Objective: To test the effects of Tanshinone IIA (Tan IIA) on cell viability, cycle, apoptosis, and autophagy of human glioma cell U251 by regulating phosphatidylinositol 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) signal pathway. Methods: Tan IIA and PI3K agonist (740 Y-P) were used to treat glioma cells U251. MTT assay was used to assess cell viability and flow cytometry was used to detect cell apoptosis and cell cycle. The expressions of apoptosis-related proteins (Bcl-2 and Bax), autophagy-related proteins (LC3B and Beclin 1) and PI3K/Akt/mTOR signal pathway-associated proteins (p-PI3K, p-Akt and p-mTOR) were evaluated by Western blotting. Results: Tan IIA decreased the expression of p-PI3K and p-Akt proteins, inhibited cell viability and promoted apoptosis. Meanwhile, the expression of Bax increased, while the expression of Bcl-2 decreased. In addition, Tan IIA promoted autophagy in U251 glioma cells and raised the expression of LC3B and Beclin 1. However, 740 Y-P played a reversed role of Tan IIA in cell viability, cycle, apoptosis, and autophagy of U251 cells. Conclusion: Tan IIA could suppress the viability of U251 cells and induce cell apoptosis and autophagy, which might be related to the inhibition of the PI3K/Akt/mTOR signal pathway.

Live probiotic-mediated therapy suffers from the contradiction between treatment efficiency and bacterial pathogenicity that is the major barrier for clinical applications. Herein, we reported a chemically enhanced strategy to promote the tumor colonization ability of probiotic Escherichia coli Nissle 1917 (EcN) by prolonging the blood reservation with a lower inflammatory reaction. The chain-transfer agent (CTA) reacted with the amino groups on the EcN surface, and PEG polymer brushes from CTA were synthesized to produce the polymer-coated bacteria (PCB). PCB has negligible differences in the morphology and viability with EcN but possesses significantly enhanced blood reservation and tumor colonization ability. The lower level of secreted cytokines and white blood cells indicated a reduced inflammatory reaction, which promoted tumor colonization. More importantly, PCB can convert prodrug 5-fluorocytosine (5-FC) into 5-fluorouridine (5-FU) for tumor treatment. The PCB + 5-FC treatment inhibited tumor growth as high as 56.1 ± 11.1%, which is significantly higher than the EcN + 5-FC treatment (19.0 ± 9.9%). This strategy promoted the safety and the efficacy of bacteria in live bacterial-mediated antitumor therapy and showed great potential for clinical applications.

Tumor recurrence commonly results from tumor-positive resection margins and metastatic lesions. The complete removal of tumor-positive margins is particularly essential in clinics. Thus, we designed a strategy based on Escherichia coli Nissle 1917 (EcN) nitroreductase (NTR) with a polyethylene glycol (PEG) polymer coating (PC-EcN-NTR) to specifically target and colonize in tumors for high-contrast tumor imaging by providing a large amount of NTR as biomarkers in situ. NTR is a favorable biomarker for tumor detection and imaging. The nfsB-encoding plasmid with a 16S promoter was transfected into EcN for the continuous and stable expression of NTR (E. coli. NfsB). PC-EcN-NTR can accumulate and proliferate for a long time in tumors to substantially express NTR. When the NTR-activated fluorescence (FL) probe was sprayed on the tumor, the tumor region showed fluorescence signals within 5 min. Compared to the tumor without colonization with bacteria, the PC-EcN-NTR-colonized tumors displayed 3.15× enhanced fluorescence signals. Furthermore, the fluorescence signals of the whole tumor can last at least 3 h, which is suitable for a long and meticulous surgical operation. More importantly, in the PC-EcN-NTR-harboring tumor, obvious FL appeared even at the very edge (approximately 200 μm away from the edge) of the tumor tissue. A TCF-Based near-infrared-II fluorescent probe (probe 2) was designed and synthesized. Results similar to those of probe 1 were observed when probe 2 was used for in vivo tumor imaging, which further proved the generality of the enhancing ability of the tumor-targeting probiotic. This strategy will hopefully guide the surgical resection of tumors via monitoring intense NTR activity. It may spur the use of tumor-targeting probiotic and enzyme-activated fluorescent probes for the processes of tumor diagnosis and image-guided surgery.