Betulinic Acid Inhibits Cell Proliferation in Human Oral Squamous Cell Carcinoma via Modulating ROS-Regulated p53 Signaling

Oral squamous cell carcinoma (OSCC) is a common cancer of the head and neck. Betulinic acid (BA) is a naturally occurring pentacyclic triterpenoid. The present study was designed to explore the effects of BA on OSCC KB cell proliferation in vitro and on implanted tumor growth in vivo and to examine the possible molecular mechanisms. The results showed that BA dose-dependently inhibited KB cell proliferation and decreased implanted tumor volume. In addition, BA significantly promoted mitochondrial apoptosis, as reflected by an increase in TUNEL(+) cells and the activities of caspases 3 and 9, an increase in Bax expression, and a decrease in Bcl-2 expression and the mitochondrial oxygen consumption rate. BA significantly increased cell population in the G(0)/G(1) phase and decreases the S phase cell number, indicating the occurrence of G(0)/G(1) cell cycle arrest. ROS generation was significantly increased by BA, and antioxidant NAC treatment markedly inhibited the effect of BA on apoptosis, cell cycle arrest, and proliferation. BA dose-dependently increased p53 expression in KB cells and implanted tumors. p53 reporter gene activity and p53 binding in the promoters of Bax were significantly increased by BA. Knockdown of p53 blocked BA-induced increase in apoptosis, cell cycle arrest, and inhibition of cell proliferation. NAC treatment suppressed BA-induced increase in p53 expression. Furthermore, phosphorylation of signal transducer and activator of transcription 3 (STAT3) was increased by BA. Taken together, the data demonstrated that ROS–p53 signaling was crucial for BA-exhibited antitumor effect in OSCC. BA may serve as a potential drug for the treatment of oral cancer.