Draft Genome Sequence of the Tumor-Targeting Salmonella enterica Serovar Typhimurium Strain SL7207

Camouflaging attenuated Salmonella by cryo-shocked macrophages for tumor-targeted therapy

Live bacteria-mediated antitumor therapies mark a pivotal point in cancer immunotherapy. However, the difficulty in reconciling the safety and efficacy of bacterial therapies has limited their application. Improving bacterial tumor-targeted delivery while maintaining biosafety is a critical hurdle for the clinical translation of live microbial therapy for cancer. Here, we developed "dead" yet "functional" Salmonella-loaded macrophages using liquid nitrogen cold shock of an attenuated Salmonella typhimurium VNP20009-contained macrophage cell line. The obtained "dead" macrophages achieve an average loading of approximately 257 live bacteria per 100 cells. The engineered cells maintain an intact cellular structure but lose their original pathogenicity, while intracellular bacteria retain their original biological activity and are delay freed, followed by proliferation. This "Trojan horse"-like bacterial camouflage strategy avoids bacterial immunogenicity-induced neutrophil recruitment and activation in peripheral blood, reduces the clearance of bacteria by neutrophils and enhances bacterial tumor enrichment efficiently after systemic administration. Furthermore, this strategy also strongly activated the tumor microenvironment, including increasing antitumor effector cells (including M1-like macrophages and CD8+ Teffs) and decreasing protumor effector cells (including M2-like macrophages and CD4+ Tregs), and ultimately improved antitumor efficacy in a subcutaneous H22 tumor-bearing mouse model. The cryo-shocked macrophage-mediated bacterial delivery strategy holds promise for expanding the therapeutic applications of living bacteria for cancer.

Transformed Salmonella typhimurium SL7207/pcDNA-CCOL2A1 as an orally administered DNA vaccine

The use of attenuated bacteria for oral delivery of DNA vaccines is a recent innovation. We designed and constructed the naked plasmid DNA vaccine pcDNA-CCOL2A1, which effectively prevented and treated a rheumatoid arthritis model by inducing immunotolerance. We aimed to ensure a reliable, controllable dosage of this oral DNA vaccine preparation and establish its stability. We transformed pcDNA-CCOL2A1 via electroporation into attenuated Salmonella typhimurium SL7207. A resistant plate assay confirmed the successful construction of the transformed strain of the SL7207/pcDNA-CCOL2A1 oral DNA vaccine. We verified its identification and stability in vitro and in vivo. Significant differences were observed in the characteristics of the transformed and blank SL7207 strains. No electrophoretic restriction patterns or direct sequencing signals were observed in the original extract of the transformed strain. However, target gene bands and sequence signals were successfully detected after PCR amplification. CCOL2A1 expression was detected in the ilea of BALB/c mice that were orally administered SL7207/pcDNA-CCOL2A1. The pcDNA-CCOL2A1 plasmid of the transformed strain was retained under the resistant condition, and the transformed strain remained stable at 4 °C for 100 days. The concentration of the strain harboring the pcDNA-CCOL2A1 plasmid was stable at 109 CFU/mL after 6-8 h of incubation. The results demonstrated that the transformed strain SL7207/pcDNA-CCOL2A1 can be expressed in vivo, has good stability, and may be used to prepare the oral DNA vaccine pcDNA-CCOL2A1 with a stable, controllable dosage and the capacity to provide oral immunization. This vehicle can effectively combine both oral immunotolerance and DNA vaccination.

Localization of Salmonella and albumin-IL-2 to the tumor microenvironment augments anticancer T cell immunity

Background

For centuries, microbial-based agents have been investigated as a therapeutic modality for the treatment of cancer. In theory, these methods would be cheap to produce, broadly applicable in a wide array of cancer types, and could synergize with other cancer treatment strategies. We aimed to assess the efficacy of combining microbial-based therapy using Salmonella SL7207 with interleukin-2 (IL-2), a potent immunostimulatory agent, in the treatment of murine colon carcinoma.

Methods

Female BALB/c mice were implanted subcutaneously with CT26 tumors, a model of colon carcinoma. Mice bearing tumors were selected and administered Albumin-IL-2 (Alb-IL2), a fusion protein, for further analysis of anticancer effect.

Results

We demonstrated that Salmonella SL7207, a genetically modified strain of Salmonella enterica serovar Typhimurium, preferentially accumulates in the tumor microenvironment, potentiating it to stimulate localized innate immunity. We delivered IL-2 as a fusion protein, Alb-IL2, which we demonstrate to have preferential accumulation properties, bringing it to the tumor and secondary lymphoid organs. Treatment of tumor-bearing mice with Salmonella + Alb-IL2 leads to superior tumor control and enhanced overall survival compared to controls. When assessing immunological factors contributing to our observed tumor control, significantly enhanced T cell population with superior effector function was observed in mice treated with Salmonella + Alb-IL2. We confirmed that these T cells were indispensable to the observed tumor control through antibody-mediated T cell depletion experiments.

Conclusions

These findings highlight the ability of Salmonella + Alb-IL2 to serve as a novel therapeutic approach to induce T cell-mediated antitumor immunity and exert long-term tumor control in a murine model of cancer.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12929-022-00841-y.

