e13084 Background: There are currently limited effective therapeutic options for metastatic breast cancer, and none target the metastatic process. MiR-10b is a major driver of breast cancer cell invasion and migration. Our lab has demonstrated its importance in metastatic cell viability, positioning miR-10b as a target for metastatic breast cancer. Our previous studies demonstrated that delivery of a novel therapeutic consisting of antisense anti-miR-10b oligomers conjugated to magnetic nanoparticles (termed MN-anti-miR10b) prevented metastases in vivo. These studies led us to hypothesize that MN-anti-miR10b affects the viability of a stem cell-like population of cells within primary tumors that otherwise would have formed metastases. Here, we investigate the relationship between miR-10b and breast cancer cell stemness and the effects of miR-10b inhibition by MN-anti-miR10b on breast cancer cell stemness. Methods: MDA-MB-231 breast cancer cells were sorted based on surface markers into stem-like (CD44+/CD24-) and non-stem-like (CD44-/CD24-) populations, and their miR-10b expression levels were quantitated. Then, unsorted MDA-MB-231 cells were treated with MN-anti-miR10b to determine the effects of miR-10b inhibition on the expression of EPCAM, a marker for cancer cell stemness. Lastly, MCF-7 breast cancer cells were cultured in mammosphere medium (which selects for stem-like cells and induces spheroid formation) and treated with MN-anti-miR10b to establish the phenotypic effect of miR-10b inhibition on cancer cell stemness. Results: We found that stem-like MDA-MB-231 cells displayed >2-fold miR-10b expression compared to non-stem-like cells. Accordingly, alongside a 70% reduction in miR-10b expression, treatment of MDA-MB-231 cells with MN-anti-miR10b reduced EPCAM expression by 65%. Treatment of MCF-7 spheroids with MN-anti-miR10b resulted in significantly greater cell dissociation from the spheroid compared to controls. Conclusions: These results support the hypothesis that inhibition of miR-10b with MN-anti-miR10b inhibits breast cancer cell stemness. This provides an explanation for the therapeutic efficacy of MN-anti-miR10b observed in mouse breast cancer metastasis models. Future studies will further investigate this relationship and shed light on how miR-10b can be optimally targeted to treat metastatic breast cancer in humans.

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