Cucurbitacin B induces mitochondrial-mediated apoptosis pathway in cholangiocarcinoma cells via suppressing focal adhesion kinase signaling
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Low efficacy and high resistance rate associated with existing chemotherapeutic drugs enforce a requirement for novel therapeutic strategies for extremely aggressive cholangiocarcinoma (CCA). In the present study, the apoptosis-inducing activity of cucurbitacin B, a compound derived from plants of Cucurbitaceae family, against KKU-100 CCA cells and the underlying mechanism mediating its effect were investigated. The results showed that cucurbitacin B significantly decreased CCA cells viability by induction of apoptosis. Increased apoptotic cell death following cucurbitacin B treatment was correlated with caspase-9 and caspase-3 activations, Bax upregulation, increased cytochrome c, apoptosis-inducing factor release, and decreased Bcl-2 and Bcl-XL levels, suggesting activation of the mitochondrial-mediated apoptosis pathway. Further molecular analyses revealed that cucurbitacin B inhibited focal adhesion kinase (FAK), which is an important regulator of the apoptosis process, and its downstream pathway, PI3K/Akt. Knockdown of FAK expression by small interfering RNA appeared to induce CCA cell apoptosis which was accompanied with elevated level of cytochrome c and cleaved caspase-9, and decreased level of Bcl-2, phospho-PI3K, and phospho-Akt. Taken together, cucurbitacin B induces an intrinsic mitochondrial apoptosis pathway in CCA cells partly through suppression of FAK-mediated oncogenic signaling. This compound should be considered as a candidate agent for CCA treatment.
KeywordsCucurbitacin B Cholangiocarcinoma Apoptosis Focal adhesion kinase
The authors would like to thank Prof. James A. Will, University of Wisconsin-Madison, for editing the manuscript via the English Editing Publication Clinic, Faculty of Medicine, Khon Kaen University, Thailand.
SiK and LS conceived and designed research and conducted experiments. VK and AP contributed new reagents or analytical tools. SiK, VK, AP, SaK, and LS analyzed data and interpreted the results. SiK and LS wrote the manuscript. All authors read and approved the manuscript.
This study was supported by the Thailand Research Fund (MRG6080008) and the grant from Khon Kaen University, Thailand (KKU592604). Sirinapha Klungsaeng holds a scholarship from Graduate School, Khon Kaen University, Thailand (581H217).
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Conflict of interest
The authors declare that they have no conflict of interest.
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