Instant Hydrogelation Inspired by Inflammasomes

Natural and Engineered Isoforms of the Inflammasome Adaptor ASC Form Noncovalent, pH-Responsive Hydrogels

The protein ASC polymerizes into intricate filament networks to assemble the inflammasome, a filamentous multiprotein complex that triggers the inflammatory response. ASC carries two Death Domains integrally involved in protein self-association for filament assembly. We have leveraged this behavior to create noncovalent, pH-responsive hydrogels of full-length, folded ASC by carefully controlling the pH as a critical factor in the polymerization process. We show that natural variants of ASC (ASC isoforms) involved in inflammasome regulation also undergo hydrogelation. To further demonstrate this general capability, we engineered proteins inspired by the ASC structure that also form hydrogels. We analyzed the structural network of the natural and engineered protein hydrogels using transmission and scanning electron microscopy and studied their viscoelastic behavior using shear rheology. Our results reveal one of the very few examples of hydrogels created by the self-assembly of globular proteins and domains in their native conformation and show that Death Domains can be used alone or as building blocks to engineer bioinspired hydrogels.

Natural and engineered isoforms of the inflammasome adaptor ASC form non-covalent, pH-responsive hydrogels

The protein ASC polymerizes into intricate filament networks to assemble the inflammasome, a filamentous multiprotein complex that triggers the inflammatory response. ASC carries two Death Domains integrally involved in protein self-association for filament assembly. We have leveraged this behavior to create non-covalent, pH-responsive hydrogels of full-length, folded ASC by carefully controlling the pH as a critical factor in the polymerization process. We show that natural variants of ASC (ASC isoforms) involved in inflammasome regulation also undergo hydrogelation. To further demonstrate this general capability, we engineered proteins inspired in the ASC structure that successfully form hydrogels. We analyzed the structural network of the natural and engineered protein hydrogels using transmission and scanning electron microscopy, and studied their viscoelastic behavior by shear rheology. Our results reveal one of the very few examples of hydrogels created by the self-assembly of globular proteins and domains in their native conformation and show that Death Domains can be used alone or as building blocks to engineer bioinspired hydrogels.

Self-Assembly, Bioactivity, and Nanomaterials Applications of Peptide Conjugates with Bulky Aromatic Terminal Groups

The self-assembly and structural and functional properties of peptide conjugates containing bulky terminal aromatic substituents are reviewed with a particular focus on bioactivity. Terminal moieties include Fmoc [fluorenylmethyloxycarbonyl], naphthalene, pyrene, naproxen, diimides of naphthalene or pyrene, and others. These provide a driving force for self-assembly due to π-stacking and hydrophobic interactions, in addition to the hydrogen bonding, electrostatic, and other forces between short peptides. The balance of these interactions leads to a propensity to self-assembly, even for conjugates to single amino acids. The hybrid molecules often form hydrogels built from a network of β-sheet fibrils. The properties of these as biomaterials to support cell culture, or in the development of molecules that can assemble in cells (in response to cellular enzymes, or otherwise) with a range of fascinating bioactivities such as anticancer or antimicrobial activity, are highlighted. In addition, applications of hydrogels as slow-release drug delivery systems and in catalysis and other applications are discussed. The aromatic nature of the substituents also provides a diversity of interesting optoelectronic properties that have been demonstrated in the literature, and an overview of this is also provided. Also discussed are coassembly and enzyme-instructed self-assembly which enable precise tuning and (stimulus-responsive) functionalization of peptide nanostructures.

Fabrication of injectable hydrogels from an anticancer peptide for local therapeutic delivery and synergistic photothermal-chemotherapy

The susceptibility of anticancer peptides to proteolytic degradation is often considered as a major weakness that limits systemic therapeutic applications. However, localized delivery of anticancer peptides via injectable hydrogels is expected to improve drug efficacy and reduce systemic toxicity. Herein, an injectable hydrogel with drug releasing properties, NIR responsiveness and pH sensitivity was developed from an anticancer peptide (KL), Fe³⁺ ions and protocatechualdehyde via dynamic and reversible interactions. Benefiting from the formation of Fe(III)-catechol complexes between Fe³⁺ ions and protocatechualdehyde within gel networks, the obtained hydrogel exhibited intrinsic NIR absorption properties for photothermal ablation of tumor cells, and remote light control of drug release. Besides, the pH-labile imine bonds between KL and protocatechualdehyde endowed the injectable gel with pH sensitivity for sustained release of KL under a mildly acidic environment, inducing membrane destabilization and facilitating the cell uptake of DOX for combinational chemotherapy. Both in vitro and in vivo experiments revealed that the injectable hydrogel exhibited a synergistic therapeutic effect on inhibiting tumor growth via combinational photothermal-chemotherapy. Therefore, this work provides a promising attempt to develop a therapeutic hydrogel from an anticancer peptide, which could work as a localized drug delivery platform for synergistic photothermal-chemotherapy.

