Effect of CYP2D6 polymorphisms on breast cancer recurrence

Pharmacogenetics of tamoxifen in breast cancer patients of African descent: Lack of data

Tamoxifen, a selective estrogen receptor modulator, is used to treat hormone receptor-positive breast cancer. Tamoxifen acts as a prodrug, with its primary therapeutic effect mediated by its principal metabolite, endoxifen. However, tamoxifen has complex pharmacokinetics involving several drug-metabolizing enzymes and transporters influencing its disposition. Genes encoding enzymes involved in tamoxifen disposition exhibit genetic polymorphisms which vary widely across world populations. This review highlights the lack of data on tamoxifen pharmacogenetics among African populations. Gaps in data are described in this study with the purpose that future research can address this dearth of research on the pharmacogenetics of tamoxifen among African breast cancer patients. Initiatives such as the African Pharmacogenomics Network (APN) are crucial in promoting comprehensive pharmacogenetics studies to pinpoint important variants in pharmacogenes that could be used to reduce toxicity and improve efficacy.

Evaluation of the effect of CYP2D6*3, *4,*10, and *17 polymorphisms on the pharmacokinetic of tamoxifen and its metabolites in patients with hormone-positive breast cancer

BACKGROUND AND OBJECTIVE

A high rate of interindividual variability in response to tamoxifen (TAM) in breast cancer patients with CYP2D6 polymorphism has been reported, which affects the patient's therapeutic outcome. The objective of this study was to investigate the pharmacogenomics of CYP2D6 genotyping in Iranian patients with breast cancer treated with adjuvant TAM.

METHODS

A peripheral blood sample was obtained to determine the steady-state plasma concentrations of TAM and its metabolites (Endoxifen (EN) and 4-Hydroxytamoxifen (4-OHT)) using high-performance liquid chromatography with fluorescence detection (HPLC-FLU) assay. We detected CYP2D6 * 3, * 4, * 10, and * 17 single nucleotide polymorphisms via polymerase chain reaction and restriction fragment length polymorphism (PCR-RFLP) method.

RESULTS

A total of 84 Iranian estrogen receptor‑positive breast cancer patients receiving the daily dose of 20 mg tamoxifen were recruited. Although a consequent decrease in the median EN and 4-OHT concentrations was observed by comparing poor or intermediate metabolizer patients with an extensive metabolizer population, this difference did not reach a significant level. The mean plasma EN concentrations in poor and intermediate metabolizers were 46.1% (95% CI, 7.4-27.8%) and 59.4% (95% CI, 11.9-37.3%) of extensive metabolizer subjects, respectively. Poor and intermediate metabolizers had the mean plasma 4-OHT concentrations that were 46.6% (95% CI, 0.9-61.7%) and 73.2% (95% CI, 2.7-93.1%) of those of subjects who were extensive metabolizer, respectively.

CONCLUSIONS

The possible role of genotyping in Iranian patients' response to treatment may explain inter-individual differences in the plasma concentrations of active metabolites of TAM.

Improving the transparency of meta-analyses with interactive web applications

Increased transparency in study design and analysis is one proposed solution to the perceived reproducibility crisis facing science. Systematic review and meta-analysis-through which individual studies on a specific association are ascertained, assessed for quality and quantitatively combined-is a critical process for building consensus in medical research. However, the conventional publication model creates static evidence summaries that force the quality assessment criteria and analytical choices of a small number of authors onto all stakeholders, some of whom will have different views on the quality assessment and key features of the analysis. This leads to discordant inferences from meta-analysis results and delayed arrival at consensus. We propose a shift to interactive meta-analysis, through which stakeholders can take control of the evidence synthesis using their own quality criteria and preferred analytic approach-including the option to incorporate prior information on the association in question-to reveal how their summary estimate differs from that reported by the original analysts. We demonstrate this concept using a web-based meta-analysis of the association between genetic variation in a key tamoxifen-metabolising enzyme and breast cancer recurrence in tamoxifen-treated women. We argue that interactive meta-analyses would speed consensus-building to the degree that they reveal invariance of inferences to different study selection and analysis criteria. On the other hand, when inferences are found to differ substantially as a function of these choices, the disparities highlight where future research resources should be invested to resolve lingering sources of disagreement.

