Biodegradable Zwitterionic Nanogels with Long Circulation for Antitumor Drug Delivery

Optimal synthesis of polyelectrolyte nanogels by electrostatic assembly directed polymerization for dye loading and release

Polyelectrolyte (PE) nanogels which combine features of nanogels and polyelectrolytes have attracted significant attention as outstanding nano-carriers. However, and crucially, any large-scale application of PE nanogels can only materialize when an efficient production method is available. We recently developed such a robust approach, namely Electrostatic Assembly Directed Polymerization (EADP), in which ionic monomers are polymerized together with cross-linker in the presence of a polyion-neutral diblock copolymer as template. Although EADP achieves efficient and scalable preparation of diverse PE nanogels, the essential factors for the optimal and controlled synthesis of nanogels have remained elusive. In this article, we investigate systematically the effects of pH, salt concentration, and cross-linker fractions on the formation and properties of a PDMAEMA nanogel prepared with PAA-b-PEO as the template. We find that the electrostatic interaction between the building blocks is crucial to obtain assembly-controlled polymerization, and we establish preferred pH, salt concentration and cross-linker fractions. The obtained PDMAEMA nanogel exhibits dual-responses to pH and salt, which allow manipulation of the positive charges of the nanogels for selective loading and controlled release of anionic substances; we demonstrate this with an anionic dye. The study presented here fully addresses the process parameters of EADP regarding optimal and controlled preparation of PE nanogels, which should allow exploration of their potential vis-a-vis a variety of applications.

Peptide-based hydrogels as delivery systems for doxorubicin

Hydrogels (HGs) and nanogels (NGs) have been recently identified as innovative supramolecular materials for many applications in biomedical field such as in tissue engineering, optoelectronic, and local delivery of active pharmaceutical ingredients (APIs). Due to their in vivo biocompatibility, synthetic accessibility, low cost, and tunability, peptides have been used as suitable building blocks for preparation of HGs and NGs formulations. Peptide HGs have shown an outstanding potential to deliver small drugs, protein therapeutics, or diagnostic probes, maintaining the efficacy of their loaded molecules, preventing degradation phenomena, and responding to external physicochemical stimuli. In this review, we discuss the possible use of peptide-based HGs and NGs as vehicles for the delivery of the anticancer drug doxorubicin (Dox). This anthracycline is clinically used for leukemia, stomach, lung, ovarian, breast, and bladder cancer therapy. The loading of Dox into supramolecular systems (liposomes, micelles, hydrogels, and nanogels) allows reducing its cardiotoxicity. According to a primary sequence classification of the constituent peptide, doxorubicin-loaded systems are here classified in short and ultra-short peptide-based HGs, RGD, or RADA-peptide-based HGs and peptide-based NGs.

Review of Contemporary Self-Assembled Systems for the Controlled Delivery of Therapeutics in Medicine

The novel and unique design of self-assembled micro and nanostructures can be tailored and controlled through the deep understanding of the self-assembly behavior of amphiphilic molecules. The most commonly known amphiphilic molecules are surfactants, phospholipids, and block copolymers. These molecules present a dual attraction in aqueous solutions that lead to the formation of structures like micelles, hydrogels, and liposomes. These structures can respond to external stimuli and can be further modified making them ideal for specific, targeted medical needs and localized drug delivery treatments. Biodegradability, biocompatibility, drug protection, drug bioavailability, and improved patient compliance are among the most important benefits of these self-assembled structures for drug delivery purposes. Furthermore, there are numerous FDA-approved biomaterials with self-assembling properties that can help shorten the approval pathway of efficient platforms, allowing them to reach the therapeutic market faster. This review focuses on providing a thorough description of the current use of self-assembled micelles, hydrogels, and vesicles (polymersomes/liposomes) for the extended and controlled release of therapeutics, with relevant medical applications. FDA-approved polymers, as well as clinically and commercially available nanoplatforms, are described throughout the paper.

