Development of Fully Degradable Phosphonium-FunctionalizedAmphiphilic Diblock Copolymers for Nucleic Acids Delivery

摘要

To expand the range of functional polymer materials to include fully hydrolytically degradable systems that bear bioinspired phosphorus-containing linkages both along the backbone and as cationic side chain moieties for packaging and delivery of nucleic acids, phosphonium-functionalized polyphosphoester-block-poly(l-lactide) copolymers of various compositions were synthesized, fully characterized, and their self-assembly into nanoparticles were studied. First, an alkyne-functionalized polyphosphoester-block-poly(l-lactide) copolymer was synthesized via a one pot sequential ring opening polymerization of an alkyne-functionalized phospholane monomer, followed by the addition of l-lactide to grow the second block. Second, the alkynyl side groups of the polyphosphoester block were functionalized via photoinitiated thiol–yne radical addition of a phosphonium-functionalized free thiol. The polymers of varying phosphonium substitution degrees were self-assembled in aqueous buffers to afford formation of well-defined core–shell assemblies with an average size ranging between30 and 50 nm, as determined by dynamic light scattering. Intracellulardelivery of the nanoparticles and their effects on cell viabilityand capability at enhancing transfection efficiency of nucleic acids(e.g., siRNA) were investigated. Cell viability assays demonstratedlimited toxicity of the assembly to RAW 264.7 mouse macrophages, exceptat high polymer concentrations, where the polymer of high degree ofphosphonium functionalization induced relatively higher cytotoxicity.Transfection efficiency was strongly affected by the phosphonium-to-phosphate(P⁺/P^–) ratios of the polymers and siRNA,respectively. The AllStars Hs Cell Death siRNA complexed to the variouscopolymers at a P⁺/P^– ratio of 10:1 inducedcomparable cell death to Lipofectamine. These fully degradable nanoparticlesmight provide biocompatible nanocarriers for therapeutic nucleic aciddelivery.