Mechanism and pathways of Glucocorticoid Receptor (GR) signaling in TNBC progression

Georgetown University, Washington DC

Investigators

Abstract

Project Summary Triple negative breast cancer (TNBC) is an aggressive BC subtype that metastasizes to multiple sites and has a prognosis of less than two years overall survival. We have reported that the presence of a small population of cells (enablers) present in TNBC can drive the bulk (responder) population of a tumor to invade and metastasize. The enabler effect on invasion of TNBC in 3D models can be markedly enhanced by glucocorticoid treatment and inhibited by glucocorticoid antagonists. One hallmark of the enabler population is high levels of expression of an isoform (D4) of the nuclear receptor coactivator oncogene AIB1. D4 is a potent coactivator of the glucocorticoid receptor (GR) and is found at glucocorticoid response elements (GREs) in both gene promoter and enhancer regions suggesting that the D4 isoform influences genomic engagement patterns of GR. Responder /enabler cell-cell contact drives significant increases in glucocorticoid dependent gene expression, especially in the D4 enabler cells and cell adhesion pathways are amongst the most highly enriched in both enabler and responder cells. This suggests one possible mechanism of glucocorticoid-mediated enabling. In this proposal we will examine the mechanism(s) of D4 enhancement of GR -induced enabling and determine the role of glucocorticoid-induced pathways in the enabling of TNBC invasion and metastasis. Aim 1: To determine how enabler/responder cellular cross talk enhances the GR Response. Using genetic (knockdown) and pharmacologic (GR antagonist Relacorilant, (Rela) approaches we will dissect the contribution of the GR to metastasis enabling determining: A) the relative role of the GR in D4 enabler vs responder cells. B) the glucocorticoid-dependent changes in genomic engagement pattern of GR and AIB1 isoforms C) the associated glucocorticoid -dependent gene expression patterns and D) the contribution of the most highly regulated pathways will be examined in different TNBC models in 3D using siRNAs and small molecule inhibitors for pathway targeting. Aim 2: To determine the effects of the glucocorticoid antagonist Relacorilant on TNBC metastatic progression and the immune microenvironment in vivo we will determine A) the effects of Rela on progression and metastasis of TNBC D4 enabled human tumor xenografts in immune compromised mice. B) the contribution of glucocorticoid antagonism and host immune function by comparing progression and metastasis of a syngeneic, immune-competent vs xenograft tumors in immune compromised mice and C) dissect signaling pathways of glucocorticoid antagonism in the xenograft and allograft models. These studies will uncover unknown vulnerabilities to exploit in a subset of TNBC tumors that harbor enabler cells and open new avenues for therapeutic targeting of this deadly cancer.