Epithelioid and fibroblastoid subsets coexist in the human sarcomatoid renal cell carcinoma (sRCC) cell line, RCC52, according to previous clonal studies. Herein, using monoclonal antibodies to CD44 and CD24 markers, we identified and isolated these two populations, and showed that CD44bright/CD24dim and CD44bright/CD24bright phenotypes correspond to epithelioid and fibroblastoid subsets, respectively. Both sorted subsets displayed different levels of tumorigenicity in xenotransplantation, indicating that each harbored its own cancer stem cells (CSCs). The CD44bright/CD24bright subset, associated with higher expression of MMP-7, -8 and TIMP-1 transcripts, showed greater migratory/invasive potential than the CD44bright/CD24dim subset, which was associated with higher expression of MMP-2, -9 and TIMP-2 transcripts. Both subsets differentially expressed stemness gene products c-Myc, Oct4A, Notch1, Notch2 and Notch3, and the RCC stem cell marker, CD105 in 4-5% of RCC52 cells. These results suggest the presence of CSCs in both sRCC subsets for the first time and should therefore be considered potential therapeutic targets for this aggressive malignancy.

As our understanding of cancer stem cell (CSC) biology improves, search for inhibitory agents of CSCs and metastatic CSCs (mCSCs) positive for CXCR4 is warranted. Withaferin A (WA), a withanolide extracted from the medicinal plant Withania somnifera, has been shown to exhibit anti-cancer effects through multiple mechanisms. Whether WA could selectively target CSCs, mCSCs, or non-CSCs of a gastrointestinal (GI) carcinoma tumor remains unclear. Methods: Side-population (SP) analysis, flow cytometric phenotyping and sorting, non-invasive imaging in conjunction with xenotransplantation, and immunohistology were used in this investigation. Results: Using the lymph node metastatic GI cancer cell line UP-LN1, consisting of CD44 high /CD24 low floating (F) and CD44 low /CD24 high adherent (A) cell subsets, this study demonstrated that as compared with parental UP-LN1 cells or A cells, WA preferentially reduced F-cell proliferation, tumor sphere formation, and SP cells in vitro in greater effi ciencies by apoptosis. This action was mechanistically mediated via the down-regulation of CXCR4/CXCL12 and STAT3/interleukin-6 axes, both of which are instrumental in the acquisition of metastatic ability. Attenuation of interferon-γ-induced CXCR4 expression in F cells by knockdown with siRNA or blocking with an anti-CXCR4 antibody, followed by Western blot analysis, showed signifi cantly reduced metastatic potential in vitro. The extent of in vitro anti-invasive effect of WA on the IFN-γ-treated F cells was signifi cantly greater than on the F cells without WA treatment, or F cells treated with control siRNA or with control IgG antibody. The observed in vitro effects of WA on the CSC and mCSC targeting were validated by data obtained with non-invasive imaging in NOD/SCID mouse xenotransplantation. Conclusion: WA could effi ciently block the formation of both CSCs and mCSCs in the UP-LN1 cell line, suggesting that WA may be considered an effective therapeutic agent for this type of GI malignancies.