Article Cite This: Chem. Mater. 2018, 30, 517−525
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ROS-Sensitive Polymeric Nanocarriers with Red Light-Activated Size Shrinkage for Remotely Controlled Drug Release Ziyang Cao,†,‡,∥ Yinchu Ma,‡,∥ Chunyang Sun,§,∥ Zidong Lu,†,∥ Zeyu Yao,⊥ Junxia Wang,† Dongdong Li,† Youyong Yuan,† and Xianzhu Yang*,† †
School of Medicine, Institutes for Life Sciences and National Engineering Research Center for Tissue Restoration and Reconstruction, South China University of Technology, Guangzhou, Guandong 510006, P. R. China ‡ School of Biological and Medical Engineering, Hefei University of Technology, Hefei, Anhui 230009, P. R. China § Department of Radiology and Tianjin Key Laboratory of Functional Imaging, Tianjin Medical University General Hospital, Tianjin 300052, P. R. China ⊥ The Affiliated High School of South China Normal University, Guangzhou 510630, P. R. China S Supporting Information *
ABSTRACT: Drug delivery systems with remotely controlled drug release capability are rather attractive options for cancer therapy. Herein, a reactive oxygen species (ROS)-sensitive polymeric nanocarrier TK-PPE@NPCe6/DOX was explored to realize remotely controlled drug release by light-activated size shrinkage. The TK-PPE@NPCe6/DOX encapsulating chlorin e6 (Ce6) and doxorubicin (DOX) was self-assembled from an innovative ROS-sensitive polymer TK-PPE with the assistance of an amphiphilic copolymer poly(ethylene glycol)-b-poly(εcaprolactone) (PEG-b-PCL). Under the 660 nm red light irradiation, ROS generated by the encapsulated Ce6 were capable of cleaving the TK linker in situ, which resulted in the rapid degradation of the TK-PPE@NPCe6/DOX core. Consequently, the size of TK-PPE@NPCe6/DOX shrank from 154 ± 4 nm to 72 ± 3 nm, and such size shrinkage affected further triggered rapid DOX release. As evidenced by both in vitro and in vivo experiments, such ROS-sensitive polymeric nanocarriers with light-induced size shrinkage capability offer remarkable therapeutic effects in cancer treatment. This concept provides new avenues for the development of light-activated drug delivery systems for remotely controlled drug release in vivo.
1. INTRODUCTION Nanocarriers with remotely controlled drug release capability have gained significant attention during the last decades due to their great potential to enhance therapeutic efficacy for cancer and minimize damage to normal tissues.1−4 Nanomaterials that respond to internal or external stimuli,5 such as pH,6 redox potentials,7 enzymes,8 ultrasound,9 magnetic field,10 and light,11 have been utilized to fabricate such smart nanocarriers for controlled drug release. Among the various types of stimuli, light is especially attractive because it can be remotely applied with high spatial and temporal resolutions.12 However, the majority of photochemical reactions must be activated by highenergy ultraviolet (UV) or blue light, which has limited tissue penetration and inevitable phototoxicity.13 Red or near-infrared (NIR) light, with wavelengths in the range of approximately 650−950 nm, is more suitable for biomedical applications because of its greater tissue penetration, reduced scattering, and minimal phototoxicity.14−16 However, the red and NIR light is difficult to cleave the chemical bond directly due to their low energy. Alternatively, current red or NIR light-responsive nanocarriers mainly utilize the photothermal effect to stimulate the release of loaded drugs.17−22 In addition, very few delivery © 2017 American Chemical Society
systems utilize upconversion nanoparticles to convert NIR to UV or visible light,23−26 which promotes the cleavage of photosensitive linkages and further stimulates drug release. Collectively, the development of nanocarriers responsive to red light or NIR light for remotely controlled drug release is still considerably desirable.27,28 Photodynamic therapy (PDT), which is based on the principle of generating reactive oxygen species (ROS) to induce cell apoptosis by photosensitizers under red or NIR light irradiation,29−31 has garnered great attention during the past decade.32−37 Recent reports have demonstrated that thioketal groups can be readily cleaved by ROS,38−42 which inspired us to integrate a nanoparticle combining photosensitizers and ROS-responsive nanomaterials for red or NIR light-controlled drug release. In light of this aim, we herein construct an innovative ROS-responsive nanocarrier to realize remotely controlled drug release by red light-activated size shrinkage. This nanocarrier TK-PPE@NPCe6/DOX comprises four compoReceived: November 11, 2017 Revised: December 20, 2017 Published: December 22, 2017 517
DOI: 10.1021/acs.chemmater.7b04751 Chem. Mater. 2018, 30, 517−525
Article
Chemistry of Materials
