Core/shell pH-sensitive micelles self-assembled from cholesterol conjugated oligopeptides for anticancer drug delivery

Targeting Peptides: The New Generation of Targeted Drug Delivery Systems

Peptides can act as targeting molecules, analogously to oligonucleotide aptamers and antibodies. They are particularly efficient in terms of production and stability in physiological environments; in recent years, they have been increasingly studied as targeting agents for several diseases, from tumors to central nervous system disorders, also thanks to the ability of some of them to cross the blood-brain barrier. In this review, we will describe the techniques employed for their experimental and in silico design, as well as their possible applications. We will also discuss advancements in their formulation and chemical modifications that make them even more stable and effective. Finally, we will discuss how their use could effectively help to overcome various physiological problems and improve existing treatments.

Evaluation of Nanoparticle Stability under Blood Flow Shear

The stability of drug-loaded nanoparticles in vivo is related to the success of the drug delivery, which is investigated as a deficiency due to the limitation of traditional experimental methods. In this study, dissipative particle dynamics (DPD), a simulation method suitable for soft matter and fluids, was used to study the stability of amphiphilic nanoparticles in the blood microenvironment. By comparing the morphology alteration of nanoparticles with various molecular topologies in the shear fluid field, we have found that branch degree and geometric symmetry would be the key factors in maintaining the nanoparticle's stability. This research could provide more theoretical guidance for drug delivery system design.

DPD simulations on mixed polymeric DOX-loaded micelles assembled from PCL-SS-PPEGMA/PDEA-PPEGMA and their dual pH/reduction-responsive release

The design of mixed polymeric micelles by a combination of two or more dissimilar polymers is a potential strategy to achieve multiple stimuli-response for anti-cancer drug delivery. However, their drug loading co-micellization behavior and multiple stimuli-responsive drug release mechanism have been poorly understood at the mesoscopic level, especially in the system that involves reduction-response due to the difficulty of simulation on the cleavage of chemical bonds. In this work, the co-micellization behavior, drug distribution regularities and dual pH/reduction-responsive drug release process of mixed micelles formed by disulfide-linked polycaprolactone-b-polyethylene glycol methyl ether methacrylate (PCL-SS-PPEGMA) and poly(ethylene glycol) methyl ether-b-poly(N,N-diethylamino ethyl methacrylate) (PDEA-PPEGMA) were studied by dissipative particle dynamics (DPD) mesoscopic simulations. A dedicated bond-breaking script was employed to accomplish the disulfide bond-breaking simulations. The results showed that PCL₅₅-SS-PPEGMA₁₀ and PDEA₃₄-PPEGMA₁₁ could be well mixed to form superior DOX-loaded micelles with good drug-loading capacity and drug-controlled release performance. To prepare the DOX-loaded micelles with optimized properties, the simulation results suggested the feed ratio of DOX:PCL₅₅-SS-PPEGMA₁₀:PDEA₃₄-PPEGMA₁₁ set to 3:4:4. Compared with the two single stimuli-response, the dual pH/reduction-response process perfectly combined both pH-response and reduction-response together, providing a higher release rate of DOX. Therefore, this study provides theoretical guidance aimed at the property optimization and micellar structure design of the dual pH/reduction-responsive mixed micelles.

Nanostructured Antimicrobial Peptides: Crucial Steps of Overcoming the Bottleneck for Clinics

The security issue of human health is faced with dispiriting threats from multidrug-resistant bacteria infections induced by the abuse and misuse of antibiotics. Over decades, the antimicrobial peptides (AMPs) hold great promise as a viable alternative to treatment with antibiotics due to their peculiar antimicrobial mechanisms of action, broad-spectrum antimicrobial activity, lower drug residue, and ease of synthesis and modification. However, they universally express a series of disadvantages that hinder their potential application in the biomedical field (e.g., low bioavailability, poor protease resistance, and high cytotoxicity) and extremely waste the abundant resources of AMP database discovered over the decades. For all these reasons, the nanostructured antimicrobial peptides (Ns-AMPs), based on a variety of nanosystem modification, have made up for the deficiencies and pushed the development of novel AMP-based antimicrobial therapies. In this review, we provide an overview of the advantages of Ns-AMPs in improving therapeutic efficacy and biological stability, reducing side effects, and gaining the effect of organic targeting and drug controlled release. Then the different material categories of Ns-AMPs are described, including inorganic material nanosystems containing AMPs, organic material nanosystems containing AMPs, and self-assembled AMPs. Additionally, this review focuses on the Ns-AMPs for the effect of biological activities, with emphasis on antimicrobial activity, biosecurity, and biological stability. The "state-of-the-art" antimicrobial modes of Ns-AMPs, including controlled release of AMPs under a specific environment or intrinsic antimicrobial properties of Ns-AMPs, are also explicated. Finally, the perspectives and conclusions of the current research in this field are also summarized.

