Structural plasticity of a transmembrane peptide allows self-assembly into biologically active nanoparticles

Peptide-Based Agents for Cancer Treatment: Current Applications and Future Directions

Peptide-based strategies have received an enormous amount of attention because of their specificity and applicability. Their specificity and tumor-targeting ability are applied to diagnosis and treatment for cancer patients. In this review, we will summarize recent advancements and future perspectives on peptide-based strategies for cancer treatment. The literature search was conducted to identify relevant articles for peptide-based strategies for cancer treatment. It was performed using PubMed for articles in English until June 2023. Information on clinical trials was also obtained from ClinicalTrial.gov. Given that peptide-based strategies have several advantages such as targeted delivery to the diseased area, personalized designs, relatively small sizes, and simple production process, bioactive peptides having anti-cancer activities (anti-cancer peptides or ACPs) have been tested in pre-clinical settings and clinical trials. The capability of peptides for tumor targeting is essentially useful for peptide-drug conjugates (PDCs), diagnosis, and image-guided surgery. Immunomodulation with peptide vaccines has been extensively tested in clinical trials. Despite such advantages, FDA-approved peptide agents for solid cancer are still limited. This review will provide a detailed overview of current approaches, design strategies, routes of administration, and new technological advancements. We will highlight the success and limitations of peptide-based therapies for cancer treatment.

Peptide-assembled nanoparticles targeting tumor cells and tumor microenvironment for cancer therapy

Tumor cells and corrupt stromal cells in the tumor microenvironment usually overexpress cancer-specific markers that are absent or barely detectable in normal cells, providing available targets for inhibiting the occurrence and development of cancers. It is noticeable that therapeutic peptides are emerging in cancer therapies and playing more and more important roles. Moreover, the peptides can be self-assembled and/or incorporated with polymeric molecules to form nanoparticles via non-covalent bond, which have presented appealing as well as enhanced capacities of recognizing targeted cells, responding to microenvironments, mediating internalization, and achieving therapeutic effects. In this review, we will introduce the peptide-based nanoparticles and their application advances in targeting tumor cells and stromal cells, including suppressive immune cells, fibrosis-related cells, and angiogenic vascular cells, for cancer therapy.

A Three-In-One Assembled Nanoparticle Containing Peptide-Radio-Sensitizer Conjugate and TLR7/8 Agonist Can Initiate the Cancer-Immunity Cycle to Trigger Antitumor Immune Response

Radiotherapy (RT) has been shown to cause immunogenic cell death (ICD) of cancer cells, which promote the release of tumor-associated antigens, and trigger the cancer-immunity cycle (CIC). However, ICD induced by RT usually does not occur in hypoxic tumor cells due to their resistance to radiation. Moreover, RT also induces programmed death ligand 1 (PD-L1) upregulation on tumor cells, which has an inhibitory effect on T lymphocytes. Therefore, therapy based on CIC must selectively target the restricted steps of antitumor immunity. Herein, the authors design a versatile three-in-one assembling nanoparticle that can simultaneously execute these obstacles. The amphiphilic peptide drug conjugate NIA-D1, containing the hydrophobic radio-sensitizer 2-(2-nitroimidazol-1-yl) acetic acid (NIA), a peptide substrate of matrix metalloproteinase-2, and a hydrophilic PD-L1 antagonist ^D PPA-1, is constructed and co-assembled with hydrophobic Toll-like receptor (TLR) 7/8 agonist R848 to form nanoparticle NIA-D1@R848. The NIA-D1@R848 nanoparticles combined with RT can trigger the apoptosis of tumor cells and initiate the CIC. In the presence of R848, it promotes the maturation of dendritic cells, which together with protein programmed cell death protein 1 (PD-1) and its ligand PD-L1  blockade to relieve T cell suppression, and amplify the antitumor immune cycle. In conclusion, a functionalized three-in-one nanoparticle NIA-D1@R848 is successfully constructed, which can induce strong systemic antitumor immune response.

Biomaterials via peptide assembly: Design, characterization, and application in tissue engineering

A core challenge in biomaterials, with both fundamental significance and technological relevance, concerns the rational design of bioactive microenvironments. Designed properly, peptides can undergo supramolecular assembly into dynamic, physical hydrogels that mimic the mechanical, topological, and biochemical features of native tissue microenvironments. The relatively facile, inexpensive, and automatable preparation of peptides, coupled with low batch-to-batch variability, motivates the expanded use of assembling peptide hydrogels for biomedical applications. Integral to realizing dynamic peptide assemblies as functional biomaterials for tissue engineering is an understanding of the molecular and macroscopic features that govern assembly, morphology, and biological interactions. In this review, we first discuss the design of assembling peptides, including primary structure (sequence), secondary structure (e.g., α-helix and β-sheets), and molecular interactions that facilitate assembly into multiscale materials with desired properties. Next, we describe characterization tools for elucidating molecular structure and interactions, morphology, bulk properties, and biological functionality. Understanding of these characterization methods enables researchers to access a variety of approaches in this ever-expanding field. Finally, we discuss the biological properties and applications of peptide-based biomaterials for engineering several important tissues. By connecting molecular features and mechanisms of assembling peptides to the material and biological properties, we aim to guide the design and characterization of peptide-based biomaterials for tissue engineering and regenerative medicine. STATEMENT OF SIGNIFICANCE: Engineering peptide-based biomaterials that mimic the topological and mechanical properties of natural extracellular matrices provide excellent opportunities to direct cell behavior for regenerative medicine and tissue engineering. Here we review the molecular-scale features of assembling peptides that result in biomaterials that exhibit a variety of relevant extracellular matrix-mimetic properties and promote beneficial cell-biomaterial interactions. Aiming to inspire and guide researchers approaching this challenge from both the peptide biomaterial design and tissue engineering perspectives, we also present characterization tools for understanding the connection between peptide structure and properties and highlight the use of peptide-based biomaterials in neural, orthopedic, cardiac, muscular, and immune engineering applications.

