Biodegradable Polymers and Polymer Composites with Antibacterial Properties

Antibiotic resistance is one of the greatest threats to global health and food security today. It becomes increasingly difficult to treat infectious disorders because antibiotics, even the newest ones, are becoming less and less effective. One of the ways taken in the Global Plan of Action announced at the World Health Assembly in May 2015 is to ensure the prevention and treatment of infectious diseases. In order to do so, attempts are made to develop new antimicrobial therapeutics, including biomaterials with antibacterial activity, such as polycationic polymers, polypeptides, and polymeric systems, to provide non-antibiotic therapeutic agents, such as selected biologically active nanoparticles and chemical compounds. Another key issue is preventing food from contamination by developing antibacterial packaging materials, particularly based on degradable polymers and biocomposites. This review, in a cross-sectional way, describes the most significant research activities conducted in recent years in the field of the development of polymeric materials and polymer composites with antibacterial properties. We particularly focus on natural polymers, i.e., polysaccharides and polypeptides, which present a mechanism for combating many highly pathogenic microorganisms. We also attempt to use this knowledge to obtain synthetic polymers with similar antibacterial activity.

Biodegradable Block Poly(ester amine)s with Pendant Hydroxyl Groups for Biomedical Applications

The article presents the results of the synthesis and characteristics of the amphiphilic block terpolymers, built of a hydrophilic polyesteramine block, and hydrophobic blocks made of lactidyl and glycolidyl units. These terpolymers were obtained during the copolymerization of L-lactide with glycolide carried out in the presence of previously produced macroinitiators with protected amine and hydroxyl groups. The terpolymers were prepared to produce a biodegradable and biocompatible material containing active hydroxyl and/or amino groups, with strong antibacterial properties and high surface wettability by water. The control of the reaction course, the process of deprotection of functional groups, and the properties of the obtained terpolymers were made based on 1H NMR, FTIR, GPC, and DSC tests. Terpolymers differed in the content of amino and hydroxyl groups. The values of average molecular mass oscillated from about 5000 g/mol to less than 15,000 g/mol. Depending on the length of the hydrophilic block and its composition, the value of the contact angle ranged from 50° to 20°. The terpolymers containing amino groups, capable of forming strong intra- and intermolecular bonds, show a high degree of crystallinity. The endotherm responsible for the melting of L-lactidyl semicrystalline regions appeared in the range from about 90 °C to close to 170 °C, with a heat of fusion from about 15 J/mol to over 60 J/mol.

Enzymatic Synthesis of Polyesters and Their Bioapplications: Recent Advances and Perspectives

This article reviews the most important advances in the enzymatic synthesis of polyesters. In first place, the different processes of polyester enzymatic synthesis, i.e., polycondensation, ring opening, and chemoenzymatic polymerizations, and the key parameters affecting these reactions, such as enzyme, concentration, solvent, or temperature, are analyzed. Then, the latest articles on the preparation of polyesters either by direct synthesis or via modification are commented. Finally, the main bioapplications of enzymatically obtained polyesters, i.e., antimicrobial, drug delivery, or tissue engineering, are described. It is intended to point out the great advantages that enzymatic polymerization present to obtain polymers and the disadvantages found to develop applied materials.

Recent advances in the synthesis of biodegradable polyesters by sustainable polymerization: lipase-catalyzed polymerization

Over the past three decades, enzymatic polymerization has dramatically developed and gradually broadened as a creative methodology in the construction of polymeric materials with tailor-made structures and properties. Compared with transition metal catalyst polymerizations, enzymatic polymerization is more attractive in the biomedicine field due to the metal-free residue, good biocompatibility, and few by-products. Meanwhile, enzymatic polymerization has far more activity towards macrolides. In this review, the synthesis of lipase-catalyzed polymer materials is systematically summarized, focusing on the synthesis of the complex and well-defined polymers. The enzymatic polyester synthesis was then discussed concerning the different reaction types, including ring-opening polymerization, polycondensation, a combination of ring-opening polymerization with polycondensation, and chemoenzymatic polymerization. Besides, exploration of novel biocatalysts and reaction media was also described, with particular emphasis on the enzymes obtained via immobilization or protein engineering strategies, green solvents, and reactors. Finally, recent developments in catalytic kinetics and mechanistic studies through the use of spectroscopy, mathematics, and computer techniques have been introduced. Besides, we addressed the remaining central issues in enzymatic polymerization and discussed current studies aimed at providing answers.

