Transdermal Gene Delivery by Functional Peptide Conjugated Cationic Gold Nanoparticle Reverses the Progression and Metastasis of Cutaneous Melanoma

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Transdermal Gene Delivery by Functional Peptide-Conjugated
Cationic Gold Nanoparticle Reverses the Progression and Metastasis
of Cutaneous Melanoma
Jie Niu,
†
Yang Chu,
†
Yan-Fen Huang,
†
Yee-Song Chong,
†
Zhi-Hong Jiang,
‡
Zheng-Wei Mao,
§
Li-Hua Peng,*
,†,‡
and Jian-Qing Gao*
,†
†
Institute of Pharmaceutics, College of Pharmaceutical Sciences, Zhejiang University, Hangzhou 310058, P. R. China
‡
State Key Laboratory of Quality Research in Chinese Medicine, Macau University of Science and Technology, Macau, P. R. China
§
MOE Key Laboratory of Macromolecular Synthesis and Functionalization, Department of Polymer Science and Engineering,
Zhejiang University, Hangzhou 310027, P. R. China
ABSTRACT: Permeability barrier imposed by stratum corneum makes an
extreme challenge for the topical delivery of plasmid DNA (pDNA), which is
widely used in gene therapy. Existing techniques to overcome the skin
barrier for bio-macromolecules delivery rely on sophisticated mechanical
devices. It is still a big challenge to treat the skin cancer, for example,
melanoma, that initiates in the dermal layer by topical gene therapy. To
facilitate the skin penetration of pDNA deeply into the melanoma tissues, we
here present a cell-penetrating peptide and cationic poly(ethyleneimine)
conjugated gold nanoparticle (AuPT) that can compact the pDNAs into
cationic nanocomplexes and penetrate through the intact stratum corneum
without any additional enhancement used. Moreover, the AuPT is highly
efficient in stimulating the intracellular uptake and nuclear targeting of the
pDNAs in cells, which guarantees the effective transfection. This study
provides evidence that penetrating peptide conjugated cationic gold
nanoparticle offers a promising vehicle for both the skin penetration and transfection of pDNAs, possessing great potential in
topical gene therapy.
KEYWORDS: stratum corneum penetration, plasmid DNA, cationic gold nanoparticle, cell-penetrating peptide, melanoma
1. INTRODUCTION
Existing techniques to overcome the skin barrier for topical
delivery of bio-macromolecules, like plasmid DNA (pDNA)
and protein, rely on sophisticated mechanical devices,
1
such as
the ultrasonic apparatus,
2
iontophoresis,
3
microneedles, and
electroporation.
4
Recently, the utilization of nanoparticles in
biomedicine holds great potential for topical drug delivery.
5,6
However, most reported topical strategies with nanoparticles
still require the combination of photoinducement, thermal
ablation, or magnetism to enhance the skin penetration
efficiency
7,8
so as to induce significant therapeutic effects.
9,10
Bio-macromolecules are usually hydrophilic with large size and
will be mostly blocked by skin. Zheng et al. have recently
reported the topical delivery of siRNA as effective treatment for
skin melisma,
11,12
which reminded us of the potential of topical
gene therapy for cutaneous melanoma. As we know, pDNAs are
frequently utilized in gene therapy because of their higher
stability than that of SiRNA, MicroRNA, and DNA.
13,14
However, until now, topical delivery of pDNAs for the
cutaneous melanoma treatment has never been reported
elsewhere.
Contributing to their small size, general nontoxicity, ease of
functionalization, and high surface-to-volume ratio, gold
nanoparticles caused increasing attention from nonviral gene
delivery and therapy. Recently, Conde et al. investigated gold
nanoparticles (AuPT)-based triple-combination therapy, con-
sisting of therapeutic gene, drugs, and photo-based treatments.
The triple-combination therapy was demonstrated to efficiently
inhibit tumor regression and reversed disease-specific traits to
prompt selective and personalized therapies for colon cancer.
15
In another study, unimer polyion complex (uPIC) was
conjugated on the gold nanoparticles surface. The intravenous
injection of uPIC-AuNPs carrying siRNA significantly
enhanced the accumulation and penetration of siRNA into
solid tumor with longer blood circulation.
16
Researchers also
invented the first example of reversible ligation of DNA on gold
nanoparticles. This conjugation can protect the DNA from
degradation, and the DNAs can be reversibly released by using
light as an external stimulus, which could potentially be widely
utilized in drug delivery, catalysis, sensing, and photonics.
17
All
this evidence reminded us of the great application potential of
gold nanoparticles in gene therapy.
Received: December 21, 2016
Accepted: March 2, 2017
Published: March 2, 2017
Research Article
www.acsami.org
© XXXX American Chemical Society ADOI: 10.1021/acsami.6b16378
ACS Appl. Mater. Interfaces XXXX, XXX, XXX−XXX

Cutaneous melanoma is one of the most deadly cancers in
clinic that is still lacking effective therapies.
18,19
Advanced
treatment options include chemotherapies, antiprogrammed
death-1, and targeted therapies like BRAF inhibitors.
20−22
These treatments have provided new options to treat this
deadly tumor but also cause serious side effects and easily
become drug-resistant. Gene therapy has emerged as a
promising technique for numerous tumor types. In gene
therapy, miRNA possesses the ability to regulate more than one
gene, which is different from siRNA and may change multiple
tumor-associated moleculessimultaneously.Muchmore
evidence has suggested that melanoma is characterized by
distinct molecular mutations, which provide unique oppor-
tunities for targeted therapy. Recently, microRNA-221
(miRNA-221) was identified to be abnormally expressed in
malignant melanoma cells, and it favors the induction of the
malignant phenotype through down-modulation of c-Kit
receptor and blocking p27 translation.
23
In the progression of
melanoma, up to 70% of metastases lack the c-Kit receptor and
can consequently escape c-Kit-triggered apoptosis.
24
Similarly,
p27 expression is lost during progression from benign nevi to
metastatic cells, and its reduction causes the poor survival,
25
because microRNA-based short hairpin still suffers from
limitations such as stability. DNA-based RNAi drugs, however,
have the potential of being stably introduced when used in
plasmid DNA.
26
Antisense sequence of miRNA-221 was
constructed and inserted into the plasmid to reduce the
expression of miRNA-221, based on the transfection of pDNA
into B16F10 cells. It was demonstrated that repression of p27 is
a consequence of direct binding of miRNA-221 sites in the
3′UTR.
27
It was shown that not only miR-222 but also miRNA-
221 was able to reduce viability and induce apoptosis mediated
by the KIT, AKT, and BCL2 signaling cascade.
28
MiRNA-221
has been proposed as a potential tumor suppressor for
melanoma therapy. Therefore, the inhibition of miRNA-221
expression that up-regulates the c-Kit receptor and p27 protein
is thought to be a novel treatment for advanced melanoma with
clinical translation.
