Knockout of cytochrome P450 3A yields new mouse models for understanding xenobiotic metabolism

Cytochrome P450 3A (CYP3A) enzymes constitute an important detoxification system that contributes to primary metabolism of more than half of all prescribed medications. To investigate the physiological and pharmacological roles of CYP3A, we generated Cyp3a-knockout (Cyp3a-/-) mice lacking all functional Cyp3a genes. Cyp3a-/- mice were viable, fertile, and without marked physiological abnormalities. However, these mice exhibited severely impaired detoxification capacity when exposed to the chemotherapeutic agent docetaxel, displaying higher exposure levels in response to both oral and intravenous administration. These mice also demonstrated increased sensitivity to docetaxel toxicity, suggesting a primary role for Cyp3a in xenobiotic detoxification. To determine the relative importance of intestinal versus hepatic Cyp3a in first-pass metabolism, we generated transgenic Cyp3a-/- mice expressing human CYP3A4 in either the intestine or the liver. Expression of CYP3A4 in the intestine dramatically decreased absorption of docetaxel into the bloodstream, while hepatic expression aided systemic docetaxel clearance. These results suggest that CYP3A expression determines impairment of drug absorption and efficient systemic clearance in a tissue-specific manner. The genetic models used in this study provide powerful tools to further study CYP3A-mediated xenobiotic metabolism, as well as interactions between CYP3A and other detoxification systems.

In vitro transport of gimatecan (7-t-butoxyiminomethylcamptothecin) by breast cancer resistance protein, P-glycoprotein, and multidrug resistance protein 2

Lipophilic camptothecin derivatives are considered to have negligible affinity for breast cancer resistance protein (BCRP; ABCG2). Gimatecan, a new orally available 7-t-butoxyiminomethyl-substituted lipophilic camptothecin derivative, has been previously reported to be not a substrate for BCRP. Using a panel of in vitro models, we tested whether gimatecan is a substrate for BCRP as well as for P-glycoprotein (MDR1) or multidrug resistance protein 2 (MRP2; ABCC2), ATP-binding cassette drug efflux transporters involved in anticancer drug resistance, and able to affect the pharmacokinetics of substrate drugs. Cell survival, drug transport, accumulation, and efflux were studied in IGROV1 and (human BCRP overexpressing) T8 cells, Madin-Darby canine kidney II (MDCKII-WT, MDCKII-Bcrp1, MDCKII-MDR1, and MDCKII-MRP2), and LLCPK (LLCPK-WT and LLCPK-MDR1) cells. Competition with methotrexate uptake was studied in Sf9-BCRP membrane vesicles. In vitro, expression of BCRP resulted in 8- to 10-fold resistance to gimatecan. In Transwell experiments, gimatecan was transported by Bcrp1 and transport was inhibited by the BCRP/P-glycoprotein inhibitors elacridar and pantoprazole. Efflux of gimatecan from MDCKII-Bcrp1 cells was faster than in WT cells. In Sf9-BCRP membrane vesicles, gimatecan significantly inhibited BCRP-mediated transport of methotrexate. In contrast, gimatecan was not transported by MDR1 or MRP2. Gimatecan is transported by BCRP/Bcrp1 in vitro, although to a lesser extent than the camptothecin analogue topotecan. Implications of BCRP expression in the gut for the oral development of gimatecan and the interaction between gimatecan and other BCRP substrate drugs and/or inhibitors warrant further clinical investigation.

Comparison of two immortalized human cell lines to study nuclear receptor-mediated CYP3A4 induction

Since CYP3A4 is responsible for the biotransformation of over 50% of all clinically used drugs, induction results in an increased clearance of many concomitantly administered drugs, thereby decreasing treatment efficacy or, in the case of prodrugs, lead to severe intoxications. CYP3A4 induction is regulated by the pregnane X receptor, constitutive androstane receptor, and vitamin D receptor. Since these nuclear receptors show large interspecies differences, accurate prediction of nuclear receptor-mediated CYP3A4 induction in humans requires the use of human systems. Because primary cultures of human hepatocytes or enterocytes have major drawbacks like poor availability and poor reproducibility, human cell lines are a good alternative. In this study, the widely used HepG2 cell line was compared with the LS180 cell line to serve as a model to study CYP3A4 induction. There was a clear difference between the cell lines with respect to CYP3A enzyme expression and induction. In LS180, CYP3A4 was expressed and was found to be induced by prototypical nuclear receptor agonists, whereas in HepG2, CYP3A4 was nonresponsive to treatment with rifampicin, CITCO [6-(4-chlorophenyl)imidazo[2,1-b][1,3]thiazole-5-carbaldehyde-O-3,4-dichlorobenzyl) oxime], or calcitriol. We subsequently evaluated whether these host-cell differences also have an effect on CYP3A4 reporter gene activity. We clearly show that there are differences in CYP3A4 reporter activity between the cell lines, and based on these results and those found on mRNA and protein level, we conclude that LS180 is a more suitable cell line to study CYP3A4 induction than the widely used HepG2.