CYP2D6*3 (A2549del), *4 (G1846A), *10 (C100T) and *17 (C1023T) genetic polymorphisms in Iranian breast cancer patients treated with adjuvant tamoxifen

There is controversy regarding the efficacy of tamoxifen in breast cancer patients who are carriers of cytochrome P450 2D6 (CYP2D6) gene polymorphisms. Poor metabolizer genotypes may not fully convert tamoxifen to its active metabolite endoxifen and thus have less exposure to anti-estrogen therapy. The present study was conducted to identify the prevalence of CYP2D6 genotypes among Iranian breast cancer patients. A total of 84 estrogen receptor-positive breast cancer patients treated at a referral center in the north of Iran were examined. A peripheral blood sample was obtained from each patient to determine the presence of *3, *4, *10 and *17 single nucleotide polymorphisms of the CYP2D6 gene by polymerase chain reaction-based restriction fragment-length polymorphism analysis. Of the four genotypes assessed, CYP2D6*4 was the most common variant and was identified in 41 (48.8%) patients as heterozygous (G/A) and 3 (3.6%) as homozygous (A/A) alleles. CYP2D6*10 heterozygous mutated alleles (C/T) were also a common genotype that presented in 22 (26.2%) of the study subjects. Variant *17 was less common and was detected only as heterozygous (C/T) in 3 patients (3.6%). No CYP2D6*3 heterozygous or homozygous mutated alleles were observed. In conclusion, the frequency of the CYP2D6 nonfunctional alleles *4 and *10 appeared relatively high in Iranian patients with hormone-sensitive breast cancer. This finding may affect the selection of an optimal hormone therapy, as patients with low CYP2D6 pathway activity may not sufficiently convert tamoxifen to its active metabolite endoxifen.

CYP2D6 gene polymorphisms in Brazilian patients with breast cancer treated with adjuvant tamoxifen and its association with disease recurrence

At present, there is controversy regarding the efficacy of tamoxifen in breast cancer patients who are carriers of cytochrome P450 2D6 (CYP2D6) gene polymorphisms, in terms of recurrence and overall survival. Thus, the aim of the present study was to investigate the association of the CYP2D6 *4, *10 and *17 gene polymorphisms with breast cancer recurrence in a Brazilian population. The cohort comprised 40 receptor-positive breast cancer patients without recurrence and 40 with distant recurrence. A 3-ml sample of peripheral blood was collected from each patient to determine the presence of the *4, *10 and *17 single nucleotide polymorphisms of the CYP2D6 gene by quantitative polymerase chain reaction analysis. There was no statistically significant difference between the two groups regarding the polymorphism frequency (P=0.246). The results revealed that intermediate metabolizers occurred in 5% of patients without recurrence and in 15% of those with distant recurrence. Poor metabolizers occurred in only 1 patient (2.5%) per group, and there was no significant difference between the groups (P=0.789). The present study concluded that the CYP2D6 gene polymorphism in women with hormone-sensitive breast cancer treated with tamoxifen was not associated with disease recurrence.

Personalized Cancer Therapy Considering Cytochrome P450 Variability

The individual variability of pharmacokinetics is underestimated and few systematic studies exist in this field. In most cases, this leads to unwanted side effects or toxicity. In polychemotherapy, prodrugs (like ifosfamide), which have to be activated by cytochrome P450 enzymes (CYPs), play an important role. If patients are poor metabolizers for these drugs, the therapy will be ineffective. Furthermore, CYPs and transporters can be (over)expressed in target tissues, which is also not examined and considered in clinical routine. Here, we present a body map showing relevant enzymes in some organs and tissues. Finally, a typical case of a Caucasian chemotherapy patient with breast cancer is presented and discussed regarding a personalized cancer therapy considering the single nucleotide polymorphisms found via genotyping.

