CYP2D6 polymorphisms and the impact on tamoxifen therapy

Potential of covalently linked tamoxifen hybrids for cancer treatment: recent update

Cancer is a complex disease and the second leading cause of death globally, and breast cancer is still a leading cause of cancer death in women. Tamoxifen is the most commonly used drug for breast cancer (ER-positive) treatment and chemoprevention, saving the lives of millions of patients every year. In addition, the tamoxifen template has been explored extensively for the development of selective estrogen receptor modulators (SERMs) applicable in breast cancer, osteoporosis, and postmenopausal symptom treatment. Numerous anticancer drugs, including tamoxifen, are in use, but the complexity and heterogeneous nature of cancer complicate the effect of conventional targeted drugs, leading to adverse reactions and resistance. One of the significant approaches to overcome these shortcomings is drug hybrids, generated by covalently linking two or more active pharmacophores. These drug hybrids are remarkably effective in acting on multiple drug targets with higher selectivity and specificity. In recent years, several tamoxifen hybrids have been discovered as potential candidates for cancer treatment. The review highlights the recent progress in developing anticancer hybrids, including organometallic, fluorescent, photocaged, and novel ligand-based tamoxifen hybrids. It also demonstrates the significance of merging various pharmacophores with tamoxifen to produce more potent, precise, and effective anticancer agents. The study offers valuable knowledge to researchers working on cancer research with the hope of enhancing drug potency and reducing drug toxicity to improve cancer patients' lives.

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.

Frequency of pharmacogenomic variants affecting efficacy and safety of anti-cancer drugs in a south Asian population from Sri Lanka

BACKGROUND

Therapy with anti-cancer drugs remain the cornerstone of treating cancer. The effectiveness and safety of anti-cancer drugs vary significantly among individuals due to genetic factors influencing the drug response and metabolism. Data on the pharmacogenomic variations in Sri Lankans related to anti-cancer therapy is sparse. As current treatment guidelines in Sri Lanka often do not consider local pharmacogenomic variants, this study aimed to explore the diversity of pharmacogenomic variants in the Sri Lankan population to pave the way for personalized treatment approaches and improve patient outcomes.

METHODS

Pharmacogenomic data regarding variant-drug pairs of genes CYP2D6, DPYD, NUDT15, EPAS1, and XRCC1 with clinical annotations labelled as evidence levels 1A-2B were obtained from the Pharmacogenomics Knowledgebase database. Their frequencies in Sri Lankans were obtained from an anonymized database that was derived from 541 Sri Lankans who underwent exome sequencing at the Human Genetics Unit, Faculty of Medicine, University of Colombo. Variations in DPYD, NUDT15, and EPAS1 genes are related to increased toxicity to fluoropyrimidines, mercaptopurines, and sorafenib respectively. Variations in CYP2D6 and XRCC1 genes are related to changes in efficacy of tamoxifen and platinum compounds, respectively. Minor allele frequencies of these variants were calculated and compared with other populations.

RESULTS

MAFs of rs1065852 c.100 C > T (CYP2D6), rs3918290 c.1905 + 1G > A (DPYD), rs56038477 c.1236G > A (DPYD), rs7557402 c.1035-7 C > G (EPAS1), rs116855232 c.415 C > T (NUDT15*3), and rs25487 c.1196 A > G (XRCC1) were: 12.9% [95%CI:10.9-14.9], 1.5% [95%CI:0.8-2.2], 1.2% [95%CI:0.5-1.8], 37.7% [95%CI:34.8-40.6], 8.3% [95%CI:6.7-10.0], and 64.0% [95%CI:61.1-66.8], respectively. Frequencies of rs1065852 c.100 C > T (CYP2D6), rs7557402 c.1035-7 C > G (EPAS1), and rs25487 (XRCC1) were significantly lower in Sri Lankans, while frequencies of rs116855232 c.415 C > T (NUDT15*3) and rs56038477 c.1236G > A (DPYD) were significantly higher in Sri Lankans when compared to some Western and Asian populations.

CONCLUSION

Sri Lankans are likely to show lower toxicity risk with sorafenib (rs7557402 c.84,131 C > G) and, higher toxicity risk with fluoropyrimidines (rs56038477 c.1236G > A) and mercaptopurine (rs116855232 c.415 C > T), and reduced effectiveness with tamoxifen (rs1065852 c.100 C > T) and platinum compounds (rs25487). These findings highlight the potential contribution of these genetic variations to the individual variability in anti-cancer dosage requirements among Sri Lankans.

The landscape of small-molecule prodrugs

Prodrugs are derivatives with superior properties compared with the parent active pharmaceutical ingredient (API), which undergo biotransformation after administration to generate the API in situ. Although sharing this general characteristic, prodrugs encompass a wide range of different chemical structures, therapeutic indications and properties. Here we provide the first holistic analysis of the current landscape of approved prodrugs using cheminformatics and data science approaches to reveal trends in prodrug development. We highlight rationales that underlie prodrug design, their indications, mechanisms of API release, the chemistry of promoieties added to APIs to form prodrugs and the market impact of prodrugs. On the basis of this analysis, we discuss strengths and limitations of current prodrug approaches and suggest areas for future development.

