pH-triggered Doxorubicin Release Research Articles

A multivalent polyphenol–metal-nanoplatform for cascade amplified chemo-chemodynamic therapy

Chemodynamic therapy (CDT), as an emerging therapeutic strategy, kills cancer cells by converting intracellular hydrogen peroxide (H2O2) into cytotoxic oxidizing hydroxyl radicals (⋅OH). However, the therapeutic efficiency of CDT is compromised due to the insufficient endogenous H2O2 and metal catalysts in tumor cells. The use of multivalent polyphenols with multiple hydroxyl functions provides a facile yet robust means for efficient CDT augmentation. For this purpose, we reported herein the construction of polyphenol–metal nanoparticles (NPs) via a phenol–metal coordination strategy. The uniqueness of this study is the preparation of only one polymer construct with multivalency that can afford various supramolecular interactions for simultaneous “one-pot” loading of different therapeutic species, i.e., doxorubicin (DOX), glucose oxidases (GOD), and Fe3+ and further co-self-assembly into a stabilized nanomedicine for cascade amplified chemo-chemodynamic therapy. Specifically, the tumor intracellular acidic pH-triggered DOX release could serve for chemotherapy as well as enhance the intracellular H2O2 level. Together with the extra H2O2 and gluconic acid produced by the GOD-triggered glucose consumption, DOX@POAD-Fe@GOD NPs promoted Fe3+participation in the Fe-mediated Fenton reaction for cascade amplified chemo-chemodynamic therapy. Notably, this formulation displayed a greater anti-tumor effect with a tumor inhibition ratio 1.6-fold higher than that of free DOX in a BALB/c mice model bearing 4T1 tumors. Overall, the multivalent polyphenol–metal nanoplatform developed herein integrates chemotherapy, starvation therapy, and CDT for synergistic enhanced anticancer efficiency, which shows great potential for clinical translations. Statement of significanceChemodynamic therapy (CDT) generally suffers from compromised therapeutic efficiency due to insufficient endogenous H2O2 and metal catalysts in tumor cells. To develop a facile yet robust strategy for efficient CDT augmentation, we reported herein construction of a multivalent polyphenol–metal nanoplatform, DOX@POAD-Fe@GOD nanoparticles (NPs) via a phenol–metal coordination strategy. This nanoplatform integrates multiple supramolecular dynamic interactions not only for simultaneously safe encapsulation of doxorubicin (DOX), Fe3+, and glucose oxidases (GOD), but also for cascade amplified chemo-chemodynamic therapy. Specifically, the intracellular acidic pH-triggered dissociation of DOX@POAD-Fe@GOD NPs promoted the release of Fe3+, DOX, and GOD for significantly increased ROS levels that can accelerate Fenton reactions for cascaded chemotherapy, starvation therapy, and CDT with amplified antitumor efficiency in vivo.

In Vitro and In Vivo Effect of pH-Sensitive PLGA-TPGS-Based Hybrid Nanoparticles Loaded with Doxorubicin for Breast Cancer Therapy.

Doxorubicin (DOX) is an antineoplastic agent clinically employed for treating breast cancer patients. Despite its effectiveness, its inherent adverse toxic side effects often limit its clinical application. To overcome these drawbacks, lipid-polymer hybrid nanoparticles (LPNP) arise as promising nanoplatforms that combine the advantages of both liposomes and polymeric nanoparticles into a single delivery system. Alpha-tocopherol succinate (TS) is a derivative of vitamin E that shows potent anticancer mechanisms, and it is an interesting approach as adjuvant. In this study, we designed a pH-sensitive PLGA-polymer-core/TPGS-lipid-shell hybrid nanoparticle, loaded with DOX and TS (LPNP_TS-DOX). Nanoparticles were physicochemically and morphologically characterized. Cytotoxicity studies, migration assay, and cellular uptake were performed in 4T1, MCF-7, and MDA-MB-231 cell lines. Antitumor activity in vivo was evaluated in 4T1 breast tumor-bearing mice. In vitro studies showed a significant reduction in cell viability, cell migration, and an increase in cellular uptake for the 4T1 cell line compared to free DOX. In vivo antitumor activity showed that LPNP-TS-DOX was more effective in controlling tumor growth than other treatments. The high cellular internalization and the pH-triggered payload release of DOX lead to the increased accumulation of the drugs in the tumor area, along with the synergic combination with TS, culminating in greater antitumor efficacy. These data support LPNP-TS-DOX as a promising drug delivery system for breast cancer treatment.

