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

Abstract

ObjectiveOverexpression 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.MethodsCell 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.ResultsATO 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.ConclusionATO may have the potential to inhibit viability of PCSCs via binding to SHH-Gli proteins in vitro and in vivo.

Arsenic Attenuates GLI Signaling, Increasing or Decreasing its Transcriptional Program in a Context-Dependent Manner

“…We have previously shown, and also demonstrate here, that short and long-term exposure to arsenic activates GLI signaling. However, a number of other groups have argued that arsenic attenuates GLI signaling rather than activates it (Fei et al, 2010;Kim et al, 2010Kim et al, , 2013Beauchamp et al, 2011;Han et al, 2013;Nakamura et al, 2013;Yang et al, 2013;You et al, 2014). We now show, in agreement with these previous groups, that arsenic can also antagonize GLI/HH signaling.…”

“…We further showed that arsenic exposure levels are positively associated with HH pathway activity in human bladder cancer, a malignancy previously linked to chronic arsenic exposure (Fei et al, 2010). More recently, other reports have shown that arsenic inhibits HH signaling initiated by either HH treatment or high GLI levels, and researchers concluded that arsenic is a functional inhibitor of HH/GLI signaling (Kim et al, 2010(Kim et al, , 2013Beauchamp et al, 2011;Han et al, 2013;Nakamura et al, 2013;Yang et al, 2013;You et al, 2014). Here, we provide in vitro and in vivo evidence suggesting that arsenic can both activate and inhibit GLI signaling, with the direction of GLI modulation dictated primarily by the starting levels of intrinsic GLI activity.…”

“…It is therefore unlikely that differential expression levels of arsenic transporters or arsenite methyltransferase is the primary mechanism responsible for the dual regulatory capacity of GLI/HH signaling by arsenic, at least in a single cell line. However, we cannot rule out that organic arsenic metabolites may be involved in the regulation of GLI activity by arsenic in more complicated systems such as human cancer patient samples, although inorganic arsenic has been reported to directly bind to GLI proteins (Beauchamp et al, 2011;Han et al, 2013), suggesting that inorganic arsenic is the main active arsenic species that modulates GLI activity.…”

Synergism between arsenic trioxide and cyclopamine in the inhibition of PC3 cell survival via the Hedgehog signaling pathway

“…Furthermore, most of Hh antagonists target Smo receptor and little target the signaling components down-stream of Smo, such as fused homolog (Sufu) or GLI [50,51]. A few recent studies have demonstrated that ATO interferes with GLI proteins in the context of a dysregulated Hh signaling pathway in many human cancers, including malignant rhabdoid tumors, pancreatic cancer stem cells, acute promyelocytic leukemia, osteosarcoma and medulloblastoma [24][25][26][27]52]. Importantly, the study of Beauchamp has shown that the underlying mechanism of the anti-tumor effect of ATO is likely through direct binding and inhibition of GLI1 and/or GLI2 transcriptional activity [29].…”

“…These evidences strongly raise the possibility of the application of ATO in teatment of PCa. A few studies have reported that ATO could inhibit tumor cell growth by blocking Hh pathway in rhabdoid tumor, osteosarcoma, Ewing sarcoma, pancreatic cancer stem cells and APL patients [24][25][26][27][28][29]. Furthermore, ATO has been established as a Hh pathway inhibitor [29] and a promising anti-tumor agent for Hedgehog-driven cancers [30].…”