Targeting of non-phagocytic tumor cells and prompt release of gene cargos upon entry into tumors are two limiting steps in the bacterial gene delivery path. To tackle these problems, the non-pathogenic Escherichia coli strain BL21(DE3) was engineered to display the anti-HER2/neu affibody on the surface. After co-incubation with tumor cells for 3 h, the anti-HER2/neu affibody-presenting E. coli strain was selectively internalized into HER2/neu-positive SKBR-3 cells. The invasion efficiency reached as high as 30%. Furthermore, the bacteria were equipped with the phage ϕX174 lysin gene E-mediated autolysis system. Carrying the transgene (e.g., eukaryotic green fluorescent protein, GFP), the tumor-targeting bacteria were subjected to the thermal shock to trigger the autolysis system upon entry into HER2/neu-positive cells. Flow cytometric analysis revealed that 3% of infected cells expressed GFP 24 h post thermal induction. Overall, the results show a promise of the proposed approach for developing bacteria as a delivery carrier.
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