EGFR-targeting Peptide Conjugated pH-sensitive Micelles as a

Potential Drug Carrier for Photodynamic Detection and Therapy of

Cancer

Cheng-Liang Peng

, Yuan-I Chen

, Ying-Hsia Shih

, Tsai-Yueh Luo

and Ming-Jium Shieh

Isotope Application Division, Institute of Nuclear Energy Research, Taoyuan, Taiwan

Institute of Biomedical Engineering, College of Medicine, National Taiwan University, Taipei, Taiwan

Keywords: Thermosensitive, Photothermal Therapy, Chemotherapy, Micelle, Control Release, Synergistic Effect.

Abstract: Multifunctional theranostics have recently been intensively explored to optimize the efficacy and safety.

Herein, we report multifunctional micelle that constructed from graft copolymer PEGMA-co-PDPA and

diblock copolymer mPEG-b-PCL as the carrier of hydrophobic photosensitizer, chlorin e6 (Ce6) for

simultaneous fluorescence imaging and photodynamic therapy. The functional inner core of PEGMA-co-

PDPA exhibited pH stimulate to accelerate drug release under slightly acidic microenvironments of tumors

and the outer shell of micelles with epidermal growth factor receptor (EGFR)-targeting GE11 peptides for

active targeting of EGFR-overexpressing cancer cells. The results demonstrate that GE11-conjugated

chlorin e6-loaded micelles (GE11-Ce6-micelles) with particle size around 100 nm and the micelles had well

defined core shell structure which was evaluated by TEM. In the in vitro cellular uptake studies, GE11-Ce6-

micelles exhibited a higher amount of intracellular uptake of chlorin e6 in HCT116 cancer cells (EGFR high

expression) via receptor-mediated endocytosis, in contrast with the time-dependent passive uptake of the

non-targeted Ce6-micelles, thereby providing a effective photocytotoxic effect on the HCT116 cancer cells.

In vivo study revealed that GE11-Ce6-micelles exhibited tumor targeting for photodynamic detection and

excellent inhibition on tumor growth after irradiation, indicating that GE11-Ce6-micelles could be

successfully applied to the effective fluorescence imaging and photodynamic therapy of cancer.

1 INTRODUCTION

Photodynamic therapy (PDT) is a novel treatment

for several diseases including age-related macular

degeneration, periodontitis and malignant cancers

(Schmidt-Erfurth and Hasan, 2000). PDT is based on

a photochemical reactions that could produces

localized tissue damage. The activation of

photosensitizers in the target tissues by suitable

wavelengths of light would lead to generations of

reactive oxygen species (ROS) to destroy cancer

cells. Important advantages of PDT over other

therapies include minimal invasiveness, repeated

PDT applicability at the same site, high therapeutic

efficacy, and less side effects in comparison with

other treatments of cancer (Wang et al., 2014a).

Chlorin e6 (Ce6) is a promising photosensitizer

for PDT with an excitation wavelength at 660 nm.

Chlorin e6 exhibits advantageous photophysical

properties including having long lifetimes in its

photoexcited triplet states and high absorption in the

red spectral region that could penetrate tissues

deeper (Wang et al., 2014b). Despite these

significant advantages, Chlorin e6 has poor

solubility in aqueous media and nonspecific

biodistribution with low tumor-targeting efficacy,

which could cause drug loss or photosensitivity in

healthy tissues (Zhang et al., 2003) .

The slight acidic microenvironment of solid

tumor is resulted from their high metabolic rate via

anaerobic glycolysis that causes accumulation of

lactic acid and carbon dioxide. Electrical and

chemical probes show that the pH of the

microenvironment is around 5.8 - 7.2, which is

lower than the physiological pH of 7.4 (Shen et al.,

2008).

To further enhance drug accumulation in tumor

sites while minimizing drug concentration in other

sites, nanoparticles are now being conjugated with

targeting ligands, such as antibodies, proteins,

Peng, C-L., Chen, Y-I., Shih, Y-H., Luo, T-Y. and Shieh, M-J.

EGFR-targeting Peptide Conjugated pH-sensitive Micelles as a Potential Drug Carrier for Photodynamic Detection and Therapy of Cancer.

