Endocrine therapy is the standard treatment for patients with luminal breast cancer. However, after treatment most patients develop hormone resistance, by mechanisms that may include deregulation of growth factor signaling pathways. Fibroblast growth factor 2 (FGF2) consists of a secreted low molecular weight form (LMW-FGF2) and several nuclear high molecular weight forms (HMW-FGF2). We previously demonstrated that FGF2-overexpression in endocrine responsive T47D cell lines, induced hormone resistance. The aim of this study was to explore the mechanisms underlying endocrine resistance.
We performed RNAseq of FGF2-overexpressing, LMW- and HMW- FGF2-T47D-YA cell lines, compared to control T47D-YA. These results were validated in T47D by qPCR and western blot. Cell proliferation was evaluated by cell counting after 6 day-treatment with enzalutamide (E, anti-androgen), dihydrotestosterone (DHT, androgen) or LGK974 (WNT inhibitor). In vivo, cell lines were subcutaneously transplanted in NSG mice and treated for 3 weeks with E and LGK974.
RNAseq analysis revealed that FGF2-overexpressing cells had a deregulated WNT signaling pathway with the upregulation of several WNT ligands. We also detected decreased estrogen receptor α (ER α) and progesterone receptors (PR) along with an increase in androgen receptors (AR), both at the mRNA and protein levels. We found a more pronounced decrease of PR isoform A (PRA) than isoform B (PRB) resulting in a low PRA/PRB ratio, which is consistent with an endocrine resistant phenotype, based on previous results from our lab. To explore the role of AR and WNT signaling pathways in FGF-triggered endocrine resistance, we evaluated the effect of DHT, E and LGK974 in LMW- and HMW-FGF2-T47D cells compared with T47D control cells. In endocrine resistant cells, DHT induced cell proliferation while blocking AR and WNT pathways inhibited cell proliferation and tumor growth. Conversely, DHT inhibited T47D control cell proliferation and blocking the AR had no significant effect on tumor growth.
Our results suggest that targeting AR and/or WNT pathways may be an alternative therapy for endocrine-resistant breast carcinomas with low PR and high AR levels.