Multiple‐Color Platinum Complex with Super‐Large Stokes Shift for Super‐Resolution Imaging of Autolysosome Escape

Enhanced Sonodynamic Therapy for Deep Tumors Using a Self-Assembled Organoplatinum(II) Sonosensitizer

Despite the promising advances in photodynamic therapy (PDT), it remains challenging to target and treat deep-seated solid tumors effectively. Herein, we developed an organoplatinum(II) complex (Pt-TPE) with self-assembly properties for sonodynamic therapy (SDT). Pt-TPE forms a nanofiber network structure through Pt-Pt and π-π stacking interactions. Notably, under ultrasound (US), Pt-TPE demonstrates unique self-assembly-induced singlet oxygen (1O2) generation due to a significantly enhanced singlet-triplet intersystem crossing (ISC). This generation of 1O2 occurs exclusively in the self-assembled state of Pt-TPE. Additionally, Pt-TPE exhibits sono-cytotoxicity against cancer cells by impairing mitochondrial membrane potential (MMP), inhibiting glucose uptake, and aerobic glycolysis. Furthermore, US-activated Pt-TPE significantly inhibits deep solid tumors in mice, achieving remarkable therapeutic efficacy even at penetration depths greater than 10 cm. This study highlights the potential of self-assembled metal complexes to enhance the efficacy of SDT for treating deep tumors.

Molecular probes for super-resolution imaging of drug dynamics

Super-resolution molecular probes (SRMPs) are essential tools for visualizing drug dynamics within cells, transcending the resolution limits of conventional microscopy. In this review, we provide an overview of the principles and design strategies of SRMPs, emphasizing their role in accurately tracking drug molecules. By illuminating the intricate processes of drug distribution, diffusion, uptake, and metabolism at a subcellular and molecular level, SRMPs offer crucial insights into therapeutic interventions. Additionally, we explore the practical applications of super-resolution imaging in disease treatment, highlighting the significance of SRMPs in advancing our understanding of drug action. Finally, we discuss future perspectives, envisioning potential advancements and innovations in this field. Overall, this review serves to inform and practitioners about the utility of SRMPs in driving innovation and progress in pharmacology, providing valuable insights for drug development and optimization.

In situ visualization of the cellular uptake and sub-cellular distribution of mussel oligosaccharides

Unlike chemosynthetic drugs designed for specific molecular and disease targets, active small-molecule natural products typically have a wide range of bioactivities and multiple targets, necessitating extensive screening and development. To address this issue, we propose a strategy for the direct in situ microdynamic examination of potential drug candidates to rapidly identify their effects and mechanisms of action. As a proof-of-concept, we investigated the behavior of mussel oligosaccharide (MOS-1) by tracking the subcellular dynamics of fluorescently labeled MOS-1 in cultured cells. We recorded the entire dynamic process of the localization of fluorescein isothiocyanate (FITC)-MOS-1 to the lysosomes and visualized the distribution of the drug within the cell. Remarkably, lysosomes containing FITC-MOS-1 actively recruited lipid droplets, leading to fusion events and increased cellular lipid consumption. These drug behaviors confirmed MOS-1 is a candidate for the treatment of lipid-related diseases. Furthermore, in a high-fat HepG2 cell model and in high-fat diet-fed apolipoprotein E (ApoE) -/- mice, MOS-1 significantly promoted triglyceride degradation, reduced lipid droplet accumulation, lowered serum triglyceride levels, and mitigated liver damage and steatosis. Overall, our work supports the prioritization of in situ visual monitoring of drug location and distribution in subcellular compartments during the drug development phase, as this methodology contributes to the rapid identification of drug indications. Collectively, this methodology is significant for the screening and development of selective small-molecule drugs, and is expected to expedite the identification of candidate molecules with medicinal effects.

