Abstract 2319: Sulforadex targets breast cancer stem-like cells in patient-derived cells and xenograft tumors
Authors: Simões Bruno M. , Alferez Denis , Eyre Rachel , Spence Kath , Santiago-Gomez Angélica , Tanaka Iris , Kohler Bertram , Howat David , Howell Sacha J. , Clarke Robert B. 
Published: August 2015

Sulforadex (SFX) is a novel therapeutic comprising synthetic sulforaphane (SFN) stabilised within α-cyclodextrin. SFN has been studied as an anti-cancer compound for many years however its development has hitherto been hampered due to its inherent instability. Breast cancer stem-like cells (CSCs) have been identified in all molecular subtypes and are believed to be the drivers of breast cancer metastasis. We investigated SFX effects on breast CSC activity using mammosphere formation and aldehyde dehydrogenase (ALDH) activity in patient samples and patient-derived xenograft (PDX) tumours.

Mammosphere formation efficiency (MFE) assessed in cells from primary (n = 12) and metastatic (n = 15) samples treated with SFX (5 μM) or vehicle control (water) showed a significant reduction in breast CSC activity following SFX treatment. A reduction greater than 50% in the MFE was observed in both primary (0.52%±0.06 vs 0.19±0.02, p&lt;0.001) and metastatic (0.93%±0.07 vs 0.43±0.04, p&lt;0.001) cells treated with SFX. Importantly, SFX also inhibits breast CSC activity of early (HBCx34) and metastatic (BB3RC31) patient-derived xenograft (PDX) tumours. Using a 14 day in vivo ‘window’ treatment, we observe that SFX (300mg/Kg/day) decreases ALDH+ cells using ALDEFLUOR assay (HBCx34 6.3%±0.4 vs 3%±0.6, p&lt;0.01; BB3RC31 3%±0.6 vs 1±0.2, p&lt;0.05) and MFE (HBCx34 0.64%±0.09 vs 0.35%±0.03, p&lt;0.01; BB3RC31 0.89%±0.06 vs 0.78±0.04).

The majority of breast cancers express the estrogen receptor (ER) but these hormone-responsive breast cancers frequently develop resistance to hormonal therapies (e.g. tamoxifen). We have established that CSCs in ER+ BC lack ER expression, representing a potential mechanism of therapeutic resistance. However, SFX targets such surviving CSCs identified by ALDH positivity and mammosphere-initiating capacity following tamoxifen treatment in vivo in ER+ PDX tumours. Combinatorial treatment of tamoxifen (10 mg/kg/day) and SFX (300mg/Kg/day) in a 14 day ‘window’ treatment reduced ALDH+ cells (HBCx34 10%±0.4 vs 4.2%±0.4, p&lt;0.01; BB3RC31 11.3%±1.1 vs 6.9±0.6, p&lt;0.05) and MFE (HBCx34 0.81%±0.07 vs 0.34%±0.02, p&lt;0.01; BB3RC31 0.47%±0.06 vs 0.27±0.04, p&lt;0.05) compared to tamoxifen treatment alone. Mechanistically SFX potently inhibited the canonical Wnt pathway in MCF-7 cells and their endocrine-resistant derivatives and future studies will explore SFX activity on other CSC regulatory pathways.

Our data demonstrate that SFX might produce clinically meaningful improvements to endocrine therapy in ER+ BC by reversing CSC mediated resistance. Clinical trials of endocrine therapy in combination with SFX are currently being planned.

Citation Format: Bruno M. Simões, Denis Alferez, Rachel Eyre, Kath Spence, Angélica Santiago-Gomez, Iris Tanaka, Bertram Kohler, David Howat, Sacha J. Howell, Robert B. Clarke. Sulforadex targets breast cancer stem-like cells in patient-derived cells and xenograft tumors. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 2319. doi:10.1158/1538-7445.AM2015-2319