Suppression of tumor invasion and migration in breast cancer cells following delivery of siRNA against Stat3 with the antimicrobial peptide PR39

PR39, a porcine cathelicidin rich in the amino acids proline and arginine can interact with the negatively charged component of the cell surface, and rapidly penetrate cell membranes. Therefore, we hypothesized that PR39, as a membrane penetrating peptide (MPP), could be exploited as a novel carrier to deliver siRNA into the cell cytoplasm in order to knockdown target gene expression. Firstly, a complex formation of PR39 with siRNA and its cellular colocalization were investigated in our studies. Further, we optimized the ratio of the PR39/siRNA complex, cell/complex incubation period and the concentration of siRNA. The results suggest that PR39 could form a complex with siRNA, and mediate translocation of the siRNA into 4T1 cells. The optimal ratio of siRNA with PR39 was 1:90 which was found to have a maximum Stat3 gene silencing effect after 48 h treatment. Moreover, 4T1 cell proliferation, cell cycle, invasion and migration were investigated. The results suggested that Stat3 knockdown could not result in 4T1 cell proliferation inhibition and cell cycle arrest, while invasion and migration of 4T1 cells were strongly inhibited. Notably, the data also showed that in addition to inhibition of carcinogenesis, single PR39 may play a role in cell invasion and migration. PR39 and Stat3 siRNA displayed synergistic biological effects in inhibiting cell invasion and migration of 4T1 cells, which was more prominent compared with the popular Lipofectamine delivery system.