Efficient down-regulation of CDK4 by novel lipid nanoparticle-mediated siRNA delivery

Background: Inhibition of cyclin-dependent kinases 4 (CDK4) activity by Small-interfering RNA (siRNA) has been demonstrated as one of the promising approaches to treat cancer. Materials and Methods: CDK4 siRNA was packaged in a lipid nanoparticle (LNP)-based delivery system that consists of an ionizable cationic lipid, helper lipid and polyethylene glycol (PEG)-lipid. The physical properties, including the size and surface charge of LNP-siRNA, were characterized by dynamic light scattering and zeta potential measurements. The biological activities of LNP-siRNA, including the cellular uptake, CDK4 expression and G₁ cell cycle arrest, in both HeLa cervical cancer and MDA-MB-468 breast cancer cells were evaluated by flow cytometry, confocal microscopy, quantitative reverse transcription PCR (qRT-PCR) and Western blotting, respectively. Results: The new LNP-mediated siRNA delivery demonstrated enhanced cellular uptake. Compared with free siRNA and lipofectamine-formulated siRNA, cells treated by LNP-CDK4 siRNA exhibited significant G₁ cell cycle arrest, which was consistent with efficient down-regulation of CDK4 at both mRNA and protein levels. Conclusion: Gene silencing of CDK4 by LNP-siRNA offers an alternative strategy for CDK4-based cancer therapy. The new LNP can be used for efficient delivery of siRNA in vitro.