Effects of Liarozole, a New Antitumoral Compound, on Retinoic Acid-induced Inhibition of Cell Growth and on Retinoic Acid Metabolism in MCF-7 Human Breast Cancer Cells

Liarozole Âis a new imidazole derivative with antitumoral properties. Effects of the compound alone and in combination with all-frans-retinoic acid on proliferation of MCF-7 human breast cancer cells were examined using a 3-(4,5-dimethylthiazoI-2-yl)-2,5-diphenyl-2//-tetrazolium bro mide assay. Following9 days of drug exposure, MCF-7 cell growth was concentra tion dependent!) inhibited by all-fra/u-retinoic acid (drug concentration resulting in 50% growth inhibition, 2 x 1(1KM), while liarozole at III'" M inhibited cell growth by only 35%. When MCF-7 cells were incubated with a combination of all-m/;ivretinoic acid and Harozole,the antiproliferative effect of all-frani-retinoic acid was clearly enhanced. This enhancement was dependent on the liarozole concentration and was more than 10-fold. A combination of 10s M Âiill-rn/nv-ri'tumiracid and IO1' M liarozole resulted in a greater antiproliferative effect than that obtained with 10' M all-fra/iA®-retinoic acid alone. When MCF-7 cells were incubated for 4 h with |'H|all-rrani-retinoic acid, the radioactivity in the supernatant consisted of unaltered retinoid. However, when cells had been pretreated with 10 '' M all-A­rans-retinoic acid overnight, they were able to substantially metabolize |'ll|Âitll-m/n\retinoic acid during a subsequent 4-h incubation. High-performance liquid chromatography analysis of the supernatants revealed that the reaction products consisted mainly of very polar metabolites. Liarozole inhibited the metabolism of all-rrans-retinoic acid in MCF-7 cells with KP" M liarozole reducing the amount of polar metabolites by 87%. It is concluded that the enhancement by liarozole of the antiprolifera tive effects of retinoic acid on MCF-7 human breast cancer cells is probably due to inhibition of retinoic acid metabolism. Further research into these effects in MCF-7 cells as well as in other cancer cell lines will provide more information concerning the exact mechanism of action of liarozole and the use of inhibitors of retinoid metabolism in cancer treatment.