Advances in Nanomedicine for the Delivery of Therapeutic Nucleic Acids

Surendra Nimesh, Ramesh Chandra, Nidhi Gupta

• Publisher: Woodhead Publishing
• Year: 2017
• Print ISBN:
  9780081005576
• eBook ISBN:
  9780081005637
• Topic: Medicina
• Subtopic: Farmacología

Advances in Nanomedicine for the Delivery of Therapeutic Nucleic Acids addresses several issues related to safe and effective delivery of nucleic acids (NAs) using nanoparticles. A further emphasis would be laid on the mechanism of delivery of NAs, the barriers encountered and the strategies adapted to combat them. An exhaustive account of the advantages as well shortcomings of all the delivery vectors being employed in delivery of various NAs will be provided. On final note the regulatory aspects of nanoparticles mediated NA would be discussed, with focus on their clinical relevance. The design and development of nucleic acid-based therapeutics for the treatment of diseases arising from genetic abnormalities has made significant progress over the past few years. NAs have been widely explored for the treatment of cancer and infectious diseases or to block cell proliferation and thereby caused diseases. Advances in synthetic oligonucleotide chemistry resulted in synthesis of NAs that are relatively stable in in vivo environments. However, cellular targeting and intracellular delivery of NAs still remains a challenge. Further development of NA-based therapeutics depends on the progress of safe and effective carriers for systemic administration. Nanomedicine has facilitated availability of vectors with diminished cytotoxicity and enhanced efficacy which are rapidly emerging as systems of choice. These vectors protect NAs from enzymatic degradation by forming condensed complexes along with targeted tissue and cellular delivery. During the past few years, a myriad reports have appeared reporting delivery of NAs mediated by nanoparticles. This book will provide an overview of nanoparticles being employed in the in vitro and in vivo delivery of therapeutically relevant NAs like DNA, siRNA, LNA, PNA, etc. - Provides a complete overview of the applicatiosn of nanomedicine in the delivery of nucleic acids, from characterization of nanoparticles, to in vitro and in vivo studies - Discusses delivery issues of less well explored nucleic acids, like PNAs, Ribozymes, DNAzymes, etc. - Summarizes the current state of research in nucleic acid delivery and underscores the future of nanomedicine in this field

1

Nanomedicine for delivery of therapeutic molecules

Surendra Nimesh¹, and Nidhi Gupta^{2 1}Central University of Rajasthan, Ajmer, India ²The IIS University, Jaipur, India

Abstract

The design and development of nucleic acid (NA)-based therapeutics for the treatment of diseases arising from genetic abnormalities have made significant progress. NAs have been widely explored for the treatment of cancer and infectious diseases or to block cell proliferation and thereby caused diseases. Advances in synthetic oligonucleotide chemistry resulted in synthesis of NAs that are relatively stable in in vivo environments. However, cellular targeting and intracellular delivery of NAs still remain a challenge. Further, development of NA-based therapeutics depends on the progress of safe and effective carriers for systemic administration. Nanomedicine has facilitated availability of vectors with diminished cytotoxicity and enhanced efficacy, which are rapidly emerging as systems of choice. These vectors protect NAs from enzymatic degradation by forming condensed complexes along with targeted tissue and cellular delivery.

Keywords

DNA; Gene delivery; Nanoparticles; Nucleic acid; siRNA

1.1. Introduction

Specificity and accuracy are two important aspects in the design and development of drug delivery strategies. In the initial stages, Paul Ehrlich had led a vision of designing “magic bullets” that would deliver drugs with the utmost specificity to the target tissue or cells. Nanotechnology is one step closer to the reality of this vision that was initiated in the beginning of the 20th century (Kayser et al., 2005). As a beginner, the best way to develop a drug delivery system (DDS) is to understand the mechanism of targeting. One simple, chemical approach for designing DDS is the use of modified forms of active drugs, also known as prodrugs, that can be cleaved enzymatically or chemically to release an active drug. The prodrugs could more easily access the target sites (Higuchi, 1975). Bioconjugate systems are also being developed that employ the use of monoclonal antibodies, polyclonal antibodies, sugars or lectins as targeting moieties, coupled chemically with drug moiety to increase target specificity of the latter. The ligand conjugated to the drug decides the fate of the coupled molecule and underlines its importance in site-specific delivery of a drug.

A number of delivery or carrier systems for drugs have found place in research since 1996, including strategies based on liposomes, nanoparticles, microparticles, and microemulsions (Aynie et al., 1999; Fattal et al., 1998; Forssen and Tokes, 1983a,b; Gregoriadis, 1990; Landfester 2001, 2009; Lee et al., 2003; Rahman et al., 1990; Tan and Gregoriadis, 1990; Zou et al., 1993a,b,c). The purpose of developing all these systems is to maximally avoid interactions with nontarget sites. Several advantages are linked with the usage of carrier-conjugated drug delivery systems, such as

1. prevention of the drug molecule from immunogenic attack and minimal exposure of the drug to normal milieu;

2. minimal renal excretion that increases the half-life of the drug;

3. the drug can be maintained in its active form;

4. at the target site, the required therapeutic concentration can be prevailed;

5. at the disease site, the drug moiety can be activated; and

6. several physiological barriers could be overcome to finally ensure cell-specific interaction.

