ABSTRACT
Acquired resistance to aromatase inhibitors (AIs) remains a major clinical problem in the treatment of estrogen receptor-positive (ER+) breast cancer. We and others have previously reported widespread changes in DNA methylation using breast cancer cell line models of endocrine resistance. Here, we show that the histone variant HIST1H2BE is hypomethylated in estrogen deprivation-resistant C4-12 and long-term estrogen-deprived (LTED) cells compared with parental MCF-7 cells. As expected, this hypomethylation associates with increased expression of HIST1H2BE in C4-12 and LTED cells. Both overexpression and downregulation of HIST1H2BE caused decreased proliferation in breast cancer cell lines suggesting the need for tightly controlled expression of this histone variant. Gene expression analysis showed varied expression of HIST1H2BE in a large panel of breast cancer cell lines, without restriction to specific molecular subtypes. Analysis of HIST1H2BE messenger RNA (mRNA) expression in ER+ AI-treated breast tumors showed significantly higher expression in resistant (n = 19) compared with sensitive (n = 37) tumors (p = 0.01). Using nanostring analysis, we measured expression of all 61 histone variants in endocrine-resistant and endocrine-sensitive tumors. We found significant overexpression of 22 variant histone genes in tumors resistant to AI therapy. In silico The Cancer Genome Atlas (TCGA) analysis showed frequent amplification of the HIST1 locus. In summary, our studies show, for the first time, that overexpression of histone variants might be important in endocrine response in ER+ breast cancer, and that overexpression is at least in part mediated via epigenetic mechanisms and amplifications. Future studies addressing endocrine response should include a potential role of these currently understudied histone variants.
Subject(s)
Antineoplastic Agents, Hormonal/pharmacology , Antineoplastic Agents, Hormonal/therapeutic use , Breast Neoplasms/drug therapy , Breast Neoplasms/genetics , Drug Resistance, Neoplasm/genetics , Genetic Variation , Histones/genetics , Adult , Aged , Aged, 80 and over , Animals , Breast Neoplasms/metabolism , Breast Neoplasms/pathology , Case-Control Studies , Cell Line, Tumor , Cell Proliferation , Cluster Analysis , Combined Modality Therapy , DNA Methylation , Female , Gene Expression , Gene Expression Profiling , Gene Knockdown Techniques , Histones/chemistry , Histones/metabolism , Humans , Middle Aged , Multigene Family , Neoplasm Grading , Neoplasm Staging , Sequence Analysis, DNAABSTRACT
Resistance to aromatase inhibitors (AIs) is a major clinical problem in the treatment of estrogen receptor (ER)-positive breast cancer. In two breast cancer cell line models of AI resistance, we identified widespread DNA hyper- and hypomethylation, with enrichment for promoter hypermethylation of developmental genes. For the homeobox gene HOXC10, methylation occurred in a CpG shore, which overlapped with a functional ER binding site, causing repression of HOXC10 expression. Although short-term blockade of ER signaling caused relief of HOXC10 repression in both cell lines and breast tumors, it also resulted in concurrent recruitment of EZH2 and increased H3K27me3, ultimately transitioning to increased DNA methylation and silencing of HOXC10. Reduced HOXC10 in vitro and in xenografts resulted in decreased apoptosis and caused antiestrogen resistance. Supporting this, we used paired primary and metastatic breast cancer specimens to show that HOXC10 was reduced in tumors that recurred during AI treatment. We propose a model in which estrogen represses apoptotic and growth-inhibitory genes such as HOXC10, contributing to tumor survival, whereas AIs induce these genes to cause apoptosis and therapeutic benefit, but long-term AI treatment results in permanent repression of these genes via methylation and confers resistance. Therapies aimed at inhibiting AI-induced histone and DNA methylation may be beneficial in blocking or delaying AI resistance.
Subject(s)
Breast Neoplasms/genetics , Cellular Reprogramming/genetics , Drug Resistance, Neoplasm/genetics , Epigenesis, Genetic/genetics , Estrogens/pharmacology , Homeodomain Proteins/genetics , Animals , Apoptosis/drug effects , Apoptosis/genetics , Aromatase Inhibitors/pharmacology , Aromatase Inhibitors/therapeutic use , Breast Neoplasms/drug therapy , Breast Neoplasms/pathology , Cell Movement/drug effects , Cell Movement/genetics , Cell Proliferation/drug effects , Cellular Reprogramming/drug effects , DNA Methylation/drug effects , DNA Methylation/genetics , Drug Resistance, Neoplasm/drug effects , Epigenesis, Genetic/drug effects , Female , Gene Expression Regulation, Neoplastic/drug effects , Gene Silencing/drug effects , Histones/metabolism , Homeodomain Proteins/metabolism , Humans , MCF-7 Cells , Mice , Neoplasm Recurrence, Local/drug therapy , Neoplasm Recurrence, Local/genetics , Neoplasm Recurrence, Local/pathology , Promoter Regions, Genetic , Xenograft Model Antitumor AssaysABSTRACT
OBJECTIVE: To describe our experience with random-start IVF with the use of GnRH agonist for final oocyte maturation, to reduce the risk of ovarian hyperstimulation syndrome. DESIGN: Case series. SETTING: University-based center for reproductive endocrinology and infertility. PATIENT(S): Patients with a new diagnosis of cancer who presented with a narrow time frame for IVF before initiating cancer therapy. INTERVENTION(S): Random-start GnRH antagonist cycles with GnRH agonist trigger for final oocyte maturation. MAIN OUTCOME MEASURE(S): Number of oocytes retrieved, fertilization rate, rates of ovarian hyperstimulation syndrome. RESULTS: Cycles were started in the late follicular or luteal phase, and the duration of controlled ovarian hyperstimulation ranged between 8-13 days. A total of 14-40 oocytes were retrieved and 5-20 embryos cryopreserved for each patient. CONCLUSION(S): Random-start IVF is a reasonable option for fertility preservation in those cancer patients for whom the treatment window may be narrow. In addition, the use of a GnRH agonist for final oocyte maturation may decrease the potential risk of ovarian hyperstimulation syndrome.