Characterization of tamoxifen and 4-hydroxytamoxifen glucuronidation by human UGT1A4 variants

Development and validation of a liquid chromatography-mass spectrometry assay for quantification of Z- and E- isomers of endoxifen and its metabolites in plasma from women with estrogen receptor positive breast cancer

The selective estrogen receptor modifier tamoxifen (TAM) is widely used for the treatment of women with estrogen receptor positive (ER+ ) breast cancer. Endoxifen (ENDX) is a potent, active metabolite of TAM and is important for TAM's clinical activity. While multiple papers have been published regarding TAM metabolism, few studies have examined or quantified the metabolism of ENDX. To quantify ENDX and its metabolites in patient plasma samples, we have developed and validated a rapid, sensitive, and specific liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the quantitative determination of the E- and Z-isomers of ENDX (0.5-500 ng/ml) and the ENDX metabolites norendoxifen (1-500 and 0.5-500 ng/ml E and Z, respectfully), ENDX catechol (3.075-307.5 and 1.92-192 ng/ml E and Z, respectfully), 4'-hydroxy ENDX (0.33-166.5 and 0.33-333.5 ng/ml E and Z, respectfully), ENDX methoxycatechol (0.3-300 and 0.2-200 ng/ml E and Z, respectfully), and ENDX glucuronide (2-200 and 3-300 ng/ml E and Z, respectfully) in human plasma. Chromatographic separation was accomplished on a HSS T3 precolumn attached to an Poroshell 120 EC-C18 analytical column using 0.1 % formic acid/water and 0.1 % formic acid/methanol as eluents followed by MS/MS detection. The analytical run time was 6.5 min. Standard curves were linear (R2 ≥ 0.98) over the concentration ranges. The intra- and inter-day precision and accuracy, determined at high-, middle-, and low-quality control concentrations for all analytes, were within the acceptable range of 85 % and 115 %. The average percent recoveries were all above 90 %. The method was successfully applied to clinical plasma samples from a Phase I study of daily oral Z-ENDX.

Electrophoretic deposition of polyaniline nanofibers on a stainless steel wire as an adsorbent for determination of tamoxifen by SPME/GC-FID in urine samples

Polyaniline nanofiber films were fabricated on the surface of stainless steel wire via a controllable and simple electrophoretic deposition route from a nonaqueous colloidal suspension consisting of polyaniline nanofibers. The prepared coating material was then characterized by field emission scanning electron microscopy equipped with energy dispersive spectroscopy and elemental mapping analysis. The fabricated polyaniline film-coated stainless steel wire was then utilized as an effective and novel sorbent phase for solid-phase microextraction of tamoxifen for subsequent gas chromatography/flame ionization detection of this anticancer drug. Parameters consisting of the temperature, extraction time, salt concentration, agitation speed, pH, temperature and time of desorption were studied and optimized using a one-at-a-time strategy. Under the optimum conditions, detection limit (S/N = 3), the limit of quantification (10/3 limit of detection), linear dynamic range, repeatability and reproducibility values of 0.51 μg L^-1 , 1.7 μg L^-1 , 2-1,130 μg L^-1 , 5.7% and 8.6% were attained, respectively. The prepared fiber can preserve 90% of its efficacy after 20 consecutive cycles, demonstrating the suitable thermal stability and cyclability of the proposed solid-phase microextraction coating material for the determination of tamoxifen by gas chromatography/flame ionization detection. The route was effectively utilized to determine tamoxifen in urine samples, with relative recoveries ranging from 89 to 106%.

Metabolic Profiles of New Unsymmetrical Bisacridine Antitumor Agents in Electrochemical and Enzymatic Noncellular Systems and in Tumor Cells

New unsymmetrical bisacridines (UAs) demonstrated high activity not only against a set of tumor cell lines but also against human tumor xenografts in nude mice. Representative UA compounds, named C-2028, C-2045 and C-2053, were characterized in respect to their physicochemical properties and the following studies aimed to elucidate the role of metabolic transformations in UAs action. We demonstrated with phase I and phase II enzymes in vitro and in tumors cells that: (i) metabolic products generated by cytochrome P450 (P450), flavin monooxygenase (FMO) and UDP-glucuronosyltransferase (UGT) isoenzymes in noncellular systems retained the compound’s dimeric structures, (ii) the main transformation pathway is the nitro group reduction with P450 isoenzymes and the metabolism to N-oxide derivative with FMO1, (iii), the selected UGT1 isoenzymes participated in the glucuronidation of one compound, C-2045, the hydroxy derivative. Metabolism in tumor cells, HCT-116 and HT-29, of normal and higher UGT1A10 expression, respectively, also resulted in the glucuronidation of only C-2045 and the specific distribution of all compounds between the cell medium and cell extract was demonstrated. Moreover, P4503A4 activity was inhibited by C-2045 and C-2053, whereas C-2028 affected UGT1A and UGT2B action. The above conclusions indicate the optimal strategy for the balance among antitumor therapeutic efficacy and drug resistance in the future antitumor therapy.

(E)-4-(3-(3-(4-Methoxyphenyl)acryloyl)phenoxy)butyl 2-Hydroxybenzoate

A new hybrid compound of chalcone-salicylate (title compound) has been successfully synthesized using a linker mode approach under reflux condition. The structure of the title compound has been established by spectroscopic analysis including UV-Vis, FT-IR, HRMS, 1D, and 2D NMR. Then, computational approach was also applied in this study through molecular docking and MD simulation to explore its potency against breast cancer. The results of the molecular docking study showed that the title compound exhibited more negative value of binding free energy (−8.15 kcal/mol) than tamoxifen (−7.00 kcal/mol). In addition, no striking change in the positioning of the interacting residues was recorded before and after the MD simulations. Based on the studies, it can be predicted that the title compound has a cytotoxic activity potency against breast cancer through ERα inhibition and it presumably can be developed as anticancer agent candidate.

Recent advances in the personalized treatment of estrogen receptor-positive breast cancer with tamoxifen: a focus on pharmacogenomics

Introduction: Tamoxifen is still an important drug in hormone-dependent breast cancer therapy. Personalization of its clinical use beyond hormone receptor positivity could improve the substantial variability of the treatment response.Areas covered: The overview of the current evidence for the treatment personalization using therapeutic drug monitoring, or using genetic biomarkers including CYP2D6 is provided. Although many studies focused on the PK aspects or the impact of CYP2D6 variability the translation into clinical routine is not clearly defined due to the inconsistent clinical outcome data.Expert opinion: We believe that at least the main candidate factors, i.e. CYP2D6 polymorphism, CYP2D6 inhibition, endoxifen serum levels may become important predictors of clinical relevance for tamoxifen treatment personalization in the future. To achieve this aim, however, further research should take into consideration more precise characterization of the disease, epigenetic factors and also utilize an appropriately powered multifactorial approach instead of a single gene evaluating studies.

Role of l- and d-Menthol in the Glucuronidation and Detoxification of the Major Lung Carcinogen, NNAL

Menthol, which creates mint flavor and scent, is often added to tobacco in both menthol and nonmenthol cigarettes. A potent tobacco carcinogen, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), is extensively metabolized to its equally carcinogenic metabolite 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) as (R)- or (S)-NNAL enantiomers. NNAL is detoxified by UDP-glucuronosyltransferase (UGT) enzymes, with glucuronidation occurring on either NNAL's pyridine ring nitrogen (NNAL-N-Gluc) or the chiral alcohol [(R)- or (S)-NNAL-O-Gluc]. To characterize a potential effect by menthol on NNAL glucuronidation, in vitro menthol glucuronidation assays and menthol inhibition of NNAL-Gluc formation assays were performed. Additionally, NNAL and menthol glucuronides (MG) were measured in the urine of smokers (n = 100) from the Southern Community Cohort Study. UGTs 1A9, 1A10, 2A1, 2A2, 2A3, 2B4, 2B7, and 2B17 all exhibited glucuronidating activity against both l- and d-menthol. In human liver microsomes, both l- and d-menthol inhibited the formation of each NNAL-Gluc, with a stereospecific difference observed between the formation of (R)-NNAL-O-Gluc and (S)-NNAL-O-Gluc in the presence of d-menthol but not l-menthol. With the exception of three nonmenthol cigarette smokers, urinary MG was detected in all menthol and nonmenthol smokers, with l-MG comprising >98% of total urinary MG. Levels of urinary NNAL-N-Gluc were significantly (P < 0.05) lower among subjects with high levels of total urinary MG; no significant changes in free NNAL were observed. These data suggest that the presence of menthol could lead to increases in alternative, activating metabolic pathways of NNAL in tobacco target tissues, increasing the opportunity for NNAL to damage DNA and lead to the development of tobacco-related cancers. SIGNIFICANCE STATEMENT: High levels of the major menthol metabolite, menthol-glucuronide, was observed in the urine of smokers of either menthol or nonmenthol cigarettes. The fact that a significant inverse correlation was observed between the levels of urinary menthol-glucuronide and NNAL-N-glucuronide, a major detoxification metabolite of the tobacco carcinogen, NNK, suggests that menthol may inhibit clearance of this important tobacco carcinogen.