The application of inductively coupled plasma mass spectrometry in clinical pharmacological oncology research

Metal-based anticancer agents are frequently used in the treatment of a wide variety of cancer types. The monitoring of these anticancer agents in biological samples is important to understand their pharmacokinetics, pharmacodynamics, and metabolism. In addition, determination of metals originating from anticancer agents is relevant to assess occupational exposure of health care personnel working with these drugs. The high sensitivity of inductively coupled plasma mass spectrometry (ICP-MS) has resulted in an increased popularity of this technique for the analysis of metal-based anticancer drugs. In addition to the quantitative analysis of the metal of interest in a sample, ICP-MS can be used as an ultrasensitive metal selective detector in combination with speciation techniques such as liquid chromatography. In the current review we provide a systematic survey of publications describing the analysis of platinum- and ruthenium-containing anticancer agents using ICP-MS, focused on the determination of total metal concentrations and on the speciation of metal compounds in biological fluids, DNA- and protein-adducts, and environmental samples. We conclude that ICP-MS is a powerful tool for the quantitative analysis of metal-based anticancer agents from multiple sample sources.

Comparison of normalisation methods for surface-enhanced laser desorption and ionisation (SELDI) time-of-flight (TOF) mass spectrometry data

Background

Mass spectrometry for biological data analysis is an active field of research, providing an efficient way of high-throughput proteome screening. A popular variant of mass spectrometry is SELDI, which is often used to measure sample populations with the goal of developing (clinical) classifiers. Unfortunately, not only is the data resulting from such measurements quite noisy, variance between replicate measurements of the same sample can be high as well. Normalisation of spectra can greatly reduce the effect of this technical variance and further improve the quality and interpretability of the data. However, it is unclear which normalisation method yields the most informative result.

Results

In this paper, we describe the first systematic comparison of a wide range of normalisation methods, using two objectives that should be met by a good method. These objectives are minimisation of inter-spectra variance and maximisation of signal with respect to class separation. The former is assessed using an estimation of the coefficient of variation, the latter using the classification performance of three types of classifiers on real-world datasets representing two-class diagnostic problems. To obtain a maximally robust evaluation of a normalisation method, both objectives are evaluated over multiple datasets and multiple configurations of baseline correction and peak detection methods. Results are assessed for statistical significance and visualised to reveal the performance of each normalisation method, in particular with respect to using no normalisation. The normalisation methods described have been implemented in the freely available MASDA R-package.

Conclusion

In the general case, normalisation of mass spectra is beneficial to the quality of data. The majority of methods we compared performed significantly better than the case in which no normalisation was used. We have shown that normalisation methods that scale spectra by a factor based on the dispersion (e.g., standard deviation) of the data clearly outperform those where a factor based on the central location (e.g., mean) is used. Additional improvements in performance are obtained when these factors are estimated locally, using a sliding window within spectra, instead of globally, over full spectra. The underperforming category of methods using a globally estimated factor based on the central location of the data includes the method used by the majority of SELDI users.

Cytoreductive surgery and intraoperative hyperthermic intraperitoneal chemotherapy with paclitaxel: a clinical and pharmacokinetic study

BACKGROUND

Intraperitoneal chemotherapy has been recommended as a treatment option for ovarian cancer with peritoneal dissemination. Although its treatment duration is significantly shorter, intraoperative hyperthermic intraperitoneal perfusion chemotherapy (HIPEC) has several advantages over simple intraperitoneal instillation chemotherapy. While platinum compounds have usually been used, only a few have administered paclitaxel during HIPEC. Its large molecular weight suggests a much more favorable pharmacokinetic profile than that of platinum compounds. The pharmacokinetics of paclitaxel during and after HIPEC have not been studied before.

METHODS

Thirteen women, mainly with ovarian cancer, underwent cytoreductive surgery and HIPEC with 175 mg/m(2) paclitaxel for 2 h. Morbidity was noted. Peritoneal fluid samples and blood samples were harvested during and until 5 days after HIPEC for pharmacokinetic study in ten patients.

RESULTS

No treatment-related mortality was noted. Overall morbidity was 38% (two wound infections, one deep venous thrombosis, two grade 1 thrombopenia, one grade 2 neutropenia, and one grade 3 pancytopenia). Mean maximal intraperitoneal paclitaxel concentration was 101 mg/L, which was an average of 1178 times higher than the peak plasma levels. The peritoneal fluid versus plasma AUC ratio was 1462 for the 2-h HIPEC duration and 366 for the total 5-day study period. Cytotoxic drug concentrations were detected in peritoneal fluid for a mean period of 2.7 days, despite drainage of the drug solution after 2 h of treatment.

