UGT1A4 Polymorphism is not Associated with a Clinically Relevant Change in Giredestrant Exposure

PURPOSE

Giredestrant is a potent, orally bioavailable, small-molecule selective estrogen receptor antagonist and degrader (SERD) that is being developed for the treatment of patients with estrogen receptor (ER)-positive breast cancer. In vitro, giredestrant was primarily metabolized by UGT1A4. The goal of this study was to investigate if UGT1A4 polymorphism had a clinically relevant impact on giredestrant exposure.

METHODS

Genotyping and pharmacokinetic data were obtained from 118 and 61 patients in two clinical studies, GO39932 [NCT03332797] and acelERA Breast Cancer [NCT04576455], respectively.

RESULTS

The overall allelic frequencies of UGT1A4*2 and UGT1A4*3 were 3.3% and 11%, respectively. Giredestrant exposure was consistent between patients with wild-type UGT1A4 and UGT1A4*2 and *3 polymorphisms, with no clinically relevant difference observed. In addition, haplotype analysis indicated that no other UGT1A4 variants were significantly associated with giredestrant exposure.

CONCLUSION

Therefore, this study indicates that UGT1A4 polymorphism status is unlikely a clinically relevant factor to impact giredestrant exposure and giredestrant can be administered at the same dose level regardless of patients' UGT1A4 polymorphism status.

Species difference in toxicokinetics and safety assessment of senecionine N-oxide in a UDP-glucuronosyltransferase 1A4 humanized mouse model

Pyrrolizidine alkaloids (PAs) are naturally occurring hepatotoxins, and herbs containing PAs are of high concern. PAs are normally found in tertiary amines and N-oxide forms (PA N-oxides), yet the latter are less evaluated for their toxicokinetics. As a continuation of our investigation into the safety assessment of PA-containing herbal medicines, the toxicity and toxicokinetic characteristics of senecionine N-oxide (a representative toxic PA N-oxide) were investigated by using the UDP-glucuronosyltransferase 1A4 humanized mouse model (hUGT1A4 mouse model) and compared with those in wild-type mice simultaneously. Results show that the toxicity caused by senecionine N-oxide exposure was evidently decreased in hUGT1A4 mice as approved by pathology and biochemistry assays. In addition, a N-glucuronidation conjugate was exclusively found in hUGT1A4 mice but not in wild-type (WT) mice. In vitro studies proved that senecionine N-oxide initially reduced to the corresponding tertiary amine alkaloid (senecionine) and then underwent N-glucuronidation via human UGT1A4. The variation in toxicokinetic characteristics was also observed between hUGT1A4 mice and WT mice with a notably enhanced clearance of senecionine N-oxide and senecionine, and accordingly less formation of pyrrole-protein adducts in hUGT1A4 mice, which finally led to the detoxification of senecionine N-oxide exposure in hUGT1A4 mice. Our results provided the first in vivo toxicity data and toxicokinetic characteristics of senecionine N-oxide in a humanized animal model and revealed that human UGT1A4 plays an important role in the detoxification of senecionine N-oxide.

Identification of Human UDP-Glucuronosyltransferase Involved in Gypensapogenin C Glucuronidation and Species Differences

Gypensapogenin C (GPC) is one of the important aglycones of Gynostemma pentaphyllum (GP), which is structurally glucuronidated and is highly likely to bind to UGT enzymes in vivo. Due to the important role of glucuronidation in the metabolism of GPC, the UDP-glucuronosyltransferase metabolic pathway of GPC in human and other species' liver microsomes is investigated in this study. In the present study, metabolites were detected using high-performance liquid chromatography-tandem mass spectrometry (LC-MS/MS). The results show that GPC could generate a metabolite through glucuronidation in the human liver microsomes (HLMs). Additionally, chemical inhibitors combined with recombinant human UGT enzymes clarified that UGT1A4 is the primary metabolic enzyme for GPC glucuronidation in HLMs according to the kinetic analysis of the enzyme. Metabolic differential analysis in seven other species indicated that rats exhibited the most similar metabolic rate to that of humans. In conclusion, UGT1A4 is a major enzyme responsible for the glucuronidation of GPC in HLMs, and rats may be an appropriate animal model to evaluate the GPC metabolism.

