Effect of alkyl length of peptide-polymer amphiphile on cargo encapsulation stability and pharmacokinetics of 3-helix micelles

Robust Electrochemical Biosensors Based on Antifouling Peptide Nanoparticles for Protein Quantification in Complex Biofluids

Peptides with distinct physiochemical properties and biocompatibility hold significant promise across diverse domains including antifouling biosensors. However, the stability of natural antifouling peptides in physiological conditions poses significant challenges to their viability for sustained practical applications. Herein, a unique antifouling peptide FFFGGGEKEKEKEK was designed and self-assembled to form peptide nanoparticles (PNPs), which possessed enhanced stability against enzymatic hydrolysis in biological fluids. The PNP-coated interfaces exhibited superior stability and antifouling properties in preventing adsorption of nonspecific materials, such as proteins and cells in biological samples. Moreover, a highly sensitive and ultralow fouling electrochemical biosensor was developed through the immobilization of the PNPs and specific aptamers onto the polyaniline nanowire-modified electrode, achieving the biomarker carcinoembryonic antigen detection in complex biofluids with reliable accuracy. This research not only addresses the challenge of the poor proteolytic resistance observed in natural peptides but also introduces a universal strategy for constructing ultralow fouling sensing devices.

Recent advances in coiled-coil peptide materials and their biomedical applications

Extensive research has gone into deciphering the sequence requirements for peptides to fold into coiled-coils of varying oligomeric states. More recently, additional signals have been introduced within coiled-coils to promote higher order assembly into biomaterials with a rich distribution of morphologies. Herein we describe these strategies for association of coiled-coil building blocks and biomedical applications. With many of the systems described herein having proven use in protein storage, cargo binding and delivery, three dimensional cell culturing and vaccine development, the future potential of coiled-coil materials to have significant biomedical impact is highly promising.

Recent advances in peptide-based nanomaterials for targeting hypoxia

Hypoxia is a prominent feature of many severe diseases such as malignant tumors, ischemic strokes, and rheumatoid arthritis. The lack of oxygen has a paramount impact on angiogenesis, invasion, metastasis, and chemotherapy resistance. The potential of hypoxia as a therapeutic target has been increasingly recognized over the last decade. In order to treat these disease states, peptides have been extensively investigated due to their advantages in safety, target specificity, and tumor penetrability. Peptides can overcome difficulties such as low drug/energy delivery efficiency, hypoxia-induced drug resistance, and tumor nonspecificity. There are three main strategies for targeting hypoxia through peptide-based nanomaterials: (i) using peptide ligands to target cellular environments unique to hypoxic conditions, such as cell surface receptors that are upregulated in cells under hypoxic conditions, (ii) utilizing peptide linkers sensitive to the hypoxic microenvironment that can be cleaved to release therapeutic or diagnostic payloads, and (iii) a combination of the above where targeting peptides will localize the system to a hypoxic environment for it to be selectively cleaved to release its payload, forming a dual-targeting system. This review focuses on recent developments in the design and construction of novel peptide-based hypoxia-targeting nanomaterials, followed by their mechanisms and potential applications in diagnosis and treatment of hypoxic diseases. In addition, we address challenges and prospects of how peptide-based hypoxia-targeting nanomaterials can achieve a wider range of clinical applications.

Designing sub-20 nm self-assembled nanocarriers for small molecule delivery: Interplay among structural geometry, assembly energetics, and cargo release kinetics