An AIEgen and Iodine Double-Ornamented Platinum(II) Complex for Bimodal Imaging-Guided Chemo-Photodynamic Combination Therapy

Real-time biodistribution monitoring and enhancing the therapeutic efficacy of platinum(II)-based anticancer drugs are urgently required to elevate their clinical performance. Herein, a tetraphenylethene derivative (TP) with aggregation-induced emission (AIE) properties and an iodine atom are selected as ligands to endow platinum (II) complex TP-Pt-I with real-time in vivo self-tracking ability by fluorescence (FL) and computerized tomography (CT) imaging, and improved anticancer efficacy by the combination of chemotherapy and photodynamic therapy. Especially, benefiting from the formation of a donor-acceptor-donor structure between the AIE photosensitizer TP and Pt-I moiety, the heavy atom effects of Pt and I, and the presence of I, TP-Pt-I displayed red-shifted absorption and emission wavelengths, enhanced ROS generation efficiency, and improved CT imaging capacity compared with the pristine TP and the control agent TP-Pt-Cl. As a result, the enhanced intratumoral accumulation of TP-Pt-I loaded nanoparticles is readily revealed by dual-modal FL and CT imaging with high contrast. Meanwhile, the TP-Pt-I nanoparticles show significantly improved tumor growth-inhibiting effects on an MCF-7 xenograft murine model by combining the chemotherapeutic effects of platinum(II) and the photodynamic effects of TP. This self-tracking therapeutic complex thus provides a new strategy for improving the therapeutic outcomes of platinum(II)-based anticancer drugs.

Enhanced optical imaging and fluorescent labeling for visualizing drug molecules within living organisms

The visualization of drugs in living systems has become key techniques in modern therapeutics. Recent advancements in optical imaging technologies and molecular design strategies have revolutionized drug visualization. At the subcellular level, super-resolution microscopy has allowed exploration of the molecular landscape within individual cells and the cellular response to drugs. Moving beyond subcellular imaging, researchers have integrated multiple modes, like optical near-infrared II imaging, to study the complex spatiotemporal interactions between drugs and their surroundings. By combining these visualization approaches, researchers gain supplementary information on physiological parameters, metabolic activity, and tissue composition, leading to a comprehensive understanding of drug behavior. This review focuses on cutting-edge technologies in drug visualization, particularly fluorescence imaging, and the main types of fluorescent molecules used. Additionally, we discuss current challenges and prospects in targeted drug research, emphasizing the importance of multidisciplinary cooperation in advancing drug visualization. With the integration of advanced imaging technology and molecular design, drug visualization has the potential to redefine our understanding of pharmacology, enabling the analysis of drug micro-dynamics in subcellular environments from new perspectives and deepening pharmacological research to the levels of the cell and organelles.

Organic Fluorophores with Large Stokes Shift for the Visualization of Rapid Protein and Nucleic Acid Assays

Organic small-molecule fluorophores, characterized by flexible chemical structure and adjustable optical performance, have shown tremendous potential in biosensing. However, classical organic fluorophore motifs feature large overlap between excitation and emission spectra, leading to the requirement of advanced optical set up to filter desired signal, which limits their application in scenarios with simple settings. Here, a series of wavelength-tunable small-molecule fluorescent dyes (PTs) bearing simple organic moieties have been developed, which exhibit Stokes shift up to 262 nm, molar extinction coefficients ranged 30,000-100,000 M-1 cm-1, with quantum yields up to 54.8 %. Furthermore, these dyes were formulated into fluorescent nanoparticles (PT-NPs), and applied in lateral flow assay (LFA). Consequently, limit of detection for SARS-CoV-2 nucleocapsid protein reached 20 fM with naked eye, a 100-fold improvement in sensitivity compared to the pM detection level for colloidal gold-based LFA. Besides, combined with loop-mediated isothermal amplification (LAMP), the LFA system achieved the visualization of single copy level nucleic acid detection for monkeypox (Mpox).

Super-resolution imaging for in situ monitoring sub-cellular micro-dynamics of small molecule drug

