Role of Insulin like Growth Factor Binding Proteins and Tamoxifen Resistance in Breast Cancer Epithelial Cells

The development of tamoxifen resistance (TR) in oestrogen-dependent breast cancer (BC) is a therapeutic challenge. Insulin-like growth factor binding proteins (IGFBPs) may play a role in this process. We have investigated the role of IGFBP proteins in TR BC. IGF axis genes were evaluated in MCF-7 (wt) cells and tamoxifen-resistant (TamR) variants using qRT-PCR and confirmed by ELISA, Western, and Ligand blotting. IGFBP-2 & -5 were knocked down by shRNA transfection, and subsequent sensitivity to 4-hydroxytamoxifen (4-HT) was determined via WST-1. Cell migration was investigated by using the Incucyte system. IGFBP-2 expression was evaluated in 424 BC cases by TMA immunohistochemistry. Five out of 10 genes of the IGF axis (IGF-IR, IGF-2R, IGFBP-2, -4 and -5) had the highest expression levels by both parental wt and TamR cells. IGFBP-5 was down-regulated by ~7-fold while IGFBP-2 was up-regulated by ~2-fold in TamR versus wt cells (mRNA and protein levels). Significantly, a knockdown of IGFBP-2 in TamR cells restored sensitivity to (4-HT), reduced ERα expression to 45 ± 11.9% and enhanced cell migration. Expression of IGFBP-2 was signicantly (P< 0.001) associated with survival advantage in TR patients. IGFBP-2 and IGFPB-5 are reciprocally regulated in the acquisition of TR by MCF-7 cells. IGFBP-2 may play a role in the development of TR in vitro and its high levels in clinical samples may predict TR.