Effect of common CYP3A4 and CYP3A5 variants on the pharmacokinetics of the cytochrome P450 3A phenotyping probe midazolam in cancer patients

CYP3A4*22 and CYP3A5*3 impact efficacy and safety of diazepam in patients with alcohol withdrawal syndrome

BACKGROUND

Diazepam is one of the most commonly prescribed pharmaceuticals for the treatment of alcohol withdrawal syndrome (AWS). However, diazepam sometimes is ineffective, and some patients experience dose-dependent adverse drug reactions (ADR). Previous studies have shown that diazepam metabolism involves the CYP3A4 and CYP3A5 isoenzymes, whose activity is highly variable between individuals, which may contribute to differences in clinical response.

PURPOSE

The study aimed to investigate the effects of the genetic polymorphisms CYP3A4*22 and CYP3A5*3 on the efficacy and safety of diazepam in patients with AWS.

MATERIALS AND METHODS

One hundred male AWS patients received 30 mg/day diazepam by intramuscular injections for 5 days. Genotyping for CYP3A4*22 (rs35599367) and CYP3A5*3 (rs776746) was performed by real-time polymerase chain reaction with allele-specific hybridization. The efficacy and safety assessments were performed using psychometric scales.

RESULTS

Patients who carry CT and TT genotypes by polymorphic marker C > T intron 6 (rs35599367) of the CYP3A4 gene had a higher risk for ADR and demonstrated lower safety of diazepam therapy (p < 0.001; two-way ANOVA).

CONCLUSION

These results suggest that genotyping for common CYP3A variants might have the potential to guide benzodiazepine withdrawal treatment.

Effects of CYP2C19*17 genetic polymorphisms on plasma and saliva concentrations of diazepam in patients with alcohol withdrawal syndrome

INTRODUCTION

Diazepam is one of the most commonly prescribed tranquilizers for the therapy of alcohol withdrawal syndrome (AWS). However, diazepam therapy often turns out to be ineffective, and some patients experience dose-dependent adverse drug reactions. Previous studies have shown that the metabolism of diazepam involves the CYP2C19 isoenzyme, whose activity is highly dependent on polymorphism of the encoding gene.

OBJECTIVE

The study aimed to investigate the effects of CYP2C19*17 genetic polymorphisms on plasma and saliva concentrations of diazepam as well as its impact on the efficacy and safety rates of therapy in patients with AWS.

MATERIAL AND METHODS

The study was conducted on 100 Russian male patients suffering from the AWS who received diazepam injections at a dosage of 30.0 mg/day for 5 days. Genotyping was performed by real-time PCR with allele-specific hybridization. The efficacy and safety assessment was performed using psychometric scales.

RESULTS

Based on the results of the study, we revealed differences in the efficacy and safety of therapy in patients with different CYP2C19 -806C>T genotypes. Therapeutic drug monitoring revealed the statistically significant difference in the levels of diazepam plasma concentration: (CC) 251.76 (214.43; 310.61) vs. (CT+TT) 89.74 (54.18; 179.13); P = 0.003, and diazepam saliva concentration: (CC) 3.86 (3.22; 5.12) vs. (CT+TT) 0.79 (0.44; 1.56); P = 0.003.

CONCLUSION

Our study showed the effects of CYP2C19*17 genetic polymorphisms on the efficacy and safety rates of diazepam. Furthermore, we revealed the statistically significant differences in plasma and saliva concentration levels of diazepam in patients carrying different genotypes.

CYP3A Activity in End-of-Life Cancer Patients Measured by 4β-Hydroxycholesterol/cholesterol Ratio, in Men and Women

Simple Summary

The elimination of drugs by enzymes in the liver may be impaired in cancer patients that are close to death (end-of-life). This could cause unwanted side effects or lack of effect of drugs and compromise the quality of life in patients. Blood samples collected in 137 deceased end-of-life cancer patients were analyzed for the marker 4β-hydroxycholesterol/cholesterol (4β-OHC/C), representing the activity of the most important drug eliminating enzyme, CYP3A. In addition, samples from young (n = 280) and elderly (n = 30) controls were analyzed for 4β-OHC/C. The average 4β-OHC/C was higher in male and female end-of-life cancer patients than in young and elderly controls without cancer. This finding may suggest that the ability to eliminate drugs by CYP3A is maintained until end of life and that drugs metabolized by CYP3 may not need dose adjustment or discontinuation in cancer patients close to death.

Abstract

More than 50% of all drugs are metabolized by the cytochrome P450 3A enzyme (CYP3A). The aim of this study was to investigate if the CYP3A activity, measured by the endogenous marker 4β-hydroxycholesterol/cholesterol ratio (4β-OHC/C), is changed during the last weeks and days of life in men and women. To this end, serum samples from 137 deceased patients (median age 70 years) collected at a single time point 1–60 days before death, were analyzed and compared to 280 young (median 27 years), and 30 elderly (median age 70 years) non-cancer controls. There were no significant differences in the 4β-OHC/C ratio between men and women in end-of-life patients (p < 0.25). The median 4β-OHC/C was significantly higher in end-of-life male patients compared to both young (p < 0.0001) and elderly (p < 0.05) male controls. In a similar manner, 4β-OHC/C in end-of-life female patients was significantly higher compared to young and elderly female controls, p < 0.0001 and p < 0.001, respectively. There was no significant correlation between 4β-OHC/C and survival time. The results from this study suggest maintained CYP3A activity to the very last days of life and even a capacity of induction of the enzyme in end-of-life cancer patients.

Investigating the influence of relevant pharmacogenetic variants on the pharmacokinetics and pharmacodynamics of orally administered docetaxel combined with ritonavir

The anticancer drug docetaxel exhibits large interpatient pharmacokinetic and pharmacodynamic variability. In this study, we aimed to assess the functional significance of 14 polymorphisms in the CYP3A, CYP1B1, ABCB1, ABCC2, and SLCO1B3 genes for the pharmacokinetics and pharmacodynamics of oral docetaxel, co-administered with ritonavir. None of the tested CYP3A, ABCB1, ABCC2, and SLCO1B3 genotypes and diplotypes showed a significant relation with an altered bioavailability or clearance of either docetaxel or ritonavir. Similarly, no clear effect of CYP1B1 genotype on clinical outcomes was observed in a subgroup of non-small cell lung cancer (NSCLC) patients. Our post hoc power analysis indicated that our pharmacogenetic-pharmacokinetic analysis was only powered for relatively high effect sizes, which were to be expected given the high interpatient variability. This makes it unlikely that future studies will explain the high observed interpatient variability in oral docetaxel pharmacokinetics as a result of any of these separate polymorphisms and diplotypes.

The rs776746 variant of CYP3A5 is associated with intravenous midazolam plasma levels and higher clearance in critically ill Mexican paediatric patients

WHAT IS KNOWN AND OBJECTIVE

Midazolam is a drug that is metabolized by cytochrome P450 (CYP450) enzymes, particularly CYP3A4 and CYP3A5. The presence of single-nucleotide polymorphisms (SNPs) in the genes encoding these enzymes, such as CYP3A4*1B which is associated with low enzyme expression and activity and CYP3A5*3, has been associated with decrease in enzymatic activity and reduced drug clearance, with potential effects on drug levels and/or toxicity. The present study was conducted to determine the frequencies of the allelic variants of the CYP3A4 (rs2740574) and CYP3A5 (rs776746) genes and their effects on the plasma levels and clearance of intravenous midazolam in critically ill Mexican paediatric patients.

METHODS

Seventy-two DNA samples were genotyped by real-time PCR with TaqMan probes. Plasma midazolam levels were determined at 3 and 24 h post infusion by high-performance liquid chromatography.

RESULTS AND DISCUSSION

The allelic variant rs776746 (CYP3A5*3) was associated with high midazolam plasma levels; the median concentration in patients with the normal genotype (CC) <0.01 ng/ml (Q₂₅ 0.01-Q₇₅ 196.09), whereas patients with the allelic variant (TT+TC) had a median midazolam concentration of 320.3 ng/ml (Q₂₅ 37.51-Q₇₅ 529.51), p = 0.001. The median pharmacokinetic clearance rates were 0.10 L/kg/h (Q₂₅ 0.01-Q₇₅ 0.34) in patients with the allelic variant (TT+TC) and 0.03 L/kg/h (Q₂₅ 0.002-Q₇₅ 0.13) in patients with the normal genotype (CC), p = 0.042.

WHAT IS NEW AND CONCLUSION

This is the first study that reports the frequency of the rs776746 polymorphism in critically ill paediatric patients, which is relevant, since carriers of the *1 allele synthesizing a functional enzyme may need higher doses to achieve adequate sedation. Our results show that compared with carriers of the normal allele, patients with the CYP3A5*3 allelic variant (rs776746) had increased plasma midazolam levels at 3 h after infusion discontinuation (320.3 ng/ml) and greater clearance (0.10 L/kg/h) of the drug.