Targeted Delivery of Secretory Promelittin via Novel Poly(lactone-co-β-amino ester) Nanoparticles for Treatment of Breast Cancer Brain Metastases

Breast cancer brain metastases (BCBM) is a devastating disease with dismal prognosis. Although chemotherapy is widely used for clinical management of most tumors, it is often ineffective for BCBM. Therefore, alternative approaches for improved treatment of BCBM are in great demand. Here, an innovative gene therapy regimen is reported that is designed for effective treatment of BCBM. First, poly(lactone-co-β-amino ester) nanoparticles that are capable of efficient gene delivery are synthesized and are engineered for targeted delivery to BCBM through surface conjugation of AMD3100, which interacts with CXCR4 enriched in the tumor microenvironment. Next, an artificial gene, proMel, is designed for the expression of secretory promelittin protein, which has limited toxicity on its own but releases cytolytic melittin after activation by MMP-2 accumulated in tumors. It is demonstrated that delivery of the proMel via the AMD3100-conjugated nanoparticles effectively inhibits tumor progression in a BCBM mouse model. This study suggests a new direction to treat BCBM through targeted delivery of promelittin-mediated gene therapy.

The protean world of non-coding RNAs in glioblastoma

Non-coding ribonucleic acids (ncRNAs) are a diverse group of RNA molecules that are mostly not translated into proteins following transcription. We review the role of ncRNAs in the pathobiology of glioblastoma (GBM), and their potential applications for GBM therapy. Significant advances in our understanding of the protean manifestations of ncRNAs have been made, allowing us to better decipher the molecular complexity of GBM. A large number of regulatory ncRNAs appear to have a greater influence on the molecular pathology of GBM than thought previously. Importantly, also, a range of therapeutic approaches are emerging whereby ncRNA-based systems may be used to molecularly target GBM. The most successful of these is RNA interference, and some of these strategies are being evaluated in ongoing clinical trials. However, a number of limitations exist in the clinical translation of ncRNA-based therapeutic systems, such as delivery mechanisms and cytotoxicity; concerted research endeavors are currently underway in an attempt to overcome these. Ongoing and future studies will determine the potential practical role for ncRNA-based therapeutic systems in the clinical management of GBM. These applications may be especially promising, given that current treatment options are limited and prognosis remains poor for this challenging malignancy.

Immobilized Candida antarctica lipase B catalyzed synthesis of biodegradable polymers for biomedical applications

Biomedical applications of biodegradable polymers synthesized via the catalysis of immobilized Candida antarctica lipase B (CALB).

Tunability of Biodegradable Poly(amine- co-ester) Polymers for Customized Nucleic Acid Delivery and Other Biomedical Applications

Gene therapy promises to treat diseases that arise from genetic abnormalities by correcting the underlying cause of the disease rather than treating the associated symptoms. Successful transfer of nucleic acids into cells requires efficient delivery vehicles that protect the cargo and can penetrate the appropriate cellular barriers before releasing their contents. Many viral vectors and synthetic polycationic vectors for nucleic acid delivery do not translate well from in vitro to in vivo applications due to their instability and toxicity. We synthesized and characterized a library of biocompatible low charge density polymers from a family of poly(amine- co-ester) (PACE) terpolymers produced via enzyme catalyzed polymerization. PACE polymers are highly customizable; we found that the terpolymer composition can be optimized to produce efficient transfection of various nucleic acids-including DNA plasmids, mRNA, and siRNA-in specific cell types with low toxicity. Our findings suggest that the unique tunability of PACEs offers new tools for gene therapy and other biomedical applications.

Chemoenzymatic synthesis of a cholesterol-g-poly(amine-co-ester) carrier for p53 gene delivery to inhibit the proliferation and migration of tumor cells

An amphiphilic cholesterol-g-poly(amine-co-ester) synthesizedviaa chemoenzymatic route has been successfully applied as a carrier in p53 gene delivery.

