Circadian variation in tamoxifen pharmacokinetics in mice and breast cancer patients.

The anti-estrogen tamoxifen is characterized by a large variability in response, partly due to pharmacokinetic differences. We examined circadian variation in tamoxifen pharmacokinetics in mice and breast cancer patients. Pharmacokinetic analysis was performed in mice, dosed at six different times (24-h period). Tissue samples were used for mRNA expression analysis of drug-metabolizing enzymes. In patients, a cross-over study was performed. During three 24-h periods, after tamoxifen dosing at 8 a.m., 1 p.m., and 8 p.m., for at least 4 weeks, blood samples were collected for pharmacokinetic measurements. Differences in tamoxifen pharmacokinetics between administration times were assessed. The mRNA expression of drug-metabolizing enzymes showed circadian variation in mouse tissues. Tamoxifen exposure seemed to be highest after administration at midnight. In humans, marginal differences were observed in pharmacokinetic parameters between morning and evening administration. Tamoxifen C(max )and area under the curve (AUC)0-8 h were 20 % higher (P < 0.001), and tamoxifen t(max) was shorter (2.1 vs. 8.1 h; P = 0.001), indicating variation in absorption. Systemic exposure (AUC0-24 h) to endoxifen was 15 % higher (P < 0.001) following morning administration. The results suggest that dosing time is of marginal influence on tamoxifen pharmacokinetics. Our study was not designed to detect potential changes in clinical outcome or toxicity, based on a difference in the time of administration. Circadian rhythm may be one of the many determinants of the interpatient and intrapatient pharmacokinetic variability of tamoxifen.

Validation of an LC-MS/MS method for simultaneous quantification of abiraterone, enzalutamide and darolutamide in human plasma.

Currently, several oral androgen receptor signalling inhibitors are available for the treatment of advanced prostate cancer. Quantification of plasma concentrations of these drugs is highly relevant for various purposes, such as Therapeutic Drug Monitoring (TDM) in oncology. Here, we report a liquid chromatography/tandem mass spectrometric (LC-MS/MS) method for the simultaneous quantification of abiraterone, enzalutamide, and darolutamide. The validation was performed according to the requirements of the U.S. Food and Drug Administration and European Medicine Agency. We also demonstrate the clinical applicability of the quantification of enzalutamide and darolutamide in patients with metastatic castration-resistant prostate cancer.

Quantification of ribociclib in dried blood spots by LC-MS/MS: Method development and clinical validation.

A reliable, specific, selective and robust liquid chromatography-tandem mass spectrometry (LC-MS/MS) method was developed for the determination of ribociclib in both dried blood spot (DBS) samples and potassium EDTA plasma. DBS samples were obtained simultaneously with a plasma sample in advanced breast cancer patients treated with ribociclib. A 6 mm disk from the central part of the dried blood spot sample was punched, followed by extraction of ribociclib using liquid-liquid extraction spiked with ribociclib-d6 as internal standard. Concentrations of ribociclib in DBS samples were correlated with corresponding plasma concentrations. From the blood sample also hematocrit was determined. The method was validated for selectivity, sensitivity, precision, lower limit of detection, linearity, stability and accuracy according to the food and drug administration (FDA) guideline. The within- and between-run precisions were ≤10.6 and ≤1.07 %, respectively; while the average accuracy ranged from 100 to 103 %. The influence of hematocrit on validation parameters was tested in the range of 0.20 - 0.40 L/L. No influence of hematocrit on validation parameters was observed. Regression analysis and a Bland-Altman plot indicated correlation between the results obtained from DBS and plasma samples. A strong correlation (R2 >0.97) between DBS samples and plasma concentration from 17 breast cancer patients was found. A number of 12 out of 17 processed DBS samples (71 %) fell inside the acceptable range of 20 % difference of simultaneously obtained plasma samples. The lower limit of quantification in DBS is 10.0 ng/mL and linearity was demonstrated up to 1000 ng/mL. In conclusion, the newly developed assay met the required standard for validation. The methods were used to study ribociclib disposition in patients with advanced breast cancer.

Quantification of afatinib, alectinib, crizotinib and osimertinib in human plasma by liquid chromatography/triple-quadrupole mass spectrometry; focusing on the stability of osimertinib.

