pH-sensitive polymeric nanoparticles for tumor-targeting doxorubicin delivery: concept and recent advances

Disulfide-bridged cleavable PEGylation in polymeric nanomedicine for controlled therapeutic delivery

PEGylation in polymeric nanomedicine has gained substantial predominance in biomedical applications due to its resistance to protein absorption, which is critically important for a therapeutic delivery system in blood circulation. The shielding layer of PEGylation, however, creates significant steric hindrance that negatively impacts cellular uptake and intracellular distribution at the target site. This unexpected effect compromises the biological efficacy of the encapsulated payload. To address this issue, one of the key strategies is to tether the disulfide bond to PEG for constructing a disulfide-bridged cleavable PEGylation. The reversible disulfide bond can be cleaved to enable selective PEG detachment. This article provides an overview on the strategy, method and progress of PEGylation nanosystem with the cleavable disulfide bond.

Metabolic changes associated with tumor metastasis, part 1: tumor pH, glycolysis and the pentose phosphate pathway

Metabolic adaptations are intimately associated with changes in cell behavior. Cancers are characterized by a high metabolic plasticity resulting from mutations and the selection of metabolic phenotypes conferring growth and invasive advantages. While metabolic plasticity allows cancer cells to cope with various microenvironmental situations that can be encountered in a primary tumor, there is increasing evidence that metabolism is also a major driver of cancer metastasis. Rather than a general switch promoting metastasis as a whole, a succession of metabolic adaptations is more likely needed to promote different steps of the metastatic process. This review addresses the contribution of pH, glycolysis and the pentose phosphate pathway, and a companion paper summarizes current knowledge regarding the contribution of mitochondria, lipids and amino acid metabolism. Extracellular acidification, intracellular alkalinization, the glycolytic enzyme phosphoglucose isomerase acting as an autocrine cytokine, lactate and the pentose phosphate pathway are emerging as important factors controlling cancer metastasis.

Smart micro/nanoparticles in stimulus-responsive drug/gene delivery systems

New achievements in the realm of nanoscience and innovative techniques of nanomedicine have moved micro/nanoparticles (MNPs) to the point of becoming actually useful for practical applications in the near future. Various differences between the extracellular and intracellular environments of cancerous and normal cells and the particular characteristics of tumors such as physicochemical properties, neovasculature, elasticity, surface electrical charge, and pH have motivated the design and fabrication of inventive "smart" MNPs for stimulus-responsive controlled drug release. These novel MNPs can be tailored to be responsive to pH variations, redox potential, enzymatic activation, thermal gradients, magnetic fields, light, and ultrasound (US), or can even be responsive to dual or multi-combinations of different stimuli. This unparalleled capability has increased their importance as site-specific controlled drug delivery systems (DDSs) and has encouraged their rapid development in recent years. An in-depth understanding of the underlying mechanisms of these DDS approaches is expected to further contribute to this groundbreaking field of nanomedicine. Smart nanocarriers in the form of MNPs that can be triggered by internal or external stimulus are summarized and discussed in the present review, including pH-sensitive peptides and polymers, redox-responsive micelles and nanogels, thermo- or magnetic-responsive nanoparticles (NPs), mechanical- or electrical-responsive MNPs, light or ultrasound-sensitive particles, and multi-responsive MNPs including dual stimuli-sensitive nanosheets of graphene. This review highlights the recent advances of smart MNPs categorized according to their activation stimulus (physical, chemical, or biological) and looks forward to future pharmaceutical applications.

The potential of protein-nanomaterial interaction for advanced drug delivery

Nanomaterials, like nanoparticles, micelles, nano-sheets, nanotubes and quantum dots, have great potentials in biomedical fields. However, their delivery is highly limited by the formation of protein corona upon interaction with endogenous proteins. This new identity, instead of nanomaterial itself, would be the real substance the organs and cells firstly encounter. Consequently, the behavior of nanomaterials in vivo is uncontrollable and some undesired effects may occur, like rapid clearance from blood stream; risk of capillary blockage; loss of targeting capacity; and potential toxicity. Therefore, protein-nanomaterial interaction is a great challenge for nanomaterial systems and should be inhibited. However, this interaction can also be used to functionalize nanomaterials by forming a selected protein corona. Unlike other decoration using exogenous molecules, nanomaterials functionalized by selected protein corona using endogenous proteins would have greater promise for clinical use. In this review, we aim to provide a comprehensive understanding of protein-nanomaterial interaction. Importantly, a discussion about how to use such interaction is launched and some possible applications of such interaction for advanced drug delivery are presented.