Chemoenzymatic Synthesis of Cholesterol-g-Poly(amine-co-ester) Amphiphilic Copolymer as a Carrier for miR-23b Delivery

The lipase-catalyzed polymerization of N-methyldiethanolamine, diethyl sebacate and ω-pentadecanolide was performed to construct a cationic poly(amine-co-ester), and a hydrophobic N-(2-bromoethyl)carbamoyl cholesterol was then grafted onto its main chain through a quaternization reaction to prepare the amphiphilic copolymer Chol-g-PMSC-PPDL. The copolymer efficiently bound and condensed miR-23b to form stable nanocomplexes, which showed favorable cellular uptake and miR-23b transfection efficacy due to the introduction of the hydrophobic segment. After miR-23b delivery, an obvious inhibition of cell proliferation could be induced, which was attributed to the induction of cell apoptosis and cell cycle arrest. Moreover, the carrier-mediated miR-23b delivery could inhibit the migration and invasion of tumor cells. Overall, the work provides a novel chemoenzymatic strategy for constructing biodegradable and biocompatible poly(amine-co-ester) derivatives, which are promising carriers for oligonucleotide delivery to achieve tumor gene therapy.

Multifunctional Poly(amine-co-ester-co-ortho ester) for Efficient and Safe Gene Delivery

Cationic polymers are used for non-viral gene delivery, but current materials lack the functionality to address the multiple barriers involved in gene delivery. Here we describe the rational design and synthesis of a new family of quaterpolymers with unprecedented multifunctionality: acid sensitivity, low cationic charge, high hydrophobicity, and biodegradability, all of which are essential for efficient and safe gene delivery. The polymers were synthesized via lipase-catalyzed polymerization of ortho ester diester, lactone, dialkyl diester, and amino diol monomers. Polymers containing ortho ester groups exhibited acid-sensitive degradation at endosomal pH (4~5), facilitated efficient endosomal escape and unpackaging of the genes, and were efficient in delivering genetic materials to HEK293 cells, human glioma cells, primary mouse melanoma cells, and human umbilical vein endothelial cells (HUVECs). We also developed a highly efficient lyophilized formulation of the nanoparticles, which could be stored for a month without loss of efficiency.

Dicarboxylic esters: Useful tools for the biocatalyzed synthesis of hybrid compounds and polymers

Dicarboxylic acids and their derivatives (esters and anhydrides) have been used as acylating agents in lipase-catalyzed reactions in organic solvents. The synthetic outcomes have been dimeric or hybrid derivatives of bioactive natural compounds as well as functionalized polyesters.

Contact-facilitated drug delivery with Sn2 lipase labile prodrugs optimize targeted lipid nanoparticle drug delivery

Sn2 lipase labile phospholipid prodrugs in conjunction with contact-facilitated drug delivery offer an important advancement in Nanomedicine. Many drugs incorporated into nanosystems, targeted or not, are substantially lost during circulation to the target. However, favorably altering the pharmacokinetics and volume of distribution of systemic drug delivery can offer greater efficacy with lower toxicity, leading to new prolonged-release nanoexcipients. However, the concept of achieving Paul Erhlich's inspired vision of a 'magic bullet' to treat disease has been largely unrealized due to unstable nanomedicines, nanosystems achieving low drug delivery to target cells, poor intracellular bioavailability of endocytosed nanoparticle payloads, and the substantial biological barriers of extravascular particle penetration into pathological sites. As shown here, Sn2 phospholipid prodrugs in conjunction with contact-facilitated drug delivery prevent premature drug diffusional loss during circulation and increase target cell bioavailability. The Sn2 phospholipid prodrug approach applies equally well for vascular constrained lipid-encapsulated particles and micelles the size of proteins that penetrate through naturally fenestrated endothelium in the bone marrow or thin-walled venules of an inflamed microcirculation. At one time Nanomedicine was considered a 'Grail Quest' by its loyal opposition and even many in the field adsorbing the pains of a long-learning curve about human biology and particles. However, Nanomedicine with innovations like Sn2 phospholipid prodrugs has finally made 'made the turn' toward meaningful translational success.

