Functional polymorphisms in UDP-glucuronosyl transferases and recurrence in tamoxifen-treated breast cancer survivors

Computer-Aided Drug Design (CADD) to De-Orphanize Marine Molecules: Finding Potential Therapeutic Agents for Neurodegenerative and Cardiovascular Diseases

Computer-aided drug design (CADD) techniques allow the identification of compounds capable of modulating protein functions in pathogenesis-related pathways, which is a promising line on drug discovery. Marine natural products (MNPs) are considered a rich source of bioactive compounds, as the oceans are home to much of the planet's biodiversity. Biodiversity is directly related to chemodiversity, which can inspire new drug discoveries. Therefore, natural products (NPs) in general, and MNPs in particular, have been used for decades as a source of inspiration for the design of new drugs. However, NPs present both opportunities and challenges. These difficulties can be technical, such as the need to dive or trawl to collect the organisms possessing the compounds, or biological, due to their particular marine habitats and the fact that they can be uncultivable in the laboratory. For all these difficulties, the contributions of CADD can play a very relevant role in simplifying their study, since, for example, no biological sample is needed to carry out an in-silico analysis. Therefore, the amount of natural product that needs to be used in the entire preclinical and clinical study is significantly reduced. Here, we exemplify how this combination between CADD and MNPs can help unlock their therapeutic potential. In this study, using a set of marine invertebrate molecules, we elucidate their possible molecular targets and associated therapeutic potential, establishing a pipeline that can be replicated in future studies.

Preliminary Pharmacogenomic-Based Predictive Models of Tamoxifen Response in Hormone-dependent Chilean Breast Cancer Patients

Tamoxifen (TAM), a selective oestrogen receptor modulator, is one of the most used treatments in oestrogen receptor-positive (ER+) early and metastatic breast cancer (BC) patients. The response to TAM has a high degree of inter-individual variability. This is mainly due to genetic variants in CYP2D6 gene, as well as other genes encoding proteins involved in the TAM pharmacokinetic and/or pharmacodynamic. Therefore, prediction of the TAM response using these genetic factors together with other non-genetic variables may be relevant to improve breast cancer treatment. Thus, in this work, we used genetic polymorphisms and clinical variables for TAM response modelling. One hundred sixty-two ER + BC patients with 2 years of TAM treatment were retrospectively recruited, and the genetic polymorphisms CYP2D6*4, CYP3A4*1B (CYP3A4*1.001), CYP3A5*3, UGT2B7*2, UGT2B15*2, SULT1A1*2, and ESRA V364E were analyzed by PCR-RFLP. Concomitantly, the therapeutic response was obtained from clinical records for association with genotypes using univariate and multivariate biostatistical models. Our results show that UGT2B15*1/*2 genotype protects against relapse (OR = 0.09; p = 0.02), CYP3A5*3/*3 genotype avoids endometrial hyperplasia (OR = 0.07; p = 0.01), SULT1A1*1/*2 genotype avoids vaginal bleeding (OR = 0.09; p = 0.03) and ESRA 364E/364E genotype increases the probability of vaginal bleeding (OR = 5.68; p = 0.02). Logistic regression models, including genomic and non-genomic variables, allowed us to obtain preliminary predictive models to explain relapse (p = 0.010), endometrial hyperplasia (p = 0.002) and vaginal bleeding (p = 0.014). Our results suggest that the response to TAM treatment in ER + BC patients might be associated with the presence of the studied genetic variants in UGT2B15, CYP3A5, SULT1A1 and ESRA genes. After clinical validation protocols, these models might be used to help to predict a percentage of BC relapse and adverse reactions, improving the individual response to TAM-based treatment.

Genetic Influences in Breast Cancer Drug Resistance

Breast cancer is the most common cancer in adult women aged 20 to 50 years. The therapeutic regimens that are commonly recommended to treat breast cancer are human epidermal growth factor receptor 2 (HER2) targeted therapy, endocrine therapy, and systemic chemotherapy. The selection of pharmacotherapy is based on the characteristics of the tumor and its hormone receptor status, specifically, the presence of HER2, progesterone receptors, and estrogen receptors. Breast cancer pharmacotherapy often gives different results in various populations, which may cause therapeutic failure. Different types of congenital drug resistance in individuals can cause this. Genetic polymorphism is a factor in the occurrence of congenital drug resistance. This review explores the relationship between genetic polymorphisms and resistance to breast cancer therapy. It considers studies published from 2010 to 2020 concerning the relationship of genetic polymorphisms and breast cancer therapy. Several gene polymorphisms are found to be related to longer overall survival, worse relapse-free survival, higher pathological complete response, and increased disease-free survival in breast cancer patients. The presence of these gene polymorphisms can be considered in the treatment of breast cancer in order to shape personalized therapy to yield better results.

