Folate-functionalized unimolecular micelles based on a degradable amphiphilic dendrimer-like star polymer for cancer cell-targeted drug delivery

Dendritic polymer prodrug-based unimolecular micelles for pH-responsive co-delivery of doxorubicin and camptothecin with synergistic controlled drug release effect

Combination chemotherapy has been recognized as a more powerful strategy for tumor treatment rather than the single chemotherapy. However, the interactive mechanism of the two hydrophobic chemotherapeutic drugs has not been explored by now. Aiming for a better synergistic effect, such interactive mechanism was investigated in the present work, by designing CPT@DOX-DPUTEA-PEG nanomedicine with encapsulated camptothecin (CPT) and conjugated doxorubicin (DOX). The synergistic controlled drug release effect was found for the two drugs loaded on the different sites of the dendritic polyurethane core. Synergism was achieved on the HepG2 cells with a combination index (CI) of 0.58 in the in vitro cellular experiments. The results demonstrated the promising application of the unimolecular micelles-based nanomedicine with independently loading of two hydrophobic chemotherapeutic drugs.

Polymeric Nanoparticles for Drug Delivery

The recent emergence of nanomedicine has revolutionized the therapeutic landscape and necessitated the creation of more sophisticated drug delivery systems. Polymeric nanoparticles sit at the forefront of numerous promising drug delivery designs, due to their unmatched control over physiochemical properties such as size, shape, architecture, charge, and surface functionality. Furthermore, polymeric nanoparticles have the ability to navigate various biological barriers to precisely target specific sites within the body, encapsulate a diverse range of therapeutic cargo and efficiently release this cargo in response to internal and external stimuli. However, despite these remarkable advantages, the presence of polymeric nanoparticles in wider clinical application is minimal. This review will provide a comprehensive understanding of polymeric nanoparticles as drug delivery vehicles. The biological barriers affecting drug delivery will be outlined first, followed by a comprehensive description of the various nanoparticle designs and preparation methods, beginning with the polymers on which they are based. The review will meticulously explore the current performance of polymeric nanoparticles against a myriad of diseases including cancer, viral and bacterial infections, before finally evaluating the advantages and crucial challenges that will determine their wider clinical potential in the decades to come.

Strategies for Targeted Delivery via Structurally Variant Polymeric Nanocarriers

The last decade has seen a meteoric rise in studies investigating polymeric aggregates as nanocarriers. When it comes to morphology, size, functionality, and immunostability, polymeric nanocarriers (PNCs) are unparalleled. With characteristics such as large surface area to volume ratio, amphiphilic nano‐environment, non‐toxic components, chemically modifiable composition, external surface alteration potential, uniform particle size, and stimuli‐dependent self‐assembly, PNCs have emerged as strong candidates for therapeutic applications. The article reviews the latest research on different challenges and strategies for targeted drug delivery and shall serve as guide to the researchers in designing site‐specific nanocarriers for application in future. The review systematically discusses the fundamental structural variation of the nanocarriers with emphasis on the influence of chemical alterations and the resulting effects on functionality; addresses the difficulties encountered with modes of administration; target selectivity and stimulus response.

Structural Engineering of Star Block Biodegradable Polymer Unimolecular Micelles for Drug Delivery in Cancer Cells

The present investigation reports the structural engineering of biodegradable star block polycaprolactone (PCL) to tailor-make aggregated micelles and unimolecular micelles to study their effect on drug delivery aspects in cancer cell lines. Fully PCL-based star block copolymers were designed by varying the arm numbers from two to eight while keeping the arm length constant throughout. Multifunctional initiators were exploited for stepwise solvent-free melt ring-opening polymerization of ε-caprolactone and γ-substituted caprolactone to construct star block copolymers having a PCL hydrophobic core and a carboxylic PCL hydrophilic shell, respectively. A higher arm number and a higher degree of branching in star polymers facilitated the formation of unimolecular micelles as opposed to the formation of conventional multimicellar aggregates in lower arm analogues. The dense core of the unimolecular micelles enabled them to load high amounts of the anticancer drug doxorubicin (DOX, ∼12-15%) compared to the aggregated micelles (∼3-4%). The star unimolecular micelle completely degraded leading to 90% release of the loaded drug upon treatment with the lysosomal esterase enzyme in vitro. The anticancer efficacies of these DOX-loaded unimolecular micelles were tested in a breast cancer cell line (MCF-7), and their IC₅₀ values were found to be much lower compared to those of aggregated micelles. Time-dependent cellular uptake studies by confocal microscopy revealed that unimolecular micelles were readily taken up by the cells, and enhancement of the drug concentration was observed at the intracellular level up to 36 h. The present work opens new synthetic strategies for building a next-generation biodegradable unimolecular micellar nanoplatform for drug delivery in cancer research.