Using Polypeptide Bearing Furan Side Chains as a General Platform to Achieve Highly Effective Preparation of Smart Glycopolypeptide Analogue-Based Nano-Prodrugs for Cancer Treatment

Although several synthetic polypeptide-based nano-prodrugs (NPDs) have entered clinical trials for cancer treatment, achieving a highly effective production of the NPDs for clinical translation remains a challenge. Herein, we develop a typical preparation of pH/glutathione (GSH) dual-responsive glycopolypeptide analogue NPDs having a high drug capsulation/loading efficiency of ca. 93% and ca. 27% even based on ring-opening polymerization (ROP) of a novel and general furan-containing N-carboxyanhydride (NCA) monomer, which facilitates the Diels-Alder (D-A) side-chain functionalization by maleimide modified chemotherapy drug without using any reactive additives. High reactivity of the D-A reaction resulting in the high preparation efficiency of the NPDs is confirmed by ¹H NMR and density functional theory (DFT) calculations. The self-assembled properties as well as the dual-responsiveness of the NPDs are systemically studied by particle size and zeta potential assay, transmission electron microscopy and drug-delivery dynamics. The cell uptake mechanism, intracellular drug distribution, in vitro/vivo antitumor activity evaluations and the main organ damages of the NPDs are all investigated. Our work can provide a good solution to solve the inefficient fabrication of the smart synthetic polypeptide-based micelles for cancer treatment by following this general and sophisticated platform.

PEG-Detachable Polymeric Micelles Self-Assembled from Amphiphilic Copolymers for Tumor-Acidity-Triggered Drug Delivery and Controlled Release

The development of an intelligent biomaterial system that can efficiently accumulate at the tumor site and release a drug in a controlled way is very important for cancer chemotherapy. PEG is widely selected as a hydrophilic shell to acquire prolonged circulation time and enhanced accumulation at the tumor site, but it also restrains the cellular transport and uptake and leads to insufficient therapeutic efficacy. In this work, a PEG-detachable pH-responsive polymer that forms micelles from copolymer cholesterol grafted poly(ethylene glycol) methyl ether- D_labile-poly(β-amino ester)- D_labile-poly(ethylene glycol) methyl ether (MPEG- D_labile-PAE- g-Chol) is developed to overcome the aforementioned challenges based on pH value changes among normal physiological, extracellular (pH_e), and intracellular (pH_i) environments. PEGylated doxorubicin (DOX)-loaded polymeric micelles (DOX-PMs) can accumulate at the tumor site via an enhanced permeability and retention effect, and the PEG shell is detachable induced by cleavage of the pH_e-labile linker between the PEG segment and the main chain. Meanwhile, the pH_i-sensitive poly(β-amino ester) segment is protonated and has a high positive charge. The detachment of PEG and protonation of PAE facilitate cellular uptake of DOX-PMs by negatively charged tumor cells, along with the escape from endo-/lysosome due to the "proton-sponge" effect. The DOX molecules are controlled release from the carriers at specific pH values. The results demonstrate that DOX-PMs have the capability of showing high therapeutic efficacy and negligible cytotoxicity compared with free DOX in vitro and in vivo. Overall, we anticipate that this PEG-detachable and tumor-acidity-responsive polymeric micelle can mediate effective and biocompatible drug delivery "on demand" with clinical application potential.

Functional biomimetic nanoparticles for drug delivery and theranostic applications in cancer treatment

Nanotechnology has been extensively utilized in the design and development of powerful strategies for drug delivery and cancer theranostic. Nanoplatforms as a drug delivery system have many advantages such as in vivo imaging, combined drug delivery, extended circulation time, and systemic controlled release. The functional biomimetic drug delivery could be realized by incorporating stimuli-responsive (pH, temperature, redox potential, etc.) properties into the nanocarrier system, allowing them to bypass biological barriers and arrive at the targeted area. In this review, we discuss the role of internal stimuli-responsive nanocarrier system for imaging and drug delivery in cancer therapy. The development of internal stimuli-responsive nanoparticles is highlighted for precision drug delivery applications, with a particular focus on in vivo imaging, drug release performance, and therapeutic benefits.

