PharmGKB summary: tamoxifen pathway, pharmacokinetics

Hormonal status affects plasma exposure of tamoxifen and its main metabolites in tamoxifen-treated breast cancer patients

Background

Tamoxifen is considered a prodrug of its active metabolite endoxifen, which is dependent on the CYP2D6 and CYP3A enzymes. Tamoxifen pharmacokinetic variability influences endoxifen exposure and, consequently, its clinical outcome. This study investigated the impact of hormonal status on the pharmacokinetics of tamoxifen and its metabolites in TAM-treated breast cancer patients.

Methods

TAM-treated breast cancer patients (n = 40) previously believed to have CYP3A activity within the normal range based on oral midazolam and phenotyped as CYP2D6 normal metabolizers using oral metoprolol were divided into two groups according to premenopausal (n = 20; aged 35–50 years) or postmenopausal (n = 20; aged 60–79 years) status. All patients were treated with 20 mg/day tamoxifen for at least three months. Serial plasma samples were collected within the 24 h dose interval for analysis of unchanged tamoxifen, endoxifen, 4-hydroxytamoxifen and N-desmethyltamoxifen quantified by LC-MS/MS. CYP activities were assessed using midazolam apparent clearance (CYP3A) and the metoprolol/alfa-hydroxymetoprolol plasma metabolic ratio (CYP2D6). CYP3A4, CYP3A5 and CYP2D6 SNPs and copy number variation were investigated using TaqMan assays.

Results

Postmenopausal status increased steady-state plasma concentrations (Css) of tamoxifen (116.95 vs 201.23 ng/mL), endoxifen (8.01 vs 18.87 ng/mL), N-desmethyltamoxifen (485.16 vs 843.88 ng/mL) and 4-hydroxytamoxifen (2.67 vs 4.11 ng/mL). The final regression models included hormonal status as the only predictor for Css of tamoxifen [β-coef ± SE, p-value (75.03 ± 17.71, p = 0.0001)] and 4-hydroxytamoxifen (1.7822 ± 0.4385, p = 0.0002), while endoxifen Css included hormonal status (8.578 ± 3.402, p = 0.02) and race (11.945 ± 2.836, p = 0.007). For N-desmethyltamoxifen Css, the final model was correlated with hormonal status (286.259 ± 76.766, p = 0.0007) and weight (− 8.585 ± 3.060, p = 0.008).

Conclusion

The premenopausal status was associated with decreased endoxifen plasma concentrations by 135% compared to postmenopausal status. Thus, the endoxifen plasma concentrations should be monitored mainly in the premenopausal period to maintain plasma levels above the efficacy threshold value.

Trial registration

RBR-7tqc7k.

Tamoxifen and Sulphoraphane for the breast cancer management: A synergistic nanomedicine approach

Breast cancer is second most leading cause of death in all over the world and not only limited to the females. Tamoxifen has been considered as the gold line therapy for estrogen receptor positive breast cancer. However, this chemopreventive approach has been focused at individuals in high risk group and limits its clinical applications to moderate and/or lower risk groups. Moreover, Tamoxifen treatment is associated with a dose related hepatotoxicity and nephrotoxicity and eventually results in poor quality of life of patients. Sulphoraphane, a naturally occurring isothiocyanate derivative has been investigated for its numerous potential biological activities including anticancer effects. The present hypothesis aims to put forward in which Tamoxifen is combined with a natural bioactive Sulphoraphane, both incorporated into a novel lipid based nanocarrier at a reduced dose, which would eventually shuttle the cargo to the target site. At the breast cancer, Sulphoraphane sensitizes the estrogen receptors and ameliorates the binding affinity of Tamoxifen to these receptors, thereby potentiating the anticancer efficacy and reducing the offsite toxicity of Tamoxifen. This dual loaded zero-dimension lipid carrier would be a value addition to the current treatment regimen for breast cancer management.

CYP2D6 Genotype Predicts Plasma Concentrations of Tamoxifen Metabolites in Ethiopian Breast Cancer Patients

Tamoxifen displays wide inter-individual variability (IIV) in its pharmacokinetics and treatment outcome. Data on tamoxifen pharmacokinetics and pharmacogenetics from black African breast cancer patient populations is lacking. We investigated the pharmacokinetic and pharmacogenetic profile of tamoxifen and its major active metabolite, endoxifen, in Ethiopian breast cancer patients. A total of 81 female breast cancer patients on adjuvant tamoxifen therapy were enrolled. Tamoxifen (Tam) and its major metabolites, N-desmethyltamoxifen (NDM), 4-hydroxy-tamoxifen (4-HT), and (Z)-endoxifen (E) were quantified using LC-MS/MS. Genotyping for CYP2D6, CYP2C9, CYP2C19, CYP3A5, POR, and ABCB1 and UGT2B15 and copy number variation for CYP2D6 were done. The proportion of patients with low endoxifen level (<5.9 ng/mL) was 35.8% (median concentration 7.94 ng/mL). The allele frequency of CYP2D6 gene deletion (*5) and duplication (*1×N or *2×N) was 4.3% and 14.8%, respectively. Twenty-six percent of the patients carried duplicated or multiplicated CYP2D6 gene. An increase in CYP2D6 activity score was associated with increased endoxifen concentration and MR_E/NDM (p < 0.001). The IIV in endoxifen concentration and MR_E/NDM was 74.6% and 59%, respectively. CYP2D6 diplotype explained 28.2% and 44% of the variability in absolute endoxifen concentration and MR_E/NDM, respectively. The explanatory power of CYP2D6 diplotype was improved among ABCB1c.4036G carriers (43% and 65.2%, respectively for endoxifen concentration and MR_E/NDM) compared to A/A genotype. CYP2C9, CYP2C19, and CYP3A5 genotypes had no significant influence on endoxifen concentration or MR_E/NDM. In conclusion, we report a high rate of low endoxifen level as well as large IIV in tamoxifen and its metabolite concentrations. CYP2D6 is significant predictor of plasma endoxifen level in a gene-dose dependent manner.

