The combination of tamoxifen and 9cis retinoic acid exerts overadditive anti-tumoral efficacy in rat hepatocellular carcinoma

Background/Aims: Medical treatment for hepatocellular carcinoma (HCC) remains elusive. While an acyclic retinoid improved tumor-free survival after hepatoma resection, tamoxifen finally proved ineffective. Combination therapy of both agents has not been investigated in vitro and in vivo. Methods: MH7777A hepatoma cells were incubated with tamoxifen (TAM) and 9-cis retinoic acid (CRA) alone or in combination. Proliferation rate and apoptosis were assessed by BrdU incorporation and flow cytometry. In vivo efficacy was studied using the Morris hepatoma model in immunocompetent rats. End points were macroscopic tumor growth, metastasis and immunohistochemistry for proliferative and apoptotic tumor cells (PCNA and TUNEL staining). Results: In vitro, CRA and TAM monotherapy was effective only in the highest concentration. Combination therapy significantly enhanced apoptosis rate and growth inhibition in hepatoma cells. While in vivo monotherapy did not reduce tumor growth or metastasis, their combination reduced tumor size after 28 days by 64.5 +/- 28%. This was paralleled by an increase in TUNEL positive and a decrease in PCNA positive cells. Conclusions: The combination of TAM and CRA enhances their anti-tumoral efficacy in vitro as well as in vivo, while monotherapy is ineffective. This combination could be a promising adjunctive therapy of HCC. (C) 2004 European Association for the Study of the Liver. Published by Elsevier B.V. All rights reserved.