Physicochemical Properties and Biological Performance of Polymethacrylate Based Gene Delivery Vector Systems: Influence of Amino Functionalities

The nanostructure of polyelectrolyte complexes of QPDMAEMA-b-POEGMA copolymers and oppositely charged polyelectrolytes, and their stability in the presence of serum albumin

Quaternized poly(2-(dimethylamino) ethyl methacrylate)-b-poly(oligo(ethyleneglycol) methyl ether methacrylate) (QPDMAEMA-b-POEGMA) is a copolymer of a positively charged block and a non-ionic hydrophilic block. The positively charged block, QPDMAEMA, electrostatically interacts with oppositely charged polymers, e.g., poly(acrylic acid) (PAA) and DNA, to form a complex. This complex is stable in aqueous solution due to the hydrophilic block, POEGMA, which provides colloidal stability and biocompatibility. Polyplexes can be used as non-viral vectors in gene therapy. Polyplexes are essential for delivering genetic materials into cells because they protect the genetic material from degradation before reaching the target cells, thus increasing the transfection efficiency. However, currently used polyplexes show a low transfection efficiency in vivo, probably because the polyplexes are exposed to blood proteins, such as serum albumin, which cause their dissociation. The main goal of this research is the morphology characterization of QPDMAEMA-b-POEGMA complexes with the sodium salt of polyacrylic acid (NaPAA), and with DNA by cryogenic transmission electron microscopy (cryo-TEM) and small-angle X-ray scattering (SAXS). These methods give qualitative and quantitative data about the morphology of the complexes. The morphology of the complexes was examined at different charge ratios (CRs). Complexes with NaPAA form core-corona spherical micelles and vesicular structures, whereas complexes with DNA form lamellar and hexagonal structures. The QPDMAEMA-b-POEGMA and DNA complexes were also examined after exposing them to bovine serum albumin (BSA). We found that BSA does not affect the complexes for seven days. This morphology characterization is essential for better design and formulation of vectors for gene therapy and polyelectrolyte complexes for biomedical applications.

Influence of DNA Type on the Physicochemical and Biological Properties of Polyplexes Based on Star Polymers Bearing Different Amino Functionalities

The interactions of two star polymers based on poly (2-(dimethylamino)ethyl methacrylate) with different types of nucleic acids are investigated. The star polymers differ only in their functionality to bear protonable amino or permanently charged quaternary ammonium groups, while DNAs of different molar masses, lengths and topologies are used. The main physicochemical parameters of the resulting polyplexes are determined. The influence of the polymer' functionality and length and topology of the DNA on the structure and properties of the polyelectrolyte complexes is established. The quaternized polymer is characterized by a high binding affinity to DNA and formed strongly positively charged, compact and tight polyplexes. The parent, non-quaternized polymer exhibits an enhanced buffering capacity and weakened polymer/DNA interactions, particularly upon the addition of NaCl, resulting in the formation of less compact and tight polyplexes. The cytotoxic evaluation of the systems indicates that they are sparing with respect to the cell lines studied including osteosarcoma, osteoblast and human adipose-derived mesenchymal stem cells and exhibit good biocompatibility. Transfection experiments reveal that the non-quaternized polymer is effective at transferring DNA into cells, which is attributed to its high buffering capacity, facilitating the endo-lysosomal escape of the polyplex, the loose structure of the latter one and weakened polymer/DNA interactions, benefitting the DNA release.

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.

Development of Double Hydrophilic Block Copolymer/Porphyrin Polyion Complex Micelles towards Photofunctional Nanoparticles

The electrostatic complexation between double hydrophilic block copolymers (DHBCs) and a model porphyrin was explored as a means for the development of polyion complex micelles (PICs) that can be utilized as photosensitive porphyrin-loaded nanoparticles. Specifically, we employed a poly(2-(dimethylamino) ethyl methacrylate)-b-poly[(oligo ethylene glycol) methyl ether methacrylate] (PDMAEMA-b-POEGMA) diblock copolymer, along with its quaternized polyelectrolyte copolymer counterpart (QPDMAEMA-b-POEGMA) and 5,10,15,20-tetraphenyl-21H,23H-porphine-p,p',p″,p'''-tetrasulfonic acid tetrasodium hydrate (TPPS) porphyrin. The (Q)PDMAEMA blocks enable electrostatic binding with TPPS, thus forming the micellar core, while the POEGMA blocks act as the corona of the micelles and impart solubility, biocompatibility, and stealth properties to the formed nanoparticles. Different mixing charge ratios were examined aiming to produce stable nanocarriers. The mass, size, size distribution and effective charge of the resulting nanoparticles, as well as their response to changes in their environment (i.e., pH and temperature) were investigated by dynamic and electrophoretic light scattering (DLS and ELS). Moreover, the photophysical properties of the complexed porphyrin along with further structural insight were obtained through UV-vis (200-800 nm) and fluorescence spectroscopy measurements.

