Pseudolaric acid B induces apoptosis in human rhabdomyosarcoma RD cells

Pseudolaric acid B (PAB) is a diterpene-type acid isolated from the root and trunk bark of Pseudolarix kaempferi Gordon of the Pinaceae family that has been demonstrated to induce apoptosis in various cell lines and autophagy in certain cell lines including murine fibrosarcoma L929, human thyroid squamous cell carcinoma SW579 and human lung fibroblast MRC5 cells. However, in human rhabdomyosarcoma RD cells, which are derived from the most common soft tissue sarcoma in children and represent a high-grade neoplasm of a skeletal myoblast type, it is not clear whether PAB induces apoptosis or autophagy. The identification of the exact mechanism of PAB is important for studying its antitumor effects and its potential application in the treatment of human rhabdomyosarcoma. To confirm the inhibitory ability of PAB on RD cells, the inhibitory ratio of PAB was analyzed, and the results of MTT assay demonstrated that PAB inhibited RD cell proliferation. Meanwhile aggregation of the microtubule fibers was found in PAB-treated RD cells compared with that in control-treated cells, which was consistent with previous studies. In addition, PAB inhibited RD cell migration, induced apoptosis and cell cycle arrest at the G2/M phase. These results suggested that the mechanism of PAB-mediated growth inhibition in RD was similar to that reported in the human breast cancer cell line MCF-7 and the neuroglioma cell line A172; however, it was different from that reported in the L929, MRC5 and SW579 cell lines. Additional experiments demonstrated that PAB regulated the activation of caspase-8 and caspase-9 to induce apoptosis and caused an upregulation of phosphorylated H2A histone family member X and cyclin B1 expression in order to induce cell cycle arrest. Therefore, PAB may be considered a potential treatment agent for human rhabdomyosarcoma.