Fig. 2. ESR1 mutant MCF7 clones grow in the absence of estrogen but show differential sensitivity to SERDs.

A, B Cells cultured in estrogen-depleted medium were treated with 10 nM estrogen, or vehicle. Shown is the fold difference in growth of individual mutant clones, relative to the growth of MCF7 cells after 9 days. The results for 10 nM estrogen addition to MCF7 cells, are shown for comparison. B Doubling times for MCF7 and mutant clones, determined from growth experiment undertaken on an Incucyte Zoom ±10 nM E2 over a 9-day period (see Supplementary Fig. 3 for the full data). Doubling times were calculated using the exponential growth equation in Graphpad Prism. C The heatmap shows relative difference in IC₅₀ values for mutant clones relative to the IC₅₀ for MCF7 cells, determined for each mutant clone. Also shown are the mRNA expression levels of mutant ER, as a percentage of total ER in each clone, determined by ddPCR (see Supplementary Figs. 4, 5 for complete data). D, E Mean growth relative to vehicle (DMSO) is shown following treatment of MCF7, MCF7-Y537S and MCF7-L536R clones for 6 days, with increasing concentrations of anti-estrogens. The graphs plot the results of three independent experiments; error bars show standard deviations (see Supplementary Fig. 4 for actual IC₅₀ values).