pH- and redox-responsive poly(ethylene glycol) and cholesterol-conjugated poly(amido amine)s based micelles for controlled drug delivery

Synthesis and characterization of dual light/temperature-responsive supramolecular injectable hydrogel based on host-guest interaction between azobenzene and starch-grafted β-cyclodextrin: Melanoma therapy with paclitaxel

Injectable stimuli-responsive hydrogels could offer an opportunity for local administration at the tumor site and a sustained drug release. In this paper, a copolymer of azobenzene derivative and N-isopropyl acrylamide (NIPAM) was synthesized, which are performed as light- and thermo-sensitive parts, respectively. The DAS@SCD/NIPAZO hydrogel was prepared upon the establishment of host-guest interactions between the hydrophobic core of CD and azobenzene moiety. The LCST of the synthesized copolymer was modified from 31.3 °C to 36.5 °C by the incorporation of the hydrophilic host moieties of the modified starch into the NIPAM copolymer structure. The LCST-based property of the hydrogel made it syringable in low temperatures and switch to a gel state after local injection. The drug release profile of the hydrogel was explored in four different conditions involving two distinct temperatures combined with two different light wavelengths to examine the light- and thermo-sensitivity of the hydrogel. Moreover, a Paclitaxel-loaded hydrogel was prepared to study the in vitro efficiency of the sample and was investigated by MTT assay against the cancerous fibroblastic cells (A-431), which revealed a sharp decline in cell viability under 365 nm light irradiation; furthermore, to evaluate the in vivo effects of the PTX-loaded hydrogel, histological studies based on staining techniques were carried out.

Polymeric Drug Delivery Systems Bearing Cholesterol Moieties: A Review

This review aims to provide an overview of polymers comprising cholesterol moiety/ies designed to be used in drug delivery. Over the last two decades, there have been many papers published in this field, which are summarized in this review. The primary focus of this article is on the methods of synthesis of polymers bearing cholesterol in the main chain or as side chains. The data related to the composition, molecular weight, and molecular weight distribution of polymers are presented. Moreover, other aspects, such as forms of carriers, types of encapsulated drugs, encapsulation efficiency and capacity, are also included.

pH-Responsive Vesicle Formation by PEGylated Cholesterol Derivatives: Physicochemical Characterization, Stability, Encapsulation, and Release Study

PEGylated vesicles are known to serve as blood-persistent drug-delivery systems (DDSs) with potential applications in intravenous drug administration. pH-responsive PEGylated vesicles are also among the most promising stimuli-responsive carriers for drug delivery and controlled release for cancer chemotherapy. Herein, we report design and synthesis of two novel pH-responsive amphiphiles by coupling a cholesterol (Chol) and poly(ethylene glycol) chain with l-cysteine amino acid through hydrolysable linkages. The objective of this work is to physicochemically characterize the nanoaggregates of the amphiphiles under different experimental conditions. We have demonstrated spontaneous vesicle formation by the amphiphiles in water using various spectroscopic, calorimetric, and microscopic techniques. The size of vesicles was observed to increase on reduction of solution pH and increase in amphiphile concentration. The vesicles were found to be sufficiently stable under physiological conditions and were shown to be able to encapsulate not only hydrophilic dyes in their aqueous core but also hydrophobic guest molecules in the bilayer membrane constituted by the Chol units. These nanosized vesicles exhibit pH-triggered release of encapsulated dye molecules in acidic pH. Thus, these spontaneously formed stable vesicles might hold potential as biocompatible DDSs in cancer chemotherapy.

Redox dual-stimuli responsive drug delivery systems for improving tumor-targeting ability and reducing adverse side effects

Cancer is a big challenge that has plagued the human beings for ages and one of the most effective treatments is chemotherapy. However, the low tumor-targeting ability limits the wide clinical application of chemotherapy. The microenvironment plays a critical role in many aspects of tumor genesis. It generates the tumor vasculature and it is highly implicated in the progression to metastasis. To maintain a suitable environment for tumor progression, there are special microenvironment in tumor cell, such as low pH, high level of glutathione (GSH) and reactive oxygen species (ROS), and more special enzymes, which is different to normal cell. Microenvironment-targeted therapy strategy could create new opportunities for therapeutic targeting. Compared to other targeting strategies, microenvironment-targeted therapy strategy will control the drug release into tumor cells more accurately. Redox responsive drug delivery systems (DDSs) are developed based on the high level of GSH in tumor cells. However, there are also GSH in normal cell though its level is lower. In order to control the release of drugs more accurately and reduce side effects, other drug release stimuli have been introduced to redox responsive DDSs. Under the synergistic reaction of two stimuli, redox dual-stimuli responsive DDSs will control the release of drugs more accurately and quickly and even increase the accumulation. This review summarizes strategies of redox dual-stimuli responsive DDSs such as pH, light, enzyme, ROS, and magnetic guide to delivery chemotherapeutic agents more accurately, aiming at providing new ideas for further promoting the drug release, enhancing tumor-targeting and improving anticancer effects. To better illustrate the redox dual-stimuli responsive DDS, preparations of carriers are also briefly described in the review.

