If not the duration, this could be a positive effect of the disulfide bond or the lower M w .
Except for SS-PA-EDA, these poly(amidoamine)s showed comparable or slightly
higher buffering capacities than branched PEI of 25 kDa. Similar results as for poly
(amidoamine)s with pendant primary amines concerning DNA retardation in gel
electrophoresis were obtained with the best polymer, SS-PA-TEPA (N:P ¼ 2).
All these polycations condensed pDNA in a similar manner as regards the diameter
of the polyplexes (<150 nm). The polyplexes of the SS-PA bearing secondary
amines in their side chain (SS-PA-DETA, SS-PA-TETA, and SS-PA-TEPA)
induced relatively high transfections, but those of SS-PA-EDA with only a terminal
primary amino group in the side chain gave only low transfection efficiency,
reinforcing the idea that a minimum chain length is needed and/or the presence of
secondary amines and higher buffering capacities of the polymers, suggesting a
more facilitated endosomal escape of their polyplexes. Enlargement of the alkyl
spacer between the amino groups in the side chain from ethylene to propylene
(SS-PA-NSpm and SS-PA-Spm) had a negative effect on transfection efficiency.
The reason was unclear given that polyplex size, surface charge, and buffering
capacity did not deviate significantly from the other SS-PA. This could be due to
their inherent cytotoxicity.
PDMAEMA and Derivatives
Poly[2-(dimethylamino)ethyl methacrylate] (PDMAEMA) is usually used as
weak polyelectrolyte for gene delivery and has the additional property of being
temperature sensitive [140, 141]. The study by Stolnik and coworkers on
PDMAEMA (Fig. 7a) emphasized the condensation behavior of PDMAEMA as a
function of pH [102]. As can be intuitively understood, the ionization of
PDMAEMA increases from pH 8 (only 24% ionization) to pH 4 (polycation nearly
completely ionized), therefore the binding of PDMAEMA with DNA is tighter
(EtBr displacement assay) at lower pH, which is “counterproductive” when it
comes to release of the genetic material. But, this effect is balanced by its buffering
capacity via the tertiary amine groups, which is favorable for endosomal escape.
PDMAEMA of various molecular weights were tested by the group of
Hennink for their transfection efficiency [142]. In COS-7 and OVCAR-3 cells,
high molecular weight polymers (M w < 300 kDa) were more efficient in transfection than the low molecular weight polymers (M w < 60 kDa), which was related to
their property as condensing agents. Low molecular weight polymers led to
polyplexes with sizes bigger than 300 nm (up to 1 μm), while high molecular
weight polymers gave polyplexes with sizes in the range 150–200 nm, and these
smaller particles seemed to enter the cells more easily.
PDMAEMA and its derivatives PDMAPMAm, PDMAPMA, PDMAEMAm,
and PTMAEMA of higher molecular weight (M n > 25 kDa) than in the first
study or of comparable molecular weight in the case of PDMAEA and PDEAEMA
(M n < 10 kDa) (Fig. 7b–e) were studied by Hennink and colleagues [143]. The
methacrylate/methacrylamide derivatives of PDMAEMA of high molecular
weight were able to condense pDNA, yielding polyplexes with sizes of
Polyelectrolyte Complexes of DNA and Polycations as Gene Delivery Vectors
141
Except for SS-PA-EDA, these poly(amidoamine)s showed comparable or slightly
higher buffering capacities than branched PEI of 25 kDa. Similar results as for poly
(amidoamine)s with pendant primary amines concerning DNA retardation in gel
electrophoresis were obtained with the best polymer, SS-PA-TEPA (N:P ¼ 2).
All these polycations condensed pDNA in a similar manner as regards the diameter
of the polyplexes (<150 nm). The polyplexes of the SS-PA bearing secondary
amines in their side chain (SS-PA-DETA, SS-PA-TETA, and SS-PA-TEPA)
induced relatively high transfections, but those of SS-PA-EDA with only a terminal
primary amino group in the side chain gave only low transfection efficiency,
reinforcing the idea that a minimum chain length is needed and/or the presence of
secondary amines and higher buffering capacities of the polymers, suggesting a
more facilitated endosomal escape of their polyplexes. Enlargement of the alkyl
spacer between the amino groups in the side chain from ethylene to propylene
(SS-PA-NSpm and SS-PA-Spm) had a negative effect on transfection efficiency.
The reason was unclear given that polyplex size, surface charge, and buffering
capacity did not deviate significantly from the other SS-PA. This could be due to
their inherent cytotoxicity.
PDMAEMA and Derivatives
Poly[2-(dimethylamino)ethyl methacrylate] (PDMAEMA) is usually used as
weak polyelectrolyte for gene delivery and has the additional property of being
temperature sensitive [140, 141]. The study by Stolnik and coworkers on
PDMAEMA (Fig. 7a) emphasized the condensation behavior of PDMAEMA as a
function of pH [102]. As can be intuitively understood, the ionization of
PDMAEMA increases from pH 8 (only 24% ionization) to pH 4 (polycation nearly
completely ionized), therefore the binding of PDMAEMA with DNA is tighter
(EtBr displacement assay) at lower pH, which is “counterproductive” when it
comes to release of the genetic material. But, this effect is balanced by its buffering
capacity via the tertiary amine groups, which is favorable for endosomal escape.
PDMAEMA of various molecular weights were tested by the group of
Hennink for their transfection efficiency [142]. In COS-7 and OVCAR-3 cells,
high molecular weight polymers (M w < 300 kDa) were more efficient in transfection than the low molecular weight polymers (M w < 60 kDa), which was related to
their property as condensing agents. Low molecular weight polymers led to
polyplexes with sizes bigger than 300 nm (up to 1 μm), while high molecular
weight polymers gave polyplexes with sizes in the range 150–200 nm, and these
smaller particles seemed to enter the cells more easily.
PDMAEMA and its derivatives PDMAPMAm, PDMAPMA, PDMAEMAm,
and PTMAEMA of higher molecular weight (M n > 25 kDa) than in the first
study or of comparable molecular weight in the case of PDMAEA and PDEAEMA
(M n < 10 kDa) (Fig. 7b–e) were studied by Hennink and colleagues [143]. The
methacrylate/methacrylamide derivatives of PDMAEMA of high molecular
weight were able to condense pDNA, yielding polyplexes with sizes of
Polyelectrolyte Complexes of DNA and Polycations as Gene Delivery Vectors
141