Probiotic Escherichia coli Nissle 1917 propelled micro-robot with pH sensitivity for hypoxia targeted intestinal tumor therapy.

Poor drug penetration in hypoxia area of solid tumor is a big challenge for intestinal tumor therapy and thus it is crucial to develop an effective strategy to overcome this challenge. Compared with other bacteria used for construction of hypoxia targeted bacteria micro-robot, the Escherichia coli Nissle 1917 (EcN) bacteria are nonpathogenic Gram-negative probiotic and can especially target and identify the signal molecules in the hypoxic region of tumor, and thus, in this study, we choose EcN to construct a bacteria propelled micro-robot for targeting intestinal tumor therapy. Firstly, the MSNs@DOX with average diameter of 200 nm were synthesized and conjugated with EcN bacteria using EDC/NHS chemical crosslinking method to construct a EcN propelled micro-robot. The motility of micro-robot was then evaluated and the motion velocity of EcN-pMSNs@DOX was 3.78 µm/s. Compared with pMSNs@DOX without EcN driven, EcN bacteria propelled micro-robot transported much more pMSNs@DOX into the inner of HCT-116 3D multicellular tumor spheroids. However, the EcN bacteria are non-intracelluar bacteria which lead to the micro-robot can not directly enter into tumor cells. Therefore, we utilized acid-labile linkers of cis-aconitic amido bone to link EcN with MSNs@DOX nanoparticles to achieve the pH sensitive separation of EcN with MSNs@DOX from the micro-robot. At 4 h of incubation, the isolated MSNs@DOX began to enter into the tumor cells through CLSM observation. In vitro live/dead staining results show that EcN-pMSNs@DOX induced much more cell death than pMSNs@DOX at 24 and 48 h of incubation with HCT-116 tumor cells in acid culture media (pH 5.3). For the validation of the therapeutic efficacy of the micro-robot for intestinal tumor, we established the HCT-116 subcutaneous transplantation tumor model. After 28 days of treatment, EcN-pMSNs@DOX dramatically inhibit tumor growth with tumor volume was around 689 mm, induce much more tumor tissues necrosis and apoptosis. Finally, the toxicity of this micro-robot was investigated by pathological analysis the liver and heart tissues. We expect that the pH sensitive EcN propelled micro-robot here we constructed may be a safe and feasible strategy for intestinal tumor therapy.