Integrin-Targeting Peptides for the Design of Functional Cell-Responsive Biomaterials

The influence of a modified p53 C-terminal peptide by using a tumor-targeting sequence on cellular apoptosis and tumor treatment

The restoration of the function of p53 in tumors is a therapeutic strategy for the highly frequent mutation of the TP53 tumor suppressor gene. P460 is a wild-type peptide derived from the p53 C-terminus and has been proven to be capable of restoring the tumor suppressor function of p53. The poor accumulation of drugs in tumors is a serious hindrance to tumor treatment. For enhancing the activity of P460, the tumor-targeting sequence Arg-Gly-Asp-Arg (RGDR, C-end rule peptide) was introduced into the C-terminus of P460 to generate the new peptide P462. P462 presented better activity than P460 in inhibiting the proliferation of cancer cells and increasing the number of tumor cells undergoing apoptosis. Cell adhesion analysis and tumor imaging results revealed that P462 showed more specific and extensive binding with tumor cells and greater accumulation in tumors than the wild-type peptide. Importantly, treatment with P462 was more efficacious than that with P460 in vivo and was associated with considerably improved tumor-homing activity. This study highlights the importance of the roles of the tumor-homing sequence RGDR in the enhancement in cell attachment and tumor accumulation. The results of this work indicate that P462 could be a novel drug candidate for tumor treatment.

One-step biofabrication of liquid core-GelMa shell microbeads for in situ hollow cell ball self-assembly

There are many instances of hollow-structure morphogenesis in the development of tissues. Thus, the fabrication of hollow structures in a simple, high-throughput and homogeneous manner with proper natural biomaterial combination is valuable for developmental studies and tissue engineering, while it is a significant challenge in biofabrication field. We present a novel method for the fabrication of a hollow cell module using a coaxial co-flow capillary microfluidic device. Sacrificial gelatin laden with cells in the inner layer and GelMa in the outer layer are used via a coaxial co-flow capillary microfluidic device to produce homogenous micro-beads. The overall and core sizes of core-shell microbeads were well controlled. When using human vein vascular endothelial cells to demonstrate how cells line the inner surface of core-shell beads, as the core liquifies, a hollow cell ball with asymmetric features is fabricated. After release from the GelMa shell, individual cell balls are obtained and deformed cell balls can self-recover. This platform paves way for complex hollow tissue modeling in vitro, and further modulation of matrix stiffness, curvature and biochemical composition to mimic in vivo microenvironments.

Conjecturing about Small-Molecule Agonists and Antagonists of α4β1 Integrin: From Mechanistic Insight to Potential Therapeutic Applications

Integrins are heterodimeric cell-surface receptors that regulate cell-cell adhesion and cellular functions through bidirectional signaling. On the other hand, anomalous trafficking of integrins is also implicated in severe pathologies as cancer, thrombosis, inflammation, allergies, and multiple sclerosis. For this reason, they are attractive candidates as drug targets. However, despite promising preclinical data, several anti-integrin drugs failed in late-stage clinical trials for chronic indications, with paradoxical side effects. One possible reason is that, at low concentration, ligands proposed as antagonists may also act as partial agonists. Hence, the comprehension of the specific structural features for ligands' agonism or antagonism is currently of the utmost interest. For α4β1 integrin, the situation is particularly obscure because neither the crystallographic nor the cryo-EM structures are known. In addition, very few potent and selective agonists are available for investigating the mechanism at the basis of the receptor activation. In this account, we discuss the physiological role of α4β1 integrin and the related pathologies, and review the few agonists. Finally, we speculate on plausible models to explain agonism vs. antagonism by comparison with RGD-binding integrins and by analysis of computational simulations performed with homology or hybrid receptor structures.

Integrin Facilitates the Internalization of TAT Peptide Conjugated to RGD Motif in Model Lipid Membranes

In recent years, targeted drug delivery has attracted a great interest for enhanced therapeutic efficiency, with diminished side effects, especially in cancer therapy. Cell penetrating peptides (CPPs) like HIV1-TAT peptides, appear to be the perfect vectors for translocating drugs or other cargoes across the plasma membrane, but their application is limited mostly due to insufficient specificity for intended targets. Although these molecules were successfully used, the mechanism by which the peptides enter the cell interior still needs to be clarified. The tripeptide motif RGD (arginine-glycine-aspartate), found in extracellular matrix proteins has high affinity for integrin receptors overexpressed in cancer and it is involved in different phases of disease progression, including proliferation, invasion and migration. Discovery of new peptides with high binding affinity for disease receptors and permeability of plasma membranes is desirable for both, development of targeted drug delivery systems and early detection and diagnosis. To complement the TAT peptide with specific targeting ability, we conjugated it with an integrin-binding RGD motif. Although the idea of RGD-CPPs conjugates is not entirely new,[1] here we describe the permeability abilities and specificity of integrin receptors of RGD-TAT peptides in model membranes. Our findings reveal that this novel RGD sequence based on TAT peptide maintains its ability to permeate lipid membranes and exhibits specificity for integrin receptors embedded in giant unilamellar vesicles. This promising outcome suggests that the RGD-TAT peptide has significant potential for applications in the field of targeted drug delivery systems.

Use of pyridazinediones for tuneable and reversible covalent cysteine modification applied to peptides, proteins and hydrogels

Reversible cysteine modification has been found to be a useful tool for a plethora of applications such as selective enzymatic inhibition, activity-based protein profiling and/or cargo release from a protein or a material. However, only a limited number of reagents display reliable dynamic/reversible thiol modification and, in most cases, many of these reagents suffer from issues of stability, a lack of modularity and/or poor rate tunability. In this work, we demonstrate the potential of pyridazinediones as novel reversible and tuneable covalent cysteine modifiers. We show that the electrophilicity of pyridazinediones correlates to the rates of the Michael addition and retro-Michael deconjugation reactions, demonstrating that pyridazinediones provide an enticing platform for readily tuneable and reversible thiol addition/release. We explore the regioselectivity of the novel reaction and unveil the reason for the fundamental increased reactivity of aryl bearing pyridazinediones by using DFT calculations and corroborating findings with SCXRD. We also applied this fundamental discovery to making more rapid disulfide rebridging agents in related work. We finally provide the groundwork for potential applications in various areas with exemplification using readily functionalised "clickable" pyridazinediones on clinically relevant cysteine and disulfide conjugated proteins, as well as on a hydrogel material.