Factors Affecting Secondary and Supramolecular Structures of Self-Assembling Peptide Nanocarriers

Self-assembling peptides are a popular vector for therapeutic cargo delivery due to their versatility, tunability, and biocompatibility. Accurately predicting secondary and supramolecular structures of self-assembling peptides is essential for de novo peptide design. However, computational modeling of such assemblies is not yet able to accurately predict structure formation for many peptide sequences. This review identifies patterns in literature between secondary and supramolecular structures, primary sequences, and applications to provide a guide for informed peptide design. An overview of peptide structures, their applications as nanocarriers, and analytical methods for characterizing secondary and supramolecular structure is examined. A top-down approach is then used to identify trends between peptide sequence and assembly structure from the current literature, including an analysis of the drivers at work, such as local and nonlocal sequence effects and solution conditions.

Design and Generation of Self-Assembling Peptide Virus-like Particles with Intrinsic GPCR Inhibitory Activity

Synthetic analogs of the second transmembrane domain (TM) containing a portion of the extracellular loop 1 of G-protein-coupled receptors (GPCR) can serve as biased antagonists of the corresponding receptor. Analogs with negative charges added to the extracellular end self-assemble into round structures. Addition of polyethylene glycol chains of defined length to the C-terminus of the peptides prevents super aggregation and results in highly uniform particles that can fuse with cell membranes spontaneously. Added PEG chains slow down cell fusion, while attachment of receptor ligands to the surface of particles results in receptor-mediated membrane fusion and cell-selective delivery. Critical assembly concentration of TM peptide particles is in the nanomolar range and thus requires nontraditional methods of determination. In this chapter, we outline sequence selection and design of self-assembling GPCR antagonists, methods of the preparation of the nanoparticles, and biophysical methods of particle characterization. The protocols allow for straightforward rational design, generation, and characterization of self-assembling GPCR antagonists for a variety of applications.

Targeting CXCR4 in AML and ALL

The interaction of acute myeloid leukemia (AML) and acute lymphoblastic leukemia (ALL) blasts with the bone marrow microenvironment regulates self-renewal, growth signaling, as well as chemotherapy resistance. The chemokine receptor, CXC receptor 4 (CXCR4), with its ligand chemokine ligand 12 (CXCL12), plays a key role in the survival and migration of normal and malignant stem cells to the bone marrow. High expression of CXCR4 on AML and ALL blasts has been shown to be a predictor of poor prognosis for these diseases. Several small molecule inhibitors, short peptides, antibodies, and antibody drug conjugates have been developed for the purposes of more effective targeting and killing of malignant cells expressing CXCR4. In this review we will discuss recent results and strategies in targeting CXCR4 with these agents in patients with AML or ALL.

Regulation of the thrombin/protease-activated receptor 1 axis by chemokine (CXC motif) receptor 4

The chemokine receptor CXCR4, a G protein-coupled receptor (GPCR) capable of heteromerizing with other GPCRs, is involved in many processes, including immune responses, hematopoiesis, and organogenesis. Evidence suggests that CXCR4 activation reduces thrombin/protease-activated receptor 1 (PAR1)-induced impairment of endothelial barrier function. However, the mechanisms underlying cross-talk between CXCR4 and PAR1 are not well-understood. Using intermolecular bioluminescence resonance energy transfer and proximity ligation assays, we found that CXCR4 heteromerizes with PAR1 in the HEK293T expression system and in human primary pulmonary endothelial cells (hPPECs). A peptide analog of transmembrane domain 2 (TM2) of CXCR4 interfered with PAR1:CXCR4 heteromerization. In HTLA cells, the presence of CXCR4 reduced the efficacy of thrombin to induce β-arrestin-2 recruitment to recombinant PAR1 and enhanced thrombin-induced Ca²⁺ mobilization. Whereas thrombin-induced extracellular signal-regulated protein kinase 1/2 (ERK1/2) phosphorylation occurred more transiently in the presence of CXCR4, peak ERK1/2 phosphorylation was increased when compared with HTLA cells expressing PAR1 alone. CXCR4-associated effects on thrombin-induced β-arrestin-2 recruitment to and signaling of PAR1 could be reversed by TM2. In hPPECs, TM2 inhibited thrombin-induced ERK1/2 phosphorylation and activation of Ras homolog gene family member A. CXCR4 siRNA knockdown inhibited thrombin-induced ERK1/2 phosphorylation. Whereas thrombin stimulation reduced surface expression of PAR1, CXCR4, and PAR1:CXCR4 heteromers, chemokine (CXC motif) ligand 12 stimulation reduced surface expression of CXCR4 and PAR1:CXCR4 heteromers, but not of PAR1. Finally, TM2 dose-dependently inhibited thrombin-induced impairment of hPPEC monolayer permeability. Our findings suggest that CXCR4:PAR1 heteromerization enhances thrombin-induced G protein signaling of PAR1 and PAR1-mediated endothelial barrier disruption.

Investigation of α/γ hybrid peptide self-assembled structures with antimicrobial and antibiofilm properties

The present work describes the synthesis and characterization of α/γ hybrid peptides, Boc-Phe-γ⁴ -Phe-Val-OMe, P1; Boc-Ala-γ⁴ -Phe-Val-OMe, P2; and Boc-Leu-γ⁴ -Phe-Val-OMe, P3 together with the formation of self-assembled structures formed by these hybrid peptides in dimethyl sulfoxide (DMSO)/water (1:1). The self-assembled structures were characterized by infrared (IR) spectroscopy, circular dichroism (CD), and scanning electron microscopy (SEM). Further, α/γ hybrid peptide self-assembled structures were evaluated for antibacterial properties. Among all, the self-assembled peptide P1 exhibited the antimicrobial activity against Escherichia coli and Klebsiella pneumoniae, while self-assembled peptide P3 inhibited the biofilms of Salmonella typhimurium and Pseudomonas aeruginosa. In this study, we have shown the significance of self-assembled structures formed from completely hydrophobic α/γ hybrid peptides in exploring the antibacterial properties together with biofilm inhibition.

