Polymer micelles with cross-linked ionic cores for delivery of anticancer drugs

Modular Synthesis of PEG-Dendritic Block Copolymers by Thermal Azide-Alkyne Cycloaddition with Internal Alkynes and Evaluation of their Self-Assembly for Drug Delivery Applications

Linear-dendritic block copolymers assemble in solution due to differences in the solubility or charge properties of the blocks. The monodispersity and multivalency of the dendritic block provide unparalleled control for the design of drug delivery systems when incorporating poly(ethylene glycol) (PEG) as a linear block. An accelerated synthesis of PEG-dendritic block copolymers based on the click and green chemistry pillars is described. The tandem composed of the thermal azide-alkyne cycloaddition with internal alkynes and azide substitution is revealed as a flexible, reliable, atom-economical, and user-friendly strategy for the synthesis and functionalization of biodegradable (polyester) PEG-dendritic block copolymers. The high orthogonality of the sequence has been exploited for the preparation of heterolayered copolymers with terminal alkenes and alkynes, which are amenable for subsequent functionalization by thiol-ene and thiol-yne click reactions. Copolymers with tunable solubility and charge were so obtained for the preparation of various types of nanoassemblies with promising applications in drug delivery.

CT and X-ray contrast agents: Current clinical challenges and the future of contrast

Computed tomography (CT) is a powerful and widely used imaging technique in modern medicine. However, it often requires the use of contrast agents to visualize structures with similar radiographic density. Unfortunately, current clinical contrast agents (CAs) for CT have remained largely unchanged for decades and come with several significant drawbacks, including serious nephrotoxicity and short circulation half-lives. The next generation of CT radiocontrast agents should strive to be long-circulating, non-toxic, and non-immunogenic. Nanoparticle contrast agents have shown promise in recent years and are likely to comprise the majority of next-generation CT contrast agents. This review highlights the fundamental mechanism and background of X-ray and contrast agents. It also focuses on the challenges associated with current clinical contrast agents and provides a brief overview of potential future agents that are based on various materials such as lipids, polymers, dendrimers, metallic, and non-metallic inorganic nanoparticles (NPs). STATEMENT OF SIGNIFICANCE: We realized a need for clarification on a number of concerns related to the use of iodinated contrast material as debates regarding the safety of these agents with patients with kidney disease, shellfish allergies, and thyroid dysfunction remain ongoing in medical practice. This review was partially inspired by debates witnessed in medical practice regarding outdated misconceptions of contrast material that warrant clarification in translational and clinical arenas. Given that conversation around currently available agents is at somewhat of a high water mark, and nanoparticle research has now reached an unprecedented number of readers, we find that this review is timely and unique in the context of recent discussions in the field.

pH-responsive intermediary layer cross-linked micelles from zwitterionic triblock copolymers and investigation of their drug-release behaviors

ABC-type triblock copolymers, namely poly[(ethylene glycol)methyl ether]-block-poly(tert-butyl methacrylate)-block-poly[2-N-(diisopropylamino)ethyl methacrylate] (MPEG-b-PBuMA-b-PDPA), were first synthesized and then the middle blocks were successfully converted into poly(methacrylic acid) to obtain MPEG-b-PMAA-b-PDPA zwitterionic triblock copolymers. These block copolymers were soluble in water and formed micellar aggregates with complex cores via hydrogen bonding interactions between MPEG and PMAA blocks below pH 4.0. When the pH was between 5.0 and 7.0, due to charge compensation between partially protonated PDPA and partially ionized PMAA blocks, micelles with polyion complex cores were observed. If the solution pH was above 8.0, deprotonation of tertiary amine groups provided a hydrophobic character to the PDPA block, which resulted in the formation of PDPA-core micelles while MPEG/anionic PMAA hybrid blocks formed hydrated coronas. Intermediary layer cross-linked (ILCL) micelles from PDPA-core micelles were also prepared by cross-linking the inner PMAA shell. The hydrophobic drug dipyridamole (DIP) was used to investigate the release profile of ILCL micelles. DIP can be loaded to the PDPA cores of the micelles in basic aqueous media. An increase in the degree of cross-linking causes slower release for the model drug. It was concluded that the more complex matrix formation in the intermediary layer of the micelles via cross-linking retards the drug release from the core.

