Determination of Endogenous Concentrations of Uracil and Dihydrouracil in Dried Saliva Spots by LC-MS/MS: Method Development, Validation, and Clinical Application.

BACKGROUND: The aim of this study was to develop and validate a liquid chromatography-tandem mass spectrometry (LC-MS/MS) assay for the measurement of uracil (U) and dihydrouracil (UH2) concentrations in dried saliva spots (DSSs), for the evaluation of dihydropyrimidine dehydrogenase (DPD) enzyme activity. RESULTS: Nine 18-mm diameter DSS discs were extracted with acetate:isopropyl alcohol (85:15, vol/vol) and analyzed by LC-MS/MS. The assay was linear in the range of 10-1000 ng·mL, with accuracy between 89% and 112% and precision between 5.7% and 13%. The metabolic ratio [UH2]/[U] was stable in DSS for up to 9 days at 45°C. Concentrations of U and UH2, as well as the metabolic ratio, were highly concordant between matrices. Using a metabolic ratio classification cutoff of 1.16 for the identification of slow DPD metabolizers, 98.7% concordance was achieved between SS and saliva. CONCLUSIONS: DSS samples could be a useful alternative for DPD activity screening, particularly in locations with limited access to highly equipped laboratories.

DPD functional tests in plasma, fresh saliva and dried saliva samples as predictors of 5-fluorouracil exposure and occurrence of drug-related severe toxicity.

OBJECTIVE: to evaluate plasma and salivary uracil (U) to dihydrouracil (UH2) ratios as tools for predicting 5-fluorouracil systemic exposure and drug-related severe toxicity, and clinically validate the use of dried saliva spots (DSS) as an alternative sampling strategy for dihydropyrimidine dehydrogenase (DPD) deficiency assessment. METHODS: Pre-chemotherapy plasma, fresh saliva and DSS samples were obtained from gastrointestinal patients (N = 40) for measurement of endogenous U and UH2 concentrations by LC-MS/MS. A second plasma sample collected during 5FU infusion was used for 5FU area under the curve (AUC) determination by HPLC-DAD. Data on toxicity was reported according to CTCAE. RESULTS: 15% of the patients developed severe 5FU-related toxicity, with neutropenia accounting for 67% of the cases. U, UH2 and [UH2,]/[U] were highly correlated between fresh and dried saliva samples (rs = 0.960; rs = 0.828; rs = 0.910, respectively). 5FU AUC ranged from 11.3 to 37.31 mg h L-1, with 46.2% of under-dosed and 10.3% over-dosed patients. The [UH2]/[U] ratios in plasma, fresh saliva and dried saliva samples were moderately correlated with 5FU AUC and adverse events grade, indicating a partial contribution of the variables to drug exposure (r = -0.412, rs = -0.373, rs = 0.377) and toxicity (r = -0.363, rs = -0.523, rs = 0.542). Metabolic ratios were lower in patients with severe toxicity (P < .01 salivary ratios, and P < .5 plasma ratios), and 5FU AUC were in average 47% higher in this group than in moderate toxicity. The diagnostic performance of [UH2]/[U] ratios in fresh saliva and DSS for the identification of patients with severe toxicity were comparable. CONCLUSIONS: The [UH2]/[U] metabolic ratios in plasma, fresh saliva and DSS were significantly associated with 5FU systemic exposure and toxicity degree. This study also demonstrated the applicability of DSS as alternative sampling for evaluating DPD activity.

Analytical and clinical validation of a dried blood spot assay for the determination of paclitaxel using high-performance liquid chromatography-tandem mass spectrometry.

