Non-viral Gene Therapy - Intracellular Delivery: Fundamentals and Applications - page 636

evidently decreased by the intravenous injection of PAGA-DNA polyplexes (15.7%),
in comparison to that of naked DNA injection (34.5%) and non-treated controls
(90.9%). Combined administration of pDNAs encoding IL-4 and IL-10 with PAGA
vector in NOD mice could also prevent the development of diabetes in 75% of the
treated animals (Ko et al. 2001 ).

3.5.2 Poly(4-Hydroxy-L-Proline Ester)

Poly(4-hydroxy-L-proline) (PHP) was synthesized by the polymerization of N-cbz-
4-hydroxy-L-proline followed by deprotection (Fig. 4b ) (Lim et al. 1999 ; Putnam
and Langer 1999 ). This polymer exhibited significantly reduced cytotoxicity as
compared to PEI25 or PLL (Putnam and Langer 1999 ). A two-stage degradation
profile was observed for PHP in aqueous solutions at a 37°C buffer condition (pH
7), and a thorough degradation took nearly 3 months. PHP-DNA polyplexes, how-
ever, showed a slower degradation profile compared to that of PHP alone.
Transfection of b-galactosidase gene into CPAE cells using PHP-DNA polyplexes
was successful, showing an efficiency that was higher than that of PLL with or
without fetal bovine serum (Lim et al. 1999 ).

3.5.3 Poly(b-Amino Ester)s

To develop safe alternatives to existing polymeric vectors, Langer's group discov-
ered a new type of degradable amine-containing polyesters, called as poly(b-amino
esters) (PAEs, Fig. 4c ) (Lynn and Langer 2000 ). These polycations possess low
cytotoxicity and can be easily synthesized by the conjugate addition of a primary
amine or bis(secondary amine) to a diacrylate (Lynn et al. 2001 ). At physiological
pH, PAEs can be completely degraded to nontoxic monomers. A large library
(>2,500) of PAE was discovered using the high-throughput semi-automated meth-
odology (Anderson et al. 2003 ). Optimizing monomers and polymerization condi-
tions resulted in a new PAE library (>500), part of which showed transfection
activities that rival PEI25 and Lipofectamine 2000 in both COS 7 and HUVEC cell
lines (Lynn et al. 2001 ; Green et al. 2006 ). In vivo delivery to xenografts in mice
showed promising results for the local treatment of cancer(Anderson et al. 2004 ).
Structure-function correlation based on the PAEs library suggested that molecular
weight and end groups significantly affected the transfection potential of these
polymers. High molecular weight and amine termination confers PAEs with high
transfection efficiency (Akinc et al. 2003 ; Zugates et al. 2007 ).
By ester exchange reactions, Park's group synthesized hyperbranched poly(amino
esters). These polymers displayed significantly lower cytotoxicity than PEI25. The
transfection efficiency of these vectors, however, was lower than that of PEI25 (Lim
et al. 2001 ). Other hyperbranched poly(amino esters) were also synthesized, and
these polymers showed significantly improved transfer activity (Li et al. 2005 ; Wu
et al. 2005, 2006 ).