Bioorganic & Medicinal Chemistry Letters
TACN-based cationic lipids with amino acid backbone and double
tails: Materials for non-viral gene delivery
⇑
⇑
Bing Wang, Wen-Jing Yi, Ji Zhang , Qin-Fang Zhang, Miao-Miao Xun, Xiao-Qi Yu
Key Laboratory of Green Chemistry and Technology (Ministry of Education), College of Chemistry, Sichuan University, Chengdu 610064, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Cationic lipids have become an efficient type of non-viral vectors for gene delivery. In this Letter, four cat-
ionic lipids containing 1,4,7-triazacyclononane (TACN) headgroup, glutamic/aspartic acid backbone and
dioleyl tails were designed and synthesized. The TACN headgroup gives these lipids excellent pH buffer-
ing capacities, which were higher than branched 25 kDa PEI. Cationic liposomes prepared from these lip-
ids and DOPE showed good DNA affinity, and full DNA condensation was found at N/P ratio of 3 via
agarose gel electrophoresis. The lipoplexes were characterized by dynamic light scattering (DLS) assay,
which gave proper particle sizes and zeta-potentials for transfection. In vitro gene transfection results
in two cell lines reveal that TAN (with aspartic acid and amide bond in the structure) shows the best
transfection efficiency, which is close to commercially available transfection agent Lipofectamine 2000.
Ó 2014 Elsevier Ltd. All rights reserved.
Received 11 November 2013
Revised 14 January 2014
Accepted 12 February 2014
Available online 22 February 2014
Keywords:
Triazacyclononane
Cationic lipids
Gene delivery
Transfection
In the past two decades, gene therapy has shown promising po-
tential to the treatment of a wide range of human diseases such as
headgroups always have one or more nitrogen atoms possessing
positive charges which trigger their interaction with negatively
charged DNA through electrostatic attraction, leading to DNA con-
1
–4
cancer, viral infection, AIDS and cardiovascular diseases.
In or-
1
4
der to smoothly transport therapeutic genes into cells, viral and
non-viral vectors were developed as two major types of carriers
used in vitro and in vivo. Although viral vectors have higher trans-
fection efficiency (TE), their clinical applications are limited owing
to safety concerns such as undesirable immune response, risk of
tumorigenesis and insertional mutagenesis.5 On the other hand,
a number of works involving non-viral gene delivery systems, such
as cationic lipids having one or two hydrophobic tails, polycations,
dendrimers and histones, were carried out. Results demonstrate
densation.
Among the headgroups, 1,4,7-triazacyclononane
(TACN) is a novel and unique one including three amine groups
1
5
with different pK
a
values. The amine with pK
a
of ꢀ11 has strong
basicity, and it is well protonated under physiological conditions.
This may benefit its affinity with electron-negative DNA via elec-
trostatic interactions. Meanwhile, more significantly, the amine
,6
with pK
a
of ꢀ6.5 may have good endosome pH buffering capacity.
At physiological pH, most of the amines with this pK
a
remain
unprotonated. After endocytosis, they would be protonated under
such more acidic environment, leading to endosomal swelling
and release of lipoplexes, and avoiding lysosomal trafficking and
degradation. This ‘proton sponge’ theory has gained widespread
acceptance despite challenges to the hypothesis.
that non-viral gene delivery may be a potential approach for the
treatment of genetic diseases.7
–11
Among various types of synthe-
sized vectors, cationic lipids can effectively compact DNA by form-
ing lipoplexes, leading to gene transfection without triggering any
adverse immune response.12 Compared with other non-viral vec-
tors, cationic lipids are also favored for many advantages such as
structural simplicity and ease of production, good repeatability
As a natural and biocompatible unit, amino acids were used as
building block in the design of cationic lipids. Kim et al. prepared a
series of cationic lipids containing lysine headgroup and aspartate
1
3
16
and biocompatibility. It is of great importance to further develop
efficient lipidic non-viral vectors, and clarify their structure–activ-
ity relationships.
backbone that gave efficient TE and reduced cytotoxicity. They
subsequently replaced aspartate moiety with glutamate and
1
7
obtained better TE. Takeoka and co-workers also synthesized
several lipids having a glutamate backbone and different amino
acids headgroup such as lysine, histidine, or arginine. Some of
them exhibited higher TE than Lipofectamine 2000.18 For the
hydrophobic groups, on the other hand, numerous efficient cat-
Cationic lipids are amphiphilic molecules and generally consist
of three parts: a hydrophobic domain, a hydrophilic headgroup,
and a spacer backbone between above two parts. The hydrophilic
1
9
20
21
ionic lipids such as DOTMA, DOTAP and DOSPA bear oleyl
tails. Many reports
2
2,23
⇑
also found that lipids with dioleyl tails
might give higher TE than those with other aliphatic chains.
960-894X/Ó 2014 Elsevier Ltd. All rights reserved.
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