Growth suppression of the hepatocellular carcinoma cell line hepa1-6 by an activatable interferon regulatory factor-1 in mice

Hepatocellular carcinoma (HCC) is a highly malignant tumor,vith a poor prognosis and few therapeutic options. The aim of the study was to evaluate the potential of IFN regulatory factor-1 (IRF-1) for cytokine gene therapy of HCC using an IRF-1/human estrogen receptor fusion protein (IRF-1hER), which is reversibly activatable by beta -estradiol (E-2). IRF-1hER stably expressing murine Hepa1-6 HCC cells (HepaIRF-1hER) were characterized by (MHC)-M-low I, (high)CD54, and lack of MHC II, CD80, and CD86 expression. Activation of HepaIRF-1hER cells induced a (MHC)-M-high I, (MHC)-M-low II, and (high)CD54 phenotype. Furthermore, they were characterized by IFN-beta secretion, decreased anchorage-independent growth in a soft agar assay, and diminished cell growth. Tumor growth in E-2-treated syngeneic C57L/J mice, but not in E-2-untreated mice, was suppressed. These E-2-treated mice were protected against rechallenge with HepaIRF-1hER and wild-type Hepa1-6 tumors even in the absence of E-2, suggesting induction of tumor specific immunity. In fact, significant CTL activity against Hepa1-6 tumors and the endogenously expressed HCC-specific self antigen alpha -fetoprotein was observed. Antitumoral effects, however, were only partially dependent on both CD4+ and CD8+ T cells. IRF-1 treatment of mice bearing HepaIRF-1hER tumors resulted in growth arrest of tumors, and a significant survival benefit was observed in comparison to E-2-untreated mice. In conclusion, our data demonstrate that IRF-1 suppresses HCC growth through both a direct antitumor growth effect and enhanced immune cell recognition of the tumor and is a promising candidate for gene therapy of HCC.