DOI: 10.5220/0005774201050110

In Proceedings of the 9th International Joint Conference on Biomedical Engineering Systems and Technologies (BIOSTEC 2016) - Volume 2: BIOIMAGING, pages 105-110

ISBN: 978-989-758-170-0

105

aptamers, and peptides (Lee et al., 2013). Peptides

are small molecules with specific receptor binding,

low immune response induction, and high stability

in vivo. These characteristics of peptides make them

better tumor targeting ligands. The epidermal growth

factor receptor (EGFR) is a cell surface receptor that

is highly expressed in human epithelial cancer cells,

including breast, lung, ovarian, and colon cancers

(Arteaga, 2002).

In this study, the structure and pH sensitivity of

multifunctional micelles were determined and

characterized. The cellular uptake efficiency was

evaluated in HCT116 cells (high EGFR expression)

and SW620 cells (low EGFR expression). At last,

the in vivo tumor-targeted PDT efficacy and

imaging were evaluated in tumor-bearing mice. The

pH-sensitive micelle conjugated with GE11 peptide

is expected to accelerate drug release under slightly

acidic microenvironments of tumors and be

internalized via EGFR-mediated endocytosis

(scheme 1). The goal of this study is to develop a

drug delivery system with enhanced tumor targeting

for cancer therapy.

2 EXPERIMENTAL SECTION

2.1 Synthesis of PEGMA-co-PDPA,

mPEG-PCL, and mal-PEG-PCL

The pH-sensitive copolymer, PEGMA-co-PDPA

(poly(ethylene glycol) methacrylate-co- poly(2-

(diisopropylamino)ethyl methacrylate) was synthesis

by free radical polymerization as described

previously (Peng et al., 2010). Briefly, PEGMA

(0.25 g) and DPA (0.5 g) were added to a flask

equipped with a magnetic stirrer and 5 ml THF. The

AIBN initiator (9.25 mg) was added to the mixture

and the solution was heated at 70 °C for 24 h in an

atmosphere of nitrogen. Unreacted monomers were

removed by dialysis against water for 3 days and the

polymer fraction was lyophilized. Copolymer

compositions were determined with FT-NMR at 500

MHz using chloroform-d (CDCl3) as the solvent.

2.2 Preparation of Chlorin E6-Loaded

Micelles

The blank micelles were prepared by dialysis

method (Chaw et al., 2004). In brief, different

weights (0~5mg) of PEGMA-co-PDPA and mPEG-

PCL were dissolved completely in 0.1N HCL and

then dialysis of base solution for 1 day. Chlorin e6-

loaded micelles (Ce6-micelles) were prepared via

the cosolvent evaporation method (Peng et al.,

2008a). Briefly, 10 mg of PEGMA-co-PDPA, 10mg

of PEG-PCL, and 2mg of mal-PEG-PCL were

dissolved in 0.5 ml THF with Chlorin e6 (1~4mg)

and then added to 5 ml of PBS with stirring at 550

rpm. The organic solvent was evaporated while

being stirred overnight and the remaining portion

was filtered through a 0.22 μm pore size Millex GS

filter to remove non-incorporated drug crystals.

2.3 Preparation of GE11-conjugated

Micelles

EGFR specific peptide (GE11, sequence:

YHWYGYTPQNVI-GGGGC) was used to

established active targeted micelles (Li et al., 2005).

The sequence of “GGGG” as an spacer while the

carboxyl terminal cysteine of the peptide conjugated

with the maleimide of the micelles (Milane et al.,

2010). The conjugation of GE11 were then just

performed by mixture of GE11 and maleimide

containing micelles with different molar ratio at 4 °C

overnight , as described previously (Olivier et al.,

2002). The unconjugated GE11 peptide were

separated by passing through PD-10 desalting

column (GE Healthcare, Uppsala, Sweden).

2.4 Characterization of Chlorin E6-

Loaded Micelles

The mean diameter and PDI of micelles were

determined using a Zetasizer Nano ZS90 apparatus

(Malvern Instruments, Worcestershire, UK). The

size and morphology of micelles were ascertained by

transmission electron microscopy (TEM) using a

model H-7650 microscope (Hitachi, Tokyo, Japan).

To prepare a TEM sample, a drop of sample solution

was placed on a 200-mesh carbon-coated copper

grid and then the excess solution was removed with

filter paper.

The pH sensitivity of micelle was recorded

through size and zeta potential measurements by

dynamic light scattering at various pH values of

PBS.

