Apoptosis-inducing activity of a fluorescent barrel-rosette M+/Cl- channel

Reversing the ion transport selectivity through arm modification of an artificial molecular hourglass

An arm modification strategy, by replacing relatively rigid, electron-deficient side arms with flexible ether chain arms and linking them onto a tetraoxacalix[2]arene[2]triazine skeleton, was utilized to design an artificial molecular hourglass. The planar bilayer experiments confirmed the unimolecular channel mechanism and suggested reversed ion selectivity from the previously reported anion selectivity to weak cation selectivity.

Supramolecular Barrel-Rosette Ion Channel Based on 3,5-Diaminobenzoic Acid for Cation-Anion Symport

The structural tropology and functions of natural cation-anion symporting channels have been continuously investigated due to their crucial role in regulating various physiological functions. To understand the physiological functions of the natural symporter channels, it is vital to develop small-molecule-based biomimicking systems that can provide mechanistic insights into the ion-binding sites and the ion-translocation pathways. Herein, we report a series of bis((R)-(-)-mandelic acid)-linked 3,5-diaminobenzoic acid based self-assembled ion channels with distinctive ion transport ability. Ion transport experiment across the lipid bilayer membrane revealed that compound 1 b exhibits the highest transport activity among the series, and it has interesting selective co-transporting functions, i.e., facilitates K+ /ClO4 - symport. Electrophysiology experiments confirmed the formation of supramolecular ion channels with an average diameter of 6.2±1 Å and single channel conductance of 57.3±1.9 pS. Selectivity studies of channel 1 b in a bilayer lipid membrane demonstrated a permeability ratio ofP C l - / P K + = 0 . 053 ± 0 . 02 ${{P}_{{Cl}^{-}}/{P}_{{K}^{+}}=0.053\pm 0.02}$ ,P C l O 4 - / P C l - = 2 . 1 ± 0 . 5 ${{P}_{{ClO}_{4}^{-}}/{P}_{{Cl}^{-}}=2.1\pm 0.5}$ , andP K + / P N a + = 1 . 5 ± 1 , ${{P}_{{K}^{+}}/{P}_{{Na}^{+}}=1.5\pm 1,}$ indicating the higher selectivity of the channel towards KClO4 over KCl salt. A hexameric assembly of a trimeric rosette of 1 b was subjected to molecular dynamics simulations with different salts to understand the supramolecular channel formation and ion selectivity pattern.

Photocontrolled activation of doubly o-nitrobenzyl-protected small molecule benzimidazoles leads to cancer cell death

Artificial biomimetic chloride anionophores have shown promising applications as anticancer scaffolds. Importantly, stimuli-responsive chloride transporters that can be selectively activated inside the cancer cells to avoid undesired toxicity to normal, healthy cells are very rare. Particularly, light-responsive systems promise better applicability for photodynamic therapy because of their spatiotemporal controllability, low toxicity, and high tunability. Here, in this work, we report o-nitrobenzyl-linked, benzimidazole-based singly and doubly protected photocaged protransporters 2a, 2b, 3a, and 3b, respectively, and benzimidazole-2-amine-based active transporters 1a-1d. Among the active compounds, trifluoromethyl-based anionophore 1a showed efficient ion transport activity (EC50 = 1.2 ± 0.2 μM). Detailed mechanistic studies revealed Cl-/NO3- antiport as the main ion transport process. Interestingly, double protection with photocages was found to be necessary to achieve the complete "OFF-state" that could be activated by external light. The procarriers were eventually activated inside the MCF-7 cancer cells to induce phototoxic cell death.

Progress and prospects toward supramolecular bioactive ion transporters

The majority of cellular physiological processes depend on natural ion channels, which are pore-forming membrane-embedded proteins that let ions flow across the cell membranes selectively. This selective movement of ions across the membranes balances the osmolality within and outside the cell. However, mutations in the genes that encode essential membrane transport proteins or structural reorganisation of these proteins can cause life-threatening diseases like cystic fibrosis. Artificial ion transport systems have opened up a way to replace dysfunctional natural ion channels to cure such diseases through channel replacement therapy. Moreover, recent research has also demonstrated the ability of these systems to kill cancer cells, reigniting interest in the field among scientists. Our contributions to the recent progress in the design and development of artificial chloride ion transporters and their effect on biological systems have been discussed in this review. This review would provide current vistas and future directions toward the development of novel ion transporters with improved biocompatibility and desired anti-cancer properties. Additionally, it strongly emphasises stimuli-responsive ion transport systems, which are crucial for obtaining target-specificity and may speed up the application of these systems in clinical therapeutics.

