Clinical pharmacokinetics of antipsychotics in pediatric populations: a scoping review focusing on dosing regimen.

INTRODUCTION: Achieving optimal clinical responses and minimizing side effects through precision dosing of antipsychotics in children and adolescents with psychiatric disorders remains a challenge. Identifying patient characteristics (covariates) that affect pharmacokinetics can inform more effective dosing strategies and ultimately improve patient outcomes. This review aims to provide greater insight into the impact of covariates on the clinical pharmacokinetics of antipsychotics in pediatric populations. AREAS COVERED: A comprehensive literature search was conducted, and the main findings regarding the effects of the covariates on the pharmacokinetics of antipsychotics in children and adolescents are presented. EXPERT OPINION: Our study highlights significant covariates, including age, sex, weight, CYP2D6 phenotype, co-medication, and smoking habits, which affect the pharmacokinetics of antipsychotics. However, the findings were generally limited by the small sample sizes of naturalistic, open-label, observational studies, and the homogeneous subgroups. Dosing based on weight and preemptive genotyping could prove beneficial for optimizing the dosing regimen in pediatric populations. Future research is needed to refine dosing recommendations and establish therapeutic reference ranges critical for precision dosing and Therapeutic Drug Monitoring (TDM). The integration of individual patient characteristics with TDM can further optimize the efficacy and safety of antipsychotics for each patient.

Cost-utility analysis of tapering strategies of biologicals in rheumatoid arthritis patients in the Netherlands.

OBJECTIVES: Current guidelines recommend tapering biological disease-modifying antirheumatoid drugs (bDMARDs) in rheumatoid arthritis (RA) if the disease is under control. However, guidelines on tapering are lacking. Assessing cost-effectiveness of different tapering strategies might provide broader input for creating guidelines on how to taper bDMARDs in patients with RA. The aim of this study is to evaluate the long-term cost-effectiveness from a societal perspective of bDMARD tapering strategies in Dutch patients with RA, namely 50% dose reduction (tapering), discontinuation and a 50% dose reduction followed by discontinuation (de-escalation). METHODS: Using a societal perspective, a Markov model with a life-time horizon of 30 years was used to simulate 3-monthly transitions between Disease Activity 28 (DAS28)-defined health states of remission (<2.6), low disease activity (2.63.2). Transition probabilities were estimated through literature search and random effects pooling. Incremental costs, incremental quality-adjusted life-years (QALYs), incremental cost-effectiveness ratios (ICERs) and incremental net monetary benefits for each tapering strategy were compared with continuation. Deterministic, probabilistic sensitivity analyses and multiple scenario analyses were performed. RESULTS: After 30 years, the ICERs were €115 157/QALY lost, €74 226/QALY lost and €67 137/QALY lost for tapering, de-escalation and discontinuation, respectively; mainly driven by bDMARD cost savings and a 72.8% probability of a loss in quality of life. This corresponds to a 76.1%, 64.3% and 60.1% probability of tapering, de-escalation and discontinuation being cost-effective, provided a willingness-to-accept threshold of €50 000/QALY lost. CONCLUSIONS: Based on these analyses, the 50% tapering approach saved the highest cost per QALY lost.

Delayed Lithium Reintoxication in a Case of Severe Multidrug Intoxication: A Case Study.

ABSTRACT: The authors present a case of severe multidrug intoxication following massive ingestion of lithium, nortriptyline, aripiprazole, lorazepam, and temazepam. After initial treatment, serum lithium levels decreased significantly. However, 28 hours post ingestion, recurrent elevated lithium levels were observed, and serum lithium level increased 0.71 mmol/L in 12 hours. The intensivist consulted a hospital pharmacist about this. After administering clearance-inducing therapy using continuous venovenous hemodialysis, the lithium level was reduced to a long-lasting nontoxic level. The occurrence of secondary elevation in lithium levels exceeding the toxic limit in cases of massive ingestion of lithium tablets, whether in combination with anticholinergic drugs, should be anticipated. Close monitoring and prompt initiation of clearance-inducing therapy can improve clinical outcomes.

