Viability of MCF-7 and LCC2 cells after tamoxifen, THZ1, or CDK7-targeting siRNA treatment individually and in combination. (a) Percentage of viable MCF-7 and LCC2 cells 48 h after treatment with the indicated concentrations of tamoxifen (TAM). (b) Percentage of viable MCF-7 and LCC2 cells after 48 h of incubation with THZ1 (2.5–50 nM). (c) (left) Viability of MCF-7 cells after treatment with the indicated concentrations of dimethyl sulfoxide (DMSO) (control), THZ1, tamoxifen, or THZ1 plus tamoxifen. (right) Viability of LCC2 cells after treatment with the indicated concentrations of dimethyl sulfoxide (DMSO), THZ1, tamoxifen, or THZ1 plus tamoxifen. (d) Cell viability after treatment with the indicated concentrations of control siRNA (CT siR) plus tamoxifen, siRNA-CDK7-2 (CDK7 siR), or siRNA-CDK7-2 plus tamoxifen in MCF-7 and LCC2 cells. The results are expressed as mean ± SD of five independent experiments performed in triplicate. Statistical significance was determined by one-way ANOVA using the Tukey multiple comparison test. *** p < 0.001. UT, untreated.