29,30
Moreover, topical delivery miRNA-221
inhibitor gene can avoid or decrease reticuloendothelial system
(RES) uptake, reduce systemic toxicity, and provide targeted
gene delivery to the tumor site located at the skin subcutaneous
layer. However, stratum corneum always poses a formidable
challenge to bio-macromolecules penetration. PDNAs, because
of their large size, hydrophilic nature, and fast degradation, are
normally precluded from percutaneous absorption.
To circumvent these problems that confront the current
methods, herein, for the first time, we present a novel strategy
for the cutaneous melanoma therapy by topical delivery of a
pDNA encoded with miRNA-221 inhibitor gene through HIV-
1 twin-arginine translocation peptide (TAT) conjugated
catonic gold nanoparticles (AuPT). In this strategy, AuPT
acts as not only the topical carrier but also the gene vector for
pDNAs. TAT as a vehicle for drug delivery has been thoroughly
investigated by many studies.
31
It was shown to be non-
immunogenic, and its use in cells and animals did not elicit
toxic responses.
32
By virtue of their strong electrostatic
interaction with anionic membrane surfaces and their some-
times amphipathic nature, TAT peptides offer “interfacial
activity”defined as the ability to bind at the bilayer−water
interface and perturb membrane structure.
33
It can coopera-
tively disrupt the vertical segregation of hydrophobic and
hydrophilic groups in a bilayer and allows the passage of polar
molecules across the membrane.
34,35
On the one hand, TAT
was so suggested as a skin-permeable protein, and it has been
demonstrated to transport the attached proteins into the skin
for strong transcutaneous immunization.
36
On the other hand,
by transient plasma membrane disruption
37
or spontaneous
translocation,
38
TAT can help the bio-macromolecules bypass
Figure 1. Schematic illustration of the transdermal delivery of pDNAs encoding microRNA-221 inhibitor gene (Mi221) by AuPT nanoparticles for
skin cutaneous melanoma treatment. The therapy consists of four major steps, including (A) preparation of AuPT/Mi221 nanocomplexes; (B)
topical application of AuPT/Mi221 and the skin penetration of AuPT/Mi221; (C) skin penetration into melanoma, and (D) gene transfection of
AuPT/Mi221 in melanoma cells for tumor therapy.
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B

the endosomal degradative environment.
39−41
In our previous
study, AuPT was shown to be highly efficient in transfecting
pDNAs in both epidermal stem cells and mesenchymal stem
cells for their in vitro directed differentiation.
42,43
In the present
study, using AuPT as a multifunctional vehicle, the penetration
of pDNAs through the different skin layers and the transfection
of these pDNAs in the melanoma cells at the subcutaneous site
were investigated. Briefly, both the penetration and distribution
of the pDNAs and gold nanoparticles in the different skin layers
after the topical application of AuPT/pDNAs were studied in
vitro and in vivo. Transfection of the pDNAs encoding miRNA-
221 inhibitor gene (Mi221) by AuPT in melanoma cells and
melanoma xenograft in mice, as well as its regulation on c-Kit
and p27 genes expression of cells and tumor tissues, were
evaluated. On the basis of that, the therapeutic effects of AuPT/
Mi221 through topical application were evaluated by
investigating the tumor cell apoptosis, metastasis, and
interference in cell cycles. The histology of the tumor tissues
was also analyzed by hematoxylin and eosin (HE), Tunel, and
EdU staining (see Figure 1A−D as a schematic design).
2. EXPERIMENTAL DETAILS
2.1. Materials. Chloroauric acid (HAuCl4), sodium borohydride
(NaBH4), poly(ethelyimine) (25 kD), amiloride-HCl, chlorpromazine
(CPZ), methyl-β-cyclodextrin (MBC), 4′,6-diamidino-2-phenylindole
(DAPI), and methylthiazoletetrazolium (MTT) were purchased from
Sigma (Sigma-Aldrich, St. Louis, MO, USA). Micro-bicinchoninic acid
(BCA) protein assay kit was purchased from Beyotime Biotechnology
Inc., China. PDNA encoding luciferase (PGL3) was obtained from
Institute of Infectious Diseases, Zhejiang University, China. PDNAs
encoding GFP and miRNA-221 inhibitor genes were purchased from
Genepharma Company. TAT peptide (H-Cys-Cys-Tyr-Gly-Arg-Lys-
Lys-Arg-Arg-Gln-Arg-Arg-Arg-OH, Mw = 1559), FITC-DNA, Cy5.5-
pDNA were constructed by Sangon Biotechnology Inc., China. Four-
week-old nude mice were supplied by Shanghai SLAC Laboratory
Animal Co. Ltd., China. B16F10 cell line was purchased from the
Institute of Biochemistry and Cell Biology, Chinese Academy of
Sciences (China). Dulbecco’s modified Eagle’s medium (DMEM),
0.25 wt % trypsin with 0.02 wt % ethylenediaminetetraacetic acid, fetal
bovine serum (FBS), streptomycin, and penicillin were obtained from
Gibco BRL (USA).
2.2. Synthesis of AuPT. HAuCl4(150 μg/mL) was reduced by
NaBH4(10 mg/mL) in the presence of PEI (3 mg/mL). The reaction
solution was stirred vigorously for 15 min at room temperature and
stored for at least 1 h to get the AuP suspension. Then AuPT was
prepared by adding TAT into the AuP solution under continuous
stirring overnight. TAT peptides were mixed with AuP (100 μg/mL)
for ligand exchange, with a variable peptide concentration of 0−100
μg/mL. Excess PEI and TAT were removed by dialysis.
2.3. Characterization of AuPT and AuPT/pDNAs Nano-
complexes. To quantify the PEI amount on the AuP nanoparticles,
thermogravimetric analysis was performed for powder samples using a
TGA/SDTA851, SWRTZER LAND thermogravimetric analyzer.
Samples between 5 and 15 mg were heated from 30 to 400 °Cata
heating rate of 10 °C/min in air. TGA derivative curves show distinct
transitions for different samples between 30 and 400 °C. To quantify
the TAT amounts on the AuPT nanoparticles, micro-BCA assay was
used to detect the amount of TAT peptide on the surface of
nanoparticles.
