Tamoxifen resistance (TamR) prevents ER-positive breast cancer patients from benefitting from endocrine therapy, and miR-221 or miR-222 plays vital roles in inducing TamR. In this study, we designed synthetic sponges to reverse TamR by targeting these two miRs. First, we established a tamoxifen resistant breast cancer cell line (MCF-7TamR), we verified the high expressing level of these two miRs in TamR cells. miR-221 or miR-222 inhibitors rendered MCF-7TamR cells responsive to tamoxifen. Next, we designed a miR-221/222 sponge, which contains total 8 multi-antisense binding sites (MBSs) for these two onco-miRs, and inserted it into CMV promoter- or hTERT promoter-driven expressing vectors. After transfected miR-221/222 sponge expressing vectors into MCF-7TamR cells, we identified a strong interaction between miR-221/222 sponge and endogenous miR-221 or miR-222 by RNA pulldown assay. We also found that miR-221/222 sponge restored the expression of ERα and PTEN, arrested cells in G1 phase, and finally resulted in reduced cell growth and cell migration. Notably, miR-221/222 sponge expressing cells abrogates tamoxifen resistance through restoring the expression of ERα, suggesting that miR-221/222 sponge gene therapy especially driven by tumor specific promoter could provide an effective therapeutic approach against TamR in breast cancer.

In the present study, authors analyzed the expression of miR-221 and miR-222 in established MCF-7TamR cells. They inserted tandem bulged miRNA binding sites targeting miR-221 and miR-222 into cytomegalovirus (CMV) promoter- and human telomerase reverse transcriptase (hTERT) promoter-driven expression vectors to generate synthetic tumor-specific miR-221/222 sponges. They investigated the roles of these sponges in cellular function and their potential application for TamR in breast cancer.

The CMV-miR-221/222 sponge and T-VISA miR-221/222 sponge restored the sensitivity of MCF-7TamR cells to tamoxifen

Article Access: https://link.springer.com/article/10.1186%2Fs43556-021-00045-0

Website for Molecular Biomedicine: https://www.springer.com/journal/43556

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