pH-responsive Doxorubicin Research Articles

Magnetic Driven Nanocarriers for pH-Responsive Doxorubicin Release in Cancer Therapy.

Doxorubicin is one of the most widely used anti-cancer drugs, but side effects and selectivity problems create a demand for alternative drug delivery systems. Herein we describe a hybrid magnetic nanomaterial as a pH-dependent doxorubicin release carrier. This nanocarrier comprises magnetic iron oxide cores with a diameter of 10 nm, enveloped in a hybrid material made of siliceous shells and ĸ-carrageenan. The hybrid shells possess high drug loading capacity and a favorable drug release profile, while the iron oxide cores allows easy manipulation via an external magnetic field. The pH responsiveness was assessed in phosphate buffers at pH levels equivalent to those of blood (pH 7.4) and tumor microenvironment (pH 4.2 and 5). The nanoparticles have a loading capacity of up to 12.3 wt.% and a release profile of 80% in 5 h at acidic pH versus 25% at blood pH. In vitro drug delivery tests on human breast cancer and non-cancer cellular cultures have shown that, compared to the free drug, the loaded nanocarriers have comparable antiproliferative effect but a less intense cytotoxic effect, especially in the non-cancer cell line. The results show a clear potential for these new hybrid nanomaterials as alternative drug carriers for doxorubicin.

Drug self-gating fluorescent nanoparticles for pH-responsive doxorubicin delivery

Intelligent drug delivery systems have attracted great attention in the field of biomedicine and cancer diagnosis. In this work, a drug delivery system that can be gated by doxorubicin itself and together with pH-responsive ability has been designed and prepared based on the upconversion nanoparticles. The drug delivery system is a special core–shell structure, consisting of upconversion nanoparticle core and mesoporous silica shell. The new system tactfully bypasses the use of auxiliary capping agents and exhibits desirable drug release at pH = 5, enhancing HeLa cells inhibition. The introduction of Schiff base plays a key role in the process of achieving pH-responsive drug release. Moreover, upconversion nanoparticles could emit bright yellow-green fluorescence (540 nm) under the irradiation of near-infrared light (980 nm) for in vivo bioimaging. This characteristic provides the possibility of locating tumor tissues and real-time tracing drug delivery.

A dual-functional HER2 aptamer-conjugated, pH-activated mesoporous silica nanocarrier-based drug delivery system provides in vitro synergistic cytotoxicity in HER2-positive breast cancer cells.

Purpose: As well as functioning as a ligand that is selectively internalized by cells overexpressing human epidermal growth factor receptor-2 (HER2), HApt can exert cytotoxic effects by inducing cross-linking and subsequent translocation of HER2 to cytoplasmic vesicles, such downregulation of HER2 inhibits cell proliferation and induces apoptosis. We aimed to exploit the potential of HApt as both a targeting agent and antagonist to maximize the efficacy of mesoporous silica nanoparticle (MSN)-based drug release systems for HER2-positive breast cancer.Materials and methods: We fabricated novel HApt aptamer-functionalized pH-sensitive β-cyclodextrin (β-CD)-capped doxorubicin (DOX)-loaded mesoporous silica nanoparticles (termed MSN-BM/CD-HApt@DOX) for targeted delivery and selective targeting of HER2-positive cells. MSN-functionalized benzimidazole (MSN-BM) was used to load and achieve pH stimuli-responsive release of the chemotherapeutic agent doxorubicin (DOX). β-cyclodextrin was introduced as a gatekeeper for encapsulated DOX and HApt as a selective HER2-targeting moiety and biotherapeutic agent.Results: Physical and chemical characterizations (FT-IR, XRD, TEM and BET) confirmed successful construction of MSN-BM/CD-HApt@DOX nanoparticles. In vitro release assays verified pH-sensitive DOX release. MSN-BM/CD-HApt@DOX (relative DOX concentration, 3.6 μg/mL) underwent HER2-mediated endocytosis and was more cytotoxic to HER2-positive SKBR3 cells than HER2-negative MCF7 cells. MSN-BM/CD-HApt@DOX also exhibited better uptake and stronger growth inhibition in SKBR3 cells than the control MSN-BM/CD-NCApt@DOX functionalized with a scrambled nucleotide sequence on CD. Overall, intracellular delivery of DOX and the biotherapeutic agent HApt resulted in synergistic cytotoxic effects in HER2-positive cancer cells in comparison to either DOX or HApt alone.Conclusion: MSN-BM/CD-HApt@DOX enables HER2-mediated targeting and biotherapeutic effects as well as pH-responsive DOX drug release, resulting in synergistic cytotoxic effects in HER2-overexpressing cells in vitro. This novel nanocarrier could potentially enable specific targeting to improve the efficacy of chemotherapy for HER2-positive cancer.

