The Histone-Deacetylase Inhibitor SAHA Potentiates Pro-Apoptotic Effects of 5-Fluorouracil and Irinotecan in Hepatoma Cells

Treatment for advanced stages of hepatocellular carcinoma (HCC) remains unsatisfactory. While 5-fluorouracil (5-FU) and Irinotecan are first-line treatment options for other gastrointestinal tumors, the effect on HCCs is low. Previously, histone-deacetylase inhibitors (HDAC-I) like suberoylanilide hydroxamic acid (SAHA) showed anti-tumoral activities in a variety of human cancers in vitro and in vivo. Here, we investigated the effect of a combination of 5-FU, Irinotecan and SAHA on growth inhibition and apoptosis induction of HCC cell lines. HepG2, Hep1B and MH–7777A hepatoma cell lines and human foreskin fibroblasts as non-transformed controls were incubated with either 5-FU, Irinotecan and SAHA alone or on combination. While single agents did not show any effects on growth of the investigated cell lines, combination of 5-FU and Irinotecan (both 10µM) lead to a moderate increase in apoptosis and proliferation inhibition. Adding 1µM SAHA increased apoptosis rates in hepatoma cell lines up to 92% after 72h, while fibroblasts showed no response (5.5% apoptosis). Induction of apoptosis was paralleled by loss of the mitochondrial transmembrane potential, down-regulation of bcl–2 expression and activation of caspase 3 but not caspase 8. In summary, SAHA sensitizes HCC cell lines for treatment with an otherwise ineffective combination of 5-FU and Irinotecan and leads to mitochondrial apoptosis induction. The triple combination could lead to optimized treatment results in vivo and needs further evaluation.