Facile Synthesis of a Redox-Responsive Hyperbranched Polymer Prodrug as a Unimolecular Micelle for the Tumor-Selective Drug Delivery

Demicellization of the self-assembled multimolecular micelles upon dilution restricts their application as drug delivery systems (DDSs) for tumor treatment. Here, a redox-responsive hyperbranched polymer prodrug (HBPP) was designed with a high drug content of 62.0% as a unimolecular micelle for the tumor-selective drug delivery, via the facile self-condensing vinyl polymerization (SCVP) of redox-responsive doxorubicin-based prodrug monomer MA-SS-DOX and poly(ethylene glycol) methacrylate (PEGMA) with p-chloromethylstyrene (CMS) as an inimer. The unimolecular micelle could be easily obtained with a hydrodynamic diameter of 122 nm, showing excellent GSH-triggered drug release performance with a cumulative release of 60.9% within 85 h but a low premature drug leakage of 3.2%. The unimolecular micelle exhibited selective tumor growth inhibition on HepG2 cells but no obvious cytotoxicity on L02 cells.

An updated review of folate-functionalized nanocarriers: A promising ligand in cancer

The uncontrolled release of drugs in conventional drug delivery systems has led to the introduction of new nanotechnology-based drug delivery systems and the use of targeted nanocarriers for cancer treatment. These targeted nanocarriers, which consist of intelligent nanoparticles modified with targeting ligands, can deliver drugs to specified locations at the right time and reduce drug doses to prevent side effects. Folate is a suitable targeting ligand for folate receptors overexpressed on cancer cells and has shown promising results in the diagnosis and treatment of cancer. In this review, we highlight the latest developments on the use of folate-conjugated nanoparticles in cancer diagnosis and treatment. Moreover, the toxicity, biocompatibility and efficacy of these nanocarriers are discussed.

Facile Construction of a Solely-DNA-Based System for Targeted Delivery of Nucleic Acids

We designed a functional drug delivery system based solely on DNA. The whole system was built with only four DNA strands. Cyclization of DNA strands excluded the formation of byproducts. DNA aptamers were equipped to endow triangular DNA nanostructures with targeting ability. The homogeneity of materials enabled not only facile construction but also convenient loading of nucleic acid-based drugs with much ease.

Dendrimer as a promising nanocarrier for the delivery of doxorubicin as an anticancer therapeutics

Dendrimers are macromolecules with high-polymeric branching capable of undergoing major modifications. These characteristics make them an efficient nanocarrier capable of encapsulating and delivering drug, antibodies, or any therapeutic gene. The failure of conventional techniques to deliver drug with higher efficacy and reduced side effects has led to the use of nanomedicines including dendrimers. Dendrimers are novel drug carriers that are modified, complexed, and conjugated with different ligands and receptors to target the delivery of drug at the specific site without impacting any of the normal cells in surrounding. Moreover, the biocompatibility and safety of the dendrimers can be altered accordingly by the process of functionalization by PEGylation, acetylation, or amination. Various dendrimers have been designed to incorporate and deliver anticancer drug either in free form or as codelivery in conjugation with other drugs or therapeutic siRNA/DNA. Doxorubicin (DOX) is one such chemotherapeutic drug that acts by disrupting the process of DNA repair in tumor cells and hence is, since long been used for anticancer therapy. Certain adverse effects such as cardiotoxicity has limited the use of conventional DOX and has shifted the focus on use of safe nanodelivery systems viz dendrimers. DOX either in free or salt form can be loaded or encapsulated accordingly within the core of the dendrimers and linked with different receptors expressed over tumor cells to improve targeting in any cancerous organ site. Positive results obtained after cytotoxicity assay and in vivo/in vitro studies on different cancerous cell lines, and grafted models suggested the potential use of multifunctional DOX-dendrimers characterized with controlled release, better penetration, improved bioavailability, and reduced organ toxicity. This review consolidates studies on different types of DOX-loaded dendrimers that were synthesized, investigated, and are currently being explored for better cancer targeting. Foreseeing the prospects of dendrimers and their compatibility with DOX (free/salt), the article was updated with all current insights.