Drug monitoring of tamoxifen metabolites predicts vaginal dryness and verifies a low discontinuation rate from the Norwegian Prescription Database

PURPOSE

Tamoxifen is an important targeted endocrine therapy in breast cancer. However, side effects and early discontinuation of tamoxifen remains a barrier for obtaining the improved outcome benefits of long-term tamoxifen treatment. Biomarkers predictive of tamoxifen side effects remain unidentified. The objective of this prospective population-based study was to investigate the value of tamoxifen metabolite concentrations as biomarkers for side effects. A second objective was to assess the validity of discontinuation rates obtained through pharmacy records with the use of tamoxifen drug monitoring.

METHODS

Longitudinal serum samples, patient-reported outcome measures and pharmacy records from 220 breast cancer patients were obtained over a 6-year period. Serum concentrations of tamoxifen metabolites were measured by LC-MS/MS. Associations between metabolite concentrations and side effects were analyzed by logistic regression and cross table analyses. To determine the validity of pharmacy records we compared longitudinal tamoxifen concentrations to discontinuation rates obtained through the Norwegian Prescription database (NorPD). Multivariable Cox regression models were performed to identify predictors of discontinuation.

RESULTS

At the 2nd year of follow-up, a significant association between vaginal dryness and high concentrations of tamoxifen, Z-4'-OHtam and tam-NoX was identified. NorPD showed a tamoxifen-discontinuation rate of 17.9% at 5 years and drug monitoring demonstrated similar rates. Nausea, vaginal dryness and chemotherapy-naive status were significant risk factors for tamoxifen discontinuation.

CONCLUSIONS

This real-world data study suggests that measurements of tamoxifen metabolite concentrations may be predictive of vaginal dryness in breast cancer patients and verifies NorPD as a reliable source of adherence data.

Potential premalignant status of gastric portion excluded after Roux en-Y gastric bypass in obese women: A pilot study

We evaluated whether the excluded stomach (ES) after Roux-en-Y gastric bypass (RYGB) can represent a premalignant environment. Twenty obese women were prospectively submitted to double-balloon enteroscopy (DBE) with gastric juice and biopsy collection, before and 3 months after RYGB. We then evaluated morphological and molecular changes by combining endoscopic and histopathological analyses with an integrated untargeted metabolomics and transcriptomics multiplatform. Preoperatively, 16 women already presented with gastric histopathological alterations and an increased pH (≥4.0). These gastric abnormalities worsened after RYGB. A 90-fold increase in the concentration of bile acids was found in ES fluid, which also contained other metabolites commonly found in the intestinal environment, urine, and faeces. In addition, 135 genes were differentially expressed in ES tissue. Combined analysis of metabolic and gene expression data suggested that RYGB promoted activation of biological processes involved in local inflammation, bacteria overgrowth, and cell proliferation sustained by genes involved in carcinogenesis. Accumulated fluid in the ES appears to behave as a potential premalignant environment due to worsening inflammation and changing gene expression patterns that are favorable to the development of cancer. Considering that ES may remain for the rest of the patient’s life, long-term ES monitoring is therefore recommended for patients undergoing RYGB.

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.

CYP2D6 as a treatment decision aid for ER-positive non-metastatic breast cancer patients: a systematic review with accompanying clinical practice guidelines

PURPOSE

Tamoxifen is one of the principal treatments for estrogen receptor (ER)-positive breast cancer. Unfortunately, between 30 and 50% of patients receiving this hormonal therapy relapse. Since CYP2D6 genetic variants have been reported to play an important role in survival outcomes after treatment with tamoxifen, this study sought to summarize and critically appraise the available scientific evidence on this topic.

METHODS

A systematic literature review was conducted to identify studies investigating associations between CYP2D6 genetic variation and survival outcomes after tamoxifen treatment. Critical appraisal of the retrieved scientific evidence was performed, and recommendations were developed for CYP2D6 genetic testing in the context of tamoxifen therapy.

RESULTS

Although conflicting literature exists, the majority of the current evidence points toward CYP2D6 genetic variation affecting survival outcomes after tamoxifen treatment. Of note, review of the CYP2D6 genotyping assays used in each of the studies revealed the importance of comprehensive genotyping strategies to accurately predict CYP2D6 metabolizer phenotypes.

CONCLUSIONS AND RECOMMENDATIONS

Critical appraisal of the literature provided evidence for the value of comprehensive CYP2D6 genotyping panels in guiding treatment decisions for non-metastatic ER-positive breast cancer patients. Based on this information, it is recommended that alternatives to standard tamoxifen treatments may be considered in CYP2D6 poor or intermediate metabolizers.

Effects of CYP2D6*10 polymorphism on tamoxifen pharmacokinetics in patients with breast cancer in Asia: a meta-analysis

PURPOSE

Insufficient serum metabolite concentrations of tamoxifen can compromise treatment efficacy in patients with breast cancer. The purpose of this meta-analysis was to explore correlations between cytochrome P450 (CYP) 2D6*10 gene polymorphisms and serum concentrations of tamoxifen and its active metabolites in patients with breast cancer in Asia.

METHODS

The study included a systematic literature search for cohort studies published before March 2018 in English databases (PubMed, Embase, Cochrane Library, and Web of Science) and Chinese databases (Chinese National Knowledge Infrastructure and Wan Fang database). The meta-analysis was performed using RevMan 5.3 software. Pooled means and standard deviations were calculated with 95% confidence intervals. Publication bias and sensitivity analyses were also performed using STATA 14.0.

