A tumor-acidity-activated charge-conversional nanogel as an intelligent vehicle for promoted tumoral-cell uptake and drug delivery

Multifunctional PEGylated multiwalled carbon nanotubes for enhanced blood pool and tumor MR imaging

Long-circulating multifunctional Gd(III)-loaded multiwalled carbon nanotubes (MWCNTs) modified with polyethylene glycol are designed and synthesized. The formed MWCNTs are water-dispersible, stable, and have good cytocompatibility and antifouling property. With the low r 2 /r 1 relaxivity ratio and relatively long blood circulation time, the multifunctional MWCNTs are able to be used as a platform for enhanced blood pool and tumor MR imaging.

Tumor-acidity activated surface charge-conversion of polymeric nanocarriers for enhanced cell adhesion and targeted drug release

The development of stimuli-responsive polymeric nanocarriers could significantly enhance drug bioavailability due to improved pharmacokinetics and biodistribution. However, in the drug delivery process, the poor cell uptake of drug-loaded carriers has greatly limited the therapeutic efficiency for anti-cancer applications. Herein, 2,3-dimethylmaleic anhydride (DMMA) is engineered into the well-defined biodegradable amphiphilic block copolymer poly(D,L-lactide)-block-poly(2-aminoethyl methacrylate) (PLA-b-PAEMA) to construct a tumor-acidity activated nanocarrier (PLA-b-PAEMA/DMMA) for potential tumor therapy. After the loading of positively charged DOX·HCl into the negatively charged corona structure through electrostatic attraction, this carrier is expected to prolong the blood circulation time and smartly convert surface charge from negative to positive for enhanced tumor cell uptake and targeted drug release. Furthermore, this carrier exhibits additional cytotoxicity for tumor cells after the tumor-acidity activated surface charge-conversion from negative to positive. Thus, this smart carrier is a feasible candidate for potential cancer therapy.

Stepwise-acid-active multifunctional mesoporous silica nanoparticles for tumor-specific nucleus-targeted drug delivery

In this paper, a novel stepwise-acid-active multifunctional mesoporous silica nanoparticle (MSN-(SA)TAT&(DMA)K11) was developed as a drug carrier. The MSN-(SA)TAT&(DMA)K11 is able to reverse its surface charge from negative to positive in the mildly acidic tumor extracellular environment. Then, the fast endo/lysosomal escape and subsequent nucleus targeting as well as intranuclear drug release can be realized after cellular internalization. Because of the difference in acidity between the tumor extracellular environment and that of endo/lysosomes, this multifunctional MSN-(SA)TAT&(DMA)K11 exhibits a stepwise-acid-active drug delivery with a tumor-specific nucleus-targeted property.

Multifunctional enveloped mesoporous silica nanoparticles for subcellular co-delivery of drug and therapeutic peptide

A multifunctional enveloped nanodevice based on mesoporous silica nanoparticle (MSN) was delicately designed for subcellular co-delivery of drug and therapeutic peptide to tumor cells. Mesoporous silica MCM-41 nanoparticles were used as the core for loading antineoplastic drug topotecan (TPT). The surface of nanoparticles was decorated with mitochondria-targeted therapeutic agent (Tpep) containing triphenylphosphonium (TPP) and antibiotic peptide (KLAKLAK)2 via disulfide linkage, followed by coating with a charge reversal polyanion poly(ethylene glycol)-blocked-2,3-dimethylmaleic anhydride-modified poly(L-lysine) (PEG-PLL(DMA)) via electrostatic interaction. It was found that the outer shielding layer could be removed at acidic tumor microenvironment due to the degradation of DMA blocks and the cellular uptake was significantly enhanced by the formation of cationic nanoparticles. After endocytosis, due to the cleavage of disulfide bonds in the presence of intracellular glutathione (GSH), pharmacological agents (Tpep and TPT) could be released from the nanoparticles and subsequently induce specific damage of tumor cell mitochondria and nucleus respectively with remarkable synergistic antitumor effect.

