[Escherichia coli outer membrane vesicles inhibit rat glioma proliferation through cell endocytosis]

To investigate the inhibitory effect of Escherichia coli outer membrane vesicles (E. coli-OMVs) on glioma proliferation and the underlying mechanism.

CCK-8 assay and EdU incorporation assay were used to determine the optimal concentrations of E. coli-OMVs and chlorpromazine (CPZ) for cell treatment. C6 glioma cells treated with 10 μg/mL E. coli-OMVs and 10 μmol/L CPZ were examined for PCNA and Ki67 expressions and cell cycle distribution using qRT-PCR, Western blotting, immunocytochemistry and flow cytometry. The expressions of β-catenin, cyclin D1, and c-Myc proteins in C6 cells were detected following treatment with OMVs in the presence or absence of CHIR99021. In a SD rat model bearing orthotopic glioma, the effects of intranasal PBS or OMVs (0.25, 0.5, 1.0 mg/kg) administration on tumor growth and PCNA and Ki67 expressions were observed using fluorescence imaging and immunohistochemistry.

E. coli-OMVs within the concentrations of 2.5-10 μg/mL dose-dependently inhibited C6 cell viability, and such inhibitory effect was attenuated by 2.5, 5, and 10 μmol/L CPZ, which was the most effective at 10 μmol/L. The OMVs at 10 μg/mL significantly reduced EdU-positive cells, downregulated mRNA and protein expressions of PCNA and Ki67, and increased G0/G1-phase and decreased S-phase cell populations. These alterations were largely reversed by 10 μmol/L CPZ. Treatment with OMVs downregulated cellular expressions of β‑catenin, Cyclin D1, and c-Myc, which were partially restored by application of CHIR99021. In the tumor-bearing mice, intranasal OMVs administration dose-dependently decreased the relative fluorescence signals, slowed tumor growth, and reduced PCNA and Ki67 expressions.

E. coli-OMVs inhibit glioma cell proliferation and delay orthotopic tumor growth in rats likely via endocytic uptake of the OMVs to cause suppression of Wnt/β-catenin signaling and cell cycle arrest.