Hyperleptinemia in obese state renders luminal breast cancers refractory to tamoxifen by coordinating a crosstalk between Med1, miR205 and ErbB

Obese women with hormone receptor-positive breast cancer exhibit poor response to therapy and inferior outcomes. However, the underlying molecular mechanisms by which obesity/hyperleptinemia may reduce the efficacy of hormonal therapy remain elusive. Obese mice with hyperleptinemia exhibit increased tumor progression and respond poorly to tamoxifen compared to non-obese mice. Exogenous leptin abrogates tamoxifen-mediated growth inhibition and potentiates breast tumor growth even in the presence of tamoxifen. Mechanistically, leptin induces nuclear translocation of phosphorylated-ER and increases the expression of ER-responsive genes, while reducing tamoxifen-mediated gene repression by abrogating tamoxifen-induced recruitment of corepressors NCoR, SMRT, and Mi2 and potentiating coactivator binding. Furthermore, in silico analysis revealed that coactivator Med1 potentially associates with 48 (out of 74) obesity-signature genes. Interestingly, leptin upregulates Med1 expression by decreasing miR-205, and increases its functional activation via phosphorylation, which is mediated by activation of Her2 and EGFR. It is important to note that Med1 silencing abrogates the negative effects of leptin on tamoxifen efficacy. In addition, honokiol or adiponectin treatment effectively inhibits leptin-induced Med1 expression and improves tamoxifen efficacy in hyperleptinemic state. These studies uncover the mechanistic insights how obese/hyperleptinemic state may contribute to poor response to tamoxifen implicating leptin-miR205-Med1 and leptin-Her2-EGFR-Med1 axes, and present bioactive compound honokiol and adipocytokine adiponectin as agents that can block leptin’s negative effect on tamoxifen.

Effect of Genetic Variability in 20 Pharmacogenes on Concentrations of Tamoxifen and Its Metabolites

Background: Tamoxifen, as a treatment of estrogen receptor positive (ER+) breast cancer, is a weak anti-estrogen that requires metabolic activation to form metabolites with higher anti-estrogenic activity. Endoxifen is the most-studied active tamoxifen metabolite, and endoxifen concentrations are highly associated with CYP2D6 activity. Associations of tamoxifen efficacy with measured or CYP2D6-predicted endoxifen concentrations have been inconclusive. Another active metabolite, 4-OHtam, and other, less active metabolites, Z-4′-endoxifen and Z-4′-OHtam, have also been reported to be associated with tamoxifen efficacy. Method: Genotype for 20 pharmacogenes was determined by VeriDose® Core Panel and VeriDose®CYP2D6 CNV Panel, followed by translation to metabolic activity phenotype following standard activity scoring. Concentrations of tamoxifen and seven metabolites were measured by UPLC-MS/MS in serum samples collected from patients receiving 20 mg tamoxifen per day. Metabolic activity was tested for association with tamoxifen and its metabolites using linear regression with adjustment for upstream metabolites to identify genes associated with each step in the tamoxifen metabolism pathway. Results: A total of 187 patients with genetic and tamoxifen concentration data were included in the analysis. CYP2D6 was the primary gene associated with the tamoxifen metabolism pathway, especially the conversion of tamoxifen to endoxifen. CYP3A4 and CYP2C9 were also responsible for the metabolism of tamoxifen. CYP2C9 especially impacted the hydroxylation to 4-OHtam, and this involved the OATP1B1 (SLCO1B1) transporter. Conclusion: Multiple genes are involved in tamoxifen metabolism and multi-gene panels could be useful to predict active metabolite concentrations and guide tamoxifen dosing.

Generating a Precision Endoxifen Prediction Algorithm to Advance Personalized Tamoxifen Treatment in Patients with Breast Cancer

Tamoxifen is an endocrine treatment for hormone receptor positive breast cancer. The effectiveness of tamoxifen may be compromised in patients with metabolic resistance, who have insufficient metabolic generation of the active metabolites endoxifen and 4-hydroxy-tamoxifen. This has been challenging to validate due to the lack of measured metabolite concentrations in tamoxifen clinical trials. CYP2D6 activity is the primary determinant of endoxifen concentration. Inconclusive results from studies investigating whether CYP2D6 genotype is associated with tamoxifen efficacy may be due to the imprecision in using CYP2D6 genotype as a surrogate of endoxifen concentration without incorporating the influence of other genetic and clinical variables. This review summarizes the evidence that active metabolite concentrations determine tamoxifen efficacy. We then introduce a novel approach to validate this relationship by generating a precision endoxifen prediction algorithm and comprehensively review the factors that must be incorporated into the algorithm, including genetics of CYP2D6 and other pharmacogenes. A precision endoxifen algorithm could be used to validate metabolic resistance in existing tamoxifen clinical trial cohorts and could then be used to select personalized tamoxifen doses to ensure all patients achieve adequate endoxifen concentrations and maximum benefit from tamoxifen treatment.