Prominent Stereoselectivity of NNAL Glucuronidation in Upper Aerodigestive Tract Tissues

Tobacco specific nitrosamines (TSNAs) are among the most potent carcinogens found in cigarettes and smokeless tobacco products. Decreases in TSNA detoxification, particularly 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK), have been associated with tobacco-related cancer incidence. NNK is metabolized by carbonyl reduction to its major carcinogenic metabolite, 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL), which is detoxified by glucuronidation at the nitrogen within the pyridine ring or at the chiral alcohol to form four glucuronide products: (R)-NNAL-O-Gluc, (S)-NNAL-O-Gluc, (R)-NNAL-N-Gluc, (S)-NNAL-N-Gluc. Stereoselective NNAL-Gluc formation and the relative expression of NNAL-glucuronidating UGTs (1A4, 1A9, 1A10, 2B7, 2B10, 2B17) were analyzed in 39 tissue specimens from the upper aerodigestive tract (esophagus (n = 13), floor of mouth (n = 4), larynx (n = 9), tongue (n = 7), and tonsil (n = 6)). All pooled tissue types preferentially formed (R)-NNAL-O-Gluc in the presence of racemic-NNAL; only esophagus exhibited any detectable formation of (S)-NNAL-O-Gluc. For every tissue type examined, UGT1A10 exhibited the highest relative expression levels among the NNAL-O-glucuronidating UGTs, ranging from 36% (tonsil) to 49% (esophagus), followed by UGT1A9 > UGT2B7 > UGT2B17. UGT1A10 also exhibited similar or higher levels of expression as compared to both NNAL-N-glucuronidating UGTs, 1A4 and 2B10. In a screening of cells expressing individual UGT enzymes, all NNAL glucuronidating UGTs exhibited some level of stereospecific preference for individual NNAL enantiomers, with UGTs 1A10 and 2B17 forming primarily (R)-NNAL-O-Gluc. These data suggest that UGTs 1A10 and 2B17 may be important enzymes in the detoxification of TSNAs like NNK in tissues of the upper aerodigestive tract.

The UDP-Glycosyltransferase (UGT) Superfamily: New Members, New Functions, and Novel Paradigms

UDP-glycosyltransferases (UGTs) catalyze the covalent addition of sugars to a broad range of lipophilic molecules. This biotransformation plays a critical role in elimination of a broad range of exogenous chemicals and by-products of endogenous metabolism, and also controls the levels and distribution of many endogenous signaling molecules. In mammals, the superfamily comprises four families: UGT1, UGT2, UGT3, and UGT8. UGT1 and UGT2 enzymes have important roles in pharmacology and toxicology including contributing to interindividual differences in drug disposition as well as to cancer risk. These UGTs are highly expressed in organs of detoxification (e.g., liver, kidney, intestine) and can be induced by pathways that sense demand for detoxification and for modulation of endobiotic signaling molecules. The functions of the UGT3 and UGT8 family enzymes have only been characterized relatively recently; these enzymes show different UDP-sugar preferences to that of UGT1 and UGT2 enzymes, and to date, their contributions to drug metabolism appear to be relatively minor. This review summarizes and provides critical analysis of the current state of research into all four families of UGT enzymes. Key areas discussed include the roles of UGTs in drug metabolism, cancer risk, and regulation of signaling, as well as the transcriptional and posttranscriptional control of UGT expression and function. The latter part of this review provides an in-depth analysis of the known and predicted functions of UGT3 and UGT8 enzymes, focused on their likely roles in modulation of levels of endogenous signaling pathways.

Meta-analysis of the Influence of UGT Genetic Polymorphisms on Lamotrigine Concentration

Uridine 5'-diphospho-glucuronosyltransferases (UGTs) are involved in the metabolism of lamotrigine, but whether the UGT1A4 and UGT2B7 genetic polymorphisms affect lamotrigine concentration remains controversial. Thus, the objective of this meta-analysis was to analyse the influence of UGT1A4 and UGT2B7 genetic polymorphisms on lamotrigine concentration. Through searching, screening, selection, data extraction and quantitative analyses, the influence of UGT1A4 and UGT2B7 genetic polymorphisms on lamotrigine concentration-to-dose ratio (CDR) was assessed by meta-analysis of nine studies. Neither UGT1A4 70C>A nor 142T>G significantly affected lamotrigine CDR values (standardized difference in means [SDM] = 0.433, 95% confidence interval [CI] = -0.380-1.302; SDM = -0.458, 95% CI = -1.141-0.224, respectively). Only the UGT2B7 -161C>T homozygous variant had significantly higher CDR values than the wild-type (WT) and heterozygous variant (SDM = 0.634, 95% CI = 0.056-1.222). In conclusion, CDR of lamotrigine was significantly higher for the UGT2B7 -161C>T homozygous variant than for the WT and heterozygous variant. Thus, UGT2B7 -161C>T homozygous variant needs to receive reduced dose.

The formation of estrogen-like tamoxifen metabolites and their influence on enzyme activity and gene expression of ADME genes

Tamoxifen, a standard therapy for breast cancer, is metabolized to compounds with anti-estrogenic as well as estrogen-like action at the estrogen receptor. Little is known about the formation of estrogen-like metabolites and their biological impact. Thus, we characterized the estrogen-like metabolites tamoxifen bisphenol and metabolite E for their metabolic pathway and their influence on cytochrome P450 activity and ADME gene expression. The formation of tamoxifen bisphenol and metabolite E was studied in human liver microsomes and Supersomes™. Cellular metabolism and impact on CYP enzymes was analyzed in upcyte® hepatocytes. The influence of 5 µM of tamoxifen, anti-estrogenic and estrogen-like metabolites on CYP activity was measured by HPLC MS/MS and on ADME gene expression using RT-PCR analyses. Metabolite E was formed from tamoxifen by CYP2C19, 3A and 1A2 and from desmethyltamoxifen by CYP2D6, 1A2 and 3A. Tamoxifen bisphenol was mainly formed from (E)- and (Z)-metabolite E by CYP2B6 and CYP2C19, respectively. Regarding phase II metabolism, UGT2B7, 1A8 and 1A3 showed highest activity in glucuronidation of tamoxifen bisphenol and metabolite E. Anti-estrogenic metabolites (Z)-4-hydroxytamoxifen, (Z)-endoxifen and (Z)-norendoxifen inhibited the activity of CYP2C enzymes while tamoxifen bisphenol consistently induced CYPs similar to rifampicin and phenobarbital. On the transcript level, highest induction up to 5.6-fold was observed for CYP3A4 by tamoxifen, (Z)-4-hydroxytamoxifen, tamoxifen bisphenol and (E)-metabolite E. Estrogen-like tamoxifen metabolites are formed in CYP-dependent reactions and are further metabolized by glucuronidation. The induction of CYP activity by tamoxifen bisphenol and the inhibition of CYP2C enzymes by anti-estrogenic metabolites may lead to drug–drug-interactions.