Engineering Chirally Blind Protein Pseudocapsids into Antibacterial Persisters

Antimicrobial resistance stimulates the search for antimicrobial forms that may be less subject to acquired resistance. Here we report a conceptual design of protein pseudocapsids exhibiting a broad spectrum of antimicrobial activities. Unlike conventional antibiotics, these agents are effective against phenotypic bacterial variants, while clearing "superbugs" in vivo without toxicity. The design adopts an icosahedral architecture that is polymorphic in size, but not in shape, and that is available in both l and d epimeric forms. Using a combination of nanoscale and single-cell imaging we demonstrate that such pseudocapsids inflict rapid and irreparable damage to bacterial cells. In phospholipid membranes they rapidly convert into nanopores, which remain confined to the binding positions of individual pseudocapsids. This mechanism ensures precisely delivered influxes of high antimicrobial doses, rendering the design a versatile platform for engineering structurally diverse and functionally persistent antimicrobial agents.

Characterization of heteromeric complexes between chemokine (C-X-C motif) receptor 4 and α1-adrenergic receptors utilizing intermolecular bioluminescence resonance energy transfer assays

Recently, we reported that chemokine (C-X-C motif) receptor 4 (CXCR4) heteromerizes with α₁-adrenergic receptors (AR) on the cell surface of vascular smooth muscle cells, through which the receptors cross-talk. Direct biophysical evidence for CXCR4:α₁-AR heteromers, however, is lacking. Here we utilized bimolecular luminescence/fluorescence complementation (BiLC/BiFC) combined with intermolecular bioluminescence resonance energy transfer (BRET) assays in HEK293T cells to evaluate CXCR4:α_1a/b/d-AR heteromerization. Atypical chemokine receptor 3 (ACKR3) and metabotropic glutamate receptor 1 (mGlu₁R) were utilized as controls. BRET between CXCR4-RLuc (Renilla reniformis) and enhanced yellow fluorescent protein (EYFP)-tagged ACKR3 or α_1a/b/d-ARs fulfilled criteria for constitutive heteromerization. BRET between CXCR4-RLuc and EYFP or mGlu₁R-EYFP were nonspecific. BRET₅₀ for CXCR4:ACKR3 and CXCR4:α_1a/b/d-AR heteromers were comparable. Stimulation of cells with phenylephrine increased BRET_max of CXCR4:α_1a/b/d-AR heteromers without affecting BRET₅₀; stimulation with CXCL12 reduced BRET_max of CXCR4:α_1a-AR heteromers, but did not affect BRET₅₀ or BRET_max/50 for CXCR4:α_1b/d-AR. A peptide analogue of transmembrane domain (TM) 2 of CXCR4 reduced BRET_max of CXCR4:α_1a/b/d-AR heteromers and increased BRET₅₀ of CXCR4:α_1a/b-AR interactions. A TM4 analogue of CXCR4 did not alter BRET. We observed CXCR4, α_1a-AR and mGlu₁R homodimerization by BiFC/BiLC, and heteromerization of homodimeric CXCR4 with proto- and homodimeric α_1a-AR by BiFC/BiLC BRET. BiFC/BiLC BRET for interactions between homodimeric CXCR4 and homodimeric mGlu₁R was nonspecific. Our findings suggest that the heteromerization affinity of CXCR4 for ACKR3 and α₁-ARs is comparable, provide evidence for conformational changes of the receptor complexes upon agonist binding and support the concept that proto- and oligomeric CXCR4 and α₁-ARs constitutively form higher-order hetero-oligomeric receptor clusters.

Self-Assembled Nanoparticles of Symmetrical Cationic Peptide Against Citrus Pathogenic Bacteria

The increasing drug resistance of phytopathogenic bacteria to conventional bactericides has driven the necessity for exploring new alternatives with a lower tendency to develop bacterial resistance. Here, we report a novel cationic symmetrical peptide P₅VP₅ (Ac- R+ LI R+ K+ V K+ R+ IL R+ -NH₂ that enables self-assembly to form nanoparticles with excellent thermal stability. An in vitro assay showed that P₅VP₅ nanoparticles exhibited excellent antibacterial activity against Xanthomonas axonopodis pv citri with a MIC value of 20 μM. Meanwhile, under an in planta condition, treatment with peptide nanoparticles demonstrated the highest ability to reduce the development of citrus canker lesions in leaves. Moreover, the nanoparticles could destroy the biofilm formation, damage the cell membranes, and affect the cell membrane permeability, ultimately leading to the death of bacteria. Taken together, these nanoparticles are a promising antibacterial agent that can be used to control citrus canker and other plant diseases caused by bacteria.

Identification and functional characterization of arginine vasopressin receptor 1A : atypical chemokine receptor 3 heteromers in vascular smooth muscle

Recent observations suggest that atypical chemokine receptor (ACKR)3 and chemokine (C-X-C motif) receptor (CXCR)4 regulate human vascular smooth muscle function through hetero-oligomerization with α₁-adrenoceptors. Here, we show that ACKR3 also regulates arginine vasopressin receptor (AVPR)1A. We observed that ACKR3 agonists inhibit arginine vasopressin (aVP)-induced inositol trisphosphate (IP₃) production in human vascular smooth muscle cells (hVSMCs) and antagonize aVP-mediated constriction of isolated arteries. Proximity ligation assays, co-immunoprecipitation and bioluminescence resonance energy transfer experiments suggested that recombinant and endogenous ACKR3 and AVPR1A interact on the cell surface. Interference with ACKR3 : AVPR1A heteromerization using siRNA and peptide analogues of transmembrane domains of ACKR3 abolished aVP-induced IP₃ production. aVP stimulation resulted in β-arrestin 2 recruitment to AVPR1A and ACKR3. While ACKR3 activation failed to cross-recruit β-arrestin 2 to AVPR1A, the presence of ACKR3 reduced the efficacy of aVP-induced β-arrestin 2 recruitment to AVPR1A. AVPR1A and ACKR3 co-internalized upon agonist stimulation in hVSMC. These data suggest that AVPR1A : ACKR3 heteromers are constitutively expressed in hVSMC, provide insights into molecular events at the heteromeric receptor complex, and offer a mechanistic basis for interactions between the innate immune and vasoactive neurohormonal systems. Our findings suggest that ACKR3 is a regulator of vascular smooth muscle function and a possible drug target in diseases associated with impaired vascular reactivity.

