Inhibition of STAT3 signaling pathway by ursolic acid suppresses growth of hepatocellular carcinoma

The signal transducer and activator of transcription 3 (STAT3) has been found to be constitutively active in liver cancer. There is no STAT3 inhibitors approved to be used clinically for the treatment or prevention of liver cancer. Some dietary compounds including ursolic acid (UA) have been reported to inhibit the growth of cancer cells. However, whether UA could inhibit STAT3 phosphorylation in hepatocellular carcinoma has not been reported. The inhibitory effects of UA on STAT3 phosphorylation, along with cell viability, migration, colony formation in vitro, as well as tumor growth in vivo were examined in human liver cancer cell lines. Our data showed that UA inhibited the P-STAT3 induced by interleukin-6 (IL-6) in Hep3B liver cancer cells which express very low basal level of P-STAT3. The constitutive STAT3 phosphorylation was also inhibited by UA in HEPG2, 7721 and Huh7 human liver cancer cell lines. UA decreased the expression of downstream target genes of STAT3, such as Bcl-2, Bcl-xl and survivin in general, with difference in these cell lines. UA also suppressed cell viability, cell migration and colony formation in liver cancer cells. Furthermore, UA suppressed STAT3 phosphorylation and HEPG2 tumor growth by oral daily treatment in vivo. UA, which exists widely in fruits and herbs, could inhibit STAT3 activation and the growth of human liver cancer cells in vitro and in vivo. It might be a potential health care product that could be used daily for prevention, as well as a promising candidate for chemotherapy of liver cancer.