Synthesis, Characterization, and Evaluation as Transfection Reagents of Double-Hydrophilic Star Copolymers: Effect of Star Architecture

Beyond Lipids: Exploring Advances in Polymeric Gene Delivery in the Lipid Nanoparticles Era

The recent success of gene therapy during the COVID-19 pandemic has underscored the importance of effective and safe delivery systems. Complementing lipid-based delivery systems, polymers present a promising alternative for gene delivery. Significant advances have been made in the recent past, with multiple clinical trials progressing beyond phase I and several companies actively working on polymeric delivery systems which provides assurance that polymeric carriers can soon achieve clinical translation. The massive advantage of structural tunability and vast chemical space of polymers is being actively leveraged to mitigate shortcomings of traditional polycationic polymers and improve the translatability of delivery systems. Tailored polymeric approaches for diverse nucleic acids and for specific subcellular targets are now being designed to improve therapeutic efficacy. This review describes the recent advances in polymer design for improved gene delivery by polyplexes and covalent polymer-nucleic acid conjugates. The review also offers a brief note on novel computational techniques for improved polymer design. The review concludes with an overview of the current state of polymeric gene therapies in the clinic as well as future directions on their translation to the clinic.

Gene-repaired iPS cells as novel approach for patient with osteogenesis imperfecta

Introduction: The benefits of patient's specific cell/gene therapy have been reported in relation to numerous genetic related disorders including osteogenesis imperfecta (OI). In osteogenesis imperfecta particularly also a drug therapy based on the administration of bisphosphonates partially helped to ease the symptoms. Methods: In this controlled trial, fibroblasts derived from patient diagnosed with OI type II have been successfully reprogrammed into induced Pluripotent Stem cells (iPSCs) using Yamanaka factors. Those cells were subjected to repair mutations found in the COL1A1 gene using homologous recombination (HR) approach facilitated with star polymer (STAR) as a carrier of the genetic material. Results: Delivery of the correct linear DNA fragment to the osteogenesis imperfecta patient's cells resulted in the repair of the DNA mutation with an 84% success rate. IPSCs showed 87% viability after STAR treatment and 82% with its polyplex. Discussion: The use of novel polymer Poly[N,N-Dimethylaminoethyl Methacrylate-co-Hydroxyl-Bearing Oligo(Ethylene Glycol) Methacrylate] Arms (P(DMAEMA-co-OEGMA-OH) with star-like structure has been shown as an efficient tool for nucleic acids delivery into cells (Funded by National Science Centre, Contract No. UMO-2020/37/N/NZ2/01125).

How does the polymer architecture and position of cationic charges affect cell viability?

Polymer chemistry, composition and molar mass are factors that are known to affect cytotoxicity, however the influence of polymer architecture has not been investigated systematically. In this study the influence of the position of the cationic charges along the polymer chain on cytotoxicity was investigated while keeping constant the other polymer characteristics. Specifically, copolymers of various architectures, based on a cationic pH responsive monomer, 2-(dimethylamino)ethyl methacrylate (DMAEMA) and a non-ionic hydrophilic monomer, oligo(ethylene glycol)methyl ether methacrylate (OEGMA) were engineered and their toxicity towards a panel of cell lines investigated. Of the seven different polymer architectures examined, the block-like structures were less cytotoxic than statistical or gradient/tapered architectures. These findings will assist in developing future vectors for nucleic acid delivery.

Polymeric Carriers for Delivery of RNA Cancer Therapeutics

As research uncovers the underpinnings of cancer biology, new targeted therapies have been developed. Many of these therapies are small molecules, such as kinase inhibitors, that target specific proteins; however, only 1% of the genome encodes for proteins and only a subset of these proteins has ‘druggable’ active binding sites. In recent decades, RNA therapeutics have gained popularity due to their ability to affect targets that small molecules cannot. Additionally, they can be manufactured more rapidly and cost-effectively than small molecules or recombinant proteins. RNA therapeutics can be synthesised chemically and altered quickly, which can enable a more personalised approach to cancer treatment. Even though a wide range of RNA therapeutics are being developed for various indications in the oncology setting, none has reached the clinic to date. One of the main reasons for this is attributed to the lack of safe and effective delivery systems for this type of therapeutic. This review focuses on current strategies to overcome these challenges and enable the clinical utility of these novel therapeutic agents in the cancer clinic.