Extracellular matrix-induced signaling pathways in mesenchymal stem/stromal cells

The extracellular matrix (ECM) is a crucial component of the stem cell microenvironment, or stem-cell niches, and contributes to the regulation of cell behavior and fate. Accumulating evidence indicates that different types of stem cells possess a large variety of molecules responsible for interactions with the ECM, mediating specific epigenetic rearrangements and corresponding changes in transcriptome profile. Signals from the ECM are crucial at all stages of ontogenesis, including embryonic and postnatal development, as well as tissue renewal and repair. The ECM could regulate stem cell transition from a quiescent state to readiness to perceive the signals of differentiation induction (competence) and the transition between different stages of differentiation (commitment). Currently, to unveil the complex networks of cellular signaling from the ECM, multiple approaches including screening methods, the analysis of the cell matrixome, and the creation of predictive networks of protein-protein interactions based on experimental data are used. In this review, we consider the existing evidence regarded the contribution of ECM-induced intracellular signaling pathways into the regulation of stem cell differentiation focusing on mesenchymal stem/stromal cells (MSCs) as well-studied type of postnatal stem cells totally depended on signals from ECM. Furthermore, we propose a system biology-based approach for the prediction of ECM-mediated signal transduction pathways in target cells. Video Abstract.

Are the integrin binding motifs within SARS CoV-2 spike protein and MHC class II alleles playing the key role in COVID-19?

The previous studies on the RGD motif (aa403-405) within the SARS CoV-2 spike (S) protein receptor binding domain (RBD) suggest that the RGD motif binding integrin(s) may play an important role in infection of the host cells. We also discussed the possible role of two other integrin binding motifs that are present in S protein: LDI (aa585-587) and ECD (661-663), the motifs used by some other viruses in the course of infection. The MultiFOLD models for protein structure analysis have shown that the ECD motif is clearly accessible in the S protein, whereas the RGD and LDI motifs are partially accessible. Furthermore, the amino acids that are present in Epstein-Barr virus protein (EBV) gp42 playing very important role in binding to the HLA-DRB1 molecule and in the subsequent immune response evasion, are also present in the S protein heptad repeat-2. Our MultiFOLD model analyses have shown that these amino acids are clearly accessible on the surface in each S protein chain as monomers and in the homotrimer complex and bind to HLA-DRB1 β chain. Therefore, they may have the identical role in SARS CoV-2 immune evasion as in EBV infection. The prediction analyses of the MHC class II binding peptides within the S protein have shown that the RGD motif is present in the core 9-mer peptide IRGDEVRQI within the two HLA-DRB1*03:01 and HLA-DRB3*01.01 strong binding 15-mer peptides suggesting that RGD motif may be the potential immune epitope. Accordingly, infected HLA-DRB1*03:01 or HLA-DRB3*01.01 positive individuals may develop high affinity anti-RGD motif antibodies that react with the RGD motif in the host proteins, like fibrinogen, thrombin or von Willebrand factor, affecting haemostasis or participating in autoimmune disorders.

Gold Half-Shell-Coated Paclitaxel-Loaded PLGA Nanoparticles for the Targeted Chemo-Photothermal Treatment of Cancer

Conventional cancer therapies suffer from nonspecificity, drug resistance, and a poor bioavailability, which trigger severe side effects. To overcome these disadvantages, in this study, we designed and evaluated the in vitro potential of paclitaxel-loaded, PLGA-gold, half-shell nanoparticles (PTX-PLGA/Au-HS NPs) conjugated with cyclo(Arg-Gly-Asp-Phe-Lys) (cyRGDfk) as a targeted chemo-photothermal therapy system in HeLa and MDA-MB-231 cancer cells. A TEM analysis confirmed the successful gold half-shell structure formation. High-performance liquid chromatography showed an encapsulation efficiency of the paclitaxel inside nanoparticles of more than 90%. In the release study, an initial burst release of about 20% in the first 24 h was observed, followed by a sustained drug release for a period as long as 10 days, reaching values of about 92% and 49% for NPs with and without near infrared laser irradiation. In in vitro cell internalization studies, targeted nanoparticles showed a higher accumulation than nontargeted nanoparticles, possibly through a specific interaction of the cyRGDfk with their homologous receptors, the ανβ3 y ανβ5 integrins on the cell surface. Compared with chemotherapy or photothermal treatment alone, the combined treatment demonstrated a synergistic effect, reducing the cell viability to 23% for the HeLa cells and 31% for the MDA-MB-231 cells. Thus, our results indicate that these multifuncional nanoparticles can be considered to be a promising targeted chemo-photothermal therapy system against cancer.