nanocarrier was capable of simultaneously encapsulating Ce6 and DOX by the nanoprecipitation method, and the amphiphilic polymer PEG-b-PCL was utilized to stabilize this formulation and provide a relatively inert particle surface. The UV−vis/NIR spectrum of TK-PPE@NPCe6/DOX (Figure 1C) showed strong absorbance at 560 and 660 nm, indicating the efficient coencapsulation of DOX and Ce6. Additionally, the loading contents of Ce6 and DOX were about 2.46 ± 0.17% and 5.88 ± 0.29%, respectively. Meantime, TK-PPE@ NPCe6/DOX maintained their diameters in phosphate buffer saline (PBS) or in PBS containing 10% fetal bovine serum (FBS) for over 7 days (Figure 1D), which might be due to stabilization by the PEG layer. According to our design, ROS produced by the encapsulated Ce6 rapidly degrades TK-PPE in situ into oligomers or small molecules upon 660 nm red light irradiation. To demonstrate it, Ce6 was encapsulated into the TK-PPE inner core with the assistance of PEG-b-PCL (TK-PPE@NPCe6), and then the TKPPE@NPCe6 was irradiated by a 660 nm laser (0.3 W/cm2, 60 min) and subjected to gel permeation chromatography (GPC) analysis. As shown in Figure 2A, PEG-b-PCL and TK-PPE exhibited two elution volume peaks at 21.7 and 24.6 min, respectively. After 660 nm laser irradiation, the peak at 24.6 min corresponded to TK-PPE almost completely disappeared, and oligomers or small molecules were observed. In contrast, the degradation did not occur in the absent of light irradiation. In addition, after irradiation at different laser power densities,
nents: ROS-responsive poly(thioketal phosphoester) (TKPPE), amphiphilic diblock copolymer poly(ethylene glycol)-bpoly(ε-caprolactone) (PEG-b-PCL), photosensitizer chlorin e6 (Ce6), and chemotherapeutic drug doxorubicin (DOX) (Figure 1A). Upon 660 nm red light irradiation, ROS produced by the
Figure 1. Preparation and characterization of the light-activated shrinkable nanoparticle TK-PPE@NPCe6/DOX. (A) Formation and mechanism of light-activated shrinkable nanoparticle TK-PPE@ NPCe6/DOX. (B) Schematic illustration of TK-PPE@NPCe6/DOX with light-activated size shrinkage for controlled DOX release. Upon 660 nm irradiation, the generated ROS was capable of degrading the TKPPE core in situ, resulting in the size shrinkage and triggered DOX release into cell nuclei for enhanced synergistic anticancer efficacy. (C) UV−vis/NIR absorption spectra of TK-PPE@NPCe6/DOX. (D) Size changes of TK-PPE@NPCe6/DOX after incubation in PBS and in PBS containing 10% FBS.
encapsulated Ce6 rapidly degrade TK-PPE core in situ into oligomers or small molecules; consequently, the nanocarriers TK-PPE@NPCe6/DOX shrink from 154 ± 4 nm into 72 ± 3 nm, which triggers the sudden burst of encapsulated DOX. Meanwhile, the generated ROS also induce tumor cell apoptosis, which combines with chemotherapy for synergistic antitumor activity (Figure 1B). Excitingly, this red lightactivated shrinkable polymeric nanocarrier exhibited great therapeutic effects in both in vitro cellular experiments and in vivo animal tumor model studies.
2. RESULTS AND DISCUSSION 2.1. Preparation and Characterization of ROS-Sensitive Polymeric Nanocarrier with Red Light-Induced Size Shrinkage Capability. To substantiate our design, we first synthesized the ROS-sensitive polymer TK-PPE using thioketal (TK) bonds as a linker between phosphoester units via condensation polymerization (Figure S1A), and successful synthesis was verified using 1H NMR spectroscopy (Figure S1B). The obtained hydrophobic TK-PPE as the inner core of
Figure 2. Red light-activated size shrinkage. (A) GPC measurement of TK-PPE@NPCe6 with or without 660 nm laser irradiation. The Mp (peak molecular weight) of the generated oligomers was marked. (B, C) Size changes of (B) TK-PPE@NPCe6 and (C) blank TK-PPE@NP plus free Ce6 after 660 nm laser irradiation at different times. (D) TEM images of TK-PPE@NPCe6 after 660 nm laser irradiation at different times. 518
DOI: 10.1021/acs.chemmater.7b04751 Chem. Mater. 2018, 30, 517−525
Article
Chemistry of Materials this TK-PPE@NPCe6 was collected and lyophilized for 1H NMR analysis. As shown in Figure S2, at a power density of 0.3 W/cm2, the peak at 1.58 ppm indicated that the CH3 in the thioketal linker of TK-PPE gradually decreased as the irradiation time increased. A similar trend was also observed at power densities of 0.15 W/cm2 (Figure S3) and 0.06 W/cm2 (Figure S4), except that the degradation rate decreased with a decrease in power density. According to these 1H NMR results, the degradation rate of TK-PPE was calculated, and it exhibited laser density and time dependencies (Figure S5). It was observed that approximately 75.3% of the thioketal linker of TK-PPE was efficiently cleaved at 0.3 W/cm2, indicating the almost complete degradation of the polymer TK-PPE, which was well consistent with the result of Figure 2A. On the contrary, about 57.9% and 31.4% of the thioketal linker was degraded at 0.15 W/cm2 and 0.06 W/cm2, respectively. After the degradation of TK-PPE under laser irradiation, the residual PEG-b-PCL shrank into smaller particles, which was observed through DLS. As shown in Figure 2B, the size of the nanoparticle continually shrank from 154 ± 4 nm to 72 ± 3 nm under 660 nm red light irradiation. Interestingly, such size shrinkage was not observed when free Ce6 and blank TKPPE@NP were separately dispersed in aqueous solution (Figure 2C), even though more ROS were generated than that of TK-PPE@NPCe6 (Figure S6). This red light-activated size shrinkage was also confirmed using transmission electron microscopy (TEM) imaging (Figure 2D), in which small particles less than 75 nm were observed after 660 nm laser irradiation. These results demonstrated that only ROS generated within the nanoparticle core can efficiently cleave the thioketal linker of TK-PPE in situ due to the short action distance (
