A strategy for enhanced tumor targeting of photodynamic therapy based on Escherichia coli-driven drug delivery system

Escherichia coli ( E. coli ) DH5α has been recognized as a non-pathogenic bacterial strain with tumor colonization ability. However, whether such a bacteria-driven drug-delivery system can improve the targeting of tumor therapy or not remains essentially untouched. Herein, a series of zinc phthalocyanine (ZnPc) photosensitizers with different numbers of charges were prepared and their electrostatic adhesion properties on E. coli were investigated via measuring their fluorescence intensities by flow cytometer. Among these ZnPc photosensitizers investigated, the ZnPc conjugate with four positive charges (named ZnPc-IR710) exhibited the highest loading capacity and the best fluorescence imaging performance of E. coli . With the help of E. coli , E. coli @ZnPc-IR710 presented a significantly enhanced cytotoxicity on human breast cancer MCF-7 cells compared with ZnPc-IR710 (survival rate of tumor cells was 39% vs . 57% at a concentration of 50 nmol L−1). Moreover, in vivo study showed that E. coli @ZnPc-IR710 remarkably inhibited the tumor growth and resulted in a complete tumor growth suppress in subcutaneous mouse 4T1 breast tumor model. These results demonstrated the great promise of bacterial-guided photodynamic therapy (PDT) in the treatment of solid tumors, and provide a unique strategy to enhance the antitumor efficacy of PDT by utilizing bacterial vectors in tumors.