Effect of side-chain length on solute encapsulation by amphiphilic heterografted brush copolymers

Anisotropic nanomaterials are non-spherical structures that possess unique shape-dependent physicochemical properties and functionalities. Inspired by the abundance of filamentous entities in nature, cylindrical nanostructures have gained significant attention due to their unique performance. Herein, we discuss the effect of side-chain length on the encapsulation properties of amphiphilic heterografted bottlebrushes. We observed that by grafting a long hydrophilic block to the double-brush, we were able to restrict solute-induced conformational changes, thus producing drug-loaded anisotropic carriers. Unimolecular encapsulation in brushes was solute-dependent as shown here for probucol and rose bengal lactone. Stabilization with an amphiphilic diblock copolymer-consisting of the same type of blocks as those comprising the heterografted brush-served to explain the solute-dependent behavior observed for brushes, suggesting that solutes with a higher propensity to nucleation could be more effectively stabilized by the anisotropic carrier in a unimolecular worm-like construct.

Use of Anticancer Platinum Compounds in Combination Therapies and Challenges in Drug Delivery

As one of the leading and most important metal-based drugs, platinum-based pharmaceuticals are widely used in the treatment of solid malignancies. Despite significant side effects and acquired drug resistance have limited their clinical applications, platinum has shown strong inhibitory effects for a wide assortment of tumors. Drug delivery systems using emerging technologies such as liposomes, dendrimers, polymers, nanotubes and other nanocompositions, all show promise for the safe delivery of platinum-based compounds. Due to the specificity of nano-formulations; unwanted side-effects and drug resistance can be largely averted. In addition, combinational therapy has been shown to be an effective way to improve the efficacy of platinum based anti-tumor drugs. This review first introduces drug delivery systems used for platinum and combinational therapeutic delivery. Then we highlight some of the recent advances in the field of drug delivery for combinational therapy; specifically progress in leveraging the cytotoxic nature of platinum-based drugs, the combinational effect of other drugs with platinum, while evaluating the drug targeting, side effect reducing and sitespecific nature of nanotechnology-based delivery platforms.

Dendrimers as efficient nanocarriers for the protection and delivery of bioactive phytochemicals

The genesis of dendrimers can be considered as a revolution in nano-scaled bioactive delivery systems. These structures possess a unique potential in encapsulating/entrapping bioactive ingredients due to their tree-like nature. Therefore, they could swiftly obtain a valuable statue in nutraceutical, pharmaceutical and medical sciences. Phytochemicals, as a large proportion of bioactives, have been studied and used by scholars in several fields of pharmacology, medical, food, and cosmetic for many years. But, the solubility, stability, and bioavailability issues have always been recognized as limiting factors in their application. Therefore, the main aim of this study is representing the use of dendrimers as novel nanocarriers for phytochemical bioactive compounds to deal with these problems. Hence, after a brief review of phytochemical ingredients, the text is commenced with a detailed explanation of dendrimers, including definitions, types, generations, synthesizing methods, and safety issues; then is continued with demonstration of their applications in encapsulation of phytochemical bioactive compounds and their active/passive delivery by dendrimers. Dendrimers provide a vast and appropriate surface to entrap the targeted phytochemical bioactive ingredients. Several parameters can affect the yield of nanoencapsulation by dendrimers, including their generation, type of end groups, surface charge, core structure, pH, and ambient factors. Another important issue of dendrimers is related to their toxicity. Cationic dendrimers, particularly PAMAM can be toxic to body cells through attaching to the cell membranes and disturbing their functions. However, a number of solutions have been suggested to decrease their toxicity.

Phenylboronic acid-functionalized unimolecular micelles based on a star polyphosphoester random copolymer for tumor-targeted drug delivery

A phenylboronic acid-functionalized unimolecular micellar drug delivery system based on a star phosphoester random copolymer synthesized by a one-pot ring-opening polymerization strategy.

