Abstract 5136: Upregulation of Salmonella motility in tumors improves dispersion, colonization and intracellular invasion of the bacteria
Authors: Raman Vishnu , Dessel Nele V. , O'Connor Owen , Forbes Neil S. 
Published: July 2017

Diffusion limitations in tumors prevent small molecule therapies from reaching cancer cells located distally from vasculature. This is one reason why some cancers become drug resistant and relapse. To circumvent these diffusional limitations, Salmonella can be used as a drug delivery vehicle. The facultative anaerobe preferentially colonizes tumor tissue over normal tissue at ratios greater than 10,000:1. Moreover, flagella allow the bacteria to penetrate deep into tumor tissue. Finally, genetically modified Salmonella can invade cancer cells and deliver a wide range of intracellularly functioning and patient specific therapies (DNA, RNA, and inhibitory peptides).

But, Salmonella must distribute homogeneously within tumors and invade a significant number of live cancer cells in order to deliver therapies uniformly within tumors. To enable this, we hypothesized that up-regulating the master motility regulator, flhDC, in Salmonella would improve intratumoral penetration, uniform colonization and intracellular invasion of cancer cells. Salmonella utilize the transcription factor complex, flhDC, to regulate flagella synthesis and thus, motility. This transcription factor complex also positively influences type three secretion system (T3SS) assembly, which, Salmonella use to intracellularly invade epithelial cells.

To test this hypothesis, we created a set of synthetic gene circuits that use arabinose for inducible expression of flhDC, the Plac promoter for constitutive expression of DSRed and the PSSEJ promoter to express GFP when Salmonella invade tumor cells. We analyzed aqueous bacterial motility with video microscopy. Finally, we administered the motility inducible Salmonella into a tumor-on-a-chip device to examine spatial and temporal tumor colonization characteristics of the bacteria.

In an aqueous environment, the flhDC induced Salmonella swam approximately 33% faster than a Salmonella control (P&lt;.01). Induction of flhDC increased the motile fraction (15-30 micrometers/second) of bacteria two-fold (P&lt;.05) while also decreasing the non-motile fraction (0-15 micrometers/second) six-fold (P&lt;.05) when compared to a Salmonella control.

In a microfluidic device, flhDC induced Salmonella exhibited increased colonization and growth in tumor tissue located far away from channels that were meant to resemble tumor microvasculature (P&lt;.05), when compared to a control. Finally, flhDC induction increased tumor cell invasion approximately two-fold in tissue located both proximal and distal to the micro-channels within the microfluidic device (P&lt;.05), when compared to a control.

Highly motile Salmonella could reduce the occurrence of drug resistant cancer relapse by delivering targeted therapies uniformly to cancer cells that would otherwise remain untreated with conventional therapy.

Citation Format: Vishnu Raman, Nele V. Dessel, Owen O'Connor, Neil S. Forbes. Upregulation of Salmonella motility in tumors improves dispersion, colonization and intracellular invasion of the bacteria [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5136. doi:10.1158/1538-7445.AM2017-5136