Targeted delivery of doxorubicin into tumor cells via MMP-sensitive PEG hydrogel-coated magnetic iron oxide nanoparticles (MIONPs)

Targeting tumors with nano-scale delivery systems shows promise to improve the therapeutic effects of chemotherapeutic drugs. However, the limited specificity of current nano-scale systems for cancer tissues prevents realization of their full clinical potential. Here, we demonstrate an effective approach to creating as targeted nanocarriers for drug delivery: MIONPs coated with integrin-targeted and matrix-metalloproteinase (MMP)-sensitive PEG hydrogel scaffolds. The functional PEG hydrogel coating has been designed for active loading as well as triggered intra-cellular release of the cancer therapeutic agent doxorubicin (DOX). Our study demonstrated that coated nanocarriers could be taken into cancer cells 11 times more efficiently than uncoated ones. Furthermore, confocal laser scanning microscopy images revealed that these targeted nanocarriers could efficiently deliver and release DOX into the nuclei of HeLa cells within 2h. Coating MIONPs with multifunctional PEG hydrogel could be a promising alternative to existing vehicles for targeted delivery of DOX into tumor tissue.

Stimuli-Responsive Materials for Controlled Release of Theranostic Agents

Stimuli-responsive materials are so named because they can alter their physicochemical properties and/or structural conformations in response to specific stimuli. The stimuli can be internal, such as physiological or pathological variations in the target cells/tissues, or external, such as optical and ultrasound radiations. In recent years, these materials have gained increasing interest in biomedical applications due to their potential for spatially and temporally controlled release of theranostic agents in response to the specific stimuli. This article highlights several recent advances in the development of such materials, with a focus on their molecular designs and formulations. The future of stimuli-responsive materials will also be explored, including combination with molecular imaging probes and targeting moieties, which could enable simultaneous diagnosis and treatment of a specific disease, as well as multi-functionality and responsiveness to multiple stimuli, all important in overcoming intrinsic biological barriers and increasing clinical viability.

Peptide Decoration of Nanovehicles to Achieve Active Targeting and Pathology-Responsive Cellular Uptake for Bone Metastasis Chemotherapy

To improve bone metastases chemotherapy, a peptide-conjugated diblock copolymer consisting of chimeric peptide, poly(ethylene glycol) and poly(trimethylene carbonate) (Pep-b-PEG-b-PTMC) is fabricated as a drug carrier capable of bone-seeking targeting as well as pathology-responsive charge reversal to ensure effective cellular uptake at the lesion sites. The chimeric peptide CKGHPGGPQAsp₈ consists of an osteotropic anionic Asp8, a cathepsin K (CTSK)-cleavable substrate (HPGGPQ) and cationic residue tethered to polymer chain. Pep-b-PEG-b-PTMC can spontaneously self-assemble into negatively charged nanomicelles (~75 nm). As to the model drug of doxorubicin, Pep-b-PEG-b-PTM shows 30.0 ± 1 % and 90.1 ± 2 % for loading content and loading efficiency, respectively. High bone binding capability is demonstrated with that 66 % of Pep-b-PEG-b-PTMC micelles are able to bind to hydroxyl apatite, whereas less than 15 % is for Pep-free micelles. The nanomicelles exhibit a negative-to-positive charge conversion from -18.5 ± 1.9 mV to 15.2 ± 1.8 mV upon exposure to CTSK, an enzyme overexpressed in bone metastatic microenvironments. Such a pathology-responsive transition would lead to remarkably enhanced cellular uptake of the nanomicelles upon reaching lesion sites, thus improving the drug efficacy as verified by the in vitro cytotoxicity assay and the in vivo study in myeloma-bearing 5TGM1 mice model.

Global gene expression analysis of cellular death mechanisms induced by mesoporous silica nanoparticle-based drug delivery system

Mesoporous silica nanoparticles (MSNs), as one of the most promising inorganic drug carriers, have attracted ever increasing attention due to their unique structural, physicochemical, and biochemical features. Drug delivery systems (DDSs) based on MSNs could easily escape from endosomes after endocytosis and protect the loaded drugs from bioerosion by stable MSN carriers, efficiently deliver drugs intracellularly in a sustained release way, and consequently kill cancer cells at enhanced efficacy. However, the underlying pathways and mechanisms of cancer cell death induced by MSN-mediated drug delivery have not been well explored. In this study, we introduce gene expression analyses to evaluate the pathways and mechanisms of cancer cell death induced by a MSN-based drug delivery system. Unique changes in gene expressions and gene ontology terms, which were caused only by the MSN-based DDS (DOX-loaded MSNs, DOX@MSNs) but not by free drug doxorubicin (DOX) and/or the carrier MSNs, were discovered and proposed to be responsible for the varied cell death mechanisms, including the greatly enhanced necrosis due to amplified oxidative stress and the apoptosis related with DNA/RNA synthesis and cell cycle inhibitions. By virtue of a certain kind of synergetic biological effect between the drug and the carrier, the DOX@MSNs DDS was found capable of increasing the intracellular levels of reactive oxygen species and triggering the mitochondria-related autophagic lysosome pathway, consequently activating a specific pathway of necrosis, which is different from those by the free drug and the carrier.