Pharmacogenetics of UGT1A4, UGT2B7 and UGT2B15 and Their Influence on Tamoxifen Disposition in Asian Breast Cancer Patients

Tamoxifen (TAM) is an established endocrine treatment for all stages of oestrogen receptor (ER)-positive breast cancer. Its complex metabolism leads to the formation of multiple active and inactive metabolites. One of the main detoxification and elimination pathways of tamoxifen and its active metabolites, 4-hydroxytamoxifen (4-OHT) and endoxifen, is via glucuronidation catalysed by uridine 5'-diphospho-glucuronosyltransferases (UGTs). However, few studies have comprehensively examined the impact of variations in the genes encoding the major hepatic UGTs on the disposition of tamoxifen and its metabolites. In the present study, we systematically sequenced exons, exon/intron boundaries, and flanking regions of UGT1A4, UGT2B7 and UGT2B15 in 240 healthy subjects of different Asian ethnicities (Chinese, Malays and Indians) to identify haplotype tagging single nucleotide polymorphisms. Subsequently, 202 Asian breast cancer patients receiving tamoxifen were genotyped for 50 selected variants in the three UGT genes to comprehensively investigate their associations with steady-state plasma levels of tamoxifen, its active metabolites and their conjugated counterparts. The UGT1A4 haplotype (containing variant 142T>G, L48 V defining the *3 allele) was strongly associated with higher plasma levels of TAM-N-glucuronide, with a twofold higher metabolic ratio of TAM-N-glucuronide/TAM observed in carriers of this haplotype upon covariate adjustment (P < 0.0001). Variants in UGT2B7 were not associated with altered O-glucuronidation of both 4-OHT and endoxifen, while UGT2B15 haplotypes had a modest effect on (E)-endoxifen plasma levels after adjustment for CYP2D6 genotypes. Our findings highlight the influence of UGT1A4 haplotypes on tamoxifen disposition in Asian breast cancer patients, while genetic variants in UGT2B7 and UGT2B15 appear to be of minor importance.

The role of glucuronidation in drug resistance

The final therapeutic effect of a drug candidate, which is directed to a specific molecular target strongly depends on its absorption, distribution, metabolism and excretion (ADME). The disruption of at least one element of ADME may result in serious drug resistance. In this work we described the role of one element of this resistance: phase II metabolism with UDP-glucuronosyltransferases (UGTs). UGT function is the transformation of their substrates into more polar metabolites, which are better substrates for the ABC transporters, MDR1, MRP and BCRP, than the native drug. UGT-mediated drug resistance can be associated with (i) inherent overexpression of the enzyme, named intrinsic drug resistance or (ii) induced expression of the enzyme, named acquired drug resistance observed when enzyme expression is induced by the drug or other factors, as food-derived compounds. Very often this induction occurs via ligand binding receptors including AhR (aryl hydrocarbon receptor) PXR (pregnane X receptor), or other transcription factors. The effect of UGT dependent resistance is strengthened by coordinate action and also a coordinate regulation of the expression of UGTs and ABC transporters. This coupling of UGT and multidrug resistance proteins has been intensively studied, particularly in the case of antitumor treatment, when this resistance is "improved" by differences in UGT expression between tumor and healthy tissue. Multidrug resistance coordinated with glucuronidation has also been described here for drugs used in the management of epilepsy, psychiatric diseases, HIV infections, hypertension and hypercholesterolemia. Proposals to reverse UGT-mediated drug resistance should consider the endogenous functions of UGT.

Stereospecific Metabolism of the Tobacco-Specific Nitrosamine, NNAL

Among the most potent carcinogens in tobacco are the tobacco-specific nitrosamines (TSNAs), with 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) being the most potent as well as one of the most abundant. NNK is extensively metabolized to the equally carcinogenic 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL). Of the two NNAL enantiomers, (S)-NNAL not only appears to be preferentially glucuronidated and excreted in humans but also exhibits higher stereoselective tissue retention in mice and humans and has been shown to be more carcinogenic in mice than its (R) counterpart. Due to the differential carcinogenic potential of the NNAL enantiomers, it is increasingly important to know which UGT enzyme targets the specific NNAL enantiomers for glucuronidation. To examine this, a chiral separation method was developed to isolate enantiomerically pure (S)- and (R)-NNAL. Comparison of NNAL glucuronides (NNAL-Glucs) formed in reactions of UGT2B7-, UGT2B17-, UGT1A9-, and UGT2B10-overexpressing cell microsomes with pure NNAL enantiomers showed large differences in kinetics for (S)- versus (R)-NNAL, indicating varying levels of enantiomeric preference for each enzyme. UGT2B17 preferentially formed (R)-NNAL-O-Gluc, and UGT2B7 preferentially formed (S)-NNAL-O-Gluc. When human liver microsomes (HLM) were independently incubated with each NNAL enantiomer, the ratio of (R)-NNAL-O-Gluc to (S)-NNAL-O-Gluc formation in HLM from subjects exhibiting the homozygous deletion UGT2B17 (*2/*2) genotype was significantly lower (p = 0.012) than that with HLM from wild-type (*1/*1) subjects. There was a significant trend (p = 0.015) toward a decreased (R)-NNAL-O-Gluc/(S)-NNAL-O-Gluc ratio as the copy number of the UGT2B17*2 deletion allele increased. These data demonstrate that variations in the expression or activity of specific UGTs may affect the clearance of specific NNAL enantiomers known to induce tobacco-related cancers.

Impacts of the Glucuronidase Genotypes UGT1A4, UGT2B7, UGT2B15 and UGT2B17 on Tamoxifen Metabolism in Breast Cancer Patients

Tamoxifen is used to prevent and treat estrogen-dependent breast cancer. It is described as a prodrug since most of its antiestrogen effects are exerted through its hydroxylated metabolites 4-OH-tamoxifen and endoxifen. In prior work, we correlated optimal plasma levels of these metabolites with certain genotypes of CYP2D6 and SULT1A2. This descriptive study examines correlations between concentrations of tamoxifen's glucuronide metabolites and genotypes UGT1A4 Pro24Thr, UGT1A4 Leu48Val, UGT2B7 His268Tyr, UGT2B15 Asp85YTyr UGT2B15 Lys523Thr and UGT2B17del in 132 patients with estrogen receptor-positive breast cancer under treatment with tamoxifen. Patients were genotyped by real-time and conventional PCR-RFLP. The glucuronides 4-OH-tamoxifen-N-glucuronide, 4-OH-tamoxifen-O-glucuronide and endoxifen-O-glucuronide were isolated from blood plasma and quantified using a high-pressure liquid chromatography-tandem mass spectrometry system. Individuals who were homozygous for UGT1A448VAL showed significantly lower mean concentrations of both glucuronide metabolites compared to subjects genotyped as wt/wt plus wt/48Val (p=0.037 and p=0.031, respectively). Women homozygous for UGT2B7268Tyr also showed mean substrate/product ratios of 4-OH-tamoxifen/4-OH-tamoxifen-O-glucuronide and 4-OH-tamoxifen/4-OH-tamoxifen-N-glucuronide indicative of reduced glucuronidase activity compared to wt homozygotes or to heterozygotes for the polymorphism (p=0.005 and p=0.003, respectively). In contrast, UGT2B15 Lys523Thr and UGT2B17del were associated with possibly increased enzyme activity. Patients with at least one variant allele UGT2B15523Thr showed significantly higher 4-OH-tamoxifen-O-glucuronide and endoxifen-glucuronide levels (p=0.023 and p=0.025, respectively) indicating a variant gene-dose effect. Higher 4-OH-tamoxifen-N-glucuronide levels observed in UGT2B17del genotypes (p=0.042) could be attributed to a mechanism that compensates for the greater expression of other genes in UGT2B17 del/del individuals. Our observations suggest that patients carrying mutations UGT1A448Val, UGT2B7268Tyr or with wt genotypes for UGT2B17nodel and UGT2B15523Lys could be the best candidates for a good response to tamoxifen therapy in terms of eliciting effective plasma active tamoxifen metabolite levels. However, additional studies examining the effects of UGT genotype on overall patient response to TAM are needed to further examine the role of UGT polymorphisms in the therapeutic efficacy of TAM.

