omega-Hydrazino linear polyethylenimine: a monoconjugation building block for nucleic acid delivery

Linear polyethylenimine as (multi) functional initiator for organocatalytic l-lactide polymerization

The preparation of polyethylenimine (PEI)–polylactide (PLA) copolymer structures is promising as these materials may find use in gene and/or drug delivery applications.

Oligobenzylethylenimine enriches linear polyethylenimine with a pH-sensitive membrane-disruptive property and leads to enhanced gene delivery activity

We report here the synthesis of a diblock linear polymer of oligo(benzylethylenimine)-b-polyethylenimine (OBzEI-PEI) and investigate its gene delivery properties. The linear copolymer OBzEI-PEI was prepared in a straightforward manner by acidic hydrolysis of a diblock polyoxazoline, which had been made by sequential polymerization of 4-benzyl-2-ethyl-2-oxazoline followed by 2-ethyl-2-oxazoline. pH titration and DNA complexation profiles of the new polymer are similar to regular linear PEIs, but with higher gene transfection efficiencies in various cell lines despite a decreased cellular uptake of plasmid DNA. Further experiments suggest that the OBzEI tail complements the intrinsic proton-sponge endosomolytic activities of PEI with an acid pH-sensitive membrane-perturbing activity.

Linear PEI nanoparticles: efficient pDNA/siRNA carriers in vitro and in vivo

Linear polyethylenimine (lPEI, 25 kDa) nanoparticles' (LPN) series was synthesized by varying percentage of cross-linking with 1,4-butanediol diglycidyl ether (BDE) and their size, surface charge, morphology, pDNA protection/release, cytotoxicity and transfection efficiency were evaluated. Synthesized nanoparticles (NPs) were spherical in shape (size: ∼109 - 235 nm; zeta potential: +38 to +16 mV). These NPs showed increased buffering capacity with increasing percent cross-linking and also exhibited excellent transfection efficiency (i.e., ∼1.3 - 14.7 folds in case of LPN-5) in comparison with lPEI and the commercial transfection agents used in this study. LPN-5 based GFP-specific siRNA delivery resulted in ∼86% suppression of targeted gene expression. These particles were relatively nontoxic in vitro (in cell lines) and in vivo (in Drosophila). In vivo gene expression studies using LPN-5 in Balb/c mice through intravenous injection showed maximum expression of the reporter gene in the spleen. These results together demonstrate the potential of these particles as efficient transfection reagents.

FROM THE CLINICAL EDITOR

The authors demonstrate a novel method of synthesizing linear PEI nanoparticles to utilize these as transfection agents.

Peptide/protein-polymer conjugates: synthetic strategies and design concepts

This feature article provides a compilation of tools available for preparing well-defined peptide/protein-polymer conjugates, which are defined as hybrid constructs combining (i) a defined number of peptide/protein segments with uniform chain lengths and defined monomer sequences (primary structure) with (ii) a defined number of synthetic polymer chains. The first section describes methods for post-translational, or direct, introduction of chemoselective handles onto natural or synthetic peptides/proteins. Addressed topics include the residue- and/or site-specific modification of peptides/proteins at Arg, Asp, Cys, Gln, Glu, Gly, His, Lys, Met, Phe, Ser, Thr, Trp, Tyr and Val residues and methods for producing peptides/proteins containing non-canonical amino acids by peptide synthesis and protein engineering. In the second section, methods for introducing chemoselective groups onto the side-chain or chain-end of synthetic polymers produced by radical, anionic, cationic, metathesis and ring-opening polymerization are described. The final section discusses convergent and divergent strategies for covalently assembling polymers and peptides/proteins. An overview of the use of chemoselective reactions such as Heck, Sonogashira and Suzuki coupling, Diels-Alder cycloaddition, Click chemistry, Staudinger ligation, Michael's addition, reductive alkylation and oxime/hydrazone chemistry for the convergent synthesis of peptide/protein-polymer conjugates is given. Divergent approaches for preparing peptide/protein-polymer conjugates which are discussed include peptide synthesis from synthetic polymer supports, polymerization from peptide/protein macroinitiators or chain transfer agents and the polymerization of peptide side-chain monomers.

Rapid optimization of gene delivery by parallel end-modification of poly(beta-amino ester)s

Poly(beta-amino ester)s are cationic degradable polymers that have significant potential as gene delivery vectors. Here we present a generalized method to modify poly(beta-amino ester)s at the chain ends to improve their delivery performance. End-chain coupling reactions were developed so that polymers could be synthesized and tested in a high-throughput manner, without the need for purification. In this way, many structural variations at the polymer terminus could be rapidly evaluated. End-modification of the terminal amine structure of a previously optimized poly(beta-amino ester), C32, significantly enhanced its in vitro transfection efficiency. In vivo, intraperitoneal (IP) gene delivery using end-modified C32 polymers resulted in expression levels over one order of magnitude higher than unmodified C32 and jet-polyethylenimine (jet-PEI) levels in several abdominal organs. The rapid end-modification strategy presented here has led to the discovery of many effective polymers for gene delivery and may be a useful method to develop and optimize cationic polymers for gene therapy.

Intracellular protein delivery with a dimerizable amphiphile for improved complex stability and prolonged protein release in the cytoplasm of adherent cell lines

Direct delivery of functionally active proteins into cells represents an emerging strategy for laboratory investigation and therapeutic applications. For this purpose, we developed a novel amphiphile (CholCSper) consisting of cholesterol linked to carboxy-spermine by a cysteine. This amphiphile is dimerizable upon mild oxidation of the thiol to disulfide and it was used in formulation with DOPE to prepare an intracellular protein delivery system. The stabilization of the CholCSper assemblies by chemical conversion of CholCSper into its gemini amphiphile afforded the production of homogeneous assemblies with proteins whose sizes are easier to control. Furthermore, the cholesterol moiety has an effect on the density of the complexes formed with proteins and leads to a prolonged protein release in the cytoplasm of cells exposed to the protein carrier assemblies.