CYP2D6 genotype, antidepressant use, and tamoxifen metabolism during adjuvant breast cancer treatment

American Cancer Society/American Society of Clinical Oncology Breast Cancer Survivorship Care Guideline

Answer questions and earn CME/CNE The purpose of the American Cancer Society/American Society of Clinical Oncology Breast Cancer Survivorship Care Guideline is to provide recommendations to assist primary care and other clinicians in the care of female adult survivors of breast cancer. A systematic review of the literature was conducted using PubMed through April 2015. A multidisciplinary expert workgroup with expertise in primary care, gynecology, surgical oncology, medical oncology, radiation oncology, and nursing was formed and tasked with drafting the Breast Cancer Survivorship Care Guideline. A total of 1073 articles met inclusion criteria; and, after full text review, 237 were included as the evidence base. Patients should undergo regular surveillance for breast cancer recurrence, including evaluation with a cancer-related history and physical examination, and should be screened for new primary breast cancer. Data do not support performing routine laboratory tests or imaging tests in asymptomatic patients to evaluate for breast cancer recurrence. Primary care clinicians should counsel patients about the importance of maintaining a healthy lifestyle, monitor for post-treatment symptoms that can adversely affect quality of life, and monitor for adherence to endocrine therapy. Recommendations provided in this guideline are based on current evidence in the literature and expert consensus opinion. Most of the evidence is not sufficient to warrant a strong evidence-based recommendation. Recommendations on surveillance for breast cancer recurrence, screening for second primary cancers, assessment and management of physical and psychosocial long-term and late effects of breast cancer and its treatment, health promotion, and care coordination/practice implications are made.

Cancer pharmacogenomics: implications on ethnic diversity and drug response

The goal of pharmacogenomic research is to discover and validate genetic variants that are predictive of drug response, for eventual implementation into clinical practice. Cancer pharmacogenomics provides the opportunity to analyze two sets of DNA, that of the tumor (somatic) and that of the host (germline). Germline variants are inherited variations and are often associated with the pharmacokinetic behavior of a drug, including drug disposition and ultimately drug efficacy and/or toxicity, whereas somatic mutations are often useful in predicting the pharmacodynamic response to drugs. Pharmacoethnicity, or ethnic diversity in drug response or toxicity, is an increasingly recognized factor accounting for interindividual variations in anticancer drug response. Pharmacoethnicity is often determined by germline pharmacogenomic factors and the distribution of single nucleotide polymorphisms across various populations, but it may also be influenced by nongenetic factors, such as environmental factors. This review aims to elucidate the importance of pharmacoethnicity in cancer pharmacogenomic research and implementation, focusing solely on germline variants.

Tamoxifen and Antidepressant Drug Interaction in a Cohort of 16,887 Breast Cancer Survivors

BACKGROUND

Controversy persists about whether certain antidepressants reduce tamoxifen's effectiveness on lowering breast cancer recurrence. We investigated whether taking tamoxifen and antidepressants (in particular, paroxetine) concomitantly is associated with an increased risk of recurrence or contralateral breast cancer.

METHODS

We examined 16 887 breast cancer survivors (TNM stages 0-II) diagnosed between 1996 and 2007 and treated with tamoxifen in two California health plans. Women were followed-up through December 31, 2009, for subsequent breast cancer. The main exposure was the percent of days of overlap when both tamoxifen and an antidepressant (paroxetine, fluoxetine, other selective serotonin reuptake inhibitors, tricyclics, and other classes) were used. Hazard ratios (HRs) and 95% confidence intervals (CIs) were estimated using multivariable Cox regression models with time-varying medication variables.

RESULTS

Of the 16 887 women, half (n = 8099) used antidepressants and 2946 women developed subsequent breast cancer during the 14-year study period. We did not find a statistically significant increased risk of subsequent breast cancer in women who concurrently used paroxetine and tamoxifen. For 25%, 50%, and 75% increases in percent overlap days between paroxetine and tamoxifen, hazard ratios were 1.06 (95% CI = 0.98 to 1.14, P = .09), 1.13 (95% CI = 0.98 to 1.30, P = .09), and 1.20 (95% CI = 0.97 to 1.49, P = .09), respectively, in the first year of tamoxifen treatment but were not statistically significant. Hazard ratios decreased to 0.94 (95% CI = 0.81 to 1.10, P = .46), 0.89 (95% CI = 0.66 to 1.20, P = .46), and 0.85 (95% CI = 0.54 to 1.32, P = .46) by the fifth year (all non-statistically significantly). Absolute subsequent breast cancer rates were similar among women who used paroxetine concomitantly with tamoxifen vs tamoxifen-only users. For the other antidepressants, we again found no such associations.

CONCLUSIONS

Using the comprehensive electronic health records of insured patients, we did not observe an increased risk of subsequent breast cancer in women who concurrently used tamoxifen and antidepressants, including paroxetine.

Personalizing chemotherapy dosing using pharmacological methods

PURPOSE

Given the toxic nature and narrow therapeutic index of traditional chemotherapeutics, better methods of dose and therapy selection are critical. Pharmacological methods, including pharmacogenomics and pharmacokinetics, offer a practical method to enrich drug exposure, reduce toxicity, and improve quality of life for patients.

METHODS

PubMed and key abstracts from the American Society of Clinical Oncology (ASCO) and American Association for Cancer Research (AACR) were searched until July 2015 for clinical data relating to pharmacogenomic- and/or pharmacokinetic-guided dosing of anticancer drugs.

RESULTS

Based on the results returned from a thorough search of the literature and the plausibility of utilizing pharmacogenomic and/or pharmacokinetic methods to personalize chemotherapy dosing, we identified several chemotherapeutic agents with the potential for therapy individualization. We highlight the available data, clinical validity, and utility of using pharmacogenomics to personalize therapy for tamoxifen, 5-fluorouracil, mercaptopurine, and irinotecan, in addition to using pharmacokinetics to personalize dosing for 5-fluorouracil, busulfan, methotrexate, taxanes, and topotecan.

CONCLUSION

A concerted effort should be made by researchers to further elucidate the role of pharmacological methods in personalizing chemotherapy dosing to optimize the risk-benefit profile. Clinicians should be aware of the clinical validity, utility, and availability of pharmacogenomic- and pharmacokinetic-guided therapies in clinical practice, to ultimately allow optimal dosing for each and every cancer patient.

Breast cancer recurrence in relation to antidepressant use

PURPOSE

Women with breast cancer frequently use antidepressants; however, questions about the effect of these medications on breast cancer recurrence remain.

METHODS

We identified 4,216 women ≥18 years with an incident stage I or II breast cancer diagnosed between 1990 and 2008 in a mixed-model healthcare delivery system linked to a cancer registry. Recurrences were ascertained from chart review. Medication exposures were extracted from electronic pharmacy records. We used multivariable Cox proportional hazards models to estimate hazard ratios (HR) and 95 % confidence intervals (CI) to assess the association between antidepressant use and breast cancer recurrence and mortality. We also conducted analyses restricted to tamoxifen users.

