Effect of ligand binding domain activating mutations of ESR1 on cellular metabolism, liver tropism, and chemotherapy resistance.

Abstract

e14506 Background: Mutations in the ligand binding domain (LBD) of estrogen receptor α (ER) confer constitutive transcriptional activity and resistance to endocrine therapies in breast cancer patients. Accumulating clinical data suggest adverse outcome for patients harboring tumors expressing these mutations. We aimed to elucidate mechanisms conferring this aggressive phenotype. Methods: Cells constitutively expressing physiologic levels of ER harboring activating LBD mutations were generated and characterized for viability, invasiveness and tumor formation in vivo. Gene expression profile was studied using RNAseq. Metabolic properties were assessed using global metabolite screen and direct measurement of metabolic activity. Response to chemotherapies was assessed using viability assays. Results: Cells expressing mutated ER showed increased proliferation, migration and in vivo tumorogenicity compared to cells expressing the WT-ER, even in the presence of estrogen. Experiments in mice revealed a more aggressive phenotype of the Y537S mutant compared to D538G as well as unique tissue predilection. Thus, 538G-ER cells exhibited liver tropism while Y537-ER cells mainly metastasized to the lungs and lymph nodes. Importantly, both mutations conferred resistance to paclitaxel and doxorubicin. Further studies indicated association of the mutated ER with upregulation of genes involved in tumor cell metabolism. Indeed, a global metabolic screen revealed distinct metabolic profile for cells harboring activating mutations, including the ability to utilize glutamine as an alternative carbon source. Moreover, we observed unique metabolic activities enabling cells to thrive in urea-reach environment of the liver, and overcome doxorubicin-induced stress responses. Conclusions: Taken together, these data indicate estrogen-independent rewiring of breast cancer cell metabolism by LBD-activating mutations, enabling aggressivene clinical behavior and chemotherapy resistance. Importantly, These unique metabolic activities may serve as a potential vulnerability and aid in the development of novel treatment strategies to overcome endocrine resistance.