RESULTS

In total, 7 studies and 552 patients were included in the meta-analysis. Serum concentrations of endoxifen were significantly different in each CYP2D6*10 genotype group (p < 0.05). The CC genotype was associated with higher concentrations of 4-OH-TAM than the CT/TT genotype (p < 0.05). However, there were no statistically significant between-group differences in serum concentrations of TAM (p > 0.05). Publication bias and sensitivity analyses confirmed that the meta-analysis results were stable and reliable.

CONCLUSIONS

CYP2D6*10 polymorphisms influence the pharmacokinetics of tamoxifen in patients with breast cancer in Asia.

Genetic polymorphisms of 3'-untranslated region of SULT1A1 and their impact on tamoxifen metabolism and efficacy

Purpose

Tamoxifen has a wide inter-variability. Recently, two SNPs in the 3′-untranslated region (UTR) of the SULT1A1 gene, rs6839 and rs1042157, have been associated with decreased SULT1A1 activity. The aim of this study is to investigate the role of the rs6839 and rs1042157 on tamoxifen metabolism and relapse-free survival (RFS) in women diagnosed with early-breast cancer receiving tamoxifen.

Methods

Samples from 667 patients collected in the CYPTAM study (NTR1509) were used for genotyping (CYP2D6, SULT1A1 rs6839 and rs1042157) and measurements of tamoxifen and metabolites. Patients were categorized in three groups depending on the decreased SULT1A1 activity due to rs6839 and rs1042157: low activity group (rs6839 (GG) and rs1042157 (TT)); high activity group (rs6839 (AA) and rs1042157 (CC)); and medium activity group (all the other combinations of rs6839 and rs1042157). Associations between SULT1A1 phenotypes and clinical outcome (RFS) were explored.

Results

In the low SULT1A1 activity group, higher endoxifen and 4-hydroxy-tamoxifen concentrations were found, compared to the medium and high activity group (endoxifen: 31.23 vs. 30.51 vs. 27.00, p value: 0.016; 4-hydroxy-tamoxifen: 5.55 vs. 5.27 vs. 4.94, p value:0.05). In terms of relapse, the low activity group had a borderline better outcome compared to the medium and high SULT1A1 activity group (adjusted Hazard ratio: 0.297; 95% CI 0.088–1.000; p value: 0.05).

Conclusion

Our results suggested that rs6839 and rs1042157 SNPs have a minor effect on the concentrations and metabolic ratios of tamoxifen and its metabolites, and RFS in women receiving adjuvant tamoxifen.

Electronic supplementary material

The online version of this article (10.1007/s10549-018-4923-7) contains supplementary material, which is available to authorized users.

Interactions between Alcohol Consumption and Adjuvant Hormone Therapy in Relation to Breast Cancer-Free Survival

Purpose

Alcohol consumption is associated with an increase in breast cancer risk, but findings on the association of alcohol with survival after breast cancer diagnosis have been inconsistent. Further, whether these associations could differ by adjuvant hormone therapy status is unknown. We examined interactions between alcohol consumption and adjuvant hormone therapy in relation to breast cancer-free survival among women with a primary breast cancer diagnosis.

Methods

Participants in this study included 1,399 women diagnosed with primary breast cancer between 2007 and 2012 at the Moffitt Cancer Center. Alcohol consumption during the year preceding diagnosis was assessed in a patient survey. Information on tumor characteristics, breast cancer treatment and outcomes was available from the Moffitt Cancer Registry. Associations were examined using Cox proportional hazards models in stratified analyses by adjuvant hormone therapy status, after adjustment for potential confounders.

Results

Overall, alcohol consumption was associated with significantly improved breast cancer-free survival (any vs. none: hazard ratio [HR], 0.77; 95% confidence interval [CI], 0.65–0.92). Among women without adjuvant hormone therapy, alcohol consumption was associated with better survival in heavy drinkers (HR, 0.63; 95% CI, 0.43–0.93). Among women with adjuvant hormone therapy, survival was better in women consuming alcohol as compared to nondrinkers (moderate: HR, 0.69, 95% CI, 0.51–0.93; heavy: HR, 0.74, 95% CI, 0.57–0.96; any: HR, 0.71, 95% CI, 0.57–0.87). There was no significant interaction between alcohol and adjuvant hormone therapy (p-interaction=0.54 for alcohol modeled as none or any and p=0.34 for alcohol modeled as none, moderate, and heavy).

Conclusion

Associations of alcohol consumption with breast cancer-free survival are similar in women with and without adjuvant hormone therapy. Future studies are warranted to elucidate potential mechanisms underlying the observed inverse associations.

The impact of pharmacokinetic gene profiles across human cancers

BACKGROUND

The right drug to the right patient at the right time is one of the ideals of Individualized Medicine (IM) and remains one of the most compelling promises of the post-genomic age. The addition of genomic information is expected to increase the precision of an individual patient's treatment, resulting in improved outcomes. While pilot studies have been encouraging, key aspects of interpreting tumor genomics information, such as somatic activation of drug transport or metabolism, have not been systematically evaluated.

METHODS

In this work, we developed a simple rule-based approach to classify the therapies administered to each patient from The Cancer Genome Atlas PanCancer dataset (n = 2858) as effective or ineffective. Our Therapy Efficacy model used each patient's drug target and pharmacokinetic (PK) gene expression profile; the specific genes considered for each patient depended on the therapies they received. Patients who received predictably ineffective therapies were considered at high-risk of cancer-related mortality and those who did not receive ineffective therapies were considered at low-risk. The utility of our Therapy Efficacy model was assessed using per-cancer and pan-cancer differential survival.

