Cationic Polymers in Regenerative Medicine: Volume 13 (Polymer Chemistry Series) - Hardcover

Hardcover

ISBN 10: 1849739374 ISBN 13: 9781849739375

Publisher: Royal Society of Chemistry, 2014

Synopsis

A comprehensive overview of the recent advances in cationic polymer synthesis, modification and the design of biomaterials with different structures for therapeutic applications.

About this title

About the Author

Dr. Sangram Keshari Samal received his PhD degree in Biomaterials from the School of Biomolecular Science, University of Pisa, Italy. During his PhD, he was a visiting fellow at BWH, HST-MIT and Tufts University, USA. He undertook his first postdoctoral research at Consiglio Nazionale delle Ricerche, Bologna, Italy. At present he is a post-doctoral fellow at the Polymer Chemistry & Biomaterials Group, Department of Organic Chemistry, University of Ghent, Belgium. His research interest is mainly focused on functionalization of polymers and evaluation of their potential for various therapeutic applications.

Prof. Peter Dubruel is currently heading a group of over 30 people and has published over 100 A1 papers. Since the start of 2006, he has been involved in several EU projects (3 FP6 and 4 FP7, 1 as a coordinator). Since end 2006, he has delivered over 20 invited lectures. He has been the spokesperson of the Young Scientist Forum (YSF) from the European Society for Biomaterials (ESB) for more than 5 years. He is part of the editorial team of BIOMAT.net and the journal Biomaterials. In 2010 and 2012, he was awarded, respectively, the YSF Excellence Award from the Romanian Society for Biomaterials and the Jean Leray Award from the ESB in 2013.

From the Back Cover

The unique physico-chemical properties of cationic polymers and their ability to be easily modified make them attractive for many biological applications. As a result there is a vast amount of research focussed on designing novel natural or synthetic cationic polymers with specific biological functionality.

Cationic Polymers in Regenerative Medicine brings together the expertise of leading experts in the field to provide a comprehensive overview of the recent advances in cationic polymer synthesis, modification and the design of biomaterials with different structures for therapeutic applications. Chapters cover recent developments in novel cationic polymer based systems including poly(L-lysine), Poly(N, N-dimethylaminoethyl methacrylate) and cationic triazine dendrimers as well as cationic polymer-coated micro- and nanoparticles and cationic cellulose and chitin nanocrystals. Applications discussed in the book include drug and gene delivery, therapeutics in thrombosis and inflammation as well as gene therapy.

Suitable both for an educational perspective for those new to the field and those already active in the field, the book will appeal to postgraduates and researchers. The broad aspects of the topics covered are suitable for polymer chemists interested in the fundamentals of the materials systems as well as pharmaceutical chemists, bioengineering and medical professionals interested in their applications.

Excerpt. © Reprinted by permission. All rights reserved.

Cationic Polymers in Regenerative Medicine

By Sangram K. Samal, Peter Dubruel

The Royal Society of Chemistry

Copyright © 2015 The Royal Society of Chemistry
All rights reserved.