Renal function after withdrawal of lithium.

OBJECTIVES: Patients on chronic lithium therapy sometimes develop chronic kidney disease. For clinical decision-making, it is important to know whether discontinuation of lithium can lead to improvement of renal function. We studied the trajectory of renal function in a population previously on chronic lithium therapy. METHODS: From a large database of patients on chronic lithium therapy, we selected a group of patients who stopped using lithium and whose creatinine values at least half a year after lithium withdrawal were available. We measured the slope of renal function (eGFR) before and after discontinuation of lithium. We compared the subgroup of patients with improvement of the renal function with those who showed further deterioration of the eGFR. RESULTS: eGFR slope significantly improved after discontinuation of lithium. Of patients with chronic kidney disease stage 3 or more (eGFR<60 ml/min), the vast majority showed an increase of eGFR or a decrease in the rate of decline after lithium withdrawal. The group of patients with further deterioration of the renal function had a mean eGFR of 32 ml/min, which was significantly lower than the patients with an improvement of the kidney function. CONCLUSIONS: Discontinuation of lithium leads in the majority of patients to improvement in renal function or at least less rapid deterioration.

The added value of H2 antagonists in premedication regimens during paclitaxel treatment.

BACKGROUND: Ranitidine, a histamine 2 blocker, is the standard of care to prevent hypersensitivity reactions (HSRs) caused by paclitaxel infusion. However, the added value of ranitidine in this premedication regimen is controversial. Therefore, we compared the incidence of HSRs during paclitaxel treatment between a standard regimen including ranitidine and a regimen without ranitidine. METHODS: This prospective, pre-post interventional, non-inferiority study compared the standard premedication regimen (N = 183) with dexamethasone, clemastine and ranitidine with a premedication regimen without ranitidine (N = 183). The primary outcome was the incidence of HSR grade ≥3. Non-inferiority was determined by checking whether the upper bound of the two-sided 90% confidence interval (CI) for the difference in HSR rates excluded the +6% non-inferiority margin. RESULTS: In both the pre-intervention (with ranitidine) and post-intervention (without ranitidine) group 183 patients were included. The incidence of HSR grade ≥3 was 4.4% (N = 8) in the pre-intervention group and 1.6% (N = 3) in the post-intervention group: difference -2.7% (90% CI: -6.2 to 0.1). CONCLUSIONS: As the upper boundary of the 90% CI does not exceed the predefined non-inferiority margin of +6%, it can be concluded that a premedication regimen without ranitidine is non-inferior to a premedication regimen with ranitidine. CLINICAL TRIAL REGISTRATION: www.trialregister.nl ; NL8173.

Chronic kidney disease in lithium-treated patients, incidence and rate of decline.

BACKGROUND: Lithium-induced nephropathy is a known long-term complication, sometimes limiting the use of lithium as mood stabilizer. The aim of this study is to establish the incidence of chronic kidney disease and the rate of decline of renal function in patients using lithium and to identify risk factors. METHODS: We selected 1012 patients treated with lithium from the laboratory database of the Antes Centre for Mental Health Care spanning a period from 2000 to 2015. Serum lithium and creatinine concentrations were retrieved and eGFR was calculated using the 4-variable CKD-EPI formula. We calculated the incidence of renal insufficiency and the rate of decline. We compared patients with and without chronic kidney disease (CKD) stage 3 regarding duration of lithium exposure. RESULTS: Incidence of chronic kidney disease was 0.012 cases per exposed patient-year. Average decline of eGFR was 1.8 ml/min/year in patients who developed chronic kidney disease stage 3. Incidence of chronic kidney disease stage 4 was only 0.0004 per patient year. No cases of end stage renal disease were found in this cohort. Odds of reaching chronic kidney disease stage 3 were increased with longer duration of lithium exposure. CONCLUSIONS: The use of lithium seems to be related to a higher incidence of chronic kidney disease. Longer duration of lithium exposure significantly increased the risk of renal failure.