RESULTS

Our simple rule-based Therapy Efficacy model classified 143 (5%) patients as high-risk. High-risk patients had age ranges comparable to low-risk patients of the same cancer type and tended to be later stage and higher grade (odds ratios of 1.6 and 1.4, respectively). A significant pan-cancer association was identified between predictions of our Therapy Efficacy model and poorer overall survival (hazard ratio, HR = 1.47, p = 6.3 × 10^- 3). Individually, drug export (HR = 1.49, p = 4.70 × 10^- 3) and drug metabolism (HR = 1.73, p = 9.30 × 10^- 5) genes demonstrated significant survival associations. Survival associations for target gene expression are mechanism-dependent. Similar results were observed for event-free survival.

CONCLUSIONS

While the resolution of clinical information within the dataset is not ideal, and modeling the relative contribution of each gene to the activity of each therapy remains a challenge, our approach demonstrates that somatic PK alterations should be integrated into the interpretation of somatic transcriptomic profiles as they likely have a significant impact on the survival of specific patients. We believe that this approach will aid the prospective design of personalized therapeutic strategies.

Clinical Pharmacogenetics Implementation Consortium (CPIC) Guideline for CYP2D6 and Tamoxifen Therapy

Tamoxifen is biotransformed by CYP2D6 to 4-hydroxytamoxifen and 4-hydroxy N-desmethyl tamoxifen (endoxifen), both with greater antiestrogenic potency than the parent drug. Patients with certain CYP2D6 genetic polymorphisms and patients who receive strong CYP2D6 inhibitors exhibit lower endoxifen concentrations and a higher risk of disease recurrence in some studies of tamoxifen adjuvant therapy of early breast cancer. We summarize evidence from the literature and provide therapeutic recommendations for tamoxifen based on CYP2D6 genotype.

Serum concentrations of active tamoxifen metabolites predict long-term survival in adjuvantly treated breast cancer patients

Background

Controversies exist as to whether the genetic polymorphisms of the enzymes responsible for the metabolism of tamoxifen can predict breast cancer outcome in patients using adjuvant tamoxifen. Direct measurement of concentrations of active tamoxifen metabolites in serum may be a more biological plausible and robust approach. We have investigated the association between CYP2D6 genotypes, serum concentrations of active tamoxifen metabolites, and long-term outcome in tamoxifen treated breast cancer patients.

Methods

From an original observational study comprising 817 breast cancer patients, 99 women with operable breast cancer were retrospectively included in the present study. This cohort of patients were adjuvantly treated with tamoxifen, had provided serum samples suitable for measuring tamoxifen metabolites, and were relapse-free at 3 years after the primary treatment commenced. The median follow-up time from this entry point to breast cancer death was 13.9 years. Patients were CYP2D6 genotyped and grouped into four CYP2D6 phenotype groups (Ultra rapid, extensive, intermediate, and poor metabolizers). Tamoxifen and nine metabolites were quantified in serum (n = 86) and compared with CYP2D6 phenotype groups and outcome.

Results

Breast cancer patients with low concentrations of Z-4-hydroxy-tamoxifen (Z-4OHtam; ≤ 3.26 nM) had a breast cancer-specific survival (BCSS) of 60% compared to 84% in patients with Z-4OHtam concentrations > 3.26 nM (p = 0.020, log-rank hazard ratio (HR) = 3.56, 95% confidence interval (CI) = 1.14–11.07). For patients with Z-4-hydroxy-N-desmethyl-tamoxifen (Z-endoxifen) levels ≤ 9.00 nM BCSS was 57% compared to 84% for patients with concentrations > 9.00 nM (p = 0.029, HR = 3.73, 95% CI = 1.05–13.22). Low concentrations of Z-4OHtam and Z-endoxifen were associated with poorer survival also after adjusting for clinically relevant variables (HR = 4.27, 95% CI = 1.35–13.58, and HR = 3.70, 95% CI = 1.03–13.25, respectively). Overall survival analysis showed similar survival differences for both active metabolites. The Antiestrogen Activity Score showed comparable effects, but did not improve the prognostic information.

Conclusions

Patients with Z-4OHtam and Z-endoxifen concentrations lower than 3.26 nM or 9.00 nM, respectively, showed an adverse outcome. Our results suggest that direct measurement of active tamoxifen metabolite concentrations could be of clinical value. Validation in larger study cohorts is warranted.

Electronic supplementary material

The online version of this article (doi:10.1186/s13058-017-0916-4) contains supplementary material, which is available to authorized users.

The effect of CYP2D6 *10 polymorphism on adjuvant tamoxifen in Asian breast cancer patients: a meta-analysis

Objective

To evaluate the effect of CYP2D6 *10 polymorphism (C 100C>T, rs1065852) on clinical outcomes of female Asian breast cancer patients with tamoxifen adjuvant treatment.

Methods

Meta-analysis of retrospective cohort studies published in July 2017 was performed. Fifteen studies with 1,794 Asian breast cancer patients were included, using strict eligibility requirements. Associations of disease-free survival (DFS), overall survival (OS) and recurrence rate after tamoxifen intake, with CYP2D6 *10 polymorphism were investigated through random effects models.

Results

CYP2D6 *10 polymorphism was found to have effect on DFS and recurrence rate in various comparison models, but not on overall survival in the female Asian breast cancer patients.

Conclusion

In conclusion, our meta-analysis suggests that significant association of *10/*10 (TT) genotype with poorer DFS and recurrence exists in female Asian breast cancer patients with tamoxifen 20 mg/day adjuvant treatment. In the future, large and well-designed studies are required to illustrate the interactions of CYP2D6 genetic variants, including *10 polymorphism and tamoxifen response on female breast cancer patients.

Effect of CYP3A4*22, CYP3A5*3, and CYP3A combined genotypes on tamoxifen metabolism

Background

Tamoxifen is one of the cornerstones of endocrine therapy for breast cancer. Recently, the decreased activity CYP3A4*22 allele and the loss of function CYP3A5*3 allele have been described as potential factors that could help to explain the inter-patient variability in tamoxifen metabolism. The aim of this study is to investigate the effect of CYP3A4*22, CYP3A5*3, and CYP3A combined genotypes on tamoxifen metabolism.