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.

PDEAEMA-based pH-sensitive amphiphilic pentablock copolymers for controlled anticancer drug delivery

The synthesis of a series of PDEAEMA-based pH-sensitive amphiphilic pentablock copolymers PEG-b-(PDEAEMA-b-PMMA)₂ with different compositions proceeded via the combination of a bromination reaction andARGET ATRP.

Targeted therapy of colorectal neoplasia with rapamycin in peptide-labeled pegylated octadecyl lithocholate micelles

Many powerful drugs have limited clinical utility because of poor water solubility and high systemic toxicity. Here, we formulated a targeted nanomedicine, rapamycin encapsulated in pegylated octadecyl lithocholate micelles labeled with a new ligand for colorectal neoplasia, LTTHYKL peptide. CPC;Apc mice that spontaneously develop colonic adenomas were treated with free rapamycin, plain rapamycin micelles, and peptide-labeled rapamycin micelles via intraperitoneal injection for 35days. Endoscopy was performed to monitor adenoma regression in vivo. We observed complete adenoma regression at the end of therapy. The mean regression rate for peptide-labeled rapamycin micelles was significantly greater than that for plain rapamycin micelles, P<0.01. On immunohistochemistry, we observed a significant reduction in phospho-S6 but not β-catenin expression and reduced tumor cell proliferation, suggesting greater inhibition of downstream mTOR signaling. We observed significantly reduced renal toxicity for peptide-labeled rapamycin micelles compared to that of free drug, and no other toxicities were found on chemistries. Together, this unique targeted micelle represents a potential therapeutic for colorectal neoplasia with comparable therapeutic efficacy to rapamycin free drug and significantly less systemic toxicity.

pH-Responsive polymeric Janus containers for controlled drug delivery

In this study, we have successfully designed and fabricated pH-responsive polymeric Janus hollow spheres for controlled drug release.

Drug release from pH-sensitive polymeric micelles with different drug distributions: insight from coarse-grained simulations

How to control the release of drugs from pH-sensitive polymeric micelles is an issue of common concern, which is important to the effectiveness of the micelles. The components and properties of polymers can notably influence the drug distributions inside micelles which is a key factor that affects the drug release from the micelles. In this work, the dissipative particle dynamics simulation method is first used to study the structural transformation of micelles during the protonation process and the drug release process from micelles with different drug distributions. And then the effects of polymer structures, including different lengths of hydrophilic blocks, pH-sensitive blocks and hydrophobic blocks, on drug release are also studied. In the end, several corresponding design principles of pH-sensitive polymers for drug delivery are proposed according to the simulation results. This work is in favor of establishing qualitative rules for the design and optimization of congener polymers for desired drug delivery, which is of great significance to provide a potential approach for the development of new multiblock pH-sensitive polymeric micelles.

pH-responsive micelles based on (PCL)2(PDEA-b-PPEGMA)2 miktoarm polymer: controlled synthesis, characterization, and application as anticancer drug carrier

Amphiphilic A2(BC)2 miktoarm star polymers [poly(ϵ-caprolactone)]2-[poly(2-(diethylamino)ethyl methacrylate)-b- poly(poly(ethylene glycol) methyl ether methacrylate)]2 [(PCL)2(PDEA-b-PPEGMA)2] were developed by a combination of ring opening polymerization (ROP) and continuous activators regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP). The critical micelle concentration (CMC) values were extremely low (0.0024 to 0.0043 mg/mL), depending on the architecture of the polymers. The self-assembled empty and doxorubicin (DOX)-loaded micelles were spherical in morphologies, and the average sizes were about 63 and 110 nm. The release of DOX at pH 5.0 was much faster than that at pH 6.5 and pH 7.4. Moreover, DOX-loaded micelles could effectively inhibit the growth of cancer cells HepG2 with IC50 of 2.0 μg/mL. Intracellular uptake demonstrated that DOX was delivered into the cells effectively after the cells were incubated with DOX-loaded micelles. Therefore, the pH-sensitive (PCL)2(PDEA-b-PPEGMA)2 micelles could be a prospective candidate as anticancer drug carrier for hydrophobic drugs with sustained release behavior.

