HUVEC cells after repeated administration compared to linear PEI (22 kDa) and
PGlu-DETA (Fig. 5b) that are non-biodegradable. Among polyaspartamides
modified with oligoethyleneimine side chains of various lengths [ethylene diamine
(PAsp-EDA) in Fig. 5c, and triethylene pentamine (PAsp-TEPA), pentaethylene
hexamine (PAsp-PEHA), and polyethyleneimine (PAsp-PEI) in Fig. 5d] [135],
PAsp-PEHA showed the highest capacity of condensation, similar to PAsp-PEI
(diameter <300 nm), while PAsp-EDA showed the lowest DNA condensation
capacity. Full retardation of DNA migration occurred at N:P ¼ 1:1 for PAspTEPA, PAsp-PEHA, and PAsp-PEI, and only at 5:1 for PAsp-EDA. This trend
was also observed for the transfection efficiency in HEK293 cells, meaning that the
length of oligoethyleneimine side chains is an important factor and that a side chain
with four ethylene imine repeating units was enough for condensation. Similar
polyaspartamide derivatives (α,β-poly[(N-2-hydroxyethyl)-D,L-aspartamide]) but
with spermine side chains (and not oligoethylene imine) were studied by the
group of Cavallaro, i.e., α,β-poly[(N-2-hydroxyethyl)-D,L-aspartamide] modified
with spermine (PHEA-Spm) (Fig. 5e) and α,β-poly[(N-2-hydroxyethyl)-D,Laspartamide] modified with spermine-butyramide (PHEA-Spm-C 4 ) (Fig. 5f)
[136]. In this case, full retardation of DNA migration was observed at C:
P ¼ 0.75 for PHEA-Spm and 2 for Spm-C 4 . The zeta-potential values became
positive at a polycation:DNA weight ratio above 1.5 for PHEA-Spm, and 2.5 for
PHEA-Spm-C 4 . These values are in agreement with the lower amount of free
primary amino groups present in PHEA-Spm-C 4 compared with PHEA-Spm.
A nearly total quenching of EtBr was reached at C:P ¼ 8 for PHEA-Spm, and
at 10 for Spm-C 4 , but at the same time the condensing ability of PHEA-Spm-C 4
was superior to that of PHEA-Spm; at C:P ¼ 1 the polyplex diameter was 600 nm
for PHEA-Spm and 130 nm for PHEA-Spm-C 4 . It seems that the introduction of
a short hydrophobic chain in the structure enabled an increased condensing
capacity, probably conferred by hydrophobic interactions with DNA, which in
turn led to a decrease in transfection efficiency, which could be due to the stability
of the polyplex (even if EtBr displacement shows equivalent performances).
Other Polyamide Backbones
Poly(amidoamine)s with pendant primary amines [amino ethane (PA-AE), amino
butane (PA-AB), and amino hexane (PA-AH)] (Fig. 6a) [137] all had a better
buffering capacity than branched PEI of 25 kDa. Those with the longest alkyl
chains had higher buffering capacity than PA-AE in the pH range 5–7, which is
important for endosomal release. Cytotoxicity in 293T and COS-7 cells was
concentration dependent and proportional to the length of the alkyl chain: the
longer the chain, the more toxic. As in the case of polyaspartamide modified with
oligoethyleneimine side chains of various lengths [135], the shortest chain showed
the lowest condensation capacity (even if no secondary amines were present in the
side chains of these poly(amidoamine)s with pendant primary amines). This
suggests that the condensation capacity (size of the polyplex) was mainly a function
of the accessibility and degree of protonation of the primary and tertiary amines.
Polyelectrolyte Complexes of DNA and Polycations as Gene Delivery Vectors
139
PGlu-DETA (Fig. 5b) that are non-biodegradable. Among polyaspartamides
modified with oligoethyleneimine side chains of various lengths [ethylene diamine
(PAsp-EDA) in Fig. 5c, and triethylene pentamine (PAsp-TEPA), pentaethylene
hexamine (PAsp-PEHA), and polyethyleneimine (PAsp-PEI) in Fig. 5d] [135],
PAsp-PEHA showed the highest capacity of condensation, similar to PAsp-PEI
(diameter <300 nm), while PAsp-EDA showed the lowest DNA condensation
capacity. Full retardation of DNA migration occurred at N:P ¼ 1:1 for PAspTEPA, PAsp-PEHA, and PAsp-PEI, and only at 5:1 for PAsp-EDA. This trend
was also observed for the transfection efficiency in HEK293 cells, meaning that the
length of oligoethyleneimine side chains is an important factor and that a side chain
with four ethylene imine repeating units was enough for condensation. Similar
polyaspartamide derivatives (α,β-poly[(N-2-hydroxyethyl)-D,L-aspartamide]) but
with spermine side chains (and not oligoethylene imine) were studied by the
group of Cavallaro, i.e., α,β-poly[(N-2-hydroxyethyl)-D,L-aspartamide] modified
with spermine (PHEA-Spm) (Fig. 5e) and α,β-poly[(N-2-hydroxyethyl)-D,Laspartamide] modified with spermine-butyramide (PHEA-Spm-C 4 ) (Fig. 5f)
[136]. In this case, full retardation of DNA migration was observed at C:
P ¼ 0.75 for PHEA-Spm and 2 for Spm-C 4 . The zeta-potential values became
positive at a polycation:DNA weight ratio above 1.5 for PHEA-Spm, and 2.5 for
PHEA-Spm-C 4 . These values are in agreement with the lower amount of free
primary amino groups present in PHEA-Spm-C 4 compared with PHEA-Spm.
A nearly total quenching of EtBr was reached at C:P ¼ 8 for PHEA-Spm, and
at 10 for Spm-C 4 , but at the same time the condensing ability of PHEA-Spm-C 4
was superior to that of PHEA-Spm; at C:P ¼ 1 the polyplex diameter was 600 nm
for PHEA-Spm and 130 nm for PHEA-Spm-C 4 . It seems that the introduction of
a short hydrophobic chain in the structure enabled an increased condensing
capacity, probably conferred by hydrophobic interactions with DNA, which in
turn led to a decrease in transfection efficiency, which could be due to the stability
of the polyplex (even if EtBr displacement shows equivalent performances).
Other Polyamide Backbones
Poly(amidoamine)s with pendant primary amines [amino ethane (PA-AE), amino
butane (PA-AB), and amino hexane (PA-AH)] (Fig. 6a) [137] all had a better
buffering capacity than branched PEI of 25 kDa. Those with the longest alkyl
chains had higher buffering capacity than PA-AE in the pH range 5–7, which is
important for endosomal release. Cytotoxicity in 293T and COS-7 cells was
concentration dependent and proportional to the length of the alkyl chain: the
longer the chain, the more toxic. As in the case of polyaspartamide modified with
oligoethyleneimine side chains of various lengths [135], the shortest chain showed
the lowest condensation capacity (even if no secondary amines were present in the
side chains of these poly(amidoamine)s with pendant primary amines). This
suggests that the condensation capacity (size of the polyplex) was mainly a function
of the accessibility and degree of protonation of the primary and tertiary amines.
Polyelectrolyte Complexes of DNA and Polycations as Gene Delivery Vectors
139