Feedback Activation Of STAT3 Confers Resistance Of HER2~+ Breast Cancer Cells To Lapatinib

Objective:To explore the role of Signal transducers and activators of transcription 3(STAT3)in lapatinib-resistant HER2-positive breast BT-474 cancer cells,and identify potential drug-resistant targets to provide the clues for treating lapatinib-resistant Her2+breast cancer.Methods 1,BT-474 cells had been treated with indicated lapatinib concentrations(0.2,0.5,1.0,2.0 and 4.0?mol/L)for 6months until the cells acquired the stable lapatinib-resistant BT-474(BT-474R)cells were established.2,Caspase 3/7 enzymatic activity levels in parental BT474 and BT-474R cells were examined using Caspase 3/7 Glo kit and the growth inhibition rate(IC50)was tested by the MTT assay.3,The expression of IL-6 and IL-6R mRNA in BT-474 parental cells and drug-resistan cells were tested by RT-qPCR.4,Western blot analysis was used to test the protein expression levels of P-gp,IL-6,p-STAT3,STAT3 and cleaved caspase 3.Inhibition of STAT3 expression by RNAi was verified by Western Blot.5,Cellular apoptosis was examined by Annexin V-FITC/PI staining and Caspase-Glo~?3/7 Assay.Results BT-474R cells displayed significantly elevated P-gp expression when compared with BT-474 cells(P<0.05)?The IC50 value of BT-474R cells was 12.7 times higher than that of BT-474 parent cells.Lapatinib treatment stimulated signal transducer and activator of transcription 3(STAT3)activity,and STAT3 activity was also upregulated in BT-474R cells.STAT3 silencing not only remarkably restored sensitivity to lapatinib and enhanced lapatinib-induced cleaved caspase 3 and caspase3/7 enzymatic activity(P<0.01),but also increased the apoptosis of BT-474R cells(P<0.01).Furthermore,lapatinib-mediated IL-6 secretion regulated STAT3 activity.Blocking IL-6 using anti-IL-6 antibody abrogated lapatinib-induced STAT3 activity.Conclusion 1,The model of lapatinib-resistant BT-474 cells were established successfully.2,The development of lapatinib-resistance was dependent on activation of STAT3.3,Lapatinib-induced IL-6 secretion could enhances the resistance against through activating STAT3 in HER2~+breast cancer cells.