BACKGROUND: Paclitaxel (PCT) is a chemotherapeutic drug widely used for the treatment of several types of tumors, and its use is associated with severe adverse events, mainly neurologic and hematopoietic toxicities. The relation between systemic exposure and clinical response to PCT was previously described, making paclitaxel a potential candidate for therapeutic drug monitoring (TDM). The use of dried blood spot (DBS) sampling could allow complex sampling schedules required for TDM of PCT. The aim of this study was to develop and validate an LC-MS/MS assay for the quantification of PCT in DBS. METHODS: PCT was extracted from one 8 mm DBS punch with a mixture of methanol and acetonitrile, followed by chromatographic separation in a Kinetex C18 (50 × 4.6 mm, 2.6 µm) column. Detection was performed in a 5500-QTRAP® mass spectrometer, with a run time of 2.3 min. RESULTS: The assay was linear in the range of 2.5 to 400 ng mL-1. Precision (CV%) and accuracy at the concentration levels of 7.5, 40 and 150 ng mL-1 were 1.69-4.9% and 106.25 to 109.92%, respectively. PCT was stable for 21 days at 25 and 45 °C. The method was applied to DBS samples obtained from 34 patients under PCT chemotherapy. The use of a simple correction factor, derived from the correlation between PCT concentrations in plasma and DBS in this set of patients, allowed unbiased estimation of PCT plasma concentrations from DBS measurements, with similar clinical decisions using either plasma or DBS measurements. CONCLUSIONS: DBS testing of PCT concentrations represents a promising alternative for the dissemination of PCT dose individualization.

Pharmacogenetic and Pharmacokinetic Dose Individualization of the Taxane Chemotherapeutic Drugs Paclitaxel and Docetaxel.

BACKGROUND: The taxane drugs paclitaxel and docetaxel, widely used on cancer chemotherapy, are currently dosed mainly based on body-surface area. This approach is associated with wide interindividual variability in drug exposure, leading to suboptimal dosing for many patients. METHODS: The available evidence supporting dose individualization strategies for paclitaxel and docetaxel were reviewed, focusing mainly on the application of therapeutic drug monitoring by a priori pharmacogenetic data or a posteriori drug measurements in biological fluids. The PubMed database was searched, in the period of 1987-2017, using the keywords pharmacogenetics, metabolic genotyping, dose individualization, therapeutic drug monitoring, personalized medicine, taxanes paclitaxel and docetaxel, either alone or in combination. RESULTS: The current knowledge of pharmacology of the taxane drugs paclitaxel and docetaxel, mainly its pharmacokinetics and the proteins responsible for their biotransformation and transport, along with the genetic polymorphism responsible for variations in the activities of these proteins, opens new opportunities for dose selection for individual patients. CONCLUSION: Considering the relation between systemic exposure to these drug and clinical responses, a posteriori TDM, with measurement of drug concentrations in plasma of treated patients, is currently the most straightforward approaches for dose individualization of paclitaxel and docetaxel.

Endogenous plasma and salivary uracil to dihydrouracil ratios and DPYD genotyping as predictors of severe fluoropyrimidine toxicity in patients with gastrointestinal malignancies.

OBJECTIVE: The aim of this study was to evaluate the use of plasma and saliva uracil (U) to dihydrouracil (UH2) metabolic ratio and DPYD genotyping, as a means to identify patients with dihydropyrimidine dehydrogenase (DPD) deficiency and fluoropyrimidine toxicity. METHODS: Paired plasma and saliva samples were obtained from 60 patients with gastrointestinal cancer, before fluoropyrimidine treatment. U and UH2 concentrations were measured by LC-MS/MS. DPYD was genotyped for alleles *7, *2A, *13 and Y186C. Data on toxicity included grade 1 to 4 neutropenia, mucositis, diarrhea, nausea/vomiting and cutaneous rash. RESULTS: 35% of the patients had severe toxicity. There was no variant allele carrier for DPYD. The [UH2]/[U] metabolic ratios were 0.09-26.73 in plasma and 0.08-24.0 in saliva, with higher correlation with toxicity grade in saliva compared to plasma (rs=-0.515 vs rs=-0.282). Median metabolic ratios were lower in patients with severe toxicity as compared to those with absence of toxicity (0.59 vs 2.83 saliva; 1.62 vs 6.75 plasma, P<0.01). A cut-off of 1.16 for salivary ratio was set (AUC 0.842), with 86% sensitivity and 77% specificity for the identification of patients with severe toxicity. Similarly, a plasma cut-off of 4.0 (AUC 0.746), revealed a 71% sensitivity and 76% specificity. CONCLUSIONS: DPYD genotyping for alleles 7, *2A, *13 and Y186C was not helpful in the identification of patients with severe DPD deficiency in this series of patients. The [UH2]/[U] metabolic ratios, however, proved to be a promising functional test to identify the majority of cases of severe DPD activity, with saliva performing better than plasma.

