(171b) Sensing the Tumor Microenvironment: Genetically Modified Bacteria Sense and Trigger Gene Expression At the Site of Solid Tumors

To improve the therapeutic specificity of bacterial cancer therapies, we have utilized chemosensory receptors coupled to the osmoporin transduction pathway to create novel a bacterial gene expression system that switches on specifically in solid tumors. We hypothesize that tumor necrosis leads to increased ribose concentrations due to the abundance of degrading DNA and RNA. It has also previously been shown that there is enhanced serine production in metastatic cancer making it a good target for specific expression within malignant tissue. A genetic circuit has been created using a previously developed fusion protein, Trz1, which couples the ribose and glucose sensing of the Trg protein to osmoporin signal transduction domain of EnvZ, from E. coli, and produces green fluorescent protein (GFP) via the porin promoter pOmpC. This genetic switch enables bacterial sensing of ribose and glucose and subsequent visualization, via fluorescence, of sugar gradients within the tumor microenvironment. In addition to this we have created a novel fusion protein, Tsz2, joining the serine sensing Tsr chemoreceptor to EnvZ to detect serine gradients within the tumor microenvironment. The ribose-glucose sensing bacterial probe responds to both glucose and ribose gradients. A previously developed in vitro 3D tumor model mimicking tumor tissue adjacent to a blood vessel was used to determine the ability of bacterial to probe the tumor microenvironment. The tumor-on-a-chip microfluidic device creates gradients in nutrients and oxygen within tumor tissue similar to in vivo conditions. Image analysis revealed gradients of the sugars within solid carcinoma tissue via the fluorescent bacterial sensors for specific gene expression. Bacterial colonization occurred in the regions of tissue with the highest sugar content as expected. The sugar gradients controlled GFP expression levels within the tissue based on bacterial density and depth within the tissue. These bacterial sensors have the potential to improve targeted cancer therapy by limiting expression to within tumors.