Triple-negative breast cancer: making the most of a misnomer

Overview on Epigenetic Re-programming: A Potential Therapeutic Intervention in Triple Negative Breast Cancers

Breast cancer treatments leads to variable responses. Hormonal therapy is beneficial to receptor positive breast cancer subtypes and display better clinical outcome than triple negative breast cancers (TNBCs) with FEC (5-Fluorouracil, Epirubicin and Cyclophosphamide) the mainstay chemotherapy regiment. Owning to their negative expressions of estrogen (ER), progesterone (PR) and HER2 receptors, disease recurrence and metastasis befalls some patients indicating resistance to FEC. Involvement of epigenetic silencing through DNA methylation, histone methylation, acetylation and sumoylation may be the key player in FEC chemoresistance. Epigenetic and molecular profiling successfully classified breast cancer subtypes, indicating potential driver mechanisms to the progression of TNBCs but functional mechanisms behind chemoresistance of these molecular markers are not well defined. Several epigenetic inhibitors and drugs have been used in the management of cancers but these attempts are mainly beneficial in hematopoietic cancers and not specifically favourable in solid tumours. Hypothetically, upon administration of epigenetic drugs, recovery of tumour suppressor genes is expected. However, high tendency of switching on global metastatic genes is predicted. Polycomb repressive complex (PRC) such as EZH2, SETD1A, DNMT, is known to have repressive effects in gene regulation and shown to inhibit cell proliferation and invasion in breast cancers. Individual epigenetic regulators may be an option to improve chemo-drug delivery in cancers. This review discussed on molecular signatures of various breast cancer subtypes and on-going attempts in understanding underlying molecular mechanisms of epigenetic regulators as well as providing insights on possible ways to utilize epigenetic enzymes/inhibitors with responses to chemotherapeutic drugs to re-program cellular and biological outcome in TNBCs.

Apigenin suppresses the stem cell-like properties of triple-negative breast cancer cells by inhibiting YAP/TAZ activity

Triple-negative breast cancer (TNBC) remains a clinical challenge because of the absence of effective therapeutic targets. In TNBC, overexpression of YAP and TAZ correlates with bioactivities of cancer stem cells (CSCs), high histological grade, resistance to chemotherapy, and metastasis. Thus, YAP/TAZ may serve as potential therapeutic targets in TNBC. To identify YAP/TAZ inhibitors, in previous experiments, we screened a library of natural compounds by using YAP/TAZ luciferase reporter assay and identified apigenin as a potential inhibitor. In this study, we demonstrated that apigenin significantly suppressed the proliferation and migration of TNBC cells. Furthermore, we demonstrated that apigenin inhibited stemness features of TNBC cells in both in vitro and in vivo assays. Our mechanism study demonstrated that apigenin decreased YAP/TAZ activity and the expression of target genes, such as CTGF and CYR61, in TNBC cells. We also showed that apigenin disrupted the YAP/TAZ-TEADs protein-protein interaction and decreased expression of TAZ sensitized TNBC cells to apigenin treatment. Collectively, our studies suggest that apigenin is a promising therapeutic agent for the treatment of TNBC patients with high YAP/TAZ activity.

siRNA-mediated suppression of collagen type iv alpha 2 (COL4A2) mRNA inhibits triple-negative breast cancer cell proliferation and migration

Triple-negative breast cancer (TNBC) is more aggressive than other breast cancer subtypes. Collagen type IV alpha 2 (COL4A2), a major component of the basement membrane, dynamically influences a wide range of biological processes, including cancer pathogenesis and progression. This study evaluated the effects of COL4A2 siRNA delivered by lentiviral vector to TNBC cells. COL4A2 siRNA lenti-viral vector was constructed and transfected into MDA-MB-231 and MDA-MB-468 cells. The COL4A2 mRNA levels were quantified by RT-PCR. CCK8 assay was performed to evaluate cell proliferation and migration. Cell migration and invasion assays were carried out using Transwell. Cell apoptosis and cell cycle analyses were conducted using flow cytometric approach. We found that COL4A2 mRNA levels were significantly down-regulated in MDA-MB-231 and MDA-MB-468 cells after transfection with COL4A2 siRNA. Furthermore, cell migration and proliferation were significantly decreased and the cell cycle was arrested. Our results indicated that COL4A2 siRNA significantly suppresses the migration and proliferation of TNBC cells. Inhibition of COL4A2 may be a new target for the prevention and treatment of TNBC.

"Triple negative breast cancer": Translational research and the (re)assembling of diseases in post-genomic medicine

The paper examines the debate about the nature and status of "Triple-negative breast cancer", a controversial biomedical entity whose existence illustrates a number of features of post-genomic translational research. The emergence of TNBC is intimately linked to the rise of molecular oncology, and, more generally, to the changing configuration of the life sciences at the turn of the new century. An unprecedented degree of integration of biological and clinical practices has led to the proliferation of bio-clinical entities emerging from translational research. These translations take place between platforms rather than between clinical and laboratory settings. The complexity and heterogeneity of TNBC, its epistemic and technical, biological and clinical dualities, result from its multiple instantiations via different platforms, and from the uneven distribution of biological materials, techniques, and objects across clinical research settings. The fact that TNBC comes in multiple forms, some of which seem to be incompatible or, at least, only partially overlapping, appears to be less a threat to the whole endeavor, than an aspect of an ongoing translational research project. Discussions of translational research that rest on a distinction between basic research and its applications fail to capture the dynamics of this new domain of activity, insofar as application is built-in from the very beginning in the bio-clinical entities that emerge from the translational research domain.