Anastrozole and Related Glucuronic Acid Conjugate are Electrophilic Species

Anastrozole (ANA), is an inhibitor of non-steroidal aromatase, widely employed for the treatment of breast cancer. However, ANA-associated liver injury cases have been documented in the application of the drug.The major purposes of the present study were to identify the structure of reactive metabolites derived from ANA and to study related metabolic pathways of ANA.We found ANA itself is an electrophilic species reactive to GSH. ANA can be metabolized to ANA-N⁺-glucuronide (1) catalyzed by UGT1A4. An ANA GSH conjugate (2) was detected in bile and livers of rats treated with ANA. UGT1A4 participated in the phase II metabolic pathway.This work allowed us to better understand the mechanisms of the hepatotoxicity of ANA and provided new avenue to define the possible role of metabolic activation in hepatotoxicity.

Lamotrigine-induced neutropenia after high-dose concomitant initiation with phenytoin

Lamotrigine has been repeatedly reported to cause hematologic toxicities, which may be associated with high initial doses or excessive escalation. A 29-year-old lady experienced profound neutropenia after two weeks of lamotrigine high initial dose, started within two days of phenytoin. The too-early dose intensification may have produced lamotrigine-induced blood dyscrasia.

UDP-glucuronosyltransferase 1A4-mediated N2-glucuronidation is the major metabolic pathway of lamotrigine in chimeric NOG-TKm30 mice with humanised-livers

Lamotrigine is a phenyltriazine anticonvulsant used to treat epilepsy and bipolar disorder, with species-dependent metabolic profiles. In this study, we investigated the metabolism of lamotrigine in chimeric NOG-TKm30 mice transplanted with human hepatocytes (humanised-liver mice).Substantial lamotrigine N2-glucuronidation activities were observed in the liver microsomes from humanised-liver mice, humans, marmosets, and rabbits, compared to those from monkeys, minipigs, guinea pigs, rats, and mice. Lamotrigine N2-glucuronidation activities in the liver microsomes from humanised-liver mice were dose-dependently inhibited by hecogenin, a specific inhibitor of the human UGT1A4.The major metabolite in the hepatocytes from humanised-liver mice and humans was lamotrigine N2-glucuronide, whereas that in mouse hepatocytes was lamotrigine N2-oxide. After a single oral dose of lamotrigine (10 mg/kg), the plasma levels of N2-glucuronide, N5-glucuronide, and N2-methyl were higher in humanised-liver mice compared to that in NOG-TKm30 mice. Lamotrigine N2-glucuronide was the most abundant metabolite in the urine in humanised-liver mice, similar to that reported in humans; whereas, lamotrigine N2-oxide was predominantly excreted in the urine in NOG-TKm30 mouse.These results suggest that humanised-liver mice may be a suitable animal model for studying the UGT1A4 mediated-lamotrigine metabolism.

A validation study of the UGT1A4 rs2011404 variant and the risk of anti-tuberculosis drug-induced hepatotoxicity in an Eastern Chinese Han population

WHAT IS KNOWN AND OBJECTIVE

Anti-tuberculosis (anti-TB) drug-induced hepatotoxicity (ATDH) is a serious adverse drug reaction. A recent study found that the rs2011404 variant of uridine 5'-diphospho-glucuronosyl-transferase 1A4 (UGT1A4) is a marker of susceptibility to ATDH. The present study aimed to validate this relationship in an Eastern Chinese Han anti-TB treatment population.

METHODS

A 1:4 matched case-control study was conducted among anti-TB treatment patients in four regions of Jiangsu. ATDH was diagnosed based on the criteria from the Chinese Society of Hepatology and the updated Roussel Uclaf Causality Assessment Method. A conditional logistic regression model was used to estimate the association between rs2011404 genotypes and the risk of ATDH using odds ratios (ORs) with 95% confidence intervals (95% CIs) and smoking, drinking, hepatoprotectant use and liver diseases as covariates.

RESULTS AND DISCUSSION

A total of 202 ATDH cases and 808 controls were matched according to age, sex and treatment history. After correcting for potential confounding factors, conditional logistic regression analysis indicated no significant differences in genotypes between the two groups (CC vs. TC: OR = 0.933, 95% CI: 0.457-1.905, p = 0.849). Subgroup analysis suggested that patients carrying the CC genotype at rs2011404 in UGT1A4 were at a reduced risk of moderate or severe liver injury (OR = 0.293, 95% CI: 0.093-0.921, p = 0.036).

