Endosomolytic Bioreducible Poly(amido amine disulfide) Polymer Conjugates for the <i>in Vivo</i> Systemic Delivery of siRNA Therapeutics

Efficient siRNA delivery is dependent not only on the ability of the delivery vehicle to target a specific organ but also on its ability to enable siRNA entry into the cytoplasm of the target cells. Polymers with endosomolytic properties are increasingly being used as siRNA delivery vehicles due to their potential to facilitate endosomal escape and intracellular delivery. Addition of disulfide bonds in the backbone of these polymers was expected to provide degradability through reduction by glutathione in cytosol. This paper describes the synthesis of new endosomolytic bioreducible poly­(amido amine disulfide) polymers whose lytic potential can be masked at physiological pH, but can be restored at acidic endosomal pH. These polymer conjugates gave good <i>in vitro</i> knockdown (KD) and did not demonstrate cytotoxicity in a MTS assay. Efficient mRNA KD for apolipoprotein B in mouse liver was observed with these polyconjugates following intravenous dosing

Novel Endosomolytic Poly(amido amine) Polymer Conjugates for Systemic Delivery of siRNA to Hepatocytes in Rodents and Nonhuman Primates

The application of small interfering (si)­RNAs as potential therapeutic agents requires safe and effective methods for their delivery to the cytoplasm of the target cells and tissues. Recent studies have shown significant progress in the development of targeting reagents that facilitate the recognition of, and siRNA delivery to, specific cell types. Among recently reported delivery approaches, polymers with amphipathic properties have been used to enable endosome escape and cytosolic delivery. Here, we describe a linear amphipathic poly­(amido amine) polymer conjugate system for the efficient siRNA delivery <i>in vitro</i> and <i>in vivo</i>. This polymer contains a novel amine bearing bis-acrylamide monomer designed for increasing amine density, which resulted in substantial improvement in liver uptake and RNAi activity compared to our previously reported poly­(amido amine disulfide) polymer. The activity for this liver targeted delivery system was demonstrated in rodents and nonhuman primates

Improving the In Vivo Therapeutic Index of siRNA Polymer Conjugates through Increasing pH Responsiveness

Polymer based carriers that aid in endosomal escape have proven to be efficacious siRNA delivery agents in vitro and in vivo; however, most suffer from cytotoxicity due in part to a lack of selectivity for endosomal versus cell membrane lysis. For polymer based carriers to move beyond the laboratory and into the clinic, it is critical to find carriers that are not only efficacious, but also have margins that are clinically relevant. In this paper we report three distinct categories of polymer conjugates that improve the selectivity of endosomal membrane lysis by relying on the change in pH associated with endosomal trafficking, including incorporation of low p<i>K</i>_a heterocycles, acid cleavable amino side chains, or carboxylic acid pH sensitive charge switches. Additionally, we determine the therapeutic index of our polymer conjugates in vivo and demonstrate that the incorporation of pH responsive elements dramatically expands the therapeutic index to 10–15, beyond that of the therapeutic index (less than 3), for polymer conjugates previously reported

Improving the In Vivo Therapeutic Index of siRNA Polymer Conjugates through Increasing pH Responsiveness

Polymer based carriers that aid in endosomal escape have proven to be efficacious siRNA delivery agents in vitro and in vivo; however, most suffer from cytotoxicity due in part to a lack of selectivity for endosomal versus cell membrane lysis. For polymer based carriers to move beyond the laboratory and into the clinic, it is critical to find carriers that are not only efficacious, but also have margins that are clinically relevant. In this paper we report three distinct categories of polymer conjugates that improve the selectivity of endosomal membrane lysis by relying on the change in pH associated with endosomal trafficking, including incorporation of low p<i>K</i>_a heterocycles, acid cleavable amino side chains, or carboxylic acid pH sensitive charge switches. Additionally, we determine the therapeutic index of our polymer conjugates in vivo and demonstrate that the incorporation of pH responsive elements dramatically expands the therapeutic index to 10–15, beyond that of the therapeutic index (less than 3), for polymer conjugates previously reported