Towards clinical adherence monitoring of oral endocrine breast cancer therapies by LC-HRMS-method development, validation, comparison of four sample matrices, and proof of concept

Oral endocrine therapies (OET) for breast cancer treatment need to be taken over a long period of time and are associated with considerable side effects. Therefore, adherence to OET is an important issue and of high clinical significance for breast cancer patients' caregivers. We hypothesized that a new bioanalytical strategy based on liquid chromatography and high-resolution mass spectrometry might be suitable for unbiased adherence monitoring (AM) of OET. Four different biomatrices (plasma, urine, finger prick blood by volumetric absorptive microsampling (VAMS), oral fluid (OF)) were evaluated regarding their suitability for AM of the OET abemaciclib, anastrozole, exemestane, letrozole, palbociclib, ribociclib, tamoxifen, and endoxifen. An analytical method was developed and validated according to international recommendations. The analytical procedures were successfully validated in all sample matrices for most analytes, even meeting requirements for therapeutic drug monitoring. Chromatographic separation of analytes was achieved in less than 10 min and limits of quantification ranged from 1 to 1000 ng/mL. The analysis of 25 matching patient samples showed that AM of OET is possible using all four matrices with the exception of, e.g., letrozole and exemestane in OF. We were able to show that unbiased bioanalytical AM of OET was possible using different biomatrices with distinct restrictions. Sample collection of VAMS was difficult in most cases due to circulatory restraints and peripheral neuropathy in fingers and OF sampling was hampered by dry mouth syndrome in some cases. Although parent compounds could be detected in most of the urine samples, metabolites should be included when analyzing urine or OF. Plasma is currently the most suitable matrix due to available reference concentrations.

Early increase in tamoxifen dose in CYP2D6 poor metaboliser breast cancer patients and survival: A propensity score matching analysis

PURPOSE

Tamoxifen is a drug used for hormone receptor-positive breast cancers, primarily metabolised by the CYP2D6 enzyme into active metabolites such as endoxifen. CYP2D6 displays varying degrees of activity depending on its genotype. This study aims to analyse the effect of an early increase in tamoxifen dose in poor metabolisers (PM) on survival.

METHODS

We enrolled 220 patients diagnosed with breast cancer who were treated with tamoxifen. CYP2D6 polymorphisms were determined, and the phenotype was estimated according to the Clinical Pharmacogenetics Implementation Consortium. Disease-free survival (DFS) and overall survival (OS) were analysed considering the entire patient group, and a subgroup of 110 patients selected by Propensity Score Matching (PSM). All women were treated with 20 mg/day of tamoxifen for 5 years, except PM, who initially received 20 mg/day for 4 months, followed by 40 mg/day for 4 months and 60 mg/day for 4 months before returning to the standard dose of 20 mg/day until completing 5 years of treatment.

RESULTS

The analysis of the influence of CYP2D6 polymorphisms in the complete group and in the PSM subgroup revealed no significant differences for DFS or OS. Furthermore, DFS and OS were analysed in relation to various covariates such as age, histological grade, nodal status, tumour size, HER-2, Ki-67, chemotherapy, and radiotherapy. Only age, histological grade, nodal status, and chemotherapy treatment demonstrated statistical significance.

CONCLUSION

An early increase in tamoxifen dose in PM patients is not associated with survival differences among CYP2D6 phenotypes.

EA, Udupa KS, Gota V, Mallayasamy S. Factors Influencing Pharmacokinetics of Tamoxifen in Breast Cancer Patients: A Systematic Review of Population Pharmacokinetic Models

BACKGROUND

Tamoxifen is useful in managing breast cancer and it is reported to have significant variability in its pharmacokinetics. This review aimed to summarize reported population pharmacokinetics studies of tamoxifen and to identify the factors affecting the pharmacokinetics of tamoxifen in adult breast cancer patients.

METHOD

A systematic search was undertaken in Scopus, Web of Science, and PubMed for papers published in the English language from inception to 20 August 2022. Studies were included in the review if the population pharmacokinetic modeling was based on non-linear mixed-effects modeling with a parametric approach for tamoxifen in breast cancer patients.

RESULTS

After initial selection, 671 records were taken for screening. A total of five studies were selected from Scopus, Web of Science, PubMed, and by manual searching. The majority of the studies were two-compartment models with first-order absorption and elimination to describe tamoxifen and its metabolites' disposition. The CYP2D6 phenotype and CYP3A4 genotype were the main covariates that affected the metabolism of tamoxifen and its metabolites. Other factors influencing the drug's pharmacokinetics included age, co-medication, BMI, medication adherence, CYP2B6, and CYP2C19 genotype.

CONCLUSION

The disposition of tamoxifen and its metabolites varies primarily due to the CYP2D6 phenotype and CYP3A4 genotype. However, other factors, such as anthropometric characteristics and menopausal status, should also be addressed when accounting for this variability. All these studies should be externally evaluated to assess their applicability in different populations and to use model-informed dosing in the clinical setting.

Endoxifen, an Estrogen Receptor Targeted Therapy: From Bench to Bedside

The selective estrogen receptor (ER) modulator, tamoxifen, is the only endocrine agent with approvals for both the prevention and treatment of premenopausal and postmenopausal estrogen-receptor positive breast cancer as well as for the treatment of male breast cancer. Endoxifen, a secondary metabolite resulting from CYP2D6-dependent biotransformation of the primary tamoxifen metabolite, N-desmethyltamoxifen (NDT), is a more potent antiestrogen than either NDT or the parent drug, tamoxifen. However, endoxifen's antitumor effects may be related to additional molecular mechanisms of action, apart from its effects on ER. In phase 1/2 clinical studies, the efficacy of Z-endoxifen, the active isomer of endoxifen, was evaluated in patients with endocrine-refractory metastatic breast cancer as well as in patients with gynecologic, desmoid, and hormone-receptor positive solid tumors, and demonstrated substantial oral bioavailability and promising antitumor activity. Apart from its potent anticancer effects, Z-endoxifen appears to result in similar or even greater bone agonistic effects while resulting in little or no endometrial proliferative effects compared with tamoxifen. In this review, we summarize the preclinical and clinical studies evaluating endoxifen in the context of breast and other solid tumors, the potential benefits of endoxifen in bone, as well as its emerging role as an antimanic agent in bipolar disorder. In total, the summarized body of literature provides compelling arguments for the ongoing development of Z-endoxifen as a novel drug for multiple indications.

