patients Treated With Clopidogrel: A Study by the International Clopidogrel Pharmacogenomics Consortium

Antiplatelet response to clopidogrel shows wide variation, and poor response is correlated with adverse clinical outcomes. CYP2C19 loss‐of‐function alleles play an important role in this response, but account for only a small proportion of variability in response to clopidogrel. An aim of the International Clopidogrel Pharmacogenomics Consortium (ICPC) is to identify other genetic determinants of clopidogrel pharmacodynamics and clinical response. A genomewide association study (GWAS) was performed using DNA from 2,750 European ancestry individuals, using adenosine diphosphate‐induced platelet reactivity and major cardiovascular and cerebrovascular events as outcome parameters. GWAS for platelet reactivity revealed a strong signal for CYP2C19*2 (P value = 1.67e−33). After correction for CYP2C19*2 no other single‐nucleotide polymorphism reached genomewide significance. GWAS for a combined clinical end point of cardiovascular death, myocardial infarction, or stroke (5.0% event rate), or a combined end point of cardiovascular death or myocardial infarction (4.7% event rate) showed no significant results, although in coronary artery disease, percutaneous coronary intervention, and acute coronary syndrome subgroups, mutations in SCOS5P1, CDC42BPA, and CTRAC1 showed genomewide significance (lowest P values: 1.07e−09, 4.53e−08, and 2.60e−10, respectively). CYP2C19*2 is the strongest genetic determinant of on‐clopidogrel platelet reactivity. We identified three novel associations in clinical outcome subgroups, suggestive for each of these outcomes.

Genome-wide and candidate gene approaches of clopidogrel efficacy using pharmacodynamic and clinical end points-Rationale and design of the International Clopidogrel Pharmacogenomics Consortium (ICPC)

RATIONALE

The P2Y12 receptor inhibitor clopidogrel is widely used in patients with acute coronary syndrome, percutaneous coronary intervention, or ischemic stroke. Platelet inhibition by clopidogrel shows wide interpatient variability, and high on-treatment platelet reactivity is a risk factor for atherothrombotic events, particularly in high-risk populations. CYP2C19 polymorphism plays an important role in this variability, but heritability estimates suggest that additional genetic variants remain unidentified. The aim of the International Clopidogrel Pharmacogenomics Consortium (ICPC) is to identify genetic determinants of clopidogrel pharmacodynamics and clinical response.

STUDY DESIGN

Based on the data published on www.clinicaltrials.gov, clopidogrel intervention studies containing genetic and platelet function data were identified for participation. Lead investigators were invited to share DNA samples, platelet function test results, patient characteristics, and cardiovascular outcomes to perform candidate gene and genome-wide studies.

RESULTS

In total, 17 study sites from 13 countries participate in the ICPC, contributing individual patient data from 8,829 patients. Available adenosine diphosphate-stimulated platelet function tests included vasodilator-stimulated phosphoprotein assay, light transmittance aggregometry, and the VerifyNow P2Y12 assay. A proof-of-principle analysis based on genotype data provided by each group showed a strong and consistent association between CYP2C19*2 and platelet reactivity (P value=5.1 × 10-40).

CONCLUSION

The ICPC aims to identify new loci influencing clopidogrel efficacy by using state-of-the-art genetic approaches in a large cohort of clopidogrel-treated patients to better understand the genetic basis of on-treatment response variability.

Multisite Investigation of Outcomes With Implementation of CYP2C19 Genotype-Guided Antiplatelet Therapy After Percutaneous Coronary Intervention

OBJECTIVES

This multicenter pragmatic investigation assessed outcomes following clinical implementation of CYP2C19 genotype-guided antiplatelet therapy after percutaneous coronary intervention (PCI).

BACKGROUND

CYP2C19 loss-of-function alleles impair clopidogrel effectiveness after PCI.

METHODS

After clinical genotyping, each institution recommended alternative antiplatelet therapy (prasugrel, ticagrelor) in PCI patients with a loss-of-function allele. Major adverse cardiovascular events (defined as myocardial infarction, stroke, or death) within 12 months of PCI were compared between patients with a loss-of-function allele prescribed clopidogrel versus alternative therapy. Risk was also compared between patients without a loss-of-function allele and loss-of-function allele carriers prescribed alternative therapy. Cox regression was performed, adjusting for group differences with inverse probability of treatment weights.

