T. van der Straaten

Effect of CYP3A4*22, CYP3A5*3, and CYP3A Combined Genotypes on Cyclosporine, Everolimus, and Tacrolimus Pharmacokinetics in Renal Transplantation

Cyclosporine, everolimus, and tacrolimus are the cornerstone of immunosuppressive therapy in renal transplantation. These drugs are characterized by narrow therapeutic windows, highly variable pharmacokinetics (PK), and metabolism by CYP3A enzymes. Recently, the decreased activity allele, CYP3A4*22, was described as a potential predictive marker for CYP3A4 activity. This study investigated the effect of CYP3A4*22, CYP3A5*3, and CYP3A combined genotypes on cyclosporine, everolimus, and tacrolimus PK in renal transplant patients. CYP3A4*22 carriers showed a significant lower clearance for cyclosporine (−15%), and a trend was observed for everolimus (−7%) and tacrolimus (−16%). Patients carrying at least one CYP3A5*1 allele had 1.5‐fold higher tacrolimus clearance compared with noncarriers; however, CYP3A5*3 appeared to be nonpredictive for everolimus and cyclosporine. CYP3A combined genotype did not significantly improve prediction of clearance compared with CYP3A5*3 or CYP3A4*22 alone. These data suggest that dose individualization of cyclosporine, everolimus, or tacrolimus therapy based on CYP3A4*22 is not indicated.

The exon-3 deleted growth hormone receptor polymorphism predisposes to long-term complications of acromegaly

OBJECTIVE The aim of the study was to evaluate the impact of the genomic deletion of exon 3 of the GH receptor (d3GHR) on long-term clinical outcome of acromegaly in a well-characterized cohort of patients with long-term remission of acromegaly. DESIGN We conducted a cross-sectional study. METHODS The presence of the d3GHR polymorphism was assessed in 86 acromegalic patients with long-term disease control and related to anthropometric parameters, cardiovascular risk factors, osteoarthritis, bone mineral density, colonic polyps and diverticulae, and dolichocolon. RESULTS Fifty-one patients had two wild-type alleles (59%), whereas 29 patients (34%) had one allele and six patients (7%) had two alleles encoding for the d3GHR isoform. Carriers of the d3GHR isoform showed increased prevalence of osteoarthritis, especially of the hip [adjusted odds ratio (OR), 5.2; 95% confidence interval (CI), 3.2-7.1], of adenomatous polyps (adjusted OR, 4.1; 95% CI, 2.4-5.6), and dolichocolon (adjusted OR, 3.2; 95% CI, 1.8-4.6). Anthropometric parameters, cardiovascular risk factors, bone mineral density, and (non)vertebral fractures were not significantly different between patients with and without the d3GHR allele. CONCLUSION In patients with long-term cured acromegaly, the d3GHR polymorphism is associated with an increased prevalence of irreversible comorbidities such as osteoarthritis, dolichocolon, and adenomatous colonic polyps, but not with other comorbidities such as cardiovascular risk factors.

Effect of genetic polymorphisms in genes encoding GST isoenzymes on BU pharmacokinetics in adult patients undergoing hematopoietic SCT

BU is used in conditioning regimens before hemopoietic SCT. High BU exposure is associated with toxicity, whereas low BU exposure leads to higher rates of therapy failure. The pharmacokinetics of BU show large interpatient variability, hypothesized to be caused by variability in BU metabolism. In this report, the effect of genetic polymorphisms in three gluthatione S-transferase genes involved in BU metabolism (hGSTA1), GSTM1 (deletion–mutation) and GSTP1 (313A/G) on the pharmacokinetics of BU in Caucasian adult patients was investigated. In all, 66 adult patients received BU as part of their conditioning regimen. After the first infusion, two serum samples were collected and measured using a HPLC assay. A one-compartment population model was used to estimate individual pharmacokinetic parameters. The genetic variants of the three glutathione S-transferase (GST) genes were determined by pyrosequencing and PCR. A reduction of 14% in BU clearance was seen for the GSTA1*B allele and an increase in BU exposure was found. No relationship was found between polymorphisms in GSTM1 and GSTP1 and BU pharmacokinetics. This study shows that an increasing number of copies of GSTA1*B allele results in a significant decrease of BU clearance.

Pharmacogenetics in the Cancer Clinic: From Candidate Gene Studies to Next‐Generation Sequencing

Genetics has significantly added to our understanding of variability in drug response, especially in cancer treatment. Pharmacogenetics, aimed at predicting a patients chance for effective and safe drug treatment by interrogating germ line genetic variants, has moved from investigating a monogenetic candidate gene to examining complex phenotype‐based genome‐wide approaches. With the rapid advances in sequencing technologies, decline in costs, and swift turnaround times, large‐scale genomic information will become available in the clinical setting, facilitating implementation of pharmacogenetics.