CONCLUSIONS

HIPEC with paclitaxel following cytoreductive surgery is feasible, relatively safe, and associated with a highly favorable pharmacokinetic profile, despite its short treatment duration. Larger studies with a more homogenous patient cohort and adequate follow-up should be performed to demonstrate its efficacy.

Comparing the old and new generation SELDI-TOF MS: implications for serum protein profiling

Background

Although the PBS-IIc SELDI-TOF MS apparatus has been extensively used in the search for better biomarkers, issues have been raised concerning the semi-quantitative nature of the technique and its reproducibility. To overcome these limitations, a new SELDI-TOF MS instrument has been introduced: the PCS 4000 series. Changes in this apparatus compared to the older one are a.o. an increased dynamic range of the detector, an adjusted configuration of the detector sensitivity, a raster scan that ensures more complete desorption coverage and an improved detector attenuation mechanism. In the current study, we evaluated the performance of the old PBS-IIc and new PCS 4000 series generation SELDI-TOF MS apparatus.

Methods

To this end, two different sample sets were profiled after which the same ProteinChip arrays were analysed successively by both instruments. Generated spectra were analysed by the associated software packages. The performance of both instruments was evaluated by assessment of the number of peaks detected in the two sample sets, the biomarker potential and reproducibility of generated peak clusters, and the number of peaks detected following serum fractionation.

Results

We could not confirm the claimed improved performance of the new PCS 4000 instrument, as assessed by the number of peaks detected, the biomarker potential and the reproducibility. However, the PCS 4000 instrument did prove to be of superior performance in peak detection following profiling of serum fractions.

Conclusion

As serum fractionation facilitates detection of low abundant proteins through reduction of the dynamic range of serum proteins, it is now increasingly applied in the search for new potential biomarkers. Hence, although the new PCS 4000 instrument did not differ from the old PBS-IIc apparatus in the analysis of crude serum, its superior performance after serum fractionation does hold promise for improved biomarker detection and identification.

P-glycoprotein and breast cancer resistance protein: two dominant transporters working together in limiting the brain penetration of topotecan

PURPOSE

The brain is a pharmacologic sanctuary site, due to the presence of the blood-brain barrier (BBB). Whereas the effect of P-glycoprotein (P-gp) at the BBB is well established, the role of breast cancer resistance protein (BCRP) that is also expressed at the BBB is not.

EXPERIMENTAL DESIGN

We have studied the effect of BCRP by administering topotecan to wild-type (WT), single Mdr1a/b(-/-) and Bcrp1(-/-), and compound Mdr1a/b(-/-)Bcrp1(-/-) knockout mice. Drug levels in plasma and tissues were determined by high-performance liquid chromatography.

RESULTS

The area under the plasma and tissue concentration-time curve (AUC) of topotecan in brains of Mdr1a/b(-/-) and Bcrp1(-/-) mice was only 1.5-fold higher compared with WT mice, but in Mdr1a/b(-/-)Bcrp1(-/-) mice, where both transporters are absent, the AUC increased by 12-fold. The AUC in plasma was approximately 0.75-, 2.4-, and 3.7-fold higher in Mdr1a/b(-/-), Bcrp1(-/-), and Mdr1a/b(-/-)Bcrp1(-/-) mice, respectively, resulting in 2.0-fold (P < 0.01), 0.65-fold (P, not significant), and 3.2-fold (P < 0.01), respectively, higher brain-to-plasma AUC ratios. Results using Mrp4(-/-) mice showed that this transporter had no effect on the brain penetration of topotecan. The P-gp/BCRP inhibitor elacridar fully inhibited P-gp-mediated transport of topotecan, whereas inhibition of Bcrp1-mediated transport by elacridar was minimal.

CONCLUSIONS

Our results using Mdr1a/b(-/-)Bcrp1(-/-) mice clearly show the effect of Bcrp1 at the BBB and also show how two drug transporters act in concert to limit the brain penetration of topotecan. We expect that this finding will also apply to other drugs that are substrates of both P-gp and BCRP. Consequently, to improve the brain penetration of such compounds for targeting intracranial malignancies in patients, it will be essential to use potent inhibitors of both drug transporters.