44
Briefly, 20 μL of various AuPT aqueous samples
containing numerous amounts of peptides were added into 96-well
plates. Each well was filled with 200 μL of micro-BCA working liquid
followed by incubating them at 37 °C for 30 min. Absorbance was
measured at 570 nm by microplate spectro-photometer. TAT
concentration of the sample was determined according to the standard
curve based on protein standard solution. The concentration of AuPT
was measured by inductively coupled plasma mass spectrometry (ICP-
MS) and adjusted to 100 μg/mL. Then different volume of
nanoparticle solution was added into a persistent bulk of pDNAs
solution (100 μg/mL) to prepare AuPT/pDNAs nanocomplexes. The
mixture immediately vortexed for 15 s and incubated for 30 min at 37
°C. The morphologies of AuPT and AuPT/pDNA nanocomplexes
(1:8, w/w) were observed by a JEM-1200EX transmission electron
microscope (TEM). The polyplex diameters were measured by
dynamic light scattering (DLS) on a Brookhaven particle size analyzer
(90plus) at room temperature. An aqueous dip cell in the automatic
mode (Zetasizer 3000, Malvern Instruments, Southborough, MA) was
used to measure the zeta potential of nanoparticles. All measurements
were performed three times.
2.4. Transfection Assay. Reporter gene pDNA-PGL3 (PGL3)
was used for the transfection assay. B16F10 cells (5 ×104) were seeded
on 24-well plate. After cells reached to 80% confluence, the cultural
medium was removed, and cells were washed with phosphate-buffered
saline (PBS) twice. Each well received 0.5 mL of DMEM without FBS.
Then different groups of AuPT/PGL3 containing 1 μg of PGL3 and
various amounts of AuPT were added to cells. Cells and nano-
complexes were incubated for 6 h at 37 °C before the cultural medium
was changed by DMEM containing FBS to remove the AuPT/PGL3
nanocomplexes. The cells were incubated for another 18 h and washed
with PBS twice. A luciferase assay kit (Beyotime, China) and a
luminometer (Promega, USA) were used to measure the PGL3
luciferase intensity. BCA protein assay reagent kit was used to measure
the total protein of each well. Final results were expressed as luciferase
intensity of per milligram of total protein of the tested cells.
2.5. Cellular Uptake. B16F10 cells were seeded on 24-well plate
with DMEM containing 10% FBS. After cells were incubated overnight
reaching 80% confluence, the medium was changed by DMEM
without FBS. Then the vector/FITC-pDNAs nanocomplexes or naked
FITC-pDNAs were added to each well. Cells were incubated with
nanocomplexes for various time periods. Before measuring the cellular
uptake of FITC-pDNAs, cells were washed twice with PBS, and flow
cytometry was used to determine the mean fluorescence intensity per
cell. To directly observe the cellular uptake of nanocomplexes at
different time points, cy5.5-labeled pDNAs were used and tracked by
confocal laser scanning microscopy (CLSM). Briefly, 3 ×104 B16F10
cells were seeded on 15 mm plate and incubated overnight. Then the
cultural solution was replaced by medium without FBS. Naked cy5.5-
labeled pDNAs or their nanocomplexes with AuPT were added to the
cells and were observed at 1, 3, 6, and 9 h, respectively. After that, cells
were washed twice and incubated with 4% paraformaldehyde and
DAPI for 15 min. Finally, cells were washed with PBS three times and
observed by CLSM.
2.6. Intracellular Pathway of AuPT/pDNAs Nanocomplexes.
For the illumination of the cellular uptake mechanism, cells were
treated with 4 °C to clarify energy dependence. Pharmacological
inhibitors like 50 μM amiloride-HCl, 10 μg/mL of chlorpromazine
(CPZ), and 10 mg/mL of methyl-β-cyclodextrin (MBC) were also
utilized for the mechanism studies. Briefly, B16F10 cells were
pretreated with these inhibitors for 30 min at 37 °C. Cells were
then incubated with AuPT/GFP (pDNAs encoded with GFP)
nanocomplexes for 6 h; then, the medium was replaced by DMEM
with 10% FBS. After another culture of 18 h, mean fluorescence
intensity per cell was accessed by flow cytometry.
2.7. Analysis of in Vitro and in Vivo Gene Expression. Total
RNA was extracted from B16F10 cells or melanoma tissues using
DxGeneTM Tissue and Cell Total RNA Extraction Kit (GenePharma,
China). MiRNA-221 was quantified by Hairpin-itTM miRNAs qPCR
quantitation kit (GenePharma, China). As for the analysis of c-Kit and
P27 expression, the primers and glyceraldehyde phosphate dehydro-
genase (GAPDH) were synthesized by Sangon Biotech (Shanghai,
China). The expressions of miRNA-221, c-Kit, and P27 were detected
with the CFX-Touch PCR detection system (Bio-Rad Laboratories,
CA, USA) complying with the manufacturer’s instructions.
2.8. Antiproliferation and Apoptosis Assays. B16F10 cells
were seeded on 96-well plate at a density of 1 ×104 cells/well and
cultivated overnight. The medium was replaced by fresh Opti-MEM
medium, and 10 μL of complexes solution with different
concentrations were added to each well cultivating for 6 h. Cells
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were incubated for 18 h further. Then the medium was replaced with
DMEM containing 3-[4, 5-dimethyl-thiazolyl-2]-2, 5-diphenol tetra-
zolium bromide (MTT, Sigma; 0.5 mg/mL). After 4 h, the supernatant
was removed, and 200 μL of dimethyl sulfoxide (DMSO, Sigma) was
added to each well. Then the plate was micro-oscillated for 30 s, and
absorbance was measured at 570 nm. The cell viability was normalized
to that of only solvent-treated cells.
2.9. Cell Cycles Analysis. After B16F10 cells were transfected
with Mi221 as mentioned above, cells were collected and fixed with
70% ethanol in 4 °C overnight. After they were washed twice with
PBS, cells were mixed with 100 μL of RNase in 37 °C for 30 min.
Then 400 μL of propidium (PI) was added in 4 °C in the dark and
incubated with the cells for another 30 min. Results were determined
by flow cytometry at the wavelength of 488 nm.
2.10. Cells Migration Assay. After different groups of trans-
fection, the cell migration was tested by Transwell assay. B16F10 cells
were digested and resuspended in serum-free medium at a density of 3
×105 cells per milliliter, and 100 μL of the cell suspension was seeded
in the upper chamber. Medium containing 10% FBS was added to the
lower chamber. The chambers were incubated at 37 °C for 72 h. After
the incubation, the medium and cells remaining in the upper chamber
were removed. Finally, crystal violet (Beyotime, Shanghai, China) was
used to stain cells left on the lower side of the membrane for 20 min.
Cells were observed and counted by light microscope (Nikon, Japan).
