The opposing effects of interferon-beta and oncostatin-M as regulators of cancer stem cell plasticity in triple-negative breast cancer.

BACKGROUND: Highly aggressive, metastatic and therapeutically resistant triple-negative breast cancers (TNBCs) are often enriched for cancer stem cells (CSC). Cytokines within the breast tumor microenvironment (TME) influence the CSC state by regulating tumor cell differentiation programs. Two prevalent breast TME cytokines are oncostatin-M (OSM) and interferon-ß (IFN-ß). OSM is a member of the IL-6 family of cytokines and can drive the de-differentiation of TNBC cells to a highly aggressive CSC state. Conversely, IFN-ß induces the differentiation of TNBC, resulting in the repression of CSC properties. Here, we assess how these breast TME cytokines influence CSC plasticity and clinical outcome. METHODS: Using transformed human mammary epithelial cell (HMEC) and TNBC cell models, we assessed the CSC markers and properties following exposure to OSM and/or IFN-ß. CSC markers included CD24, CD44, and SNAIL; CSC properties included tumor sphere formation, migratory capacity, and tumor initiation. RESULTS: There are three major findings from our study. First, exposure of purified, non-CSC to IFN-ß prevents OSM-mediated CD44 and SNAIL expression and represses tumor sphere formation and migratory capacity. Second, during OSM-induced de-differentiation, OSM represses endogenous IFN-ß mRNA expression and autocrine/paracrine IFN-ß signaling. Restoring IFN-ß signaling to OSM-driven CSC re-engages IFN-ß-mediated differentiation by repressing OSM/STAT3/SMAD3-mediated SNAIL expression, tumor initiation, and growth. Finally, the therapeutic use of IFN-ß to treat OSM-driven tumors significantly suppresses tumor growth. CONCLUSIONS: Our findings suggest that the levels of IFN-ß and OSM in TNBC dictate the abundance of cells with a CSC phenotype. Indeed, TNBCs with elevated IFN-ß signaling have repressed CSC properties and a better clinical outcome. Conversely, TNBCs with elevated OSM signaling have a worse clinical outcome. Likewise, since OSM suppresses IFN-ß expression and signaling, our studies suggest that strategies to limit OSM signaling or activate IFN-ß signaling will disengage the de-differentiation programs responsible for the aggressiveness of TNBCs.

The Critical, Clinical Role of Interferon-Beta in Regulating Cancer Stem Cell Properties in Triple-Negative Breast Cancer.

Triple-negative breast cancer (TNBC) the deadliest form of this disease currently lacks a targeted therapy and is characterized by increased risk of metastasis and presence of therapeutically resistant cancer stem cells (CSC). Recent evidence has demonstrated that the presence of an interferon (IFN)/signal transducer of activated transcription 1 (STAT1) gene signature correlates with improved therapeutic response and overall survival in TNBC patients. In agreement with these clinical observations, our recent work has demonstrated, in a cell model of TNBC that CSC have intrinsically repressed IFN signaling. Administration of IFN-ß represses CSC properties, inducing a less aggressive non-CSC state. Moreover, an elevated IFN-ß gene signature correlated with repressed CSC-related genes and an increased presence of tumor-infiltrating lymphocytes in TNBC specimens. We therefore propose that IFN-ß be considered as a potential therapeutic option in the treatment of TNBC, to repress the CSC properties responsible for therapy failure. Future studies aim to improve methods to target delivery of IFN-ß to tumors, to maximize therapeutic efficacy while minimizing systemic side effects.

Interferon-beta represses cancer stem cell properties in triple-negative breast cancer.

Triple-negative breast cancer (TNBC), the deadliest form of this disease, lacks a targeted therapy. TNBC tumors that fail to respond to chemotherapy are characterized by a repressed IFN/signal transducer and activator of transcription (IFN/STAT) gene signature and are often enriched for cancer stem cells (CSCs). We have found that human mammary epithelial cells that undergo an epithelial-to-mesenchymal transition (EMT) following transformation acquire CSC properties. These mesenchymal/CSCs have a significantly repressed IFN/STAT gene expression signature and an enhanced ability to migrate and form tumor spheres. Treatment with IFN-beta (IFN-ß) led to a less aggressive epithelial/non-CSC-like state, with repressed expression of mesenchymal proteins (VIMENTIN, SLUG), reduced migration and tumor sphere formation, and reexpression of CD24 (a surface marker for non-CSCs), concomitant with an epithelium-like morphology. The CSC-like properties were correlated with high levels of unphosphorylated IFN-stimulated gene factor 3 (U-ISGF3), which was previously linked to resistance to DNA damage. Inhibiting the expression of IRF9 (the DNA-binding component of U-ISGF3) reduced the migration of mesenchymal/CSCs. Here we report a positive translational role for IFN-ß, as gene expression profiling of patient-derived TNBC tumors demonstrates that an IFN-ß metagene signature correlates with improved patient survival, an immune response linked with tumor-infiltrating lymphocytes (TILs), and a repressed CSC metagene signature. Taken together, our findings indicate that repressed IFN signaling in TNBCs with CSC-like properties is due to high levels of U-ISGF3 and that treatment with IFN-ß reduces CSC properties, suggesting a therapeutic strategy to treat drug-resistant, highly aggressive TNBC tumors.

Cancer Stem Cell Plasticity Drives Therapeutic Resistance.

The connection between epithelial-mesenchymal (E-M) plasticity and cancer stem cell (CSC) properties has been paradigm-shifting, linking tumor cell invasion and metastasis with therapeutic recurrence. However, despite their importance, the molecular pathways involved in generating invasive, metastatic, and therapy-resistant CSCs remain poorly understood. The enrichment of cells with a mesenchymal/CSC phenotype following therapy has been interpreted in two different ways. The original interpretation posited that therapy kills non-CSCs while sparing pre-existing CSCs. However, evidence is emerging that suggests non-CSCs can be induced into a transient, drug-tolerant, CSC-like state by chemotherapy. The ability to transition between distinct cell states may be as critical for the survival of tumor cells following therapy as it is for metastatic progression. Therefore, inhibition of the pathways that promote E-M and CSC plasticity may suppress tumor recurrence following chemotherapy. Here, we review the emerging appreciation for how plasticity confers therapeutic resistance and tumor recurrence.