Coordination bonding-based Fe3O4@PDA-Zn2+-doxorubicin nanoparticles for tumor chemo-photothermal therapy

Multistimuli-responsive vehicles that deliver drugs in temporal-, spatial- and dosage-controlled manners have developed as a potential platform in tumor therapy. However, how to integrate these functions in one single carrier effectively still presents a lot of challenge. Here, we developed a strategy to construct a photothermal and pH responsive platform based on Zn2+ coordination with doxorubicin (DOX) and polydopamine (PDA) on the surface of magnetic nanoparticles (Fe3O4@PDA-Zn2+-DOX NPs). In this architecture, Fe3O4@PDA nanoparticles triggered photothermal effects for tumor hyperthermia, and Zn2+ coordinated DOX was released in responding to the thermal effect to achieve chemotherapy simultaneously. Moreover, DOX release was further promoted at acidic environment due to the pH sensitivity of Zn2+ coordination. Therefore, our system possesses multiple effects in tumor treatment: photothermal therapy with near infrared lighting (NIR), thermosensitive DOX release for chemotherapy, and pH-responsive DOX release to enhance deeper therapy in tumor acidic microenvironment. Our in vivo results provide the evidence that Fe3O4@PDA-Zn2+-DOX NPs upon laser exposure have effective anti-tumor therapeutic activity, indicating this platform is suitable for enhanced chemo-photothermal synergistic tumor therapy.

Polymer Brush Decorated MOF Nanoparticles Loaded with AIEgen, Anticancer Drug, and Supramolecular Glue for Regulating and In Situ Observing DOX Release.

UiO-66-based metal-organic framework nanoparticles functionalized with abundant polycationic segments as polymer brushes on surface are created to load negatively charged functional entities composed of anticancer drug, doxorubicin (DOX), and aggregation-induced emissive luminogen, a tetraphenylethene (TPE) derivative, followed by further modification with cucurbit[7]uril (CB[7]) as a supramolecular glue with the aim of pursuing a pH-responsive release function of the loaded functional components. The subsequent investigations verified the constructed formulation capable of promoting the stability and cellular uptake of the nanoparticles. The fluorescence resonance energy transfer between TPE donor and DOX acceptor enables in situ observation of pH-responsive DOX release. Significantly, CB modification appears to facilitate intracellular release of the DOX payload, eventually accounting for potent cytotoxicity to the treated cells.

PEGylated hydrazided gold nanorods for pH-triggered chemo/photodynamic/photothermal triple therapy of breast cancer