Preparation of thermo/redox/pH-stimulative poly(N-isopropylacrylamide-co-N,N'-dimethylaminoethyl methacrylate) nanogels and their DOX release behaviors

Stimuli-sensitive drug delivery systems show beneficial features of both medical and pharmaceutical fields. In this article, polymeric nanogel P (N-isopropylacrylamide-N,N '-dimethylaminoethyl methacrylate [NIPAM-DMAEMA]) (PND) with pH/redox/thermo-responsivenesses was synthesized by the in situ polymerization of NIPAM and DMAEMA for the controlled release of doxorubicin hydrochloride (DOX) and N,N '-bis(acryloyl)cystamine (BAC) and N,N '-methylenebisacrylamide (MBA) act as the crosslinkers, respectively. The structure, size, and zeta potential of PND-BAC and PND-MBA were further characterized. Moreover, after loading DOX, the encapsulation efficiency and the in vitro release behavior of PND-BAC/DOX and PND-MBA/DOX nanogels were discussed in detail. Compared to PND-MBA NGs, PND-BAC nanogels have redox degradability due to the presence of the crosslinker BAC. After loading DOX, the PND-BAC/DOX nanogel showed a higher encapsulation efficiency (81.6 ± 1.2)% and thermo- and pH-responsiveness as well as redox-responsive in vitro release. These properties together with excellent environmentally sensitive properties make PND-BAC as an attractive candidate for application in drug nanocarriers for the targeted drug delivery of model payloads. © 2018 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 1195-1203, 2019.

Degradable redox-responsive disulfide-based nanogel drug carriers via dithiol oxidation polymerization

Stimuli-responsive nanogels are important drug and gene carriers that mediate the controlled release of therapeutic molecules. Herein, we report the synthesis of fully degradable disulfide cross-linked nanogel drug carriers formed by oxidative radical polymerization of 2,2'-(ethylenedioxy)diethanethiol (EDDET) as a monomer with different cross-linkers, including pentaerythritol tetramercaptoacetate (PETMA). Because the poly(EDDET) backbone repeat structure and cross-linking junctions are composed entirely of disulfide bonds, these nanogels specifically degrade to small molecule dithiols intracellularly in response to the reducing agent glutathione present inside of cells. Cross-linked nanogels were synthesized using controlled microfluidic mixing in the presence of a nonionic Pluronic surfactant PLU-127 to increase the nanogel stability. Adjusting the monomer to cross-linker ratio from 5 : 1 to 100 : 1 (mol/mol) tuned the cross-linking density, resulting in swelling ratios from 1.65 to >3. Increasing the amount of stabilizing Pluronic surfactant resulted in a decrease of nanogel diameter, as expected due to increased surface area of the resulting nanogels. The monomer to cross-linker ratio in the feed had no effect on the formed nanogel diameter, providing a way to control cross-linking density with constant nanogel size but tunable drug release kinetics. Nanogels exhibited an entrapment efficiency of up to 75% for loading of Rhodamine B dye. In vitro studies showed low cytotoxicity, quick uptake, and fast degradation kinetics. Due to the ease of synthesis, rapid gelation times, and tunable functionality, these non-toxic and fully degradable nanogels offer potential for use in a variety of drug delivery applications.

Cholesterol and vitamin E-conjugated PEGylated polymeric micelles for efficient delivery and enhanced anticancer activity of curcumin: evaluation in 2D monolayers and 3D spheroids

