Silybum marianum seed disrupts mitosis by reducing polo-like kinase 1 in breast cancer cells

Background: Silybum marianum (SM) seeds contain a family of flavonolignans. Many studies have revealed the role of SM in regulating cancer cell proliferation and apoptosis, but research has rarely focused on the correlation between cancer cell regulation and SM seed (SMS). Breast cancer is the most commonly diagnosed cancer in women worldwide. In addition to clinical treatments, natural products reportedly act as auxiliary agents or treatments for breast cancer. Purpose: This study investigated the effect of SMS water extract (SMSWE) on breast cancer and explored the potential molecular mechanism of its effect. Methods: We used SMSWE to treat breast cancer cells and animals orthotopically injected with breast cancer cells. Results: The results indicated that SMSWE decreased breast cancer cell viability by disrupting mitosis. The mechanism was modulated by the downregulation of proteins involved in spindle assembly, including polo-like kinase 1 (PLK1) and the EXTAH complex (Eg5, XMAP215, Tpx2, Aurora A, and HURP). In mice orthotopically injected with breast cancer cells and treated with SMSWE, tumor growth significantly decreased and PLK1 expression decreased compared with controls. Conclusions: These current evidences provide that SMSWE treatment can decelerate breast cancer cell growth, and the possible mechanism involves mitosis disruption through decreased PLK1 expression.