An Overview of Methods and Tools for Transfection of Eukaryotic Cells in vitro

Transfection is a powerful analytical tool enabling studies of gene products and functions in eukaryotic cells. Successful delivery of genetic material into cells depends on DNA quantity and quality, incubation time and ratio of transfection reagent to DNA, the origin, type and the passage of transfected cells, and the presence or absence of serum in the cell culture. So far a number of transfection methods that use viruses, non-viral particles or physical factors as the nucleic acids carriers have been developed. Among non-viral carriers, the cationic polymers are proposed as the most attractive ones due to the possibility of their chemical structure modification, low toxicity and immunogenicity. In this review the delivery systems as well as physical, biological and chemical methods used for eukaryotic cells transfection are described and discussed.

Nonviral DNA Delivery System with Supramolecular PEGylation Formed by Host-Guest Pseudo-Block Copolymers

A cationic supramolecular system based on host-guest pseudoblock copolymers was developed for nonviral DNA delivery. In this system, the macromolecular host was a cationic star-shaped polymer composed of a β-cyclodextrin (β-CD) core and multiple poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) chains grafted on the core, while the macromolecular guest was a linear adamantyl-ended poly(ethylene glycol) (mPEG-Ad). Pseudoblock copolymers were self-assembled from the polymeric host-guest pairs (typically, 1:1 molar ratio) in aqueous media through the inclusion of an adamantyl group at the end of guest polymer into the β-CD cavity of host polymers. Through such an approach, the resultant supramolecular system was integrated with not only a superior DNA condensing ability due to the host polymer but also an outstanding polyplex-stabilizing ability as well as biocompatibility due to the guest polymer. The cationic star-shaped host polymers alone were capable of condensing plasmid DNA efficiently into nanoparticles (70-100 nm) with positive surface charge. They showed obviously lower cytotoxicity than PEI 25K (commercial branched polyethylenimine with a molecular weight around 25 kDa) in cell lines of L929, MB231, and Hela under high dose. In serum-free or serum-containing culture conditions, these host polymers exhibited either higher or lower in vitro DNA transfection efficiency as compared with PEI 25K in the three cell lines under study, which was dependent on the N/P ratios and PDMAEMA arm length. Upon incorporation of the PEG block through host-guest complexation with mPEG-Ad (i.e., supramolecular PEGylation), the resulting host-guest supramolecular systems exhibited even lower cytotoxicity than the host polymers alone. The polyplexes between plasmid DNA (pDNA) and the host-guest systems showed significantly improved stability in BSA-PBS buffer solution (pH 7.4) and enhanced in vitro DNA transfection efficiency in the cases of higher N/P ratios or longer PDMAEMA arms in all tested cell lines under both serum-free and serum-containing culture conditions, as compared with the corresponding polyplexes without supramolecular PEGylation. Further, through forming pseudoblock copolymer, the DNA transfection ability of the supramolecular system can be easily modulated and optimized either by changing the ratio between the guest and host or by using different hosts with varied PDMAEMA arm lengths.

Star polymer-based nanolayers with immobilized complexes of polycationic stars and DNA for deposition gene delivery and recovery of intact transfected cells

We designed a novel thermoresponsive system of nanolayers composed of star poly[oligo(ethylene glycol) methacrylate]s (S-POEGMA) covalently bonded to a solid support and covered with polyplexes of cationic star polymers and plasmid DNA (pDNA). S-POEGMA stars were attached to the solid support via a UV-mediated "grafting to" method. To the best of our knowledge, for the first time, the conformational changes of obtained star nanolayers, occurring with changes in temperature, were studied using a quartz crystal microbalance technique. Next, the polyplexes of star poly[N,N'-dimethylaminoethyl methacrylate-ran-di(ethylene glycol) methacrylate] (S-P(DMAEMA-DEGMA)) with pDNA, exhibiting a phase transition temperature (T_CP) in culture medium DMEM, were deposited on S-POEGMA layers when the temperature increased above the T_CP of polyplex. The thermoresponsivity of the system was then the main mechanism for controlling the adhesion, proliferation, transfection and detachment of HT-1080 cells. The nanolayers promoted the effective cell culture and delivered nucleic acids into cells, with a transfection efficiency several times higher than that of the control. The detachment of the transfected cells was regulated only by the change of temperature. The studies demonstrated that we obtained a novel and effective system, based on a star polymer architecture, useful for gene delivery and tissue engineering applications.

Star polymers with acid-labile diacetal-based cores synthesized by aqueous RAFT polymerization for intracellular DNA delivery

Facile low temperature aqueous heterogeneous RAFT polymerization for preparation of novel star polymers with acid-labile diacetal-based cores for DNA delivery.