ROLE OF CYCLIN D1 IN THE MECHANISMS OF TAMOXIFEN RESISTANCE

Hormone-receptor positive breast cancer is the most common molecular subtype and represents 60–75 % of all breast cancers (BC). The presence of specific molecular targets such as the estrogen/progesterone receptor determines the use of hormone therapy for patients with this subtype. Tamoxifen, a selective estrogen receptor modulator, remains the first adjuvant treatment choice for the hormone-receptor positive BC patients. However, tamoxifen resistance is the major limitation of its efficacy. In this regard, the study of drug resistance mechanisms as well as search for biological prognostic markers of tamoxifen efficacy is very important. Cyclin D1 is a representative of the regulatory protein family, which plays a central role in the cell cycle regulation. The data on the association between cyclin D1 and estrogen-dependent signaling as well as the characteristics of CCND1 gene and its most studied polymorphic loci, were presented. The prognostic significance of cyclin D1 in hormone-receptor positive BC receptor-positive breast cancer was described. The experimental and clinical studies data on the association between the cyclin D1 expression level and tamoxifen efficacy are analyzed. Current approaches to overcoming hormone resistance based on cyclin D1 studies were considered.

The CYP2C19 rs4917623 single nucleotide polymorphism to predict tamoxifen efficacy in estrogen receptor-positive breast cancer patients.

e12001 Background: Tamoxifen is a selective estrogen receptor modulator that is widely used to treat estrogen receptor (ER)-positive breast cancer. However, not all patients benefit from the incorporation of tamoxifen into an adjuvant therapy. This is also the case when tamoxifen is used in chemoprevention, since only half of participants benefit from the drug. In order to improve treatment response, we attempted to identify single nucleotide polymorphisms (SNPs) that correlated with tamoxifen efficacy. Methods: ER-positive breast cancer patients at our hospital were enrolled on this study between January 2007 and September 2010. The primary endpoint was ER-positive breast cancer-free survival. We examined 17 SNPs in these patients. The survival benefit associated with each genotype was determined with a log-rank test, and the hazard ratio was analyzed using a Cox proportional-hazards model. Results: The median follow-up time of the 320 patients enrolled on the study was 3298 days. Of 240 patients who received any endocrine therapy, ER-positive breast cancer-free survival in patients with the 2q35 rs13387042 AA genotype was significantly shorter than in those who had the AG or GG genotype (p < 0.0001), and the hazard ratio was significantly higher (HR 8.83; 95% CI 2.09–25.53, p = 0.0064). Of the 145 patients who received tamoxifen therapy, there was a trend among ER-positive breast cancer patients with the CYP2C19 rs4917623 TT genotype to have a shorter disease-free period (p = 0.0635) when compared to patients with TC or CC genotypes. Similarly, there was a trend for the TT genotype patients to exhibit a higher hazard ratio (HR 2.62; 95% CI 0.86–7.55, p = 0.0861). Conclusions: The rs4917623 SNP in the CYP2C19 gene, which encodes a metabolic enzyme, predicts tamoxifen efficacy. This finding will facilitate selection of ER-positive breast cancer patients for tamoxifen treatment; it may also be useful for selection of patients most likely to benefit from tamoxifen-dependent chemoprevention.

Relation of EGFR/PI3K/AKT signaling components with tamoxifen efficacy in patients with estrogen-dependent breast cancer

Background. It is generally accepted that crosstalk between the growth factor receptor and ER pathways implicated in tamoxifen resistance. The aim of the study was to examine the relationship between mRNA level, protein expression and gene polymorphism of the EGFR/PI3K/AKT signaling components with tamoxifen efficacy in patients with estrogen-dependent breast cancer. Materials and methods. The study included 95 breast cancer patients who had received adjuvant tamoxifen, of which 31 patients developed recurrence/metastasis after tamoxifen treatment (tamoxifen resistance group), 64 patients did not develop any diseases progression (tamoxifen sensitive group) during the 5 years of follow-up. Genotypes for ESR1 (rs2077647, rs2228480, rs1801132), EGFR (rs1468727, rs2227983), AKT1 (rs1130233) and PTEN (rs11202592) were analyzed using a TaqMan assay. Using reverse transcription-PCR, the relative expression of mRNA for ESR1, EGFR, AKT1 and PTEN was determined. ERα, EGFR, Akt (pS473) and PTEN expression level was evaluated using immunohistochemistry. Progression-free survival (PFS) was estimated by Kaplan – Meier analysis. Results. The minor allele of ESR1 rs2077647 was more prevalent in tamoxifen sensitive tumors compared to tamoxifen resistant tumors (p = 0.044). We found high AKT1 mRNA expression level in tamoxifen sensitive group compared with tamoxifen resistance patients (7.27 ± 5.29 and 0.02 ± 0.01, respectively, p = 0.014). ESR1 rs2228480 was significantly associated with tamoxifen resistance (p = 0.028). EGFR and Akt (pS473) protein expression level was significantly higher in the tamoxifen resistance group compared to tamoxifen sensitive breast cancer patients (p = 0.006 and 0.037, respectively). Patients carrying mutant genotypes of ESR1 rs2228480 had a poorer progression-free survival than those carrying wild and heterozygous variants (log rank p = 0.043). Positive EGFR tumor expression as well as positive Akt (pS473) expression were significantly associated with shorter PFS (log rank p = 0.014 and 0.048, respectively). Conclusion. Polymorphic sites of the ESR1 gene, AKT1 mRNA expression, EGFR expression level and Akt (pS473) protein expression can be potential molecular markers associated with tumor sensitivity/resistance to tamoxifen treatment.