Biological constraints in diseased tissues have motivated the need for small nanocarriers (10-30 nm) to achieve sufficient vascular extravasation and pervasive tumor penetration. This particle size limit is only an order of magnitude larger than small molecules, such that cargo loading is better described by co-assembly processes rather than simple encapsulation. Understanding the structural, kinetic, and energetic contributions of carrier-cargo co-assembly is thus critical to achieve molecular-level control towards predictable in vivo behavior. These interconnected set of properties were systematically examined using sub-20 nm self-assembled nanocarriers known as three-helix micelles (3HM). Both hydrophobicity and the "geometric packing parameter" dictate small molecule compatibility with 3HM's alkyl tail core. Planar obelisk-like apomorphine and doxorubicin (DOX) molecules intercalated well within the 3HM core and near the core-shell interface, forming an integral component to the co-assembly, as corroborated by small-angle X-ray and neutron-scattering structural studies. DOX promoted crystalline alkyl tail ordering, which significantly increased (+63%) the activation energy of 3HM subunit exchange. Subsequently, 3HM-DOX displayed slow-release kinetics (t_1/2 = 40 h) at physiological temperatures, with ~50× greater cargo preference for the micelle core as described by two drug partitioning coefficients (micellar core/shell K_p1 ~ 24, and shell/bulk solvent K_p2 ~ 2). The geometric and energetic insights between nanocarrier and their small molecule cargos developed here will aid in broader efforts to deconvolute the interconnected properties of carrier-drug co-assemblies. Adding this knowledge to pharmacological and immunological explorations will expand our understanding of nanomedicine behavior throughout all the physical and in vivo processes they are intended to encounter.

Design of 18 nm Doxorubicin-Loaded 3-Helix Micelles: Cellular Uptake and Cytotoxicity in Patient-Derived GBM6 Cells

The fate of nanocarrier materials at the cellular level constitutes a critical checkpoint in the development of effective nanomedicines, determining whether tissue level accumulation results in therapeutic benefit. The cytotoxicity and cell internalization of ∼18 nm 3-helix micelle (3HM) loaded with doxorubicin (DOX) were analyzed in patient-derived glioblastoma (GBM) cells in vitro. The half-maximal inhibitory concentration (IC₅₀) of 3HM-DOX increased to 6.2 μg/mL from <0.5 μg/mL for free DOX in patient-derived GBM6 cells, to 15.0 μg/mL from 6.5 μg/mL in U87MG cells, and to 21.5 μg/mL from ∼0.5 μg/mL in LN229 cells. Modeling analysis of previous 3HM biodistribution results predicts that these cytotoxic concentrations are achievable with intravenous injection in rodent GBM models. 3HM-DOX formulations were internalized intact and underwent intracellular trafficking distinct from free DOX. 3HM was quantified to have an internalization half-life of 12.6 h in GBM6 cells, significantly longer than that reported for some liposome and polymer systems. 3HM was found to traffic through active endocytic processes, with clathrin-mediated endocytosis being the most involved of the pathways studied. Inhibition studies suggest substantial involvement of receptor recognition in 3HM uptake. As the 3HM surface is PEG-ylated with no targeting functionalities, protein corona-cell surface interactions, such as the apolipoprotein-low-density lipoprotein receptor, are expected to initiate internalization. The present work gives insights into the cytotoxicity, pharmacodynamics, and cellular interactions of 3HM and 3HM-DOX relevant for ongoing preclinical studies. This work also contributes to efforts to develop predictive mathematical models tracking the accumulation and biodistribution kinetics at a systemic level.

Molecular Modeling and Simulations of Peptide–Polymer Conjugates

Peptide–polymer conjugates are a class of soft materials composed of covalently linked blocks of protein/polypeptides and synthetic/natural polymers. These materials are practically useful in biological applications, such as drug delivery, DNA/gene delivery, and antimicrobial coatings, as well as nonbiological applications, such as electronics, separations, optics, and sensing. Given their broad applicability, there is motivation to understand the molecular and macroscale structure, dynamics, and thermodynamic behavior exhibited by such materials. We focus on the past and ongoing molecular simulation studies aimed at obtaining such fundamental understanding and predicting molecular design rules for the target function. We describe briefly the experimental work in this field that validates or motivates these computational studies. We also describe the various models (e.g., atomistic, coarse-grained, or hybrid) and simulation methods (e.g., stochastic versus deterministic, enhanced sampling) that have been used and the types of questions that have been answered using these computational approaches.