ISBN: 978-1-84973-937-5

Contents

Chapter 1 Functionalization of Cationic Polymers for Drug Delivery Applications Ilja Tabujew and Kalina Peneva, 1, 
Chapter 2 Synthesis and Properties of Polyalkylenimines Bryn D. Monnery and Richard Hoogenboom, 30, 
Chapter 3 Well-Defined Cationic Polymers for Nucleic Acid Delivery Marya Ahmed and Ravin Narain, 62, 
Chapter 4 Poly(L-lysine)-Based Copolymers: Synthetic Strategies and Biomedical Applications Ivaylo V. Dimitrov, 99, 
Chapter 5 Stimuli-Responsive Cationic Microgels and Hydrogels Based on Poly(N,N-dimethylaminoethyl methacrylate) Jie Wei and Liang-Yin Chu, 133, 
Chapter 6 Stimuli-Responsive Structures from Cationic Polymers for Biomedical Applications Maria Teresa Calejo, Nesrin Hasirci, Shahla, 149, 
Chapter 7 Cationic Polysaccharides in Regenerative Medicine: Challenges and Perspectives Stefan Spirk and Tamilselvan Mohan, 178, 
Chapter 8 Cationic Cellulose and Chitin Nanocrystals for Novel Therapeutic Applications Seyedeh Parinaz Akhlaghi, Masuduz Zaman, Baoliang Peng, 197, 
Chapter 9 Cationic Polysaccharides in Gene Delivery Anjali Jain, Eameema Muntimadugu, Abraham J. Domb and Wahid Khan, 228, 
Chapter 10 Cationic Triazine Dendrimers: Synthesis, Characterization, and Biological Applications Eric E. Simanek and Alan E. Enciso, 249, 
Chapter 11 Cationic Polymer Nanoparticles for Drug and Gene Delivery Erem Bilensoy, Gamze ISik and Cem Varan, 268, 
Chapter 12 Cationic Polymers in Drug Delivery Anna Karewicz, Krzysztof Szczubia!ka and Maria Nowakowska, 296, 
Chapter 13 Cationic Dendritic Systems as Non-viral Vehicles for Gene Delivery Applications Paula Ortega, Javier Sánchez-Nieves, Marta Martínez-Bonet, A. Judith Perisé-Barrios, Rafael Gómez, M. Ángeles Muñoz-Fernández and F. Javier de la Mata, 321, 
Chapter 14 Cationic Polymers for Intracellular Delivery of Proteins Grégory Coué and Johan F. J. Engbersen, 356, 
Chapter 15 Cationic Polymers for Gene Delivery into Mesenchymal Stem Cells as a Novel Approach to Regenerative Medicine Sante Di Gioia, Adriana Trapani, Annalucia Carbone, Stefano Castellani, Carla Colombo, Giuseppe Trapani and Massimo Conese, 386, 
Chapter 16 Cationic Polymers as Gene-Activated Matrices for Biomedical Applications Mamoni Dash, David L. Kaplan, Peter Dubruel and Sangram K. Samal, 438, 
Chapter 17 Cationic Polymers in the Central Nervous System: Past, Present and Future Asha Mathew, Mangesh Morey and Abhay Pandit, 463, 
Chapter 18 Interactions of Cationic Polymers with Cells Matthew J. Ware, Huw D. Summers and Biana Godin, 479, 
Chapter 19 Cationic Polymer-Based Non-viral Gene Delivery Systems and their Application in Gene-Engineered Stem Cells Bing Huang, Cai-Xia He, Jun Lin and Jian-Qing Gao, 512, 
Chapter 20 Cationic Polymers as Carriers through the Blood-Brain Barrier Sangram K. Samal, Mamoni Dash, Peter Dubruel, Klaus Müllen and Jayakumar Rajadas, 539, 
Chapter 21 Natural Cationic Polymers for Advanced Gene and Drug Delivery Sheng Dai, 557, 
Chapter 22 Effects of Cationic Polymers on Cell Functions Guoping Chen, 583, 
Subject Index, 592, 

CHAPTER 1

Functionalization of Cationic Polymers for Drug Delivery Applications

ILJA TABUJEW AND KALINA PENEVA

Max Planck Institute for Polymer Research, Ackermannweg 10, 55128 Mainz, Germany

1.1 Introduction and Classification of Cationic Polymers

Cationic polymers can be defined as macromolecules that bear positive charges, which can be either intrinsically present in the polymer backbone and/or in the side chains. Most cationic polymers possess primary, secondary or tertiary amine functional groups that can be protonated. They also differ widely in their polymeric structure (linear, branched, hyperbranched and dendrimer-like) and can be further differentiated by the placement of the positive charges (backbone or side chains). The cationic polymers that will be discussed in this chapter are divided into three categories according to their origin: natural, semi-synthetic and synthetic (Figure 1.1). This chapter will focus only on the most prominent examples which have been shown to have applications in drug delivery rather than trying to include all existing cationic polymers.

1.1.1 Natural

Natural cationic polymers are derived from renewable sources and possess inherent positive charges. They are biodegradable and often possess low immunogenicity and low toxicity. Numerous natural cationic polymers have functional groups like carboxylic acid groups that can be further modified to carry therapeutic molecules.