Induction of UDP-glucuronosyltransferase 2B15 gene expression by the major active metabolites of tamoxifen, 4-hydroxytamoxifen and endoxifen, in breast cancer cells

We previously reported upregulation of UGT2B15 by 17β-estradiol in breast cancer MCF7 cells via binding of the estrogen receptor α (ERα) to an estrogen response unit (ERU) in the proximal UGT2B15 promoter. In the present study, we show that this ERα-mediated upregulation was significantly reduced by two ER antagonists (fulvestrant and raloxifene) but was not affected by a third ER antagonist, 4-hydroxytamoxifen (4-OHTAM), a major active tamoxifen (TAM) metabolite. Furthermore, we found that, similar to 17β-estradiol, 4-OHTAM and endoxifen (another major active TAM metabolite) elevated UGT2B15 mRNA levels, and that this stimulation was significantly abrogated by fulvestrant. Further experiments using 4-OHTAM revealed a critical role for ERα in this regulation. Specifically; knockdown of ERα expression by anti-ERα small interfering RNA reduced the 4-OHTAM-mediated induction of UGT2B15 expression; 4-OHTAM activated the wild-type but not the ERU-mutated UGT2B15 promoter; and chromatin immunoprecipitation assays showed increased ERα occupancy at the UGT2B15 ERU in MCF7 cells upon exposure to 4-OHTAM. Together, these data indicate that both 17β-estradiol and the antiestrogen 4-OHTAM upregulate UGT2B15 in MCF7 cells via the same ERα-signaling pathway. This is consistent with previous observations that both 17β-estradiol and TAM upregulate a common set of genes in MCF7 cells via the ER-signaling pathway. As 4-OHTAM is a UGT2B15 substrate, the upregulation of UGT2B15 by 4-OHTAM in target breast cancer cells is likely to enhance local metabolism and inactivation of 4-OHTAM within the tumor. This represents a potential mechanism that may reduce TAM therapeutic efficacy or even contribute to the development of acquired TAM resistance.

Frequencies of UGT1A4*2 (P24T) and *3 (L48V) and their effects on serum concentrations of lamotrigine

The gene encoding uridine diphosphate glucuronosyltransferase (UGT) 1A4 shows considerable polymorphism. Several common drugs are metabolised by UGT1A4, among them lamotrigine (LTG). Experimental and clinical studies suggest that certain variants of UGT1A4 are associated with altered enzyme activity. However, results are conflicting. This clinical study aimed to investigate the frequencies of two common UGT1A4 variants, *2 (P24T) and *3 (L48V), and their potential effects on serum concentrations of LTG. The *2 variant was associated with a trend towards higher serum concentrations, while the *3 variant was associated with significantly lower serum concentrations of LTG. The calculated allele frequencies were in the same range as in earlier studies on Caucasian populations. To our knowledge, this is the first study suggesting a clinical effect of UGT1A4*2. Further study is needed to confirm this finding.

Transcriptional regulation of human UDP-glucuronosyltransferase genes

Glucuronidation is an important metabolic pathway for many small endogenous and exogenous lipophilic compounds, including bilirubin, steroid hormones, bile acids, carcinogens and therapeutic drugs. Glucuronidation is primarily catalyzed by the UDP-glucuronosyltransferase (UGT) 1A and two subfamilies, including nine functional UGT1A enzymes (1A1, 1A3-1A10) and 10 functional UGT2 enzymes (2A1, 2A2, 2A3, 2B4, 2B7, 2B10, 2B11, 2B15, 2B17 and 2B28). Most UGTs are expressed in the liver and this expression relates to the major role of hepatic glucuronidation in systemic clearance of toxic lipophilic compounds. Hepatic glucuronidation activity protects the body from chemical insults and governs the therapeutic efficacy of drugs that are inactivated by UGTs. UGT mRNAs have also been detected in over 20 extrahepatic tissues with a unique complement of UGT mRNAs seen in almost every tissue. This extrahepatic glucuronidation activity helps to maintain homeostasis and hence regulates biological activity of endogenous molecules that are primarily inactivated by UGTs. Deciphering the molecular mechanisms underlying tissue-specific UGT expression has been the subject of a large number of studies over the last two decades. These studies have shown that the constitutive and inducible expression of UGTs is primarily regulated by tissue-specific and ligand-activated transcription factors (TFs) via their binding to cis-regulatory elements (CREs) in UGT promoters and enhancers. This review first briefly summarizes published UGT gene transcriptional studies and the experimental models and tools utilized in these studies, and then describes in detail the TFs and their respective CREs that have been identified in the promoters and/or enhancers of individual UGT genes.

A potential role for human UDP-glucuronosyltransferase 1A4 promoter single nucleotide polymorphisms in the pharmacogenomics of tamoxifen and its derivatives

Tamoxifen (Tam) is a selective estrogen receptor modulator used to inhibit breast tumor growth. Tam can be directly N-glucuronidated via the tertiary amine group or O-glucuronidated after cytochrome P450-mediated hydroxylation. In this study, the glucuronidation of Tam and its hydroxylated and/or chlorinated derivatives [4-hydroxytamoxifen (4OHTam), toremifene (Tor), and 4-hydroxytoremifene (4OHTor)] was examined using recombinant human UDP-glucuronosyltransferases (UGTs) from the 1A subfamily and human hepatic microsomes. Recombinant UGT1A4 catalyzed the formation of N-glucuronides of Tam and its derivatives and was the most active UGT enzyme toward these compounds. Therefore, it was hypothesized that single nucleotide polymorphisms (SNPs) in the promoter region of UGT1A4 have the ability to significantly decrease the glucuronidation rates of Tam metabolites in the human liver. In vitro activity of 64 genotyped human liver microsomes was used to determine the association between the UGT1A4 promoter and coding region SNPs and the glucuronidation rates of Tam, 4OHTam, Tor, and 4OHTor. Significant decreases in enzymatic activity were observed in microsomes for individuals heterozygous for -163G/A and -217T/G. These alterations in glucuronidation may lead to prolonged circulating half-lives and may potentially modify the effectiveness of these drugs in the treatment of breast cancer.

High-throughput and combinatorial gene expression on a chip for metabolism-induced toxicology screening

Differential expression of various drug-metabolizing enzymes (DMEs) in the human liver may cause deviations of pharmacokinetic profiles, resulting in interindividual variability of drug toxicity and/or efficacy. Here, we present the 'Transfected Enzyme and Metabolism Chip' (TeamChip), which predicts potential metabolism-induced drug or drug-candidate toxicity. The TeamChip is prepared by delivering genes into miniaturized three-dimensional cellular microarrays on a micropillar chip using recombinant adenoviruses in a complementary microwell chip. The device enables users to manipulate the expression of individual and multiple human metabolizing-enzyme genes (such as CYP3A4, CYP2D6, CYP2C9, CYP1A2, CYP2E1 and UGT1A4) in THLE-2 cell microarrays. To identify specific enzymes involved in drug detoxification, we created 84 combinations of metabolic-gene expressions in a combinatorial fashion on a single microarray. Thus, the TeamChip platform can provide critical information necessary for evaluating metabolism-induced toxicity in a high-throughput manner.

UGT2B gene expression analysis in multiple tobacco carcinogen-targeted tissues

The UDP-glucuronosyltransferase (UGT) 2B subfamily of enzymes plays an important role in the metabolism of numerous endogenous and exogenous compounds, including various carcinogens present in tobacco smoke. The goal of the present study was to examine the levels of expression of individual UGT2B genes in various tissues that are targets for tobacco carcinogenesis. Using MT-ATP6 as the experimentally validated housekeeping gene, the highest extrahepatic expression of UGT2B genes was observed in human tonsil, with UGT2B expression levels similar to that observed in human liver. UGT2B17 exhibited high relative expression in most tissues examined, including lung, most tissues of the aerodigestive tract, and pancreas. UGT2B7 expression was highest in pancreas but low or undetectable in most other tissues examined. UGT2B10 expression was high in both tonsil and tongue. There was wide variability between individuals in the magnitude of expression in each tissue site, and there were strong correlations between UGT2B expression levels in different individuals within many of the tissue sites, suggesting coordinated regulation of UGT2B gene expression in extrahepatic tissues. In the liver, UGTs 2B4, 2B7, 2B10, and 2B15 were significantly correlated with each other (all r(2) > 0.70, P < 0.0001). In all examined tissues of the aerodigestive tract, UGTs 2B10, 2B11, and 2B17 exhibited a strong correlation with each other (all r(2) > 0.75, P < 0.05). UGTs 2B7 and 2B10 exhibited a strong inverse correlation in the pancreas (r(2) = -0.95, P < 0.01). These data suggest that specific UGT2B enzymes important in tobacco carcinogen metabolism are expressed and coordinately regulated in various target sites for tobacco-related cancers.

