Melamine Functionalized Copolymer for Sequence Specific siRNA Loading and Ligand-Driven Delivery

Triamino triazine, also termed melamine, presents three identical interfaces that are capable of recognizing U/T with three hydrogen bonds. When displayed on a polymeric chain, melamine displaying polymers are capable of condensing structureless U/T tracts into triple-stranded structures, which have been conferred with enhanced tolerance towards nuclease degradation and preserved biological function. In this study, a mixed-block copolymer with alternating display of N-Acetylgalactosamine (GalNAc) and melamine p(GM)_(10) is synthesized via reversible addition-fragmentation chain transfer (RAFT). The polymer has been demonstrated to sequence specifically load the 27-mer dicer substrate siRNA targeting ApoB-100 precursor mRNA that is appended with U stretches. The loaded siRNA can be efficiently processed by recombinant dicer, and readily uptaken by HepG2 cells via receptor mediated endocytosis, eliciting an IC 50 of 5 nM. Further, the copolymer is immunologically tolerant as the result of carbohydrate decoration, and induces minimum cytokine release syndrome. Hence, melamine displaying polymer offers a novel siRNA delivery strategy with enhanced RNAi potency; further, RAFT polymerization has been demonstrated to be a versatile platform for synthesizing tailored delivery system with tissue/disease-specific ligand conjugations.