Iron-Tannin Coating\nReduces Clearance and Increases\nTumor Colonization of Systemically Delivered Bacteria

Engineered bacteria offer a novel approach to targeted\ncancer therapy,\nbut challenges remain in delivering enough bacteria safely for effective\ntreatment. Previous efforts have used either a native or synthetic\ncoating to achieve better control over the half-life of bacteria in\nthe body but have limitations in delivery or versatility. In this\nwork, we optimized and evaluated a synthetic coating for probiotic Escherichia coli Nissle 1917 to increase its half-life\nin blood and thereby increase the bioavailability of intravenous doses\nof bacteria to colonize and treat tumors. Using a simple one-pot chemical\nprocess, we coated bacteria with iron and tannic acid (FeTA) to form\na temporary adhesive protective coating surrounding the bacterial\ncell surface. The iron to tannic acid ratio of the coating was optimized\nfor intravenous use, and FeTA-coated bacteria of several different\ngenetic backgrounds showed 15-fold higher survival in blood survival\nassays for up to 4 hours. We found that the FeTA coating reduced both\ncomplement-mediated bacterial killing and phagocyte-mediated bacterial\nkilling <i>in vitro</i>. As a result, systemic delivery\nof attenuated bacteria had up to 60% colonization efficiency of FeTA-coated\nbacteria in an orthotopic breast cancer mouse model compared to 10%\nfor the non-coated control, all the while maintaining a two-fold decrease\nin weight loss of attenuated bacteria compared to wild-type. Altogether,\nwe show that an optimized FeTA coating significantly extends the half-life\nand colonization efficiency of engineered bacteria, overcoming a key\nlimitation of their application in cancer therapy.