2.5 In Vivo Fluorescence Imaging

To observe biodistribution of Chlorin e6, female

BALB/c athymic (nut/nut) mice (5-6 weeks old)

were purchased from the National Laboratory

Animal Center (Taipei, Taiwan). HCT-116 cells

(1×106) and SW620 celles (1×106) were inoculated

subcutaneously on the right and left flanks of nude

BIOIMAGING 2016 - 3rd International Conference on Bioimaging

106

mice, respectively. When the tumors reached a

volume of 150 to 200 mm3, mice received an

intravenous injection of Ce6-miccelles or GE11-

Ce6-miccelles (equivalent to 5 mg/kg of Ce6). The

in vivo biodistribution of Ce6 were imaged at 3 and

24 after intravenous injection using an IVIS imaging

system (Xenogen, Alameda, CA, USA). The tumor-

bearing mice were sacrificed 24 h post-injection,

major organs and tumors were excised for isolated

organ imaging to estimate the tissue distribution of

Ce6-miccelles or GE11-Ce6-miccelles.

2.6 In Vivo Photodynamic Therapy

HCT116 cells (1 × 10

cells) were implanted

subcutaneously into the right flanks of mice. When

tumors grew to approximately 150-200 mm3 in

volume, 200-500 μl of PBS containing Ce6-micelles

or GE11-Ce6-micelles (equivalent to 5 mg/kg of

Ce6) were injected via tail vein (n = 4 per each

group). At 24 h after injection, tumor tissues were

irradiated by 670 nm diode laser (634 mW/cm2) for

10 min.

3 RESULTS AND DISCUSSION

3.1 Synthesis and Characterization of

Polymers

In this study, the pH-responsive micelles assembled

from mixture of graft copolymer PEGMA-co-PDPA

and diblock copolymer mPEG-PCL were developed

to control drug delivery and enhance the antitumor

efficacy of photodynamic therapy. Synthesis of

PEGMA-co-PDPA and mPEG-b-PCL were carried

out as shown in Figure 1. The potentiometric

measurements was performed to determine the pKa

of the PEGMA-co-PDPA copolymers, each of the

DPA-based copolymers presented a sharp

protonation transition in the pH range 6.0 to 7.0.

According to the pH transition of PEGMA-co-

PDPA, the pH-responsive micelles can deliver

successfully the anticancer drugs to target tumor

tissue but minimize the drug release at normal

tissues. The diblock copolymer, mPEG-PCL were

synthesized by ring-opening polymerization (Peng et

al., 2009).

The micelles ranged from 91.05 to 142.37 nm in

size with various polydispersity indices (Table 1).

Figure 1: Schematic diagram illustrates the fabrication of

GE11-Ce6-micelles.

3.2 Characterization of Chlorin

E6-Loaded Micelles

Chlorin e6 as an photosensitizer was efficiently

encapsulated into the pH-responsive micelles, due to

the hydrophobic interactions between chlorin e6 and

hydrophobic group as DPA or PCL of micelles.

Table 1 lists the results of the loading efficiency,

drug contents, and sizes of the chlorin e6 loaded pH

responsive micelles. After incorporating various

amounts of chlorin e6, all of the samples had a

narrow PDI from 0.109-0.154 and ranged in size

from 96.6-103.1 nm. Chlorin e6-loaded micelles

with a D/P ratio of 1/10 were used and the

encapsulation efficiency was 86.25%. When the

micelles with a D/P ratio of 1/5 or 1/20 were

employed, the encapsulation efficiency was lower

Table 1: Characteristics of micelles.

Sample

D/P

ratio

encapsulation

efficiency (%)

drug content

(%)

Mean size

/nm(PDI)

micelles - - - 91.1 (0.239)

Ce6-

micelles

1/5 75.52 12.09 96.6 (0.109)

Ce6-

micelles

1/10 86.25 7.82 96.7 (0.125)

Ce6-

micelles

1/20 74.35 3.54

103.1

(0.154)

Mal-

micelles

- - -

105.7

(0.222)

Ce6-Mal-

micelles

1/10 85.9 7.81

110.0

(0.184)

GE11-Ce6-

micelles

1/10 78.8 7.16

105.1

(0.293)

EGFR-targeting Peptide Conjugated pH-sensitive Micelles as a Potential Drug Carrier for Photodynamic Detection and Therapy of Cancer

107

than those with a D/P ratio of 1/10. Figure 2 showed

the morphology of the nanoparticles with or without

chlorin e6 as observed by TEM. The images

indicated that micelles with different conditions

were uniform, spherical, and the particle size agreed

with the results measured by dynamic light

scattering (DLS).Absorbance and fluorescence

spectra of chlorin e6-loaded mixed micelles (Ce6-

micelles), and GE11-conjugated chlorin e6-loaded

mixed micelles (GE11-Ce6-micelles) revealed that

free chlorin e6 exhibited a relatively broad and weak

fluorescence, while the fluorescence of chlorin e6-

loaded mixed micelles was strong and reached a

maximum at 670 nm as show in Figure 3.

