Objective  TRAIL-Mu3 was obtained by mutating the N-terminus of human tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) gene to an eight continuous arginine sequence. The present study was designed to explore the antitumor effect of this soluble mutant protein and the underlying mechanisms.

  Methods  The inhibitory effect of TRAIL-Mu3 on the proliferation of lung cancer cell lines NCI-H460, A549, NCI-H1299 and calu-1 was tested by CCK8 assay. The apoptotic rates of A549 and NCI-H460 treated by TRAIL-Mu3 were detected by flow cytometer (FCM). The expressions of apoptosis related proteins death receptor (DR) 4, DR5, Caspase-3, Caspase-8 and X-linked inhibitor of apoptosis protein (XIAP) were detected by Western blot. Moreover, a subcutaneous xenograft tumor mouse model of NCI-H460 was established and treated with TRAIL-Mu3 daily or every other day or three times a week. The expressions of DR4, DR5, Caspase-3, Caspase-8 and XIAP were detected by immunohistochemical staining.

  Results  The in vitro study demonstrated that as compared to the TRAIL, the TRAIL-Mu3 was more toxic and pro-apoptotic by up-regulation of the expression and activity of DR4, Caspase-3 and Caspase-8. Also, the animal study showed a similar antitumor effect between treatment with TRAIL-Mu3 every other day and three time a week, which was better than daily use. All treatments significantly suppressed the growth of xenograft tumor, increased the expression or activity of DR4 and Caspase-3, and down-regulated the expression of XIAP (P<0.05).

  Conclusion  TRAIL-Mu3 could improve antitumor activity in vivo and in vitro through elevating DR4 expression, activating Caspase-3/-8, and inhibiting XIAP activation.