ABC transporters Mdr1a/1b, Bcrp1, Mrp2 and Mrp3 determine the sensitivity to PhIP/DSS-induced colon carcinogenesis and inflammation.

2-Amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) is an abundant dietary carcinogen, formed during high-temperature cooking of meat. In this study, we investigated whether clinically relevant ATP-binding cassette (ABC) efflux transporters can modulate PhIP-induced colorectal carcinogenesis in vivo using wild-type (WT), Bcrp1-/-; Mrp2-/-; Mrp3-/- and Bcrp1-/-; Mdr1a/b-/-; Mrp2-/- mice. We used a physiological mouse model of colorectal cancer; a combination of a single high-dose oral PhIP administration (200 mg/kg), followed by administering a colonic inflammatory agent, dextran sodium sulfate (DSS), in drinking water for 7 days. Pilot experiments showed that both knockout strains were more sensitive to DSS-induced colitis compared to WT mice. Lack of these transporters in mice also led to clearly altered disposition of activated PhIP metabolites after a high-dose oral PhIP administration. The results suggest that Mdr1a/1b, Bcrp1 and Mrp2 contributed to biliary excretion and Mrp3 to sinusoidal secretion of the pre-carcinogenic metabolite N2-OH-PhIP. The levels of a genotoxicity marker, PhIP-5-sulphate, were at least 4- and 17-fold reduced in the intestinal tissue and intestinal content of both knockout strains compared to WT mice. In line with these findings, the level of colon carcinogenesis was reduced by two- to four-fold in both knockout strains compared to WT mice when PhIP and DSS treatments were combined. Thus, perhaps counterintuitively, reduced activity of these ABC transporters may in part protect from PhIP-induced colon carcinogenesis. Collectively, these data suggest that ABC transporters are important in protecting the body from inflammatory agents such as DSS, in the disposition of carcinogenic metabolites, and in determining the sensitivity to dietary PhIP-induced carcinogenesis.

Investigational study of tamoxifen phase I metabolites using chromatographic and spectroscopic analytical techniques.

A comprehensive overview is presented of currently known phase I metabolites of tamoxifen consisting of their systematic name and molecular structure. Reference standards are utilized to elucidate the MS(n) fragmentation patterns of these metabolites using a linear ion trap mass spectrometer. UV-absorption spectra are recorded and absorption maxima are defined. Serum extracts from ten breast cancer patients receiving 40mg tamoxifen once daily were qualitatively analyzed for tamoxifen phase I metabolites using a liquid chromatography-tandem mass spectrometry set-up. In total, 19 metabolites have been identified in these serum samples. Additionally a synthetic method for the preparation of the putative metabolite 3',4'-dihydroxytamoxifen is described.

Development and validation of a quantitative assay for the determination of tamoxifen and its five main phase I metabolites in human serum using liquid chromatography coupled with tandem mass spectrometry.

A sensitive bioanalytical assay for the quantitative determination of tamoxifen and five of its phase I metabolites (N-desmethyltamoxifen, N-desmethyl-4-hydroxytamoxifen, N-desmethyl-4'-hydroxytamoxifen, 4-hydroxytamoxifen and 4'-hydroxytamoxifen) in serum is described. The method has been fully validated at ranges covering steady-state serum concentrations in patients receiving therapeutic dosages of tamoxifen. The bioanalytical assay is based on reversed phase liquid chromatography coupled with tandem mass spectrometry in the positive ion mode using multiple reaction monitoring for drug (-metabolite) quantification. The sample pretreatment consists of protein precipitation with acetonitrile using only 50 µL of serum. In the past, numerous assays have been developed by other groups for the quantification of tamoxifen and its phase I metabolites. However, the number of metabolites included in these studies is very limited and only very few of these assays have been fully validated. A liquid chromatography tandem mass spectrometry assay for the quantification of tamoxifen and four phase I metabolites in human serum that was previously developed by our group is now explicitly improved and described herein. Time of analysis has been reduced by 50% and sensitivity was increased by a reduction of the lower limit of quantification from 1.0 to 0.2 ng/mL for 4-hydroxytamoxifen and 4'-hydroxytamoxifen. Additionally, two phase I metabolites that have never been quantified in human serum hitherto, namely 4'-hydroxytamoxifen and N-desmethyl-4'-hydroxytamoxifen, were included in this assay. Validation results demonstrate an accurate and precise quantification of tamoxifen, N-desmethyltamoxifen, N-desmethyl-4-hydroxytamoxifen, N-desmethyl-4'-hydroxytamoxifen, 4-hydroxytamoxifen and 4'-hydroxytamoxifen in human serum. The applicability of the assay was demonstrated and it is now successfully used to support clinical studies in which patient-specific dose optimization is performed based on serum concentrations of tamoxifen metabolites.

Development and validation of a liquid chromatography-tandem mass spectrometry assay for the analysis of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) and its metabolite 2-hydroxyamino-1-methyl-6-phenylimidazo[4,5-b]pyridine (N-OH-PhIP) in plasma, urine, bile, intestinal contents, faeces and eight selected tissues from mice.

