Impact of P-glycoprotein (ABCB1) and breast cancer resistance protein (ABCG2) gene dosage on plasma pharmacokinetics and brain accumulation of dasatinib, sorafenib, and sunitinib.

Low brain accumulation of anticancer drugs due to efflux transporters may limit chemotherapeutic efficacy, necessitating a better understanding of the underlying mechanisms. P-glycoprotein (Abcb1a/1b) and breast cancer resistance protein (Abcg2) combination knockout mice often display disproportionately increased brain accumulation of shared drug substrates compared with single transporter knockout mice. Recently developed pharmacokinetic models could explain this phenomenon. To experimentally test these models and their wider relevance for tyrosine kinase inhibitors and other drugs, we selected dasatinib, sorafenib, and sunitinib because of their divergent oral availability and brain accumulation profiles: the brain accumulation of dasatinib is mainly restricted by Abcb1, that of sorafenib mainly by Abcg2, and that of sunitinib equally by Abcb1 and Abcg2. We analyzed the effect of halving the efflux activity of these transporters at the blood-brain barrier by generating heterozygous Abcb1a/1b;Abcg2 knockout mice and testing the plasma and brain levels of the drugs after oral administration at 10 mg/kg. Real-time reverse transcription-polymerase chain reaction analysis confirmed the ∼2-fold decreased expression of both transporters in brain. Interestingly, whereas complete knockout of the transporters caused 24- to 36-fold increases in brain accumulation of the drugs, the heterozygous mice only displayed 1.6- to 1.9-fold increases of brain accumulation relative to wild-type mice. These results are well in line with the predictions of the pharmacokinetic models and provide strong support for their validity for a wider range of drugs. Moreover, retrospective analysis of fetal accumulation of drugs across the placenta in Abcb1a/1b heterozygous knockout pups suggests that these models equally apply to the maternal-fetal barrier.

The bioanalysis of the major Echinacea purpurea constituents dodeca-2E,4E,8Z,10E/Z-tetraenoic acid isobutylamides in human plasma using LC-MS/MS.

Alkylamides are a group of active components of the widely used herb Echinacea purpurea (E. purpurea), which have immunostimulatory and anti-inflammatory effects. For the most abundant alkylamides, dodeca-2E,4E,8Z,10E/Z-tetraenoic acid isobutylamides (DTAI), an LC-MS/MS assay has been developed and validated for quantification in human plasma. This assay will be used to support a clinical interaction study with E. purpurea. A 300 µL plasma aliquot underwent liquid-liquid extraction with diethylether-n-hexane (50:50, v/v). After evaporization and reconstitution in 100 µL of acetonitrile-water (50:50, v/v) 20 µL of sample were injected into the HPLC system. Chromatographic separation was achieved with a Polaris 3 C18-A column (50 mm × 2 mm ID, particle size 3 µm), a flow rate of 0.3 mL/min and isocratic elution with acetonitrile-water (50:50, v/v) containing 0.1% formic acid during the first 5 min. Hereafter, gradient elution was applied for 0.5 min, followed by restoration of the initial isocratic conditions. The total run time was 7.5 min. The assay was validated over a concentration range from 0.01 to 50 ng/mL for DTAI, with a lower limit of quantification of 0.01 ng/mL. Validation results show that DTAI can be accurately and precisely quantified in human plasma. DTAI also demonstrated to be chemically stable under relevant conditions. Finally, the applicability of this assay has been successfully demonstrated by measuring the plasma concentration of DTAI in patients after ingestion of a commercial extract of E. purpurea.

Liquid chromatography-tandem mass spectrometric assay for diclofenac and three primary metabolites in mouse plasma.

The first liquid chromatography-tandem mass spectrometric assay for the simultaneous determination of diclofenac, 4'-hydroxy-diclofenac, 5-hydroxy-diclofenac and diclofenac-acyl-glucuronide in mouse plasma, using a simple sample pre-treatment procedure, was developed and validated. Analytes in plasma were stabilized using acetic acid and ascorbic acid. After addition of the internal standard D(4)-diclofenac to a 10 microl sample volume and protein precipitation with acetonitrile, the supernatant was supplemented with an equal volume of water and injected into the chromatographic system. A polar embedded reversed-phase column with gradient elution using formic acid and ammonium acetate in water-methanol were used. The eluate was totally transferred into an electrospray interface with positive ionization and the analytes were quantified using triple quadrupole mass spectrometry. The assay was validated in the ranges 10-5000 ng/ml for 4'-hydroxy-diclofenac and 20-10,000 ng/ml for the other analytes, the lowest levels of these ranges (10 or 20 ng/ml) being the lower limits of quantification. Within day precisions were < or = 10%, between day precisions < or = 13% and accuracies were between 90 and 108%. The analytes were chemically stable under all relevant conditions. The assay was successfully applied in a pharmacokinetic study with diclofenac in mice.

Population pharmacokinetics and pharmacodynamics of mitomycin during intraoperative hyperthermic intraperitoneal chemotherapy.

BACKGROUND: During recent years, cytoreductive surgery combined with hyperthermic intraperitoneal chemotherapy (HIPEC) with mitomycin has been used for various malignancies. OBJECTIVE: To characterise the population pharmacokinetics and pharmacodynamics of mitomycin during HIPEC. METHODS: Forty-seven patients received mitomycin 35 mg/m2 intraperitoneally as a perfusion over 90 minutes. Mitomycin concentrations were determined in both the peritoneal perfusate and plasma. The observed concentration-time profiles were used to develop a population pharmacokinetic model using nonlinear mixed-effect modelling (NONMEM). The area under the plasma concentration-time curve (AUC) was related to the haematological toxicity. RESULTS: Concentration-time profiles of mitomycin in perfusate and plasma were adequately described with one- and two-compartment models, respectively. The average volume of distribution of the perfusate compartment (V1) and rate constant from the perfusate to the systemic circulation (k12) were 4.5 +/- 1.1L and 0.014 +/- 0.003 min(-1), respectively (mean +/- SD, n = 47). The average volume of distribution of the central plasma compartment (V2), clearance from the central compartment (CL) and volume of distribution of the peripheral plasma compartment (V3) were 28 +/- 16L, 0.55 +/- 0.18 L/min and 36 +/- 8L, respectively. The relationship between the AUC in plasma and degree of leucopenia was described with a sigmoidal maximum-effect (Emax) model. CONCLUSIONS: The pharmacokinetics of mitomycin during HIPEC could be fitted successfully to a multicompartment model. Relationships between plasma exposure and haematological toxicity were quantified. The developed pharmacokinetic-pharmacodynamic model can be used to simulate different dosage schemes in order to optimise mitomycin administration during HIPEC.