Tamoxifen and oxidative stress: an overlooked connection

Tamoxifen is the gold standard drug for the treatment of breast cancer in pre and post-menopausal women. Its journey from a failing contraceptive to a blockbuster is an example of pharmaceutical innovation challenges. Tamoxifen has a wide range of pharmacological activities; a drug that was initially thought to work via a simple Estrogen receptor (ER) mechanism was proven to mediate its activity through several non-ER mechanisms. Here in we review the previous literature describing ER and non-ER targets of tamoxifen, we highlighted the overlooked connection between tamoxifen, tamoxifen apoptotic effects and oxidative stress.

Recent advances in prodrug-based nanoparticle therapeutics

Extensive research into prodrug modification of active pharmaceutical ingredients and nanoparticle drug delivery systems has led to unprecedented levels of control over the pharmacological properties of drugs and resulted in the approval of many prodrug or nanoparticle-based therapies. In recent years, the combination of these two strategies into prodrug-based nanoparticle drug delivery systems (PNDDS) has been explored as a way to further advance nanomedicine and identify novel therapies for difficult-to-treat indications. Many of the PNDDS currently in the clinical development pipeline are expected to enter the market in the coming years, making the rapidly evolving field of PNDDS highly relevant to pharmaceutical scientists. This review paper is intended to introduce PNDDS to the novice reader while also updating those working in the field with a comprehensive summary of recent efforts. To that end, first, an overview of FDA-approved prodrugs is provided to familiarize the reader with their advantages over traditional small molecule drugs and to describe the chemistries that can be used to create them. Because this article is part of a themed issue on nanoparticles, only a brief introduction to nanoparticle-based drug delivery systems is provided summarizing their successful application and unfulfilled opportunities. Finally, the review's centerpiece is a detailed discussion of rationally designed PNDDS formulations in development that successfully leverage the strengths of prodrug and nanoparticle approaches to yield highly effective therapeutic options for the treatment of many diseases.

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.

Medical applications of clustered regularly interspaced short palindromic repeats (CRISPR/Cas) tool: A comprehensive overview

Since the discovery of the double helix and the introduction of genetic engineering, the possibility to develop new strategies to manipulate the genome has fascinated scientists around the world. Currently scientists have the knowledge andabilitytoedit the genomes. Several methodologies of gene editing have been established, all of them working like "scissor", creating double strand breaks at specific spots. The introduction of a new technology, which was adapted from the clustered regularly interspaced short palindromic repeats (CRISPR)/Cas bacterial immune system, has revolutionized the genetic therapy field, as it allows a much more precise editing of gene than the previously described tools and, therefore, to prevent and treat disease in humans. This review aims to revisit the genome editing history that led to the rediscovery of the CRISPR/Cas technology and to explore the technical aspects, applications and perspectives of this fascinating, powerful, precise, simpler and cheaper technology in different fields.

Influence of CYP2D6, CYP3A5, ABCB1, APOE polymorphisms and nongenetic factors on donepezil treatment in patients with Alzheimer's disease and vascular dementia

PURPOSE

This study aims to evaluate the influence of genetic polymorphisms of CYP2D6, CYP3A5, ABCB1, and APOE genes and nongenetic factors on steady-state plasma concentrations (Cpss) of donepezil and therapeutic outcomes in Thai patients with Alzheimer's disease (AD) and vascular dementia (VAD).

PATIENTS AND METHODS

Eighty-five dementia patients who received donepezil for at least six months were recruited. CYP2D6, CYP3A5, ABCB1, and APOE polymorphisms were genotyped. Cpss of donepezil was measured. Association of genetic and non-genetic factors with Cpss and clinical outcomes of donepezil (cognitive function as measured by the Thai Mental State Examination score; TMSE) were determined by using univariate and multivariate analysis.

RESULTS

Both univariate and multiple linear regression analysis indicated that only CYP2D6*10 allele was associated with higher Cpss (p-value =0.029 and B =0.478, p-value =0.032, respectively) that might influence the clinical outcomes of donepezil. ie, TMSE (p-value =0.010 and B =4.527, p-value =0.001) and ΔTMSE (p-value =0.023 and B =4.107, p-value =0.002), especially in patients with AD. Interestingly, concomitant use of memantine was found to be associated with increased Cpss of donepezil (p-value =0.007 and B =0.511, p-value =0.014). Whereas, co-medication with antidepressant drugs attenuated clinical responses in patients with AD (TMSE: B =-2.719, p-value =0.013 and ΔTMSE: B =-2.348, p-value =0.028). Age was a significant predictor of donepezil response in VAD patients. No significant association of CYP3A5*3, ABCB1 3435C>T or ABCB1 1236C>T, and APOE ε4 genotypes with Cpss or clinical outcomes of donepezil was found in this study.

CONCLUSION

Our results suggests that CYP2D6*10 strongly influences Cpss and there is a trend toward better outcomes of donepezil in patients with AD. Nongenetic factors including concomitant drugs treatment might alter Cpss of donepezil or clinical outcomes.

