Nanoparticles for drug delivery prepared from amphiphilic PLGA zwitterionic block copolymers with sharp contrast in polarity between two blocks

Integrated zwitterionic conjugated poly(carboxybetaine thiophene) as a new biomaterial platform

An integrated zwitterionic conjugated polymer-based biomaterial platform was designed and studied to address some of the key challenges of conjugated polymers in biomedical applications. This biomaterial platform consists of conjugated polymer backbones and multifunctional zwitterionic side chains. Zwitterionic materials gain electrical conductivity and interesting optical properties through conjugated polymer backbones, and non-biocompatible conjugated polymers obtain excellent antifouling properties, enhanced electrical conductivity, functional groups of bioconjugation and response to environmental stimuli via multifunctional zwitterionic side chains. This platform can potentially be adapted to a wide range of applications (e.g. bioelectronics, tissue engineering and biofuel cell), which require high performance conducting materials with excellent antifouling/biocompatibility at biointerfaces.

Antibiofouling polymer interfaces: poly(ethylene glycol) and other promising candidates

This review highlights antibiofouling polymer interfaces with emphasis on the latest developments using poly(ethylene glycol) and the design new polymeric structures.

Reductively-sheddable cationic nanocarriers for dual chemotherapy and gene therapy with enhanced release

The development of a versatile strategy to synthesize cationic nanocarriers capable of co-delivery and enhanced release of drugs and oligonucleotides is promising for synergic dual chemotherapy and gene therapy. Herein, we report a novel cationic amphiphilic diblock copolymer having a single reduction-responsive disulfide linkage at a junction between a FDA-approved polylactide (PLA) block and a cationic methacrylate block (C-ssABP). The amphiphilic design of the C-ssABP enables the formation of cationic micellar aggregates possessing hydrophobic PLA cores, encapsulating anticancer drugs; cationic coronas, ensuring complementary complexation with negatively-charged oligonucleotides through electrostatic interactions; and disulfides at interfaces, leading to enhanced release of both encapsulated drugs and complexed oligonucleotides. The reduction-responsive intracellular trafficking results from flow cytometry, confocal laser scanning microscopy, and cell viability, as well as in vitro gene transfection assay suggest that C-ssABP offers versatility as an effective nanocarrier platform for dual chemotherapy and gene therapy.

Biocompatible long-circulating star carboxybetaine polymers

Polyethylene glycol (PEG) is considered to be the most effective material to prolong the circulation time of nanoparticles by reducing non-specific protein adsorption in blood. However, it is recognized that PEG decomposes in most physiological solutions, and an anti-PEG antibody has been detected in some normal blood donors as a response to injection with PEGylated polymer particles. Zwitterionic polymers are potential alternatives to PEG for biomedical applications because of their super resistance to non-specific protein adsorption. Thus, finding one polymer with a long circulation time and resistance to the immune response is of significant importance. Here, we prepared four star carboxybetaine polymers of different molecular weights via atom transfer radical polymerization (ATRP) from a β-cyclodextrin (β-CD) initiator for investigating the biocompatibility of carboxybetaine polymer, a typical zwitterionic polymer. The circulation half-life of the largest star polymer (123 kDa) in mice was prolonged to 40 h in vivo, with no appreciable damage or inflammation observed in the major organ tissues. Furthermore, the circulation time of repeat injections showed similar results to the first injection, with no obvious increase in the amount of antibody in blood. The internalization of the star carboxybetaine polymers by macrophage cells was a relatively slow process. The high cell viability in the presence of star carboxybetaine polymers up to 2 mg mL^-1 was maintained. The hemolytic activity of the star carboxybetaine polymers at 5 mg mL^-1 was almost undetectable. In vitro results prove a key prediction of excellent biocompatibility in vivo. All the results suggest that the carboxybetaine polymer, perhaps even most of the zwitterionic ones, might be a good alternative to PEG in the development of a drug delivery system.

