LAUSR

BACKGROUND AND AIMS Hepatocellular carcinoma (HCC) is a leading cause of cancer-related death. c-Rel, an NF-κB transcription factor family subunit is typically pro-tumourigenic, however, it has recently been reported as a tumour suppressor. Here we investigated the role of c-Rel in HCC. APPROACH AND RESULTS Histological and transcriptional studies confirmed expression of c-Rel in human HCC patients, but low c-Rel expression correlated with increased tumour cell proliferation, mutational burden, and was associated with advanced disease. In vivo, global (Rel-/- ) and epithelial specific (RelAlb ) c-Rel knockout mice develop more tumours, with a higher proliferative rate and increased DNA damage, than wild type (WT) controls 30 weeks post-diethylnitrosamine (DEN) injury. However, tumour burden was comparable when c-Rel was deleted in hepatocytes once tumours were established, suggesting c-Rel signalling is important in preventing HCC initiation after genotoxic injury, rather than for HCC progression. In vitro, Rel-/- hepatocytes were more susceptible to genotoxic injury than WT controls. ATM-CHK2 DNA damage response pathway proteins were supressed in Rel-/- hepatocytes following genotoxic injury, suggesting that c-Rel is required for effective DNA repair. To determine if c-Rel inhibition sensitises cancer cells to chemotherapy, by preventing repair of chemotherapy-induced DNA damage, thus increasing tumour-cell death, we administered single or combination doxorubicin and IT-603 (c-Rel inhibitor) therapy in an orthotopic HCC model. Indeed, combination therapy was more efficacious than doxorubicin alone. CONCLUSION Hepatocyte c-Rel signalling limits genotoxic injury, and subsequent HCC burden. Inhibiting c-Rel as an adjuvant therapy increased the effectiveness of DNA damaging agents and reduced HCC growth.