Functional Nucleic Acids-Engineered Bio-Barcode Nanoplatforms for Targeted Synergistic Therapy of Multidrug-Resistant Cancer

Rational design of multifunctional nanomedicines has revolutionized the therapeutic efficacy of cancers. Herein, we have constructed the functional nucleic acids (FNAs)-engineered nanoplatforms based on the concept of a bio-barcode (BBC) for synergistic targeted therapy of multidrug-resistant (MDR) cancer. In this study, the platinum(IV) prodrug is synthesized to covalently link two kinds of FNAs at a rational ratio to fabricate three-dimensional BBC-like DNA nanoscaffolds, accompanied by the one-pot encapsulation of ZnO nanoparticles (NPs) through electrostatic interaction. The multivalent AS1411 aptamers equipped in ZnO@BBCs facilitate specific and efficient endocytosis into MDR human lung adenocarcinoma cells (A549/DDP). In response to the intracellular environment of A549/DDP cells, such as the lysosome-acidic pH and overexpressed GSH, the ZnO NPs are degraded into Zn²⁺ ions for generating reactive oxygen species (ROS), while the Pt(IV) prodrugs are reduced into Pt(II) active species by glutathione (GSH), followed by the release of therapeutic DNAzymes for chemotherapy and gene therapy. In particular, the designed system plays an important role in remodeling the intracellular environment to reverse cancer MDR. On the one hand, the depletion of GSH promotes the downregulation of glutathione peroxidase 4 (GPX4) for amplifying oxidative stress and increasing lipid peroxidation (LPO), resulting in the activation of ferroptosis. On the other hand, the silence of early growth response protein 1 (Egr-1) mRNA by Zn²⁺-dependent DNAzymes directly inhibits the proliferation and migration of MDR cells, which further suppresses the P-glycoprotein (P-gp)-mediated drug efflux. Thus, the proposed nanoplatforms show great promise for the development of versatile therapeutic tools and personalized nanomedicines for MDR cancers.

Polymeric core-crosslinked particles prepared via a nanoemulsion-mediated process: from particle design and structural characterization to in vivo behavior in chemotherapy

Various polymeric nanoparticles have been used as drug carriers in drug delivery systems (DDSs). Most of them were constructed from dynamic self-assembly systems formed via hydrophobic interactions and from structures that are unstable in an in vivo environment owing to their relatively weak formation forces. As a solution to this issue, physically stabilized core-crosslinked particles (CP) with chemically crosslinked cores have received attention as alternatives to the dynamic nanoparticles. This focused review summarizes recent advances in the construction, structural characterization, and in vivo behavior of polymeric CPs. First, we introduce a nanoemulsion-mediated method to create polyethylene glycol (PEG)-bearing CPs and their structural characterization. The relationship between the PEG chain conformations in the particle shell and the in vivo fate of the CPs is also discussed. After that, the development and advantages of zwitterionic amino acid-based polymer (ZAP)-bearing CPs are presented to address the poor penetration and the internalization of PEG-based CPs into tumor tissues and cells, respectively. Finally, we conclude and discuss prospects for application of polymeric CPs in the DDS field.

Double-hydrophilic block copolymer-metal ion associations: Structures, properties and applications

Hybrid polyionic complexes (HPICs), constructed from double-hydrophilic block copolymers and metal ions, have been largely developed with increasing interest in the past decade in the fields of catalysis, materials science and biological applications. The chemical natures of both blocks are very versatile, but one block should be able to interact with ions, and the second one should be neutral. Many metals have been used to form HPICs, which have, in their simplest architectural form, a core-shell structure of a few tens of nanometers in radius with an external shell made of the neutral block of the copolymer. In this review, we focus our discussion on the stability, shape, size and inner structure of these hybrid micelles. We then describe the most recent applications of HPICs, as reported in the literature, and point out the current challenges, missing structural information and future perspectives for this class of organized structures.

An injectable thermosensitive hydrogel for dual delivery of diclofenac and Avastin® to effectively suppress inflammatory corneal neovascularization

Corneal neovascularization (CNV) is a sequela of anterior segment inflammation, which could lead to vision impairment and even blindness. In the present study, the dual delivery of anti-inflammatory agent (i.e., diclofenac; DIC) and anti-VEGF antibody (i.e., Avastin®; Ava) by the thermosensitive hydrogel (Poly(dl-lactide)-poly(ethylene glycol)-poly(dl-lactide); PDLLA-PEG-PDLLA) is expected to effectively inhibit CNV via their synergistic effects. The optimal DIC micelles were formulated and then mixed with Ava and PDLLA-PEG-PDLLA aqueous solution to generate various DIC@Ava-loaded hydrogels. The co-encapsulation of DIC micelles and Ava did not influence the gelling behavior of the system, and the resulting DIC@Ava-loaded hydrogel provided sustained drug release of both DIC and Ava without compromising their pharmacological activity over 19 days. As indicated by in vitro cytotoxicity and in vivo ocular biocompatibility test, the proposed PDLLA-PEG-PDLLA hydrogel caused minimal cytotoxicity against all tested cell lines at a polymeric concentration ranging from 0.05 mg/mL to 0.8 mg/mL and demonstrated good ocular biocompatibility after a single subconjunctival injection. Using the rabbit CNV model, we documented the superior anti-angiogenic effects of the DIC@Ava-loaded hydrogel over Ava alone medication (treatment with Ava solution and Ava-loaded hydrogel) due to synergistic effects of anti-VEGF and anti-inflammatory action. Overall, the proposed DIC@Ava-loaded hydrogel might be a powerful strategy to reduce CNV.