Development of a Systematic Strategy toward Promotion of α-Synuclein Aggregation Using 2-Hydroxyisophthalamide-Based Systems

Establishing a potent scheme against α-synuclein aggregation involved in Parkinson's disease has been evaluated as a promising route to identify compounds that either inhibit or promote the aggregation process of α-synuclein. In the last two decades, this perspective has guided a dramatic increase in the efforts, focused on developing potent drugs either for retardation or promotion of the self-assembly process of α-synuclein. To address this issue, using a chemical kinetics platform, we developed a strategy that enabled a progressively detailed analysis of the molecular events leading to protein aggregation at the microscopic level in the presence of a recently synthesized 2-hydroxyisophthalamide class of small organic molecules based on their binding affinity. Furthermore, qualitatively, we have developed a strategy of disintegration of α-synuclein fibrils in the presence of these organic molecules. Finally, we have shown that these organic molecules effectively suppress the toxicity of α-synuclein oligomers in neuron cells.

Ion Channels and Transporters as Therapeutic Agents: From Biomolecules to Supramolecular Medicinal Chemistry

Ion channels and transporters typically consist of biomolecules that play key roles in a large variety of physiological and pathological processes. Traditional therapies include many ion-channel blockers, and some activators, although the exact biochemical pathways and mechanisms that regulate ion homeostasis are yet to be fully elucidated. An emerging area of research with great innovative potential in biomedicine pertains the design and development of synthetic ion channels and transporters, which may provide unexplored therapeutic opportunities. However, most studies in this challenging and multidisciplinary area are still at a fundamental level. In this review, we discuss the progress that has been made over the last five years on ion channels and transporters, touching upon biomolecules and synthetic supramolecules that are relevant to biological use. We conclude with the identification of therapeutic opportunities for future exploration.

Effects of butein on human osteosarcoma cell proliferation, apoptosis, and autophagy through oxidative stress

PURPOSE

Osteosarcoma (OS) is a primary malignant bone tumor, and the cure rate has stagnated in the past three decades. Butein, a plant polyphenol extracted from many herbs, has been proved to possess anti-tumor activity. However, the effect of butein on human OS and the underlying mechanisms remain to be elucidated.

MATERIALS AND METHODS

The OS cell line 143B was used. The effects of butein were evaluated through the cell proliferation assay, flow cytometry, florescence and transmission electron microscopy, and western blotting. All statistical analyses were performed using GraphPad Prism 7.0.

RESULTS

Butein was found to inhibit cell proliferation by causing G2/ M phase arrest in the 143B cells. In addition, butein suppressed the invasion of 143B cells upon IL-6 treatment. Additionally, we found that butein inhibited the invasion of 143B cells stimulated with IL-6 via the p-STAT3-MMP9 signaling pathway. Remarkably, butein triggered extrinsic and intrinsic apoptosis and autophagy of 143B cells. The process of autophagy may have tumor-supporting effects. Furthermore, butein induced oxidative stress as evidenced by ROS generation, increase in malondialdehyde (MDA) level, and decrease in GSH/GSSH ratio and GPX4 expression. N-acetylcysteine can reverse the change of ROS. Further experiments indicated apoptosis and autophagy could be attenuated by the N-acetyl-L-cysteine and c-Jun N-terminal kinase (JNK) inhibitor SP600125. Additionally, butein inhibited the Akt/mammalian target of rapamycin (mTOR) signaling pathway, and suppressed the Akt kinase activity increased apoptosis and autophagy.

CONCLUSION

Our results revealed butein induced apoptosis and autophagy by regulating oxidative stress, activating the JNK signaling pathway and blocking the Akt/mTOR signaling pathway in OS cells. Additionally, butein inhibited the invasion of 143B cells stimulated with IL-6 through the pSTAT3- MMP9 signaling pathway. In view of these results, butein may be a potential anti-tumor drug targeting osteosarcoma.

