Abstract P1-12-12: The insulin like growth factor axis and development of tamoxifen resistance in breast cancer

Abstract

Abstract Background Insulin-like growth factors (IGF). IGFs are potent mitogens for breast epithelial cells that modulate the action of AKT, which has been reported to be associated with tamoxifen resistance. To date, however, anti-IGF strategies have proved disappointing in clinical trials We have investigated whether the IGFBP family of proteins, which modulate the activity of IGF, may play a role in tamoxifen resistance, opening up the route for alternative anti-IGF based therapies. Methodology We investigated the expression of IGF axis genes in parental and tamoxifen-resistant (TamR) MCF-7 cells using qRT-PCR. Gene and protein expression was confirmed using ELISA, Western, and ligand blotting. shRNA transfection was used to silence candidate IGF axis genes in both cell lines. Cell sensitivity 4-hydroxytamoxifen (4-HT) was investigated by WST-1 cell proliferation assay. Results IGF-IR, IGF-2R, IGFBP-2, -4 and -5 genes had the highest expression levels. IGFBP-5 was down-regulated 7-fold while IGFBP-2 was up-regulated by 2-fold in TamR v wt cells. Changes in IGFBP-5 and IGFBP-2 gene expression were mirrored in protein levels measured in conditioned media by ELISA, Western and Ligand blot. Importantly knock down of IGFBP-2 in TamR cells restored sensitivity to 4-HT suggesting a causal role for IGFBP-2 in the acquisition of tamoxifen resistance. Conclusion IGFBP-5 and IGFPB-2 are reciprocally regulated on the acquisition of tamoxifen resistance by MCF-7 cells. Preliminary studies suggest that IGFBP-2 may play a role in the development of tamoxifen resistance in vitro. Citation Format: Yousef M Hawsawi, James Beattie, Reem El-Gendy, Valerie Speirs, Christopher Twelves. The insulin like growth factor axis and development of tamoxifen resistance in breast cancer [abstract]. In: Proceedings of the Thirty-Seventh Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2014 Dec 9-13; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2015;75(9 Suppl):Abstract nr P1-12-12.