Emodin (Frangula emodin) is a naturally occurring anthraquinone present in the roots and barks of numerous plants; exerts antiproliferative effects in Y cells that are regulated by different signaling pathways.

Emodin, an anthraquinone derivative, selectively inhibits casein kinase II(CKII), a Ser/Thr kinase, as a competitive inhibitor. Emodin inhibits CKII activity with IC50 of 2 μM, which is two to three orders of magnitude lower than those against the other kinases. Enzyme kinetic assays show that Emodin inhibits CKII activity as acompetitive inhibitor against ATP with Ki of 7.2 μM[1]. Emodin is a broad-spectrum inhibitory agent of cancer cells, including leukemia, lung cancer, human tongue squamous cancer, colon cancer, gallbladder cancer, pancreatic cancer, breast cancer, human cervical cancer and hepatic carcinoma cells. Emodin inhibits A549, HepG2, OVCAR-3, HeLa and Madin-Darby Canine Kidney (MDCK) cells with IC50 of 19.54, 12.79, 25.82, 12.14 and 5.81 μg/mL. The anticancer mechanisms of Emodin are involved in many biological pathways, such as casein kinase Ⅱ and ERK1/2[2]. Emodin is applied as a Reactive oxygen species (ROS) generator in combination with cisplatin in T24 and J82 human bladder cancer cells. Emodin kills T24 and J82 cells in the dose-dependent and time-dependent manner, and it is less toxic to HCV-29 cells. The concentration of 20 and 15 μM is selected as appropriate doses for investigating chemotherapeutic sensitivity of T24 and J82 cells at 24 h, respectively[3].

Mice treated with Emodin (50 mg/kg) and Cisplatin (1 mg/kg) have significantly smaller tumors than those from the other groups. In addition, no notable differences on the body weight loss are observed among groups and no obvious necrosis and abnormity are observed in the sections of liver, kidney and heart. These results demonstrate that Emodin/cisplatin co-treatment can significantly suppress tumor growth in vivo with no distinct side effects. Consistent with in vitro experiment, TUNEL assay shows that Emodin/cisplatin combination significantly increased cell apoptosis in xenograft tumors. Emodin/Cisplatin co-treatment group also has lower MRP1 expression than the other groups[3].

Emodin is prepared in DMSO and stored, and then diluted with appropriate medium before use[3]. The T24 human bladder cancer cells, the HCV-29 normal bladder epithelial cells and J82 human bladder cancer cells are are cultured in RPMI 1640 medium supplemented with 10 % fetal bovine serum at 37°C in a humidified atmosphere containing 5 % CO2. Cells are seeded in 96-well plates with 2×104 cells per well. The cells are incubated with Emodin for 24 h at different concentrations (0, 5, 10, 20, 30, 40, 50, 60, 70 μM) and chose the critical concentration (20 μM) treated with cells for 0, 6, 12, 24, 48, 72, 96 h. The cells are incubated with cisplatin for 24 h at different concentrations (0, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0 μg/mL). MTT assay is used to analyze the cell viability. Cells are treated with drugs for 24 h and apoptotic rates are assessed with flow cytometry using AnnexinV-fluorescein isothiocyanate (AnnexinV-FITC)/propidium iodide (PI) kit. Samples are prepared according to the manufacturer's instruction and analyzed by a flow cytometry (FCM) Calibur[3].