Background Current studies show that exosomal miRNAs become an important factor in cancer metastasis. Among the many miRNA studies, miR-7-5p has not been thoroughly investigated in breast cancer metastasis. Methods Bioinformatic screening was performed using extant data from the GEO database, and miR-7-5p expression levels in breast cancer cell lines and exosomes were further examined using real-time quantitative PCR (qRT-PCR). The extracted exosomes were characterised by transmission electron microscopy (TEM), particle size analysis and marker protein determination. Cell migration and invasion were then examined using wound healing assays and Transwell assays, respectively. Correlation between miR-7-5p and receptor-like tyrosine kinase (RYK) was analysed by luciferase reporter. The effect of miR-7-5p against RYK-related downstream factors was verified using western blot assays. Results In this study, we found that the expression of miR-7-5p was significantly different in exosomes secreted from breast cancer cell lines with different high and low invasiveness. Further experiments revealed that miR-7-5p has an important role in inhibiting the migration and invasion of breast cancer. In terms of mechanism of action, miR-7-5p was found to target the RYK, leading to its reduced expression, which in turn caused a reduction in the phosphorylation level of the downstream factor JNK. Reduced levels of phosphorylated JNK factors lead to reduced levels of phosphorylation of c-Jun protein, which in turn leads to increased expression of EMT transcription factors, thereby inhibiting the epithelial–mesenchymal transition (EMT) process to suppress the invasion of breast cancer. Conclusion Thus, we demonstrated that exosomes loaded with high levels of miR-7-5p emitted from less aggressive breast cancers can participate in the atypical WNT pathway by targeting the RYK gene and thus inhibit breast cancer metastasis.

The aim of this study is to design a novel pH and photothermal dual-responsive nanodrug delivery system with high biocompatibility and tumor targeting. Based on the high loading rate and good photothermal properties of graphene oxide (GO), we selected GO modified with chitosan (CO) and γ-polyglutamic acid (γ-PGA) as nanocarriers. CO and γ-PGA increased the dispersion of GO and improved the solubility of GO-CO-γ-PGA (G-C-P) in solution. To further improve the targeting of the system, the nucleic acid aptamer NH2-AS1411 (APT), which targets the nucleolin (C23), was attached to G-C-P and the targeted nano-delivery system APT-GO-CO-γ-PGA (A-G-C-P) was prepared by amidation. The synthesized samples were characterized using Fourier transform infrared spectroscopy (FTIR), Ultraviolet-visible spectrophotometer (UV-Vis), X-ray diffraction (XRD), Transmission electron microscopy (TEM), Dynamic light scattering (DLS) and Zeta potential, and their good biocompatibility and stable photothermal conversion properties were demonstrated experimentally. The nanocarrier can act as a photothermal agent, generating high temperatures to induce cell damage. The lower hemolysis rate reflects the good biocompatibility of the carrier. Doxorubicin hydrochloride (DOX) was selected as the model drug with a nanocarrier loading of 37.0 ± 0.74%, showing dual response drug release characteristics of pH and NIR light. The cytotoxicity and photothermal toxicity of the nanocarrier A-G-C-P and the drug delivery system APT-GO-CO-γ-PGA-DOX (A-G-C-P-D) on HeLa cells were investigated in cellular experiments. It was found that A-G-C-P had almost no toxic side effects on the cells, and the killing effect of A-G-C-P-D with the application of near-infrared light irradiation was more obvious, proving its good photothermal therapeutic effect, and further demonstrating that the combined effect of chemotherapy and photothermal treatment is significant than that of single treatment. Confocal microscopy and flow cytometry determined the distribution of DOX in the cells to different degrees after cell internalization. In vivo anti-tumor experiments were conducted to further investigate the therapeutic effects and safety of the targeted nano-drug delivery system in concert with photothermal. Compared with the weight loss and heart tissue damage caused by free DOX, A-G-C-P-D and NIR light irradiation did not cause any tissue damage and toxic side effects in nude mice, and have good biosafety; A-G-C-P-D and NIR light irradiation can inhibit tumor growth, cause damage to tumor tissue, significantly reduce Ki67 expression and increase Caspase-3 expression, all of which prove their good anti-tumor effects. This relatively non-invasive approach may provide a good direction for targeted drug delivery and chemotherapeutic photothermal treatment of tumors, greatly reducing the side effects of chemotherapy. The therapeutic effect of this nano-drug delivery system provides new ideas for clinical treatment strategies with potential applications and reference values, offering a broad prospect for biological applications.