Bacterial extracellular vesicles-based therapeutic strategies for bone and soft tissue tumors therapy

Abstract

Bone and soft tissue tumors are complex mesenchymal neoplasms that seriously endanger human health. Over the past decade, the relationship between microorganisms and human health and diseases is getting more attention. The extracellular vesicles derived from bacteria have been shown to regulate bacterial-host cell communication by transferring their contents, including nucleic acids, proteins, metabolites, lipopolysaccharides, and peptidoglycans. Bacteria extracellular vesicles (BEVs) are promising lipid-bilayer nanocarriers for the treatment of many diseases due to their low toxicity, drug loading capacity, ease of modification and industrialization. Specially, BEVs-based cancer therapy has attracted much attention because of their ability to effectively stimulate immune responses. In this review, we provide an overview of the biogenesis, composition, isolation, classification, and internalization of BEVs. We then comprehensively summarize the sources of BEVs in cancer therapy and the BEVs-related cancer treatment strategies. We further highlight the great potential of BEVs in bone and soft tissue tumors. Finally, we conclude the major advantages and challenges of BEVs-based cancer therapy. We believe that the comprehensive understanding of BEVs in the field of cancer therapy will generate innovative solutions to bone and soft tissue tumors and achieve clinical applications.

Keywords: Bacteria extracellular vesicles; Bone and soft tissue tumors; Immunotherapy; Nanotechnology; Synergistic therapy.

Figure 1

BEVs-based cancer therapy is of great significance. BEVs are derived from Gram-positive and Gram-negative bacteria and can be designed as functionalized BEVs for tumor therapy by engineering approaches. The resulting BEVs have shown great promise against various tumors, including bone and soft tissue tumors. Figure was created with https://app.biorender.com/.

Figure 2

Overview of biogenesis, composition, and classification of BEVs. The Gram-positive bacteria can generate CMVs by the mechanism of bubbling cell death. In contrast, the Gram-negative bacteria have two kinds of mechanisms to generate BEVs. The OMVs are produced by the mechanism of blebbing of the outer membrane; the OIMVs and EOMVs are resulted from explosive lysis. In general, BEVs contain many inclusions such as nucleic acids (DNA/RNA), proteins, and metabolites, etc. IM: Inner membrane, OM: other membrane, PG: peptidoglycan, LPS: lipopolysaccharide.

Figure 3

A set of isolation method applicable to the vast majority of bacteria. After proper culture, the isolation of BEVs is generally divided into three steps: 1) Removal of bacteria and their debris; 2) Removal of non-BEVs proteins and concentration; 3) Isolation and purification. Finally, the collected BEVs are characterized by TEM, NTA, and WB, if necessary.

Figure 4

The internalization of BEVs. Three major internalization pathways for BEVs internalization have been proposed: 1) Receptor-mediated signaling; 2) Endocytosis via endocytosis via phagocytosis, macropinocytosis, lipid raft, and caveolae; 3) Membrane fusion. Figures were created with https://app.biorender.com/.

Figure 5

Summarization of BEVs-based cancer treatment strategies. Immunotherapy is an important therapy in the field of BEV-based cancer therapy. In addition to immunotherapy, BEVs have been applied to the combination with chemotherapy, gene therapy, and photothermal therapy to amplify antitumor efficacy. Nanostructured BEVs enable efficient lymphatic drainage when injected subcutaneously and enhance localization to solid tumors through passive targeting effect when injected systemically. More importantly, the targeting ability of BEVs can be enhanced by displaying specific proteins on the membrane surface, which can greatly enhance local drug concentration and reduce side effects. Figure was created with https://app.biorender.com/.

Figure 6

BEVs-based immunotherapy. (A) Schematic illustration of the antitumor mechanism and characterization of BEVs-PD1 for cancer immunotherapy. Adapted with permission from , copyright 2020, American Chemical Society. (B) Schematic illustration of the construction of EcN into ΔE-CHy and its application. Adapted with permission from , copyright 2022, Wiley-VCH GmbH. EcN, E. coli Nissle 1917; ΔE, EcN with the deletion of nlpI; CHy, ClyA-Hy. (C) Schematic illustration of the construction and the mechanism of multifunctional modified biomimetic BEVs. Adapted with permission from , copyright 2021, Wiley-VCH GmbH. It is worth noting that the author uses OMV to represent the extracellular vesicles produced by bacteria, which is not exactly the same as the OMVs described in “2.1 Biogenesis, composition, and classification of BEVs”. In order to maintain the consistency of the article, we use BEVs to represent the extracellular vesicles produced by bacteria, and the explanation will not be repeated later.

Figure 7

BEVs-based immunotherapy and chemotherapy. (A) Schematic illustration of the construction of bioengineered BEVs-coated polymeric micelles and the effect of combination of immunotherapy and chemotherapy. Adapted with permission from , copyright 2020, American Chemical Society.

Figure 8

BEVs-based immunotherapy and gene therapy. (A) Schematic representation of the BEVs-based siRNA delivery system, which displays HER2 affibody in the outer membrane to specifically target tumors. Adapted with permission from , copyright 2014, American Chemical Society. (B) Schematic representation of the BEV-based mRNA delivery system and innate immunity activation and antigen presentation. Adapted with permission from , copyright 2022, Wiley-VCH GmbH.

Figure 9

BEVs-based immunotherapy and photothermal therapy. (A-B) Schematic illustration of BEV-Mel production. Adapted with permission from , copyright 2019, Springer Nature. (C-D) Schematic illustration of the construction of HPDA@BEV-CC NPs and their antitumor immune responses after PTT. Adapted with permission from , copyright 2020, American Chemical Society.

Figure 10

The potential role of BEVs in BSTTs. Displaying proteins or antigens on the membranes, loading therapeutic agents (such as chemotherapeutics, miRNA, siRNA, and PTAs), and hybridizing other functionalized biological membranes (such as lipopolymers and tumor membranes) can be used to enrich the therapeutic and targeting functions of BEVs for BSTTs. Moreover, oral administration of BEVs or BEVs-based symbiotic bacteria will be one of the promising directions of BEVs-based cancer therapy. In addition, another important application area of BEVs is the diagnostic biomarker in tumor liquid biopsies. Figure was created with https://app.biorender.com/.