Antifouling gold surfaces grafted with aspartic acid and glutamic acid based zwitterionic polymer brushes

We report two new amino acid based antifouling zwitterionic polymers, poly(N(4)-(2-methacrylamidoethyl)asparagine) (pAspAA) and poly(N(5)-(2-methacrylamidoethyl)glutamine) (pGluAA). The vinyl monomers were developed from aspartic acid and glutamic acid. Surface-initiated photoiniferter-mediated polymerization was employed to graft polymer brushes from gold surfaces. Different thickness of polymer brushes was controlled by varying UV irradiation time. The nonspecific adsorption from undiluted human blood serum and plasma was studied by surface plasmon resonance (SPR). With the polymer film as thin as 11-12 nm, the adsorption on pAspAA from serum and plasma was as low as 0.75 and 5.18 ng/cm(2), respectively, and 1.88 and 10.15 ng/cm(2), respectively, for pGluAA. The adsorption amount is comparable to or even better than other amino acid based zwitterionic polymers such as poly(serine methacrylate), poly(lysine methacrylamide), and poly(ornithine methacrylamide) and other widely used antifouling polymers such as poly(sulfobetaine methacrylate), even under thinner polymer film thickness. The pAspAA and pGluAA grafted surfaces also showed strong resistance to endothelial cell attachment. The possession of both zwitterionic structure and hydrophilic amide groups, biomimetic property, and multifunctionality make pAspAA and pGluAA promising candidates for biocompatible antifouling functionalizable materials.

Zwitterionic nanoparticles constructed with well-defined reduction-responsive shell and pH-sensitive core for "spatiotemporally pinpointed" drug delivery

Enabling nanocarriers to complete the sophisticated journey from the initial injection site to the targeted tumor cells and achieve "spatiotemporally pinpointed" drug release intracellularly is a challenging task in anticancer drug delivery. Herein, versatile shell-cross-linked nanoparticles (SCNPs) were prepared by one-step assembly of triblock zwitterionic copolymers, polycarboxybetaine methacrylate-block-poly(N-(2-(2-pyridyl disulde) ethyl methacrylamide-block-poly(2-(diisopropylamino) ethyl methacrylate) (PCB-b-PDS-b-PDPA, termed as PCSSD), which was well-defined via reversible additive fragment transfer (RAFT) polymerization, followed by functionalization with Arg-Gly-Asp (RGD). Thus, the RGD-PCSSD SCNPs cooperatively combine the ultra pH-sensitive PDPA core for efficient drug loading and pH-responsive drug release, the disulfide-cross-linked PDS shell that prevents premature drug release, the zwitterionic PCB corona to stabilize the SCNPs and prolong its systemic circulation, the RGD ligand for active tumor targeting and receptor-mediated endocytosis. Doxorubicin (DOX) was loaded as a model medicine (termed as RGD-PCSSD/DOX SCNPs). The dual-sensitivity studies showed that the pH-sensitivity of PDPA core could be adjusted by the shell-cross-linking density, accompanied by better control over premature drug release. Furthermore, results obtained by flow cytometry and fluorescence microscopy analysis demonstrated that once the RGD-PCSS10D/DOX SCNPs were internalized into tumor cells via receptor-mediated endocytosis, boost drug release was observed with considerable cytotoxicity in vitro. The results of ex vivo imaging studies further confirmed the successful drug delivery from the injection site to the tumor tissue. In summary, the well-constructed RGD-PCSS10D/DOX SCNPs with cooperative multifunctionality showed great potential as novel nanocarriers for tumor targeted anticancer drug delivery.

Integrin-targeted zwitterionic polymeric nanoparticles with acid-induced disassembly property for enhanced drug accumulation and release in tumor

Reasonably structural design of nanoparticles (NPs) to combine functions of prolonged systemic circulation, enhanced tumor targeting and specific intracellular drug release is crucial for antitumor drug delivery. Combining advantages of Arg-Gly-Asp (RGD) for active tumor targeting, zwitterionic polycarboxybetaine methacrylate (PCB) for prolonged systemic circulation, poly(2-(diisopropylamino) ethyl methacrylate) (PDPA) for acid-triggered intracellular release, novel RGD-PCB-b-PDPA (RGD-PCD) block copolymers were prepared via reversible addition-fragmentation chain transfer (RAFT) polymerization and followed by functionalization with RGD. Doxorubicine (DOX) was encapsulated within the RGD-PCD NPs as model medicine (RGD-PCD/DOX NPs). With ultra pH-sensitivity of PDPA, the drug release was restrained at pH 7.4 for only 24% within 36 h, which was increased to 60% at pH 6.0 within 24 h, and released more rapidly at pH 5.0 for 100% within 5 h, indicating that the RGD-PCD/DOX NPs were able to turn drug release "off" at neutral pH (e.g., systemic circulation) whereas "on" under acidic conditions (e.g., inside endo/lysosomes). Furthermore, the results of fluorescence microscopy and flow cytometry analysis demonstrated improved internalization of RGD-PCD/DOX NPs in HepG2 cells via integrin-mediated endocytosis with rapid DOX release intracellularly. Consequently, the RGD-PCD/DOX NPs showed considerable cytotoxicity against HepG2 and HeLa cells in comparison with free DOX. Importantly, the RGD-PCD/DOX NPs exhibited little protein adsorption property with excellent serum stability, which led to prolonged systemic circulation and enhanced tumor accumulation in tumor-bearing nude mice. Therefore, this multifunctional RGD-PCD NPs, which represented the flexible design approach, showed great potential for the development of novel nanocarriers in tumor-targeted drug delivery.

