Abstract P5-03-05: Model of acquired resistance to the tyrphostin NT157 in hormone receptor-positive breast cancer

Abstract

Abstract As previously reported, the small-molecule tyrphostin NT157 binds to the type I insulin-like growth factor-1 receptor (IGF-1R) beta subunit (IGF-IRβ) resulting in degradation of the insulin receptor substrate (IRS) adaptor proteins and inhibits growth of tamoxifen sensitive and resistant ER+ breast cancer cells (Yang, Y. et al. Horm Canc, in press). To investigate effects related to long-term NT157 exposure on IGF signaling, we incubated T47D parental cells in increasing concentrations of NT157 for 20 months. This prolonged exposure resulted in resistant cells (T47D-NTR). Monolayer growth assays showed parental cells inhibited at 0.7 μM of NT157 whereas resistant cells were suppressed by 8 μM of NT157. In parental cells, NT157 caused G0-G1 arrest and an increase in the sub-G1 fraction. However, resistant cells did not show these cell cycle changes after exposure to NT157. Furthermore, the antiproliferative effect of prolonged exposure to 96 hours of NT157 was correlated with decreased activation of Akt/S6k signaling axis and reduction of cyclin D1 expression in T47D parental cells. 48 hours treatment with 5 μM of NT157 resulted in a decrease of IGF-IR and insulin receptor (InR) expression level at 33% and 39% respectively, along with the downregulation of the adaptor proteins IRS-1/2 in only the parental cell line. In resistant cells, the NT157 treatment induced minimal IGF-1R suppression and a 21% increase of IR expression. Additionally, the T47D-NTR cells-maintained IRS protein levels at 10 μM. This absence of IRS protein degradation observed in NT157-resistant cells correlated with the continued expression of estrogen receptor-alpha (ERα), suggesting functional changes within IGF and ERα complex. IGF ligands (IGF-1 or IGF-2) and estradiol (E2) stimulated growth in both cell lines. When NT157 was removed from T47D-NTR cells, they were not re-sensitized to NT157 nor were they affected by IGF dependent growth in the re-introduction of NT157. These findings suggest that resistance to NT157 is mediated by the maintained expression of the IRS adaptor proteins. The continued responsiveness to estradiol and IGF ligands could be due to either a decrease in the drug's half-life or possible changes in NT157 binding to the beta subunit of IGF-IR in resistant cells. Citation Format: Ekyalongo RC, Abdelwahab R, Holtz A, Sabet A, Yee D. Model of acquired resistance to the tyrphostin NT157 in hormone receptor-positive breast cancer [abstract]. In: Proceedings of the 2018 San Antonio Breast Cancer Symposium; 2018 Dec 4-8; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2019;79(4 Suppl):Abstract nr P5-03-05.