Recent advancements of nanoparticles application in cancer and neurodegenerative disorders: At a glance

Nanoscale engineering is one of the innovative approaches to heal multitudes of ailments, such as varieties of malignancies, neurological problems, and infectious illnesses. Therapeutics for neurodegenerative diseases (NDs) may be modified in aspect because of their ability to stimulate physiological response while limiting negative consequences by interfacing and activating possible targets. Nanomaterials have been extensively studied and employed for cancerous therapeutic strategies since nanomaterials potentially play a significant role in medical transportation. When compared to conventional drug delivery, nanocarriers drug delivery offers various benefits, such as excellent reliability, bioactivity, improved penetration and retention impact, as well as precise targeting and administering. Upregulation of drug efflux transporters, dysfunctional apoptotic mechanisms, and a hypoxic atmosphere are all elements that lead to cancer treatment sensitivity in humans. It has been possible to target these pathways using nanoparticles and increase the effectiveness of multidrug resistance treatments. As innovative strategies of tumor chemoresistance are uncovered, nanomaterials are being developed to target specific pathways of tumor resilience. Scientists have recently begun investigating the function of nanoparticles in immunotherapy, a field that is becoming increasingly useful in the care of malignancies. Nanoscale therapeutics have been explored in this scientific literature and represent the most current approaches to neurodegenerative illnesses and cancer therapy. In addition, current findings and various biomedical nanomaterials' future promise for tissue regeneration, prospective medication design, and the synthesis of novel delivery approaches have been emphasized.

Natural and Synthetic Micelles for Delivery of Small Molecule Drugs, Imaging Agents and Nucleic Acids

The poor solubility, lack of targetability, quick renal clearance, and degradability of many therapeutic and imaging agents strongly limit their applications inside the human body. Amphiphilic copolymers having self-assembling properties can form core-shell structures called micelles, a promising nanocarrier for hydrophobic drugs, plasmid DNA, oligonucleotides, small interfering RNAs (siRNAs) and imaging agents. Fabrication of micelles loaded with different pharmaceutical agents provides numerous advantages including therapeutic efficacy, diagnostic sensitivity, and controlled release to the desired tissues. Moreover, due to their smaller particle size (10-100 nm) and modified surfaces with different functional groups (such as ligands) help them to accumulate easily in the target location, enhancing cellular uptake and reducing unwanted side effects. Furthermore, the release of the encapsulated agents may also be triggered from stimuli-sensitive micelles at different physiological conditions or by an external stimulus. In this review article, we discuss the recent advancement in formulating and targeting different natural and synthetic micelles including block copolymer micelles, cationic micelles, and dendrimers-, polysaccharide- and protein-based micelles for the delivery of different therapeutic and diagnostic agents. Finally, their applications, outcomes, and future perspectives have been summarized.

Double hydrophilic copolymers - synthetic approaches, architectural variety, and current application fields

Solubility and functionality of polymeric materials are essential properties determining their role in any application. In that regard, double hydrophilic copolymers (DHC) are typically constructed from two chemically dissimilar but water-soluble building blocks. During the past decades, these materials have been intensely developed and utilised as, e.g., matrices for the design of multifunctional hybrid materials, in drug carriers and gene delivery, as nanoreactors, or as sensors. This is predominantly due to almost unlimited possibilities to precisely tune DHC composition and topology, their solution behavior, e.g., stimuli-response, and potential interactions with small molecules, ions and (nanoparticle) surfaces. In this contribution we want to highlight that this class of polymers has experienced tremendous progress regarding synthesis, architectural variety, and the possibility to combine response to different stimuli within one material. Especially the implementation of DHCs as versatile building blocks in hybrid materials expanded the range of water-based applications during the last two decades, which now includes also photocatalysis, sensing, and 3D inkjet printing of hydrogels, definitely going beyond already well-established utilisation in biomedicine or as templates.

Efficient, enzyme responsive and tumor receptor targeting gelatin nanoparticles decorated with concanavalin-A for site-specific and controlled drug delivery for cancer therapy