3.3 Cellular Uptake and Localization of

Chlorin E6-Loaded Micelles

Subcellular localization of EGFR-targeted GE11-

Ce6-micelles or non-targeted Ce6-micelles were

evaluated by using fluorescence microscopy as

shown in Figure 4. After 5 h incubation, the GE11-

Ce6-micelles were rapidly taken up by the HCT116

cells, as that could be observed from the green

fluorescence of FITC-labeled micelles accumulated

in cells. Intracellular drug release by targeted

micelles and non-targeted micelles could be

projected by red fluorescence of chlorin e6.

Figure 2: Transmission electron micrographs images of (a)

PEGMA-co-DPA micelles, (b) mixed micelles, (c) chlorin

e6 loaded mixed micelles (Ce6-micelles), and (d) chlorin

e6 loaded GE11-conjugated mixed micelles (GE11-Ce6-

micelles).

The fluorescence of GE11-Ce6-micelles

significantly accumulated in the cytoplasm but not in

the nucleus. Furthermore, the most fluorescence of

chlorin e6 in HCT116 celles were colocalized with

the fluorescence of micelles. However, the

fluorescence intensity of chlorin e6 in HCT116 cells

remarkably decreased when cells treated with GE11-

Ce6-micelles and excess amount of free GE11

peptides, indicated that the specific uptake of GE11-

Ce6-micelles into tumor cells through EGFR-

mediated endocytosis.

3.4 In Vivo Fluorescence Imaging

To compare the in vivo biodistribution of EGFR-

targeted GE11-Ce6-micelles or non-targeted Ce6-

micelles (equivalent to 5mg/kg of chlorin e6) was

injected intravenously into HCT116 (high

expression EGFR) and SW620 (low expression

EGFR) tumor-bearing mice. The in vivo

biodistribution of chlorin e6 could be directly

monitored by non-invasive and real-time

fluorescence imaging of the whole body, because

chlorin e6 can emit strong near infrared (NIR)

fluorescence for efficient tracking (Koo et al., 2010).

Figure 3: (a) Absorbance spectra of free chlorin e6 (Ce6),

chlorin e6-loaded mixed micelles (Ce6-micelles), and

GE11-conjugated chlorin e6-loaded mixed micelles

(GE11-Ce6-micelles) (b) fluorescence spectra of GE11-

Ce6-mixed micelles in difference pH values of buffers, (c)

fluorescence spectra of chlorin e6-loaded mPEG-b-PCL

micelles in difference pH values of buffers (equivalent to

2 μg/ml of chlorin e6). The fluorescence spectra were

measured with an excitation of 403 nm and emissions in

the 600–800 nm range. (d) Singlet oxygen generation of

GE11-Ce6-micelles in various pH Tris buffer solutions.

Figure 4: Subcellular localization of chlorin e6 in HCT116

cells treated with EGFR-targeted GE11-Ce6-micelles or

non-targeted Ce6-micelles.

BIOIMAGING 2016 - 3rd International Conference on Bioimaging

108

The results demonstrated that GE11-Ce6-micelles

were effectively accumulated in the HCT116 tumor,

compared to non-targeted mixed micelles (Figure 5).

At 3 h post-injection, significant fluorescence

emitted from the GE11-Ce6-micelles injected mice

was observed in the HCT116 tumor but not SW620

tumor.

Figure 5: In vivo and ex vivo fluorescence imaging of

HCT116 and SW620 tumor-bearing mice administrated

with EGFR-targeted GE11-Ce6-micelles and non-targeted

Ce6-micelles. (a) Whole body fluorescence images of

tumor-bearing mice treated with GE11-Ce6-micelles and

Ce6-micelles. Arrows indicate tumor sites. (b) Ex vivo

fluorescence images of organs and tumors were acquired

after 24 h injection of GE11-Ce6-micelles. The total

fluorescent photon counts of chlorin e6 in (c) HCT116

tumor and (d) SW620 tumor in the corresponding

fluorescence images in Figure 8a was quantified.

Meanwhile, there are also fluorescence signal in

the other tissues. At 24 h post-injection, the

fluorescence of GE11-Ce6-micelles was maintained

in HCT116 tumor, indicating that it were not subject

to rapid excretion from the mice. Additionally, the

total fluorescent photon counts of chlorin e6 in

tumor with GE11-Ce6-micelles was about 2-2.5 fold

higher than that with Ce6-micelles at 3 h and 24h

post-injection in HCT116 tumor.