Evaluation of endometrial thickness and bone mineral density based on CYP2D6 polymorphisms in Turkish breast cancer patients receiving tamoxifen treatment

BACKGROUND

Several previous studies have examined the effect of CYP2D6 gene polymorphism on the efficacy and metabolism of tamoxifen (Tamoxifen Teva, Nolvadex) in the treatment of breast cancer. In the present study, the metabolic profiles associated with various CYP2D6 genotypes were evaluated.

METHOD

In the present study 92 Turkish breast cancer patients with early-stage hormone receptor-positive tumors treated with adjuvant tamoxifen (20 mg) were evaluated for CYP2D6 genotype and metabolic profiles. Known side effects of tamoxifen treatment, including endometrial thickening, changes in serum lipid levels and bone density, and hepatosteatosis, were evaluated according to the CYP2D6 polymorphism.

RESULT

The distribution of metabolic characteristics in the Turkish population was as follows: 77.1% normal metabolism, 11.5% intermediate metabolism, 5.2% ultrarapid metabolism, and 2.1% poor metabolism. The CYP2D6 genotypes associated with rapid metabolism were CYP2D6 3X*1/*1 duplication (DUP) and CYP2D6 2X*1/*2, while poor metabolism was associated with the genotypes CYP2D6 *3/*4 and CYP2D6 *6/*6. There was no statistically significant relationship between metabolic characteristics and bone density or hepatosteatosis. A statistically significant difference in total cholesterol and triglycerides was detected in lipid profile analysis (p = 0.003, p = 0.02). Assessment of endometrial thickness revealed a significant association of hyperplasia and poor metabolism, and an association between atrophy and ultrarapid metabolism (p = 0.01).

CONCLUSION

Significant development of endometrial hyperplasia was identified among individuals with poor tamoxifen metabolism. As a result, tamoxifen may be a significant predictor of endometrial thickening among individuals with poor metabolic characteristics.

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

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

CYP2D6 genotype and tamoxifen response for breast cancer: a systematic review and meta-analysis

OBJECTIVE

To evaluate evidence on the association between CYP2D6 genotype and tamoxifen response through.

DESIGN

Systematic review and meta-analysis of prospective, cross-sectional and case-control studies published to 2012. For each study, relative risks and 95% confidence intervals were extracted and pooled with a fixed and random effects model. Heterogeneity, publication bias, subgroup, and meta-regression analyses were performed.

DATA SOURCES

PubMed (inception-2012) and EMBASE (inception-2012).

ELIGIBILITY CRITERIA FOR SELECTING STUDIES

Criteria for inclusion were studies reporting breast cancer outcomes in patients treated with tamoxifen and genotyped for polymorphisms in the CYP2D6 gene.

RESULTS

Twenty-five studies of 13,629 individuals were identified, of which 22 investigated the association of CYP2D6 genotype with outcomes in breast cancer women all receiving tamoxifen treatment ("treatment-only" design). Three randomized trials evaluated the effect of CYP2D6 genotype on tamoxifen response ("effect modification" design). In analysis of treatment-only studies, the relative risk (RR) of all-cause mortality (>307 events in 4,936 patients) for carriers of a CYP2D6 reduced function allele was 1.11 (95% confidence interval (CI): 0.94 to 1.31) compared to individuals with normal/increased function CYP2D6 alleles. When we investigated a composite outcome including all-cause mortality and surrogate endpoints for overall survival (>307 events in 6,721 patients), carriers of a CYP2D6 reduced function allele had a RR of 1.27 (95% CI: 1.11 to 1.45). From two randomized trials that permitted effect-modification analysis, one had only 154 patients and showed evidence of effect modification of tamoxifen by CYP2D6 genotype for distant recurrence but was directionally opposite to that predicted, whereas a larger trial of 2,537 patients failed to show evidence of effect modification for breast cancer-free interval (P values for interaction 0.02 and 0.44, respectively).

CONCLUSIONS

Based on these findings, there is insufficient evidence to recommend CYP2D6 genotyping to guide tamoxifen treatment.

