Two new studies published in the New England Journal of Medicine found that patients with reduced-function alleles of CYP2C19 who had been treated with the popular anti-platelet drug clopidogrel experienced diminished platelet inhibition and a higher rate of major cardiovascular events compared to clopidogrel-treated patients without the alleles.
These studies are particularly meaningful since the US Food and Drug Administration has said it is looking to update labeling for Bristol-Myer’s Squibb/Sanofi-Aventis’ Plavix (clopidogrel) with genetic risk association information [see PGx Reporter 10-22-2008].
The first study, “Cytochrome P-450 Polymorphisms and Response to Clopidogrel,” by Mega et al., found that patients with certainCYP2C19 alleles “had significantly lower levels of the active metabolite of clopidogrel, diminished platelet inhibition, and a higher rate of major adverse cardiovascular events, including stent thrombosis, than did noncarriers.”
Mega et al. was funded with research grants from Daiichi Sankyo and Eli Lilly, codevelopers of the anti-platelet prasugrel (Effient), which is currently under review at the FDA and stands to compete with Plavix.
With $4.8 billion in worldwide sales last year, Plavix is BMS’ top-selling drug. BMS did not respond to questions regarding the studies prior to deadline.
The second study, “Genetic Determinants of Response to Clopidogrel and Cardiovascular Events,” by Simon et al. found that patients with an acute myocardial infarction who were receiving clopidogrel and were carrying CYP2C19 loss-of-function alleles had a “higher rate of subsequent cardiovascular events than those who were not.” According to the paper, cardiovascular events were notably high among patients undergoing percutaneous coronary intervention.
Simon et al. was conducted by investigators from French Registry of Acute ST-Elevation and Non-ST-Elevation Myocardial Infarction (FAST-MI), a registry affiliated with the French Society of Cardiology. The study was funded by unrestricted grants from Pfizer and Servier for FAST-MI, and a research grant from the French Caisse Nationale d'Assurance Maladie.
Based on these studies and other data, if the FDA decides to update Plavix’s label with genetic risk association data, then the patient population for the drug will certainly shrink, which in turn stands to benefit BMS’ competitors.
Mega et al.
Researchers in Mega et al. looked at the link between functional genetic variants in CYP genes, plasma concentrations of active drug metabolite, and platelet inhibition in 162 healthy subjects treated with clopidogrel.
According to the paper, carriers of at least one CYP2C19 reduced-function allele, comprising 30 percent of the study population, had a 32 percent relative reduction in plasma exposure to the active metabolite of clopidogrel compared with noncarriers of the allele. Carriers of CYP2C19 reduced-function alleles also experienced an absolute reduction in maximal platelet aggregation in response to clopidogrel that was 9 percent less than the effect seen in noncarriers. Both of these findings reached statistical significance (P<0.001).
“We found that patients with particular gene variants do not optimally respond to clopidogrel and therefore face a significantly higher risk of having a major cardiac event,” Jessica Mega, lead author and an instructor of medicine at Harvard Medical School, said in a statement. “The identification of this link could be an important part of targeting medicine to individual patients rather than treating everyone with one-size-fits-all therapies.”
“Our data suggest that knowing this information could be useful to clinicians.”
In Mega et al., researchers also looked at the relationship between CYP2C19 loss-of-function alleles and cardiovascular events in a separate cohort of 1,477 clopidogrel-treated patients with acute coronary syndromes in the Trial to Assess Improvement in Therapeutic Outcomes by Optimizing Platelet Inhibition with Prasugrel–Thrombolysis in Myocardial Infarction (TRITON–TIMI) 38.
In TRITON-TIMI 38, a head-to-head study of Lilly/Daiichi’s Effient and BMS’ Plavix, prasugrel was found to be more efficacious than clopidogrel in preventing deaths from blood clots, non-fatal heart attacks, and non-fatal strokes in patients receiving stents. However, in the more than 13,000-patient study, those receiving Effient had a greater risk of life-threatening bleeding than those taking Plavix (1.4 percent versus 0.9 percent, respectively).
When Mega et al. looked at TRITON–TIMI 38, they found that carriers of CYP2C19 reduced-function alleles treated with clopidogrel had a 53 percent increase in the risk of death from cardiovascular causes, myocardial infarction, or stroke, as compared with noncarriers, and an increase by a factor of 3 in the risk of stent thrombosis.
Mega et al. does not discuss the relationship between CYP2C19 reduced-function alleles and cardiovascular events in Effient-treated patients in TRITON-TIMI 38. However, in a study conducted by Lilly and published in the Journal of Thrombosis and Haemostasis last year, Brandt et al. found that the “common loss of function polymorphisms of CYP2C19 and CYP2C9 are associated with decreased exposure to the active metabolite of clopidogrel but not prasugrel,” and that “decreased exposure to [clopidogrel’s] active metabolite is associated with a diminished pharmacodynamic response to” the drug.
In Mega et al., researchers identified 54 alleles for CYP2C19, CYP2C9, CYP2B6, CYP3A5, CYP3A4,and CYP1A2. “Of note,the tested alleles in CYP3A4 were not polymorphic, which leftfive genes for analysis,” the study authors report in the paper.