1.1.1.1 Gelatine

Gelatine is a thermally denatured collagen extracted from porcine skin or bovine bone and is commonly used for pharmaceutical and medical applications because of its biodegradability. Being categorized as a safe excipient by the US Food and Drug Administration (FDA), gelatine has shown great promise as a component of biomaterials in many medical applications. For example, gelatine nanoparticles have been successfully utilized for non-viral plasmid DNA delivery and cationic gelatine plasmid DNA polyplexes, i.e. complexes formed by the electrostatic interactions of positively charged polymer molecules and negatively charged DNA, were applied for transfection studies on monocyte-derived immature dendritic cells. The mode of action of non-viral vectors for gene and RNA delivery will be discussed in detail in the next chapters of this book and will therefore not be examined in depth here. In contrast to other cationic polymers, gelatine also possesses carboxyl groups and therefore can have an overall negative charge, depending on the pH of the environment. The isoelectric point of gelatine at physiological pH can be modified during its extraction to yield either negatively charged acidic gelatine using alkaline treatment (classified as B) or positively charged basic gelatine (denoted as A) by acidic treatment. This differentiation is necessary because the extraction process using a base leads to hydrolysis of the amide groups of glutamine and asparagine residues, which increases the content of carboxylic groups in the polymer. As a result of this treatment the isoelectric point of gelatine is lowered (IEP1/44.7–5.4) while the acidic extraction does not change the intrinsic properties of the collagen (IEP1/46–9). Furthermore, aminated gelatine can be prepared in a one-pot reaction using 1-ethyl-3-(3-dimethylaminopropyl)-carbodiimide hydrochloride (EDC) and diamine. It has been demonstrated that this additional modification technique leads to improved release control in the delivery of acidic peptide/protein drugs.

1.1.2 Semi-synthetic

This group of cationic polymers includes all those natural polymers that require further modification in order to acquire a cationic character. Therefore, they differ from the biopolymers with inherent cationic properties and those cationic polymers that are produced artificially using polymerization methods. Such polymers often retain their biodegradability, while the introduction of positive charges leads to increased cytotoxicity and therefore decreased biocompatibility.

1.1.2.1 Chitosan

Chitosan is a copolymer consisting of statistically distributed N- acetylglucosamine and D-glucosamine. Deacetylation of chitin, the second most abundant polysaccharide in nature, with concentrated alkali solution at elevated temperatures leads to the production of chitosan. The carbohydrate backbone is similar to cellulose and consists of β-1,4-linked D-glucosamine, except that the acetylamino group replaces the hydroxyl group on the C2 position. Thus, chitosan is a copolymer consisting of N-acetyl-2-amino-2-deoxy-D-glucopyranose and 2-amino-2-deoxy-D-glucopyranose, where the two types of repeating units are linked by (1[right arrow]4)-β-glycosidic bonds. Chitosan has proved to be a safe excipient in drug formulations over recent decades, being a non-toxic, biodegradable and biocompatible polymer with antioxidant and antibacterial properties. Additionally, it can increase the cellular permeability and improve the bioavailability of orally administered protein drugs, due to its mucoadhesive properties. Furthermore, chitosan possesses the versatile trait of pH esponsiveness in the pH range 6–6.5. By altering the degree of deacetylation and the molecular weight of the polymer, which can be achieved by varying the temperature of the deacetylation process, the charge density of the polymer can be additionally adjusted. It is important to mention that chitosan is poorly soluble at physiological pH and it readily swells in aqueous solutions, resulting in rapid drug release in its application as a continuous matrix for controlled drug release. Numerous colloidal delivery systems based on chitosan have been reported for the mucosal delivery of hydrophilic drugs, peptides, proteins, vaccines and DNA. Chitosan is a polycationic polymer that has two hydroxyl groups in the repeating glucosidic residue and one amino group. The primary amino groups present on the polymer backbone provide reactive sites for a variety of side-group attachments by employing only mild reaction conditions.

1.1.2.2 Cationic Cyclodextrin

Cyclodextrins (CDs) are sugar derivatives that are produced by enzymatic degradation of starch. CDs are cyclic oligosaccharides composed of six to eight α-1,4-linked glucose units. They feature a bulb-shaped topology with a hydrophobic cavity, which is enclosed by a hydrophilic exterior. Based on the amount of glucose units in these cyclic molecules (6, 7 or 8), CDs are divided into three groups (α, β or γ). As biodegradable monodisperse molecules with low toxicity, low immunogenicity and a high number of hydroxyl groups, which can be used for further modification, CDs have attracted increasing attention for medical applications. The straightforward chemical modification of CDs has led to the generation of a large number of CD–polymer conjugates such as star-shaped polymers using α-CD as the core equipped with oligomeric ethylenimine arms utilizing 1,1'-carbonyldiimidazole chemistry. The incorporation of CDs into cationic polymers has led to improved electrostatic complexation of DNA molecules. Amphiphilic CD-based systems are valuable carriers for gene delivery, as they can be tuned at will to change the density of cationic groups and introducing or decreasing hydrogen bonding functionalities can alter the flexibility of the polymer chains. Besides the examples described above, other diverse modifications have been prepared such as "click clusters", polyCDplexes for DNA compaction and chiral separation of anionic drug molecules or amino acids by utilizing the host–guest concept.