Impact of metabolizing enzymes on drug response of endocrine therapy in breast cancer

Estrogen-receptor positive breast cancer accounts for 75% of diagnosed breast cancers worldwide. There are currently two major options for adjuvant treatment: tamoxifen and aromatase inhibitors. Variability in metabolizing enzymes determines their pharmacokinetic profile, possibly affecting treatment response. Therefore, prediction of therapy outcome based on genotypes would enable a more personalized medicine approach, providing optimal therapy for each patient. In this review, the authors will discuss the current evidence on the most important metabolizing enzymes in endocrine therapy, with a special focus on CYP2D6 and its role in tamoxifen metabolism.

Pharmacogenetics-based population pharmacokinetic analysis of etravirine in HIV-1 infected individuals

OBJECTIVES

Etravirine (ETV) is metabolized by cytochrome P450 (CYP) 3A, 2C9, and 2C19. Metabolites are glucuronidated by uridine diphosphate glucuronosyltransferases (UGT). To identify the potential impact of genetic and non-genetic factors involved in ETV metabolism, we carried out a two-step pharmacogenetics-based population pharmacokinetic study in HIV-1 infected individuals.

MATERIALS AND METHODS

The study population included 144 individuals contributing 289 ETV plasma concentrations and four individuals contributing 23 ETV plasma concentrations collected in a rich sampling design. Genetic variants [n=125 single-nucleotide polymorphisms (SNPs)] in 34 genes with a predicted role in ETV metabolism were selected. A first step population pharmacokinetic model included non-genetic and known genetic factors (seven SNPs in CYP2C, one SNP in CYP3A5) as covariates. Post-hoc individual ETV clearance (CL) was used in a second (discovery) step, in which the effect of the remaining 98 SNPs in CYP3A, P450 cytochrome oxidoreductase (POR), nuclear receptor genes, and UGTs was investigated.

RESULTS

A one-compartment model with zero-order absorption best characterized ETV pharmacokinetics. The average ETV CL was 41 (l/h) (CV 51.1%), the volume of distribution was 1325 l, and the mean absorption time was 1.2 h. The administration of darunavir/ritonavir or tenofovir was the only non-genetic covariate influencing ETV CL significantly, resulting in a 40% [95% confidence interval (CI): 13-69%] and a 42% (95% CI: 17-68%) increase in ETV CL, respectively. Carriers of rs4244285 (CYP2C19*2) had 23% (8-38%) lower ETV CL. Co-administered antiretroviral agents and genetic factors explained 16% of the variance in ETV concentrations. None of the SNPs in the discovery step influenced ETV CL.

CONCLUSION

ETV concentrations are highly variable, and co-administered antiretroviral agents and genetic factors explained only a modest part of the interindividual variability in ETV elimination. Opposing effects of interacting drugs effectively abrogate genetic influences on ETV CL, and vice-versa.

Important and critical scientific aspects in pharmacogenomics analysis: lessons from controversial results of tamoxifen and CYP2D6 studies

Tamoxifen contributes to decreased recurrence and mortality of patients with hormone receptor-positive breast cancer. As this drug is metabolized by phase I and phase II enzymes, the interindividual variations of their enzymatic activity are thought to be associated with individual responses to tamoxifen. Among these enzymes, CYP2D6 is considered to be a rate-limiting enzyme in the generation of endoxifen, a principal active metabolite of tamoxifen, and the genetic polymorphisms of CYP2D6 have been extensively investigated in association with the plasma endoxifen concentrations and clinical outcome of tamoxifen therapy. In addition to CYP2D6, other genetic factors including polymorphisms in various drug-metabolizing enzymes and drug transporters have been implicated to their relations to clinical outcome of tamoxifen therapy, but their effects would be small. Although the results of association studies are controversial, accumulation of the evidence has revealed us the important and critical issues in the tamoxifen pharmacogenomics study, namely the quality of genotyping, the coverage of genetic variations, the criteria for sample collection and the source of DNAs, which are considered to be common problematic issues in pharmacogenomics studies. This review points out common critical issues in pharmacogenomics studies through the lessons we have learned from tamoxifen pharmacogenomics, as well as summarizes the results of pharmacogenomics studies for tamoxifen treatment.

Glucuronidation of the second-generation antipsychotic clozapine and its active metabolite N-desmethylclozapine. Potential importance of the UGT1A1 A(TA)₇TAA and UGT1A4 L48V polymorphisms

INTRODUCTION

Clozapine (CLZ) is an FDA approved second-generation antipsychotic for refractory schizophrenia, and glucuronidation is an important pathway in its metabolism. The aim of this study was to fully characterize the CLZ glucuronidation pathway and examine whether polymorphisms in active glucuronidating enzymes could contribute to variability in CLZ metabolism.

METHODS

Cell lines overexpressing wild-type or variant uridine diphosphate-glucuronosyltransferase (UGT) enzymes were used to determine which UGTs show activity against CLZ and its major active metabolite N-desmethylclozapine (dmCLZ). Human liver microsomes (HLM) were used to compare hepatic glucuronidation activity against the UGT genotype.

RESULTS

Several UGTs including 1A1 and 1A4 were active against CLZ; only UGT1A4 showed activity against dmCLZ. UGT1A1 showed a 2.1-fold (P <0.0001) higher V(max)/K(M) for formation of the CLZ-N⁺-glucuronide than UGT1A4; UGT1A4 was the only UGT for which CLZ-5-N-glucuronide kinetics could be determined. The UGT1A4(24Pro/48Val) variant showed a 5.2-, 2.0-, and 3.4-fold (P < 0.0001 for all) higher V(max)/K(M) for the formation of CLZ-5-N-glucuronide, CLZ-N⁺-glucuronide, and dmCLZ-5-N-glucuronide, respectively, as compared with that of wild-type UGT1A4(24Pro/48Leu). There was a 37% (P< 0.05) decrease in the rate of CLZ-N⁺-glucuronide formation in HLM with the UGT1A1 (*28/*28)/UGT1A4 (*1/*1) genotype, and a 2.2- and 1.8-fold (P < 0.05 for both) increase in the formation of CLZ-5-N-glucuronide and CLZ-N⁺-glucuronide in UGT1A1 (*1/*1)/UGT1A4 (*3/*3) HLM compared with UGT1A1 (*1/*1)/UGT1A4 (*1/*1) HLM. The UGT1A1*28 allele was a significant (P = 0.045) predictor of CLZ-N⁺-glucuronide formation; the UGT1A4*3 allele was a significant (P < 0.0001) predictor of CLZ-5-N-glucuronide and dmCLZ-glucuronide formation.

CONCLUSION

These data suggest that the UGT1A1*28 and UGT1A4*3 alleles contribute significantly to the interindividual variability in CLZ and dmCLZ metabolism.

