Enhancing Chemosensitivity of Breast Cancer Stem Cells by Downregulating SOX2 and ABCG2 Using Wedelolactone-encapsulated Nanoparticles.

A major caveat in the treatment of breast cancer is disease recurrence after therapeutic regime at both local and distal sites. Tumor relapse is attributed to the persistence of chemoresistant cancer stem cells (CSC), which need to be obliterated along with conventional chemotherapy. Wedelolactone, a naturally occurring coumestan, demonstrates anticancer effects in different cancer cells, although with several limitations, and is mostly ineffective against CSCs. To enhance its biological activity in cancer cells and additionally target the CSCs, wedelolactone-encapsulated PLGA nanoparticles (nWdl) were formulated. Initial results indicated that nanoformulation of wedelolactone not only increased its uptake in breast cancer cells and the CSC population, it enhanced drug retention and sustained release within the cells. Enhanced drug retention was achieved by downregulation of SOX2 and ABCG2, both of which contribute to drug resistance of the CSCs. In addition, nWdl prevented epithelial-to-mesenchymal transition, suppressed cell migration and invasion, and reduced the percentage of breast cancer stem cells (BCSC) in MDA-MB-231 cells. When administered in combination with paclitaxel, which is known to be ineffective against BCSCs, nWdl sensitized the cells to the effects of paclitaxel and reduced the percentage of ALDH⁺ BCSCs and mammospheres. Furthermore, nWdl suppressed growth of solid tumors in mice and also reduced CD44⁺/CD24^-/low population. Taken together, our data imply that nWdl decreased metastatic potential of BCSCs, enhanced chemosensitivity through coordinated regulation of pluripotent and efflux genes, and thereby provides an insight into effective drug delivery specifically for obliterating BCSCs.