Adam W. York

Facile Synthesis of Multivalent Folate-Block Copolymer Conjugates via Aqueous RAFT Polymerization: Targeted Delivery of siRNA and Subsequent Gene Suppression

Cell specific delivery of small interfering ribonucleic acid (siRNA) using well-defined multivalent folate-conjugated block copolymers is reported. Primary amine functional, biocompatible, hydrophilic-block-cationic copolymers were synthesized via aqueous reversible addition-fragmentation chain transfer (RAFT) polymerization. N-(2-hydroxypropyl)methacrylamide) (HPMA), a permanently hydrophilic monomer, was copolymerized with a primary amine containing monomer, N-(3-aminopropyl)methacrylamide (APMA). Poly(HPMA) confers biocompatibility, while APMA provides amine functionality, allowing conjugation of folate derivatives. HPMA-stat-APMA was chain extended with a cationic block, poly(N-[3-(dimethylamino)propyl]methacrylamide), to promote electrostatic complexation between the copolymer and the negatively charged phosphate backbone of siRNA. Notably, poly(HPMA) stabilizes the neutral complexes in aqueous solution, while APMA allows the conjugation of a targeting moiety, thus, dually circumventing problems associated with the delivery of genes via cationically charged complexes (universal transfection). Fluorescence microscopy and gene down-regulation studies indicate that these neutral complexes can be specifically delivered to cancer cells that overexpress folate receptors.

Synthetic Routes to Stimuli‐Responsive Micelles, Vesicles, and Surfaces via Controlled/Living Radical Polymerization∗

Controlled/living polymerization (CLRP) techniques have recently been developed that offer unprecedented opportunities for synthesis of materials with precisely tailored nano‐ and micro‐scale features. This account focuses on significant developments in the field of stimuli‐responsive block copolymers with immediate and future utility in advanced formulation and surface science. Specifically, stable free radial polymerization (SFRP), atom transfer polymerization (ATRP), and reversible addition fragmentation chain transfer (RAFT) polymerization techniques for preparation of responsive micelles and vesicles, stabilized nanoparticles, thin films, polymer brushes, and other ordered structures are described. Conformational changes in response to external stimuli are manifested in changes in physiochemical properties including surface wetting, adsorption, adhesion, lubricity, and permeability. *Paper number 120 in a series entitled Water Soluble Polymers.

Tailored Design of Au Nanoparticle-siRNA Carriers Utilizing Reversible Addition-Fragmentation Chain Transfer Polymers

The facile synthesis of polymer-stabilized Au nanoparticles (AuNPs) capable of forming neutral, sterically stable complexes with small interfering RNA (siRNA) is reported. The amine-containing cationic block of poly(N-2-hydroxypropyl methacrylamide(70)-block-N-[3-(dimethylamino)propyl] methacrylamide(24)) [P(HPMA(70)-b-DMAPMA(24))] was utilized to promote the in situ reduction of Au(3+) to AuNPs and subsequently bind small interfering RNA, while the nonimmunogenic, hydrophilic block provided steric stabilization. The ratio of [DMAPMA](0)/[Au(3+)](0) utilized in the reduction reaction was found to be critical to the production of polymer-stabilized AuNPs capable of complexing siRNA. Significant protection ( approximately 100 times) against nucleases was demonstrated by enzymatic tests, while gene down-regulation experiments indicated successful delivery of siRNA to cancerous cells.

Chiroptical Properties of Homopolymers and Block Copolymers Synthesized From the Enantiomeric Monomers N-acryloyl-L-alanine and N-acryloyl-D-alanine Using Aqueous RAFT Polymerization

Chiral homo- and block copolymers based on the enantiomeric monomers N-acryloyl-l-alanine (ALAL) and N-acryloyl-d-alanine (ADAL) were prepared directly in water using controlled reversible addition–fragmentation chain transfer (RAFT) polymerization. The polymerization of the chiral monomers proceeded in a controlled fashion producing the respective homopolymers, block copolymers, and a statistical copolymer with targeted molecular weights and narrow molecular weight distributions. The chiroptical activity of these biomimetic polymers and their analogous model compounds was investigated using circular dichroism (CD). P(ALAL) and P(ADAL) were shown to be optically active exhibiting mirror image CD spectra. In addition, statistical and enantiomeric block copolymers prepared at 1:1 stochiometric ratios exhibited virtually no optical activity.

Facile, modular transformations of RAFT block copolymers via sequential isocyanate and thiol -ene reactions

We describe a robust strategy utilizing reversible addition-fragmentation chain transfer (RAFT) polymerization and sequential transformations involving carbamate formation and thiol-ene click addition to synthesize well-defined functional block copolymers. The hydroxy-functional block copolymer scaffold, poly[(N,N-dimethylacrylamide)-b-(N-(2-hydroxyethyl)acrylamide)] (PDMAn-b-PHEAm) was first prepared via RAFT, requiring no protecting group chemistry. The hydroxyl groups of the HEA block were then reacted with 2-(acryloyloxy)ethylisocyanate (AOI) or allylisocyanate (AI) resulting in acrylate- and allyl-functionalized copolymer precursors, respectively. The efficiencies of both Michael and free radical-mediated thiol-ene addition reactions were investigated using model thiol compounds having alkyl, aryl, hydroxyl, carboxylic acid, amine and amino acid functionalities. The steps of RAFT polymerization, isocyanate-hydroxyl coupling and thiol-ene addition can be accomplished under mild conditions, thus offering a facile, modular route to the synthesis of functional copolymers from a single polymeric precursor.