Cyclic RGD targeting nanoparticles with pH sensitive polymer–drug conjugates for effective treatment of melanoma

Cyclic RGD targeting polymeric nanomedicines prepared from pH sensitive polymer–drug conjugates for effective treatment of melanoma.

pH-sensitive amphiphilic copolymer brush Chol-g-P(HEMA-co-DEAEMA)-b-PPEGMA: synthesis and self-assembled micelles for controlled anti-cancer drug release

A novel pH-sensitive amphiphilic copolymer Chol-g-P(HEMA-co-DEAEMA)-b-PPEGMA and its micelles were developed as a promising anti-cancer drug carrier.

pH-sensitive nano-systems for drug delivery in cancer therapy

Nanotechnology has been widely used in the development of new strategies for drug delivery and cancer therapy. Compared to traditional drug delivery systems, nano-based drug delivery system have greater potential in a variety of areas, such as multiple targeting functionalization, in vivo imaging, combined drug delivery, extended circulation time, and systemic control release. Nano-systems incorporating stimulus-responsive materials have remarkable properties which allow them to bypass biological barriers and achieve targeted intracellular drug delivery. As a result of the active metabolism of tumor cells, the tumor microenvironment (TME) is highly acidic compared to normal tissues. pH-Sensitive nano-systems have now been developed in which drug release is specifically triggered by the acidic tumor environment. Studies have demonstrated that novel pH-sensitive drug delivery systems are capable of improving the efficiency of cancer treatment. A number of these have been translated from bench to clinical application and have been approved by the Food and Drug Administration (FDA) for treatment of various cancerous diseases. Herein, this review mainly focuses on pH-sensitive nano-systems, including advances in drug delivery, mechanisms of drug release, and possible improvements in drug absorption, with the emphasis on recent research in this field. With deeper understanding of the difference between normal and tumor tissues, it might be possible to design ever more promising pH-responsive nano-systems for drug delivery and cancer therapy in the near future.

Dissipative particle dynamics studies of doxorubicin-loaded micelles assembled from four-arm star triblock polymers 4AS-PCL-b-PDEAEMA-b-PPEGMA and their pH-release mechanism

Dissipative particle dynamics (DPD) simulation was applied to investigate the microstructures of the micelles self-assembled from pH-sensitive four-arm star triblock poly(ε-caprolactone)-b-poly(2-(diethylamino)ethyl methacrylate)-b-poly(poly(ethylene glycol) methyl ether methacrylate) (4AS-PCL-b-PDEAEMA-b-PPEGMA). In the optimized system, the micelles have a core-mesosphere-shell three-layer structure. The drug-loading process and its distribution at different formulations in the micelles were studied. The results show that DOX molecules distributed in the core and the interface between the core and the mesosphere, suggesting the potential encapsulation capacity of DOX molecules. More drugs were loaded in the micelles with the increase in DOX, and the size of micelles became larger. However, some openings start to generate on the PEG shell when the DOX reaches a certain concentration. By changing the pH values of the system, different morphologies of the micelles were acquired after the pH-sensitive blocks PDEAEMA were protonated, the mechanism of which was also analyzed through correlating functions. The results indicated that the sudden increase in solubility parameter of the pH-sensitive blocks and the swelling of the micelles were the key factors on the change of morphologies. Furthermore, with the decrease in pH value, the number and size of the cracks on the surface of the micelles were larger, which may have a direct effect on the drug release. In conclusion, 4AS-PCL-b-PDEAEMA-b-PPEGMA has great promising applications in delivering hydrophobic anticancer drugs for improved cancer therapy.

pH-sensitive micelles self-assembled from multi-arm star triblock co-polymers poly(ε-caprolactone)-b-poly(2-(diethylamino)ethyl methacrylate)-b-poly(poly(ethylene glycol) methyl ether methacrylate) for controlled anticancer drug delivery