DBS sampling in imatinib therapeutic drug monitoring: from method development to clinical application.

BACKGROUND: Imatinib (IM) is widely used in treatment of chronic myeloid leukemia with target trough plasma concentrations above 1000 ng ml(-1). DBS can increase access to IM therapeutic drug monitoring. RESULTS: IM was measured in the range 50-4000 ng ml(-1) by UHPLC-MS/MS using one 6 mm DBS in a fully validated method. IM was stable at DBS maintained at 40°C for 36 days. Plasma and DBS concentrations were highly correlated (r > 0.96). The use of a IM concentration target of 765 ng ml(-1) in DBS identified 93% of patients with plasma concentration below 1000 ng ml(-1). CONCLUSION: IM can be measured in DBS using UHPLC-MS/MS with results comparable to those obtained in blood plasma.

CYP3A4*22 is related to increased plasma levels of 4-hydroxytamoxifen and partially compensates for reduced CYP2D6 activation of tamoxifen.

AIM: To evaluate the impact of CYP3A4*22 in the formation of endoxifen (EDF) and hydroxytamoxifen (HTF), under different CYP2D6 genotypic backgrounds. MATERIALS & METHODS: 178 patients were enrolled in the study. CYP2D6 and CYP3A4 genotyping and tamoxifen (TAM) and metabolites quantification were performed. RESULTS: EDF concentrations were lower in poor (2.77 ng ml(-1)) and CYP2D6 intermediate metabolizers (5.84 ng ml(-1)), comparing to functional group (EM-F) (10.67 ng ml(-1), p < 0.001). HTF and TAM levels were respectively 47 and 53% higher in CYP3A4*22 carriers compared with *1/*1 patients in the whole group. Patients with impaired CYP2D6 metabolism and carriers of CYP3A4*22 had EDF levels comparable to CYP2D6 EM-F group (9.06 and 10.67 ng ml(-1), p = 0.247). CONCLUSION: The presence of CYP3A4*22 might compensate the reduction of EDF concentrations related to CYP2D6 inactivity, especially due to increased HTF concentrations.

Influence of CYP2D6 and CYP3A4 Phenotypes, Drug Interactions, and Vitamin D Status on Tamoxifen Biotransformation.

OBJECTIVE: In view of the large variability on therapeutic response and the multiple factors associated to tamoxifen (TAM) metabolic activation, this study aimed to evaluate the effect of CYP2D6 and CYP3A4 phenotypes, drug interactions, and vitamin D exposure on TAM metabolism in a group of breast cancer patients. METHODS: Trough blood samples were collected from 116 patients. TAM and metabolites endoxifen (EDF), N-desmethyltamoxifen, and 4-hydroxytamoxifen (HTF) were measured in plasma by liquid chromatography-tandem mass spectrometry. CYP2D6 and CYP3A4 phenotyping were obtained according to [dextromethorphan]/[dextrorphan] and [omeprazole]/[omeprazole sulfone] metabolic ratios, measured by high-performance liquid chromatography in plasma collected 3 hours after oral administration of 33 mg of dextromethorphan and 20 mg of omeprazole. Vitamin D3 was measured in plasma by high-performance liquid chromatography-ultraviolet. Data on concomitant use of drug considered as CYP2D6 and CYP3A4 inhibitor or inducer and vitamin D supplementation were recorded. RESULTS: About 20% of patients had reduced CYP2D6 metabolic activity and 7% CYP3A4 impaired metabolism. EDF levels diminished proportionally to the reduction of CYP2D6 metabolic activity (poor metabolizer 2.79 ng·mL, intermediate metabolizer (IM) 5.36 ng·mL, and extensive metabolizer 10.65 ng·mL, P < 0.01). Median plasma levels of TAM (161.50 ng·mL) and HTF (1.32 ng·mL) in CYP2D6 IM/CYP3A4 poor metabolizer patients were higher (P < 0.05) than those from CYP2D6 IM/CYP3A4 extensive metabolizer patients (122.07 ng·mL and 0.61 ng·mL, respectively). Seasons contributed to the interpatient variability of EDF and HTF levels; summer concentrations were 24% and 42% higher compared with winter. Vitamin D3 was not associated to CYP3A4 metabolic activity, indicating that other mechanisms might be involved in the relation between TAM metabolism and vitamin D exposure. CONCLUSIONS: CYP3A4 contributes to the bioactivation of TAM through formation of HTF and becomes increasingly important in case of reduced or absent CYP2D6 activity. EDF and HTF exposure were associated to seasonal variations, with considerable higher plasma concentrations during summer.