Adequacy of a hospital-wide standard dose of 7mg/kg bodyweight gentamicin sufficient to achieve an adequate prophylactic maximum serum concentration (Cmax) in burn patients undergoing surgical burn wound treatment.

INTRODUCTION: Pharmacokinetics of drugs can be significantly altered in burn patients. The aim of our study was to validate if the current hospital-wide standard dosage of 7mg/kg total bodyweight gentamicin is sufficient to achieve an adequate prophylactic Cmax (Cmax≥20mg/L). MATERIALS AND METHODS: A prospective observational cohort pharmacokinetic study was conducted in burn patients undergoing surgical burn wound treatment. RESULTS: 36/40 (90%) burn patients undergoing surgical burn wound treatment at Rotterdam Burn Centre (Maasstad Hospital), the Netherlands, achieved adequate prophylactic serum concentrations (Cmax≥20mg/L) after a single prophylactic intravenous dose of 7mg/kg total bodyweight gentamicin. Total Body Surface Area (TBSA) burned and total bodyweight were statistically significantly correlated with the Cmax, with correlation coefficients of -0.316, 0.443 and p values of 0.047, 0.004, respectively. Other covariates (age, time after injury, serum creatinine, dose, gender, intensive care admittance) were not statistically significantly correlated. Occurrence of postoperative infection was limited (n=1), no statistically significant difference was observed between patients with a therapeutic and patients with a subtherapeutic serum concentration. CONCLUSION: The current hospital-wide standard dosage of 7mg/kg total bodyweight is sufficient to achieve an adequate prophylactic Cmax in burn patients undergoing surgical burn wound treatment.

[Lithium: only acceptable with careful monitoring]. / Lithium, alleen verantwoord met zorgvuldige controle.

In the Netherlands, lithium is the mood stabilizer of choice for patients with bipolar disorder. Long-term treatment with lithium can only be implemented safely with frequent and appropriate monitoring of serum lithium concentrations. Here we use 3 cases to illustrate that severe complications can arise when careful monitoring is not performed: a 47-year-old woman with symptoms of a lithium intoxication with therapeutic plasma levels; a 73-year-old woman with chronic lithium intoxication; and a 56-year-old woman with end-stage renal failure after many years of probable toxic lithium levels.

Effects of cyclosporine a on single-dose pharmacokinetics of intravenous itraconazole in patients with hematologic malignancies.

An open-label, clinical pilot study was performed to study the effect of cyclosporine A (CsA) on single-dose pharmacokinetics of itraconazole in patients with a hematologic malignancy. Patients (n = 10), admitted for allogeneic stem cell transplantation, received a single dose of 200 mg itraconazole in a 1-hour intravenous infusion during their treatment period before initiation of CsA. This was repeated during the period that CsA was administered and a steady-state concentration of CsA was achieved (trough whole blood level 200-400 ng/mL). After both administrations of itraconazole, serum pharmacokinetics of itraconazole and hydroxy (OH) itraconazole were determined during 24 hours. The results were compared with each patient acting as his or her own control. Exposure to itraconazole, as measured by the AUC[0-24h], was not significantly altered when combined with CsA. Large interindividual variations were observed in area under the concentration curve values among patients. In contrast, exposure to OH-itraconazole was significantly increased when itraconazole was coadministered with CsA (median increase of AUC[0-24h] 49%) with significant prolongation of T(max) and T1/2 (median increase of T(max) 37% and T1/2 176%). These differences may be the result of variability in affinity of itraconazole, OH-itraconazole, and CsA for the cytochrome P450 3A4 metabolic system and the occurrence of P-glycoprotein polymorphisms. In conclusion, exposure to OH-itraconazole, but not to itraconazole, is increased when itraconazole is coadministered with CsA. Although the interaction profile of itraconazole and CsA remains complex, these findings may be of importance in patients in whom monitoring of itraconazole serum levels is warranted, for example, in those with life-threatening fungal infections or in those who receive concurrent cytochrome inducers or inhibitors.

Pharmacogenomics of drug-metabolizing enzymes and drug transporters in chemotherapy.