Polymeric siRNA gene delivery - transfection efficiency versus cytotoxicity

Within the field of gene therapy, there is a considerable need for the development of non-viral vectors that are able to compete with the efficiency obtained by viral vectors, while maintaining a good toxicity profile and not inducing an immune response within the body. While there have been many reports of possible polymeric delivery systems, few of these systems have been successful in the clinical setting due to toxicity, systemic instability or gene regulation inefficiency, predominantly due to poor endosomal escape and cytoplasmic release. The objective of this review is to provide an overview of previously published polymeric non-coding RNA and, to a lesser degree, oligo-DNA delivery systems with emphasis on their positive and negative attributes, in order to provide insight in the numerous hurdles that still limit the success of gene therapy.

Effect of block copolymer architecture and composition on gold nanoparticle fabrication

Gold nanoparticles (AuNPs) fabricated via the self-assembly of block copolymers of various architectures.

Synthesis, Characterization and Cytotoxicity of Novel Thermoresponsive Star Copolymers of N,N'-Dimethylaminoethyl Methacrylate and Hydroxyl-Bearing Oligo(Ethylene Glycol) Methacrylate

Novel, nontoxic star copolymers of N,N-dimethylaminoethyl methacrylate (DMAEMA) and hydroxyl-bearing oligo(ethylene glycol) methacrylate (OEGMA-OH) were synthesized via atom transfer radical polymerization (ATRP) using hyperbranched poly(arylene oxindole) as the macroinitiator. Stars with molar masses from 100,000 g/mol to 257,000 g/mol and with various amounts of OEGMA-OH in the arms were prepared. As these polymers can find applications, e.g., as carriers of nucleic acids, drugs or antibacterial or antifouling agents, in this work, much attention has been devoted to exploring their solution behavior and their stimuli-responsive properties. The behavior of the stars was studied in aqueous solutions under various pH and temperature conditions, as well as in PBS buffer, in Dulbecco's modified Eagle's medium (DMEM) and in organic solvents for comparison. The results indicated that increasing the content of hydrophilic OEGMA-OH units in the arms up to 10 mol% increased the cloud point temperature. For the stars with an OEGMA-OH content of 10 mol%, the thermo- and pH-responsivity was switched off. Since cytotoxicity experiments have shown that the obtained stars are less toxic than homopolymer DMAEMA stars, the presented studies confirmed that the prepared polymers are great candidates for the design of various nanosystems for biomedical applications.

pH-Responsive polymers

This review summarizes pH-responsive monomers, polymers and their derivative nano- and micro-structures including micelles, cross-linked micelles, microgels and hydrogels.

Co-self-assembly of cationic microparticles to deliver pEGFP-ZNF580 for promoting the transfection and migration of endothelial cells

The gene transfection efficiency of polyethylenimine (PEI) varies with its molecular weight. Usually, high molecular weight of PEI means high gene transfection, as well as high cytotoxicity in gene delivery in vivo. In order to enhance the transfection efficiency and reduce the cytotoxicity of PEI-based gene carriers, a novel cationic gene carrier was developed by co-self-assembly of cationic copolymers. First, a star-shaped copolymer poly(3(S)-methyl-morpholine-2,5-dione-co-lactide) (P(MMD-co-LA)) was synthesized using D-sorbitol as an initiator, and the cationic copolymer (P(MMD-co-LA)-g-PEI) was obtained after grafting low-molecular weight PEI. Then, by co-self-assembly of this cationic copolymer and a diblock copolymer methoxy-poly(ethylene glycol) (mPEG)-b-P(MMD-co-LA), microparticles (MPs) were formed. The core of MPs consisted of a biodegradable block of P(MMD-co-LA), and the shell was formed by mPEG and PEI blocks. Finally, after condensation of pEGFP-ZNF580 by these MPs, the plasmids were protected from enzymatic hydrolysis effectively. The result indicated that pEGFP-ZNF580-loaded MP complexes were suitable for cellular uptake and gene transfection. When the mass ratio of mPEG-b-P(MMD-co-LA) to P(MMD-co-LA)-g-PEI reached 3/1, the cytotoxicity of the complexes was very low at low concentration (20 μg mL-1). Additionally, pEGFP-ZNF580 could be transported into endothelial cells (ECs) effectively via the complexes of MPs/pEGFP-ZNF580. Wound-healing assay showed that the transfected ECs recovered in 24 h. Cationic MPs designed in the present study could be used as an applicable gene carrier for the endothelialization of artificial blood vessels.