RESULTS

Antidepressants overall, tricyclic antidepressants, and selective serotonin reuptake inhibitors were not associated with risk of breast cancer recurrence or mortality. Women taking paroxetine only (adjusted HR: 1.66; 95 % CI 1.02, 2.71) and trazodone only (adjusted HR: 1.76; 95 % CI 1.06, 2.92), but not fluoxetine only (adjusted HR: 0.92; 95 % CI 0.55, 1.53), had higher recurrence risks than antidepressant nonusers. There was some suggestion of an increased recurrence risk with concurrent paroxetine and tamoxifen use compared with users of tamoxifen only (adjusted HR: 1.49; 95 % CI 0.79, 2.83).

CONCLUSIONS

In general, antidepressants did not appear increase risk of breast cancer recurrence, though there were some suggested increases in risk that warrant further investigation in other datasets. Our results combined systematically and quantitatively with results from other studies may be useful for patients and providers making decisions about antidepressant use after breast cancer diagnosis.

The pharmacological and hormonal therapy of hot flushes in breast cancer survivors

The side effects of oncological treatment, which appear during or after therapy, are sometimes very annoying for patients and are not adequately treated by physicians. Among the symptoms experienced by breast cancer patients are hot flushes, which result from a natural or cancer therapy-induced menopause. The intensity of hot flushes in breast cancer patients may be more severe than those experienced by women undergoing a natural menopause. Taking into account the incidence of breast cancer and long-lasting hormone-suppression therapies, the problem of hot flushes will affect many women. Hormonal replacement therapy, the most effective therapeutic means for alleviating hot flushes, is usually contraindicated for breast cancer patients. For intense and severe hot flushes, pharmacological treatment using agents from a group of selective serotonin reuptake inhibitors and serotonin and norepinephrine reuptake inhibitors such as venlafaxine or citalopram may be introduced. Other agents from different pharmacological groups, such as clonidine, gabapentin, or pregabalin, have also proved to be effective in treating hot flushes. The efficacy of phytoestrogens has not been proven in randomized clinical trials. The importance of the placebo effect in decreasing vasomotor symptoms has also been reported in many research papers. Educating breast cancer patients in lifestyle changes which decrease the frequency and intensity of vasomotor symptoms can offer significant help too. This paper reviews the current state of research in order to assess the options for the treatment of hot flushes in breast cancer survivors.

CYP2D6 genotype- and endoxifen-guided tamoxifen dose escalation increases endoxifen serum concentrations without increasing side effects

Breast cancer patients with absent or reduced CYP2D6 activity and consequently low endoxifen levels may benefit less from tamoxifen treatment. CYP2D6 poor and intermediate metabolizers may need a personalized increased tamoxifen dose to achieve effective endoxifen serum concentrations, without increasing toxicity. From a prospective study population of early breast cancer patients using tamoxifen (CYPTAM: NTR1509), 12 CYP2D6 poor and 12 intermediate metabolizers were selected and included in a one-step tamoxifen dose escalation study during 2 months. The escalated dose was calculated by multiplying the individual’s endoxifen level at baseline relative to the average endoxifen concentration observed in CYP2D6 extensive metabolizers by 20 mg (120 mg maximum). Endoxifen levels and tamoxifen toxicity were determined at baseline and after 2 months, just before patients returned to the standard dose of 20 mg. Tamoxifen dose escalation in CYP2D6 poor and intermediate metabolizers significantly increased endoxifen concentrations (p < 0.001; p = 0.002, respectively) without increasing side effects. In intermediate metabolizers, dose escalation increased endoxifen to levels comparable with those observed in extensive metabolizers. In poor metabolizers, the mean endoxifen level increased from 24 to 81 % of the mean concentration in extensive metabolizers. In all patients, the endoxifen threshold of 5.97 ng/ml (=16.0 nM) reported by Madlensky et al. was reached following dose escalation. CYP2D6 genotype- and endoxifen-guided tamoxifen dose escalation increased endoxifen concentrations without increasing short-term side effects. Whether such tamoxifen dose escalation is effective and safe in view of long-term toxic effects is uncertain and needs to be explored.

Limited predictive value of achieving beneficial plasma (Z)-endoxifen threshold level by CYP2D6 genotyping in tamoxifen-treated Polish women with breast cancer

BACKGROUND

Tamoxifen, the most frequently used drug for treating estrogen receptor-positive breast cancer, must be converted into active metabolites to exert its therapeutic efficacy, mainly through CYP2D6 enzymes. The objective of this study was to investigate the impact of CYP2D6 polymorphisms on (Z)-endoxifen-directed tamoxifen metabolism and to assess the usefulness of CYP2D6 genotyping for identifying patients who are likely to have insufficient (Z)-endoxifen concentrations to benefit from standard therapy.

METHODS

Blood samples from 279 Polish women with breast cancer receiving tamoxifen 20 mg daily were analyzed for CYP2D6 genotype and drug metabolite concentration. Steady-state plasma levels of tamoxifen and its 14 metabolites were measured by using the ultra-performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) method.

RESULTS

In nearly 60 % of patients, including over 30 % of patients with fully functional CYP2D6, (Z)-endoxifen concentration was below the predefined threshold of therapeutic efficacy. The most frequently observed CYP2D6 genotype was EM/PM (34.8 %), among which 83.5 % of patients had a combination of wild-type and *4 alleles. Plasma concentration of five metabolites was significantly correlated with CYP2D6 genotype. For the first time, we identified an association between decreased (E/Z)-4-OH-N-desmethyl-tamoxifen-β-D-glucuronide levels (r (2) = 0.23; p < 10(-16)) and increased CYP2D6 functional impairment. The strongest correlation was observed for (Z)-endoxifen, whose concentration was significantly lower in groups of patients carrying at least one CYP2D6 null allele, compared with EM/EM patients. The CYP2D6 genotype accounted for plasma level variability of (Z)-endoxifen by 27 % (p < 10(-16)) and for the variability of metabolic ratio indicating (Z)-endoxifen-directed metabolism of tamoxifen by 51 % (p < 10(-43)).

CONCLUSIONS

The majority of breast cancer patients in Poland may not achieve a therapeutic level of (Z)-endoxifen upon receiving a standard dose of tamoxifen. This finding emphasizes the limited value of CYP2D6 genotyping in routine clinical practice for identifying patients who might not benefit from the therapy. In its place, direct monitoring of plasma steady-state (Z)-endoxifen concentration should be performed to personalize and optimize the treatment.

