Intestinal probiotics Nissle 1917 as a targeted vehicle for delivery of p53 and Tum-5 to solid tumors for cancer therapy.

Traditional cancer therapies, such as surgery treatment, radiotherapy, and chemotherapy, often fail to completely eliminate tumor cells in an anaerobic microenvironment of tumor regions. In contrast to these traditional cancer therapies, the use of targeted delivery vectors to deliver anticancer genes or antitumor drugs to hypoxic areas in tumors is the most clinically promising cancer treatment with rapid development in recent years. In this study, Nissle 1917 (EcN), an intestinal probiotic, was utilized as a targeted transport vector to deliver p53 and Tum-5 protein to tumor hypoxic regions. The tumor-targeting characteristics of EcN were investigated using luciferase CDABE operon, and the results demonstrated that EcN could specifically accumulate in the solid tumor areas of SMMC-7721 tumor-bearing BALB/c nude mice. The Tum 5-p53 bifunctional proteins were initially constructed and then delivered to solid tumor regions by using the targeted transporter EcN for cancer therapy. The antitumor effect and safety of three engineered bacteria, namely, EcN (Tum-5), EcN (p53), and EcN (Tum 5-p53), were also examined. The calculated tumor volume and tumor weight indicated that these three engineered bacteria could inhibit the growth of human hepatoma SMMC-7721 cells, and the antitumor effect of EcN (Tum 5-p53) expressing the Tum 5-p53 fusion protein was significantly better than those of EcN (Tum-5) and EcN (p53) alone. Immunofluorescence demonstrated that the expression of Ki-67, a nuclear proliferation-related protein, was inhibited in the tumor areas of the groups treated with the engineered bacteria, whereas the expression of caspase-3 was upregulated. The expression trends of Ki-67 and caspase-3 were consistent with the different antitumor efficacies of these three engineered bacteria. EcN did not elicit obvious side effects on mice. This research not only provids a foundation for tumor-targeted therapy but also contributes greatly to the development of antitumor agents and anticancer proteins.