Gene Delivery Using Chemical Methods - Challenges in Delivery of Therapeutic Genomics and Proteomics - page 182

nanospheres encapsulating pDNA encoding for cystic fibrosis transport regulator were
effectively transfected in cultured human tracheal epithelial cells (HTEo). Expression
of cystic fibrosis transport regulator was observed in 50% of the cells when trans-
fected with gelatin nanospheres [383] . The same group proposed the solvent pre-
cipitation method under controlled conditions of temperature and pH for gelatin
encapsulating pDNA [384] . Gelatin was modified with PEG to impart long circulating
characteristics. Reporter pDNA encoding for -galactosidase (pCMV-) was encapsu-
lated in gelatin and PEGylated gelatin NPs. -galactosidase expression was sustained
for 96 h when evaluated against Lewis lung carcinoma cells. Various nonviral (chemi-
cal) vectors used in gene therapy clinical trials are shown in Table 4.1 .
4.8 Conclusion
The last two decades have witnessed tremendous progress in the design and synthe-
sis of nonviral vectors for gene delivery. Structure property relation and common
design principles have been applied in the development of nonviral vectors. The field
of gene delivery continues to advance, and expands to address issues pertinent to
any nonviral method of gene delivery. Usually, all synthetic vectors form complexes
with DNA owing to its positive charge imparted by an amine group or other cationic
group. Although increasing the number and charge density of the amines typically
improves transfection efficiency, the increased charge density generally promotes
high cytotoxicity. The cytotoxicity can be reduced by incorporating guanidine or his-
tidine functional groups that better distribute the positive charge that results in higher
transfection efficiency. Quaternization of amines is one of the approaches to achieve
higher transfection efficiency. However, it is not universal because quaternization of
PEI, CD, and polyamidoamine gives a negative effect.
The therapeutic applications of these nonviral gene delivery systems are still lim-
ited despite the progress in vector design and in understanding of transfection biol-
ogy. Few results of clinical trials demonstrate that the in vitro and in vivo animal
model data can be translated into clinical benefit, and interestingly, no major clini-
cal toxicities have been reported with nonviral delivery systems. But principally, the
standard requirements for clinical use have not been met in terms of efficiency and
specificity.
Practically, cationic lipids, cationic polymers, and other naturally occurring com-
pounds have proven to be extremely effective for in vitro gene delivery. Inclusion of
PEG-lipids, target ligands, endosomolytic peptides, and nuclear peptides into DNA
complexes, to convert a simple DNA complex into a more sophisticated multicom-
ponent gene vector, appears to be a reasonable approach to equip the complexes with
more function. Gene delivery is a multistep process, in which an appropriate prop-
erty of vector is required to go through each step. Hence, rationally designed multi-
functional vectors capable of overcoming a series of extra- and intracellular barriers
should be designed at a molecular level. Also, suitable plasmid design may avoid
immunogenic response.