Actionable pharmacogenetic markers for prediction and prognosis in breast cancer

Breast cancer is a heterogeneous disease that necessitates proper patient classification to direct surgery, pharmacotherapy, and radiotherapy. Despite patients within the same subgroup receiving similar pharmacotherapy, substantial variation in clinical outcomes is observed. Pharmacogenetic variations with direct effect on pharmacokinetics and pharmacodynamics play a central role in clinical outcomes. Pharmacogenetic markers associated with clinical outcome are known as biomarkers. They are termed prognostic biomarkers when their presence is associated with a specific clinical outcome. If the presence of such biomarkers guides treatment, they are termed predictive biomarkers. A number of pharmacogenetic markers have been described in relation to breast cancer pharmacotherapy both in the adjuvant and neoadjuvant setting. CYP2D6 allelic variants produce variable rates of tamoxifen metabolism and are associated with survival outcomes. Other biomarkers have been described in relation to other forms of endocrine therapy and trastuzumab. In neoadjuvant and adjuvant breast cancer chemotherapy, specific biomarkers were correlated with clinical outcomes and risk of drug toxicity. This review highlights key biomarkers in breast cancer pharmacotherapy with the potential of translating such study outcomes into clinical practice.

Assessing the Risks Associated with Antidepressant Use in Plastic Surgery: A Systematic Review

BACKGROUND

Antidepressant use has increased dramatically over the past decade. Although there is no question about the benefits of these medications, uncertainty exists with regard to the implications of antidepressant treatment surrounding plastic surgery. This systematic review collates all of the available literature that evaluates the risks of patient antidepressant treatment, in relation to plastic surgery.

METHODS

A comprehensive literature review of the PubMed and Cochrane databases was conducted. Articles were assessed by two independent reviewers using predefined data fields and selected using specific inclusion criteria. The two authors independently reviewed the literature and extracted data from included reviews, and discrepancies were resolved by consensus.

RESULTS

Twenty-six articles were included in the analysis and were categorized into five groups for comparison: risk of bleeding, risk of breast cancer, risk of breast cancer recurrence, breast enlargement, and miscellaneous (unique complications). Extracted information included study type, statistical analyses, conclusion, and limitations.

CONCLUSIONS

This review does not support the cessation of antidepressants in patients before plastic surgery, as the numbers needed to harm are low and the implications of withdrawal may prove to be detrimental to postoperative management. However, the use of antidepressants for mental disorders may also implicate key patient risk factors for surgical complications, and sufficient exploration into the patient's indications for the prescription is crucial. Evidence so far does not suggest that antidepressants increase the risk of breast cancer or recurrence in general, but caution should be exercised for those specifically on concurrent tamoxifen and paroxetine treatment.

Impacts of the Glucuronidase Genotypes UGT1A4, UGT2B7, UGT2B15 and UGT2B17 on Tamoxifen Metabolism in Breast Cancer Patients

Tamoxifen is used to prevent and treat estrogen-dependent breast cancer. It is described as a prodrug since most of its antiestrogen effects are exerted through its hydroxylated metabolites 4-OH-tamoxifen and endoxifen. In prior work, we correlated optimal plasma levels of these metabolites with certain genotypes of CYP2D6 and SULT1A2. This descriptive study examines correlations between concentrations of tamoxifen's glucuronide metabolites and genotypes UGT1A4 Pro24Thr, UGT1A4 Leu48Val, UGT2B7 His268Tyr, UGT2B15 Asp85YTyr UGT2B15 Lys523Thr and UGT2B17del in 132 patients with estrogen receptor-positive breast cancer under treatment with tamoxifen. Patients were genotyped by real-time and conventional PCR-RFLP. The glucuronides 4-OH-tamoxifen-N-glucuronide, 4-OH-tamoxifen-O-glucuronide and endoxifen-O-glucuronide were isolated from blood plasma and quantified using a high-pressure liquid chromatography-tandem mass spectrometry system. Individuals who were homozygous for UGT1A448VAL showed significantly lower mean concentrations of both glucuronide metabolites compared to subjects genotyped as wt/wt plus wt/48Val (p=0.037 and p=0.031, respectively). Women homozygous for UGT2B7268Tyr also showed mean substrate/product ratios of 4-OH-tamoxifen/4-OH-tamoxifen-O-glucuronide and 4-OH-tamoxifen/4-OH-tamoxifen-N-glucuronide indicative of reduced glucuronidase activity compared to wt homozygotes or to heterozygotes for the polymorphism (p=0.005 and p=0.003, respectively). In contrast, UGT2B15 Lys523Thr and UGT2B17del were associated with possibly increased enzyme activity. Patients with at least one variant allele UGT2B15523Thr showed significantly higher 4-OH-tamoxifen-O-glucuronide and endoxifen-glucuronide levels (p=0.023 and p=0.025, respectively) indicating a variant gene-dose effect. Higher 4-OH-tamoxifen-N-glucuronide levels observed in UGT2B17del genotypes (p=0.042) could be attributed to a mechanism that compensates for the greater expression of other genes in UGT2B17 del/del individuals. Our observations suggest that patients carrying mutations UGT1A448Val, UGT2B7268Tyr or with wt genotypes for UGT2B17nodel and UGT2B15523Lys could be the best candidates for a good response to tamoxifen therapy in terms of eliciting effective plasma active tamoxifen metabolite levels. However, additional studies examining the effects of UGT genotype on overall patient response to TAM are needed to further examine the role of UGT polymorphisms in the therapeutic efficacy of TAM.

Rethinking tamoxifen in the management of melanoma: New answers for an old question

The use of the antiestrogen tamoxifen in melanoma therapy is controversial due to the unsuccessful outcomes and a still rather unclarified mechanism of action. It seemed that the days of tamoxifen in malignant melanoma therapy were close to an end, but new evidence may challenge this fate. On one hand, it is now believed that metabolism is a major determinant of tamoxifen clinical outcomes in breast cancer patients, which is a variable that has yet to be tested in melanoma patients, since the tamoxifen active metabolite endoxifen demonstrated superior cytostatic activity over the parent drug in melanoma cells; on the other hand, new evidence has emerged regarding estrogen-mediated signaling in melanoma cells, including the methylation of the estrogen receptor-α gene promoter and the expression of the G protein coupled estrogen receptor. The expression of estrogen receptor-α and G protein coupled estrogen receptor, as well as the cytochrome P450 (CYP) 2D6 genotype, may be used as predictive biomarkers to select the patients that may respond to antiestrogens based on specific traits of their tumors. This review focused on these new evidences and how they may contribute to shed new light on this long-lasting controversy, as well as their possible implications for future investigations.

Critical appraisal of paroxetine for the treatment of vasomotor symptoms

Background

Vasomotor symptoms (VMS), characterized by hot flashes and night sweats, are the most commonly reported symptoms associated with estrogen deficiency during menopause and occur in up to 70% of women. The goal of treatment is to reduce the frequency and severity of symptoms. Although hormone therapy (HT) is generally recommended as first-line treatment, it is not appropriate for all patients. Antidepressants, specifically selective serotonin reuptake inhibitors, have been evaluated and utilized internationally for alternative treatment for VMS. In 2013, paroxetine mesylate (Brisdelle^®) received a US Food and Drug Administration-labeled indication for moderate-to-severe hot flashes, making it the first nonhormonal treatment for VMS associated with menopause. The objective of this review is to critically evaluate available clinical data regarding the efficacy and safety of paroxetine for the treatment of VMS in menopausal women.