Functionalized Moringa oleifera Gum as pH-Responsive Nanogel for Doxorubicin Delivery: Synthesis, Kinetic Modelling and In Vitro Cytotoxicity Study

Environment-responsive-cum-site-specific delivery of therapeutic drugs into tumor cells is a foremost challenge for chemotherapy. In the present work, Moringa oleifera gum-based pH-responsive nanogel (MOGN) was functionalized as a doxorubicin (DOX) carrier. It was synthesized via free radical polymerization through the γ-irradiation method using acrylamide and N,N'-MBA followed by hydrolysis, sonication, and ultracentrifugation. The swelling behavior of MOGN as a function of pH was assessed using a gravimetric method that revealed its superabsorbent nature (365.0 g/g). Furthermore, MOGN showed a very high loading efficiency (98.35 %L) of DOX by MOGN. In vitro release studies revealed that DOX release from DOX-loaded MOGN was 91.92% at pH 5.5 and 12.18% at 7.4 pH, thus favorable to the tumor environment. The drug release from nanogel followed Korsmeyer-Peppas model at pH 5.5 and 6.8 and the Higuchi model at pH 7.4. Later, the efficient DOX release at the tumor site was also investigated by cytotoxicity study using Rhabdomyosarcoma cells. Thus, the synthesized nanogel having high drug loading capacity and excellent pH-triggered disintegration and DOX release performance in a simulated tumor environment could be a promising candidate drug delivery system for the targeted and controlled release of anticancer drugs.

Antitumor Activity of the Zinc Oxide Nanoparticles Coated with Low-Molecular-Weight Heparin and Doxorubicin Complex In Vitro and In Vivo.

Various metal oxide nanomaterials have been widely used as carriers to prepare pH-sensitive nanomedicines to respond to the acidic tumor microenvironment promoting antitumor efficiency. Herein, we used zinc oxide nanoparticles (ZnO NPs) as metal oxide nanomaterial coated with low-molecular-weight heparin (LMHP) and doxorubicin (DOX) complex (LMHP-DOX) to prepare ZnO-LD NPs for controllable pH-triggered DOX release on the targeted site. Our results indicated that the released DOX from ZnO-LD NPs was pH-sensitive. The oxygen produced by ZnO-LD NPs in H2O2 solution was observed in in vitro experiment. The ZnO-LD NPs entered into both PC-3M and 4T1 tumor cells via clathrin-mediated endocytosis and micropinocytosis pathway. The intracellular reactive oxygen species (ROS) generated by ZnO-LD NPs could significantly increase the caspase 3/7 level, leading to tumor cell apoptosis. The in vitro and in vivo antitumor activity was confirmed in PC-3M and 4T1 cell lines or tumor-bearing mice models. The in vivo and in vitro tumor images via second-order nonlinearity of ZnO-LD NPs indicated that ZnO-LD NPs could penetrate deep into the tumor tissues. Therefore, the ZnO-LD NPs developed in our study could provide an efficient approach for the preparation of pH-sensitive nano delivery systems suitable for tumor therapy and imaging.