Novel peptide nanoparticle-biased antagonist of CCR3 blocks eosinophil recruitment and airway hyperresponsiveness

BACKGROUND

Chemokine signaling through CCR3 is a key regulatory pathway for eosinophil recruitment into tissues associated with allergic inflammation and asthma. To date, none of the CCR3 antagonists have shown efficacy in clinical trials. One reason might be their unbiased mode of inhibition that prevents receptor internalization, leading to drug tolerance.

OBJECTIVE

We sought to develop a novel peptide nanoparticle CCR3 inhibitor (R321) with a biased mode of inhibition that would block G protein signaling but enable or promote receptor internalization.

METHODS

Self-assembly of R321 peptide into nanoparticles and peptide binding to CCR3 were analyzed by means of dynamic light scattering and nuclear magnetic resonance. Inhibitory activity on CCR3 signaling was assessed in vitro by using flow cytometry, confocal microscopy, and Western blot analysis in a CCR3+ eosinophil cell line and blood eosinophils. In vivo effects of R321 were assessed by using a triple-allergen mouse asthma model.

RESULTS

R321 self-assembles into nanoparticles and binds directly to CCR3, altering receptor function. Half-maximal inhibitory concentration values for eotaxin-induced chemotaxis of blood eosinophils are in the low nanomolar range. R321 inhibits only the early phase of extracellular signal-regulated kinase 1/2 activation and not the late phase generally associated with β-arrestin recruitment and receptor endocytosis, promoting CCR3 internalization and degradation. In vivo R321 effectively blocks eosinophil recruitment into the blood, lungs, and airways and prevents airway hyperresponsiveness in a mouse eosinophilic asthma model.

CONCLUSIONS

R321 is a potent and selective antagonist of the CCR3 signaling cascade. Inhibition through a biased mode of antagonism might hold significant therapeutic promise by eluding the formation of drug tolerance.

Simultaneous Occurrence of Nanospheres and Nanofibers Self-Assembled from Achiral Tripeptides

The achiral tripeptide Boc‐Aib‐MABA‐Aib‐OMe has the ability to co‐exist as nanospheres and as a network of nanofibers in methanol. Furthermore, AFM and TEM images show the presence of bulges in the network of nanofibers. Interestingly, the formation of nanofibers is seen to emerge from the outer boundary of the spherical structures. Some of the nanofibers curl up at the tip and later result in the formation of hollow nanospheres with thick boundaries. The presence of β‐turn‐like structures with hydrogen bonding is observed using FT‐IR studies. The presence of hydrogen bonding is also demonstrated by using NMR studies.

Peptide Nanomaterials Designed from Natural Supramolecular Systems

Natural supramolecular assemblies exhibit unique structural and functional properties that have been optimized over the course of evolution. Inspired by these natural systems, various bio-nanomaterials have been developed using peptides, proteins, and nucleic acids as components. Peptides are attractive building blocks because they enable the important domains of natural protein assemblies to be isolated and optimized while retaining the original structures and functions. Furthermore, the peptide subunits can be conjugated with exogenous molecules such as peptides, proteins, nucleic acids, and metal nanoparticles to generate advanced functions. In this personal account, we summarize recent progress in the construction of peptide-based nanomaterial designed from natural supramolecular systems, including (1) artificial viral capsids, (2) self-assembled nanofibers, and (3) protein-binding motifs. The peptides inspired by nature should provide new design principles for bio-nanomaterials.

Biased antagonism of CXCR4 avoids antagonist tolerance

Repeated dosing of drugs targeting G protein-coupled receptors can stimulate antagonist tolerance, which reduces their efficacy; thus, strategies to avoid tolerance are needed. The efficacy of AMD3100, a competitive antagonist of the chemokine receptor CXCR4 that mobilizes leukemic blasts from the bone marrow into the blood to sensitize them to chemotherapy, is reduced after prolonged treatment. Tolerance to AMD3100 increases the abundance of CXCR4 on the surface of leukemic blasts, which promotes their rehoming to the bone marrow. AMD3100 inhibits both G protein signaling by CXCR4 and β-arrestin1/2-dependent receptor endocytosis. We demonstrated that biased antagonists of G protein-dependent chemotaxis but not β-arrestin1/2 recruitment and subsequent receptor endocytosis avoided tolerance. The peptide antagonist X4-2-6, which is derived from transmembrane helix 2 and extracellular loop 1 of CXCR4, limited chemotaxis and signaling but did not promote CXCR4 accumulation on the cell surface or cause tolerance. The activity of X4-2-6 was due to its distinct mechanism of inhibition of CXCR4. The peptide formed a ternary complex with the receptor and its ligand, the chemokine CXCL12. Within this complex, X4-2-6 released the portion of CXCL12 critical for receptor-mediated activation of G proteins but enabled the rest of the chemokine to recruit β-arrestins to the receptor. In contrast, AMD3100 displaced all components of the chemokine responsible for CXCR4 activation. We further identified a small molecule with similar biased antagonist properties to those of X4-2-6, which may provide a viable alternative to patients when antagonist tolerance prevents drugs from reaching efficacy.