Integration of multimodal therapies into one nanoplatform holds great promise to overcome the drawbacks of conventional single-modal therapy and pursues enhanced anticancer efficacy. Herein, we developed a PEGylated gold nanorods (GNRs)-based nanoplatform (GNRs-MPH-ALA/DOX-PEG) with pH-responsive drug release property for triple-combined chemotherapy (CT), photodynamic therapy (PDT) and photothermal therapy (PTT) of breast cancer. GNRs were first decorated with mercaptopropionylhydrazide (MPH) and thiol-terminated monomethoxyl poly(ethylene glycol) (mPEG-SH) via Au-thiol linkage, and subsequently conjugated with chemotherapeutant doxorubicin (DOX) and pro-photosensitizer 5-aminolevulinic acid (ALA) through acid-liable hydrazone bonds between drugs and MPH molecules. The resulting nanoplatform GNRs-MPH-ALA/DOX-PEG exhibited excellent stability in physiological solutions and pH-responsive DOX and ALA release behaviors. In vitro studies showed that GNRs-MPH-ALA/DOX-PEG could efficiently enter human breast cancer MCF-7 cells and release DOX and ALA into cytoplasm. Furthermore, DOX could locate in the cell nucleus and ALA was productively metabolized into protoporphyrin IX (PpIX). Upon near-infrared (NIR) irradiation, PpIX produced enough reactive oxygen species for PDT and meanwhile GNRs could efficiently induce hyperthermia for PTT. Compared with single CT and dual-modal CT/PDT or CT/PTT treatment, the triple-combined CT/PDT/PTT treatment could more efficiently kill MCF-7 cells via a superadditive antitumor effect. Furthermore, the circulation half-life of GNRs-MPH-ALA/DOX-PEG in the blood was as long as approximately 52 min and it exhibited a tumor accumulation of 3.3%. The triple-combined CT/PDT/PTT treatment could completely suppress tumor growth without obvious systemic toxicity. Our study paves a new avenue for multimodal therapy of breast cancer. Statement of significanceThe development of a simple but effective strategy to construct a versatile nanoplatform for multi-combined therapy still remains an enormous challenge. In this work, we developed a novel and simple nanoplatform GNRs-MPH-ALA/DOX-PEG with pH-responsive drug release for triple-combined chemotherapy (CT), photodynamic therapy (PDT) and photothermal therapy (PTT) of breast cancer. The nanoplatform could be efficiently internalized by MCF-7 cells. The intracellular GNRs-MPH-ALA/DOX-PEG could release DOX for CT, induce hyperthermia for PTT and generate high levels of ROS for PTT. Compared with single CT and dual-modal CT/PDT or CT/PTT treatments, the triple-combined CT/PDT/PTT treatment could more efficiently kill MCF-7 cells via a superadditive antitumor effect. Furthermore, upon triple-combined CT/PDT/PTT treatment, the tumor growth was completely suppressed without obvious systemic toxicity.

Design, Synthesis, and Characterization of Schiff Base Bond-Linked pH-Responsive Doxorubicin Prodrug Based on Functionalized mPEG-PCL for Targeted Cancer Therapy.

The side effects of doxorubicin (DOX) extremely limit its application in the treatment of malignant tumors. Nano-sized polymeric drugs based on the acidic microenvironment of tissular- or intra- tumor have attracted ample attention because of their potential in reducing side effects. In this research, an amphiphilic diblock copolymer based on poly (ethylene glycol) (PEG) and functionalized polycaprolactone (PCL) was synthesized and utilized as the drug carrier. DOX was chemically conjugated with the polymer via acid-cleavable imine bonds to obtain a novel pH-sensitive DOX prodrug (mPEG-PCL-Imi-DOX). mPEG-PCL-Imi-DOX (24.2 wt % DOX content) formed micelles with an average diameter of 125 nm through a simple solvent evaporation method. The in vitro release profile demonstrated that DOX release of the prodrug micelles was pH-responsive and able to be accelerated with the decrease of pH. In vitro cytotoxicity assay tests revealed that the pH-sensitive DOX prodrug micelles exhibited relatively lower toxicity and similar antitumor efficacy towards MCF-7 cells compared with free DOX. Hence, the DOX prodrug micelles with imine bonds can offer a carrier with great potential for chemo-therapeutics.

