D proteins differentiates between elisidepsin-sensitive and elisidepsin-resistant cell lines. b-actin was used as an internal control. These western blots were performed in triplicate. B) 548-04-9 web Expression levels of HER1, HER2, HER3, HER4, pAkt, and pMAPK were analyzed by western blot using 50 mg of protein cell lysate. The membranes were stripped and reprobed with anti-b-actin to verify equal protein loading. C, control; R, resistance. doi:10.1371/journal.pone.0053645.ghave been proposed to be involved in the cellular response to elisidepsin treatment, such as fatty acid-containing ceramides, 25033180 fatty acid 2-hydroxylase (FA2H), lysosomes, lipid rafts and epithelial growth factor receptors, including the HER receptors [10,29,30,31,32,33].In the present study we explored whether basal levels of EMT markers and HER receptor proteins could be predictive markers for elisidepsin treatment. The role of the cell membrane as an important target of elisidepsin was studied in breast and pancreas cancer cell lines. Basal levels of EMT protein 
expression markersEMT and HER3 Predicts Elisidepsin SensitivityFigure 6. Loss of HER3 expression decreases the sensitivity to elisidepsin treatment. Cell viability after treatment with various concentrations of elisidepsin for 72 h was determined in SKBR3 (A), MCF-7 (B), MDA-MB-231 (C), MDA-MB-435 (D), BT474 (E), BxPC-3 (F), HPAC (G) and AsPC-1 (H) cells. HER3 expression was downregulated with shRNA (grey squares); LUC shRNA transfected cells were used as the control (black diamonds). Mean, SD, and IC50 values are shown from three independent experiments. Cell viability was measured using a crystal violet assay. Before performing the viability experiments, all cell lines were checked by western blot using 50 mg of protein to confirm their levels of HER3 expression. doi:10.1371/journal.pone.0053645.gshowed a significant correlation with the cell viability response to elisidepsin treatment in a panel of 12 different cancer cell lines. The epithelial marker E-cadherin protein was significantly expressed in the sensitive cell lines (p 
= 0.0364) while expression of the mesenchymal markers vimentin, Twist-1 and Snail, was found in all cell lines with reduced sensitivity to the drug. ��-Sitosterol ��-D-glucoside biological activity Furthermore, this study showed that continuous exposure to elisidepsin correlates with a downregulation of epithelial markers in 4 different cancer cell types (breast, pancreas, lung and 1326631 colon). Loss of epithelial markers was further evidenced by the detection of morphological changes in the cells. These changes, which were observed after continuous long-term exposure of different cell types to elisidepsin, suggest that the drug is able to modify the composition of the plasma membrane. This behavior was further accompanied by signaling changes, resulting in the upregulation of mesenchymal markers. This analysis confirmed that acquired resistance to elisidepsin is associated with a switch to the EMT state.On the other hand, regarding HER family receptors, we observed an association between HER3 protein expression and sensitivity to elisidepsin treatment in a variety of cell lines (p = 0.0091). The other members of the HER family were also checked by western blotting and we did not find any significant correlation. Interestingly, HER4 expression was observed in 4 out of 5 elisidepsin-sensitive breast cancer cell lines, and further studies that include more breast cancer cell lines are necessary to establish the potential predictive marker of the HE.D proteins differentiates between elisidepsin-sensitive and elisidepsin-resistant cell lines. b-actin was used as an internal control. These western blots were performed in triplicate. B) Expression levels of HER1, HER2, HER3, HER4, pAkt, and pMAPK were analyzed by western blot using 50 mg of protein cell lysate. The membranes were stripped and reprobed with anti-b-actin to verify equal protein loading. C, control; R, resistance. doi:10.1371/journal.pone.0053645.ghave been proposed to be involved in the cellular response to elisidepsin treatment, such as fatty acid-containing ceramides, 25033180 fatty acid 2-hydroxylase (FA2H), lysosomes, lipid rafts and epithelial growth factor receptors, including the HER receptors [10,29,30,31,32,33].In the present study we explored whether basal levels of EMT markers and HER receptor proteins could be predictive markers for elisidepsin treatment. The role of the cell membrane as an important target of elisidepsin was studied in breast and pancreas cancer cell lines. Basal levels of EMT protein expression markersEMT and HER3 Predicts Elisidepsin SensitivityFigure 6. Loss of HER3 expression decreases the sensitivity to elisidepsin treatment. Cell viability after treatment with various concentrations of elisidepsin for 72 h was determined in SKBR3 (A), MCF-7 (B), MDA-MB-231 (C), MDA-MB-435 (D), BT474 (E), BxPC-3 (F), HPAC (G) and AsPC-1 (H) cells. HER3 expression was downregulated with shRNA (grey squares); LUC shRNA transfected cells were used as the control (black diamonds). Mean, SD, and IC50 values are shown from three independent experiments. Cell viability was measured using a crystal violet assay. Before performing the viability experiments, all cell lines were checked by western blot using 50 mg of protein to confirm their levels of HER3 expression. doi:10.1371/journal.pone.0053645.gshowed a significant correlation with the cell viability response to elisidepsin treatment in a panel of 12 different cancer cell lines. The epithelial marker E-cadherin protein was significantly expressed in the sensitive cell lines (p = 0.0364) while expression of the mesenchymal markers vimentin, Twist-1 and Snail, was found in all cell lines with reduced sensitivity to the drug. Furthermore, this study showed that continuous exposure to elisidepsin correlates with a downregulation of epithelial markers in 4 different cancer cell types (breast, pancreas, lung and 1326631 colon). Loss of epithelial markers was further evidenced by the detection of morphological changes in the cells. These changes, which were observed after continuous long-term exposure of different cell types to elisidepsin, suggest that the drug is able to modify the composition of the plasma membrane. This behavior was further accompanied by signaling changes, resulting in the upregulation of mesenchymal markers. This analysis confirmed that acquired resistance to elisidepsin is associated with a switch to the EMT state.On the other hand, regarding HER family receptors, we observed an association between HER3 protein expression and sensitivity to elisidepsin treatment in a variety of cell lines (p = 0.0091). The other members of the HER family were also checked by western blotting and we did not find any significant correlation. Interestingly, HER4 expression was observed in 4 out of 5 elisidepsin-sensitive breast cancer cell lines, and further studies that include more breast cancer cell lines are necessary to establish the potential predictive marker of the HE.