2.11. In Vitro Skin Penetration Test. The skins of nude mice
(four weeks old) were used for in vitro penetration test with Franz
diffusion cells. Mice were anesthetized using 10% chloral hydrate, and
then the dorsal skin hair of all mice was removed using hair removal
cream. The skin was used once it was removed from mice. Skin was
cut to a suitable size and mounted on the receptor compartment of the
diffusion cell containing PBS buffer (pH 7.4). The receptor was
maintained at 37 °C and constantly stirred with a magnetic bar. The
amount of total FITC-pDNAs was 10 μg, and the ratio between
vectors to FITC-pDNAs was 1:8 (w/w). The concentration of vectors
was adjusted to 100 μg/mL. Then different vectors solution was added
into FITC-pDNAs solution (100 μg/mL), incubating for 30 min
before adding into donor cells. PBS was added to the diffusion
chamber without bubble. Vector solution loaded with FITC-pDNAs
(0.5 mL) was added to each donor cell. Samples (100 μL) were
withdrawn from diffusion chamber at different intervals (1, 3, 6, 9, and
24 h), and fresh PBS was replenished. The samples were extracted
onto 96-well solid black microplate, and then fluorescence intensity
was detected by fluorescence microplate reader. Other skin samples
that treated with FITC-pDNAs were fixed to glass coverslips and
observed by CLSM at 24 h.
2.12. Penetration and Distribution of Vector/pDNAs Nano-
complexes in Xenograft Tumor Tissue. Transdermal and
distribution of vector/pDNA in the tumor tissues were imaged with
TEM. For the TEM observation, tumor samples were washed twice
with PBS and then fixed for 1 h with 3.5% (v/v) glutaraldehyde.
Postfixation was performed for 1.5 h in 1% (v/v) osmium tetroxide at
room temperature. The samples were dehydrated in graded series of
ethanol and propylene oxide. Then the samples were embedded in
Durcupan (Fluka, Sigma-Aldrich). Thickness of section was ∼60 μm.
Sections were mounted on nickel grids and stained with uranyl acetate
before examination under a JEM-1200EX microscope.
2.13. In Vivo Transdermal Delivery of Mi221 and Anti-
Tumor Effects. Nude mice (four weeks old) were purchased from
Figure 2. (A) Weight loss of AuPT nanoparticle at 400 °C with different TAT feeding concentrations. (B) TAT contents on the AuPT
nanoparticles. (C) Diameters and polydispersity indices of the AuPT nanoparticles. (D) Zeta potentials of AuPT nanoparticles. (E) Mean
fluorescence intensity per cell (derived from the expressed GFP in transfected cells) of B16F10 cells after transfection at different TAT
concentrations, **p< 0.01. (F) Diameters of AuPT/pDNA nanocomplexes at different weight ratios of vector to pDNA.
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Shanghai SLAC Laboratory Animal Co. Ltd., China. All animal
experimental procedures were performed in obedience to guidelines
and protocols of the Animal Experimental Ethics Committee of
Zhejiang University. B16F10 cells (1 ×106)wereinoculated
subcutaneously at right flank of nude mice to set up the melanoma
model. The melanoma-bearing nude mice were then randomly divided
into six groups, and each group included six nude mice. For the
preparation of AuPT/Mi221, AuP/Mi221, and AuPT/shNC samples,
vectors were purified by dialysis to remove excess ligand molecules.
The concentrations of AuP and AuPT were adjusted to 100 μg/mL
and verified by inductively coupled plasma mass spectrometry (ICP-
MS). Vectors (12.5 μL) were added into pDNAs solution including 10
μg of pDNAs, vortexed for 15 s, and incubated for 20 min prior to
applying to the dorsal skin of the mice, under which the melanoma
xenograft existed. Nude mice were given topical treatment with AuPT/
Mi221, AuP/Mi221, AuPT, AuPT/shNC, naked Mi221, or PBS,
respectively, twice a day. The therapy dose was 100 μL containing 10
μg of Mi221 or shNC. The body weights of nude mice were tested
every day. All mice were well-tolerated with the tested treatments over
the course of research with no noticeable body weight loss or any signs
of poisonousness such as diarrhea or edema.
2.14. H&E, TUNEL, and EdU staining. On the last day of
treatment, tumors were collected and prepared into paraffin and frozen
in slices 6 μm thick by standardized protocols. Afterward, the paraffin
slices were analyzed by H&E and TUNEL staining. The processed
paraffin slices were imaged and analyzed using a light microscope.
Frozen slices were fixed using 4% paraformaldehyde. Consistent with
the manufacturer’sinstructions(Beyotime,Shanghai,China),
fluorimetric TUNEL (TdT-mediated dUTP Nick-End Labeling)
staining was used to detect the presence of apoptotic cells. The brief
procedure was that frozen sections were treated with 20 μg/mL of
proteinase K. Then a nucleotide mixture of fluorescein-12-dUTP and
terminal deoxynucleotidyl transferase (TdT) was added to the frozen
sections incubating for 90 min. After cell nucleus was stained by DAPI
(1 μg/mL), fluorescence images of apoptotic cells (red) and cell nuclei
(blue) were obtained by CLSM analysis. EdU (keyFluor488 Click-iT
EdU Kit, keygen BioTECH, Nanjing, China) was used to label cells
nuclei that have undergone S phase of DNA synthesis. Briefly, tumor
sections were fixed with 4% paraformaldehyde for 15 min. Next, Click-
iT reaction mixture containing CuSO4, keyFluor 488 azide, and
buffering was prepared according to the instructions of Click-iT EdU
Kit. Then the prepared mixture was incubated with each tumor section
for 30 min in darkness. Sections were finally washed with PBS twice
and observed under CLSM.
2.15. Statistical Analysis. Data are expressed as mean ±standard
deviation (SD). A statistically significant value was set as p< 0.05
based on the Student’sttest.
3. RESULTS AND DISCUSSION
3.1. Characterization of AuPT Nanoparticles and
AuPT/pDNAs Polyplexes. PEI was proved to be densely
conjugated on the surface of gold nanoparticles (Figure 2A),
indicating ∼150 PEI molecules were covered on the gold
surface (0.8 molecule per square nanometer). PEI conjugated
to the nanogold could stabilize the hydrophobic gold
Figure 3. (A) Luciferase activity per milligram of total protein expressed by the transfected B16F10 cells with the tested vectors/pDNAs. (B) Mean
FITC fluorescence intensity per B16F10 cell after incubation with various vectors/FITC-pDNAs. Co-localization of the cy5.5-pDNAs and DAPI
stained nucleus at 1, 3, 6, and 9 h of the naked pDNAs (C1−C4), PEI/pDNAs (D1−D4), AuP/pDNAs (E1−E4), and AuPT/pDNAs (F1−F4) treated
group, respectively. Scale bar is 10 μm. (G) B16F10 cells were pretreated with various endocytosis inhibitors and then transfected with AuPT/
pDNAs. *and ** indicate the significant difference at p< 0.05 and p< 0.01, respectively.
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nanoparticles and kept the nanogold colloid system stable. TAT
peptides could replace PEI on the surface of gold nanoparticles
under the reaction of ligand exchange as TAT peptide
sequences contain thiol. During ligand-exchange process, the
capping ligands are displaced by thiol-TAT due to a stronger
Au−S linkage and an energy gain associated with the
intermolecular interaction. And this stronger Au−S linkage
has been proved by many scientists in previous studies.