Methods

DNA from 667 women enrolled in the CYPTAM study (NTR1509) was genotyped (CYP2D6, CYP3A4*22, and CYP3A5*3). Tamoxifen and metabolite concentrations were measured in serum, and metabolic ratios were calculated. The effect of the CYP3A4*22, CYP3A5*3, and CYP3A combined genotypes in addition to the CYP2D6 genotypes was examined by multiple linear regression analysis.

Results

CYP3A4*22 carriers reached significant higher concentrations of tamoxifen, N-desmethyl-tamoxifen, and 4-hydroxy-tamoxifen compared to non-carriers, whereas a tendency toward increased endoxifen levels was observed (p = 0.088). The metabolic ratio tamoxifen/N-desmethyl-tamoxifen was significantly higher in CYP3A4*22 individuals (0.59 vs. 0.52, p < 0.001). At the same time, CYP3A4*22 genotype contributed to improving the inter-variability [R² of the (log-transformed) metabolic ratio tamoxifen/N-desmethyl-tamoxifen improved from 21.8 to 23.9%, p < 0.001]. CYP3A5*3 marginally improved the explained variability of the (log transformed) metabolic ratio 4-hydroxy-tamoxifen/endoxifen (from 44.9 to 46.2%, p < 0.038).

Conclusion

Our data demonstrate that CYP3A genotype has a minor effect to explaining the variability between patients in tamoxifen metabolism and has no added value in addition to CYP2D6 genotype.

Electronic supplementary material

The online version of this article (10.1007/s00228-017-2323-2) contains supplementary material, which is available to authorized users.

Effects of CYP2D6 and CYP3A5 polymorphisms on tamoxifen and its metabolites in Thai breast cancer patients

Purpose

This study aimed to determine the effects of CYP2D6 and CYP3A5 polymorphisms on the levels of tamoxifen (TAM) and its metabolites in the plasma of breast cancer patients. The protocol was designed to test the associations between CYP2D6, CYP3A5 genotypes and phenotypes (extensive metabolizer [EM], intermediate metabolizer [IM] and poor metabolizer [PM]) and TAM, N-desmethyl tamoxifen (NDMT), endoxifen (END) and 4-hydroxytamoxifen (4OHT) concentrations.

Patients and methods

One hundred and thirty-four Thai breast cancer patients from the Thai Tamoxifen Project undergoing TAM treatment who met the inclusion/exclusion criteria were recruited. Plasma samples were assessed for the concentrations of TAM and its metabolites using high-performance liquid chromatography. The data are presented as actual values and metabolic ratios (MR). The hypotheses were tested using Kruskal–Wallis or Mann–Whitney U test, including the simple main effects analysis.

Results

The patients had stage 0–IV breast cancer. The mean age and body mass index were 51.6±11.6 years and 24.0±4.3, respectively. Also, 53.0% of them were premenopausal, 10.4% were perimenopausal and 36.6% were postmenopausal, while 23.1% were CYP2D6-EM/CYP3A5-EM and 20.9% carried only CYP2D6 and CYP3A5 incomplete alleles. The median concentrations of TAM, NDMT, END and 4OHT were 374.7 (interquartile range [IQR] 230.2) ng/mL, 1,064.9 (IQR 599.6) ng/mL, 54.5 (IQR 52.5) ng/mL and 5.0 (IQR 3.1) ng/mL, respectively. MR (TAM-NDMT) and MR (NDMT-END) were statistically different (p=0.013 and p=0.014, respectively), while MR (4OHT-END) was not statistically different within the CYP2D6 phenotype (p=0.594). MR (TAM-4OHT) was not statistically different within the CYP2D6 phenotype (p=0.079), but it was potentially different from CYP3A5-PM (p=0.056). None of the MR was statistically different within the CYP3A5 phenotype.

Conclusion

CYP2D6 polymorphisms appear to affect END concentration through an NDMT subpathway and potentially affect 4OHT concentrations through a 4OHT subpathway in CYP3A5-PM group.

Catalpol protects glucose-deprived rat embryonic cardiac cells by inducing mitophagy and modulating estrogen receptor

Catalpol, a bioactive component from Rehmannia glutinosa (Di Huang), has been widely used to protect cardiomyocytes against myocardial ischemia. The aim of the present study was to investigate the anti-apoptotic and anti-oxidative effects of Catalpol on glucose-starved H9c2 cells for cardio-protection and to elucidate the underlying mechanisms. Here, we showed that Catalpol protected the glucose-starved H9c2 cells through reducing apoptosis and attenuating oxidative damage. Moreover, the increases of autophagic lysosomes, LC3, autophagic flux and autophagic vacuole were observed in Catalpol-treated cells using flow cytometer and fluorescence microscope. Western blotting analyses showed that the autophagy-related proteins (LC3, Beclin1 and ULK) were markedly increased in Catalpol-treated cells, suggesting that Catalpol up-regulated autophagy in glucose starved H9c2 cells. Mechanistic investigations revealed that the autophagy inhibitor 3-MA markedly abrogated Catalpol's anti-apoptotic and anti-oxidative effects and prevented Catalpol-induced mitophagy. Furthermore, the estrogen receptor inhibitor tamoxifen significantly abolished Catalpol up-regulation of mitophagic related proteins (LC3, Beclin 1, p62, ATG5). Collectively, these data revealed that Catalpol inhibited apoptosis and oxidative stress in glucose-deprived H9c2 cell through promoting cell mitophagy and modulating estrogen receptor, supporting the notion that Catalpol could be a novel drug candidate against myocardial ischemia for the treatment of cardiovascular diseases.

