RETRACTED: Hypoxia-inducible factors are required for chemotherapy resistance of breast cancer stem cells

Abstract

Triple negative breast cancers (TNBCs) are defined by the lack of estrogen receptor (ER), progesterone receptor (PR), and human epidermal growth factor receptor 2 expression, and are treated with cytotoxic chemotherapy such as paclitaxel or gemcitabine, with a durable response rate of less than 20%. TNBCs are enriched for the basal subtype gene expression profile and the presence of breast cancer stem cells, which are endowed with self-renewing and tumor-initiating properties and resistance to chemotherapy. Hypoxia-inducible factors (HIFs) and their target gene products are highly active in TNBCs. Here, we demonstrate that HIF expression and transcriptional activity are induced by treatment of MDA-MB-231, SUM-149, and SUM-159, which are human TNBC cell lines, as well as MCF-7, which is an ER + /PR + breast cancer line, with paclitaxel or gemcitabine. Chemotherapy-induced HIF activity enriched the breast cancer stem cell population through interleukin-6 and interleukin-8 signaling and increased expression of multidrug resistance 1. Coadministration of HIF inhibitors overcame the resistance of breast cancer stem cells to paclitaxel or gemcitabine, both in vitro and in vivo, leading to tumor eradication. Increased expression of HIF-1α or HIF target genes in breast cancer biopsies was associated with decreased overall survival, particularly in patients with basal subtype tumors and those treated with chemotherapy alone. Based on these results, clinical trials are warranted to test whether treatment of patients with TNBC with a combination of cytotoxic chemotherapy and HIF inhibitors will improve patient survival.digoxin | mammary fat pad implantation | tumor relapse

Chemotherapy triggers HIF-1–dependent glutathione synthesis and copper chelation that induces the breast cancer stem cell phenotype

“…Compared with other breast cancer subtypes, xCT and GCLM mRNA levels were significantly increased in basal breast cancers (Fig. S1C), in which hypoxia-inducible factor (HIF)-target gene expression is also increased (10). A detailed comparison of xCT and GCLM mRNA levels with those of CXCR3, L1CAM, BNIP3, PLOD1, P4HA1, P4HA2, VEGFA, SLC2A1, and CA9 mRNA, which are all HIFregulated gene products in TNBC cells, showed a significant correlation of xCT and GCLM expression with six of nine and eight of A B C D E F Fig.…”

“…We recently demonstrated that paclitaxel treatment increases the percentage of BCSCs in a HIF-dependent manner (10). xCT and GCLM expression in breast cancer cell lines is correlated with expression of CD44, an important BCSC marker (20,24).…”

“…In addition, BCSCs have increased resistance to chemotherapy through expression of drug transporter proteins, expression of survival factors, and other mechanisms (7). BCSCs are enriched in response to chemotherapy, further potentiating the risk of tumor recurrence and metastasis (8)(9)(10). The enrichment of BCSCs can be measured by the Aldefluor assay, which is based on the high aldehyde dehydrogenase activity (ALDH) in BCSCs (11), or by the mammosphere assay, which is based on the ability of BCSCs to generate multicellular spheroids in suspension culture (12).…”

“…Hypoxiainducible factors (HIFs) are transcription factors that serve as master regulators of cellular responses to hypoxia (14) and are associated with chemotherapy resistance in breast cancer (10,15). Chemotherapy induces HIF-dependent expression of interleukin (IL)-6 and IL-8, which promote the BCSC phenotype, and of multidrug resistance protein 1 (MDR-1), which mediates chemotherapy efflux from BCSCs, such that the percentage of BCSCs is increased following treatment with paclitaxel or gemcitabine (10). Coadministration of digoxin, which inhibits HIF-1α protein accumulation, blocked chemotherapy-induced expression of IL-6, IL-8, and MDR-1, and blocked BCSC enrichment (10).…”

Hypoxia induces the breast cancer stem cell phenotype by HIF-dependent and ALKBH5-mediated m 6 A-demethylation of NANOG mRNA

“…In hypoxic breast cancer cells, HIFs activate the transcription of target genes that play important roles in tumor growth, angiogenesis, metabolic reprogramming, motility, invasion, metastasis, and resistance to chemotherapy (15,16). Recent studies have demonstrated that HIFs are required for the specification and/or maintenance of BCSCs in response to hypoxia (17)(18)(19)(20)(21) or chemotherapy (22,23), leading to direct or indirect transcriptional regulation of genes encoding the pluripotency factors NANOG, SOX2, and KLF4. In addition, HIF-1α is required for hypoxia-induced epithelial-mesenchymal transition (24), which is also linked to the BCSC phenotype (25).…”