Journal of Biomaterials and Nanobiotechnology, 2011, 2, 622-625
doi:10.4236/jbnb.2011.225074 Published Online December 2011 (http://www.scirp.org/journal/jbnb)
A Novel Targeting Drug Delivery System Based on
Self-Assembled Peptide Hydrogel
Liang Liang1*, Jun Yang1, Qinghua Li1, Ming Huo1, Fagang Jiang2, Xiaoding Xu3,
Xianzheng Zhang3
1Department of Ophthalmology, The First College of Clinical Medical Science, China Three Gorges University, Yichang, China;
2Department of Ophthalmology, Union Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan,
China; 3Key Laboratory of Biomedical Polymers of Ministry of Education & Department of Chemistry, Wuhan University, Wuhan,
China.
Received September 12th, 2011; revised October 24th, 2011; accepted November 25th, 2011.
ABSTRACT
In the last two decades, 5-fluorouracil (5-FU) is widely used in clinica l practice to inhibit the fibrob lasts to proliferate
and improve the success rate of glaucoma-filtering surgery, but 5-FU has many toxic effects to normal ocular tissues.
The self-assembled peptide hydrogels may serve as a new class of biomaterials for applications including tissue engi-
neering and drug delivery. How to deliver 5-FU quickly and precisely to the target sites of ocular tissue by a self-as-
sembled peptide hydrogel remains unexplored. RGD (arginine-glycine-aspartic acid) sequence is cell attachment site in
extracellular matrix (ECM). Thus, If the self-assembled peptide hydrogel containing the RGD sequence that act as a
specific attachment site for the pro liferated fibroblasts adhesion could be d esigned, after integrated 5-FU, a novel tar-
geting drug delivery system will be put into practice in the future.
Keywords: Dr ug Delivery System, Self-Assembly, Filtering Surgery
1. Introduction
The success rate of glaucoma-filtering surgery unfortu-
nately has been limited by postoperative scarring [1].
Scar formation results from infiltration of fibroblasts into
damaged areas, proliferation of those fibroblasts, and
synthesis of ECM glycoproteins. For treatment of scar
formation, 5-FU was widely reported as adjunct to im-
prove surgical results by inhibiting the postoperative pro-
liferation of fibroblasts of the filtering site [2-4]. Yet, It
was reported toxic effects of 5-FU included toxicity on
the conjunctival and corneal epithelium, wound dehis-
cence, and wound leaks [2], some of which are vision
threatening [3]. If a drug delivery system could be de-
signed to specifically target the proliferated fibroblasts
after the filtering surgery, not only the success rate of
surgery will be significantly improved, but also the pos-
sible toxic effects of 5-FU to the surrounding normal
ocular tissues will be avoided eventually.
A family of peptides has been developed whose ability
to self-assemble into supramolecular hydrogel material is
directly linked to their intramolecularly folded state.
These peptides adopt random coil conformations in aque-
ous solution and are freely soluble until intramolecular
folding is triggered by the addition of a stimulus. Upon
folding, the peptides adopt a conformation conducive to
self-assembly. Assembly ultimately leads to the forma-
tion of a structurally hydrogel without the need for in-
corporation of covalent crosslinks [5]. This self-assem-
bled peptide hydrogels may serve as a new class of bio-
materials for applications including tissue engineering
and drug delivery system [6-9]. Given that the degrada-
tion products consist of the drug and amino acid, this
drug delivery system has an advantage over polymer-
based drug delivery system that generate polymer frag-
ments with heterogeneous chain lengths upon degrada-
tion that may present complex toxicity profiles [10].
The RGD sequence was discovered as cell attachment
site in ECM some 20 years ago [11], and the receptors
for these RGD sequence were identified and organized in
the integrin family. The integrin family is one of the most
important cell adhesion molecules which are found on
the cell surface that act as receptors for cell-to-cell and
cell- ECM adhesion [12-14].
Whether can we design a novel targeting drug delivery

A Novel Targeting Drug Delivery System Based on Self-Assembled Peptide Hydrogel623
system based on self-assembled peptide hydrogel which
contains the RGD peptide sequence that act as a specific
receptor for the proliferated fibroblasts adhesion?
We hypothesized that a novel peptide containing a
bioactive RGD sequence was designed and prepared.
When dissolving the peptide in distilled water, a su-
pramolecular hydrogel with nanofibers was formed
through the self-assembly of the peptide. In addition, this
self-assembled peptide hydrogel could integrate 5-FU
into its nanofibers during the process of self-assembly of
the peptide. The proliferated fibroblasts can be attached
in the peptide hydrogel through the recognition of the
RGD sequence, and 5-FU is delivered to the fibroblasts
by this model of targeting of drugs (Figure 1).
In the past decade, hydrogels formed from self-as-
sembled proteins or peptides have attracted considerable
attention. Unlike the conventional polymeric hydrogels
that are made of covalently crosslinked polymers, pro-
tein- or peptide- based hydrogel is composed of peptide
molecules that self-assemble from aqueous solution into
cylindrical nanofibers that display bioactive epitopes on
their surfaces [15]. The bioactive epitopes could be rec-
ognized by some receptors on cell surface, allowing cell
adhesion to self-assembled peptide hydrogel [14]. In ad-
dition, this self-assembled peptide hydrogel forms a net-
work of nanofibers that are similar in scale to the natural
ECM and therefore provides an “in vivo” environment
for cell growth, migration, and differentiation [5]. Actu-
ally, much recent effort has been focused on the synthe-
sis of short peptides to create a new generation of
self-assembled materials for the use in biomedical appli-
cations. One of the well studied short peptides is the
build block comprising of a specific peptide sequence
Figure 1. The novel model of targeting of drug based on
peptide hydrogel with nanofibers.
and a hydrophobic aromatic tail such as the popular
N-Fluorenyl-9-methoxycarbonyl (FMOC) group, which
has an ability to self-assemble into hydrogel by taking
advantage of π-π stacking interactions [16,17].