Enhanced resolution triple-quadrupole mass spectrometry for ultra-sensitive and quantitative analysis of the investigational anticancer agent EO9 (apaziquone) and its metabolite EO5a in human and dog plasma to support (pre)-clinical studies of EOquin given intravesically

A highly sensitive and selective liquid chromatography/tandem mass spectrometric (LC/MS/MS) method was developed to quantify the experimental anticancer agent EO9 and its metabolite EO5a in biological matrices. A 200-microL aliquot of human/dog plasma was spiked with a mixture of deuterated internal standards EO9-d3 and EO5a-d4 and extracted with 1.25 mL of ethyl acetate. Dried extracts were reconstituted in 0.1 M ammonium acetate/methanol (7:3, v/v) and 20-microL volumes were injected onto the LC system. Separation was achieved on a 150 x 2.1 mm C18 column using an alkaline eluent (1 mM ammonium hydroxide/methanol (gradient system)). The detection was performed by a Finnigan TSQ Quantum Ultra equipped with an electrospray ionization source operated in positive mode and enhanced mass resolution capability. It demonstrated improved sensitivity with a factor 10-20 for EO9 and EO5a over a 3-decades dynamic range, with acceptable accuracy and precision, when compared with the previously described assay for EO9 and EO5a, developed by our group, using an API 2000. The assay quantifies a range from 0.5 to 500 ng/mL for EO9 and EO5a using 200-microL human plasma and dog samples. The described mass resolution method was successfully applied for the evaluation of the pharmacokinetic profile of EO9 and its metabolite EO5a in human and dog plasma.

A pharmacokinetic and pharmacogenetic study of efavirenz in children: dosing guidelines can result in subtherapeutic concentrations

BACKGROUND

Our main objectives were to study the population pharmacokinetics of efavirenz and to explore the adequacy of dosing guidelines.

METHODS

A total of 33 HIV-1-infected patients were recruited from the Emma Children's Hospital (Amsterdam, the Netherlands). Gender, age, drug formulation, the presence of the c.516G>T polymorphism in the CYP2B6 gene and the quantitation of liver enzymes alanine aminotransferase and aspartate aminotransferase at baseline were collected. A non-linear mixed effect pharmacokinetic model was developed.

RESULTS

CYP2B6 genotype and drug formulation significantly influenced efavirenz pharmacokinetics. Clearance was 29.7% lower in children carrying the CYP2B6-516-G/T genotype compared with children carrying the G/G genotype. Relative bioavailiability of the oral liquid compared with tablets or capsules was 46.6%. Children carrying the CYP2B6-516-G/G genotype had a 50-70% probability of developing a subtherapeutic trough level of efavirenz and only 1-3% probability of developing a trough level >4 mg/l. To reduce the probability of developing a subtherapeutic trough concentration, we propose to give an adult efavirenz dose to children weighing > or =25 kg and to allometrically scale doses for other weight levels a priori. The dose of the oral solution should be twice the dose of capsules.

CONCLUSIONS

Population pharmacokinetics of efavirenz in children were adequately described. Current dosing guidelines can result in subtherapeutic concentrations in children carrying the CYP2B6-516-G/G genotype and with the liquid formulation. A priori dose adaptations in the paediatric population seem feasible and need prospective validation.

Midazolam metabolism in cytochrome P450 3A knockout mice can be attributed to up-regulated CYP2C enzymes

The cytochrome P450 3A (CYP3A) enzymes represent one of the most important drug-metabolizing systems in humans. Recently, our group has generated cytochrome P450 3A knockout mice to study this drug-handling system in vivo. In the present study, we have characterized the Cyp3a knockout mice by studying the metabolism of midazolam, one of the most widely used probes to assess CYP3A activity. We expected that the midazolam metabolism would be severely reduced in the absence of CYP3A enzymes. We used hepatic and intestinal microsomal preparations from Cyp3a knockout and wild-type mice to assess the midazolam metabolism in vitro. In addition, in vivo metabolite formation was determined after intravenous administration of midazolam. We were surprised to find that our results demonstrated that there is still marked midazolam metabolism in hepatic (but not intestinal) microsomes from Cyp3a knockout mice. Accordingly, we found comparable amounts of midazolam as well as its major metabolites in plasma after intravenous administration in Cyp3a knockout mice compared with wild-type mice. These data suggested that other hepatic cytochrome P450 enzymes could take over the midazolam metabolism in Cyp3a knockout mice. We provide evidence that CYP2C enzymes, which were found to be up-regulated in Cyp3a knockout mice, are primarily responsible for this metabolism and that several but not all murine CYP2C enzymes are capable of metabolizing midazolam to its 1'-OH and/or 4-OH derivatives. These data illustrate interesting compensatory changes that may occur in Cyp3a knockout mice. Such flexible compensatory interplay between functionally related detoxifying systems is probably essential to their biological role in xenobiotic protection.

Population pharmacokinetics and pharmacodynamics of paclitaxel and carboplatin in ovarian cancer patients: a study by the European organization for research and treatment of cancer-pharmacology and molecular mechanisms group and new drug development group

PURPOSE

Paclitaxel and carboplatin are frequently used in advanced ovarian cancer following cytoreductive surgery. Threshold models have been used to predict paclitaxel pharmacokinetic-pharmacodynamics, whereas the time above paclitaxel plasma concentration of 0.05 to 0.2 micromol/L (t(C > 0.05-0.2)) predicts neutropenia. The objective of this study was to build a population pharmacokinetic-pharmacodynamic model of paclitaxel/carboplatin in ovarian cancer patients.