Construction of a tumor microenvironment pH-responsive cleavable PEGylated hyaluronic acid nano-drug delivery system for colorectal cancer treatment

In order to improve active tumor targeting, tumor cell uptake efficiency and circulation time of doxorubicin (DOX) in vivo, we constructed a cleavable PEGylated hyaluronic acid nano-drug delivery system (HA-mPEG2k-DOX) based on a tumor microenvironment pH-responsive imine bond. In this study, HA-mPEG2k-DOX can self-assemble into stable nanoparticles (HA-mPEG2k-DOX NPs) with a particle size of 50 nm. And the NPs can efficiently target CD44 positive CT26 cells and the pH-responsive cleavable PEG shell can be detached under weakly acidic environments and effectively promote the cellular uptake of HA-DOX NPs. Compared with DOX·HCl, the HA-mPEG2k-DOX NPs can significantly increase the DOX circulation time by 12.5 times, efficiently target the tumor tissues of CT26 tumor-bearing mice and remain for 72 hours. Therefore, the antitumor results in vivo indicated that the HA-mPEG2k-DOX NPs have the best anti-tumor effect while reducing the toxicity of the DOX. Overall, the cleavable PEGylated HA-mPEG2k-DOX NPs responding to pH-sensitive imine bonds, while actively targeting CD44-positive tumor cells, improve the dilemma of cellular uptake and delivery by the PEGylated nano delivery system.

Novel zwitterionic vectors: Multi-functional delivery systems for therapeutic genes and drugs

Zwitterions consist of equal molar cationic and anionic moieties and thus exhibit overall electroneutrality. Zwitterionic materials include phosphorylcholine, sulfobetaine, carboxybetaine, zwitterionic amino acids/peptides, and other mix-charged zwitterions that could form dense and stable hydration shells through the strong ion-dipole interaction among water molecules and zwitterions. As a result of their remarkable hydration capability and low interfacial energy, zwitterionic materials have become ideal choices for designing therapeutic vectors to prevent undesired biosorption especially nonspecific biomacromolecules during circulation, which was termed antifouling capability. And along with their great biocompatibility, low cytotoxicity, negligible immunogenicity, systematic stability and long circulation time, zwitterionic materials have been widely utilized for the delivery of drugs and therapeutic genes. In this review, we first summarized the possible antifouling mechanism of zwitterions briefly, and separately introduced the features and advantages of each type of zwitterionic materials. Then we highlighted their applications in stimuli-responsive "intelligent" drug delivery systems as well as tumor-targeting carriers and stressed the multifunctional role they played in therapeutic gene delivery.

A phosphorylcholine-based zwitterionic copolymer coated ZIF-8 nanodrug with a long circulation time and charged conversion for enhanced chemotherapy

In recent years, zeolitic imidazolate framework-8 (ZIF-8) has become an attractive metal organic framework (MOF) material in drug delivery for cancer chemotherapy. However, as a drug delivery system, ZIF-8 still shows some disadvantages, such as short blood circulation time and poor tumor targeting, leading to reduced drug delivery efficiency and unsatisfactory treatment. Herein, we developed a phosphorylcholine-based zwitterionic copolymer coated ZIF-8 nanodrug (DOX@ZIF-8@P(MPC-co-C7A)), and the obtained nanodrug was prepared via a charge-conversional zwitterionic copolymer coating on DOX@ZIF-8 composites. In this system, DOX was encapsulated in the framework of ZIF-8, which could reduce the drug leakage in the bloodstream. The phosphorylcholine-based zwitterionic copolymer effectively extended the blood circulation time, resulting in enhanced tumor accumulation of the nanodrug. Once the nanodrug reached the tumor site, the surface charge of the system could rapidly convert to positive, resulting in an enhanced tumor cellular uptake. Finally, in the acidic environment inside intracellular organelles, DOX will be released rapidly for chemotherapy owing to the fast disintegration of ZIF-8 frameworks. Therefore, the obtained nanodrug could effectively inhibit the growth of A549-bearing tumors (93.2% tumor inhibition rate) with negligible side effects. Overall, this work significantly improved the drug delivery efficiency of ZIF-8, which may pave the way for the biomedical applications of ZIF-8 crystals in anti-tumor drug delivery.

