The objective of this study was to identify and characterize a self-renewing subpopulation of human ovarian tumor cells (ovarian cancer-initiating cells, OCICs) fully capable of serial propagation of their original tumor phenotype in animals.

There have been major advances in our understanding of the cellular and molecular biology of the human malignancies collectively referred to as ovarian cancer. At a recent Helene Harris Memorial Trust meeting, an international group of researchers considered actions that should be taken to improve the outcome for women with ovarian cancer. Nine major recommendations are outlined in this Perspective.

High-grade serous ovarian cancer (HGSOC) accounts for 70-80% of ovarian cancer deaths, and overall survival has not changed significantly for several decades. In this Opinion article, we outline a set of research priorities that we believe will reduce incidence and improve outcomes for women with this disease. This ‘roadmap’ for HGSOC was determined after extensive discussions at an Ovarian Cancer Action meeting in January 2015.

The involvement of the MET oncogene in de novo and acquired resistance of non-small cell lung cancers (NSCLC) to tyrosine kinase inhibitors (TKIs) has been reported, but the precise mechanism by which MET overexpression contributes to TKI-resistant NSCLC remains unclear. MicroRNAs (miRNAs) negatively regulate gene expression and their dysregulation has been implicated in tumorigenesis. To understand the role of microRNAs in TKI-resistant NSCLC, we examined TK receptor-mediated microRNA changes. Here we report that miR-30b/c and miR-221/222, modulated by both EGF and MET receptors, and miR-103, -203, controlled only by MET, play important roles in gefitinib-induced apoptosis and epithelial-mesenchymal transition (EMT) of NSCLC cells, in vitro and in vivo, by inhibiting the expression of Bim, APAF-1, PKC-ε and SRC genes. The finding suggests that modulation of specific microRNAs may provide a therapeutic approach for future treatment of NSCLC.

Preclinical studies have shown that hypomethylating agents reverse platinum resistance in ovarian cancer. In this phase II clinical trial, based upon the results of our phase I dose defining study, we tested the clinical and biologic activity of low-dose decitabine administered before carboplatin in platinum-resistant ovarian cancer patients. Among 17 patients with heavily pretreated and platinum-resistant ovarian cancer, the regimen induced a 35% objective response rate (RR) and progression-free survival (PFS) of 10.2 months, with nine patients (53%) free of progression at 6 months. Global and gene-specific DNA demethylation was achieved in peripheral blood mononuclear cells and tumors. The number of demethylated genes was greater (P < 0.05) in tumor biopsies from patients with PFS more than 6 versus less than 6 months (311 vs. 244 genes). Pathways enriched at baseline in tumors from patients with PFS more than 6 months included cytokine–cytokine receptor interactions, drug transporters, and mitogen-activated protein kinase, toll-like receptor and Jak-STAT signaling pathways, whereas those enriched in demethylated genes after decitabine treatment included pathways involved in cancer, Wnt signaling, and apoptosis (P < 0.01). Demethylation of MLH1, RASSF1A, HOXA10, and HOXA11 in tumors positively correlated with PFS (P < 0.05). Together, the results of this study suggest that low-dose decitabine altered DNA methylation of genes and cancer pathways, restoring sensitivity to carboplatin in patients with heavily pretreated ovarian cancer and resulting in a high RR and prolonged PFS.

These findings suggest that the negative regulatory loop involving miR-221-222 and ERalpha may confer proliferative advantage and migratory activity to breast cancer cells and promote the transition from ER-positive to ER-negative tumors.

The development of targeted therapies for antiestrogenresistant breast cancer requires a detailed understanding of its molecular characteristics. To further elucidate the molecular events underlying acquired resistance to the antiestrogens tamoxifen and fulvestrant, we established drug-resistant sublines from a single colony of hormonedependent breast cancer MCF7 cells. These model systems allowed us to examine the cellular and molecular changes induced by antiestrogens in the context of a uniform clonal background. Global changes in both basal and estrogeninduced gene expression profiles were determined in hormonesensitive and hormonal-resistant sublines using Affymetrix Human Genome U133 Plus 2.0 Arrays. Changes in DNA methylation were assessed by differential methylation hybridization, a high-throughput promoter CpG island microarray analysis. By comparative studies, we found distinct gene expression and promoter DNA methylation profiles associated with acquired resistance to fulvestrant versus tamoxifen. Fulvestrant resistance was characterized by pronounced upregulation of multiple growth-stimulatory pathways, resulting in estrogen receptor A (ERA)-independent, autocrineregulated proliferation. Conversely, acquired resistance to tamoxifen correlated with maintenance of the ERA-positive phenotype, although receptor-mediated gene regulation was altered. Activation of growth-promoting genes, due to promoter hypomethylation, was more frequently observed in antiestrogen-resistant cells compared with gene inactivation by promoter hypermethylation, revealing an unexpected insight into the molecular changes associated with endocrine resistance. In summary, this study provides an in-depth understanding of the molecular changes specific to acquired resistance to clinically important antiestrogens. Such knowledge of resistance-associated mechanisms could allow for identification of therapy targets and strategies for resensitization to these well-established antihormonal agents. (Cancer Res 2006; 66(24): 11954-66)

Fulvestrant is a selective estrogen receptor downregulator (SERD) and highly effective antagonist to hormone-sensitive breast cancers following failure of previous tamoxifen or aromatase inhibitor therapies. However, after prolonged fulvestrant therapy, acquired resistance eventually occurs in the majority of breast cancer patients, due to poorly understood mechanisms. To examine a possible role(s) of aberrantly expressed microRNAs (miRNAs) in acquired fulvestrant resistance, we compared antiestrogen-resistant and -sensitive breast cancer cells, revealing the over-expression of miR-221/222 in the SERD-resistant cell lines. Fulvestrant treatment of estradiol (E2)- and fulvestrant-sensitive MCF7 cells resulted in increased expression of endogenous miR-221/222. Ectopic upregulation of miR-221/222 in estrogen receptor-α (ERα)-positive cell lines counteracted the effects of E2 depletion or fulvestrant-induced cell death, thus also conferring hormone-independent growth and fulvestrant resistance. In cells with acquired resistance to fulvestrant, miR-221/222 expression was essential for cell growth and cell cycle progression. To identify possible miR-221/222 targets, miR-221- or miR-222- induced alterations in global gene expression profiles and target gene expression at distinct time points were determined, revealing that miR-221/222 overexpression resulted in deregulation of multiple oncogenic signaling pathways previously associated with drug resistance. Activation of β-catenin by miR-221/222 contributed to estrogen-independent growth and fulvestrant resistance, whereas TGF-β-mediated growth inhibition was repressed by the two miRNAs. This first in-depth investigation into the role of miR-221/222 in acquired fulvestrant resistance, a clinically important problem, demonstrates that these two ‘oncomirs’ may represent promising therapeutic targets for treating hormone-independent, SERD-resistant breast cancer.