Bioengineered bacterial outer membrane vesicles encapsulated Polybia–mastoparan I fusion peptide as a promising nanoplatform for bladder cancer immune-modulatory chemotherapy

Background Nanosized bacterial outer membrane vesicles (OMVs) secreted by Gram-negative bacteria have emerged as a novel antitumor nanomedicine reagent due to their immunostimulatory properties. The encapsulated bacterial composition in OMVs can be edited via manipulating bioengineering technology on paternal bacteria, allowing us to design an ingenious antitumor platform by loading the Polybia–mastoparan I (MPI) fusion peptide into OMVs. Methods OMVs containing the MPI fusion peptide were obtained from bioengineered Escherichia coli transformed with recombinant plasmid. The antitumor efficacy of bioengineered OMVs in vitro was verified by performing cell viability and wound-healing and apoptosis assays using MB49 and UMUC3 cells, respectively. Subcutaneous MB49 tumor-bearing mice were involved to investigate the tumor inhibition ability of bioengineered OMVs. Moreover, the activated immune response in tumor and the biosafety were also evaluated in detail. Results The resulting OMVs had the successful encapsulation of MPI fusion peptides and were subjected to physical characterization for morphology, size, and zeta potential. Cell viabilities of bladder cancer cells including MB49 and UMUC3 rather than a non-carcinomatous cell line (bEnd.3) were decreased when incubated with bioengineered OMVs. In addition, bioengineered OMVs restrained migration and induced apoptosis of bladder cancer cells. With intratumor injection of bioengineered OMVs, growths of subcutaneous MB49 tumors were significantly restricted. The inherent immunostimulation of OMVs was demonstrated to trigger maturation of dendritic cells (DCs), recruitment of macrophages, and infiltration of cytotoxic T lymphocytes (CTLs), resulting in the increased secretion of pro-inflammatory cytokines (IL-6, TNF-α, and IFN-γ). Meanwhile, several lines of evidence also indicated that bioengineered OMVs had satisfactory biosafety. Conclusion Bioengineered OMVs fabricated in the present study were characterized by strong bladder cancer suppression and great biocompatibility, providing a new avenue for clinical bladder cancer therapy.