Metabolism of tamoxifen by recombinant human cytochrome P450 enzymes: formation of the 4-hydroxy, 4'-hydroxy and N-desmethyl metabolites and isomerization of trans-4-hydroxytamoxifen

Benzylidene-isophorone hybrids with strong anticancer activity

Isophorone is a cyclic ketone that has gained significant attention in the field of organic chemistry due to its versatile reactivity and structural attributes. Derivatives of isophorone offer a broad spectrum of applications ranging from pharmaceuticals to polymer chemistry. With the aim of developing novel hybrid structures based on benzylidene by combining with isophorone scaffold, we report 3 derivatives of the benzylidene-isophorone hybrids and its potent anticancer activity. In order to optimize the anticancer activity of hybrids di-substitution of -Cl group in C2 and C6 position of phenyl ring (compound1), -OCH3 group in C2 and C5 position of phenyl ring (compound2), and -OCH3 group in C2 and C3 position of phenyl ring (compound3) of benzylidene (PhCH=) moiety were made. The structure of Compounds1,2 and 3 were elucidated using spectral and XRD methods. Compounds1,2 and 3 exhibit space group P c a 21, P-1, and P 1 21/n 1 respectively. Compounds1,2 and 3 were tested for the potent anticancer activity on MDA MB-231 cell line. All the three compounds exhibit good anticancer activity on the breast cancer cells. The parent hybrid with ortho, ortho directing -Cl (1) exhibits strong antiproliferation effect (IC50 = 0.028 µM) on MDA-MB 231 cell line. However, hybrid structures with ortho, meta directing -OCH3 (2) group showed moderate effect (IC50 = 0.061 µM) and hybrid with ortho, meta directing -OCH3 (3) substitution showed the least potent anticancer activity (IC50 = 0.074 µM). The benzylidene-isophorone hybrids exhibit anticancer effects in the following order: 1 > 2 > 3.

Systemic oncological therapy in breast cancer patients on dialysis

The advancement of renal replacement therapy has significantly enhanced the survival rates of patients with end-stage renal disease (ESRD) over time. However, this prolonged survival has also been associated with a higher likelihood of cancer diagnoses among these patients including breast cancer. Breast cancer treatment typically involves surgery, radiation, and systemic therapies, with approaches tailored to cancer type, stage, and patient preferences. However, renal replacement therapy complicates systemic therapy due to altered drug clearance and the necessity for dialysis sessions. This review emphasizes the need for optimized dosing and administration strategies for systemic breast cancer treatments in dialysis patients, aiming to ensure both efficacy and safety. Additionally, challenges in breast cancer screening and diagnosis in this population, including soft-tissue calcifications, are highlighted.

Formation of potentially toxic metabolites of drugs in reactions catalyzed by human drug-metabolizing enzymes

Data are presented on the formation of potentially toxic metabolites of drugs that are substrates of human drug metabolizing enzymes. The tabular data lists the formation of potentially toxic/reactive products. The data were obtained from in vitro experiments and showed that the oxidative reactions predominate (with 96% of the total potential toxication reactions). Reductive reactions (e.g., reduction of nitro to amino group and reductive dehalogenation) participate to the extent of 4%. Of the enzymes, cytochrome P450 (P450, CYP) enzymes catalyzed 72% of the reactions, myeloperoxidase (MPO) 7%, flavin-containing monooxygenase (FMO) 3%, aldehyde oxidase (AOX) 4%, sulfotransferase (SULT) 5%, and a group of minor participating enzymes to the extent of 9%. Within the P450 Superfamily, P450 Subfamily 3A (P450 3A4 and 3A5) participates to the extent of 27% and the Subfamily 2C (P450 2C9 and P450 2C19) to the extent of 16%, together catalyzing 43% of the reactions, followed by P450 Subfamily 1A (P450 1A1 and P450 1A2) with 15%. The P450 2D6 enzyme participated in an extent of 8%, P450 2E1 in 10%, and P450 2B6 in 6% of the reactions. All other enzymes participate to the extent of 14%. The data show that, of the human enzymes analyzed, P450 enzymes were dominant in catalyzing potential toxication reactions of drugs and their metabolites, with the major role assigned to the P450 Subfamily 3A and significant participation of the P450 Subfamilies 2C and 1A, plus the 2D6, 2E1 and 2B6 enzymes contributing. Selected examples of drugs that are activated or proposed to form toxic species are discussed.

Pre- and Postoperative Antioxidant Use, Aryl Hydrocarbon Receptor (AhR) Activation and Clinical Outcome in Different Treatment Groups of Breast Cancer Patients

BACKGROUND

Cancer patients often use antioxidants that may interact with adjuvant treatments. The purpose was to investigate pre- and postoperative antioxidant use in relation to clinicopathological characteristics and prognosis in different breast cancer treatment groups.

METHODS AND PATIENTS

Pre- and postoperative antioxidant (vitamin A, C, E, carotenoids, or Q10) or multivitamin use was self-reported by patients from Lund (n = 1855) and Helsingborg (n=478), Sweden. Patients were followed for up to 15 years. Clinical data were obtained from patient charts. The aryl hydrocarbon receptor (AhR) was evaluated in tumor tissue arrays from 915 patients from Lund and with Western blot in MCF-7 and MDA-MB-231 cells.

RESULTS

About 10% of patients used antioxidants. Nuclear AhR (AhRnuc) positivity was twice as common in preoperative antioxidant users compared to non-users. In mechanistic studies vitamin C increased AhR levels and its downstream target CYP1B1, indicating AhR activation. There were significant interactions between tumor AhRnuc status and preoperative antioxidant use in relation to clinical outcome. In all patients, antioxidant use (other than multivitamins) at both visits was associated with poorer prognosis, while use only at the follow-up visit was associated with better prognosis, compared with no use at either visit.

CONCLUSION

The clinical impact of antioxidants depended on antioxidant type, timing of use, and tumor AhR activation. Antioxidants may influence clinical outcome by activation of the master regulator AhR in addition to interference with free radicals. Further studies are needed to identify breast patients that might improve or worsen their prognosis when using antioxidants postoperatively.

Lipidome and metabolome analyses reveal metabolic alterations associated with MCF-7 apoptosis upon 4-hydroxytamoxifen treatment

4-hydroxytamoxifen (OHT) is an anti-cancer drug that induces apoptosis in breast cancer cells. Although changes in lipid levels and mitochondrial respiration have been observed in OHT-treated cells, the overall mechanisms underlying these metabolic alterations are poorly understood. In this study, time-series metabolomics and lipidomics were used to analyze the changes in metabolic profiles induced by OHT treatment in the MCF-7 human breast cancer cell line. Lipidomic and metabolomic analyses revealed increases in ceramide, diacylglycerol and triacylglycerol, and decreases in citrate, respectively. Gene expression analyses revealed increased expression of ATP-dependent citrate lyase (ACLY) and subsequent fatty acid biosynthetic enzymes, suggesting that OHT-treated MCF-7 cells activate citrate-to-lipid metabolism. The significance of the observed metabolic changes was evaluated by co-treating MCF-7 cells with OHT and ACLY or a diacylglycerol O-acyltransferase 1 (DGAT1) inhibitor. Co-treatment ameliorated cell death and reduced mitochondrial membrane potential compared to that in OHT treatment alone. The inhibition of cell death by co-treatment with an ACLY inhibitor has been observed in other breast cancer cell lines. These results suggest that citrate-to-lipid metabolism is critical for OHT-induced cell death in breast cancer cell lines.