Codelivery of Hydrophobic and Hydrophilic Drugs by Graphene-Decorated Magnetic Dendrimers

In this study, a nanocarrier was prepared for the codelivery of a hydrophilic drug (doxorubicin) and a hydrophobic drug (curcumin) to cancer cells. In this nanocarrier, the edges of graphene oxide sheets were decorated with a magnetic-functionalized polyamidoamine dendrimer with hydrazone groups at the end of the polymer. The edge functionalization of graphene sheets not only improved the solubility and dispersibility of graphene sheets but also imparted the magnetic properties to the nanocarrier. The resulting nanocarrier was loaded with doxorubicin through the covalent linkage and curcumin through π-π stacking. The nanocarrier showed a pH-sensitive release for both drugs, and the drug release behavior was also improved by the coimmobilization of both drugs. The cytotoxicity assay of nanocarrier showed low toxicity toward MCF-7 cell compared to unmodified graphene oxide, which was attributed to the presence of a magnetic dendrimer. Besides, the drug-loaded nanocarrier was highly toxic for cells even more than for free drugs. The cellular uptake images revealed higher drug internalization for coloaded nanocarrier than for the nanocarrier loaded with one drug alone. All of the results showed that the codelivery of curcumin and doxorubicin in the presence of the nanocarrier was more effective in chemotherapy than the nanocarrier loaded with one drug.

Targeting Groups Employed in Selective Dendrons and Dendrimers

The design of compounds with directed action to a defined organ or tissue is a very promising approach, since it can decrease considerably the toxicity of the drug/bioactive compound. For this reason, this kind of strategy has been greatly important in the scientific community. Dendrimers, on the other hand, comprise extremely organized macromolecules with many peripheral functionalities, stepwise controlled synthesis, and defined size. These nanocomposites present several biological applications, demonstrating their efficiency to act in the pharmaceutical field. Considering that, the main purpose of this review was describing the potential of dendrons and dendrimers as drug targeting, applying different targeting groups. This application has been demonstrated through interesting examples from the literature considering the last ten years of publications.

Folic Acid-Conjugated Cellulose Nanocrystals Show High Folate-Receptor Binding Affinity and Uptake by KB and Breast Cancer Cells

The study evaluates cellulose nanocrystals (CNCs) as nanocarriers for targeted, intracellular delivery of molecular agents. CNCs were labeled with fluorescein-5'-isothiocyanate as an imaging agent and conjugated to folic acid (FA) as a targeting ligand. The CNC conjugates were characterized by UV-vis spectroscopy, ζ-potential analysis, dynamic light scattering, and atomic force microscopy. Cellular binding/uptake of the FA-conjugated CNCs by KB and MDA-MB-468 cells was quantified with cellular uptake assays. Internalization of the particles was confirmed by confocal microscopy. Uptake mechanisms were determined by inhibition studies with chlorpromazine and genistein. Binding affinity was qualitatively assessed with a free folate inhibition assay. Both KB and MDA-MB-468 cells exhibited significant and folate-receptor specific binding/uptake of FA-conjugated CNCs. Clathrin-mediated endocytosis was a significant uptake mechanism in both cell types, whereas caveolae-mediated endocytosis only played a significant role in MDA-MB-468 cells. Uptake inhibition of FA-conjugated CNCs by KB cells required high concentrations (>1 mM) of free FA. The observed FR-specific internalization of FA-conjugated CNCs by FR-positive cancer cells and tumors and their remarkable high affinity for the FR demonstrate the great potential of CNCs as novel nanocarriers for imaging agents and chemotherapeutics in the early detection and treatment of cancer.

Biodegradable polyester unimolecular systems as emerging materials for therapeutic applications

Unimolecular micelles, as a class of single-molecular micelles, are structurally stable regardless of their concentrations or alterations of the outer environment such as pH, temperature, ion strength etc. in comparison with conventional polymeric micelles. Polyester unimolecular micelles are extensively applied in bio-medical fields because of their stability, biocompatibility, biodegradability, structural-controllabilty etc. In this review, the most recent developments in polyester unimolecular micelle designs in terms of Boltorn polymer H40 core, cyclodextrin, dendrimer or dendrimer-like polymer, or polyhedral oligomeric silsesquioxane (POSS) based polyester unimolecular micelles are presented. The significance and application in biomedical fields including drug delivery, bio-imaging and theranostics are also classified in this review. Finally, the remaining challenges and future perspectives for further development of unimolecular micelles as therapeutic materials are also discussed.

A review on core-shell structured unimolecular nanoparticles for biomedical applications

Polymeric unimolecular nanoparticles (NPs) exhibiting a core-shell structure and formed by a single multi-arm molecule containing only covalent bonds have attracted increasing attention for numerous biomedical applications. This unique single-molecular architecture provides the unimolecular NP with superior stability both in vitro and in vivo, a high drug loading capacity, as well as versatile surface chemistry, thereby making it a desirable nanoplatform for therapeutic and diagnostic applications. In this review, we surveyed the architecture of various types of polymeric unimolecular NPs, including water-dispersible unimolecular micelles and water-soluble unimolecular NPs used for the delivery of hydrophobic and hydrophilic agents, respectively, as well as their diverse biomedical applications. Future opportunities and challenges of unimolecular NPs were also briefly discussed.

