Looking for synergy or additivity between 188Re and sorafenib on hepatoma cell lines.

Abstract

247 Background: In case of non resectable HCC, radioembolization and sorafenib (S) are therapeutic options respectively for intermediate and advanced stages. In some other cancers, there is an increase of efficacy when external beam radiotherapy is done concomitantly with systemic chemotherapy or targeted therapies. So we wondered if there could be a synergistic or an additive activity when S is combined with a radionuclide. Methods: Hepatoma cell lines N1S1 (murine HCC), HepG2 (human hepatoblastoma) and HepaRG (human HCC) were treated with increasing concentrations of rhenium-188 (188Re) or S. On each cell line, we have studied the cellular toxicities of S and 188Re using Tetrazolium dye test, extra-cellular medium LDH level and morphologic analysis. This was done for different dosage of S and 188Re. We measured the lethal concentration killing 25% of cells (LC25) with the results of the Tetrazolium dye test. Secondly, we looked for synergy or additivity on cellular toxicity of these two compounds according to cell lines by combined treatment. Synergy or additivity was estimated with the combination index (CI) method (synergy if CI lower than 1, additivity if CI = 1, antagonism if CI upper to 1) based on the Tetrazolium dye test’s results. Results: Monotherapy dose-dependent toxicities were observed for all three cell lines with 188Re and for the N1S1 and HepG2 cell lines only with S. Combined treatment with 188Re and S showed synergy on HepaRG and N1S1 cell lines and additivity on the HepG2 cell line. Conclusions: The additive, and even synergistic, interest of a combined treatment with 188Re and S is demonstrated in vitro (for the first time to our knowledge) on hepatoma cell lines. This results, in particular for the HepaRG cell line (human HCC), could be explained by the down-regulation of the hepatic drug transporters which are responsible for the Sorafenib efflux in case of simultaneous DNA damages due to a radionuclide exposition. This promising approach now needs to be confirmed in vivo. [Table: see text]