P53 AND CYCLIN B1 MEDIATE APOPTOTIC EFFECTS OF APIGENIN AND RUTIN IN ER+-BREAST CANCER MCF-7 CELLS

Tamoxifen is an effective treatment for estrogen receptor alpha positive (ERa+)-breast cancer, however patients who received the treatment for five years have greater mortality risk compared to those who did not receive tamoxifen. Furthermore, patients treated with tamoxifen developed resistance to the drug which mediated through p53 and PTEN. Therefore, the study is undertaken to determine the potential adjuvant properties of flavonoids, apigenin and rutin to promote the anticancer activity induced by tamoxifen using ERa+-breast cancer MCF-7 cell lines. MCF-7 and non-transformed breast MCF-10A cells were treated separately with apigenin, rutin, tamoxifen or the combination of each flavonoids with tamoxifen. Anti-proliferative activity and respective IC50 concentrations were determined using MTT assay. The respective IC50 concentrations obtained were used in the subsequent experiments. The anti-proliferative mechanism was determined using Annexin V-FITC morphological staining and DNA fragmentation assays. The effect on tumor suppressor (p53 and PTEN) and cell cycle related genes (p21, CDK1 and Cyclin B1) were determined by QuantiGene Plex assay. Our results showed that MCF-7 cells were more sensitive to both apigenin and rutin compared to MCF-10A cells. Both cells were sensitive to tamoxifen. Apigenin and rutin synergistically enhanced tamoxifen anti-proliferative effect in MCF-7. Meanwhile rutin protects MCF-10A against the toxicity of tamoxifen. Our results indicate that the anti-proliferative mechanism of apigenin and rutin is mediated by apoptosis signals. In MCF-7 cells, both tumor suppressor (p53 and PTEN) and cell cycle related genes (p21 and CDK1) were up regulated by apigenin and rutin, contrary to tamoxifen. Apigenin and rutin induced G2/M arrest and apoptosis in MCF-7 cells through p53-dependent pathway. Both flavonoids are suggested as potential adjuvant agents to enhance tamoxifen efficacy in ERa+-breast cancer treatment.

Expression of estrogen receptor beta isoforms in pancreatic adenocarcinoma.

337 Background: There have been several limited trials in which tamoxifen efficacy was tested in patients with pancreatic adenocarcinoma (PAC). Most of these studies were small series of patients with unresectable PAC and reported mixed results. In these studies, patients were not stratified by estrogen receptor status because estrogen receptor beta (ER-b) had not yet been identified, and PAC did not express the traditional ER-alpha. Recent studies showed that the effects of estrogens, phytoestrogens and tamoxifen on PAC cell lines depended on ER-b expression. The aim of this study was to investigate ER-b expression in human PAC and whether such expression correlates with any clinicopathologic parameters. Methods: Sections of tissue microarray containing 18 formalin fixed and paraffin embedded human PAC were stained by immunohistochemistry (IHC) using monoclonal antibodies to ER-b isoforms 1, 2, and 5 (ER-b1, ER-b2, and ER-b5, respectively), and for Cyclin A. The levels of ER-b isoform expression in tumor cells and the S-phase fraction (SPF) were determined using a quantitative digital image analysis solution (OTMIAS). Results: All isoforms were expressed in PAC, although at different levels. Higher mean ER-b2 levels correlated with male sex (p = 0.057), older age (p = 0.005), and lower pT stage (p = 0.008), but not with grade, pN stage, or SPF. Mean ER-b5 levels correlated negatively with SPF (p = 0.021), but not with sex, age, grade, pT or pN. Mean ER-b1 expression did not correlate with any of the above mentioned clinicopathologic factors. Conclusions: ER-b1, ER-b2, and ER-b5 are expressed in PAC. Higher ER-b2 and ER-b5 levels of expression are significantly correlated with lower tumor pT stage and with lower SPF, respectively, suggesting that they may play a tumor suppressive role in PAC. The association between ER-b2 levels and patient sex and age suggest that it could be influenced by endogenous/exogenous hormonal exposure.