Engineering a probiotic strain of <i>Escherichia coli</i> to induce the regression of colorectal cancer through production of 5‐aminolevulinic acid

Bacterial vectors can be engineered to generate microscopic living therapeutics to produce and deliver anticancer agents. Escherichia coli Nissle 1917 (Nissle 1917) is a promising candidate with probiotic properties. Here, we used Nissle 1917 to develop a metabolic strategy to produce 5-aminolevulinic acid (5-ALA) from glucose as 5-ALA plays an important role in the photodynamic therapy of cancers. The coexpression of hemA^M and hemL using a low copy-number plasmid led to remarkable accumulation of 5-ALA. The downstream pathway of 5-ALA biosynthesis was inhibited by levulinic acid (LA). Small-scale cultures of engineered Nissle 1917 produced 300 mg l^-1 of 5-ALA. Recombinant Nissle 1917 was applied to deliver 5-ALA to colorectal cancer cells, in which it induced the accumulation of antineoplastic protoporphyrin X (PpIX) and specific cytotoxicity towards colorectal cancer cells irradiated with a 630 nm laser. Moreover, this novel combination therapy proved effective in a mouse xenograft model and was not cytotoxic to normal tissues. These findings suggest that Nissle 1917 will serve as a potential carrier to effectively deliver 5-ALA for cancer therapy.