IR780 loaded sulfobetaine methacrylate-functionalized albumin nanoparticles aimed for enhanced breast cancer phototherapy

New insights about nanomaterials' biodistribution revealed their ability to achieve tumor accumulation by taking advantage from the dynamic vents occurring in tumor's vasculature. This paradigm-shift emphasizes the importance of extending nanomaterials' blood circulation time to enhance their tumor uptake. The classic strategy to improve nanomaterials' stability during circulation relies on their functionalization with poly(ethylene glycol). However, recent reports have been showing that PEGylated nanomaterials can suffer from the accelerated blood clearance phenomenon, emphasizing the importance of developing novel coatings for functionalizing the nanomaterials. To address this limitation, the modification of natural carriers' surface to enhance their stability appears to be a promising strategy. Herein, sulfobetaine methacrylate (SBMA)-functionalized bovine serum albumin (BSA) was synthesized for the first time to investigate the capacity of this modification to improve the resulting nanoparticles' physicochemical properties, colloidal stability and in vitro performance. This novel polymer was then employed in the formulation of nanoparticles loaded with IR780 for application in breast cancer phototherapy (IR/SBMA-BSA NPs). When compared to their non-functionalized equivalents, the IR/SBMA-BSA NPs presented a neutral surface charge and a higher stability in biologically relevant media. Due to these features, the IR/SBMA-BSA NPs could achieve a 1.9-fold greater uptake by breast cancer cells than IR/BSA NPs. Furthermore, the IR/SBMA-BSA NPs were cytocompatible towards normal cells and reduced breast cancer cells' viability up to 42%. The phototherapy mediated by IR/SBMA-BSA NPs could further decrease cancer cells' viability to about 12%. Overall, the IR/SBMA-BSA NPs have enhanced features that propel their application in breast cancer phototherapy.

Dihydroartemisinin-Loaded Magnetic Nanoparticles for Enhanced Chemodynamic Therapy

Recently, chemodynamic therapy (CDT) has represented a new approach for cancer treatment with low toxicity and side effects. Nonetheless, it has been a challenge to improve the therapeutic effect through increasing the amount of reactive oxygen species (ROS). Herein, we increased the amount of ROS agents in the Fenton-like reaction by loading dihydroartemisinin (DHA) which was an artemisinin (ART) derivative containing peroxide groups, into magnetic nanoparticles (MNP), thereby improving the therapeutic effect of CDT. Blank MNP were almost non-cytotoxic, whereas three MNP loading ART-based drugs, MNP-ART, MNP-DHA, and MNP-artesunate (MNP-AS), all showed significant killing effect on breast cancer cells (MCF-7 cells), in which MNP-DHA were the most potent. What's more, the MNP-DHA showed high toxicity to drug-resistant breast cancer cells (MCF-7/ADR cells), demonstrating its ability to overcome multidrug resistance (MDR). The study revealed that MNP could produce ferrous ions under the acidic condition of tumor microenvironment, which catalyzed DHA to produce large amounts of ROS, leading to cell death. Further experiments also showed that the MNP-DHA had significant inhibitory effect on another two aggressive breast cancer cell lines (MDA-MB-231 and MDA-MB-453 cells), which indicated that the great potential of MNP-DHA for the treatment of intractable breast cancers.

Zwitterionic Polymer Coating of Sulfur Dioxide-Releasing Nanosystem Augments Tumor Accumulation and Treatment Efficacy

Multiple drug resistance (MDR) exhibited by cancer cells and low intratumor accumulation of chemotherapeutics are the main obstacles in cancer chemotherapy. Herein, the preparation of a redox-responsive sulfur dioxide (SO₂ )-releasing nanosystem, with high SO₂ -loading capacity, aimed at improving the treatment efficacy of cancers exhibiting MDR is described. The multifunctional nanomedicine (MON-DN@PCBMA-DOX) is designed and constructed by coating mesoporous organosilica nanoparticles with a zwitterionic polymer, poly(carboxybetaine methacrylate) (PCBMA), which can concurrently load SO₂ prodrug molecules (DN, 2,4-dinitrobenzenesulfonylchloride) and chemotherapeutics (DOX, doxorubicin). The generated SO₂ molecules can sensitize cells to chemotherapy and overcome the MDR by downregulating the expression of P-glycoprotein. Furthermore, the PCBMA coating prolongs the blood circulation time of the inner core, leading to an increased intratumor accumulation of the nanomedicine. Owing to the prolonged blood circulation, enhanced tumor accumulation, and SO₂ sensitization of cells to chemotherapy, the nanomedicine exhibits excellent tumor suppression with a tumor inhibition rate of 94.8%, and might provide a new platform for cancer therapy.

