Gene Delivery Using Chemical Methods - Challenges in Delivery of Therapeutic Genomics and Proteomics - page 141

Figure 4.6 Chemical structures of gene vectors based
on polyesters.

O

O

n

O

O

n

H 2 N

PHP PAGA

reported separately by both Park et al. and Langer et al. ( Fig. 4.6 ) [84,85] . PHP was
synthesized by polymerization of N -cbz-4-hydroxy-L-proline followed by deprot-
ection [86] . Although initially PHP was reduced to half of its molecular weight in
2 h due to aminolysis by the secondary amine groups in an aqueous solution of pH
7.0 at 37°C, complete degradation of monomeric units occurs in about 3 months.
Accumulations of degradation product in vitro slow down the degradation hydrolysis
by decreasing pH of the solution. PHP forms polyanion complex with DNA. The
complex demonstrated stability for a minimum up to 4 h presence of nucleases. The
PHP was degraded at a much slower rate when bound with DNA [84] .
PHP could condense DNA efficiently at a polymer-DNA ratio of 3:1(w:w). The
transfection efficiency of PHP polyplexes was comparable to that of PLL. In addi-
tion, serum proteins did not affect the transfection efficiency of PHP-based poly-
plexes. Importantly, PHP significantly reduced cytotoxicity as compared to PEI or
PLL [85] . It was demonstrated that DNA-loaded microspheres prepared by copoly-
merization of PHP with D,L-lactide were capable of sustained gene expression for a
period of 1 week [87] .
Poly[-(4-aminobutyl)-L-glycolic acid] (PAGA) is an amine-substituted polyester
synthesized by Lim et al. [88,89] . The degradation behavior of PAGA, rapid initial
degradation followed by slow hydrolysis for several months, is similar to PHP. PAGA
reduced to one-third of its molecular weight in 30 min in aqueous solution and com-
plete hydrolysis of monomers occurs in 6 months at 37°C. PAGA could efficiently
condense a pDNA to form nanoparticles with an average size of 326 nm [89] . The
PAGA-DNA complexes revealed stability similar to PHP. PAGA-DNA complexes
were stable for 8 h and dissociated completely in 1 day, showing their favorability for
gene expression [88] .
PAGA polyplexes demonstrated threefold higher transfection activity compared
to PLL polyamide analogue of PAGA, in vitro without any cytotoxicity in the con-
centration range tested. Animal studies performed in 3-week-old NOD mice after
IV administration of PAGA-pCAGGS mouse IL-10 complexes demonstrated maxi-
mum serum level at 5 days followed by detectable serum level for more than 9 weeks
[90,91] . The combined systemic administration of PAGA-IL-4 pDNA complexes
and PAGA-IL-10 pDNA complexes to 32-week NOD mice demonstrated the preven-
tion of diabetes in 75% of the treated animals [92] . Local administration of plasmid
encoding IL-12 using PAGA to tumor-bearing mice appreciably increased the attrac-
tion of natural killer (NK) cells, CD4 () T cells, and professional antigen presenting