RESULTS

Among 1,815 patients, 572 (31.5%) had a loss-of-function allele. The risk for major adverse cardiovascular events was significantly higher in patients with a loss-of-function allele prescribed clopidogrel versus alternative therapy (23.4 vs. 8.7 per 100 patient-years; adjusted hazard ratio: 2.26; 95% confidence interval: 1.18 to 4.32; p = 0.013). Similar results were observed among 1,210 patients with acute coronary syndromes at the time of PCI (adjusted hazard ratio: 2.87; 95% confidence interval: 1.35 to 6.09; p = 0.013). There was no difference in major adverse cardiovascular events between patients without a loss-of-function allele and loss-of-function allele carriers prescribed alternative therapy (adjusted hazard ratio: 1.14; 95% confidence interval: 0.69 to 1.88; p = 0.60).

CONCLUSIONS

These data from real-world observations demonstrate a higher risk for cardiovascular events in patients with a CYP2C19 loss-of-function allele if clopidogrel versus alternative therapy is prescribed. A future randomized study of genotype-guided antiplatelet therapy may be of value.

The Pharmacogenomics Research Network Translational Pharmacogenetics Program: Outcomes and Metrics of Pharmacogenetic Implementations Across Diverse Healthcare Systems

Numerous pharmacogenetic clinical guidelines and recommendations have been published, but barriers have hindered the clinical implementation of pharmacogenetics. The Translational Pharmacogenetics Program (TPP) of the National Institutes of Health (NIH) Pharmacogenomics Research Network was established in 2011 to catalog and contribute to the development of pharmacogenetic implementations at eight US healthcare systems, with the goal to disseminate real-world solutions for the barriers to clinical pharmacogenetic implementation. The TPP collected and normalized pharmacogenetic implementation metrics through June 2015, including gene-drug pairs implemented, interpretations of alleles and diplotypes, numbers of tests performed and actionable results, and workflow diagrams. TPP participant institutions developed diverse solutions to overcome many barriers, but the use of Clinical Pharmacogenetics Implementation Consortium (CPIC) guidelines provided some consistency among the institutions. The TPP also collected some pharmacogenetic implementation outcomes (scientific, educational, financial, and informatics), which may inform healthcare systems seeking to implement their own pharmacogenetic testing programs.

Implementation of pharmacogenetics: the University of Maryland Personalized Anti-platelet Pharmacogenetics Program

Despite a substantial evidence base, implementation of pharmacogenetics into routine patient care has been slow due to a number of non-trivial practical barriers. We implemented a Personalized Anti-platelet Pharmacogenetics Program (PAP3) for cardiac catheterization patients at the University of Maryland Medical Center and the Baltimore Veterans Administration Medical Center Patients' are offered CYP2C19 genetic testing, which is performed in our Clinical Laboratory Improvement Amendment (CLIA)-certified Translational Genomics Laboratory. Results are returned within 5 hr along with clinical decision support that includes interpretation of results and prescribing recommendations for anti-platelet therapy based on the Clinical Pharmacogenetics Implementation Consortium guidelines. Now with a working template for PAP3, implementation of other drug-gene pairs is in process. Lessons learned as described in this article may prove useful to other medical centers as they implement pharmacogenetics into patient care, a critical step in the pathway to personalized and genomic medicine.

The relation between CYP2C19 genotype and phenotype in stented patients on maintenance dual antiplatelet therapy

Both high platelet reactivity (HPR) and CYP2C19 genotyping have been proposed to stratify cardiovascular event risk and to personalize maintenance dual antiplatelet therapy (DAPT) in stented patients. However, how well CYP2C19 genotype correlates with HPR in patients on maintenance DAPT is less clear. We determined the association of CYP2C19 loss-of-function (*2) and gain-of-function (*17) allele status with platelet reactivity in 118 stented patients on DAPT ≥2 weeks and in 143 patients with stable coronary artery disease on aspirin therapy alone. Thirty-three percent and 39% carried at least 1 copy of *2 and *17 alleles, respectively. Neither allele was associated with platelet reactivity in patients on aspirin therapy alone. On DAPT, platelet aggregation was higher in those with *2 allele than noncarriers (P ≤ .01) but did not differ between those with the *17 allele and noncarriers. The prevalence of HPR using the 20 μM adenosine diphosphate-induced aggregation cutpoint was 34% in the total population: 26% in *1/*1 homozygotes, 49% in those with the *2 allele, and 20% in those with the *17 allele (P = .006). Determination of diplotype status enhanced identification of HPR. However, platelet function on DAPT is highly variable within diplotype groups. Therefore, CYP2C19 genotype and HPR are imperfect correlates of each other. Because both predict cardiovascular events with similar risk ratios, CYP2C19 genotyping and HPR may provide complementary information to stratify risk and personalized DAPT in stented patients than either alone.