The tumor targeting and stimuli responsiveness behavior of intelligent drug delivery systems imparts effective therapeutic delivery and decreases the toxicity of conventional chemotherapeutic agents in off-target organs. To achieve the receptor targeting and smart drug release, several strategies have been employed to engineer nano-carrier with stimulus sensitivity. In this work, mannose receptor-targeted and matrix metalloproteinase (MMP) responsive gelatin nanoparticles were developed and assessed for its receptor targeting and "on-demand" controlled drug delivery in lung cancer therapeutics. MMPs are protease enzymes and over-expressed in tumorous tissues in all the stages of cancer. The cancer cells also have over-expressed mannose receptors on the cell surface. The surface decoration of gelatin nanoparticles with concanavalin A (con-A) tends to bind with mannose moiety of cell surface glycoproteins which enhances the cancer cell-specific higher uptake of nanoparticles. Gelatin nanoparticles have attracted significant attraction in recent years as a potential drug carrier because of its good biocompatibility and versatile physicochemical properties desirable to deliver the drug. Cisplatin was complexed with the gelatin matrix (CG-NP) to evaluate stimuli responsiveness with the lung cancer cells and its release pattern. In this smart inhalable delivery system, cisplatin loaded gelatin nanoparticles were surface decorated with con-A (CCG-NP). In tumorous cells, con-A coating is expected to enhance mannose receptor-specific cellular internalization of CCG-NP, and subsequently high level of MMP in tumor tissues would help to release cisplatin in response and ensures controlled drug release. The synthesized CCG-NP has shown enzyme triggered drug release and favorable endocytosis after incubation of 12 h compare to uncoated nanoparticles. The efficacy of CCG-NP significantly increased in presence of MMP-2 enzyme in lung cancer cell line A549 cells. It also significantly enhanced reactive oxygen species generation, cell cycle arrest in S and G₂/M phase, and apoptosis in cancer cells. Therefore, inhalable CCG-NP promises a pragmatic approach to construct a receptor targeting and an "on-demand" drug delivery system to efficiently deliver the drug at the tumor site only.

Nucleic acid peptide nanogels for the treatment of bacterial keratitis

Cage-shaped nucleic acid nanocarriers are promising molecular scaffolds for the organization of polypeptides. However, there is an unmet need for facile loading strategies that truly emulate nature's host-guest systems to drive encapsulation of antimicrobial peptides (AMPs) without loss of biological activity. Herein, we develop DNA nanogels with rapid in situ loading of L12 peptide during the thermal annealing process. By leveraging the binding affinity of L12 to the polyanionic core, we successfully confine the AMPs within the DNA nanogel. We report that the thermostability of L12 in parallel with the high encapsulation efficiency, low toxicity and sustained drug release of the pre-loaded L12 nanogels can be translated into significant antimicrobial activity. Using an S. aureus model of infectious bacterial keratitis, we observe fast resolution of clinical symptoms and significant reduction of bacterial bioburden. Collectively, this study paves the way for the development of DNA nanocarriers for caging AMPs with immense significance to address the rise of resistance.

Real time monitoring of peptide delivery in vitro using high payload pH responsive nanogels

A pH responsive pMAA nanogel that demonstrates high loading capacity and rapid intracellular delivery of hydrophilic peptides.

The effective treatment of multi-drug resistant tumors with self-assembling alginate copolymers

Alginates of two different chain lengths were alkyne functionalized on the hydroxyl group, leaving all carboxylic groups intact.

Nano-Based Systems and Biomacromolecules as Carriers for Metallodrugs in Anticancer Therapy

Since the discovery of cisplatin and its potency in anticancer therapy, the development of metallodrugs has been an active area of research. The large choice of transition metals, oxidation states, coordinating ligands, and different geometries, allows for the design of metal-based agents with unique mechanisms of action. Many metallodrugs, such as titanium, ruthenium, gallium, tin, gold, and copper-based complexes have been found to have anticancer activities. However, biological application of these agents necessitates aqueous solubility and low systemic toxicity. This minireview highlights the emerging strategies to facilitate the in vivo application of metallodrugs, aimed at enhancing their solubility and bioavailability, as well as improving their delivery to tumor tissues. The focus is on encapsulating the metal-based complexes into nanocarriers or coupling to biomacromolecules, generating efficacious anticancer therapies. The delivery systems for complexes of platinum, ruthenium, copper, and iron are discussed with most recent examples.

Fabrication of Polymer-Protein Hybrids

Rapid developments in organic chemistry and polymer chemistry promote the synthesis of polymer-protein hybrids with different structures and biofunctionalities. In this feature article, recent progress achieved in the synthesis of polymer-protein conjugates, protein-nanoparticle core-shell structures, and polymer-protein nanogels/hydrogels is briefly reviewed. The polymer-protein conjugates can be synthesized by the "grafting-to" or the "grafting-from" approach. In this article, different coupling reactions and polymerization methods used in the synthesis of bioconjugates are reviewed. Protein molecules can be immobilized on the surfaces of nanoparticles by covalent or noncovalent linkages. The specific interactions and chemical reactions employed in the synthesis of core-shell structures are discussed. Finally, a general introduction to the synthesis of environmentally responsive polymer-protein nanogels/hydrogels by chemical cross-linking reactions or molecular recognition is provided.