Small molecule drugs play a pivotal role in the arsenal of anticancer pharmacological agents. Nonetheless, their small size poses a challenge when directly visualizing their localization, distribution, mechanism of action (MOA), and target engagement at the subcellular level in real time. We propose a strategy for developing triple-functioning drug beacons that seamlessly integrate therapeutically relevant bioactivity, precise subcellular localization, and direct visualization capabilities within a single molecular entity. As a proof of concept, we have meticulously designed and constructed a boronic acid fluorescence drug beacon using coumarin-hemicyanine (CHB). Our CHB design includes three pivotal features: a boronic acid moiety that binds both adenosine triphosphate (ATP) and adenosine diphosphate (ADP), thus depleting their levels and disrupting the energy supply within mitochondria; a positively charged component that targets the drug beacon to mitochondria; and a sizeable conjugated luminophore that emits fluorescence, facilitating the application of structured illumination microscopy (SIM). Our study indicates the exceptional responsiveness of our proof-of-concept drug beacon to ADP and ATP, its efficacy in inhibiting tumor growth, and its ability to facilitate the tracking of ADP and ATP distribution around the mitochondrial cristae. Furthermore, our investigation reveals that the micro-dynamics of CHB induce mitochondrial dysfunction by causing damage to the mitochondrial cristae and mitochondrial DNA. Altogether, our findings highlight the potential of SIM in conjunction with visual drug design as a potent tool for monitoring the in situ MOA of small molecule anticancer compounds. This approach represents a crucial advancement in addressing a current challenge within the field of small molecule drug discovery and validation.

Synthesis and anticancer mechanisms of four novel platinum(II) 4'-substituted-2,2':6',2''-terpyridine complexes

Mitophagy, a selective autophagic process, has emerged as a pathway involved in degrading dysfunctional mitochondria. Herein, new platinum(II)-based chemotherapeutics with mitophagy-targeting properties are proposed. Four novel binuclear anticancer Pt(II) complexes with 4'-substituted-2,2':6',2''-terpyridine derivatives (tpy1-tpy4), i.e., [Pt2(tpy1)(DMSO)2Cl4]·CH3OH (tpy1Pt), [Pt(tpy2)Cl][Pt(DMSO)Cl3]·CH3COCH3 (tpy2Pt), [Pt(tpy3)Cl][Pt(DMSO)Cl3] (tpy3Pt), and [Pt(tpy4)Cl]Cl·CH3OH (tpy4Pt), were designed and prepared. Moreover, their potential antitumor mechanism was studied. Tpy1Pt-tpy4Pt exhibited more selective cytotoxicity against cisplatin-resistant SK-OV-3/DDP (SKO3cisR) cancer cells compared with those against ovarian SK-OV-3 (SKO3) cancer cells and normal HL-7702 liver (H702) cells. This selective cytotoxicity of Tpy1Pt-tpy4Pt was better than that of its ligands (i.e., tpy1-tpy4), the clinical drug cisplatin, and cis-Pt(DMSO)2Cl2. The results of various experiments indicated that tpy1Pt and tpy2Pt kill SKO3cisR cancer cells via a mitophagy pathway, which involves the disruption of the mitophagy-related protein expression, dissipation of the mitochondrial membrane potential, elevation of the [Ca2+] and reactive oxygen species levels, promotion of mitochondrial DNA damage, and reduction in the adenosine triphosphate and mitochondrial respiratory chain levels. Furthermore, in vivo experiments indicated that the dinuclear anticancer Pt(II) coordination compound (tpy1Pt) has remarkable therapeutic efficiency (ca. 52.4%) and almost no toxicity. Therefore, the new 4'-substituted-2,2':6',2''-terpyridine Pt(II) coordination compound (tpy1Pt) is a potential candidate for next-generation mitophagy-targeting dinuclear Pt(II)-based anticancer drugs.

Mitochondrial nucleoid condensates drive peripheral fission through high membrane curvature

Mitochondria are dynamic organelles that undergo fusion and fission events, in which the mitochondrial membrane and DNA (mtDNA) play critical roles. The spatiotemporal organization of mtDNA reflects and impacts mitochondrial dynamics. Herein, to study the detailed dynamics of mitochondrial membrane and mtDNA, we rationally develop a dual-color fluorescent probe, mtGLP, that could be used for simultaneously monitoring mitochondrial membrane and mtDNA dynamics via separate color outputs. By combining mtGLP with structured illumination microscopy to monitor mitochondrial dynamics, we discover the formation of nucleoid condensates in damaged mitochondria. We further reveal that nucleoid condensates promoted the peripheral fission of damaged mitochondria via asymmetric segregation. Through simulations, we find that the peripheral fission events occurred when the nucleoid condensates interacted with the highly curved membrane regions at the two ends of the mitochondria. Overall, we show that mitochondrial nucleoid condensates utilize peripheral fission to maintain mitochondrial homeostasis.