The effect of elinogrel on high platelet reactivity during dual antiplatelet therapy and the relation to CYP2C19*2 genotype: first experience in patients

To study the effect of a new direct acting reversible P2Y(12) inhibitor, elinogrel (PRT060128), and the relation to cytochrome P450 (CYP) polymorphisms in patients with high platelet reactivity (HPR) on standard dual antiplatelet therapy.

METHODS AND RESULTS

We studied the pharmacodynamic and pharmacokinetic effects of a single 60-mg oral dose of elinogrel in 20 of 45 previously stented stable patients with HPR. We also genotyped for CYP2C19*2,3,5,17 and CYP3A5*3. Platelet reactivity fell within 4 h of dosing, the earliest time point evaluated as measured by the following assays: maximum 5 and 10 microM ADP LTA (P < 0.001 for both vs. predosing); maximum 20 microM ADP LTA (P < 0.05); VerifyNow (P < 0.001); thrombelastography (P < 0.05); VASP phosphorylation (P < 0.01); and perfusion chamber assay (P < 0.05); this was reversible within 24 h in these same assays (P = ns vs. predosing for all assays). CYP2C19*2 was present in 44% of all patients but was more frequent in HPR patients (77% vs. 16%, P = 0.0004).

CONCLUSIONS

HPR is reversibly overcome by a single 60-mg oral dose of elinogrel, a drug now being investigated in a phase 2 trial. CYP2C19*2 was associated with HPR during conventional dual antiplatelet therapy.

The genetic response to short-term interventions affecting cardiovascular function: rationale and design of the Heredity and Phenotype Intervention (HAPI) Heart Study

BACKGROUND

The etiology of cardiovascular disease (CVD) is multifactorial. Efforts to identify genes influencing CVD risk have met with limited success to date, likely because of the small effect sizes of common CVD risk alleles and the presence of gene by gene and gene by environment interactions.

METHODS

The HAPI Heart Study was initiated in 2002 to measure the cardiovascular response to 4 short-term interventions affecting cardiovascular risk factors and to identify the genetic and environmental determinants of these responses. The measurements included blood pressure responses to the cold pressor stress test and to a high salt diet, triglyceride excursion in response to a high-fat challenge, and response in platelet aggregation to aspirin therapy.

RESULTS

The interventions were carried out in 868 relatively healthy Amish adults from large families. The heritabilities of selected response traits for each intervention ranged from 8% to 38%, suggesting that some of the variation associated with response to each intervention can be attributed to the additive effects of genes.

CONCLUSIONS

Identifying these response genes may identify new mechanisms influencing CVD and may lead to individualized preventive strategies and improved early detection of high-risk individuals.

The contraceptive effects of etoprine on male mice and rats

We had previously found that 2,4-diaminopyrimidines affected spermatogenesis, possibly through the inhibition of testicular dihydrofolate reductase (DHFR). The current study examined the effects of etoprine, a highly lipophilic 2,4-diaminopyrimidine that is also a potent DHFR inhibitor, on the fertility of male mice at various dosages (0.1-50 mg/kg/day) for 55 days and male rats at 5 mg/kg/day for 65 days. Two other substituted diaminopyrimidines were tested at dosages of 50 mg/kg/day for 55 days. Results of breeding trials along with assessment of various parameters indicative of male fertility were noted. We found that of the compounds tested, etoprine is a potent antifertility agent that causes complete infertility at doses of > or = 5 mg/kg/day in mice with a threshold of effectiveness occurring between 1 and 5 mg/kg/day. The antifertility action of etoprine may be related to its capacity to inhibit testicular DHFR and its high degree of lipophilicity.

The effect of ketoconazole on endocrine and reproductive parameters in male mice and rats

Ketoconazole has been shown to reduce steroidogenesis by inhibiting the cytochrome P-450 enzymes in these pathways. This finding, along with the observation that the compound reduces sperm motility, led us to study the effectiveness of ketoconazole as a male contraceptive agent administered in acute and chronic studies of both rats and mice. Four hours after a single administration, male rats showed significant reductions in both serum testosterone and corticosterone levels that completely recovered (testosterone) or nearly recovered (corticosterone) 24 hours after administration. Chronic administration of ketoconazole to male rats and mice resulted in steroid levels comparable with those of control animals. Epididymal sperm motility was only slightly reduced in male mice 4 hours after administration of the drug. No effect on sperm motility was noted after chronic administration in either species studied. In vitro exposure of epididymal sperm to ketoconazole resulted in a significant reduction of sperm motility. Breeding trials after ketoconazole administration resulted in normal fertility and fecundity even at the highest dosage studied. The lack of correlation between steroid levels and sperm immobilization, along with rapid in vivo and in vitro effects on sperm motility, suggests that the reduction in sperm motility is not related to a decrease in steroid levels. From these data, the authors conclude that ketoconazole is probably not a viable approach to the development of a male contraceptive.