Rapid preparation of hyperbranched β-CD functionalized hydroxyapatite based on host-guest reaction for cell imaging and drug delivery

Improving the biocompatibility and water dispersibility of hydroxyapatite (HAP) is an effective way to expand its application in biomedicine. Here, we present a nanosystem (HAP-β-CD-HPG) that is constructed by riboflavin sodium phosphate (HE) functionalized hydroxyapatite (HAP) and hyperbranched β-cyclodextrin (β-CD-HPG) through a simple, mild and rapid approach. Firstly, the successful construction of HAP-β-CD-HPG nanosystem is confirmed by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and so on. Next, Doxorubicin (DOX) is loaded onto HAP-β-CD-HPG with a high encapsulation potency (60.3%) and further use for the simultaneously cell-imaging and controlled release of the cytotoxic drug DOX. Furthermore, the pH-triggered DOX release process in A549 cancer cells can be visualized dynamically by tracking the fluorescence of HAP-β-CD-HPG and DOX. This work both provides a new protocol for the construction of dual-function nanosystem for imaging of cell cytoplasm and drug delivery via a simple approach and promotes a potential application of this diagnosis-therapy integrated system for cancer treatment in the future.

Coassembling functionalized glycopolypeptides to prepare pH-responsive self-indicating nanocomplexes to manipulate self-assembly/drug delivery and visualize intracellular drug release

The pH-responsive polymeric micelles (PMs) have been widely used as smart nano drug delivery systems to treat tumors. However, synchronously manipulating these PMs' self-assembly properties, drug release dynamics and tracing their pH-dependent intracellular fate remain challenges. Herein, we have first synthesized hyaluronic acid (HA) based glycopolypeptides modified by tetraphenylethylene (TPE) and a pH-sensitive doxorubicin (DOX) prodrug through Diels-Alder reaction, respectively. Then, the pH-responsive nanocomplexes (NCs) were prepared by coassembling the two obtained glycopolypeptides with different formulations. Controllable size within the range of 60–125 nm and morphologies like spherical, vesicular and oblate micelles can be easily accomplished by using this method; High drug encapsulating and loading efficiency can be easily realized and adjusted within a range of 86–97% and 7–25%, respectively; Acid sensitive drug release dynamics of these NCs are also tunable by using this way. Additionally, the programmed drug release induced by subtle pH variations can be extracellularly self-indicated by detecting the blue AIE changes of the TPE units through fluorescence resonance energy transfer (FRET) effect between DOX and TPE. More importantly, the dynamic pH-triggered DOX release can be easily traced inside the tumor cells by visualizing blue emission changes of the TPE through the FRET effect. In addition, both the size and the shape can affect the endocytic routes of the NCs; The HA coated NCs targeting the tumor cells can effectively inhibit the proliferation of the HeLa cells. This work can provide a new route to acquire the stimuli-responsive self-indicating PMs with the ability to adjust their self-assembly properties and their pH-triggered drug release dynamics, and even to simultaneously visualize the PMs' intracellular fate in a real-time.

Biomimetic hydrogels based on L-Dopa conjugated gelatin as pH-responsive drug carriers and antimicrobial agents

Biomimetic hydrogels which possess good biocompatibility, high degradability, and low toxicity as well as good antibacterial activity against various bacteria would potentially be promising for biomaterial applications, such as wound healing, tissue engineering, and payload delivery systems. Herein, we report the synthesis and hydrogelation of L-Dopa conjugated (GPLD) polypeptides via a versatile strategy including enzymatic cross-linking or coordinated/oxidized cross-linking with Fe3+ ions and demonstrated the feasibility of loading cancer drug and metal NPs in hydrogel matrix. The drug-loaded hydrogel was simply prepared via coordinated/oxidized cross-linking by Fe3+ and H2O2 within short gelation time. Doxorubicin (DOX) was encapsulated in the hydrogel network through the formation of metal-DOX/catechol complexes. The catechol groups acted not only as the complexing depots for DOX encapsulation but also as cross-linking depots for hydrogel formation. The mechanical strength, swelling ratio, and degradability behavior could be tuned by varying Fe3+/H2O2 or enzyme/H2O2 concentration. The as-prepared hydrogel exhibited excellent pH-responsive drug release behavior and the ability to effectively kill cancer cells by pH-triggered release of DOX. We also demonstrated that the enzymatically cross-linked hydrogels loaded with metal nanoparticles (NPs) exhibiting excellent antimicrobial activities. This multifunctional hydrogel is promising for drug delivery and antimicrobial applications.

PH-responsive intramolecular FRET-based self-tracking polymer prodrug nanoparticles for real-time tumor intracellular drug release monitoring and imaging.

