itself seemed to be far less toxic than the diblock to HEK293T cells (at 0.5 mg mL
À1
there was nearly 100% cell viability versus 55% for the diblock). Following the
trends of DNA complexation, the diblock copolymer was more efficient for
transfection than the triblock at lower N:P ratio, with a bell-shaped dependence
of the transfection efficiency as a function of the N:P ratio (Fig. 15d). For the range
studied (N:P ratios of 1:1 to 15:), the maximum efficiency for PDMAEMA-bPOEGMA was reached at N:P ¼ 3, while for PDMAEMA-b-POEGMA-bPDMAEMA, the maximum seemed to be reached at N:P ¼ 15, but it could also
be a bell-shaped dependence shifted to higher ratios.
PDMAEMA-b-PEG-b-PDMAEMA and PHEMA-b-PDMAEMA-b-PEG-bPDMAEMA-b-PHEMA with 113 EG units in the central block and on each side
33, 48, or 61 DMAEMA units (used to complex DNA) and eventually ~15 more
HEMA units on each side (Fig. 12d) were studied by Kang and colleagues
[196]. At a polymer:plasmid weight ratio above 5, all polymers condensed DNA
into particles of less than 200 nm in size and more than 25 mV in zeta potential. The
triblocks PDMAEMA-b-PEG-b-PDMAEMA showed increased DNA complexing
ability as well as transfection efficiency with increasing number of DMAEMA
units. Adding short PHEMA blocks to the triblocks (leading to the pentablocks
PHEMA-b-PDMAEMA-b-PEG-b-PDMAEMA-b-PHEMA) did not significantly
impede the complexation ability of the polymers compared to the triblock and led
to higher transfection than PDMAEMA. By comparison, a random block copolymer of similar component composition could not condense DNA efficiently,
showing the importance of the architecture of the polycation.
Linear PEI Derivatives
PEG 45 -b-linear PEI 600 (Fig. 16a) (M w ¼ 51 kDa) was obtained by complete hydrolysis of a block copolymer PEG-b-poly(ethyl oxazoline-co-methyl oxazoline)
[197]. PEG 45 -b-linear PEI 600 inhibited DNA migration at a polymer:DNA weight
ratio of 1 under physiological ionic strength, while linear PEI of 22 kDa achieved it
at a ratio of 0.75. The levels of reporter gene expression obtained with the diblock
copolymer were similar to those obtained for the linear PEI although at higher
weight ratio, while the cytotoxicity as well as solubility were comparable, which
was probably due to the relatively short length of the PEG block. Therefore,
perhaps a longer PEG block should be introduced in order to see the benefits.
PHEMA-g-(linear PEI-b-PEG) (Fig. 16b) (M w ¼ 509 kDa) adopted a cylindrical brush topology at pH 5.0 [198] and completely retarded DNA migration at
N:P ratio of 2, whereas efficient condensation started at an N:P ratio of 10, leading
to small particles of 150 nm in diameter with a positive zeta potential of 20 mV.
PHEMA-g-(linear PEI-b-PEG) was well tolerated by HEK293 cells up to a dose
of 125 μg mL
À1 , whereas exposure of the cells to PEI25K (branched) led to 50%
viability at 16 μg mL
À1 . PHEMA-g-(linear PEI-b-PEG)/pDNA complexes
were internalized by BT474 cells to a greater extent than PEI25K/DNA
complexes at the same ratio (N:P ¼ 10) and led to a higher transfection efficiency
in a variety of cell lines.
Polyelectrolyte Complexes of DNA and Polycations as Gene Delivery Vectors
161
À1
there was nearly 100% cell viability versus 55% for the diblock). Following the
trends of DNA complexation, the diblock copolymer was more efficient for
transfection than the triblock at lower N:P ratio, with a bell-shaped dependence
of the transfection efficiency as a function of the N:P ratio (Fig. 15d). For the range
studied (N:P ratios of 1:1 to 15:), the maximum efficiency for PDMAEMA-bPOEGMA was reached at N:P ¼ 3, while for PDMAEMA-b-POEGMA-bPDMAEMA, the maximum seemed to be reached at N:P ¼ 15, but it could also
be a bell-shaped dependence shifted to higher ratios.
PDMAEMA-b-PEG-b-PDMAEMA and PHEMA-b-PDMAEMA-b-PEG-bPDMAEMA-b-PHEMA with 113 EG units in the central block and on each side
33, 48, or 61 DMAEMA units (used to complex DNA) and eventually ~15 more
HEMA units on each side (Fig. 12d) were studied by Kang and colleagues
[196]. At a polymer:plasmid weight ratio above 5, all polymers condensed DNA
into particles of less than 200 nm in size and more than 25 mV in zeta potential. The
triblocks PDMAEMA-b-PEG-b-PDMAEMA showed increased DNA complexing
ability as well as transfection efficiency with increasing number of DMAEMA
units. Adding short PHEMA blocks to the triblocks (leading to the pentablocks
PHEMA-b-PDMAEMA-b-PEG-b-PDMAEMA-b-PHEMA) did not significantly
impede the complexation ability of the polymers compared to the triblock and led
to higher transfection than PDMAEMA. By comparison, a random block copolymer of similar component composition could not condense DNA efficiently,
showing the importance of the architecture of the polycation.
Linear PEI Derivatives
PEG 45 -b-linear PEI 600 (Fig. 16a) (M w ¼ 51 kDa) was obtained by complete hydrolysis of a block copolymer PEG-b-poly(ethyl oxazoline-co-methyl oxazoline)
[197]. PEG 45 -b-linear PEI 600 inhibited DNA migration at a polymer:DNA weight
ratio of 1 under physiological ionic strength, while linear PEI of 22 kDa achieved it
at a ratio of 0.75. The levels of reporter gene expression obtained with the diblock
copolymer were similar to those obtained for the linear PEI although at higher
weight ratio, while the cytotoxicity as well as solubility were comparable, which
was probably due to the relatively short length of the PEG block. Therefore,
perhaps a longer PEG block should be introduced in order to see the benefits.
PHEMA-g-(linear PEI-b-PEG) (Fig. 16b) (M w ¼ 509 kDa) adopted a cylindrical brush topology at pH 5.0 [198] and completely retarded DNA migration at
N:P ratio of 2, whereas efficient condensation started at an N:P ratio of 10, leading
to small particles of 150 nm in diameter with a positive zeta potential of 20 mV.
PHEMA-g-(linear PEI-b-PEG) was well tolerated by HEK293 cells up to a dose
of 125 μg mL
À1 , whereas exposure of the cells to PEI25K (branched) led to 50%
viability at 16 μg mL
À1 . PHEMA-g-(linear PEI-b-PEG)/pDNA complexes
were internalized by BT474 cells to a greater extent than PEI25K/DNA
complexes at the same ratio (N:P ¼ 10) and led to a higher transfection efficiency
in a variety of cell lines.
Polyelectrolyte Complexes of DNA and Polycations as Gene Delivery Vectors
161