WHAT IS NEW AND CONCLUSION

Based on a 1:4 individual matched case-control study, possessing the CC genotype at rs2011404 of the UGT1A4 gene reduces the risk of moderate or severe liver injury in Eastern Chinese Han patients receiving anti-TB treatment. Further research is warranted to explain the role of the UGT1A4 gene and its contribution to individual differences in susceptibility to ATDH.

[Study on hereditary susceptibility genetic markers to anti-tuberculosis drug induced liver injury in Chinese population]

To systematically study the susceptible genetic markers for liver injury induced by anti-tuberculosis drugs in the Chinese population, 109 genes related to drug metabolism, transport and immunity were captured by Haloplex capture technique from DNA samples of 41 patients with liver injury induced by anti-tuberculosis drugs and 39 healthy controls, and sequenced completely. Association study was conducted using Plink software. To verify the significant candidate SNPs, the χ ² study was expanded to the control group from the 1000-person Genome Project of the East Asian population. SIFT and Polyphen2 software were used to predict the functional significance of the associated SNPs. Our results identified the UGT1A4 rs2011404 (χ ² = 4.6809, P = 0.0305) as a susceptible genetic marker for liver injury induced by anti-tuberculosis drugs, and rs2011404 mutation might contribute to UGT1A4 protein dysfunction. This study has provided a potentially useful reference for establishing the precision medicine in rational uses of anti-tuberculosis drugs in the clinic.

The association of genetic polymorphisms in CYP1A2, UGT1A4, and ABCB1 with autonomic nervous system dysfunction in schizophrenia patients treated with olanzapine

BACKGROUND

Use of the antipsychotic drug olanzapine by patients with schizophrenia is associated with autonomic nervous system (ANS) dysfunction. It is presumed that there are interindividual differences in ANS dysfunction that correspond to pharmacogenetics. In this study, we investigated whether genetic polymorphisms in ABCB1, CYP1A2, and UGT1A4 are associated with this observed ANS dysfunction.

METHODS

A total of 91 schizophrenia patients treated with olanzapine monotherapy participated in this study. A power spectral analysis of heart rate variability was used to assess ANS activity. The TaqMan system was used to genotype seven single nucleotide polymorphisms (SNPs) in CYP1A2 (rs2069514 and rs762551), UGT1A4 (rs2011425), and ABCB1 (rs1045642, rs1128503, rs2032582, rs2235048).

RESULTS

Sympathetic nervous activity was significantly higher in individuals with the UGT1A4 rs2011425 G allele than in those with the UGT1A4 rs2011425 non-G allele (sympathetic activity, p = .001). Furthermore, sympathetic nervous activity was also significantly associated with UGT1A4 rs2011425 genotype as revealed by multiple regression analysis (sympathetic activity, p = .008).

CONCLUSIONS

We suggest that the UGT1A4 rs2011425 polymorphism affects olanzapine tolerability because it is associated with the observed side effects of olanzapine in schizophrenia patients, namely sympathetic dysfunction.

Association between ESR1, ESR2, HER2, UGT1A4, and UGT2B7 polymorphisms and breast Cancer in Jordan: a case-control study

Background

Breast cancer risk, development, and treatment are influenced by genetic variation in certain genes, namely those involved in cell proliferation, tumor suppression, and drug metabolism. In turn, the relevance of the aforementioned genetic variation to cancer depends on the ethnic group in question, highlighting the need for population-specific association studies. Therefore, the objective of the present study was to investigate the association between certain ESR1, ESR2, HER2, UGT1A4, and UGT2B7 single nucleotide polymorphisms and breast cancer.

Methods

Blood samples were collected from 437 Jordanian-Arab breast cancer patients and healthy volunteers and subject to genotyping using the Sequenom MassARRAY® system (iPLEX GOLD).

Results

Our findings show a significant association between breast cancer and the allelic (P = 0.02486879) and genotypic (P = 0.04793066) frequencies of the ESR1 polymorphism rs3798577, a result which was confirmed in different genetic models. No other investigated polymorphism showed a significant association with breast cancer itself in Jordanian Arabs, but the Rare Hz (GG) vs Het (AG) genetic model revealed an association of the disease with the ESR1 polymorphism rs3798577. However, several associations were found between certain polymorphisms and breast cancer’s prognostic factors.

Conclusion

This study suggests that certain polymorphisms may increase the risk of breast cancer in the Jordanian-Arab population. Future research and clinical translation could incorporate the current results in preventative breast cancer approaches tailored for Jordanian-Arab patients.

