Do oestrogens induce chromosome specific aneuploidy in vitro, similar to the pattern of aneuploidy seen in breast cancer?

Role of aneuploidy in the carcinogenic process: Part 3 of the report of the 2017 IWGT workgroup on assessing the risk of aneugens for carcinogenesis and hereditary diseases

Aneuploidy is regarded as a hallmark of cancer, however, its role is complex with both pro- and anti-carcinogenic effects evident. In this IWGT review, we consider the role of aneuploidy in cancer biology; cancer risk associated with constitutive aneuploidy; rodent carcinogenesis with known chemical aneugens; and chemotherapy-related malignant neoplasms. Aneuploidy is seen at various stages in carcinogenesis. However, the relationship between induced aneuploidy occurring after exposure and clonal aneuploidy present in tumours is not clear. Recent evidence indicates that the induction of chromosomal instability (CIN), may be more important than aneuploidy per se, in the carcinogenic process. Down Syndrome, trisomy 21, is associated with altered hematopoiesis in utero which, in combination with subsequent mutations, results in an increased risk for acute megakaryoblastic and lymphoblastic leukemias. In contrast, there is reduced cancer risk for most solid tumours in Down Syndrome. Mouse models with high levels of aneuploidy are also associated with increased cancer risk for particular tumours with long latencies, but paradoxically other types of tumour often show decreased incidence. The aneugens reviewed that induce cancer in humans and animals all possess other carcinogenic properties, such as mutagenicity, clastogenicity, cytotoxicity, organ toxicities, hormonal and epigenetic changes which likely account for, or interact with aneuploidy, to cause carcinogenesis. Although the role that aneuploidy plays in carcinogenesis has not been fully established, in many cases, it may not play a primary causative role. Tubulin-disrupting aneugens that do not possess other properties linked to carcinogenesis, were not carcinogenic in rodents. Similarly, in humans, for the tubulin-disrupting aneugens colchicine and albendazole, there is no reported association with increased cancer risk. There is a need for further mechanistic studies on agents that induce aneuploidy, particularly by mechanisms other than tubulin disruption and to determine the role of aneuploidy in pre-neoplastic events and in early and late stage neoplasia.

BRCA1 Promoter Methylation and Expression - Associations with ER+, PR+ and HER2+ Subtypes of Breast Carcinoma

Introduction: Considering the increasing trend in incidence rates, morbidity and mortality of breast cancer, there is an urgent need to identify and validate new biomarkers for early detection and better management. The purpose of the study was to investigate BRCA1 protein expression and promoter methylation of the BRCA1 gene and their association with molecular subtypes based on estrogen receptor (ER), progesterone receptor (PR) and human epidermal growth factor receptor 2 (HER2) positivity. Materials and Methods: A total of 114 breast cancer tissue biopsies were collected for methylation specific PCR (MSP) and immunohistochemical (IHC) analysis. Results: Seven tissue microarrays were constructed. BRCA1 protein expression was reduced in 55/114 (48.2%) and in the majority of ER-negative tumors (73.3%) (p<0.001). Similarly BRCA1 expression was reduced in the majority of PR-negative tumors (69.2%) but without statistical significance (p value=0.083). BRCA1 methylation was positive in 59.6% cases. A subset regarding ER+, PR+ and HER2+ was identified which consisted of 31.6% in which an inverse relationship between BRCA1 methylation and protein expression was noted. Conclusion: Reduced expression was associated with ER and PR negative status which is linked with a poor prognosis. BRCA1 protein expression might thus be used as a prognostic indicator to predict treatment response to hormone therapy.