Identification and functional characterization of a novel UDP-glucuronosyltransferase 2A1 splice variant: potential importance in tobacco-related cancer susceptibility

UDP-glucuronosyltransferase (UGT) 2A1 is a respiratory and aerodigestive tract-expressing phase II detoxifying enzyme that metabolizes various xenobiotics including polycyclic aromatic hydrocarbons (PAHs). In the present study, a novel exon 3 deletion splice variant was identified for UGT2A1 (UGT2A1Δexon3). As determined by reverse transcription-polymerase chain reaction (PCR), UGT2A1Δexon3 was shown to be expressed in various tissues including lung, trachea, larynx, tonsil, and colon. The ratio of UGT2A1Δexon3/wild-type UGT2A1 expression was highest in colon (0.79 ± 0.08) and lung (0.42 ± 0.12) as determined by real-time PCR; an antibody specific to UGT2A1 showed splice variant protein (UGT2A1_i2) to wild-type protein (UGT2A1_i1) ratios in the range of 0.5 to 0.9 in these tissues. Using ultra-pressure liquid chromatography, we found that homogenates prepared from UGT2A1_i2-overexpressing human embryonic kidney 293 cells exhibited no glucuronidation activity against PAHs, including benzo[a]pyrene-7,8-dihydrodiol (B[a]P-7,8-diol). An inducible in vitro system was created to determine the effect of UGT2A1_i2 expression on UGT2A1_i1 activity. Increasing UGT2A1_i2 levels resulted in a significant (p < 0.01) decrease in the UGT2A1_i1 V(max) against 1-hydroxy (OH)-pyrene, 3-OH-benzo[a]pyrene, and B[a]P-7,8-diol; no significant changes in K(M) were observed for any of the three substrates. Coimmunoprecipitation experiments suggested the formation of UGT2A1_i1 and UGT2A1_i2 hetero-oligomers and UGT2A1_i1 homo-oligomers; coexpression of UGT2A1_i1 or UGT2A1_i2 with other UGT1A or UGT2B enzymes caused no change in UGT1A or UGT2B glucuronidation activity. These data suggest that a novel UGT2A1 splice variant regulates UGT2A1-mediated glucuronidation activity via UGT2A1-specific protein-protein interactions, and expression of this variant could play an important role in the detoxification of carcinogens within target tissues for tobacco carcinogenesis.

A pharmacogenetics study of the human glucuronosyltransferase UGT1A4

BACKGROUND

UGT1A4 is primarily expressed in the liver and exhibits catalytic activities for various drugs. Amongst the few UGT1A4 polymorphisms evaluated, studies support the alteration of UGT1A4-mediated glucuronidation by a few variations including the Pro²⁴Thr and Leu⁴⁸Val variants (referred to as UGT1A4*2 and *3).

METHODS

We therefore investigated genetic mechanisms that might contribute to interindividual variation in UGT1A4 expression and activity. The UGT1A4 gene was sequenced from -4963 bp relative to the ATG to 2000 bp after the first exon in 184 unrelated Caucasians and African-Americans.

RESULTS

We identified a large number of genetic variations, including 13 intronic, 39 promoter, as well as 14 exonic polymorphisms, with 10 that lead to amino-acid changes. Of the nucleotide variations found in the -5 kb promoter region, five are located in the proximal region (first 500 bp), and positioned in putative HNF-1 and OCT-1 binding sites. Four of these variants, placed at -163, -219, -419 and -463, are in complete linkage disequilibrium with the Leu⁴⁸Val coding region variant and with several variants in the upstream region of the promoter. Transient transfections of reference and variant promoter constructs (from position -500 to +1) in different cell lines with or without co-expression of HNF-1 and/or OCT-1 showed limited effect of these variations.

CONCLUSION

Additional functional studies on promoter variants are still required to predict their potential influence on UGT1A4 expression in vivo. Besides, several coding variants significantly modified the enzyme kinetics for tamoxifen and Z-4-hydroxytamoxifen (Val⁴⁸, Asp⁵⁰, Gln⁵⁶, Phe¹⁷⁶, Asn²⁵⁰, Leu²⁷⁶) and are expected to have a potential in vivo effect.

Contributions of human enzymes in carcinogen metabolism

Considerable support exists for the roles of metabolism in modulating the carcinogenic properties of chemicals. In particular, many of these compounds are pro-carcinogens that require activation to electrophilic forms to exert genotoxic effects. We systematically analyzed the existing literature on the metabolism of carcinogens by human enzymes, which has been developed largely in the past 25 years. The metabolism and especially bioactivation of carcinogens are dominated by cytochrome P450 enzymes (66% of bioactivations). Within this group, six P450s--1A1, 1A2, 1B1, 2A6, 2E1, and 3A4--accounted for 77% of the P450 activation reactions. The roles of these P450s can be compared with those estimated for drug metabolism and should be considered in issues involving enzyme induction, chemoprevention, molecular epidemiology, interindividual variations, and risk assessment.

Functional impact and prevalence of polymorphisms involved in the hepatic glucuronidation of valproic acid

Metabolism of valproic acid, a widely used drug, is only partially understood. It is mainly metabolized through glucuronidation and acts as a substrate for various UDP-glucuronosyltransferases (UGTs). UGTs metabolizing valproic acid in the liver are UGT1A3, UGT1A4, UGT1A6, UGT1A9 and UGT2B7, with UGT1A6 and UGT2B7 being the most prominent. Polymorphisms in genes expressing these enzymes may have clinical consequences, regarding dosing, blood levels of the drug and adverse reactions. Not all genes are well studied and studies, where they exist, report conflicting results. Prevalence of polymorphisms and various haplotypes is also of great importance, as it may suggest different therapeutic approaches in various populations. Presented here is a review of currently known polymorphisms, their functional impact, when known, and their prevalence in different populations, highlighting the current state of understanding and areas where there is a lack of data and suggesting new perspectives for further research.

SULT1A1 rs9282861 polymorphism-a potential modifier of efficacy of the systemic adjuvant therapy in breast cancer?

Background

Sulfotransferase 1A1 (SULT1A1) participates in the elimination of 4-hydroxy-tamoxifen (4-OH-TAM), which is one of the major active metabolites of tamoxifen (TAM). Homozygous SULT1A1 variant allele genotype has been associated with lower catalytic activity and thermostability of the enzyme. Previous clinical studies suggest that the SULT1A1 rs9282861 polymorphism may influence the survival of breast cancer patients treated with TAM in the adjuvant setting. We investigated the effect of rs9282861 genotypes on the survival of Finnish breast cancer patients treated with adjuvant chemotherapy or TAM.

Methods

The rs9282861 genotypes of 412 Finnish breast cancer patients with early breast cancer were identified by using PCR-RFLP method. Seventy six patients were treated with adjuvant cyclophosphamide based chemotherapy only, 65 patients received adjuvant TAM, and four patients were treated with both adjuvant chemotherapy and TAM. Overall long-term survival (OS), breast cancer specific survival (BCSS), and relapse-free survival (RFS) by rs9282861 genotypes were evaluated by the Kaplan-Meier method and Cox regression analysis.

Results

The multivariate analysis of 145 patients receiving either adjuvant TAM or chemotherapy showed a statistically significantly improved OS in patients with the rs9282861 homozygous variant AA genotype (hazard ratio [HR] = 0.50, 95% confidence interval [CI] = 0.29-0.88, P = 0.015). In the separate analyses of patients receiving only chemotherapy or adjuvant TAM, there were no statistically significant differences in survival.

Conclusions

In this prospective study, we observed a previously unreported association between the SULT1A1 rs9282861 genotype and OS of breast cancer patients treated with adjuvant chemotherapy or TAM. This novel finding suggests that the rs9282861 polymorphism modifies the long-term clinical outcome of patients receiving adjuvant TAM or chemotherapy.

UDP-glucuronosyltransferase 1A4 (UGT1A4) polymorphisms in a Jordanian population

Glucuronidation is one of the most important phase II metabolic pathways. It is catalyzed by a family of UDP-glucuronosyltransferase enzymes (UGTs). One of the subfamilies is UGT1A. Allele frequencies in UGT1A4 differ among ethnic groups. The aim of this study was to determine the allelic frequency of two most common defective alleles: UGT1A4*2 and UGT1A4*3 in a Jordanian population. A total of 216 healthy Jordanian Volunteers (165 males and 51 females) were included in this study. Genotyping for UGT1A4*1, UGT1A4*2 and UGT1A4*3 was done using a well established polymerase chain reaction-restriction fragment length polymorphism test. Among 216 random individuals studied for UGT1A4*2 mutation there were 26 individuals who were heterozygous, giving a prevalence of 12% and an allele frequency of 6.5%. Only one individual was homozygous for UGT1A4*2. The UGT1A4*3 mutation was detected as heterozygous in 9 of 216 individuals indicating a prevalence of 4.2% and allele frequency of 3.5%. Three individuals were homozygous for the UGT1A4*3 indicating a prevalence of 1.4%. The prevalence of UGT1A4*2 is similar to the Caucasians but different from other populations whilst the UGT1A4*3 prevalence in the Jordanian population is distinct from other populations. Our results provide useful information for the Jordanian population and for future genotyping of Arab populations in general.