Transition of Nano-Architectures Through Self-Assembly of Lipidated β3-Tripeptide Foldamers

β³-peptides consisting exclusively of β³-amino acids adopt a variety of non-natural helical structures and can self-assemble into well-defined hierarchical structures by axial head-to-tail self-assembly resulting in fibrous materials of varying sizes and shapes. To allow control of fiber morphology, a lipid moiety was introduced within a tri-β³-peptide sequence at each of the three amino acid positions and the N-terminus to gain finer control over the lateral assembly of fibers. Depending on the position of the lipid, the self-assembled structures formed either twisted ribbon-like fibers or distinctive multilaminar nanobelts. The nanobelt structures were comprised of multiple layers of peptide fibrils as revealed by puncturing the surface of the nanobelts with an AFM probe. This stacking phenomenon was completely inhibited through changes in pH, indicating that the layer stacking was mediated by electrostatic interactions. Thus, the present study is the first to show controlled self-assembly of these fibrous structures, which is governed by the location of the acyl chain in combination with the 3-point H-bonding motif. Overall, the results demonstrate that the nanostructures formed by the β³-tripeptide foldamers can be tuned via sequential lipidation of N-acetyl β³-tripeptides which control the lateral interactions between peptide fibrils and provide defined structures with a greater homogeneous population.

Stable micelles based on a mixture of coiled-coils: the role of different oligomeric states

Homomeric micelles with tunable size, shape and stability have been extensively studied for biomedical applications such as drug carriers. However, designing the local valency and self-assembled morphology of nanophase-separated multicomponent micelles with varied ligand binding possibilities remains challenging. Here, we present micelles self-assembled from amphiphilic peptide-PEG-lipid hybrid conjugates, where the peptides can be either a 3-helix or 4-helix coiled-coil. We demonstrate that the micelle size and sphericity can be controlled based on the coiled-coil oligomeric state. Using theory and coarse-grained dissipative particle dynamics (DPD) simulations in an explicit solvent simulation, we studied the distribution of 3-helix and 4-helix conjugates within the mixed micelles and observed self-organization into nanodomains within the mixed micelle. We discovered that the phase separation behavior is dictated by the geometry mismatch in the alkyl chain length from different coiled-coil oligomeric states. Our analyses of the self-assembly tendency and drug delivery potency of mixed micelles with controlled multivalency provide important insights into the assembly and formation of nanophase-separated micelles.

Importance of Evaluating Dynamic Encapsulation Stability of Amphiphilic Assemblies in Serum

In targeted drug delivery systems, it is desirable that the delivery of hydrophobic drugs to a cell or tissue is achieved with little to no side effects. To ensure that the drugs do not leak during circulation, encapsulation stability of the drug carrier in serum is critical. In this paper, we report on a modified FRET-based method to evaluate encapsulation stability of amphiphilic assemblies and cross-linked polymer assemblies in serum. Our results show that serum components can act as reservoirs for hydrophobic molecules. We also show that serum albumin is likely to be the primary determinant of this property. This work highlights the importance of assessing encapsulation stability in terms of dynamics of guest molecules, as it provides the critical distinction between hydrophobic molecules bound inside amphiphilic assemblies and the molecules that are bound to the hydrophobic pockets of serum albumin.

Responsive Hybrid (Poly)peptide-Polymer Conjugates

(Poly)peptide-polymer conjugates continue to garner significant interest in the production of functional materials given their composition of natural and synthetic building blocks that confer select and synergistic properties. Owing to opportunities to design predefined architectures and structures with different morphologies, these hybrid conjugates enable new approaches for producing micro- or nanomaterials. Their modular design enables the incorporation of multiple responsive properties into a single conjugate. This review presents recent advances in (poly)peptide-polymer conjugates for drug-delivery applications, with a specific focus on the utility of the (poly)peptide component in the assembly of particles and nanogels, as well as the role of the peptide in triggered drug release.

pH-responsive nanoparticle assembly from peptide amphiphiles for tumor targeting drug delivery

In this paper, the peptide amphiphiles (PA) which consists of RGDSEEEEEEEEEEK as pH-sensitive segment and stearic acid as hydrophobic segment named RGDS-E₁₀-Lys(C₁₈) was successfully synthesized. TEM images showed that uniformly dispersed nanoparticles could be formed by PA molecules in pH 7.4 medium, however, disintegrated in pH 5.0 medium. Circular dichroism (CD) spectrum indicated that polypeptide adopted a random-coil conformation in neutral medium (pH 7.4). The CD signal was significantly attenuate for decreased solubility of PA in medium with pH 5.0. As expected, the prepared RGDS-E₁₀-Lys(C₁₈) assembly showed high pH-sensitive property which demonstrated a much more rapid drug release from micelles in tumor tissue (acidic environment) than in physiological environment (neutral environment). After DOX-loaded micelles incubated with tumor cells, the cytotoxicity of the micelles against Hela cells was increased obviously, indicating the great potential of micelles developed here as promising vehicle for targeted pH-responsive drug delivery.