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.

Monocytes mediate Salmonella Typhimurium-induced tumor growth inhibition in a mouse melanoma model

The use of bacteria as an alternative cancer therapy has been reinvestigated in recent years. SL7207: an auxotrophic Salmonella enterica serovar Typhimurium aroA mutant with immune-stimulatory potential has proven a promising strain for this purpose. Here, we show that systemic administration of SL7207 induces melanoma tumor growth arrest in vivo, with greater survival of the SL7207-treated group compared to control PBS-treated mice. Administration of SL7207 is accompanied by a change in the immune phenotype of the tumor-infiltrating cells toward pro-inflammatory, with expression of the TH 1 cytokines IFN-γ, TNF-α, and IL-12 significantly increased. Interestingly, Ly6C+ MHCII+ monocytes were recruited to the tumors following SL7207 treatment and were pro-inflammatory. Accordingly, the abrogation of these infiltrating monocytes using clodronate liposomes prevented SL7207-induced tumor growth inhibition. These data demonstrate a previously unappreciated role for infiltrating inflammatory monocytes underlying bacterial-mediated tumor growth inhibition. This information highlights a possible novel role for monocytes in controlling tumor growth, contributing to our understanding of the immune responses required for successful immunotherapy of cancer.

NLRC4 inflammasome-dependent cell death occurs by a complementary series of three death pathways and determines lethality in mice

Inflammasome is an innate immune defense mechanism, but its overactivation can lead to host death. Here, we show that cell death dictates mouse death caused by NLRC4 inflammasome overactivation. To execute NLRC4-dependent cell death, three death pathways complement each other in a specific order: Pyroptosis pathway requiring caspase-1 and GSDMD is the default path; impairment of it initiates ASC-mediated caspase-8–dependent apoptosis; when these two pathways are blocked, caspase-1 triggers intrinsic apoptotic pathway. Blocking one or two of these death pathways inhibits induction of various cytokines and lipid mediators, but mice still succumb, and only genetic deletions that block all death paths prevent NLRC4-mediated cell death, tissue damage, and mice death. In addition, infection of nonpropagative Salmonella-caused mice death is attenuated by blocking these death pathways. Thus, to reduce the lethality of infection-related diseases, preventing cell death might be necessary when propagation of infected pathogen was controlled by other means.

Hyaluronidase-Expressing Salmonella Effectively Targets Tumor-Associated Hyaluronic Acid in Pancreatic Ductal Adenocarcinoma

In pancreatic ductal adenocarcinoma (PDAC), the extracellular matrix (ECM) surrounding cancer cells forms a barrier that often limits the ability of chemotherapeutic drugs and cytotoxic immune subsets to penetrate and eliminate tumors. The dense stromal matrix protecting cancer cells, also known as desmoplasia, results from the overproduction of major ECM components such as collagens and hyaluronic acid (HA). Although candidate drugs targeting ECM components have shown promise in increasing penetration of chemotherapeutic agents, severe adverse effects associated with systemic depletion of ECM in peripheral healthy tissues limits their use at higher, more effective doses. Currently, few strategies exist that preferentially degrade ECM in tumor tissue over healthy tissues. In light of this, we have developed an attenuated, tumor-targeting Salmonella typhimurium (ST) expressing functional bacterial hyaluronidase (bHs-ST), capable of degrading human HA deposited within PDAC tumors. Our data show that bHs-ST (i) targets and colonizes orthotopic human PDAC tumors following systemic administration and (ii) is efficiently induced in vivo to deplete tumor-derived HA, which in turn (iii) significantly increases diffusion of Salmonella typhimurium within desmoplastic tumors. BHs-ST represents a promising new tumor ECM-targeting strategy that may be instrumental in minimizing off-tumor toxicity while maximizing drug delivery into highly desmoplastic tumors.

Increasing the bactofection capacity of a mammalian expression vector by removal of the f1 ori

Bacterial-mediated cancer therapy has shown great promise in in vivo tumour models with increased survival rates post-bacterial treatment. Improving efficiency of bacterial-mediated tumour regression has focused on controlling and exacerbating bacterial cytotoxicity towards tumours. One mechanism that has been used to carry this out is the process of bactofection where post-invasion, bacteria deliver plasmid-borne mammalian genes into target cells for expression. Here we utilised the cancer-targeting Salmonella Typhimurium strain, SL7207, to carry out bactofection into triple negative breast cancer MDA-MB-231 cells. However, we noted that post-transformation with the commonly used mammalian expression vector pEGFP, S. Typhimurium became filamentous, attenuated and unable to invade target cells efficiently. Filamentation did not occur in Escherichia coli-transformed with the same plasmid. Further investigation identified the region inducing S. Typhimurium filamentation as being the f1 origin of replication (f1 ori), an artefact of historic use of mammalian plasmids for single stranded DNA production. Other f1 ori-containing plasmids also induced the attenuated phenotype, while removal of the f1 ori from pEGFP restored S. Typhimurium virulence and increased the bactofection capacity. This work has implications for interpretation of prior bactofection studies employing f1 ori-containing plasmids in S. Typhimurium, while also indicating that future use of S. Typhimurium in targeting tumours should avoid the use of these plasmids.