45,46
As
the result of ligand exchange with TAT peptide, the amount of
TAT on AuPT increased from 0% to 6.7% with the TAT
feeding concentration increased (Figure 2B). No significant
change was observed for the diameters and zeta potentials of
the AuP nanoparticles after the TAT anchoring on them
(Figure 2C,D). So, AuP nanoparticles with different amounts of
TAT conjugation were further tested with transfection
efficiency in B16F10 cells to determine the best TAT feeding
concentration. It was found that highest fluorescence intensity
derived from GFP expression appeared when TAT concen-
tration reached 25 μg/mL (Figure 2E). The results
demonstrated that certain amount of TAT could help improve
the transfection efficiency, while too much TAT may exchange
more PEI molecules and reduce the ability of AuPT in gene
delivery. As Duchardt et al. had investigated the influence of
different kinds of cell-penetrating peptides (concentration)
including TAT in cellular uptake, it was found that when cells
were incubated with the TAT at concentrations of 1−5μM
(equal to 1.5−7.5 μg/mL), the peptide was kept being located
only in vesicles, which could not enhance the transfection
efficiency significantly. However, above a concentration thresh-
old of 2−40 μM, which was nearly equivalent to 3−60 μg/mL,
this peptide could, on the one hand, internalize predominantly
through a process that leads to a rapid distribution of peptides
into the cytoplasm and nucleus.
47
On the other hand, according
to our previous study,
42
too much TAT will inhibit the
transfection efficiency. Therefore, this concentration range of
0−100 μg/mL was selected for investigation in the present
study. However, according to Figure 2F, diameters of AuPT/
pDNAs nanocomplexes decreased with the increase of AuPT.
The smallest diameter of AuPT/pDNAs polyplex was 199 ±
7.76 nm, and PDI was 0.27 ±0.02 when the weight ratio of
AuPT to pDNA was 1:8.
3.2. In Vitro Transfection of B16F10 with Reporter
pDNAs. B16F10 is known as a hard-to-transfect murine tumor
cell line.
48,49
However, from Figure 3A, transfection efficiency
of AuPT in B16F10 reached highest of 1.71 ×107RLU/mg
total protein when the ratio of vector to pDNA is 1:8 (w/w).
The zeta potential of the nanocomplexes with this ration was
16.81 ±0.56 mV. Along with the priority of nanoparticles with
small size in transdermal delivery, this ratio was further
investigated in the following study. This transfection efficiency
is significantly higher than those of AuP, PEI, and Lipofect-
amine 2000 (Lipo 2k) by 1.3-fold (p< 0.01), 2.5-fold (p<
0.01), and 1.9-fold (p< 0.01), respectively. To clarify the
transfection mechanism, cellular uptake kinetics, nuclear
targeting property, and intracellular pathway of AuPT/
pDNAs in B16F10 were investigated. As shown in Figure 3B,
the average fluorescence intensity per cell increased along with
the prolongation of culture time and took up much more
pDNAs than the naked pDNAs, PEI/pDNAs, and AuP/pDNAs
treated groups within the tested 9 h. This might be attributed to
the attachment of TAT peptides on the AuP surface, which
resulted in higher TAT local concentration and subsequently
enhanced cell penetrating ability. This consequence was also
clearly observed in CLSM images. As shown in Figure 3C−F,
cells obviously ingested much more fluorescent cy5.5-pDNAs
(Figure 3F1−F4) with many localized at the nucleus, as white
arrows indicated. By contrast, no obvious fluorescence in
B16F10 cells could be observed in the naked pDNA-treated
group (Figure 3C1−C4). Even with the PEI/cy5.5-pDNAs
(Figure 3D1−D4) and AuP/cy5.5-pDNAs (Figure 3E1−E4)
treatment, less cy5.5-pDNAs were identified in the cytoplasm
without nuclear targeting property (Figure 3D1−D4,E1−E4).
These results reminded us that AuPT could disrupt the
endosomal membrane and release the pDNAs to cytoplasm, as
well as translocate them to the nucleus. The endosome escape
effect of AuPT might be partly contributed to the conjugation
of PEI, which was a well-known polymer capable of protonation
and can disturb the lysosomes.
50
A comprehensive evaluation of
the PEI/TAT/pDNA (as a control group), including the
characterization, toxicity, transfection efficiency, and targeting
ability to cell nucleus was investigated in our previous study.
42
It was shown that the PEI-TAT/pDNA complexes had lower
zeta potential, larger particle size, higher toxicity, and lower
transfection efficiency in cells than Au-PEI-TAT/pDNA.
AuPT/pDNA-based vectors can deliver pDNA not only into
cells but also target to cell nucleus. On the contrary, the
fluorescence observed in PEI-TAT/pDNA group expressed
limited cell penetrating and gene transfection ability, although
they have similar ability to condense pDNA and generate
vector/pDNA complexes. The results suggested that only
tethered TAT molecules on AuP gold nanoparticle can
generate pores on cell membrane and facilitate cellular uptake
and gene transfection due to locally enhanced concentration.
Additionally, the larger particle size of PEI-TAT/pDNA
complexes was not advantageous for the transdermal efficiency.
PEI/TAT/pDNA was so not set as a control group in this
study.
Pharmacological inhibitors are often used to investigate
which endocytic mechanism is responsible for cellular uptake of
the various nanoparticles. Different pharmacological inhibitors
have been discussed and summarized by Iversen. Many
endocytosis pathways have been reported including caveolae
pinching, RhoA-mediated endocytosis, raft-mediated endocy-
tosis, macropinocytosis, and clathrin-independent and choles-
terol-dependent endocytosis.
51
Several different types of
endocytosis have been well-investigated in the intracellular
mechanisms of vesicles derived from plasma membrane, which
are clathrin-independent endocytosis (CIE), raft-mediated
endocytosis, and micropinocytosis. Especially, methyl-β-cyclo-
dextrin (MBC) is a cyclic oligomer of glucopyranoside that
inhibits cholesterol-dependent endocytic processes by rever-
sibly extracting the steroid out of the plasma membrane. MBC
is regularly used to determine whether endocytosis is
dependent on the integrity of lipid rafts.
52
Chlorpromazine is
a cationic amphiphilic drug that is believed to inhibit clathrin-
coated pit formation by a reversible translocation of clathrin
and its adapter proteins from the plasma membrane to
intracellular vesicles.
53
It has been known for years that
amiloride and amiloride derivatives block micropinocytosis.
These chemicals, known to inhibit the Na+/H+ exchanger,
were shown to inhibit the initiation of micropinocytosis by
lowering the pH locally, close to the membrane, and thereby
inhibit recruitment of Rac.