Effects of 7-ketocholesterol on tamoxifen efficacy in breast carcinoma cell line models in vitro

Oxysterols play significant roles in many physiological and pathological processes including cancer. They modulate some of the cancer hallmarks pathways, influence the efficacy of anti-cancer drugs, and associate with patient survival. In this study, we aimed to analyze the role of 7-ketocholesterol (7-KC) in breast carcinoma cells and its potential modulation of the tamoxifen effect. 7-KC effects were studied in two estrogen receptor (ER)-positive (MCF-7 and T47D) and one ER-negative (BT-20) breast cancer cell lines. First, we tested the viability of cells in the presence of 7-KC. Next, we co-incubated cells with tamoxifen and sublethal concentrations of 7-KC. We also tested changes in caspase 3/7 activity, deregulation of the cell cycle, and changes in expression of selected genes/proteins in the presence of tamoxifen, 7-KC, or their combination. Finally, we analyzed the effect of 7-KC on cellular migration and invasion. We found that the presence of 7-KC slightly decreases the efficacy of tamoxifen in MCF-7 cells, while an increased effect of tamoxifen and higher caspase 3/7 activity was observed in the BT-20 cell line. In the T47D cell line, we did not find any modulation of tamoxifen efficacy by the presence of 7-KC. Expression analysis showed the deregulation in CYP1A1 and CYP1B1 with the opposite trend in MCF-7 and BT-20 cells. Moreover, 7-KC increased cellular migration and invasion potential regardless of the ER status. This study shows that 7-KC can modulate tamoxifen efficacy as well as cellular migration and invasion, making 7-KC a promising candidate for future studies.

Towards Evidence-Based Implementation of Pharmacogenomics in Southern Africa: Comorbidities and Polypharmacy Profiles across Diseases

Pharmacogenomics may improve patient care by guiding drug selection and dosing; however, this requires prior knowledge of the pharmacogenomics of drugs commonly used in a specific setting. The aim of this study was to identify a preliminary set of pharmacogenetic variants important in Southern Africa. We describe comorbidities in 3997 patients from Malawi, South Africa, and Zimbabwe. These patient cohorts were included in pharmacogenomic studies of anticoagulation, dyslipidemia, hypertension, HIV and breast cancer. The 20 topmost prescribed drugs in this population were identified. Using the literature, a list of pharmacogenes vital in the response to the top 20 drugs was constructed leading to drug-gene pairs potentially informative in translation of pharmacogenomics. The most reported morbidity was hypertension (58.4%), making antihypertensives the most prescribed drugs, particularly amlodipine. Dyslipidemia occurred in 31.5% of the participants, and statins were the most frequently prescribed as cholesterol-lowering drugs. HIV was reported in 20.3% of the study participants, with lamivudine/stavudine/efavirenz being the most prescribed antiretroviral combination. Based on these data, pharmacogenes of immediate interest in Southern African populations include ABCB1, CYP2B6, CYP2C9, CYP2C19, CYP2D6, CYP3A4, CYP3A5, SLC22A1, SLCO1B1 and UGT1A1. Variants in these genes are a good starting point for pharmacogenomic translation programs in Southern Africa.

Administration of Secretome Derived from Human Mesenchymal Stem Cells Induces Hepatoprotective Effects in Models of Idiosyncratic Drug-Induced Liver Injury Caused by Amiodarone or Tamoxifen

Drug-induced liver injury (DILI) is one of the leading causes of acute liver injury. While many factors may contribute to the susceptibility to DILI, obese patients with hepatic steatosis are particularly prone to suffer DILI. The secretome derived from mesenchymal stem cell has been shown to have hepatoprotective effects in diverse in vitro and in vivo models. In this study, we evaluate whether MSC secretome could improve DILI mediated by amiodarone (AMI) or tamoxifen (TMX). Hepatic HepG2 and HepaRG cells were incubated with AMI or TMX, alone or with the secretome of MSCs obtained from human adipose tissue. These studies demonstrate that coincubation of AMI or TMX with MSC secretome increases cell viability, prevents the activation of apoptosis pathways, and stimulates the expression of priming phase genes, leading to higher proliferation rates. As proof of concept, in a C57BL/6 mouse model of hepatic steatosis and chronic exposure to AMI, the MSC secretome was administered endovenously. In this study, liver injury was significantly attenuated, with a decrease in cell infiltration and stimulation of the regenerative response. The present results indicate that MSC secretome administration has the potential to be an adjunctive cell-free therapy to prevent liver failure derived from DILI caused by TMX or AMI.

Construction of a fused grid-based CYP2C19-Template system and the application

A ligand-accessible space in the CYP2C19 active site was reconstituted as a fused grid-based Template with the use of structural data of the ligands. An evaluation system of CYP2C19-mediated metabolism has been developed on Template with the introduction of the idea of Trigger-residue initiated ligand-movement and fastening. Reciprocal comparison of the data of simulation on Template with experimental results suggested a unified way of the interaction of CYP2C19 and its ligands through the simultaneous plural-contact with Rear-wall of Template. CYP2C19 was expected to have a room for ligands between vertically standing parallel walls termed Facial-wall and Rear-wall, which were separated by a distance corresponding to 1.5-Ring (grid) diameter size. The ligand sittings were stabilized through contacts with Facial-wall and the left-side borders of Template including specific Position 29 or Left-end after Trigger-residue initiated ligand-movement. Trigger-residue movement is suggested to force ligands to stay firmly in the active site and then to initiate CYP2C19 reactions. Simulation experiments for over 450 reactions of CYP2C19 ligands supported the system established.

Predicting disruptions to drug pharmacokinetics and the risk of adverse drug reactions in non-alcoholic steatohepatitis patients

The liver plays a central role in the pharmacokinetics of drugs through drug metabolizing enzymes and transporters. Non-alcoholic steatohepatitis (NASH) causes disease-specific alterations to the absorption, distribution, metabolism, and excretion (ADME) processes, including a decrease in protein expression of basolateral uptake transporters, an increase in efflux transporters, and modifications to enzyme activity. This can result in increased drug exposure and adverse drug reactions (ADRs). Our goal was to predict drugs that pose increased risks for ADRs in NASH patients. Bibliographic research identified 71 drugs with reported ADRs in patients with liver disease, mainly non-alcoholic fatty liver disease (NAFLD), 54 of which are known substrates of transporters and/or metabolizing enzymes. Since NASH is the progressive form of NAFLD but is most frequently undiagnosed, we identified other drugs at risk based on NASH-specific alterations to ADME processes. Here, we present another list of 71 drugs at risk of pharmacokinetic disruption in NASH, based on their transport and/or metabolism processes. It encompasses drugs from various pharmacological classes for which ADRs may occur when used in NASH patients, especially when eliminated through multiple pathways altered by the disease. Therefore, these results may inform clinicians regarding the selection of drugs for use in NASH patients.

CYP1B1: A Novel Molecular Biomarker Predicts Molecular Subtype, Tumor Microenvironment, and Immune Response in 33 Cancers

BACKGROUND

Cytochrome P450 Family 1 Subfamily B Member 1 (CYP1B1) is a critical metabolic enzyme of melatonin. Although melatonin has been identified to exhibit tumor suppressing activity, the role and mechanism of the clinical and immunological characteristics of CYP1B1 in cancer remain unclear.