Based on this point, a novel peptide containing a bio-
active RGD sequence and FMOC tail could be synthe-
sized and the corresponding hydrogel formed subse-
quently. The specific experiments include the peptide
synthesis and peptide hydrogels preparation.
The peptide was synthesized manually in 1.98 mmol
scale on the 2-chlorotrityl chloride resin employing a
standard FMOC solid phase peptide synthesis (SPPS)
method. Before the reaction, the resin was washed with
CH2Cl2 (three times) and DMF (three times) and then
immersed in DMF for 30 min. After draining off DMF
solution, a DMF solution of the mixture of FMOC pro-
tected amino acid (4 equiv relative to resin loading) and
DiEA (6 equiv) was added to the resin and shaken for 2 h
at room temperature. After removing the reaction solu-
tion, the resin was washed with DMF (three times). Sub-
sequently, 20% piperdine/DMF (V/V) solution was in-
troduced to the resin to remove the FMOC protected
groups. After shaking for 30 min at room temperature,
the reaction solution was drained off and the resin was
washed with DMF (three times). The presence of free
amino groups was indicated by a blue color in the Kaiser
test. Thereafter, a DMF solution of the mixture of FMOC
protected amino acid (4 equiv), HBTU (4 equiv), HOBt
(4 equiv) and DiEA (6 equiv) was added. After shaking
for 1.5 h at room temperature, the reaction solution was
drained off and the resin was washed with DMF (three
times). The absence of free amino groups was indicated
by a yellow color in the Kaiser test. After repetition of
the deprotection and acylation reaction, the resin was
finally washed with DMF (three times) and CH2Cl2
(three times) and dried under vacuum for 24 h. Cleavage
of the expected peptide and the removal the protected
groups of side chains from the dried resin were per-
formed using a mixture of TFA, deionized water, and
TIS in the ratio of 95:2.5:2.5. After 2 h shaking at room
temperature, the cleavage mixture and three subsequent
TFA washing were collected. The combined solution was
concentrated to a viscous solution by rotary evaporation.
Cold ether was added to precipitate the product. After
washing with cold ether (five times) to remove TFA re-
sidual, the precipitate was dissolved in distilled water and
then freeze-dried under vacuum for 3 days. The obtained
crude products were purified by high-pressure liquid
chromatography (HPLC) with a C18 column and using a
linear gradient of acetonitrile and DI water containing
0.1% TFA. IR: ~3470 cm amide A band, ~1657 cm−1
amide I band, ~1558 cm−1 amide II band; ESI-MS:
1009.4, found: 1008.4 (M-H)-.

A Novel Targeting Drug Delivery System Based on Self-Assembled Peptide Hydrogel 624
After peptide synthesis, peptide was well dissolved in
ultra purified water to form 1.5 wt% peptide solution and
subsequently filtrated for the sterilization. After placing
at room temperature for 30 min, a well defined peptide
hydrogel appeared based on the self-assembly of the pep-
tide molecules.
Simultaneously, it is possible to design this kind of
novel peptide containing a bioactive RGD sequence to
specifically bind the fibroblasts due to the expression of
high level of 1 integrin in proliferated fibroblastsɑ [18].
Because hydrogels have been widely applied as intelli-
gent carriers in controlled drug delivery systems [19-21],
5-FU could be integrated into this self-assembled peptide
hydrogel and released upon enzyme-mediated hydrogel
degradation [10].
Currently, filtration surgery has been recognized as a
standard therapy for glaucoma, which involves generat-
ing a filtration fistula to allow the escape of aqueous
humor to reduce the intraocular pressure (IOP). The suc-
cess rate of glaucoma filtration surgery is limited by the
postoperative scarring formation. The scarring formation
is usually attributed to the proliferation of fibroblasts at
the surgical site after glaucoma filtering surgery, leading
to the scleral flap fibrosis and eventual filtration failure.
In the case of evaluation of effect of this novel targeting
drug delivery system in filtering surgery of rabbit eye,
we chose the clinical observation and pathology analysis
that could test the decrease amount of intraocular pres-
sure, the duration of bleb, the present of filtration fistula
and the proliferated status of fibroblasts in surgical site.
After administrating this self-assembled peptide hy-
drogel containing 5-FU in filtering surgery intraopera-
tively, the success rate of surgery will be improved by a
localized and targeting delivery of a very small yet effi-
cient amount of the antifibroblastic agent 5-FU, offering
potential benefits to decrease the toxic side effects in
patients who are at high risk of failed filtering surgery.
2. Conflicts of In t e r e st S t a t e m e nt
The authors have no conflict of interests.
3. Acknowledgements
Financial support was obtained from National Natural
Science Foundation of China (30772382, 50633020) and
National Key Basic Research Program of China
(2005CB623903).
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