Cation-free siRNA micelle knockdown of EPHA2 improves sensitivity of imatinib for osteosarcoma treatment

• Covalent attachment of siRNA to PDPA polymers to form cation-free siRNA micelles . • Cation-free siRNA micelles biocompatible and nontoxic. • RNAi combined with chemotherapeutic agents to treat osteosarcoma . Nanoparticle-based small interfering RNA (siRNA) therapeutics have revealed potential applications in the treatment of osteosarcoma. Nevertheless, charge-related toxicity and nuclease clearance severely limit the applicability of siRNAs in osteosarcoma therapeutic field. Herein, a GSH-responsive diblock copolymer siRNA-disulfide-poly(2-(diisopropylamino)ethyl methacrylate) (siRNA-SS-PDPA) is designed and synthesized, of which the siRNA micelles are generated via self-assembly strategy. Specifically, the derived siRNA micelles not only possess the features of effective cellular internalization, endosomal escape, prolonged blood circulation time, stable and efficient release, and no charge toxicity, but also effectively knock down the EPHA2 gene that mediates the insensitivity of tumor cells to imatinib (IMA). Resultantly, EPHA2 is capable of being knocked down by siRNA micelles, which enhances the sensitivity of MG63 cell line to imatinib, synergistically inhibiting the PI3K-AKT pathway and inducing apoptosis in combination with IMA. Simultaneously, the siRNA micelles demonstrate favorable biosafety in both cell lines and animal experiments, which significantly inhibit the in-situ growth of MG63 xenograft osteosarcoma by synergizing with IMA and markedly improve the survival rate. Conclusively, such cation-free siRNA micelles provide a novel drug-encoded delivery platform for GSH-triggered synergistic treatment of osteosarcoma with RNAi and chemotherapeutic agents.