Systematic design and application of unimolecular star-like block copolymer micelles: a coarse-grained simulation study

Unimolecular polymeric micelles have several features, such as thermodynamic stability, small particle size, biocompatibility, and the ability to internalize hydrophobic molecules. These micelles have recently attracted significant attention in various applications, such as nano-reactors, catalysis, and drug delivery. However, few attempts have explored the formation mechanisms and conditions of unimolecular micelles due to limited experimental techniques. In this study, a unimolecular micelle system formed from β-cyclodextrin-graft-{poly(lactide)-block-poly(2-(dimethylamino) ethyl multimethacrylate)-block-poly[oligo (2-ethyl-2-oxazoline) methacrylate]} β-CD-g-(PLA-b-PDMAEMA-b-PEtOxMA) star-like block copolymers in aqueous media was investigated by dissipative particle dynamics (DPD) to explore the formation process of unimolecular micelles. The simulation results showed that using longer hydrophobic or pH-sensitive chains, shorter hydrophilic backbones, smaller hydrophilic side chain grafting density, and fewer polymer arms resulted in micellar aggregation. Furthermore, this unimolecular polymeric micelle could be used for encapsulating gold nanoparticles, whose mesoscopic structure was also explored. The gold nanoparticles tended to distribute in the middle layer formed by PDMAEMA, and the unimolecular micelles were capable of impeding gold nanoparticle aggregation. This study could help understand the formation mechanism of unimolecular micelles formed from star-like block copolymers in dilute solutions and offer a theoretical guide to the design and preparation of promising unimolecular polymeric micelles with targeting properties.

Doxorubicin-Loaded Unimolecular Micelle-Stabilized Gold Nanoparticles as a Theranostic Nanoplatform for Tumor-Targeted Chemotherapy and Computed Tomography Imaging

Current research is mainly trending toward addressing the development of multifunctional nanocarriers that could precisely reach disease sites, release drugs in a controlled-manner, and act as an imaging agent for both diagnosis and targeted therapy. In this study, a pH-sensitive theranostic nanoplatform as a promising dual-functional nanovector for tumor therapy and computed tomography (CT) imaging was developed. The 21-arm star-like triblock polymer of β-cyclodextrin-{poly(ε-caprolactone)-poly(2-aminoethyl methacrylate)-poly[poly(ethylene glycol) methyl ether methacrylate]}₂₁ [β-CD-(PCL-PAEMA-PPEGMA)₂₁] with stable unimolecular micelles formed in aqueous solution was first synthesized by combined ROP with ARGET ATRP techniques and then was used as a template for fabricating gold nanoparticles (AuNPs) with uniform sizes and excellent colloidal stability in situ followed by the encapsulation of doxorubicin (DOX) with maximum entrapment efficiency up to 60% to generate the final product β-CD-(PCL-PAEMA-PPEGMA)₂₁/AuNPs/DOX. Furthermore, dissipative particle dynamics (DPD) simulations revealed further details of the formation process of unimolecular micelles and the morphologies and distributions of AuNPs and DOX. Almost 80% of DOX was released in 120 h in an acidic tumoral environment in an in vitro drug release experiment, and the experiments both in vitro and in vivo demonstrated the fact that β-CD-(PCL-PAEMA-PPEGMA)₂₁/AuNPs/DOX exhibited similar antitumor efficacy to free DOX and effective CT imaging performance. Therefore, we believe this structurally stable unimolecular micelle-based nanoplatform synergistically integrated with anticancer drug delivery and CT imaging capabilities hold great promise for future cancer theranostics.