Probing the dynamic crosstalk of lysosomes and mitochondria with structured illumination microscopy

Structured illumination microscopy (SIM) is a super-resolution technology for imaging living cells and has been used for studying the dynamics of lysosomes and mitochondria. Recently, new probes and analyzing methods have been developed for SIM imaging, enabling the quantitative analysis of these subcellular structures and their interactions. This review provides an overview of the working principle and advances of SIM, as well as the organelle-targeting principles and types of fluorescence probes, including small molecules, metal complexes, nanoparticles, and fluorescent proteins. Additionally, quantitative methods based on organelle morphology and distribution are outlined. Finally, the review provides an outlook on the current challenges and future directions for improving the combination of SIM imaging and image analysis to further advance the study of organelles. We hope that this review will be useful for researchers working in the field of organelle research and help to facilitate the development of SIM imaging and analysis techniques.

A general design of pyridinium-based fluorescent probes for enhancing two-photon microscopy

Two-photon absorbing fluorescent probes have emerged as powerful imaging tools for subcellular-level monitoring of biological substances and processes, offering advantages such as deep light penetration, minimal photodamage, low autofluorescence, and high spatial resolution. However, existing two-photon absorbing probes still face several limitations, such as small two-photon absorption cross-section, poor water solubility, low membrane permeability, and potentially high toxicity. Herein, we report three small-molecule probes, namely MSP-1arm, Lyso-2arm, and Mito-3arm, composed of a pyridinium center (electron-acceptor) and various methoxystyrene "arms" (electron-donor). These probes exhibit excellent fluorescence quantum yield and decent aqueous solubility. Leveraging the inherent intramolecular charge transfer and excitonic coupling effect, these complexes demonstrate excellent two-photon absorption in the near-infrared region. Notably, Lyso-2arm and Mito-3arm exhibit distinct targeting abilities for lysosomes and mitochondria, respectively. In two-photon microscopy experiments, Mito-3arm outperforms a commercial two-photon absorbing dye in 2D monolayer HeLa cells, delivering enhanced resolution, broader NIR light excitation window, and higher signal-to-noise ratio. Moreover, the two-photon bioimaging of 3D human forebrain organoids confirms the successful deep tissue imaging capabilities of both Lyso-2arm and Mito-3arm. Overall, this work presents a rational design strategy in developing competent two-photon-absorbing probes by varying the number of conjugated "arms" for bioimaging applications.

Dual-Emissive Monoruthenium Complexes of N(CH3)-Bridged Ligand: Synthesis, Characterization, and Substituent Effect

Three monoruthenium complexes 1(PF6)2-3(PF6)2 bearing an N(CH3)-bridged ligand have been synthesized and characterized. These complexes have a general formula of [Ru(bpy)2(L)](PF6)2, where L is a 2,5-di(N-methyl-N'-(pyrid-2-yl)amino)pyrazine (dapz) derivative with various substituents, and bpy is 2,2'-bipyridine. The photophysical and electrochemical properties of these compounds have been examined. The solid-state structure of complex 3(PF6)2 is studied by single-crystal X-ray analysis. These complexes show two well-separated emission bands centered at 451 and 646 nm (Δλmax = 195 nm) for 1(PF6)2, 465 and 627 nm (Δλmax = 162 nm) for 2(PF6)2, and 455 and 608 nm (Δλmax = 153 nm) for 3(PF6)2 in dilute acetonitrile solution, respectively. The emission maxima of the higher-energy emission bands of these complexes are similar, while the lower-energy emission bands are dependent on the electronic nature of substituents. These complexes display two consecutive redox couples owing to the stepwise oxidation of the N(CH3)-bridged ligand and ruthenium component. Moreover, these experimental observations are analyzed by computational investigation.

