Efficiency of Conditionally Attenuated Salmonella enterica Serovar Typhimurium in Bacterium-Mediated Tumor Therapy

Abstract

Increasing numbers of cancer cases generate a great urge for new treatment options. Applying bacteria like Salmonella enterica serovar Typhimurium for cancer therapy represents an intensively explored option. These bacteria have been shown not only to colonize solid tumors but also to exhibit an intrinsic antitumor effect. In addition, they could serve as tumor-targeting vectors for therapeutic molecules. However, the pathogenic S. Typhimurium strains used for tumor therapy need to be attenuated for safe application. Here, lipopolysaccharide (LPS) deletion mutants (ΔrfaL, ΔrfaG, ΔrfaH, ΔrfaD, ΔrfaP, and ΔmsbB mutants) of Salmonella were investigated for efficiency in tumor therapy. Of such variants, the ΔrfaD and ΔrfaG deep rough mutants exhibited the best tumor specificity and lowest pathogenicity. However, the intrinsic antitumor effect was found to be weak. To overcome this limitation, conditional attenuation was tested by complementing the mutants with an inducible arabinose promoter. The chromosomal integration of the respective LPS biosynthesis genes into the araBAD locus exhibited the best balance of attenuation and therapeutic benefit. Thus, the present study establishes a basis for the development of an applicably cancer therapeutic bacterium.

Optimizing the restored chemotactic behavior of anticancer agent Salmonella enterica serovar Typhimurium VNP20009

“…This result allows the conclusion that the major contributors to the chemotaxis phenotype of VNP20009 cheY + result from the msbB and Suwwan deletions. This result is contrary to previously reported chemotaxis assays of 14028 msbB − , where no significant difference was observed between the 14028 msbB mutant and 14028 wild type (Frahm et al, 2015). A possible explanation for our result is that we measured swim ring diameters after 12 h, whereas in Frahm et al (Frahm et al, 2015), the measured time point was at 4 h.…”

“…Although the lipid A modification by MsbB is essential for attenuation of VNP20009, it is not ideal for the downstream application of exploring the role of bacterial chemotaxis in tumor colonization. Research questions on utilizing bacterial chemotaxis for improved tumor targeting might be better suited in strains that have been attenuated by other means, such as auxotrophy or modifications of LPS with a less detrimental effect as described by Frahm et al (Frahm et al, 2015). However, gene targets for auxotrophy should be chosen carefully.…”

Rescuing chemotaxis of the anticancer agent Salmonella enterica serovar Typhimurium VNP20009

“…VNP20009 has a slight growth defect compared to the parental strain due to its msbB deletion, even in the presence of extragenic suppressors of growth defects such as the lack of somA (Murray et al, 2001). However, a recent study reported that a 14028 msbB mutant performed equally well on swim plates than its parental strain (Frahm et al, 2015). We cannot exclude that the VNP20009 Suwwan deletion, a spontaneous homologous recombination event causing the loss of several metabolic traits (Murray et al, 2004), affects spreading of cells in swim plates.…”

Part I: Fighting Cancer with Deadly Bacteria

“…They grew their modified Salmonella in the presence of arabinose to express wild-type LPS and injected this strain into tumor-bearing mice. Although mouse health suffered more with these bacteria, the mice survived the treatment and showed tumor cell death (3). …”