Synergistic effects of integrin binding peptide (RGD) and photobiomodulation therapies on bone-like microtissues to enhance osteogenic differentiation

Bone tissue engineering aims to diversify and enhance the strategies for bone regeneration to overcome bone-related health problems. Bone mimetic peptides such as Gly-Arg-Gly-Asp-Ser (RGD) are useful tools for osteogenic differentiation. Similarly, photobiomodulation (PBM) at 600-800 nm of wavelength range improves bone tissue healing via the production of intracellular reactive oxygen species (ROS), ATP synthesis, and nitric oxide (NO) release. Besides, traditional monolayer cell culture models have limited conditions to exhibit the details of a mechanism such as a peptide or PBM therapy. However, scaffold-free microtissues (SFMs) can mimic a tissue more properly and be an efficient way to understand the mechanism of therapy via cell-cell interaction. Thus, the synergistic effects of RGD peptide (1 mM) and PBM applications (1 J/cm² energy density at 655 nm of wavelength and 5 J/cm² energy density at 808 nm of wavelength) were evaluated on SFMs formed with the co-culture of Human Bone Marrow Stem Cells (hBMSC) and Human Umbilical Vein Endothelial Cells (HUVEC) for osteogenic differentiation. Cell viability assays, mechanistic analysis, and the evaluation of osteogenic differentiation markers were performed. Combined therapies of RGD and PBM were more successful to induce osteogenic differentiation than single therapies. Especially, RGD + PBM at 655 nm group exhibited a higher capability of osteogenic differentiation via ROS production, ATP synthesis, and NO release. It can be concluded that the concomitant use of RGD and PBM may enhance bone regeneration and become a promising therapeutic tool to heal bone-related problems in clinics.

Design, Pharmacological Characterization, and Molecular Docking of Minimalist Peptidomimetic Antagonists of α4β1 Integrin

Integrin receptors mediate cell-cell interactions via the recognition of cell-adhesion glycoproteins, as well as via the interactions of cells with proteins of the extracellular matrix, and upon activation they transduce signals bi-directionally across the cell membrane. In the case of injury, infection, or inflammation, integrins of β₂ and α₄ families participate in the recruitment of leukocytes, a multi-step process initiated by the capturing of rolling leukocytes and terminated by their extravasation. In particular, α₄β₁ integrin is deeply involved in leukocyte firm adhesion preceding extravasation. Besides its well-known role in inflammatory diseases, α₄β₁ integrin is also involved in cancer, being expressed in various tumors and showing an important role in cancer formation and spreading. Hence, targeting this integrin represents an opportunity for the treatment of inflammatory disorders, some autoimmune diseases, and cancer. In this context, taking inspiration from the recognition motives of α₄β₁ integrin with its natural ligands FN and VCAM-1, we designed minimalist α/β hybrid peptide ligands, with our approach being associated with a retro strategy. These modifications are expected to improve the compounds' stability and bioavailability. As it turned out, some of the ligands were found to be antagonists, being able to inhibit the adhesion of integrin-expressing cells to plates coated with the natural ligands without inducing any conformational switch and any activation of intracellular signaling pathways. An original model structure of the receptor was generated using protein-protein docking to evaluate the bioactive conformations of the antagonists via molecular docking. Since the experimental structure of α₄β₁ integrin is still unknown, the simulations might also shed light on the interactions between the receptor and its native protein ligands.

Design of Functional Pluronic-Based Precursors for Tailoring Hydrogel Thermoresponsiveness and Cell-Adhesive Properties

In this study, functional Pluronic F127 precursors were designed and synthesized for the preparation of thermosensitive hydrogels. Using linear Pluronic thioacetate and Pluronic multi-acrylate precursors, F127-based hydrogels were prepared through thioacetate deprotection-mediated Michael-type addition. The properties of these gels were compared to those obtained through free radical crosslinking of F127 diacrylate. Temperature was found to have a clear influence on gel swelling as a result of F127 thermoresponsiveness. The macromolecular architecture and functionality of the precursors were also optimized and characterized in terms of gelation kinetics and drug diffusion. In vitro tests were conducted on fibroblasts and endothelial cells to assess their response to cellular adhesion with Pluronic gels that were functionalized with an RGD peptide or pretreated with serum proteins to promote cell adhesion. This study provides a method for creating tailored hydrogels suitable for various biomedical applications, such as soft-tissue engineering, cell encapsulation, wound healing, and sustained delivery of therapeutic molecules.

Design and Pharmacological Characterization of α4β1 Integrin Cyclopeptide Agonists: Computational Investigation of Ligand Determinants for Agonism versus Antagonism

α₄β₁ integrin is a cell adhesion receptor deeply involved in the migration and accumulation of leukocytes. Therefore, integrin antagonists that inhibit leukocytes recruitment are currently regarded as a therapeutic opportunity for the treatment of inflammatory disorder, including leukocyte-related autoimmune diseases. Recently, it has been suggested that integrin agonists capable to prevent the release of adherent leukocytes might serve as therapeutic agents as well. However, very few α₄β₁ integrin agonists have been discovered so far, thus precluding the investigation of their potential therapeutic efficacy. In this perspective, we synthesized cyclopeptides containing the LDV recognition motif found in the native ligand fibronectin. This approach led to the discovery of potent agonists capable to increase the adhesion of α₄ integrin-expressing cells. Conformational and quantum mechanics computations predicted distinct ligand-receptor interactions for antagonists or agonists, plausibly referable to receptor inhibition or activation.

Molecular Modeling Insights into the Structure and Behavior of Integrins: A Review

Integrins are heterodimeric glycoproteins crucial to the physiology and pathology of many biological functions. As adhesion molecules, they mediate immune cell trafficking, migration, and immunological synapse formation during inflammation and cancer. The recognition of the vital roles of integrins in various diseases revealed their therapeutic potential. Despite the great effort in the last thirty years, up to now, only seven integrin-based drugs have entered the market. Recent progress in deciphering integrin functions, signaling, and interactions with ligands, along with advancement in rational drug design strategies, provide an opportunity to exploit their therapeutic potential and discover novel agents. This review will discuss the molecular modeling methods used in determining integrins' dynamic properties and in providing information toward understanding their properties and function at the atomic level. Then, we will survey the relevant contributions and the current understanding of integrin structure, activation, the binding of essential ligands, and the role of molecular modeling methods in the rational design of antagonists. We will emphasize the role played by molecular modeling methods in progress in these areas and the designing of integrin antagonists.