Methods

MEDLINE, PubMed, and Google Scholar were searched using the keywords paroxetine, vasomotor symptoms, hot flashes, and menopause. Searches were limited to humans, English language, and clinical trial design with a primary outcome of hot flash/vasomotor changes.

Results

Paroxetine (hydrochloride and mesylate) has been associated with a 33%–67% reduction in hot flash frequency with 6–12 weeks of treatment compared to 13.7%–37.8% reductions with placebo in patients both with and without a history of breast cancer. It was also associated with significant reductions in hot flash severity. Benefits of treatment persisted through 24 weeks in the study of the longest duration. Most adverse effects reported were of mild-to-moderate severity, with improved tolerability associated with lower doses (7.5–12.5 mg/day).

Conclusion

Paroxetine is a safe and effective therapy for the treatment of VMS during menopause. Paroxetine (7.5–12.5 mg/day) should be considered a first-line therapy option for VMS in patients when HT is either inappropriate or intolerable.

Venlafaxine in management of hot flashes in women with breast cancer: a systematic review and meta-analysis

Toxicity due to treatment causes a negative impact on quality of life in breast cancer survivors. Hot flash symptoms, described as intense sensations of heat, sweating and flushing occur in more than 50 % of breast cancer patients taking tamoxifen. We hypothesized that venlafaxine, a selective-norepinephrine reuptake inhibitor drug, was effective for reducing patient-reported hot flash scores among women treated for breast cancer compared to other non-hormonal treatments. We searched Medline, Scopus, and Cochrane Central Register of Controlled Trials from inception till May 2015 for venlafaxine (75 mg once daily or greater) with non-hormonal comparators for the treatment of hot flashes in female breast cancer patients. The primary outcome was hot flash score (derived from patient-reported hot flash severity and frequency) in randomized controlled trials. Standardized mean differences (SMD) were calculated for each study due to variation in the outcome measures. Heterogeneity was determined using I (2) statistics, and publication bias was assessed using a contour funnel plot and Egger's tests. Pooled analyses demonstrated that venlafaxine significantly reduced hot flash scores compared to the trial comparators (overall SMD 2.06; 95% confidence interval (CI) [0.40, 3.72]). There was significant heterogeneity among these studies (I (2) = 98.7%, P < 0.001). Asymmetry in the contour funnel plot suggests the presence of publication bias and a trend towards small study effects (Egger's test, P = 0.096). Venlafaxine is efficacious in managing hot flashes among women with breast cancer. This review highlights methodological issues that arise from eligible trials and recommends a collaborative approach in survivorship studies.

Targeted therapies for ER+/HER2- metastatic breast cancer

The majority of breast cancers present with estrogen receptor (ER)-positive and human epidermal growth factor receptor (HER2)-negative features and might benefit from endocrine therapy. Although endocrine therapy has notably evolved during the last decades, the invariable appearance of endocrine resistance, either primary or secondary, remains an important issue in this type of tumor. The improvement of our understanding of the cancer genome has identified some promising targets that might be responsible or linked to endocrine resistance, including alterations affecting main signaling pathways like PI3K/Akt/mTOR and CCND1/CDK4-6 as well as the identification of new ESR1 somatic mutations, leading to an array of new targeted therapies that might circumvent or prevent endocrine resistance. In this review, we have summarized the main targeted therapies that are currently being tested in ER+ breast cancer, the rationale behind them, and the new agents and combinational treatments to come.

Comparative metabolic study between two selective estrogen receptor modulators, toremifene and tamoxifen, in human liver microsomes

Toremifene (TOR) and Tamoxifen (TAM) are widely used as endocrine therapy for estrogen receptor positive breast cancer. Poor metabolizers of TAM are likely to have worse clinical outcomes than patients who exhibit normal TAM metabolism due to lower plasma level of its active metabolite, 4-hydroxy-N-desmethyl (4OH-NDM) tamoxifen (endoxifen). In this study, we examined the role of individual cytochrome P450 (CYP) isoforms in the metabolism of TOR to N-desmethyl (NDM), 4-hydroxy (4OH) and 4OH-NDM metabolites in comparison with TAM using human liver microsomes (HLMs) with selective chemical inhibitors for each CYP isoform and recombinant CYP proteins. Similar levels of NDM metabolites were formed for both TOR and TAM, and N-demethylation of both compounds was primarily carried out by CYP3A4. We found that the formation of 4OH-NDM-TOR was catalyzed both by CYP2C9 and CYP2D6, whereas the formation of 4OH-TAM and endoxifen was specifically catalyzed by CYP2D6 in HLMs. Our results suggest that the potential contribution of CYP2D6 in the bioactivation pathway of TOR may be lower compared to TAM, and may have a different impact on clinical outcome than CYP2D6 polymorphisms.

Quantification of tamoxifen in pharmaceutical formulations using micellar liquid chromatography

This paper describes a micellar liquid chromatographic method used to analyze tamoxifen (TAMO) in pharmaceutical formulations, while focusing in its interesting features. Solid samples were solved in a micellar solution, irradiated at 254 nm, filtered and injected. Extraction steps were avoided and thus expediting the procedure. Tamoxifen was resolved in <5 min, using a mobile phase containing 0.15 M sodium dodecyl sulfate-7% pentanol at pH 3, running at 1.5 mL/min under an isocratic mode at 40°C through a C18 column. Detection was achieved by fluorescence by excitation at 260 nm and emission at 380 nm. The validation was performed following the requirements of the International Conference on Harmonization (ICH) Tripartite Guidelines in terms of: specificity, sensitivity, calibration range (0.2 - 20 mg/L), accuracy (98.8 - 101.7%), precision (<1.5%) and robustness (<6.2%). The method was applied to quantify TAMO in TAMO citrate tablets supplied in Spain, and was found appropriate for the quality control of TAMO formulations.

Role of single nucleotide polymorphisms in pharmacogenomics and their association with human diseases

Global statistical data shed light on an alarming trend that every year thousands of people die due to adverse drug reactions as each individual responds in a different way to the same drug. Pharmacogenomics has come up as a promising field in drug development and clinical medication in the past few decades. It has emerged as a ray of hope in preventing patients from developing potentially fatal complications due to adverse drug reactions. Pharmacogenomics also minimizes the exposure to drugs that are less/non-effective and sometimes even found toxic for patients. It is well reported that drugs elicit different responses in different individuals due to variations in the nucleotide sequences of genes encoding for biologically important molecules (drug-metabolizing enzymes, drug targets and drug transporters). Single nucleotide polymorphisms (SNPs), the most common type of polymorphism found in the human genome is believed to be the main reason behind 90% of all types of genetic variations among the individuals. Therefore, pharmacogenomics may be helpful in answering the question as to how inherited differences in a single gene have a profound effect on the mobilization and biological action of a drug. In the present review, we have discussed clinically relevant examples of SNP in associated diseases that can be utilized as markers for "better management of complex diseases" and attempted to correlate the drug response with genetic variations. Attention is also given towards the therapeutic consequences of inherited differences at the chromosomal level and how associated drug disposition and/or drug targets differ in various diseases as well as among the individuals.