The power of the ring: a pH-responsive hydrophobic epoxide monomer for superior micelle stability

We developed micelles with superior stability by integrating a novel hydrophobic, pH-responsive epoxide monomer, tetrahydropyranyl glycidyl ether.

Understanding Peptide Oligomeric State in Langmuir Monolayers of Amphiphilic 3-Helix Bundle-Forming Peptide-PEG Conjugates

Coiled-coil peptide-polymer conjugates are an emerging class of biomaterials. Fundamental understanding of the coiled-coil oligomeric state and assembly process of these hybrid building blocks is necessary to exert control over their assembly into well-defined structures. Here, we studied the effect of peptide structure and PEGylation on the self-assembly process and oligomeric state of a Langmuir monolayer of amphiphilic coiled-coil peptide-polymer conjugates using X-ray reflectivity (XR) and grazing-incidence X-ray diffraction (GIXD). Our results show that the oligomeric state of PEGylated amphiphiles based on 3-helix bundle-forming peptide is surface pressure dependent, a mixture of dimers and trimers was formed at intermediate surface pressure but transitions into trimers completely upon increasing surface pressure. Moreover, the interhelical distance within the coiled-coil bundle of 3-helix peptide-PEG conjugate amphiphiles was not perturbed under high surface pressure. Present studies provide valuable insights into the self-assembly process of hybrid peptide-polymer conjugates and guidance to develop biomaterials with controlled multivalency of ligand presentation.

Cancer-Targeted Nanotheranostics: Recent Advances and Perspectives

Cancer-targeted nanotechnology is experiencing the trend of finding new materials with multiple functions for imaging and therapeutic applications. With the rapid development of the related fields, there exists a large number of reports regarding theranostic nanomedicine, decreasing the gap between cancer diagnosis and treatment with minimized separate comprehensions. In order to present an overview on the cancer-targeted nanotheranostics, we first describe their essential building blocks, including platforms, therapeutic agents and imaging agents, and then the recently rapidly developed multimodal theranostic systems. Finally we discuss the major challenges and the perspectives of future development of nanotheranostics toward clinical translations and personalized nanomedicine.

Fluorophore exchange kinetics in block copolymer micelles with varying solvent-fluorophore and solvent-polymer interactions

Fluorescence spectroscopy was employed to characterize the kinetics of guest exchange in diblock copolymer micelles composed of poly(ethylene oxide-b-ε-caprolactone) (PEO-PCL) diblock copolymers in water/tetrahydrofuran (THF) mixtures which encapsulated fluorophores. The solvent composition (THF content) of the micelle solution was varied as a means of modulating the strength of interactions between the fluorophore and solvent as well as between the micelle core and solvent. A donor-acceptor fluorophore pair was employed consisting of 3,3'-dioctadecyloxacarbocyanine perchlorate (DiO, the donor) and 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI, the acceptor). Through the process of Förster resonance energy transfer (FRET), energy was transferred from the donor to acceptor when the fluorophores were in close proximity. A micelle solution containing DiO was mixed with a micelle solution containing DiI at t = 0, and the emission spectra of the mixed solution were monitored over time (at an excitation wavelength optimized for the donor). In micelle solutions containing 5 and 10 vol% THF in the bulk solvent, an increase in the acceptor peak intensity maximum occurred over time in the post-mixed solution, accompanied by a decrease in the donor peak intensity maximum, indicating the presence of energy transfer from the donor to the acceptor. At long times, the FRET ratios (acceptor peak intensity divided by the sum of the acceptor and donor peak intensities) were indistinguishable from that determined from pre-mixed micelle solutions of the same THF content (in pre-mixed solutions, DiO and DiI were encapsulated within the same micelle cores). In the micelle solution containing 20 vol% THF, the fluorophore exchange process occurred too quickly to be observed (the FRET ratios measured from the solutions mixed at t = 0 were commensurate to that measured from the pre-mixed solution). A time constant describing the guest exchange process was extracted from the time-dependence of the FRET ratio through fit of an exponential decay. An increase in the THF content in the micelle solution resulted in a decrease in the time constant, and the time constant varied over five orders of magnitude as the THF content was varied from 5-20 vol%.

