Abstract A57: miR-125a-induced cellular switch elicits a response to anti-HER2 targeted therapy in breast cancer cells
Authors: Ninio-Many Lihi , Hikri Elad , Stemmer Salomon M. , Shalgi Ruth , Ben-Aharon Irit 
Published: May 2016

Background: The EGFR/HER2 signaling network emerges as an effective therapeutic target for Her2 enriched cancers, which is known by its aggressive biological course. Nevertheless, there is evidence that the EGFR/HER2 network may play a key role not only in the HER2-enriched subtype of breast cancer, but also in the similarly aggressive basal-like subtype. We had formerly demonstrated the involvement of miR-125a-3p in the EGFR pathway in prostate cancer. We aimed to study the effect of miR-125a-3p as a potential modulator of the ERBB2/HER2 pathway in basal-like breast cancer subtype.

Methods: Using qPCR we calibrated estrogen receptor (ER), ERBB2 (HER2), miR-125a-3p/5p (two isoforms) expression in three cell lines: MDA-MB-231, MCF-7 and SKBR3 (represent the basal-like subtype, ER positive subtype and HER2-enriched subtype respectively). We generated stable MDA-MB-231 cells that overexpress miR-125a-3p and control cells that overexpress scrambled miRNA. In parallel, we established an in vivo platform by injection of miR-125a-3p-overexpressing MDA-MB-231 breast cancer cells to the mammary pad of NUDE mice and evaluated traits of the induced tumors compared with scrambled miRNA-expressing cells (control mice) and response to potential targeted therapy.

Results: miR-125a-3p was endogenously expressed in all cell lines, though its expression in MDA-MB-231 cells was significantly lower than in MCF-7 or in SKBR3 cells. Following transfection of cells with miR-125a-3p, MDA-MB-231 cells showed a significant increase in the expression level of ERBB2 mRNA and protein as well as a stronger immunofluorescence staining of ErbB2 than in control cells. Combined treatment of miR-125a-3p-overexpressing cells and trastuzumab induces apoptosis and reduces migration of MDA-MB-231 cells. By tracking Erbb2 internalization and its localization to the lysosoms/the functionality of erbb2 receptor, we determined that trastuzumab caused internalization of ErbB2 and a subsequent lysosomal lysis. In the experimental in vivo platform, starting one week post cells injection/tumor formation?, mice were treated twice a week, for the next 28 days, with 10 mg/Kg trastuzumab or saline as a control. Response to treatment was evaluated by measurement of the tumor size/volume by computerized tomography (CT) or calliper. Both measurements indicated that that the tumors in the miR-125a-3p group that were treated with trastuzumab were significantly smaller than in other groups.

Conclusion: our results indicate that miR-125a-3p is capable of inducing a shift in the involvement of key cellular pathway - the ERBB2 pathway that may convert the cell fate and dispose it to anti-HER2 therapies. In an era of personalized medicine, our study proposes a means to enlarge the patient population that may benefit from anti-HER2 therapies.

Citation Format: Lihi Ninio-Many, Elad Hikri, Salomon M. Stemmer, Ruth Shalgi, Irit Ben-Aharon. miR-125a-induced cellular switch elicits a response to anti-HER2 targeted therapy in breast cancer cells. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr A57.