Downregulation of STAT3 and activation of MAPK are involved in the induction of apoptosis by HNK in glioblastoma cell line U87

Honokiol [3,5-di-(2-propenyl)-1,1-biphenyl-2,2-diol; HNK], a natural bioactive molecular compound isolated from the Magnolia officinalis, exhibits potent antitumor activity against a variety of human cancer cell lines. However, few studies have reported the antineoplastic effects of HNK on glioblastoma cells. It remains unknown how apoptosis is induced by HNK in glioblastoma cells and through which associated pathway this compound acts. The present study confirmed that HNK inhibited proliferation of glioblastoma cells by inducing a slight G0/G1 phase cell cycle arrest and apoptosis. We demonstrated for the first time that HNK triggered apoptosis of glioblastoma cells through both caspase-independent and caspase-dependent pathways, the latter including the extrinsic pathway and intrinsic pathway. Moreover, the inhibition of STAT3 signaling, ERK1/2 as well as activation of the p38 MAPK signaling pathway may be involved in apoptosis induced by HNK in U87 cells. Our findings suggest that HNK treatment could be a promising therapeutic strategy in human glioblastoma.