Ultrasound-Triggered Phase-Transition Cationic Nanodroplets for Enhanced Gene Delivery

Ultrasound as an external stimulus for enhanced gene transfection represents a safe, noninvasive, cost-effective delivery strategy for gene therapy. Herein, we have developed an ultrasound-triggered phase-transition cationic nanodroplet based on a novel perfluorinated amphiphilic poly(amino acid), which could simultaneously load perfluoropentane (PFP) and nucleic acids. The heptadecafluoroundecylamine (C11F17-NH2) was chosen to initiate β-benzyl-L-aspartate N-carboxyanhydride (BLA-NCA) ring-opening polymerization to prepare C11F17-poly(β-benzyl-L-aspartate) (C11F17-PBLA). Subsequently, C11F17-poly{N-[N'-(2-aminoethyl)]aspartamide} [C11F17-PAsp(DET)] was synthesized by aminolysis reaction of C11F17-PBLA with diethylenetriamine (DET). PFP/pDNA-loaded nanodroplets PFP-TNDs [PFP/C11F17-PAsp(DET)/LucDNA/γ-PGA or poly(glutamic acid)-g-MeO-poly(ethylene glycol) (PGA-g-mPEG) ternary nanodroplets] were primarily formulated by an oil/water emulsification method, followed by surface modification with PGA-g-mPEG. The average diameter of PFP-TNDs ranged from 300 to 400 nm, and transmission electron microscopy images showed that the nanodroplets were nearly spherical in shape. The ζ potential of the nanodroplets dramatically decreased from +54.3 to +15.3 mV after modification with PGA-g-mPEG, resulting in a significant increase of the stability of the nanodroplets in the serum-containing condition. With ultrasound irradiation, the gene transfection efficiency was enhanced 14-fold on HepG2 cells, and ultrasound-triggered phase-transition cationic nanodroplets also displayed a good ultrasound contrast effect. These results suggest that the PFP/DNA-loaded phase-transition cationic nanodroplets can be utilized as efficient theranostic agents for targeting gene delivery.

Enzymatic synthesis of poly(ω-pentadecalactone-co-butylene-co-3,3′-dithiodipropionate) copolyesters and self-assembly of the PEGylated copolymer micelles as redox-responsive nanocarriers for doxorubicin delivery

The PEG-polyester copolymers bearing disulfide groups were synthesized to serve as redox-responsive anticancer drug carriers with an enhanced efficacy.

Multifunctional non-viral gene vectors with enhanced stability, improved cellular and nuclear uptake capability, and increased transfection efficiency

We have developed a new multifunctional, non-viral gene delivery platform consisting of cationic poly(amine-co-ester) (PPMS) for DNA condensation, PEG shell for nanoparticle stabilization, poly(γ-glutamic acid) (γ-PGA) and mTAT (a cell-penetrating peptide) for accelerated cellular uptake, and a nuclear localization signal peptide (NLS) for enhanced intracellular transport of DNA to the nucleus. In vitro study showed that coating of the binary PPMS/DNA polyplex with γ-PGA promotes cellular uptake of the polyplex particles, particularly by γ-glutamyl transpeptidase (GGT)-positive cells through the GGT-mediated endocytosis pathway. Conjugating PEG to the γ-PGA led to the formation of a ternary PPMS/DNA/PGA-g-PEG polyplex with decreased positive charges on the surface of the polyplex particles and substantially higher stability in serum-containing aqueous medium. The cellular uptake rate was further improved by incorporating mTAT into the ternary polyplex system. Addition of the NLS peptide was designed to facilitate intracellular delivery of the plasmid to the nucleus--a rate-limiting step in the gene transfection process. As a result, compared with the binary PPMS/LucDNA polyplex, the new mTAT-quaternary PPMS/LucDNA/NLS/PGA-g-PEG-mTAT system exhibited reduced cytotoxicity, remarkably faster cellular uptake rate, and enhanced transport of DNA to the nucleus. All these advantageous functionalities contribute to the remarkable gene transfection efficiency of the mTAT-quaternary polyplex both in vitro and in vivo, which exceeds that of the binary polyplex and commercial Lipofectamine™ 2000/DNA lipoplex. The multifunctional mTAT-quaternary polyplex system with improved efficiency and reduced cytotoxicity represents a new type of promising non-viral vectors for the delivery of therapeutic genes to treat tumors.

