Pharmacological inhibition or small interfering RNA targeting acid ceramidase sensitizes hepatoma cells to chemotherapy and reduces tumor growth in vivo

Ceramidases (CDases) play a key role in cancer therapy through enhanced conversion of ceramide into sphingosine 1-phosphate (S1P), but their involvement in hepatocarcinogenesis is unknown. Here, we report that daunorubicin (DNR) activated acid CDase post-transcriptionally in established human (HepG2 cells) or mouse (Hepa1c1c7) hepatoma cell lines as well as in primary cells from murine liver tumors, but not in cultured mouse hepatocytes. Acid CDase silencing by small interfering RNA (siRNA) or pharmacological inhibition with N-oleoylethanolamine (NOE) enhanced the ceramide to S1P balance compared to DNR alone, sensitizing hepatoma cells (HepG2, Hep-3B, SK-Hep and Hepa1c1c7) to DNR-induced cell death. DNR plus NOE or acid CDase siRNA-induced cell death was preceded by ultrastructural changes in mitochondria, stimulation of reactive oxygen species generation, release of Smac/DIABLO and cytochrome c and caspase-3 activation. In addition, in vivo siRNA treatment targeting acid CDase reduced tumor growth in liver tumor xenografts of HepG2 cells and enhanced DNR therapy. Thus, acid CDase promotes hepatocarcinogenesis and its antagonism may be a promising strategy in the treatment of liver cancer.