Using the CYP3A Activity Evaluation to Predict the Efficacy and Safety of Diazepam in Patients With Alcohol Withdrawal Syndrome

BACKGROUND

Diazepam is one of the most commonly prescribed tranquilizers for the therapy of alcohol withdrawal syndrome (AWS). Despite its popularity, there is currently no precise information on the effect of genetic polymorphisms on the efficacy and safety of diazepam therapy.

OBJECTIVE

The objective of our study was to study the effect of CYP3A isoenzymes activity on the efficacy and safety of diazepam in patients with AWS.

METHODS

The study was conducted on 30 Russian male patients suffering from the AWS who received diazepam in injections at a dosage of 30.0 mg / day for 5 days. The efficacy and safety assessment was performed using psychometric scales and scales for assessing the severity of adverse drug reactions.

RESULTS

Based on the results of the study, we revealed the differences in the efficacy of therapy in patients with different CYP3A4 C>T intron 6 (rs35599367) genotypes: (CC) -9.0 [-13.0; -5.0], (CT+TT) -13.5 [-15.0; -10.0], p = 0.014. The scores on the UKU scale, which was used to evaluate the safety of therapy, were also different: (CC) 7.5 [6.0; 11.0], (CT+TT) 11.0 [8.0; 12.0], p = 0.003.

CONCLUSION

Possible relationship between the CYP3A activity, evaluated by the content of the urinary endogenous substrate of the given isoenzyme and its metabolite, the 6-beta-hydroxy cortisol (6-β-HC) / cortisol ratio, and the efficacy of diazepam was demonstrated. This possible relationship was also supported by the genotyping results. This should be taken into consideration when prescribing this drug to such patients in order to reduce the risk of pharmacoresistance.

How do CYP2C19*2 and CYP2C19*17 genetic polymorphisms affect the efficacy and safety of diazepam in patients with alcohol withdrawal syndrome?

Background Diazepam is one of the most commonly prescribed tranquilizers for therapy of alcohol withdrawal syndrome (AWS). Despite its popularity, there is currently no precise information on the effect of genetic polymorphisms on its efficacy and safety. The objective of our study was to investigate the effect of CYP2C19*2 and CYP2C19*17 genetic polymorphisms on the efficacy and safety of diazepam in patients with AWS. Methods The study was conducted on 30 Russian male patients suffering from the AWS who received diazepam in injections at a dosage of 30.0 mg/day for 5 days. The efficacy and safety assessment was performed using psychometric scales and scales for assessing the severity of adverse drug reactions. Results Based on the results of the study, we revealed the differences in the efficacy of therapy in patients with different CYP2C19 681G>A (CYP2C19*2, rs4244285) genotypes: (CYP2C19*1/*1) -8.5 [-15.0; -5.0], (CYP2C19*1/*2 and CYP2C19*2/*2) -12.0 [-13.0; -9.0], p = 0.021. The UKU scale scores, which were used to evaluate the safety of therapy, were also different: (CYP2C19*1/*1) 7.0 [6.0; 12.0], (CYP2C19*1/*2 and CYP2C19*2/*2) 9.5 [8.0; 11.0], p = 0.009. Patients carrying different CYP2C19 -806C>T (CYP2C19*17, rs12248560) genotypes also demonstrated differences in therapy efficacy and safety rates. Conclusions Thus, the effects of CYP2C19*2 and CYP2C19*17 genetic polymorphisms on the efficacy of diazepam were demonstrated.

Pharmacokinetics of midazolam in sevoflurane-anesthetized cats

OBJECTIVE

To estimate the pharmacokinetics of midazolam and 1-hydroxymidazolam after midazolam administration as an intravenous bolus in sevoflurane-anesthetized cats.

STUDY DESIGN

Prospective pharmacokinetic study.

ANIMALS

A group of six healthy adult, female domestic cats.

METHODS

Anesthesia was induced and maintained with sevoflurane. After 30 minutes of anesthetic equilibration, cats were administered midazolam (0.3 mg kg^-1) over 15 seconds. Venous blood was collected at 0, 1, 2, 4, 8, 15, 30, 45, 90, 180 and 360 minutes after administration. Plasma concentrations for midazolam and 1-hydroxymidazolam were measured using high-pressure liquid chromatography. The heart rate (HR), respiratory rate (f_R), rectal temperature, noninvasive mean arterial pressure (MAP) and end-tidal carbon dioxide (Pe'CO₂) were recorded at 5 minute intervals. Population compartment models were fitted to the time-plasma midazolam and 1-hydroxymidazolam concentrations using nonlinear mixed effect modeling.

RESULTS

The pharmacokinetic model was fitted to the data from five cats, as 1-hydroxymidazolam was not detected in one cat. A five-compartment model best fitted the data. Typical values (% interindividual variability where estimated) for the volumes of distribution for midazolam (three compartments) and hydroxymidazolam (two compartments) were 117 (14), 286 (10), 705 (14), 53 (36) and 334 mL kg^-1, respectively. Midazolam clearance to 1-hydroxymidazolam, midazolam fast and slow intercompartmental clearances, 1-hydroxymidazolam clearance and 1-hydroxymidazolam intercompartment clearance were 18.3, 63.5 (15), 22.1 (8), 1.7 (67) and 3.8 mL minute^-1 kg^-1, respectively. No significant changes in HR, MAP, f_R or Pe'CO₂ were observed following midazolam administration.

CONCLUSION AND CLINICAL RELEVANCE

In sevoflurane-anesthetized cats, a five-compartment model best fitted the midazolam pharamacokinetic profile. There was a high interindividual variability in the plasma 1-hydroxymidazolam concentrations, and this metabolite had a low clearance and persisted in the plasma for longer than the parent drug. Midazolam administration did not result in clinically significant changes in physiologic variables.

CYP3A4/5 Activity Probed with Testosterone and Midazolam: Correlation between Two Substrates at the Microsomal and Enzyme Levels

Testosterone (TST) and midazolam (MDZ) are widely used as probes to detect CYP3A4/5 activity, but the data acquired with these two substrates do not correlate well at the microsomal level (per milligram of microsomal protein), and the reason is unclear. In this study, CYP3A4/5 activity was probed with TST and MDZ at the microsomal and enzyme levels (per picomole of CYP3A4/5) in 72 human liver samples. Correlation coefficients were lower in V_max and CL_int at the microsomal level, as compared with those at the enzyme level ( V_max 0.658 vs 0.883; CL_int no correlation vs 0.796). Compared with TST, MDZ was found to correlate better with the content of CYP3A4/5 (no correlation vs 0.431) and CYP3A5 (no correlation vs 0.447), and huge variations in enzyme content existed among different genotypes, which explained the lower degree of correlation at the microsomal level. In addition, different genotypes had varying effects on activity at the enzyme level, whereas the difference between activity at the enzyme level probed with TST and that probed with MDZ was not obvious ( P > 0.05), indicating that the effect of gene polymorphisms on correlation between activity probed with these two substrates was limited at the enzyme level. In conclusion, our study demonstrates a high degree of correlation between CYP3A4/5 activity probed with TST and MDZ at the enzyme level but not at the microsomal level and allows us to correctly understand the influence of gene polymorphisms on the correlations.

Development and validation of a sensitive assay for analysis of midazolam, free and conjugated 1-hydroxymidazolam and 4-hydroxymidazolam in pediatric plasma: Application to Pediatric Pharmacokinetic Study

Pharmacokinetic, pharmacodynamic and pharmacogenomic studies of midazolam are currently being performed in critically ill children to find suitable dose regimens. Sensitive assays using small volumes of plasma are necessary to determine the concentrations of midazolam and its respective metabolites in pediatric studies. Midazolam is metabolized to hydroxylated midazolam isomers, which are present as free as well as the corresponding glucuronide conjugates. A high-performance liquid chromatographic method with tandem mass spectrometry has been developed and validated for the quantification of midazolam, and free and total 1-hydroxymidazolam and 4-hydroxymidazolam metabolites in small volumes of plasma. Cleanup consisted of 96-well μ-elution solid phase extraction (SPE). The analytes were separated by gradient elution using a C₁₈ analytical column with a total run time of 5min. Multiple reaction monitoring was employed using precursor to product ion transitions of m/z 326.2→291.3 for midazolam, m/z 342.1→203.0 for 1-hydroxymidazolam, m/z 342.1→325.1 for 4-hydroxymidazolam and m/z 330.2→295.3 for ²H₄-midazolam (internal standard). Since authentic hydroxymidazolamglucuronide standards are not available, samples were hydrolyzed with β-glucuronidase under optimized conditions. Assay conditions were modified and optimized to provide appropriate recovery and stability because 4-hydroxymidazolam was very acid sensitive. Standard curves were linear from 0.5 to 1000ng/mL for all three analytes. Intra- and inter day accuracy and precision for quality control samples (2, 20, 200 and 800ng/mL) were within 85-115% and 15% (coefficient of variation), respectively. Stability in plasma and extracts were sufficient under assay conditions. Plasma samples were processed and analyzed for midazolam, and free 1-hydroxymidazolam and 4-hydroxymidazolam metabolites. Plasma samples that were hydrolyzed with β-glucuronidase were processed and analyzed for midazolam, and total 1-hydroxymidazolam and 4-hydroxymidazolam metabolites under the same assay conditions. The difference in concentration between the total and free hydroxymidazolam metabolites provided an estimate of conjugated hydroxymidazolam metabolites. The combination of 96-well μ-elution SPE and LC-MS/MS allows reliable quantification of midazolam and its metabolites in small volumes of plasma for pediatric patients. This assay is currently being successfully utilized for analysis of samples from ongoing clinical trials.