A green four-component synthesis of zwitterionic alkyl/benzyl pyrazolyl barbiturates and their photophysical studies

A novel series of unsymmetrically substituted alkyl/benzyl pyrazolyl barbiturates incorporating highly biologically active pyrazolone and barbiturate moieties was synthesized by four-component reactions of a mixture of ethyl acetoacetate, hydrazine hydrate, aldehydes and barbituric acid/thiobarbituric acid in ethanol without using a catalyst. The photophysical properties of the newly designed alkyl/benzyl pyrazolyl barbiturates were studied, and good quantum yield of some products indicated a definitive scope in the field of biochemical applications. Single-crystal X-ray crystallographic studies revealed that the newly synthesized compounds exist in zwitterionic form. The zwitterionic nature of the new chimera makes them interesting candidates for drug delivery as zwitterionic drugs are known to have highly water soluble properties, specific protein absorption, slow recognition by immune system, slow blood clearance from body and can constantly diffuse and deposit throughout the physiological pH.

Polymeric nanotherapeutics: clinical development and advances in stealth functionalization strategies

Long-circulating polymeric nanotherapeutics have garnered increasing interest in research and in the clinic owing to their ability to improve the solubility and pharmacokinetics of therapeutic cargoes. Modulation of carrier properties promises more effective drug localization at the disease sites and can lead to enhanced drug safety and efficacy. In the present review, we highlight the current development of polymeric nanotherapeutics in the clinic. In light of the importance of stealth properties in therapeutic nanoparticles, we also review the advances in stealth functionalization strategies and examine the performance of different stealth polymers in the literature. In addition, we discuss the recent development of biologically inspired "self" nanoparticles, which present a differing stealth concept from conventional approaches.

Ultrastable core–shell structured nanoparticles directly made from zwitterionic polymers

A one-step method to create ultra-stable core–shell nanoparticles directly from zwitterionic polymers.

Polymeric topology and composition constrained polyether-polyester micelles for directional antitumor drug delivery

Amphiphilic linear and dumbbell-shaped poly(ethylene glycol)-poly(lactide-co-glycolide) (PEG-PLGA) copolymers were simply synthesized by the ring-opening polymerization of lactide and glycolide using PEG or tetrahydroxyl-functionalized PEG as the macroinitiator and stannous octoate as the catalyst. The copolymers spontaneously self-assembled into spherical micelles in phosphate-buffered saline at pH 7.4. The self-assembly behavior was dependent on both the polymeric topology and composition. Doxorubicin (DOX), an anthracycline antitumor drug, was loaded into micelles through nanoprecipitation. The in vitro release behavior could be adjusted by regulating the topology or composition of the copolymer, or the pH of the release medium. The effective intracellular DOX release from DOX-loaded micelles was confirmed by confocal laser scanning microscopy and flow cytometry in vitro. DOX-loaded micelles displayed great cellular proliferation inhibition efficacies after incubation for 24, 48 or 72 h. The hemolysis ratio of DOX was significantly reduced by the presence of copolymer. These properties indicated that the micelles derived from linear or dumbbell-shaped copolymers were promising candidates as smart antitumor drug carriers for malignancy therapy.

Stealth properties to improve therapeutic efficacy of drug nanocarriers

Over the last few decades, nanocarriers for drug delivery have emerged as powerful tools with unquestionable potential to improve the therapeutic efficacy of anticancer drugs. Many colloidal drug delivery systems are underdevelopment to ameliorate the site specificity of drug action and reduce the systemic side effects. By virtue of their small size they can be injected intravenously and disposed into the target tissues where they release the drug. Nanocarriers interact massively with the surrounding environment, namely, endothelium vessels as well as cells and blood proteins. Consequently, they are rapidly removed from the circulation mostly by the mononuclear phagocyte system. In order to endow nanosystems with long circulation properties, new technologies aimed at the surface modification of their physicochemical features have been developed. In particular, stealth nanocarriers can be obtained by polymeric coating. In this paper, the basic concept underlining the "stealth" properties of drug nanocarriers, the parameters influencing the polymer coating performance in terms of opsonins/macrophages interaction with the colloid surface, the most commonly used materials for the coating process and the outcomes of this peculiar procedure are thoroughly discussed.

