Breast cancer (BC) is the most common cause of cancer-related death in females in Saudi Arabia. BC in Saudi women tend to behave more aggressively than breast cancer in the West. Therefore, identification of new molecular targets and treatment strategies are highly warranted to improve patient outcome. FoxM1 has been shown to play a critical role in pathogenesis of various malignancies. In this study, we explored the prevalence and clinical implication of FoxM1 overexpression in Saudi breast cancer. FoxM1 protein overexpression was seen in 79% (770/975) of BC tissues and was associated with aggressive clinical parameters such as younger age (< 30 yrs) (p = 0.0172), high grade (p < 0.0001), mucinous histology (p < 0.0001) and triple negative phenotype (p < 0.0001). Overexpression of FoxM1 was significantly associated with activated AKT (p < 0.0001), Ki67 expression (p < 0.0001), VEGF (p < 0.0001), MMP-9 (p < 0.0001), XIAP (p < 0.0001) and Bcl-xL (p = 0.0300). Importantly, FoxM1 overexpression is found to be an independent prognostic marker in multivariate analysis in advanced stage (Stage III and IV) breast cancer (p = 0.0298). In vitro data using BC cell lines showed that down-regulation of FoxM1 using specific inhibitor, thiostrepton or siRNA inhibited cell migration, invasion and angiogenesis. In addition, treatment of BC cell lines with thiostrepton resulted in inhibition of proliferation and induction of apoptosis in a dose-dependent manner. In vivo, thiostrepton treatment regressed MDA-MB-231 cells generated xenografts via down-regulation of FoxM1 and its downstream targets. Our results suggest that FoxM1 may be a potential therapeutic target for the treatment of aggressive breast cancers.
Keywords: FoxM1; apoptosis; breast cancer; invasion; thiostrepton.