54
From Figure 3G, with 4 °Cor
methylated β-cyclodextrin pretreatments, the transfection
efficiency of AuPT/pDNA was significantly decreased. These
results indicated that caveolin-mediated endocytotic pathway
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also contributed to the ingestion of AuPT/pDNA in melanoma
cells besides energy-dependent process.
PEI-capped gold nanoparticles can increase the transfection
efficiency compared with PEI. This result had been previously
proved,
42
and the mechanism has been explained by some
scientists.
55,56
(1) The conjugating PEI to gold nanoparticles
would increase its effective molecular weight, consequently
enhancing pDNA binding and condensation and therefore
improving the transfection. (2) The super gene transfection
performance is also likely due to the biomimetic design of the
particles that has a size more or less similar to the nucleosome
core proteins, having a large proportion of basic residues that
form electrostatic bonding with the phosphate backbone of
pDNA. Those PEI-capped gold nanoparticles may redirect the
intracellular distributions of nucleic acid drug and enhance the
gene therapy effect of nucleic acid drug compared with PEI. (3)
PEI-capped gold nanoparticles showed good cytocompatibility,
which suggests that PEI-capped gold nanoparticles are suitable
for transfecting cells with lower toxicity leading to better
cellular state.
3.3. Gene Interference in B16F10 by Mi221 Trans-
fection. To investigate whether Mi221 could regulate gene
expression of melanoma cells, resulting in inhibition of cell
cycles and cell migrations to induce cytotoxicity in vitro,
different groups carrying Mi221 treated B16F10 cells. The
results were in agreement with gene transfection consequences
mentioned above. From Figure 4A,B, the AuPT/Mi221
transfection significantly decreased the miRNA-221 level
along with the obvious up-regulation of c-Kit and p27
expression in B16F10 cells. However, PEI/Mi221 and AuP/
Mi221 groups did not express regulating ability as effectively as
AuPT/Mi221. In addition, control groups nearly had no
influence on B16F10 cells, which proved the regulation of
miRNA-221 was intervention result of Mi221. It has been
found that inhibition of c-Kit receptor permits uncontrolled cell
proliferation leading to melanoma progression.
57
P27 plays an
important role in regulating the cell cycle transition from G1 to
Figure 4. (A) MiRNA-221 gene expression levels, (B) P27 and c-Kit genes expression in the melanoma cells after 24 h of transfection. (C) Cell
cycles percentage of the tested cells after transfection. (D) Cell viability after the 24 h of transfection. (E) Cells migrations after the 24 h of
transfection. (F) Migrated cell numbers in each group were quantified. Scale bar = 100 μm. *and ** indicate significant difference at p< 0.05 and p
< 0.01, respectively.
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S phase.
58
From Figure 4C, in contrast to the normal cells,
PEI/Mi221 and AuP/Mi221 treated cells, of which the cell
distributions in G1 and S phases were ∼70.0% and 20.0%, the
AuPT/Mi221 transfected cell distributions in G1 and S phases
were 79.3% and 14.1%, respectively, demonstrating more cells
were detained in G1 phases. This result gave evidence that
much more AuPT/Mi221 treated B16F10 cells were retarded
in G1 phase and that the cells in S phase were significantly
decreased. Subsequently, cell viability was decreased to 68.7%,
62.2%, and 48.2%, respectively, for the PEI/Mi221, AuP/
Mi221, and AuPT/Mi221 treated cells (Figure 4D). As the
AuPT vector control, AuPT/shNC and naked Mi221 had no
cytotoxicity (Figure 4D), the antiproliferation effect was
identified to be induced by the decrease of miRNA-221 level
and the up-regulation of c-Kit and p27 genes, which initiated
the apoptosis.
B16F10 is a melanoma cell with highly aggressive property
and may metastasize from a primary subcutaneous site to the
lungs, bones, etc.
59
The invasion of the transfected cells was
evaluated by transwell assay. From Figure 4E,F, in contrast to
the blank control, cells treated with naked Mi221 or AuPT/
shNC, the migration of PEI/Mi221, AuP/Mi221, and AuPT/
Mi221 transfected cells were significantly decreased with 79.1%,
85.0%, and 89.1%, respectively, as black arrows headed. This
Figure 5. Skin penetration of the FITC-pDNAs delivered in vitro and in vivo. (A) TEM images of AuPT nanoparticles, (B) AuPT/pDNAs
nanocomplexes, and (C) higher magnification micrograph of AuPT/pDNAs nanocomplexes. (D) CLSM images of the lateral skin sections. Scale bar
= 100 μm. (E) Quantitative analysis of the FITC-pDNAs that had penetrated through the skins by in vitro skin diffusion test. Data refer to average
value of three times. TEM images of the melanoma xenograft tissues collected from the mice after treated with blank (F1,G
1), naked Mi221 (F2,G
2),
AuPT (F3,G
3), AuPT/shNC (F4,G
4), AuP/Mi221 (F5,G
5), and AuPT/Mi221 (F6,G
6). Black arrows indicated the Au nanoparticles distributed in
melanoma tissues. Scale bars of F1−F6and G1−G6represent 2 μm and 200 nm, respectively. ** indicates significant difference at p< 0.01.
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migrating inhibition effect of AuPT/Mi221 provides a great
priority for its application in preventing the clinical melanoma
metastasis.
3.4. Skin Penetration of pDNAs by AuPT Delivery.
Round-shaped nanoparticles were also found in skin follicles by
CLSM (Figure 5D), which permits simultaneous examination
of the distribution of fluorescent dye inside skin.
8,60
The xz
optical sections of the skin after treatment with FITC-pDNAs
were shown in Figure 5D. Images starting from 40 μm were
collected, because obvious fluorescence could be tested until
the depth of z-axle reached 40 μm at the tested time point. In
the naked FITC-pDNAs, PEI/FITC-pDNAs, and AuP/FITC-
pDNAs treated groups, weak FITC fluorescence was only
observed at ∼40 and 60 μm in depth of the skin (Figure 5D).
By contrast, when the same dose of FITC-pDNAs was
condensed by AuPT and applied to the skin, strong
fluorescence was observed beyond the epidermis and into the
dermal layer up to 80 μm(Figure 5D). In the images of Figure
5D as white arrows headed, a large amount of round-shaped
AuPT/FITC-pDNAs complexes uniformly dispersed in the hair
follicles without aggregation, which provided robust evidence
that AuPT was an excellent transdermal vehicle for bio-
macromolecules, utilizing the hair follicle duct as a transport
route. Transmission electron microscope (TEM) image (Figure
5A) showed that AuPT nanoparticles are round in shape and
well-dispersed with no aggregation observed. The average
diameter of AuPT is ∼18 nm. In Figure 5B, AuPT was shown
to closely attach to the surface of pDNA and condense them
into round nanostructures. All the pDNAs were incorporated in
the center of the vector/pDNAs nanocomplexes (see Figure 5C
as an enlarged view), whose round shape was consistent with
images shown in Figure 5D. The plasmid DNA was negatively
charged, so it would be condensed and surrounded by
positively charged gene vector AuPT, whose zeta potential
was ∼35 mV as shown in Figure 5B,C. Gold nanoparticles are
adsorbed in the outermost layer of AuPT/pDNA complexes, so
the color of the outermost layer was black. However, the pDNA
do not have high electron density; therefore, pDNA was almost
transparent under TEM
61,62
and was wrapped in the core of
complexes. Considering the protection and gene transfection
effects were attributed to PEI and TAT modified on the surface
of gold nanoparticles, PEI and TAT may not dissociate upon
the addition of pDNA. It has also been proved by Z. Chen that
shielded PEI on Au-PEI/pDNA complex not only condensed
pDNA completely but also protected DNA from DNase I
enzymatic degradation.