The majority of the genotyping was conducted with Affymetrix’s Targeted Human DMET 1.0 Assay. In thecase of CYP2C19*17 or a no-call on the DMET chip, which occurred in 2 percent of samples, genotyping was performed with bidirectional sequencing or exon-specificPCR amplification, followed by the useof standard agarose-gel electrophoresis to resolve restriction-fragment-lengthpolymorphisms, study authors note.
Mega et al. was conducted by investigators from the Thrombolysis in Myocardial Infarction (TIMI) Study Group, Brigham and Women's Hospital and Harvard Medical School, Eli Lilly Research Laboratories, and Daiichi Sankyo. Many of the investigators reported receiving research grants, consulting fees, and lecture fees from BMS, Sanofi-Aventis, Lilly, Daiichi, and other firms.
If FDA decides to recommend that doctors genotype patients prior to prescribing Plavix, as they have done recently for the anticoagulant warfarin and the HIV drug abacavir, then sales for BMS’ blockbuster will certainly be impacted. Such a recommendation from the FDA would be particularly good news for competitors looking to cut into Plavix’s market share. Clopidogrel goes off patent in 2011.
In the paper, the study authors note several limitations of the study.
For instance, although researchers looked at multiple known functional variants in CYP genes, rare functional variants were not observed in the study population. “We cannot exclude meaningful effects of these and other genetic variants that either were not identified or had incomplete functional characterization,” the study authors wrote. “Moreover, since variations in non-CYP genes may also have an effect on responsiveness to clopidogrel and the likelihood of ischemic events, such variations also merit study.”
Also, due to the “complexity” of sample handling and assays, researchers were unable to “widely implement’ pharmacokinetic and pharmacodynamic assessments in TRITON-TIMI 38. As a result, in Mega et al., platelet-aggregation studies were done in healthy subjects, not in patients with coronary disease.
However, researchers attempted to control for elements that might confound baseline platelet activity, such as multiple genetic and environmental factors, by examining the change in platelet aggregation after the administration of clopidogrel.
Lastly, although researchers expected to observe a lower rate of bleeding among carriers of a CYP2C19 reduced-function allele than among noncarriers treated with clopidogrel, there was a low rate of bleeding events, and thus, the power to detect significant differences in bleeding on the basis of genotype was limited in TRITON-TIMI 38.
Lead author Mega told Pharmacogenomics Reporter that “none of the limitations impact the conclusions of the study.”
Mega added that the researchers had submitted their findings to the FDA.
“Our data suggest that knowing this information could be useful to clinicians,” she noted.
Although Mega acknowledges that this research can help doctors target Plavix to the subset of patients least likely to see cardiac events, she would not elaborate on potential discussions with sponsors on the development of a companion diagnostic.
Such discussions would be “separate from the paper,” was all Mega said.
Simon et al.
The second study by Simon et al., also published in the NEJM on Dec. 22, essentially confirms the link Mega et al. reported between risk of cardiovascular events and certain allelic variations in CYP2C19 in patients treated with clopidogrel.
In Simon et al., researchers followed for one year 2,208 patients in a nationwide French registry, who had an acute myocardial infarction and were treated with clopidogrel, to assess how allelic variants of genes modulating clopidogrel absorption (ABCB1), metabolic activation (CYP3A5 and CYP2C19), and biologic activity (P2RY12 and ITGB3), impacted their risk of death from any cause, nonfatal stroke, or myocardial infarction.
During the follow-up period, 225 patients died and 94 experienced non-fatal myocardial infarction or stroke. None of the selected SNPs in CYP3A5, P2RY12, or ITGB3 were associated with a risk of an adverse outcome. However, 16 percent of patients with two variant alleles of ABCB1 (TT at nucleotide 3435) and 11 percent of patients with ABCB1 wild-type genotype (CC at nucleotide 3435) had cardiovascular events at one year.
Patients carrying any two CYP2C19 loss-of-function alleles (*2, *3, *4, or *5), had a higher adverse event rate than non-carriers (approximately 22 percent versus vs. 13 percent). In Mega et al., researchers compared cardiovascular event rates with carriers of CYP2C19 loss-of-function alleles *1A, *2A, *3, *4, *5A, *6, *7, *8, *9, *10, *12, *13, *14, and *17.
According to Simon et al. out of the 1,535 patients who underwent percutaneous coronary intervention during hospitalization, “the rate of cardiovascular events among patients with two CYP2C19 loss-of-function alleles was 3.58 times the rate among those with none.”
Genomic DNA was extracted from whole-blood specimens with Roche’s MagNA Pure Compact Instrument and genotyping for CYP2C19, CYP3A5, ABCB1 and P2RY12 was performed with Applied Biosystem’s oligonucleotide ligation assay SNPlex, after initial amplification by PCR involving two primers for the variant alleles CYP2C19*2 (rs4244285), CYP2C19*3 (rs4986893), CYP3A5*3 (rs776746), ABCB1 (rs1045642), and P2RY12 (rs16846673, rs6809699, and rs6785930).
Genotyping for known variants of CYP2C19 and ITGB3, CYP2C19*4 (rs28399504), CYP2C19*5, CYP2C19*17 (rs12248560), and ITGB3 (rs5918), was performed with a custom TaqMan assay and ABI’s prism 7900HT Sequence Detection System.