METHODS

In this study, RNA expression and clinical data were obtained from The Cancer Genome Atlas (TCGA) across 33 solid tumors. The expression, survival, immune subtype, molecular subtype, tumor mutation burden (TMB), microsatellite instability (MSI), biological pathways, and function in vitro and vivo were evaluated. The predictive value of CYP1B1 in immune cohorts was further explored.

RESULTS

We found the dysregulated expression of CYP1B1 was associated with the clinical stage and tumor grade. Immunological correlation analysis showed CYP1B1 was positively correlated with the infiltration of lymphocyte, immunomodulator, chemokine, receptor, and cancer-associated fibroblasts (CAFs) in most cancer. Meanwhile, CYP1B1 was involved in immune subtype and molecular subtype, and was connected with TMB, MSI, neoantigen, the activation of multiple melatonergic and immune-related pathways, and therapeutic resistance.

CONCLUSIONS

Together, this study comprehensively revealed the role and mechanism of CYP1B1 and explored the significant association between CYP1B1 expression and immune activity. These findings provide a promising predictor and molecular target for clinical immune treatment.

Limitations of Tamoxifen Application for In Vivo Genome Editing Using Cre/ERT2 System

Inducible Cre-dependent systems are frequently used to produce both conditional knockouts and transgenic mice with regulated expression of the gene of interest. Induction can be achieved by doxycycline-dependent transcription of the wild type gene or OH-tamoxifen-dependent nuclear translocation of the chimeric Cre/ER^T2 protein. However, both of these activation strategies have some limitations. We analyzed the efficiency of knockout in different tissues and found out that it correlates with the concentration of the hydroxytamoxifen and endoxifen-the active metabolites of tamoxifen-measured by LC-MS in these tissues. We also describe two cases of Cdk8^{floxed/floxed}/Rosa-Cre-ER^T2 mice tamoxifen-induced knockout limitations. In the first case, the standard scheme of tamoxifen administration does not lead to complete knockout formation in the brain or in the uterus. Tamoxifen metabolite measurements in multiple tissues were performed and it has been shown that low recombinase activity in the brain is due to the low levels of tamoxifen active metabolites. Increase of tamoxifen dosage (1.5 fold) and duration of activation (from 5 to 7 days) allowed us to significantly improve the knockout rate in the brain, but not in the uterus. In the second case, knockout induction during embryonic development was impossible due to the negative effect of tamoxifen on gestation. Although DNA editing in the embryos was achieved in some cases, the treatment led to different complications of the pregnancy in wild-type female mice. We propose to use doxycycline-induced Cre systems in such models.

Role of Genetic Polymorphisms in Drug-Metabolizing Enzyme-Mediated Toxicity and Pharmacokinetic Resistance to Anti-Cancer Agents: A Review on the Pharmacogenomics Aspect

The inter-individual differences in cancer susceptibility are somehow correlated with the genetic differences that are caused by the polymorphisms. These genetic variations in drug-metabolizing enzymes/drug-inactivating enzymes may negatively or positively affect the pharmacokinetic profile of chemotherapeutic agents that eventually lead to pharmacokinetic resistance and toxicity against anti-cancer drugs. For instance, the CYP1B1*3 allele is associated with CYP1B1 overexpression and consequent resistance to a variety of taxanes and platins, while 496T>G is associated with lower levels of dihydropyrimidine dehydrogenase, which results in severe toxicities related to 5-fluorouracil. In this context, a pharmacogenomics approach can be applied to ascertain the role of the genetic make-up in a person's response to any drug. This approach collectively utilizes pharmacology and genomics to develop effective and safe medications that are devoid of resistance problems. In addition, recently reported genomics studies revealed the impact of many single nucleotide polymorphisms in tumors. These studies emphasized the importance of single nucleotide polymorphisms in drug-metabolizing enzymes on the effect of anti-tumor drugs. In this review, we discuss the pharmacogenomics aspect of polymorphisms in detail to provide an insight into the genetic manipulations in drug-metabolizing enzymes that are responsible for pharmacokinetic resistance or toxicity against well-known anti-cancer drugs. Special emphasis is placed on different deleterious single nucleotide polymorphisms and their effect on pharmacokinetic resistance. The information provided in this report may be beneficial to researchers, especially those who are working in the field of biotechnology and human genetics, in rationally manipulating the genetic information of patients with cancer who are undergoing chemotherapy to avoid the problem of pharmacokinetic resistance/toxicity associated with drug-metabolizing enzymes.

Targeting the tamoxifen receptor within sodium channels to block osteoarthritic pain

Voltage-gated sodium channels (NaV) in nociceptive neurons initiate action potentials required for transmission of aberrant painful stimuli observed in osteoarthritis (OA). Targeting NaV subtypes with drugs to produce analgesic effects for OA pain management is a developing therapeutic area. Previously, we determined the receptor site for the tamoxifen analog N-desmethyltamoxifen (ND-Tam) within a prokaryotic NaV. Here, we report the pharmacology of ND-Tam against eukaryotic NaVs natively expressed in nociceptive neurons. ND-Tam and analogs occupy two conserved intracellular receptor sites in domains II and IV of NaV1.7 to block ion entry using a "bind and plug" mechanism. We find that ND-Tam inhibition of the sodium current is state dependent, conferring a potent frequency- and voltage-dependent block of hyperexcitable nociceptive neuron action potentials implicated in OA pain. When evaluated using a mouse OA pain model, ND-Tam has long-lasting efficacy, which supports the potential of repurposing ND-Tam analogs as NaV antagonists for OA pain management.

Comprehensive Network Analysis of Dysregulated Genes Revealed MNX1‐AS1/ hsa‐miR‐4697‐3p/ HOXB13 Axis in OC Chemotherapy Response

Poor chemotherapy response is the main obstacle of ovarian cancer (OC) treatment. Platinum‐refractory and ‐resistant patients are associated with a worse outcome than platinum‐sensitive and partially sensitive patients, but the comprehensive similarities and differences among them are not yet clear. In this study, we analyzed the data of patients with different chemotherapy response in The Cancer Genome Atlas. We found a minority of altered genes were overlapped in refractory and resistant groups, as did the enriched pathways and Gene Ontology terms. We noticed that the neural signaling and drug metabolism enzymes were more significantly enriched and the protein–protein interaction supported these results. The transcription analysis highlighted PDX1 as the common and central transcription factor in both refractory and resistant groups. The competing endogenous RNA (ceRNA) network shared no common ceRNA pairs, indicating a major difference in noncoding RNA post‐transcriptional regulation. In the end, we validated the expression, regulation, binding, and effect on chemotherapy response for selected MNX1‐AS1/hsa‐miR‐4697‐3p/HOXB13 in OC cell lines. Our study offered a novel and comprehensive insight into chemotherapy response, and potential targets for improving chemotherapy response in OC.

Inhibition of Cytochrome P450s by Strobilanthes crispus Sub-Fraction (F3): Implication for Herb-Drug Interaction

BACKGROUND AND OBJECTIVE

Strobilanthes crispus Blume sub-fraction (F3) has been reported to be cytotoxic against cancer cells and to cause murine mammary tumor regression. Potential utilization of F3 as an adjuvant in breast cancer treatment to alleviate chemotherapeutic drug resistance is currently hampered by potential cytochrome P450 (CYP)-mediated herb-drug interactions (HDIs). The current study assessed the inhibitory potency of F3 towards five CYP enzymes involved in tamoxifen metabolism.

METHODS

Potential CYP inhibition by F3 was first determined using fluorescence assays, using known CYP inhibitors as reference. To further ascertain the inhibitory potency and mode of inhibition, high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS) analysis of specific metabolites of a CYP probe substrate was conducted.