A Series of Planar Phosphorescent Cyclometalated Platinum(II) Complexes as New Anticancer Theranostic Agents That Induce Oncosis

Herein, four planar cyclometalated platinum(II) complexes with a main ligand of enlarged aromatic rings have been assessed as effective anticancer theranostic agents for the first time. With an increased number of aromatic rings in the N∧N ligand, 1a-1d exhibit increased lipophilicity and cytotoxicity selectivity. The intensity of the Pt-Pt interaction of each complex can be indicated by an enhanced near-infrared (NIR) emission in phosphate-buffered saline (PBS), their binding activity with biomolecules of bovine serum albumin (BSA) is accompanied by a vivid turn-on green emission, and the intensity gradually decreased from 1a to 1d, which is consistent with the docking of two complexes with BSA. Both "turn-on" NIR and green emission of 1d can be mainly observed in nuclei of living cell within 24 h, while two phosphorescence traces of 1b were recorded in lysosomes by confocal imaging. Moreover, 1d shows the highest efficiency in inducing oncosis of Hela cells, and the relative process was investigated.

Organic-Platinum Hybrids for Covalent Binding of G-Quadruplexes: Structural Basis and Application to Cancer Immunotherapy

G-quadruplexes (G4s) have been revived as promising therapeutic targets with the development of immunotherapy, but the G4-mediated immune response remains unclear. We designed a novel class of G4-binding organic-platinum hybrids, L1 -cispt and L1 -transpt, with spatial matching for G4 binding and G4 DNA reactivity for binding site locking. The solution structure of L1 -transpt-MYT1L G4 demonstrated the effectiveness of the covalent binding and revealed the covalent binding-guided dynamic balance, accompanied by the destruction of the A5-T17 base pairs to achieve the covalent binding of the platinum unit to N7 of the G6 residue. Furthermore, L1 -cispt- and L1 -transpt-mediated genomic dysfunction could activate the retinoic acid-induced gene I (RIG-I) pathway and induce immunogenic cell death (ICD). The use of L1 -cispt/L1 -transpt-treated dying cells as therapeutic vaccines stimulated a robust immune response and effectively inhibited tumor growth in vivo. Our findings highlight the importance of the rational combination of specific spatial recognition and covalent locking in G4-trageting drug design and their potential in immunotherapy.

Reversible and irreversible stimuli-responsive chromism of a square-planar platinum(ii) salt

A new simple Pt(ii) terpyridyl salt that shows reversible response towards acetonitrile and irreversible response towards methanol has been reported, accompanied with the colorimetric/luminescent changing from red to yellow. Experimentally and theoretically, the spectroscopic change derives from the hydrogen bonds between crystal water in the Pt(ii) terpyridyl salt and external organic molecules, and the different strength of hydrogen bond leads either reversible or irreversible stimuli-response. Furthermore, this Pt(ii) terpyridyl salt has been on one hand applied as a probe for sensing acetonitrile in water solution, with high selectivity, good reversibility, proper sensitivity and fast response rate, and on the other hand as advanced anticounterfeiting materials. The current study provides a new approach to acquire and design either reversible or irreversible stimuli-responsive luminescent materials.

Aggregation-Induced Emission (AIE), Life and Health

Light has profoundly impacted modern medicine and healthcare, with numerous luminescent agents and imaging techniques currently being used to assess health and treat diseases. As an emerging concept in luminescence, aggregation-induced emission (AIE) has shown great potential in biological applications due to its advantages in terms of brightness, biocompatibility, photostability, and positive correlation with concentration. This review provides a comprehensive summary of AIE luminogens applied in imaging of biological structure and dynamic physiological processes, disease diagnosis and treatment, and detection and monitoring of specific analytes, followed by representative works. Discussions on critical issues and perspectives on future directions are also included. This review aims to stimulate the interest of researchers from different fields, including chemistry, biology, materials science, medicine, etc., thus promoting the development of AIE in the fields of life and health.

Advanced imaging techniques for tracking drug dynamics at the subcellular level

Optical microscopes are an important imaging tool that have effectively advanced the development of modern biomedicine. In recent years, super-resolution microscopy (SRM) has become one of the most popular techniques in the life sciences, especially in the field of living cell imaging. SRM has been used to solve many problems in basic biological research and has great potential in clinical application. In particular, the use of SRM to study drug delivery and kinetics at the subcellular level enables researchers to better study drugs' mechanisms of action and to assess the efficacy of their targets in vivo. The purpose of this paper is to review the recent advances in SRM and to highlight some of its applications in assessing subcellular drug dynamics.

