Arsenic trioxide inhibits viability of pancreatic cancer stem cells in culture and in a xenograft model via binding to SHH-Gli.

OBJECTIVE: Overexpression of the sonic hedgehog (SHH) signaling pathway is an essential characteristic of pancreatic cancer stem cells (PCSCs) and arsenic trioxide (ATO) is described as a SHH inhibitor. This study evaluates whether ATO has the potential to inhibit viability of PCSCs via binding to SHH-Gli proteins. METHODS: Cell counting kit-8 and flow cytometry were used for analyzing apoptosis in cells in vitro. The animal model was an athymic nude mouse model bearing subcutaneous xenografts of SW1990 pancreatic cancer cells. The terminal deoxynucleotidyl transferase dUTP nick end labeling assay and immunohistochemistry were used for tumor tissue analysis. The interaction between Gli1 and ATO was examined by a confocal system and an ultraviolet absorption spectrum assay. RESULTS: ATO induced apoptosis in pancreatic cancer cells, especially CD24(+)CD44(+) cells in vitro. Combination treatment of ATO and low dose gemcitabine inhibited tumor growth by 60.9% (P = 0.004), and decreased the expression of CD24, CD44, and aldehyde dehydrogenase 1 family, member A1 significantly in vivo. ATO changed the structure of the recombinant Gli1 zinc finger peptides in a cell-free condition and the binding action of ATO to recombinant Gli1 was observed in cultured pancreatic cancer cells. CONCLUSION: ATO may have the potential to inhibit viability of PCSCs via binding to SHH-Gli proteins in vitro and in vivo.

Advances in Smoothened-targeting therapies for pancreatic cancer: implication for drug discovery from herbal medicines.

Smoothened (SMO) is a member of sonic hedgehog homology (SHH) signaling pathway. It plays a key role as a bridge between patched-1 (PTCH-1) and Gli. Aberrant SHH expression can be detected in various malignant tissues, and the expression in pancreatic cancer stem cells is higher apparently. SHH signals are closely associated with self-duplication of cancer stem cells, formation of tumor vessels as well as matrixes. SMO antagonists such as cyclopamine, GDC-0449 and so on show potential to inhibit activity of SHH signaling, and arrest the growth as well as metastases of tumors. Recently, a few of SMO antagonists have been studied in phase I clinical trials and some are in phase II, meanwhile, phase I or II trials of SMO antagonists to treat pancreatic cancer are performed currently. As the classical SMO antagonist, cyclopamine is extracted from a medicinal plant. Perhaps researchers may be able to determine more effective SMO-targeting drugs from herbal medicines in the future.