Curcumin analog EF24 induces apoptosis and downregulates the mitogen activated protein kinase/extracellular signal-regulated signaling pathway in oral squamous cell carcinoma

Oral squamous cell carcinoma (OSCC) is one of the most common malignancies worldwide. Diphenyldifluoroketone (EF24) is a curcumin analog that has been demonstrated to improve anticancer activity; however, its therapeutic potential and mechanisms in oral cancer remain unknown. In the present study, the effect of EF24 on apoptosis induction and its potential underlying mechanism in the CAL-27 human OSCC cell line was investigated. To achieve this, various concentrations of cisplatin or EF24 were administrated to CAL-27 cells for 24 h, and cell viability, apoptotic DNA fragmentation, and cleaved caspase 3 and 9 levels were evaluated. To investigate the potential underlying mechanism, the levels of mitogen-activated protein kinase kinase 1 (MEK1) and extracellular signal-regulated kinase (ERK), two key proteins in the mitogen-activated protein kinase/ERK signaling pathway, were additionally examined. The results indicated that EF24 and cisplatin treatment decreased cell viability. EF24 treatment increased the levels of activated caspase 3 and 9, and decreased the phosphorylated forms of MEK1 and ERK. Sequential treatments of EF24 and 12-phorbol-13-myristate acetate, a MAPK/ERK activator, resulted in a significant increase of activated MEK1 and ERK, and reversed cell viability. These results suggested that EF24 has potent anti-tumor activity in OSCC via deactivation of the MAPK/ERK signaling pathway. Further analyses using animal models are required to confirm these findings in vivo.