Exploring the Solid State Properties of Enzymatic Poly(amine-co-ester) Terpolymers to Expand their Applications in Gene Transfection

Polymers bearing amino functional groups are an important class of materials capable of serving as non-viral carriers for DNA delivery to living cells. In this work biodegradable poly(amine-co-ester) terpolymers were synthesized via ring-opening and polycondensation copolymerization of lactone (ε-caprolactone (CL), ω-dodecalactone, ω-pentadecalactone (PDL), and ω-hexadecalactone) with diethyl sebacate (DES) and N-methyldiethanolamine (MDEA) in diphenyl ether, catalyzed by Candida antarctica lipase B (CALB). All lactone-DES-MDEA terpolymers had random distributions of lactone, sebacate, MDEA repeat units in the polymer chains. PDL-DES-MDEA terpolymers were studied in the composition range from 21 mol% to 90 mol% PDL whereas the terpolymers with other lactones were investigated at a single composition (80 mol% lactone). DSC and WAXS analyses showed that all investigated terpolymers crystallize in their respective homopolylactone crystal lattice. Terpolymers with large lactones and a high lactone content melt well above room temperature and are hard solids, whereas terpolymers with small lactones (e.g. CL) or with a low lactone content melt below/around ambient temperature and are waxy/gluey materials. Given the importance of hydrophobicity in influencing gene delivery, water contact angle measurements were carried out on lactone-DES-MDEA terpolymers showing that it is possible to tune the hydrophilic-to-hydrophobic balance by varying polymer composition and size of lactone units. To demonstrate the feasibility of using solid terpolymers as nanocarriers for DNA delivery, PDL-DES-MDEA copolymers with 65-90% PDL were successfully transformed into free-standing nanoparticles with average particle size ranging from 163 to 175 nm. Our preliminary results showed that LucDNA-loaded nanoparticles of the terpolymer with 65% PDL were effective for luciferase gene transfection of HEK293 cells.

A highly efficient synthetic vector: nonhydrodynamic delivery of DNA to hepatocyte nuclei in vivo

Multifunctional membrane-core nanoparticles, composed of calcium phosphate cores, arginine-rich peptides, cationic and PEGylated lipid membranes, and galactose targeting ligands, have been developed as synthetic vectors for efficient nuclear delivery of plasmid DNA and subsequent gene expression in hepatocytes in vivo. Targeted particles exhibited rapid and extensive hepatic accumulation and were predominantly internalized by hepatocytes, while the inclusion of such peptides in LCP was sufficient to elicit high degrees of nuclear translocation of plasmid DNA. Monocyclic CR8C significantly enhanced in vivo gene expression over 10-fold more than linear CR8C, likely due to a release-favoring mechanism of the DNA/peptide complex. Though 100-fold lower in activity than that achieved via hydrodynamic injection, this formulation presents as a much less invasive alternative. To our knowledge, this is the most effective synthetic vector for liver gene transfer.

A dual-functionally modified chitosan derivative for efficient liver-targeted gene delivery

Galactosylated chitosan-hydroxypropyltrimethylammonium (gal-HTCC) was synthesized by galactosylating and quaternizing chitosan to endue chitosan with targeting specificity for potential applications as gene vectors. The composition and physicochemical properties of gal-HTCC were characterized by FT-IR, (1) H NMR, elemental analysis, X-ray diffraction, and turbidity measurement. It was found that water-soluble gal-HTCC showed a more amorphous structure than chitosan, and it also had a much better plasmid condensation capability than galactosylated chitosan. Cytotoxicity measurements revealed that gal-HTCC showed significantly lower cytotoxicity in HepG2 and HeLa cell lines compared to branched polyethylenimine (bPEI, 25 kDa) which was used as a positive control. The nanoparticles (NPs) consisted of gal-HTCC and plasmid DNA had desirable particle size (around 250 nm) with a narrow size distribution. Confocal laser scanning microscopy confirmed that NPs could be internalized and transported to the nucleus efficiently within 6 h. In vitro gene transfection results indicated that gal-HTCC had significantly higher transfection efficiency (7- to 32-fold) compared to chitosan and gal-chitosan for targetable delivery of pGL3 luciferase plasmid to HepG2, and its transfection efficiency was highly inhibited in the presence of galactose (20 mM). All these results suggest that gal-HTCC can function as a promising nonviral gene vector for efficient liver-targeted gene delivery.