3.5 In Vivo Photodynamic Therapy

In vivo photodynamic therapeutic efficacy of GE11-

Ce6-micelles or Ce6-micelles (equivalent to 5mg/kg

of chlorin e6) with laser irradiation was evaluated by

measuring tumor growth in HCT116 tumor-bearing

mice. After 24h injection, the tumors were irradiated

with a red laser (670 nm, 634 mW/cm2) for 10 min

and the tumor size was monitored for 22 days.

Figure 6a showed the therapeutic efficacy of each

treatment was monitored by evaluating the relative

tumor volume for 22 days. The PDT mediated by

GE11-Ce6-micelles reduced relative tumor volume

compared with control tumors and tumors treated

with Ce6-micelles plus laser irradiation.. The body

weight were not significantly different between

control mice and PDT-treated mice, indicating that

photodynamic therapy mediated by Ce6-micelles or

GE11-Ce6-micelles did not result in unacceptable

toxicity(Figure 6b).

4 CONCLUSIONS

We have prepared and characterized pH-resposive

micelle constructed from graft copolymer PEGMA-

co-DPA and diblock copolymer mPEG-b-PCL as

drug delivery carrier for simultaneous photodynamic

imaging and therapy. In vitro and in vivo studies

confirmed that EGFR-targeted o GE11-Ce6-micelles

enhanced specific uptake by cancer cells via receptor

mediated endocytosis pathway and improved PDT

of EGFR overexpressing cancer cells. Moreover, the

tumor targeted delivery of GE11-Ce6-micelles

allowed detection of EGFR tumors by near infrared

imaging. In tumor-bearing mice models, GE11-Ce6-

micelles could effectively suppress the tumor growth

compared to non-targeted Ce6-micelles. In

conclusion, GE11-Ce6-micelles could be

successfully applied to fluorescence imaging and

effective photodynamic therapy of cancer.

Figure 6: In vivo photodynamic therapeutic efficacy of

Ce6-micelles or GE11-Ce6-micelles in HCT116 tumor-

bearing mice. (a) The tumor volumes and (b) body weights

were measured during the 22-day evaluation period in

mice were treated with PBS (Control), Ce6-micelles plus

laser irradiation, or GE11-Ce6-micelles plus laser

irradiation. Data indicate means and standard errors.

EGFR-targeting Peptide Conjugated pH-sensitive Micelles as a Potential Drug Carrier for Photodynamic Detection and Therapy of Cancer

109

REFERENCES

Arteaga, C. L. 2002. Epidermal Growth Factor Receptor

Dependence In Human Tumors: More Than Just

Expression? The Oncologist, 7, 31-39.

Chaw, C.-S., Chooi, K.-W., Liu, X.-M., Tan, C.-W.,

Wang, L. & Yang, Y.-Y. 2004. Thermally Responsive

Core-Shell Nanoparticles Self-Assembled From

Cholesteryl End-Capped And Grafted

Polyacrylamides:: Drug Incorporation And In Vitro

Release. Biomaterials, 25, 4297-4308.

Huang, P., Xu, C., Lin, J., Wang, C., Wang, X. S., Zhang,

C. L., Zhou, X. J., Guo, S. W. & Cui, D. X. 2011.

Folic Acid-Conjugated Graphene Oxide Loaded With

Photosensitizers For Targeting Photodynamic

Therapy. Theranostics, 1, 240-250.

Koo, H., Lee, H., Lee, S., Min, K. H., Kim, M. S., Lee, D.

S., Choi, Y., Kwon, I. C., Kim, K. & Jeong, S. Y.

2010. In Vivo Tumor Diagnosis And Photodynamic

Therapy Via Tumoral Ph-Responsive Polymeric

Micelles. Chemical Communications, 46, 5668-5670.

Lee, P.-C., Chiou, Y.-C., Wong, J.-M., Peng, C.-L. &

Shieh, M.-J. 2013. Targeting Colorectal Cancer Cells

With Single-Walled Carbon Nanotubes Conjugated To

Anticancer Agent Sn-38 And Egfr Antibody.

Biomaterials, 34, 8756-8765.

Li, Z., Zhao, R., Wu, X., Sun, Y., Yao, M., Li, J., Xu, Y.

