| Summary: | Sinomenine, the main alkaloid extracted from the medicinal plant Sinomenium acutum, is known for its anti-inflammatory effects. Recent studies have suggested its anti-cancer effect in synovial sarcoma, lung cancer and hepatic cancer. However, the underlying molecular mechanism for its anti-cancer effect still remains unclear. This study investigated the anti-tumor activity of sinomenine hydrochloride (SH), a hydrochloride form of sinomenine, in human breast cancer cells in vitro and in vivo. We found that SH potently inhibited cell viability of a broad panel of breast cancer cell lines. Two representative breast cancer cell lines, namely ER(−)/PR(−) MDA-MB-231 and ER(+)/PR(+) MCF-7, were used for further investigation. The results showed that SH induced G1/S cell cycle arrest, caused apoptosis and induced ATM/Chk2- and ATR/Chk1-mediated DNA-damage response in MDA-MB-231 and MCF-7. The anti-cancer effect of SH was regulated by increased expression levels of p-ERK, p-JNK and p-38 MAPK. Further studies showed that SH resulted in an increase in reactive oxygen species (ROS) and inhibition of ROS by N-acetyl-L-cysteine (NAC) almost blocked SH-induced DNA damage but only mitigated SH-induced MAPK expression changes, suggesting that both ROS-dependent and -independent pathways were involved in MAPK-mediated SH-induced breast cancer cell death. The in vivo study demonstrated that SH effectively inhibited tumor growth without showing significant toxicity. In conclusion, SH induced breast cancer cell death through ROS-dependent and -independent pathways with an upregulation of MAPKs, indicating that SH may be a potential anti-tumor drug for breast cancer treatment.
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