EXPERIMENTAL DESIGN

One hundred thirty-nine ovarian cancer patients received paclitaxel (175 mg/m(2)) over 3 h followed by carboplatin area under the concentration-time curve 5 mg/mL*min over 30 min. Plasma concentration-time data were measured, and data were processed using nonlinear mixed-effect modeling. Semiphysiologic models with linear or sigmoidal maximum response and threshold models were adapted to the data.

RESULTS

One hundred five patients had complete pharmacokinetic and toxicity data. In 34 patients with measurable disease, objective response rate was 76%. Neutrophil and thrombocyte counts were adequately described by an inhibitory linear response model. Paclitaxel t(C > 0.05) was significantly higher in patients with a complete (91.8 h) or partial (76.3 h) response compared with patients with progressive disease (31.5 h; P = 0.02 and 0.05, respectively). Patients with paclitaxel t(C > 0.05) > 61.4 h (mean value) had a longer time to disease progression compared with patients with paclitaxel t(C > 0.05) < 61.4 h (89.0 versus 61.9 weeks; P = 0.05). Paclitaxel t(C > 0.05) was a good predictor for severe neutropenia (P = 0.01), whereas carboplatin exposure (C(max) and area under the concentration-time curve) was the best predictor for thrombocytopenia (P < 10(-4)).

CONCLUSIONS

In this group of patients, paclitaxel t(C > 0.05) is a good predictive marker for severe neutropenia and clinical outcome, whereas carboplatin exposure is a good predictive marker for thrombocytopenia.

Determination of imatinib mesylate and its main metabolite (CGP74588) in human plasma and murine specimens by ion-pairing reversed-phase high-performance liquid chromatography

A sensitive reversed-phase high-performance liquid chromatographic (HPLC) method has been developed and validated for the determination of imatinib, a tyrosine kinase inhibitor, and its main metabolite N-desmethyl-imatinib (CGP74588) in human plasma and relevant murine biological matrices. A simple HPLC assay for the individual quantification of imatinib and CGP74588 in murine specimens has not been reported to date. Sample pre-treatment involved liquid-liquid extraction with tert-butyl-methyl ether. Imatinib, CGP74588 (metabolite) and the internal standard 4-hydroxybenzophenone were separated using a narrow bore (2.1 x 150 mm) stainless steel Symmetry C(18) column and detected by UV at 265 nm. The mobile phase consisted of 28% (v/v) acetonitrile in 50 mM ammonium acetate buffer pH 6.8 containing 0.005 M 1-octane sulfonic acid and was delivered at 0.2 mL/min. The calibration curve was prepared in blank human plasma and was linear over the dynamic range 10 ng/mL to 10 microg/mL). The accuracy was close to 100% and the within-day and between-day precisions were within the generally accepted 15% range. The validation results showed that the assay was selective and reproducible. This method was applied to study the pharmacokinetics of imatinib and its main metabolite in human and mice.

PK/PD model of indisulam and capecitabine: interaction causes excessive myelosuppression

The anticancer agent indisulam was evaluated in a dose-escalation study in combination with capecitabine. Severe myelotoxicity was observed after multiple treatment cycles. We hypothesized that capecitabine inhibits the synthesis of CYP2C9, which metabolizes indisulam. The objectives were to develop a pharmacokinetic/pharmacodynamic (PK/PD) model for the combination treatment and to estimate the impact of a drug-drug interaction on the safety of various dose levels. NONMEM was used to develop a PK/PD model, including the impact of capecitabine coadministration on indisulam pharmacokinetics. A simulation study was performed to evaluate the risk of dose-limiting neutropenia. A time-dependent pharmacokinetic drug-drug interaction resulted in increased exposure to indisulam and in increased myelotoxicity. The risk of dose-limiting neutropenia increased with treatment duration and with dose. The excessive myelosuppression after multiple cycles may be explained by a pharmacokinetic interaction between indisulam and capecitabine. The combination of 550 mg/m(2) indisulam and 1,250 mg/m(2) capecitabine twice daily was considered safe.

Identification of responders and reactive domains to rivastigmine in Alzheimer's disease

PURPOSE

Presently, it is unclear which patients suffering from Alzheimer's Disease (AD) respond to rivastigmine and if rivastigmine acts on specific cognitive domains. The aims of this study are thus to investigate treatment effects of rivastigmine on specific cognitive domains and to find possible responsive subpopulations to rivastigmine cognitive effects.