Amorphous Solid Dispersion of Epigallocatechin Gallate for Enhanced Physical Stability and Controlled Release

Epigallocatechin gallate (EGCG) has been recognized as the most prominent green tea extract due to its healthy influences. The high instability and low bioavailability, however, strongly limit its utilization in food and drug industries. This work, for the first time, develops amorphous solid dispersion of EGCG to enhance its bioavailability and physical stability. Four commonly used polymeric excipients are found to be compatible with EGCG in water-dioxane mixtures via a stepwise mixing method aided by vigorous mechanical interference. The dispersions are successfully generated by lyophilization. The physical stability of the dispersions is significantly improved compared to pure amorphous EGCG in stress condition (elevated temperature and relative humidity) and simulated gastrointestinal tract environment. From the drug release tests, one of the dispersions, EGCG-Soluplus^® 50:50 (w/w) shows a dissolution profile that only 50% EGCG is released in the first 20 min, and the remains are slowly released in 24 h. This sustained release profile may open up new possibilities to increase EGCG bioavailability via extending its elimination time in plasma.

Block ionomer micellar nanoparticles from double hydrophilic copolymers, classifications and promises for delivery of cancer chemotherapeutics

A class of double hydrophilic copolymers comprising ionic and nonionic water-soluble blocks, which are also called block ionomers, represent an interesting type of polymer assembly forming stable, homogeneous core-corona dispersions. They exhibit the solution behavior of normal polyelectrolytes, whereas assembly into micelle, vesicle or disk morphology happens by an external stimulus (pH, temperature or ionic strength) or complex formation with metal ions, ionic surfactants, polyelectrolytes, etc. Temperature, pH, redox or salt sensitivity affords a unique opportunity to control the triggered release of payloads accommodated through electrostatic interaction, coordination or chemical conjugation. Moreover, the non-ionic block provides the surface passivation, prolongation of the blood circulation and tumor accumulation, supporting targeted delivery of chemotherapeutic agents based on pathophysiology of tumor microenvironment. Potentiation of antitumor activity, sensitization of the resistant tumors, increased tolerated dose and translation into clinical practice are among their most intriguing characteristics. Their high functionality has been suggested for co-delivery of multiple agents for reversal of chemo-resistance as well as simultaneous therapy and diagnostics. Nevertheless, some stability concerns may be raised due to the polymer disassembly beyond a critical concentration of pH, salt and polyion concentration that can be modulated by introducing crosslinks between the polymer chains (Nano-networks).

Rational Design of Cancer Nanomedicine: Nanoproperty Integration and Synchronization

Current cancer nanomedicines can only mitigate adverse effects but fail to enhance therapeutic efficacies of anticancer drugs. Rational design of next-generation cancer nanomedicines should aim to enhance their therapeutic efficacies. Taking this into account, this review first analyzes the typical cancer-drug-delivery process of an intravenously administered nanomedicine and concludes that the delivery involves a five-step CAPIR cascade and that high efficiency at every step is critical to guarantee high overall therapeutic efficiency. Further analysis shows that the nanoproperties needed in each step for a nanomedicine to maximize its efficiency are different and even opposing in different steps, particularly what the authors call the PEG, surface-charge, size and stability dilemmas. To resolve those dilemmas in order to integrate all needed nanoproperties into one nanomedicine, stability, surface and size nanoproperty transitions (3S transitions for short) are proposed and the reported strategies to realize these transitions are comprehensively summarized. Examples of nanomedicines capable of the 3S transitions are discussed, as are future research directions to design high-performance cancer nanomedicines and their clinical translations.

Strategies for improving the payload of small molecular drugs in polymeric micelles

In the past few years, substantial efforts have been made in the design and preparation of polymeric micelles as novel drug delivery vehicles. Typically, polymeric micelles possess a spherical core-shell structure, with a hydrophobic core and a hydrophilic shell. Consequently, poorly water-soluble drugs can be effectively solubilized within the hydrophobic core, which can significantly boost their drug loading in aqueous media. This leads to new opportunities for some bioactive compounds that have previously been abandoned due to their low aqueous solubility. Even so, the payload of small molecular drugs is still not often satisfactory due to low drug loading and premature release, which makes it difficult to meet the requirements of in vivo studies. This problem has been a major focus in recent years. Following an analysis of the published literature in this field, several strategies towards achieving polymeric micelles with high drug loading and stability are presented in this review, in order to ensure adequate drug levels reach target sites.

Encapsulation of cisplatin in a pegylated calcium phosphate nanoparticle (CPNP) for enhanced cytotoxicity to cancerous cells

HYPOTHESIS

Exchange of the chloride ion (Cl^-) ligands of cisplatin with carboxylates is widely used in fabricating cisplatin loaded nanoparticles for improved cancer therapy. However, the dynamic exchange may cause premature cisplatin release and even disintegration of the nanoparticles in Cl^--containing medium such as in plasma. Molecules bearing carboxylates are capable of mediating the mineralization process of calcium phosphate; therefore, it is possible to overcome the disadvantage by sequestering cisplatin in a calcium phosphate nanoparticle (CPNP).