RESULTS

The half-maximal inhibitory concentration (IC₅₀) values indicate that F3 exhibited relatively weak inhibition on CYP2B6, CYP2C19, CYP2D6, and CYP3A4. Highest susceptibility to inhibition by F3 was observed for CYP2C9, where the IC₅₀ value from fluorescence-based assay was 35-fold higher than control. Further analysis by HPLC-MS/MS revealed relatively weak mixed-type inhibition of F3 on CYP2C9, as indicated by IC₅₀ and inhibition constant (K_I) values. The risk of clinically significant CYP2C9 inhibition by F3 was then predicted based on the attained K_I value and the presumed amount of F3 absorbed from S. crispus leaves following consumption. The calculated maximum plasma concentration to inhibition constant C_max/K_I) ratio suggests that F3 consumption could potentially result in clinically significant drug interactions with medications metabolized by CYP2C9.

CONCLUSION

Taken together, the results revealed a low probability of inhibition by F3 on CYP enzymes involved in tamoxifen metabolism. However, further in vivo investigation is necessary for potential F3 interaction with CYP2C9. The utility of a preliminary in vitro approach in the assessment of potential HDI was demonstrated in this study.

Pharmacogenetics of Drugs Used in the Treatment of Cancers

Pharmacogenomics is based on the understanding of the individual differences in drug use, the response to drug therapy (efficacy and toxicity), and the mechanisms underlying variable drug responses. The identification of DNA variants which markedly contribute to inter-individual variations in drug responses would improve the efficacy of treatments and decrease the rate of the adverse side effects of drugs. This review focuses only on the impact of polymorphisms within drug-metabolizing enzymes on drug responses. Anticancer drugs usually have a very narrow therapeutic index; therefore, it is very important to use appropriate doses in order to achieve the maximum benefits without putting the patient at risk of life-threatening toxicities. However, the adjustment of the appropriate dose is not so easy, due to the inheritance of specific polymorphisms in the genes encoding the target proteins and drug-metabolizing enzymes. This review presents just a few examples of such polymorphisms and their impact on the response to therapy.

Association between genetic polymorphisms in cytochrome P450 enzymes and survivals in women with breast cancer receiving adjuvant endocrine therapy: a systematic review and meta-analysis

Tamoxifen is commonly prescribed for preventing recurrence in patients with breast cancer. However, the responses of the patients on tamoxifen treatment are variable. Cytochrome P450 genetic variants have been reported to have a significant impact on the clinical outcomes of tamoxifen treatment but no tangible conclusion can be made up till now. The present review attempts to provide a comprehensive review on the associative relationship between genetic polymorphisms in cytochrome P450 enzymes and survival in breast cancer patients on adjuvant tamoxifen therapy. The literature search was conducted using five databases, resulting in the inclusion of 58 studies in the review. An appraisal of the reporting quality of the included studies was conducted using the assessment tool from the Effective Public Health Practice Project (EPHPP). Meta-analyses were performed on CYP2D6 studies using Review Manager 5.3 software. For other studies, descriptive analyses were performed. The results of meta-analyses demonstrated that shorter overall survival, disease-free survival and relapse-free survival were found in the patients with decreased metabolisers when compared to normal metabolisers. The findings also showed that varying and conflicting results were reported by the included studies. The possible explanations for the variable results are discussed in this review.

Manipulating Estrogenic/Anti-Estrogenic Activity of Triphenylethylenes towards Development of Novel Anti-Neoplastic SERMs

Selective estrogen receptor modulators (SERMs) act as estrogen receptor (ERα) agonists or antagonists depending on the target issue. Tamoxifen (TAM) (a non-steroidal triphenylethylene derivative) was the first SERM approved as anti-estrogen for the treatment of metastatic breast cancer. On the hunt for novel SERMs with potential growth inhibitory activity on breast cancer cell lines yet no potential to induce endometrial carcinoma, we designed and synthesized 28 novel TAM analogs. The novel analogs bear a triphenylethylene scaffold. Modifications on rings A, B, and C aim to attenuate estrogenic/anti-estrogenic activities of the novel compounds so they can potentially inhibit breast cancer and provide positive, beneficial estrogenic effects on other tissues with no risk of developing endometrial hyperplasia. Compound 12 (E/Z-1-(2-{4-[1-(4-Chloro-phenyl)-2-(4-methoxy-phenyl)-propenyl]-phenoxy}-ethyl)-piperidine) showed an appreciable relative ERα agonistic activity in a yeast estrogen screen (YES) assay. It successfully inhibited the growth of the MCF-7 cell line with GI₅₀ = 0.6 µM, and it was approximately three times more potent than TAM. It showed no potential estrogenicity on Ishikawa endometrial adenocarcinoma cell line via assaying alkaline phosphatase (AlkP) activity. Compound 12 was tested in vivo to assess its estrogenic properties in an uterotrophic assay in an ovariectomized rat model. Compared to TAM, it induced less increase in wet uterine wet weight and showed no uterotrophic effect. Compound 12 is a promising candidate for further development due to its inhibition activity on MCF-7 proliferation with moderate AlkP activity and no potential uterotrophic effects. The in vitro estrogenic activity encourages further investigations toward potential beneficial properties in cardiovascular, bone, and brain tissues.

Bacterial Biosynthetic P450 Enzyme PikCD50N: A Potential Biocatalyst for the Preparation of Human Drug Metabolites

Human drug metabolites (HDMs) are important chemicals widely used in drug-related studies. However, acquiring these enzyme-derived and regio-/stereo-selectively modified compounds through chemical approaches is complicated. PikC is a biosynthetic P450 enzyme involved in pikromycin biosynthesis from the bacterium Streptomyces venezuelae. Here, we identify the mutant PikC_D50N as a potential biocatalyst, with a broad substrate scope, diversified product profile, and high catalytic efficiency, for preparation of HDMs. Remarkably, PikC_D50N can mediate the drug-metabolizing reactions using the low-cost H₂O₂ as a direct electron and oxygen donor.

Enriching Medication Review with a Pharmacogenetic Profile - A Case of Tamoxifen Adverse Drug Reactions

Pharmacogenotyping is applied to determine the hereditable component of a patient's susceptibility to experience therapy failure and/or adverse drug reactions (ADRs). We present the case of a female patient diagnosed with breast cancer and treated with tamoxifen as recurrence therapy who experienced various ADRs. Pharmacogenotyping revealed variants in the cytochrome P450 (CYP) enzymes CYP2D6, CYP2C9, and CYP2C19. The observed genotype was associated with a risk for lower tamoxifen efficacy. Aside from the tamoxifen therapy, the comedication was reviewed for the influence of the patient’s pharmacogenetic profile. As a result of this pharmacist-led medication review with pharmacogenetic analyses, concrete genotype-driven recommendations for the treating gynecologist were compiled. This case revealed the added value of a large pharmacogenetic panel and the complexity of integrating a pharmacogenetic profile into a recommendation.