METHODS

Mini Mental State Examination (MMSE) and Cambridge Cognitive Examination (CAMCOG) were administered at baseline and after 6 months in 83 rivastigmine users and 96 historical controls, representing natural decline. Treatment effects on different subsections of the CAMCOG and in different subpopulations were investigated by linear regression analyses.

RESULTS

Rivastigmine showed effectiveness on total CAMCOG (p < 0.001), CAMCOG non-memory subsection (p < 0.001) and subscales of language (p = 0.002), attention/calculation (p = 0.043), abstract thinking (p < 0.001) and perception (p = 0.031). In patients with baseline MMSE < or =19 rivastigmine showed significant and favourable effects compared to historical controls on total CAMCOG (p < 0.001) and both non-memory (p < 0.001) and memory subsections (p = 0.002).

CONCLUSION

Rivastigmine showed primarily effectiveness on the non-memory section of the CAMCOG and patients with a baseline MMSE < or = 19 appeared to show greater responses to rivastigmine compared to patients with baseline MMSE > or = 20.

Quantitative and selective assay of 5-methylindirubine, an inhibitor of cyclin-dependent kinases, in murine plasma using coupled liquid chromatography and electrospray tandem mass spectrometry

A sensitive and rapid LC-MS/MS assay for the quantitative determination of 5-methylindirubine (5-MI) in murine plasma is described. A 50-microL-murine plasma aliquot was spiked with an internal standard, indirubine-3-monoxime (IMO), and extracted with 1.25 mL diethyl ether. Dried extracts were reconstituted in methanol-water (8:2, v/v) and 10 microL-volumes were injected onto the HPLC system. Separation was achieved on a Gemini C18 column (150 mm x 2.1 mm ID, particle size 5 microm) using an alkaline eluent (10 mM ammonium hydroxide-methanol (5:95, v/v)). Detection was performed by negative ion electrospray followed by tandem mass spectrometry. The assay quantifies 5-MI in a range from 1 to 500 ng/mL using 50 microL of murine EDTA plasma samples. Validation results demonstrate that 5-MI concentrations can be accurately and precisely quantified in murine plasma. This assay is used to support pre-clinical pharmacologic studies with 5-MI.

CYP2C9 and CYP2C19 polymorphic forms are related to increased indisulam exposure and higher risk of severe hematologic toxicity

PURPOSE

The anticancer agent indisulam is metabolized by the cytochrome P450 of enzymes CYP2C9 and CYP2C19. Polymorphisms of these enzymes may affect the elimination rate of indisulam. Consequently, variant genotypes may be clinically relevant predictors for the risk of developing severe hematologic toxicity. The purposes of this study were to evaluate the effect of genetic variants of CYP2C9 and CYP2C19 on the pharmacokinetics of indisulam and on clinical outcome and to assess the need for pharmacogenetically guided dose adaptation.

EXPERIMENTAL DESIGN

Pharmacogenetic screening of CYP2C polymorphisms was done in 67 patients treated with indisulam. Pharmacokinetic data were analyzed with a population pharmacokinetic model, in which drug elimination was described by a linear and a Michaelis-Menten pathway. The relationships between allelic variants and the elimination pharmacokinetic parameters (CL, V(max), K(m)) were tested using nonlinear mixed-effects modeling. Polymorphisms causing a high risk of dose-limiting neutropenia were identified in a simulation study.

RESULTS

The Michaelis-Menten elimination rate (V(max)) was decreased by 27% (P<0.0001) for heterozygous CYP2C9*3 mutants. Heterozygous CYP2C19*2 and CYP2C19*3 mutations reduced the linear elimination rate (CL) by 38% (P < 0.0001). The risk of severe neutropenia was significantly increased by these mutations and dose reductions of 50 to 100 mg/m(2) per mutated allele may be required to normalize this risk.

CONCLUSIONS

CYP2C9*3, CYP2C19*2, and CYP2C19*3 polymorphisms resulted in a reduced elimination rate of indisulam. Screening for these CYP2C polymorphisms and subsequent pharmacogenetically guided dose adaptation may assist in the selection of an optimized initial indisulam dosage.

Development of a bladder instillation of the indoloquinone anticancer agent EO-9 using tert-butyl alcohol as lyophilization vehicle