Interethnic Variability in CYP2D6, CYP2C9, and CYP2C19 Genes and Predicted Drug Metabolism Phenotypes Among 6060 Ibero- and Native Americans: RIBEF-CEIBA Consortium Report on Population Pharmacogenomics

Pharmacogenetic variation in Latin Americans is understudied, which sets a barrier for the goal of global precision medicine. The RIBEF-CEIBA Network Consortium was established to characterize interindividual and between population variations in CYP2D6, CYP2C9, and CYP2C19 drug metabolizing enzyme genotypes, which were subsequently utilized to catalog their "predicted drug metabolism phenotypes" across Native American and Ibero American populations. Importantly, we report in this study, a total of 6060 healthy individuals from Ibero-America who were classified according to their self-reported ancestry: 1395 Native Americans, 2571 Admixed Latin Americans, 96 Afro-Latin Americans, 287 white Latin Americans (from Cuba), 1537 Iberians, and 174 Argentinean Ashkenazi Jews. Moreover, Native Americans were grouped into North-, Central-, and South Amerindians (from Mexico, Costa Rica, and Peru, respectively). All subjects were studied for the most common and functional CYP2D6, CYP2C9, and CYP2C19 allelic variants, and grouped as genotype-predicted poor or ultrarapid metabolizer phenotypes (gPMs and gUMs, respectively). Native Americans showed differences from each ethnic group in at least two alleles of CYP2D6, CYP2C9, and CYP2C19. Native Americans had higher frequencies of wild-type alleles for all genes, and lower frequency of CYP2D6*41, CYP2C9*2, and CYP2C19*17 (p < 0.05). Native Americans also showed less CYP2C19 gUMs than the rest of the population sample. In addition, differences within Native Americans (mostly North vs. South) were also found. The interethnic differences described supports the need for population-specific personalized and precision medicine programs for Native Americans. To the best of our knowledge, this is the largest study carried out in Native Americans and other Ibero-American populations analyzing CYP2D6, CYP2C9, and CYP2C19 genetic polymorphisms. Population pharmacogenomics is a nascent field of global health and warrants further research and education.

Characterization of in vitro and in vivo metabolism of leelamine using liquid chromatography-tandem mass spectrometry

Leelamine is a diterpene compound found in the bark of pine trees and has garnered considerable interest owing to its potent anticancer properties. The aim of the present study was to investigate the metabolic profile of leelamine in human liver microsomes (HLMs) and mice using liquid chromatography-tandem mass spectrometry (LC-MS/MS). We found that leelamine undergoes only Phase I metabolism, which generates one metabolite that is mono-hydroxylated at the C9 carbon of the octahydrophenanthrene ring (M1) both in vitro and in vivo. The structure and metabolic pathway of M1 were determined from the MSⁿ fragmentation obtained by collision-induced dissociation using LC-MS/MS in HLMs. Cytochrome p450 (CYP) 2D6 was found to be the dominant CYP enzyme involved in the biotransformation of leelamine to its hydroxylated metabolite, whereas CYP2C19, CYP1A1, and CYP3A4 contributed to some extent. Moreover, we identified only one metabolite M1, in the urine, but none in the feces. In conclusion, leelamine was metabolized to a mono-hydroxyl metabolite by CYP2D6 and mainly excreted in the urine.

Tumoral expression of drug and xenobiotic metabolizing enzymes in breast cancer patients of different ethnicities with implications to personalized medicine

Drug and xenobiotic metabolizing enzymes (DXME) play important roles in drug responses and carcinogenesis. Recent studies have found that expression of DXME in cancer cells significantly affects drug clearance and the onset of drug resistance. In this study we compared the expression of DXME in breast tumor tissue samples from patients representing three ethnic groups: Caucasian Americans (CA), African Americans (AA), and Asian Americans (AS). We further combined DXME gene expression data with eQTL data from the GTEx project and with allele frequency data from the 1000 Genomes project to identify SNPs that may be associated with differential expression of DXME genes. We identified substantial differences among CA, AA, and AS populations in the expression of DXME genes and in activation of pathways involved in drug metabolism, including those involved in metabolizing chemotherapy drugs that are commonly used in the treatment of breast cancer. These data suggest that differential expression of DXME may associate with health disparities in breast cancer outcomes observed among these three ethnic groups. Our study suggests that development of personalized treatment strategies for breast cancer patients could be improved by considering both germline genotypes and tumor specific mutations and expression profiles related to DXME genes.

Personalized in vitro cancer models to predict therapeutic response: Challenges and a framework for improvement

Personalized cancer therapy focuses on characterizing the relevant phenotypes of the patient, as well as the patient's tumor, to predict the most effective cancer therapy. Historically, these methods have not proven predictive in regards to predicting therapeutic response. Emerging culture platforms are designed to better recapitulate the in vivo environment, thus, there is renewed interest in integrating patient samples into in vitro cancer models to assess therapeutic response. Successful examples of translating in vitro response to clinical relevance are limited due to issues with patient sample acquisition, variability and culture. We will review traditional and emerging in vitro models for personalized medicine, focusing on the technologies, microenvironmental components, and readouts utilized. We will then offer our perspective on how to apply a framework derived from toxicology and ecology towards designing improved personalized in vitro models of cancer. The framework serves as a tool for identifying optimal readouts and culture conditions, thus maximizing the information gained from each patient sample.

Molecular mechanisms and mode of tamoxifen resistance in breast cancer

Breast cancer is one of the most common cancers in women around the globe Tamoxifen is used for the last 40 years as an endocrine therapy for breast cancer. This resulted in the reduction of mortality rate by 30% and it still remains one of the most effective therapies against breast cancer. However, resistance against tamoxifen is still one of the major hurdles in the effective management of breast cancer. Intense research has been conducted in the past decade to further explore its resistance mechanism, but still a lot of research will be needed to effectively alleviate this problem. Several biochemical factors and molecular pathways, such as the modulation of ER signaling, upregulation of growth factors had been observed as key factors for tamoxifen resistance (TR). After, initial therapy of five to ten years, breast cancer patients develops resistance towards this drug. The resistance leads to the development of other cancers like uterine cancer. Here, we briefly explore all the molecular events related to tamoxifen resistance and focus on its mechanism of action as well as other pharmacological approaches to better its beneficial effects in the treatment of breast carcinoma.