A self-assembled pH/enzyme dual-responsive prodrug with PEG deshielding for multidrug-resistant tumor therapy

Multidrug resistance (MDR) is one of the major obstacles for tumor therapy. Intake by receptor-mediated endocytosis enables molecules to bypass ABC transporter efflux, which is the primary mechanism of MDR. Here, we developed a novel pH/enzyme dual-responsive polypeptide prodrug to reverse multidrug resistance. This drug is composed of pH/MMP2-sensitive nanoparticles (MSNPs) self-assembled from mPEG-peptide-DOX. MSNPs can overcome sequential physiological barriers of multidrug resistance by prolonging the circulation time through PEGylation, enhancing tumor accumulation through passive targeting, increasing tumor penetration by enzyme-sensitive PEG deshielding, bypassing ABC transporter efflux by undergoing receptor-mediated endocytosis, and inducing sufficient DOX release from nanoparticles triggered by lysosomal pH. The reversal of MDR by MSNPs was evaluated in MCF-7/ADR cells and nude mice bearing tumors consisting of MCF-7/ADR cells. Both in vitro and in vivo studies showed that the MSNPs can effectively reverse MDR. Thus, MSNPs may constitute a potentially promising strategy for overcoming MDR in clinical applications.

Sulfobetaine methacrylate-functionalized graphene oxide-IR780 nanohybrids aimed at improving breast cancer phototherapy

The application of Graphene Oxide (GO) in cancer photothermal therapy is hindered by its lack of colloidal stability in biologically relevant media and modest Near Infrared (NIR) absorption. In this regard, the colloidal stability of GO has been improved by functionalizing its surface with poly(ethylene glycol) (PEG), which may not be optimal due to the recent reports on PEG immunogenicity. On the other hand, the chemical reduction of GO using hydrazine hydrate has been applied to enhance its photothermal capacity, despite decreasing its cytocompatibility. In this work GO was functionalized with an amphiphilic polymer containing [2-(methacryloyloxy)ethyl]dimethyl-(3-sulfopropyl)ammonium hydroxide (SBMA) brushes and was loaded with IR780, for the first time, aiming to improve its colloidal stability and phototherapeutic capacity. The attained results revealed that the SBMA-functionalized GO displays a suitable size distribution, neutral surface charge and adequate cytocompatibility. Furthermore, the SBMA-functionalized GO exhibited an improved colloidal stability in biologically relevant media, while its non-SBMA functionalized equivalent promptly precipitated under the same conditions. By loading IR780 into the SBMA-functionalized GO, its NIR absorption increased by 2.7-fold, leading to a 1.2 times higher photothermal heating. In in vitro cell studies, the combination of SBMA-functionalized GO with NIR light only reduced breast cancer cells' viability to 73%. In stark contrast, by combining IR780 loaded SBMA-functionalized GO and NIR radiation, the cancer cells' viability decreased to 20%, hence confirming the potential of this nanomaterial for cancer photothermal therapy.

IR780 loaded SBMA-coated GO displayed an improved colloidal stability in biologically relevant media and an enhanced photothermal capacity.

Diselenide-crosslinked zwitterionic nanogels with dual redox-labile properties for controlled drug release

We developed a diselenide-crosslinked zwitterionic nanogel based on poly(2-methacryloyloxyethyl phosphorylcholine), which has sensitive dual redox-degradability and high colloidal stability.

