NSC 74859‐mediated inhibition of STAT 3 enhances the anti‐proliferative activity of cetuximab in hepatocellular carcinoma

Background Cetuximab [an epidermal growth factor receptor ( EGFR ) inhibitor], which was shown to be effective in rectal and non‐small cell lung cancers ( NSCLC s), was only modestly effective in clinical trials of hepatocellular carcinoma ( HCC ). STAT 3, which is thought to be a determinant of HCC sensitivity to antitumour drugs, may be involved. Aims To evaluate the efficacy of combination therapy using cetuximab and NSC 74859 (a novel STAT 3 inhibitor) in EGFR and STAT 3 overexpressing hepatoma cells. Methods Hepatoma cell lines were treated with cetuximab, NSC 74859 or a combination of both drugs. Efficacy of treatment was evaluated by determining cell viability using MTT assays and proliferation by cell counting. Expression and activation of STAT 3 were determined using Western blot analysis. We evaluated the role of STAT 3 in single and combination therapy using si RNA ‐mediated knock‐down of STAT 3 or STAT 3 overexpression strategies. Results HepG 2 and Huh ‐7 cells, which had lower levels of pSTAT 3 than SK ‐ HEP 1 cells, were more sensitive to cetuximab treatment when compared with SK ‐ HEP 1 cells. Although none of these cell lines was sensitive to NSC 74859 alone, NSC 74859 potentiated the antiproliferative effect of cetuximab in all three cell lines. siRNA knock‐down of STAT 3 increased the sensitivity of these cell lines to cetuximab, whereas STAT 3 overexpression antagonized these effects. Conclusions Enhanced growth inhibition in hepatoma cells treated with both NSC 74859 and cetuximab suggests that cetuximab resistance is probably mediated via STAT 3. Combination therapy using both inhibitors of EGFR and STAT 3 signalling warrants further investigation under in vivo condition.