The development and full validation of a sensitive and selective ultra-performance liquid chromatography/tandem mass spectrometry (UPLC-MS/MS) method are described for the simultaneous analysis of afatinib, alectinib, crizotinib and osimertinib in human lithium heparinized plasma. Afatinib-d6, crizotinib-d5 and erlotinib-d6 were used as internal standards. Given osimertinib's instability in plasma and whole blood at ambient temperature, samples should be solely processed on ice (T = 0 °C). Chromatographic separation was obtained on an Acquity UPLC ® BEH C18; 2.1 × 50 mm, 1.7 µm column, which was eluted with 0.400 mL/minute flow on a linear gradient, consisting of 10 mM ammonium formate (pH 4.5) and acetonitrile. Calibration curves for all compounds were linear for concentration ranges of 1.00 to 100 ng/mL for afatinib and 10.0 to 1000 ng/mL for alectinib, crizotinib and osimertinib, herewith validating the lower limits of quantification at 1.00 ng/mL for afatinib and 10.0 ng/mL for alectinib, crizotinib and osimertinib. Within-run and between-run precision measurements fell within 10.2%, with accuracy ranging from 89.2 to 110%.

Relationship Between Sunitinib Pharmacokinetics and Administration Time: Preclinical and Clinical Evidence.

BACKGROUND AND OBJECTIVE: Circadian rhythms may influence the pharmacokinetics of drugs. This study aimed to elucidate whether the pharmacokinetics of the orally administered drug sunitinib are subject to circadian variation. METHODS: We performed studies in male FVB-mice aged 8-12 weeks, treated with single-dose sunitinib at six dosing times. Plasma and tissue samples were obtained for pharmacokinetic analysis and to monitor messenger RNA (mRNA) expression of metabolizing enzymes and drug transporters. A prospective randomized crossover study was performed in which patients took sunitinib once daily at 8 a.m., 1 p.m., and 6 p.m at three subsequent courses. Patients were blindly randomized into two groups, which determined the sequence of the sunitinib dosing time. The primary endpoint in both studies was the difference in plasma area under the concentration-time curve (AUC) of sunitinib and its active metabolite SU12662 between dosing times. RESULTS: Sunitinib and SU12662 plasma AUC in mice followed an ~12-h rhythm as a function of administration time (p ≤ 0.04). The combined AUC from time zero to 10 h (AUC10) was 14-27 % higher when sunitinib was administered at 4 a.m. and 4 p.m. than at 8 a.m. and 8 p.m. Twenty-four-hour rhythms were seen in the mRNA levels of drug transporters and metabolizing enzymes. In 12 patients, sunitinib trough concentrations (C trough) were higher when the drug was taken at 1 p.m. or 6 p.m. than when taken at 8 a.m. (C trough-1 p.m. 66.0 ng/mL; C trough-6 p.m. 58.9 ng/mL; C trough-8 a.m. 50.7 ng/mL; p = 0.006). The AUC was not significantly different between dosing times. CONCLUSIONS: Our results indicate that sunitinib pharmacokinetics follow an ~12-h rhythm in mice. In humans, morning dosing resulted in lower C trough values, probably resulting from differences in elimination. This can have implications for therapeutic drug monitoring.

Effect of omeprazole on the pharmacokinetics and toxicities of irinotecan in cancer patients: a prospective cross-over drug-drug interaction study.

BACKGROUND: Omeprazole is one of the most prescribed medications worldwide and within the class of proton pump inhibitors, it is most frequently associated with drug interactions. In vitro studies have shown that omeprazole can alter the function of metabolic enzymes and transporters that are involved in the metabolism of irinotecan, such as uridine diphosphate glucuronosyltransferase subfamily 1A1 (UGT1A1), cytochrome P-450 enzymes subfamily 3A (CYP3A) and ATP-binding cassette drug-transporter G2 (ABCG2). In this open-label cross-over study we investigated the effects of omeprazole on the pharmacokinetics and toxicities of irinotecan. METHODS: Fourteen patients were treated with single agent irinotecan (600mg i.v., 90min) followed 3weeks later by a second cycle with concurrent use of omeprazole 40mg once daily, which was started 2weeks prior to the second cycle. Plasma samples were obtained up to 55h after infusion and analysed for irinotecan and its metabolites 7-ethyl-10-hydroxycampothecin (SN-38), SN-38-glucuronide (SN-38G), 7-ethyl-10-[4-(1-piperidino)-1-amino]-carbonyloxycamptothecin (NPC) and 7-ethyl-10-[4-N-(5-aminopentanoic acid)-1-piperidino]-carbonyloxycamptothecin (APC) by high-performance liquid chromatography (HPLC). Non-compartmental modelling was performed. Toxicities were monitored during both cycles. Paired statistical tests were performed with SPSS. RESULTS: The exposure to irinotecan and its metabolites was not significantly different between both cycles. Neither were there significant differences in the absolute nadir and percentage decrease of WBC and ANC, nor on the incidence and severity of neutropenia, febrile neutropenia, diarrhoea, nausea and vomiting when irinotecan was combined with omeprazole. CONCLUSION: Omeprazole 40mg did not alter the pharmacokinetics and toxicities of irinotecan. This widely used drug can, therefore, be safely administered during a 3-weekly single agent irinotecan schedule.