Synthesis and properties of stimuli-sensitive heterografted toothbrush-like terpolymers with a linear handle and two types of V-shaped grafts

Straightforward syntheses were performed to generate amphiphilic heterograftedPNIPAM(PAA)_2m(PCL)_2mcopolymers, which could self-assemble into versatile nanoobjects for thermo, pH and additive triggered controlled release of doxorubicin.

PDEAEMA-based pH-sensitive amphiphilic pentablock copolymers for controlled anticancer drug delivery

The synthesis of a series of PDEAEMA-based pH-sensitive amphiphilic pentablock copolymers PEG-b-(PDEAEMA-b-PMMA)₂ with different compositions proceeded via the combination of a bromination reaction andARGET ATRP.

Stable and pH-responsive polyamidoamine based unimolecular micelles capped with a zwitterionic polymer shell for anticancer drug delivery

Zwitterionic dendrimer based unimolecular micelles for anticancer drug delivery were prepared, exhibiting excellent stability in complex biological media.

Synthesis and properties of an acid-labile dual-sensitive ABCD star quaterpolymer

Copolymer aggregates formed from an amphiphilic ABCD star could exhibit acid-induced topological and morphological transformations and stimuli-triggered drug delivery properties.

Self-assembled micelles of PEG–poly(disulfide carbamate amine) copolymers for intracellular dual-responsive drug delivery

Self-assembled nanomicelles based on biodegradable poly(carbamate) copolymers are applicable for pH and redox dual-responsive release of doxorubicin (Dox) and cancer chemotherapy.

Facile Construction of pH- and Redox-Responsive Micelles from a Biodegradable Poly(β-hydroxyl amine) for Drug Delivery

Here we demonstrate a type of pH and reduction dual-sensitive biodegradable micelles, which were self-assembled by a cationic polymer in an aqueous solution. Due to tumor cells or tissues showing low pH and high reduction concentration, these micelles possessed specific tumor targetability and maximal drug-release controllability inside tumor cells upon changes in physical and chemical environments, but presented good stability at physiological conditions. CCK-8 assay showed that the DOX-loaded micelles had a similar cytotoxicity for MCF-7 tumor cells as free DOX, and blank micelles had a very low cytotoxicity to the cells. Fluorescent microscopy observation revealed that the drug-loaded micelles could be quickly internalized by endosomes to inhibit cancer cell growth. These results indicated these biodegradable micelles, as a novel and effective pH- and redox-responsive nanocarrier, have a potential to improve drug delivery and enhance the antitumor efficacy.

Stromal barriers and strategies for the delivery of nanomedicine to desmoplastic tumors

Nanoparticle based delivery formulations have become a leading delivery strategy for cancer imaging and therapy. The success of nanoparticle-based therapy relies heavily on their ability to utilize the enhanced permeability and retention (EPR) effect and active targeting moieties to their advantage. However, these methods often fail to enable a uniform NP distribution across the tumor, and lead to insufficient local concentrations of drug. Oftentimes, this heterogeneous drug distribution is one of the primary reasons for suboptimal treatment efficacy in NP delivery platforms. Herein, we seek to examine the biophysical causes of heterogeneous NP distribution in stroma-rich desmoplastic tumors; namely the abnormal tumor vasculature, deregulated extracellular matrix and high interstitial hypertension associated with these tumors. It is suggested that these factors help explain the discrepancy between promising outlooks for many NP formulations in preclinical studies, but suboptimal clinical outcomes for most FDA approved nanoformulations. Furthermore, examination into the role of the physicochemical properties of NPs on successful drug delivery was conducted in this review. In light of the many formidable barriers against successful NP drug delivery, we provided possible approaches to mitigate delivery issues from the perspective of stromal remodeling and NP design. In all, this review seeks to provide guidelines for optimizing nanoparticle-based cancer drug delivery through both modified nanoparticle design and alleviation of biological barriers to successful therapy.

