[Frontiers in Bioscience E3, 515-528, January 1, 2011]

Sulforaphane synergizes with quercetin to inhibit self-renewal capacity of pancreatic cancer stem cells

Rakesh K. Srivastava1, Su-Ni Tang1, Wenyu Zhu1, Daniel Meeker1, Sharmila Shankar2

1Department of Pharmacology, Toxicology and Therapeutics, and Medicine, The University of Kansas Cancer Center, The University of Kansas Medical Center, 3901 Rainbow Boulevard, Kansas City, KS, 66160, USA, 2Department of Pathology and Laboratory Medicine, The University of Kansas Cancer Center, The University of Kansas Medical Center, 3901 Rainbow Boulevard, Kansas City, KS, 66160, USA

TABLE OF CONTENTS

1. Abstract
2. Introduction
3. Materials and Methods
3.1. Reagents
3.2. Cell culture 3.3. Tumor spheroid assay 3.4. Soft agar colony assay for assessment of tumorigenic potential in vitro
3.5. Lentiviral vector-mediated transduction of pancreatic cancer stem cells
3.6. Western blot analysis
3.12. Statistical analysis
4. Results
4.1. Sulforaphane inhibits the growth of cancer stem cells isolated from human pancreatic cancer cell lines.
4.2. Sulforaphane inhibits the formation of primary and secondary tumor spheroids and cell viability of pancreatic cancer stem cells
4.3. Sulforaphane inhibits the growth of colonies formed by pancreatic cancer stem cells
4.4. Inhibition of Nanog enhances the effects of sulforaphane on spheroid formation by human pancreatic cancer stem cells
4.5. Sulforaphane inhibits the expression of XIAP and Bcl-2 and phosphorylation of FKHR, and cleaves caspase-3 in human pancreatic cancer stem cells
4.6. Sulforaphane inhibits the expression of epithelial-mesenchymal transition markers (EMT) in human pancreatic cancer stem cells
4.7. Quercetin enhances the effects of sulforaphane on spheroid and colony formation by pancreatic cancer stem cells
5. Discussion
6. Acknowledgements
7. References

1. ABSTRACT

According to the cancer stem cell hypothesis, the aggressive growth and early metastasis of cancer may arise through dysregulation of self-renewal of stem cells. The objectives of this study were to examine the molecular mechanisms by which sulforaphane (SFN, an active compound in cruciferous vegetables) inhibits self-renewal capacity of pancreatic cancer stem cells (CSCs), and synergizes with quercetin, a major polyphenol and flavonoid commonly detected in many fruits and vegetables. Our data demonstrated that SFN inhibited self-renewal capacity of pancreatic CSCs. Inhibition of Nanog by lentiviral-mediated shRNA expression enhanced the inhibitory effects of sulforaphane on self-renewal capacity of CSCs. SFN induced apoptosis by inhibiting the expression of Bcl-2 and XIAP, phosphorylation of FKHR, and activating caspase-3. Moreover, SFN inhibited expression of proteins involved in the epithelial-mesenchymal transition (β-catenin, vimentin, twist-1, and ZEB1), suggesting the blockade of signaling involved in early metastasis. Furthermore, the combination of quercetin with SFN had synergistic effects on self-renewal capacity of pancreatic CSCs. These data suggest that SFN either alone or in combination with quercetin can eliminate cancer stem cell-characteristics.