Self-assembled 20-nm (64)Cu-micelles enhance accumulation in rat glioblastoma

There is an urgent need to develop nanocarriers for the treatment of glioblastoma multiforme (GBM). Using co-registered positron emission tomography (PET) and magnetic resonance (MR) images, here we performed systematic studies to investigate how a nanocarrier's size affects the pharmacokinetics and biodistribution in rodents with a GBM xenograft. In particular, highly stable, long-circulating three-helix micelles (3HM), based on a coiled-coil protein tertiary structure, were evaluated as an alternative to larger nanocarriers. While the circulation half-life of the 3HM was similar to 110-nm PEGylated liposomes (t1/2=15.5 and 16.5h, respectively), the 20-nm micelles greatly enhanced accumulation within a U87MG xenograft in nu/nu rats after intravenous injection. After accounting for tumor blood volume, the extravasated nanoparticles were quantified from the PET images, yielding ~0.77%ID/cm(3) for the micelles and 0.45%ID/cm(3) for the liposomes. For GBM lesions with a volume greater than 100mm(3), 3HM accumulation was enhanced both within the detectable tumor and in the surrounding brain parenchyma. Further, the nanoparticle accumulation was shown to extend to the margins of the GBM xenograft. In summary, 3HM provides an attractive nanovehicle for carrying treatment to GBM.

Micelle stabilization via entropic repulsion: balance of force directionality and geometric packing of subunit

Nanoparticles, 10-30 nm in size, have shown great prospects as nanocarriers for drug delivery. We designed amphiphiles based on 3-helix peptide-PEG conjugate forming 15 nm micelles (defined as "3-helix micelles") with good in vivo stability. Here, we investigated the effect of the site of PEG conjugation on the kinetic stability and showed that the conjugation site affects the PEG chain conformation and the overall molecular architecture of the subunit. Compared to the original design where the PEG chain is located in the middle of the 3-helix bundle, micelle kinetic stability was reduced when the PEG chain was attached near the N-terminus (t(1/2) = 35 h) but was enhanced when the PEG chain was attached near the C-terminus (t(1/2) = 80 h). Quantitative structural and kinetic analysis suggest that the kinetic stability was largely dictated by the combined effects of entropic repulsion associated with PEG chain conformation and the geometric packing of the trimeric subunits. The modular design approach coupled with a variety of well-defined protein stucture and functional polymers will significantly expand the utility of these materials as nanocarriers to meet current demands in nanomedine.

Synergistic effect of sandwich polyoxometalates and copper–imidazole complexes for enhancing the peroxidase-like activity

Two inorganic–organic hybrids based on copper(ii)–imidazole complex modified sandwich-type tungstobismuthate or tungstoantimonite, have been synthesized, demonstrating higher peroxidase-like activity using TMB as a peroxidase substrate.

Solvent effects on kinetic mechanisms of self-assembly by peptide amphiphiles via molecular dynamics simulations

Peptide amphiphiles are known to form a variety of distinctive self-assembled nanostructures (including cylindrical nanofibers in hydrogels) dependent upon the solvent conditions. Using a novel coarse-grained model, large-scale molecular dynamics simulations are performed on a system of 800 peptide amphiphiles (sequence, palmitoyl-Val3Ala3Glu3) to elucidate kinetic mechanisms of molecular assembly as a function of the solvent conditions. The assembly process is found to occur via a multistep process with transient intermediates that ultimately leads to the stabilized nanostructures including open networks of β-sheets, cylindrical nanofibers, and elongated micelles. Different kinetic mechanisms are compared in terms of peptide secondary structures, solvent-accessible surface area, radius of gyration, relative shape anisotropy, intra/intermolecular interactions, and aggregate size dynamics to provide insightful information for the design of functional biomaterials.