Abstract 2173: Sulforaphane suppresses the growth of triple-negative breast cancer stem cells in vitro and in vivo
Authors: Castro Nadia P. , Rangel Maria Cristina , Merchant Anand S. , Saylor Karen , Salomon David , Kim Young 
Published: July 2016

Triple-negative breast cancer (TNBC) represents the poorest prognosis among the breast cancer subtypes and no current standard therapy. TNBC tumors are enriched with stem-like cells that are resistant to standard targeted drugs. Thus, it is urgent to develop new agents that are non-toxic and specifically efficacious against these cancer stem cells (CSCs) that are suggested to be responsible for the initiation and maintenance of tumors. Here, we show that sulforaphane (SFN), which is a dietary component abundant in broccoli and its sprouts, inhibits cell proliferation and sphere formation of the CSC population in TNBC cells and also reduces mammary tumor growth.

To evaluate the effects of SFN in TNBC we isolated CSC population from MDA-MB-231 Luci D3H1 human cells using fluorescently activated cell sorting (FACS) analysis. The population containing CD49f+, CD24-/CD44high showed the ability to form mammospheres, which is a characteristic of stemness. When these cells were treated with natural dietary constituent SFN at the concentration of 7.5 μM, they lost the property to form mammospheres in vitro. In vivo, when BalbC/nude mice were supplemented with SFN before and after cell inoculation (daily i.p. injection of 50mg SFN/kg for 5 and 3 weeks respectively), they exhibited reduced tumor volume. The suppressive effect of SFN on the tumor volume was higher when the treatment started before tumor implantation with a thirty percent reduction for pre- (n = 20, 5 weeks) and fourteen for post-treated (n = 20, 3 weeks) group compared to respective controls (saline treated group, n = 20). These results suggest that SFN could be used as a chemopreventive agent considering its nontoxicity and efficacy. Next, we examined the effects of SFN in CSC during tumor growth using a panel of 192 stem cell markers by Nanostring mRNA analysis. The results showed that 95% of the genes were down- regulated in the pre-treatment group (n = 10) compared with the control group (n = 10). Twenty-seven genes presented p value &lt;0.02 and fold change &gt;1.5. We selected 8 genes for further real time validation confirming reduced gene expression of FOXD3, FDZ10, GAS1, WNT3, and NOTCH4 in pre-treatment group (n = 10) compared with control (n = 10). By real time only, we also found the same gene expression pattern for two CSC markers of our interest, CRIPTO-1 and NFkB.

Our results indicated that SFN suppresses the formation of triple negative mammospheres and tumor development both in vitro (7.5uM) and in vivo (50mg/kg) possibly by targeting a CSC population. Further analysis on gene expression revealed that SFN particularly decreased the expression of stem cell markers. These results suggest that the use of SFN for chemoprevention of TNBC is plausible and warrant further clinical evaluation.

Citation Format: Nadia P. Castro, Maria Cristina Rangel, Anand S. Merchant, Karen Saylor, David Salomon, Young Kim. Sulforaphane suppresses the growth of triple-negative breast cancer stem cells in vitro and in vivo. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2173.