Conformational Conversion during Controlled Oligomerization into Nonamylogenic Protein Nanoparticles

Protein materials are rapidly gaining interest in materials sciences and nanomedicine because of their intrinsic biocompatibility and full biodegradability. The controlled construction of supramolecular entities relies on the controlled oligomerization of individual polypeptides, achievable through different strategies. Because of the potential toxicity of amyloids, those based on alternative molecular organizations are particularly appealing, but the structural bases on nonamylogenic oligomerization remain poorly studied. We have applied spectrofluorimetry and spectropolarimetry to identify the conformational conversion during the oligomerization of His-tagged cationic stretches into regular nanoparticles ranging around 11 nm, useful for tumor-targeted drug delivery. We demonstrate that the novel conformation acquired by the proteins, as building blocks of these supramolecular assemblies, shows different extents of compactness and results in a beta structure enrichment that enhances their structural stability. The conformational profiling presented here offers clear clues for understanding and tailoring the process of nanoparticle formation through the use of cationic and histidine rich stretches in the context of protein materials usable in advanced nanomedical strategies.

Sequentially Responsive Therapeutic Peptide Assembling Nanoparticles for Dual-Targeted Cancer Immunotherapy

Combination therapeutic regimen is becoming a primary direction for current cancer immunotherapy to broad the antitumor response. Functional nanomaterials offer great potential for steady codelivery of various drugs, especially small molecules, therapeutic peptides, and nucleic acids, thereby realizing controllable drug release, increase of drug bioavailability, and reduction of adverse effects. Herein, a therapeutic peptide assembling nanoparticle that can sequentially respond to dual stimuli in the tumor extracellular matrix was designed for tumor-targeted delivery and on-demand release of a short d-peptide antagonist of programmed cell death-ligand 1 (^DPPA-1) and an inhibitor of idoleamine 2,3-dioxygenase (NLG919). By concurrent blockade of immune checkpoints and tryptophan metabolism, the nanoformulation increased the level of tumor-infiltrated cytotoxic T cells and in turn effectively inhibited melanoma growth. To achieve this, an amphiphilic peptide, consisting of a functional 3-diethylaminopropyl isothiocyanate (DEAP) molecule, a peptide substrate of matrix metalloproteinase-2 (MMP-2), and ^DPPA-1, was synthesized and coassembled with NLG919. The nanostructure swelled when it encountered the weakly acidic tumor niche where DEAP molecules were protonated, and further collapsed due to the cleavage of the peptide substrate by MMP-2 that is highly expressed in tumor stroma. The localized release of ^DPPA-1 and NLG919 created an environment which favored the survival and activation of cytotoxic T lymphocytes, leading to the slowdown of melanoma growth and increase of overall survival. Together, this study offers new opportunities for dual-targeted cancer immunotherapy through functional peptide assembling nanoparticles with design features that are sequentially responsive to the multiple hallmarks of the tumor microenvironment.

Antimicrobial peptide capsids of de novo design

The spread of bacterial resistance to antibiotics poses the need for antimicrobial discovery. With traditional search paradigms being exhausted, approaches that are altogether different from antibiotics may offer promising and creative solutions. Here, we introduce a de novo peptide topology that—by emulating the virus architecture—assembles into discrete antimicrobial capsids. Using the combination of high-resolution and real-time imaging, we demonstrate that these artificial capsids assemble as 20-nm hollow shells that attack bacterial membranes and upon landing on phospholipid bilayers instantaneously (seconds) convert into rapidly expanding pores causing membrane lysis (minutes). The designed capsids show broad antimicrobial activities, thus executing one primary function—they destroy bacteria on contact.

With the growing threat of antibiotic resistance, unconventional approaches to antimicrobial discovery are needed. Here, the authors present a peptide topology that mimics virus architecture and assembles into antimicrobial capsids that disrupt bacterial membranes upon contact.

α1-Adrenergic Receptors Function Within Hetero-Oligomeric Complexes With Atypical Chemokine Receptor 3 and Chemokine (C-X-C motif) Receptor 4 in Vascular Smooth Muscle Cells

Background

Recently, we provided evidence that α₁‐adrenergic receptors (ARs) in vascular smooth muscle are regulated by chemokine (C‐X‐C motif) receptor (CXCR) 4 and atypical chemokine receptor 3 (ACKR3). While we showed that CXCR4 controls α₁‐ARs through formation of heteromeric receptor complexes in human vascular smooth muscle cells (hVSMCs), the molecular basis underlying cross‐talk between ACKR3 and α₁‐ARs is unknown.

Methods and Results

We show that ACKR3 agonists inhibit inositol trisphosphate production in hVSMCs on stimulation with phenylephrine. In proximity ligation assays and co‐immunoprecipitation experiments, we observed that recombinant and endogenous ACKR3 form heteromeric complexes with α_1A/B/D‐AR. While small interfering RNA knockdown of ACKR3 in hVSMCs reduced α_1B/D‐AR:ACKR3, CXCR4:ACKR3, and α_1B/D‐AR:CXCR4 complexes, small interfering RNA knockdown of CXCR4 reduced α_1B/D‐AR:ACKR3 heteromers. Phenylephrine‐induced inositol trisphosphate production from hVSMCs was abolished after ACKR3 and CXCR4 small interfering RNA knockdown. Peptide analogs of transmembrane domains 2/4/7 of ACKR3 showed differential effects on heteromerization between ACKR3, α_1A/B/D‐AR, and CXCR4. While the transmembrane domain 2 peptide interfered with α_1B/D‐AR:ACKR3 and CXCR4:ACKR3 heteromerization, it increased heteromerization between CXCR4 and α_1A/B‐AR. The transmembrane domain 2 peptide inhibited ACKR3 but did not affect α_1b‐AR in β‐arrestin recruitment assays. Furthermore, the transmembrane domain 2 peptide inhibited phenylephrine‐induced inositol trisphosphate production in hVSMCs and attenuated phenylephrine‐induced constriction of mesenteric arteries.