Polyelectrolyte brushes: theory, modelling, synthesis and applications

Polyelectrolyte (PE) brushes are a special class of polymer brushes (PBs) containing charges. Polymer chains attain "brush"-like configuration when they are grafted or get localized at an interface (solid-fluid or liquid-fluid) with sufficiently close proximity between two-adjacent grafted polymer chains - such a proximity triggers a particular nature of interaction between the adjacent polymer molecules forcing them to stretch orthogonally to the grafting interface, instead of random-coil arrangement. In this review, we discuss the theory, synthesis, and applications of PE brushes. The theoretical discussion starts with the standard scaling concepts for polymer and PE brushes; following that, we shed light on the state of the art in continuum modelling approaches for polymer and PE brushes directed towards analysis beyond the scaling calculations. A special emphasis is laid in pinpointing the cases for which the PE electrostatic effects can be de-coupled from the PE entropic and excluded volume effects; such de-coupling is necessary to appropriately probe the complicated electrostatic effects arising from pH-dependent charging of the PE brushes and the use of these effects for driving liquid and ion transport at the interfaces covered with PE brushes. We also discuss the atomistic simulation approaches for polymer and PE brushes. Next we provide a detailed review of the existing approaches for the synthesis of polymer and PE brushes on interfaces, nanoparticles, and nanochannels, including mixed brushes and patterned brushes. Finally, we discuss some of the possible applications and future developments of polymer and PE brushes grafted on a variety of interfaces.

Biocompatible nanoparticles sensing the matrix metallo-proteinase 2 for the on-demand release of anticancer drugs in 3D tumor spheroids

The balance between dose-dependent tolerability, effectiveness and toxicity of systemically administered antitumor drugs is extremely delicate. This issue highlights the striking need for targeted release of chemotherapeutic drugs within tumors. In this work, a smart strategy of drug targeting to tumors relying upon biodegradable/biocompatible nanoparticles releasing cytotoxic drugs after sensing physiological variations intrinsic to the very nature of tumor tissues is exploited. Here, the well-known over-expression of matrix metallo-proteinase 2 (MMP2) enzyme in tumors has been chosen as a trigger for the release of a cytotoxic drug. Nanoparticles made up of a biodegradable poly(D,L-lactic-co-glycolic acid) (PLGA)--block--polyethylene glycol (PEG) copolymer (namely PELGA), blended with a tumor-activated prodrug (TAP) composed of a MMP2-sensitive peptide bound to doxorubicin (Dox) and to PLGA chain have been produced. The obtained devices are able to release Dox specifically upon MMP2 cleavage of the TAP. More interestingly, they can sense the differences in the expression levels of endogenous MMP2 protein, thus modulating drug penetration within a three-dimensional (3D) tumor spheroid matrix, accordingly. Therefore, the proposed nanoparticles hold promise as a useful tool for in vivo investigations aimed at an improved therapeutic efficacy of the conjugated drug payload.

Tumor-targeting, pH-sensitive nanoparticles for docetaxel delivery to drug-resistant cancer cells

The attachment of polyethylene glycol (PEG) increases the circulation time of drug-containing nanoparticles; however, this also negatively affects cellular uptake. To overcome this problem, unique lipid polymer hybrid (LPH) nanoparticles were developed with a pH-responsive PEG layer that detached prior to cell uptake. Docetaxel (DTX) was incorporated into the lipid core of the nanoparticles, which was then shielded with the pH-responsive block co-polymer polyethylene glycol-b-polyaspartic acid (PEG-b-PAsp) using a modified emulsion method. The optimized LPH nanoparticles were ~200 nm and had a narrow size distribution. Drug release from DTX-loaded LPH (DTX-LPH) nanoparticles was pH-sensitive, which is beneficial for tumor targeting. More importantly, DTX-LPH nanoparticles were able to effectively induce apoptosis in cancer cells. The negative surface charge and PEG shell of vehicle remarkably enhanced the blood circulation and physiological activity of DTX-LPH nanoparticles compared with that of free DTX. The nanoparticles were also found to reduce the size of tumors in tumor-bearing xenograft mice. The in vivo anticancer effect of DTX-LPH nanoparticles was further confirmed by the elevated levels of caspase-3 and poly ADP ribose polymerase found in the tumors after treatment. Thus, the results suggest that this novel LPH system could be an effective new treatment for cancer.