Cationic polymers and their therapeutic potential

The last decade has witnessed enormous research focused on cationic polymers. Cationic polymers are the subject of intense research as non-viral gene delivery systems, due to their flexible properties, facile synthesis, robustness and proven gene delivery efficiency. Here, we review the most recent scientific advances in cationic polymers and their derivatives not only for gene delivery purposes but also for various alternative therapeutic applications. An overview of the synthesis and preparation of cationic polymers is provided along with their inherent bioactive and intrinsic therapeutic potential. In addition, cationic polymer based biomedical materials are covered. Major progress in the fields of drug and gene delivery as well as tissue engineering applications is summarized in the present review.

Novel delivery strategies for glioblastoma

Brain tumors--particularly glioblastoma multiforme--pose an important public health problem in the United States. Despite surgical and medical advances, the prognosis for patients with malignant gliomas remains grim: current therapy is insufficient with nearly universal recurrence. A major reason for this failure is the difficulty of delivering therapeutic agents to the brain: better delivery approaches are needed to improve treatment. In this article, we summarize recent progress in drug delivery to the brain, with an emphasis on convection-enhanced delivery of nanocarriers. We examine the potential of new delivery methods to permit novel drug- and gene-based therapies that target brain cancer stem cells and discuss the use of nanomaterials for imaging of tumors and drug delivery.

Biodegradable poly(amine-co-ester) terpolymers for targeted gene delivery

Many synthetic polycationic vectors for non-viral gene delivery show high efficiency in vitro, but their usually excessive charge density makes them toxic for in vivo applications. Here we describe the synthesis of a series of high molecular weight terpolymers with low charge density, and show that they exhibit efficient gene delivery, some surpassing the efficiency of the commercial transfection reagents Polyethylenimine and Lipofectamine 2000. The terpolymers were synthesized via enzyme-catalyzed copolymerization of lactone with dialkyl diester and amino diol, and their hydrophobicity adjusted by varying the lactone content and by selecting a lactone comonomer of specific ring size. Targeted delivery of the pro-apoptotic TRAIL gene to tumour xenografts by one of the terpolymers results in significant inhibition of tumour growth, with minimal toxicity both in vitro and in vivo. Our findings suggest that the gene delivery ability of the terpolymers stems from their high molecular weight and increased hydrophobicity, which compensates for their low charge density.

C/EBP-α and C/EBP-β-mediated adipogenesis of human mesenchymal stem cells (hMSCs) using PLGA nanoparticles complexed with poly(ethyleneimmine)

In this study, to drive efficient adipogenic differentiation, the adipogenic transcription factors C/EBP-α and C/EBP-β fused to green fluorescent protein (GFP) or red fluorescent protein (RFP) were complexed with poly-ethyleneimine (PEI) coupled with biodegradable PLGA nanospheres and delivered to human mesenchymal stem cell (hMSC). FACS analysis revealed that the transfection efficiency of C/EBP-α, C/EBP-β, or both genes complexed with PEI-coated PLGA nanospheres was 12.59%, 21.74%, and 28.96% of hMSCs. Expression and localization of C/EBP-α and C/EBP-β were confirmed by Western blotting and confocal laser microscopy. Overexpression of exogenous C/EBP-α and C/EBP-β significantly elevated adipogenic differentiation processes as indicated by RT-PCR, real-time PCR, Western blotting, histology, and immunofluorescence microscopy. During adipogenesis, PEI-coupled PLGA nanospheres complexed with C/EBP-α and C/EBP-β greatly increased the adipogenic capability of in vitro cultured cells, as well of in vivo transplanted cells. The expression of genes and proteins specific to adipogenic differentiation in hMSCs was significantly elevated compared to the controls.