Pharmacogenetics of tamoxifen therapy in Asian populations: from genetic polymorphism to clinical outcomes

BACKGROUND

Compared with western countries, Asian breast cancer patients have unique pathological and biological characteristics. Most of them are premenopausal women with HR positive. Tamoxifen as the first-line drug for premenopausal women with HR+ is involved in multiple enzymes and transporters during metabolizing and transporting process. Variants that cause decreased or inactive gene products leading to abnormal responses in tamoxifen therapy have well been studied in western countries, whereas such information is much less reported in Asian populations.

OBJECTIVE

In order to elucidate the relationship between genetic variants and tamoxifen-induced individual drug reactions in different Asian populations and further identify genotypes/phenotypes with potential therapeutic significance.

METHODS

We reviewed the frequencies of genetic variants in major enzymes and transporter genes involved in the metabolism and transport of tamoxifen across Asian populations as well as significant correlations between genotypes/metabolic phenotypes and metabolites concentrations or BC clinical outcomes.

RESULTS

Significant inter-ethnic differences in allele frequencies was found among Asian populations, such as CYP2D6*4, *10, *41, CYP2C9*2, ABCB1 C3435T and SLCO1B1*5, and CYP2D6*10/*10 is the most common genotype correlated with adverse clinical outcomes. Moreover, we summarized the barriers and controversies of implementing pharmacogenetics in tamoxifen therapy and concluded that more population-specific pharmacogenetic studies are needed in the future.

CONCLUSION

This review revealed more systematic pharmacogenomics of genes involved in the metabolism and transport besides CYP2D6, are required to optimize the genotyping strategies and guide the personalized tamoxifen therapy in Asian populations.

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.

Multi-drug resistance protein 2 (MRP2) expression, adjuvant tamoxifen therapy, and risk of breast cancer recurrence: a Danish population-based nested case-control study

BACKGROUND

Adjuvant tamoxifen therapy approximately halves the risk of recurrence in estrogen receptor-positive (ER+) breast cancer patients, but many women respond insufficiently to therapy. Expression of multi-drug resistance protein 2 (MRP2) in breast cancer may potentiate tamoxifen resistance. Thus, we investigated the expression of MRP2 in breast cancer as a predictor of tamoxifen therapy effectiveness.

MATERIAL AND METHODS

We conducted a case-control study nested in the Danish Breast Cancer Group clinical database. The study included women aged 35-69 years diagnosed with stage l-lll breast cancer during 1985-2001, in Jutland, Denmark. We identified 541 recurrent breast cancers (cases) among women with estrogen receptor positive (ER+) disease treated with tamoxifen for at least 1 year (ER+/TAM+) and 300 cases among women with estrogen receptor-negative (ER-) disease, never treated with tamoxifen (ER-/TAM-). We matched one recurrence-free control to each recurrent case. We retrieved paraffin-embedded primary tumor tissue for all patients, and all available recurrent tumor tissue from pathology archives. MRP2 expression was evaluated using immunohistochemistry. We computed odds ratios (ORs) and 95% confidence intervals (95% CIs) associating MRP2 expression (positive vs. none) with breast cancer recurrence in conditional logistic regression models. We compared MRP2 expression in paired primary- and recurrent tumors.

RESULTS

MRP2 expression was more prevalent in the ER+/TAM + group, than in the ER-/TAM - group. No predictive utility of MRP2 for breast cancer recurrence was found in the ER+/TAM + group (OR_adj = 0.96, 95% CI 0.70, 1.33). Further, no prognostic utility was found in the ER-/TAM - group (OR_adj = 0.81, 95% CI 0.53, 1.23). MRP2 expression was not increased in recurrent versus primary tumors.

CONCLUSIONS

MRP2 expression is neither a predictive marker of tamoxifen effectiveness nor a prognostic marker in breast cancer.

Cohort Profile: the Predictors of Breast Cancer Recurrence (ProBe CaRE) Premenopausal Breast Cancer Cohort Study in Denmark

PURPOSE

The Predictors of Breast Cancer Recurrence (ProBe CaRe) study was established to evaluate modification of tamoxifen (TAM) effectiveness in premenopausal women through reduced activity of TAM-metabolising enzymes. It comprehensively evaluates the effects of pharmacogenetic variants, use of concomitant medications and biomarkers involved in oestrogen metabolism on breast cancer recurrence risk.