Conclusions

α₁‐ARs form hetero‐oligomeric complexes with the ACKR3:CXCR4 heteromer, which is required for α_1B/D‐AR function, and activation of ACKR3 negatively regulates α₁‐ARs. G protein–coupled receptor hetero‐oligomerization is a dynamic process, which depends on the relative abundance of available receptor partners. Endogenous α₁‐ARs function within a network of hetero‐oligomeric receptor complexes.

Small amphipathic peptides are responsible for the assembly of cruciferin nanoparticles

Amphipathic peptides are versatile building blocks for fabricating well-ordered nanostructures, which have gained much attention owing to their enormous design possibilities and bio-functionalities. However, using amphipathic peptides from natural proteins to create tunable nanostructures is challenging because of their heterogeneity and great tendency to form aggregates. Here we fabricated two well-defined nanoparticles from cruciferin amphipathic peptides by integrating top-down and bottom-up approach. Alkali hydrolysis (pH 12, 120 °C for 30 min) was introduced to break down intact cruciferin into peptides (top–down). The cruciferin peptides and their fractions were then assembled into nanoparticles (bottom–up) in the presence of calcium ions. The permeate fraction from 10 kDa cut-off membrane formed smaller nanoparticles (F1-NPs) (around 82 nm) than that of unfractionated cruciferin peptides (CRU-NPs, around 185 nm); the electrostatic and hydrophobic interactions were the main driving forces for particle formation. LC-MS/MS analysis characterised that the small amphipathic peptides (X_n1Z_n2X_n3Z_n4, n_1–4 = 0~5), composed of alternating hydrophobic (X) and hydrophilic (Z) amino acid with a length of 5–15 and 5–20 residues for F1-NPs and CRU-NPs, respectively, were responsible for particle formation. Our study established the mechanism of particle formation of the cold gelation is through assembly of amphipathic peptides.

Tumor Microenvironment Targeting and Responsive Peptide-Based Nanoformulations for Improved Tumor Therapy

The tumor microenvironment participates in all stages of tumor progression and has emerged as a promising therapeutic target for cancer therapy. Rapid progress in the field of molecular self-assembly using various biologic molecules has resulted in the fabrication of nanoformulations that specifically target and regulate microenvironment components to inhibit tumor growth. This inhibition process is based on differentiating between biophysicochemical cues guiding tumor and normal tissue microenvironments. Peptides and peptide derivatives, owing to their biocompatibility, chemical versatility, bioactivity, environmental sensitivity, and biologic recognition abilities, have been widely used as building blocks to construct multifunctional nanostructures for targeted drug delivery and controlled release. Several groups of peptides have been identified as having the ability to penetrate plasma membranes, regulate the essential signaling pathways of angiogenesis and immune reactions, and recognize key components in the tumor microenvironment (such as vascular systems, stromal cells, and abnormal tumor biophysicochemical features). Thus, using different modules, various functional peptides, and their derivatives can be integrated into nanoformulations specifically targeting the tumor microenvironment with increased selectivity, on-demand response, elevated cellular uptake, and improved tumor therapy. In this review, we introduce several groups of functional peptides and highlight peptide-based nanoformulations that specifically target the tumor microenvironment. We also provide our perspective on the development of smart drug-delivery systems with enhanced therapeutic efficacy.

Smart materials on the way to theranostic nanorobots: Molecular machines and nanomotors, advanced biosensors, and intelligent vehicles for drug delivery

BACKGROUND

Theranostics, a fusion of two key parts of modern medicine - diagnostics and therapy of the organism's disorders, promises to bring the efficacy of medical treatment to a fundamentally new level and to become the basis of personalized medicine. Extrapolating today's progress in the field of smart materials to the long-run prospect, we can imagine future intelligent agents capable of performing complex analysis of different physiological factors inside the living organism and implementing a built-in program thereby triggering a series of therapeutic actions. These agents, by analogy with their macroscopic counterparts, can be called nanorobots. It is quite obscure what these devices are going to look like but they will be more or less based on today's achievements in nanobiotechnology.

SCOPE OF REVIEW

The present Review is an attempt to systematize highly diverse nanomaterials, which may potentially serve as modules for theranostic nanorobotics, e.g., nanomotors, sensing units, and payload carriers.

MAJOR CONCLUSIONS

Biocomputing-based sensing, externally actuated or chemically "fueled" autonomous movement, swarm inter-agent communication behavior are just a few inspiring examples that nanobiotechnology can offer today for construction of truly intelligent drug delivery systems.

GENERAL SIGNIFICANCE

The progress of smart nanomaterials toward fully autonomous drug delivery nanorobots is an exciting prospect for disease treatment. Synergistic combination of the available approaches and their further development may produce intelligent drugs of unmatched functionality.

Suppression of Breast Cancer Cell Migration by Small Interfering RNA Delivered by Polyethylenimine-Functionalized Graphene Oxide

The carbon-based nanomaterial graphene can be chemically modified to associate with various molecules such as chemicals and biomolecules and developed as novel carriers for drug and gene delivery. In this study, a nonviral gene transfection reagent was produced by functionalizing graphene oxide (GO) with a polycationic polymer, polyethylenimine (PEI), to increase the biocompatibility of GO and to transfect small interfering RNA (siRNA) against C-X-C chemokine receptor type 4 (CXCR4), a biomarker associated with cancer metastasis, into invasive breast cancer cells. PEI-functionalized GO (PEI-GO) was a homogeneous aqueous solution that remained in suspension during storage at 4 °C for at least 6 months. The particle size of PEI-GO was 172 ± 4.58 and 188 ± 5.00 nm at 4 and 25 °C, respectively, and increased slightly to 262 ± 17.6 nm at 37 °C, but remained unaltered with time. Binding affinity of PEI-GO toward siRNA was assessed by electrophoretic mobility shift assay (EMSA), in which PEI-GO and siRNA were completely associated at a PEI-GO:siRNA weight ratio of 2:1 and above. The invasive breast cancer cell line, MDA-MB-231, was transfected with PEI-GO in complex with siRNAs against CXCR4 (siCXCR4). Suppression of the mRNA and protein expression of CXCR4 by the PEI-GO/siCXCR4 complex was confirmed by real-time PCR and western blot analysis. In addition, the metastatic potential of MDA-MB-231 cells was attenuated by the PEI-GO/siCXCR4 complex as demonstrated in wound healing assay. Our results suggest that PEI-GO is effective in the delivery of siRNA and may contribute to targeted gene therapy to suppress cancer metastasis.

