Selective ERβ agonist LY500307 enhances ERβ signaling and reduces cell viability in CTCL cells, sparing noncancerous skin cells. (A) ERβ protein expression in CTCL cells was determined by performing western blots; 50 μg of protein was loaded for each sample, and glyceraldehyde-3-phosphate dehydrogenase (GAPDH) served as a loading control (Ctrl). The data shown are from 3 independent experiments. (B) CTCL cells were transfected with ERE-luc plasmid. After 6 hours, the cells were treated with either vehicle or LY500307 for additional 24 hours, and then reporter activity was measured. (C) Antiproliferative effect of LY500307 compared with placebo in CTCL cells, determined by performing MTS assays. Cells were treated for 48 hours with increasing compound concentrations, from which 50% inhibitory concentration (IC₅₀) values and Hill slopes were calculated. Cell growth was normalized to cells treated with dimethyl sulfoxide (DMSO; untreated Ctrl). Mean values of minimum 3 independent experiments with standard deviation (SD) are plotted. (D) Isolated malignant cells from samples of patients (Pts) with SS (n = 5; left) and CD4⁺ T cells isolated from peripheral blood of healthy volunteers (n = 4; middle) were incubated with increasing concentrations of LY500307 for 72 hours, and cell viability was assessed using MTS assays. Cell growth was normalized to cells treated with DMSO (untreated Ctrl). Mean values of at least 3 replicates with SD are plotted. A comparison is presented of the average cell viability between malignant and healthy cells across the tested LY500307 concentrations (right). (E) Antiproliferative effect of LY500307 compared with placebo in HaCaT cells, primary human keratinocytes, and fibroblasts, determined by performing MTS assays. Cells were treated for 48 hours with increasing compound concentrations. Cell growth was normalized to cells treated with DMSO (untreated Ctrl). Mean values of a minimum of 3 independent experiments with SD are plotted. ∗P < .5; ∗∗P < .01; ∗∗∗P < .001; ∗∗∗∗P < .0001.