Bioselectivity of silk protein-based materials and their bio-inspired applications

Adhesion to material surfaces is crucial for almost all organisms regarding subsequent biological responses. Mammalian cell attachment to a surrounding biological matrix is essential for maintaining their survival and function concerning tissue formation. Conversely, the adhesion and presence of microbes interferes with important multicellular processes of tissue development. Therefore, tailoring bioselective, biologically active, and multifunctional materials for biomedical applications is a modern focus of biomaterial research. Engineering biomaterials that stimulate and interact with cell receptors to support binding and subsequent physiological responses of multicellular systems attracted much interest in the last years. Further to this, the increasing threat of multidrug resistance of pathogens against antibiotics to human health urgently requires new material concepts for preventing microbial infestation and biofilm formation. Thus, materials exhibiting microbial repellence or antimicrobial behaviour to reduce inflammation, while selectively enhancing regeneration in host tissues are of utmost interest. In this context, protein-based materials are interesting candidates due to their natural origin, biological activity, and structural properties. Silk materials, in particular those made of spider silk proteins and their recombinant counterparts, are characterized by extraordinary properties including excellent biocompatibility, slow biodegradation, low immunogenicity, and non-toxicity, making them ideally suited for tissue engineering and biomedical applications. Furthermore, recombinant production technologies allow for application-specific modification to develop adjustable, bioactive materials. The present review focusses on biological processes and surface interactions involved in the bioselective adhesion of mammalian cells and repellence of microbes on protein-based material surfaces. In addition, it highlights the importance of materials made of recombinant spider silk proteins, focussing on the progress regarding bioselectivity.

Molecular dynamics simulations of cRGD-conjugated PEGylated TiO2 nanoparticles for targeted photodynamic therapy

The conjugation of high-affinity cRGD-containing peptides is a promising approach in nanomedicine to efficiently reduce off-targeting effects and enhance the cellular uptake by integrin-overexpressing tumor cells. Herein we utilize atomistic molecular dynamics simulations to evaluate key structural-functional parameters of these targeting ligands for an effective binding activity towards α_Vβ₃ integrins. An increasing number of cRGD ligands is conjugated to PEG chains grafted to highly curved TiO₂ nanoparticles to unveil the impact of cRGD density on the ligand's presentation, stability, and conformation in an explicit aqueous environment. We find that a low density leads to an optimal spatial presentation of cRGD ligands out of the "stealth" PEGylated layer around the nanosystem, favoring a straight upward orientation and spaced distribution of the targeting ligands in the bulk-water phase. On the contrary, high densities favor over-clustering of cRGD ligands, driven by a concerted mechanism of enhanced ligand-ligand interactions and reduced water accessibility over the ligand's molecular surface. These findings strongly suggest that the ligand density modulation is a key factor in the design of cRGD-targeting nanodevices to maximize their binding efficiency into over-expressed α_Vβ₃ integrin receptors.

Craft of Co-encapsulation in Nanomedicine: A Struggle To Achieve Synergy through Reciprocity

Achieving synergism, often by combination therapy via codelivery of chemotherapeutic agents, remains the mainstay of treating multidrug-resistance cases in cancer and microbial strains. With a typical core-shell architecture and surface functionalization to ensure facilitated targeting of tissues, nanocarriers are emerging as a promising platform toward gaining such synergism. Co-encapsulation of disparate theranostic agents in nanocarriers-from chemotherapeutic molecules to imaging or photothermal modalities-can not only address the issue of protecting the labile drug payload from a hostile biochemical environment but may also ensure optimized drug release as a mainstay of synergistic effect. However, the fate of co-encapsulated molecules, influenced by temporospatial proximity, remains unpredictable and marred with events with deleterious impact on therapeutic efficacy, including molecular rearrangement, aggregation, and denaturation. Thus, more than just an art of confining multiple therapeutics into a 3D nanoscale space, a co-encapsulated nanocarrier, while aiming for synergism, should strive toward achieving a harmonious cohabitation of the encapsulated molecules that, despite proximity and opportunities for interaction, remain innocuous toward each other and ensure molecular integrity. This account will inspect the current progress in co-encapsulation in nanocarriers and distill out the key points toward accomplishing such synergism through reciprocity.

Structural Requirements for the Binding of a Peptide to Prohibitins on the Cell Surface of Monocytes/Macrophages

The screening of phage peptide libraries resulted in the identification of a sequence (named NW peptide, NWYLPWLGTNDW) that specifically binds to human monocytes and macrophages. Although the NW peptide can be used for the targeted delivery of therapeutics without knowledge of its receptor(s), the identification of-its binding partners will support future clinical applications-Here, we used the biotinylated NW peptide for cross-linking cell surface receptor(s) on live cells or as bait in pull-down assays with membrane proteins isolated from monocytes or human THP-1 cells differentiated into macrophages. Proteomic analysis of the captured proteins identified cell surface prohibitins (PHB1 and PHB2) and modified albumin as binding partners. Using flow cytometry and pull-down methods, we demonstrated that PHB1 and PHB2 interact directly with the NW peptide. Confocal imaging showed co-localization of the peptide with PHB1 on the surface of monocytes. Single replacement of either tryptophan or leucine with alanine completely inhibited binding, whereas the replacement of asparagine at position 1 or 10 and aspartic acid at position 11 with alanine did not affect the binding of the peptide variants. Neutral amino acid replacement of tryptophan at positions 2, 6, and 12 with tyrosine or phenylalanine also abolished the binding, implying that the indole ring of tryptophan is indispensable for the NW peptide to bind. Overall, the data suggest that membrane-associated prohibitins might be a useful target for the delivery of therapeutics to monocytes/macrophages and that tryptophan and leucine are key residues for peptide binding.

