Stimuli-responsive
polycations have been developed for improved
nucleic acid transfection and enhanced therapeutic efficacy. The most reported mechanisms for controlled release of
siRNA are based on
polyelectrolyte exchange reactions in the cytoplasm and the degradation of
polycations initiated by specific triggers. However, the degradation strategy has not always been sufficient due to unsatisfactory kinetics and binding of cationic fragments to
siRNA, which limits the gene silencing effect. In this study, a new strategy that combines degradation and charge reversal is proposed. Methods: We prepared a polycation (CrossPPA) by crosslinking of
phenylboronic acid (PBA)-grafted 1.8k PEI with
alginate. It was compared with 25k PEI, 1.8k PEI and 1.8k PEI-PBA on
siRNA encapsulation,
ATP-responsive behavior and mechanism, cytotoxicity, cell uptake,
siRNA transfection, in vivo biodistribution and in vivo anti-
tumor efficacy. The in vitro and in vivo experiments were performed on 4T1 murine
breast cancer cells and 4T1
tumor model separately. Results: The crosslinking strategy obviously improve the
siRNA loading ability of 1.8k PEI. We validated that intracellular levels of
ATP could trigger CrossPPA disassembly and charge reversal, which resulted in efficient and rapid
siRNA release due to electrostatic repulsion. Besides, CrossPPA/
siRNA showed strong cell uptake in 4T1 cells compared with 1.8k PEI/
siRNA. Notably, the cytotoxicity of CrossPPA was pretty low, which was owing to its biodegradability. Furthermore, the crosslinked polyplexes significantly enhanced
siRNA transfection and improved
tumor accumulation. The high gene silencing ability of CrossPPA polyplex led to strong anti-
tumor efficacy when using Bcl2-targeted
siRNA. Conclusion: These results indicated that the
ATP-triggered disassembly and charge reversal strategy provided a new way for developing stimuli-responsive
siRNA carriers and showed potential for
nucleic acid delivery in the treatment of
cancer.