Association of CYP2C19 and UGT1A4 polymorphisms with voriconazole-induced liver injury

Aim: This study investigated the association between voriconazole-induced liver injury and gene polymorphisms of CYP2C19 and UGT1A4. Materials & methods: Thirty-eight adult patients who received voriconazole therapy were included in the study. Genotype of CYP2C19 was detected using gene chip hybrid analysis. The UGT1A4 142T>G was genotyped using PCR-RFLP analysis. Results: Ten patients (26.3%) had voriconazole-induced liver injury and were considered as the case group There was no significant difference between the two groups in genotype and allele frequencies of CYP2C19*2 and UGT1A4 142T>G (p > 0.05), however, the GA frequency of CYP2C19 *3 in the drug-induced liver injury case group was higher than that in the control group (p < 0.05). Compared with patients carrying *1/*1 or *1/*2, there was no significant difference in voriconazole trough concentration of the patients with *1/*3 (p > 0.05). Conclusion: There was no significant correlation between voriconazole-induced liver injury and gene polymorphisms of CYP2C19 and UGT1A4.

[Relationship between UGT1A4 142T>G polymorphism and serum concentration of lamotrigine in Chinese epileptic patients: a meta-analysis]

Objective: To investigate the relationship between the polymorphism of Uridine diphosphate glucuronosyltransferases (UGT)1A4 142T>G (*3, L48V, rs 2011425)and serum concentration of lamotrigine(LTG) in Chinese epileptic patients. Methods: Databases including Cochrane Library, PubMed, Embase, CNKI, VIP and Wanfang were searched for the studies on the relationship of the polymorphisms of UGT1A4 142T>G with concentration of LTG (from the establishment a database to December 1, 2017). Meta-analysis was performed by RevMan 5.3. Results: We pooled data from 6 literatures, including 903 Chinese epileptic patients. Meta-analysis: In terms of the effect of UGT1A4 142T>G polymorphism on the serum concentration/dose ratio(CDR)of LTG, there was no significant difference between the wild-type(TT genotype)group and mutant-type (TG+ GG genotype) group (MD=-0.08, 95% CI (-0.40-0.23)). Further subgroup analysis was performed on LTG monotherapy or valproic acid(VPA)co-administration. For patients treated with LTG as monotherapy, difference was not statistically significant between the 2 groups(MD=0.16, 95% CI(-0.25-0.57)). But in children treated with VPA co-administration, difference was statistically significant between the 2 groups (MD=-0.50, 95% CI(-0.75--0.26)). Conclusion: UGT1A4 142T>G polymorphism has an effect on LTG concentration only with VPA co-administration in Chinese epileptic pediatric patients and those children with wild-type (TT genotype) have a tendency to have a lower serum concentration of lamotrigine.

The Genetic Polymorphism UGT1A4*3 Is Associated with Low Posaconazole Plasma Concentrations in Hematological Malignancy Patients Receiving the Oral Suspension

The metabolism of posaconazole is mediated mainly by uridine 5'-diphospho-glucuronosyltransferase (UGT) enzymes, especially UGT1A4. The aim of this study was to investigate the effects of genetic polymorphisms on the posaconazole plasma concentration (PPC). This prospective study was conducted from September 2014 to August 2016. We enrolled patients with acute myeloid leukemia or myelodysplastic syndrome treated with posaconazole oral suspension (200 mg) three times daily for fungal prophylaxis. The patients were examined for the multidrug resistance gene 1 3435C>T and 2677G>T/A variations and the UGT1A4*3 allele by direct sequencing of DNA from peripheral whole-blood samples. We defined poor absorbers to be those with PPCs of <200 ng/ml and the optimal PPC to be ≥700 ng/ml on day 8. The associations between genetic polymorphisms and the PPC were evaluated using multivariate logistic regression analysis including clinical variables. During the study period, 132 patients were enrolled. Six patients (4.5%) were defined as poor absorbers, and 49 patients (37.1%) did not reach the optimal PPC on day 8. In multivariate analysis, the independent risk factors for a poor absorber were at least one UGT1A4*3 allele (adjusted odds ratio [aOR], 18.81; 95% confidence interval [CI], 1.09 to 324.44; P = 0.043) and poor oral food intake (aOR per -100 kcal, 1.44; 95% CI, 1.04 to 1.99; P = 0.029). There was no statistically significant association between the genetic polymorphisms and achievement of the optimal PPC on day 8. The UGT1A4*3 polymorphism is an independent risk factor for being a poor absorber of posaconazole oral suspension in patients with hematological malignancies.

