Acetyl-11-keto-β-boswellic acid triggers premature senescence via induction of DNA damage accompanied by impairment of DNA repair genes in hepatocellular carcinoma cells in vitro and in vivo.

Cellular senescence, a state of irreversible growth arrest, occurs in all somatic cells and causes the cells to exhaust replicative capacity. Recently, cellular senescence has been emerging as one of the principal mechanisms of tumor suppression, which can be induced by low doses of therapeutic drugs in cancer cells. Acetyl-11-keto-beta-boswellic acid (AKBA), an active ingredient isolated from the plant Boswellia serrata, has been identified to induce apoptosis in hepatocellular carcinoma (HCC) cells. In this study, we found that low concentrations of AKBA treatment triggered cell growth arrest at G0/G1 phase with features of premature cellular senescence phenotype in both HCC cell lines HepG2 and SMMC7721, as observed by enlarged and flattened morphology, significant increase in cells with senescence-associated beta-galactosidase staining, and decrease in cell proliferation and DNA synthesis. Furthermore, cellular senescence induced by AKBA occurred via activation of DNA damage response and impairment of DNA repair, as evidenced by strong induction of gamma H2AX and p53, and downregulated expressions of multiple DNA repair associated genes. Induction of p53 by AKBA caused a significant increase in p21(CIP1), which had a critical involvement in the induction of cellular senescence. Additionally, in vivo study demonstrated that induction of senescence contributed to the anticancer efficacy of AKBA. Therefore, our findings suggested that induction of premature senescence by AKBA through DNA damage response accompanied by impairment of DNA repair genes defines a novel mechanism contributing to its growth suppression in HCC cells.