cytoskeleton br Conflicts of interest br Acknowledgements Th
Conflicts of interest
Acknowledgements This work was supported, in part or in whole, by the grants from the National Natural Science Foundation of China (11802056, 11772088), the China Postdoctoral Science Foundation (2018M640904), and the Fundamental Research Funds for the Central Universities (ZYGX2017KYQD180).
Introduction Breast cancer is the leading malignant tumor in women worldwide . It has been demonstrated that there are multiple hallmarks in cancer cells, including sustained proliferation signaling, especially in triple-negative breast cancer (TNBC) . TNBC, is one of the molecular types of breast cancer, and does not respond to endocrine therapy and anti-human epidermal growth factor receptor 2 (HER2) therapy, as it does not express the estrogen receptor (ER), progesterone receptor (PR) or HER2. As a result, TNBC has the highest risk of recurrence of all breast cancers; therefore, the identification of potential adjuvant therapy for TNBC is essential . It is well known that Akt and ERK signaling are dysregulated or mutated in breast cancers, especially in TNBC [, , , ]. Downregulation of phosphorylated Akt or ERK levels induce cell apoptosis, cytoskeleton arrest and cell senescence in several cancers, including breast cancer [, , , , , ]. However, the crosstalk between these two signaling pathways may lead to attenuation of the effect of single inhibition . This suggests that dual inhibition of Akt and ERK signaling may achieve greater induction of cellular senescence and tumor suppression than single inhibition . Norcantharidin (NCTD), the demethylated analog of cantharidin, retains the antitumor features of cantharidin with less toxicity . It was demonstrated that NCTD suppresses tumor cell proliferation, cell migration and invasion, and induces cell apoptosis and cell cycle arrest by inhibiting the Akt or ERK signaling pathways in several carcinomas [, , ]. Moreover, NCTD inhibits tumor growth and angiogenesis by abrogating the ERK signaling pathway, but has little effect on the phosphorylation of Akt . Furthermore, NCTD induces cell senescence by repressing YAP signaling in non-small lung cancer cells . However, there is little research concerning the effect of NCTD on TNBC. In addition, crosstalk between the Akt and ERK signaling pathwaysin cell senescence and how to simultaneously suppress Akt and ERK signaling are unclear in TNBC. In this study, we demonstrate that NCTD induces cell senescence, cell apoptosis and cell cycle arrest by simultaneously down-regulating the Akt and ERK signaling pathways in vitro and in vivo. However, NCTD upregulates the level of soluble signaling factors of the senescence-associated secretory phenotype (SASP) in a NF-κB-independent manner. These findings suggest that NCTD may be used as a potential adjuvant therapy for TNBC.
Materials and methods
Discussion It is well known that Akt and ERK signaling are crucial regulators in cell biological processes such as the cell cycle, proliferation, survival, cell senescence and metabolism, and are mutated, self-activated and interact with each other in breast cancer, especially in triple-negative breast cancer (TNBC) [, , , ]. Due to the complexity of signaling pathways, inhibition of one signaling pathway may cause compensatory activation of other signaling pathways . As a result, how to simultaneously suppress Akt and ERK signaling is unclear. In this study, the results showed that norcantharidin (NCTD) suppressed cell proliferation in vitro and in vivo, and induced cell apoptosis, cell cycle arrest and cell senescence mainly by simultaneously suppressing pAkt and pERK1/2 signaling and activating p21 and p16. Following the confirmation of potential crosstalk of the pAkt and pERK1/2 signaling pathways, the combination of LY294002 and U0126 was assessed and was shown to induce a similar effect to that of NCTD. These findings indicate that NCTD induces cell apoptosis, cell cycle arrest and cell senescence mainly via dual inhibition of pAkt and pERK1/2 signaling in TNBC.