Redox-responsive hollow mesoporous silica nanoparticles constructed via host-guest interactions for controllable drug release

A novel redox-responsive hollow mesoporous silica (HMS) was constructed by host-guest interaction between β-cyclodextrin modified hollow mesoporus silica nanoparticles (HMS@β-CD) and the ferrocene-containing amphiphilic block copolymer PEG-b-PMAFc (PPFc), the prepared HMS@β-CD@PPFc system was used to control drug delivery in targeted cancer therapy through redox stimulus. The self-assembled morphology was investigated by transmission electron microscopy (TEM) and dynamic light scattering (DLS). Intracellular localization of DOX-loaded HMS@β-CD@PPFc in A549 cells was further investigated by confocal laser scanning microscopy (CLSM), and the results indicated that DOX-loaded HMS@β-CD@PPFc was ingested by A549 cells effectively. Furthermore, the redox agent H₂O₂ was used to trigger the release of DOX. The cytotoxicity evaluated by MTT method indicated that HMS@β-CD@PPFc had good biocompatibility and was promising as the drug carrier.

Nanogels and Microgels: From Model Colloids to Applications, Recent Developments, and Future Trends

Nanogels and microgels are soft, deformable, and penetrable objects with an internal gel-like structure that is swollen by the dispersing solvent. Their softness and the potential to respond to external stimuli like temperature, pressure, pH, ionic strength, and different analytes make them interesting as soft model systems in fundamental research as well as for a broad range of applications, in particular in the field of biological applications. Recent tremendous developments in their synthesis open access to systems with complex architectures and compositions allowing for tailoring microgels with specific properties. At the same time state-of-the-art theoretical and simulation approaches offer deeper understanding of the behavior and structure of nano- and microgels under external influences and confinement at interfaces or at high volume fractions. Developments in the experimental analysis of nano- and microgels have become particularly important for structural investigations covering a broad range of length scales relevant to the internal structure, the overall size and shape, and interparticle interactions in concentrated samples. Here we provide an overview of the state-of-the-art, recent developments as well as emerging trends in the field of nano- and microgels. The following aspects build the focus of our discussion: tailoring (multi)functionality through synthesis; the role in biological and biomedical applications; the structure and properties as a model system, e.g., for densely packed arrangements in bulk and at interfaces; as well as the theory and computer simulation.

Degradable and Thermosensitive Microgels Synthesized via Simultaneous Quaternization and Siloxane Condensation

Degradable and thermosensitive microgels were successfully prepared via simultaneous quaternization and siloxane condensation during surfactant-free emulsion polymerization, with N-vinylcaprolactam as the main monomer and 1-vinylimidazole (VIM) as the comonomer, in the presence of (3-bromopropyl)trimethoxysilane (BPTMOS). The formation mechanism of cross-linking network was attributed to the hydrolysis and condensation of the methoxysilyl groups of BPTMOS and the quaternization of imidazole moiety of VIM by the bromine group of BPTMOS, leading to the microgels. The microgels were spherical in shape with a narrow size distribution, stable in an acidic buffer solution, but degradable in neutral and alkaline solutions. The presence of quaternized imidazolium in the same chain segment of Si-O-Si cross-linking points promoted the decomposition of Si-O-Si bonds and hence the degradation of the microgels. The obtained microgels could load and release the model drug, doxorubicin. The size, thermosensitivity, stability, degradation rate, and drug release behavior of the resultant microgels could be tuned by controlling the cross-linking degree, chemical composition, and degradation medium.

Dual carrier-cargo hydrophobization and charge ratio optimization improve the systemic circulation and safety of zwitterionic nano-polyplexes

