The aim of the present study was to clarify the activation of ferroptosis in different breast cancer cells by sulfasalazine (SAS) and to explore the relationship between the estrogen receptor (ER) and the transferrin receptor (TFRC). MDA-MB-231 and T47D cells were treated with SAS for 24 h. Changes in cell morphology were observed under a microscope. CCK-8 was used to detect the proliferation inhibition rate and determine the IC 50 values. Western blotting was used to detect the expression of glutathione peroxidase 4 (GPX4) and xCT. Flow cytometry was used to identify changes in the production of reactive oxygen species (ROS). Mitochondrial morphological changes in T47D were observed using transmission electron microscopy. Changes in the mitochondrial membrane potential (MMP) were observed using confocal fluorescence microscopy. RT-PCR was used to detect the mRNA expression levels of TFRC and divalent metal transporter 1 (DMT1). Bioinformatics analysis was performed on TFRC expression in 1,208 breast cancer samples and its relationship with ER. TFRC expression was detected in various breast cancer tissues using immunohistochemistry and in various breast cancer cells using western blotting. Small interfering RNA (siRNA) knocked down ER expression in T47D cells, and changes in the TFRC mRNA and protein levels were observed. RT-PCR was used to detect TFRC expression in 87 clinical specimens. The results of the present study revealed that SAS could inhibit breast cancer cell viability, which was accompanied by an abnormal increase in ROS and a depletion of GPX4 and system x c-. Liproxstatin-1 reversed the SAS-induced increase in ROS. The cells treated with SAS had shrunken mitochondria and decreased MMP. SAS upregulated TFRC and DMT1. Knockdown of the ER increased TFRC expression in breast cancer cells. Immunohistochemistry indicated that TFRC expression was lower in ER + tissues than in ERtissues. After confirmation with RT-PCR in 87 clinical specimens, TFRC expression in ERtissue was revealed to be significantly higher than that of ER + tissue. In conclusion SAS could trigger ferroptosis in breast cancer cells, especially in cells with low ER expression. Therefore, SAS is a potential agent for breast cancer treatment.

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Background: Triple-negative breast cancer (TNBC) was characterized by breast cancers that do not express estrogen receptor (ER), progesterone receptor (PR), or human epidermal growth factor receptor (HER)-2 genes. TNBC patients are associated with a shorter median time to relapse and death for the lack of available treatment targets. Long non-coding RNAs (LncRNAs) have been reported to play an important role in the development of TNBC. We identified a novel breast-specific long non-coding RNA LINC00993, but less was known about its expression pattern and functional role in TNBC. Methods: LINC00993 RNA expression was detected across different types of clinical breast cancer samples by using qRT-PCR. Bioinformatic methods "guilt by association" and gene set enrichment analysis (GSEA) were used to predict LINC00993 functions. Subcellular localization of LINC00993 in cells was detected by RNA fluorescence in situ hybridization (FISH). Effect of LINC00993 on cell growth was measured by plate colony formation assays, typical growth curve, and an in vivo tumor model. Cell cycle analysis was done by flow cytometry analysis. Key cell cycle regulators were detected by Western blot. Results: LINC00993 was largely downregulated in TNBC, and higher expression indicated better outcome. LINC00993 located mainly in the nucleus. LINC00993 suppressed TNBC growth both in vitro and in vivo. LINC00993 was predicted to be involved in cell cycle pathways by using "guilt by association" and GSEA methods. Key cell cycle regulators like p16 INK4A , p14 ARF , p53, and p21 were affected by LINC00993 overexpression. Conclusions: A new breast-specific lincRNA LINC00993 was identified with a tumorsuppressive feature and with prognostic value. This is the first research on LINC00993 function. Our results suggest that controlling LINC00993 level may be beneficial for breast cancer treatment.

HORMA domain-containing protein 1 (HORMAD1), is normally expressed only in the germline, but is frequently re-activated in human triple-negative breast cancer (TNBC); however, its function in TNBC is largely unknown. In the present study, the expression and biological significance of HORMAD1 in human TNBC was evaluated. Bioinformatics analysis and reverse transcription-quantitative PCR were used to evaluate HORMAD1 expression in datasets and cell lines. HORMAD1 protein expression was detected in TNBC samples using immunohistochemical assays, and the effect of HORMAD1 on cell proliferation was determined using Cell Counting Kit-8, plate colony formation and standard growth curve assays. Cell cycle, reactive oxygen species (ROS) and apoptosis analyses were conducted using flow cytometry. The activity of caspases was measured using caspase activity assay kit. The levels of key apoptosis regulators and autophagy markers were detected by western blot analysis. TNBC cell survival and apoptosis were not influenced by small interfering RNA targeting HORMAD1 alone; however, HORMAD1 knockdown enhanced autophagy and docetaxel (Doc)-induced apoptosis, compared with the control group. Furthermore, higher ROS levels and caspase-3, -8 and -9 activity were detected in MDA-MB-436 TNBC cells with HORMAD1 knockdown upon exposure to Doc. The levels of the induced DNA damage marker γH2AX were also higher, while those of the DNA repair protein RAD51 were lower in TNBC cells with HORMAD1 knockdown compared with the controls. Furthermore, the expression of the autophagy marker P62 was enhanced in MDA-MB-231 cells in response to HORMAD1 overexpression. Notably, Doc-induced apoptosis was similarly increased by both HORMAD1 overexpression and treatment with the autophagy inhibitor, 3-methyladenine (3MA); however, the Doc-induced increase in autophagy was not inhibited by 3MA. The present data indicated that HORMAD1 was involved in autophagy and that the inhibition of autophagy can partially enhance the induction of apoptosis by Doc. The role of HORMAD1 in the DNA damage tolerance of tumor cells may be the main reason for Doc resistance; hence, HORMAD1 could be an important therapeutic target in TNBC.

Tamoxifen (TAM) resistance is a major challenge in the treatment of estrogen receptor-positive (ER +) breast cancer. To date, to the best of our knowledge, there are only a few studies available examining the response of patients with TAM-resistant breast cancer to chemotherapy, and the guidelines do not specify recommended drugs for these patients. In the present study, TAM-resistant cells were shown to exhibit increased proliferation and invasion compared with the parent cells, and the increased expression of c-MYC was demonstrated to play an important role in TAM resistance. Furthermore, the TAM-resistant cells were significantly more sensitive to cisplatin compared with the parent cells, and the silencing of c-MYC expression desensitized the cells to cisplatin through the inhibition of the cell cycle. An increased c-MYC expression was observed in 28 pairs of primary and metastatic tumors from patients treated with TAM, and the clinical remission rate of cisplatin-based chemotherapy was significantly higher compared with other chemotherapy-based regimens in 122 patients with TAM resistant breast cancer. Taken together, the data of the present study demonstrated that although c-MYC was involved in TAM resistance, it increased the sensitivity of ER + breast cancer to cisplatin. Thus, cisplatin may be a preferred chemotherapeutic agent for the treatment of patients with TAM-resistant breast cancer, particularly in patients where the rapid control of disease progression is required.

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