Objective: To investigate therapeutic potential of TRAIL in hepatocellular carcinoma (HCC) and the mechanism of sTRAIL resistance and to reverse the resistance to sTRAIL-inducing apoptosis.
Methods: The expression profiles of TRAILR were determined 60 HCC samples, in 20 normal liver tissues and 2 HCC cell lines HepG2 and SMMC-7721 by in situ hybridization. Cellular effects of sTRAIL in promoting apoptosis on HCC cell lines HepG2 and SMMC-7721 were analyzed after exposure to recombinant protein and after transfection with a cDNA expression construct. In vivo effects of sTRAIL on tumor growth were investigated using a nude mice HCC model of hepG2. Furthermore, the expression of survivin in HCC was detected, and treatment with antisence oligonucleotide was accepted. Finally, therapeutic effect on HCC by combining sTRAIL and interleukin-12 (IL-12) was detected.
Results: Both DR4 and DR5 were present in all HCC tissues as well as normal hepatic tissues. In contrast, 54 HCC tissues did not express DcR1 and 25 did not express DcR2. But both DcR were detectable in all of the normal liver tissues. The expression patterns of DR and DcR in HCC samples were quite different from those in normal tissue. DR5, DR4, and DcR2 expressed in both cell lines, while no DcR1 expression was detected. Recombinant sTRAIL alone was found to have a slight activity as it killed a maximum of 15% of HCC cells within 24 h while killing over 70% of Jurkat cells. In vivo administration of the TRAIL gene couldn't inhibit tumor growth in a nude mice HCC model. Mostly, HCC tissue and both HCC cell lines expressed survivin, whereas normal liver tissue did not express survivin. Treatment with antisence oligonucleotide enhanced sTRAIL-inducing apoptosis. IL-12 significantly augmented sTRAIL-inducing apoptosis and inhibited survivin expression.
Conclusions: HCC cells are insensitive towards TRAIL-mediated apoptosis. Survivin may play a role in resistance to TRAIL-induced apoptosis in HCC, and antisence oligonucleotide could partly reverse the resistance to TRAIL-inducing apoptosis. IL-12 may sensitize HCC cells to TRAIL-induced apoptosis by preventing survivin. Combining gene therapy strategy such as combining gene therapy of TRAIL with IL-12 may be a promising maneuver to HCC.