Polymeric micelles encapsulating pH-responsive doxorubicin prodrug and glutathione-activated zinc(II) phthalocyanine for combined chemotherapy and photodynamic therapy

A series of polymeric micelles encapsulating different ratios of doxorubicin (DOX) and zinc(II) phthalocyanine (ZnPc) have been prepared for dual chemotherapy and photodynamic therapy (PDT). The amphiphilic block copolymers consist of methoxypolyethylene glycol (PEG) and poly(β-benzyl-l-aspartate) (PBLA), in which DOX and ZnPc were conjugated to the aspartate side chain through an acid-labile hydrazone linker and a redox-responsive disulfide linker, respectively. The polymers were self-assembled into spherical polymeric micelles with diameters of about 160–180 nm and their surface charges were found to be nearly neutral due to the outermost PEG layer. These polymeric micelles exhibited excellent stability and silenced fluorescence in aqueous media. The controlled release of DOX and ZnPc was studied in phosphate solution under acidic and reducing environments, respectively. In vitro study demonstrated that these polymeric micelles could be internalized into HepG2 human hepatocellular carcinoma cells, showing the fluorescence of DOX in the nucleus and fluorescence of ZnPc in the cytoplasm. This observation suggested that the acidic and reducing intracellular environments could trigger the release of DOX and ZnPc by cleaving the corresponding linkers. These micelles exhibited different degree of dark- and photo-cytotoxicity on the HepG2 cells due to the chemocytotoxic DOX and the singlet oxygen generated upon irradiation of the ZnPc. With a certain ratio of DOX and ZnPc, they caused a synergistic cytotoxicity as calculated by combination index. The DOX-ZnPc-micelles-2, which has a DOX/ZnPc molar ratio of 3.8, could induce cell death mainly through apoptosis and exhibit preferential tumor retention in tumor-bearing mice via the enhanced permeability and retention effect. The results suggest that these polymeric micelles are promising nanoplatforms for the delivery of anticancer drugs and photosensitizers for dual therapy.

Polyaspartic acid-anchored mesoporous silica nanoparticles for pH-responsive doxorubicin release.

BackgroundNanotechnology-based drug delivery systems exhibit promising therapeutic efficacy in cancer chemotherapy. However, ideal nano drug carriers are supposed to be sufficiently internalized into cancer cells and then release therapeutic cargoes in response to certain intracellular stimuli, which has never been an easy task to achieve.ObjectiveThis study is to design mesoporous silica nanoparticles (MSNs)-based pH-responsive nano drug delivery system that is effectively internalized into cancer cells and then release drug in response to lysosomal/endosomal acidified environment.MethodsWe synthesized MSNs by sol-gel method. Doxorubicin (DOX) was encapsulated into the pores as a model drug. Polyaspartic acid (PAsA) was anchored on the surface of mesoporous MSNs (P-MSNs) as a gatekeeper via amide linkage and endowed MSNs with positive charge.ResultsIn vitro release analysis demonstrated enhanced DOX release from DOX-loaded PAsA-anchored MSNs (DOX@P-MSNs) under endosomal/lysosomal acidic pH condition. Moreover, more DOX@P-MSNs were internalized into HepG2 cells than DOX-loaded MSNs (DOX@MSNs) and free DOX revealed by flow cytometry. Likewise, confocal microscopic images revealed that DOX@P-MSNs effectively released DOX and translocated to the nucleus. Much stronger cytotoxicity of DOX@P-MSNs against HepG2 cells was observed compared with DOX@MSNs and free DOX.ConclusionDOX@P-MSNs were successfully fabricated and achieved pH-responsive DOX release. We anticipated this nanotherapeutics might be suitable contenders for future in vivo cancer chemotherapeutic applications.

PH Responsive Doxorubicin Delivery by Fluorous Polymers for Cancer Treatment.