Nanotechnology-Assisted, Single-Chromophore-Based White-Light-Emitting Organic Materials with Bioimaging Properties

White-light-emitting (WLE) organic materials, especially small molecules comprising a single chromophoric unit, have received much attention due to their tremendous use in modern-day electronic devices and biomaterials. They can increase the efficiency and lifetime of devices compared to the currently used combination approach. Herein, we explored a small symmetric push-pull organic molecule Hexyl-TCBD with a single 1,1,4,4-tetracyanobuta-1,3-diene (TCBD) chromophoric unit containing urea as a key functional group on an acceptor-donor∼donor-acceptor (A-D∼D-A) backbone for its ability to show white-light emission in solution as well as in the solid state. The luminescence was absent in the solid state due to the H-bonding- and π-stacking-driven quenching processes, while emission behavior in solution was tunable with variable CIE chromaticity index values via hydrogen (H)-bonding-governed disaggregation phenomena. Translation of WLE from the Hexyl-TCBD solution to a solid state was demonstrated by utilizing nonemissive polystyrene (80 wt % with respect to the chromophore) as the matrix to obtain WLE nanofibers (made by the electrospun technique) via segregating the molecules. The optical microscopy study validated the WLE nanofibers. The presence of multicolor photoluminescence, including white light, could be fine-tuned through various excitation wavelengths, solvent polarities, and polystyrene matrices. Furthermore, the detailed photophysical studies, including lifetime measurements, indicated that the inherent intramolecular charge transfer (ICT) bands of Hexyl-TCBD exhibit better ICT state stabilization by space charge distribution through the modulation of H-bonding between urea groups. Finally, a cytotoxicity study was performed for Hexyl-TCBD on normal and cancer cell lines using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay to explore bioimaging applications in biosystems. MTT results revealed significant toxicity toward cancer cells, whereas normal cells exhibited good biocompatibility.

Molecular Self-Assembly as a Tool to Construct Transmembrane Supramolecular Ion Channels

Self-assembly has become a powerful tool for building various supramolecular architectures with applications in material science, environmental science, and chemical biology. One such area is the development of artificial transmembrane ion channels that mimic naturally occurring channel-forming proteins to unveil various structural and functional aspects of these complex biological systems, hoping to replace the defective protein channels with these synthetically accessible moieties. This account describes our recent approaches to construct supramolecular ion channels using synthetic molecules and their applications in medicinal chemistry.

Cation-chloride cotransport mediated by an ion pair transporter

Ion transport mediated by an ion pair receptor 1 bearing both cation and anion binding sites is presented. The ion pair binding property was revealed by means of ¹H NMR titrations in organic solutions and X-ray analysis in the solid state. Single crystal structures demonstrated that 1 and CaI₂ formed a solvent-separated ion-pair complex with two iodides each interacting with a triazine ring through anion-π interactions, whereas the calcium ion is bound by a pentaethylene glycol moiety. The ion transport activity was studied by monitoring the efflux of ions from salt-loaded EYPC large unilamellar vesicles (EYPC-LUVs) using ion selective electrodes. Chloride transport across the membrane mediated by the ion pair receptor through K⁺/Cl^- or Na⁺/Cl^- cotransport with a selectivity towards the K⁺/Cl^- symport was realized.

Recent Advances in Bioactive Artificial Ionophores

Several life-threatening diseases, also known as 'Channelopathies' are linked to irregularities in ion transport proteins. Significant research efforts have fostered the development of artificial transport systems that facilitates to restore the functions of impaired natural transport proteins. Indeed, a few of these artificial ionophores demonstrate the rare combination of transmembrane ion transport and important biological activity, offering early promises of suitability in 'channel replacement therapy'. In this review, structural facets and functions of both cationophores and anionophores are discussed. Ionophores that are toxic to various bacteria and yeast, could be exploited as antimicrobial agent. Nevertheless, few non-toxic ionophores offer the likelihood of treating a wide range of genetic diseases caused by the gene mutations. In addition, their ability to disrupt cellular homeostasis and to alter lysosomal pH endow ionophores as promising candidates for cancer treatment. Overall, critically outlining the advances in artificial ionophores in terms of in vitro ion transport, possible modes of action and biological activities enables us to propose possible future roadmaps in this research area.