High viability of cells encapsulated in degradable poly(carboxybetaine) hydrogels

In this study, we report a degradable poly(carboxybetaine) (pCB) hydrogel, produced via a thiol-disulfide exchange reaction for cell encapsulation. A pCB dithiol was synthesized as a cross-linker and reacted with a pyridyl dithiol-containing CB copolymer to form a hydrogel. We evaluated the biocompatibility of the pCB-based hydrogel via encapsulation of three cell types, including NIH3T3 fibroblasts, MG63 osteoblast-like cells, and HepG2 hepatocarcinoma cells. Up to 90% of cells retained their viability in the pCB hydrogel even at low cell-seeding densities under serum-free conditions after a 9-day culture. Results are compared with a degradable poly(ethylene glycol) methacrylate (PEGMA) hydrogel, which showed very low cell viability under serum-free condition after a 3-day culture. We incorporated an RGD peptide into the CB hydrogel using a cysteine-terminated cross-linker, which was shown to promote cell proliferation.

Prolonged in vivo circulation time by zwitterionic modification of magnetite nanoparticles for blood pool contrast agents

Long circulation time is critical for blood pool contrast agents used in high-resolution magnetic resonance angiography. For iron oxide particle contrast agents, size and surface properties significantly influence their in vivo performance. We developed a novel long-circulating blood pool contrast agent by introducing zwitterionic structure onto the particle surface. Zwitterionic structure was fabricated by 3-(diethylamino)propylamine (DEAPA) grafted onto the surface of ployacrylic acid coated magnetite nanoparticles via EDC/NHS [N-(3-dimethylaminopropyl)-N'-ethylcarbo-diimide hydrochloride/N-hydroxysuccinimide] coupling chemistry. Zwitterionic particles demonstrated five times lower macrophage cell uptake than the original particles and low cell toxicity. Magnetic resonance angiography indicated that zwitterionic nanoparticles had much longer in vivo circulation time than the original particles and were an ideal candidate for blood pool contrast agent. We suppose that zwitterionic modification by DEAPA and EDC/NHS can be used generally for coating nanoparticles with carboxyl surface and to prolong their circulating time.

Synthesis and in vivo pharmacokinetic evaluation of degradable shell cross-linked polymer nanoparticles with poly(carboxybetaine) versus poly(ethylene glycol) surface-grafted coatings

Nanoparticles with tunable pharmacokinetics are desirable for various biomedical applications. Poly(ethylene glycol) (PEG) is well-known to create "stealth" effects to stabilize and extend the blood circulation of nanoparticles. In this work, poly(carboxybetaine) (PCB), a new nonfouling polymer material, was incorporated as surface-grafted coatings, conjugated onto degradable shell cross-linked knedel-like nanoparticles (dSCKs) composed of poly(acrylic acid)-based shells and poly(lactic acid) cores, to compare the in vivo pharmacokinetics to their PEG-functionalized analogues. A series of five dSCKs was prepared from amphiphilic block copolymers, having different numbers and lengths of either PEG or PCB grafts, by supramolecular assembly in water followed by shell cross-linking, and then studied by a lactate assay to confirm their core hydrolytic degradabilities. Each dSCK was also conjugated with 1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid macrocyclic chelators and tyramine moieties to provide for (64)Cu and/or radiohalogen labeling. The high specific activity of (64)Cu radiolabeling ensured nanogram administration of dSCKs for in vivo evaluation of their pharmacokinetics. Biodistribution studies demonstrated comparable in vivo pharmacokinetic profiles of PCB-grafted dSCKs to their PEG-conjugated counterparts. These results indicated that PCB-functionalized dSCKs have great potential as a theranostic platform for translational research.

Surface charge switchable nanoparticles based on zwitterionic polymer for enhanced drug delivery to tumor

Two faced nanoparticles: A zwitterionic polymer-based nanoparticle with response to tumor acidity is developed for enhanced drug delivery to tumors. The nanoparticles are neutrally charged at physiological conditions and show prolonged circulation time; after leaking into tumor sites, in the acidic extracellular tumor environment (pH(e) ), nanoparticles are activated and become positively charged and are therefore efficiently taken up by tumor cells, leading to enhanced therapeutic effects in cancer treatment.

