Abstract P6-05-15: Glucocorticoids has diverse effect on the tumorigenicity in estrogen receptor positive and estrogen recptor negative cancer cells

Abstract

Abstract Background: Glucocorticoids (GCs) exerts its biologic effects via GC receptor (GR), which has been linked to signal transduction pathways inducing apoptosis in many hematological malignancies. Generally, GCs are considered not affecting the growth of gross tumor of most non-hematological solid tumor. However, a recent study using meta-analysis of primary breast tumor gene expression from 1378 early breast cancer patients with long-term follow-up, showing that high levels of GR expression significantly correlated with shorter relapse-free survival in estrogen receptor (ER) negative patients. On the contrary, in ER+ breast cancer patients, high levels of GR expression in tumors were significantly associated with better outcome relative to low levels of GR expression. (Cancer Res. 2011, 15;71: 6360–70). We hypothesized that GC has differential effect on the tumorigenicity in ER+ and ER− breast cancer cells. Methods: Twelve ER− breast cancer cell lines and 5 ER+ breast cancer cell lines were tested. MTT assay, clonogenic assay and soft agar assay was performed with cancer cells treated with or without dexamethasone (DEX). Flow cytometry were applied to detect the effect of DEX on the expression of cancer stem cell markers after treatment with DEX. Nude mice tail vein injection assay of cancer metastasis was performed to evaluate the in vivo tumorigenicity. Transfection with ER expression vector to MDA-MB231, a triple negative cancer cell, by lipofectamine was carried to determine the role of ER in this scenario. Results. DEX significantly enhanced colony forming ability and/or tumorigenicity in 12 ER− breast cancer cell lines. However, DEX did not affect the proliferation rate of these cancer cells according to MTT assay. We further explored whether DEX could affect the population of cancer stem-like cell, and thereby resulted in increase of tumorigenicity. By flow cytometry study, we found treatment of DEX significantly increased the number stem cell marker + (for examples, ALDH+) cells in ER− cancer cell lines, but not in ER+ cell lines. Sorting and collection of these stem cell marker + cells demonstrated that they had much higher colony forming efficiency and tumorigenicity. Further, in nude mice model by tail vein injection with MDA-MB-231-Lu2 (derived from lung metastasis of MDA-MB-231 cells after two in vivo passages in nude mice using intracardiac injection), treatment of DEX significantly increased the lung metastatic foci number and size. In contrast, DEX significantly decreased the colony forming ability and tumorigenicity in 5 ER+ cancer cell lines. Short term exposure (72hr) of DEX resulted in increased p21 expression and cell cycle G1 arrest in MCF7, an ER+ cancer cell. Prolong incubation of MCF7 cells with DEX (more than 10 days) induced cell apoptosis. When MDA-MB231 cells were stably transfected with ER, MDA-MB231/ER cells showed similar phenotype as those of ER+ cancer cell lines, i.e., DEX decreased the clonogenic and tumorigenicity ability. Studies on underlying mechanisms are ongoing, and preliminary result showed that there is cross talk between ER and GR. Conclusions: GC increased tumorigenicity in ER− breast cancer cells, but decrease tumorigenicity in ER+ cancer cells. Citation Information: Cancer Res 2012;72(24 Suppl):Abstract nr P6-05-15.