An intramolecular fluorescence resonance energy transfer (FRET)-based macromolecular theranostic prodrug was designed by directly conjugating Doxorubicin (DOX) as the FRET acceptor onto the naphthalimide side groups in the fluorescent copolymer PPEGMA20-PNAP8 as the FRET energy donor via an acid-labile imine bond, without a fluorogenic linker. The proposed PPEGMA20-PNAP8-DOX theranostic prodrug showed a high DOX content of 24.3% owing to a conjugation efficiency of>93% under mild conjugation conditions. It could easily self-assemble into unique theranostic nanoparticles with a Dh of 71nm. The theranostic nanoparticles showed excellent pH-triggered DOX release performance with very low premature drug leakage of 6.3% in normal physiological medium over 129h, while>91% of the conjugated DOX was released in the acidic tumor intracellular microenvironment. MTT assays indicated the enhanced antitumor efficacy of the proposed theranostic nanoparticles compared with free DOX. Furthermore, because drug release was triggered by pH, orange fluorescence was restored to the blue fluorescence of the backbone copolymer. Such self-tracking pH-responsive colorful fluorescence variations during intracellular drug delivery and release are expected to allow real-time tumor intracellular drug release monitoring and imaging diagnosis.

DOX-conjugated CQD-based nanosponges for tumor intracellular pH-triggered DOX release and imaging

Novel tumor nanotheranostics were designed by conjugating doxorubicin (DOX) onto the hydrazine-functionalized crosslinked carbon quantum dots (CQDs)/polyethylene glycol bisacrylate (PEGBA) (C-CQDPEGBA-Hy) nanosponges via an acid-labile imine bond for the tumor intracellular real-time imaging and pH-triggered DOX release. The proposed prodrug nanotheranostics with a DOX content of 14.57 % and a mean hydrodynamic diameter around 116 nm showed excellent pH-triggered drug release performance, with a cumulative release of 52.71 % in the simulated tumor intracellular microenvironment in 4 days, while a premature drug leakage of 7.09 % in the simulated normal physiological medium. Besides, the fluorescence could be recovered during the drug release, indicating the potential application for tumor intracellular real-time imaging.

Light-Switchable Yolk-Mesoporous Shell UCNPs@MgSiO3 for Nitric Oxide-Evoked Multidrug Resistance Reversal in Cancer Therapy.

Gas therapy has emerged as a forceful strategy for augmenting the effects of chemotherapeutic drugs against cancer cells. However, it remains extremely challenging to effectively deliver gas into tissues of interest and unravel its underlying mechanisms. Herein, we designed a near-infrared (NIR) light-switchable nitric oxide (NO) delivery nanosystem for high-efficacy multidrug resistance (MDR) reversal in cancer therapy based on a yolk-shell upconverting nanoparticles@magnesium silica (UCNP@MgSiO3). The internal hollow cavity and flower-like mesoporous shell of UCNPs@MgSiO3 not only enabled a significantly high encapsulation capacity for the NO precursor (BNN6) and doxorubicin (DOX) but also allowed the enhanced cellular uptake, resulting in NIR-triggered NO generation and low pH-triggered DOX release in cancer cells. Mechanistically, intracellular NO can downregulate the drug efflux-related P-glycoprotein and adenosine 5'-triphosphate-binding cassette transporters, thereby increasing the DOX accumulation in the cell nuclei. Such combination therapy of NO and DOX induced the apoptosis of MDR cells and completely inhibited in vivo MDR tumor growth. We further elucidated the therapy mechanism via proteomic profiling, showcasing the downregulation of the ubiquitin-proteasome pathway and nuclear factor kappa-B signaling pathway in the NO-treated MDR cells. Therefore, our findings develop a promising nanoscale gas/drug delivery paradigm for fighting MDR tumors and providing molecular insights into cancer therapy.