An ER-targeted "reserve-release" fluorogen for topological quantification of reticulophagy

The endoplasmic reticulum's (ER) dynamic nature, essential for maintaining cellular homeostasis, can be influenced by stress-induced damage, which can be assessed by examining the morphology of ER dynamics and, more locally, ER properties such as hydrophobicity, viscosity, and polarity. Although numerous ER-specific chemical probes have been developed to monitor the ER's physical and chemical parameters, the quantitative detection and super-resolution imaging of its local hydrophobicity have yet to be explored. Here, we describe a photostable ER-targeted probe with high signal-to-noise ratio for super-resolution imaging that can specifically respond to changes in ER hydrophobicity under stress based on a "reserve-release" mechanism. The probe shows an excellent ability to target ER over commercial ER dyes and can be used to track local changes of hydrophobicity by fluorescence intensity and morphology during the selective autophagy of ER (i.e., reticulophagy). By correlating the level and location of ER damage with the distribution of fluorescence intensity, we were able to assess reticulophagy at the subcellular level. Beyond that, we developed a topological analytical tool adaptable to any ER probe for detecting structural changes in ER and thus quantitatively identifying reticulophagy. The algorithm-assisted tool can also be adapted to a wide range of molecular probes and organelles. Altogether, the new probe and analytical strategy described here show promise for the quantitative detection and analysis of subtle ER damage and stress.

Bioinspired large Stokes shift small molecular dyes for biomedical fluorescence imaging

Long Stokes shift dyes that minimize cross-talk between the excitation source and fluorescent emission to improve the signal-to-background ratio are highly desired for fluorescence imaging. However, simple small molecular dyes with large Stokes shift (more than 120 nanometers) and near-infrared (NIR) emissions have been rarely reported so far. Here, inspired by the chromophore chemical structure of fluorescent proteins, we designed and synthesized a series of styrene oxazolone dyes (SODs) with simple synthetic methods, which show NIR emissions (>650 nanometers) with long Stokes shift (ranged from 136 to 198 nanometers) and small molecular weight (<450 daltons). The most promising SOD9 shows rapid renal excretion and blood-brain barrier passing properties. After functioning with the mitochondrial-targeted triphenylphosphonium (TPP) group, the resulting SOD9-TPP can be engineered for head-neck tumor imaging, fluorescence image-guided surgery, brain neuroimaging, and on-site pathologic analysis. In summary, our findings add an essential small molecular dye category to the classical dyes.

Luminescent and Photofunctional Transition Metal Complexes: From Molecular Design to Diagnostic and Therapeutic Applications

There has been emerging interest in the exploitation of the photophysical and photochemical properties of transition metal complexes for diagnostic and therapeutic applications. In this Perspective, we highlight the major recent advances in the development of luminescent and photofunctional transition metal complexes, in particular, those of rhenium(I), ruthenium(II), osmium(II), iridium(III), and platinum(II), as bioimaging reagents and phototherapeutic agents, with a focus on the molecular design strategies that harness and modulate the interesting photophysical and photochemical behavior of the complexes. We also discuss the current challenges and future outlook of transition metal complexes for both fundamental research and clinical applications.

Conformationally Confined Emissive Cationic Macrocycle with Photocontrolled Organelle-Specific Translocation

The optimization of molecular conformation and aggregation modes is of great significance in creation of new luminescent materials for biochemical research and medical diagnostics. Herein, a highly emissive macrocycle (1) is reported, which is constructed by the cyclization reaction of triphenylamine with benzyl bromide and exhibits very distinctive photophysical performance both in aqueous solution and the solid state. Structural analysis reveals that the 1 can form self-interpenetrated complex and emit bright yellow fluorescence in the crystal lattice. The distorted yet symmetrical structure can endow 1 with unique two-photon absorption property upon excitation by near-infrared light. Also, 1 can be utilized as an efficient photosensitizer to produce singlet oxygen (1 O2 ) both in inanimate milieu and under cellular environment. More intriguingly, due to the strong association of 1 with negatively charged biomacromolecules, organelle-specific migration is achieved from lysosome to nucleus during the 1 O2 -induced cell apoptosis process. To be envisaged, this conformationally confined cationic macrocycle with photocontrolled lysosome-to-nucleus translocation may provide a feasible approach for in situ identifying different biospecies and monitoring physiological events at subcellular level.

