Abstract 3687: Benzyl isothiocyanate downregulates Ronβ and sfRon to inhibit self-renewal of breast cancer stem cells.

Abstract

Abstract Recent studies suggest that cancer stem cells play a major role not only in the initiation and maintenance of breast cancer but also in clinical response to therapy. Breast cancer stem cells (bCSC) are characterized by their ability to self-renew (asymmetrical division into a daughter bCSC and a progeny), form spheres under ultra-low attachment conditions in vitro, and express unique cell-surface markers (eg, CD44, ESA). Elimination of both therapy-resistant bCSC and therapy-sensitive epithelial tumor cells may be required for effective prevention of breast cancers. We have shown previously that dietary administration of benzyl isothiocyanate (BITC), a small molecule constituent of many edible cruciferous vegetables (eg, garden cress), significantly inhibits mammary cancer development in a transgenic mouse model (MMTV-neu) in association with apoptosis induction and tumor infiltration of T cells. The present study was undertaken to determine the effect of BITC on bCSC. Exposure of MCF-7 (an estrogen-responsive cell line) and SUM159 (a triple-negative cell line) human breast cancer cells to pharmacologic doses of BITC (0.5-2.5 μM) resulted in inhibition of mammosphere formation (first generation after BITC treatment and subsequent generations without BITC treatment), aldehyde dehydrogenase 1 (ALDH1) activity, and CD44high/CD24low/ESA+ population. Inhibition of bCSC self-renewal resulting from BITC exposure was accompanied by down-regulation of urokinase-type plasminogen activator (uPAR), Bmi-1, and Ron (Ronβ and sfRon) proteins in vitro and in MDA-MB-231 xenografts in vivo (uPAR and Bmi-1). Ectopic expression of uPAR alone was sufficient to drive stemness in MCF-7 and MDA-MB-468 cells. However, the BITC-mediated inhibition of mammosphere formation and ALDH1 activity was sustained even after stable overexpression of uPAR in MCF-7 or MDA-MB-468 cells. Similarly, Bmi-1 overexpression was largely dispensable for BITC-mediated suppression of bCSC. On the other hand, overexpression of Ron (full-length) as we as sfRon in MCF-7 cells conferred significant protection against BITC-mediated inhibition of bCSC self-renewal. Ectopic expression of sfRon, but not Ron, resulted in nearly 4-fold increase in ALDH1 activity compared with control cells. Novel conclusions of the present study are: (a) overexpression of sfRon is sufficient to drive stemness at least in MCF-7 cells (b) mammary cancer prevention by BITC likely involves removal of bCSC, and (c) BITC-mediated inhibition of bCSC is caused by suppression of Ron signaling. This study was supported by the grant CA129347-06 awarded by the National Cancer Institute. Citation Format: Su-Hyeong Kim, Anuradha Sehrawat, Shivendra V. Singh. Benzyl isothiocyanate downregulates Ronβ and sfRon to inhibit self-renewal of breast cancer stem cells. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3687. doi:10.1158/1538-7445.AM2013-3687