Polymeric nanoparticles have emerged as valuable drug delivery vehicles as they improve solubility of hydrophobic drugs, enhance circulation lifetime, and can improve the biodistribution profile of small-molecule therapeutics. These nanoparticles can take on a host of polymer architectures including polymersomes, hyperbranched nanoparticles, and dendrimers. We have recently reported that simple low molecular weight fluorous copolymers can self-assemble into nanoparticles and show exceptional passive targeting into multiple tumor models. Given the favorable biodistribution of these particles, we sought to develop systems that enable selective delivery in acidic environments, such as the tumor microenvironment or the lysosomal compartment. In this report, we describe the synthesis and in vitro biological studies of a pH-responsive doxorubicin (DOX) fluorous polymer conjugate. A propargyl DOX hydrazone was synthesized and covalently attached to a water-dispersible fluorous polymer composed of trifluoroethyl methacrylate (TFEMA) and oligo(ethylene glycol) methyl ether methacrylate (OEGMEMA) using the ligand-accelerated copper-catalyzed azide-alkyne cycloaddition. Driven by the high fluorine content of the copolymer carrier, the DOX-copolymer formed stable micelles under aqueous conditions with a hydrodynamic diameter of 250 nm. The DOX-copolymer showed internalization into multiple in vitro models for breast and ovarian cancer. Cytotoxicity assays demonstrated efficacy in both breast and ovarian cancer with overall efficacy being highly dependent on the cell line chosen. Taken together, these results present a platform for the pH-triggered delivery of DOX from a fluorous micelle carrier effective against multiple cancer models in vitro.

Polymeric nanovesicles as simultaneous delivery platforms with doxorubicin conjugation and elacridar encapsulation for enhanced treatment of multidrug-resistant breast cancer.

Multidrug resistance (MDR) is one of the major obstacles hindering the successful chemotherapy of cancer. Overexpression of drug efflux transporters such as P-glycoprotein (P-gp) is an important factor responsible for MDR. In this study, a novel copolymer methoxy-poly(ethylene glycol)-poly[(N-(6-hydroxyhexyl)-g-doxorubicin-l-aspartamide)-(β-benzyl-l-aspartate)] (mPEG-P[Asp(HPA-g-DOX)-BLA)] was synthesized and utilized to assemble into nanovesicles with hydrophilic P-gp inhibitor elacridar hydrochloride (Ela) encapsulated into the aqueous lumen. Doxorubicin (DOX) was covalently conjugated onto the polymer chain via a pH-cleavable amide linkage, leading to a pH responsive DOX release as well as disintegration of the nanovesicles in the lysosome of tumor cells. In vitro studies demonstrated that the DOX and Ela co-delivered nanovesicles showed superior cytotoxicity and enhanced anti-tumor properties as compared to single DOX-delivery nanosystems in MCF-7/ADR cancer, which was attributed to the P-gp bioactivity inhibition as investigated by a cell immunofluorescence assay. In vivo studies showed that the polymeric nanovesicles effectively accumulated at the tumor site and the co-delivered DOX and Ela effectively suppressed the MCF-7/ADR tumor growth. All the results indicated that the acid-liable nanovesicles had a synergistic effect to enhance antitumor efficacy for multidrug-resistant breast cancer treatment.

Chitosan capped nanoscale Fe-MIL-88B-NH2 metal-organic framework as drug carrier material for the pH responsive delivery of doxorubicin

In recent years nanoscale metal-organic frameworks (NMOFs) are contributing as an effective material for use in drug delivery and imaging applications due to their porous surfaces and easy surface modifications. In this work, Fe-MIL-88B-NH2 NMOFs were successfully synthesized on facile hydrothermal route and 2-aminoterephthalic acid (NH2-BDC) was employed as a bridging ligand to activate amine functional groups on the surface. Amine functional groups not only serve as a structure stabilizing agent but also enhance the loading efficiency of the doxorubicin (DOX) anticancer drug. A pH responsive DOX release was realized by introducing a positively charged chitosan (Chi) capping layer. Upon Chi-coating, cleavage was observed in the Fe-MIL-88B-NH2 structure at acidic pH, while gel-like insoluble structure was formed at basic pH. By utilizing this phenomenon, a pH responsive DOX release system was developed by using Chi capped Fe-MIL-88B-NH2 NMOFs under the designed pH (4.0–8.0). The results suggest the Chi capped Fe-MIL-88B-NH2 can be a promising candidate for future pH responsive drug delivery systems.

