Controlling intracellular protein delivery, tumor colonization and tissue distribution using the master regulator flhDC in a clinically relevant ΔsseJ Salmonella strain

Effectively targeting intracellular pathways in cancers requires a system that specifically delivers to tumors and internalizes into cancer cells. To achieve this goal, we developed intracellular-delivering (ID) Salmonella with controllable expression of flhDC to regulate flagella production and cell invasion. We hypothesized that controlling flhDC would overcome the poor colonization seen in prior clinical trials. To test this hypothesis, we incorporated the aspirin-responsive Psal promoter and tuned flhDC expression with ssra degradation tags. In tumor-bearing mice, controlling flhDC increased protein release, tissue dispersion, and tumor colonization more than 10 million times. We discovered that inducing flhDC increases escape from intracellular vacuoles; however, deleting sseJ prevented escape and further increased protein delivery. Delivering constitutively active caspase-3 with ID-f-s Salmonella (ΔsseJ and induced Psal-flhDC) induced cell death in pancreatic, breast, and liver cancer cells and reduced the growth of breast tumors. This clinically ready strain preferentially colonized metastatic breast tissue 280 and 800 times more than surrounding healthy tissue in the lung and liver, respectively. By precisely controlling tumor colonization and cell invasion, this strain overcomes critical limitations of bacterial therapy and will enable treatment of many hard-to-treat cancers. [Display omitted] Targeting intracellular pathways selectively within cancer cells unlocks therapeutic potential. Forbes and colleagues created a clinically applicable bacteria-based delivery vector that selectively colonizes tumors. An over-the-counter dose of aspirin triggers the intratumoral bacteria to deliver cancer therapies inside tumor cells and reduces disease burden without causing systemic toxicity.