**3. Gene delivery**

**1. Introduction**

in solutions [1].

or cure many diseases [3–10].

**2.1. Plasmid DNA**

**2.2. RNA interference**

**2.3. Small interfering RNA**

infectious diseases and cancers [11–14].

**2. Various gene delivery mechanisms**

gene is translated to protein, which is then expressed from the cell.

responsible for post-translational regulation of protein expression.

immune compatibility, and cellular uptake.

14 Advanced Technology for Delivering Therapeutics

Drug and gene delivery system include organic, inorganic, polymeric and lipid-based nanobiomaterials. Binding of the nanobiomaterials to the receptors to target cells/tissues can be improved by surface modification. This surface modification may increase solubility,

Various nano drug delivery systems include nanoparticles, nanocapsules, nanotubes, nanogels, and dendrimers. They can be used to deliver both small molecule drugs and various classes of biomacromolecules, such as peptides, proteins, plasmid DNA, and synthetic oligodeoxynucleotides. Antisense oligonucleotide (AS-ODN) and small interfering RNA (siRNA) are shown as promise one in gene delivery and good therapeutic agents, but it can be used directly due to their limitations such as sequence size, length, charge, half-life, or stability

Various diseases are occurred in human beings due to mutations or deletions in genes lead to metabolic pathway disorder, regulation of cell cycle, protein function and its structure, function of receptor, and cell skeleton [2]. This can be treated effectively through gene delivery system. Gene delivery is a term used when referring to the delivery of genetic material such as DNA plasmids, RNA, and siRNA into target cells either encapsulated inside or conjugated to the NPs to express or suppress the biosynthesis of proteins (also called transfection) to treat

It is currently the most commonly investigated nucleic acid in gene delivery applications. When the pDNA is entering into the nucleus, the pDNA strand is transcribed, and the coding

It is triggered by double-stranded RNA (dsRNA), activates the anti-viral interferon leads to shutdown of protein synthesis by degradation of messenger RNA (mRNA). Another mechanism involves the use of microRNAs (miRNA), which are small non-coding nucleic acids

Small interfering RNA comprises around 21–23 nucleotides, which can be designed to be better targeted than long dsRNA and can eliminate the activation of the response of the interferon while still inhibiting target gene expression. The gene expression can be able to control/block transected siRNA into mammalian cells; this specific gene block can be used to treat certain

In gene delivery, a vector/carrier is essential in order to carry the hydrophilic, negatively charged DNA through the hydrophobic and negatively charged cell membrane. The therapeutic efficiency depends upon the efficient delivery of DNA into the target site. Barriers including cellular like intracellular uptake, endosomal escape, DNA release, and nuclear uptake and extracellular barriers like avoidance of particle clearance mechanisms, targeting to specific tissues and/or cells of interest, and protection of DNA from degradation are present in the system [16–19]. One main hurdle in gene delivery is the delivery of therapeutic polynucleotides crossing the plasma membrane and delivering into the cells of interest. This is the limitation one in the gene delivery for efficient and safe delivery into the cells. A good gene delivery vector should be able to effectively compact and protect DNA, sufficient stability during bypassing the immune system of the host, traverse the plasma membrane (typically through endocytosis), disrupt the endosomal membrane, and deliver the DNA into the nucleus [20–22]. Successful gene transfer requires sufficient stability of DNA during the extracellular delivery phase, transportation through cell membranes, cytoplasm, and eventual disassembly and nuclear delivery.

Gene delivery systems can be divided into two general categories:


Initially, viruses were used for gene delivery. The disadvantages of viral vectors limited their application in gene delivery like due to its size of DNA that they can carry, low loading capacity, large-scale manufacturing, quality control cost, and safety factor such as immunogenicity and potential oncogenicity [23].

Hence, more attention has been paid to develop non-viral vectors as an alternative one for gene delivery [6, 8–10, 24].

Nonviral delivery systems have advantages like easy to prepare, amenable to synthetic manipulations of polymer properties, cell/tissue targeting, less immunogenic and oncogenic, no potential of virus recombination and limitation on the size of a transferred gene, virtually no limitation on the unrestricted plasmid size that can be delivered and the cost of production is relatively low [25]. Moreover, they can be consigned readily to carry genetic materials to target cells by virtue of their size, charge and structurally modifying the vectors [26]. Difference between viral and nonviral gene delivery is based on the various gene transfer and its complementary mechanisms. The mechanism includes in the viral gene delivery is the ability of virus to circulate in the blood, bind to cell surface receptors, gain entry into the cell, avoid lysosomal destruction, survive degradation in the cytosol, and deliver genetic material to the nucleus. In the nonviral gene delivery overcoming biological barriers in the circulation or inside the target cell and transferring the gene vector is based on the molecular weight of the vector, ratio between the vector nitrogens and the DNA phosphates (termed the N:P ratio) and the salt concentration of the buffer solution. [27–30].

Nonviral gene delivery systems are typically composed of plasmid DNA condensed into nanoparticles by a cationic polymer [31].

Nonviral vectors are categories into lipid- and polymer-based one. Whereas the polymeric based nonviral vectors have the advantage over lipid-based one due to its modification property.

The steps involved in the polymeric gene delivery are given below:

