To confirm the role of cathelicidin (LL-37) in the internalization of bacille Calmette-Guérin (BCG) into bladder cancer cells.

Enzyme-linked immunosorbent assay and reverse transcription polymerase chain reaction analysis evaluated the changes in protein and messenger ribonucleic acid (RNA) expression with BCG incubation after LL-37 pretreatment in 5637 and T24 human bladder cancer cells. The internalization rate was evaluated by a double immunofluorescence assay, and confocal microscopy confirmed the function of LL-37 in BCG internalization. We also investigated the difference in internalization rates and cell viability between LL-37, anti–LL-37 antibody, and LL-37 plus anti–LL-37 antibody.

The levels of LL-37 increased after BCG exposure in bladder cancer cells in dose- and time-dependent manners. Increasing LL-37 levels using recombinant LL-37 protein further dose dependently decreased BCG internalization in both cell lines. The internalization rates of BCG after LL-37 instillation were lower compared with the controls, and the internalization rate of BCG after anti–LL-37 antibody instillation was significantly higher compared with the controls in both cell lines (P <.05). Viability of LL-37 plus BCG group was higher compared with the BCG-alone group. The anti–LL-37 antibody plus BCG group had decreased cell viability compared with the BCG-alone group in both cell lines.

Bladder cancer cells produce cathelicidin when infected with BCG and upregulate cathelicidin to defend against BCG by inhibiting its internalization. Blocking the action of cathelicidin may increase the internalization and effectiveness of BCG in reducing bladder cancer cell proliferation.