Pterostilbene, a bioactive component of blueberries, suppresses the generation of breast cancer stem cells within tumor microenvironment and metastasis via modulating NF-κB/microRNA 448 circuit

Scope: Tumor-associated macrophages (TAMs) have been shown to promote metastasis and malignancy. Pterostilbene, a natural stilbene isolated from blueberries, has been suggested for anti-cancer effects. Here, we explored the potential cancer stem cells (CSCs)/TAM modulating effects of pterostilbene in breast cancer. Methods and results: Using flowcytometric and Boyden chamber assay, we showed MCF7 and MDA-MB-231 cells cocultured with M2 TAMs exhibited increased percentage of CD44(+)/CD24(-) CSC population and migratory/invasive abilities. RT-PCR results showed that CD44(+)/CD24(-) cells expressed an increased level of HIF-1 alpha, beta-catenin, Twist1, and NF-kappa B and enhanced tumor sphere forming ability. Additionally, pterostilbene treatment dose dependently overcame M2 TAM-induced enrichment of CSCs and metastatic potential of breast cancer cells. Mechanistically, pterostilbene suppressed NF kappa B, Twist1, vimentin, and increased E-cadherin expression. Using siRNA technique, we demonstrated that pterostilbene-mediated NF kappa B downregulation was correlated to an increased amount of microRNA 448. Finally, pterostilbene-mediated suppression in tumorigenesis and metastasis was validated by noninvasive bioluminescence in mice bearing M2 TAM cocultured MDA-MB-231 tumor. Conclusion: Pterostilbene effectively suppresses the generation of CSCs and metastatic potential under the influence of M2 TAMs via modulating EMT associated signaling pathways, specifically NF-kappa B/miR488 circuit. Thus, pterostilbene could be an ideal anti-CSC agent in clinical settings.