Programmable probiotics for detection of cancer in urine

Probiotics programmed to generate specific metabolites traffic from the gut to tumors and enable cancer detection through the urine. Synthetic bacteria for tumor detection Tumors often harbor bacteria, and Danino et al. have taken advantage of this peculiar fact to design a method to detect liver metastases. An E. coli strain was carefully engineered to carry β-galactosidase, an enzyme that can metabolize numerous substrates. When fed to mice, these bacteria transited the gut epithelium to enter the bloodstream and then traveled to the liver, where they take up residence in any tumor colonies that are present. At that point, the mice were fed LuGal, a combined luciferin and galactose molecule. When the LuGal reached the bacteria in the tumors, the bacterial β-galactosidase metabolized it to luciferin, which was then excreted in the urine. The amount of luciferin, an easily detectible molecule, revealed the tumor burden carried in the liver. It remains to be seen whether this noninvasive approach to cancer detection can be applied to other tumor types and locations, but the versatility conferred by control of the enzymes in the E. coli and the substrates fed to the animal bodes well for future application. Rapid advances in the forward engineering of genetic circuitry in living cells has positioned synthetic biology as a potential means to solve numerous biomedical problems, including disease diagnosis and therapy. One challenge in exploiting synthetic biology for translational applications is to engineer microbes that are well tolerated by patients and seamlessly integrate with existing clinical methods. We use the safe and widely used probiotic Escherichia coli Nissle 1917 to develop an orally administered diagnostic that can noninvasively indicate the presence of liver metastasis by producing easily detectable signals in urine. Our microbial diagnostic generated a high-contrast urine signal through selective expansion in liver metastases (106-fold enrichment) and high expression of a lacZ reporter maintained by engineering a stable plasmid system. The lacZ reporter cleaves a substrate to produce a small molecule that can be detected in urine. E. coli Nissle 1917 robustly colonized tumor tissue in rodent models of liver metastasis after oral delivery but did not colonize healthy organs or fibrotic liver tissue. We saw no deleterious health effects on the mice for more than 12 months after oral delivery. Our results demonstrate that probiotics can be programmed to safely and selectively deliver synthetic gene circuits to diseased tissue microenvironments in vivo.