There is wide variability in the response of individuals to standard doses of drug therapy. This is an important problem in clinical practice, where it can lead to therapeutic failures or adverse drug events. Polymorphisms in genes coding for metabolizing enzymes and drug transporters can affect drug efficacy and toxicity. Pharmacogenomics aims to identify individuals predisposed to high risk of toxicity and low response from standard doses of anticancer drugs. This chapter focuses on the clinical significance of polymorphisms in drug-metabolizing enzymes and drug transporters in influencing efficacy and toxicity of anticancer therapy. The most important examples to demonstrate the influence of pharmacogenomics on anticancer therapy are thiopurine methyltransferase (TPMT), UGT (uridine diphosphate glucuronosyltransferase) 1A1*28, and DPD (dihydropyrimidine dehydrogenase) *2A, respectively, for 6-mercaptopurine, irinotecan, and 5-fluorouracil therapy. However, in most other anticancer therapies no clear association has been found for polymorphisms in drug-metabolizing enzymes and drug transporters and pharmacokinetics or pharmacodynamics of anticancer drugs. Evaluation of different regimens and tumor types showed that polymorphisms can have different, sometimes even contradictory, pharmacokinetic and pharmacodynamic effects in different tumors in response to different drugs. The clinical application of pharmacogenomics in cancer treatment therefore requires more detailed information regarding the different polymorphisms in drug-metabolizing enzymes and drug transporters. A greater understanding of complexities in pharmacogenomics is needed before individualized therapy can be applied on a routine basis.

Rapid detection of the DPYD IVS14+1G>A mutation for screening patients to prevent fluorouracil-related toxicity.

BACKGROUND: Deficiency of dihydropyrimidine dehydrogenase (DPD) has been linked to severe or lethal fluorouracil (FU)-related toxicity. The most prominent mutation in the DPYD gene is the IVS14+1G>A mutation, which causes skipping of exon 14 in the messenger RNA (mRNA) and results in DPD enzyme deficiency. Several methods have been described to detect this mutation, but all are labor intensive and low throughput. OBJECTIVE Our aim was to develop a high-throughput real-time PCR assay to screen patients for the IVS14+1G>A mutation. METHODS: Primers and probes were developed and several reaction conditions were tested. In total, 165 individuals were screened for this mutation, with DNA sequencing as a reference method. RESULTS: Results of the real-time PCR assay and DNA sequencing were 100% identical. In total, eight heterozygous individuals were identified, of which six were patients with severe FU-related toxicity after FU or capecitabine treatment and two were healthy volunteers. CONCLUSION: This new real-time PCR assay with a high throughput is particularly suitable for large-scale screening for the IVS14+1G>A mutation in patients selected for treatment with fluoropyrimidines in order to prevent severe FU-related toxicity.

Antiviral activity of HIV type 1 protease inhibitors nelfinavir and indinavir in vivo is not influenced by P-glycoprotein activity on CD4+ T cells.

P-glycoprotein (P-gp) can compromise the antiretroviral effect of a protease inhibitor (PI)-containing regimen for HIV-1, but can also reduce HIV-1 replication. We studied the net effect of P-gp on the intracellular HIV-1 RNA and DNA load in vivo. CD4(+) T cells were isolated from 27 HIV-1 patients (13 without and 14 with a PI-containing regimen) and subsequently sorted in CD45RO(-) (naive) and CD45RO(+) (memory) subsets with either high (P-gp(high)) or low (P-gp(low)) P-gp activity. Unspliced HIV-1 RNA and HIV-1 DNA load were determined. For each patient P-gp(high) and P-gp(low) subsets were compared. In patients on a PI-containing regimen, intracellular unspliced HIV-1 RNA was significantly lower in P-gp(high)-naive CD4(+) cells compared to P-gp(low)-naive CD4(+) cells (p = 0.04). The same trend was seen in naive CD4(+) cells of treatment naive patients. In both treated and untreated patients HIV-1 DNA levels were significantly lower in P-gp(high) than in P-gp(low) memory CD4(+) cells (p = 0.02 and p = 0.04). High cellular P-gp activity coincided with a reduced intracellular HIV-1 load in vivo, both in therapy-naive and in PI-treated patients. Therefore we conclude that the potential efflux function of P-gp on PIs may be clinically less relevant than the effect of P-gp on intracellular HIV-1 replication.