'Smart' nanoparticles as drug delivery systems for applications in tumor therapy

INTRODUCTION

In the therapy of clinical diseases such as cancer, it is important to deliver drugs directly to tumor sites in order to maximize local drug concentration and reduce side effects. This objective may be realized by using 'smart' nanoparticles (NPs) as drug delivery systems, because they enable dramatic conformational changes in response to specific physical/chemical stimuli from the diseased cells for targeted and controlled drug release.

AREAS COVERED

In this review, we first briefly summarize the characteristics of 'smart' NPs as drug delivery systems in medical therapy, and then discuss their targeting transport, transmembrane and endosomal escape behaviors. Lastly, we focus on the applications of 'smart' NPs as drug delivery systems for tumor therapy.

EXPERT OPINION

Biodegradable 'smart' NPs have the potential to achieve maximum efficacy and drug availability at the desired sites, and reduce the harmful side effects for healthy tissues in tumor therapy. It is necessary to select appropriate NPs and modify their characteristics according to treatment strategies of tumor therapy.

Stable and efficient Paclitaxel nanoparticles for targeted glioblastoma therapy

Development of efficient nanoparticles (NPs) for cancer therapy remains a challenge. NPs are required to have high stability, uniform size, sufficient drug loading, targeting capability, and ability to overcome drug resistance. In this study, the development of a NP formulation that can meet all these challenging requirements for targeted glioblastoma multiform (GBM) therapy is reported. This multifunctional NP is composed of a polyethylene glycol-coated magnetic iron oxide NP conjugated with cyclodextrin and chlorotoxin (CTX) and loaded with fluorescein and paclitaxel (PTX) (IONP-PTX-CTX-FL). The physicochemical properties of the IONP-PTX-CTX-FL are characterized by transmission electron microscope, dynamic light scattering, and high-performance liquid chromatography. The cellular uptake of NPs is studied using flow cytometry and confocal microscopy. Cell viability and apoptosis are assessed with the Alamar Blue viability assay and flow cytometry, respectively. The IONP-PTX-CTX-FL had a uniform size of ≈44 nm and high stability in cell culture medium. Importantly, the presence of CTX on NPs enhanced the uptake of the NPs by GBM cells and improved the efficacy of PTX in killing both GBM and GBM drug-resistant cells. The IONP-PTX-CTX-FL demonstrated its great potential for brain cancer therapy and may also be used to deliver PTX to treat other cancers.

Facile construction of dual-bioresponsive biodegradable micelles with superior extracellular stability and activated intracellular drug release

It is still a major challenge for targeted cancer chemotherapy to design stable biodegradable micellar drug delivery systems which show a rapid and complete intracellular drug release. Here, reversibly core-crosslinked pH-responsive biodegradable micelles were developed based on poly(ethylene glycol)-poly(2,4,6-trimethoxybenzylidene-pentaerythritol carbonate-co-pyridyl disulfide carbonate) [PEG-P(TMBPEC-co-PDSC)] copolymers and investigated for intracellular doxorubicin (DOX) release. PEG-P(TMBPEC-co-PDSC) copolymers formed micelles with a small size of 58.6nm were readily crosslinked by the addition of dithiothreitol (DTT). Notably, in vitro release studies showed that under physiological conditions only ca. 19.9% of DOX was released from the reversibly crosslinked micelles in 24h at a low micelle concentration of 40μg/mL. The release of DOX was accelerated at pH5.0 or in the presence of 10mM glutathione (GSH) at pH7.4, in which 64.2% and 44.1% of DOX was released, respectively, in 24h. The drug release was further boosted at pH5.0 and 10mM GSH, with 98.8% of DOX released in 12h. Moreover, DOX release was also facilitated by a 4h incubation at pH5.0 followed by incubation at pH7.4 with 10mM GSH. Confocal microscopy indicated that DOX was delivered and released into the nuclei of RAW 264.7 cells following a 12h incubation with DOX-loaded reversibly crosslinked micelles. MTT assays revealed that DOX-loaded reversibly crosslinked micelles had much higher antitumor activity than irreversibly crosslinked controls, with low IC50 values of 1.65 and 1.14μg/mL for HeLa and RAW 264.7 cells, respectively, following a 48h incubation. The blank crosslinked micelles had a low cytotoxicity of up to a concentration of 0.8mg/mL. These reversibly crosslinked pH-sensitive biodegradable micelles with superior extracellular stability but activated intracellular drug release provide a novel platform for tumor-targeting drug delivery.