Amphiphilic Copolymer-Lipid Chimeric Nanosystems as DNA Vectors

Lipid-polymer chimeric (hybrid) nanosystems are promising platforms for the design of effective gene delivery vectors. In this regard, we developed DNA nanocarriers comprised of a novel poly[(stearyl methacrylate-co-oligo(ethylene glycol) methyl ether methacrylate] [P(SMA-co-OEGMA)] amphiphilic random copolymer, the cationic 1,2-dioleoyl-3-(trimethylammonium) propane (DOTAP), and the zwitterionic L-α-phosphatidylcholine, hydrogenated soybean (soy) (HSPC) lipids. Chimeric HSPC:DOTAP:P[(SMA-co-OEGMA)] nanosystems, and pure lipid nanosystems as reference, were prepared in several molar ratios of the components. The colloidal dispersions obtained presented well-defined physicochemical characteristics and were further utilized for the formation of lipoplexes with a model DNA of linear topology containing 113 base pairs. Nanosized complexes were formed through the electrostatic interaction of the cationic lipid and phosphate groups of DNA, as observed by dynamic, static, and electrophoretic light scattering techniques. Ultraviolet-visible (UV-Vis) and fluorescence spectroscopy disclosed the strong binding affinity of the chimeric and also the pure lipid nanosystems to DNA. Colloidally stable chimeric/lipid complexes were formed, whose physicochemical characteristics depend on the N/P ratio and on the molar ratio of the building components. Cryogenic transmission electron microscopy (Cryo-TEM) revealed the formation of nanosystems with vesicular morphology. The results suggest the successful fabrication of these novel chimeric nanosystems with well-defined physicochemical characteristics, which can form stable lipoplexes.

Hydrophilic Random Cationic Copolymers as Polyplex-Formation Vectors for DNA

Research on the improvement and fabrication of polymeric systems as non-viral gene delivery carriers is required for their implementation in gene therapy. Random copolymers have not been extensively utilized for these purposes. In this regard, double hydrophilic poly[(2-(dimethylamino) ethyl methacrylate)-co-(oligo(ethylene glycol) methyl ether methacrylate] [P(DMAEMA-co-OEGMA)] random copolymers were synthesized via reversible addition-fragmentation chain transfer (RAFT) polymerization. The copolymers were further modified by quaternization of DMAEMA tertiary amine, producing the cationic P(QDMAEMA-co-OEGMA) derivatives. Fluorescence and ultraviolet-visible (UV-vis) spectroscopy revealed the efficient interaction of copolymers aggregates with linear DNAs of different lengths, forming polyplexes, with the quaternized copolymer aggregates exhibiting stronger binding affinity. Light scattering techniques evidenced the formation of polyplexes whose size, molar mass, and surface charge strongly depend on the N/P ratio (nitrogen (N) of the amine group of DMAEMA/QDMAEMA over phosphate (P) groups of DNA), DNA length, and length of the OEGMA chain. Polyplexes presented colloidal stability under physiological ionic strength as shown by dynamic light scattering. In vitro cytotoxicity of the empty nanocarriers was evaluated on HEK293 as a control cell line. P(DMAEMA-co-OEGMA) copolymer aggregates were further assessed for their biocompatibility on 4T1, MDA-MB-231, MCF-7, and T47D breast cancer cell lines presenting high cell viability rates.

Direct Surface Modification of Polycaprolactone-Based Shape Memory Materials to Introduce Positive Charge Aiming to Enhance Cell Affinity

In this study, the introduction of a positive charge on the surface of a shape memory material was investigated to enhance cell affinity. To achieve this, the direct chemical modification of a material surface was proposed. Sheet-type, crosslinked poly(caprolactone-co-α-bromo-ɤ-butyrolactone) (poly(CL-co-BrBL)) were prepared, and the direct reaction of amino compounds with bromo groups was conducted on the material surface with a positive charge. Branched poly(CL-co-BrBL) was prepared, followed by the introduction of methacryloyl groups to each chain end. Using the branched macromonomers, stable and sheet-type materials were derived through UV-light irradiation. Then, the materials were soaked in an amino compound solution to react with the bromo groups under various conditions. Differential scanning calorimetry and surface analysis of the modified materials indicated that 10 vol% of N, N-dimethylethylenediamine in n-hexane and 1 h soaking time were optimal to maintain the inherent thermal properties. The achievement of increased luminance and a positive zeta potential proved that the direct modification method effectively introduced the positive charge only on the surface, thereby enhancing cell affinity.

Functional Polyglycidol-Based Block Copolymers for DNA Complexation

Gene therapy is an attractive therapeutic method for the treatment of genetic disorders for which the efficient delivery of nucleic acids into a target cell is critical. The present study is aimed at evaluating the potential of copolymers based on linear polyglycidol to act as carriers of nucleic acids. Functional copolymers with linear polyglycidol as a non-ionic hydrophilic block and a second block bearing amine hydrochloride pendant groups were prepared using previously synthesized poly(allyl glycidyl ether)-b-polyglycidol block copolymers as precursors. The amine functionalities were introduced via highly efficient radical addition of 2-aminoethanethiol hydrochloride to the alkene side groups. The modified copolymers formed loose aggregates with strongly positive surface charge in aqueous media, stabilized by the presence of dodecyl residues at the end of the copolymer structures and the hydrogen-bonding interactions in polyglycidol segments. The copolymer aggregates were able to condense DNA into stable and compact nanosized polyplex particles through electrostatic interactions. The copolymers and the corresponding polyplexes showed low to moderate cytotoxicity on a panel of human cancer cell lines. The cell internalization evaluation demonstrated the capability of the polyplexes to successfully deliver DNA into the cancer cells.