EXPERIMENTS

With the hypothesis, precipitation reaction of calcium nitrate and disodium hydrogen phosphate was performed in a solution of poly(ethylene glycol)-poly(acrylic acid) block copolymers with their carboxylates partly conjugated with cisplatin. Then, structure, physicochemical properties, and bioactivity of the product were carefully investigated with multiple characterization methods.

FINDINGS

It was revealed a pegylated, cisplatin encapsulated CPNP was prepared; and with appropriate mole ratio of cisplatin to carboxylates, the nanoparticle encapsulated cisplatin efficiently (>90%), was stable and almost entirely prevented the cisplatin release in Cl^--containing medium at pH 7.4 but released them in an acidic condition, and showed moderately and greatly enhanced cytotoxicities to the lung cancer cell line A549 and its cisplatin resistance form A549R respectively in comparison with the free cisplatin.

Core cross-linked double hydrophilic block copolymer micelles based on multiple hydrogen-bonding interactions

Facile preparation and characterization of core cross-linked micelles via strong multiple hydrogen bonds using well-defined thermo-responsive double hydrophilic block copolymers.

Metal-containing and related polymers for biomedical applications

A survey of the most recent progress in the biomedical applications of metal-containing polymers is given. Due to the unique optical, electrochemical, and magnetic properties, at least 30 different metal elements, most of them transition metals, are introduced into polymeric frameworks for interactions with biology-relevant substrates via various means. Inspired by the advance of metal-containing small molecular drugs and promoted by the great progress in polymer chemistry, metal-containing polymers have gained momentum during recent decades. According to their different applications, this review summarizes the following biomedical applications: (1) metal-containing polymers as drug delivery vehicles; (2) metal-containing polymeric drugs and biocides, including antimicrobial and antiviral agents, anticancer drugs, photodynamic therapy agents, radiotherapy agents and biocides; (3) metal-containing polymers as biosensors, and (4) metal-containing polymers in bioimaging.

Folate-Mediated Targeted Delivery of Combination Chemotherapeutics Loaded Reduced Graphene Oxide for Synergistic Chemo-Photothermal Therapy of Cancers

PURPOSE

Larger surface area for drug incorporation and superior optical activity makes reduced graphene oxide (rGO) a suitable drug carrier for combination chemotherapeutics delivery. And folate receptors are potential mediators for cancer targeted delivery. This study mainly aimed to prepare irinotecan (IRI)- and docetaxel (DOC)-loaded, folate (FA)-conjugated rGO (FA-P407-rGO/ID) for synergistic cancer therapy.

METHODS

FA-P407-rGO/ID was prepared as aqueous dispersion. Characterization was performed using high performance liquid chromatography (HPLC), transmission electron microscopy (TEM), atomic force microscopy (AFM), ultraviolet/visible spectroscopy, fourier transform infrared spectroscopy (FTIR) and drug release. In vitro cellular studies were performed using 3-(4,5-dimethylthiazol-2-yl)-5-(3-carboxymethoxyphenyl)-2-(4-sulfophenyl)-2H-tetrazolium (MTS), fluorescence-activated cell sorting (FACS) and western blot analyses.

RESULTS

Our results revealed successful preparation of stable FA-P407-rGO/ID formulation with enhanced drug release profiles in acidic microenvironment. In vitro cytotoxicity of the formulation on folate receptor-expressing human mammary carcinoma (MCF-7) cells was higher than that when free IRI/DOC combination (ID) was used; such increased cytotoxicity was not observed in folate receptor-negative hepatocellular carcinoma (HepG2) cells. Cellular uptake of FA-P407-rGO/ID in MCF-7 cells was higher than in HepG2 cells. Further, FACS and western blot analysis revealed better apoptotic effects of the formulation in MCF-7 cells than in HepG2 cells, suggesting the important role of folate receptors for targeted chemotherapy delivery to cancer cells. Near infrared irradiation further enhanced the apoptotic effect in cancer cells, resulting from the photothermal effects of rGO.

CONCLUSIONS

Hence, FA-P407-rGO/ID can be considered as a potential formulation for folate-targeted chemo-photothermal therapy in cancer cells.

Toxicity reduction of imidazolium-based ionic liquids by the oxygenation of the alkyl substituent

Five different salicylate based ionic liquids were prepared in order to study their toxicity. Aquatic organisms (A. salina) and a human non-tumor cell line (normal fetal lung fibroblasts, MRC-5) were used for that purpose.

