Tailoring diblock copolymers for efficient siPLK1 delivery and enhanced gene therapy of orthotopic osteosarcoma

Osteosarcoma (OS) is a primary malignant bone tumor characterized by its aggressive local destruction and high metastatic potential. RNA interference (RNAi)-based therapeutics show great promise for treating OS; yet the challenge lies in developing safe and efficient delivery systems that can achieve effective siRNA delivery and therapeutic outcomes, particularly in orthotopic OS models. Herein, we introduce a diblock copolymer with precisely designed block composition and length that simultaneously fulfills the multiple requirements for siRNA delivery, both <i>in vitro</i> and <i>in vivo</i>. We selected siPLK1 as the active RNA and defined the copolymer as PEG₁₁₃-<i>b</i>-P(AAPBA₂₀-<i>co</i>-DMAPMA₂₀), containing boronic acid (PBA) and <i>N</i>-(3-dimethylaminopropyl) (DMAP) pendant units. Both AAPBA and DMAPMA can bind to siRNA, but only their random combination with appropriate block length formed well-defined NPs that facilitated efficient endocytosis. Adequate endosomal escape and siRNA release were then achieved through the cationic PAM and responsive PBA units, respectively. The shielding PEG block, further modified with an alendronate sodium (AS) moiety, enabled OS-targeted delivery of siPLK1. The designed copolymer achieved 83.9% <i>in vitro</i> PLK1 gene silencing, outperforming Lipo3000 (49.3%), and demonstrated superior anti-tumor (74.6% inhibition rate) and anti-metastasis effects in a highly metastatic orthotopic 143B OS model.