Spermatic cord torsion. Contralateral testicular degeneration at various ages in the rat

Unilateral spermatic cord torsion causes damage to the contralateral testis in humans and animals models. It is now known, however, at what age an animal's reproductive capacity is most susceptible to this type of trauma. To determine if the animal's age is a factor in its susceptibility to reproductive damage, rats at 30 to 70 days of age were subjected to unilateral spermatic cord torsion. Rats of the same ages underwent sham surgery and served as controls. The animals were allowed to recover from the surgery and to attain puberty before a period of fertility testing. Fertility, serum testosterone, organ weight, and testicular histologic data were obtained after the breeding period. Our data indicate that animals undergoing torsion at the youngest (30 days) and oldest (70 days) ages exhibited no change in the parameters studied. Animals between the ages of 35 and 50 days are highly susceptible to reproductive damage due to unilateral spermatic cord torsion, and the 35-day-old animals exhibit the most susceptibility. The stages of testicular development occurring during this period are such that damage to one testicle will result in degeneration of both organs. However, once the animal is older than 50 days, its reproductive capacity is not affected by spermatic cord torsion. The specific period of susceptibility in the development of human testes is yet to be defined.

Spermatic cord torsion: effects of cyclosporine and prednisone on fertility and the contralateral testis in the rat

Unilateral spermatic cord torsion results in contralateral degeneration and reduced fertility in the prepubertal male rat. This study was conducted to investigate the use of immunosuppression with cyclosporine and prednisone to prevent these untoward effects. Thirty-five-day-old male rats were subjected to 720 degrees unilateral spermatic cord torsion of 9 hours duration. At the time of detorsion, animals were given a subcutaneous injection of i) cyclosporine, ii) prednisone, or iii) cyclosporine combined with prednisone. Control groups included: i) animals undergoing orchiectomy of the ipsilateral testis following the torsion period, ii) hemicastration in the absence of torsion and iii) sham surgery. Orchiectomy at the end of the torsion period prevented the torsion induced reduction of fertility, contralateral seminiferous tubule diameter and testis weight. Treatment with cyclosporine combined with prednisone significantly increased these parameters above detorsion alone. These data indicate that short term immunosuppression with cyclosporine alone or in combination with prednisone limits the adverse effects of unilateral spermatic cord torsion as does removal of the damaged organ at the end of the torsion period.

The effect of various degrees of unilateral spermatic cord torsion on fertility in the rat

Unilateral spermatic cord torsion has been shown to cause damage to the contralateral testis in humans and animal models. In an attempt to explain conflicts among various laboratories concerning the extent of this contralateral effect and to determine the importance of the extent of torsion, prepubertal rats (35 to 40 days) were subjected to unilateral spermatic cord torsion of various degrees (zero to 1440 degrees). Sham surgeries were performed and served as controls (0 degrees of torsion). The animals were allowed to recover from the surgeries and to attain puberty before a period of fertility testing. Fertility, fecundity, organ weight and testicular histological data were obtained after the breeding period. Our data indicate that animals undergoing 360 degrees of torsion exhibited no changes in the parameters studied. However, if 720 degrees, 1080 degrees or 1440 degrees of torsion was induced, a significantly lower percentage of fertile males and pregnant females resulted for each of these experimental groups when compared to those values for the 0 degrees controls. These data indicate that the extent of contralateral testicular degeneration is dependent upon the degree of spermatic cord torsion to which the ipsilateral testis is subjected. The induction of unilateral spermatic cord torsion at 720 degrees or more causes a significant reduction of subsequent fertility while torsion of a lesser degree has little or no effect in the development of this phenomenon.

Pyrimethamine: an approach to the development of a male contraceptive

With the human population of the world currently more than 5.2 billion and growing at an explosive rate, the need for additional forms of readily available contraception appears paramount. To date, contraception techniques in the male have been very limited. The present study demonstrates the ability of pyrimethamine (PYR) to cause spermatogenic arrest and male infertility in mice in a dose-dependent manner. Furthermore, upon cessation of drug administration all animals returned to normal fertility status. It is also suggested that the action of PYR is due to its antifolate action. Thus, PYR represents another approach toward development of a male contraceptive.