Chemotherapy does not have a prominent role in the treatment of hepatoma. However, an acyclic retinoid prevented tumor recurrence post-hepatectomy, and tamoxifen (TAM) induced apoptosis in tumor cells. Combination therapy of these agents on proliferation and apoptosis of hepatoma cells has not been explored. HepG2, Hep1B, Hepa1-6 and MH1C1 hepatoma cells were incubated with TAM, 9-cis- and all-trans retinoic acid (CRA, ATRA, respectively) alone or in combination. Proliferation rate was assessed and apoptosis was analyzed by flow cytometry, immunostaining, caspase activity assays and the expression of apoptosis- and/or cell cycle-related molecules. CRA and TAM, but not ATRA monotherapy were moderately effective. Apoptosis was accompanied by upregulation of caspase 3 and 8 activity, and increased p27, bax, caspase 3 expression, while the levels of p21cip/waf and bcl-2 were unchanged or decreased. Combination therapy enhanced apoptosis from a maximum of 60% after monotherapy to more than 90% after 96 h in all cell types. Pro-apoptotic effects were paralleled by inhibition of proliferation. Combination of TAM and CRA, but not ATRA, have an additive to synergistic anti-proliferative and pro-apoptotic effect on HCC cells. This justifies trials for HCC using combinations of these biological response modifiers.

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