Effects of SULT1A1 Copy Number Variation on Estrogen Concentration and Tamoxifen-Associated Adverse Drug Reactions in Premenopausal Thai Breast Cancer Patients: A Preliminary Study

Tamoxifen is a pharmacological estrogen inhibitor that binds to the estrogen receptor (ER) in breast cells. However, it shows an estrogenic effect in other organs, which causes adverse drug reactions (ADRs). The sulfotransferase 1A1 (SULT1A1) enzyme encoded by the SULT1A1 gene is involved in estrogen metabolism. Previous research has suggested that the SULT1A1 copy number is linked with the plasma estradiol (E2) concentration. Here, a total of 34 premenopausal breast cancer patients, selected from the Thai Tamoxifen (TTAM) Project, were screened for their SULT1A1 copy number, plasma E2 concentration and ADRs. The mean age was 44.3±11.1 years, and they were subtyped as ER+/ progesterone receptor (PR) + (28 patients), ER+/ PR- (5 patients) and ER-/PR- (1 patient). Three patients reported ADRs, which were irregular menstruation (2 patients) and vaginal discharge (1 patient). Most (33) patients had two SULT1A1 copies, with one patient having three copies. The median plasma E2 concentration was 1,575.6 (IQR 865.4) pg/ml. Patients with ADRs had significantly higher plasma E2 concentrations than those patients without ADRs (p = 0.014). The plasma E2 concentration was numerically higher in the patient with three SULT1A1 copies, but this lacked statistical significance.

Synergistic disruption of ERα/HER2 crosstalk by endoxifen and lapatinib in breast cancer cells

BACKGROUND

Despite decades of clinical success, tamoxifen therapy is complicated by inter-individual variability due to CYP450 polymorphism and resistance attributed to ERα/HER2 crosstalk. Direct administration of endoxifen shows promise in circumventing obligatory CYP450 bioactivation while maintaining efficacy. Separately, disruption of the crosstalk using probe antagonists against ERα (tamoxifen) and HER2 (e.g., lapatinib) has been explored clinically. However, the efficacy of this combination may be confounded by lapatinib, a potent inactivator of CYP3A4/5 which could negate the bioactivation of tamoxifen to the active metabolite endoxifen. Additionally, in a manner analogous to tamoxifen, endoxifen is similarly not immune to the development of ERα/HER2 crosstalk that could result in resistance. Simultaneous antagonism of ERα and HER2 using endoxifen and lapatinib could overcome these problems.

METHODS

Metabolism studies were performed in human liver microsomes to determine the extent of inhibition of tamoxifen bioactivation by lapatinib. Synergism of endoxifen and lapatinib was assessed using the combination index design in a panel of cell models exhibiting either a priori ERα/HER2 crosstalk (BT474) or acquired ERα/HER2 crosstalk (TAM-R and MCF-7/HER2).

RESULTS

Lapatinib inhibited tamoxifen bioactivation by up to 1.8-fold. Synergistic activity was uncovered for lapatinib and endoxifen against BT474, TAM-R and MCF-7/HER2 models of ERα/HER2 crosstalk. Western blot confirmed that endoxifen and lapatinib disrupted this crosstalk.

CONCLUSION

This forward-looking study extends the success of tamoxifen by exploring the effectiveness of combining the next-generation tamoxifen derivative, endoxifen with an anti-HER2 agent to combat ERα/HER2 crosstalk, and at the same time provides a solution to the predicted pharmacokinetic antagonism between lapatinib and tamoxifen.

Chemical and toxicological characterisation of anticancer drugs in hospital and municipal wastewaters from Slovenia and Spain

Anticancer drugs are continuously released into hospital and urban wastewaters, where they, most commonly, undergo conventional treatment in wastewater treatment plants (WWTPs). Wastewaters contain complex mixtures of substances including parent compounds, their metabolites and transformation products (TPs). In this study, samples of hospital effluents and WWTP influents and effluents from Slovenia and Spain were analyzed for twenty-two selected anticancer drugs, their metabolites and transformation products. Acute and chronic toxicity tests were performed on the crustacean Ceriodaphnia dubia, genotoxicity was determined with Tradescantia and Allium cepa micronucleus (MN) assays and in vitro comet assay in zebrafish (Danio rerio) liver cell line (ZFL cells). Sixty of the two hundred-twenty determinations revealed detectable levels of anticancer drug residues. Among the targeted compounds, platinum based were most frequently detected (90%). Furthermore, erlotinib was detected in 80%, cyclophosphamide and tamoxifen in 70% and methotrexate in 60% of the samples. Seven of ten samples were toxic to C. dubia after acute exposure, whereas after chronic exposure all samples reduced reproduction of C. dubia at high sample dilutions. Allium cepa proved insensitive to the potential genotoxicity of the tested samples, while in Tradescantia increased MN frequencies were induced by a hospital effluent and WWTP influents. In ZFL comet assay all but one sample induced a significant increase of DNA strand breaks. Correlations of chemotherapeutics or their TPs were detected for all bioassays except for Allium cepa genotoxicity test, however for each test the highest correlations were found for different substances indicating differential sensitivities of the test organisms.

The pharmacoepigenetics of drug metabolism and transport in breast cancer: review of the literature and in silico analysis

The focus of this manuscript is on DNA methylation and miRNA regulation of drug-metabolizing enzymes and drug transporters involved in the disposition of drugs commonly used in breast cancer. We start with a review of the available scant literature and follow with an in silico analysis of the CpG islands and miRNA binding sites of genes of interest. We make the case that there is room for further research to include more genes and miRNAs despite the extensive sharing of miRNA targets by candidate genes of interest. We also stress on the role of peripheral blood as a source of pharmacoepigenetic biomarkers, and point out the lack of toxicoepigenetic studies in breast cancer.