Acid-labile anhydride-linked doxorubicin-doxorubicin dimer nanoparticles as drug self-delivery system with minimized premature drug leakage and enhanced anti-tumor efficacy

Acid-labile anhydride-linked doxorubicin-doxorubicin dimers (D-DOX) were designed as doxorubicin-doxorubicin conjugate-based drug self-delivery systems (DSDSs) with high drug content for tumor intracellular pH-triggered release, by conjugating doxorubicin (DOX) with various anhydrides, such as maleic anhydride (MAH), succinic anhydride (suc), and 2,3-dimethylmaleic anhydride (DMMAH). With the similar diameter of about 200 nm, the D-DOXMAH showed better pH-triggered DOX release and was thus selected for the further investigation. The D-DOX-5 nanoparticles with desirable average hydrodynamic diameter (Dh) of 162 nm and high drug content of 51.20% were obtained via self-assembly by a facile dialysis technique, with the PEGylated dimer (D-DOXMAH-S-PEG) as surfactant. The cumulative DOX release from the proposed D-DOX nanoparticles reached 40.6% within 36 h in the simulated tumor intracellular acidic micro-environment, while the premature drug leakage was only 4.5% in the simulated normal physiological medium. The MTT results indicated the proposed DSDS possessed an enhanced anti-tumor efficacy for the HepG2 cancer cell than the free DOX.

Smart micelles self-assembled from four-arm star polymers as potential drug carriers for pH-triggered DOX release

A series of amphiphilic four-arm star polymers poly(e-caprolactone)-b-poly(2-(diethylamino)ethylmethacrylate) (4AS-PCL-b-PDMAEMA) were developed by a combination of ring opening polymerization (ROP) and continuous activators regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP). The molecular structures of the copolymers were confirmed with 1H NMR, FT-IR and gel permeation chromatography (GPC). The critical micelle concentration (CMC) values of the star polymers in aqueous solution were extremely low (3.0–4.1 mg/L).In aqueous solution, the copolymers self-assemble into blank and doxorubicin (DOX)-loaded micelles with an average size of 56–150 nm measured by scanning electron microscopy (SEM) and dynamic light scattering (DLS), which consist of outer shell with blocks PDMAEMA and inner core with blocks PCL. The core block PCL was used to contain drug molecules and shell block PDMAEMA could protonize responding to acidic condition. The in vitro release behavior showed that the micelle structure remains basically unchanged, and the drug cumulative release was only 24.5% at pH 7.4, and at pH 5.0, PDMAEMA is protonated and the micelles swell, which accelerates the release rate of DOX and the cumulative release is higher than pH 7.4. Through the semi-empirical model, the mechanism of drug release process was analyzed, and the mechanism of drug release from polymer micelles was further explored. The in vitro cytotoxicity indicated that the 4AS-PCL-b-PDMAEMA materials had low toxicity, but the DOX-loaded micelles had an obvious inhibitory effect on the HepG2 cells. The results indicate the four-arm star polymers 4AS-PCL-b-PDMAEMA may be a potential drug carriers for pH-triggered DOX release.

Poly(ethylene glycol) shell-sheddable TAT-modified core cross-linked nano-micelles: TAT-enhanced cellular uptake and lysosomal pH-triggered doxorubicin release