Towards better dose individualisation: metabolic phenotyping to predict cabazitaxel pharmacokinetics in men with prostate cancer

BACKGROUND

Cabazitaxel is approved for treatment of castration-resistant metastatic prostate cancer. The current dosing strategy of cabazitaxel is based on body surface area (BSA). Body surface area is known as a poor predictor for total systemic exposure to drugs, since it does not take into account variability in activity of metabolising enzymes, necessary for clearance of drugs. As exposure to cabazitaxel is related to treatment response, it is essential to develop a better individualised dosing strategy.

METHODS

Ten patients with metastatic castration-resistant prostate cancer, who received cabazitaxel dosed on BSA as a part of routine palliative care, were enrolled in this study. Midazolam was administered as phenotyping probe for cytochrome P450 isoenzyme 3A (CYP3A). The relationship between midazolam and cabazitaxel clearance was investigated using non-linear mixed effects modelling.

RESULTS

The clearance of Midazolam highly correlated with cabazitaxel clearance (R=0.74). Midazolam clearance significantly (P<0.004) explained the majority (∼60%) of the inter-individual variability in cabazitaxel clearance in the studied population.

CONCLUSIONS

Metabolic phenotyping of CYP3A using midazolam is a promising strategy to individualise cabazitaxel dosing. Before clinical application, a randomised study is warranted.

Relation of Transcriptional Factors to the Expression and Activity of Cytochrome P450 and UDP-Glucuronosyltransferases 1A in Human Liver: Co-Expression Network Analysis

Cytochrome P450 (CYPs) and UDP-glucuronosyltransferases (UGTs) play important roles in the metabolism of exogenous and endogenous compounds. The gene transcription of CYPs and UGTs can be enhanced or reduced by transcription factors (TFs). This study aims to explore novel TFs involved in the regulatory network of human hepatic UGTs/CYPs. Correlations between the transcription levels of 683 key TFs and CYPs/UGTs in three different human liver expression profiles (n = 640) were calculated first. Supervised weighted correlation network analysis (sWGCNA) was employed to define hub genes among the selected TFs. The relationship among 17 defined TFs, CYPs/UGTs expression, and activity were evaluated in 30 liver samples from Chinese patients. The positive controls (e.g., PPARA, NR1I2, NR1I3) and hub TFs (NFIA, NR3C2, and AR) in the Grey_sWGCNA Module were significantly and positively associated with CYPs/UGTs expression. And the cancer- or inflammation-related TFs (TEAD4, NFKB2, and NFKB1) were negatively associated with mRNA expression of CYP2C9/CYP2E1/UGT1A9. Furthermore, the effect of NR1I2, NR1I3, AR, TEAD4, and NFKB2 on CYP450/UGT1A gene transcription translated into moderate influences on enzyme activities. To our knowledge, this is the first study to integrate Gene Expression Omnibus (GEO) datasets and supervised weighted correlation network analysis (sWGCNA) for defining TFs potentially related to CYPs/UGTs. We detected several novel TFs involved in the regulatory network of hepatic CYPs and UGTs in humans. Further validation and investigation may reveal their exact mechanism of CYPs/UGTs regulation.

Docetaxel-induced neuropathy: a pharmacogenetic case-control study of 150 women with early-stage breast cancer

BACKGROUND

Docetaxel is a highly effective treatment of a wide range of malignancies but is often associated with peripheral neuropathy. The genetic variability of genes involved in the transportation or metabolism of docetaxel may be responsible for the variation in docetaxel-induced peripheral neuropathy (DIPN). The main purpose of this study was to investigate the impact of genetic variants in GSTP1 and ABCB1 on DIPN.

MATERIAL AND METHODS

DNA was extracted from whole blood from 150 patients with early-stage breast cancer who had received adjuvant docetaxel from February 2011 to May 2012. Two polymorphisms in GSTP1 and three in ABCB1 were selected for the primary analysis, and a host of other candidate genes was explored and compared between 75 patients with clinician-reported DIPN grade ≥ 2 and 75 patients without DIPN.

RESULTS

Patients with the genetic variants GSTP1 rs1138272 C/T or T/T (114Ala/114Val or 114Val/114Val) genotype had an adjusted odds ratio of 3.82; 95% confidence interval 1.34-11.09 of developing DIPN. This result was confirmed in both analysis of cumulated docetaxel dose and haplotype analysis. None of the explorative genes investigated were significantly correlated with DIPN. Patients with a BMI ≥ 30 were five-fold more likely to have DIPN than patients with BMI < 25.

CONCLUSION

We found that GSTP1 Ala114Val polymorphism is associated with occurrence of DIPN. This supports the theory that oxidative stress is involved in DIPN pathophysiology. If confirmed, this may be helpful in the risk assessment of DIPN and perhaps help to achieve better management of neurotoxicity.

Pharmacokinetic interaction of intravenous fentanyl with ketoconazole

Fentanyl is primarily metabolized by CYP3A, but has also been suggested to act as a weak inhibitor of CYP3A. We investigated the influence of CYP3A inhibition by ketoconazole on the pharmacokinetics of intravenously administered fentanyl and the effect of fentanyl on CYP3A activity. A prospective, open-label, randomized, monocentre, crossover study was conducted in 16 healthy volunteers. They received fentanyl alone (5 microgram per kilogram) or fentanyl plus ketoconazole (200 milligram orally B.I.D. over 2 days). Naloxone (2 × 0.2 milligram i.v.) was given simultaneously with fentanyl to mitigate any opioid effect. Midazolam was administered as a CYP3A probe drug. Fentanyl and its metabolites were quantified by LC/MS/MS in blood and urine samples obtained over 24 hour. Exposure of fentanyl (AUC0- ∞ ) was significantly increased to 133% and systemic clearance was reduced to 78% by ketoconazole, norfentanyl formation was significantly delayed and partial metabolic clearance decreased to 18%. Fentanyl had no influence on midazolam exposure and CYP3A activity whereas ketoconazole decreased CYP3A activity to 13%. Although fentanyl N-dealkylation is substantially inhibited by ketoconazole, exposure of fentanyl itself increased by one third only. Clinically fentanyl dosage adjustments may become necessary when ketoconazole or other strong CYP3A inhibitors are given simultaneously. Fentanyl itself does not influence CYP3A activity.

Comparison of two endogenous biomarkers of CYP3A4 activity in a drug-drug interaction study between midostaurin and rifampicin

PURPOSE

Midostaurin, a multitargeted tyrosine kinase inhibitor, is primarily metabolized by CYP3A4. This midostaurin drug-drug interaction study assessed the dynamic response and clinical usefulness of urinary 6β-hydroxycortisol to cortisol ratio (6βCR) and plasma 4β-hydroxycholesterol (4βHC) for monitoring CYP3A4 activity in the presence or absence of rifampicin, a strong CYP3A4 inducer.

METHODS

Forty healthy adults were randomized into groups for either placebo or treatment with rifampicin 600 mg QD for 14 days. All participants received midostaurin 50 mg on day 9. Midostaurin plasma pharmacokinetic parameters were assessed. Urinary 6βCR and plasma 4βHC levels were measured on days 1, 9, 11, and 15.

RESULTS

Both markers remained stable over time in the control group and increased significantly in the rifampicin group. In the rifampicin group, the median increases (vs day 1) on days 9, 11, and 15 were 4.1-, 5.2-, and 4.7-fold, respectively, for 6βCR and 3.4-, 4.1-, and 4.7-fold, respectively, for 4βHC. Inter- and intrasubject variabilities in the control group were 45.6 % and 30.5 %, respectively, for 6βCR, and 33.8 % and 7.5 %, respectively, for 4βHC. Baseline midostaurin area under the concentration-time curve (AUC) correlated with 4βHC levels (ρ = -0.72; P = .003), but not with 6βCR (ρ = 0.0925; P = .6981).

CONCLUSIONS

Both 6βCR and 4βHC levels showed a good dynamic response range upon strong CYP3A4 induction with rifampicin. Because of lower inter- and intrasubject variability, 4βHC appeared more reliable and better predictive of CYP3A4 activity compared with 6βCR. The data from our study further support the clinical utility of these biomarkers.