Bioengineered PLEKHA7 nanodelivery regularly induces behavior alteration and growth retardation of acute myeloid leukemia

Acute myeloid leukemia (AML) is the most lethal leukemia with an extremely poor prognosis and high relapse rates. In leukemogenesis, adhesion abnormalities can readily guide an imbalance between hematopoietic progenitor cells and bone marrow stromal cells, altering the normal hematopoietic bone marrow microenvironment into leukemic transformation that enhances leukemic proliferation. Here, we have firstly studied the PLEKHA7 expression in leukemic cells to assess their growth capability affected by the restoration of PLEKHA7 in the cells. The efficacy of PLEKHA7-loaded cRGD-mediated PEGylated cationic lipid nanoparticles for efficient PLEKHA7 delivery in leukemic cells as well as the effect of PLEKHA7 on the regulated induction of AML behavior and growth alterations were investigated. PLEKHA7 re-expression diminished colony-forming ability and reinforced the incidence of growth retardation without apoptosis in AML cell lines. PLEKHA7 regulated the restoration of cell surface adhesion and integrity during normal homeostasis. Our findings revealed that PLEKHA7 functions as a behavior and growth modulator in AML. To our knowledge, the role of PLEKHA7 in AML had not been studied previously and our data could be exploited for further mechanistic studies and insights into altering human AML behavior and growth.

Liposomes and Extracellular Vesicles as Drug Delivery Systems: A Comparison of Composition, Pharmacokinetics, and Functionalization

Over the past decades, lipid-based nanoparticle drug delivery systems (DDS) have caught the attention of researchers worldwide, encouraging the field to rapidly develop improved ways for effective drug delivery. One of the most prominent examples is liposomes, which are spherical shaped artificial vesicles composed of lipid bilayers and able to encapsulate both hydrophilic and hydrophobic materials. At the same time, biological nanoparticles naturally secreted by cells, called extracellular vesicles (EVs), have emerged as promising more complex biocompatible DDS. In this review paper, the differences and similarities in the composition of both vesicles are evaluated, and critical mediators that affect their pharmacokinetics are elucidate. Different strategies that have been assessed to tweak the pharmacokinetics of both liposomes and EVs are explored, detailing the effects on circulation time, targeting capacity, and cytoplasmic delivery of therapeutic cargo. Finally, whether a hybrid system, consisting of a combination of only the critical constituents of both vesicles, could offer the best of both worlds is discussed. Through these topics, novel leads for further research are provided and, more importantly, gain insight in what the liposome field and the EV field can learn from each other.

The Galapagos Chip Platform for High-Throughput Screening of Cell Adhesive Chemical Micropatterns

In vivo cells reside in a complex extracellular matrix (ECM) that presents spatially distributed biochemical and -physical cues at the nano- to micrometer scales. Chemical micropatterning is successfully used to generate adhesive islands to control where and how cells attach and restore cues of the ECM in vitro. Although chemical micropatterning has become a powerful tool to study cell-material interactions, only a fraction of the possible micropattern designs was covered so far, leaving many other possible designs still unexplored. Here, a high-throughput screening platform called "Galapagos chip" is developed. It contains a library of 2176 distinct subcellular chemical patterns created using mathematical algorithms and a straightforward UV-induced two-step surface modification. This approach enables the immobilization of ligands in geometrically defined regions onto cell culture substrates. To validate the system, binary RGD/polyethylene glycol patterns are prepared on which human mesenchymal stem cells are cultured, and the authors observe how different patterns affect cell and organelle morphology. As proof of concept, the cells are stained for the mechanosensitive YAP protein, and, using a machine-learning algorithm, it is demonstrated that cell shape and YAP nuclear translocation correlate. It is concluded that the Galapagos chip is a versatile platform to screen geometrical aspects of cell-ECM interaction.

Thy-1 (CD90), Integrins and Syndecan 4 are Key Regulators of Skin Wound Healing

Acute skin wound healing is a multistage process consisting of a plethora of tightly regulated signaling events in specialized cells. The Thy-1 (CD90) glycoprotein interacts with integrins and the heparan sulfate proteoglycan syndecan 4, generating a trimolecular complex that triggers bi-directional signaling to regulate diverse aspects of the wound healing process. These proteins can act either as ligands or receptors, and they are critical for the successful progression of wound healing. The expression of Thy-1, integrins, and syndecan 4 is controlled during the healing process, and the lack of expression of any of these proteins results in delayed wound healing. Here, we review and discuss the roles and regulatory events along the stages of wound healing that support the relevance of Thy-1, integrins, and syndecan 4 as crucial regulators of skin wound healing.

Surface Functionalization of Poly(l-lactide-co-glycolide) Membranes with RGD-Grafted Poly(2-oxazoline) for Periodontal Tissue Engineering

Bone tissue defects resulting from periodontal disease are often treated using guided tissue regeneration (GTR). The barrier membranes utilized here should prevent soft tissue infiltration into the bony defect and simultaneously support bone regeneration. In this study, we designed a degradable poly(l-lactide-co-glycolide) (PLGA) membrane that was surface-modified with cell adhesive arginine-glycine-aspartic acid (RGD) motifs. For a novel method of membrane manufacture, the RGD motifs were coupled with the non-ionic amphiphilic polymer poly(2-oxazoline) (POx). The RGD-containing membranes were then prepared by solvent casting of PLGA, POx coupled with RGD (POx_RGD), and poly(ethylene glycol) (PEG) solution in methylene chloride (DCM), followed by DCM evaporation and PEG leaching. Successful coupling of RGD to POx was confirmed spectroscopically by Raman, Fourier transform infrared in attenuated reflection mode (FTIR-ATR), and X-ray photoelectron (XPS) spectroscopy, while successful immobilization of POx_RGD on the membrane surface was confirmed by XPS and FTIR-ATR. The resulting membranes had an asymmetric microstructure, as shown by scanning electron microscopy (SEM), where the glass-cured surface was more porous and had a higher surface area then the air-cured surface. The higher porosity should support bone tissue regeneration, while the air-cured side is more suited to preventing soft tissue infiltration. The behavior of osteoblast-like cells on PLGA membranes modified with POx_RGD was compared to cell behavior on PLGA foil, non-modified PLGA membranes, or PLGA membranes modified only with POx. For this, MG-63 cells were cultured for 4, 24, and 96 h on the membranes and analyzed by metabolic activity tests, live/dead staining, and fluorescent staining of actin fibers. The results showed bone cell adhesion, proliferation, and viability to be the highest on membranes modified with POx_RGD, making them possible candidates for GTR applications in periodontology and in bone tissue engineering.