Rational design of polyion complex nanoparticles to overcome cisplatin resistance in cancer therapy

Rationally designed PIC nanoparticles as next-generation delivery system: we have developed a core-shell-corona PIC nanoparticle (⊕) NP/Pt@PPC-DA as a next-generation delivery system. (⊕) NP/Pt@PPC-DA exhibits prolonged circulation and enhanced drug accumulation in tumors. Subsequently, tumor pH leads to the release of (⊕) NP/Pt, which facilitates cellular uptake followed by rapid intracellular cisplatin release. Using this delivery strategy cisplatin-resistant tumor growth in a murine xenograft model has been successfully suppressed.

Morpholino-decorated long circulating polymeric micelles with the function of surface charge transition triggered by pH changes

Micelles with surface morpholino groups were stealthy at blood and normal tissue pH (7.4) due to the unprotonated hydrophilic morpholino groups on the surfaces. At tumor pH (<7), the micelle surfaces were positively charged because of the protonation of the morpholino groups, which promoted the cellular uptake of the micelles.

Dual Stimuli - Dual Response Nanoassemblies Prepared from a Simple Homopolymer

A dual stimuli responsive nanogel-polyelectrolyte complex based on electrostatic coating has been developed. The nanoassembly is designed to elicit two disparate responses (viz. surface property change and guest encapsulation stability) from two different stimuli (viz. pH and redox variations). The components of the nanogel and the polyelectrolyte have been conveniently achieved from a simple homopolymer, poly(pentafluorophenylacrylate).

Magnetic and pH sensitive drug delivery system through NCA chemistry for tumor targeting

Magnetic- and pH- dually sensitive drug delivery system.

Hydrogen-bonding strategy for constructing pH-sensitive core–shell micelles with hydrophilic polymer as the shell and hydrophobic drug as the core

pH-sensitive micelles with hydrophilic polymer as the shell and hydrophobic drug as the core.

Synthesis and in vitro evaluation of charge reversal photoresponsive quinoline tethered mesoporous silica for targeted drug delivery

We developed excellent charge reversal photoresponsive nanoparticles for targeted delivery of the anticancer drug chlorambucil.

A charge-switchable, four-armed polymeric photosensitizer for photodynamic cancer therapy

A water-soluble, charge-switchable, four-armed polymeric photosensitizer (C4P-PS), in which charge switching is pH dependent, has been designed as a new class of photosensitizer for photodynamic cancer therapy.

Biodegradable multiblock polyurethane micelles with tunable reduction-sensitivity for on-demand intracellular drug delivery

Biodegradable polyurethanes bearing varied amounts of disulfide linkages in the backbone can rapidly enter tumor cells and efficiently transport the encapsulated payloads into cytosol, resulting in controlled inhibition effects against cancer cells. The nanocarriers are promising candidates for on-demand intracellular drug delivery applications.

Self-assembly behaviors of thermal- and pH- sensitive magnetic nanocarriers for stimuli-triggered release