This study aimed to develop sheddable polyethylene glycol (PEG) shells with TAT-modified core cross-linked nanomicelles as drug-delivery carriers of doxorubicin (DOX) to establish a programmed response against the tumor microenvironment, enhanced endocytosis, and lysosomal pH-triggered DOX release. First, poly(L-succinimide) (PSI) underwent a ring-opening reaction with ethylenediamine to generate poly(N-(2-aminoethyl)-l-aspartamide) (P(ae-Asp)). Next, the thiolytic cleavable PEG, 3,4-dihydroxyphenylacetic acid, and TAT were grafted onto P(ae-Asp) to synthesize the amphiphilic graft copolymer of mPEG-SS-g-P(ae-Asp)-MCA-DA-TAT. In aqueous solution, the amphiphilic polymer self-assembled into nanomicelles, encapsulating DOX into the hydrophobic core of micelles. TAT was shielded by the PEG corona during circulation to avoid non-specific transmembrane interaction with normal cells, while the tumor redox environment-responsive shedding of PEG could expose TAT to promote internalization of tumor cells. In order to improve the stability of nanomicelles and achieve pH-triggered drug release, a core cross-linking strategy based on the coordination of catechol and Fe3+ was adopted. In vitro studies demonstrated that core cross-linked nanomicelles maintained the nanostructure in 100 times dilution in pH 7.4 phosphate-buffered saline (PBS). Moreover, DOX release from DOX-loaded core cross-linked nanomicelles (DOX-TAT-CCLMs) was favored at simulated lysosomal conditions over simulated plasma conditions, indicating that these nanomicelles demonstrate characteristics of pH-triggered DOX release. The TAT modification considerably enhanced the mean fluorescence intensity of the nanomicelles endocytosed by MCF-7/ADR cells by 8 times, compared with DOX·HCl after 8 h of incubation. Notably, the IC50 value of nanomicelles (11.61 ± 0.95 μg/mL) was nearly 4 times lower than that of DOX·HCl against MCF-7/ADR cells, implying that the nanomicelles could overcome drug resistance observed in MCF-7/ADR cells. Furthermore, the DOX-TAT-CCLMs reported superior tumor growth suppression in a 4T1 tumor-bearing mouse model. Thus, the redox- and pH- stimuli stepwise-responsive novel nanomicelles fabricated from the mPEG-SS-g-P(ae-Asp)-MCA-DA-TAT graft copolymer exhibited multifunctionality and displayed great potential for drug delivery.

A bio-responsive 6-mercaptopurine/doxorubicin based "Click Chemistry" polymeric prodrug for cancer therapy.

A novel bio-responsive co-delivery system based on Poly(DEA)-b-Poly(ABMA-co-OEGMA) (PDPAO, prepared by reversible addition-fragmentation chain transfer (RAFT) polymerization) copolymers was constructed for enhanced cellular internalization and effective combination therapy. Reduction-sensitive 6-mercaptopurine (6MP) based prodrug and pH-sensitive doxorubicin (DOX) based prodrug were grafted onto PDPAO by an azide-alkyne "Click Chemistry" reaction to acquire a pH/reduction-sensitive polymeric prodrug (PDPAO@imine-DOX/cis-6MP), which was able to self-aggregate to form polymeric micelles (M(DOX/6MP)) with an average particle size of 116±2nm in the water. The resultant micelles could maintain a stable sphere structure and show stability with a small particles' dispersion index in the blood. Importantly, it has been observed that the pH-sensitive surface charge-conversion accompanied pH-triggered DOX release in the biomimetic extracellular acidic environment of tumor tissue and a rapid dual-drug release triggered by pH and GSH in the intracellular environment. The in vitro evaluation of micelles on human cervical cancer (HeLa) and human promyelocytic leukemia (HL-60) cells showed an enhanced cellular uptake because of charge-conversion and exhibited a higher cell-killing performance. Moreover, the graft ratio of DOX and 6MP showed the ability to adjust the cytotoxicity; the micelles with a graft ratio of 2: 1 (M(DOX2/6MP)) displayed the higher cellular inhibition on either HeLa (combination index (CI)=0.62) or HL-60 (CI=0.35) cells. Overall, this novel dual-drug-conjugated delivery system might have important potential applications for combination therapy of cancer.

Cleavable Multifunctional Targeting Mixed Micelles with Sequential pH-Triggered TAT Peptide Activation for Improved Antihepatocellular Carcinoma Efficacy.

