Quorum-sensing Salmonella selectively trigger protein expression within tumors.

Area of Science:

• Microbiology
• Biotechnology
• Cancer Therapy

Background:

• Salmonella engineered to secrete anticancer proteins show tumor elimination potential.
• Nonspecific protein expression by Salmonella can damage healthy tissues.
• A density-dependent switch is needed to confine therapeutic protein expression to tumors.

Purpose of the Study:

• To engineer Salmonella with a density-dependent switch for targeted anticancer protein expression.
• To determine the critical bacterial density required for protein expression using the lux quorum-sensing (QS) system.
• To evaluate the in vivo efficacy and safety of QS Salmonella in a mouse tumor model.

Main Methods:

• Cloned the lux quorum-sensing (QS) system and a GFP reporter into nonpathogenic Salmonella.
• Measured fluorescence and bacterial density in vitro and in a tumor-on-a-chip device.
• Quantified GFP expression in vivo in 4T1 tumor-bearing mice using immunofluorescence and bacterial counts.

Main Results:

• QS Salmonella exhibited minimal GFP expression below 0.6 × 10(10) cfu/g, with significant expression above 4.2 × 10(10) cfu/g.
• GFP expression was dependent on bacterial density and inversely related to the distance between bacteria (no expression > 155 µm).
• Liver bacterial density was below the critical threshold for expression, indicating targeted action.

Conclusions:

• QS Salmonella effectively target protein expression to tumor sites based on bacterial density.
• This system prevents therapeutic protein release in healthy tissues like the liver.
• QS Salmonella represent a promising strategy for targeted cancer therapy with reduced side effects.