Emerging antitumor applications of extracellularly reengineered polymeric nanocarriers

Recently, polymeric nanocarriers with shielding surfaces, e.g., poly(ethylene glycol) and small molecules, have been widely applied in antitumor drug delivery mainly because of their stealth during blood circulation. However, the shielding shell greatly hinders the tumor penetration, drug release, and cell internalization of the nanocarriers, which leads to unsatisfactory therapeutic efficacy. To integrate the extended blood circulation time and the enhanced drug transmission in one platform, some extracellularly stimuli-mediated shell-sheddable polymeric nanocarriers have been exploited. The systems are stealthy and stable during blood circulation, and as soon as they reach tumor tissue, the shielding matrices are removed, which is triggered by extracellular endogenous stimuli (e.g., pH or enzymes) or exogenous excitations (e.g., light or voltage). This review mainly focuses on recent advances in the designs and emerging antitumor applications of extracellularly reengineered polymeric nanocarriers for directional drug delivery, as well as perspectives for future developments.

pH-Responsive chimaeric pepsomes based on asymmetric poly(ethylene glycol)-b-poly(l-leucine)-b-poly(l-glutamic acid) triblock copolymer for efficient loading and active intracellular delivery of doxorubicin hydrochloride

pH-Responsive chimaeric polypeptide-based polymersomes (refer to as pepsomes) were designed and developed from asymmetric poly(ethylene glycol)-b-poly(l-leucine)-b-poly(l-glutamic acid) (PEG-PLeu-PGA, PEG is longer than PGA) triblock copolymers for efficient encapsulation and triggered intracellular delivery of doxorubicin hydrochloride (DOX·HCl). PEG-PLeu-PGA was conveniently prepared by sequential ring-opening polymerization of l-leucine N-carboxyanhydride and γ-benzyl-l-glutamate N-carboxyanhydride using PEG-NH2 as an initiator followed by deprotection. Pepsomes formed from PEG-PLeu-PGA had unimodal distribution and small sizes of 64-71 nm depending on PLeu block lengths. Interestingly, these chimaeric pepsomes while stable at pH 7.4 were quickly disrupted at pH 5.0, likely due to alternation of ionization state of the carboxylic groups in PGA that shifts PGA blocks from hydrophilic and random coil structure into hydrophobic and α-helical structure. DOX·HCl could be actively loaded into the watery core of pepsomes with a high loading efficiency. Remarkably, the in vitro release studies revealed that release of DOX·HCl was highly dependent on pH, in which about 24.0% and 75.7% of drug was released at pH 7.4 and 5.0, respectively, at 37 °C in 24 h. MTT assays demonstrated that DOX·HCl-loaded pepsomes exhibited high antitumor activity, similar to free DOX·HCl in RAW 264.7 cells. Moreover, they were also potent toward drug-resistant MCF-7 cancer cells (MCF-7/ADR). Confocal microscopy studies showed that DOX·HCl-loaded pepsomes delivered and released drug into the cell nuclei of MCF-7/ADR cells in 4 h, while little DOX·HCl fluorescence was observed in MCF-7/ADR cells treated with free drug under otherwise the same conditions. These chimaeric pepsomes with facile synthesis, efficient drug loading, and pH-triggered drug release behavior are an attractive alternative to liposomes for targeted cancer chemotherapy.