63
In conclusion, these nanostructures
will protect nucleic acids from enzymatic degradation, increase
the bioavailability of miRNA-221 inhibitor, and enhance their
target delivery to specific cells.
As we all know, stratum corneum is a challenging barrier for
the transdermal/topical drug delivery. Hair follicles directly
penetrate into the dermal layer, which could help the
nanoparticles reach deeply into the subcutaneous tissues.
64−66
For the transdermal mechanism of the cationic gold nano-
particles, on the one hand, AuP and AuPT can interact with the
negatively charged skin lipids by electrostatic interaction, and
TAT may help cause membrane destabilization. On the other
hand, the small size of the metal gold particles with good
stability is also advantageous for the skin penetration. As shown
in Figure 5D, compared with other control groups, AuPT
stimulated much more entrapped FITC-pDNAs to diffuse into
the deeper layers of skin tissues. Accordingly, significantly
higher FITC-pDNAs concentrations were detected in the
diffusion solution of AuPT/FITC-pDNAs than that of other
control groups within the 24 h (Figure 5E). In vivo studies
were also performed to testify if the AuPT/pDNAs complexes
Figure 6. Antitumor effects in skin melanoma xenograft-bearing mice. (A) Tumor volumes were monitored every day (*p< 0.05). (B) Body weights
were assessed after the first treatment every day. (C) MicroRNA-221 gene expression level in the tumor tissues collected on day 8 by qRT-PCR (**p
< 0.01). (D) P27 and c-Kit gene expression levels were analyzed for the tumor tissues collected on day 8 by qRT-PCR (**p< 0.01).
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could penetrate deeply into melanoma tissues. With the TEM
observation, from Figure 5F,G, nanocomplexes with several
hundreds of nanometers (black arrows headed) were found to
be localized in the tumor slices of AuPT (Figure 5G3,F3),
AuPT/shNC (Figure 5G4,F4), AuP/Mi221 (Figure 5G5,F5),
and AuPT/Mi221 (Figure 5G6,F6) treated groups, which were
absent in the blank (Figure 5G1,F1) and naked Mi221 (Figure
5G2,F2) control groups. These results together demonstrated
the strong efficacy of AuPT in stimulating the skin penetration
of pDNAs into the subcutaneous tissues.
Gold nanoparticles have been indicated for their nano-
biological interactions with membrane lipids to enhance
transdermal efficiency.
67,68
The nanoparticles have also been
proved to modulate membrane lipid phase transitions so as to
increase the lipid fluidity.
69,70
Because the skin barrier is
actually governed by the physical state and structural
organization of stratum corneum extracellular lipids, the lipid-
fluidizing functions of nanoparticles play an important role in
their ability to alter skin permeability.
71
Metal-based nano-
particles, including gold nanoparticles,
5
quantum dots
72
and
iron oxide nanoparticles,
73,74
were revealed to be capable of
penetrating through intact skin, due largely to the interaction
with the lipid in extracellular space, which was absent for
polymers such as PEI. Hence, the altered condition of skin
accompanied by percutaneous penetration of nanoparticles
leads to the breach of skin barrier as the result of usage of gold
nanoparticles in our study.
3.5. In Vivo Anti-Tumor Effects. As shown in Figure 6A,
despite that no significance was obtained, AuP/Mi221
expressed a certain tumor inhibition trend. Compared with
the blank group, AuP/Mi221 treatment inhibited the tumor
growth with 11.5%−38.7% at the tested period. By contrast, the
tumor inhibition rates expressed by AuPT/Mi221-treated
group were 38.5%−52.3%, with significance received at day 2,
4, and 8 (p< 0.05). AuPT-treated group showed a similar
profile to that of saline group, which indicated that metal
particles themselves have no influence on the tumor growth.
Neither significant tumor inhibition was observed in the naked
Mi221 nor AuPT/shNC treated group. On the one hand, these
results provided the evidence that the AuPT/Mi221 trans-
fection played important role in the antitumor effect. Of which,
TAT was critical in promoting the skin penetration and gene
transfection of the pDNAs by AuP in topical application. On
the other hand, mice in all the tested groups showed similar
body weights growth (Figure 6B), indicating that the topical
delivery of AuPT/Mi221 and other control groups had no
cytotoxic effect on the animals. The MicroRNA-221 regulated
target genes expression in vivo was also identified and shown in
Figure 6C,D. In accord with the observed delay in tumor
growth, the miRNA-221 expression of melanoma in the AuPT/
Mi221 and AuPT/Mi221 treated groups were inhibited, while
p27 and c-Kit were up-regulated obviously compared with
other control groups.
In keeping with this, a further examination of tumor tissues
was conducted by H&E staining. As shown in Figure 7A1−A4,
Figure 7. H&E staining images of the tumor tissues harvested from mice treated with (A1) blank, (A2) naked Mi221, (A3) AuPT, (A4) AuPT/shNC,
(A5) AuP/Mi221, and (A6) AuPT/Mi221, on day 8. Scale bar represents 100 μm. TUNEL staining (red fluorescence) images of the tumor tissues
harvested from mice treated with (B1) blank, (B2) naked Mi221, (B3) AuP, (B4) AuPT/shNC, (B5) AuP/Mi221, and (B6) AuPT/Mi221. EdU
staining (green fluorescence) images of the tumor tissues harvested from mice treated with (C1) blank, (C2) naked Mi221, (C3) AuP, (C4) AuPT/
shNC, (C5) AuP/Mi221, and (C6) AuPT/Mi221. Scale bar represents 50 μm. (D) Quantification of the number of melanoma cells with positive
stain in TUNEL assay. (E) Quantification of the number of melanoma cells with positive stain in EdU assay. H&E stain was observed by light
microscope. TUNEL and EdU stains were observed.