Although tumor-targeting nanovehicles for hepatocellular carcinoma (HCC) chemotherapy have attracted great research and clinic interest, the poor cancer penetration, inefficient cellular uptake, and slow intracellular drug release greatly compromise their therapeutic outcomes. In this work, a multifunctional mixed micellar system, consisting of glycyrrhetinic acid (GA) for specific liver-targeting, trans-activator of transcription (TAT) peptide for potent cell penetration, and pH-sensitive poly(β-amino ester) polymers for acidic-triggered drug release, was developed to provide HCC-targeting delivery and pH-triggered release of doxorubicin (DOX). These micelles were hypothesized to efficaciously accumulate in HCC site by the guide of GA ligands, enter into cancer cells facilitated by the activated TAT peptide on the micellar surface, and finally rapidly release DOX in cytoplasm. To demonstrate this design, DOX was initially loaded in micelles modified with both GA and TAT (DOX/GA@TAT-M) with high drug loading efficiency and pH-sensitive drug release profiles. The HCC-targeting cellular uptake and synergetic anticancer efficacy were tested, indicating DOX/GA@TAT-M could be specifically and effectively internalized into HCC cells by the effect of GA targeting and TAT penetrating with enhanced cytotoxicity. In addition, the prolonged circulation time and enhanced accumulation in tumor facilitated its potent tumor growth inhibition activity in vivo. These results demonstrated that the cleavable multifunctional mixed micelles with tumor targeting, controlled TAT peptide activation, and sequential pH-sensitive drug release could be an efficient strategy for HCC treatment.

Block copolymeric micelles of poly(ethylene oxide)-b-poly(glycidyl methacrylate) for pH-triggered drug release

ABSTRACTA pH-triggered drug release system of poly(ethylene oxide)-b-poly(glycidyl methacrylate) (PEO-b-PGMA) micelles was described. The PEO-b-PGMA block copolymers were synthesized by the reversible addition-fragmentation chain transfer (RAFT) polymerization of GMA with the PEO-macroinitiator. Subsequently, the hydroxyl groups were introduced to the block copolymer by epoxide ring-opening reaction of PGMA parts. The hydrophobic anticancer drug, doxorubicin (DOX), was conjugated to the polymer by acid cleavable hydrazone bonds, resulting in a pH-responsive controlled release system. The block copolymer and core-shell structure of DOX bearing PEO-b-PGMA were characterized by using FT-IR, 1H NMR, and TEM analyses. The pH-triggered release of DOX from the micellar core was investigated at pH 5.0 and 7.4, indicating a controlled drug delivery characteristic.

Peptide-Based Stealth Nanoparticles for Targeted and pH-Triggered Delivery.

Stealth agents are extensively investigated as a means by which to prolong nanostructure residence time in the bloodstream by avoiding uptake by the reticuloendothelial system. Unfortunately, commonly used agents such as poly(ethylene glycol) can adversely impact targeting efficiency and promote immune reaction by the host organism. Therefore, there is an increasing interest in developing biocompatible, non-PEGylated organic nanostructures able to perform targeted delivery to increase the efficacy of liposomal technology. Here, a lipopeptide is presented that can be mixed with lipids commonly used in liposomal formulations in percentages ranging from 20% to 60% w/w. The resulting vesicles are thermally and chemically stable. The peptide coating limits serum-protein adsorption even upon prolonged incubation in pure serum in physiological conditions, outperforming PEGylated liposomes. This architecture can be easily modified to allow straightforward derivatization by standard bio-orthogonal conjugation. Upon derivatization with an anti-transferrin receptor aptamer, these vesicles show highly selective cellular internalization with minimal nonspecific uptake and pH-triggered doxorubicin release.

Fluorescent Copolymer-Based Prodrug for pH-Triggered Intracellular Release of DOX.

A novel water-soluble pH stimuli-responsive fluorescent copolymer of P(PEGMA-b-(MAH-co-Rh6GEAm)) was synthesized by two-step sequential RAFT polymerization. The prodrug with drug content of 0.1560 mg/mg was prepared by coupling doxorubicin (DOX) onto the copolymer via acid-cleavable hydrazone bond, formed between the carbonyl group of DOX and abundant hydrazide functional groups in the copolymer. The amphiphilic DOX-conjugated prodrug (P(PEGMA-b-(MAH-DOX-co-Rh6GEAm))) could easily form a micelle in water with Dh of less than 100 nm. It could be transported into HepG2 cells and release DOX without burst release, while the leakage of DOX can be avoided in the simulated normal physiological media. Furthermore, its fluorescence intensity experienced a reversible change with the transformation of the media pH. The better biocompatibility, pH stimuli-responsiveness, and the strong fluorescence at low pH media make the nanoparticles a potential platform for the controlled release of anticarcinogens and real-time fluorescent imaging of tumor tissues.