Olanzapine metabolism and the significance of UGT1A448V and UGT2B1067Y variants

OBJECTIVES

Olanzapine is an antipsychotic used in the treatment of schizophrenia, bipolar disorder, and treatment-resistant depression. Glucuronidation by the UDP-glucuronosyltransferase (UGT) family of enzymes is the major mode of olanzapine metabolism, and polymorphisms in these enzymes could contribute to interindividual variability in olanzapine metabolism and therapeutic response.

METHODS

Cell lines overexpressing individual UGT enzymes were used to determine which UGTs have enzymatic activity against olanzapine, characterize the kinetics of this reaction, and examine the effects of UGT variants on olanzapine metabolism. A bank of 105 human liver microsomes (HLM) were used to perform a phenotype-genotype study comparing glucuronidation activity against UGT genotype.

RESULTS

Cell lines overexpressing the individual UGTs 1A4 and 2B10 exhibited glucuronidation activity against olanzapine. The UGT1A4 variant exhibited a 3.7-fold (P<0.0001) higher Vmax/KM for the formation of the olanzapine-10-N-glucuronide isomer 1, and a 4.3-fold (P<0.0001) higher Vmax/KM for the formation of the olanzapine-10-N-glucuronide isomer 2 than wild-type UGT1A4. The UGT2B10 variant exhibited no glucuronidation activity against olanzapine. In a screening of 105 HLM specimens, there was a 2.1-fold (P=0.04) and 1.6-fold (P=0.0017) increase in the rate of olanzapine-10-N-glucuronide isomer 1 and olanzapine-4'-N-glucuronide formation, and a 2-fold (P=0.02) increase in the overall olanzapine glucuronidation formation, in HLM with the UGT1A4 (*3/*3)/UGT2B10 (*1/*1) genotype compared with HLM with the UGT1A4 (*1/*1)/UGT2B10 (*1/*1) genotype. There was a 1.9-fold (P<0.003) decrease in the formation of both isomers of the olanzapine-10-N-glucuronide, a 2.7-fold (P<0.0001) decrease in olanzapine-4'-N-glucuronide formation, and a 2.1-fold (P=0.0002) decrease in the overall olanzapine glucuronide formation in HLM with at least one UGT2B10*2 allele. In regression analysis, the UGT1A4*3 (P<0.02) and UGT2B10*2 (P<0.002) alleles were significant predictors of the formation of all olanzapine glucuronide isomers.

CONCLUSION

The UGTs 1A4 and 2B10 glucuronidate olanzapine and functional variants of these UGTs significantly alter olanzapine glucuronidation in vitro. These data suggest that the UGT1A4*3 and UGT2B10*2 alleles contribute significantly to interindividual variability in olanzapine metabolism.

Functional analysis of UGT1A4P24T and UGT1A4L48V variant enzymes

Aim: To investigate the effects of two nonsynonymous SNPs, UGT1A4*2 (rs#: 6755571, 70C>A, P24T) and UGT1A4*3 (rs#: 2011425, 142T>G, L48V), on the function of UGT1A4 against dihydrotestosterone (DHT), transandrosterone (t-AND), lamotrigine (LTG) and tamoxifen (TAM). Materials & methods: Detailed kinetic experiments were conducted with recombinant UGT1A4wild-type, UGT1A4P24T and UGT1A4L48V, which were overexpressed in HEK293 cell lines. The kinetic profiles and kinetic parameters (Km, Vmax and CLint) obtained with either UGT1A4P24T or UGT1A4L48V were compared with those obtained with the wild-type enzyme. The interaction of TAM on UG1A4-catalyzed DHT glucuronidation was also investigated with the three UGT1A4 polymorphic enzymes. Results: UGT1A4L48V had higher enzyme efficiency (CLint) compared with wild-type UGT1A4 on DHT glucuronidation; UGT1A4P24T and UGT1A4L48V had lower CLint than wild-type UGT1A4 for t-AND and LTG glucuronidation. The TAM CLint with UGT1A4P24T and UGT1A4L48V glucuronidation and the UGT1A4P24T-catalyzed DHT glucuronidation were, on the other hand, similar to those of the wild-type enzyme. With all three enzymes, TAM activated UGT1A4-catalyzed DHT glucuronidation in a concentration-dependent fashion. Conclusion: Decreased CLint of UGT1A4P24T and UGT1A4L48V on LTG glucuronidation may lead to interindividual variations in LTG metabolism in vivo. However, it is less likely that these polymorphisms would have impact on DHT and t-AND metabolism in vivo because these compounds are glucuronidated by multiple enzymes.

Original submitted 31 May 2011; Revision submitted 19 July 2011

Screening of multiple hormonal activities in surface water and sediment from the Pearl River system, South China, using effect-directed in vitro bioassays

This paper reports screening of multiple hormonal activities (estrogenic and androgenic activities, antiestrogenic and antiandrogenic activities) for surface water and sediment from the Pearl River system (Liuxi, Zhujiang, and Shijing rivers) in South China, using in vitro recombinant yeast bioassays. The detection frequencies for estrogenic and antiandrogenic activities were both 100% in surface water and 81 and 93% in sediment, respectively. The levels of estrogenic activity were 0.23 to 324 ng 17β-estradiol equivalent concentration (EEQ)/L in surface water and 0 to 101 ng EEQ/g in sediment. Antiandrogenic activities were in the range of 20.4 to 935 × 10(3) ng flutamide equivalent concentration (FEQ)/L in surface water and 0 to 154 × 10(3) ng FEQ/g in sediment. Moreover, estrogenic activity and antiandrogenic activity in sediment showed good correlation (R(2) = 0.7187), suggesting that the agonists of estrogen receptor and the antagonists of androgen receptor co-occurred in sediment. The detection frequencies for androgenic and antiestrogenic activities were 41 and 29% in surface water and 61 and 4% in sediment, respectively. The levels of androgenic activities were 0 to 45.4 ng dihydrotestosterone equivalent concentration (DEQ)/L in surface water, and the potency was very weak in the only detected sediment site. The levels of antiestrogenic activity were 0 to 1,296 × 10(3) ng tamoxifen equivalent concentration (TEQ)/L in surface water and 0 to 89.5 × 10(3) ng TEQ/g in sediment. The Shijing River displayed higher levels of hormonal activities than the Zhujiang and Liuxi rivers, indicating that the Shijing River had been suffering from heavy contamination with endocrine-disrupting chemicals. The equivalent concentrations of hormonal activities in some sites were greater than the lowest-observed-effect concentrations reported in the literature, suggesting potential adverse effects on aquatic organisms.

Pharmacogenetics of anti-estrogen treatment of breast cancer

A major effort is underway to select genetic polymorphisms potentially relevant to the clinical efficacy and safety of endocrine treatment of breast cancer. Genetic factors of the host that affect the metabolism of tamoxifen, a widely used drug for the adjuvant treatment of breast cancer, have received particular attention. Cytochrome P450 isoform 2D6 (CYP2D6) is a key step in the metabolism of tamoxifen to its active moiety endoxifen. Women with functionally deficient genetic variants of CYP2D6 who are given drugs that inhibit CYP2D6 are exposed to low endoxifen plasma levels and may enjoy reduced benefits from tamoxifen treatment. Therefore, CYP2D6 status may be an important predictor of the benefits of tamoxifen to an individual; unfortunately, the data are not uniformly concordant, and definitive evidence that would suggest the routine analysis of CYP2D6 before commencing tamoxifen treatment is not yet available. Recent research has focused on the role UDP-glucuronosyltransferases, a family of metabolizing enzymes that play an important role in the metabolic clearance of tamoxifen and of the aromatase inhibitors as well, and how interindividual differences in these enzymes may play a role in the clinical outcome upon administration of anti-estrogen treatment. In conclusion, whether a pharmacogenetic profile should be obtained prior to initiating tamoxifen therapy is currently a matter of debate, although summing up all the scientific evidence available on this issue it appears that the genetic screening would be an useful support for clinical decision making in selected patients.