CYP3A4 intron 6 C>T SNP (CYP3A4*22) encodes lower CYP3A4 activity in cancer patients, as measured with probes midazolam and erythromycin

AIM

The CYP3A4*22 allele was recently reported to be associated with reduced CYP3A4 activity. We investigated the impact of this allele on the metabolism of the CYP3A-phenotyping probes, midazolam (MDZ) and erythromycin.

PATIENTS & METHODS

Genomic DNA from 108 cancer patients receiving intravenous MDZ and 45 undergoing the erythromycin breath test was analyzed for CYP3A4*22 (rs35599367 C>T) and CYP3A5*3.

RESULTS

The MDZ metabolic ratio (1´-OH-MDZ:MDZ) was 20.7% (95% CI: -36.2 to -6.2) lower for CYP3A4*22 carriers compared with CYP3A4*1/*1 patients (p = 0.01). Combining CYP3A4*22 and CYP3A5*3 genotypes showed a 38.7% decrease (95% CI: -50.0 to -27.4; p < 0.001) in 1´-OH-MDZ:MDZ for poor (CYP3A4*22-CYP3A5*3/*3) and 28.0% (95% CI: -33.3 to -22.6; p < 0.001) for intermediate (CYP3A4*1/*1-CYP3A5*3/*3) metabolizers, compared with extensive (CYP3A4*1/*1-CYP3A5*1) CYP3A metabolizers. CYP3A4 erythromycin N-demethylation activity was 40% lower in CYP3A4*22 carriers compared with CYP3A4*1/*1 patients (p = 0.032).

CONCLUSION

The CYP3A4*22 allele is associated with decreased CYP3A4-mediated metabolism, as verified by CYP3A-phenotyping probes.

Scaling of pharmacokinetics across paediatric populations: the lack of interpolative power of allometric models

AIM

The objective of this investigation was to assess the performance of an allometric model as the basis for interpolating drug exposure in the context of pharmacokinetic bridging across paediatric subpopulations.

METHODS

Midazolam was selected as a paradigm compound. Two nonlinear mixed effects models were developed to describe midazolam pharmacokinetics in infants, toddlers and adults (model 1) and in children and adolescents (model 2). Subsequently, systemic drug exposure, expressed in terms of the area under the concentration vs. time curve (AUC), in children and adolescents was interpolated based on pharmacokinetic parameter distributions obtained from the model describing infants, toddlers and adults (model 1). Results were compared with the values obtained from modelling of the data in the corresponding population (model 2).

RESULTS

The two pharmacokinetic models accurately described midazolam exposure in the population on which they were built. However, the model based on data from infants, toddlers and adults failed to predict the exposure observed in children and adolescents: the mean difference between the predicted and estimated AUC(0-180) was of -17.8%, with a range of -6.8 to -38.4%.The discrepancy between estimated and interpolated exposure increased proportionally with body weight.

CONCLUSIONS

The current results indicate that irrespective of whether extrapolation or interpolation methods are to be applied during paediatric drug development, model predictions beyond the range of the data used for parameter estimation may be biased. For accurate inter- or extrapolation to different populations, the assumption of identical parameter-covariate correlations across age groups may not be taken for granted.

Microarray-assisted pathway analysis identifies MT1X & NFκB as mediators of TCRP1-associated resistance to cisplatin in oral squamous cell carcinoma

We recently reported that TCRP1, a novel multidrug-resistance associated human gene, can mediate cisplatin resistance in OSCC cells. However, the molecular mechanism underlying this role of TCRP1 remained to be elucidated. In this study, by using Human Toxicology and Drug Resistance Microarray, we identified 30 genes with significantly different expression levels between Tca/PYM and TCRP1 knockdown cell lines. Co-immunoprecipitation experiments and GST-pull down assays showed that metallothionein1X (MT1X) and Akt interact with TCRP1. siRNA-mediated knockdown of TCRP1 and MT1X was found to sensitize cells to cisplatin, leading to increased apoptosis and inhibition of cell proliferation. These functions of TCRP1 may be caused at least in part via activation of the PI3K/Akt/NF-κB signaling pathway. Taken together, our findings indicate that TCRP1 may be an important drug target for improvement of the treatment and survival of patients with oral squamous cell carcinoma.

In vivo CYP3A4 activity, CYP3A5 genotype, and hematocrit predict tacrolimus dose requirements and clearance in renal transplant patients

Tacrolimus is metabolized by CYP3A4 and CYP3A5 and is characterized by a narrow therapeutic index and highly variable pharmacokinetics. This cross-sectional study in 59 renal transplant patients investigated the relationship among in vivo CYP3A4 activity (assessed using midazolam as a drug probe), CYP3A5 genotype on the one hand, and tacrolimus pharmacokinetics on the other hand, taking into account other potential determinants of tacrolimus disposition. In vivo CYP3A4 activity and CYP3A5 genotype explain 56-59% of variability in tacrolimus dose requirements and clearance, contributing ~25 and 30%, respectively. Hematocrit explains an additional 4-14%. These data indicate that CYP3A4- and CYP3A5-mediated tacrolimus metabolisms are major determinants of tacrolimus disposition in vivo and explain a substantial part of the clinically observed high interindividual variability in tacrolimus pharmacokinetics. Furthermore, these data provide a potential basis for a comprehensive approach to predicting tacrolimus dose requirement in individual patients and hence provide a strategy to tailor immunosuppressive therapy in transplant recipients.

Rate of onset of inhibition of gut-wall and hepatic CYP3A by clarithromycin

AIMS

To determine the extent and time-course of hepatic and intestinal cytochrome P450 3A (CYP3A) inactivation due to the mechanism-based inhibitor clarithromycin.

METHODS

Intestinal and hepatic CYP3A inhibition was examined in 12 healthy volunteers following the administration of single and multiple doses of oral clarithromycin (500 mg). Intestinal biopsies were obtained under intravenous midazolam sedation at baseline and after the first dose, on days 2-4, and on days 6-8 of the clarithromycin treatment. The formation of 1'-hydroxymidazolam in biopsy tissue and the serum 1'-hydroxymidazolam:midazolam ratio were indicators of intestinal and hepatic CYP3A activity, respectively.

RESULTS

Intestinal CYP3A activity decreased by 64 % (p = 0.0029) following the first dose of clarithromycin, but hepatic CYP3A activity did not significantly decrease. Repeated dosing of clarithromycin caused a significant decrease in hepatic CYP3A activity (p = 0.005), while intestinal activity showed little further decline. The CYP3A5 or CYP3A4*1B genotype were unable to account for inter-individual variability in CYP3A activity.

CONCLUSIONS

Following the administration of clarithromycin, the onset of hepatic CYP3A inactivation is delayed compared to that of intestinal CYP3A. The time-course of drug-drug interactions due to clarithromycin will vary with the relative contribution of intestinal and hepatic CYP3A to the clearance and bioavailability of a victim substrate.

Population pharmacokinetic analysis of sorafenib in patients with solid tumours

WHAT IS ALREADY KNOWN ABOUT THIS SUBJECT

Sorafenib is a multikinase inhibitor with activity against B-raf, C-raf, VEGFR2, PDGFRβ and FGFR1. Sorafenib is clinically approved for the treatment of renal cell carcinoma (RCC) and hepatocellular carcinoma (HCC). The pharmacokinetics (PK) of sorafenib are highly variable between subjects. Sorafenib exposure increases less than dose proportionally (likely due to limited solubility). Sorafenib undergoes enterohepatic recycling (EHC).

WHAT THIS STUDY ADDS

This is the first study to characterize the PK of sorafenib using a model based on sorafenib's known disposition characteristics such as delayed/solubility-limited GI absorption and EHC. The parameterization of the EHC model used a square wave function to describe the gall bladder emptying. This study evaluated the effect of baseline bodyweight, BSA, age, gender, liver function parameters, kidney function parameters and genotype with respect to CYP3A4*1B, CYP3A5*3C, UGT1A9*3 and UGT1A9*5 on sorafenib PK. No clinically important covariates were identified. This model can be used to simulate and explore alternative dosing regimens and to develop exposure-response relationships for sorafenib.

AIMS

To characterize the pharmacokinetics (PK) of sorafenib in patients with solid tumours and to evaluate the possible effects of demographic, clinical and pharmacogenetic (CYP3A4*1B, CYP3A5*3C, UGT1A9*3 and UGT1A9*5) covariates on the disposition of sorafenib.

METHODS

PK were assessed in 111 patients enrolled in five phase I and II clinical trials, where sorafenib 200 or 400 mg was administered twice daily as a single agent or in combination therapy. All patients were genotyped for polymorphisms in metabolic enzymes for sorafenib. Population PK analysis was performed by using nonlinear mixed effects modelling (NONMEM). The final model was validated using visual predictive checks and nonparametric bootstrap analysis.