Quantum-Dot-Based Theranostic Micelles Conjugated with an Anti-EGFR Nanobody for Triple-Negative Breast Cancer Therapy

A quantum-dot (QD)-based micelle conjugated with an anti-epidermal growth factor receptor (EGFR) nanobody (Nb) and loaded with an anticancer drug, aminoflavone (AF), has been engineered for EGFR-overexpressing cancer theranostics. The near-infrared (NIR) fluorescence of the indium phosphate core/zinc sulfide shell QDs (InP/ZnS QDs) allowed for in vivo nanoparticle biodistribution studies. The anti-EGFR nanobody 7D12 conjugation improved the cellular uptake and cytotoxicity of the QD-based micelles in EGFR-overexpressing MDA-MB-468 triple-negative breast cancer (TNBC) cells. In comparison with the AF-encapsulated nontargeted (i.e., without Nb conjugation) micelles, the AF-encapsulated Nb-conjugated (i.e., targeted) micelles accumulated in tumors at higher concentrations, leading to more effective tumor regression in an orthotopic triple-negative breast cancer xenograft mouse model. Furthermore, there was no systemic toxicity observed with the treatments. Thus, this QD-based Nb-conjugated micelle may serve as an effective theranostic nanoplatform for EGFR-overexpressing cancers such as TNBCs.

Dendrimer and dendrimer–conjugate protein complexes and protein coronas

Dendrimers and dendrimer conjugates are widely employed for biological applications such as bio-imaging and drug delivery. Understanding the interaction between dendrimers and their biological environment is key to evaluating the efficacy and safety of these materials. Proteins can form an adsorbed layer, termed a “protein corona”, on dendrimers in either a non-specific or specific fashion. A tight-binding, non-exchangeable corona is defined as a “hard” corona, whereas a loosely bound, highly exchangeable corona is called a “soft” corona. Recent research indicates that small molecules conjugated to the polymer surface can induce protein structural change, leading to tighter protein–dendrimer binding and further protein aggregation. This “triggered” corona formation on dendrimer and dendrimer conjugates is reviewed and discussed along with the existing hard or soft corona model. This review describes the triggered corona model to further the understanding of protein corona formation.

Unimolecular Micelle-Based Hybrid System for Perivascular Drug Delivery Produces Long-Term Efficacy for Neointima Attenuation in Rats

At present, there are no clinical options for preventing neointima-caused (re)stenosis after open surgery such as bypass surgery for treating flow-limiting vascular disease. Perivascular drug delivery is a promising strategy, but in translational research, it remains a major challenge to achieve long-term (e.g., > 3 months) anti(re)stenotic efficacy. In this study, we engineered a unique drug delivery system consisting of durable unimolecular micelles, formed by single multiarm star amphiphilic block copolymers with only covalent bonds, and a thermosensitive hydrogel formed by a poly(lactide-co-glycolide)-poly(ethylene glycol)-poly(lactide-co-glycolide) triblock copolymer (abbreviated as triblock gel) that is stable for about 4 weeks in vitro. The drug-containing unimolecular micelles (UMs) suspended in Triblock gel were able to sustain rapamycin release for over 4 months. Remarkably, even 3 months after perivascular application of the rapamycin-loaded micelles in Triblock gel in the rat model, the intimal/medial area ratio (a restenosis measure) was still 80% inhibited compared to the control treated with empty micelle/gel (no drug). This could not be achieved by applying rapamycin in Triblock gel alone, which reduced the intimal/medial ratio only by 27%. In summary, we created a new UM/Triblock gel hybrid system for perivascular drug delivery, which produced a rare feat of 3-month restenosis inhibition in animal tests. This system exhibits a real potential for further translation into an anti(re)stenotic application with open surgery.

Next Generation Precision-Polyesters Enabling Optimization of Ligand-Receptor Stoichiometry for Modular Drug Delivery

The success of receptor-mediated drug delivery primarily depends on the ability to optimize ligand-receptor stoichiometry. Conventional polyesters such as polylactide (PLA) or its copolymer, polylactide-co-glycolide (PLGA), do not allow such optimization due to their terminal functionality. We herein report the synthesis of 12 variations of the PLA-poly(ethylene glycol) (PEG) based precision-polyester (P2s) platform, permitting 5-12 periodically spaced carboxyl functional groups on the polymer backbone. These carboxyl groups were utilized to achieve variable degrees of gambogic acid (GA) conjugation to facilitate ligand-receptor stoichiometry optimization. These P2s-GA combined with fluorescent P2s upon emulsification form nanosystems (P2Ns) of size <150 nm with GA expressed on the surface. The P2Ns outclass conventional PLGA-GA nanosystems in cellular uptake using caco-2 intestinal model cultures. The P2Ns showed a proportional increase in cellular uptake with an increase in relative surface GA density from 0 to 75%; the slight decline for 100% GA density was indicative of receptor saturation. The intracellular trafficking of P2Ns in live caco-2 cells demonstrated the involvement of endocytic pathways in cellular uptake. The P2Ns manifest transferrin receptor (TfR) colocalization in ex vivo intestinal tissue sections, despite blocking of the receptor with transferrin (Tf) noncompetitively, i.e., independently of receptor occupation by native ligand. The in vivo application of P2Ns was demonstrated using cyclosporine (CsA) as a model peptide. The P2Ns exhibited modular release in vivo, as a function of surface GA density. This approach may contribute to the development of personalized dose regimen.