A pH-targeted and NIR-responsive NaCl-nanocarrier for photothermal therapy and ion-interference therapy

Transport ions into cells through nanocarrier to achieve ion-interference therapy provides new inspiration for cancer treatment. In this work, a pH-targeted and NIR-responsive NaCl-nanocarrier is prepared using surfactant Vitamin E-O(EG₂-Glu) and modified with polydopamine (PDA) and pH-sensitive zwitterionic chitosan (ZWC). The NaCl-nanocarrier is decorated with NH₄HCO₃ and IR-780 to introduce near-infrared (NIR)-responsive performance and imaging. Once the NaCl-nanocarrier is exposed to NIR laser, the temperature rises rapidly because of the excellent photothermal conversion ability of PDA, then NH₄HCO₃ is decomposed into NH₃ and CO₂, which burst the nanocarrier, resulting in Cl^- and Na⁺ "bomb-like" release. This pH-targeted nanocarrier accumulates more at tumor site and when irradiating the site with NIR light, the temperature rises and excessive Cl^- and Na⁺ are released to destroy the ion homeostasis and inhibit tumor growth effectively. Through this strategy, the unique combination of ion interference therapy and photothermal therapy is achieved.

Supramolecular chemistry in lipid bilayer membranes

Lipid bilayer membranes form compartments requisite for life. Interfacing supramolecular systems, including receptors, catalysts, signal transducers and ion transporters, enables the function of the membrane to be controlled in artificial and living cellular compartments. In this perspective, we take stock of the current state of the art of this rapidly expanding field, and discuss prospects for the future in both fundamental science and applications in biology and medicine.

A Pyridyl-Linked Benzimidazolyl Tautomer Facilitates Prodigious H+/Cl- Symport through a Cooperative Protonation and Chloride Ion Recognition

We report two pyridyl-linked benzimidazolyl hydrazones as HCl cotransporters that are 5 and 2 times superior to prodigiosin, a natural product whose transport efficiency has never been routed by synthetic molecules. These hydrazones provide a suitable HCl binding site through a cooperative protonation and chloride ion recognition. HCl transport by the most active compound induces lysosome deacidification. Viability assays confirmed that the compounds induce cytotoxicity toward human breast cancer MCF-7 cells but are relatively nontoxic toward noncancerous HEK293T cells.

Ligand Induced CuII Transport Restricts Cancer and Mycobacterial Growth: Towards a Plug-and-Select Ion Channel Scaffold

Synthetic channels with high ion selectivity are attractive drug targets for diseases involving ion dysregulation. Achieving selective transport of divalent ions is highly challenging due their high hydration energies. A small tripeptide amphiphilic scaffold installed with a pybox ligand selectively transports Cu^II ions across membranes. The peptide forms stable dimeric pores in the membrane and transports ions by a Cu²⁺ /H⁺ antiport mechanism. The ligand-induced excellent Cu^II selectivity as well as high membrane permeability of the peptide is exploited to promote cancer cell death. The peptide's ability to restrict mycobacterial growth serves as seeds to evolve antibacterial strategies centred on selectively modulating ion homeostasis in pathogens. This simple peptide can potentially function as a universal, yet versatile, scaffold wherein the ion selectivity can be precisely controlled by modifying the ligand at the C terminus.

Tetrapodal Anion Transporters

Synthetic anion transporters that facilitate chloride transport are promising candidates for channelopathy treatments. However, most anion transporters exhibit an undesired side effect of facilitating proton transport via interacting with fatty acids present in the membrane. To address the limitation, we here report the use of a new tetrapodal scaffold to maximize the selective interaction with spherical chloride over binding the carboxylate headgroup of fatty acids. One of the new transporters demonstrated a high selectivity for chloride uniport over fatty acid-induced proton transport while being >10 times more active in chloride uniport than strapped calixpyrroles that were previously the only class of compounds known to possess similar selectivity properties.

Advances in anion transport and supramolecular medicinal chemistry

Advances in anion transport by synthetic supramolecular systems are discussed in this article. Developments in the design of discrete molecular carriers for anions and supramolecular anion channels are reviewed followed by an overview of the use of these systems in biological systems as putative treatments for diseases such as cystic fibrosis and cancer.

Macrocyclic Transmembrane Anion Transporters via a One-Pot Condensation Reaction

Synthetic chloride transporters are potential therapeutic agents for cystic fibrosis and cancer. Reported herein are macrocyclic transmembrane chloride transporters prepared by a one-pot condensation reaction. The most efficient macrocycle possesses a fine balance of hydrophobicity for membrane permeation and hydrophilicity for ion recognition. The macrocycle transports chloride ions by forming channels in the membrane. Hydrogen bonds and anion-π interactions assist chloride transport.