RESULTS

A one compartment model with four transit absorption compartments and enterohepatic circulation (EHC) adequately described sorafenib disposition. Baseline bodyweight was a statistically significant covariate for distributional volume, accounting for 4% of inter-individual variability (IIV). PK model parameter estimates (range) for an 80 kg patient were clearance 8.13 l h(-1) (3.6-22.3 l h(-1) ), volume 213 l (50-1000 l), mean absorption transit time 1.98 h (0.5-13 h), fraction undergoing EHC 50% and average time to gall bladder emptying 6.13 h.

CONCLUSIONS

Overall, population PK analysis was consistent with known biopharmaceutical/PK characteristics of oral sorafenib. No clinically important PK covariates were identified.

The interactions of age, genetics, and disease severity on tacrolimus dosing requirements after pediatric kidney and liver transplantation

Purpose

In children, data on the combined impact of age, genotype, and disease severity on tacrolimus (TAC) disposition are scarce. The aim of this study was to evaluate the effect of these covariates on tacrolimus dose requirements in the immediate post-transplant period in pediatric kidney and liver recipients.

Methods

Data were retrospectively collected describing tacrolimus disposition, age, CYP3A5 and ABCB1 genotype, and pediatric risk of mortality (PRISM) scores for up to 14 days post-transplant in children receiving liver and renal transplants. Initial TAC dosing was equal in all patients and adjusted using therapeutic drug monitoring. We determined the relationship between covariates and tacrolimus disposition.

Results

Forty-eight kidney and 42 liver transplant recipients (median ages 11.5 and 1.5 years, ranges 1.5–17.7 and 0.05–14.8 years, respectively) received TAC post-transplant. In both transplant groups, younger children (<5 years) needed higher TAC doses than older children [kidney: 0.15 (0.07–0.35) vs. 0.09 (0.02–0.20) mg/kg/12h, p = 0.046, liver: 0.12 (0.04–0.32) vs. 0.09 (0.01–0.18) mg/kg/12h, p = 0.038]. In kidney but not liver transplants, CYP3A5 expressors needed significantly higher TAC doses than nonexpressors [0.15 (0.07–0.20) vs. 0.09 (0.02–0.35) mg/kg/12h, P = 0.001]. In these patients, age and CYP3A5 genotype were independently associated with TAC dosing requirement. In liver, but not kidney transplant patients, homozygous ABCB1 T-T-T haplotype carriers needed higher TAC doses than noncarriers [0.26 (0.15–0.32) vs. 0.11 (0.01–0.25) mg/kg/12h, p = 0.013].

Conclusion

CYP3A5 genotype may explain variation in tacrolimus disposition early after transplant in pediatric kidney recipients, independent of age-related variation. In contrast, in pediatric liver recipients, variation in tacrolimus disposition appears related to age and ABCB1 genotype. These findings illustrate the importance of the interplay among age, genotype, and transplant organ on tacrolimus disposition.

Effect of ABCC2 (MRP2) transport function on erythromycin metabolism

The macrolide antiobiotic erythromycin undergoes extensive hepatic metabolism and is commonly used as a probe for cytochrome P450 (CYP) 3A4 activity. By means of a transporter screen, erythromycin was identified as a substrate for the transporter ABCC2 (MRP2) and its murine ortholog, Abcc2. Because these proteins are highly expressed on the biliary surface of hepatocytes, we hypothesized that impaired Abcc2 function may influence the rate of hepatobiliary excretion and thereby enhance erythromycin metabolism. Using Abcc2 knockout mice, we found that Abcc2 deficiency was associated with a significant increase in erythromycin metabolism, whereas murine Cyp3a protein expression and microsomal Cyp3a activity were not affected. Next, in a cohort of 108 human subjects, we observed that homozygosity for a common reduced-function variant in ABCC2 (rs717620) was also linked to an increase in erythromycin metabolism but was not correlated with the clearance of midazolam. These results suggest that impaired ABCC2 function can alter erythromycin metabolism, independent of changes in CYP3A4 activity.

Pharmacologic and phenotypic study of docetaxel in patients with ovarian or primary peritoneal cancer

PURPOSE

The objectives of this study were to determine whether the midazolam clearance predicted docetaxel pharmacokinetics, CA-125 change, and response and to assess the impact of cytochrome P450 (CYP) 3A5 and ATP-binding cassette, subfamily B, member 1 (ABCB1) genotypes on docetaxel pharmacokinetics and pharmacodynamics in ovarian or primary peritoneal cancer patients.

METHODS

Thirty-four patients with advanced ovarian and primary peritoneal cancer were administered docetaxel at 75 mg/m(2) as a 1-h infusion in combination with carboplatin IV over 30 min at a target AUC of 5 mg/ml min. Cycles were repeated every 21 days for 6 cycles. Midazolam was administered at 2 mg as a 30-min IV infusion the day prior to cycle one of docetaxel administration. Pharmacokinetic studies of docetaxel and CYP3A5 and ABCB1 genotype studies were performed.

RESULTS

There was an inverse relationship between midazolam clearance (CL) and CA-125 level after cycle 6 where a higher midazolam CL was associated with a CA-125 <10 U/ml (P = 0.007) and CA-125 <15 U/ml (P = 0.048). The CA-125 categories were associated with response achieved (complete response/partial response) (CR/PR), stable disease (SD), and progressive disease (PD) at the end of therapy (P = 0.0173). Docetaxel CL was not related to midazolam CL or genotype. Docetaxel exposure and genotypes were not related to toxicity or response (P > 0.05).

CONCLUSIONS

The midazolam CL predicted CA-125 levels and response that was independent of other factors including docetaxel pharmacokinetics. Future studies need to evaluate the mechanism for the relationship between midazolam CL and response in patients with ovarian cancer.

Interaction of sorafenib and cytochrome P450 isoenzymes in patients with advanced melanoma: a phase I/II pharmacokinetic interaction study

BACKGROUND

In vitro data indicate that the sorafenib is a moderate inhibitor of cytochrome P450 (CYP) enzymes, including CYP3A4, CYP2C19, and CYP2D6. This phase I/II study in patients with advanced melanoma evaluated the potential effect of sorafenib on the pharmacokinetics of midazolam, omeprazole, and dextromethorphan, specific substrates of CYP3A4, CYP2C19, and CYP2D6, respectively.

METHODS

Twenty-one patients received sorafenib 400 mg twice daily for 28 consecutive days. On days 1 and 28, a cocktail containing midazolam 2 mg, omeprazole 20 mg, and dextromethorphan 30 mg was administered. Pharmacokinetic analyses were performed on day 1 without sorafenib and day 28 after steady-state sorafenib exposure; sorafenib pharmacokinetics were evaluated on day 28. We defined an interaction to be excluded if the 90% confidence interval of the ratio of all day 28:day 1 analyses fell within a range from 0.80 to 1.25.

RESULTS

In all, 18 patients were evaluable. On day 28, area under the plasma concentration-time curve from time 0 to 12 h (AUC(0-12)) and maximum plasma concentration (C(max)) for sorafenib were 38.1 mg h/l and 4.9 mg/l, respectively. Day 28:day 1 ratios for AUC from time 0 extrapolated to infinity (AUC(0-inf)) and C(max) for midazolam were 0.85 and 0.98, respectively. Day 28:day 1 ratio for 5-OH-omeprazole:omeprazole plasma concentration at 3 h postdose was 1.26, slightly outside of the 0.80-1.25 range. Thus, an interaction could not be excluded, but is considered unlikely to be clinically significant. Day 28:day 1 ratio for dextromethorphan:dextrorphan concentration in urine was 0.94. Sorafenib had an acceptable safety profile. The most frequently observed grade 3-4 toxicities in cycle 1 included elevated lipase (19%) and hypertension (10%).

CONCLUSIONS

In this patient population, our results demonstrate that exposures of probes of CYP3A4, CYP2D6, or CYP2C19 activity are potentially altered by administration of sorafenib at 400 mg twice daily. However, these differences are sufficiently small that a clinically significant inhibition or induction of these important drug metabolizing P450 isoenzymes is unlikely. Clinical and, where possible, drug level monitoring may still be appropriate for drugs of narrow therapeutic range co-administered with sorafenib.

Pharmacokinetic design optimization in children and estimation of maturation parameters: example of cytochrome P450 3A4

The aim of this work was to determine whether optimizing the study design in terms of ages and sampling times for a drug eliminated solely via cytochrome P450 3A4 (CYP3A4) would allow us to accurately estimate the pharmacokinetic parameters throughout the entire childhood timespan, while taking into account age- and weight-related changes. A linear monocompartmental model with first-order absorption was used successively with three different residual error models and previously published pharmacokinetic parameters ("true values"). The optimal ages were established by D-optimization using the CYP3A4 maturation function to create "optimized demographic databases." The post-dose times for each previously selected age were determined by D-optimization using the pharmacokinetic model to create "optimized sparse sampling databases." We simulated concentrations by applying the population pharmacokinetic model to the optimized sparse sampling databases to create optimized concentration databases. The latter were modeled to estimate population pharmacokinetic parameters. We then compared true and estimated parameter values. The established optimal design comprised four age ranges: 0.008 years old (i.e., around 3 days), 0.192 years old (i.e., around 2 months), 1.325 years old, and adults, with the same number of subjects per group and three or four samples per subject, in accordance with the error model. The population pharmacokinetic parameters that we estimated with this design were precise and unbiased (root mean square error [RMSE] and mean prediction error [MPE] less than 11% for clearance and distribution volume and less than 18% for k(a)), whereas the maturation parameters were unbiased but less precise (MPE < 6% and RMSE < 37%). Based on our results, taking growth and maturation into account a priori in a pediatric pharmacokinetic study is theoretically feasible. However, it requires that very early ages be included in studies, which may present an obstacle to the use of this approach. First-pass effects, alternative elimination routes, and combined elimination pathways should also be investigated.