Super paramagnetic Norbornene Copolymer Functionalized with Biotin and Doxorubicin: A Potential Unique Site-Specific Theranostic Agent

Polymer-based nanosystems have been extensively explored either as therapeutic agents or bioimaging probes in the cancer diagnosis. However, very few systems are successful in combining both therapy and imaging. Herein, a new class of norbornene based copolymer, Nor-Dox-Cob-Btn is proposed as potential theranostics agent for tumor diagonosis. The copolymer (Nor-Dox-Cob-Btn) with doxorubicin, cobalt carbonyl complex, and biotin as pendent functionalized group is synthesized, using ring opening metathesis polymerization (ROMP). The cell viability, drug release, NMR relaxation, NMR 1-D image and Epi fluorescence microscopy studies on Nor-Dox-Cob-Btn nanocarrier are thoroughly studied. The effect of nanocarrier on transverse relaxation (T2) of water molecule and NMR 1-D image suggest that the nanocarrier has the potential application in magnetic resonance imaging agent. The T2-weighted MRI agent, along with biotin receptor assisted pH responsive doxorubicin release from Nor-Dox-Cob-Btn, prompts us to envision...

Theranostic pH responsive doxorubicin loaded nanoparticles inducing active targeting and apoptosis for advanced gastric cancer

Theranostic pH responsive doxorubicin loaded nanoparticles inducing active targeting and apoptosis for advanced gastric cancer

Amphiphilic Diblock Terpolymer PMAgala-b-P(MAA-co-MAChol)s with Attached Galactose and Cholesterol Grafts and Their Intracellular pH-Responsive Doxorubicin Delivery.

In this work, a series of diblock terpolymer poly(6-O-methacryloyl-D-galactopyranose)-b-poly(methacrylic acid-co-6-cholesteryloxy hexyl methacrylate) amphiphiles bearing attached galactose and cholesterol grafts denoted as the PMAgala-b-P(MAA-co-MAChol)s were designed and prepared, and these terpolymer amphiphiles were further exploited as a platform for intracellular doxorubicin (DOX) delivery. First, employing a sequential RAFT strategy with preliminarily synthesized poly(6-O-methacryloyl-1,2:3,4-di-O-isopropylidene-d-galactopyranose) (PMAIpGP) macro-RAFT initiator and a successive trifluoroacetic acid (TFA)-mediated deprotection, a series of amphiphilic diblock terpolymer PMAgala-b-P(MAA-co-MAChol)s were prepared, and were further characterized by NMR, Fourier transform infrared spectrometer (FTIR), gel permeation chromatography (GPC), differential scanning calorimetry (DSC), and a dynamic contact angle testing instrument (DCAT). In aqueous media, spontaneous micellization of the synthesized diblock terpolymer amphiphiles were continuously examined by critical micellization concentration assay, dynamic light scattering (DLS), and transmission electron microscopy (TEM), and the efficacies of DOX loading by these copolymer micelles were investigated along with the complexed nanoparticle stability. Furthermore, in vitro DOX release of the drug-loaded terpolymer micelles were studied at 37 °C in buffer under various pH conditions, and cell toxicities of as-synthesized diblock amphiphiles were examined by MTT assay. Finally, with H1299 cells, intracellular DOX delivery and localization by the block amphiphile vectors were investigated by invert fluorescence microscopy. As a result, it was revealed that the random copolymerization of MAA and MAChol comonomers in the second block limited the formation of cholesterol liquid-crystal phase and enhanced DOX loading efficiency and complex nanoparticle stability, that ionic interactions between the DOX and MAA comonomer could be exploited to trigger efficient DOX release under acidic condition, and that the diblock terpolymer micellular vector could alter the DOX trafficking in cells. Hence, these suggest the pH-sensitive PMAgala-b-P(MAA-co-MAChol)s might be further exploited as a smart nanoplatform toward efficient antitumor drug delivery.

