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. 2020 Jul 31;2(4):e190053. doi: 10.1148/rycan.2020190053

Figure 8:

Acidic pH specifically and reversibly stimulates the STM Tn:1787 promoter. A, Bacteria were cultured in media of different pH values, and reporter activation by Salmonella library clones in low pH media (pH 6) were compared with reporter activation in normal pH (pH 7.5). Genes identified in the tumor cell coculture screen were activated in the context of acidic pH compared with pH 7.5. pMAAC001 and luxCDABE constitutively express plasmid-encoded and chromosomally encoded luxCDABE imaging reporters, respectively. Data were normalized as the ratio of the signal in media pH 6.0 to signal in media pH 7.5. Error bars correspond to standard error of the mean. B, Mice bearing B16F10 flank tumor xenografts were injected intratumorally with tumor-activated bioluminescent (Tn:1787+pluxCDE) or constitutively bioluminescent (Tn:27.8+pluxCDE) Salmonella. The excised tumors were then imaged hourly, and data are presented as the normalized signal at each time point. The normalized signal represents the ratio of the mean of the fold-initial signal of two Tn:1787+pluxCDE-colonized tumors to the mean of the fold-initial signal of two constitutive Tn:27.8+pluxCDE-colonized tumors. C, Representative tumor imaging ex vivo shows reversibility of the bioluminescent signal in the tumor-activated Salmonella. Images on the left show Salmonella-infected tumor explants after 6 hours of incubation at the indicated pH (pH 6.0, top; pH 7.5, bottom). Two hours later (8 hours total), media were removed and replaced with media of the indicated pH (pH 7.5, top; pH 6.0, bottom). Images on the right show Salmonella-infected tumor explants 4 hours after the pH of the media was changed. Note the reversibility of the bioluminescent signal (107). (Reprinted, with permission, from reference 107.)

Acidic pH specifically and reversibly stimulates the STM Tn:1787 promoter. A, Bacteria were cultured in media of different pH values, and reporter activation by Salmonella library clones in low pH media (pH 6) were compared with reporter activation in normal pH (pH 7.5). Genes identified in the tumor cell coculture screen were activated in the context of acidic pH compared with pH 7.5. pMAAC001 and luxCDABE constitutively express plasmid-encoded and chromosomally encoded luxCDABE imaging reporters, respectively. Data were normalized as the ratio of the signal in media pH 6.0 to signal in media pH 7.5. Error bars correspond to standard error of the mean. B, Mice bearing B16F10 flank tumor xenografts were injected intratumorally with tumor-activated bioluminescent (Tn:1787+pluxCDE) or constitutively bioluminescent (Tn:27.8+pluxCDE) Salmonella. The excised tumors were then imaged hourly, and data are presented as the normalized signal at each time point. The normalized signal represents the ratio of the mean of the fold-initial signal of two Tn:1787+pluxCDE-colonized tumors to the mean of the fold-initial signal of two constitutive Tn:27.8+pluxCDE-colonized tumors. C, Representative tumor imaging ex vivo shows reversibility of the bioluminescent signal in the tumor-activated Salmonella. Images on the left show Salmonella-infected tumor explants after 6 hours of incubation at the indicated pH (pH 6.0, top; pH 7.5, bottom). Two hours later (8 hours total), media were removed and replaced with media of the indicated pH (pH 7.5, top; pH 6.0, bottom). Images on the right show Salmonella-infected tumor explants 4 hours after the pH of the media was changed. Note the reversibility of the bioluminescent signal (107). (Reprinted, with permission, from reference 107.)