Physiologically-based pharmacokinetic modelling of a CYP2C19 substrate, BMS-823778, utilizing pharmacogenetic data

AIMS

Previous studies demonstrated direct correlation between CYP2C19 genotype and BMS-823778 clearance in healthy volunteers. The objective of the present study was to develop a physiologically-based pharmacokinetic (PBPK) model for BMS-823778 and use the model to predict PK and drug-drug interaction (DDI) in virtual populations with multiple polymorphic genes.

METHODS

The PBPK model was built and verified using existing clinical data. The verified model was simulated to predict PK of BMS-823778 and significance of DDI with a strong CYP3A4 inhibitor in subjects with various CYP2C19 and UGT1A4 genotypes.

RESULTS

The verified PBPK model of BMS-823778 accurately recovered observed PK in different populations. In addition, the model was able to capture the exposure differences between subjects with different CYP2C19 genotypes. PK simulation indicated higher exposures of BMS-823778 in CYP2C19 poor metabolizers who were also devoid of UGT1A4 activity, compared to those with normal UGT1A4 functionality. Moderate DDI with itraconazole was predicted in subjects with wild-type CYP2C19 or UGT1A4. However, in subjects without CYP2C19 or UGT1A4 functionality, significant DDI was predicted when BMS-823778 was coadministered with itraconazole.

CONCLUSIONS

A PBPK model was developed using clinical data that accurately predicted human PK in different population with various CYP2C19 phenotypes. Simulations with the verified PBPK model indicated that UGT1A4 was probably an important clearance pathway in CYP2C19 poor metabolizers. DDI with itraconazole is likely to be dependent on the genotypes of CYP2C19 and UGT1A4.

N-glucuronidation catalyzed by UGT1A4 and UGT2B10 in human liver microsomes: Assay optimization and substrate identification

N-glucuronidation is an important pathway for metabolism and disposition of tertiary amines in humans. This reaction is mainly catalyzed by the enzymes UGT1A4 and UGT2B10. However, the metabolic patterns of UGT1A4- and UGT2B10-mediated N-glucuronidation are not fully clear. In this study, we first optimized in vitro reaction conditions for N-glucuronidation by using specific substrates (i.e., trifluoperazine for UGT1A4, cotinine and amitriptyline for UGT2B10). Furthermore, we found that hepatic N-glucuronidation showed significant species differences. In addition, UGT1A4 and UGT2B10 were primarily responsible for N-glucuronidation of many tertiary amines, including asenapine, loxapine, clozapine, chlorpromazine, dothiepin, doxepin, mirtazapine, mianserin, chlorcyclizine, cyclizine, promethazine, cyclobenzaprine, imatinib, retrorsine, strychnine and brucine. In conclusion, this study provides an in vitro assay system for evaluating N-glucuronidation of amines. Also, UGT1A4- and UGT2B10-mediated N-glucuronidation might play significant roles in metabolism and detoxification of tertiary amines in humans.

No association between non-bullous skin reactions from lamotrigine and heterozygosity of UGT1A4 genetic variants *2(P24T) or *3(L48V) in Norwegian patients

PURPOSE

High initial serum concentrations increase the risk of cutaneous adverse reactions. Genetic variants of the main metabolizing isoenzyme, uridine diphosphate glucuronosyltransferase (UGT) 1A4 influence the elimination of lamotrigine (LTG). Our aim was to investigate the potential association between the two best studied variants, *2 (P24T) and *3 (L48V), and the occurrence non-bullous skin reactions from LTG.

METHOD

The study included 29 patients of Caucasian ethnicity with a history of non-bullous skin reactions from LTG. 184 subjects tolerant to LTG for at least three months were used as controls. UGT1A4 genotyping was performed in all patients and controls by sequencing of the first part of exon 1. Six controls were excluded due to rare genetic variants.

RESULTS

Two of 29 subjects (7%) with rash from LTG were heterozygous for UGT1A4 *2, compared to 23 of 178 (13%) tolerant controls (p=0.54). Four of 29 subjects (14%) with rash from LTG were heterozygous for UGT1A4 *3 compared to 25 of 178 (14%) tolerant controls (p=0.97).

