Date Published: July 14, 2017
Publisher: Public Library of Science
Author(s): Eun-Kyung Kim, Jae Hee Cho, EuiJoo Kim, Yoon Jae Kim, Aamir Ahmad.
The regulation of reactive oxygen species (ROS) exists as a therapeutic target for cancer treatments. Previous studies have shown that ursodeoxycholic acid (UDCA) suppresses the proliferation of colon cancer cells. The aim of this study was to evaluate the effect of UDCA upon the proliferation of colon cancer cells as a direct result of the regulation of ROS.
Colon cancer cell lines (HT29 and HCT116) were treated with UDCA. The total number of cells and the number of dead cells were determined using cell counters. A fluorescein isothiocyanate-bromodeoxyuridine flow kit was used to analyze cell cycle variations. Upon exposure to UDCA, the protein levels of p27, p21, CDK2, CDK4 and CDK6 were determined using western blotting, and qRT-PCR was used to determine levels of mRNA. We preformed dichlorofluorescindiacetate (DCF-DA) staining to detect alteration of intracellular ROS using fluorescence activated cell sorting (FACS). Colon cancer stem-like cell lines were generated by tumorsphere culture and treated with UDCA for seven days. The total number of tumorspheres was determined using microscopy.
We found that UDCA reduced the total number of colon cancer cells, but did not increase the number of dead cells. UDCA inhibited the G1/S and G2/M transition phases in colon cancer cells. UDCA induced expression of cell cycle inhibitors such as p27 and p21. However, it was determined that UDCA suppressed levels of CDK2, CDK4, and CDK6. UDCA regulated intracellular ROS generation in colon cancer cells, and induced activation of Erk1/2. Finally, UDCA inhibited formation of colon cancer stem-like cells.
Our results indicate that UDCA suppresses proliferation through regulation of oxidative stress in colon cancer cells, as well as colon cancer stem-like cells.
Colorectal cancer (CRC) is the third-leading diagnosed cancer in males and second-leading diagnosed cancer among females. Diagnosis rates have gradually increased and can be attributed to changes in diet, environmental factors, and genetic susceptibility. Despite advances in screening and treatment, CRC remains a leading cause of cancer-related death. Similar to other solid tumors, the main treatment methods for colon cancer are radiotherapy, surgery, and chemotherapy. Recently, treatment with specific monoclonal antibodies was also applied to advance CRC. However, new drugs or drug targets are needed for better treatment.
Several studies have suggested that UDCA has a chemo-preventive and anticancer effect on gastrointestinal tract cancers that extends beyond its role as a bile acid[16–18]. Wuang et al. reported that UDCA reduces the risk of colon cancer development in a cohort study on liver disease. Akare et al. reported that UDCA exhibits a chemo-preventive effect via modulation of chromatin by inducing hypoacetylation and differentiation of colon cancer cells. Histone deacetylase inhibitor (HDAC) 6 is upregulated by UDCA and plays a role in UDCA-induced senescence, although p53, p21 and Rb were not affected after UDCA treatment. Several UDCA-mediated mechanisms that could potentially repress the growth of cancer cells have been identify, however, the inhibitory molecular mechanism of proliferation by UDCA has not been completely elucidated.