Clinical association between pharmacogenomics and adverse drug reactions

Adverse drug reactions (ADRs) are a major public health concern and cause significant patient morbidity and mortality. Pharmacogenomics is the study of how genetic polymorphisms affect an individual's response to pharmacotherapy at the level of a whole genome. This article updates our knowledge on how genetic polymorphisms of important genes alter the risk of ADR occurrence after an extensive literature search. To date, at least 244 pharmacogenes identified have been associated with ADRs of 176 clinically used drugs based on PharmGKB. At least 28 genes associated with the risk of ADRs have been listed by the Food and Drug Administration as pharmacogenomic biomarkers. With the availability of affordable and reliable testing tools, pharmacogenomics looks promising to predict, reduce, and minimize ADRs in selected populations.

Breast cancer screening utilization and understanding of current guidelines among rural U.S. women with private insurance

Women living in rural areas of the U.S. face disparities in screening mammography and breast cancer outcomes. We sought to evaluate utilization of mammography, awareness of screening guidelines, and attitudes towards screening among rural insured U.S. women. We conducted a cross-sectional self-administered anonymous survey among 2000 women aged 40-64 insured by the National Rural Electric Cooperative Association, a non-profit insurer for electrical utility workers in predominantly rural areas across the U.S. Outcomes included mammographic screening in the past year, screening interval, awareness of guidelines, and perceived barriers to screening. 1588 women responded to the survey (response rate 79.4 %). 74 % of respondents lived in a rural area. Among women aged 40-49, 66.5 % reported mammographic screening in the past year. 46 % received annual screening, 32 % biennial screening, and 22 % rare/no screening. Among women aged 50-64, 77.1 % reported screening in the past year. 63 % received annual screening, 25 % biennial screening, and 12 % rare/no screening. The majority of women (98 %) believed that the mammography can find breast cancer early and save lives. Less than 1 % of younger women, and only 14 % of women over age 50 identified the recommendations of the U.S. Preventative Services Screening Task Force as the current expert recommendations for screening. Screening practices tended to follow perceived guideline recommendations. When rural U.S. women over age 40 have insurance, most receive breast cancer screening. The screening guidelines of cancer advocacy groups and specialty societies appear more influential and widely recognized than those of the U.S. preventative services taskforce.

Boronic prodrug of endoxifen as an effective hormone therapy for breast cancer

As a prodrug, tamoxifen is activated by the P450 enzyme CYP2D6 that is responsible for converting it to the active metabolites, 4-hydroxytamoxifen and endoxifen. Patients with genetic polymorphisms of CYP2D6 may not receive the full benefit of tamoxifen therapy. There is increasing evidence that poor metabolizer patients have lower plasma concentrations of endoxifen and suffer worse disease outcome, although some clinical studies reported no correlation between CYP2D6 polymorphism and tamoxifen therapy outcome. Endoxifen is currently undergoing clinical trials as a potentially improved and more potent SERM (Selective Estrogen Receptor Modulator) for endocrine therapy that is independent of CYP2D6 status in patients. However, direct administration of endoxifen may present the problem of low bioavailability due to its rapid first-pass metabolism via O-glucuronidation. We have designed and synthesized ZB483, a boronic prodrug of endoxifen suitable for oral administration with greatly enhanced bioavailability by increasing the concentration of endoxifen in mouse blood. Our study demonstrated that ZB483 potently inhibited growth of ER+ breast cancer cells in vitro and was efficiently converted to endoxifen in cell culture media by oxidative deboronation. This metabolic conversion is equally efficient in vivo as indicated in the pharmacokinetic study in mice. Moreover, when administered at the same dose, oral ZB483 afforded a 30- to 40-fold higher plasma level of endoxifen in mice than oral administration of endoxifen. The significantly enhanced bioavailability of endoxifen conferred by the boronic prodrug was further validated in an in vivo efficacy study. ZB483 was demonstrated to be more efficacious than endoxifen in inhibiting xenograft tumor growth in mice at equal dosage but more so at lower dosage. Together, these preclinical studies demonstrate that ZB483 is a promising endocrine therapy agent with markedly enhanced bioavailability in systemic circulation and superior efficacy compared to endoxifen.

Biotransformation of xenobiotics in the human colon and rectum and its association with colorectal cancer

In humans, the liver is generally considered to be the major organ contributing to drug metabolism, but studies during the last years have suggested an important role of the extra-hepatic drug metabolism. The gastrointestinal tract (GI-tract) is the major path of entry for a wide variety of compounds including food, and orally administered drugs, but also compounds - with neither nutrient nor other functional value - such as carcinogens. These compounds are metabolized by a large number of enzymes, including the cytochrome P450 (CYP), the glutathione S-transferase (GST) family, the uridine 5'-diphospho- glucuronosyltransferase (UDP-glucuronosyltransferase - UGT) superfamily, alcohol-metabolizing enzymes, sulfotransferases, etc. These enzymes can either inactivate carcinogens or, in some cases, generate reactive species with higher reactivity compared to the original compound. Most data in this field of research originate from animal or in vitro studies, wherein human studies are limited. Here, we review the human studies, in particular the studies on the phenotypic expression of these enzymes in the colon and rectum to get an impression of the actual enzyme levels in this primary organ of exposure. The aim of this review is to give a summary of currently available data on the relation between the CYP, the GST and the UGT biotransformation system and colorectal cancer obtained from clinical and epidemiological studies in humans.