Structural analysis of binding functionality of folic acid-PEG dendrimers against folate receptor

Dendrimers functionalized with folic acid (FA) are drug delivery systems that can selectively target cancer cells with folate receptors (FR-α) overexpression. Incorporation of polyethylene glycol (PEG) can enhance dendrimers solubility and pharmacokinetics, but ligand-receptor binding must not be affected. In this work we characterized, at atomic level, the binding functionality of conventional site-specific dendrimers conjugated with FA with PEG 750 or PEG 3350 as a linker. After Molecular Dynamics simulation, we observed that both PEG's did not interfere over ligand-receptor binding functionality. Although binding kinetics could be notably affected, the folate fragment from both dendrimers remained exposed to the solvent before approaching selectively to FR-α. PEG 3350 provided better solubility and protection from enzymatic degradation to the dendrimer than PEG 750. Also, FA-PEG3350 dendrimer showed a slightly better interaction with FR-α than FA-PEG750 dendrimer. Therefore, theoretical evidence supports that both dendrimers are suitable as drug delivery systems for cancer therapies.

Star Polymers

Recent advances in controlled/living polymerization techniques and highly efficient coupling chemistries have enabled the facile synthesis of complex polymer architectures with controlled dimensions and functionality. As an example, star polymers consist of many linear polymers fused at a central point with a large number of chain end functionalities. Owing to this exclusive structure, star polymers exhibit some remarkable characteristics and properties unattainable by simple linear polymers. Hence, they constitute a unique class of technologically important nanomaterials that have been utilized or are currently under audition for many applications in life sciences and nanotechnologies. This article first provides a comprehensive summary of synthetic strategies towards star polymers, then reviews the latest developments in the synthesis and characterization methods of star macromolecules, and lastly outlines emerging applications and current commercial use of star-shaped polymers. The aim of this work is to promote star polymer research, generate new avenues of scientific investigation, and provide contemporary perspectives on chemical innovation that may expedite the commercialization of new star nanomaterials. We envision in the not-too-distant future star polymers will play an increasingly important role in materials science and nanotechnology in both academic and industrial settings.

Unimolecular Micelles from Layered Amphiphilic Dendrimer-Like Block Copolymers

In this report, we synthesized layered amphiphilic dendrimer-like block copolymers containing a polystyrene core and poly(p-tert-butoxystyrene)/poly(p-hydroxylstyrene) shell (coded G4-PtBOS/G4-PHOS). The synthetic method is easy involving anionic polymerization, epoxidation, ring-opening reaction and hydrolysis reaction. The hydrolyzed G4-PtBOS was soluble in alkaline water and behaved as unimolecular micelle, as demonstrated by the results of DLS, cryo- and normal TEM, and pyrene entrapping experiment. The stability of the unimolecular micelles was investigated via ζ-potential measurements.

Pluronic F127–chondroitin sulfate micelles prepared through a facile method for passive and active tumor targeting

Micelles based on Pluronic F127 and chondroitin sulfate with targeting properties were fabricated to specifically deliver DOX to tumors.

Unimolecular micelles from graft copolymer with binary side chains

A novel amphiphilic binary graft copolymer was synthesized and used to prepare unimolecular micelles by intramolecular association.

Thermosensitive tribrachia star-shaped s-P(NIPAM-co-DMAM) random copolymer micelle aggregates: Preparation, characterization, and drug release applications

Tribrachia star-shaped random copolymers with tunable thermosensitive phase transition temperature were designed and synthesized via a simple one-pot ammonolysis reaction approach with trimesic acid as cores. The self-assembly micellization behavior of the copolymers in aqueous solution was examined by surface tension, UV-vis transmittance, transmission electron microscope, and dynamic light scattering measurements, etc. The results indicated that the resultant copolymers formed thermosensitive micelle aggregates through hydrophobic interactions among the isopropyl groups of poly(N-isopropylacrylamide) PNIPAM chains and inter-star association at a polymer concentration above critical aggregation concentrations from 4.06 to 6.55 mg L(-1), with a cloud point range from 36.6℃ to 52.1℃, and homogeneously distributed micelle size below 200 nm. The arm length and the compositional ratios of the two comonomers had effect on physicochemical properties of the polymer micelle aggregates. Particularly, the cloud point values were enhanced as the (N,N-dimethylacrylamide) DMAM monomer was introduced and reached to 36.6℃ and 41.0℃-44.7℃ when the mass ratio of NIPAM to DMAM was 90:10 and 80:20, respectively. The thermo-triggered drug release and cytotoxicity were evaluated to confirm the applicability of the random copolymer micelle aggregates as novel drug targeted release carriers.

