Phosphobisaromatic motifs enable rapid enzymatic self-assembly and hydrogelation of short peptides

Multicomponent supramolecular hydrogels composed of cationic phenylalanine derivatives and anionic amino acids

Supramolecular hydrogels composed of self-assembled fluorenylmethoxycarbonyl phenylalanine (Fmoc-Phe) derivatives have been the focus of intense study as novel materials for biological applications that include drug delivery, tissue engineering, and regenerative medicine. Cationic Fmoc-Phe derivatives functionalized with diaminopropane (Fmoc-Phe-DAP) have been shown to undergo self-assembly and hydrogelation upon an increase in solution ionic strength by the addition of inorganic salts that provide cation-shielding counterions. Further, the identity of the inorganic salts modifies the assembly morphology and emergent viscoelastic properties of the resulting materials. Herein, we report multicomponent hydrogels composed of Fmoc-Phe-DAP derivatives in which hydrogelation is promoted by the addition of anionic amino acids, monosodium aspartate or monosodium glutamate. Aspartate and glutamate salts both support supramolecular gelation of Fmoc-Phe-DAP derivatives, although only the glutamate gels remain stable over periods longer than one hour. The assemblies formed by Fmoc-Phe-DAP derivatives in the presence of aspartate and glutamate are morphologically distinct relative to those formed in the presence of sodium chloride. The viscoelastic properties of stable glutamate/Fmoc-Phe-DAP derivative hydrogels are sensitive to the ratios of glutamate to Fmoc-Phe-DAP derivative, with increased concentrations of glutamate corresponding to higher viscoelastic strength. These multicomponent systems demonstrate that comixing unfunctionalized amino acids with self-assembling Fmoc-Phe-DAP derivatives is yet another effective method to modify the emergent properties of the resulting materials.

Self-Assembly of Noncanonical Peptides: A New Frontier in Cancer Therapeutics and Beyond

In addition to the 20 standard amino acids that form the building blocks of proteins, nature employs alternative amino acids to create specialized "noncanonical peptides." These unique peptides, found in organisms from bacteria to humans, often exhibit unconventional structures and functionalities, playing critical roles in modulating cellular processes, particularly as antibiotics. Their potential has attracted significant interest for designing novel functional materials based on noncanonical peptides. This review highlights recent advances in the generation and application of noncanonical peptide assemblies. It begins with a definition of noncanonical peptides, including classic examples that showcase their distinct structures and useful biological activities. Then the applications of noncanonical peptide assemblies in developing anticancer therapeutics are discussed, focusing on recent and representative studies that demonstrate their efficacy and versatility in targeting tumor cells. Beyond oncology, it is explored how noncanonical peptide assemblies have been utilized in biomaterials, regenerative medicine, molecular imaging and catalysis. Finally, perspectives are offered on future directions in this rapidly evolving field, emphasizing exciting opportunities and remaining challenges that will drive continued innovation in designing and applying noncanonical peptide-based assemblies.

Therapeutic Supramolecular Polymers: Designs and Applications

The self-assembly of low-molecular-weight building motifs into supramolecular polymers has unlocked a new realm of materials with distinct properties and tremendous potential for advancing medical practices. Leveraging the reversible and dynamic nature of non-covalent interactions, these supramolecular polymers exhibit inherent responsiveness to their microenvironment, physiological cues, and biomolecular signals, making them uniquely suited for diverse biomedical applications. In this review, we intend to explore the principles of design, synthesis methodologies, and strategic developments that underlie the creation of supramolecular polymers as carriers for therapeutics, contributing to the treatment and prevention of a spectrum of human diseases. We delve into the principles underlying monomer design, emphasizing the pivotal role of non-covalent interactions, directionality, and reversibility. Moreover, we explore the intricate balance between thermodynamics and kinetics in supramolecular polymerization, illuminating strategies for achieving controlled sizes and distributions. Categorically, we examine their exciting biomedical applications: individual polymers as discrete carriers for therapeutics, delving into their interactions with cells, and in vivo dynamics; and supramolecular polymeric hydrogels as injectable depots, with a focus on their roles in cancer immunotherapy, sustained drug release, and regenerative medicine. As the field continues to burgeon, harnessing the unique attributes of therapeutic supramolecular polymers holds the promise of transformative impacts across the biomedical landscape.

