Abstract P6-10-22: miR363-3p mediates maintenance of breast cancer stem cells (BCSCs) and predicts resistance to neoadjuvant chemotherapy and disease recurrence
Authors: Renaud Stephanie , Stravodimou Athina , Fiche Maryse , Xenarios Ioannis , Valentina Scabia , Dormoy Valerian , Galmiche Marie , Brisken Cathrin , Delaloye Jean-Francois , Treboux Assia , Meuwly Jean-Yves , Mermod Nicolas , Zaman Khalil 
Published: March 2020

Background Increasing data support the role of BCSCs in recurrence and resistance to chemotherapy. However, detecting these cells specifically and targeting them therapeutically remain challenging. We set to identify miRNAs involved in chemoresistance of BCSCs in vitro and the results were assessed in the sera of healthy donors and breast cancer patients treated with neoadjuvant chemotherapy (NAC). Methods In vitro experiments were conducted in the MCF7 cell line grown as mammospheres (MS) in order to enrich a BCSC phenotype. After treatment with 5FU or Paclitaxel (Pac), microRNA profile of chemoresistant cells was analyzed by microarray. The results were compared to miRNAs found in immortalized non-tumorigenic MCF10A cells in order to exclude miRNAs related to normal stem cells. A signature of 6 miRNAs was identified. miR-363-3p, appearing the most relevant, was chosen for further assessment. By RT-qPCR, miR363-3p levels were 20- and 100-fold higher in ALDH+ sorted cells compared to ALDH- MCF7 and MDA-MB-231 cells, respectively. Moreover, overexpression of miR363-3p in MCF7 cells correlated with an increased number of ALDH+ cells and 1.5 more MS formed. In contrast, downregulation of miR363-3p levels induced a decrease in MS size and 2-fold reduction in number. Consistently, miR-363-3p downregulation decreased tumor growth and metastasis of MCF7 cells in an intraductal human-in-mice transplantation model. miRNA was quantified by RT-qPCR in tissue and sera collected prospectively from 40 breast cancer patients before and after NAC (anthracycline-taxane) and also from 25 healthy donors. Results Fifty percent of the patients had luminal A and B tumors (n=20), 32,5% (n=13) had triple negative breast cancer (TNBC), and 17.5% (n=7) had HER2 positive BC. Excluding one patient, who refused the surgical resection, 40% achieved pathological complete response (pCR). Six patients presented disease recurrence. In patients’ tumor before and after NAC, a higher level of miR363-3p was observed compared with benign tissue. In sera of the BC patients, miR363-3p levels were significantly higher than that of healthy donors. After NAC, the levels of miR363-3p remained high among patients who relapsed, whereas they were equivalent to the healthy donors in patients who remained in remission. No correlation between Ki-67, grade 1 or 2 and miR363-3p levels was observed. However, in grade 3 BC, low level of miR363-3p before and after NAC was correlated with pCR and remission. The level of miR363-3p correlated with remission and pCR in patients with TNBC and HER2 BC. Conclusions Assessment in the sera of patients and healthy donors confirms our previous data supporting the role of miR363-3p as predictive factor of resistance to neoadjuvant chemotherapy and disease recurrence. Further investigations are warranted to confirm the role of miR363-3p as a biomarker and potential therapeutic target.

Citation Format: Stephanie Renaud, Athina Stravodimou, Maryse Fiche, Ioannis Xenarios, Scabia Valentina, Valerian Dormoy, Marie Galmiche, Cathrin Brisken, Jean-Francois Delaloye, Assia Treboux, Jean-Yves Meuwly, Nicolas Mermod, Khalil Zaman. miR363-3p mediates maintenance of breast cancer stem cells (BCSCs) and predicts resistance to neoadjuvant chemotherapy and disease recurrence [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P6-10-22.