Relationship between the functional exon 3 deleted growth hormone receptor polymorphism and symptomatic osteoarthritis in women

Background Several studies suggest a role of the growth hormone (GH)/insulin-like growth factor-1 (IGF-1) axis in the pathophysiology of primary osteoarthritis (OA). A common polymorphism of the GH receptor (exon 3 deletion, d3-GHR) is associated with increased GH/IGF-1 activity. Objective To study associations between the d3-GHR polymorphism and symptomatic OA. Methods In the GARP (Genetics, osteoARthritis and Progression) study, we compared the d3-GHR polymorphism between OA patients and controls. GARP patients were genotyped for seven single nucleotide polymorphisms encompassing the d3-GHR gene, using rs4590183 as proxy for d3-GHR (pairwise r2=1). Binary logistic regression models with robust SEs were performed, stratified by sex. For replication, rs4590183 was tested in three additional cohorts. Fixed- and random-effects combined analyses were performed. Results In female GARP patients with severe familial OA, d3-GHR was associated with OA (adjusted OR 1.36 (95% CI 1.01 to 1.83), p=0.043), independently of age and body mass index. Combined analysis of all studies showed suggestive evidence for association between d3-GHR and OA (OR=1.17 (95% CI 1.04 to 1.30), p=0.008). Evidence was strongest in hip OA cases, without any evidence for heterogeneity. Conclusions In women, the d3-GHR polymorphism was associated with symptomatic OA, especially at the hip site.

Pharmacogenetics in transplant patients: mind the mix.

To the Editor: Several consortia have published guidelines to aid clinicians with the interpretation of pharmacogenetic test results,1,2 and an increasing number of medical centers are implementing prospective genotyping.3 Among these, there are many highly specialized care centers with complex patient populations. These patients may present unexpected challenges, as demonstrated by this case.

Response: Limited sampling strategies for once daily tacrolimus exposure monitoring

Dear Sir, We thankDr. Antonio J. Carcas-Sansuán for his valuable comments. However, there is an important difference between the Madrid models and the Leiden models. In their article (Almeida-Paulo et al.) [1], linear regression limited sampling strategies for AUC12 prediction were developed and not limited sampling maximum a priori (MAP) Bayesian estimation models. Linear regression limited sampling strategies are inconvenient in a way that it requires strict adherence to set times for blood sample collection which is almost impossible in clinical practice. Erroneous predictions will occur if the sampling times are not exactly as requested in the sampling protocol. In contrast, maximum a priori (MAP) Bayesian population pharmacokinetic models as we have developed in our recent article [2] are far more flexible and can handle sampling times which deviate from the sampling protocol without resulting in erroneous predictions. Although these models require more complex calculations and the development of a population pharmacokinetic model, we believe these models are superior to linear regression limited sampling formulas when used in clinical practice. Currently different software packages are available to support these population phamacokinetic models in clinical practice and have been evaluated recently [3]. Furthermore, different more user friendly web-based initiatives are emerging such as Dose Me [4] and Insight-rx [5]. In our University Medical Center, we have used these kinds of models for over a decade in routine clinical practice for prediction of cyclosporine, tacrolimus, and mycophenolic acid exposure for all renal and liver transplant recipients with satisfactory results. Furthermore, Størset et al. [6, 7] recently showed that computerized dose individualization improved target concentration achievement of tacrolimus after renal transplantation potentially improve long-term outcome. We agree with Dr. Antonio J. Carcas-Sansuán that hard evidence that AUC12 monitoring of tacrolimus is superior to troughmonitoring is still lacking when looking at clinical endpoints. However, based on theory and examples from clinical practice, we strongly believe that AUC12 monitoring of tacrolimus is more informative and accurate and should therefore be applied. The development of dried blood spot techniques [8, 9] has also made the limited sampling AUC12 for patient less burdensome because the blood sampling can now be performed at home. To gain more evidence with respect to improvement of clinical outcome using these models, we would suggest to set up a two arm randomized clinical trial in a high acute rejection risk patient population to evaluate the differences in acute rejection episodes and renal function decline over a period of for instance 5 years between the trough monitoring arm and the limited sampling AUC12 monitoring arm. Such a study would be able to provide indisputable evidence for potential additional value of AUC12 over trough monitoring; however, it will be challenging to finance such a study with a high sample size and long-term follow-up. * D. J. A. R Moes d.j.a.r.moes@lumc.nl

PHC-014 Exploratory Analysis of 1,936 SNPs in 225 ADME Genes For Association with Busulfan Clearance in Adult Hematopoietic Stem Cell Recipients

Background Busulfan is used in preparative regimens prior to stem cell transplantation (SCT). There is significant inter-patient variability in busulfan pharmacokinetics (PK) and outcome is related to exposure. To date, only polymorphisms in genes encoding for glutathione-S-transferases have been studied; they could only explain a small portion of the variability in PK. Purpose To investigate the role of other genetic variants on busulfan clearance by interrogating 1,936 variants in 225 genes that are involved in drug absorption, distribution, metabolism and excretion (ADME). Materials and Methods 62 adult patients who received busulfan were genotyped using the Drug Metabolizing Enzymes and Transporters (DMET) array. Busulfan clearance was estimated with a limited sampling (t = 2.5, 4 hrs) PK model. Individual SNPs were associated with busulfan clearance. Top SNPs and haplotypes were replicated in an independent cohort (n = 78). Results In the discovery cohort 7 variants (3 SNPs and 4 haplotypes) explained 64% (adjusted R2) of variance in busulfan clearance (p < 0.001). These genetic variants, located in GSTA5, CYP2C19, CYP39A1 (2 haplotypes), ABCB4, SLC22A4 and SLC7A8, were replicated in the second cohort. One haplotype in GSTA5 (rs4715354 and rs7746993) remained statistically significant (P = 0.025) for correlation with busulfan clearance. Conclusions This is the first study using an exploratory pharmacogenetic approach in 225 genes involved in ADME to explain the inter-individual variability in busulfan clearance. The GSTA5 haplotype was significantly correlated with busulfan clearance, both in the discovery and replication cohort. No additional genetic markers involved in drug metabolism and transport appear to be associated with busulfan clearance. No conflict of interest.