Acetylbritannilactone is a potent synergist of celecoxib to inhibit cyclooxygenase‐2 expression and to induce apoptosis in human breast cancer cells

Abstract

The use of cyclooxygenase‐2 (COX‐2) inhibitors is associated with a significant decrease in breast cancer risk. However, recent studies show that the long‐term use might be limited due to undesired side effects. Our previous study has demonstrated that acetylbritannilactone (ABL), isolated from Chinese herb Inula Britannica L, inhibit COX‐2 expression via blockade of nuclear factor‐kappa B (NF‐κB) activation. Here, the effects of ABL and celecoxib as single and their combination were examined in breast cancer cells, and CalcuSyn software was used to assess synergistic inhibition. Celecoxib (5 μM) and ABL (25–50 μM) synergistically inhibited cell growth and induced cell apoptosis. The results showed that ABL augmented celecoxib inhibition of COX‐2 expression and prostaglandin E2 synthesis. To confirm the mechanism by which ABL and celecoxib synergistically attenuate COX‐2 expression. Furthermore, the promoter activity of COX‐2 gene was analyzed by chromatin immunoprecipitation and DNA affinity protein‐binding assays. We found that the combination of ABL with celecoxib at lower concertration resulted in reduction of binding of CREB‐1, ATF‐2 and c‐fos to the COX‐2 promoter, and then decreased activity of promoter reporter gene. In addition, inhibition of Akt and p38 signaling pathways was required for the synergism, as a constitutively active Akt and p38 abrogated the reduction of COX‐2 transcription and protected cells against apoptosis induced by the combination. Taken together, the combination of ABL with celecoxib elicited significantly greater inhibition of cell growth and more apoptosis, compared with either drug alone. Thus, ABL is expected to be a potent synergist of celecoxib for treatment of breast cancer.