G-quadruplex stabilizer Tetra-Pt(bpy) disrupts telomere maintenance and impairs FAK-mediated migration of telomerase-positive cells

G-quadruplex regulates a wide spectrum of biological processes, including telomere maintenance, DNA replication and transcription. The development of small molecules to selectively target G-quadruplex and their application remain hotspots in cancer therapy. Here, we explored the biological effect of G-quadruplexes stabilizer Tetra-Pt(bpy) in telomerase-positive cancer cells. Telomere maintenance was evaluated by telomerase repeat amplification protocol, chromosome orientation fluorescence in situ hybridization and telomere restriction fragment assays. We found that Tetra-Pt(bpy) accelerates telomere shortening through dual inhibition of telomerase activity and telomere sister chromatin exchanges mediated by telomeric G-quadruplexes. Consequently, Tetra-Pt(bpy)-treated cancer cells became enriched with extremely short telomeres and produced a strong telomeric DNA damage response following long-term treatment, leading to cell proliferation inhibition and senescence. Experimental evidence from RNA seq and cell migration-related assays showed that Tetra-Pt(bpy) decreased cell-matrix adhesion and inhibited the migration of non-senescent tumor cells. Mechanistically, Tetra-Pt(bpy) induced the formation of G-quadruplexes in focal adhesion kinase (FAK)-encoding gene PTK2, resulting in FAK transcription inhibition. Tetra-Pt(bpy) reduced xenograft tumor formation and inhibited tumor cell growth and migration in mice. This study further elucidates the function of G-quadruplexes in the human genome and reveals the potential of Tetra-Pt(bpy) as a novel chemotherapeutic agent for targeting telomerase-positive cancer cells.

Development of a novel light-up probe for detection of G-quadruplexes in stress granules

G-quadruplexes (G4s) regulate various biological processes in cells. However, cellular imaging of dynamically forming G4s in biomolecular condensates using small molecules has been poorly investigated. Herein, we present a fluorescent light-up probe with the ability to selectively stabilize G4s and enhance fluorescence upon G4 binding. The foci of the probe were mainly observed in the nucleoli. These were co-localized with anti-fibrillarin antibodies and anti-G4 antibodies (BG4). Moreover, we tested detection of G4 in stress granules using the developed probe. Stress granules were induced through treatment with not only thapsigargin, but also known G4 ligands (pyridostatin, RHPS4, and BRACO-19). In the stress granules, co-localization between the probe, BG4, and stress granule markers (TIA1 and G3BP1) was detected. We present a practical light-up probe for G4s in stress granules, providing potential targets for G4 ligands.

Luminescent Metal Complexes for Bioassays in the Near-Infrared (NIR) Region

Near-infrared (NIR, 700-1700 nm) luminescent imaging is an emerging bioimaging technology with low photon scattering, minimal autofluorescence, deep tissue penetration, and high spatiotemporal resolution that has shown fascinating promise for NIR imaging-guided theranostics. In recent progress, NIR luminescent metal complexes have attracted substantially increased research attention owing to their intrinsic merits, including small size, anti-photobleaching, long lifetime, and metal-centered NIR emission. In the past decade, scientists have contributed to the advancement of NIR metal complexes involving efforts to improve photophysical properties, biocompatibility, specificity, pharmacokinetics, in vivo visualization, and attempts to exploit new ligand platforms. Herein, we summarize recent progress and provide future perspectives for NIR metal complexes, including d-block transition metals and f-block lanthanides (Ln) as NIR optical molecular probes for bioassays.