A newly synthesized PEGylated cholesterol/α-tocopheryl succinate (α-TOS) linked polymer (CV) was self-assembled and loaded with curcumin to form a micellar system (C-CVM). The tri-functionalized amphiphilic polymer was constituted of hydrophobic cholesterol and α-TOS connected to hydrophilic PEG via a lysine linker. The synthesized polymer and the micelles were characterized by ¹H NMR, DLS, zeta potentiometer, TEM, CMC determination and hemolysis studies. CVM displayed low CMC value of 15 µM with extent of hemolysis as less than 4%. The stable C-CVM with optimum % drug loading (14.2 ± 0.24) displayed Z average of 175.8 ± 0.68 nm with PDI (0.248 ± 0.075) and released curcumin in sustained manner in the in vitro drug release study. C-CVM demonstrated dose-dependent cellular uptake and cytotoxicity in murine melanoma, B16F10 and human breast cancer, MDA-MB-231 cell lines. CV exhibited marked reversal of drug resistance as indicated by significantly higher retention of P-glycoprotein substrate, rhodamine-123 in the resistant B16F10 cell line compared to standard P-glycoprotein inhibitor, verapamil. C-CVM demonstrated significantly higher spheroidal growth inhibition compared to C-PPM. The results provide strong evidence for CVM as promising drug delivery system and confirm the potential of C-CVM as chemotherapy in cancer.

Enzymatic PEG-Poly(amine-co-disulfide ester) Nanoparticles as pH- and Redox-Responsive Drug Nanocarriers for Efficient Antitumor Treatment

We have designed and constructed novel multifunctional nanoparticle drug-delivery systems that are stable under physiological conditions and responsive to tumor-relevant pH and intracellular reduction potential. The nanoparticles were fabricated from enzymatically synthesized poly(ethylene glycol) (PEG)-poly(ω-pentadecalactone-co-N-methyldiethyleneamine-co-3,3'-dithiodipropionate) (PEG-PPMD) and PEG-poly(ε-caprolactone-co-N-methyldiethyleneamine-co-3,3'-dithiodipropionate) (PEG-PCMD) block copolymers via self-assembly processes in aqueous solution. At acidic pH and in the presence of a reductant (e.g., d,l-dithiothreitol or glutathione), the nanosized micelle particles rapidly swell and disintegrate due to the protonation of amino groups and reductive cleavage of disulfide bonds in the micelle cores. Consistently, docetaxel (DTX)-loaded PEG-PPMD and PEG-PCMD micelles can be triggered synergistically by acidic endosomal pH and a high intracellular reduction potential to rapidly release the drug for efficient killing of cancer cells. The drug formulations based on PEG-PPMD and PEG-PCMD copolymers exhibited a substantially higher potency than free DTX in inhibiting tumor growth in mice, whereas their therapeutic effects on important organ tissues were minimal. These results demonstrate that PEG-PPMD and PEG-PCMD nanoparticles have a great potential to serve as site-specific, controlled drug-delivery vehicles for safe and efficient antitumor treatment.

Cholesterol-conjugated poly(D, L-lactide)-based micelles as a nanocarrier system for effective delivery of curcumin in cancer therapy

Polymeric micelles have been widely explored preclinically as suitable delivery systems for poorly soluble chemotherapeutic drugs in cancer therapy. The present study reported the development of cholesterol (Ch)-conjugated poly(D,L-Lactide) (PLA)-based polymeric micelles (mPEG–PLA-Ch) for effective encapsulation and delivery of curcumin (CUR) at the tumor site. Cholesterol conjugation dramatically affected the particle size and improved drug loading (DL) and encapsulation efficiency (EE). mPEG–PLA-Ch-CUR showed bigger hydrodynamic diameter (104.6 ± 2.1 nm, and 169.3 ± 1.52 nm for mPEG–PLA and mPEG–PLA-Ch, respectively) due to increased size of the hydrophobic core. The newly developed polymer exhibited low critical micelles concentration (CMC) (25 μg/mL) which is close to lipid-based polymer, PEG-phosphatidyl ethanolamine (12.5 μg/mL) compared to mPEG–PLA (50 μg/mL). mPEG–PLA-Ch micelles exhibited relatively higher EE (93.74 ± 1.6%) and DL (11.86 ± 0.8%) compared to mPEG–PLA micelles (EE 91.89 ± 1.2% and DL 11.06 ± 0.8%). mPEG–PLA-Ch micelles were internalized by the cancer cells effectively and exhibited higher cytotoxicity compared to free CUR in both, murine melanoma (B16F10) and human breast cancer (MDA-MB-231) cells. mPEG–PLA-Ch exhibited satisfactory hemocompatibility indicating their potential for systemic application. Further, mPEG–PLA-Ch-CUR demonstrated higher rate of reduction of tumor volume in B16F10-xenografted tumor-bearing mice compared to free CUR. At the end of 22 days, the tumor reduced to 1.87-fold (627.72 ± 0.9 mm³ versus 1174.68 ± 1.64 mm³) compared to the treatment with free CUR. In conclusion, the experimental data in vitro and in vivo indicated that the newly developed CUR-mPEG–PLA-Ch micelles may have promising applications in solid tumors.