Star Polymers

Recent advances in controlled/living polymerization techniques and highly efficient coupling chemistries have enabled the facile synthesis of complex polymer architectures with controlled dimensions and functionality. As an example, star polymers consist of many linear polymers fused at a central point with a large number of chain end functionalities. Owing to this exclusive structure, star polymers exhibit some remarkable characteristics and properties unattainable by simple linear polymers. Hence, they constitute a unique class of technologically important nanomaterials that have been utilized or are currently under audition for many applications in life sciences and nanotechnologies. This article first provides a comprehensive summary of synthetic strategies towards star polymers, then reviews the latest developments in the synthesis and characterization methods of star macromolecules, and lastly outlines emerging applications and current commercial use of star-shaped polymers. The aim of this work is to promote star polymer research, generate new avenues of scientific investigation, and provide contemporary perspectives on chemical innovation that may expedite the commercialization of new star nanomaterials. We envision in the not-too-distant future star polymers will play an increasingly important role in materials science and nanotechnology in both academic and industrial settings.

Water soluble stimuli-responsive star copolymers with multiple encapsulation and release properties

Stimuli-responsive, water soluble, nontoxic, star-copolymers showing reversible encapsulation and release of hydrophobic dye/drug molecule with increasing temperature and decreasing pH.

Nonviral Plasmid DNA Carriers Based on N,N'-Dimethylaminoethyl Methacrylate and Di(ethylene glycol) Methyl Ether Methacrylate Star Copolymers

Star polymers with random and block copolymer arms made of cationic N,N'-dimethylaminoethyl methacrylate (DMAEMA) and nonionic di(ethylene glycol) methyl ether methacrylate (DEGMA) were synthesized via atom transfer radical polymerization (ATRP) and used for the delivery of plasmid DNA in gene therapy. All stars were able to form polyplexes with plasmid DNA. The structure and size of the polyplexes were precisely determined using light scattering and cryo-TEM microscopy. The hydrodynamic radius of a complex of DNA with star was dependent on the architecture of the star arms, the DEGMA content and the number of amino groups in the star compared to the number of phosphate groups of the nucleic acid (N/P ratio). The smallest polyplexes (Rh90°∼50 nm) with positive zeta potentials (∼15 mV) were formed of stars with N/P=6. The introduction of DEGMA into the star structure caused a decrease of polyplex cytotoxicity in comparison to DMAEMA homopolymer stars. The overall transfection efficiency using HT-1080 cells showed that the studied systems are prospective gene delivery agents. The most promising results were obtained for stars with random copolymer arms of high DEGMA content.

The influence of polymer architecture on in vitro pDNA transfection

In the field of polymer-based gene delivery, the tuning potential of polymers by using different architectures like graft- and star-shaped polymers as well as self-assembled block copolymers is immense. In the last years numerous new polymer designs showed enhanced transfections properties in combination with a good biocompatibility.

Bioreducible POSS-cored star-shaped polycation for efficient gene delivery

The bioreducible star-shaped gene vector (POSS-(SS-PDMAEMA)8) with well-defined structure and relatively narrow molecular weight distribution was synthesized via atom transfer radical polymerization (ATRP) of (2-dimethylamino)ethyl methacrylate (DMAEMA) from a polyhedral oligomeric silsesquioxane (POSS) macroinitiator. POSS-(SS-PDMAEMA)8 was composed of a biocompatible POSS core and eight disulfide-linked PDMAEMA arms, wherein the PDMAEMA chain length could be adjusted by controlling polymerization time. POSS-(SS-PDMAEMA)8 can effectively bind pDNA into uniform nanocomplexes with appropriate particle size and zeta potential. The incorporation of disulfide bridges gave the POSS-(SS-PDMAEMA)8 material facile bioreducibility. In comparison with POSS-(PDMAEMA)8 without disulfide linkage, POSS-(SS-PDMAEMA)8 exhibited much lower cytotoxicity and substantially higher transfection efficiency. The present work would provide useful information for the design of new POSS-based drug/gene carriers.