Self-Assembled Monomethoxy (Polyethylene Glycol)-b-P(D,L-Lactic-co-Glycolic Acid)-b-P(L-Glutamic Acid) Hybrid-Core Nanoparticles for Intracellular pH-Triggered Release of Doxorubicin.

Triblock copolymers, Monomethoxy (Polyethylene glycol)-b-P(D,L-lactic-co-glycolic acid)-b-P(L-glutamic acid) (mPEG-PLGA-PGlu) with different molecular weights, were synthesized and mPEG(5k)-PLGA(20.5k)-PGlu(7.9k) were self-assembled into negatively charged nanoparticles with a hybrid core of PLGA and PGlu, and a stealth PEG shell. Because of electrostatic interaction with the negative hybrid-core, the model drug, doxorubicin (DOX), could be easily loaded into the hybrid-core nanoparticles with a high drug loading of ca. 25%. The hydrophobic interaction provided by PLGA could increase the stability of drug-loaded nanoparticles with no change in particle size for at least 3 days and only minor drug leakage (< 0.5%) in pH7.4 physiological media. Due to protonation of PGlu block in pH5.0 medium, the hybrid-core of these nanoparticles was destroyed, as shown by transmission electron microscopy, and this resulted in an increase in the pH-triggered release of DOX from 38.9% in pH7.4 release medium to 71% in pH5.0 release medium at 24 h. In vitro cytotoxicity testing involving MCF-7 and NCI-H460 cells showed that DOX-loaded nanoparticles were more cytotoxic to both types of cells than free DOX. Time-dependent cellular uptake of the drug-loaded nanoparticles was observed and at least 4 hours was required for rapid internalization through caveolinmediated endocytosis and macropinocytosis by MCF-7 cells into the endosomes where pH-trigged release of DOX from the nanoparticles occurred. The hybrid-core nanoparticles represent a potentially useful therapeutic delivery system for cationic drugs due to their high drug loading, high stability in physiological media and intracellular pH-triggered release.

Matrix metalloproteinase-sensitive size-shrinkable nanoparticles for deep tumor penetration and pH triggered doxorubicin release

Nanocarriers are widely used for delivering drugs to tumors and are progressing in a stable trend. The enhanced permeability and retention (EPR) effect has been a key rationale for the development of stimulus-responsive nanocarriers to solid tumor. In this study, we developed a kind of novel nanocarrier, G-AuNPs-DOX-PEG, which was constructed with shrinkable gelatin nanoparticles coated, doxorubicin (DOX) tethered gold nanoparticles and long chain polyethylene glycol (PEG). The particle size of G-AuNPs-DOX-PEG was 186.5 nm with a zeta potential of −4.21 mV and the DOX loading capacity was 9.22%. In vitro, the G-AuNPs-DOX-PEG could be degraded by MMP-2 proteins with a size shrink from 186.5 nm to 59.3 nm. The release of DOX from G-AuNPs-DOX-PEG was in a pH- and time-dependent manner. At pH 5.0, the release of DOX was much quicker than that at high pH value and the cumulative release rate of DOX from G-AuNPs-DOX-PEG was approach 90.9%. Cellular uptake demonstrated that G-AuNPs-DOX-PEG could be internalized via the endosome-mediated pathway. Tumor spheroid penetration and collagen gel diffusion showed G-AuNPs-DOX-PEG with pre-incubation with MMP-2 could significantly enhance its penetrating efficiency. In vivo and ex vivo imaging exhibit that G-AuNPs-DOX-PEG could distribute into 4T1 and B16F10 tumor at a highest intensity. Correspondingly, 4T1 and B16F10 tumor bearing mice treated with G-AuNPs-DOX-PEG displayed the lowest tumor growth rate. In summary, the tumor microenvironment sensitive size-shrinkable G-AuNPs-DOX-PEG could deliver into deep tumor region and then release DOX, resulting in a best anti-tumor effect.