Development of bacterial vectors for tumor-targeted gene therapy

Bacterially mediated drug delivery and therapeutics: Strategies and advancements

It was already clinically apparent 150 years ago that bacterial therapy could alleviate diseases. Recently, a burgeoning number of researchers have been using bacterial regimens filled with microbial therapeutic leads to diagnose and treat a wide range of disorders and diseases, including cancers, inflammatory diseases, metabolic disorders and viral infections. Some bacteria that were designed to have low toxicity and high efficiency in drug delivery have been used to treat diseases successfully, especially in tumor therapy in animal models or clinical trials, thanks to the progress of genetic engineering and synthetic bioengineering. Therefore, genetically engineered bacteria can serve as efficient drug delivery vehicles, carrying nucleic acids or genetic circuits that encode and regulate therapeutic payloads. In this review, we summarize the development and applications of this approach. Strategies for genetically modifying strains are described in detail, along with their objectives. We also describe some controlled strategies for drug delivery and release using these modified strains as carriers. Furthermore, we discuss treatment methods for various types of diseases using engineered bacteria. Tumors are discussed as the most representative example, and other diseases are also briefly described. Finally, we discuss the challenges and prospects of drug delivery systems based on these bacteria.

Attenuated Salmonella typhimurium-mediated tumour targeting imaging based on peptides

Attenuated bacteria-mediated tumor targeting diagnosis will provide a novel strategy for further cancer treatments owing to the intrinsic facultative anaerobic characteristic of bacteria and rapid proliferation in the tumor sites. In this work, we firstly investigate the in vivo behaviour of the attenuated Salmonella typhimurium (S. typhimuriumΔppGpp/lux) after intravenous injection. S. typhimurium exhibits rapid proliferation in tumor sites after three days of injection through bioluminescence imaging, the Luria-Bertani plate and the Gram-staining assay. In contrast, S. typhimurium does not proliferate in the normal tissues and could be excreted from the body of mice. Afterwards, a targeting peptide ubiquicidin (UBI) labeled with fluorescent dye Cy5.5 or radionuclide ¹²⁵I was intravenously injected into the mice with or without S. typhimurium treatments for in vivo fluorescence imaging and single-photon emission computed tomography (SPECT/CT) imaging, respectively. The results show that the peptide UBI could specifically target the two independent bacteria-infected tumor models, the 4T1 murine breast cancer model and the CT26 mouse colon cancer model, realizing the sensitive multimodal imaging of tumors. Such a strategy (bacteria-mediated tumor targeting) may further improve the sensitivity to early diagnosis of tumors. We hope that our developed strategy could further be extended to cancer theranostics in the future, bringing good news for cancer patients.

The antitumor effect of suicide gene therapy using Bifidobacterium infantis-mediated herpes simplex virus thymidine kinase/ganciclovir in a nude mice model of renal cell carcinoma

OBJECTIVE

To confirm the effectivity of Bifidobacterium infantis-mediated herpes simplex virus thymidine kinase/ganciclovir suicide gene system on the treatment of renal cell carcinoma in nude mice and further explore the mechanisms.

MATERIALS AND METHODS

A B infantis thymidine kinase (B infantis-TK) suicide gene system was constructed in our previous study. Tumor-bearing nude mice were randomized into 4 groups and injected with normal saline, B infantis, B infantis/pGEX-1λT, and B infantis-TK, respectively, via tail vein, followed by intraperitoneal injection of ganciclovir. The treatment effects were evaluated by the terminal deoxynucleotidyl transferase-mediated deoxynucleotide triphosphate nick end labeling assay, quantitative reverse transcriptase polymerase chain reaction, and Western blotting. Side effects were also recorded.

RESULTS

Compared with the other 3 treatments, the treatment with B infantis-TK resulted in a significant effective antitumor activity and stronger apoptotic response. Western blot analysis showed that the expression levels of Rel A and Bcl-xL were significantly lower, whereas those of caspase 3 and Bax were significantly higher in tumor tissues resected from group B infantis-TK, which were consistent with the quantitative reverse transcriptase-polymerase chain reaction results.

CONCLUSION

The B infantis-TK/ganciclovir therapy system exhibits an effective antitumor activity by promoting tumor cell apoptosis through both the intrinsic and the extrinsic apoptotic pathways.

Inhibitory effect of Bifidobacterium infantis-mediated sKDR prokaryotic expression system on angiogenesis and growth of Lewis lung cancer in mice

BACKGROUND

To construct the Bifidobacterium infantis-mediated soluble kinase insert domain receptor (sKDR) prokaryotic expression system and to observe its inhibitory effect on growth of human umbilicus vessel endothelial cells (HUVECs) in vitro and Lewis lung cancer (LLC) on mice in vivo.

METHODS

The Bifidobacterium infantis-mediated sKDR prokaryotic expression system was constructed through electroporation and subsequently identified through PCR and Western blot analysis. HUVECs were added to the products of this system to evaluate the anti-angiogenesis effect through MTT assay in vitro. The LLC mice models were divided into three groups: one group treated with saline (group a); one group treated with recombinant Bifidobacterium infantis containing pTRKH2-PsT plasmid group (group b); and one group treated with recombinant Bifidobacterium infantis containing pTRKH2-PsT/sKDR plasmid group (group c). The quality of life and survival of mice were recorded. Tumor volume, tumor weight, inhibitive rate, and necrosis rate of tumor were also evaluated. Necrosis of tumor and signals of blood flow in tumors were detected through color Doppler ultrasound. In addition, microvessel density (MVD) of the tumor tissues was assessed through CD31 immunohistochemical analysis.

RESULTS

The positively transformed Bifidobacterium infantis with recombinant pTRKH2-PsT/sKDR plasmid was established, and was able to express sKDR at gene and protein levels. The proliferation of HUVECs cultivated with the extract of positively transformed bacteria was inhibited significantly compared with other groups (P < 0. 05). The quality of life of mice in group c was better than in group a and b. The recombinant Bifidobacterium infantis containing pTRKH2-PsT/sKDR plasmid enhanced the efficacy of tumor growth suppression and prolongation of survival, increased the necrosis rate of tumor significantly, and could obviously decrease MVD and the signals of blood flow in tumors.

CONCLUSION

The Bifidobacterium infantis-mediated sKDR prokaryotic expression system was constructed successfully. This system could express sKDR at gene and protein levels and significantly inhibit the growth of HUVECs induced by VEGF in vitro. Moreover, it could inhibit tumor growth and safely prolong the survival time of LLC C57BL/6 mice.

Myristoylation negative msbB-mutants of probiotic E. coli Nissle 1917 retain tumor specific colonization properties but show less side effects in immunocompetent mice

Specific colonization of solid tumors by bacteria opens the way to novel approaches in both tumor diagnosis and therapy. However, even non-pathogenic bacteria induce responses by the immune system, which could be devastating for a tumor bearing patient. As such effects are caused e.g., by the lipid A moiety of the lipopolysaccharide, a msbB-mutant of the probiotic E. coli Nissle 1917 strain was investigated. Bacteria of the mutant strain did not show any growth defects in culture media when compared to wild-type E. coli Nissle 1917 but were unable to myristoylate lipid A, had less toxic effects on immunocompetent BALB/c mice, and were still able to specifically colonize tumors. Therefore, the modification of lipid A could result in bacterial strains that might be better suited for diagnosis and therapy of tumors than the corresponding wild-type strains, even if those are not considered pathogenic or are of probiotic background.