Human Family 1-4 cytochrome P450 enzymes involved in the metabolic activation of xenobiotic and physiological chemicals: an update

This is an overview of the metabolic activation of drugs, natural products, physiological compounds, and general chemicals by the catalytic activity of cytochrome P450 enzymes belonging to Families 1-4. The data were collected from > 5152 references. The total number of data entries of reactions catalyzed by P450s Families 1-4 was 7696 of which 1121 (~ 15%) were defined as bioactivation reactions of different degrees. The data were divided into groups of General Chemicals, Drugs, Natural Products, and Physiological Compounds, presented in tabular form. The metabolism and bioactivation of selected examples of each group are discussed. In most of the cases, the metabolites are directly toxic chemicals reacting with cell macromolecules, but in some cases the metabolites formed are not direct toxicants but participate as substrates in succeeding metabolic reactions (e.g., conjugation reactions), the products of which are final toxicants. We identified a high level of activation for three groups of compounds (General Chemicals, Drugs, and Natural Products) yielding activated metabolites and the generally low participation of Physiological Compounds in bioactivation reactions. In the group of General Chemicals, P450 enzymes 1A1, 1A2, and 1B1 dominate in the formation of activated metabolites. Drugs are mostly activated by the enzyme P450 3A4, and Natural Products by P450s 1A2, 2E1, and 3A4. Physiological Compounds showed no clearly dominant enzyme, but the highest numbers of activations are attributed to P450 1A, 1B1, and 3A enzymes. The results thus show, perhaps not surprisingly, that Physiological Compounds are infrequent substrates in bioactivation reactions catalyzed by P450 enzyme Families 1-4, with the exception of estrogens and arachidonic acid. The results thus provide information on the enzymes that activate specific groups of chemicals to toxic metabolites.

Impact of Human SULT1E1 Polymorphisms on the Sulfation of 17β-Estradiol, 4-Hydroxytamoxifen, and Diethylstilbestrol by SULT1E1 Allozymes

BACKGROUND AND OBJECTIVES

Previous studies have revealed that sulfation, as mediated by the estrogen-sulfating cytosolic sulfotransferase (SULT) SULT1E1, is involved in the metabolism of 17β-estradiol (E2), 4-hydroxytamoxifen (4OH-tamoxifen), and diethylstilbestrol in humans. It is an interesting question whether the genetic polymorphisms of SULT1E1, the gene that encodes the SULT1E1 enzyme, may impact on the metabolism of E2 and these two drug compounds through sulfation.

METHODS

In this study, five missense coding single nucleotide polymorphisms of the SULT1E1 gene were selected to investigate the sulfating activity of the coded SULT1E1 allozymes toward E2, 4OH-tamoxifen, and diethylstilbestrol. Corresponding cDNAs were generated by site-directed mutagenesis, and recombinant SULT1E1 allozymes were bacterially expressed, affinity-purified, and characterized using enzymatic assays.

RESULTS

Purified SULT1E1 allozymes were shown to display differential sulfating activities toward E2, 4OH-tamoxifen, and diethylstilbestrol. Kinetic analysis revealed further distinct K_m (reflecting substrate affinity) and V_max (reflecting catalytic activity) values of the five SULT1E1 allozymes with E2, 4OH-tamoxifen, and diethylstilbestrol as substrates.

CONCLUSIONS

Taken together, these findings highlighted the significant differences in E2-, as well as the drug-sulfating activities of SULT1E1 allozymes, which may have implications in the differential metabolism of E2, 4OH-tamoxifen, and diethylstilbestrol in individuals with different SULT1E1 genotypes.

Optimization of tamoxifen-induced Cre activity and its effect on immune cell populations

Tamoxifen (TAM) inducible Cre recombinase system is an essential tool to study gene function when early ablation or overexpression can cause developmental defects or embryonic lethality. However, there remains a lack of consensus on the optimal route and dosage of TAM administration in vivo. Here, we assessed dosage and delivery of TAM for activation of Cre in immune cell subsets assessed longitudinally and spatially using transgenic mice with ubiquitously expressed Cre/ER and the Cre-inducible fluorescent reporter YFP. After comparing two TAM delivery methods (intraperitoneal versus oral gavage) and different doses, we found that 3 mg of TAM administered orally for five consecutive days provides maximal reporter induction with minimal adverse effects in vivo. Serum levels of TAM peaked 1 week after initiating treatment then slowly decreased, regardless of dosing and delivery methods. TAM concentration in specific tissues (liver, spleen, lymph nodes, and thymus) was also dependent on delivery method and dose. Cre induction was highest in myeloid cells and B cells and substantially lower in T cells, and double-positive thymocytes had a notably higher response to TAM. In addition to establishing optimal dose and administration of TAM, our study reveals a disparate activity of Cre in different cell immune populations when using Cre/ER models.

Ratite oils for local transdermal therapy of 4-OH tamoxifen: development, characterization, and ex vivo evaluation

The anti-inflammatory property of ratite oils as well as its ability to act as a penetration enhancer makes it an ideal agent to be used in transdermal formulations. The present study aims to develop an effective transfersomal delivery of 4-hydroxytamoxifen (4-OHT), an anti-cancer drug, using ratite oil as a carrier agent for the treatment of breast cancer (BC). The 4-OHT transfersomes were prepared with and without ratite oils using soy phosphatidylcholine and three different edge activators (EAs) in five different molar ratios using the rotary evaporation-ultrasonication method. Optimal transfersome formulations were selected using physical-chemical characterization and ex vivo studies. Results from physical-chemical characterization of the developed formulations found sodium taurocholate to be the most suitable EA, which recorded highest entrapment efficiency of 95.1 ± 2.70% with 85:15, (w/w) and lowest vesicle size of 82.3 ± 0.02 nm with 75:25, (w/w) molar ratios. TEM and DSC studies showed that the vesicles were readily identified and present in a nearly perfect spherical shape. In addition, formulations with emu oil had better stability than formulations with ostrich oil. Physical stability studies at 4 °C showed that ratite oil transfersomes were stable up to 4 weeks, while transfersomes without ratite oils were stable for 8 weeks. Ex vivo permeability studies using porcine skin concluded that 4-OHT transfersomal formulations with (85:15, w/w) without emu oil have the potential to be used in transdermal delivery approach to enhance permeation of 4-OHT, which may be beneficial in the treatment of BC.

Quantifying drug-induced structural toxicity in hepatocytes and cardiomyocytes derived from hiPSCs using a deep learning method

Cardiac and hepatic toxicity result from induced disruption of the functioning of cardiomyocytes and hepatocytes, respectively, which is tightly related to the organization of their subcellular structures. Cellular structure can be analyzed from microscopy imaging data. However, subtle or complex structural changes that are not easily perceived may be missed by conventional image-analysis techniques. Here we report the evaluation of PhenoTox, an image-based deep-learning method of quantifying drug-induced structural changes using human hepatocytes and cardiomyocytes derived from human induced pluripotent stem cells. We assessed the ability of the deep learning method to detect variations in the organization of cellular structures from images of fixed or live cells. We also evaluated the power and sensitivity of the method for detecting toxic effects of drugs by conducting a set of experiments using known toxicants and other methods of screening for cytotoxic effects. Moreover, we used PhenoTox to characterize the effects of tamoxifen and doxorubicin-which cause liver toxicity-on hepatocytes. PhenoTox revealed differences related to loss of cytochrome P450 3A4 activity, for which it showed greater sensitivity than a caspase 3/7 assay. Finally, PhenoTox detected structural toxicity in cardiomyocytes, which was correlated with contractility defects induced by doxorubicin, erlotinib, and sorafenib. Taken together, the results demonstrated that PhenoTox can capture the subtle morphological changes that are early signs of toxicity in both hepatocytes and cardiomyocytes.