Induction of CYP3A4 by vinblastine: Role of the nuclear receptor NR1I2

BACKGROUND

Several microtubule targeting agents are capable of inducing CYP3A4 via activation of the pregnane X receptor (PXR; NR1I2).

OBJECTIVE

To evaluate the CYP3A4 induction potential of vinblastine both clinically and in vitro and determine the involvement of the nuclear receptors NR1I2 and the constitutive androstane receptor (NR1I3).

METHODS

Midazolam pharmacokinetics were evaluated in 6 patients who were enrolled in a Phase 1/2 study of infusional vinblastine given in combination with the ABCB1 (P-glycoprotein) antagonist valspodar (PSC 833) and received the CYP3A4 phenotyping probe midazolam on more than 1 occasion. Genotyping was conducted in CYP3A4, CYP3A5, and ABCB1 to rule out potential pharmacogenetic influences. Clinical data were followed-up by Western blotting and reporter assays in HepG2 and NIH3T3 cells treated with vinblastine over a dose range of 150-4800 ng/mL for 48 hours.

RESULTS

In 6 patients with cancer, vinblastine increased the median (95% CI) clearance of the CYP3A4 phenotyping probe midazolam from 21.7 L/h (12.6 to 28.1) to 32.3 L/h (17.3 to 53.9) (p = 0.0156, Wilcoxon signed-rank test). No obvious effect of polymorphisms in CYP3A4, CYP3A5, and ABCB1 on midazolam clearance was observed. In vitro, vinblastine induced CYP3A4 protein. Furthermore, cell-based reporter gene assays using transiently transfected HepG2 and NIH3T3 cells indicated that vinblastine (150-4800 ng/mL) weakly activated human and mouse full-length NR1I2, but had no influence on NR1I3.

CONCLUSIONS

Collectively, these findings suggest that vinblastine is able to induce CYP3A4, at least in part, via an NR1I2-dependent mechanism, and thus has the potential to facilitate its own elimination and cause interactions with other CYP3A4 substrates.

A phase I clinical study of high dose ketoconazole plus weekly docetaxel for metastatic castration resistant prostate cancer

PURPOSE

This phase I study of high dose ketoconazole and docetaxel was designed against castration resistant prostate cancer to determine the maximum tolerated doses, side effects, and pharmacokinetic interaction of co-administered docetaxel and ketoconazole.

MATERIALS AND METHODS

Patients with metastatic castration resistant prostate cancer received weekly docetaxel for 3 of every 4 weeks plus daily ketoconazole. Pharmacokinetic studies were performed on day 1 (docetaxel alone) and day 16 (after ketoconazole).

RESULTS

The study enrolled 42 patients at 9 different dose levels. The combination regimens investigated included docetaxel weekly, increasing from 5 to 43 mg/m(2), with starting doses of 600, 800 or 1,200 mg ketoconazole daily. Decreases in prostate specific antigen of 50% or greater were seen in 62% of patients. Of 25 patients with soft tissue disease 7 (28%) had a partial response. Median overall survival was 22.8 months and was significantly greater in docetaxel naïve patients than in patients pretreated with docetaxel (36.8 vs 10.3 months, p = 0.0001). The most frequently observed adverse events were anemia, edema, fatigue, diarrhea, nausea, sensory neuropathy and elevated liver function tests. The fractional change in docetaxel clearance correlated significantly with ketoconazole exposure (p <0.01). Concomitant ketoconazole increased docetaxel exposure 2.6-fold with 1,200 mg daily, 1.6-fold with 800 mg daily and approximately 1.3 to 1.5-fold with 600 mg daily.

CONCLUSIONS

Combination regimens using 600 mg ketoconazole daily were fairly well tolerated and the maximum tolerated dose of docetaxel was 32 mg/m(2). Results suggest that the combination has significant antitumor activity in castration resistant prostate cancer. The long survival in the docetaxel naïve cohort warrants additional, larger trials of docetaxel with ketoconazole or possibly CYP17A1 inhibitors such as abiraterone.

A pharmacogenetic study of docetaxel and thalidomide in patients with castration-resistant prostate cancer using the DMET genotyping platform

The anticancer agent docetaxel shows significant inter-individual variation in its pharmacokinetic and toxicity profile. Thalidomide is an active anticancer agent and also shows wide pharmacological variation. Past pharmacogenetic research has not explained this variation. Patients with prostate cancer enrolled in a randomized phase II trial using docetaxel and thalidomide versus docetaxel alone were genotyped using the Affymetrix DMET 1.0 platform, which tests for 1256 genetic variations in 170 drug disposition genes. Genetic polymorphisms were analyzed for associations with clinical response and toxicity. In all, 10 single-nucleotide polymorphisms (SNPs) in three genes were potentially associated with response to therapy: peroxisome proliferator-activated receptor-delta (PPAR-delta), sulfotransferase family, cytosolic, 1C, member 2 (SULT1C2) and carbohydrate (chondroitin 6) sulfotransferase 3 (CHST3). In addition, 11 SNPs in eight genes were associated with toxicities to treatment: spastic paraplegia 7 (pure and complicated autosomal recessive) (SPG7), CHST3, cytochrome P450, family 2, subfamily D, polypeptide 6 (CYP2D6), N-acetyltransferase 2 (arylamine N-acetyltransferase) (NAT2), ATP-binding cassette, sub-family C (CFTR/MRP), member 6 (ABCC6), ATPase, Cu++ transporting, alpha polypeptide (ATP7A), cytochrome P450, family 4, subfamily B, polypeptide 1 (CYP4B1) and solute carrier family 10 (sodium/bile acid cotransporter family), member 2 (SLC10A2). Genotyping results between drug metabolizing enzymes and transporters (DMET) and direct sequencing showed >96% of concordance. These findings highlight the role that non-CYP450 metabolizing enzymes and transporters may have in the pharmacology of docetaxel and thalidomide.

Effect of Telavancin on the pharmacokinetics of the cytochrome P450 3A probe substrate midazolam: a randomized, double-blind, crossover study in healthy subjects

STUDY OBJECTIVE

To examine the effect of telavancin, a lipoglycopeptide antibiotic with potent gram-positive activity, on the pharmacokinetics of midazolam, a cytochrome P450 (CYP) 3A probe substrate. Design. Phase I, randomized, double-blind, placebo-controlled, crossover study. Setting. Clinical research center.

PARTICIPANTS

Sixteen healthy adult volunteers. Intervention. Subjects were randomly assigned to receive an intravenous infusion of telavancin 10 mg/kg or placebo once/day for 7 days. On day 7, a single dose of intravenous midazolam 1 mg was given immediately after completion of the last infusion of telavancin or placebo. Patients crossed over to the alternate treatment regimen after a washout period of at least 7 days.

MEASUREMENTS AND MAIN RESULTS

Pharmacokinetic sampling was performed on study days 7 and 21. Blood was collected before telavancin or placebo dosing and at 0.25, 0.5, 1, 2, 3, 4, 6, 8, 10, 12, and 24 hours after midazolam administration. Formal equivalence analysis using the two one-sided t test method showed that the geometric mean ratios for maximum plasma concentration (C(max)) and areas under the plasma concentration-time curve (AUC) for midazolam coadministered with telavancin versus midazolam coadministered with placebo were close to unity. The 90% confidence intervals (CIs) around the ratios fell within the 0.8-1.25 bioequivalence bounds (geometric mean ratio for AUC from time zero to the last measured plasma concentration 0.95, 90% CI 0.910-0.984; C(max) geometric mean ratio 1.03, 90% CI 0.956-1.11). The multiple-dose pharmacokinetic profile of telavancin with concomitant administration of midazolam (C(max) 97 microg/ml, concentration 24 hrs after completion of telavancin infusion 9 microg/ml, terminal-phase elimination half-life 8.9 hrs, clearance 13.3 ml/hr/kg) was consistent with data from earlier studies.

CONCLUSION

These pharmacokinetic data show that intravenous telavancin administered at the intended therapeutic dose does not affect the pharmacokinetics of intravenous midazolam. The results indicate that telavancin is unlikely to inhibit hepatic CYP3A activity to a clinically meaningful extent.

The missing linkage: what pharmacogenetic associations are left to find in CYP3A?