Chitosan crosslinking with pyridoxal 5-phosphate vitamer toward biocompatible hydrogels for in vivo applications

Vitamin B6 is an essential micronutrient in the mammalian diet, with role of coenzyme and synergistic effect with some antibiotics and antitumor drugs. Based on these, we hypothesized that its use for the preparation of hydrogels can yield multifunctional biomaterials suitable for in vivo applications. To this aim, chitosan was reacted with the active form of vitamin B6, pyridoxal 5-phosphate, via acid condensation, when clear hydrogels were obtained. Their investigation by structural characterization methods proved that the hydrogelation was a consequence of both covalent imine formation and physical interactions. The novel hydrogels had microporous morphology and showed shrinking effect in phosphate buffer, indicating good shape preservation and slow dissolution in in vivo environment. Their enzymatic biodegradation could be controlled by the imination degree, varying from 40 to 61% in 21 days. They demonstrated very good in vitro cytocompatibility on normal human dermal fibroblasts cells and no harmful effect on experimental mice, confirming their safely use for in vivo application.

Recent Progress in the Design and Application of Supramolecular Peptide Hydrogels in Cancer Therapy

Supramolecular peptide hydrogel (SPH) is a class of biomaterials self-assembled from peptide-based gelators through non-covalent interactions. Among many of its biomedical applications, the potential of SPH in cancer therapy has been vastly explored in the past decade, taking advantage of its good biocompatibility, multifunctionality, and injectability. SPHs can exert localized cancer therapy and induce systemic anticancer immunity to prevent tumor recurrence, depending on the design of SPH. This review first gives a brief introduction to SPH and then outlines the major types of peptide-based gelators that have been developed so far. The methodologies to tune the physicochemical properties and biological activities are summarized. The recent advances of SPH in cancer therapy as carriers, prodrugs, or drugs are highlighted. Finally, the clinical translation potential and main challenges in this field are also discussed.

Assemblies of Peptides in a Complex Environment and their Applications

Using peptide assemblies with emergent properties to achieve elaborate functions has attracted increasing attention in recent years. Besides tailoring the self-assembly of peptides in vitro, peptide research is advancing into a new and exciting frontier: the rational design of peptide assemblies (or their derivatives) for biological functions in a complex environment. This Minireview highlights recent developments in peptide assemblies and their applications in biological systems. After introducing the unique merits of peptide assemblies, we discuss the recent progress in designing peptides (or peptide derivatives) for self-assembly with conformational control. Then, we describe biological functions of peptide assemblies, with an emphasis on approach-instructed assembly for spatiotemporal control of peptide assemblies, in the cellular context. Finally, we discuss the future promises and challenges of this exciting area of chemistry.

Nucleopeptide Assemblies Selectively Sequester ATP in Cancer Cells to Increase the Efficacy of Doxorubicin

Herein, we report that assemblies of nucleopeptides selectively sequester ATP in complex conditions (for example, serum and cytosol). We developed assemblies of nucleopeptides that selectively sequester ATP over ADP. Counteracting enzymes interconvert ATP and ADP to modulate the nanostructures formed by the nucleopeptides and the nucleotides. The nucleopeptides, sequestering ATP effectively in cells, slow down efflux pumps in multidrug-resistant cancer cells, thus boosting the efficacy of doxorubicin, an anticancer drug. Investigation of 11 nucleopeptides (including d- and l-enantiomers) yields five more nucleopeptides that differentiate ATP and ADP through either precipitation or gelation. As the first example of assemblies of nucleopeptides that interact with ATP and disrupt intracellular ATP dynamics, this work illustrates the use of supramolecular assemblies to interact with small and essential biological molecules for controlling cell behavior.

Regulating Higher-Order Organization through the Synergy of Two Self-Sorted Assemblies

The extracellular matrix (ECM) is the natural fibrous scaffold that regulates cell behavior in a hierarchical manner. By mimicking the dynamic and reciprocal interactions between ECM and cells, higher-order molecular self-assembly (SA), mediated through the dynamic growth of scaffold-like nanostructures assembled by different molecular components, was developed. Designed and synthesized were two self-sorted coumarin-based gelators, a peptide molecule and a benzoate molecule, which self-assemble into nanofibers and nanobelts, respectively, with different dynamic profiles. Upon the dynamic growth of the fibrous scaffold assembled from peptide gelators, nanobelts assembled from benzoate gelators transform into a layer-by-layer nanosheet, reaching ninefold increase in height. By using light and an enzyme, the spatial-temporal growth of the scaffold can be modified, leading to in situ height regulation of the higher-order architecture.

Hydrogen sulfide induced supramolecular self-assembly in living cells

A gasotransmitter mediated reduction instructs supramolecular self-assembly in multiple living cell lines, revealing the variation in intracellular H₂S production.