Genetically Engineered Oncolytic Salmonella typhimurium
Ananda M. Chakrabarty, Arsénio M. Fialho in Microbial Infections and Cancer Therapy, 2019
Wild-type S. typhimurium is extremely toxic when administered directly to animals, but very low doses are usually insufficient to induce notable anticancer effects. Thus, these bacteria must be attenuated by genetic engineering before their application to cancer research. Several approaches have been used to generate attenuated S. typhimurium strains with decreased toxicity and increased tumor targeting. Bacterial components can be modified to reduce inflammatory stimulation of the host immune system. For example, the LPS mutant strain VNP20009, with deletions of purl and msbB from the bacterial chromosome, showed a 10,000-fold increase in LD50 in animals [4].Nutrient auxotrophs can be generated by depleting certain genes, such as leucine, arginine, and aromatic acid synthetases [10, 21], making the growth of these strains dependent on the extracellular nutrient supply. However, in the tumor microenvironment, small molecular nutrients released from apoptotic/necrotic cancer cells may enhance the ability of these attenuated S. typhimurium strains to colonize and proliferate in tumor tissues.The expression of toxic genes can be inactivated or down-regulated. Deletions of relA and spoT suppressed the synthesis of ppGpp, markedly down-regulating the expression of various virulence genes, including those encoded on Salmonella pathogenicity island 1 (SPI1) that are required for the invasion of host cells and induction of macrophage apoptosis [22].Advantage can be taken of the tumor microenvironment, with hypoxia utilized to express essential bacterial genes, such as asd, which encode the enzyme aspartate-semialdehyde dehydrogenase and are under the control of hypoxia-inducible promoter (HIP)-1. Thus, these bacteria can survive only under hypoxic conditions, greatly reducing their cytotoxicity to normal tissues and increasing their tumor-specific proliferation [23].
Salmonella enterica Typhimurium engineered for nontoxic systemic colonization of autochthonous tumors
Published in Journal of Drug Targeting, 2021
Lance B. Augustin, Liming Milbauer, Sara E. Hastings, Arnold S. Leonard, Daniel A. Saltzman, Janet L. Schottel
Bacterial strains, including relevant genotypes and sources are listed in Table 1. S. Typhimurium strain VNP20009 was obtained from the American Type Culture Collection (ATCC #202165). Strain SL3261 was obtained from the Salmonella Genetic Stock Centre (SGSC #439). Strain BCT1 was constructed by deletion of the aspartate-semialdehyde dehydrogenase (asd) gene from the chromosome of SL3261 using the phage λ Red recombinase method [22] and two PCR primers DSfwd and DSrev (Table 2). When measuring tumour colonisation, the bacteria were transformed with plasmids that contain the lux operon [23] for bioluminescence. S. Typhimurium strain BCT2 was constructed by deleting the fliC, fljB, fimH, and rfaL genes from χ11091 [24], and introducing a single nucleotide change into the pgtE promoter in the χ11091 chromosome. Oligonucleotide primers used to introduce these mutations into χ11091 by the DIRex method [25] are listed in Table 2.
Related Knowledge Centers
- Catalysis
- Chemical Reaction
- Enzyme
- Glycine
- Nicotinamide Adenine Dinucleotide Phosphate
- Phosphate
- Substrate
- L-Aspartic-4-Semialdehyde
- Product
- Oxidoreductase