IMPORTANCE OF THE FIELD

An enormous amount of drugs and endogenous substrates are metabolized by the enzymes encoded in the CYP3A gene cluster, making variation at this locus of utmost importance in the field of pharmacogenetics. However, the identification of genetic variation that contributes to the wide phenotypic variability at this locus has been elusive. While dozens of studies have investigated the effects of coding variants, none have found the definitive answer to what variant or variants explain the distribution of enzyme activity and clinical effects seen with the drug metabolized by these genes.

AREAS COVERED IN THIS REVIEW

This review highlights the recent pharmacogenetic work at the CYP3A locus, in particular studies on known functional variants in CYP3A4 and CYP3A5. In addition, common pharmacogenetic strategies as well as considerations specific to the CYP3A locus are discussed.

WHAT THE READER WILL GAIN

The reader will gain a greater understanding of the complexities involved in studying the CYP3A locus, population differences that may affect pharmacogenetic studies at this locus and the importance of variation that affect gene regulation.

TAKE HOME MESSAGE

More innovative and comprehensive methods to assay this region are needed, with particular attention paid to the role of gene regulation and non-coding sequence.

Population pharmacokinetics of romidepsin in patients with cutaneous T-cell lymphoma and relapsed peripheral T-cell lymphoma

PURPOSE

Romidepsin is a potent histone deacetylase inhibitor under clinical development. The objective of this study was to evaluate the effect of demographic, clinical, and pharmacogenetic covariates on the pharmacokinetics of romidepsin in patients with T-cell lymphoma.

EXPERIMENTAL DESIGN

Pharmacokinetic assessment was done in 98 patients enrolled in a phase II study who received 14 or 18 mg/m2 of romidepsin as a 4-hour infusion on day 1 during their first treatment cycle. Population modeling was done using a nonlinear mixed effects modeling approach to explore the effects of polymorphic variations in CYP3A4, CYP3A5, SLCO1B3, and ABCB1, all of which encode genes thought to be involved in romidepsin disposition.

RESULTS

A two-compartment model with linear kinetics adequately described the romidepsin disposition. Population clearance was 15.9 L/h with between-patient variability of 37%. ABCB1 2677G>T/A variant alleles tended toward a reduced clearance and lower volume of tissue distribution, but this was not supported by a statistical significance. Genetic variations in CYP3A4/5 and SCLO1B3 had no effect on the systemic exposure.

CONCLUSION

The population pharmacokinetic analysis indicates moderate interindividual variability in romidepsin pharmacokinetics and no clinically relevant covariates associated with the unexplained pharmacokinetic variability of romidepsin in this population.

Hypnosedative-induced complex behaviours : incidence, mechanisms and management

A number of news items and case reports describing complex behaviours (e.g. sleep driving, sleep cooking, sleep eating, sleep conversations, sleep sex) associated with the use of hypnosedative medications have recently received considerable attention. Regulatory agencies examining these reports have subsequently issued warnings regarding the potential of hypnosedative agents to produce complex behaviours. Despite these warnings, little is known about the likelihood, presentation, treatment or prevention of hypnosedative-induced complex behaviours. The purpose of this review is to evaluate the published evidence regarding the clinical presentation, incidence, mechanism and management of sleep-related behaviours induced by nonbenzodiazepine receptor agonists (NBRAs).Review of the literature identified ten published case reports of NBRA-induced complex behaviours involving 17 unique patients. Fifteen of the 17 patients described in the case reports had taken zolpidem, one had taken zaleplon and one had taken zopiclone. The complex behaviours most commonly reported were sleep eating, sleepwalking with object manipulation, sleep conversations, sleep driving, sleep sex and sleep shopping. Elevated serum concentrations resulting from increased medication dose or drug-drug interactions appeared to play a role in some but not all cases. Sex, age, previous medication exposure and concomitant disease states were not consistently found to be related to the risk of experiencing a medication-induced complex behaviour.From a pharmacological standpoint, enhancement of GABA activity at GABAA receptors (particularly alpha1-GABAA receptors) is a possible mechanism for hypnosedative complex behaviours and amnesia. Evidence suggests that complex behaviour risk may increase with both dose and binding affinity at alpha1-GABAA receptors. The amnesia that accompanies complex behaviours is possibly due to inhibition of consolidation of short- to long-term memory, suggesting that the risk may extend to non-GABAergic hypnosedatives. While amnesia and GABA-related receptor actions are the most frequently discussed mechanisms for complex behaviours in the literature, they do not fully explain such behaviours, suggesting that other mechanisms and factors probably play a role.A number of potential strategies are available to manage or prevent hypnosedative-induced complex behaviours. These include lowering the dose of, or stopping, the offending hypnosedative, switching to a different hypnosedative, treating patients with other classes of medications, using nonpharmacological treatment strategies for patients with sleep disorders, examining drug regimens for potential drug interactions that may predispose patients to experiencing complex behaviours, administering hypnosedative medications appropriately and selecting patients more carefully for treatment in terms of their likelihood of experiencing medication adverse effects.

Dose calculation of anticancer drugs

BACKGROUND

Anticancer drugs are characterized by a narrow therapeutic window and significant inter-patient variability in therapeutic and toxic effects. Current body surface area (BSA)-based dosing fails to standardize systemic anticancer drug exposure and other alternative dosing strategies also have their limitations. Just as important as the initial dose selection is the subsequent dose revision to ensure the dose is correct.

OBJECTIVE

To provide an insight into the different dose individualization and dose adjustment methods, their feasibility and applicability in daily oncology practice and to suggest a practical framework for dose calculation and a basis for future research.

METHODS

Review of relevant literature related to dose calculation of anticancer drugs.

RESULTS

Strategies using clinical parameters, genotype and phenotype markers, and therapeutic drug monitoring all have potential and each has a role for specific drugs. However, no one method is a practical dose calculation strategy for many or all drugs.

CONCLUSION

Given that BSA-dosing leads to significant underdosing it is not reasonable to use this as the sole method of dose calculation. Because of wide disparity in individual patient characteristics and elimination mechanisms, we are unlikely to find the 'Holy Grail' of a single individualized dosing strategy for every patient and anticancer drug in the near future. We propose a pragmatic, although invalidated system for initial dose calculation using dose clusters and structured subsequent dose revision based on treatment-related toxicities and therapeutic drug monitoring. These models need to be tested in clinical trials.

Prediction of CYP3A4 enzyme activity using haplotype tag SNPs in African Americans

The CYP3A locus encodes hepatic enzymes that metabolize many clinically used drugs. However, there is marked interindividual variability in enzyme expression and clearance of drugs metabolized by these enzymes. We utilized comparative genomics and computational prediction of transcriptional factor binding sites to evaluate regions within CYP3A that were most likely to contribute to this variation. We then used a haplotype tagging single-nucleotide polymorphisms (htSNPs) approach to evaluate the entire locus with the fewest number of maximally informative SNPs. We investigated the association between these htSNPs and in vivo CYP3A enzyme activity using a single-point IV midazolam clearance assay. We found associations between the midazolam phenotype and age, diagnosis of hypertension and one htSNP (141689) located upstream of CYP3A4. 141689 lies near the xenobiotic responsive enhancer module (XREM) regulatory region of CYP3A4. Cell-based studies show increased transcriptional activation with the minor allele at 141689, in agreement with the in vivo association study findings. This study marks the first systematic evaluation of coding and noncoding variation that may contribute to CYP3A phenotypic variability.

Pharmacogenetic pathway analysis of docetaxel elimination

The purpose of this study was to evaluate the affinity of docetaxel for 14 transporter proteins and assess the functional significance of 17 variants in five genes involved in drug elimination. Among the transfected models investigated, OATP1B3 (SLCO1B3) was identified as the most efficient influx transporter for docetaxel. None of the observed genotypes (SLCO1B3, ABCB1, and ABCC2) was related with docetaxel clearance in 92 white patients (P > 0.17). However, the simultaneous presence of the CYP3A4*1B and CYP3A5*1A alleles was associated with a 64% increase in docetaxel clearance (P = 0.0015), independent of both sex and CYP3A activity (as determined using the erythromycin breath test). This haplotype was also associated with increased midazolam clearance in another population (P = 0.0198). An analysis of the CYP3A locus among CEPH-HapMap samples revealed that CYP3A4*1B is present exclusively among a subset of CYP3A5 expressors. Therefore, future studies should first stratify the population on the basis of CYP3A5 genotype and then compare CYP3A activity between individuals with and without the CYP3A4*1B allele.

Inflammation and CYP3A4-mediated drug metabolism in advanced cancer: impact and implications for chemotherapeutic drug dosing

BACKGROUND

The inability to accurately predict treatment outcomes for cancer patients in terms of tumour response and anticancer drug toxicity is a severe limitation inherent in current approaches to chemotherapy. Many anticancer drugs are metabolically cleared by cytochrome P450 3A4 (CYP3A4), the predominant CYP expressed in liver. CYP3A4 expression exhibits marked interindividual variation and is repressed in acute inflammatory states.

