Understanding and predicting the association of intrinsic and extrinsic factors of pharmacokinetic variability in the context of precision medicine: impact of genetic polymorphisms on CYP2D6-mediated drug-drug interactions

La variabilité pharmacocinétique est une source majeure de variabilité de réponse aux médicaments, via notamment le métabolisme des médicaments par les cytochromes P450 (CYP). Parmi ceux-ci, le CYP2D6 représente un intérêt clinique considérable, en raison du grand nombre de médicaments qu’il métabolise et d’un polymorphisme important, principalement expliqué par des variations génétiques (facteur intrinsèque) ainsi que par des interactions médicamenteuses (facteur extrinsèque). Ce travail de thèse consiste en l’étude de l’impact du polymorphisme génétique sur les interactions médicamenteuses impliquant le CYP2D6. La thèse est divisée en trois volets majeurs: étude clinique mettant en évidence un effet du polymorphisme génétique sur l’amplitude des interactions médicamenteuses, étude in vitro investiguant les mécanismes des interactions gène-médicament-médicament, étude in silico de prédiction des interactions gène-médicament-médicament. Le présent travail souligne la nécessité de prise en compte des différents facteurs intrinsèques et extrinsèques de variabilité pharmacocinétique pour l’optimisation thérapeutique dans le contexte de la médecine de précision

The effect of proton pump inhibitors on platelet activity: An ex-vivo study

Clinical studies have pointed out a possible interaction between aspirin and omeprazole. In a recent study in aspirin treated patients, proton pump inhibitors (PPIs) were linked to an increased risk of adverse cardiovascular events. A recent proteomic study has described the presence of proton pumps in human platelets. This work looked into the modulation of aspirin antiplatelet effect by omeprazole and the effect of omeprazole alone on platelet activity. Incubation of omeprazole with aspirin, compared to aspirin alone, showed no significant difference on thromboxane A2 generation (p>0.05). However, it significantly (p>0.05) decreased platelet aggregation and granular secretion. Incubation of omeprazole in plasma caused a significant decrease of TxA2 generation and platelet granular secretion compared to control conditions, but aggregation remained unchanged. Omeprazole may enhance the antiplatelet effect of aspirin by another mechanism than COX-1 inhibition. The hypothesis about proton pumps role in the growth and stabilisation of the platelet plug is a given, but further studies are needed

Genotype-sensitive reversible and time-dependent CYP2D6 inhibition in human liver microsomes

Cytochrome P450 (CYP) 2D6 metabolizes a wide range of xenobiotics and is characterized by a huge interindividual variability. A recent clinical study highlighted differential magnitude of CYP inhibition as a function of CYP2D6 genotype. The aim of this study was to investigate the effect of CYP2D6 genotype on the inhibition of dextromethorphan O-demethylation by duloxetine and paroxetine in human liver microsomes (HLMs). The study focused on genotypes defined by the combination of two fully functional alleles (activity score 2, AS 2, n = 6), of one fully functional and one reduced allele (activity score 1.5, AS 1.5, n = 4) and of one fully functional and one non-functional allele (activity score 1, AS 1, n = 6), which all predict extensive metabolizer phenotype. Kinetic experiments showed that maximal reaction velocity was affected by CYP2D6 genotype, with a decrease in 33% of Vmax in AS 1 HLMs compared to AS 2 (P = 0.06). No difference in inhibition parameters Ki , KI and kinact was observed neither with the competitive inhibitor duloxetine nor with the time-dependent inhibitor paroxetine. Among the genotypes tested, we found no difference in absolute CYP2D6 microsomal levels with ELISA immunoquantification. Therefore, our results suggest that genotype-sensitive magnitude of drug-drug interactions recently observed in vivo is likely to be due to differential amounts of functional enzymes at the microsomal level rather than to a difference in inhibition potencies across genotypes, which motivates for further quantitative proteomic investigations of functional and variant CYP2D6 alleles

Physiologically-based pharmacokinetic modeling for the prediction of CYP2D6-mediated gene-drug-drug interactions

The aim of this work was to predict the extent of Cytochrome P450 2D6 (CYP2D6)-mediated drug-drug interactions (DDIs) in different CYP2D6 genotypes using physiologically-based pharmacokinetic (PBPK) modeling. Following the development of a new duloxetine model and optimization of a paroxetine model, the effect of genetic polymorphisms on CYP2D6-mediated intrinsic clearances of dextromethorphan, duloxetine, and paroxetine was estimated from rich pharmacokinetic profiles in activity score (AS)1 and AS2 subjects. We obtained good predictions for the dextromethorphan-duloxetine interaction (Ratio of predicted over observed area under the curve (AUC) ratio (Rpred/obs ) 1.38-1.43). Similarly, the effect of genotype was well predicted, with an increase of area under the curve ratio of 28% in AS2 subjects when compared with AS1 (observed, 33%). Despite an approximately twofold underprediction of the dextromethorphan-paroxetine interaction, an Rpred/obs of 0.71 was obtained for the effect of genotype on the area under the curve ratio. Therefore, PBPK modeling can be successfully used to predict gene-drug-drug interactions (GDDIs). Based on these promising results, a workflow is suggested for the generic evaluation of GDDIs and DDIs that can be applied in other situations

Pharmacogenomics of Oral Antithrombotic Drugs

Pharmacogenomics is a relatively recent yet rapidly expanding field of study examining how genetic variations influence responses to drugs. Antithrombotic drugs include the anticoagulant and antiplatelet compounds widely prescribed for the treatment and prevention of cardiovascular diseases. However, there is a large variability in response to antithrombotics, and this can modify the benefit/risk ratio of taking such medications. This variability can be explained by clinical factors such as age, sex, and drug-drug interactions, but also by genetic variants. In recent years, several genetic polymorphisms have been associated with variable biological responses to antithrombotics. Relevant polymorphisms related to antithrombotics have included target genes and genes that participate in the drugs' pharmacokinetics. This article provides a comprehensive review of the published literature about the pharmacogenomics of antithrombotic drugs, including well-studied compounds such as vitamin K antagonists (e.g., warfarin, acenocoumarol, and phenprocoumon), aspirin, and clopidogrel, as well as more recently approved compounds such as prasugrel, ticagrelor, and direct oral anticoagulants