Genetic variants of CYP2D6 gene and cancer risk: a HuGE systematic review and meta-analysis

OBJECTIVE

Genetic polymorphisms in metabolic enzymes are associated with numerous cancers. A large number of single nucleotide polymorphisms (SNPs) in the CYP2D6 gene have been reported to associate with cancer susceptibility. However, the results are controversial. The aim of this Human Genome Epidemiology (HuGE) review and meta-analysis was to summarize the evidence for associations.

METHODS

Studies focusing on the relationship between CYP2D6 gene polymorphisms and susceptibility to cancer were selected from the Pubmed, Cochrane library, Embase, Web of Science, Springerlink, CNKI and CBM databases. Data were extracted by two independent reviewers and the meta-analysis was performed with Review Manager Version 5.1.6 and STATA Version 12.0 software. Odds ratios (ORs) with 95% confidence intervals (95%CIs) were calculated.

RESULTS

According to the inclusion criteria, forty-three studies with a total of 7,009 cancer cases and 9,646 healthy controls, were included in the meta-analysis. The results showed that there was a positive association between heterozygote (GC) of rs1135840 and cancer risk (OR=1.92, 95%CI: 1.14-3.21, P=0.01). In addition, we found that homozygote (CC) of rs1135840 might be a protective factor for cancer (OR=0.58, 95%CI: 0.34-0.97, P=0.04). Similarly, the G allele and G carrier (AG + GG) of rs16947 and heterozygote (A/del) of rs35742686 had negative associations with cancer risk (OR=0.69, 95%CI: 0.48-0.99, P=0.04; OR=0.60, 95%CI: 0.38-0.94, P=0.03; OR=0.50, 95%CI: 0.26-0.95, P=0.03; respectively).

CONCLUSION

This meta-analysis suggests that CYP2D6 gene polymorphisms are involved in the pathogenesis of various cancers. The heterozygote (GC) of rs1135840 in CYP2D6 gene might increase the risk while the homozygote (CC) of rs1135840, G allele and G carrier (AG + GG) of rs16947 and heterozygote (A/del) of rs35742686 might be protective factors.

Influence of CYP2D6-genotype on tamoxifen efficacy in advanced breast cancer

The influence of CYP2D6 genotype on the efficacy of tamoxifen (Tam) has been extensively analyzed in early breast cancer with conflicting results. However, there is only scarce data regarding this potential influence in advanced breast cancer (ABC). We hypothesize that Tam is more effective in patients with a functional CYP2D6 allele than in patients with impaired CYP2D6 activity. ABC patients with prior or ongoing palliative Tam treatment (20 mg/d) were eligible. Genomic DNA was extracted from blood (n = 51) and formalin-fixed, paraffin-embedded tissue (n = 43). CYP2D6*2, *3, *4, *5, *6, *10, *17, *29, *41, CYP2D6 duplication and multiplication were determined in blood and CYP2D6*4 in tissue samples. Primary endpoint was progression free survival (PFS); secondary endpoints included clinical benefit (CB), and overall survival (OS). The clinical charts were retrospectively analyzed regarding survival and treatment effects. Genotyping was performed blinded and clinical data were analyzed separately. 94 patients were identified with a median age of 59 years (29-90 years). In 6 patients genotyping did not show conclusive results, therefore these patients were excluded from further analysis. Genotyping results were as follows: 1.1 % ultrarapid, 84.1 % extensive, 3.4 % intermediate, and 11.4 % poor metabolizers. Patients without any fully functional allele (IM/IM, IM/PM, PM/PM) had a significant shorter PFS and OS compared to patients with at least one functional allele (EM/EM, EM/IM, EM/PM) (PFS: p = 0.017; HR = 2.19; 95 % CI 1.15-4.18; OS: p = 0.028; HR = 2.79; 95 % CI 1.12-6.99). The CB rate was 73 % for EM-group and 38.5 % for IM + PM-group (p = 0.019). Our results show a significant influence of the CYP2D6 genotype on the efficacy of Tam in the treatment of ABC. In contrast to the adjuvant setting, the evidence in the palliative setting is congruent. CYP2D6 testing in ABC should be considered.