OBJECTIVES

(1) To review the relevance of CYP3A4 variability to drug metabolism in the setting of cancer and to understand how inflammation associated with malignancy contributes to both this variability and to adverse treatment outcomes. (2) To examine the relationship between tumour-induced inflammation and repression of CYP3A4 and to explore methods of dosing of anticancer drugs in the setting of advanced cancer.

METHODS

Review of relevant literature covering both human and animal studies as well as in vitro mechanistic studies.

RESULTS/CONCLUSIONS

Interindividual variability in CYP3A4 expression is a major confounding factor for effective cancer treatment and methods to predict CYP3A4-mediated drug clearance may have clinical utility in this setting. Although acute inflammation has long been recognised to repress drug metabolism, it is now becoming apparent that cancer patients exhibiting clinical and laboratory features of an inflammatory response have reduced expression of CYP3A4 and possibly other genes relevant to anticancer drug disposition.

Inflammation and altered drug clearance in cancer: transcriptional repression of a human CYP3A4 transgene in tumor-bearing mice

A tumor-associated inflammatory response has recently been found to contribute to the considerable interindividual variability in cytotoxic drug clearance seen in cancer patients. Circulating inflammatory markers, such as C-reactive protein (CRP) and interleukin-6 (IL-6), correlate with excessive drug toxicity caused by reduced CYP3A4-mediated metabolism. This article outlines the use of a transgenic mouse model of human CYP3A4 regulation to demonstrate that extrahepatic tumors elicit an inflammatory response, leading to transcriptional repression of the CYP3A4 gene as well as of other drug clearance pathways.

Regulation of drug-metabolizing enzymes and transporters in infection, inflammation, and cancer

This article is a report on a symposium sponsored by the American Society for Pharmacology and Experimental Therapeutics and held at the Experimental Biology 07 meeting in Washington, DC. The presentations discussed the phenomenology, clinical consequences, and underlying mechanisms of cytochrome P450 and drug transporter regulation by inflammatory and infectious stimuli. Although considerable insights into the links between inflammatory mediators and altered hepatic drug clearance pathways have been gained from previous studies with acute inflammatory stimuli, this symposium highlighted recent advances in understanding how these processes operate in other organs and chronic inflammatory states relevant to human diseases. The development of mouse models of live bacterial infection provides excellent opportunities to explore the impact of infection on drug metabolism beyond the well characterized effects of bacterial endotoxin. Altered levels of cytochromes P450 and especially drug transporters due to inflammation in brain, intestine, and placenta have significant implications for the use of many drugs in diverse clinical settings. The consequences of inflammatory cytokine production by tumors for drug safety and efficacy in cancer patients were outlined. Repression of drug clearance pathways by tumor-derived cytokines may result in extreme toxicity to chemotherapy, compromising treatment of many cancers. It is fitting that, in honoring the career contributions and achievements of Dr. Kenneth W. Renton, this symposium reinforced the clinical relevance of this field.

Influence of garlic (Allium sativum) on the pharmacokinetics of docetaxel

PURPOSE

The herbal supplement garlic (Allium sativum) is commonly used by cancer patients. Preclinical studies have shown that allicin, a major component of garlic, may affect cytochrome P450 3A4 (CYP3A4) activity. This study examines the influence of garlic supplementation on the pharmacokinetics of docetaxel, a CYP3A4 substrate.

EXPERIMENTAL DESIGN

Women with metastatic breast cancer were treated with docetaxel (30 mg/m(2)) given weekly for 3 of 4 weeks. Three days after the initial dose of docetaxel, patients received 600 mg of garlic twice daily for 12 consecutive days. Docetaxel pharmacokinetics were assessed during the first three administrations.

RESULTS

In 10 evaluable patients, the mean baseline clearance of docetaxel was 30.8 L/h/m(2) [95% confidence intervals (95% CI), 16.7-44.9]. Coadministration of garlic reduced mean clearance of docetaxel to 23.7 L/h/m(2) (95% CI, 15.5-31.8) and 20.0 L/h/m(2) (95% CI, 13.3-26.7) on days 8 and 15, respectively (P = 0.17). Additional pharmacokinetic variables of docetaxel, including peak concentration (P = 0.79), area under the curve (P = 0.36), volume of distribution (P = 0.84), and half-life (P = 0.36), were also not statistically significantly different. The mean area under the curve ratio between day 15 and day 1 was 3.74 in three individuals with the CYP3A5*1A/*1A genotype (all African American) compared with 1.02 in six individuals with the CYP3A5*3C/*3C genotype (all Caucasian).

CONCLUSIONS

This study indicates that garlic does not significantly affect the disposition of docetaxel. However, it cannot be excluded that garlic decreases the clearance of docetaxel in patients carrying a CYP3A5*1A allele.

Impact of the CYP3A5 genotype on midazolam pharmacokinetics and pharmacodynamics during intensive care sedation

OBJECTIVE

Information is lacking on whether the CYP3A5 genotype affects the disposition and effects of midazolam during the long-term intensive care sedation of patients. This study was undertaken to estimate whether the CYP3A5 genotype can explain a relevant portion of pharmacokinetic interindividual variability.

METHODS

We determined the CYP3A5 genotype in 71 Caucasian patients who underwent long-term sedation during intensive care treatment. We then assessed the relation between the genotype and both the plasma concentrations of midazolam and 1'-OH-midazolam in 645 plasma samples and the simultaneously estimated Ramsay sedation score, both of which were recorded during routine midazolam drug monitoring.

RESULTS

Eight patients had the CYP3A5*1/*3 genotype and 63 patients the CYP3A5*3/*3 genotype. The concentration-dose ratio [C/D; plasma concentration of midazolam (ng/ml) divided by the rate of infusion (mg/h); expressed as the mean (95% confidence interval)] was 87.4 (70.8, 108.9) for the *3/*3 patients and 79.0 (48.9, 129.0) for *1/*3 patients. The corresponding data for infusion rate (IR; in mg/h), Ramsay score (RS) and the ratio 1'-OH-midazolam concentration/midazolam concentration (ROH) for *3/*3 and *1/*3 patients were IR 7.4 (6.2, 8.6) vs. 11.4 (4.9, 17.9), RS 5.4 (5.2, 5.6) vs. 5.3 (4.2, 6.0) and ROH 0.11 (0.09, 0.13) vs. 0.17 (0.11, 0.26), respectively.

CONCLUSIONS

The CYP3A5*1/*3 genotype did not lead to an apparently lower midazolam concentration/dose ratio or Ramsay score values. As the present sedation procedure during intensive care therapy may be described as a physician closed-loop titration towards Ramsay scores of 4 +/- 1, our data do not indicate that prior determination of the genotype will result in better care or economic savings.

Influence of CYP3A5 genotype on the pharmacokinetics and pharmacodynamics of the cytochrome P4503A probes alfentanil and midazolam

The hepatic and first-pass cytochrome P4503A (CYP3A) probe alfentanil (ALF) is also metabolized in vitro by CYP3A5. Human hepatic microsomal ALF metabolism is higher in livers with at least one CYP3A5*1 allele and higher CYP3A5 protein content, compared with CYP3A5*3 homozygotes with little CYP3A5. The influence of CYP3A5 genotype on ALF pharmacokinetics and pharmacodynamics was studied, and compared to midazolam (MDZ), another CYP3A probe. Healthy volunteers (58 men, 41 women) were genotyped for CYP3A5 *1, *3, *6, and *7 alleles. They received intravenous MDZ then ALF, and oral MDZ and ALF the next day. Plasma MDZ and ALF concentrations were determined by mass spectrometry. Dark-adapted pupil diameters were determined coincident with blood sampling. In CYP3A5(*)3/(*)3 (n=62), (*)1/(*)3 (n=28), and (*)1/(*)1 (n=8) genotypes, systemic clearances of ALF were 4.6+/-1.8, 4.8+/-1.7, and 3.9+/-1.7 ml/kg/min and those of MDZ were 7.8+/-2.3, 7.7+/-2.3, and 6.0+/-1.4 ml/kg/min, respectively (not significant), and apparent oral clearances were 11.8+/-7.2, 13.3+/-6.1, and 12.6+/-8.2 ml/kg/min for ALF and 35.2+/-19.0, 36.4+/-15.7, and 29.4+/-9.3 ml/kg/min for MDZ (not significant). Clearances were not different between African Americans (n=25) and Whites (n=68), or between CYP3A5 genotypes within African Americans. ALF pharmacodynamics was not different between CYP3A5 genotypes. There was consistent concordance between ALF and MDZ, in clearances and extraction ratios. Thus, in a relatively large cohort of healthy subjects with constitutive CYP3A activity, CYP3A5 genotype had no effect on the systemic or apparent oral clearances, or pharmacodynamics, of the CYP3A probes ALF and MDZ, despite affecting their hepatic microsomal metabolism.