The foremost goal of controlled drug delivery is to deliver a particular drug to a target site or a specific population of cells within a particular organ or tissue. For designing a new system for the target-specific delivery of a drug, the following factors should be taken into consideration:

1. The system should have the capability to differentiate between target and nontarget sites, ultimately minimizing the toxic effects.

2. The system should be free of any toxic compounds on prolonged retention in the system.

3. The carrier system deployed should be biodegradable after its role imparted at the target site, and the degraded components produced should be nontoxic to the system to which it is administered.

The major problem faced during the process of the delivery of polymeric nanoparticulate carriers in the body is the systemic scavenging machinery such as the reticuloendothelial system (RES). Herein, the nanoparticles or any other foreign body entering into the vasculature system get surrounded or coated by various plasma proteins and glycoproteins called opsonins by the process termed “opsonization.” Consequently, the RES removes the carrier system from the blood circulation similar to the mechanism followed in the removal of pathogens, dying cells, and foreign bodies from the blood circulation by phagocytosis (Müller and Wallis, 1993). In addition, the Kupffer cells, spleen, lungs, and circulating macrophages also play a significant role in the removal of opsonized particles. It has been observed that the RES mainly depends on the size and surface properties of the particles. As a result, the particulates with greater hydrophobic surfaces get efficiently coated with opsonins and are rapidly cleared from the circulation, whereas hydrophilic particle experiences prolonged circulation as it escapes being recognized by the opsonins (Storm et al., 1995).

In the current scenario, antisense nucleotides such as siRNA have been employed for the treatment of several infectious and inflammatory diseases including cancer (Stephenson and Zamecnik, 1978; Zamecnik and Stephenson, 1978). This nucleic acid (NA) therapeutics is considered to be more efficient compared to conventional therapeutics as it works at the level of gene expression, inhibiting the expression of target protein. Also, NA offers unique prospects in its therapeutic activity on intractable targets, such as regulation of transcription factors for the expression of entire groups of genes. Thus, NA could be either employed for incorporating desired function or inhibition of the function at the molecular level known as gene therapy (Scanlon, 2004). In gene therapy, generally large NA molecules are used for expressing a desired protein, whereas small and specific NA sequences are used for inhibiting target gene function. Though the therapeutic use of NA is considered to display several benefits, it is hampered by challenges such as limited stability and poor cellular internalization. Hence, there is a need of a carrier capable of administering NA in vitro and in vivo efficiently, safely, and repeatedly that can be attained by applying the use of nanoparticles.

Nanotechnology generally deals with the design, synthesis and application of materials in the nanometer range (usually 100 nm or smaller). Previous studies have shown that nanocarriers could be used for successful delivery of drugs to the target tissue with greater potential, penetration and improved efficacy. Among most of the nanoparticles available, polymeric nanoparticles have evolved as one of the most promising candidates, with rapid progress as vectors for targeted drug and gene delivery (Peer et al., 2007). Thus polymeric nanocarriers could be exploited for the delivery of several therapeutic agents such as low molecular weight drugs and macromolecules involving proteins or NA. These nanocarriers could be categorized as (1) nanospheres, spherical nanometer range particles where the desired molecules can either be entrapped inside the sphere or adsorbed on the outer surface or both (Fig. 1.1) or (2) nanocapsules, solid polymeric shells with an inner liquid core, and the desired molecules entrapped inside (Fig. 1.1) (Fattal et al., 1998; Mao et al., 2010; Reischl and Zimmer, 2009). Basically, the fate of nanoparticles within the body is governed by its size, shape, surface charge, and nature (hydrophobic or hydrophilic) of the polymer (Alexis et al., 2008). So far, natural and synthetic polymers investigated for NA delivery include chitosan, polyethylenimine (PEI), cyclodextrin-based polycations, and polyethylene glycol (PEG), etc.

Figure 1.1 Types of nanoparticles.

1.2. Properties of nanoparticles

Size of particles has been a major concern during the preparation of various formulation systems such as DNA/polymers, lipid complexes, and liposomes. The size of nanoparticles has been observed to be one of the critical factors that significantly influences the transfectivity (Dauty et al., 2001; Lee et al., 2001; Sakurai et al., 2000). A plethora of reports have shown tha...

Table of contents

• Cover image
• Title page
• Table of Contents
• Related titles
• Copyright
• List of contributors
• Foreword
• Preface
• Acknowledgments
• 1. Nanomedicine for delivery of therapeutic molecules
• 2. Nanoparticles as nucleic acid delivery vectors
• 3. Methods for characterization of nanoparticles
• 4. Nanoparticles for DNA delivery
• 5. Nanoparticles for siRNA-mediated gene silencing
• 6. Nanoparticles for locked nucleic acid delivery
• 7. Nanoparticles for ribozymes delivery
• 8. Nanoparticles for DNAzymes delivery
• 9. Pharmacokinetics and biodistribution of the nanoparticles
• 10. Nanotoxicology: Evaluation of toxicity potential of nanoparticles
• 11. Regulatory aspects of nanoparticulate mediated nucleic acid delivery systems
• 12. Clinical studies and future prospects
• Index