In the present work, we prepare thermo- and pH-sensitive polymer-based nanoparticles incorporating with magnetic iron oxide as the remote-controlled, stimuli-response nanocarriers. Well-defined, dual functional tri-block copolymer poly[(acrylic acid)-block-(N-isopropylacrylamide)-block-(acrylic acid)], was synthesized via reversible addition-fragmentation chain-transfer (RAFT) polymerization with S,S'-bis(α,α'-dimethyl-α″-acetic acid)trithiocarbonate (CMP) as a chain transfer agent (CTA). With the aid of using 3-aminopropyltriethoxysilane, the surface-modified iron oxides, Fe3O4-NH2, was then attached on the surface of self-assembled tri-block copolymer micelles via 1-[3-(dimethylamino)propyl]-3-ethylcarbodiimide hydrochloride/N-hydroxysuccinamide (EDC/NHS) crosslinking method in order to furnish not only the magnetic resources for remote control but also the structure maintenance for spherical morphology of our nanocarriers. The nanocarrier was characterized by transmission electron microscope (TEM), Fourier transform infrared spectroscopy (FT-IR), and ultraviolet-visible (UV/Vis) spectral analysis. Rhodamine 6G (R6G), as the modeling drugs, was encapsulated into the magnetic nanocarriers by a simple swelling method for fluorescence-labeling and controlled release monitoring. Biocompatibility of the nanocarriers was studied via 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay, which revealed that neither the pristine nanocarrier nor the R6G-loaded nanocarriers were cytotoxic to the normal fibroblast cells (L-929 cells). The in vitro stimuli-triggered release measurement showed that the intelligent nanocarriers were highly sensitive to the change of pH value and temperature rising by the high-frequency magnetic field (HFMF) treatment, which provided the significant potential to apply this technology to biomedical therapy by stimuli-responsive controlled release.

Doxorubicin-loaded amphiphilic polypeptide-based nanoparticles as an efficient drug delivery system for cancer therapy

An amphiphilic anionic copolymer, methoxy poly(ethylene glycol)-b-poly(l-glutamic acid-co-l-phenylalanine) (mPEG-b-P(Glu-co-Phe)), with three functionalized domains, was synthesized and used as a nanovehicle for cationic anticancer drug doxorubicin hydrochloride (DOX·HCl) delivery via electrostatic interactions for cancer treatment. The three domains displayed distinct functions: PEG block chain for prolonged circulation; poly(phenylalanine) domain for stabilizing the nanoparticle construct through hydrophobic/aromatic interactions; and the poly(glutamic acid) domain for providing electrostatic interactions with the cationic drug to be loaded. The copolymer could self-assemble into micellar-type nanoparticles, and DOX was successfully loaded into the interior of nanoparticles by simple mixing of DOX·HCl and the copolymer in the aqueous phase. DOX-loaded mPEG-b-P(Glu-co-Phe) nanoparticles (DOX-NP) had a superior drug-loading content (DLC) (21.7%), a high loading efficiency (almost 98%) and a pH-triggered release of DOX. The size of DOX-NP was ∼140 nm, as determined by dynamic light scattering measurements and transmission electron microscopy. In vitro assays showed that DOX-NP exhibited higher cell proliferation inhibition and higher cell uptake in A549 cell lines compared with free DOX·HCl. Maximum tolerated dose (MTD) studies showed that DOX-NP demonstrated an excellent safety profile with a significantly higher MTD (15 mg DOX kg(-1)) than that of free DOX·HCl (5 mg DOX kg(-1)). The in vivo studies on the subcutaneous non-small cell lung cancer (A549) xenograft nude mice model confirmed that DOX-NP showed significant antitumor activity and reduced side effects, and then enhanced tumor accumulation as a result of the prolonged circulation in blood and the enhanced permeation and retention effect, compared with free DOX, indicating its great potential for cancer therapy.

Targeted polysaccharide nanoparticle for adamplatin prodrug delivery

A series of conjugated hyaluronic acid particles (HAP), composed of a hydrophobic anticancer drug core and hydrophilic cyclodextrin/hyaluronic acid shell, were prepared through self-assembling and characterized by (1)H NMR titration, electron microscopy, zeta potential, and dynamic light-scattering experiments. The nanometer-sized HAP thus prepared was biocompatible and biodegradable and was well-recognized by the hyaluronic acid receptors overexpressed on the surface of cancer cells, which enabled us to exploit HAP as an efficient targeted delivery system for anticancer drugs. Indeed, HAP exhibited anticancer activities comparable to the commercial anticancer drug cisplatin but with lower side effects both in vitro and in vivo.