Metabolism of trabectedin (ET-743, Yondelis) in patients with advanced cancer.

PURPOSE: Trabectedin (ET-743, Yondelis) is a novel anti-cancer drug currently undergoing phase II-III evaluation, that has shown remarkable activity in pre-treated patients with soft tissue sarcoma. Despite extensive pharmacokinetic studies, the human disposition and metabolism of trabectedin remain largely unknown. We aimed to determine the metabolic profile of trabectedin and to identify its metabolites in humans. METHODS: We analysed urine and faeces (the major excretory route) from eight cancer patients after a 3 or 24 h intravenous administration of [14C]trabectedin. Using liquid chromatography with tandem quadrupole mass spectrometric detection (LC-MS/MS) and radiochromatography with off-line radioactivity detection by liquid scintillation counting (LC-LSC), we characterised the metabolic profile in 0-24 h urine and 0-120 h faeces. RESULTS: By radiochromatography, a large number of trabectedin metabolites were detected. Incubation with beta-glucuronidase indicated the presence of a glucuronide metabolite in urine. Trabectedin, ET-745, ET-759A, ETM-259, ETM-217 (all available as reference compounds) and a proposed new metabolite coined ET-731 were detected using LC-MS/MS. The inter-individual differences in radiochromatographic profiles were small and did not correlate with polymorphisms in drug-metabolising enzymes (CYP2C9, 2C19, 2D6, 2E1, 3A4, GST-M1, P1, T1 and UGT1A1 2B15) as determined by genotyping. CONCLUSIONS: Trabectedin is metabolically converted to a large number of compounds that are excreted in both urine and faeces. In urine and faeces we have confirmed the presence of trabectedin, ET-745, ET-759A, ETM-259, ETM-217 and ETM-204. In addition we have identified a putative new metabolite designated ET-731. Future studies should be aimed at further identification of possible metabolites and assessment of their activity.

Pharmacogenetic screening of CYP3A and ABCB1 in relation to population pharmacokinetics of docetaxel.

PURPOSE: Despite the extensive clinical experience with docetaxel, unpredictable interindividual variability in efficacy and toxicity remain important limitations associated with the use of this anticancer drug. Large interindividual pharmacokinetic variability has been associated with variation in toxicity profiles. Genetic polymorphisms in drug-metabolizing enzymes and drug transporters could possibly explain the observed pharmacokinetic variability. The aim of this study was therefore to investigate the influence of polymorphisms in the CYP3A and ABCB1 genes on the population pharmacokinetics of docetaxel. EXPERIMENTAL DESIGN: Whole blood samples were obtained from patients with solid tumors and treated with docetaxel to quantify the exposure to docetaxel. DNA was collected to determine polymorphisms in the CYP3A and ABCB1 genes with DNA sequencing. A population pharmacokinetic analysis of docetaxel was done using nonlinear mixed-effect modeling. RESULTS: In total, 92 patients were assessable for pharmacokinetic analysis of docetaxel. A three-compartmental model adequately described the pharmacokinetics of docetaxel. Several polymorphisms in the CYP3A and ABCB1 genes were found, with allele frequencies of 0.54% to 48.4%. The homozygous C1236T polymorphism in the ABCB1 gene (ABCB1*8) was significantly correlated with a decreased docetaxel clearance (-25%; P = 0.0039). No other relationships between polymorphisms and pharmacokinetic variables reached statistical significance. Furthermore, no relationship between haplotypes of CYP3A and ABCB1 and the pharmacokinetics could be identified. CONCLUSIONS: The polymorphism C1236T in the ABCB1 gene was significantly related to docetaxel clearance. Our current finding may provide a meaningful tool to explain interindividual differences in docetaxel treatment in daily practice.