PARTICIPANTS

The ProBe CaRe study was established using resources from the Danish Breast Cancer Group (DBCG), including 5959 premenopausal women diagnosed with stage I-III primary breast cancer between 2002 and 2010 in Denmark. Eligible participants were divided into two groups based on oestrogen receptor alpha (ERα) expression and receipt of TAM therapy, 4600 are classified as ERα+/TAM+ and 1359 are classified as ERα-/TAM-. The ProBe CaRe study is a population-based cohort study nested in a nearly complete source population, clinical, tumour and demographic data were abstracted from DBCG registry data. Linkage to Danish registries allows for abstraction of information regarding comorbid conditions, comedication use and mortality. Formalin-fixed paraffin-embedded tissue samples have been prepared for DNA extraction and immunohistochemical assay.

FINDINGS TO DATE

To mitigate incorrect classification of patients into specific categories, we conducted a validation substudy. We compared data acquired from registry and from medical record review to calculate positive predictive values (PPVs) and negative predictive values. We observed PPVs near 100% for tumour size, lymph node involvement, receptor status, surgery type, receipt of radiotherapy, receipt of chemotherapy and TAM treatment. We found that the PPVs were 96% (95% CI 83% to 100%) for change in endocrine therapy and 61% (95% CI 42% to 77%) for menopausal transition.

FUTURE PLANS

The ProBeCaRe cohort study is well positioned to comprehensively examine pharmacogenetic variants. We will use a Bayesian pathway analysis to evaluate the complete TAM metabolic path to allow for gene-gene interactions, incorporating information of other important patient characteristics.

Tamoxifen and CYP2D6: A Controversy in Pharmacogenetics

Tamoxifen reduces the rate of breast cancer recurrence by about one-half. It is converted to more active metabolites by enzymes encoded by polymorphic genes, including cytochrome P450 2D6 (CYP2D6) and transported by ATP-binding cassette transporters. Genetic polymorphisms that confer reduced CYP2D6 activity or concurrent use of CYP2D6-inhibiting drugs may reduce the clinical efficacy of tamoxifen. The issue of the clinical utility of CYP2D6 genotype testing is subject to considerable and ongoing academic and clinical controversy. In this chapter, we outline tamoxifen's clinical pharmacology and give an overview of the research to date on the association between CYP2D6 inhibition and tamoxifen effectiveness. Based on the evidence to date, the impact of drug-induced and/or gene-induced inhibition of CYP2D6 activity is likely to be null or small, or at most moderate in subjects carrying two reduced function alleles. Future research should examine the effect of polymorphisms in genes encoding enzymes in tamoxifen's complete metabolic pathway, should comprehensively evaluate other biomarkers that affect tamoxifen effectiveness, such as the transport enzymes, and focus on subgroups of patients, such as premenopausal breast cancer patients, for whom tamoxifen is the only guideline approved endocrine therapy.

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.

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.

Metabolism and transport of tamoxifen in relation to its effectiveness: new perspectives on an ongoing controversy

Tamoxifen reduces the rate of breast cancer recurrence by approximately a half. Tamoxifen is metabolized to more active metabolites by enzymes encoded by polymorphic genes, including cytochrome P450 2D6 (CYP2D6). Tamoxifen is a substrate for ATP-binding cassette transporter proteins. We review tamoxifen's clinical pharmacology and use meta-analyses to evaluate the clinical epidemiology studies conducted to date on the association between CYP2D6 inhibition and tamoxifen effectiveness. Our findings indicate that the effect of both drug-induced and/or gene-induced inhibition of CYP2D6 activity is likely to be null or small, or at most moderate in subjects carrying two reduced function alleles. Future research should examine the effect of polymorphisms in genes encoding enzymes in tamoxifen's complete metabolic pathway, should comprehensively evaluate other biomarkers that affect tamoxifen effectiveness, such as the transport enzymes, and focus on subgroups of patients, such as premenopausal breast cancer patients, for whom tamoxifen is the only guideline endocrine therapy.

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.

Phase two steroid metabolism and its roles in breast and prostate cancer patients

Breast and prostate cancer are diseases in which steroids and steroid metabolism could markedly influence clinical outcomes for patients. In both malignancies the modification of ketone and hydroxyl groups attached to the steroid backbone (phase one metabolism) has been examined in detail but the conjugation reactions (phase two metabolism) have not been extensively studied. Therefore, in this review we aim to summarize phase two metabolism in breast and prostate cancers from a number of perspectives, including the impact of variation in serum levels of conjugated steroids, tissue, and pathology specific expression of phase two enzymes, and consequences of genetic variations of these conjugation enzymes. In addition to this biological perspective, we will also address current pharmacological efforts to manipulate phase two metabolism as a potential therapy for hormone dependent cancers, including clinical trials of STS inhibitors and preclinical STS inhibitor development. While this review is not intended to cover any one particular area in great technical depth, it is intended as an introduction to and/or update on the importance of variance in phase two metabolic pathways in breast and prostate cancers.