CONCLUSION

It is unlikely that heterozygosity of the UGT1A4 genetic variants *2(P24T) or *3(L48V) influences the risk of non-bullous skin reactions in patients treated with LTG.

Identification of Human UDP-Glucuronosyltransferase 1A4 as the Major Isozyme Responsible for the Glucuronidation of 20(S)-Protopanaxadiol in Human Liver Microsomes

20(S)-protopanaxadiol (PPD), one of the representative aglycones of ginsenosides, has a broad spectrum of pharmacological activities. Although phase I metabolism has been investigated extensively, information regarding phase II metabolism of this compound remains to be elucidated. Here, a glucuronidated metabolite of PPD in human liver microsomes (HLMs) and rat liver microsomes (RLMs) was unambiguously identified as PPD-3-O-β-d-glucuronide by nuclear magnetic resonance spectroscopy and high resolution mass spectrometry. The chemical inhibition and recombinant human UDP-Glucuronosyltransferase (UGT) isoforms assay showed that the PPD glucuronidation was mainly catalyzed by UGT1A4 in HLM, whereas UGT1A3 showed weak catalytic activity. In conclusion, PPD-3-O-β-d-glucuronide was first identified as the principal glucuronidation metabolite of PPD in HLMs, which was catalyzed by UGT1A4.

Diethylstilbestrol can effectively accelerate estradiol-17-O-glucuronidation, while potently inhibiting estradiol-3-O-glucuronidation

This in vitro study investigates the effects of diethylstilbestrol (DES), a widely used toxic synthetic estrogen, on estradiol-3- and 17-O- (E2-3/17-O) glucuronidation, via culturing human liver microsomes (HLMs) or recombinant UDP-glucuronosyltransferases (UGTs) with DES and E2. DES can potently inhibit E2-3-O-glucuronidation in HLM, a probe reaction for UGT1A1. Kinetic assays indicate that the inhibition follows a competitive inhibition mechanism, with the Ki value of 2.1±0.3μM, which is less than the possible in vivo level. In contrast to the inhibition on E2-3-O-glucuronidation, the acceleration is observed on E2-17-O-glucuronidation in HLM, in which cholestatic E2-17-O-glucuronide is generated. In the presence of DES (0-6.25μM), Km values for E2-17-O-glucuronidation are located in the range of 7.2-7.4μM, while Vmax values range from 0.38 to 1.54nmol/min/mg. The mechanism behind the activation in HLM is further demonstrated by the fact that DES can efficiently elevate the activity of UGT1A4 in catalyzing E2-17-O-glucuronidation. The presence of DES (2μM) can elevate Vmax from 0.016 to 0.81nmol/min/mg, while lifting Km in a much lesser extent from 4.4 to 11μM. Activation of E2-17-O-glucuronidation is well described by a two binding site model, with KA, α, and β values of 0.077±0.18μM, 3.3±1.1 and 104±56, respectively. However, diverse effects of DES towards E2-3/17-O-glucuronidation are not observed in liver microsomes from several common experimental animals. In summary, this study issues new potential toxic mechanisms for DES: potently inhibiting the activity of UGT1A1 and powerfully accelerating the formation of cholestatic E2-17-O-glucuronide by UGT1A4.

Effects of UGT1A4 genetic polymorphisms on serum lamotrigine concentrations in Chinese children with epilepsy

Lamotrigine (LTG) is widely used in the treatment of children with epilepsy. Genetic polymorphisms in genes encoding drug-metabolizing enzymes may be an important source of interindividual variability in LTG metabolism. The aim of this study was to evaluate the effects of genetic polymorphisms of uridine diphosphate glucuronosyltransferase (UGT) 1A4 (UGT1A4) gene on LTG serum concentrations in children with epilepsy. The UGT1A4 142T > G in the coding regions and -219C > T/-163G > A in the 5'-upstream regions were genotyped using polymerase chain reaction amplification followed by direct automated DNA sequencing in 148 patients treated with polytherapy with LTG and valproic acid (VPA). Our data showed that patients carrying the variant UGT1A4 -219C > T/-163G > A genotypes or alleles had significantly higher adjusted LTG concentrations than those carrying the wild-type genotypes or alleles. However, the significant association was abrogated after adjusted by age, body weight, and adjusted VPA concentration. No associations were detected between the UGT1A4 142T > G genotypes or alleles and adjusted LTG concentrations. Taken together, these results suggest that the -219C > T/-163G > A mutations in the 5'-upstream regions of the UGT1A4 gene affect LTG pharmacokinetics, with which is potentially interfered by age, body weight, and concomitant VPA administration.