& Gu, J. 2005. Identification And Characterization Of

A Novel Peptide Ligand Of Epidermal Growth Factor

Receptor For Targeted Delivery Of Therapeutics. The

Faseb Journal, 19, 1978-1985.

Milane, L., Duan, Z. & Amiji, M. 2010. Development Of

Egfr-Targeted Polymer Blend Nanocarriers For

Combination Paclitaxel/Lonidamine Delivery To Treat

Multi-Drug Resistance In Human Breast And Ovarian

Tumor Cells. Molecular Pharmaceutics, 8, 185-203.

Min, K. H., Kim, J.-H., Bae, S. M., Shin, H., Kim, M. S.,

Park, S., Lee, H., Park, R.-W., Kim, I.-S., Kim, K.,

Kwon, I. C., Jeong, S. Y. & Lee, D. S. 2010. Tumoral

Acidic Ph-Responsive Mpeg-Poly(Β-Amino Ester)

Polymeric Micelles For Cancer Targeting Therapy.

Journal Of Controlled Release, 144, 259-266.

Olivier, J.-C., Huertas, R., Lee, H. J., Calon, F. &

Pardridge, W. M. 2002. Synthesis Of Pegylated

Immunonanoparticles. Pharmaceutical Research, 19,

1137-1143.

Peng, C.-L., Shieh, M.-J., Tsai, M.-H., Chang, C.-C. &

Lai, P.-S. 2008a. Self-Assembled Star-Shaped

Chlorin-Core Poly(Ɛ-Caprolactone)–Poly(Ethylene

Glycol) Diblock Copolymer Micelles For Dual

Chemo-Photodynamic Therapies. Biomaterials, 29,

3599-3608.

Peng, C.-L., Yang, L.-Y., Luo, T.-Y., Lai, P.-S., Yang, S.-

J., Lin, W.-J. & Shieh, M.-J. 2010. Development Of

Ph Sensitive 2-(Diisopropylamino)Ethyl Methacrylate

Based Nanoparticles For Photodynamic Therapy.

Nanotechnology, 21, 155103.

Peng, C. L., Lai, P. S., Lin, F. H., Wu, S. Y. H. & Shieh,

M. J. 2009. Dual Chemotherapy And Photodynamic

Therapy In An Ht-29 Human Colon Cancer Xenograft

Model Using Sn-38-Loaded Chlorin-Core Star Block

Copolymer Micelles. Biomaterials, 30, 3614-3625.

Peng, C. L., Shieh, M. J., Tsai, M. H., Chang, C. C. & Lai,

P. S. 2008b. Self-Assembled Star-Shaped Chlorin-

Core Poly(C-Caprolactone)-Poly(Ethylene Glycol)

Diblock Copolymer Micelles For Dual Chemo-

Photodynamic Therapies. Biomaterials, 29, 3599-

3608.

Schmidt-Erfurth, U. & Hasan, T. 2000. Mechanisms Of

Action Of Photodynamic Therapy With Verteporfin

For The Treatment Of Age-Related Macular

Degeneration. Survey Of Ophthalmology, 45, 195-

214.

Shen, Y., Tang, H., Radosz, M., Van Kirk, E. & Murdoch,

W. 2008. Ph-Responsive Nanoparticles For Cancer

Drug Delivery. In: Jain, K. (Ed.) Drug Delivery

Systems. Humana Press.

Wang, M., Chen, Z., Zheng, W., Zhu, H., Lu, S., Ma, E.,

Tu, D., Zhou, S., Huang, M. & Chen, X. 2014a.

Lanthanide-Doped Upconversion Nanoparticles

Electrostatically Coupled With Photosensitizers For

Near-Infrared-Triggered Photodynamic Therapy.

Nanoscale, 6, 8274-8282.

Wang, X., Liu, K., Yang, G., Cheng, L., He, L., Liu, Y.,

Li, Y., Guo, L. & Liu, Z. 2014b. Near-Infrared Light

Triggered Photodynamic Therapy In Combination

With Gene Therapy Using Upconversion

Nanoparticles For Effective Cancer Cell Killing.

Nanoscale.

Zhang, G.-D., Harada, A., Nishiyama, N., Jiang, D.-L.,

Koyama, H., Aida, T. & Kataoka, K. 2003. Polyion

Complex Micelles Entrapping Cationic Dendrimer

Porphyrin: Effective Photosensitizer For

Photodynamic Therapy Of Cancer. Journal Of

Controlled Release, 93, 141-150.

BIOIMAGING 2016 - 3rd International Conference on Bioimaging

110