Limitations of Systemic Oncological Therapy in Breast Cancer Patients with Chronic Kidney Disease

Breast cancer is the most common malignancy, affecting middle-age and older women frequently suffering from other chronic diseases, including chronic kidney disease. The risk of breast cancer development in women on renal replacement therapy (peritoneal dialysis and haemodialysis) is higher than in the general population. Chronic kidney disease does not limit surgical treatment or radiotherapy; however, it affects the pharmacokinetics of drugs used in the systematic treatment to a different extent, increasing their toxicity and the risk of adverse drug reactions. This article summarizes the current knowledge (published studies accessed through PUBMED) on drugs used in chemotherapy, hormone therapy, anti-HER2 drugs, CDK4/6 inhibitors, PARP inhibitors, and immune therapy in breast cancer patients undergoing dialysis. We discuss the data, the optimal choice of the chemotherapeutic protocol, and the administration of drugs in a specific time relation to the haemodialysis session to ensure the most effective and safe treatment to breast cancer patients.

Synthesis of novel flexible tamoxifen analogues to overcome CYP2D6 polymorphism and their biological evaluation on MCF-7 cell line

Tamoxifen (TAM) is currently the endocrine treatment of choice for all stages of breast cancer; it has proven success in ER positive and ER negative patients. TAM is activated by endogenous CYP450 enzymes to the more biologically active metabolites 4-hydroxytamoxifen and endoxifen mainly via CYP2D6 and CYP3A4/5. CYP2D6 has been investigated for polymorphism; there is a large interindividual variation in the enzyme activity, this drastically effects clinical outcomes of tamoxifen treatment. Here in we report the design and synthesis of 10 novel compounds bearing a modified tamoxifen skeleton, ring C is substituted with different ester groups to bypass the CYP2D6 enzyme metabolism and employ esterase enzymes for activation. All compounds endorse flexibility on ring A. Compounds (II-X) showed MCF-7% growth inhibition >50% at a screening dose of 10 μM. These results were validated by yeast estrogen screen (YES) and E-Screen assay combined with XTT assay. Compound II (E/Z 4-[1-4-(3-Dimethylamino-propoxy)-phenyl)-3-(4-methoxy-phenyl)-2-methyl-propenyl]-phenol) showed nanomolar antiestrogenic activity (IC₅₀ = 510 nM in YES assay) and was five times more potent in inhibiting the growth of MCF-7 BUS (IC₅₀ = 96 nM) compared to TAM (IC₅₀ = 503 nM). Esterified analogues VI, VII were three times more active than TAM on MCF-7 BUS (IC₅₀ = 167 nM). Novel analogues are prodrugs that can ensure equal clinical outcomes to all breast cancer patients.

Pharmacogenomics in the Nigerian population: the past, the present and the future

The Nigerian population exhibits huge ethnic and genetic diversity, typical of African populations, which can be harnessed for improved drug-response and disease management. Existing data on genes relevant to drug response, so far generated for the population, indeed confirm the prevalence of some clinically significant pharmacogenes. These reports detail prevailing genetic alleles and metabolic phenotypes of vital drug metabolizing monooxygenases, transferases and drug transporters. While the utilization of existing pharmacogenomic data for healthcare delivery remains unpopular, several past and on-going studies suggest that a future shift toward genotype-stratified dosing of drugs and disease management in the population is imminent. This review discusses the present state of pharmacogenomics in Nigeria and the potential benefits of sustained research in this field for the population.

CYP enzymes, expressed within live human suspension cells, are superior to widely-used microsomal enzymes in identifying potent CYP1A1/CYP1B1 inhibitors: Identification of quinazolinones as CYP1A1/CYP1B1 inhibitors that efficiently reverse B[a]P toxicity and cisplatin resistance

Microsomal cytochrome P450 (CYP) enzymes, isolated from recombinant bacterial/insect/yeast cells, are extensively used for drug metabolism studies. However, they may not always portray how a developmental drug would behave in human cells with intact intracellular transport mechanisms. This study emphasizes the usefulness of human HEK293 kidney cells, grown in 'suspension' for expression of CYPs, in finding potent CYP1A1/CYP1B1 inhibitors, as possible anticancer agents. With live cell-based assays, quinazolinones 9i/9b were found to be selective CYP1A1/CYP1B1 inhibitors with IC₅₀ values of 30/21 nM, and > 150-fold selectivity over CYP2/3 enzymes, whereas they were far less active using commercially-available CYP1A1/CYP1B1 microsomal enzymes (IC₅₀, >10/1.3-1.7 μM). Compound 9i prevented CYP1A1-mediated benzo[a]pyrene-toxicity in normal fibroblasts whereas 9b completely reversed cisplatin resistance in PC-3/prostate, COR-L23/lung, MIAPaCa-2/pancreatic and LS174T/colon cancer cells, underlining the human-cell-assays' potential. Our results indicate that the most potent CYP1A1/CYP1B1 inhibitors would not have been identified if one had relied merely on microsomal enzymes.

Predicting the Effects of Different Triazole Antifungal Agents on the Pharmacokinetics of Tamoxifen

Tamoxifen is an antiestrogen drug that is widely used in the adjuvant chemotherapy of estrogen receptor-α (ERα)-positive breast cancer. Chemotherapy could suppress immune function in breast cancer patients, which may cause invasive fungal infections (IFIs). Triazoles (voriconazole, fluconazole, and itraconazole) were commonly used for IFI. The physiologically based pharmacokinetic (PBPK) models were developed to investigate the influence of different triazoles on tamoxifen pharmacokinetics in this paper. To investigate the influence of different triazoles (voriconazole, fluconazole, itraconazole) on tamoxifen pharmacokinetics. Adjusted physicochemical data and pharmacokinetic parameters of voriconazole, fluconazole, itraconazole, and tamoxifen were obtained from published literatures. PBPK models were built and verified in healthy subjects using GastroPlus™. Voriconazole, itraconazole, and tamoxifen were administered orally. Fluconazole was administered intravenously. Simulated plasma concentration-time curves of the voriconazole, fluconazole, itraconazole, and tamoxifen showed good agreement with the observed profiles, respectively. The DDI simulations showed that the pharmacokinetic parameters of tamoxifen were increased by various degrees when coadministered with different triazoles. In healthy subjects, the area under the plasma concentration-time curve from 0 to t h (AUC_0-t) of tamoxifen was increased by 41%, 5%, and1% when coadministrated with voriconazole, fluconazole, and itraconazole, respectively. The PBPK models adequately characterized the pharmacokinetics of tamoxifen and triazoles. Among the three triazoles, voriconazole exhibited the greatest effect on tamoxifen pharmacokinetics. In clinical practice, an effective dosage adjustment of tamoxifen may need to be considered and TDM for tamoxifen is advisable to guide dosing and optimize therapy when coadministered with voriconazole.

Tamoxifen inhibits the proliferation of non‑melanoma skin cancer cells by increasing intracellular calcium concentration

Tamoxifen is an estrogen receptor (ER) antagonist used as first-line chemotherapy in breast cancer. Recent studies suggest that tamoxifen may be effective not only for ER‑positive but also for ER‑negative cancer cases. The aim of the present study was to investigate the antiproliferative effect of tamoxifen against human non‑melanoma skin cancer cells. Tamoxifen inhibited the proliferation of the skin squamous cell carcinoma (SCC) cell lines A431, DJM‑1 and HSC‑1. A431 cells did not express ER‑α or -β, suggesting that tamoxifen may exert antiproliferative effects on skin SCC cells via a non‑ER‑mediated pathway. Tamoxifen increased the intracellular calcium concentration of skin SCC cells, and this increase in intracellular calcium concentration by calcium ionophore A23187 suppressed the proliferation of skin SCC cells. These data indicate that tamoxifen inhibited the proliferation of human skin SCC cells via increasing intracellular calcium concentration. Voltage-gated calcium channels and non‑selective cation channels are involved in the increase in intracellular calcium concentration induced by tamoxifen. The broad-spectrum protein kinase C (PKC) inhibitor phloretin significantly attenuated the antiproliferative effect of tamoxifen on skin SCC cells. From these data, it may be concluded that tamoxifen inhibits the proliferation of skin SCC cells by induction of extracellular calcium influx via calcium channels in the plasma membrane and by subsequent activation of PKC.