The CYP2C19*2 genotype predicts tamoxifen treatment outcome in advanced breast cancer patients

AIMS

Tamoxifen is metabolized by cytochrome P450s, with an important role for CYP2D6. Recently, we demonstrated in 80 patients that CYP2C19*2 is associated with increased survival in breast cancer patients using tamoxifen. Here, we aimed to confirm this in a large group of 499 patients.

MATERIALS & METHODS

A total of 499 estrogen receptor-positive primary breast tumor specimens of advanced disease patients treated with first-line tamoxifen were genotyped for CYP2C19*2 and *17 variant alleles, with primary end point time-to-treatment failure (TTF). Effects of CYP2C19, independent of treatment, were analyzed in 243 primary systematic untreated patients.

RESULTS

CYP2C19*2 hetero- and homozygote patients combined showed significantly longer TTFs (hazard ratio [HR]: 0.72; 95% CI: 0.57-0.90; p = 0.004). In multivariate analysis, including CYP2D6*4 status, CYP2C19*2 remained independently associated with TTF (HR: 0.73; 95% CI: 0.58-0.91; p = 0.007). In untreated patients, the CYP2C19*17 allele was significantly associated with a longer disease-free interval (HR: 0.66; 95%CI: 0.46-0.95; p = 0.025).

CONCLUSION

CYP2C19 genotyping is potentially important for tamoxifen therapy for advanced disease and for breast cancer prognosis.

First-pass metabolism via UDP-glucuronosyltransferase: a barrier to oral bioavailability of phenolics

Glucuronidation mediated by UDP-glucuronosyltransferases (UGTs) is a significant metabolic pathway that facilitates efficient elimination of numerous endobiotics and xenobiotics, including phenolics. UGT genetic deficiency and polymorphisms or inhibition of glucuronidation by concomitant use of drugs are associated with inherited physiological disorders or drug-induced toxicities. Moreover, extensive glucuronidation can be a barrier to oral bioavailability as the first-pass glucuronidation (or premature clearance by UGTs) of orally administered agents usually results in the poor oral bioavailability and lack of efficacies. This review focused on the first-pass glucuronidation of phenolics including natural polyphenols and pharmaceuticals. The complexity of UGT-mediated metabolism of phenolics is highlighted with species-, gender-, organ- and isoform-dependent specificity, as well as functional compensation between UGT1A and 2B subfamily. In addition, recent advances are discussed with respect to the mechanisms of enzymatic actions, including the important properties such as binding pocket size and phosphorylation requirements.

Activity levels of tamoxifen metabolites at the estrogen receptor and the impact of genetic polymorphisms of phase I and II enzymes on their concentration levels in plasma

The therapeutic effect of tamoxifen depends on active metabolites, e.g., cytochrome P450 2D6 (CYP2D6) mediated formation of endoxifen. To test for additional relationships, 236 breast cancer patients were genotyped for CYP2D6, CYP2C9, CYP2B6, CYP2C19, CYP3A5, UGT1A4, UGT2B7, and UGT2B15; also, plasma concentrations of tamoxifen and 22 of its metabolites, including the (E)-, (Z)-, 3-, and 4'-hydroxymetabolites as well as their glucuronides, were quantified using liquid chromatography-tandem mass spectrometry (MS). The activity levels of the metabolites were measured using an estrogen response element reporter assay; the strongest estrogen receptor inhibition was found for (Z)-endoxifen and (Z)-4-hydroxytamoxifen (inhibitory concentration 50 (IC50) 3 and 7 nmol/l, respectively). CYP2D6 genotypes explained 39 and 9% of the variability of steady-state concentrations of (Z)-endoxifen and (Z)-4-hydroxytamoxifen, respectively. Among the poor metabolizers, 93% had (Z)-endoxifen levels below IC90 values, underscoring the role of CYP2D6 deficiency in compromised tamoxifen bioactivation. For other enzymes tested, carriers of reduced-function CYP2C9 (*2, *3) alleles had lower plasma concentrations of active metabolites (P < 0.004), pointing to the role of additional pathways.

Automation and Miniaturization of the Bioluminescent UGT-Glo Assay for Screening of UDP-Glucuronosyltransferase Inhibition by Various Compounds

The uridine 5'-diphospho-glucuronosyltransferase (UGT) family of enzymes is involved in the metabolism of various compounds. These enzymes transfer a hydrophilic glucuronic acid moiety to their substrates, rendering them more water soluble and amenable to excretion. The UGTs act on various endogenous substrates, such as bilirubin, 17β-estradiol, and testosterone, and drugs and other xenobiotics. The function of these enzymes is essential for the clearance of drugs and toxicants, and alteration of UGT activity is a potential cause of adverse drug—drug interactions in vivo. This has stimulated an increased interest in the study of UGT function and inhibition, and the desire to profile new drug entities against UGT enzymes, similar to CYP450 profiling. However, certain factors have hindered the development of a robust method for UGT profiling. Current methods for assessing UGT enzyme activity are laborious and involve protein precipitation and/or chromatographic separation steps, which are not amenable to rapid screening applications for UGT inhibitors or substrates. The approach presented here is a bioluminescent assay for measuring UGT enzyme activity and inhibition in vitro. Using flexible, robust instrumentation in a 384-well microplate format, this study highlights the quick and easy assay implementation for estimation of inhibition kinetics with a variety of known and suspected UGT substrates and inhibitors.

Potential role of UGT pharmacogenetics in cancer treatment and prevention: focus on tamoxifen and aromatase inhibitors

Tamoxifen (TAM) is a selective estrogen-receptor modulator that is widely used in the prevention and treatment of estrogen-receptor-positive breast cancer. Its use has significantly contributed to a decline in breast cancer mortality, since breast cancer patients treated with TAM for 5 years exhibit a 30-50% reduction in both the rate of disease recurrence after 10 years of patient follow-up and in the occurrence of contralateral breast cancer. However, in patients treated with TAM, there is substantial interindividual variability in the development of resistance to TAM therapy and in the incidence of TAM-induced adverse events, including deep-vein thrombosis, hot flashes, and the development of endometrial cancer. Aromatase inhibitors (AIs) have emerged as a viable alternative to TAM, working by inhibiting aromatase activity and blocking estrone/estrodiol biosynthesis in postmenopausal women. The current third-generation AIs, anastrozole, exemestane, and letrozole, were used initially for the treatment of metastatic breast cancer, demonstrating similar or greater benefit but less toxicity, compared with TAM, and are now being employed as adjuvant treatment for early breast cancer in postmenopausal women. This article will focus on the UDP-glucuronosyltransferases, a family of metabolizing enzymes that play an important role in the deactivation and clearance of TAM, anastrazole, and exemestane, and how interindividual differences in these enzymes may play a role in patient response to these agents.

Uridine 5'-diphospho-glucuronosyltransferase genetic polymorphisms and response to cancer chemotherapy

Pharmacogenetics aims to elucidate how genetic variation affects the efficacy and side effects of drugs, with the ultimate goal of personalizing medicine. Clinical studies of the genetic variation in the uridine 5'-diphosphoglucuronosyltransferase gene have demonstrated how reduced-function allele variants can predict the risk of severe toxicity and help identify cancer patients who could benefit from reduced-dose schedules or alternative chemotherapy. Candidate polymorphisms have also been identified in vitro, although the functional consequences of these variants still need to be tested in the clinical setting. Future approaches in uridine 5'-diphosphoglucuronosyltransferase pharmacogenetics include genetic testing prior to drug treatment, genotype-directed dose-escalation studies, study of genetic variation at the haplotype level and genome-wide studies.