Effect of age on functional P-glycoprotein in the blood-brain barrier measured by use of (R)-[(11)C]verapamil and positron emission tomography.

INTRODUCTION: P-glycoprotein (P-gp) is an efflux transporter responsible for the transport of various drugs across the blood-brain barrier (BBB). Loss of P-gp function with age may be one factor in the development and progression of neurodegenerative diseases. The aim of this study was to assess the effect of aging on BBB P-gp function. Furthermore, the relationship between BBB P-gp activity and peripheral P-gp activity in CD3-positive leukocytes was investigated. Finally, plasma pharmacokinetics of carbon 11-labeled (R)-verapamil was evaluated. METHODS: (R)-[(11)C]verapamil and positron emission tomography were used to assess gray matter P-gp function. Because (R)-[(11)C]verapamil is a substrate for P-gp, the volume of distribution of (R)-[(11)C]verapamil in the brain inversely reflects P-gp function in the BBB. RESULTS: Mean volume of distribution values for 5 young healthy volunteers (age range, 21-27 years) and 5 elderly healthy volunteers (age range, 59-68 years) were 0.62+/-0.10 and 0.73+/-0.07, respectively (P=.03). The activity index of P-gp activity in CD3-positive leukocytes was 2.88+/-0.77 in young volunteers and 1.76+/-0.58 in elderly volunteers (P=.02). CONCLUSION: This study showed decreased P-gp activity during aging. Consequently, the brain may be exposed to higher drug and toxin levels in elderly subjects.

Genetic polymorphisms of drug-metabolising enzymes and drug transporters in the chemotherapeutic treatment of cancer.

There is wide variability in the response of individuals to standard doses of drug therapy. This is an important problem in clinical practice, where it can lead to therapeutic failures or adverse drug reactions. Polymorphisms in genes coding for metabolising enzymes and drug transporters can affect drug efficacy and toxicity. Pharmacogenetics aims to identify individuals predisposed to a high risk of toxicity and low response from standard doses of anti-cancer drugs. This review focuses on the clinical significance of polymorphisms in drug-metabolising enzymes (cytochrome P450 [CYP] 2C8, CYP2C9, CYP2C19, CYP2D6, CYP3A4, CYP3A5, dihydropyrimidine dehydrogenase, uridine diphosphate glucuronosyltransferase [UGT] 1A1, glutathione S-transferase, sulfotransferase [SULT] 1A1, N-acetyltransferase [NAT], thiopurine methyltransferase [TPMT]) and drug transporters (P-glycoprotein [multidrug resistance 1], multidrug resistance protein 2 [MRP2], breast cancer resistance protein [BCRP]) in influencing efficacy and toxicity of chemotherapy. The most important example to demonstrate the influence of pharmacogenetics on anti-cancer therapy is TPMT. A decreased activity of TPMT, caused by genetic polymorphisms in the TPMT gene, causes severe toxicity with mercaptopurine. Dosage reduction is necessary for patients with heterozygous or homozygous mutation in this gene. Other polymorphisms showing the influence of pharmacogenetics in the chemotherapeutic treatment of cancer are discussed, such as UGT1A1*28. This polymorphism is associated with an increase in toxicity with irinotecan. Also, polymorphisms in the DPYD gene show a relation with fluorouracil-related toxicity; however, in most cases no clear association has been found for polymorphisms in drug-metabolising enzymes and drug transporters, and pharmacokinetics or pharmacodynamics of anti-cancer drugs. The studies discussed evaluate different regimens and tumour types and show that polymorphisms can have different, sometimes even contradictory, pharmacokinetic and pharmacodynamic effects in different tumours in response to different drugs. The clinical application of pharmacogenetics in cancer treatment will therefore require more detailed information of the different polymorphisms in drug-metabolising enzymes and drug transporters. Larger studies, in different ethnic populations, and extended with haplotype and linkage disequilibrium analysis, will be necessary for each anti-cancer drug separately.

Screening for polymorphisms in the PXR gene in a Dutch population.