1.1.2.3 Cationic Dextran

Dextran is a versatile and widely available natural polymer that exhibits biodegradability and biocompatibility. These properties are due to its water solubility irrespective of the pH of the solution and of its polysaccharide structure consisting of α-1,6-linked glucose units as well. The polysaccharide glycogen, which is commonly found in animals and fungi as an energy storage molecule, possesses the same kind of bond. Utilizing a debranching enzyme, living organisms are able to cleave this chemically stable bond. The three accessible hydroxyl moieties, found on every monomer unit, facilitate modifications such as the incorporation of amino groups. (Diethylaminoethyl)dextran and dextran-spermine are well-described examples, especially since dextran-spermine exhibits high transfection efficiency for DNA.

1.1.2.4 Cationic Cellulose

Cellulose is a biopolymer with a polysaccharide structure of β-1,4-conjugated glucose units and as the main component in the cell wall of plants it is in fact the most common organic compound in the world. Therefore it is understandable that this biodegradable polymer became the focus of attention in the modern age of renewable resources. The hydroxyl moieties of cellulose are the chemical target for modification and functionalization. In the case of cationic cellulose these functional groups are usually reacted with glycidyl ammonium salts or by utilizing in situ epoxidation. While these modifications are convenient for introducing desired properties like hydrophilicity or antibacterial activity, it needs to be mentioned that cellulose is poorly soluble in both polar and non-polar solvents. This negative aspect of derivative synthesis is due to the strong intra- and intermolecular hydrogen bonding of cellulose molecules. In spite of this disadvantage, several cationic derivatives of cellulose have been prepared and analyzed for medical application, such as the self-assembling micelles based on hydrophobically modified quaternized cellulose (HMQC) for the delivery of poorly water-soluble drugs, as well as derivatives with short quaternized poly[2-(N, N-dimethylamino)ethyl methacrylate] (PDMAEMA; see below) or poly(ethylene oxide) (PEO) polymer chains grafted onto the cellulose backbone for enhanced cationic character of the biopolymer.

1.1.3 Synthetic

Synthetic products have acquired a negative association due to synthetic food additives, but they show many valuable properties, especially in medical applications. Synthetic polymers are valuable for therapeutic use since they can be produced in a well-defined and controlled fashion, overcoming the greatest setback of natural polymers: the batch-to-batch variation. Synthetic polymers often exhibit increased cytotoxicity due to the strong positive charge, but since they can be freely modified in order to introduce desired properties, their biocompatibility can be improved, for example by incorporation of biodegradable linkers and bioactive functionalities.

1.1.3.1 Polyethylenimine

Polyethylenimine (PEI) is the most outstanding example for synthetic cationic polymers because of its wide range of applications. It can be synthesized in linear (LPEI) as well as in branched (BPEI) structures. LPEI possesses primary and secondary amino groups, whereas BPEI also features tertiary amino groups. BPEI usually has a ratio of primary to secondary to tertiary amino functionalities of 1 : 2 : 1 and up to 25% of these amino groups are protonated under physiological conditions. Such buffer capability can also be utilized for endosomal escape mechanisms. The amino functionalities are, nevertheless, first and foremost the target for further modification in order to introduce therapeutic molecules or to alter the undesired properties of PEI such as the cytotoxicity, the low hemocompatibility and the lack of biodegradability. In order to overcome the fact that PEI is non-biodegradable, several strategies have been developed. By incorporation of reducible/cleavable disulfide linkages into the polymer, utilizing biodegradable linkers to graft short PEI chains onto other polymer backbones and by introducing acid-labile ester bonds in the polymer chain, the biocompatibility can be increased. Other modifications such as the acid-degradable amino ketal branches grafted onto LPEI, which were originally introduced for endosomal escape, also increased the buffering capability and the transfection efficiency. Modification methods such as drug conjugation and the introduction of other polymeric chains are also viable pathways to acquire a tailor-made polymer for drug delivery. This aspect is most prominent in the example of PEI-g-PEG-RGD, which has an incorporated integrin-binding peptide (RGD) for more efficient gene delivery through endothelial cell-targeting. Besides their susceptibility for modification and functionalization, the amino groups are also an important asset in order to acquire polyplexes, since they can be protonated and therefore equipped with a cationic charge, depending on the pH of the medium. It has been demonstrated that BPEI of high molecular weight forms enzymatically stable polyplexes of small size and high transfection efficiency.

