Cyclin-dependent kinase 4 (CDK4) siRNA packaged in a lipid NP (LNP)-based delivery system that consists of an ionizable cationic lipid, helper lipid, and polyethylene glycol (PEG)-lipid showed a 16-fold increase in intracellular uptake of siRNA by BC cells and a significant G1 cell cycle arrest due to efficient down-regulation of CDK4 at both mRNA and protein levels [210]. Here, CDK4 is linked to breast cancer.