Effect of molar ratio and concentration on the rheological properties of two-component supramolecular hydrogels: tuning of the morphological and drug releasing behaviour

Self-assembled supramolecular hydrogels offer great potential as biomaterials and drug delivery systems. Specifically, peptide-based multicomponent hydrogels are promising materials due to their advantage that their mechanical and physical properties can be tuned to enhance their functionalities and broaden their applications. Herein, we report two-component assembly and formation of hydrogels containing inexpensive complementary anionic, BUVV-OH (A), and cationic, KFFC12 (B), peptide amphiphiles. Individually, neither of these components formed a hydrogel, while mixtures with compositions 1 : 1, 1 : 2, and 2 : 1 (molar ratio) as A : B show hydrogel formation (Milli-Q water, at pH = 6.79). These hydrogels displayed a good shear-thinning behaviour with different mechanical stabilities and nano-fibrous network structures. The 1 : 1 hydrogel shows good cell viability for human embryonic kidney (HEK-293) cells and CHO cells indicating its non-cytotoxicity. The biocompatible, thixotropic 1 : 1 hydrogel with a nanofiber network structure shows the highest mechanical strength with a storage modulus of 3.4 × 103 Pa. The hydrogel is able to encapsulate drugs including antibiotics amoxicillin and rifampicin, and anticancer drug doxorubicin, and it exhibits sustainable release of 76%, 70%, and 81% respectively in vitro after 3 days. The other two mixtures (composition 1 : 2 and 2 : 1) are unable to form a hydrogel when they are loaded with these drugs. Interestingly, it is noticed that with an increase in concentration, the mechanical strength of a 1 : 1 hydrogel is significantly enhanced, showing potential that may act as a scaffold for tissue engineering. The two-component gel offers tunable mechanical properties, thixotropy, injectability, and biocompatibility and has great potential as a scaffold for sustained drug release and tissue engineering.

Mechanistic Insights into Hyaluronic Acid Induced Peptide Nanofiber Organization in Supramolecular Hydrogels

Composite hydrogels composed of low-molecular-weight peptide self-assemblies and polysaccharides are gaining great interest as new types of biomaterials. Interactions between polysaccharides and peptide self-assemblies are well reported, but a molecular picture of their impact on the resulting material is still missing. Using the phosphorylated tripeptide precursor Fmoc-FFpY (Fmoc, fluorenylmethyloxycarbonyl; F, phenylalanine; Y, tyrosine; p, phosphate group), we investigated how hyaluronic acid (HA) influences the enzyme-assisted self-assembly of Fmoc-FFY generated in situ in the presence of alkaline phosphatase (AP). In the absence of HA, Fmoc-FFY peptides are known to self-assemble in nanometer thick and micrometer long fibers. The presence of HA leads to the spontaneous formation of bundles of several micrometers thickness. Using fluorescence recovery after photobleaching (FRAP), we find that in the bundles both (i) HA colocalizes with the peptide self-assemblies and (ii) its presence in the bundles is highly dynamic. The attractive interaction between negatively charged peptide fibers and negatively charged HA chains is explained through molecular dynamic simulations that show the existence of hydrogen bonds. Whereas the Fmoc-FFY peptide self-assembly itself is not affected by the presence of HA, this polysaccharide organizes the peptide nanofibers in a nematic phase visible by small-angle X-ray scattering (SAXS). The mean distance d between the nanofibers decreases by increasing the HA concentration c, but remains always larger than the diameter of the peptide nanofibers, indicating that they do not interact directly with each other. At a high enough HA concentration, the nematic organization transforms into an ordered 2D hexagonal columnar phase with a nanofiber distance d of 117 Å. Depletion interaction generated by the polysaccharides can explain the experimental power law variation d ∼ c - 1 / 4 and is responsible for the bundle formation and organization. Such behavior is thus suggested for the first time on nano-objects using polymers partially adsorbing on self-assembled peptide nanofibers.

