TNBC invasion: downstream of STAT3

Recent advances in targeted strategies for triple-negative breast cancer

Triple-negative breast cancer (TNBC), a highly aggressive subtype of breast cancer, negatively expresses estrogen receptor, progesterone receptor, and the human epidermal growth factor receptor 2 (HER2). Although chemotherapy is the main form of treatment for patients with TNBC, the effectiveness of chemotherapy for TNBC is still limited. The search for more effective therapies is urgent. Multiple targeted therapeutic strategies have emerged according to the specific molecules and signaling pathways expressed in TNBC. These include PI3K/AKT/mTOR inhibitors, epidermal growth factor receptor inhibitors, Notch inhibitors, poly ADP-ribose polymerase inhibitors, and antibody-drug conjugates. Moreover, immune checkpoint inhibitors, for example, pembrolizumab, atezolizumab, and durvalumab, are widely explored in the clinic. We summarize recent advances in targeted therapy and immunotherapy in TNBC, with the aim of serving as a reference for the development of individualized treatment of patients with TNBC in the future.

Zinc complex of 3,5-di-tert-butyl salicylate inhibits viability, migration, and invasion in triple-negative breast cancer cells

The zinc complex of 3,5-di-tert-butyl salicylate (Zn{[CH₃)₃C]₂Sal}₂²⁻) is a zinc ion chelate of salicylate. In this study, we found that this compound inhibits viability, invasion, and migration and induces apoptosis in triple-negative breast cancer 4T1 cells. RNA-seq showed that the expression of 17 genes was upregulated and 26 genes were downregulated significantly by Zn{[CH₃)₃C]₂Sal}₂²⁻ treatment. Further GO and KEGG analysis showed that the activity of Zn{[CH₃)₃C]₂Sal}₂²⁻ against triple-negative breast cancer cells may be involved in the JAK-STAT3, HIF-1, and TNF signaling pathways. The expression of key genes was verified by RT–PCR. The phosphorylation of STAT3 and its upstream SRC decreased drastically upon Zn{[CH₃)₃C]₂Sal}₂²⁻ treatment, as demonstrated by western blot. Our results indicate that Zn{[CH₃)₃C]₂Sal}₂²⁻ inhibits the activity of TNBC cells by downregulating the STAT3 signaling through the SRC pathway.

Anticancer effect of nor-wogonin (5, 7, 8-trihydroxyflavone) on human triple-negative breast cancer cells via downregulation of TAK1, NF-κB, and STAT3

BACKGROUND

Nor-wogonin, a polyhydroxy flavone, has been shown to possess antitumor activity. However, the mechanisms responsible for its antitumor activity are poorly studied. Herein, we investigated the mechanisms of nor-wogonin actions in triple-negative breast cancer (TNBC) cells.

METHODS

Effects of nor-wogonin on cell proliferation and viability of four TNBC cell lines (MDA-MB-231, BT-549, HCC70, and HCC1806) and two non-tumorigenic breast cell lines (MCF-10A and AG11132) were assessed by BrdU incorporation assays and trypan blue dye exclusion tests. Cell cycle and apoptosis analyses were carried out by flow cytometry. Protein expression was analyzed by immunoblotting.

RESULTS

Nor-wogonin significantly inhibited the growth and decreased the viability of TNBC cells; however, it exhibited no or minimal effects in non-tumorigenic breast cells. Nor-wogonin (40 μM) was a more potent anti-proliferative and cytotoxic agent than wogonin (100 μM) and wogonoside (100 μM), which are structurally related to nor-wogonin. The antitumor effects of nor-wogonin can be attributed to cell cycle arrest via reduction of the expression of cyclin D1, cyclin B1, and CDK1. Furthermore, nor-wogonin induced mitochondrial apoptosis, (as evidenced by the increase in % of cells that are apoptotic), decreases in the mitochondrial membrane potential (ΔΨm), increases in Bax/Bcl-2 ratio, and caspase-3 cleavage. Moreover, nor-wogonin attenuated the expression of the nuclear factor kappa-B and activation of signal transducer and activator of transcription 3 pathways, which can be correlated with suppression of transforming growth factor-β-activated kinase 1 in TNBC cells.

CONCLUSION

These results showed that nor-wogonin might be a potential multi-target agent for TNBC treatment.

Ganoderma lucidum extract (GLE) impairs breast cancer stem cells by targeting the STAT3 pathway

The aggressive nature of triple negative breast cancer (TNBC) may be explained in part by the presence of breast cancer stem cells (BCSCs), a subpopulation of cells, which are involved in tumor initiation, progression, metastasis, recurrence, and therapy resistance. The signal transducer and activator of transcription 3 (STAT3) pathway participates in the development and progression of BCSCs, but its role in TNBC remains unclear. Here, we report that Ganoderma lucidum extract (GLE), a medicinal mushroom with anticancer activity, acts on BCSCs in vitro and in TNBC pre-clinical animal tumor models by downregulating the STAT3 pathway. We show that GLE significantly reduces TNBC cell viability, and down-regulates total and phosphorylated STAT3 expression. This is consistent with the reduction of OCT4, NANOG and SOX2 expression, reduction in the BCSC population by loss of the ALDH1 and CD44⁺/CD24^– population, the deformation of mammospheres, and the strong reduction in animal tumor volume and tumor weight. Analysis of the BCSC compartment in tumors revealed that GLE decreases the STAT3 pathway and the expression of OCT4, NANOG, and SOX2 in BCSCs. These findings demonstrate that the anti-cancer activity of GLE targets BCSCs of TNBC through the downregulation of the STAT3 pathway.