Drug cocktail optimization in chemotherapy of cancer

BACKGROUND

In general, drug metabolism has to be considered to avoid adverse effects and ineffective therapy. In particular, chemotherapeutic drug cocktails strain drug metabolizing enzymes especially the cytochrome P450 family (CYP). Furthermore, a number of important chemotherapeutic drugs such as cyclophosphamide, ifosfamide, tamoxifen or procarbazine are administered as prodrugs and have to be activated by CYP. Therefore, the genetic variability of these enzymes should be taken into account to design appropriate therapeutic regimens to avoid inadequate drug administration, toxicity and inefficiency.

OBJECTIVE

The aim of this work was to find drug interactions and to avoid side effects or ineffective therapy in chemotherapy.

DATA SOURCES AND METHODS

Information on drug administration in the therapy of leukemia and their drug metabolism was collected from scientific literature and various web resources. We carried out an automated textmining approach. Abstracts of PubMed were filtered for relevant articles using specific keywords. Abstracts were automatically screened for antineoplastic drugs and their synonyms in combination with a set of human CYPs in title or abstract.

RESULTS

We present a comprehensive analysis of over 100 common cancer treatment regimens regarding drug-drug interactions and present alternatives avoiding CYP overload. Typical concomitant medication, e.g. antiemetics or antibiotics is a preferred subject to improvement. A webtool, which allows drug cocktail optimization was developed and is publicly available on http://bioinformatics.charite.de/chemotherapy.

Insulin-like growth factor 1 attenuates antiestrogen- and antiprogestin-induced apoptosis in ER+ breast cancer cells by MEK1 regulation of the BH3-only pro-apoptotic protein Bim

Introduction

In this pre-clinical in vitro study conducted in estrogen receptor positive (ER+) breast cancer cells, we have characterized the effects of insulin-like growth factor I (IGF-1) on the cytostatic and cytotoxic action of antiestrogen treatment when used as a single agent or in combination with the antiprogestin mifepristone (MIF). Our goal was to identify new molecular targets to improve the efficacy of hormonal therapy in breast cancer patients that have a poor response to hormonal therapy, in part, due to high circulating levels of unbound insulinIGF-1.

Methods

IGF-1-mediated effects on cytostasis and apoptotic cell death were determined with cell counts conducted in the presence and absence of trypan blue; enzyme-linked immunosorbent assays to determine the intracellular levels of cleaved cytokeratin 18, a marker of epithelial cancer cell apoptosis; and immunoblot analysis to determine the levels of cleaved poly-ADP ribose polymerase (PARP) and lamin A that result from caspase-dependent apoptosis. Cytotoxicity was further characterized by determination of the levels of reactive oxygen species (ROS) and the percent of mitochondrial membrane depolarization in cell populations treated with the different hormones in the presence and absence of IGF-1. Small molecule inhibitors of the dual-specificity protein kinase MEK1, MEK1 siRNA, Bim siRNA, and vectors overexpressing MEK1 wild type and mutant, dominant negative cDNA were used to identify key IGF-1 downstream prosurvival effectors.

Results

IGF-1, at physiologically relevant levels, blocked the cytotoxic action(s) of the antiestrogens 4-hydroxytamoxifen (4-OHT) and tamoxifen (TAM) when used as single agents or in combination with the antiprogestin MIF. The antiapoptotic action of IGF-1 was mediated primarily through the action of MEK1. MEK1 expression reduced the levels of ROS and mitochondrial membrane depolarization induced by the hormonal treatments via a mechanism that involved the phosphorylation and proteasomal turnover of the proapoptotic BH3-only Bcl-2 family member Bim. Importantly, small-molecule inhibitors of MEK1 circumvented the prosurvival action of IGF-1 by restoring Bim to levels that more effectively mediated apoptosis in ER⁺ breast cancer cells.

Conclusion

his study provides strong support for the use of MEK1 inhibitors in combination with hormonal therapy to effectively affect cytostasis and activate a Bim-dependent apoptotic pathway in ER⁺ breast cancer cells. We discuss that MEK1 blockade may be a particularly effective treatment for women with high circulating levels of IGF-1, which have been correlated to a poor prognosis.