Purpose: Our purpose was to explore the contribution of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)/TRAIL receptor pathway to antitumor effects of IFNα and 5-fluorouracil (5-FU) combination therapy for hepatocellular carcinoma (HCC). Experimental Design: Susceptibility of HCC cell lines to TRAIL and/or 5-FU was examined by 3-(4,5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide assay. The effects of 5-FU, IFNα, or both on the expression of TRAIL receptors (R1, R2, R3, and R4) on HCC cells or TRAIL in peripheral blood mononuclear cells (PBMC) were examined by flow cytometry. IFNα-induced cytotoxic effects of PBMC on HCC cell lines were examined by 51Cr release assay. TRAIL expression in peripheral blood mononuclear cells and liver tissue from patients was examined by real-time reverse transcription-PCR or immunohistochemistry. Results: HLE and HepG2 were sensitive to TRAIL, but HuH7, PLC/PRF/5, and HLF were resistant. 5-FU had synergistic effect on TRAIL in HLF and additive effect in four other HCC cell lines. TRAIL receptors on HCC cells were up-regulated by 5-FU, and IFNα induced TRAIL on CD4+ T cells, CD14+ monocytes, and CD56+ NK cells. Treatment of effector cells by IFNα and target HCC cells by 5-FU enhanced the cytotoxicity of CD14+ monocytes and CD56+ NK cells against HCC cells via a TRAIL-mediated pathway. TRAIL mRNA overexpression was noted in PBMC of HCC patients who clinically responded to IFNα/5-FU combination therapy, and TRAIL+ mononuclear cells were found in cancer tissue of a responder. Conclusion: Our results suggest that modulation of TRAIL/TRAIL receptor-mediated cytotoxic pathway might partially contribute to the anti-HCC effect of IFNα and 5-FU combination therapy.
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