Synthesis and functions of well-defined polymer-drug conjugates as efficient nanocarriers for intravesical chemotherapy of bladder cancer(a).

Novel poly(ethylene glycol) and poly(N-(2-hydroxypropyl)methacrylamide) block copolymer (PEG-b-PHPMA) with well-defined composition was synthesized by RAFT polymerization. Folate and doxorubicin (DOX) were quantitatively introduced into the copolymer. The influences of folate content and pH value on folate receptor (FR) mediated cell endocytosis and pH-responsive DOX release were studied. It has been demonstrated that minimum folate content is needed for the enrichment of hydrophobic folate on the hydrophilic part of polymer conjugates. The cytotoxicity of targetable polymer drug conjugates was much higher than that of non-targetable ones and free DOX. It could be concluded that the folate plays a significant role in targeting and internalization of the conjugates against bladder cancer cells.

Coordinate Bonding Strategy for Molecularly Imprinted Hydrogels: Toward pH-Responsive Doxorubicin Delivery

Molecularly imprinted hydrogel (MIH) as drug delivery system has been studied. It still remains a challenge to construct the stimuli-responsive MIH. Here, we report a coordinate bond strategy for imprinting doxorubicin (Dox) in hydrogel capable of pH-responsive and sustained drug delivery. The imprinting condition such as template-monomer interactions induced by metal ion was carefully investigated by spectroscopic methods. The obtained Dox-MIH was evaluated by absorption and in vitro release experiments. It has been demonstrated that the cupric ion mediated interaction between Dox and 4-vinyl pyridine via coordination and the optimal coordinate ratio of Dox/Cu(2+) was 2:1. The rebinding amount of MIH to Dox was 2.7-fold that of nonimprinted hydrogel and the Dox-loaded MIH showed a pH-responsive release property. Not more than 10% of loaded drug was released from Dox-MIH at pH 7.2 during a time course of 7 days. However, near to 60% of loaded drug was sustainedly released at pH 5.0 during the same period. These results indicated that Dox-MIH with pH-responsive behavior possessed great promising as sustained-release delivery system of anticancer drug.

Intracellularly monitoring/imaging the release of doxorubicin from pH-responsive nanoparticles using Förster resonance energy transfer

Stimuli-responsive nanoparticles (NPs) have been receiving much attention as a drug-delivery vehicle for therapeutic applications; once internalized into cells, the intracellular fate of NPs and their drug release behavior in response to local stimuli must be understood for efficient delivery of therapeutics. In this study, we prepared pH-responsive doxorubicin (DOX)-loaded NPs, made of N-palmitoyl chitosan bearing a Cy5 moiety (Cy5–NPCS), as an anticancer delivery device. The results of our molecular dynamic simulations showed that the ability of Cy5–NPCS to self-associate offered the close proximity between the donor (DOX) and the acceptor (Cy5) required for Förster resonance energy transfer (FRET), while the pH-driven structure transition prescribed the on-to-off switch of the energy transfer. The caveolae-mediated pathway played a major role in the internalization of NPCS NPs. Using the concept of FRET, we found that the DOX fluorescence in the cytosol was first seen when NPCS NPs were present in the slightly acidic early endosomes. Following NPCS NPs trafficking into a more acidic organelle (late endosomes/lysosomes), a more evident release of DOX into the cytosol was observed; the released DOX was then gradually accumulated in the cell nuclei, leading to a significant cytotoxicity. Understanding the fate of NPs with respect to their intracellular localization and drug release behavior is crucial for the rational design of drug carriers.