Prevalence of CYP2D6*2, CYP2D6*4, CYP2D6*10, and CYP3A5*3 in Thai breast cancer patients undergoing tamoxifen treatment

Background

Tamoxifen (TAM) is used in breast cancer treatment, but interindividual variabilities in TAM-metabolizing enzymes exist and have been linked to single nucleotide polymorphisms in the respective encoding genes. The different alleles and genotypes of these genes have been presented for Caucasians and Asians. This study aimed to explore the prevalence of the incomplete functional alleles and genotypes of the CYP2D6 and CYP3A5 genes in Thai breast cancer patients undergoing TAM treatment.

Patients and methods

In total, 134 Thai breast cancer patients were randomly invited to join the Thai Tamoxifen Project. Their blood samples were collected and extracted for individual DNA. The alleles and genotypes were determined by real-time polymerase chain reaction with TaqMan^® Drug Metabolism Genotyping Assays.

Results

The patients were aged from 27.0 years to 82.0 years with a body mass index range from 15.4 to 40.0, with the majority (103/134) in the early stage (stages 0–II) of breast cancer. The median duration of TAM administration was 17.2 months (interquartile range 16.1 months). Most (53%) of the patients were premenopausal with an estrogen receptor (ER) and progesterone receptor (PR) status of ER+/PR+ (71.7%), ER+/PR− (26.9%), ER−/PR+ (0.7%), and ER−/PR− (0.7%). The allele frequencies of CYP2D6*1, CYP2D6*2, CYP2D6*4, CYP2D6*10, CYP3A5*1, and CYP3A5*3 were 72.9%, 3.2%, 1.1%, 22.8%, 37.3%, and 62.7%, respectively, while the genotype frequencies of CYP2D6*1/*1, CYP2D6*1/*2, CYP2D6*2/*2, CYP2D6*4/*4, CYP2D6*1/*10, CYP2D6*2/*10, CYP2D6*4/*10, CYP2D6*10/*10, CYP3A5*1/*1, CYP3A5*1/*3, and CYP3A5*3/*3 were 9.7%, 2.2%, 3.7%, 1.5%, 15.7%, 9.7%, 3.7%, 53.7%, 13.4%, 47.8%, and 38.8%, respectively.

Conclusion

The majority (97.8%) of Thai breast cancer patients undergoing TAM treatment carry at least one incomplete functional allele, including 20.9% of the patients who carry only incomplete functional alleles for both the CYP2D6 and CYP3A5 genes. This research indicates the high prevalence of these defective alleles that are involved in TAM-metabolic pathways that might further affect TAM treatment.

A pooled analysis of CYP2D6 genotype in breast cancer prevention trials of low-dose tamoxifen

Decreased CYP2D6 activity is associated with lower levels of active tamoxifen metabolites. We examined the impact of CYP2D6 genotype on tamoxifen pharmacokinetics, biomarker activity, and efficacy in a pooled analysis of low-dose tamoxifen. Four randomized breast cancer prevention trials of very-low-dose (1 mg/day, n = 52 or 10 mg/week, n = 152) or low-dose tamoxifen (5 mg/day, n = 171) were pooled. DNA from 367 subjects was genotyped for CYP2D6 alleles associated with absent (PM allele: *3, *4, *5, *6, *7, *8, *12, and *14), reduced (IM allele: *9, *10, *17, *29, *41), normal (EM allele), or increased (UM: *XN) enzyme activity. Associations of tamoxifen, metabolites, activity biomarkers, and event-free survival with rapid (UM/EM, UM/IM, EM/EM, EM/IM, or EM/PM alleles) versus slow metabolizers (PM/IM or PM/PM) were investigated through random effects models, with 'study' as the random factor, and Cox regression models, adjusting for confounders. Rapid metabolizers had higher endoxifen levels than slow metabolizers: 15.3 versus 12.2 ng/mL (P = 0.018) with 5 mg/day, and 3.8 versus 2.8 ng/mL (P = 0.004) with 1 mg/day or 10 mg/week tamoxifen. The IGF-I decrease correlated with endoxifen (P = 0.002) and 4-hydroxytamoxifen levels, demonstrating steeper decreases at higher metabolite levels (P = 0.001). After a median follow-up of 12 years, rapid metabolizers with prior history of breast neoplasms allocated to tamoxifen 5 mg/day had a 60 % reduction of risk of recurrences (HR = 0.40, 95 % CI: 0.16-0.99) compared to slow metabolizers. CYP2D6 genotype may have an impact on tamoxifen efficacy at low doses. Trials investigating tamoxifen dose adjustments based on the woman's hormonal context and CYP2D6 genotype are warranted.

Evaluating the impact of missenses mutations in CYP2D6*7 and CYP2D6*14A: does it compromise tamoxifen metabolism?

CYP2D6 is a high polymorphic enzyme from P450, responsible for metabolizing almost 25% of drugs. The distribution of different mutations among CYP2D6 alleles has been associated with poor, intermediate, extensive and ultra-metabolizers.

AIM

To evaluate how missenses mutations in CYP2D6*7 and CYP2D6*14A poor metabolizer alleles affect CYP2D6 stability and function.

MATERIALS & METHODS

CYPalleles database was used to collect polymorphisms data present in 105 alleles. We selected only poor metabolizers alleles that presented exclusively missenses mutations. They were analyzed through seven algorithms to predict the impact on CYP2D6 structure and function.

RESULTS

H324P, the unique mutation in CYP2D6*7, has high impact in enzyme function due to its occurrence between two alpha-helixes involved in active site dynamics. G169R, a mutation that occurs only in CYP2D6*14A, leads to the gain of solvent accessibility and severe protein destabilization.

CONCLUSION

Our in silico analysis showed that missenses mutations in CYP2D6*7 and CYP2D6*14A cause CYP2D6 dysfunction.

