PyEG 11% ) (Fig. 10c-R 1 ) [161], primary amine in P(DMAEG 85% -co-AEG 15%
(Fig. 10e-R 1 ), imidazole in P(DMAEG-co-HisG) (Fig. 10e-R 2 ), and ethylguanidine
in P(DMAEG 83% -co-AgmG 17%) (Fig. 10e-R 3 ) [162] and compared them with
PDMAEG and P(DEAEG 67% -co-LLys 33% ) (Fig. 10b) [161] as well as with PHisG
(Fig. 10d) and poly[(histamino-L-glutamine) 73% -co-(agmatino-L-glutamine) 27% ]
(P(HisG-co-AgmG); Fig. 10f) [162]. The mass per charge for all the copolymers
was in the range 222–290 Da. The highest condensations (EtBr) were obtained
for PDMAEG and P(DEAEG-co-LLys) compared to P(DMAEG-co-PyEG) and
P(DMAEG-co-Glu) (but all gave <50% EtBr fluorescence), respectively, because
of the highest percentage of tertiary amines among the PDMAEG derivatives and the
presence of the primary amines of PLL [161]. All the copolymers were degradable
under biologically relevant conditions in a time frame varying from hours to days,
and formed polyplexes with DNA with a diameter <100 nm. The most potent
polymers in transfection studies in HEK293 cells were the polymers containing
pyridine and acid groups (by a factor of ten) and not PDMAEG or P(DEAEG-coLLys) [162]. The explanation for the better performances of the pyridine derivatives
was not clear, given that the pyridine moiety did not provide extra buffering capacity.
The potency of the polymers containing a carboxylic acid group could be because it
eventually destabilized the cell membranes in its carboxylate form.
Polymers containing more than 70% imidazole were not able to condense DNA
(>50% EtBr fluorescence), i.e., PHisG, P(HisG 73% -co-Agm 27% ), or the copolymers
from the P(DMAEG-co-HisG) series [162]. PDMAEG, P(DMAEG 85% -co-AEG 15% ),
P(DMAEG 82% -co-HisG 18% ), and P(DMAEG 64% -co-HisG 36% ) all possessed a similar charge ratio, causing 50% reduction of EtBr fluorescence (+/À around 0.8), and
this value increased with increasing imidazole content; P(DMAEG 84% -coAgmG 16% ) showed a higher value than P(DMAEG 85% -co-AEG 15% ). According
to the authors, this might be due to the longer distance between the charged
guanidine group and the main polymer chain in comparison with the polymers
containing tertiary and primary amines, resulting in a weaker electrostatic interaction between the polymer and the DNA. On the same line, the smallest complexes
were formed with P(DMAEG 85% -co-AEG 15% ), probably because of the primary
amines that allow a better interaction with the DNA in comparison with the tertiary
amines (less steric hindrance, higher protonation degree). PHisG and P(His 73% -coAgmG 27% ) formed the largest complexes. In the case of pHisG, the large size could
be due to the weak interaction between the polycation and the DNA (few imidazole
functions are protonated). The large complexes formed with P(His 73% -coAgmG 27% ) could be explained by the fact that the zeta potential of the complexes
was close to neutrality, leading to aggregation of the complexes. All the polyplexes,
except those based on P(HisG 73% -co-AgmG 27% ), had low transfection efficiency
in COS-1 cells, which could be due to their poor ability to interact with the
membrane of the cells and thus the polyplexes were not taken up by the cells
[163]. On the other hand, polyplexes based on PHisG 73% -co-PAgmG 27% (more
cytotoxic) at a ratio of 8:1 were more efficient than PEI-DNA at a ratio of 2:1,
which may be due to the presence of the guanidine functions (more pronounced
148
A. Bertin
(Fig. 10e-R 1 ), imidazole in P(DMAEG-co-HisG) (Fig. 10e-R 2 ), and ethylguanidine
in P(DMAEG 83% -co-AgmG 17%) (Fig. 10e-R 3 ) [162] and compared them with
PDMAEG and P(DEAEG 67% -co-LLys 33% ) (Fig. 10b) [161] as well as with PHisG
(Fig. 10d) and poly[(histamino-L-glutamine) 73% -co-(agmatino-L-glutamine) 27% ]
(P(HisG-co-AgmG); Fig. 10f) [162]. The mass per charge for all the copolymers
was in the range 222–290 Da. The highest condensations (EtBr) were obtained
for PDMAEG and P(DEAEG-co-LLys) compared to P(DMAEG-co-PyEG) and
P(DMAEG-co-Glu) (but all gave <50% EtBr fluorescence), respectively, because
of the highest percentage of tertiary amines among the PDMAEG derivatives and the
presence of the primary amines of PLL [161]. All the copolymers were degradable
under biologically relevant conditions in a time frame varying from hours to days,
and formed polyplexes with DNA with a diameter <100 nm. The most potent
polymers in transfection studies in HEK293 cells were the polymers containing
pyridine and acid groups (by a factor of ten) and not PDMAEG or P(DEAEG-coLLys) [162]. The explanation for the better performances of the pyridine derivatives
was not clear, given that the pyridine moiety did not provide extra buffering capacity.
The potency of the polymers containing a carboxylic acid group could be because it
eventually destabilized the cell membranes in its carboxylate form.
Polymers containing more than 70% imidazole were not able to condense DNA
(>50% EtBr fluorescence), i.e., PHisG, P(HisG 73% -co-Agm 27% ), or the copolymers
from the P(DMAEG-co-HisG) series [162]. PDMAEG, P(DMAEG 85% -co-AEG 15% ),
P(DMAEG 82% -co-HisG 18% ), and P(DMAEG 64% -co-HisG 36% ) all possessed a similar charge ratio, causing 50% reduction of EtBr fluorescence (+/À around 0.8), and
this value increased with increasing imidazole content; P(DMAEG 84% -coAgmG 16% ) showed a higher value than P(DMAEG 85% -co-AEG 15% ). According
to the authors, this might be due to the longer distance between the charged
guanidine group and the main polymer chain in comparison with the polymers
containing tertiary and primary amines, resulting in a weaker electrostatic interaction between the polymer and the DNA. On the same line, the smallest complexes
were formed with P(DMAEG 85% -co-AEG 15% ), probably because of the primary
amines that allow a better interaction with the DNA in comparison with the tertiary
amines (less steric hindrance, higher protonation degree). PHisG and P(His 73% -coAgmG 27% ) formed the largest complexes. In the case of pHisG, the large size could
be due to the weak interaction between the polycation and the DNA (few imidazole
functions are protonated). The large complexes formed with P(His 73% -coAgmG 27% ) could be explained by the fact that the zeta potential of the complexes
was close to neutrality, leading to aggregation of the complexes. All the polyplexes,
except those based on P(HisG 73% -co-AgmG 27% ), had low transfection efficiency
in COS-1 cells, which could be due to their poor ability to interact with the
membrane of the cells and thus the polyplexes were not taken up by the cells
[163]. On the other hand, polyplexes based on PHisG 73% -co-PAgmG 27% (more
cytotoxic) at a ratio of 8:1 were more efficient than PEI-DNA at a ratio of 2:1,
which may be due to the presence of the guanidine functions (more pronounced
148
A. Bertin