Cell-Compatible Nanoprobes for Imaging Intracellular Phosphatase Activities

Alkaline phosphatase (ALP) activatable small molecule-based prodrugs for cancer theranostics

Highly water-soluble small molecule-based prodrugs (5-FUPD and SAHAPD) are formulated. They comprise a phosphate group to lock the active drug payload (5-fluorouracil and SAHA) along with a turn-on fluorophore consisting of a glutathione (GSH) depletory feature. Installation of the phosphate group along with purification of final product has been accomplished in an operationally facile manner. Activation of the prodrugs is facilitated by alkaline phosphatase (ALP)-mediated hydrolysis of the phosphate group followed by 1,8-elimination. The prodrugs were found to be highly effective against ALP flared human cervical cancer (HeLa) and liver cancer (HepG2) cell lines. Most notably, they were found to be innocuous to normal liver cells (WRL-68).

Designing bioresponsive nanomaterials for intracellular self-assembly

Supramolecular assemblies are essential components of living organisms. Cellular scaffolds, such as the cytoskeleton or the cell membrane, are formed via secondary interactions between proteins or lipids and direct biological processes such as metabolism, proliferation and transport. Inspired by nature’s evolution of function through structure formation, a range of synthetic nanomaterials has been developed in the past decade, with the goal of creating non-natural supramolecular assemblies inside living mammalian cells. Given the intricacy of biological pathways and the compartmentalization of the cell, different strategies can be employed to control the assembly formation within the highly crowded, dynamic cellular environment. In this Review, we highlight emerging molecular design concepts aimed at creating precursors that respond to endogenous stimuli to build nanostructures within the cell. We describe the underlying reaction mechanisms that can provide spatial and temporal control over the subcellular formation of synthetic nanostructures. Showcasing recent advances in the development of bioresponsive nanomaterials for intracellular self-assembly, we also discuss their impact on cellular function and the challenges associated with establishing structure–bioactivity relationships, as well as their relevance for the discovery of novel drugs and imaging agents, to address the shortfall of current solutions to pressing health issues.

Creating artificial nanostructures inside living cells requires the careful design of molecules that can transform into active monomers within a complex cellular environment. This Review explores the recent development of bioresponsive precursors for the controlled formation of intracellular supramolecular assemblies.

Bioorthogonal Disassembly of Tetrazine Bearing Supramolecular Assemblies Inside Living Cells

Supramolecular assemblies are an emerging class of nanomaterials for drug delivery systems (DDS), while their unintended retention in the biological milieu remains largely unsolved. To realize the prompt clearance of supramolecular assemblies, the bioorthogonal reaction to disassemble and clear the supramolecular assemblies within living cells is investigated here. A series of tetrazine-capped assembly precursors which can self-assemble into nanofibers and hydrogels upon enzymatic dephosphorylation are designed. Such an enzyme-instructed supramolecular assembly process can perform intracellularly. The time-dependent accumulation of assemblies elicits oxidative stress and induces cellular toxicity. Tetrazine-bearing assemblies react with trans-cyclooctene derivatives, which lead to the disruption of π-π stacking and induce disassembly. In this way, the intracellular self-assemblies disassemble and are deprived of potency. This bioorthogonal disassembly strategy leverages the biosafety aspect in developing nanomaterials for DDSs.

Multifunctional AIE iridium (III) photosensitizer nanoparticles for two-photon-activated imaging and mitochondria targeting photodynamic therapy

Developing novel photosensitizers for deep tissue imaging and efficient photodynamic therapy (PDT) remains a challenge because of the poor water solubility, low reactive oxygen species (ROS) generation efficiency, serve dark cytotoxicity, and weak absorption in the NIR region of conventional photosensitizers. Herein, cyclometalated iridium (III) complexes (Ir) with aggregation-induced emission (AIE) feature, high photoinduced ROS generation efficiency, two-photon excitation, and mitochondria-targeting capability were designed and further encapsulated into biocompatible nanoparticles (NPs). The Ir-NPs can be used to disturb redox homeostasis in vitro, result in mitochondrial dysfunction and cell apoptosis. Importantly, in vivo experiments demonstrated that the Ir-NPs presented obviously tumor-targeting ability, excellent antitumor effect, and low systematic dark-toxicity. Moreover, the Ir-NPs could serve as a two-photon imaging agent for deep tissue bioimaging with a penetration depth of up to 300 μm. This work presents a promising strategy for designing a clinical application of multifunctional Ir-NPs toward bioimaging and PDT.

A Crowding Barrier to Protein Inhibition in Colloidal Aggregates

Small molecule colloidal aggregates adsorb and partially denature proteins, inhibiting them artifactually. Oddly, this inhibition is typically time-dependent. Two mechanisms might explain this: low concentrations of the colloid and enzyme might mean low encounter rates, or colloid-based protein denaturation might impose a kinetic barrier. These two mechanisms should have different concentration dependencies. Perplexingly, when enzyme concentration was increased, incubation times actually lengthened, inconsistent with both models and with classical chemical kinetics of solution species. We therefore considered molecular crowding, where colloids with lower protein surface density demand a shorter incubation time than more crowded colloids. To test this, we grew and shrank colloid surface area. As the surface area shrank, the incubation time lengthened, while as it increased, the converse was true. These observations support a crowding effect on protein binding to colloidal aggregates. Implications for drug delivery and for detecting aggregation-based inhibition will be discussed.