Nanotechnology-based intelligent drug design for cancer metastasis treatment

Traditional chemotherapy used today at clinics is mainly inherited from the thinking and designs made four decades ago when the Cancer War was declared. The potency of those chemotherapy drugs on in-vitro cancer cells is clearly demonstrated at even nanomolar levels. However, due to their non-specific effects in the body on normal tissues, these drugs cause toxicity, deteriorate patient's life quality, weaken the host immunosurveillance system, and result in an irreversible damage to human's own recovery power. Owing to their unique physical and biological properties, nanotechnology-based chemotherapies seem to have an ability to specifically and safely reach tumor foci with enhanced efficacy and low toxicity. Herein, we comprehensively examine the current nanotechnology-based pharmaceutical platforms and strategies for intelligent design of new nanomedicines based on targeted drug delivery system (TDDS) for cancer metastasis treatment, analyze the pros and cons of nanomedicines versus traditional chemotherapy, and evaluate the importance that nanomaterials can bring in to significantly improve cancer metastasis treatment.

Reversal of multidrug resistance by stimuli-responsive drug delivery systems for therapy of tumor

Multidrug resistance (MDR) is a major obstacle to successful cancer therapy, especially for chemotherapy. The new drug delivery system (DDS) provides promising approaches to reverse MDR, for which the poor cellular uptake and insufficient intracellular drug release remain rate-limiting steps for reaching the drug concentration level within the therapeutic window. Stimulus-coupled drug delivery can control the drug-releasing pattern temporally and spatially, and improve the accumulation of chemotherapeutic agents at targeting sites. In this review, the applications of DDS which is responsive to different types of stimuli in MDR cancer therapy is introduced, and the design, construction, stimuli-sensitivity and the effect to reverse MDR of the stimuli-responsive DDS are discussed.

Manganese-loaded dual-mesoporous silica spheres for efficient T1- and T2-weighted dual mode magnetic resonance imaging

A novel class of manganese-based dual-mode contrast agents (DMCAs) based on the core-shell structured manganese-loaded dual-mesoporous silica spheres (Mn-DMSSs) for simultaneous T1- and T2-weighted magnetic resonance imaging (MRI) has been successfully reported. The in vitro MR tests demonstrate that the Mn-based DMCAs display an excellent simultaneous T1-weighted and T2-weighted MR imaging effect with a noticeably high T1 relaxivity (r1) of 10.1 mM(-1) s(-1) and a moderately high T2 relaxivity (r2) of 169.7 mM(-1) s(-1). The Mn-based DMCAs exhibit negligible cytotoxicity with >80% cell viability at a concentration of up to 200 μg/mL in human liver carcinoma (HepG2) and mouse macrophage (RAW264.7) cells after 24 h. Confocal laser scanning microscopy (CLSM) results show that the Mn-DMSSs were internalized via endocytosis and located in the cytoplasm but not in the nucleus. The in vivo experiment shows that the signals of rat liver increased by 29% under T1-weighted imaging mode and decreased by 28% under T2-weighted imaging mode in 5 min postinjection of Mn-DMSSs, which reveal that the novel Mn-loaded DMSSs can be used as both positive (T1-weighted) and negative (T2-weighted) MR contrast agents in further biomedical applications.

One-pot construction of functional mesoporous silica nanoparticles for the tumor-acidity-activated synergistic chemotherapy of glioblastoma

Mesoporous silica nanoparticles (MSNs) have proved to be an effective carrier for controlled drug release and can be functionalized easily for use as stimuli-responsive vehicles. Here, a novel intelligent drug-delivery system (DDS), camptothecin (CPT)-loaded and doxorubicin (DOX)-conjugated MSN (CPT@MSN-hyd-DOX), is reported via a facile one-pot preparation for use in synergistic chemotherapy of glioblastoma. DOX was conjugated to MSNs via acid-labile hydrazone bonds, and CPT was loaded in the pores of the MSNs. At pH 6.5 (analogous to the pH in tumor tissues), a fast DOX release was observed that was attributed to the hydrolysis of the hydrazone bonds. In addition, a further burst release of DOX was found at pH 5.0 (analogous to the pH in lyso/endosomes of tumor cells), leading to a strong synergistic effect. In all, CPT and DOX could be delivered simultaneously into tumor cells, and this intelligent DDS has great potential for tumor-trigged drug release for use in the synergistic chemotherapy of tumors.