Far beyond the usual biomarkers in breast cancer: a review

Research investigating biomarkers for early detection, prognosis and the prediction of treatment responses in breast cancer is rapidly expanding. However, no validated biomarker currently exists for use in routine clinical practice, and breast cancer detection and management remains dependent on invasive procedures. Histological examination remains the standard for diagnosis, whereas immunohistochemical and genetic tests are utilized for treatment decisions and prognosis determinations. Therefore, we conducted a comprehensive review of literature published in PubMed on breast cancer biomarkers between 2009 and 2013. The keywords that were used together were breast cancer, biomarkers, diagnosis, prognosis and drug response. The cited references of the manuscripts included in this review were also screened. We have comprehensively summarized the performance of several biomarkers for diagnosis, prognosis and predicted drug responses of breast cancer. Finally, we have identified 15 biomarkers that have demonstrated promise in initial studies and several miRNAs. At this point, such biomarkers must be rigorously validated in the clinical setting to be translated into clinically useful tests for the diagnosis, prognosis and prediction of drug responses of breast cancer.

Inhibitory effects of phytochemicals on metabolic capabilities of CYP2D6(*)1 and CYP2D6(*)10 using cell-based models in vitro

AIM

Herbal products have been widely used, and the safety of herb-drug interactions has aroused intensive concerns. This study aimed to investigate the effects of phytochemicals on the catalytic activities of human CYP2D6(*)1 and CYP2D6(*)10 in vitro.

METHODS

HepG2 cells were stably transfected with CYP2D6(*)1 and CYP2D6(*)10 expression vectors. The metabolic kinetics of the enzymes was studied using HPLC and fluorimetry.

RESULTS

HepG2-CYP2D6(*)1 and HepG2-CYP2D6(*)10 cell lines were successfully constructed. Among the 63 phytochemicals screened, 6 compounds, including coptisine sulfate, bilobalide, schizandrin B, luteolin, schizandrin A and puerarin, at 100 μmol/L inhibited CYP2D6(*)1- and CYP2D6(*)10-mediated O-demethylation of a coumarin compound AMMC by more than 50%. Furthermore, the inhibition by these compounds was dose-dependent. Eadie-Hofstee plots demonstrated that these compounds competitively inhibited CYP2D6(*)1 and CYP2D6(*)10. However, their Ki values for CYP2D6(*)1 and CYP2D6(*)10 were very close, suggesting that genotype-dependent herb-drug inhibition was similar between the two variants.

CONCLUSION

Six phytochemicals inhibit CYP2D6(*)1 and CYP2D6(*)10-mediated catalytic activities in a dose-dependent manner in vitro. Thus herbal products containing these phytochemicals may inhibit the in vivo metabolism of co-administered drugs whose primary route of elimination is CYP2D6.

Personalized medicine in breast cancer: tamoxifen, endoxifen, and CYP2D6 in clinical practice

Tamoxifen is metabolized into endoxifen, a potent antagonist of the estrogen receptor, in part through cytochrome p450 (CYP) 2D6. Genotypic variation in CYP2D6 affects endoxifen levels, and some have argued that patients who do not efficiently metabolize tamoxifen might wish to consider alternative hormonal treatments. This study evaluated an algorithm in which endoxifen levels and CYP2D6 genotypes were used to make hormonal therapy recommendations for patients on adjuvant tamoxifen for breast cancer. Patients with stage I-III breast cancer who had been taking adjuvant tamoxifen for 8-56 weeks were eligible. At enrollment, baseline whole blood and serum were sent for genotyping by Amplichip and endoxifen measurement, respectively, and endoxifen levels were also measured 3 weeks later. Results were returned to oncologists along with an algorithm-generated treatment recommendation. The algorithm recommended that participants with poor metabolizer genotype and/or baseline endoxifen level <6 ng/mL consider alternative endocrine therapy. A medical record review evaluated actual treatment decisions. Of 99 patients on study, 18 (18 %) had findings that triggered algorithm-based recommendations to consider a change in endocrine therapy due to endoxifen <6 ng/mL (all 18 patients) and/or poor metabolizer CYP2D6 genotype (2 of the 18). Endoxifen levels were ≥6 ng/mL in four of them 3 weeks later. Seven (39 % of 18) switched to a different treatment (one based on toxicity, not the algorithm). Hot flash burden was not found to be significantly associated with endoxifen <6 ng/mL or genotype. Prospective testing of tamoxifen metabolism as gauged by CYP2D6 genotype and serum endoxifen levels is feasible. Future studies of tamoxifen metabolism and efficacy should consider including measurement of serial endoxifen levels. Although clinical evidence at present is insufficient to warrant routine CYP2D6 or endoxifen testing, some clinicians and patients did utilize this predefined algorithm to inform clinical decisions regarding optimal adjuvant endocrine therapy.

Identification of compounds by high-content screening that induce cytoplasmic to nuclear localization of a fluorescent estrogen receptor α chimera and exhibit agonist or antagonist activity in vitro

We have completed a robust high-content imaging screen for novel estrogen receptor α (ERα) agonists and antagonists by quantitation of cytoplasmic to nuclear translocation of an estrogen receptor chimera in 384-well plates. The screen was very robust, with Z' values >0.7 and coefficients of variation (CV) <5%. The screen utilized a stably transfected green fluorescent protein-tagged glucocorticoid/estrogen receptor (GFP-GRER) chimera, which consisted of the N-terminus of the glucocorticoid receptor fused to the human ERα ligand binding domain. The GFP-GRER exhibited cytoplasmic localization in the absence of ERα ligands and translocated to the nucleus in response to stimulation with ERα agonists and antagonists. The BD Pathway 435 imaging system was used for image acquisition, analysis of translocation dynamics, and cytotoxicity measurements. We screened 224,891 samples from our synthetic, pure natural product libraries, prefractionated natural product extracts library, and crude natural product extracts library, which produced a 0.003% hit rate. In addition to identifying several known ER ligands, five compounds were discovered that elicited significant activity in the screen. Transactivation potential studies demonstrated that two hit compounds behave as agonists, while three compounds elicited antagonist activity in MCF-7 cells.