Aneuploidy: a common and early evidence-based biomarker for carcinogens and reproductive toxicants

Aneuploidy, defined as structural and numerical aberrations of chromosomes, continues to draw attention as an informative effect biomarker for carcinogens and male reproductive toxicants. It has been well documented that aneuploidy is a hallmark of cancer. Aneuploidies in oocytes and spermatozoa contribute to infertility, pregnancy loss and a number of congenital abnormalities, and sperm aneuploidy is associated with testicular cancer. It is striking that several carcinogens induce aneuploidy in somatic cells, and also adversely affect the chromosome compliment of germ cells. In this paper we review 1) the contributions of aneuploidy to cancer, infertility, and developmental abnormalities; 2) techniques for assessing aneuploidy in precancerous and malignant lesions and in sperm; and 3) the utility of aneuploidy as a biomarker for integrated chemical assessments of carcinogenicity, and reproductive and developmental toxicity.

Effect of low doses of estradiol and tamoxifen on breast cancer cell karyotypes

Evidence supports a role of 17&-estradiol (E2) in carcinogenesis and the large majority of breast carcinomas are dependent on estrogen. The anti-estrogen tamoxifen (TAM) is widely used for both treatment and prevention of breast cancer; however, it is also carcinogenic in human uterus and rat liver, highlighting the profound complexity of its actions. The nature of E2- or TAM-induced chromosomal damage has been explored using relatively high concentrations of these agents, and only some numerical aberrations and chromosomal breaks have been analyzed. This study aimed to determine the effects of low doses of E2 and TAM (10(&8 )mol L(&1) and 10(&6 )mol L(&1) respectively) on karyotypes of MCF7, T47D, BT474, and SKBR3 breast cancer cells by comparing the results of conventional karyotyping and multi-FISH painting with cell proliferation. Estrogen receptor (ER)-positive (+) cells showed an increase in cell proliferation after E2 treatment (MCF7, T47D, and BT474) and a decrease after TAM treatment (MCF7 and T47D), whereas in ER& cells (SKBR3), no alterations in cell proliferation were observed, except for a small increase at 96 h. Karyotypes of both ER+ and ER& breast cancer cells increased in complexity after treatments with E2 and TAM leading to specific chromosomal abnormalities, some of which were consistent throughout the treatment duration. This genotoxic effect was higher in HER2+ cells. The ER&/HER2+ SKBR3 cells were found to be sensitive to TAM, exhibiting an increase in chromosomal aberrations. These in vitro results provide insights into the potential role of low doses of E2 and TAM in inducing chromosomal rearrangements in breast cancer cells.

Possible influence of menstrual cycle on lymphocyte X chromosome mosaicism

PURPOSE

Estrogens are known to selectively influence cell proliferation. Physiological variations of blood hormone concentration might play a role in regulating the level of X chromosome aneuploidy. In this study we observed the percentages of X aneuploid cells in standard lymphocyte cultures from blood samples obtained in relation to the menstrual cycle, noting whether collection occurred during either the follicular or the luteal phase.

METHODS

A study consisting of 28 women with X mosaicism and recurrent pregnancy loss, and 28 age-matched healthy controls. Cytogenetic studies were carried out on peripheral blood samples according to standard procedures.

RESULTS

A significant difference in the percentage of X aneuploidy was found in blood samples obtained during different phases of the menstrual cycle. In the case group, the mean value of aneuploid cells in the follicular and luteal phase samples was 10.0 and 6.3 % respectively and in the control group, it was 2.8 and 1.0 % (P < 0.0001). The difference in the case group varied between 0 and 8 % (3.6 ± 2.1 %) and in the control group between 0 and 4 % (1.7 ± 1.1 %). The specificity for detecting true X mosaicism was 0.875. We estimate that the initial diagnosis of X mosaicism could be correct in 68 % of patients with recurrent pregnancy loss.

CONCLUSIONS

This observational study establishes that the time of blood sampling in relation to the menstrual cycle can influence lymphocyte X chromosome mosaicism. The results, further proven by additional controlled studies, would have practical implications for genetic counselling and fertility treatment.

