Sonic Hedgehog Signaling Inhibition Provides Opportunities for Targeted Therapy by Sulforaphane in Regulating Pancreatic Cancer Stem Cell Self-Renewal

Abstract

Dysregulation of the sonic hedgehog (Shh) signaling pathway has been associated with cancer stem cells (CSC) and implicated in the initiation of pancreatic cancer. Pancreatic CSCs are rare tumor cells characterized by their ability to self-renew, and are responsible for tumor recurrence accompanied by resistance to current therapies. The lethality of these incurable, aggressive and invasive pancreatic tumors remains a daunting clinical challenge. 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. 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 induced apoptosis by inhibition of BCL-2 and activation of caspases. Our data reveal the essential role of Shh-Gli signaling in controlling the characteristics of pancreatic CSCs. We propose that pancreatic cancer preventative effects of SFN may result from inhibition of the Shh pathway. Thus Sulforaphane potentially represents an inexpensive, safe and effective alternative for the management of pancreatic cancer.

Deguelin inhibits proliferation and migration of human pancreatic cancer cells in vitro targeting hedgehog pathway

“…The components of the Shh pathway are highly expressed in PC cell lines (28,29). Our results revealed that deguelin inhibits PC cells proliferation by suppressing the Hh pathway.…”

Dietary Sulforaphane in Cancer Chemoprevention: The Role of Epigenetic Regulation and HDAC Inhibition

“…After sulforaphane treatment, inhibition of SHH signaling has been demonstrated, and may contribute to the regulation of the self-renewal capacity of human pancreatic cancer stem cells (167,233). In an in vitro model, sulforaphane was shown to inhibit the SHH signaling pathway, and reduced the expression of Smo, Gli1, and Gli2 (233).…”

New insights into pancreatic cancer stem cells

“…Recently, mounting evidence supports hedgehog signaling activation in pancreatic CSCs. Hedgehog pathway plays a significant role by regulating pluripotency maintaining factors like Oct4, Nanog, c-Myc, and Sox2 to the maintenance of stemness [61][62][63][64][65][66] . Apart from hedgehog, increasing evidence suggests that Notch signaling activation was associated with molecular characteristics of CSCs in PC cases [67,68] .…”

“…More preclinical animal and human clinical studies are warranted to evaluate the drugs for their specificity in targeting CSCs to inhibit the progression of PC. Combination of epigallocatechin-3 gallate (EGCG) and quercetin, and, Sulforaphane inhibited the selfrenewal capacity of pancreatic CSCs via attenuation of the Hedgehog pathway [62][63][64][65] . The GANT-61 is a Gli transcription factor inhibitor that inhibits pancreatic CSC viability and induces apoptosis [61] .…”