**4.2 Polyplex (polysaccharides/cationic polymers)**

A wide range of polymeric vectors have been utilized to deliver therapeutic genes *in vivo.* The modification of polymeric vectors has also shown successful improvements in achieving target-specific delivery and in promoting intracellular gene transfer efficiency [Park et al., 2006, Ogris and Wagner, 2002]. Various systemic and cellular barriers, including serum proteins in blood stream, cell membrane, endosomal compartment and nuclear membrane, were successfully avoided by designing polymer carriers having a smart molecular structure [Park et al., 2006; Ogris and Wagner, 2002]. Vectors based on a complex of polymers with DNA are called polyplexes. Most of them consist of cationic polymers and their production is regulated by ionic interactions [Gardlik et al., 2005].

In contrast to lipoplexes, some polyplexes (polylysin) are not able to release intracellular DNA into the cytoplasm [Gardlik et al., 2005]. For this purpose, co-transfection with endosome-lytic agents (inactivated *adenovirus*) is needed. On the other hand, polymers such as polyethylenimine have a mechanism of endosome disruption and there is thus no need for transfection with endosome-lytic agents. Polyethylenimine is used as a vector in aerosol inhalation gene therapy. It is a non-invasive and relatively effective gene transfer, especially into the respiratory tract, with permanent gene expression in this target region without undesirable expression in other tissues [Gardlik et al., 2005]. The size of the polymer determines the transfection efficiency and is specific for each individual gene transfer. Furthermore, the size of the aerosol particles determines the place of action, and thus the specificity of inhalation gene therapy [Gardlik et al., 2005]. An alternative to polyplexes can also be the use of polymer nanoparticles. Two types of such complexes have been characterized as gelatin-DNA and chitosan-DNA. In comparison with naked DNA, transfection using nanoparticles shows increased expression *in vivo* when administrated intratracheally or intramuscularly. Some polymeric vectors are summarized in the following sections:

#### **Poly (L-lysine) (PLL)-based gene delivery systems**

PLL has been widely used as a non-viral gene carrier since the formation of polyelectrolyte complexes between PLL and DNA was identified [Park et al., 2006]. Although, PLLs with high molecular weight have some properties suitable for a gene carrier, the PLL/DNA complexes showed a relatively high cytotoxicity and a tendency to aggregate and precipitate depending on the ionic strength. PEGylation [PEG: polyethylene glycol] of cationic polymers is known to greatly improve the problems of cytotoxicity, aggregation and nonspecific protein adsorption *in vivo* [Park et al., 2006]. Some examples are mentioned as following:

• **Sugar-conjugated PLL:** Lactose and galactose have been used as conjugation partners with polymeric gene carriers for targeting asialoglycoprotein of hepatocytes. Lac-PEG-PLL showed much less cytotoxicity and higher stability and solubility in a physiological condition compared to PLL [Park et al., 2006].

Toll-like receptors (TLRs), which may result in the generation of anti-tumor natural killer (NK) cell and T-cell responses by the innate immune system. In addition, as a vaccine adjuvant, this agent may induce a strong cytotoxic T-lymphocyte (CTL) response to co-administered antigen. The efficacy of JVRS-100 has been evaluated in phase I clinical trials for the treatment of patients with Relapsed or Refractory Leukemia [ID:

A wide range of polymeric vectors have been utilized to deliver therapeutic genes *in vivo.* The modification of polymeric vectors has also shown successful improvements in achieving target-specific delivery and in promoting intracellular gene transfer efficiency [Park et al., 2006, Ogris and Wagner, 2002]. Various systemic and cellular barriers, including serum proteins in blood stream, cell membrane, endosomal compartment and nuclear membrane, were successfully avoided by designing polymer carriers having a smart molecular structure [Park et al., 2006; Ogris and Wagner, 2002]. Vectors based on a complex of polymers with DNA are called polyplexes. Most of them consist of cationic polymers and their production

In contrast to lipoplexes, some polyplexes (polylysin) are not able to release intracellular DNA into the cytoplasm [Gardlik et al., 2005]. For this purpose, co-transfection with endosome-lytic agents (inactivated *adenovirus*) is needed. On the other hand, polymers such as polyethylenimine have a mechanism of endosome disruption and there is thus no need for transfection with endosome-lytic agents. Polyethylenimine is used as a vector in aerosol inhalation gene therapy. It is a non-invasive and relatively effective gene transfer, especially into the respiratory tract, with permanent gene expression in this target region without undesirable expression in other tissues [Gardlik et al., 2005]. The size of the polymer determines the transfection efficiency and is specific for each individual gene transfer. Furthermore, the size of the aerosol particles determines the place of action, and thus the specificity of inhalation gene therapy [Gardlik et al., 2005]. An alternative to polyplexes can also be the use of polymer nanoparticles. Two types of such complexes have been characterized as gelatin-DNA and chitosan-DNA. In comparison with naked DNA, transfection using nanoparticles shows increased expression *in vivo* when administrated intratracheally or intramuscularly. Some polymeric vectors are summarized in the following

PLL has been widely used as a non-viral gene carrier since the formation of polyelectrolyte complexes between PLL and DNA was identified [Park et al., 2006]. Although, PLLs with high molecular weight have some properties suitable for a gene carrier, the PLL/DNA complexes showed a relatively high cytotoxicity and a tendency to aggregate and precipitate depending on the ionic strength. PEGylation [PEG: polyethylene glycol] of cationic polymers is known to greatly improve the problems of cytotoxicity, aggregation and nonspecific protein adsorption *in vivo* [Park et al., 2006]. Some examples are mentioned as

• **Sugar-conjugated PLL:** Lactose and galactose have been used as conjugation partners with polymeric gene carriers for targeting asialoglycoprotein of hepatocytes. Lac-PEG-PLL showed much less cytotoxicity and higher stability and solubility in a physiological

NCT00860522].

sections:

following:

**4.2 Polyplex (polysaccharides/cationic polymers)** 

is regulated by ionic interactions [Gardlik et al., 2005].

**Poly (L-lysine) (PLL)-based gene delivery systems** 

condition compared to PLL [Park et al., 2006].

