Acquired Tumor Necrosis Factor-Related Apoptosis-Inducing Ligand (TRAIL) Resistance of Human Colorectal Cancer Cells Is Linked to Histone Acetylation and Is Synergistically Ameliorated by Combination with HDAC Inhibitors

Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is an attractive target for the treatment of various malignancies; however, its therapeutic potential is limited because of the frequent occurrence of tumor cell resistance. In this study, we determined whether TRAIL resistance acquired by repeated administration could be overcome by HDAC inhibition in human colorectal cancer cells.

TRAIL-resistant HCT116 human colorectal cancer cells (HCT116-TR) were generated by repeated treatment with 10 and 25 ng/mL TRAIL twice weekly for 28 days.

The resulting TRAIL-resistant cells were noncross-resistant to other chemotherapeutic agents. The levels of histone acetylation-related proteins, such as ac-histone H4 and HDAC1, were altered in HCT116-TR cells compared with the parental HCT116 cell line. The combined treatment with TRAIL and HDAC inhibitors significantly increased apoptosis in HCT116-TR cells and indicated a synergistic effect. The mechanism by which HDAC inhibition sensitizes HCT116-TR cells to TRAIL is dependent on the intrinsic pathway. In addition, we found that HDAC inhibition enhanced the sensitivity of cells to TRAIL through mitogen-activated protein kinases/CCAAT/enhancer-binding protein homologs of protein-dependent upregulation of death receptor 5.

These results suggest that histone acetylation is responsible for acquired TRAIL resistance after repeated exposure and acquired resistance to TRAIL may be overcome by combination therapies with HDAC inhibitors.