Fig. 6. BRCA1 levels predict response to the ERα antagonist, Fulvestrant.

A) Dose response curves demonstrate that siRNA-mediated inhibition of endogenous BRCA1 results in increased resistance to the ERα antagonist Fulvestrant (ICI 182, 780) compared to scrambled controls (SCR) in T47D and MCF-7 cells. Western blot analysis confirms the reduction in ERα protein expression levels with siRNA-mediated inhibition of endogenous BRCA1 in T47D and MCF-7 cells (top). Reprobing for GAPDH confirmed equal loading. In parallel, cells were treated with a range of concentrations of Fulvestrant. IC₅₀ and IC₄₀ values were calculated from the respective sigmoidal dose response curves. The results are shown as the average ± SD (n=3) of three independent experiments. B) Dose response curves showing that transient reconstitution of BRCA1-depleted T47D and MCF-7 cells with exogenous ERα re-sensitises cells to Fulvestrant (ICI 182, 780). Western blot analysis demonstrates ERα expression levels in BRCA1 siRNA treated cells following transfection of pcDNA3.1 EV or pcDNA3.1 ERα expression vectors. Reprobing for GAPDH confirmed equal loading. In parallel, cells were treated with a range of concentrations of Fulvestrant. IC₄₀ values were calculated from the respective sigmoidal dose response curves. The results are shown as the average ± SD (n=3) of three independent experiments.