Anti-cancer effect of cucurbitacin B on cholangiocarcinoma cells

The treatment of cholangiocarcinoma (CCA) is still ineffective and the search for a novel and more effective treatment is required. Cucurbitacin B (CuB) is a natural tetracyclic triterpene that possesses anti-cancer activity across a wide array of cancers. In this study, we explored the effect of CuB isolated from the Thai herb Trichosanthes cucumerina L on the proliferation of two CCA cell lines using MTT test. The results demonstrated that CuB exhibited potent anti-proliferation effect in a doseand time-dependent fashion. IC50 values were 0.048, 0.036 and 0.032 μM for KKU-213 and 0.088, 0.053 and 0.04 μM for KKU-214 cell line at 24, 48 and 72 h of incubation, respectively. Flow cytometric analysis revealed that CuB induced G2/M phase cell cycle arrest in a dose dependent manner. Concomitantly, subG1 population was observed when the cells treated with 0.2 μM CuB in both cell lines. Western blotting demonstrated that CuB at the concentration of 0.2 μM enhanced the expression of cell cycle inhibitory proteins namely p21 and p27. On the other hand, it downregulated the expression of cell cycle driving proteins namely phosphorylated retinoblastoma protein (pRB), cyclin D1, and cyclin E. Taken together, it is suggested that CuB may inhibit CCA cell growth through suppression of cell cycle progression. The detailed molecular mechanisms underlying CuB effect on CCA cells both in vitro and in vivo should be further explored with the hope that this promising compound derived from Thai herb might be an alternative treatment for CCA.