Controlled release of cisplatin from pH-thermal dual responsive nanogels

In this study, a pH-thermal dual responsive nanogel was applied for cisplatin (CDDP) delivery. CDDP was loaded into the nanogels via conjugation with the carboxyl groups in the nanogels. The conjugation was confirmed by FTIR and XPS. The bonding between CDDP and COOH can be broken by the H(+) or Cl(-). We found that the CDDP released much faster at more acidic environment. The Cl(-) concentration in the human body is about 95-105 mm. The conjugated bond could be easily attacked by Cl(-) while the nanosystem is injected into the body. In order to diminish the Cl(-) triggering release of CDDP from the nanogels, we introduced a thermal-responsive units-NIPAm into the nanogel structure. After NIPAm introduced, the CDDP released much slower from the nanogels at 37 °C in pH = 7.38 buffer in the present of Cl(-) (150 mm) than that without NIPAm. And the CDDP also released slower from the nanogels at 37 °C than at 25 °C. By in vitro release behavior studying, we found that CDDP release from the NIPAm containing nanogels can be accelerated by H(+) attacking and reduced by temperature arising. By cellular uptake observation, we found that the nanogels were mainly localized in the cytoplasm of the cancer cells. The CDDP-loaded nanogels exhibited longer circulation time in vivo while compared to free CDDP. And it has better anti-cancer performance than free CDDP in vivo therapy of breast cancer in mice model. Furthermore, some side effects of CDDP, such as renal toxicity, phlebitis, bone marrow suppression etc. have also been reduced by nanogels loading. The in vitro and in vivo results demonstrated that the dual responsible nanogel is a suitable CDDP delivery candidate.

Tumor extracellular acidity-activated nanoparticles as drug delivery systems for enhanced cancer therapy

pH-responsive nanoparticles (NPs) are currently under intense development as drug delivery systems for cancer therapy. Among various pH-responsiveness, NPs that are designed to target slightly acidic extracellular pH environment (pHe) of solid tumors provide a new paradigm of tumor targeted drug delivery. Compared to conventional specific surface targeting approaches, the pHe-targeting strategy is considered to be more general due to the common occurrence of acidic microenvironment in solid tumors. This review mainly focuses on the design and applications of pHe-activated NPs, with special emphasis on pHe-activated surface charge reversal NPs, for drug and siRNA delivery to tumors. The novel development of NPs described here offers great potential for achieving better therapeutic effects in cancer treatment.

Boronate-dextran: an acid-responsive biodegradable polymer for drug delivery

Stimuli-responsive drug carriers have great potential to deliver bioactive materials on demand and to a specific location within the human body. Acid-responsive drug carriers can specifically release their payload in the acidic microenvironments of tumors or in the endosomal or lysosomal compartments within a cell. Here we describe an approach to functionalize vicinal diols of dextran with hydrophobic boronate esters in order to produce a water insoluble boronate dextran polymer (B-Dex), which spontaneously forms acid-responsive nanoparticles in water. We show the encapsulation of a hydrophobic anticancer drug doxorubicin into the particles. Hydrolysis of the boronate esters under mild acidic conditions recovers the hydrophilic hydroxyl groups of the dextran and disrupts the particles into water soluble fragments thereby leading to a pH-responsive release of the drug. According to dynamic light scattering (DLS) and UV/Vis spectroscopy, mild acidic conditions (pH 5.0) lead to a three-fold increase in the degradation of the particles and a four-fold increase in the release of the drug compared to the behavior of particles at pH 7.4. In vitro tests in Hela cells show no toxicity of the empty B-Dex nanoparticles, while the toxicity of doxorubicin-loaded B-Dex nanoparticles is comparable to that of the doxorubicin · HCl drug. Confocal fluorescence microscopy reveals that 100% of the Hela cells uptake doxorubicin-loaded B-Dex nanoparticles with a preferential accumulation of the nanoparticles in the cytoplasm.