Bioorthogonal Strategy for Bioprocessing of Specific-Site-Functionalized Enveloped Influenza-Virus-Like Particles

Virus-like particles (VLPs) constitute a promising platform in vaccine development and targeted drug delivery. To date, most applications use simple nonenveloped VLPs as human papillomavirus or hepatitis B vaccines, even though the envelope is known to be critical to retain the native protein folding and biological function. Here, we present tagged enveloped VLPs (TagE-VLPs) as a valuable strategy for the downstream processing and monitoring of the in vivo production of specific-site-functionalized enveloped influenza VLPs. This two-step procedure allows bioorthogonal functionalization of azide-tagged nascent influenza type A hemagglutinin proteins in the envelope of VLPs through a strain-promoted [3 + 2] alkyne–azide cycloaddition reaction. Importantly, labeling does not influence VLP production and allows for construction of functionalized VLPs without deleterious effects on their biological function. Refined discrimination and separation between VLP and baculovirus, the major impurity of the process, is achieved when this technique is combined with flow cytometry analysis, as demonstrated by atomic force microscopy. TagE-VLPs is a versatile tool broadly applicable to the production, monitoring, and purification of functionalized enveloped VLPs for vaccine design trial runs, targeted drug delivery, and molecular imaging.

A De Novo Virus-Like Topology for Synthetic Virions

A de novo topology of virus-like assembly is reported. The design is a trifaceted coiled-coil peptide helix, which self-assembles into ultrasmall, monodisperse, anionic virus-like shells that encapsulate and transfer both RNA and DNA into human cells. Unlike existing artificial systems, these shells share the same physical characteristics of viruses being anionic, nonaggregating, abundant, hollow, and uniform in size, while effectively mediating gene silencing and transgene expression. These are the smallest virus-like structures reported to date, both synthetic and native, with the ability to adapt and transfer small and large nucleic acids. The design thus offers a promising solution for engineering bespoke artificial viruses with desired functions.

New Insights into Mechanisms and Functions of Chemokine (C-X-C Motif) Receptor 4 Heteromerization in Vascular Smooth Muscle

Recent evidence suggests that C-X-C chemokine receptor type 4 (CXCR4) heteromerizes with α_1A/B-adrenoceptors (AR) and atypical chemokine receptor 3 (ACKR3) and that CXCR4:α_1A/B-AR heteromers are important for α₁-AR function in vascular smooth muscle cells (VSMC). Structural determinants for CXCR4 heteromerization and functional consequences of CXCR4:α_1A/B-AR heteromerization in intact arteries, however, remain unknown. Utilizing proximity ligation assays (PLA) to visualize receptor interactions in VSMC, we show that peptide analogs of transmembrane-domain (TM) 2 and TM4 of CXCR4 selectively reduce PLA signals for CXCR4:α_1A-AR and CXCR4:ACKR3 interactions, respectively. While both peptides inhibit CXCL12-induced chemotaxis, only the TM2 peptide inhibits phenylephrine-induced Ca²⁺-fluxes, contraction of VSMC and reduces efficacy of phenylephrine to constrict isolated arteries. In a Cre-loxP mouse model to delete CXCR4 in VSMC, we observed 60% knockdown of CXCR4. PLA signals for CXCR4:α_1A/B-AR and CXCR4:ACKR3 interactions in VSMC, however, remained constant. Our observations point towards TM2/4 of CXCR4 as possible contact sites for heteromerization and suggest that TM-derived peptide analogs permit selective targeting of CXCR4 heteromers. A molecular dynamics simulation of a receptor complex in which the CXCR4 homodimer interacts with α_1A-AR via TM2 and with ACKR3 via TM4 is presented. Our findings further imply that CXCR4:α_1A-AR heteromers are important for intrinsic α₁-AR function in intact arteries and provide initial and unexpected insights into the regulation of CXCR4 heteromerization in VSMC.

Potential of CXCR4/CXCL12 Chemokine Axis in Cancer Drug Delivery

This review discusses the potential of CXCR4 chemokine receptor in the design of anticancer and antimetastatic drug delivery systems. The role of CXCR4 in cancer progression and metastasis is discussed in the context of the development of several types of drug delivery strategies. Overview of drug delivery systems targeted to cancers that overexpress CXCR4 is provided, together with the main types of CXCR4-binding ligands used in targeting applications. Drug delivery applications that take advantage of CXCR4 inhibition to achieve enhanced anticancer and antimetastatic activity of combination treatments are also discussed.

Structurally plastic peptide capsules for synthetic antimicrobial viruses

A conceptual design for artificial antimicrobial viruses is described. The design emulates viral assembly and function to create self-assembling peptide capsules that promote efficient gene delivery and silencing in mammalian cells. Unlike viruses, however, the capsules are antimicrobial, which allows them to exhibit a dual biological function: gene transport and antimicrobial activity. Unlike other antimicrobials, the capsules act as pre-concentrated antimicrobial agents that elicit rapid and localised membrane-disrupting responses by converting into individual pores at their precise landing positions on membranes. The concept holds promise for engineering virus-like scaffolds with biologically tuneable properties.

Peptide self-assembly for nanomaterials: the old new kid on the block

Peptide self-assembly is an increasingly attractive tool for nanomaterials. Perfected in biology peptide self-assembling systems have impacted on nearly any conceivable nanomaterial type. However, with all the information available to us commercialisation of peptide materials remains in its infancy. In an attempt to better understand the reasons behind this shortcoming we categorise peptide self-assembled materials in relation to their non-peptide counterparts. A particular emphasis is placed on the versatility of peptide self-assembly in terms of modularity, responsiveness and functional diversity, which enables direct comparisons with more traditional material chemistries.