Complex Drug-Drug-Gene-Disease Interactions Involving Cytochromes P450: Systematic Review of Published Case Reports and Clinical Perspectives

Drug pharmacokinetics (PK) is influenced by multiple intrinsic and extrinsic factors, among which concomitant medications are responsible for drug-drug interactions (DDIs) that may have a clinical relevance, resulting in adverse drug reactions or reduced efficacy. The addition of intrinsic factors affecting cytochromes P450 (CYPs) activity and/or expression, such as genetic polymorphisms and diseases, may potentiate the impact and clinical relevance of DDIs. In addition, greater variability in drug levels and exposures has been observed when such intrinsic factors are present in addition to concomitant medications perpetrating DDIs. This variability results in poor predictability of DDIs and potentially dramatic clinical consequences. The present review illustrates the issue of complex DDIs using systematically searched published case reports of DDIs involving genetic polymorphisms, renal impairment, cirrhosis, and/or inflammation. Current knowledge on the impact of each of these factors on drug exposure and DDIs is summarized and future perspectives for the management of such complex DDIs in clinical practice are discussed, including the use of advanced Computerized Physician Order Entry (CPOE) systems, the development of model-based dose optimization strategies, and the education of healthcare professionals with respect to personalized medicine

Evaluation of Pupillometry for CYP2D6 Phenotyping in Children Treated with Tramadol

Following the contraindication of codeine use in children, increasing use of tramadol has been observed in pain management protocols. However, tramadol’s pharmacokinetics (PK) and pharmacodynamics are influenced by cytochrome P450 (CYP)2D6 activity, similarly to codeine. Previous studies in adults have demonstrated a correlation between pupillary response and tramadol PK. Our objective was to evaluate pupillometry as a phenotyping method to assess CYP2D6 activity in children treated with tramadol. We included 41 children (mean age 11 years) receiving a first dose of tramadol (2 mg/kg) in the emergency room (ER) as part of their routine care. CYP2D6 phenotyping and genotyping were performed. The concentrations of tramadol and its active metabolite, M1, were measured, and static and dynamic pupillometry was conducted using a handheld pupillometer at the time of tramadol administration and during the ER stay. Pupillometric measurements were obtained for 37 children. Tramadol affected pupillary parameters, with a decrease in pupil diameter in 83.8% of children (p = 0.002) (mean decrease 14.1 ± 16.7%) and a decrease in reflex amplitude constriction in 78.4% (p = 0.011) (mean decrease 17.7 ± 34.5%) at T150 compared to T0. We were unable to identify a correlation between pupillometry measurements and CYP2D6 activity. Likely confounding factors include light intensity, pain, and stress, making the procedure less feasible in paediatric emergency settings

The Association of Combined GSTM1 and CYP2C9 Genotype Status with the Occurrence of Hemorrhagic Cystitis in Pediatric Patients Receiving Myeloablative Conditioning Regimen Prior to Allogeneic Hematopoietic Stem Cell Transplantation

Hemorrhagic cystitis (HC) is one of the complications of busulfan-cyclophosphamide (BU-CY) conditioning regimen during allogeneic hematopoietic stem cell transplantation (HSCT) in children. Identifying children at high risk of developing HC in a HSCT setting could facilitate the evaluation and implementation of effective prophylactic measures. In this retrospective analysis genotyping of selected candidate gene variants was performed in 72 children and plasma Sulfolane (Su, water soluble metabolite of BU) levels were measured in 39 children following treatment with BU-CY regimen. The cytotoxic effects of Su and acrolein (Ac, water soluble metabolite of CY) were tested on human urothelial cells (HUCs). The effect of Su was also tested on cytochrome P 450 (CYP) function in HepaRG hepatic cells. Cumulative incidences of HC before day 30 post HSCT were estimated using Kaplan-Meier curves and log-rank test was used to compare the difference between groups in a univariate analysis. Multivariate Cox regression was used to estimate hazard ratios with 95% confidence intervals (CIs). Multivariate analysis included co-variables that were significantly associated with HC in a univariate analysis. Cumulative incidence of HC was 15.3%. In the univariate analysis, HC incidence was significantly (p 40 vs. <11%) or in carriers of both functional GSTM1 and CYP2C9 (33.3 vs. 6.3%) compared to the other group. In a multivariate analysis, combined GSTM1 and CYP2C9 genotype status was associated with HC occurrence with a hazards ratio of 4.8 (95% CI: 1.3-18.4; p = 0.02). Ac was found to be toxic to HUC cells at lower concentrations (33 μM), Su was not toxic to HUC cells at concentrations below 1 mM and did not affect CYP function in HepaRG cells. Our observations suggest that pre-emptive genotyping of CYP2C9 and GSTM1 may aid in selection of more effective prophylaxis to reduce HC development in pediatric patients undergoing allogeneic HSCT. Article summary: (1) Children carrying functional alleles in GSTM1 and CYP2C9 are at high risk for developing hemorrhagic cystitis following treatment with busulfan and cyclophosphamide based conditioning regimen. (2) Identification of children at high risk for developing hemorrhagic cystitis in an allogeneic HSCT setting will enable us to evaluate and implement optimal strategies for its prevention. Trial registration: This study is a part of the trail "clinicaltrials.gov identifier: NCT01257854.