Effect of CYP2C19 and CYP2D6 genotype on tamoxifen treatment outcome indicates endogenous and exogenous interplay

Aim: We investigated the interaction of CYP2C19 and CYP2D6 genotype on clinical outcome in tamoxifen-treated breast cancer patients. Materials & methods: A cohort of 306 patients on tamoxifen treatment for a minimum of 1 year were employed to analyze the effect of genotype-predicted phenotype on relapse-free survival. Results & conclusion: We show that the group with worst outcome and highest risk of relapse is that of 2C19↑–2D6↓ (hazard ratio: 2.94), when adjusting for age, Nottingham prognostic index and adjuvant chemotherapy. Furthermore, the effect of 2C19↑–2D6↓genotype-predicted phenotype is greatly enhanced in premenopausal patients (hazard ratio: 21.08). We hypothesize that poor bioactivation of tamoxifen in patients with low CYP2D6 activity and high CYP2C19 metabolism represents a tamoxifen-treated patient group that has the worst clinical outcome.

Recombinant production of eukaryotic cytochrome P450s in microbial cell factories

Cytochrome P450s (P450s) comprise one of the largest known protein families. They occur in every kingdom of life and catalyze essential reactions, such as carbon source assimilation, synthesis of hormones and secondary metabolites, or degradation of xenobiotics. Due to their outstanding ability of specifically hydroxylating complex hydrocarbons, there is a great demand to use these enzymes for biocatalysis, including applications at an industrial scale. Thus, the recombinant production of these enzymes is intensively investigated. However, especially eukaryotic P450s are difficult to produce. Challenges are faced due to complex cofactor requirements and the availability of a redox-partner (cytochrome P450 reductase, CPR) can be a key element to get active P450s. Additionally, most eukaryotic P450s are membrane bound which complicates the recombinant production. This review describes current strategies for expression of P450s in the microbial cell factories Escherichia coli, Saccharomyces cerevisiae, and Pichia pastoris.

Density Functional Theory Study on the Demethylation Reaction between Methylamine, Dimethylamine, Trimethylamine, and Tamoxifen Catalyzed by a Fe(IV)-Oxo Porphyrin Complex

In this work, we studied computationally the N-demethylation reaction of methylamine, dimethylamine, and trimethylamine as archetypal examples of primary, secondary, and tertiary amines catalyzed by high-field low-spin Fe-containing enzymes such as cytochromes P450. Using DFT calculations, we found that the expected C-H hydroxylation process was achieved for trimethylamine. When dimethylamine and methylamine were studied, two different reaction mechanisms (C-H hydroxylation and a double hydrogen atom transfer) were computed to be energetically accessible and both are equally preferred. Both processes led to the formation of formaldehyde and the N-demethylated substrate. Finally, as an illustrative example, the relative contribution of the three primary oxidation routes of tamoxifen was rationalized through energetic barriers obtained from density functional calculations and docking experiments involving CYP3A4 and CYP2D6 isoforms. We found that the N-demethylation process was the intrinsically favored one, whereas other oxidation reactions required most likely preorganization imposed by the residues close to the active sites.

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

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

CYP2C19*2 and CYP2C19*17 variants and effect of tamoxifen on breast cancer recurrence: Analysis of the International Tamoxifen Pharmacogenomics Consortium dataset

The role of cytochrome P450 drug metabolizing enzymes in the efficacy of tamoxifen treatment of breast cancer is subject to substantial interest and controversy. CYP2D6 have been intensively studied, but the role of CYP2C19 is less elucidated, and we studied the association of CYPC19 genotype and recurrence of breast cancer. We used outcome and genotyping data from the large publicly available International Tamoxifen Pharmacogenomics Consortium (ITPC) dataset. Cox regression was used to compute the hazard ratios (HRs) for recurrence. CYP2C19 genotype data was available for 2 423 patients and the final sample cohort comprised 2 102 patients. CYP2C19*2 or *19 alleles did not influence DFS. For the CYP2C19*2 allele, the HR was 1.05 (CI 0.78–1.42) and 0.79 (CI 0.32–1.94) for hetero- and homozygote carriers, respectively. The corresponding HR for hetero- and homozygote carriers of the CYP2C19*17 allele were 1.02 (CI 0.71–1.46) and 0.57 (CI 0.26–1.24), respectively. Accounting for CYP2D6 genotype status did not change these estimates. We found no evidence to support a clinically meaningful role of CYP2C19 polymorphisms and response to tamoxifen in breast cancer patients and, consequently, CYP2C19 genotype status should not be included in clinical decisions on tamoxifen treatment.

Rifampin-Mediated Induction of Tamoxifen Metabolism in a Humanized PXR-CAR-CYP3A4/3A7-CYP2D6 Mouse Model

Animals are not commonly used to assess drug-drug interactions due to poor clinical translatability arising from species differences that may exist in drug-metabolizing enzymes and transporters, and their regulation pathways. In this study, a transgenic mouse model expressing human pregnane X receptor (PXR), constitutive androstane receptor (CAR), CYP3A4/CYP3A7, and CYP2D6 (Tg-composite) was used to investigate the effect of induction mediated by rifampin on the pharmacokinetics of tamoxifen and its metabolites. In humans, tamoxifen is metabolized primarily by CYP3A4 and CYP2D6, and multiple-day treatment with rifampin decreased tamoxifen exposure by 6.2-fold. Interestingly, exposure of tamoxifen metabolites 4-hydroxytamoxifen (4OHT), N-desmethyltamoxifen (NDM), and endoxifen also decreased. In the Tg-composite model, pretreatment with rifampin decreased tamoxifen area under the time-concentration curve between 0 and 8 hours (AUC_0-8) from 0.82 to 0.20 µM*h, whereas AUC_0-8 of 4OHT, NDM, and endoxifen decreased by 3.4-, 4.7-, and 1.3-fold, respectively, mirroring the clinic observations. In the humanized PXR-CAR (hPXR-CAR) model, rifampin decreased AUC_0-8 of tamoxifen and its metabolites by approximately 2-fold. In contrast, no significant modulation by rifampin was observed in the nonhumanized C57BL/6 (wild-type) animals. In vitro kinetics determined in microsomes prepared from livers of the Tg-composite animals showed that, although K_m values were not different between vehicle- and rifampin-treated groups, rifampin increased the V_max for the CYP3A4-mediated pathways. These data demonstrate that, although the hPXR-CAR model is responsive to rifampin, the extent of the clinical rifampin-tamoxifen interaction is better represented by the Tg-composite model. Consequently, the Tg-composite model may be a suitable tool to examine the extent of rifampin-mediated induction for other compounds whose metabolism is mediated by CYP3A4 and/or CYP2D6.

