Evidence for Enhanced Exosome Production in Aromatase Inhibitor-Resistant Breast Cancer Cells.

Giuseppina Augimeri,Balázs Győrffy,Cinzia Giordano,Stefania Catalano,Sebastiano Andò,Salvatore Panza,Luca Gelsomino,Ines Barone,Daniela Bonofiglio,Diego Sisci,Catia Morelli,Giusi La Camera

doi:10.3390/ijms21165841

Abstract

Aromatase inhibitors (AIs) represent the standard anti-hormonal therapy for post-menopausal estrogen receptor-positive breast cancer, but their efficacy is limited by the emergence of AI resistance (AIR). Exosomes act as vehicles to engender cancer progression and drug resistance. The goal of this work was to study exosome contribution in AIR mechanisms, using estrogen-dependent MCF-7 breast cancer cells as models and MCF-7 LTED (Long-Term Estrogen Deprived) subline, modeling AIR. We found that exosome secretion was significantly increased in MCF-7 LTED cells compared to MCF-7 cells. MCF-7 LTED cells also exhibited a higher amount of exosomal RNA and proteins than MCF-7 cells. Proteomic analysis revealed significant alterations in the cellular proteome. Indeed, we showed an enrichment of proteins frequently identified in exosomes in MCF-7 LTED cells. The most up-regulated proteins in MCF-7 LTED cells were represented by Rab GTPases, important vesicle transport-regulators in cancer, that are significantly mapped in “small GTPase-mediated signal transduction”, “protein transport” and “vesicle-mediated transport” Gene Ontology categories. Expression of selected Rab GTPases was validated by immunoblotting. Collectively, we evidence, for the first time, that AIR breast cancer cells display an increased capability to release exosomes, which may be associated with an enhanced Rab GTPase expression. These data provide the rationale for further studies directed at clarifying exosome’s role on endocrine therapy, with the aim to offer relevant markers and druggable therapeutic targets for the management of hormone-resistant breast cancers.

Highlights

According to the GLOBOCAN statistics in 2018, breast cancer represents the most commonly diagnosed cancer and the deadliest type of malignancy among the female population on a world scale, showing morbidity and mortality rates of ~25% and ~15%, respectively [1]
When we analyzed the concentration of the secreted vesicles by using Nanoparticle Tracking Analysis (NTA), we found that the numbers of the exosomes released in the conditioned medium of MCF-7 Long-term estrogen deprived (LTED) cells increased about six-fold compared to those of exosomes isolated from parental cells (6.09 × 1010 ± 0.48 × 1010 versus 1.01 × 1010 ± 1.96 × 108) (Figure 1c)
Exosome secretion was significantly increased in MCF-7 LTED cells compared to MCF-7 cells, further indicating that AI resistance (AIR) phenotype might be associated with an enhanced capability of breast cancer cells to release exosomes

Summary

Introduction

According to the GLOBOCAN statistics in 2018, breast cancer represents the most commonly diagnosed cancer and the deadliest type of malignancy among the female population on a world scale, showing morbidity and mortality rates of ~25% and ~15%, respectively [1]. Clinical decisions are generally dependent on disease stage and expression of estrogen (ER) and progesterone (PR) receptors, epidermal growth factor 2 receptor (HER2) and Ki-67. Hormone receptor-positive breast carcinomas account for almost 70–80% of all cancer cases and mainly overlap with luminal molecular subtypes [2]. In these tumors, endocrine-targeted treatments using aromatase inhibitors (AIs, i.e., letrozole, anastrozole and exemestane) represent the mainstay of the standard care both in the adjuvant and recurrent settings. Despite major advances in our understanding of these molecular events, we are still unable to effectively treat hormone-resistant diseases, highlighting the need to explore novel, clinically relevant markers and therapeutic targets

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