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.

Fulvestrant up regulates UGT1A4 and MRPs through ERα and c-Myb pathways: a possible primary drug disposition mechanism

Fulvestrant (Faslodex™) is a pure antiestrogen that is effective in treating estrogen receptor-(ER) positive breast cancer tumors that are resistant to selective estrogen receptor modulators such as tamoxifen. Clinical trials investigating the utility of adding fulvestrant to other therapeutics have not been shown to affect cytochrome P450-mediated metabolism. Effects on phase II metabolism and drug resistance have not been explored. This study demonstrates that fulvestrant up regulates the expression of UDP glucuronosyltransferase 1A4 (UGT1A4) >2.5- and >3.5-fold in MCF7 and HepG2 cells, respectively. Up regulation occurred in a time- and concentration-dependent manner, and was inhibited by siRNA silencing of ERα. Fulvestrant also up regulates multidrug resistance-associated proteins (MRPs). There was an up regulation of MRP2 (1.5- and 3.5-fold), and MRP3 (5.5- and 4.5-fold) in MCF7 and HepG2 cell lines, respectively, and an up regulation of MRP1 (4-fold) in MCF7 cells. UGT1A4 mRNA up regulation was significantly correlated with UGT1A4 protein expression, anastrozole glucuronidation, ERα mRNA expression and MRP mRNA expression, but not with ERα protein expression. Genetic variants in the UGT1A4 promoter (-163A, -217G and -219T) reduced the basal activity of UGT1A4 by 40-60%. In silico analysis indicated that transcription factor c-Myb binding capacity may be affected by these variations. Luciferase activity assays demonstrate that silencing c-Myb abolished UGT1A4 up regulation by fulvestrant in promoters with the common genotype (-163G, -217 T and -219C) in MCF7 cells. These data indicate that fulvestrant can influence the disposition of other UGT1A4 substrates. These findings suggest a clinically significant role for UGT1A4 and MRPs in drug efficacy.

Expression and functional relevance of UGT1A4 in a cohort of human drug-resistant epileptic brains

PURPOSE

Brain drug bioavailability is regulated by the blood-brain barrier (BBB). It was recently suggested that cytochrome P450 (CYP) enzymes could act in concert with multidrug transporter proteins to regulate drug penetration and distribution into the diseased brain. The possibility that phase II metabolic enzymes could be expressed in the epileptic brain has been not evaluated. Phase II enzymes are involved in the metabolism of common antiepileptic drugs (AEDs).

METHODS

Phase II enzyme UGT1A4 brain expression was evaluated in temporal lobe resections from patients with epilepsy. UGT1A4 expression was determined by western blot and immunocytochemistry in primary cultures of human drug-resistant brain endothelial human brain epileptic endothelial cells (EPI-EC)s and commercially available control cells human brain microvascular endothelial cells (HBMECs). Lack of DNA condensation measured by 4',6-diamidino-2-phenylindole (DAPI) was used as a surrogate marker of cell viability and was correlated to UGT1A4 expression high performance liquid chromatography ultraviolet detection (HPLC-UV) was used to quantify lamotrigine metabolism by EPI-EC and HBMEC. The appearance of the specific lamotrigine metabolite, 2-n glucuronide (MET-1), was also evaluated. Lamotrigine and MET-1 levels were measured in selected surgical brain and matched blood samples.

KEY FINDINGS

UGT1A4 expression was observed in BBB endothelial cells and neurons. Our quantification study revealed variable levels of UGT1A4 expression across the brain specimens analyzed. Neurons devoid of UGT1A4 expression displayed nuclear DAPI condensation, a sign of cellular distress. UGT1A4 overexpression in EPI-EC, as compared to HBMEC, was reflected by a proportional increase in lamotrigine metabolism. The lamotrigine metabolite, MET-1, was formed in vitro by EPI-EC and, to a lesser extent, by HBMEC. HPLC-UV measurements of brain and blood samples obtained from patients receiving lamotrigine prior to surgery revealed the presence of lamotrigine and its metabolites in the brain.

SIGNIFICANCE

These initial results suggest the presence of a phase II enzyme in the epileptic brain. Further studies are required to fully describe the pattern of brain UGT1A4 expression in relation to clinical variables and drug resistance.