A series of amphiphilic 4- and 6-armed star triblock co-polymers poly(ε-caprolactone)-b-poly(2-(diethylamino)ethyl methacrylate)-b-poly(poly(ethylene glycol) methyl ether methacrylate) (4/6AS-PCL-b-PDEAEMA-b-PPEGMA) were developed by a combination of ring opening polymerization and continuous activators regenerated by electron transfer atom transfer radical polymerization. The critical micelle concentration values of the star co-polymers in aqueous solution were extremely low (2.2-4.0mgl(-1)), depending on the architecture of the co-polymers. The self-assembled blank and doxorubicin (DOX)-loaded three layer micelles were spherical in shape with an average size of 60-220nm determined by scanning electron microscopy and dynamic light scattering. The in vitro release behavior of DOX from the three layer micelles exhibited pH-dependent properties. The DOX release rate was significantly accelerated by decreasing the pH from 7.4 to 5.0, due to swelling of the micelles at lower pH values caused by the protonation of tertiary amine groups in DEAEMA in the middle layer of the micelles. The in vitro cytotoxicity of DOX-loaded micelles to HepG2 cells suggested that the 4/6AS-PCL-b-PDEAEMA-b-PPEGMA micelles could provide equivalent or even enhanced anticancer activity and bioavailability of DOX and thus a lower dosage is sufficient for the same therapeutic efficacy. The results demonstrate that the pH-sensitive multilayer micelles could have great potential application in delivering hydrophobic anticancer drugs for improved cancer therapy.

Synthesis and physicochemical characterization of amphiphilic triblock copolymer brush containing pH-sensitive linkage for oral drug delivery

A novel and well-defined pH-sensitive amphiphilic triblock copolymer brush poly(lactide)-b-poly(methacrylic acid)-b-poly(poly(ethylene glycol) methyl ether monomethacrylate) (PLA-b-PMAA-b-PPEGMA) and its self-assembled micelles were developed for oral administration of hydrophobic drugs. The copolymer and its precursors were synthesized by the combination of activators regenerated by electron transfer atom transfer radical polymerization (ARGET ATRP) and ring-opening polymerization (ROP) techniques. The molecular structures and characteristics were confirmed by GPC, (1)H NMR, and FT-IR. The critical micelle concentration (CMC) values of PLA-b-PMAA-b-PPEGMA in aqueous medium varied from 1.4 to 2.6 mg/L, and the partition equilibrium constant (K(v)) of pyrene in micellar solutions ranged from 2.873 × 10(5) to 3.312 × 10(5). The average sizes of the self-assembled blank and drug-loaded micelles were 140-250 nm determined by DLS in aqueous solution. The morphology of the micelles was found to be spherical by SEM. Nifedipine (NFD), a poorly water-soluble drug, was selected as the model drug and wrapped into the core of micelles via dialysis method. The in vitro release behavior of NFD from the micelles was pH-dependent. In simulated gastric fluid (SGF, pH 1.2), the cumulative release percent of NFD was relative low, while in simulated intestinal fluid (SIF, pH 7.4), more than 96% was released within 24 h. All the results showed that the pH-sensitive PLA-b-PMAA-b-PPEGMA micelle may be a prospective candidate as oral drug delivery carrier for hydrophobic drugs with controlled release behavior.

Mesoscopic simulations on the aggregation behavior of pH-responsive polymeric micelles for drug delivery

Computer simulations, dissipative particle dynamics (DPD) and mesoscopic dynamics (MesoDyn), are performed to study the aggregation behavior of pH-sensitive micelles self-assembled from amphiphilic polymer poly(methyl methacrylate-co-methacrylic acid)-b-poly(poly-(ethylene glycol) methyl ether monomethacrylate), P(MMA-co-MAA)-b-PPEGMA. Ibuprofen (IBU) is selected as the model drug. It can be seen from DPD simulations that P(MMA-co-MAA)-b-PPEGMA and IBU form spherical core-shell micelles at certain compositions, and IBU molecules distribute inside the core formed by hydrophobic MMA. The polymer molecules aggregate first, and then IBU diffuses into the aggregate, forming drug-loaded nanoparticles. With different compositions of polymer and IBU, aggregate morphologies in water are observed as sphere, column and lamella. From MesoDyn results, with less hydrophobic MMA beads, the polymer chains are more difficult to form ordered aggregates, and the order parameters get equilibrated in a longer time. The pH value also affects the aggregate process. At pH<5, the polymer could form traditional core-shell micelles. But at pH>5, the morphology of micelles is found to be anomalous and loose for releasing drug. MAA aggregates on the surface, instead of the inside. The simulation results are qualitatively consistent with the experimental results.