In Vivo Anchoring Bis-Pyrene Probe for Molecular Imaging of Early Gastric Cancer by Endoscopic Techniques

With the development of blue laser endoscopy (BLE) technique, it's often used to diagnose early gastric cancer (EGC) by the morphological changes of blood vessels through BLE. However, EGC is still not obvious to identify, resulting in a high rate of missed diagnosis. Molecular imaging can show the changes in early tumors at molecular level, which provides a possibility for diagnosing EGC. Therefore, developing a probe that visually monitors blood vessels of EGC under BLE is particularly necessary. Herein, a bis-pyrene (BP) based nanoprobe (BP-FFVLK-(PEG)-RGD, M1 ) is designed, which can target angiogenesis and self-assemble into fibers in situ, resulting in stable and long-term retention in tumor. Moreover, M1 probe can emit yellow-green fluorescence for imaging under BLE. M1 probe is confirmed to steadily remain in tumor for up to 96 hours in mice transplanted subcutaneously. In addition, the M1 probe is able to target angiogenesis for molecular imaging of isolated human gastric cancer tissue under BLE. Finally, M1 probe i.v. injected into primary gastric cancer model rabbits successfully highlighted the tumor site under BLE, which is confirmed by pathological analysis. It's the first time to develop a probe for diagnosing EGC by visualizing angiogenesis under BLE, showing great clinical significance.

Switching the Mode of Drug Release from a Reaction-Coupled Low-Molecular-Weight Gelator System by Altering Its Reaction Pathway

Low-molecular-weight hydrogels are attractive scaffolds for drug delivery applications because of their modular and facile preparation starting from inexpensive molecular components. The molecular design of the hydrogelator results in a commitment to a particular release strategy, where either noncovalent or covalent bonding of the drug molecule dictates its rate and mechanism. Herein, we demonstrate an alternative approach using a reaction-coupled gelator to tune drug release in a facile and user-defined manner by altering the reaction pathway of the low-molecular-weight gelator (LMWG) and drug components through an acylhydrazone-bond-forming reaction. We show that an off-the-shelf drug with a reactive handle, doxorubicin, can be covalently bound to the gelator through its ketone moiety when the addition of the aldehyde component is delayed from 0 to 24 h, or noncovalently bound with its addition at 0 h. We also examine the use of an l-histidine methyl ester catalyst to prepare the drug-loaded hydrogels under physiological conditions. Fitting of the drug release profiles with the Korsmeyer-Peppas model corroborates a switch in the mode of release consistent with the reaction pathway taken: increased covalent ligation drives a transition from a Fickian to a semi-Fickian mode in the second stage of release with a decreased rate. Sustained release of doxorubicin from the reaction-coupled hydrogel is further confirmed in an MTT toxicity assay with MCF-7 breast cancer cells. We demonstrate the modularity and ease of the reaction-coupled approach to prepare drug-loaded self-assembled hydrogels in situ with tunable mechanics and drug release profiles that may find eventual applications in macroscale drug delivery.

Self-assembly hydrogels of therapeutic agents for local drug delivery

Advanced drug delivery systems are of vital importance to enhance therapeutic efficacy. Among various recently developed formulations, self-assembling hydrogels composed of therapeutic agents have shown promising potential for local drug delivery owing to their excellent biocompatibility, high drug-loading efficiency, low systemic toxicity, and sustained drug release behavior. In particular, therapeutic agents self-assembling hydrogels with well-defined nanostructures are beneficial for direct delivery to the target site via injection, not only improving drug availability, but also extending their retention time and promoting cellular uptake. In brief, the self-assembly approach offers better opportunities to improve the precision of pharmaceutical treatment and achieve superior treatment efficacies. In this review, we intend to cover the recent developments in therapeutic agent self-assembling hydrogels. First, the molecular structures, self-assembly mechanisms, and application of self-assembling hydrogels are systematically outlined. Then, we summarize the various self-assembly strategies, including the single therapeutic agent, metal-coordination, enzyme-instruction, and co-assembly of multiple therapeutic agents. Finally, the potential challenges and future perspectives are discussed. We hope that this review will provide useful insights into the design and preparation of therapeutic agent self-assembling hydrogels.