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

PURPOSE

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

METHODS

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

RESULTS

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

CONCLUSION

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

Synthesis of a photocaged tamoxifen for light-dependent activation of Cre-ER recombinase-driven gene modification

We report the design of a water-soluble, quaternized tamoxifen photoprobe and demonstrate its application in light-controlled induction of green fluorescent protein expression via a Cre-ER recombinase system.

Endoxifen levels and its association with CYP2D6 genotype and phenotype: evaluation of a southern Brazilian population under tamoxifen pharmacotherapy

BACKGROUND

An association between CYP2D6 variation and clinical outcomes among women with breast cancer treated with tamoxifen (TAM) has been demonstrated, such that the presence of 2 functional CYP2D6 alleles was associated with better clinical outcomes. This association is mainly due to the CYP2D6-mediated hydroxylation of N-desmethyltamoxifen (NDT) to yield endoxifen (EDF), which because of its high antiestrogenic potency, is mainly responsible for the therapeutic efficacy of TAM. The aim of this study was to evaluate the relation of CYP2D6 genotyping and phenotyping with EDF levels and [NDT]/[EDF] metabolic ratio in breast cancer patients from South of Brazil under TAM therapy.

METHODS

Trough blood samples were collected from 97 patients. CYP2D6 genotyping was performed with a luminex assay and calculation of genotypic activity scores. Tamoxifen and metabolites EDF, NDT, and 4-hydroxy-TAM were measured in plasma by high performance liquid chromatography with photo diode array detector. CYP2D6 phenotyping was performed by the determination of dextromethorphan (DMT) and dextrorphan (DTF) by high-performance liquid chromatography with fluorescence detection at plasma collected 3 hours after oral administration of 33 mg of DMF. Phenotypes were given according to [DMT]/[DTF] metabolic ratio.

RESULTS

CYP2D6 genotyping indicated a prevalence of 4.1% poor metabolizer, 4.1% intermediate metabolizer, 49.5% extensive metabolizer slow activity, 39.2% extensive metabolizer fast activity, and 3.1% ultrarapid metabolizer. Genotype (genotypic activity scores) was significantly correlated with phenotype ([DMT]/[DTF]), with a moderate association (rs = -0.463; P < 0.001). Median plasma concentrations (nanograms per milliliter; N = 97) were TAM 57.17; 4-hydroxy-TAM 1.01; EDF 6.21; NDT 125.50. EDF levels were lower in poor metabolizers than that in extensive metabolizers (P < 0.05). Phenotype showed stronger, but still moderate, association with EDF and [NDT]/[EDF] than genotype (r = -0.507, r = 0.625, P < 0.001 versus r = 0.356, r = 0.516, P < 0.01). Phenotype accounted for 26% of the variability in EDF levels and 38% of [NDT]/[EDF], whereas genotype accounted for 12% and 27%, respectively.

CONCLUSIONS

CYP2D6 genotyping and/or phenotyping could not fully predict EDF concentrations. Monitoring EDF itself could be considered during TAM therapy.

Cytochrome P450-activated prodrugs

A prodrug is a compound that has negligible, or lower, activity against a specified pharmacological target than one of its major metabolites. Prodrugs can be used to improve drug delivery or pharmacokinetics, to decrease toxicity, or to target the drug to specific cells or tissues. Ester and phosphate hydrolysis are widely used in prodrug design because of their simplicity, but such approaches are relatively ineffective for targeting drugs to specific sites. The activation of prodrugs by the cytochrome P450 system provides a highly versatile approach to prodrug design that is particularly adaptable for targeting drug activation to the liver, to tumors or to hypoxic tissues.

Some applications of pharmacogenomics and epigenetics in drug development and use in pursuit of personalized medicine

Personalized medicine has become the most recent mantra of the pharmaceutical industry. While truly affordable bespoke drugs may never be totally achievable, pharmacogenomics and epigenetics will play significant roles in developing targeted therapy tailored to subpopulations of disease sufferers most likely to benefit. Personalized medicine is a very attractive concept, but an extremely difficult reality to achieve due to theoretical and practical considerations. Foremost among the theoretical reasons is our dearth of knowledge of individual physiology and metabolism, as well as the interactions of genetics and environment in the development of most diseases. Amongst the practical reasons, there is the cost of new drug development, considered to be about 800 million to one billion dollars (J Health Econ 22:151-185, DiMasi et al. 2003; Health Econ 19:130-141, Adams and Vu Brantner 2010) and the fact that many drugs now on the market do display reasonable efficacy in large segments of the population with acceptable side effects. Thus, the market for "personalized" drugs may not be large enough to support the costs of development. Another factor is the limitations put on healthcare by governments and insurance companies which promote the use of generics rather than the creation of new chemical entities. Finally, there are the social and ethical considerations of turning individual biology into noughts and ones with the possibility of such information becoming public and/or being used to constrain the way one lives or the care one receives (Nat Rev Drug Discov 1:300-308, Issa 2002). That said, to the degree that personalized medicine does become possible, pharmacogenomics and epigenetics will play significant roles in drug development and use.

A new frontier in personalized cancer therapy: mapping molecular changes

Mutations in the genome of a normal cell can affect the function of its many genes and pathways. These alterations could eventually transform the cell from a normal to a malignant state by allowing an uncontrolled proliferation of the cell and formation of a cancer tumor. Each tumor in an individual patient can have hundreds of mutated genes and perturbed pathways. Cancers clinically presenting as the same type or subtype could potentially be very different at the molecular level and thus behave differently in response to therapy. The challenge is to distinguish the key mutations driving the cancer from the background of mutational noise and find ways to effectively target them. The promise is that such a molecular approach to classifying cancer will lead to better diagnostic, prognostic and personalized treatment strategies. This article provides an overview of advances in the molecular characterization of cancers and their applications in therapy.

