Gene therapy

Potential Applications of Nanotechnology

Surendra Nimesh

• Publisher: Woodhead Publishing
• Year: 2013
• Print ISBN: 9781907568404
• eBook ISBN: 9781908818645
• Topic: Biological Sciences
• Subtopic: Genetics & Genomics
• Index: Biological Sciences

Gene therapy is emerging as a new class of therapeutics for the treatment of inherited and acquired diseases. However, poor cellular uptake and instability of DNA in the physiological milieu limits its therapeutic potential, hence a vector which can protect and efficiently transport DNA to the target cells must be developed. Nanotechnology-based non-viral vectors have been proposed as potential candidates. Various polymeric nanoparticles have been shown to be suitable, with high cellular uptake efficiencies and reduced cytotoxicity. These delivery vectors form condensed complexes with DNA which result in shielding against enzymatic degradation and enhanced cellular targeting. Advantages including easy manipulatibility, high stability, low cost and high payload, mean that nanoparticles from various polymers have been exploited. Gene therapy gives a systematic account of the many aspects of nanotechnology mediated gene therapy, from the preparation of nanoparticles to physicochemical characterization, and follows with applications in in vitro and in vivo models. This book emphasizes the various aspects of nanotechnology-based gene therapy, with initial chapters detailing the tools and techniques available for preparation and in vitro and in vivo characterization of nanoparticles. Later chapters provide exhaustive details on polymeric systems employed for gene therapy.- Provides an overview of nanotechnology applications in gene therapy, from preparation of nanoparticles to in vitro and in vivo studies- Details the tools and techniques available for preparation, characterization and in vitro and in vivo study of nanoparticles- Details the limitations of nanoparticle-mediated gene therapy and proposes ways in which they may be overcome

1

Nanotechnology: an introduction

Abstract:

The term “nanotechnology” was coined by Norio Taniguchi (1974) and defined as: Nanotechnology mainly consists of the processing of separation, consolidation, and deformation of materials by one atom or one molecule. Nanotechnology enables the production and application of physical, chemical, and biological systems at sizes ranging from individual atoms or molecules to submicron dimensions. Nanomedicine is one of the most significant implications of nanotechnology; it is used to collectively mention liposomes, quantum dots, polymeric micelles, polymer-drug conjugates, dendrimers, inorganic nanoparticles, biodegradable nanoparticles, and other materials in nanoscale size with therapeutic relevance. This chapter provides some basic introduction to nanotechnology and various drug and gene delivery systems.

Key words

nanotechnology

nanomedicine

nanoparticles

nanocapsules

nanospheres

liposomes

quantum dots

1.1 Introduction

In the quest to develop an efficient drug delivery system with desired therapeutic effect, several approaches have been proposed. Upon administration, the fate of drug distribution in the body depends on the physico-chemical properties and molecular structure of the drug. However, the uneven distribution of the drug results in only a small amount of the administered dose reaching the desired site of action. Further, deposition of the drug at non-specific sites may lead to adverse and toxic side effects. Hence, it has been a challenging task to design and develop novel delivery systems with maximal therapeutic effect and minimal toxic effects. To develop better drug targeting strategies it is imperative to fully explore the nature of the target and the mechanism of targeting. A number of drug delivery systems have been developed in order to engineer a system that can efficiently and specifically deliver drugs to target sites. One early approach was the use of prodrugs, which are modified forms of the active drugs that can reach the target site and be cleaved enzymatically or chemically to release the active drug moiety. More recently, several biomolecule-based vectors have been investigated, including polyclonal antibodies, monoclonal antibodies, sugars and lectins, as targeting molecules to which the drug can be chemically coupled.

The primary objective of controlled drug delivery systems is to deliver a drug to a target site, which could be an organ, a tissue or a particular population of cells within a tissue. Regarding development of newer target-specific delivery systems, the following points are noteworthy:

the system should be capable of distinguishing between target and non-target sites, to diminish the side effects;

the system should not exhibit toxic effects on prolonged in vivo administration;

the vector should be biodegradable, i.e. it should degrade after achieving drug delivery and the degraded components thus formed should not be toxic.

The site-specific delivery of a drug can be significantly influenced by the choice of delivery system. Recent decades have witnessed the evolution of several carrier systems, such as microparticles, microemulsions, liposomes and nanoparticles. These systems were designed to deliver drug at the target sites and diminish any interactions with non-target sites, thereby leading to enhanced therapeutic effect. These novel carrier systems offer explicit advantages, such as:

maintenance of drug activity;

maintenance of therapeutic drug concentration at target sites;

protection of drug from being eliminated by the host defense system.