Tamoxifen resistance in breast cancer

Tamoxifen is a central component of the treatment of estrogen receptor (ER)-positive breast cancer as a partial agonist of ER. It has been clinically used for the last 30 years and is currently available as a chemopreventive agent in women with high risk for breast cancer. The most challenging issue with tamoxifen use is the development of resistance in an initially responsive breast tumor. This review summarizes the roles of ER as the therapeutic target of tamoxifen in cancer treatment, clinical values and issues of tamoxifen use, and molecular mechanisms of tamoxifen resistance. Emerging knowledge on the molecular mechanisms of tamoxifen resistance will provide insight into the design of regimens to overcome tamoxifen resistance and discovery of novel therapeutic agents with a decreased chance of developing resistance as well as establishing more efficient treatment strategies.

miRNA-34b as a tumor suppressor in estrogen-dependent growth of breast cancer cells

Introduction

Estrogen is involved in several physiological and pathological processes through estrogen receptor (ER)-mediated transcriptional gene regulation. miRNAs (miRs), which are noncoding RNA genes, may respond to estrogen and serve as posttranscriptional regulators in tumorigenic progression, especially in breast cancer; however, only limited information about this possibility is available. In the present study, we identified the estrogen-regulated miR-34b and investigated its functional role in breast cancer progression.

Methods

Estrogen-regulated miRNAs were identified by using a TaqMan low density array. Our in vivo Tet-On system orthotopic model revealed the tumor-suppressive ability of miR-34b. Luciferase reporter assays and chromatin immunoprecipitation assay demonstrated miR-34b were regulated by p53-ER interaction.

Results

In this study, we identified one such estrogen downregulated miRNA, miR-34b, as an oncosuppressor that targets cyclin D1 and Jagged-1 (JAG1) in an ER+/wild-type p53 breast cancer cell line (MCF-7), as well as in ovarian and endometrial cells, but not in ER-negative or mutant p53 breast cancer cell lines (T47D, MBA-MB-361 and MDA-MB-435). There is a negative association between ERα and miR-34b expression levels in ER+ breast cancer patients. Tet-On induction of miR-34b can cause inhibition of tumor growth and cell proliferation. Also, the overexpression of miR-34b inhibited ER+ breast tumor growth in an orthotopic mammary fat pad xenograft mouse model. Further validation indicated that estrogen's inhibition of miR-34b expression was mediated by interactions between ERα and p53, not by DNA methylation regulation. The xenoestrogens diethylstilbestrol and zeranol also showed similar estrogenic effects by inhibiting miR-34b expression and by restoring the protein levels of the miR-34b targets cyclin D1 and JAG1 in MCF-7 cells.

Conclusions

These findings reveal that miR-34b is an oncosuppressor miRNA requiring both ER+ and wild-type p53 phenotypes in breast cancer cells. These results improve our ability to develop new therapeutic strategies to target the complex estrogenic pathway in human breast cancer progression through miRNA regulation.

Anastrozole Use in Early Stage Breast Cancer of Post-Menopausal Women

The majority of breast cancers express the estrogen receptor and depend on estradiol (E2) for their growth. Hormonal therapy aims at depriving estrogen signaling either by using selective estrogen receptor modulators (SERM)-that interfere with the binding of E2 to its receptor (ER)-or aromatase inhibitors (AI)-that block the aromatase-dependent synthesis of E2. While SERMs are recommended for both pre- and post-menopausal patients, AIs are indicated only for post-menopausal patients. For the past 20 years, the SERM tamoxifen has been considered the "gold standard" for the treatment of hormone receptor positive breast cancers. However, tamoxifen's role is now challenged by third generation AIs, such as anastrozole, which exhibit greater efficacy in the adjuvant setting in several recently reported trials. This review will focus on anastrozole's mechanism of action, dosing, pharmacology, pharmacokinetics, and clinical applications. It will briefly discuss the clinical trials that determined anastrozole's efficacy in the treatment of advanced breast cancer (ABC) and in the neoadjuvant setting. Finally, it will present the clinical trials that established anastrozole as a frontline agent in the treatment of post-menopausal women with hormone receptor positive early breast cancer.