Pharmacogenomic testing: relevance in medical practice: why drugs work in some patients but not in others

Genetics may account for much of the variability in our patients' responses to drug therapies. This article offers the clinician an up-to-date overview of pharmacogenomic testing, discussing implications and limitations of emerging validated tests relevant to the use of warfarin (Coumadin), clopidogrel (Plavix), statins, tamoxifen (Nolvadex), codeine, and psychotropic drugs. It also discusses the future role of pharmacogenomic testing in medicine.

Enzyme-based amperometric platform to determine the polymorphic response in drug metabolism by cytochromes P450

"Personalized medicine" is a new concept in health care, one aspect of which defines the specificity and dosage of drugs according to effectiveness and safety for each patient. Dosage strongly depends from the rate of metabolism which is primarily regulated by the activity of cytochrome P450. In addition to the need for a genetic characterization of the patients, there is also the necessity to determine the drug-clearance properties of the polymorphic P450 enzyme. To address this issue, human P450 2D6 and 2C9 were engineered and covalently linked to an electrode surface allowing fast, accurate, and reliable measurements of the kinetic parameters of these phase-1 drug metabolizing polymorphic enzymes. In particular, the catalytic activity of P450 2C9 on the electrode surface was found to be improved when expressed from a gene-fusion with flavodoxin from Desulfovibrio vulgaris (2C9/FLD). The results are validated using marker drugs for these enzymes, bufuralol for 2D6, and warfarin for 2C9/FLD. The platform is able to measure the same small differences in K(M), and it allows a fast and reproducible mean to generated the product identified by HPLC from which the k(cat) is calculated.

Development of a new generation of 4-aminoquinoline antimalarial compounds using predictive pharmacokinetic and toxicology models

Among the known antimalarial drugs, chloroquine (CQ) and other 4-aminoquinolines have shown high potency and good bioavailability. Yet complications associated with drug resistance necessitate the discovery of effective new antimalarial agents. ADMET prediction studies were employed to evaluate a library of new molecules based on the 4-aminoquinolone-related structure of CQ. Extensive in vitro screening and in vivo pharmacokinetic studies in mice helped to identify two lead molecules, 18 and 4, with promising in vitro therapeutic efficacy, improved ADMET properties, low risk for drug-drug interactions, and desirable pharmacokinetic profiles. Both 18 and 4 are highly potent antimalarial compounds, with IC(50) values of 5.6 and 17.3 nM, respectively, against the W2 (CQ-resistant) strain of Plasmodium falciparum (for CQ, IC(50) = 382 nM). When tested in mice, these compounds were found to have biological half-lives and plasma exposure values similar to or higher than those of CQ; they are therefore desirable candidates to pursue in future clinical trials.

Molecular epidemiology and its current clinical use in cancer management

The revelation of the entire human DNA sequence in 2001, and the launching of the international haplotype map (HapMap) project, made the identification of common markers of disease possible, dramatically transforming molecular epidemiology. In recent years, the development of, and discoveries within, human genome research have been rapid, highlighted by the current explosion of genome-wide association studies (GWAS). GWAS aim at finding germline changes that increase cancer risk. An equally important and rapid development had been seen in cancer genomics, with great strides being made in our understanding of somatic mutations that allow and accompany cancer development. In this review we discuss whether it is currently possible to use these new discoveries to aid the reduction of cancer mortality by reducing risk of disease, improving prognosis, and keeping complications due to treatment to a minimum. Findings from GWAS have mostly been used to predict risk, but there is the potential to use them for prognostication and even treatment prediction. Expression arrays have identified prognostic patterns for breast cancer, but few reliable patterns are available for treatment prediction. More importantly, virtually no genetic signatures are available to predict morbidity from treatment. Thus, there is a need to bring different biological techniques together and integrate them with existing clinical oncological care for a simultaneous risk and outcome assessment.

FGFR4 Arg388 genotype is associated with pathological complete response to neoadjuvant chemotherapy for primary breast cancer

BACKGROUND

A single-nucleotide polymorphism (SNP) in the FGFR4 gene is associated with poor prognosis in solid tumors. A recent study presented the first evidence that FGFR4 Arg388 could predict resistance to adjuvant chemotherapy in breast cancer. The present study evaluates the potential of this SNP to predict response to neoadjuvant chemotherapy (NCT) for primary breast cancer (PBC).

METHODS

As part of a randomized phase II trial, 257 patients received either doxorubicin-cyclophosphamide (AC) or doxorubicin-pemetrexed (AP) followed by docetaxel (Doc; Taxotere) as NCT for T2-4/N0-2/M0 PBC. FGFR4 genotype analyzed on germline DNA was correlated with clinicopathologic variables, clinical response, and pathological complete response (pCR) using univariate and multivariate analyses.

RESULTS

Only axillary lymph node status was associated with FGFR4 Arg388 [odds ratio (OR) 1.82, P = 0.03]. Joint analysis of both treatment arms revealed a correlation of FGFR4 Arg388 with clinical response (OR 2.14, P = 0.03) but not with pCR. In the AC-Doc arm, however, FGFR4 Arg388 was a strong predictor of pCR in the multivariate analysis (OR 3.79, P = 0.03). A significant interaction between FGFR4 genotype and treatment (P = 0.01) was found, indicating a therapy-specific effect.

CONCLUSION

We provide the evidence that FGFR4 388Arg is an independent predictor of pCR following AC-Doc as NCT in PBC.