A bioluminescent transposon reporter-trap identifies tumor-specific microenvironment-induced promoters in Salmonella for conditional bacterial-based tumor therapy.
Salmonella specifically localize to malignant tumors in vivo, a trait potentially exploitable as a delivery system for cancer therapeutics. To characterize mechanisms and genetic responses of Salmonella during interaction with living neoplastic cells, we custom-designed a promoterless transposon reporter containing bacterial luciferase. Analysis of a library containing 7,400 independent Salmonella transposon insertion mutants in coculture with melanoma or colon carcinoma cells identified five bacterial genes specifically activated by cancer cells: adiY, yohJ, STM1787, STM1791, and STM1793. Experiments linked acidic pH, a common characteristic of the tumor microenvironment, to a strong, specific, and reversible stimulus for activation of these Salmonella genes in vitro and in vivo. Indeed, a Salmonella reporter strain encoding a luciferase transgene regulated by the STM1787 promoter, which contains a tusp motif, showed tumor-induced bioluminescence in vivo. Furthermore, Salmonella expressing Shiga toxin from the STM1787 promoter provided potent and selective antitumor activity in vitro and in vivo, showing the potential for a conditional bacterial-based tumor-specific therapeutic.


CONCLUSIONS
Salmonella, which often encounter acidic environments during classical host infection, may co-opt evolutionarily conserved pathways for tumor colonization in response to the acidic tumor microenvironment. We identified specific promoter sequences that provide a platform for targeted Salmonella-based tumor therapy in vivo.
BRIGHT Institute, Washington University School of Medicine, St. Louis, Missouri 63110, USA.
Kelly
K
Flentie
Brandon
B
Kocher
Seth T
ST
Gammon
Deborah V
DV
Novack
Jeffrey S
JS
McKinney
David
D
Piwnica-Worms
D000818:Animals; D045744:Cell Line, Tumor; D004251:DNA Transposable Elements / Q000235:genetics*; D015870:Gene Expression; D018014:Gene Transfer Techniques; D005798:Genes, Bacterial / Q000235:genetics; D015316:Genetic Therapy / Q000379:methods; D045325:HCT116 Cells; D006367:HeLa Cells; D006801:Humans; D008156:Luciferases / Q000235:genetics* / Q000378:metabolism; D008163:Luminescent Measurements / Q000379:methods; D051379:Mice; D008819:Mice, Nude; D009369:Neoplasms / Q000235:genetics / Q000473:pathology / Q000628:therapy*; D011401:Promoter Regions, Genetic / Q000235:genetics*; D012486:Salmonella typhimurium / Q000235:genetics*; D059016:Tumor Microenvironment / Q000235:genetics; D023041:Xenograft Model Antitumor Assays / Q000379:methods
D004251:DNA Transposable Elements; D008156:Luciferases