The host defense mechanism, which consists of the reticuloendothelial system (RES), poses one of the major challenges in the development of polymeric nanoparticulate vectors. When a carrier molecule, or any other foreign moiety, enters the vascular system, it is rapidly conditioned (or coated) by elements in circulation, such as plasma proteins and glycoproteins called “opsonins”, in a process known as “opsonization”. This opsonization process enables easy identification of the carrier materials by the RES, as in the case of other foreign bodies, pathogens, or dying cells, and cleared from the blood circulation by phagocytosis by the macrophages.¹ The macrophage cells of the liver (Kupffer cells), spleen and lung, and circulating macrophages, all play a significant role in the removal of the opsonized particles. Recognition of the particles by the RES is dictated by size and surface properties. Particulates with large hydrophobic surfaces are efficiently coated with opsonins and are rapidly cleared from circulation. However, particles with hydrophilic surfaces escape recognition by opsonins, leading to prolonged time in circulation.²

Several strategies have been proposed for the modification of surface properties of delivery vectors.³ Coating of polystyrene nanoparticles with positively-charged polylysyl-gelatin led to the reduction in liver uptake and an increase in spleen and lung uptake. In the early 1980s, Illum and Davis observed that particles can be largely protected from scavenging and clearance by the RES by chemical modification, which consists of coating the particles with block copolymers.² This approach proved to be highly effective in alteration of the biodistribution of radiolabeled colloidal particles. The polystyrene particles coated with block copolymer poloxamer 338 largely escaped (by up to 50%) the normally predominant liver and spleen uptake, but could not escape removal by RES cells. However, coating the particles with poloxamine 908, which totally prevents RES capture, led to prolonged circulation times. Some of the other strategies proposed to circumvent these problems include coating the carrier molecules with surfactants, gangliosides and polymers like polyethylene glycol (PEG) or polyethylene oxide (PEO). Studies with surfactant coated carrier molecules led to reduced liver uptake and increase in their concentration in blood and other non-RES organs.⁴ However, such strategies are not considered to be applicable in clinical practice, since repeated suppression can lead to impaired RES function.

Particle based drug carriers have been engineered to enhance the bioavailability of drug at the desired site and to explore the therapeutic relevance of the controlled release of drug and drug targeting. It is highly desirable to control the size of the polymeric matrix, to achieve the desired therapeutic response of the entrapped drug molecules. According to size, the particles can be broadly categorized as:

macroparticles (50–200 μm),

microparticles (1–50 μm),

nanoparticles (1–1000 nm).

Microparticles and nanoparticles have been employed in numerous studies of drug and gene delivery. Although microparticles have been observed to circulate in the blood and are capable of passing through the heart, due to their large size they cannot enter capillaries and thus cannot reach tissue sinusoids. However, the drug encapsulated molecules accumulate in the nearby tissues surrounding the capillaries and release the drug slowly. These accumulated microparticles can be used as a depot system and can be delivered by various routes, such as intra-arterial, subcutaneous, intravenous or intraperitoneal. Thus, the drug is not only released slowly and continuously but is also protected from in vivo degradation. Efficient drug release is achieved by the use of a polymer properly engineered with regard to its pore size, swelling properties and degradation. Considering these key parameters, biodegradable microparticles of starch, albumin, polylactic acid and ethyl cellulose have been designed and implicated for chemoembolization.

Advances in drug delivery studies have suggested that micron sized particles are rapidly cleared by the RES defense mechanism. However,...

Table of contents

• Cover image
• Title page
• Table of Contents
• Copyright
• Dedication
• List of figures and tables
• Acknowledgments
• Foreword
• Preface
• About the author
• Chapter 1: Nanotechnology: an introduction
• Chapter 2: Methods of nanoparticle preparation
• Chapter 3: Tools and techniques for physico-chemical characterization of nanoparticles
• Chapter 4: Characterization of nanoparticles: in vitro and in vivo
• Chapter 5: Theory and limitations to gene therapy
• Chapter 6: Targeted gene delivery mediated by nanoparticles
• Chapter 7: Polymeric nanoparticles for gene delivery
• Chapter 8: Poly-L-lysine nanoparticles
• Chapter 9: Chitosan nanoparticles
• Chapter 10: Polyethylenimine nanoparticles
• Chapter 11: Atelocollagen
• Chapter 12: Protamine nanoparticles
• Chapter 13: Dendrimers
• Chapter 14: Cyclodextrins and cyclodextrin-containing polymers
• Chapter 15: Poly(D,L-lactide-co-glycolide)-based nanoparticles
• Chapter 16: Metallic and inorganic nanoparticles
• Index