Retinoids have been effectively used as chemotherapeutic agents to treat certain types of cancer. To investigate the potential therapeutic effect of retinoids on human hepatocellular carcinoma (HCC), the apoptotic effects of a panel of carotenoids and retinoids were evaluated in three human hepatocellular carcinoma cell lines. Retinoid-dependent and cell type-specific apoptosis was observed. Fenretinide, [N-(4-hydroxyphenyl) retinamide or 4-HPR] was the most potent retinoid in inducing apoptosis in Huh-7 cells. Seventy-two hour treatment of fenretinide decreased cell number by 79% in Huh7 and 80% in Hep3B cells compared to the control and induced caspase-3 cleavage in Huh-7 and Hep3B cells, but not in HepG2 cells. Membrane lipid phosphatidylserine translocation in Huh7 cells was detected 24 hours after fenretinide treatment and reached 6.5- fold and 17- fold over the control at 48 hours and 72 hours, respectively. In contrast, no phosphatidylserine translocation was detected in fenretinide-treated HepG2 cells. To further examine the mechanism underlying the sensitivity of Huh-7 cells and resistance of HepG2 cells to fenretinide treatment, expression of eleven nuclear receptors was evaluated in the three cell lines. Huh-7 cells has the highest basal level of RARβ mRNA followed by Hep3B cells, whereas no RARβ mRNA was detected in HepG2 cells. Moreover, in Huh-7 cells, RARβ mRNA level was increased as early as 2 hours after fenretinide treatment and reached 13- and 34-fold over the control at 24 hours and 48 hours, respectively. In contrast, in HepG2 cells, the RARβ mRNA was only moderately increased at 6 hours and the induction was not sustained after a longer period of treatment. Consistent with the differential inducibility of the RARβ gene by fenretinide in Huh-7 and HepG2 cells, fenretinide activated RXRα/RARβ-mediated transactivation through a retinoic acid response element (RARE) in Huh-7 cells, but not in HepG2 cells. Most importantly, siRNA knockdown of RARβ gene expression in Huh-7 cells significantly reduced DNA double-strand breaks following fenretinide treatment. In conclusion, the basal level as well as the inducibility of the RARβ gene is essential for fenretinide-induced apoptosis in human hepatoma cells. (NIH CA 53596, AA14147, P20RR021940)

98th AACR Annual Meeting-- Apr 14-18, 2007; Los Angeles, CA