While polymeric nano-formulations for RNAi therapeutics hold great promise for molecularly-targeted, personalized medicine, they possess significant systemic delivery challenges including rapid clearance from circulation and the potential for carrier-associated toxicity due to cationic polymer or lipid components. Herein, we evaluated the in vivo pharmacokinetic and safety impact of often-overlooked formulation parameters, including the ratio of carrier polymer to cargo siRNA and hydrophobic siRNA modification in combination with hydrophobic polymer components (dual hydrophobization). For these studies, we used nano-polyplexes (NPs) with well-shielded, zwitterionic coronas, resulting in various NP formulations of equivalent hydrodynamic size and neutral surface charge regardless of charge ratio. Doubling nano-polyplex charge ratio from 10 to 20 increased circulation half-life five-fold and pharmacokinetic area under the curve four-fold, but was also associated with increased liver enzymes, a marker of hepatic damage. Dual hydrophobization achieved by formulating NPs with palmitic acid-modified siRNA (siPA-NPs) both reduced the amount of carrier polymer required to achieve optimal pharmacokinetic profiles and abrogated liver toxicities. We also show that optimized zwitterionic siPA-NPs are well-tolerated upon long-term, repeated administration in mice and exhibit greater than two-fold increased uptake in orthotopic MDA-MB-231 xenografts compared to commercial transfection reagent, in vivo-jetPEI®. These data suggest that charge ratio optimization has important in vivo implications and that dual hydrophobization strategies can be used to maximize both NP circulation time and safety.

Zwitterionic shielded polymeric prodrug with folate-targeting and pH responsiveness for drug delivery

Zwitterionic polymers are a class of polymers that acts as both Lewis base and Lewis acid in solution. These polymers not only have excellent properties of hydration, anti-bacterial adhesion, charge reversal and easy chemical modification, but also have characteristics of long-term circulation and suppress nonspecific protein adsorption in vivo. Here, we describe a novel folate-targeted and acid-labile polymeric prodrug under the microenvironment of tumor cells, abbreviated as FA-P(MPC-co-PEGMA-BZ)-g-DOX, which was synthesized via a combination of reversible addition-fragmentation chain transfer (RAFT) copolymerization, Schiff-base reaction, Click chemistry, and a reaction between the amine group of doxorubicin (DOX) and aldehyde functionalities of P(MPC-co-PEGMA-BZ) pendants, wherein MPC and PEGMA-BZ represent 2-(methacryloyloxy)ethyl phosphorylcholine and polyethylene glycol methacrylate ester benzaldehyde, respectively. The polymeric prodrug could self-assemble into nanoparticles in an aqueous solution. The average particle size and morphologies of the prodrug nanoparticles were observed by dynamic light scattering (DLS) and transmission electron microscopy (TEM), respectively. We also investigated the in vitro drug release behavior and observed rapid prodrug nanoparticle dissociation and drug release under a mildly acidic microenvironment. The methyl thiazolyl tetrazolium (MTT) assay verified that the P(MPC-co-PEGMA-BZ) copolymer possessed good biocompatibility and the FA-P(MPC-co-PEGMA-BZ)-g-DOX prodrug nanoparticles showed higher cellular uptake than those prodrug nanoparticles without the FA moiety. The results of cytotoxicity and the intracellular uptake of non-folate/folate targeted prodrug nanoparticles further confirmed that FA-P(MPC-co-PEGMA-BZ)-g-DOX could be efficiently accumulated and rapidly internalized by HeLa cells due to the strong interaction between multivalent phosphorylcholine (PC) groups and cell membranes. This kind of multifunctional FA-P(MPC-co-PEGMA-BZ)-g-DOX prodrug nanoparticle with combined target-ability and pH responsiveness demonstrates promising potential for cancer chemotherapy.

POSS-based supramolecular amphiphilic zwitterionic complexes for drug delivery

A novel POSS-based supramolecular amphiphilic zwitterionic polymer exhibited excellent stability in both extracellular and intracellular pH environments and well encapsulated the antitumor drug DOX, and has the potential to improve smart drug delivery and enhance antitumor efficacy for biomedical applications.

Cholesterol-induced physicochemical changes in dodecylamine-based metallosomes: drug entrapping ability and interactions with biological molecules

Multivesicular metallosomes have been synthesized from metal functionalized amphiphiles. They have been thoroughly characterized and explored for their entrapment efficiency towards drug and other biomolecules.

Poly(cystine–PCL) based pH/redox dual-responsive nanocarriers for enhanced tumor therapy

Illustration of pH/redox dual-responsive poly(cystine–PCL)/PTX NPs for tumor therapy.