Nanoparticle-based immunotherapy for cancer

The design of nanovaccines capable of triggering effective antitumor immunity requires an understanding of how the immune system senses and responds to threats, including pathogens and tumors. Equally important is an understanding of the mechanisms employed by tumor cells to evade immunity and an appreciation of the deleterious effects that antitumor immune responses can have on tumor growth, such as by skewing tumor cell composition toward immunologically silent tumor cell variants. The immune system and tumors engage in a tug-of-war driven by competition where promoting antitumor immunity or tumor cell death alone may be therapeutically insufficient. Nanotechnology affords a unique opportunity to develop therapeutic compounds than can simultaneously tackle both aspects, favoring tumor eradication. Here, we review the current status of nanoparticle-based immunotherapeutic strategies for the treatment of cancer, ranging from antigen/adjuvant delivery vehicles (to professional antigen-presenting cell types of the immune system) to direct tumor antigen-specific T-lymphocyte-targeting compounds and their combinations thereof.

Tuning of hydrogen peroxide-responsive polymeric micelles of biodegradable triblock polycarbonates as a potential drug delivery platform with ratiometric fluorescence signaling

Two micelles of amphiphilic triblock polycarbonates with different H₂O₂-reactive core-forming blocks manifest disparate H₂O₂-induced disaggregation behaviors of micelles.

Thermo and pH dual-controlled charge reversal amphiphilic graft copolymer micelles for overcoming drug resistance in cancer cells

A novel thermo and pH dual-controlled charge reversal PSMA₈₉-g-P(DMA₁₆-co-SD₅₆) graft copolymer micelle was developed with effectively enhanced cellular uptake for overcoming multi-drug resistance in cancer cells.

Micellization of antineoplastic agent to significantly upregulate efficacy and security

The amphiphilic diblock copolymer composed of methoxy poly(ethylene glycol) and racemic oligoleucine was synthesized which formed into micelle with uniform size in aqueous environment. Doxorubicin (DOX) was loaded into micelle aided by noncovalent interactions with high drug loading efficiency. The DOX-loaded micelle (referred as M-DOX) demonstrated the sustained drug release in vitro and excellent antiproliferative capability toward both MG63 and Saos-2 cells. Furthermore, for both MG63 and Saos-2-xenografted BALB/c nude mouse models, M-DOX exhibited enhanced intratumoral distribution, improved antitumor efficacy, and reduced side effects compared with free DOX. Therefore, the polypeptide micelle showed a bright prospect for controlled delivery of antitumor drugs in vivo.

Nanomedical engineering: shaping future nanomedicines

Preclinical research in the field of nanomedicine continues to produce a steady stream of new nanoparticles with unique capabilities and complex properties. With improvements come promising treatments for diseases, with the ultimate goal of clinical translation and better patient outcomes compared with current standards of care. Here, we outline engineering considerations for nanomedicines, with respect to design criteria, targeting, and stimuli-triggered drug release strategies. General properties, clinical relevance, and current research advances of various nanomedicines are discussed in light of how these will realize their potential and shape the future of the field.

Tumor-homing, size-tunable clustered nanoparticles for anticancer therapeutics

We present herein a pH-responsive dynamic DNA nanocluster based on gold nanoparticles with highly packed nucleic acid assembly and evaluate its potential as a drug delivery vehicle with tumor-specific accumulation. Each gold nanoparticle was readily functionalized with various functional DNA sequences; in particular, we modified the surface of gold nanoparticles with bcl-2 antisense and i-motif binding sequences. Clustering of the gold nanoparticles induced by hybridization of each DNA sequence via i-motif DNA provided tumor targeting and drug loading capabilities. After cellular uptake, the drug was released by disassembly of the gold nanoparticle cluster into single gold nanoparticles in response to the pH decrease in the late endosome. Furthermore, the antiapoptotic Bcl-2 protein was down-regulated by the antisense-modified gold nanoparticles; thus, drug-mediated apoptosis was significantly accelerated by sensitizing the cancer cells to the drug. Our size-tunable clustered nucleic acid-grafted gold nanoparticles provide tumor homing in the blood circulation and are thus a potential multifunctional therapeutic agent in vivo as well as in vitro.