1.1.3.2 Poly(L-lysine)

Poly(L-lysine) (PLL) was one of the first polycations investigated for the formation of polyplexes with nucleic acids. It possesses a high number of primary amino groups, which enable efficient complexation of polyanions, and it is well suited for gene delivery, in spite of the fact that the ε-amino groups of the L-lysine monomers are only partially protonated in physiological environment due to the neighbouring group effect. Although PLL with high molecular weight shows cytotoxic properties, it is a valuable and widely researched polymer, as most of these drawbacks can be overcome using different modification methods. The precipitation of the PLL polyplexes, for example, has been elucidated using PEG blocks that have increased the water solubility of the complexes. The introduction of an artery wall-binding peptide to the PLL-b-PEG copolymer led to a specific targeting and drastically increased the transfection efficiency by 18 000% compared to the PLL-b-PEG copolymer without the covalently bound peptide. Similar targeting properties were achieved by introducing a leukaemia-specific JL1 antigen to the PLL backbone. PLL dendrimers and their PEGylated derivatives, including a pH-sensitive linker molecule for the release of the drug, have been prepared and applied for drug delivery purposes. Biodegradability was achieved by incorporating succinimidyldipropyldiamine (SPN) into the PLL dendrimers, and by using octa(3-aminopropyl)silsesquioxane as the dendrimer core the transfection efficiency was successfully increased. Utilizing a 3-(hydrazinosulfonyl)-benzoic acid linker and the terminal amino groups of lysine or SPN, PLL dendrimer derivatives as well as conjugates have been prepared, such as the guanidine end-caped PLL dendrigraft or the PEGylated dendrimers that were further equipped with doxorubicin, a DNA intercalating anthracycline used in cancer chemotherapy.

1.1.3.3 Polyamidoamine

The cationic polymer polyamidoamine (PAA) offers a variety of advantageous properties, such as biocompatibility, biodegradability, water solubility and lower inherent cytotoxicity, than other cationic polymers. The large number of tertiary amino and amido groups on the backbone of PAA makes it an excellent scaffold for further chemical functionalization. PAA is usually synthesized by a Michael-type polyaddition or by using "green" catalysts (salts of alkaline earth metals such as CaCl2). Structural variations (linear vs. branched) can be introduced just by varying the monomers used for the polymerization. This straighforward method can also be utilized in order to influence the polymer properties and to introduce the desired functionalities. For example, incorporating ketals and acetals into the polymer backbone leads to pH-sensitive PAA, which hydrolyzes more quickly under the non-physiological conditions found in tumour tissue. Another method of increasing the biocompatibility of the polymer is by introducing reducable disulfide bonds into the backbone of linear PAA using oligoamines and disulfide-containing cystamine bisacrylamide as reactants in the polyaddition. The disulfide bond is cleavable under the influence of glutathione, a common antioxidant in nature, which can be found at elevated concentrations in tumour cells. It has also been shown that, besides its effect on biodegradability, this modification increases the DNA condensation and transfection efficiency. This approach has been further improved by introducing PEG side-chains to the disulfide bond containing PAA in order to induce a stealth effect. The cleavage of the disulfide bond, once the PAA drug carrier reaches the tumour enviroment, enhances this effect even further. PAA can be functionaized via copolymerizing monomers with diamines, which have N-triphenylmethyl-protected primary amino functionalities. It has been shown that 2,2-bis(acrylamido)acetic acid (BAC) or 1,4-bis (acryloyl)piperazine (BP) can be copolymerized with N-triphenylmethyl -monosubstituted 1,2-diamines to form almost monodisperse polymers (PDI of 1.16) (Scheme 1.1). These pendant amino groups can then be used for conjugation chemistry. Utilizing this method, doxorubicin was successfully coupled to PAA carrier molecules.

(Continues...)

Excerpted from Cationic Polymers in Regenerative Medicine by Sangram K. Samal, Peter Dubruel. Copyright © 2015 The Royal Society of Chemistry. Excerpted by permission of The Royal Society of Chemistry.
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Edition details

• Publisher: Royal Society of Chemistry
• Publication date: 2014
• Language: English
• ISBN 10: 1849739374
• ISBN 13: 9781849739375
• Binding: Hardcover
• Number of pages: 638
• Editor: Sangram K. Samal