Different types of degradable vectors from low-molecular-weight polycation-functionalized poly(aspartic acid) for efficient gene delivery

Poly(aspartic acid) (PAsp) has been employed as the potential backbone for the preparation of efficient gene carriers, due to its low cytotoxicity, good biodegradability and excellent biocompatibility. In this work, the degradable linear or star-shaped PBLA was first prepared via ring-opining polymerization of β-benzyl-L-aspartate N-carboxy anhydride (BLA-NCA) initiated by ethylenediamine (ED) or ED-functionalized cyclodextrin cores. Then, PBLA was functionalized via aminolysis reaction with low-molecular-weight poly(2-(dimethylamino)ethyl methacrylate) with one terminal primary amine group (PDMAEMA-NH2), followed by addition of excess ED or ethanolamine (EA) to complete the aminolysis process. The obtained different types of cationic PAsp-based vectors including linear or star PAsp-PDM-NH2 and PAsp-PDM-OH exhibited good condensation capability and degradability, benefiting gene delivery process. In comparison with gold standard polyethylenimine (PEI, ∼ 25 kDa), the cationic PAsp-based vectors, particularly star-shaped ones, exhibited much better transfection performances.

Molecular weight and architectural dependence of well-defined star-shaped poly(lysine) as a gene delivery vector

A series of well-defined star-shaped polypeptides were successfully synthesised by the ring opening polymerisation (ROP) of the N-carboxyanhydride (NCA) of ε-carbobenzyloxy-l-lysine (ZLL) using a range of generations of polypropylene imine (PPI) dendrimers as multifunctional initiators. The monomer feed ratio and dendrimer generation were varied to afford a series of polypeptide dendrimer hybrids with superior structural versatility and functionality. Subsequent protecting group removal yielded star-shaped poly(lysine) of controlled variation in polypeptide chain length and arm multiplicity. Star-shaped PLL polymers were used to prepare pDNA and siRNA to form "polyplexes" to determine their ability to complex different nucleic acid cargoes and were compared with linear PLL polyplex controls. Significant differences in size and surface charge were seen between star-shaped PLL polyplexes and linear PLL polyplexes for both cargoes. The star-shaped polypeptides were capable of more effective complexation of both nucleic acids at low N/P ratios compared to linear PLL as evidenced by zeta potential and electrophoretic data. This was particularly evident in siRNA polyplexes as linear PLL failed to completely complex siRNA into nanocomplexes of appropriate size for cell transfection i.e. <200 nm in size, while star poly(lysine) formed siRNA polyplexes <100 nm at certain N/P ratios, albeit strongly dependent on the particular molecular weight and architecture, as analysed by dynamic light scattering (DLS). Atomic force microscopy (AFM) identified discrete spherically shaped polyplexes for all star-shaped polypeptide-based polyplexes while linear PLL formed elongated irregular shaped complexes. This difference in morphology may go some way towards explaining the 300-fold increase in luciferase expression seen for star-shaped PLL polyplexes G5(64)-PLL₄₀ compared to linear PLL pGLuc polyplexes in epithelial cells. Each of the PPI-PLL polymers appeared to be capable of protecting the nucleic acid cargoes from degradation by the relevant nuclease enzyme as effectively as the positive control polyethyleneimine (PEI) polyplexes. Overall the promising nucleic acid complexation, sizing, morphology and protection capacity of two different genetic "cargoes" highlight the potential of polypeptide dendrimer hybrids as gene delivery vectors.

Polymeric theranostics: using polymer-based systems for simultaneous imaging and therapy

Polymer-based nanomedicine is a large and fast growing field. Polymer-based systems have been extensively used as therapeutic carriers as well as bioimaging agents for example in tumour diagnosis. However, fewer polymeric systems have been able to combine both therapy and imaging in a new field that is called theranostics (theragnostics). This review aims to summarise the recent developments and trends on polymeric theranostics. Four different types of therapies/treatments are examined namely drug delivery, gene delivery, photodynamic therapy and hyperthermia treatment combined with different imaging moieties like magnetic resonance imaging agents, fluorescent agents and microbubbles for ultrasound imaging.

Star polymers with a cationic core prepared by ATRP for cellular nucleic acids delivery

Poly(ethylene glycol) (PEG)-based star polymers with a cationic core were prepared by atom transfer radical polymerization (ATRP) for in vitro nucleic acid (NA) delivery. The star polymers were synthesized by ATRP of 2-(dimethylamino)ethyl methacrylate (DMAEMA) and ethylene glycol dimethacrylate (EGDMA). Star polymers were characterized by gel permeation chromatography, zeta potential, and dynamic light scattering. These star polymers were combined with either plasmid DNA (pDNA) or short interfering RNA (siRNA) duplexes to form polyplexes for intracellular delivery. These polyplexes with either siRNA or pDNA were highly effective in NA delivery, particularly at relatively low star polymer weight or molar ratios, highlighting the importance of NA release in efficient delivery systems.