cRGD-directed, NIR-responsive and robust AuNR/PEG-PCL hybrid nanoparticles for targeted chemotherapy of glioblastoma in vivo

cRGD-directed, NIR-responsive and robust AuNR/PEG-PCL hybrid nanoparticles (cRGD-HNs) were designed and developed for targeted chemotherapy of human glioma xenografts in mice. As expected, cRGD-HNs had excellent colloidal stability. The in vitro release studies showed that drug release from DOX-loaded cRGD-HNs (cRGD-HN-DOX) was minimal under physiological conditions but markedly accelerated upon NIR irradiation at a low power density of 0.2 W/cm2, due to photothermally induced phase transition of PCL regime. MTT assays showed that the antitumor activity of cRGD-HN-DOX in αvβ3 integrin over-expressed human glioblastoma U87MG cells was greatly boosted by mild NIR irradiation, which was significantly more potent than non-targeting HN-DOX counterpart under otherwise the same conditions and was comparable or superior to free DOX, supporting receptor-mediated endocytosis mechanism. The in vivo pharmacokinetics studies showed that cRGD-HN-DOX had much longer circulation time than free DOX. The in vivo imaging and biodistribution studies revealed that cRGD-HN-DOX could actively target human U87MG glioma xenograft in nude mice. The therapeutic studies in human U87MG glioma xenografts exhibited that cRGD-HN-DOX in combination with NIR irradiation completely inhibited tumor growth and possessed much lower side effects than free DOX. The Kaplan-Meier survival curves showed that all mice treated with cRGD-HN-DOX plus NIR irradiation survived over an experimental period of 48 days while control groups treated with PBS, cRGD-HN-DOX, cRGD-HNs with NIR irradiation, free DOX, or HN-DOX with NIR irradiation (non-targeting control) had short life spans of 15-40 days. Ligand-directed AuNR/PEG-PCL hybrid nanoparticles with evident tumor-targetability as well as superior spatiotemporal and rate control over drug release have emerged as an appealing platform for cancer chemotherapy in vivo.

Synthesis and characterization of dendritic star-shaped zwitterionic polymers as novel anticancer drug delivery carriers

In this work, a novel dendritic star-shaped zwitterionic polymer, polyamidoamine-graft-poly[3-dimethyl (methacryloyloxyethyl) ammonium propanesulfonate] (PAMAM-g-PDMAPS), was synthesized. PAMAM dendrimers (generation 2, G2) were firstly prepared and then converted into the PAMAM-Br macroinitiator with 2-bromoisobutyryl bromide for ATRP. Finally, ATRP of zwitterionic DMAPS was carried out to obtain the dendritic star-shaped polymers PAMAM-g-PDMAPS with different PDMAPS chain lengths. Fourier transform-infrared spectroscopy, (1)H NMR, dynamic laser light scattering (DLS), and TEM were used to characterize the polymers. Encapsulation of adriamycin (ADR) by PAMAM-g-PDMAPS nanoparticles and ADR release behavior from ADR-loaded PAMAM-g-PDMAPS nanoparticles were investigated in detail. PAMAM-g-PDMAPS polymers, even starting from low-generation PAMAM core (G2), were found to show high loading efficiency for ADR because ADR existed not only within G2 PAMAM cores but also in PDMAPS layers. The release profile of ADR from ADR-loaded PAMAM-g-PDMAPS nanoparticles was pH-sensitive and could be controlled by the length of PDMAPS chains. Cell viability studies indicated that ADR-loaded PAMAM-g-PDMAPS could effectively restrain the growth of HepG2 cells and even kill them, whereas PAMAM-g-PDMAPS exhibited nontoxicity. All these results demonstrated that dendritic star-shaped zwitterionic polymers PAMAM-g-PDMAPS are attractive candidates as anticancer drug delivery carriers.