The purpose of this research was to develop a stable bladder instillation of EO-9 for the treatment of superficial bladder cancer. First, stability and dissolution studies were performed. Subsequently, the freeze-drying process was optimized by determination of the freeze-drying characteristics of the selected cosolvent/water system and differential scanning calorimetry analysis of the formulation solution. Furthermore, the influence of the freeze-drying process on crystallinity and morphology of the freeze-dried product was determined with x-ray diffraction analysis and scanning electron microscopy, respectively. Subsequently, a reconstitution solution was developed. This study revealed that tert-butyl alcohol (TBA) can be used to both dramatically improve the solubility and stability of EO-9 and to shorten the freeze-drying cycle by increasing the sublimation rate. During freeze drying, 3 TBA crystals were found: TBA hydrate-ice crystals, crystals of TBA hydrate, and a third crystal, probably composed of TBA hydrate crystals containing approximately 90% to 95% TBA. Furthermore, it was shown that crystallization of TBA hydrate was inhibited in the presence of both sodium bicarbonate (NaHCO3) and mannitol. Addition of an annealing step resulted in a minor increase in the crystallinity of the freeze-dried product and formation of the delta-polymorph of mannitol. A stable bladder instillation was obtained after reconstitution of the freeze-dried product (containing 8 mg of EO-9, 20 mg of NaHCO3, and 50 mg of mannitol per vial) to 20 mL with a reconstitution solution composed of propylene glycol/water for injection (WfI)/NaHCO3/sodium edetate 60%/40%/2%/0.02% vol/vol/wt/wt, followed by dilution with WfI to a final volume of 40 mL.

Phase I Pharmacokinetic Study of the Safety and Tolerability of Lapatinib (GW572016) in Combination with Oxaliplatin/Fluorouracil/Leucovorin (FOLFOX4) in Patients with Solid Tumors

PURPOSE

This phase I study was designed to determine the optimally tolerated regimen (OTR), safety, and clinical activity of lapatinib in combination with FOLFOX4 [oxaliplatin/leucovorin/5-fluorouracil (5-FU)] in patients with solid tumors. Furthermore, the pharmacokinetics of lapatinib, oxaliplatin, and 5-FU when given alone and in combination were evaluated.

EXPERIMENTAL DESIGN

This study was conducted in two parts. Part 1 was designed to determine the OTR and part 2 was the pharmacokinetic part of the study. Lapatinib was administered once daily for the entire duration of the study. Leucovorin and oxaliplatin were given concurrently over 2 h as an i.v. infusion, after which 5-FU was given as a bolus followed by continuous infusion over 22 h on day 1. 5-FU and leucovorin administration were repeated in an identical manner on day 2. Cycles were repeated every 2 weeks. Once the OTR was determined, it was to become the dose level for patients included in the pharmacokinetic part of the study.

RESULTS

A total of 34 patients was treated in this study. No dose-limiting toxicities were observed and the OTR was established at 1,500 mg/d lapatinib in combination with the standard FOLFOX4 regimen. Nonhematologic toxicities consisted mainly of nausea, diarrhea, vomiting, fatigue, neuropathy, and mucositis. The most important hematologic toxicity was neutropenia. No drug-drug interactions between lapatinib and the FOLFOX4 regimen were observed.

CONCLUSION

Lapatinib can be safely administered in combination with the standard FOLFOX4 regimen. Further studies are warranted to explore the potential additive antitumor effect of lapatinib in combination with the FOLFOX4 regimen.

Liquid chromatography–tandem mass spectrometric assays for salinomycin in mouse plasma, liver, brain and small intestinal contents and in OptiMEM cell culture medium

Fast and sensitive liquid chromatography-tandem mass spectrometric assays for the determination of salinomycin in mouse plasma, liver, brain and small intestinal contents and in OptiMEM cell culture medium, were developed and validated using simple sample pre-treatment procedures. Tissue samples were homogenized with phosphate buffered saline or, for high levels in liver, with human plasma. After addition of monensin as the internal standard to plasma, homogenate or culture medium and acetonitrile extraction for tissue and plasma, the diluted medium or the supernatant was directly injected into the isocratic chromatographic system using a polar embedded reversed-phase column and formic acid in water-acetonitrile as the eluent. The eluate was completely led into an electrospray interface with positive ionization and the analytes were quantified using triple quadrupole mass spectrometry. The assays were successfully validated in the ranges 10-2000 ng/ml for OptiMEM cell culture medium, 1-2000 ng/ml for plasma and 3-2000 ng/g in liver brain and small intestinal contents. At the lowest levels, the intra-day precisions were < or =9%, inter-day precisions were < or =14% and accuracies were between 91 and 112%. The analytes were chemically stable under all relevant conditions and the assays were applied in different in vitro transport studies and in pharmacokinetic and tissue distribution studies with salinomycin in mice.

