ABSTRACT
However, in order to act as ideal gene vectors, there are numerous barriers that need to be conquered from administration to effective transfection in vivo. And the choice of polymers, the preparation method, and the characteristics of prepared micro/nanospheres need to be adjusted carefully with these barriers in consideration. The ideal vectors should be able to improve the stability of pDNA or siRNA, help these large molecules into cells, and release them for the nucleus entry. Moreover, the material used should be biodegradable and biocompatible in order to avoid any side effects or immunogenic responses to the vector itself. In this chapter, the main barriers to gene delivery, characteristics of used polymers, preparation methods, and parts of application fields using polymer micro/nanospheres as gene vectors will be illustrated. 10.2 The Main Barriers for Micro/Nanospheres
as Gene VectorsThe transfection process of a gene includes being delivered in vivo; being taken by cellular endocytosis; escaping from the endosomal compartments; being transported through the cytosol; and localizing in cell nucleus as shown in Fig. 10.1. During this process, there were many enzymes which tend to degrade genetic material both in extracellular and intercellular circumstances. By adopting micro/nanospheres as gene vector, the encapsulation of DNA could avoid direct contact between the genetic material and the external surroundings. Yu et al. prepared poly(ethylene-glycol)- poly(γ-benzyl-l-glutamate) nanospheres with a mean diameter around 80 nm to load the drug. After being incubated with DNase I for 16 h, nearly half of the DNA in the nanospheres remained intact, while almost all of the naked plasmid was digested (8). Adopting polymers with buffering ability was another way to avoid enzymatic degradation, which promotes the escape of the vectors from endosomes prior to fusion with lysosomes (9). Compared with DNA, RNA is more labile due to ubiquitous RNase activity and chemical degradation. It is hard to protect RNA integrity by the conventional methods used to prevent DNA from degradation (10,11,12). Yagi et al. designed a novel nanosphere system called “wrapsome” to deliver siRNA in vivo, which had a core-shell structure. siRNA and a cationic lipofection complex were inserted
Figure 10.1 Simplified transfection process: (A) Extracellular trafficking; (1) Loading gene on the vector; (B) Cell membrane attachment; (2) Cellular endocytosis; (C) Intracellular trafficking; (3) Escape from the endosomal compartments; (4) Nuclear entry; (D) Gene expression; (5) Dissociation of the vector and release of the gene; (6) ARNm transcription from the gene; (7) Protein translation from ARNm (2). Reprinted from Mansouri Ref. 12 with permission from Elsevier BV.