Enzyme-manipulated hydrogelation of small molecules for biomedical applications

Enzyme-manipulated hydrogelation based on self-assembly of small molecules is an attractive methodology for development of functional biomaterials. Upon the catalysis of enzymes, small-molecular precursors are converted into assemblable building blocks, which arrange into high-ordered nanofibers via non-covalent interactions at the molecular level, and further trap water to form hydrogels at the macroscopic level. Such approach has numerous advantages of region- and enantioselectivity, and mild reaction conditions for encapsulation of biomedications or cells that are fragile to environmental change. In addition to the common applications as drug reservoirs or cell scaffolds, the utilization of endogenous enzymes as stimuli to initiate self-assembly in the living cells and tissue is considered as an intelligent spatiotemporally controllable hydrogelation strategy for biomedical applications. The enzyme-instructed in situ self-assembly and hydrogelation can modulate the cell behavior, and even present therapeutic bioactivities, which provides a new perspective in the field of disease treatment. In this review, we categorize distinct enzymatic stimuli and elaborate substrate design, catalytic characteristics, and mechanisms of self-assembly and hydrogelation. The biomedical applications in drug delivery, tissue engineering, bioimaging, and in situ gelation-produced bioactivity are outlined. Advantages and limitations regarding the state-of-the-art enzyme-driven hydrogelation technologies and future perspectives are also discussed. STATEMENT OF SIGNIFICANCE: Hydrogel is a semi-solid soft material containing a large amount of water. Due to the features of adjustable flexibility, extremely porous architecture, and the high similarity of structure to natural extracellular matrices, the hydrogel has broad application prospects in biomedicine. In recent 20 years, enzyme-manipulated hydrogelation based on self-assembly of small molecules has developed rapidly as an attractive methodology for the construction of functional biomaterials. Upon the catalysis of enzymes, small-molecular precursors are converted into assemblable building blocks, which arrange into high-ordered nanofibers via non-covalent interactions at the molecular level, and further trap water to form hydrogels at the macroscopic level. This review summarized the characteristics of enzymatic hydrogel, as well as the traditional application and emerging prospect of enzyme-instructed self-assembly and hydrogelation.

Enzyme Responsive Rigid-Rod Aromatics Target "Undruggable" Phosphatases to Kill Cancer Cells in a Mimetic Bone Microenvironment

Bone metastasis remains a challenge in cancer treatment. Here we show enzymatic responsive rigid-rod aromatics acting as the substrates of "undruggable" phosphatases to kill cancer cells in a mimetic bone microenvironment. By phosphorylation and conjugating nitrobenzoxadiazole (NBD) to hydroxybiphenylcarboxylate (BP), we obtained pBP-NBD (1P) as a substrate of both acid and alkaline phosphatases. 1P effectively kills both metastatic castration-resistant prostate cancer cells (mCRPCs) and osteoblast mimic cells in their coculture. 1P enters Saos2 almost instantly to target the endoplasmic reticulum (ER) of the cells. Co-culturing with Saos2 cells boosts the cellular uptake of 1P by mCRPCs. Cryo-EM reveals the nanotube structures of both 1P (2.4 Å resolution, pH 5.6) and 1 (2.2 Å resolution, pH 7.4). The helical packing of both nanotubes is identical, held together by strong pi-stacking interactions. Besides reporting the atomistic structure of nanotubes formed by the assembly of rigid-rod aromatics, this work expands the pool of molecules for designing EISA substrates that selectively target TME.

Localized Enzyme-Assisted Self-Assembly of low molecular weight hydrogelators. Mechanism, applications and perspectives

Nature uses systems of high complexity coordinated by the precise spatial and temporal control of associated processes, working from the molecular to the macroscopic scale. This living organization is mainly ensured by enzymatic actions. Herein, we review the concept of Localized Enzyme-Assisted Self-Assembly (LEASA). It is defined and presented as a straightforward and insightful strategy to achieve high levels of control in artificial systems. Indeed, the use of immobilized enzymes to drive self-assembly events leads not only to the local formation of supramolecular structures but also to tune their kinetics and their morphologies. The possibility to design tailored complex systems taking advantage of self-assembled networks through their inherent and emergent properties offers new perspectives for the design of novel, more adaptable materials. As a result, some applications have already been developed and are gathered in this review. Finally, challenges and perspectives of LEASA are introduced and discussed.

Enzymatic noncovalent synthesis of peptide assemblies generates multimolecular crowding in cells for biomedical applications

Enzymatic noncovalent synthesis enables the spatiotemporal control of multimolecular crowding in cells, thus offering a unique opportunity for modulating cellular functions. This article introduces some representative enzymes and molecular building blocks for generating peptide assemblies as multimolecular crowding in cells, highlights the relevant biomedical applications, such as anticancer therapy, molecular imaging, trafficking proteins, genetic engineering, artificial intracellular filaments, cell morphogenesis, and antibacterial, and briefly discusses the promises of ENS as a multistep molecular process in biology and medicine.