Current advances in self-assembled nanogel delivery systems for immunotherapy

Since nanogels (nanometer-sized gels) were developed two decades ago, they were utilized as carriers of innovative drug delivery systems. In particular, immunological drug delivery via self-assembled nanogels (self-nanogels) owing to their nanometer size and molecular chaperon-like ability to encapsulate large biomolecules is one of the most well studied and successful applications of nanogels. In the present review, we focus on self-nanogel applications as immunological drug delivery systems for cancer vaccines, cytokine delivery, nasal vaccines, and nucleic acid delivery, including several clinical trials. Cancer vaccines were the first practical application of self-nanogels as vehicles for drug delivery. After successful pre-clinical studies, phase I clinical trials were conducted, and it was found that vaccines consisting of self-nanogels could be administered repeatedly to humans without serious adverse effects, and self-nanogel vaccines induced antigen-specific cellular and humoral immunity. Cytokine delivery via self-nanogels led to the sustained release of IL-12, suppressed tumor growth, and increased Th1-type immune responses. Cationic self-nanogels were effective in penetrating the nasal mucosa and resulted in successful nasal vaccines in mice and nonhuman primates. Cationic self-nanogels were also used for the intracellular delivery of proteins and nucleic acids, and were successfully used to knockdown tumor growth factor expression using short interfering RNA with the immunological effect. These studies suggest that self-nanogels are currently one of the most unique and attractive immunological drug delivery systems and are edging closer to practical use.

Cytotoxic Activity of Salicylic Acid-Containing Drug Models with Ionic and Covalent Binding

Three different types of drug delivery platforms based on imidazolium ionic liquids (ILs) were synthesized in high preparative yields, namely, the models involving (i) ionic binding of drug and IL; (ii) covalent binding of drug and IL; and (iii) dual binding using both ionic and covalent approaches. Seven ionic liquids containing salicylic acid (SA-ILs) in the cation or/and in the anion were prepared, and their cytotoxicity toward the human cell lines CaCo-2 (colorectal adenocarcinoma) and 3215 LS (normal fibroblasts) was evaluated. Cytotoxicity of SA-ILs was significantly higher than that of conventional imidazolium-based ILs and was comparable to the pure salicylic acid. It is important to note that the obtained SA-ILs dissolved in water more readily than salicylic acid, suggesting benefits of possible usage of traditional nonsoluble active pharmaceutical ingredients in an ionic liquid form.

Polymeric nanoparticles and microparticles for the delivery of peptides, biologics, and soluble therapeutics

Biologically derived therapeutics, or biologics, are the most rapidly growing segment of the pharmaceutical marketplace. However, there are still unmet needs in improving the delivery of biologics. Injectable polymeric nanoparticles and microparticles capable of releasing proteins and peptides over time periods as long as weeks or months have been a major focus in the effort to decrease the frequency of administration. These particle systems fit broadly into two categories: those composed of hydrophilic and those composed of hydrophobic polymeric scaffolds. Here we review the factors that contribute to the slow and controlled release from each class of particle, as well as the effects of synthesis parameters and product design on the loading, encapsulation efficiency, biologic integrity, and release profile. Generally, hydrophilic scaffolds are ideal for large proteins while hydrophobic scaffolds are more appropriate for smaller biologics without secondary structure. Here we also introduce a Flash NanoPrecipitation method that has been adopted for encapsulating biologics in nanoparticles (40-200nm) at high loadings (50-75wt.%) and high encapsulation efficiencies. The hydrophilic gel interior and hydrophobic shell provide an opportunity to combine the best of both classes of injectable polymeric depots.

A micelle-like structure of poloxamer-methotrexate conjugates as nanocarrier for methotrexate delivery

The purpose of this study was to develop a novel featured and flexible methotrexate (MTX) formulation, in which MTX was physically entrapped and chemically conjugated in the same drug delivery system. A series of poloxamer-MTX (p-MTX) conjugates was synthesized, wherein MTX was grafted to poloxamer through an ester bond. p-MTX conjugates could self-assemble into micelle-like structures in aqueous environment and the MTX end was in the inner-core of micelles. Moreover, free MTX could be physically entrapped into p-MTX micelles hydrophobic core region to increase the total drug loading. Importantly, the resulting MTX-loaded p-MTX micelles showed a biphasic release of MTX, with a relative fast release of the entrapped MTX (about 6-7h) followed by a sustained release of the conjugated MTX. The pharmacokinetics study showed that the mean residence time (MRT) was extended in the case of MTX-loaded p-MTX micelles, indicating a delayed MTX elimination from the bloodstream and prolonged in vivo residence time. Besides, the area under curve (AUC) of MTX-loaded p-MTX micelles was greater than free MTX, indicating a drug bioavailability improvement. Overall, MTX-loaded p-MTX micelles might be a promising nanosized drug delivery system for the cancer therapy.

An unexpected increase of toxicity of amino acid-containing ionic liquids

The influence of the structure of cations and anions on the biological activity of ionic liquids is addressed.