Polyamidoamine and polyglycerol; their linear, dendritic and linear–dendritic architectures as anticancer drug delivery systems

This review covers the latest advances in the conjugation of chemotherapeutics such as doxorubicin, paclitaxel, methotrexate, fluorouracil and cisplatin to dendritic polymers, including polyamidoamine dendrimers, hyperbranched polyglycerols and their linear analogues, with a focus on their cytotoxicity, biodistribution and biodegradability.

PNIPAM-based heteroarm star-graft quarterpolymers: synthesis, characterization and pH-dependent thermoresponsiveness in aqueous media

We report the design of PS_n(P2VP-b-PAA-g-PNIPAM)_n heteroarm star-graft quarterpolymers, the thermoresponsiveness of which is strongly dependent on pH ionic strength, and their macromolecular features, e.g. arm number and grafting density.

Encapsulation of anticancer drug by hydrogen-bonded multilayers of tannic acid

Tannic acid (TA)-based multilayer assemblies have attracted increasing interest for biomedical applications. Here we explore properties of TA-poly(N-vinylpyrrolidone) (TA-PVPON) hydrogen-bonded multilayers for drug encapsulation and long-term storage. We demonstrate that the small molecular weight anticancer drug, doxorubicin (DOX), can be successfully loaded into (TA-PVPON) capsules with high encapsulation efficiency. We have also found that the encapsulated DOX can be efficiently stored inside the capsules for the pH range from pH = 7.4 to pH = 5. We show that the chemical and functional stability of TA at neutral and basic pH values is achieved through complexation with PVPON. The UV-vis spectrophotometry and in situ ellipsometry analyses of the hydrogen bonding interactions between TA and PVPON at different pH values reveal pH-dependent behavior of TA-PVPON capsules for the pH range from pH = 7.4 to pH = 5. Increasing deposition pH value from pH = 5 to pH = 7.4 leads to a 2-fold decrease in capsule thickness. However, this trend is reversed when salt concentration of the deposition solutions is increased from 0.01 M to 0.1 M NaCl. We have also demonstrated that the permeability of (TA-PVPON) capsules prepared using low salt deposition conditions and pH = 7.4 can be increased 2-fold by exposure of the capsules to 0.1 M NaCl salt solutions at the same pH. Our work opens new perspectives for design of novel polymer carriers for controlled drug delivery in cancer therapy.

Quantitative control of active targeting of nanocarriers to tumor cells through optimization of folate ligand density

The active targeting delivery system has been widely studied in cancer therapy by utilizing folate (FA) ligands to generate specific interaction between nanocarriers and folate receptors (FRs) on tumor cell. However, there is little work that has been published to investigate the influence of the definite density of the FA ligands on the active targeting of nanocarriers. In this study, we have combined magnetic-guided iron oxide nanoparticles with FA ligands, adjusted the FA ligand density and then studied the resulting effects on the active targeting ability of this dual-targeting drug delivery system to tumor cells. We have also optimized the FA ligand density of the drug delivery system for their active targeting to FR-overexpressing tumor cells in vitro. Prussian blue staining, semi-thin section of cells observed with transmission electron microscopy (TEM) and inductively coupled plasma-atomic emission spectroscopy (ICP-AES) have shown that the optimal FA density is from 2.3 × 10(18) to 2.5 × 10(18) per gram nanoparticles ((g·NPs)(-1)). We have further tried to qualitatively and quantitatively control the active targeting and delivering of drugs to tumors on 4T1-bearing BALB/c mice. As expected, the in vivo experimental results have also demonstrated that the FA density of the magnetic nanoparticles (MNPs) could be optimized for a more easily binding to tumor cells via the multivalent linkages and more readily internalization through the FR-mediated endocytosis. Our study can provide a strategy to quantitatively control the active targeting of nanocarriers to tumor cells for cancer therapy.