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no indication of necrotic or apoptotic regions were observed in
the robust tumor tissues of saline, naked Mi221, AuPT, and
AuPT/shNC treated groups. By contrast, significant cell
necrosis and big vacuoles were observed in the tumors of
AuPT/Mi221 and AuP/Mi221 treated group (Figure 7A5−A6,
black arrows headed), which might be contributing to the
apoptosis of cells inside the tumor. The enhanced inhibition in
xenografted melanoma expressed by the AuPT/Mi221 treat-
ment can be partly attributed to the enhanced skin penetration
and increased transfection of Mi221 in the tumor cells. High in
vivo transdermal efficiency of AuPT/pDNAs nanocomplexes
had been previously proven in Figure 5F,G.
DNA fragmentation in apoptosis is usually associated with
ultrastructural changes in cellular morphology.
75
Apoptosis
resulting from DNA fragmentation can be examined by TdT-
mediated dUTP Nick-End Labeling (TUNEL) assay. It was
shown that many apoptotic cells indicated by the red
fluorescence (white arrows headed) in AuP/Mi221 and
AuPT/Mi221 tumor slices were observed (Figure 7B5−B6).
On the contrary, only a small amount of red fluorescence was
identified in other four control groups (Figure 7B1−B4, white
arrows headed). Quantitatively, there are 14% cell that were
apoptotic in tumor slices of AuPT/Mi221-treated group, which
is 1.3-fold (P< 0.01) and 7-fold (P< 0.01) higher than that of
AuP/Mi221 and control groups, respectively (Figure 7D).
Apoptosis is usually associated with cell cycle inhibition, which
was so examined by Click-iT EdU assay. Particularly, cells in S-
phase of DNA synthesis were stained to express green
fluorescence, and subsequent visualization by fluorescent
microscopy gives biologically important data about cell cycle.
As shown in Figure 7C1−C4, the four control groups
demonstrated massive green fluorescence (white arrows
headed), suggesting many cells were in S-phase of DNA
synthesis. A certain amount of proliferation signal was observed
from the AuP/Mi221 and AuPT/Mi221 tumor slices groups,
but the intensity is much less than that of the control groups
(Figure 7C5,C6, white arrows headed). The EdU positive cells
were calculated and shown in Figure 7E. It was found that only
8% melanoma cells of AuPT/Mi221 group were in S phases,
compared with the 10% in AuP/Mi221 group and ∼18% in
other control groups, suggesting more cells were retarded in G1
phase upon AuP/Mi221 or AuPT/Mi221 treatment. These
results also suggested the highest transfect efficiency of AuPT,
which induced the strongest MicroRNA-221 inhibition,
resulting in the inhibition of DNA synthesis in the cells.
Collectively, these results provided further evidence for the
efficiency of AuPT as a vehicle for the in vivo transdermal
delivery of pDNAs and as the vector for the pDNAs
transfection in vivo.
Melanoma has poor prognosis with high mortality when
patients are in advanced stages.
76−78
Current therapeutic ways
for skin melanoma were usually not effective resulting in only
less than 10% survival rate. Two main reasons explained the
poor efficiency. The first one lies in that chemotherapeutic ways
would easily cause drug resistance and make melanoma
insensitive to them. The other reason is that melanoma is
associated with multiple gene changes, so targeting only one
gene is not easy to receive satisfactory antitumor effects.
23,79
Therefore, in the present study, we use miRNA, which can
control multiple targets involved in melanoma by mainly
targeting c-Kit and p27 simultaneously. Multiple genes
regulation can influence a series of protein amount in
melanoma cells and change signaling pathways. Such synergy
can achieve better antitumor results theoretically. What’s more,
latest studies have explored the expression of microRNA in
drug-resistant cancer cells. They found drug-resistant mecha-
nism was closely associated with miRNA levels. In two kinds of
drug-resistant cancer cell lines, the expression of a certain
miRNA was significantly higher than those of drug-sensitive cell
lines.
80
In addition, Denmark Santaris pharma has started the
phase I clinical trials to target miRNA molecules (miR-122),
suggesting miRNA was a promising target in cancer gene
therapy.
81
All this research progress reminded us of the great
potential of miRNA-based novel gene therapy in cancer gene
therapy. In the present study, we aim to deliver miRNA by a
novel strategy, transdermal delivery, for the topical skin cancer.
Until recently, transdermal bio-macromolecules delivery is
reported scarcely and less than the delivery by other strategies
like injection and oral administrations. Siu et al. have recently
reported the design and application of noncovalently function-
alized carbon nanotubes (CNT) in topical siRNA delivery, in
which, PEI was conjuguated to CNT to deliver siRNA.
Through transdermal method, the target gene in the tumor
tissue was silenced effectively.
82
Another study formulated the
effective cationic lipid−polymer hybrid nanoparticles compris-
ing of an anti-inflammatory drug Cap and siRNA against TNF-
αto treat difficult skin inflammatory conditions in vivo.
83
These
two studies both prepared nanoparticles carrying siRNA with
favorable transdermal ability. But it was known that pDNAs are
used more often in clinic as it remained stable in vivo. However,
transdermal delivery of pDNAs with higher molecular weight
faced much bigger challenge than siRNA. In this study, AuPT
was first reported to deliver the pDNAs by transdermal
pathway. AuPT played two indispensable roles in not only
enhancing the transdermal ability of pDNAs, making the
AuPT/pDNAs can enter into deep skin layers, but also acting
as the efficient nonviral vector to transfect the melanoma cells.
The in vitro transfection efficiency and mechanism of AuPT in
difficult-to-transfect cells (bone marrow derived mesenchymal
stem cells) were investigated in our precious work.
42
In the
present study, the transdermal efficiency and in vivo application
of AuPT was systematically investigated. Considering the scarce
report on transdermal pDNA delivery, the present study also
provides, for the first time, the evidence for the new way in
utilizing the transdermal pDNAs delivery for gene therapy.
4. CONCLUSIONS
Transmembrane peptide-conjugated cationic gold nanoparticles
(AuPT) was shown a highly efficient carrier for the transdermal
delivery of pDNAs. Along with the robust gene transfection
efficiency of AuPT, transdermal delivery of AuPT/pDNA-
Mi221 provides a novel topical gene therapy strategy for skin
cancer with great priority to reverse both the progression and
metastasis of advanced melanoma.
■AUTHOR INFORMATION
Corresponding Authors
*E-mail: lhpeng@zju.edu.cn. Phone:+86-571-88208437. (L.-
H.P.)
*E-mail: gaojianqing@zju.edu.cn. (J.-Q.G.)
ORCID
Li-Hua Peng: 0000-0001-9763-383X
Notes
The authors declare no competing financial interest.
ACS Applied Materials & Interfaces Research Article
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K

■ACKNOWLEDGMENTS
The study was supported by National Natural Science
Foundation of China (Project No. 81473145) and the Macau
Science and Technology Development Fund, Macau Special
Administrative Region, China (Open Project of State Key
Laboratory of Quality Research in Chinese Medicine, Macau
University of Science and Technology, Project No. MUST-
SKL-2016-11).
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