OBJECTIVE: Cytochrome P450 3A4 (CYP3A4) is involved in the metabolism of over 50% of all drugs currently in use. However, CYP3A4 expression shows a large inter-individual variation that cannot only be explained by genetic polymorphisms identified in this gene. The pregnane X receptor (PXR) has been identified as a transcriptional regulator of CYP3A4. Single nucleotide polymorphisms (SNPs) in the PXR gene could influence PXR activity and thereby CYP3A4 expression. This study was therefore aimed at determining the frequencies of known SNPs and detecting yet unknown SNPs in the PXR gene in a Dutch population. METHODS: Genomic DNA was isolated from blood samples obtained from 100 healthy volunteers and subjected to PCR amplification, followed by DNA sequencing. The population, of which the ethnicity was 93% Caucasian, consisted of 79 female individuals and 21 males. RESULTS: A total of 24 SNPs were found in the PXR gene, eight of which are previously unknown. The allelic frequencies found in this population varied from 0.5 to 73%. Most of the previously detected SNPs were located in introns. One new SNP, T8555G in exon 8, causes an amino acid change of C379G and is located in the Ligand Binding Domain of PXR. CONCLUSION: Several SNPs were detected in the PXR gene, one of which is located in the ligand binding domain (LBD). These SNPs may influence PXR-mediated CYP3A4 induction.

Validation of in vitro cell models used in drug metabolism and transport studies; genotyping of cytochrome P450, phase II enzymes and drug transporter polymorphisms in the human hepatoma (HepG2), ovarian carcinoma (IGROV-1) and colon carcinoma (CaCo-2, LS180) cell lines.

Human cell lines are often used for in vitro biotransformation and transport studies of drugs. In vivo, genetic polymorphisms have been identified in drug-metabolizing enzymes and ABC-drug transporters leading to altered enzyme activity, or a change in the inducibility of these enzymes. These genetic polymorphisms could also influence the outcome of studies using human cell lines. Therefore, the aim of our study was to pharmacogenotype four cell lines frequently used in drug metabolism and transport studies, HepG2, IGROV-1, CaCo-2 and LS180, for genetic polymorphisms in biotransformation enzymes and drug transporters. The results indicate that, despite the presence of some genetic polymorphisms, no real effects influencing the activity of metabolizing enzymes or drug transporters in the investigated cell lines are expected. However, this characterization will be an aid in the interpretation of the results of biotransformation and transport studies using these in vitro cell models.

Detection of single nucleotide polymorphisms in the ABCG2 gene in a Dutch population.

BACKGROUND: ABCG2 is a drug transporter involved in the protection of tissues by actively transporting toxic substances and xenobiotics out of cells. Cancer cells overexpressing the ABCG2 gene show multidrug resistance to mitoxantrone-, methotrexate-, doxorubicin-, and camptothecin-based anticancer drugs, such as topotecan and SN-38. Large interindividual differences have been shown in oral availability and clearance of drugs that are substrates for ABCG2. Variation in the ABCG2 gene, such as single nucleotide polymorphisms (SNPs), can possibly explain the variability in pharmacokinetics of ABCG2 substrates. AIM: This study was performed to screen for SNPs in the ABCG2 gene to determine the frequencies of currently known and previously unknown SNPs in a Dutch population. METHODS: Blood samples were obtained from 100 healthy volunteers to isolate genomic DNA. PCR amplification was performed, followed by DNA sequencing. The population, of which the ethnicity was 93% Caucasian, consisted of 79 female individuals and 21 males. RESULTS: In total, 19 SNPs were found in the ABCG2 gene, of which 7 were previously unknown. The SNPs G8883A in exon 5 and C44168T in exon 14 cause an amino acid change of R160Q and R575X, respectively. Most of the previously unknown SNPs were found in introns. CONCLUSIONS: The results will be used in future studies to explore the influence of the different SNPs on ABCG2 protein expression, activity, and substrate specificity. In addition, the results can be used to study the effects of genetic polymorphisms in the ABCG2 gene on the pharmacokinetic profile of anticancer drugs.