Analysis of miRNA expression profile induced by zoledronic acid in breast cancer cells

Zoledronic acid (ZOL), a third generation bisphosphonate able to significantly inhibit bone resorption, is currently used for the treatment of breast cancer patients with osteolytic bone metastases. Our previous work showed an effective anticancer role of low-dose ZOL in the inhibition of several processes, such as cell adhesion, invasion, cytoskeleton remodelling and proliferation, in MCF-7 breast cancer cell line. The main aim of our study was to investigate the molecular mechanisms and signaling pathways by which ZOL exerts its anti-tumor effects in breast cancer cells focusing our attention on miRNA expression profile. Using a TaqMan Low Density Array A human microRNA microarray analysis, the expression profile of 377 miRNAs was analyzed in MCF7 cells treated for 24 h with 10 µM ZOL with respect to untreated cells. In addition, the expression of miRNAs specifically induced by ZOL was analyzed in MCF-7, MDA-MB-231 and SkBr3 cells using Real-time PCR analyses. A subset of miRNAs was shown to be differentially expressed following the low-dose ZOL treatment, and several cancer-related pathways, including PI3/Akt, MAPK, Wnt, Jak-STAT, TGF-&bgr;, and mTOR signaling, were predicted as potential targets of these deregulated miRNAs, using the DIANA tool mirPath software. In particular, a set of 54 miRNAs resulted significantly altered after ZOL exposure, with a group of them being up- or down-regulated, and others induced or silenced by treatment. Most of these miRNAs are unexamined in breast cancer cells. These data are perfectly in agreement with the recent results reported in literature regarding some miRNAs involved in proliferation, bone metastasis development, invasion and therapy resistance in breast cancer. This work establishes, for the first time, a link between anticancer effects of ZOL and miRNA expression changes, suggesting the involvement of some miRNAs in molecular pathways mediating ZOL activity in breast cancer.