Antiproliferative activity of the CTet formulated in γ-cyclodextrin aqueous solution. Estrogen receptor-positive (MCF-7 and BT-474) and triple-negative (MDA-MB-231 and BT-20) human breast cancer cell lines were exposed to increased concentrations of CTet. Cell proliferation was evaluated by [3H]thymidine incorporation into cellular DNA after 72 hours of treatment. Results are shown as the percentage of [3H]thymidine incorporation in treated cells compared with control cells (vehicle only). Data are expressed as mean ± standard error of the mean of at least three separate experiments. CTet, indole-3-carbinol cyclic tetrameric derivative.