Enhanced retention and cellular uptake of nanoparticles in tumors by controlling their aggregation behavior

Effective accumulation of nanoparticles (NPs) in tumors is crucial for NP-assisted cancer diagnosis and treatment. With the hypothesis that aggregation of NPs stimulated by tumor microenvironment can be utilized to enhance retention and cellular uptake of NPs in tumors, we designed a smart NP system to evaluate the effect of aggregation on NPs' accumulation in tumor tissue. Gold nanoparticles (AuNPs, ~16 nm) were facilely prepared by surface modification with mixed-charge zwitterionic self-assembled monolayers, which can be stable at the pH of blood and normal tissues but aggregate instantly in response to the acidic extracellular pH of solid tumors. The zwitterionic AuNPs exhibited fast, ultrasensitive, and reversible response to the pH change from pH 7.4 to pH 6.5, which enabled the AuNPs to be well dispersed at pH 7.4 with excellent stealth ability to resist uptake by macrophages, while quickly aggregating at pH 6.5, leading to greatly enhanced uptake by cancer cells. An in vivo study demonstrated that the zwitterionic AuNPs had a considerable blood half-life with much higher tumor accumulation, retention, and cellular internalization than nonsensitive PEGylated AuNPs. A preliminary photothermal tumor ablation evaluation suggested the aggregation of AuNPs can be applied to cancer NIR photothermal therapy. These results suggest that controlled aggregation of NPs sensitive to tumor microenvironment can serve as a universal strategy to enhance the retention and cellular uptake of inorganic NPs in tumors, and modifying NPs with a mixed-charge zwitterionic surface can provide an easy way to obtain stealth properties and pH-sensitivity at the same time.

Photolabile plasmonic vesicles assembled from amphiphilic gold nanoparticles for remote-controlled traceable drug delivery

We have developed a new type of photo-responsive plasmonic vesicles that allow for active delivery of anticancer payloads to specific cancer cells and personalized drug release regulated by external photo-irradiation. Our results show that amphiphilic gold nanoparticles carrying hydrophilic poly(ethylene glycol) (PEG) and photo-responsive hydrophobic poly(2-nitrobenzyl acrylate) (PNBA) can assemble into plasmonic vesicles with gold nanoparticles embedded in the hydrophobic shell of PNBA, which can be converted into hydrophilic poly(acrylic acid) upon photo exposure. Benefiting from the interparticle plasmonic coupling of gold nanoparticles in close proximity, the plasmonic vesicles assembled from amphiphilic gold nanoparticles exhibit distinctively different optical properties from single nanoparticle units, which offer the opportunity to track the photo-triggered disassembly of the vesicles and the associated cargo release by plasmonic imaging. We have shown the dense layer of PEG grafts on the vesicles not only endow plasmonic vesicles with excellent colloidal stability, but also serve as flexible spacers for bioconjugation of targeting ligands to facilitate the specific recognition of cancer cells. The targeted delivery of model anticancer drug doxorubicin, investigated by dual-modality plasmonic and fluorescence imaging and toxicity studies, clearly demonstrated the potential of photolabile plasmonic vesicles as multi-functional drug carriers.

Self-reinforced endocytoses of smart polypeptide nanogels for "on-demand" drug delivery

The pH and reduction dual-responsive polypeptide nanogels with self-reinforced endocytoses were prepared through ring-opening polymerization of l-glutamate N-carboxyanhydrides, deprotection of benzyl group and subsequent quaternization reaction between γ-2-chloroethyl-l-glutamate unit in polypeptide block and 2,2'-dithiobis(N,N-dimethylethylamine). The nanogels were revealed to exhibit smart pH and reduction dual-responsiveness, and excellent biocompatibilities, which expressed great potential as antitumor drug nanocarriers. Doxorubicin (DOX) as a model antitumor drug was loaded into nanogels through dispersion. DOX-loaded nanogels displayed a stable core-cross-linked structure under normal physiological condition (pH7.4), while rapidly releasing the payloads in the mimicking endosomal (pH5.3), tumor tissular (pH6.8) or intracellular reductive microenvironments (10.0mM glutathione). Confocal fluorescence microscopy demonstrated that DOX-loaded nanogels could deliver DOX into HepG2 cells (a human hepatoma cell line) more efficiently than the parent DOX-loaded micelle and free DOX. The enhanced cellular internalizations of DOX-loaded nanogels were more significant under tumor tissular acidic condition (pH6.8) ascribed to the quaternary ammonium groups in the cores. In addition, DOX-loaded nanogels exhibited improved in vitro and in vivo antitumor activities, and in vivo securities compared with DOX-loaded micelle and free DOX. These excellent features of the smart nanogels with quaternary ammonium groups were endowed with a bright prospect for intracellular targeting antitumor drug delivery.