Multigenerational effects of the anticancer drug tamoxifen and its metabolite 4-hydroxy-tamoxifen on Daphnia pulex

Tamoxifen and its metabolite 4-hydroxy-tamoxifen (4OHTam) are two potent molecules that have anticancer properties on breast cancers. Their medical use is expected to increase with the increasing global cancer rate. After consumption, patients excrete tamoxifen and the 4OHTam metabolite into wastewaters, and tamoxifen has been already detected in wastewaters and natural waters. The concentrations of 4OHTam in waters have never been reported. A single study reported 4OHTam effects on the microcrustacean Daphnia pulex. The effects of tamoxifen and 4OHTam over more than two generations are unknown in aquatic invertebrates. The main goal of this study was to assess the long-term sensitivity of the microcrustacean D. pulex over four generations, based on size, reproduction, viability and the intrinsic rate of natural increase (r). Additional experiments were carried out to observe whether the effects of tamoxifen and 4OHTam were reversible in the next generation after descendants were withdrawn from chemical stress (i.e., recovery experiment), and whether the lowest test concentration of each chemical induced toxic effects when both concentrations were combined (i.e., mixture experiments). Our results showed that tamoxifen and 4OHTam induced the adverse effects at environmentally relevant concentrations. Tamoxifen and 4OHTam impaired size, viability, reproduction and the r in four generations of treated D. pulex, but these effects were not clearly magnified over generations. Tamoxifen was more potent than 4OHTam on D. pulex. When used in a mixture, the combination of tamoxifen and 4OHTam induced effects in offspring, whereas no effects were observed when these chemicals were tested individually. In the recovery experiment, the reproduction and size were reduced in offspring withdrawn from chemical exposures. Our results suggested that tamoxifen and its metabolite may be a relevant pharmaceutical to consider in risk assessment.

No effect on pharmacokinetics of tamoxifen and 4-hydroxytamoxifen by multiple doses of red clover capsule in rats

Tamoxifen is used in clinical practice for breast cancer patients and to prevent osteoporosis. Red clover (Trifolium pratense) preparations are consumed worldwide as dietary supplements for relieving postmenopausal symptoms. In the present study we investigated the possible herb-drug interaction between red clover and tamoxifen in rats. 15 days pre-treatment with red clover did not alter the tamoxifen and its active metabolite 4-hydroxytamoxifen pharmacokinetics significantly (p > 0.05). Therefore the therapeutic efficacy of the tamoxifen may not be compromised by the co-administration with red clover. Tamoxifen metabolism is primarily mediated by CYP2D6, CYP3A4 with minor contribution from CYP2C9, CYP2E1 and CYP1A2 isoforms. Although, red clover pre-treatment significantly (p < 0.05) decreased the mRNA expression and activity of CYP3a2, no effect on CYP2d4 and increased expression and activity of CYP2c11 could be the plausible reasons for lack of effect on tamoxifen and its metabolite pharmacokinetics in rats. CYP1a1 and CYP2b2 mRNA expression and activity were also significantly reduced by red clover. To extend the clinical utility of the present study, effect of red clover extract on major CYPs using human liver microsomes and HepG2 cell lines were also determined. Similar finding were observed in the human liver preparations as in rats.

In vivo assessment of the metabolic activity of CYP2D6 diplotypes and alleles

AIMS

A prospectively enrolled patient cohort was used to assess whether the prediction of CYP2D6 phenotype activity from genotype data could be improved by reclassification of diplotypes or alleles.

METHODS

Three hundred and fifty-five patients receiving tamoxifen 20 mg were genotyped for CYP2D6 and tamoxifen metabolite concentrations were measured. The endoxifen : N-desmethly-tamoxifen metabolic ratio, as a surrogate of CYP2D6 activity, was compared across four diplotypes (EM/IM, EM/PM, IM/IM, IM/PM) that are typically collapsed into an intermediate metabolizer (IM) phenotype. The relative metabolic activity of each allele type (UM, EM, IM, and PM) and each EM and IM allele was estimated for comparison with the activity scores typically assigned, 2, 1, 0.5 and 0, respectively.

RESULTS

Each of the four IM diplotypes have distinct CYP2D6 activity from each other and from the EM and PM phenotype groups (each P < 0.05). Setting the activity of an EM allele at 1.0, the relative activities of a UM, IM and PM allele were 0.85, 0.67 and 0.52, respectively. The activity of the EM alleles were statistically different (P < 0.0001), with the CYP2D6*2 allele (scaled activity = 0.63) closer in activity to an IM than an EM allele. The activity of the IM alleles were also statistically different (P = 0.014).

CONCLUSION

The current systems for translating CYP2D6 genotype into phenotype are not optimally calibrated, particularly in regards to IM diplotypes and the *2 allele. Additional research is needed to improve the prediction of CYP2D6 activity from genetic data for individualized dosing of CYP2D6 dependent drugs.

Progress towards the integration of pharmacogenomics in practice

Understanding the role genes and genetic variants play in clinical treatment response continues to be an active area of research with the goal of common clinical use. This goal has developed into today's industry of pharmacogenomics, where new drug-gene relationships are discovered and further characterized, published and then curated into national and international resources for use by researchers and clinicians. These efforts have given us insight into what a pharmacogenomic variant is, and how it differs from human disease variants and common polymorphisms. While publications continue to reveal pharmacogenomic relationships between genes and specific classes of drugs, many challenges remain toward the goal of widespread use clinically. First, the clinical guidelines for pharmacogenomic testing are still in their infancy. Second, sequencing technologies are changing rapidly making it somewhat unclear what genetic data will be available to the clinician at the time of care. Finally, what and when to return data to a patient is an area under constant debate. New innovations such as PheWAS approaches and whole genome sequencing studies are enabling a tsunami of new findings. In this review, pharmacogenomic variants, pharmacogenomic resources, interpretation clinical guidelines and challenges, such as WGS approaches, and the impact of pharmacogenomics on drug development and regulatory approval are reviewed.