New star-shaped carriers composed of β-cyclodextrin cores and disulfide-linked poly(glycidyl methacrylate) derivative arms with plentiful flanking secondary amine and hydroxyl groups for highly efficient gene delivery

The biocleavable star-shaped vectors (CD-SS-PGEAs) consisting of nonionic β-cyclodextrin (β-CD) cores and disulfide-linked low-molecular-weight poly(glycidyl methacrylate) (PGMA) derivative arms with plentiful flanking secondary amine and hydroxyl groups were successfully proposed for highly efficient gene delivery. A simple two-step method was first adopted to introduce reduction-sensitive disulfide-linked initiation sites of atom transfer radical polymerization (ATRP) onto β-CD cores. The disulfide-linked PGMA arms prepared subsequently via ATRP were functionalized via the ring-opening reaction with ethanolamine (EA) to produce the cationic EA-functionalized PGMA (PGEA) arms with plentiful secondary amine and nonionic hydroxyl units. The cationic PGEA arms can be readily cleavable from the β-CD cores under reducible conditions. Such biocleavable star-shaped CD-SS-PGEA vectors possessed the good pDNA condensation ability, low cytotoxicity, and efficient gene delivery ability.

Optimization of brush-like cationic copolymers for nonviral gene delivery

Polyethylenimine (PEI) is one of the most broadly used polycations for gene delivery due to its high transfection efficiency and commercial availability but materials are cytotoxic and often polydisperse. The goal of current work is to develop an alternative family of polycations based on controlled living radical polymerization (CLRP) and to optimize the polymer structure for efficient gene delivery. In this study, well-defined poly(glycidyl methacrylate)(P(GMA)) homopolymers were synthesized using reversible addition-fragmentation chain transfer (RAFT) polymerization followed by decoration using three different types of oligoamines, i.e., tetraethylenepentamine (TEPA), pentaethylenehexamine (PEHA), and tris(2-aminoethyl)amine (TREN), respectively, to generate various P(GMA-oligoamine) homopolycations. The effect of P(GMA) backbone length and structure of oligoamine on gene transfer efficiency was then determined. The optimal polymer, P(GMA-TEPA)(50), provided comparable transfection efficiency but lower cytotoxicity than PEI. P(GMA-TEPA)(50) was then used as the cationic block in diblock copolymers containing hydrophilic N-(2-hydroxypropyl) methacrylamide (HPMA) and oligo(ethylene glycol) monomethyl ether methacrylate (OEGMA). Polyplexes of block copolymers were stable against aggregation in physiological salt condition and in Opti-MEM due to the shielding effect of P(HPMA) and P(OEGMA). However, the presence of the HPMA/OEGMA block significantly decreased the transfection efficacy of P(GMA-TEPA)(50) homopolycation. To compensate for reduced cell uptake caused by the hydrophilic shell of polyplex, the integrin-binding peptide, RGD, was conjugated to the hydrophilic chain end of P(OEGMA)(15)-b-P(GMA-TEPA)(50) copolymer by Michael-type addition reaction. At low polymer to DNA ratios, the RGD-functionalized polymer showed increased gene delivery efficiency to HeLa cells compared to analogous polymers lacking RGD.

Multiarm cationic star polymers by atom transfer radical polymerization from β-cyclodextrin cores: influence of arm number and length on gene delivery

Controlled β-cyclodextrin (β-CD) core-based cationic star polymers have attracted considerable attention as non-viral gene carriers. Atom transfer radical polymerization (ATRP) could be readily used to produce the star-shaped polymers. The precise control of the number of initiation sites on the multifunctional core was of crucial importance to the investigation of the structure-property relationship of the functional star gene carriers. Herein, the controlled multiarm star polymers consisting of a β-CD core and various arm lengths of poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) were prepared via ATRP from the chloroacetylated β-CD with well-designed initiation sites. Generally, these star polycations can condense plasmid DNA into 100-150 nm nanoparticles with positive zeta potentials of 30-40 mV at N/P ratios (star polymer to DNA ratios) of 17 or higher. The effects of arm numbers and lengths on gene delivery were investigated in detail. With a fixed length of the PDMAEMA arm, the fewer the number of arms, the lower the toxicity. The star polycations with suitable arm numbers possess the best transfection ability. On the other hand, with the fixed molecular weights, the shorter the arms, the lower the toxicity. The polymers with 21 arms possess the lowest transfection efficiency.