Surfactant-Free Emulsion-Based Preparation of Redox-Responsive Nanogels

A surfactant-free emulsion-based approach is developed for preparation of nanogels. A water-in-oil emulsion is generated feasibly from a mixture of water and a solution of disulfide-containing hyperbranched PEGylated poly(amido amine)s, poly(BAC2-AMPD1)-PEG, in chloroform. The water droplets in the emulsion are stabilized and filled with poly(BAC2-AMPD1)-PEG, and the crosslinked poly(amido amine)s nanogels are formed via the intermolecular disulfide exchange reaction. FITC-dextran is loaded within the nanogels by dissolving the compound in water before emulsification. Transmission electron microscopy and dynamic light scattering are applied to characterize the emulsion and the nanogels. The effects of the homogenization rate and the ratio of water/polymer are investigated. Redox-induced degradation and FITC-dextran release profile of the nanogels are monitored, and the results show efficient loading and redox-responsive release of FITC-dextran. This is a promising approach for the preparation of nanogels for drug delivery, especially for neutral charged carbohydrate-based drugs.

Reduction-sensitive polymeric nanocarriers in cancer therapy: a comprehensive review

Redox potential is regarded as a significant signal to distinguish between the extra-cellular and intra-cellular environments, as well as between tumor and normal tissues. Taking advantage of this physiological differentiation, various reduction-sensitive polymeric nanocarriers (RSPNs) have been designed and explored to demonstrate excellent stability during blood circulation but rapidly degrade and effectively trigger drug release in tumor cells. Therefore, this smart RSPN delivery system has attracted much attention in recent years, as it represents one of the most promising drug delivery strategies in cancer therapy. In this review, we will provide a comprehensive overview of RSPNs with various reducible linkages and functional groups up to date, including their design and synthetic strategies, preparation methods, drug release behavior, and their in vitro and in vivo efficacy in cancer therapy. In addition, dual- and triple-sensitive nanocarriers based on reducible disulfide bond-containing linkages will also be discussed.

Trigger responsive polymeric nanocarriers for cancer therapy

Conventional chemotherapy for the treatment of cancer has limited specificity when administered systemically and is often associated with toxicity issues. Enhanced accumulation of polymeric nanocarriers at a tumor site may be achieved by passive and active targeting. Incorporation of trigger responsiveness into these polymeric nanocarriers improves the anticancer efficacy of such systems by modulating the release of the drug according to the tumor environment. Triggers used for tumor targeting include internal triggers such as pH, redox and enzymes and external triggers such as temperature, magnetic field, ultrasound and light. While internal triggers are specific cues of the tumor microenvironment, external triggers are those which are applied externally to control the release. This review highlights the various strategies employed for the preparation of such trigger responsive polymeric nanocarriers for cancer therapy and provides an overview of the state of the art in this field.

pH- and redox-responsive self-assembly of amphiphilic hyperbranched poly(amido amine)s for controlled doxorubicin delivery

Vinyl-terminated hyperbranched poly(amido amine)s is obtained by Michael addition polymerization of 4-(aminomethyl)piperidine (AMPD) with a double molar N,N-cystaminebis(acrylamide) (BAC). Then an amphiphilic hyperbranched poly(BAC2-AMPD1)-PEG is produced via converting the vinyl groups to amines followed by PEGylation. Transmission electron microscopy (TEM), dynamic light scattering (DLS), and (1)H nuclear magnetic resonance (NMR) results indicate that the micelles can be obtained via self-assembly of hyperbranched poly(BAC2-AMPD1)-PEG. Further an anti-cancer drug, doxorubicin (DOX), can be loaded into the micelles. pH- and redox-response of the micelles of hyperbranched poly(BAC2-AMPD1)-PEG without and with DOX are investigated. The results of confocal microscopy and flow cytometry reflect that FITC tagged or DOX loaded micelles of hyperbranched poly(BAC2-AMPD1)-PEG can enter HepG2 and MCF-7 cells, and DOX can be observed in the nucleus of the cells. The cytotoxicity of the micelles without and with DOX is evaluated in HepG2 and MCF-7 cells, and the efficacy to kill the cancer cells is discussed in comparison with free DOX.

A facile synthetic approach to a biodegradable polydisulfide MRI contrast agent

A biodegradable novel polydisulfide MRI contrast agent forming self-assembly in aqueous solution with a low cytotoxicity and a higherr₁is promising for producing better MRI imaging with fewer side effects.