Is complementary and alternative therapy effective for women in the climacteric period?

Vasomotor symptoms start about 2 years prior to menopause in women who are approaching menopause, and early menopause symptoms appear including emotional disturbance and anxiety, followed by physical changes such as vaginal dryness, urinary incontinence and skin wrinkles. As time progresses, osteoporosis, cardiovascular diseases, and dementia occur consecutively. Hormone therapy is primarily considered for the relief of menopause symptoms in postmenopausal women. However, as hormone replacement has emerged as a therapy that increases the potential risk of thrombosis, cerebral infarction and breast cancer, complementary and alternative medicine has drawn much attention. This study aimed to examine the types and effects of evidence-based complementary and alternative therapies that are currently used.

Tailored Tamoxifen Treatment for Breast Cancer Patients: A Perspective

Tamoxifen, an endocrine agent, is widely used in the treatment of estrogen receptor-positive breast cancer. It has greatly reduced disease recurrence and mortality rates of breast cancer patients, however, not all patients benefit from tamoxifen treatment because in approximately 25% to 30% of the patients the disease recurs. Many researchers have sought to find factors associated with endocrine treatment outcome in the past years, however, this quest has not been finished. In this article, we focus on a factor that might influence outcome of tamoxifen treatment: interpatient variability in tamoxifen pharmacokinetics. In recent years it has become clear that tamoxifen undergoes extensive metabolism and that some of the formed metabolites are much more pharmacologically active than tamoxifen itself. Despite the wide interpatient variability in tamoxifen pharmacokinetics and pharmacodynamics, all patients receive a standard dose of 20 mg tamoxifen per day. Different approaches can be pursued to individualize tamoxifen dosing: genotyping, phenotyping, and therapeutic drug monitoring. Therapeutic drug monitoring seems to be the most direct and promising approach, however, further clinical research is warranted to establish the added value of individual dosing in tamoxifen treatment optimization.

Personalized medicine and the clinical laboratory

Personalized medicine is the use of biomarkers, most of them molecular markers, for detection of specific genetic traits to guide various approaches for preventing and treating different conditions. The identification of several genes related to heredity, oncology and infectious diseases lead to the detection of genetic polymorphisms that are involved not only in different clinical progression of these diseases but also in variations in treatment response. Currently, it is possible to detect these polymorphisms using several methodologies: detection of single nucleotide polymorphisms using polymerase chain reaction methods; nucleic acid microarray detection; and nucleic acid sequencing with automatized DNA sequencers using Sanger-derived methods and new generation sequencing. Personalized medicine assays are directed towards detecting genetic variations that alter interactions of drugs with targets or the metabolic pathways of drugs (upstream and downstream) and can be utilized for the selection of drug formulations and detect different immunogenicities of the drug. Personalized medicine applications have already been described in different areas of Medicine and allow specific treatment approaches to be applied to each patient and pathology according to the results of these assays. The application of such a protocol demands an increasing interaction between the clinical laboratory and the clinical staff. For its implementation, a coordinated team composed of basic researchers and physicians highly specialized in their areas supported by a highly specialized team of clinical analysts particularly trained in molecular biology assays is necessary.

How the Probability and Potential Clinical Significance of Pharmacokinetically Mediated Drug-Drug Interactions Are Assessed in Drug Development: Desvenlafaxine as an Example

OBJECTIVE

The avoidance of adverse drug-drug interactions (DDIs) is a high priority in terms of both the US Food and Drug Administration (FDA) and the individual prescriber. With this perspective in mind, this article illustrates the process for assessing the risk of a drug (example here being desvenlafaxine) causing or being the victim of DDIs, in accordance with FDA guidance.

DATA SOURCES/STUDY SELECTION

DDI studies for the serotonin-norepinephrine reuptake inhibitor desvenlafaxine conducted by the sponsor and published since 2009 are used as examples of the systematic way that the FDA requires drug developers to assess whether their new drug is either capable of causing clinically meaningful DDIs or being the victim of such DDIs. In total, 8 open-label studies tested the effects of steady-state treatment with desvenlafaxine (50-400 mg/d) on the pharmacokinetics of cytochrome (CYP) 2D6 and/or CYP 3A4 substrate drugs, or the effect of CYP 3A4 inhibition on desvenlafaxine pharmacokinetics. The potential for DDIs mediated by the P-glycoprotein (P-gp) transporter was assessed in in vitro studies using Caco-2 monolayers.

DATA EXTRACTION

Changes in area under the plasma concentration-time curve (AUC; CYP studies) and efflux (P-gp studies) were reviewed for potential DDIs in accordance with FDA criteria.

RESULTS

Desvenlafaxine coadministration had minimal effect on CYP 2D6 and/or 3A4 substrates per FDA criteria. Changes in AUC indicated either no interaction (90% confidence intervals for the ratio of AUC geometric least-squares means [GM] within 80%-125%) or weak inhibition (AUC GM ratio 125% to < 200%). Coadministration with ketoconazole resulted in a weak interaction with desvenlafaxine (AUC GM ratio of 143%). Desvenlafaxine was not a substrate (efflux ratio < 2) or inhibitor (50% inhibitory drug concentration values > 250 μM) of P-gp.

CONCLUSIONS

A 2-step process based on FDA guidance can be used first to determine whether a pharmacokinetically mediated interaction occurs and then to assess the potential clinical significance of the DDI. In the case of the drug tested in this series of studies, the potential for clinically meaningful DDIs mediated by CYP 2D6, CYP 3A4, or P-gp was found to be low.

Genetic polymorphisms of CYP2D6*10 and the effectiveness of combined tamoxifen citrate and testosterone undecanoate treatment in infertile men with idiopathic oligozoospermia

Tamoxifen citrate, as the first line of treatment for infertile men with idiopathic oligozoospermia, was proposed by the World Health Organization (WHO), and testosterone undecanoate has shown benefits in semen values. Our objective was to assess the effectiveness of treatment with tamoxifen citrate and testosterone undecanoate in infertile men with idiopathic oligozoospermia, and whether the results would be affected by polymorphisms of CYP2D6*10. A total of 230 infertile men and 147 controls were included in the study. Patients were treated with tamoxifen citrate and testosterone undecanoate. Sex hormone, sperm parameters, and incidence of spontaneous pregnancy were detected. There were no significant differences between the control and patient groups with respect to CYP2D6*10 genotype frequencies (P>0.05). The follicle-stimulation hormone (FSH), luteinizing hormone (LH), and testosterone (T) levels were raised, and sperm concentration and motility were increased at 3 months and became significant at 6 months, and they were higher in the wild-type allele (C/C) than in the heterozygous variant allele (C/T) or homozygous variant allele (T/T) subgroups (P<0.05). In addition, the percentage of normal morphology was raised at 6 months, and represented the highest percentage in the C/C subgroup (P<0.05). The incidence of spontaneous pregnancy in the C/C subgroup was higher than that in the C/T or T/T subgroups (P<0.01). This study showed that the CYP2D6*10 variant genotype demonstrated worse clinical effects in infertile men with idiopathic oligozoospermia.