Effects of CYP2D6 and UGT2B7 polymorphisms on pharmacokinetics of tamoxifen in Thai breast cancer patients

PURPOSE

The objective of this study was to evaluate the impact of CYP2D6 and UGT2B7 polymorphisms on tamoxifen (TAM) pharmacokinetics in Thai breast cancer patients.

METHODS

Thai female breast cancer patients treated with TAM were included in the study. Patients were genotyped for CYP2D6 and UGT2B7 polymorphism, and plasma levels of TAM and its potent active metabolite endoxifen (END), at steady state, were identified.

RESULTS

Fifty-nine female breast cancer patients were included in the study. The average age was 50 ± 9.3 years old; 76% were premenopausal and 85% had estrogen receptor-positive breast cancer. The allele frequencies of CYP2D6*10 and UGT2B7*2 were 53% and 28%, respectively. Patients with CYP2D6*10/*10 had lower END concentrations compared with CYP2D26*1/*10 and CYP2D6*1/*1 (9.62 ng/mL versus 15.67 ng/mL and 21.55 ng/mL, respectively, P = 0.045). Polymorphisms of UGT2B7 alone did not have any impact on TAM metabolism. However, among 20 patients with CYP2D6*10/*10, one with UGT2B7*2/*2 had higher END concentrations compared against patients with UGT2B7*1/*1 and UGT2B7*1/*2 (31.36 ng/mL versus 7.86 ng/mL, respectively, P = 0.023).

CONCLUSION

Results from this study confirmed the impacts of CYP2D6 polymorphisms on the pharmacokinetics of TAM, while UGT2B7 polymorphisms tended to have impact on TAM metabolism in patients with homozygous CYP2D6*10.

Variants in tamoxifen metabolizing genes: a case-control study of contralateral breast cancer risk in the WECARE study

Tamoxifen has been shown to greatly reduce risk of recurrence and contralateral breast cancer (CBC). Still, second primary contralateral breast cancer is the most common malignancy to follow a first primary breast cancer. Genetic variants in CYP2D6 and other drug-metabolizing enzymes that alter the metabolism of tamoxifen may be associated with CBC risk in women who receive the drug. This is the first study to investigate the impact of this variation on risk of CBC in women who receive tamoxifen. From the population-based Women's Environment Cancer and Radiation Epidemiology (WECARE) Study, we included 624 Caucasian women with CBC (cases) and 1,199 women with unilateral breast cancer (controls) with complete information on tumor characteristics and treatment. Conditional logistic regression was used to assess the risk of CBC associated with 112 single nucleotide polymorphisms (SNPs) in 8 genes involved in the metabolism of tamoxifen among tamoxifen users and non-users. After adjustment for multiple testing, no significant association was observed between any of the genotyped variants and CBC risk in either tamoxifen users or non-users. These results suggest that when using a tagSNP approach, common variants in selected genes involved in the metabolism of tamoxifen are not associated with risk of CBC among women treated with the drug.

Functional polymorphisms in xenobiotic metabolizing enzymes and their impact on the therapy of breast cancer

Breast cancer is the top cancer among women, and its incidence is increasing worldwide. Although the mortality tends to decrease due to early detection and treatment, there is great variability in the rates of clinical response and survival, which makes breast cancer one of the most appealing targets for pharmacogenomic studies. The recognition that functional CYP2D6 polymorphisms affect tamoxifen pharmacokinetics has motivated the attempts of using CYP2D6 genotyping for predicting breast cancer outcomes. In addition to tamoxifen, the chemotherapy of breast cancer includes combinations of cytotoxic drugs, which are substrates for various xenobiotic metabolizing enzymes. Because of these drugs’ narrow therapeutic window, it has been postulated that impaired biotransformation could lead to increased toxicity. In the present review, we performed a systematic search of all published data exploring associations between polymorphisms in xenobiotic metabolizing enzymes and clinical outcomes of breast cancer. We retrieved 43 original articles involving either tamoxifen or other chemotherapeutic protocols, and compiled all information regarding response or toxicity. The data indicate that, although CYP2D6 polymorphisms can indeed modify tamoxifen pharmacokinetics, CYP2D6 genotyping alone is not enough for predicting breast cancer outcomes. The studies involving other chemotherapeutic protocols explored a great diversity of pharmacogenetic targets, but the number of studies for each functional polymorphism is still very limited, with usually no confirmation of positive associations. In conclusion, the application of pharmacogenetics to predict breast cancer outcomes and to select one individual’s chemotherapeutic protocol is still far from clinical routine. Although some very interesting results have been produced, no clear practical recommendations are recognized yet.