Doxorubicin-conjugated Escherichia coli Nissle 1917 swimmers to achieve tumor targeting and responsive drug release

The use of bacteria as drug carriers meets several challenges, such as biocompatibility, motility deterioration after drug loading and lack of in vivo verification. Escherichia coli Nissle 1917 (EcN) is one of the best studied probiotic strains, and doxorubicin (DOX) is conjugated onto EcN in the current study via acid-labile linkers of cisaconitic anhydride (EcN-ca-Dox), realizing the bacteria-directed accumulation and acid-responsive release of anticancer drugs in tumors. The drug conjugation has maintained the bacterial motion profiles of over 9 mu m/s and cell viability of over 70%. After 3 h and 3 days of intravenous injection of EcN-ca-Dox, DOX accumulations in tumors are determined as 12.9% and 6.4% of the injected doses per gram of tissue, respectively, which are much higher than the commonly used nanocarriers. Compared with free DOX and DOX-conjugated EcN via stable linkers of succinic anhydride, the EcN-ca-Dox treatment improves the antitumor efficacy with respect to the tumor growth inhibition, prolongation of animal survivals, and apoptosis induction of tumor cells. In addition, EcN has been cleaned off from tumors and other tissues after antimicrobial treatment. Thus, the acid-labile EcN conjugates provide a safe and concise strategy to enhance the temporal and spatial controllability of anticancer drugs.