Molecular self-assembly of a tyroservatide-derived octapeptide and hydroxycamptothecin for enhanced therapeutic efficacy

Tyroservatide (YSV) belongs to a class of bioactive peptides that have drawn considerable attention in the field of drug discovery, yet it displays limited potency and often requires a millimolar concentration to execute its cellular functions. To enhance the potency of the drug through a self-assembling strategy, we designed and synthesized a series of octapeptides through conjugation of YSV with a pentapeptide sequence bearing alternating hydrophobic and hydrophilic amino acids to promote their self-assembling capabilities. Initial screening for hydrogelation gave a novel octapeptide (denoted as 1-YSV hereafter) that was capable of self-assembling under physiological conditions to afford supramolecular nanofibers with enhanced anti-cancer efficacy compared to YSV itself. Interestingly, 1-YSV formed a robust co-assembly with the anticancer drug hydroxycamptothecin (HCPT) to afford 1-YSV/HCPT hydrogel, which not only greatly improved the viscoelastic properties of hydrogels, but also stabilized HCPT in the hydrogel matrix and avoided the agglomeration of drug molecules. Compared to HCPT solution, the hydrogel formulation of 1-YSV/HCPT demonstrated better efficacy against the proliferation of non-small cell lung cancer A549 cells both in vitro and in vivo. Finally, thanks to the pure amino acid-based composition, the 1-YSV/HCPT formulation exhibited excellent biocompatibility, giving a low hemolytic rate to red blood cells, with mild local tissue reactions and negligible systematic toxicities in mice.

Pathological environment directed in situ peptidic supramolecular assemblies for nanomedicines

Peptidic self-assembly provides a powerful method to build biomedical materials with integrated functions. In particular, pathological environment instructed peptidic supramolecular have gained great progress in treating various diseases. Typically, certain pathology related factors convert hydrophilic precursors to corresponding more hydrophobic motifs to assemble into supramolecular structures. Herein, we would like to review the recent progress of nanomedicines based on the development of instructed self-assembly against several specific disease models. Firstly we introduce the cancer instructed self-assembly. These assemblies have exhibited great inhibition efficacy, as well as enhanced imaging contrast, against cancer models both in vitro and in vivo. Then we discuss the infection instructed peptidic self-assembly. A number of different molecular designs have demonstrated the potential antibacterial application with satisfied efficiency for peptidic supramolecular assemblies. Further, we discuss the application of instructed peptidic self-assembly for other diseases including neurodegenerative disease and vaccine. The assemblies have succeeded in down-regulating abnormal Aβ aggregates and immunotherapy. In summary, the self-assembly precursors are typical two-component molecules with (1) a self-assembling motif and (2) a cleavable trigger responsive to the pathological environment. Upon cleavage, the self-assembly occurs selectively in pathological loci whose targeting capability is independent from active targeting. Bearing the novel targeting regime, we envision that the pathological conditions instructed peptidic self-assembly will lead a paradigm shift on biomedical materials.

Recent advances in quinazolinones as an emerging molecular platform for luminescent materials and bioimaging

This review summarized recent advances relating to the luminescence properties of quinazolinones and their applications in fluorescent probes, biological imaging and luminescent materials. Their future outlook is also included.

Biomaterials based on noncovalent interactions of small molecules

Unlike conventional materials that covalent bonds connecting atoms as the major force to hold the materials together, supramolecular biomaterials rely on noncovalent intermolecular interactions to assemble. The reversibility and biocompatibility of supramolecular biomaterials render them with diverse range of functions and lead to rapid development in the past two decades. This review focuses on the noncovalent and enzymatic control of supramolecular biomaterials, with the introduction to various triggering mechanism to initiate self-assembly. Representative applications of supramolecular biomaterials are highlighted in four categories: tissue engineering, cancer therapy, drug delivery, and molecular imaging. By introducing various applications, we intend to show enzymatic control and noncovalent interactions as a powerful tool for achieving spatiotemporal control of biomaterials both invitro and in vivo for biomedicine.

Enzyme-Instructed Self-Assembly for Cancer Therapy and Imaging

Enzymatic reactions and self-assembly are two fundamental attributes of cells. It is not surprising that one can use enzyme-instructed self-assembly (EISA)-the integration of enzymatic transformation and molecular self-assembly-to modulate the emergent properties of supramolecular assemblies for controlling cell behaviors. The exploration of EISA for developing cancer therapy and imaging has made considerable progress over the last five years. In this Topical Review, we discuss these exciting results and the future promise of EISA. After describing several key studies to illustrate the progress of EISA in developing cancer therapy, we discuss the use of EISA for molecular imaging. Then, we give the outlook of EISA for developing supramolecular anticancer medicine that inhibits multiple hallmark capabilities of cancer.

Enzymatic Noncovalent Synthesis of Supramolecular Soft Matter for Biomedical Applications

Enzymatic noncovalent synthesis (ENS), a process that integrates enzymatic reactions and supramolecular (i.e., noncovalent) interactions for spatial organization of higher-order molecular assemblies, represents an emerging research area at the interface of physical and biological sciences. This review provides a few representative examples of ENS in the context of supramolecular soft matter. After a brief comparison of enzymatic covalent and noncovalent synthesis, we discuss ENS of man-made molecules for generating supramolecular nanostructures (e.g., supramolecular hydrogels) in cell-free conditions. Then, we introduce ENS in a cellular environment. To illustrate the unique merits for applications, we discuss intercellular, peri- or intracellular, and subcellular ENS for cell morphogenesis, molecular imaging, cancer therapy, and targeted delivery. Finally, we provide an outlook on the potential of ENS. We hope that this review offers a new perspective for scientists who develop supramolecular soft matter to address societal needs at various frontiers.