Dysregulation of the sonic hedgehog (Shh) signaling pathway has been associated with cancer stem cells (CSC) and implicated in the initiation of pancreatic cancer. The lethal nature of pancreatic cancer stems from its propensity to rapidly disseminate accompanied by resistance to current therapies contributes to the high mortality in patients with pancreatic cancer. Thus, the objective of this study was to investigate the role of Shh pathway in pancreatic cancer and to examine the molecular mechanisms by which sulforaphane (SFN), an active compound in cruciferous vegetables, inhibits self-renewal capacity of human pancreatic CSCs. Interestingly, we demonstrate here that Shh pathway is highly activated in pancreatic CSCs and plays important role in maintaining stemness by regulating the expression of stemness genes.
Given the requirement for Hedgehog in pancreatic cancer, we investigated whether hedgehog blockade by SFN could target the stem cell population in pancreatic cancer. In an in vitro model, human pancreatic CSCs derived spheres were significantly inhibited on treatment with SFN, suggesting the clonogenic depletion of the CSCs. Interestingly, SFN inhibited the components of Shh pathway and Gli transcriptional activity. Interference of Shh-Gli signaling significantly blocked SFN-induced inhibitory effects demonstrating the requirement of an active pathway for the growth of pancreatic CSCs. We also show here for the first time, that sulforaphane treatment resulted in a significant reduction in the tumor growth, of orthotopically implanted primary pancreatic CSCs isolated from human pancreatic tumors into the pancreas of NOD/SCID/IL2Rgamma mice, which is mediated through the modulation of Sonic hedgehog-GLI signaling. Hedgehog pathway blockade by SFN at a dose of 20 mg/kg resulted in a 45% reduction in growth of pancreatic cancer tumors. SFN also inhibited downstream targets of Gli transcription by suppressing the expression of pluripotency maintaining factors (Nanog and Oct-4) as well as PDGFRα and Cyclin D1. Furthermore, SFN treatment resulted in a significant reduction in EMT markers Zeb-1, which correlated with increase in E-Cadherin expression suggesting the blockade of signaling involved in early metastasis. Interestingly, SFN downregulated the expression of Bcl-2 and XIAP to induce apoptosis.
Our data reveal the essential role of Shh-Gli signaling in controlling the characteristics of pancreatic CSCs. Such information will not only allow rational design of SFN-based strategies for prevention and/ or treatment of pancreatic cancer but could also facilitate development of mechanism-driven protocols for optimal clinical effects. Thus Sulforaphane potentially represents an inexpensive, safe and effective alternative for the management of pancreatic cancer.
Citation Format: Rakesh Srivastava, Sharmila Shankar. Exploiting sonic hedgehog pathway in pancreatic carcinogenesis as a potential target for chemoprevention. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 4123. doi:10.1158/1538-7445.AM2014-4123