Pharmacogenomics toward personalized tamoxifen therapy for breast cancer

Tamoxifen has been used not only for the treatment or prevention of recurrence in patients with estrogen receptor positive breast cancers but also for recurrent breast cancer. Because CYP2D6 is known to be an important enzyme responsible for the generation of the potent tamoxifen metabolite, ‘endoxifen’, lots of studies reported that genetic variation which reduced its enzyme activity were associated with poor clinical outcome of breast cancer patients treated with tamoxifen. However, there are some discrepant reports questioning the association between CYP2D6 genotype and clinical outcome after tamoxifen therapy. Dose-adjustment study of tamoxifen based on CYP2D6 genotypes provides the evidence that dose adjustment is useful for the patients carrying reduced or null allele of CYP2D6 to maintain the effective endoxifen level. This review describes critical issues in pharmacogenomic studies as well as summarizes the results of the association of CYP2D6 genotype with tamoxifen efficacy.

Pharmacogenomic biomarkers for personalized cancer treatment

Personalized medicine involves the selection of the safest and most effective pharmacological treatment based on the molecular characteristics of the patient. In the case of anticancer drugs, tumour cell alterations can have a great impact on drug activity and, in fact, most biomarkers predicting response originate from these cells. On the other hand, the risk of developing severe toxicity may be related to the genetic background of the patient. Thus, understanding the molecular characteristics of both the tumour and the patient, and establishing their relation with drug outcomes will be critical for the identification of predictive biomarkers and to provide the basis for individualized treatments. This is a complex scenario where multiple genes as well as pathophysiological and environmental factors are important; in addition, tumours exhibit large inter- and intraindividual variability in space and time. Against this background, the huge amounts of biological and genetic data generated by the high-throughput technologies will facilitate pharmacogenomic progress, suggest novel druggable molecules and support the design of future strategies aimed at disease control. Here, we will review the current challenges and opportunities for pharmacogenomic studies in oncology, as well as the clinically established biomarkers. Lung and renal cancer, two areas in which huge progress has been made in the last decade, will be used to illustrate advances in personalized cancer treatment; we will review EGFR mutation as the paradigm of targeted therapies in lung cancer, and discuss the dissection of lung cancer into clinically relevant molecular subsets and novel advances that suggest an important role of single nucleotide polymorphisms in the response to antiangiogenic agents, as well as the challenges that remain in these fields. Finally, we will present new approaches and future prospects for personalizing medicine in oncology.

Tamoxifen metabolism predicts drug concentrations and outcome in premenopausal patients with early breast cancer

Tamoxifen is the standard-of-care treatment for estrogen receptor-positive premenopausal breast cancer. We examined tamoxifen metabolism via blood metabolite concentrations and germline variations of CYP3A5, CYP2C9, CYP2C19 and CYP2D6 in 587 premenopausal patients (Asians, Middle Eastern Arabs, Caucasian-UK; median age 39 years) and clinical outcome in 306 patients. N-desmethyltamoxifen (DM-Tam)/(Z)-endoxifen and CYP2D6 phenotype significantly correlated across ethnicities (R(2): 53%, P<10(-77)). CYP2C19 and CYP2C9 correlated with norendoxifen and (Z)-4-hydroxytamoxifen concentrations, respectively (P<0.001). DM-Tam was influenced by body mass index (P<0.001). Improved distant relapse-free survival (DRFS) was associated with decreasing DM-Tam/(Z)-endoxifen (P=0.036) and increasing CYP2D6 activity score (hazard ratio (HR)=0.62; 95% confidence interval (CI), 0.43-0.91; P=0.013). Low (<14 nM) compared with high (>35 nM) endoxifen concentrations were associated with shorter DRFS (univariate P=0.03; multivariate HR=1.94; 95% CI, 1.04-4.14; P=0.064). Our data indicate that endoxifen formation in premenopausal women depends on CYP2D6 irrespective of ethnicity. Low endoxifen concentration/formation and decreased CYP2D6 activity predict shorter DRFS.

Role of cytochrome P450 genes in breast cancer etiology and treatment: effects on estrogen biosynthesis, metabolism, and response to endocrine therapy

PURPOSE

The cytochrome P450 (CYP) genes are oxygenases involved in estrogen biosynthesis and metabolism, generation of DNA damaging procarcinogens, and response to anti-estrogen therapies. Since lifetime estrogen exposure is an established risk factor for breast cancer, determining the role of CYP genes in breast cancer etiology may provide critical information for understanding tumorigenesis and response to treatment.

METHODS

This review summarizes literature available in PubMed published between 1993 and 2013 that focuses on studies evaluating the effects of DNA variants in CYP genes on estrogen synthesis, metabolism, and generation of procarcinogens in addition to response to anti-estrogen therapies.

RESULTS

Evaluation of DNA variants in estrogen metabolism genes was largely inconclusive. Meta-analyses of data from CYP19A1 support an association between the number of (TTTA) n repeats in intron 4 and breast cancer risk, but the biological mechanism for this relationship is unknown. Associations between single nucleotide polymorphism in CYP1B1 and DNA damage caused by procarcinogenic estrogen metabolites were ambiguous. Variants in CYP2D6 are associated with altered metabolism tamoxifen; however, current data do not support widespread clinical testing. The effect of variants in CYP19A1 in response to aromatase inhibitors is also questionable.

CONCLUSION

Evaluation of DNA variants in CYP genes involved with estrogen metabolism or treatment response has been inconclusive, reflecting small samples sizes, tumor heterogeneity, and differences between populations. Better-powered studies that account for genetic backgrounds and tumor phenotypes are thus necessary.

Cytochrome P450 in Cancer Susceptibility and Treatment

Cytochrome 450 (CYP450) designates a group of enzymes abundant in smooth endoplasmic reticulum of hepatocytes and epithelial cells of small intestines. The main function of CYP450 is oxidative catalysis of various endogenous and exogenous substances. CYP450 are implicated in phase I metabolism of 80% of drugs currently in use, including anticancer drugs. They are also involved in synthesis of various hormones and influence hormone-related cancers. CYP450 genes are highly polymorphic and their variants play an important role in cancer risk and treatment. Association studies and meta-analyses have been performed to decipher the role of CYP450 polymorphisms in cancer susceptibility. Cancer treatment involves multimodal therapies and evaluation of CYP450 polymorphisms is necessary for pharmacogenetic assessment of anticancer therapy outcomes. In addition, CYP450 inhibitors are being evaluated for improved pharmacokinetics and oral formulation of several anticancer drugs.