Heteromerization of chemokine (C-X-C motif) receptor 4 with α1A/B-adrenergic receptors controls α1-adrenergic receptor function

Recent evidence suggests that chemokine (C-X-C motif) receptor 4 (CXCR4) contributes to the regulation of blood pressure through interactions with α1-adrenergic receptors (ARs) in vascular smooth muscle. The underlying molecular mechanisms, however, are unknown. Using proximity ligation assays to visualize single-molecule interactions, we detected that α1A/B-ARs associate with CXCR4 on the cell surface of rat and human vascular smooth muscle cells (VSMC). Furthermore, α1A/B-AR could be coimmunoprecipitated with CXCR4 in a HeLa expression system and in human VSMC. A peptide derived from the second transmembrane helix of CXCR4 induced chemical shift changes in the NMR spectrum of CXCR4 in membranes, disturbed the association between α1A/B-AR and CXCR4, and inhibited Ca(2+) mobilization, myosin light chain (MLC) 2 phosphorylation, and contraction of VSMC upon α1-AR activation. CXCR4 silencing reduced α1A/B-AR:CXCR4 heteromeric complexes in VSMC and abolished phenylephrine-induced Ca(2+) fluxes and MLC2 phosphorylation. Treatment of rats with CXCR4 agonists (CXCL12, ubiquitin) reduced the EC50 of the phenylephrine-induced blood pressure response three- to fourfold. These observations suggest that disruption of the quaternary structure of α1A/B-AR:CXCR4 heteromeric complexes by targeting transmembrane helix 2 of CXCR4 and depletion of the heteromeric receptor complexes by CXCR4 knockdown inhibit α1-AR-mediated function in VSMC and that activation of CXCR4 enhances the potency of α1-AR agonists. Our findings extend the current understanding of the molecular mechanisms regulating α1-AR and provide an example of the importance of G protein-coupled receptor (GPCR) heteromerization for GPCR function. Compounds targeting the α1A/B-AR:CXCR4 interaction could provide an alternative pharmacological approach to modulate blood pressure.

Exploring thermodynamically downhill nanostructured peptide libraries: from structural to morphological insight

Biocatalytic evolution of thermodynamically downhill nanostructured peptide libraries in hydrogel states are envisaged.

In situ generation of redox active peptides driven by selenoester mediated native chemical ligation

Redox active peptides synthesized via selenoester mediated native chemical ligation with a propensity to self-assemble in aqueous medium. A gel–sol transition of self-assembled peptide in a reducing environment makes it a versatile candidate for the development of functional biomaterials.

Dendritic cell-based nanovaccines for cancer immunotherapy

Cancer immunotherapy critically relies on the efficient presentation of tumor antigens to T-cells to elicit a potent anti-tumor immune response aimed at life-long protection against cancer recurrence. Recent advances in the nanovaccine field have now resulted in formulations that trigger strong anti-tumor responses. Nanovaccines are assemblies that are able to present tumor antigens and appropriate immune-stimulatory signals either directly to T-cells or indirectly via antigen-presenting dendritic cells. This review focuses on important aspects of nanovaccine design for dendritic cells, including the synergistic and cytosolic delivery of immunogenic compounds, as well as their passive and active targeting to dendritic cells. In addition, nanoparticles for direct T-cell activation are discussed, addressing features necessary to effectively mimic dendritic cell/T-cell interactions.

Supplementing with non-glycoside hydrolase proteins enhances enzymatic deconstruction of plant biomass

The glycoside hydrolases (GH) of Caldicellulosiruptor bescii are thermophilic enzymes, and therefore they can hydrolyze plant cell wall polysaccharides at high temperatures. Analyses of two C. bescii glycoside hydrolases, CbCelA-TM1 and CbXyn10A with cellulase and endoxylanase activity, respectively, demonstrated that each enzyme is highly thermostable under static incubation at 70°C. Both enzymes, however, rapidly lost their enzymatic activities when incubated at 70°C with end-over-end shaking. Since crowding conditions, even at low protein concentrations, seem to influence enzymatic properties, three non-glycoside hydrolase proteins were tested for their capacity to stabilize the thermophilic proteins at high temperatures. The three proteins investigated were a small heat shock protein CbHsp18 from C. bescii, a histone MkHistone1 from Methanopyrus kandleri, and bovine RNase A, from a commercial source. Fascinatingly, each of these proteins increased the thermostability of the glycoside hydrolases at 70°C during end-over-end shaking incubation, and this property translated into increases in hydrolysis of several substrates including the bioenergy feedstock Miscanthus. Furthermore, MkHistone1 and RNase A also altered the initial products released from the cello-oligosaccharide cellopentaose during hydrolysis with the cellodextrinase CbCdx1A, which further demonstrated the capacity of the three non-GH proteins to influence hydrolysis of substrates by the thermophilic glycoside hydrolases. The non-GH proteins used in the present report were small proteins derived from each of the three lineages of life, and therefore expand the space from which different polypeptides can be tested for their influence on plant cell wall hydrolysis, a critical step in the emerging biofuel industry.

The structure of monomeric components of self-assembling CXCR4 antagonists determines the architecture of resulting nanostructures

Self-assembling peptides play increasingly important roles in the development of novel materials and drug delivery vehicles. Understanding mechanisms governing the assembly of nanoarchitectures is essential for the generation of peptide-based nanodevices. We find that a cone-shaped derivative of the second transmembrane domain of CXCR4 receptor, x4-2-6 self-assembles into nanospheres, while a related cylindrical peptide, x4-2-9 forms fibrils. Stronger intermolecular interactions in nanospheres than in fibrils result in slow rates of particle disassembly and protection against proteolytic degradation.