Interdisciplinary Approaches for Molecular and Cellular Life Sciences Expansion of Breast Cancer Stem Cells with Fi Brous Scaff Olds M E D L I N E ! Expansion of Breast Cancer Stem Cells with Fibrous Scaffolds †

a Cancer stem cells (CSCs) are hypothesized as tumor-initiating cells within tumors and main contributors of tumor growth, metastasis and recurrence. Mammary cancer cells, MCF-7 cells, were cultured on 3D polycaprolactone (PCL) fibrous scaffolds, showing an increased proportion of CSCs. The expression of stem cell markers, including OCT3/4 and SOX2, and breast CSC-specific markers, SOX4 and CD49f, was significantly upregulated, and the mammosphere-forming capability in cells cultured on PCL fibrous scaffolds increased. The fibrous scaffolds also induced the elongation of MCF-7 cells and extended cell proliferation. The increase of CSC properties after being cultured on fibrous scaffolds was further confirmed with two luminal-type mammary cell lines, T47D and SK-BR-3, and a basal-type cell line, MDA-MB-231, by ALDEFLUOR assay and mammosphere formation assay. Moreover, we observed the upregulation of epithelial to mesenchymal transition and increased invasive capability in cells cultured on PCL fibrous scaffolds. These data suggest that the increase of CSC proportion in a 3D culture system may account for the enhanced malignancy. Therefore, our PCL fibrous scaffolds can potentially be used for CSCs enrichment and anti-cancer drug screening. Three dimensional (3D) culture systems have been utilized in studies of cancer metastasis and anti-tumor drug screening. Accumulating evidence indicates that cancer cells in 3D culture displayed higher malignancy and invasive capability compared to their counterparts in two-dimensional culture. In the present paper, we have fabricated a 3D polycaprolactone fibrous scaffold using an electrospinning process to evaluate how CSCs proportion in breast cancer cell lines responds to this 3D culture. Functional assay and gene profiling together indicate that culture on fibrous scaffolds increased CSCs and induced epithelial-mesenchymal-transition. This work provides a better understanding of how a 3D culture condition affects cancer cells behavior as a mixture of CSCs and non-CSCs. Thus, this knowledge potentially enlightens the design of novel biomaterials for the enrichment of CSCs, and eventually for drug screening targeting CSCs.