A repetitive mutation and selection system for bacterial evolution to increase the specific affinity to pancreatic cancer cells

It is difficult to target and kill cancer cells. One possible approach is to mutate bacteria to enhance their binding to cancer cells. In this study, Gram-negative bacteria Escherichia coli and Gram-positive bacteria Bacillus subtilis were randomly mutated, and then were positively and negatively selected for binding cancer and normal cells. With repetitive mutation and selection both bacteria successfully evolved to increase affinity to the pancreatic cancer cell line (Mia PaCa-2) but not normal cells (HPDE: immortalized human pancreatic ductal epithelial cell line). The mutant E. coli and B. subtilis strains could bind to Mia PaCa-2 cells about 10 and 25 times more than to HPDE cells. The selected E. coli , strain had mutations in biofilm-related genes and the regulatory region for a type I pilus gene. Consistent with type I pili involvement, mannose could inhibit the binding to cells. However, the results suggest that weak but specific binding is involved in the initial step of adhesion. To kill Mia PaCa-2 cells, hemolysin was expressed in the mutant strain. The hemolysin that was released from the mutant strain could kill Mia PaCa-2 cells. This type of mutation/selection strategy may be applicable to other combinations of cancer cells and bacterial species.