Nanogel Carrier Design for Targeted Drug Delivery

Polymer-based nanogel formulations offer features attractive for drug delivery, including ease of synthesis, controllable swelling and viscoelasticity as well as drug loading and release characteristics, passive and active targeting, and the ability to formulate nanogel carriers that can respond to biological stimuli. These unique features and low toxicity make the nanogels a favorable option for vascular drug targeting. In this review, we address key chemical and biological aspects of nanogel drug carrier design. In particular, we highlight published studies of nanogel design, descriptions of nanogel functional characteristics and their behavior in biological models. These studies form a compendium of information that supports the scientific and clinical rationale for development of this carrier for targeted therapeutic interventions.

Stimuli-responsive one-dimensional copolymer nanostructures fabricated by metallogel template polymerization and their adsorption of aspirin

pH responsive poly(N,N'-methylenebisacrylamide-co-4-vinylpyridine) (P(MBA-4VP)) one dimensional (1D) nanostructures have been prepared by metallogel template copolymerization, which was carried out in an Ag(i)-coordinated organogel with benzoyl peroxide (BPO) as the initiator. The product has been characterized using infrared spectroscopy, scanning electron microscopy and transmission electron microscopy. The experimental results reveal that the gel fiber is a crucial template for polymerization. Due to the degradation of the template in copolymerization, nanofibers of metallogel were transcribed to copolymer nanowires. The introduction of co-monomer 4-vinylpyridine (4VP) imparts to the 1D copolymer nanostructures pH sensitivity and the possible use as an adsorption material of aspirin. Adsorbed 1D copolymer nanostructures could be regenerated using proton solvent, acid medium and salt solution. In addition, silver nanoparticle loaded copolymer nanowires have been produced from the reduction of silver ions instead of template removal, where silver ions act both as the template and as the nanoparticle growth substrate.

Sequential optimization of methotrexate encapsulation in micellar nano-networks of polyethyleneimine ionomer containing redox-sensitive cross-links

A functional polycation nanonetwork was developed for delivery of water soluble chemotherapeutic agents. The complexes of polyethyleneimine grafted methoxy polyethylene glycol (PEI-g-mPEG) and Zn(2+) were utilized as the micellar template for cross-linking with dithiodipropionic acid, followed by an acidic pH dialysis to remove the metal ion from the micellar template. The synthesis method was optimized according to pH, the molar ratio of Zn(2+), and the cross-link ratio. The atomic force microscopy showed soft, discrete, and uniform nano-networks. They were sensitive to the simulated reductive environment as determined by Ellman's assay. They showed few positive ζ potential and an average hydrodynamic diameter of 162±10 nm, which decreased to 49±11 nm upon dehydration. The ionic character of the nano-networks allowed the achievement of a higher-loading capacity of methotrexate (MTX), approximately 57% weight per weight, depending on the cross-link and the drug feed ratios. The nano-networks actively loaded with MTX presented some suitable properties, such as the hydrodynamic size of 117±16 nm, polydispersity index of 0.22, and a prolonged swelling-controlled release profile over 24 hours that boosted following reductive activation of the nanonetwork biodegradation. Unlike the PEI ionomer, the nano-networks provided an acceptable cytotoxicity profile. The drug-loaded nano-networks exhibited more specific cytotoxicity against human hepatocellular carcinoma cells if compared to free MTX at concentrations above 1 μM. The enhanced antitumor activity in vitro might be attributed to endocytic entry of MTX-loaded nano-networks that was found in the epifluorescence microscopy experiment for the fluorophore-labeled nano-networks.

Photo-inducible crosslinked nanoassemblies for pH-controlled drug release

PURPOSE

To control drug release from block copolymer nanoassemblies by variation in the degree of photo-crosslinking and inclusion of acid sensitive linkers.

METHODS

Poly(ethylene glycol)-poly(aspartate-hydrazide-cinnamate) (PEG-CNM) block copolymers were prepared and conjugated with a model drug, doxorubicin (DOX), through acid sensitive hydrazone linkers. The block copolymers formed photo-inducible, self-assembled nanoassemblies (piSNAs), which were used to produce photo-inducible crosslinked nanoassemblies (piCNAs) through UV crosslinking. The nanoassemblies were characterized to determine particle size, surface charge, pH- and crosslinking-dependent DOX release, in vitro cytotoxicity, and intracellular uptake as a function of photo-crosslinking degree.

RESULTS

Nanoassemblies with varying photo-crosslinking degrees were successfully prepared while retaining particle size and surface charge. Photo-crosslinking caused no noticeable change in DOX release from the nanoassemblies at pH 7.4, but the DOX-loaded nanoassemblies modulated drug release as a function of crosslinking at pH 6.0. The nanoassemblies showed similar cytotoxicity regardless of crosslinking degrees, presumably due to the low cellular uptake and cell nucleus drug accumulation.

CONCLUSIONS

Photo-crosslinking is useful to control drug release from pH-sensitive block copolymer nanoassemblies as a function of crosslinking without altering the particle properties, and thus providing unique tools to investigate the pharmaceutical effects of drug release on cellular response.