Cytotoxic Activity of Boesenbergia rotunda Extracts against Nasopharyngeal Carcinoma Cells (HK1). Cardamonin, a Boesenbergia rotunda Constituent, Inhibits Growth and Migration of HK1 Cells by Inducing Caspase-Dependent Apoptosis and G2/M-Phase Arrest.

Boesenbergia rotunda (L.) Mansf. is an edible herb that is commonly used in the cuisine of several Asian countries. Studies have shown that it possesses high bioactivity against a variety of cancer cells. In this study, we investigated the cytotoxic activity of Boesenbergia rotunda rhizomes and some of its constituents on nasopharyngeal carcinoma cells (HK1). MTT assay results showed that the methanolic and hexane extracts of Boesenbergia rotunda decreased HK1 cell viability with IC50 values of 136 µg/ml and 66 µg/ml, respectively. Cardamonin, a constituent of Boesenbergia rotunda, exhibited the highest cytotoxic activity with an IC50 value of 27 μg/ml. Further studies on cardamonin revealed that it inhibited the migration of HK1 cells, caused G2/M-phase arrest and induced apoptosis. Apoptosis was induced via activating caspase-8 and caspase-3, but independent of caspase-9. This indicated that cardamonin induced extrinsic apoptosis. Western blot analysis further showed that cardamonin caused extrinsic apoptosis, as the expression levels of intrinsic apoptosis-related proteins (Bcl-XL, Bcl-2 and Bax), were not affected. Finally, JC-1 staining of HK1 cells revealed an increase in the mitochondrial membrane potential after treatment, further proving that cardamonin did not induce apoptosis via the intrinsic pathway. These results reflect cardamonin's potential as an anticancer agent.