Marsdenia tenacissima extract induces G0/G1 cell cycle arrest in human esophageal carcinoma cells by inhibiting mitogen-activated protein kinase (MAPK) signaling pathway

Marsdenia tenacissima extract (MTE, trade name: Xiao-Ai-Ping injection) is an extract of a single Chinese plant medicine. It has been used for the treatment of cancer in China for decades, especially for esophageal cancer and other cancers in the digestive tract. In the present study, the potential mechanism for MTE's activity in esophageal cancer was explored. The effects of MTE on the proliferation of human esophageal cancer cells (KYSE150 and Eca-109) were investigated by the MTT assay, the BrdU (bromodeoxyuridine) incorporation immunofluorescence assay, and flow cytometric analysis. MTE inhibited cell proliferation through inducing G(0)/G(1) cell cycle arrest in KYSE150 and Eca-109. Western blot analysis was employed to determine protein levels in the MTE treated cells. Compared with the control cells, the expression levels of the cell cycle regulatory proteins cyclin Dl/D2/D3, cyclin El, CDK2/4/6 (CDK: cyclin dependent kinase), and p-Rb were decreased significantly in the cells treated with MTE at 40 mg.mL(-1). In addition, MTE had an inhibitory effect on the MAPK (mitogen-activated protein kinase) signal transduction pathway, including ERK (extracellular signal-regulated kinase), JNK (c-Jun N-terminal kinase), and p38MAPK. Moreover, MTE showed little additional effects on the regulation of cyclin Dl/D3, CDK4/6, and p-Rb when the ERK pathway was already inhibited by the specific ERK inhibitor U0126. In conclusion, these data suggest that MTE inhibits human esophageal cancer cell proliferation through regulation of cell cycle regulatory proteins and the MAPK signaling pathways, which is probably mediated by the inhibition of ERK activation.