Evaluation of in vivo antitumor effects of low‐frequency ultrasound‐mediated miRNA‐133a microbubble delivery in breast cancer

MicroRNAs (miRNAs), as a novel class of small noncoding RNAs, have been identified as important transcriptional and posttranscriptional inhibitors of gene expression. Ultrasound‐targeted microbubble destruction (UTMD) is a noninvasive method for microRNA delivery. We aimed to investigate the effect of UTMD of miR‐133a on breast cancer treatment. It has been reported that miRNA‐133a is involved in various cancers. miR‐133a was lowly expressed in breast cancer tissues and breast cancer cell lines MCF‐7 and MDA‐MB‐231. The miR‐133a expression was significantly upregulated under exogenous miRNA‐133a treatment in MCF‐7 and MDA‐MB‐231 cells analyzed by qRT‐PCR. Exogenous miR‐133a promoted the cell proliferation as determined by diphenyl tetrazolium bromide (MTT) assay and 5‐ethynyl‐2′‐deoxyuridine (EdU) staining. Epidermal growth factor receptor (EGFR) expression and Akt phosphorylation were significantly suppressed after miR‐133a transfection by western blot detection. We prepared the miR‐133a‐microbubble and injected it into breast cancer xenografts. The miR‐133a‐microbubble injection prolonged miR‐133a circulatory time by detecting the amount of miRNA‐133a in the plasma. No significant toxicity was observed on alanine aminotransferase (ALT) and aspartate aminotransferase (AST) levels at liver and albumin, blood urea nitrogen, or creatine kinase levels at kidney after miR‐133a‐microbubble injection. The tumor size of miR‐133a‐microbubble‐injected mice was smaller than that of the control group. Furthermore, the delivery efficiency of miR‐133a with low frequency was higher than that with common frequency. miR‐133a suppressed cell proliferation by suppressing the expression of EGFR and the phosphorylation of Akt. UTMD of miR‐133a inhibited the tumor growth and improved the survival rate in breast cancer mice. Our study provides new evidence that UTMD of miRNA is a promising platform for breast cancer therapy.