Associations between CYP1A1 rs1048943 A > G and rs4646903 T > C genetic variations and colorectal cancer risk: Proof from 26 case-control studies

Cytochrome P450 1A1 (CYP1A1) enzyme is one of the most important metabolizing enzymes responsible for the metabolism of numerous xenobiotics. Numerous individual case-control studies have investigated the associations between the CYP1A1 rs1048943 A > G and rs4646903 T > C genetic variations and colorectal cancer (CRC) risk, but the conclusions were controversial. To obtain a scientific conclusion, we performed a meta-analysis based on a total of 26 publications, including 20 studies with 8665 cases and 9953 controls on rs1048943 A > G and 19 studies with 6416 cases and 7551 controls on rs4646903 T > C, respectively. The pooled analysis indicated that rs1048943 A > G was associated with an increased risk of CRC (G vs. A: OR = 1.28, 95% CI = 1.08-1.52; GG vs. AA: OR = 1.54, 95% CI = 1.25-1.91; GA vs. AA: OR = 1.26, 95% CI = 1.00-1.60; GG/GA vs. AA: OR = 1.31, 95% CI = 1.05-1.64; GG vs. GA/AA. OR = 1.56, 95% CI = 1.26-1.91). Stratification analysis showed the association between rs1048943 A > G and CRC risk was more obvious in studies with the population-based (PB) design or high quality score. The association between rs4646903 T > C and CRC risk did not reach statistical significance in the pooled analysis as well as stratification analysis. This meta-analysis demonstrated CYP1A1 rs1048943 A > G may increase the susceptibility to CRC instead of rs4646903 T > C. This conclusion suggested CYP1A1 may contribute to the pathogenesis of CRC.

A case report of QT prolongation with glycopyrronium bromide in a patient with chronic tamoxifen use

Background

Glycopyrronium bromide has recently been approved as a once daily maintenance inhalation therapy for moderate to severe chronic obstructive pulmonary disease (COPD). Efficacy and safety trial data have found rare cases of significant QT prolongation. To our knowledge, we describe the first case report of QT prolongation >600 ms with initiation of glycopyrronium bromide in a real world setting.

Case presentation

A 78-year-old female with moderate COPD recently started on glycopyrronium bromide, presented to Emergency Department (ED) with syncope. Her past medical history was significant for a left total mastectomy and she had been on Tamoxifen for 9 months. One day prior to her presentation, she had visited a naturopathic clinic for a vitamin infusion resulting in emesis. The following day she continued to feel dizzy and had a witnessed syncopal episode without any reported cardiac or neurological symptoms preceding the event or after regaining consciousness. In the emergency department, she reported dizziness and was found to be hypotensive. Her symptoms completely resolved with intravenous fluids. Lab work was normal however her electrocardiogram (ECG) demonstrated a QTc interval of 603 and 631 ms (Friderica and Bazett’s respectively) with a normal QT interval on her baseline ECG prior to initiating Tamoxifen. She was admitted to the Cardiology service for further work-up of QT prolongation. Her syncope was felt to be due to orthostatic hypotension and the QT prolongation secondary to medications, which were both discontinued during her admission. After 2 days, her QT interval normalized consistent with the half-life of Glycopyrronium bromide (13–57 h) compared to Tamoxifen (8–14 days).

Conclusion

Glycopyrronium bromide is guideline recommended as first line therapy for prevention of exacerbation in moderate to severe COPD however safety data had been limited to select populations. This case report highlights the need for future studies to identify high-risk populations at potential risk of life-threatening arrhythmias who may benefit from periodic ECG surveillance.

Epidermal Growth Factor Receptor Kinase Inhibitors Synergize with TCDD to Induce CYP1A1/1A2 in Human Breast Epithelial MCF10A Cells

CYP1A1 and CYP1A2 are transcriptionally activated in the human normal breast epithelial cell line MCF10A following exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). Shifting MCF10A cultures to medium deficient in serum and epidermal growth factor (EGF) caused rapid reductions in the activated (i.e., phosphorylated) forms of extracellular regulated kinases (ERKs) and the epidermal growth factor receptor (EGFR). Shifting to serum/EGF-deficient medium also enhanced TCDD-mediated induction of cytochrome P450 (CYP)1A1 Treatment of cells cultured in complete medium with the EGFR inhibitors gefitinib (Iressa), AG1478, and CI-1033 resulted in concentration-dependent reductions of active EGFR and ERKs, and increased CYP1A1 mRNA content ∼3- to 18-fold above basal level. EGFR inhibitors synergized with TCDD and resulted in transient CYP1A1 and CYP1A2 mRNA accumulations ∼8-fold greater (maximum at 5 hours) than that achieved with only TCDD. AG1478, gefitinib, and TCDD individually induced small increases (∼1.2- to 2.5-fold) in CYP1A1 protein content but did not cause additive or synergistic accumulations of CYP1A1 protein when used in combination. The mitogen-activated protein kinase kinase inhibitor PD184352 inhibited ERK and EGFR activation in a concentration-dependent fashion without causing CYP1A1 mRNA accumulation. However, cotreatment with PD184352 potentiated TCDD-mediated CYP1A1 induction. TCDD-mediated induction of CYP1A1 in MCF7-TET on-EGFR cells, a MCF7 variant in which EGFR expression can be controlled, was not affected by the activity status of EGFR or ERKs. Hence, EGFR signaling mutes both basal and ligand-induced expression of two aryl hydrocarbon receptor-responsive P450s in MCF10A cultures. However, these effects are cell context-dependent. Furthermore, CYP1A1 mRNA and protein abundance are not closely coupled in MCF10A cultures.

Dose Escalation of Tamoxifen in Patients with Low Endoxifen Level: Evidence for Therapeutic Drug Monitoring-The TADE Study

PURPOSE

Endoxifen is the major mediator of tamoxifen effect and endoxifen levels <15 nmol/L may be associated with increased risk of breast cancer recurrence. We increased tamoxifen dose in breast cancer patients with low endoxifen levels and assessed the influence of various parameters on reaching 15 nmol/L and 30 nmol/L endoxifen levels.

EXPERIMENTAL DESIGN

Tamoxifen dose was increased in those with endoxifen levels below 30 nmol/L. Toxicity, including hot flash score, was measured. CYP2D6 metabolizer status was classified as ultra-rapid (UM), extensive (EM), intermediate (IM), or poor (PM) based genotype of somatic DNA.

RESULTS

Dosage was escalated in 68 of 122 participants. On 20 mg tamoxifen, 24% had endoxifen levels below 15 nmol/L and this reduced to 6% following dose escalation. In over 50% of cases, there was no identified cause for low endoxifen. Low baseline endoxifen level, and not CYP2D6 metabolizer status, independently predicted reaching threshold targets for both the 15 nmol/L and 30 nmol/L targets (P = 0.04 and 0.003 respectively). The 15 nmol/L target was reached in all UM/EM and IM patients, 63% of PM patients, and 58% of those with baseline endoxifen of <10 nmol/L. There was no correlation between hot flash score and genotype or any tamoxifen metabolite level including endoxifen (R = 0.07).

CONCLUSIONS

Low endoxifen on standard dose tamoxifen was the only independent predictor of failure to achieve potentially therapeutic levels. Trials examining tamoxifen dose escalation and breast cancer outcome should be guided by endoxifen levels alone, without reference to CYP2D6 genotype or presence of hot flashes. Clin Cancer Res; 22(13); 3164-71. ©2016 AACRSee related commentary by Hertz and Rae, p. 3121.