Erythrocyte-inspired delivery systems

Herein recent progress in developing red blood cell (RBC)-inspired delivery systems is reviewed, with an emphasis on how our growing understanding of fundamental biological properties of natural RBCs has been applied in the design and engineering of these delivery systems. Specifically, progress achieved in developing carrier RBCs, a class of delivery vehicles engineered by directly loading natural RBCs with therapeutic agents, will be reviewed. Then alternative approaches to engineering synthetic vehicles through mimicking the mechanobiological and chemico-biological properties of natural RBCs will be considered. The synthesis and application of RBC membrane-derived vesicles, of which the natural RBC membranes are collected and directly utilized to prepare drug carriers, will then be discussed. Finally, a recent approach in engineering RBC membrane-camouflaged nanoparticle systems that combine advantages of natural RBCs and synthetic biomaterials will be highlighted. These developments indicate that RBC-inspired delivery systems will result in next-generation nanomedicine with extensive medical applications.

Superhydrophilic zwitterionic polymers stabilize liposomes

Nonionic polyethylene glycol (PEG) as a stealth polymer destabilizes liposomes due to its amphiphilic property. As a result, PEGylated liposomes have to be further stabilized, such as by using a large amount cholesterol. This is a long existing dilemma faced by PEG. In this work, we show that zwitterionic poly(carboxybetaine) (PCB) stabilizes liposomes because of its superhydrophilic nature, thus solving this dilemma. Specifically, PCB-modified liposomes without cholesterol exhibited good retention of hydrophilic drug and long blood circulating characteristics in vivo. To further validate this new PCB chemistry, PCB liposomal doxorubicin without cholesterol was compared with DOXIL for their antitumor therapeutic efficacies.

Carrier-free, functionalized drug nanoparticles for targeted drug delivery

We demonstrate a new concept of carrier-free functionalized drug nanoparticles for targeted drug delivery. It exhibits significantly enhanced drug efficacy to folate receptor-positive cells with high selectivity and a high drug loading content up to more than 78%.

Docetaxel nanotechnology in anticancer therapy

Taxanes have been recognized as a family of very efficient anticancer drugs, but the formulation in use for the two main taxanes-Taxol for paclitaxel and Taxotere for docetaxel-have shown dramatic side effects. Whereas several new formulations for paclitaxel have recently appeared, such as Abraxane and others currently in various phases of clinical trials, there is no new formulation in clinical trials for the other main taxane, docetaxel, except BIND-014, a polymeric nanoparticle, which recently entered phase I clinical testing. Therefore, we review herein the state of the art and recent abundance in published results of academic approaches toward nanotechnology-based drug-delivery systems containing nanocarriers and targeting agents for docetaxel formulations. These efforts will certainly enrich the spectrum of docetaxel treatments in the near future. Taxotere's systemic toxicity, low water solubility, and other side effects are significant problems that must be overcome. To avoid the limitations of docetaxel in clinical use, researchers have developed efficient drug-delivery assemblies that consist of a nanocarrier, a targeting agent, and the drug. A wide variety of such engineered nanosystems have been shown to transport and eventually vectorize docetaxel more efficiently than Taxotere in vitro, in vivo, and in pre-clinical administration. Recent progress in drug vectorization has involved a combined therapy and diagnostic ("theranostic") approach in a single drug-delivery vector and could significantly improve the efficiency of such an anticancer drug as well as other drug types.

Recent advances in stealth coating of nanoparticle drug delivery systems

Modifying surfaces of nanoparticles (NPs) with polyethylene glycol (PEG), the so-called PEGylation, is the most commonly used method for reducing premature clearance of NPs from the circulation. However, several reports point out that PEGylation may negatively influence the performance of NPs as a drug carrier. Alternative surface modification strategies, including substitute polymers, conditional removal of PEG, and biomimetic surface modification, may provide solutions for the limitations of PEG.

Poly(zwitterionic)protein conjugates offer increased stability without sacrificing binding affinity or bioactivity

Treatment with therapeutic proteins is an attractive approach to targeting a number of challenging diseases. Unfortunately, the native proteins themselves are often unstable in physiological conditions, reducing bioavailability and therefore increasing the dose that is required. Conjugation with poly(ethylene glycol) (PEG) is often used to increase stability, but this has a detrimental effect on bioactivity. Here, we introduce conjugation with zwitterionic polymers such as poly(carboxybetaine). We show that poly(carboxybetaine) conjugation improves stability in a manner similar to PEGylation, but that the new conjugates retain or even improve the binding affinity as a result of enhanced protein-substrate hydrophobic interactions. This chemistry opens a new avenue for the development of protein therapeutics by avoiding the need to compromise between stability and affinity.