Ultra-high performance liquid chromatography tandem mass spectrometric method for the determination of tamoxifen, N-desmethyltamoxifen, 4-hydroxytamoxifen and endoxifen in dried blood spots--development, validation and clinical application during breast cancer adjuvant therapy.

A LC-MSMS method for the simultaneous determination of tamoxifen, N-desmethyltamoxifen, 4-hydroxytamoxifen and endoxifen in dried blood spots samples was developed and validated. The method employs an ultrasound-assisted liquid extraction and a reversed phase separation in an Acquity(®) C18 column (150×2.1 mm, 1.7 µm). Mobile phase was a mixture of formic acid 0.1% (v/v) pH 2.7 and acetonitrile (gradient from 60:40 to 50:50, v/v). Total analytical run time was 8 min. Precision assays showed CV % lower than 10.75% and accuracy in the range 94.5 to 110.3%. Mean analytes recoveries from DBS ranged from 40% to 92%. The method was successfully applied to 91 paired clinical DBS and plasma samples. Dried blood spots concentrations were highly correlated to plasma, with rs>0.83 (P<0.01). Median estimated plasma concentrations after hematocrit and partition factor adjustment were: TAM 123.3 ng mL(-1); NDT 267.9 ng mL(-1), EDF 10.0 ng mL(-1) and HTF 1.3 ng mL(-1,) representing in average 98 to 104% of the actually measured concentrations. The DBS method was able to identify 96% of patients with plasma EDF concentrations below the clinical threshold related to better prognosis (5.9 ng mL(-1)). The procedure has adequate analytical performance and can be an efficient tool to optimize adjuvant breast cancer treatment, especially in resource limited settings.

Development, validation and clinical application of a HPLC-FL method for CYP2D6 phenotyping in South Brazilian breast cancer patients.

OBJECTIVE: To develop and validate a method for determination of dextromethorphan (DMT) and dextrorphan (DTP) in plasma samples using HPLC-FL and to apply it to CYP2D6 phenotyping of a population from the South of Brazil. METHODS: Samples were prepared by hydrolysis and liquid-liquid extraction. Analysis was conducted in a reversed phase column, with isocratic elution and fluorescence detection. One hundred and forty patients being treated with tamoxifen were given 30 mg of dextromethorphan and their CYP2D6 phenotypes were determined on the basis of [DMT]/[DTP] metabolic ratios in plasma samples collected after 3h. RESULTS: Total chromatography running time was 12 min. Precision (CV%) was below 9.7% and accuracy was between 92.1 and 106.9%. The lower limits of quantification were 1 ng mL(-1) for DMT and 10 ng mL(-1) for DTP. Mean extraction yield of analytes was 86.6%. Mean age of patients was 55.7 years. Phenotype frequencies were as follows: 7.1% poor metabolizers, 13.6% intermediate metabolizers, 77.1% extensive metabolizers and 2.1 ultra-rapid metabolizers. Metabolic ratios for patients on strong (n=11) and weak (n=16) CYP2D6 activity inhibitors were different from each other and also different from ratios for patients not taking enzyme inhibitors (n=113). CONCLUSIONS: A sensitive method for determination of dextromethorphan and its metabolite in plasma samples was developed and successfully applied, providing evidence of the impact that CYP2D6 inhibitors have on the enzyme's metabolic capacity.