Surface Labeling with Adhesion Protein FimH Improves Binding of Immunotherapeutic Agent Salmonella Ty21a to the Bladder Epithelium

BACKGROUND: Bladder cancer is the ninth most common cancer in men. 70% of these tumors are classified as non-muscle invasive bladder cancer and those patients receive 6 intravesical instillations with Mycobacterium bovis BCG after transurethral resection. However, 30% of patients show recurrences after treatment and experience severe side effects that often lead to therapy discontinuation. Recently, another vaccine strain, Salmonella enterica typhi Ty21a, demonstrated promising antitumor activity in vivo. Here we focus on increasing bacterial retention in the bladder in order to reduce the number of instillations required and improve antitumor activity. OBJECTIVE: To increase the binding of Ty21a to the bladder wall by surface labeling of the bacteria with adhesion protein FimH and to study its effect in a bladder cancer mouse model. METHODS: Binding of Ty21a with surface-labeled FimH to the bladder wall was analyzed in vitro and in vivo. The antitumor effect of a single instillation of Ty21a+FimH in treatment was determined in a survival experiment. RESULTS: FimH-labeled Ty21a showed significant (p < 0.0001) improved binding to mouse and human cell lines in vitro. Furthermore, FimH labeled bacteria showed ∼5x more binding to the bladder than controls in vivo. Enhanced binding to the bladder via FimH labeling induced a modest improvement in median but not in overall mice survival. CONCLUSIONS: FimH labeling of Ty21a significantly improved binding to bladder tumor cells in vitro and the bladder wall in vivo. The improved binding leads to a modest increase in median survival in a single bladder cancer mouse study.