Personalizing medicine in geriatric oncology

Minimizing toxicity while maximizing efficacy is a common goal in the treatment of any condition but its importance is underscored in the discipline of oncology because of the serious nature of many chemotherapeutic toxicities and the risk of cancer recurrence or disease progression. The challenge of achieving an optimal therapeutic index is especially augmented in the elderly population because of age-related metabolism changes and interacting concurrent medications. Additional factors, such as germline mutations in drug-metabolizing enzymes and other pharmacogenomic alterations, may have more pronounced effects in elderly patients, given their predisposition to altered pharmacokinetics and pharmacodynamics with resulting increased risk of toxicity. Examples of the possible interplay of these factors will be discussed using tamoxifen, paclitaxel, codeine, and fluorouracil as starting points. Limited participation of the elderly in many cancer trials, especially trials assessing drug exposure, makes much knowledge on the interaction of these patient and environmental factors speculative in nature but presents an opportunity for future research to achieve better optimization of chemotherapeutic agents in the elderly.

Prediction of tamoxifen outcome by genetic variation of CYP2D6 in post-menopausal women with early breast cancer

The question of whether genetic polymorphisms of CYP2D6 can affect treatment outcome in patients with early post-menopausal oestrogen receptor (ER)-positive breast cancer has been a matter of debate over the past few years. In this article we revisit the hypothesis of CYP2D6 being a potential tamoxifen outcome predictor and provide detailed insight into the ongoing controversy that prevented the CYP2D6 marker from being accepted by the scientific and clinical community. We summarize the available pharmacokinetic, pharmacodynamic and pharmacogenetic evidence and resolve the controversy based on the recognized methodological and statistical issues. The cumulative evidence suggests that genotyping for CYP2D6 is clinically relevant in post-menopausal women. This is important, because the clarification of this issue has the potential to resolve a clinical management question that is relevant to hundreds of thousands of women diagnosed with ER-positive breast cancer each year, who should not be denied effective endocrine therapy.

Comparative uterotrophic effects of endoxifen and tamoxifen in ovariectomized Sprague-Dawley rats

Endoxifen (4-hydroxy-N-desmethyl-tamoxifen), one of the major active metabolites of tamoxifen, has substantially greater estrogen antagonist properties and antiproliferative effects in breast tumor cells than tamoxifen, a mixed estrogen agonist/antagonist. An associated risk of endometrial cancer and hyperplasia has been linked to the estrogen agonist properties of tamoxifen. We evaluated endoxifen using a classic uterotrophic effects method. Rats were given endoxifen or tamoxifen orally for 3 days. Estradiol was the positive control. Endoxifen and tamoxifen plasma levels exceeded those previously observed clinically. Uterine weight was 3-fold higher in the estradiol group than in the tamoxifen or endoxifen groups, which did not differ from vehicle controls. Tamoxifen and endoxifen caused a greater increase in luminal epithelial cell height than estradiol. Both tamoxifen and endoxifen produced an increase in the stromal BrdU labeling index (LI) that was ≤ estradiol and inversely related to dose, but did not affect luminal epithelial cell BrdU LI. As expected, estradiol increased luminal epithelial cell proliferation. These results indicate that endoxifen induces uterotrophic effects, but is less potent than estradiol in eliciting these effects. Given prior preclinical observations that endoxifen has superior antitumor activity than tamoxifen, the observations of similar uterine effects suggest that the endoxifen risk/benefit ratio may be superior to tamoxifen.

Pharmacogenomic diversity of tamoxifen metabolites and estrogen receptor genes in Hispanics and non-Hispanic whites with breast cancer

Ethnic differences in patient genetics and breast cancer (BC) biology contribute to ethnic disparities in cancer presentation and patient outcome. We prospectively evaluated SNPs within phase I and phase II tamoxifen (TAM) metabolizing enzymes, and the estrogen receptor gene (ESR1), aiming to identify potential pharmacogenomic ethnicity patterns in an ER-positive BC cohort constituted of Hispanic and Non-Hispanic White (NHW) women in South Texas. Plasma concentrations of TAM/metabolites were measured using HPLC. CYP2C9, CYP2D6 and SULT1A1 genotypes were determined by DNA sequencing/Pyrosequencing technology. ESR1 PvuII and XbaI SNPs were genotyped using Applied Biosystems Taqman Allelic Discrimination Assay. Hispanics had higher levels of TAM, 4-hydroxytamoxifen, and endoxifen than NHWs. There was a higher prevalence of CYP2D6 EM within Hispanics than NHWs, which corresponded to higher endoxifen levels, but no differences were verified with regard to CYP2C9 and SULT1A1. We found a higher incidence of the wild type forms of the ESR1 in Hispanics than NHWs. The performance status, the disease stage at diagnosis, and the use of aromatase inhibitors might have overcome the overall favorable pharmacogenomics profile of Hispanics when compared to NHWs in relation to TAM therapy responsiveness. Our data strongly point to ethnical peculiarities related to pharmacogenomics and demographic features of TAM treated Hispanics and NHWs. In the era of pharmacogenomics and its ultimate goal of individualized, efficacious and safe therapy, cancer studies focused on the Hispanic population are warranted because this is the fastest growing major demographic group, and an understudied segment in the U.S.

Association of SULT1A1 Arg²¹³His polymorphism with male breast cancer risk: results from a multicenter study in Italy

Male breast cancer (MBC) is rare and poorly understood. Like female breast cancer (FBC), MBCs are highly sensitive to hormonal changes, and hyperestrogenism, specifically, represents a major risk factor for MBC. MBC is considered similar to late-onset, post-menopausal estrogen/progesteron receptors positive FBC (ER+/PR+). Sulfotransferase 1A1 (SULT1A1) is an enzyme involved in the metabolism of estrogens. Recently, SULT1A1 common functional polymorphism Arg(213)His (638G>A) variant has been found to be associated with increased breast cancer (BC) risk, particularly in post-menopausal women. For this reason, we decided to explore whether SULT1A1 Arg(213)His could exert an effect on MBC development. The primary aim of this study was to evaluate the influence of the SULT1A1 Arg(213)His polymorphism on MBC risk. The secondary aim was to investigate possible associations with relevant clinical-pathologic features of MBC. A total of 394 MBC cases and 786 healthy male controls were genotyped for SULT1A1 Arg(213)His polymorphism by PCR-RFLP and high-resolution melting analysis. All MBC cases were characterized for relevant clinical-pathologic features. A significant difference in the distribution of SULT1A1 Arg(213)His genotypes was found between MBC cases and controls (P < 0.0001). The analysis of genotype-specific risk showed a significant increased MBC risk in individuals with G/A (OR 1.97, 95% CI 1.50-2.59; P < 0.0001) and A/A (OR 3.09, 95% CI 1.83-5.23; P < 0.0001) genotypes in comparison to wild-type genotype, under co-dominant model. A significant association between SULT1A1 risk genotypes and HER2 status emerged. Results indicate that SULT1A1 Arg(213)His may act as a low-penetrance risk allele for developing MBC and could be associated with a specific tumor subtype associated with HER2 overexpression.