Myeloid cell leukemia-1 is an important apoptotic survival factor in triple-negative breast cancer

Breast cancer is the second-most frequently diagnosed malignancy in US women. The triple-negative breast cancer (TNBC) subtype, which lacks expression of the estrogen receptor, progesterone receptor and human epidermal growth factor receptor-2, afflicts 15% of patients and is refractory to current targeted therapies. Like many cancers, TNBC cells often deregulate programmed cell death by upregulating anti-apoptotic proteins of the B-cell CLL/lymphoma 2 (Bcl-2) family. One family member, myeloid cell leukemia-1 (Mcl-1), is commonly amplified in TNBC and correlates with a poor clinical prognosis. Here we show the effect of silencing Mcl-1 and Bcl-2-like protein 1 isoform 1 (Bcl-xL) expression on viability in a panel of seventeen TNBC cell lines. Cell death was observed in a subset upon Mcl-1 knockdown. In contrast, Bcl-xL knockdown only modestly reduced viability, indicating that Mcl-1 is a more important survival factor. However, dual silencing of both Mcl-1 and Bcl-xL reduced viability in most cell lines tested. These proliferation results were recapitulated by BH3 profiling experiments. Treatment with a Bcl-xL and Bcl-2 peptide had only a moderate effect on any of the TNBC cell lines, however, co-dosing an Mcl-1-selective peptide with a peptide that inhibits Bcl-xL and Bcl-2 was effective in each line tested. Similarly, the selective Bcl-xL inhibitor WEHI-539 was only weakly cytotoxic across the panel, but sensitization by Mcl-1 knockdown markedly improved its EC50. ABT-199, which selectively inhibits Bcl-2, did not synergize with Mcl-1 knockdown, indicating the relatively low importance of Bcl-2 in these lines. Mcl-1 sensitivity is not predicted by mRNA or protein levels of a single Bcl-2 family member, except for only a weak correlation for Bak and Bax protein expression. However, a more comprehensive index composed of Mcl-1, Bcl-xL, Bim, Bak and Noxa protein or mRNA expression correlates well with Mcl-1 sensitivity in TNBC and can also predict Mcl-1 dependency in non-small cell lung cancer cell lines.

Combined phosphoproteomics and bioinformatics strategy in deciphering drug resistant related pathways in triple negative breast cancer

Because of the absence of a clear therapeutic target for triple negative breast cancer (TNBC), conventional chemotherapy is the only available systemic treatment option for these patients. Despite chemotherapy treatment, TNBC patients still have worse prognosis when compared with other breast cancer patients. The study is to investigate unique phosphorylated proteins expressed in chemoresistant TNBC cell lines. In the current study, twelve TNBC cell lines were subjected to drug sensitivity assays against chemotherapy drugs docetaxel, doxorubicin, gemcitabine, and cisplatin. Based on their half maximal inhibitory concentrations, four resistant and two sensitive cell lines were selected for further analysis. The phosphopeptides from these cells were enriched with TiO2 beads and fractionated using strong cation exchange. 1,645 phosphoprotein groups and 9,585 unique phosphopeptides were identified by a high throughput LC-MS/MS system LTQ-Orbitrap. The phosphopeptides were further filtered with Ascore system and 1,340 phosphoprotein groups, 2,760 unique phosphopeptides, and 4,549 unique phosphosites were identified. Our study suggested that differentially phosphorylated Cdk5, PML, AP-1, and HSF-1 might work together to promote vimentin induced epithelial to mesenchymal transition (EMT) in the drug resistant cells. EGFR and HGF were also shown to be involved in this process.

Enhancing the antitumor activity of berberine hydrochloride by solid lipid nanoparticle encapsulation

Berberine hydrochloride (BH) is an isoquinolin alkaloid with promising anticancer efficacies. Nevertheless, further development and application of this compound had been hampered by its poor aqueous solubility, low gastrointestinal absorption, and rapid metabolism in the body. In this study, a solid lipid nanoparticle (SLN)-based system was developed for efficient incorporation and persistent release of BH. The drug-loading SLNs (BH-loaded SLNs) were stable, with a mean particle size of 81.42 ± 8.48 nm and zeta potential of -28.67 ± 0.71 mV. BH-loaded SLNs showed desirable drug entrapment efficiency and drug-loaded, and the release of BH from SLNs was significantly slower than free BH. Importantly, our in vitro study indicated that BH-loaded SLNs more significantly inhibited cell proliferation on MCF-7, HepG 2, and A549 cancer cells. Meanwhile, clone formation, cellular uptake, cell cycle arrest, and cell apoptosis studies also demonstrated that BH-loaded SLNs enhanced the antitumor efficacies of BH on MCF-7 cancer cells. Taken together, our results suggest that this SLN formulation may serve as a novel, simple, and efficient system for the delivery of BH.