Core-Shell Microcapsules: Biofabrication and Potential Applications in Tissue Engineering and Regenerative Medicine

The construction of biomaterial scaffolds that accurately recreate the architecture of living tissues in vitro is a major challenge in the field of tissue engineering and regenerative medicine. Core-shell microcapsules...

Mesenchymal stem cell-based nanoparticles and scaffolds in regenerative medicine

Mesenchymal stem cells (MSCs) are adult stem cells owing to their regenerative potential and multilineage potency. MSCs have wide-scale applications either in their native cellular form or in conjugation with specific biomaterials as nanocomposites. Majorly, these natural or synthetic biomaterials are being used in the form of metallic and non-metallic nanoparticles (NPs) to encapsulate MSCs within hydrogels like alginate or chitosan or drug cargo loading into MSCs. In contrast, nanofibers of polymer scaffolds such as polycaprolactone (PCL), poly-lactic-co-glycolic acid (PLGA), poly-L-lactic acid (PLLA), silk fibroin, collagen, chitosan, alginate, hyaluronic acid (HA), and cellulose are used to support or grow MSCs directly on it. These MSCs based nanotherapies have application in multiple domains of biomedicine including wound healing, bone and cartilage engineering, cardiac disorders, and neurological disorders. This study focused on current approaches of MSCs-based therapies and has been divided into two major sections. The first section elaborates on MSC-based nano-therapies and their plausible applications including exosome engineering and NPs encapsulation. The following section focuses on the various MSC-based scaffold approaches in tissue engineering. Conclusively, this review mainly focused on MSC-based nanocomposite's current approaches and compared their advantages and limitations for building effective regenerative medicines.

Developing biomaterials to mediate the spatial distribution of integrins

Innovation in material design to regulate cell behavior and function is one of the primary tasks in materials science. Integrins, a family of cell surface-adhesion receptors that mechanically connect the extracellular matrix (ECM) to the intracellular cytoskeleton, have long served as primary targets for the design of biomaterials because their activity is not only critical to a wide range of cell and tissue functions but also subject to very tight and complex regulations from the outside environment. To review the recent progress of material innovations targeting the spatial distribution of integrins, we first introduce the interaction mechanisms between cells and the ECM by highlighting integrin-based cell adhesions, describing how integrins respond to environmental stimuli, including variations in ligand presentation, mechanical cues, and topographical variations. Then, we overview the current development of soft materials in guiding cell behaviors and functions via spatial regulation of integrins. Finally, we discuss the current limitations of these technologies and the advances that may be achieved in the future. Undoubtedly, synthetic soft materials that mediate the spatial distribution of integrins play an important role in biomaterial innovations for advancing biomedical applications and addressing fundamental biological questions.

Possible Treatment of Myocardial Infarct Based on Tissue Engineering Using a Cellularized Solid Collagen Scaffold Functionalized with Arg-Glyc-Asp (RGD) Peptide

Currently, the clinical impact of cell therapy after a myocardial infarction (MI) is limited by low cell engraftment due to low cell retention, cell death in inflammatory and poor angiogenic infarcted areas, secondary migration. Cells interact with their microenvironment through integrin mechanoreceptors that control their survival/apoptosis/differentiation/migration and proliferation. The association of cells with a three-dimensional material may be a way to improve interactions with their integrins, and thus outcomes, especially if preparations are epicardially applied. In this review, we will focus on the rationale for using collagen as a polymer backbone for tissue engineering of a contractile tissue. Contractilities are reported for natural but not synthetic polymers and for naturals only for: collagen/gelatin/decellularized-tissue/fibrin/Matrigel™ and for different material states: hydrogels/gels/solids. To achieve a thick/long-term contractile tissue and for cell transfer, solid porous compliant scaffolds are superior to hydrogels or gels. Classical methods to produce solid scaffolds: electrospinning/freeze-drying/3D-printing/solvent-casting and methods to reinforce and/or maintain scaffold properties by reticulations are reported. We also highlight the possibility of improving integrin interaction between cells and their associated collagen by its functionalizing with the RGD-peptide. Using a contractile patch that can be applied epicardially may be a way of improving ventricular remodeling and limiting secondary cell migration.

Design of α/β-Hybrid Peptide Ligands of α4β1 Integrin Equipped with a Linkable Side Chain for Chemoselective Biofunctionalization of Microstructured Materials

Arg-Gly-Asp (RGD)-binding integrins, e.g., αvβ3, αvβ1, αvβ5 integrins, are currently regarded as privileged targets for the delivery of diagnostic and theranostic agents, especially in cancer treatment. In contrast, scarce attention has been paid so far to the diagnostic opportunities promised by integrins that recognize other peptide motifs. In particular, α4β1 integrin is involved in inflammatory, allergic, and autoimmune diseases, therefore, it represents an interesting therapeutic target. Aiming at obtaining simple, highly stable ligands of α4β1 integrin, we designed hybrid α/β peptidomimetics carrying linkable side chains for the expedient functionalization of biomaterials, nano- and microparticles. We identified the prototypic ligands MPUPA-(R)-isoAsp(NHPr)-Gly-OH (12) and MPUPA-Dap(Ac)-Gly-OH (13) (MPUPA, methylphenylureaphenylacetic acid; Dap, 2,3-diamino propionic acid). Modification of 12 and 13 by introduction of flexible linkers at isoAsp or Dap gave 49 and 50, respectively, which allowed for coating with monolayers (ML) of flat zeolite crystals. The resulting peptide–zeolite MLs were able to capture selectively α4β1 integrin-expressing cells. In perspective, the α4β1 integrin ligands identified in this study can find applications for preparing biofunctionalized surfaces and diagnostic devices to control the progression of α4β1 integrin-correlated diseases.