Concise Review: Clinical Relevance of Drug–Drug and Herb–Drug Interactions Mediated by the ABC Transporter ABCB1 (MDR1, P‐glycoprotein)

The importance of P-glycoprotein (P-gp) in drug-drug interactions is increasingly being identified. P-gp has been reported to affect the pharmacokinetics of numerous structurally and pharmacologically diverse substrate drugs. Furthermore, genetic variability in the multidrug resistance 1 gene influences absorption and tissue distribution of drugs transported. Inhibition or induction of P-gp by coadministered drugs or food as well as herbal constituents may result in pharmacokinetic interactions leading to unexpected toxicities or undertreatment. On the other hand, modulation of P-gp expression and/or activity may be a useful strategy to improve the pharmacological profile of anticancer P-gp substrate drugs. In recent years, the use of complementary and alternative medicine (CAM), like herbs, food, and vitamins, by cancer patients has increased significantly. CAM use substantially increases the risk for interactions with anticancer drugs, especially because of the narrow therapeutic window of these compounds. However, for most CAMs, it is unknown whether they affect metabolizing enzymes and/or drug transporter activity. Clinically relevant interactions are reported between St John's wort or grapefruit juice and anticancer as well as nonanticancer drugs. CAM-drug interactions could explain, at least in part, the large interindividual variation in efficacy and toxicity associated with drug therapy in both cancer and noncancer patients. The study of drug-drug, food-drug, and herb-drug interactions and of genetic factors affecting pharmacokinetics and pharmacodynamics is expected to improve drug safety and will enable individualized drug therapy. Disclosure of potential conflicts of interest is found at the end of this article.

Phase I Pharmacokinetic and Pharmacodynamic Study of the Oral Protein Kinase C β-Inhibitor Enzastaurin in Combination with Gemcitabine and Cisplatin in Patients with Advanced Cancer

PURPOSE

Enzastaurin targets the protein kinase C and phosphatidylinositol 3-kinase/AKT pathways to reduce tumor angiogenesis and cell proliferation and to induce cell death. A phase I trial was conducted to evaluate the feasibility of combining enzastaurin with gemcitabine and cisplatin.

EXPERIMENTAL DESIGN

Patients with advanced cancer received a 14-day lead-in treatment with oral enzastaurin followed by subsequent 21-day cycles of daily enzastaurin, gemcitabine on days 1 and 8, and cisplatin on day 1. Enzastaurin doses were escalated between 350 mg once daily to 500 mg twice daily, whereas gemcitabine doses were either 1,000 or 1,250 mg/m(2) and cisplatin doses were either 60 or 75 mg/m(2). Circulating endothelial cell numbers and CD146 and CD133 mRNA expression were evaluated as pharmacodynamic markers.

RESULTS

Thirty-three patients (median age, 58 years) were enrolled in seven dose levels. The maximum tolerated dose was not identified. Two dose-limiting toxicities (grade 2 QT interval corrected for heart rate prolongation and grade 3 fatigue) were reported. Other toxicities included grade 3/4 neutropenia (3 of 6 patients), thrombocytopenia (1 of 6 patients), grade 3 leukopenia (2 patients), and fatigue (5 patients). Enzastaurin twice daily (> or =250 mg) resulted in more discontinuations and low-grade toxicities. In the combination, enzastaurin exposures decreased slightly but remained above the target of 1,400 nmol/L, whereas gemcitabine/cisplatin exposures were unaltered. Three patients (9.1%) had partial responses and 13 (39.4%) had stable disease. Measurement of circulating endothelial cell numbers and CD146 and CD133 mRNA expression did not contribute to decision-making on dose escalation.

CONCLUSIONS

Recommended phase II dose is 500 mg enzastaurin once daily, 1,250 mg/m(2) gemcitabine, and 75 mg/m(2) cisplatin. This regimen is well tolerated with no significant alterations in the pharmacokinetic variables of any drug.

Enzymatic digestion as a tool for the LC–MS/MS quantification of large peptides in biological matrices: Measurement of chymotryptic fragments from the HIV-1 fusion inhibitor enfuvirtide and its metabolite M-20 in human plasma

The use of enzymatic digests of the peptide HIV-1 fusion inhibitor enfuvirtide as a tool for the absolute quantification of this polypeptide (MW 4492 Da) in human plasma by LC-MS/MS has been evaluated. Two different methods applying digestion of enfuvirtide with chymotrypsin after solid phase extraction (SPE) of the plasma samples have therefore been developed and validated. One method used a stable isotopically labeled analog of the complete peptide (d60-enfuvirtide) as internal standard (IS) and could use as much as four different chymotryptic fragments for the quantification of enfuvirtide in a range of 100-10,000 ng/ml. Intra- and inter-assay precisions and deviations from the nominal concentrations varied for the different fragments, but were below 9% when the four results were averaged. The other method used a stable isotopically labeled chymotryptic fragment of the peptide (d10-ASLW) as IS. Although this IS does not correct for variations in digestion recovery, it allows the selective quantification of enfuvirtide (100-10,000 ng/ml), besides the quantification of the sum of enfuvirtide and its de-amidated metabolite M-20 (120-12,000 ng/ml). Both methods were suitable for the absolute quantification of enfuvirtide and M-20 in plasma, but proper selection of the fragment(s) used for the quantification appeared crucial when the deuterated fragment was used as IS.