Increased seizure threshold related to tamoxifen

Both animal and human evidence suggest that estrogen has a modulatory role in seizure threshold, although there have been no reports to date suggesting the relevance of this to ECT practice. We describe the case of a woman who had been receiving maintenance ECT for several years with a stable seizure threshold. She developed breast cancer and ultimately agreed to begin estrogen deprivation therapy with tamoxifen; this treatment regimen resulted in an increased seizure threshold, necessitating an increase in stimulus power settings. ECT practitioners should be aware that estrogen deprivation therapy may have the potential to alter seizure threshold.

Pharmacogenetics of SULT1A1

Cytosolic SULT1A1 participates in the bioconversion of a plethora of endogenous and xenobiotic substances. Genetic variation in this important enzyme such as SNPs can vary by ethnicity and have functional consequences on its activity. Most SULT1A1 genetic variability studies have been centered on the SULT1A1*1/2 SNP. Highlighted here are not only this SNP, but other genetic variants associated with SULT1A1 that could modify drug efficacy and xenobiotic metabolism. Some studies have investigated how differential metabolism of xenobiotic substances influences susceptibility to or protection from cancer in multiple sites. This review will focus primarily on the impact of SULT1A1 genetic variation on the response to anticancer therapeutic agents and subsequently how it relates to environmental and dietary exposure to both cancer-causing and cancer-preventative compounds.

Pharmacokinetics of endoxifen and tamoxifen in female mice: implications for comparative in vivo activity studies

BACKGROUND

Reduced CYP2D6 metabolism and low Z-endoxifen (ENDX) concentrations may increase the risk of breast cancer recurrence in tamoxifen (TAM)-treated women. Little is known regarding the differences between TAM and ENDX murine pharmacokinetics or the effect of administration route on plasma concentrations of each drug.

METHODS

The pharmacokinetics of TAM and ENDX were characterized in female mice.

RESULTS

For subcutaneous [s.c.] and oral TAM (4, 10 and 20 mg/kg), TAM AUC increased in a linear manner, but concentrations of the active metabolites [ENDX and 4-hydroxytamoxifen (4HT)] remained low. For oral TAM (20 mg), 4HT concentrations were tenfold greater (>25 ng/ml) than achievable in TAM-treated humans. Both oral (10-200 mg/kg) and s.c. (2.5-25 mg/kg) ENDX·HCl resulted in a greater than dose-proportional increase in AUC, with eightfold greater ENDX concentrations than an equivalent TAM dose. ENDX accumulated in plasma after 5-day dosing of 25 or 100 mg/kg ENDX·HCl and exceeded target concentrations of 0.1 and 1.0 μM, respectively, by twofold to fourfold.

CONCLUSIONS

In murine models, oral ENDX yields substantially higher ENDX concentrations, compared to TAM. The low 4HT and ENDX concentrations observed in mice receiving s.c. TAM mirror the TAM pharmacokinetics in humans with impaired CYP2D6 metabolism. These data support the ongoing development of ENDX as a novel agent for the endocrine treatment of ER-positive breast cancer.

Pharmacological relevance of endoxifen in a laboratory simulation of breast cancer in postmenopausal patients

BACKGROUND

Tamoxifen is metabolically activated via a CYP2D6 enzyme system to the more potent hydroxylated derivatives 4-hydroxytamoxifen and endoxifen. This study addresses the pharmacological importance of endoxifen by simulating clinical scenarios in vitro.

METHODS

Clinical levels of tamoxifen metabolites in postmenopausal breast cancer patients previously genotyped for CYP2D6 were used in vitro along with clinical estrogen levels (estrone and estradiol) in postmenopausal patients determined in previous studies. The biological effects on cell growth were evaluated in a panel of estrogen receptor-positive breast cancer cell lines via cell proliferation assays and real-time polymerase chain reaction (PCR). Data were analyzed with one- and two-way analysis of variance and Student's t test. All statistical tests were two-sided.

RESULTS

Postmenopausal levels of estrogen-induced proliferation of all test breast cancer cell lines (mean fold induction ± SD vs vehicle control: MCF-7 = 11 ± 1.74, P < .001; T47D = 7.52 ± 0.72, P < .001; BT474 = 1.75 ± 0.23, P < .001; ZR-75-1 = 5.5 ± 1.95, P = .001. Tamoxifen and primary metabolites completely inhibited cell growth regardless of the CYP2D6 genotype in all cell lines (mean fold induction ± SD vs vehicle control: MCF-7 = 1.57 ± 0.38, P = .54; T47D = 1.17 ± 0.23, P = .79; BT474 = 0.96 ± 0.2, P = .98; ZR-75-1 = 0.86 ± 0.67, P = .99). Interestingly, tamoxifen and its primary metabolites were not able to fully inhibit the estrogen-stimulated expression of estrogen-responsive genes in MCF-7 cells (P < .05 for all genes), but the addition of endoxifen was able to produce additional antiestrogenic effect on these genes.

CONCLUSIONS

The results indicate that tamoxifen and other metabolites, excluding endoxifen, completely inhibit estrogen-stimulated growth in all cell lines, but additional antiestrogenic action from endoxifen is necessary for complete blockade of estrogen-stimulated genes. Endoxifen is of supportive importance for the therapeutic effect of tamoxifen in a postmenopausal setting.

Determination of CYP2D6 *3, *4, and *10 frequency in women with breast cancer in São Luís, Brazil, and its association with prognostic factors and disease-free survival

The CYP2D6 enzyme is crucial for the metabolism of tamoxifen. The CYP2D6 gene is highly polymorphic, and individuals can be extensive, intermediate, or poor tamoxifen metabolizers. The aim of this study was to determine the frequencies of the CYP2D6 *3, *4, and *10 alleles in women with breast cancer who were treated with tamoxifen and analyze the association of enzyme activity with prognostic factors and disease-free survival. We observed a high frequency of CYP2D6 *10, with an allelic frequency of 0.14 (14.4%). The *3 allele was not present in the studied population, and *4 had an allelic frequency of 0.13 (13.8%). We conclude that patients with reduced CYP2D6 activity did not present worse tumor characteristics or decreased disease-free survival than women with normal enzyme activity, as the difference was not statistically significant. We also observed a high frequency of CYP2D6 *10, which had not been previously described in this specific population. This study is the first in north-northeastern Brazil that aimed to contribute to the knowledge of the Brazilian regional profile for CYP2D6 polymorphisms and their phenotypes. These findings add to the knowledge of the distribution of different polymorphic CYP2D6 alleles and the potential role of CYP2D6 genotyping in clinical practice prior to choosing therapeutic protocols.