Partial contribution of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL)TRAIL receptor pathway to antitumor effects of interferon-α/5-fluorouracil against hepatocellular carcinoma

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.