The development and validation of a bioanalytical assay is described for the simultaneous analysis of 2-amino-1-methyl-6-phenylimidazo[4-5-b]pyridine (PhIP) and its main metabolite 2-hydroxyamino-1-methyl-6-phenylimidazo[4,5-b]pyridine (N-OH-PhIP) in plasma, urine, faeces, bile, liver, kidney, testis, spleen, brain, as well as colon-, cecum- and small intestinal tissue and contents from mice. The effect of the matrix on the accuracy of the method was extensively investigated. The bioanalytical assay is based on reversed phase liquid chromatography coupled with tandem mass spectrometry in the positive ion mode using multiple reaction monitoring for analyte quantification. The assay is validated from 1 to 250 ng/mL and the sample pretreatment consists of protein precipitation with acetonitrile using only 100 microL matrix (plasma, bile diluted in 4% (m/v) BSA, intestinal contents, faeces and tissue samples homogenized in 4% (m/v) BSA). The measured concentrations of PhIP and N-OH-PhIP in homogenates were expressed in ng/mL. Based on the weight of the isolated intestinal contents, faeces or tissue the amount of PhIP and N-OH-PhIP per mass unit intestinal content, faeces or tissue was calculated. The validated range for PhIP in urine is from 10 to 1000 ng/mL using 20 microL urine. For N-OH-PhIP quantification, mouse urine was diluted 100 x in blank human urine to compensate for matrix effects. The developed method is simple, robust and reproducible. The applicability of the method was demonstrated and the assay could be successfully used to support in vivo toxicokinetics studies of PhIP and N-OH-PhIP in mice.

Review on the analysis of 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine and its phase I and phase II metabolites in biological matrices, foodstuff and beverages.

The heterocyclic aromatic amine, 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP), has been shown to be carcinogenic in rodents, mice and rats. Following phase I N-hydroxylation and phase II esterification PhIP exerts its carcinogenic effect by binding to DNA purines. Quantitative and qualitative analysis of its bioactivated metabolites as well as it detoxification products is important in studying its biological effects and inter- and intra-individual exposures. A review is presented with an extensive coverage of publications specifically reporting on the analysis of PhIP and its phase I and II metabolites in biological matrices, foodstuff and beverages. Analytical techniques such as liquid and gas chromatography coupled with various detection techniques (mass spectrometry, ultraviolet or fluorescence detection) were mostly applied. We conclude that since the initial identification of PhIP in 1986 a large set of assays has been developed for the analysis of PhIP and its phase I and phase II metabolites in a wide range of matrices, these included food products and biological samples such as plasma, urine and faeces. In addition, it was shown that numerous metabolites were recovered and identified. Thus, we conclude that liquid chromatography coupled to mass spectrometry is clearly the method of choice for sensitive qualitative as well as quantitative analysis with high selectivity and reaching lower quantification levels in the sub pg/mL range. The main aim of this review is that it can be used by other researchers as a resource for method development and optimization of analytical methods of PhIP and its carcinogenic or detoxification products.

Bioanalytical methods for determination of tamoxifen and its phase I metabolites: a review.

The selective estrogen receptor modulator tamoxifen is used in the treatment of early and advanced breast cancer and in selected cases for breast cancer prevention in high-risk subjects. The cytochrome P450 enzyme system and flavin-containing monooxygenase are responsible for the extensive metabolism of tamoxifen into several phase I metabolites that vary in toxicity and potencies towards estrogen receptor (ER) alpha and ER beta. An extensive overview of publications on the determination of tamoxifen and its phase I metabolites in biological samples is presented. In these publications techniques were used such as capillary electrophoresis, liquid, gas and thin layer chromatography coupled with various detection techniques (mass spectrometry, ultraviolet or fluorescence detection, liquid scintillation counting and nuclear magnetic resonance spectroscopy). A trend is seen towards the use of liquid chromatography coupled to mass spectrometry (LC-MS). State-of-the-art LC-MS equipment allowed for identification of unknown metabolites and quantification of known metabolites reaching lower limit of quantification levels in the sub pg mL(-1) range. Although tamoxifen is also metabolized into phase II metabolites, the number of publications reporting on phase II metabolism of tamoxifen is scarce. Therefore the focus of this review is on phase I metabolites of tamoxifen. We conclude that in the past decades tamoxifen metabolism has been studied extensively and numerous metabolites have been identified. Assays have been developed for both the identification and quantification of tamoxifen and its metabolites in an array of biological samples. This review can be used as a resource for method transfer and development of analytical methods used to support pharmacokinetic and pharmacodynamic studies of tamoxifen and its phase I metabolites.

Development and validation of a quantitative assay for the analysis of tamoxifen with its four main metabolites and the flavonoids daidzein, genistein and glycitein in human serum using liquid chromatography coupled with tandem mass spectrometry.

The development and validation of a bioanalytical assay is described for the simultaneous analysis in human serum of tamoxifen, four of its main metabolites and three flavonoids, which are known constituents in alternative medicine and dietary supplements often used by breast cancer patients. The method has been fully validated at linear ranges covering steady-state serum concentrations in patients who receive therapeutic dosages of tamoxifen. The wide range also allows for quantification of large inter-patient fluctuations of flavonoid concentrations. The bioanalytical assay is based on reversed phase liquid chromatography coupled with tandem mass spectrometry in the positive ion mode using multiple reaction monitoring for drug (-metabolite) quantification. The sample pretreatment consists of a protein precipitation with acetonitrile using only 50 microL serum. The described method is simple, robust and reproducible with inter- and intra-assay accuracies within 85-115%. The applicability of the assay was demonstrated and it is now successfully used to study the in vivo pharmacokinetics of tamoxifen, its main metabolites and flavonoids in human serum of patients receiving tamoxifen.