Inhibiting survivin expression enhances TRAIL-induced tumoricidal activity in human hepatocellular carcinoma via cell cycle arrest

Human Hepatocellular carcinoma (HCC) cell types exhibit a major resistance to tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)-induced cell death, and the key determinants of mechanisms accounting for TRAIL susceptibility, still remain controversial. Our previous studies showed that overexpression of survivin reduced sensitivity of HCC cells to TRAIL. The aim of this study is to investigate how tumor cells escape TRAIL-mediated surveillance through survivin expression and how to reverse the resistance of TRAIL-inducing apoptosis. Seven tumor cell lines were treated with or without TRAIL protein and antisense oligodeoxynucleotides (ODNs) against survivin in culture. HepG₂ and SMMC7721 cells were treated with mimosine, thymidine or nocodazole to synchronize their cell cycle phases and then used to test their sensitivity to TRAIL. In vivo effects of TRAIL plasmid alone or in combination with survivin antisense ODNs on tumor growth were evaluated in a nude mouse hepatoma model of HepG₂ cell grafts. Varied levels of survivin mRNA in various cell lines were evaluated and negatively correlated to TRAIL-induced apoptosis. Hepatoma HepG₂ and SMMC7721 cells in G₁ or S phase are more sensitive to TRAIL than those in G₂ phase. Treatment with survivin antisense ODNs caused S phase arrest and significantly enhanced TRAIL-induced apoptosis. TRAIL protein caused G₂/M arrest and resulted in an increase of survivin in HepG₂ cells. Combined TRAIL plasmid and survivin antisense ODNs significantly supressed the growth of tumor xenografts as compared to TRAIL plamid or antisense ODNs alone during four weeks of observation. The findings indicate that survivin may play a role in tumor cell resistance to TRAIL-induced apoptosis, at least in part, through cell cycle regulation. Manipulation of survivin expression levels may sensitizes tumor cells to TRAIL-induced apoptosis.