Scaffolds in Periodontal Regenerative Treatment

Successful periodontal regeneration requires the hierarchical reorganization of multiple tissues including periodontal ligament, cementum, alveolar bone, and gingiva. The limitation of conventional regenerative therapies has been attracting research interest in tissue engineering-based periodontal therapies where progenitor cells, scaffolds, and bioactive molecules are delivered. Scaffolds offer not only structural support but also provide geometrical clue to guide cell fate. Additionally, functionalization improves bioactive properties to the scaffold. Various scaffold designs have been proposed for periodontal regeneration. These include the fabrication of biomimetic periodontal extracellular matrix, multiphasic scaffolds with tissue-specific layers, and personalized 3D printed scaffolds. This review summarizes the basic concept as well as the recent advancement of scaffold designing and fabrication for periodontal regeneration and provides an insight of future clinical translation.

Peptide-Based Drug Delivery Systems

Peptide-based drug delivery systems have many advantages when compared to synthetic systems in that they have better biocompatibility, biochemical and biophysical properties, lack of toxicity, controlled molecular weight via solid phase synthesis and purification. Lysosomes, solid lipid nanoparticles, dendrimers, polymeric micelles can be applied by intravenous administration, however they are of artificial nature and thus may induce side effects and possess lack of ability to penetrate the blood-brain barrier. An analysis of nontoxic drug delivery systems and an establishment of prospective trends in the development of drug delivery systems was needed. This review paper summarizes data, mainly from the past 5 years, devoted to the use of peptide-based carriers for delivery of various toxic drugs, mostly anticancer or drugs with limiting bioavailability. Peptide-based drug delivery platforms are utilized as peptide–drug conjugates, injectable biodegradable particles and depots for delivering small molecule pharmaceutical substances (500 Da) and therapeutic proteins. Controlled drug delivery systems that can effectively deliver anticancer and peptide-based drugs leading to accelerated recovery without significant side effects are discussed. Moreover, cell penetrating peptides and their molecular mechanisms as targeting peptides, as well as stimuli responsive (enzyme-responsive and pH-responsive) peptides and peptide-based self-assembly scaffolds are also reviewed.

Peptide-Conjugated Nano Delivery Systems for Therapy and Diagnosis of Cancer

Peptides are strings of approximately 2-50 amino acids, which have gained huge attention for theranostic applications in cancer research due to their various advantages including better biosafety, customizability, convenient process of synthesis, targeting ability via recognizing biological receptors on cancer cells, and better ability to penetrate cell membranes. The conjugation of peptides to the various nano delivery systems (NDS) has been found to provide an added benefit toward targeted delivery for cancer therapy. Moreover, the simultaneous delivery of peptide-conjugated NDS and nano probes has shown potential for the diagnosis of the malignant progression of cancer. In this review, various barriers hindering the targeting capacity of NDS are addressed, and various approaches for conjugating peptides and NDS have been discussed. Moreover, major peptide-based functionalized NDS targeting cancer-specific receptors have been considered, including the conjugation of peptides with extracellular vesicles, which are biological nanovesicles with promising ability for therapy and the diagnosis of cancer.

Peptide-Assisted Nucleic Acid Delivery Systems on the Rise

Concerns associated with nanocarriers' therapeutic efficacy and side effects have led to the development of strategies to advance them into targeted and responsive delivery systems. Owing to their bioactivity and biocompatibility, peptides play a key role in these strategies and, thus, have been extensively studied in nanomedicine. Peptide-based nanocarriers, in particular, have burgeoned with advances in purely peptidic structures and in combinations of peptides, both native and modified, with polymers, lipids, and inorganic nanoparticles. In this review, we summarize advances on peptides promoting gene delivery systems. The efficacy of nucleic acid therapies largely depends on cell internalization and the delivery to subcellular organelles. Hence, the review focuses on nanocarriers where peptides are pivotal in ferrying nucleic acids to their site of action, with a special emphasis on peptides that assist anionic, water-soluble nucleic acids in crossing the membrane barriers they encounter on their way to efficient function. In a second part, we address how peptides advance nanoassembly delivery tools, such that they navigate delivery barriers and release their nucleic acid cargo at specific sites in a controlled fashion.

Key Roles of RGD-Recognizing Integrins During Cardiac Development, on Cardiac Cells, and After Myocardial Infarction

Cardiac cells interact with the extracellular matrix (ECM) proteins through integrin mechanoreceptors that control many cellular events such as cell survival, apoptosis, differentiation, migration, and proliferation. Integrins play a crucial role in cardiac development as well as in cardiac fibrosis and hypertrophy. Integrins recognize oligopeptides present on ECM proteins and are involved in three main types of interaction, namely with collagen, laminin, and the oligopeptide RGD (Arg-Gly-Asp) present on vitronectin and fibronectin proteins. To date, the specific role of integrins recognizing the RGD has not been addressed. In this review, we examine their role during cardiac development, their role on cardiac cells, and their upregulation during pathological processes such as heart fibrosis and hypertrophy. We also examine their role in regenerative and angiogenic processes after myocardial infarction (MI) in the peri-infarct area. Specific targeting of these integrins may be a way of controlling some of these pathological events and thereby improving medical outcomes.

