Oleanolic acid enhanced the anticancer effect of fluorouracil by regulating Ca2+ levels in liver cancer cells

Oleanolic acid (OA) serves as an anticancer drug like the common chemotherapeutic agents in the clinic. However, the effect of OA on regulating cancer cell sensitivity to fluorouracil (5FU) has not yet been reported. This study aims to investigate the impact of OA/5FU co-treatment on liver cancer cells and explore its underlying mechanism. In this study, by using the MTT and colony formation assays, OA/5FU co-treatment significantly reduced the proliferation of HEPG2 liver cancer cells in vitro compared with OA or 5FU alone. Moreover, OA/5FU co-treatment had a stronger ability to induce apoptosis than treatment alone, which is determined by Hoechst 33342 staining and Western Blot. The results of the Ca2+ fluorescent probes and Western Blot analysis showed that OA/5FU co-treatment increased the Ca2+ level in the liver cancer cells compared with OA or 5FU alone. Furthermore, the inhibitory effect of OA/5FU cotreatment on cell proliferation was partially inhibited by 2-Aminoethyl diphenylborinate (2-APB) which is a calcium channel inhibitor. The OA/5FU cotreatment inducing apoptosis of HEPG2 liver cancer cells was also partially reversed by 2-APB. Collectively, OA and 5FU worked synergistically to regulate the Ca2+ signaling in liver cancer cells, inducing apoptosis and inhibiting the proliferation of liver cancer cells. This study sheds new light on improving the anticancer effect of 5FU by using the natural product OA.