A Review on Toxicity and Challenges in Transferability of Surface-functionalized Metallic Nanoparticles from Animal Models to Humans

Abstract The unique size and surface morphology of nanoparticles (NPs) have substantially influenced all aspects of human life, making nanotechnology a novel and promising field for various applications in biomedical sciences. Metallic NPs have gained immense interest over the last few decades due to their promising optical, electrical, and biological properties. However, the aggregation and the toxic nature of these NPs have restricted their utilization in more optimized applications. The optimum selection of biopolymers and biological macromolecules for surface functionalization of metallic NPs will significantly improve their biological applicability and biocompatibility. The present mini-review attempts to stress the overview of recent strategies involved in surface functionalization of metallic NPs, their specific biomedical applications, and comparison of their in vitro, ex vivo, and in vivo toxicities with non-functionalized metallic NPs. In addition, this review also discusses the various challenges for metallic NPs to undergo human clinical trials.

Spidroin Silk Fibers with Bioactive Motifs of Extracellular Proteins for Neural Tissue Engineering

The interaction of neural progenitor cells (NPCs) with the extracellular matrix (ECM) plays an important role in neural tissue regeneration. Understanding which motifs of the ECM proteins are crucial for normal NPC adhesion, proliferation, and differentiation is important in order to create more adequate tissue engineered models of neural tissue and to efficiently study the central nervous system regeneration mechanisms. We have shown earlier that anisotropic matrices prepared from a mixture of recombinant dragline silk proteins, such as spidroin 1 and spidroin 2, by electrospinning are biocompatible with NPCs and provide good proliferation and oriented growth of neurites. This study objective was to find the effects of spidroin-based electrospun materials, modified with peptide motifs of the extracellular matrix proteins (RGD, IKVAV, and VAEIDGIEL) on adhesion, proliferation, and differentiation of directly reprogrammed neural precursor cells (drNPCs). The structural and biomechanical studies have shown that spidroin-based electrospun mats (SBEM), modified with ECM peptides, are characterized by a uniaxial orientation and elastic moduli in the swollen state, comparable to those of the dura mater. It has been found for the first time that drNPCs on SBEM mostly preserve their stemness in the growth medium and even in the differentiation medium with brain-derived neurotrophic factor and glial cell line-derived neurotrophic factor, while addition of the mentioned ECM-peptide motifs may shift the balance toward neuroglial differentiation. We have demonstrated that the RGD motif promotes formation of a lower number of neurons with longer neurites, while the IKVAV motif is characterized by formation of a greater number of NF200-positive neurons with shorter neurites. At the same time, all the studied matrices preserve up to 30% of neuroglial progenitor cells, phenotypically similar to radial glia derived from the subventricular zone. We believe that, by using this approach and modifying spidroin by various ECM-motifs or other substances, one may create an in vitro model for the neuroglial stem cell niche with the potential control of their differentiation.

Targeted delivery of neural progenitor cell-derived extracellular vesicles for anti-inflammation after cerebral ischemia

Ischemic stroke remains a major cause of death, and anti-inflammatory strategies hold great promise for preventing major brain injury during reperfusion. In the past decade, stem cell-derived extracellular vesicles (EVs) have emerged as novel therapeutic effectors in immune modulation. However, the intravenous delivery of EVs into the ischemic brain remains a challenge due to poor targeting of unmodified EVs, and the costs of large-scale production of stem cell-derived EVs hinder their clinical application.

Methods: EVs were isolated from a human neural progenitor cell line, and their anti-inflammatory effects were verified in vitro. To attach targeting ligands onto EVs, we generated a recombinant fusion protein containing the arginine-glycine-aspartic acid (RGD)-4C peptide (ACDCRGDCFC) fused to the phosphatidylserine (PS)-binding domains of lactadherin (C1C2), which readily self-associates onto the EV membrane. Subsequently, in a middle cerebral artery occlusion (MCAO) mouse model, the RGD-C1C2-bound EVs (RGD-EV) were intravenously injected through the tail vein, followed by fluorescence imaging and assessment of proinflammatory cytokines expression and microglia activation.

Results: The neural progenitor cell-derived EVs showed intrinsic anti-inflammatory activity. The RGD-EV targeted the lesion region of the ischemic brain after intravenous administration, and resulted in a strong suppression of the inflammatory response. Furthermore, RNA sequencing revealed a set of 7 miRNAs packaged in the EVs inhibited MAPK, an inflammation related pathway.

Conclusion: These results point to a rapid and easy strategy to produce targeting EVs and suggest a potential therapeutic agent for ischemic stroke.

Molecular Delivery of Cytotoxic Agents via Integrin Activation

Integrins are cell adhesion receptors overexpressed in tumor cells. A direct inhibition of integrins was investigated, but the best inhibitors performed poorly in clinical trials. A gained attention towards these receptors arouse because they could be target for a selective transport of cytotoxic agents. Several active-targeting systems have been developed to use integrins as a selective cell entrance for some antitumor agents. The aim of this review paper is to report on the most recent results on covalent conjugates between integrin ligands and antitumor drugs. Cytotoxic drugs thus conjugated through specific linker to integrin ligands, mainly RGD peptides, demonstrated that the covalent conjugates were more selective against tumor cells and hopefully with fewer side effects than the free drugs.

Redirecting cytotoxic T cells with chemically programmed antibodies

T-cell engaging bispecific antibodies (T-biAbs) mediate potent and selective cytotoxicity by combining specificities for target and effector cells in one molecule. Chemically programmed T-biAbs (cp-T-biAbs) are precisely assembled compositions of (i) small molecules that govern cancer cell surface targeting with high affinity and specificity and (ii) antibodies that recruit and activate T cells and equip the small molecule with confined biodistribution and longer circulatory half-life. Conceptually similar to cp-T-biAbs, switchable chimeric antigen receptor T cells (sCAR-Ts) can also be put under the control of small molecules by using a chemically programmed antibody as a bispecific adaptor molecule. As such, cp-T-biAbs and cp-sCAR-Ts can endow small molecules with the power of cancer immunotherapy. We here review the concept of chemically programmed antibodies for recruiting and activating T cells as a promising strategy for broadening the utility of small molecules in cancer therapy.