Cancer Cell Membrane Labeling Fluorescent Doppelganger Enables In Situ Photoactivated Membrane Dynamics Tracking via Two-Photon Fluorescence Imaging Microscopy

Various suborganelles are delimited by lipid bilayers, in which high spatial and temporal morphological changes are essential to many physiological and pathological processes of cells. However, almost all the amphiphilic fluorescent molecules reported until now are not available for in situ precise tracking of membrane dynamics in cell apoptosis. Here, the MO (coumarin pyridine derivatives) was devised by engineering lipophilic coumarin and cationic pyridine salt, which not only lastingly anchored onto the plasma membrane in dark due to appropriate amphipathicity and electrostatic interactions but also in situ reflected the membrane damage and heterogeneity with secretion of extracellular vesicles (EVs) under reactive oxygen species regulation and was investigated by two-photon fluorescence lifetime imaging microscopy. This work opens up a new avenue for the development of plasma membrane staining and EV-based medicines for the early diagnosis and treatment of disease.

De Novo Design of A Membrane-Anchored Probe for Multidimensional Quantification of Endocytic Dynamics

As a process of cellular uptake, endocytosis, with gradient acidity in different endocytic vesicles, is vital for the homeostasis of intracellular nutrients and other functions. To study the dynamics of endocytic pathway, a membrane-anchored pH probe, ECGreen, is synthesized to visualize endocytic vesicles under structured illumination microscopy (SIM), a super-resolution technology. Being sensitive to acidity with increasing fluorescence at low pH, ECGreen can differentiate early and late endosomes as well as endolysosomes. Meanwhile, membrane anchoring not only improves the durability of ECGreen, but also provides an excellent anti-photobleaching property for long-time imaging with SIM. Moreover, by taking these advantages of ECGreen, a multidimensional analysis model containing spatial, temporal, and pH information is successfully developed for elucidating the dynamics of endocytic vesicles and their interactions with mitochondria during autophagy, and reveals a fast conversion of endosomes near the plasma membrane.

Efficient Synthesis of 2,3'-Spirobi (Indolin)-2'-Ones and Preliminary Evaluation of Their Damage to Mitochondria in HeLa Cells

A novel formal (4 + 1) annulation between N-(o-chloromethyl)aryl amides and 3-chlorooxindoles through in situ generated aza-ortho-QMs with 3-chlorooxindoles is reported for the synthesis of a series of 2,3'-spirobi (indolin)-2'-ones in high yields. Under structured illumination microscopy, compound 3a is found to change the mitochondrial morphology and induce mitophagy pathway, which might then trigger mitophagy in cancer cells.

Novel Pyrazine-Bridged D-A-D Type Charge Neutral Probe for Membrane Permeable Long-Term Live Cell Imaging

A novel donor-acceptor-donor (D-A-D) type compound containing pyrazine as the acceptor and triphenylamine as the donor has been designed and synthesized. The photophysical properties and biocompatibility of this probe, namely (OMeTPA)2-Pyr for live cell imaging were systematically investigated, with observed large Stokes shifts, high photostability, and low cytotoxicity. Furthermore, we demonstrated that (OMeTPA)2-Pyr could permeate live cell membranes for labeling. The proposed mechanism of this probe was the binding and shafting through membrane integral transport proteins by electrostatic and hydrophobic interactions. These salient and novel findings can facilitate the strategic design of new pyrazine-fused charge-neutral molecular platforms as fluorescent probes, for long-term in situ dynamic monitoring in live cells.

A deep-red-emission antimony(III) chloride with dual-cations: extremely large Stokes shift due to high [SbCl6] distortion

Compound [C₅mim][Mim]₂[SbCl₆] (1; [C₅mim]⁺ = 1-pentyl-3-methylimidazolium; [Mim]⁺ = N-methylimidazolium) with dual cations exhibits the first case of deep-red emission in [SbCl₆]^3--based 0D OIMHs. Anion distortion due to high disequilibrium of supramolecular interactions is revealed to be responsible for the extremely large Stokes shift of 335 nm and FWHM of 210 nm in the emission.

A Carbonic Anhydrase IX (CAIX)-Anchored Rhenium(I) Photosensitizer Evokes Pyroptosis for Enhanced Anti-Tumor Immunity

An ideal cancer treatment should not only destroy primary tumors but also improve the immunogenicity of the tumor microenvironment to achieve a satisfactory anti-tumor immune effect. We designed a carbonic anhydrase IX (CAIX)-anchored rhenium(I) photosensitizer, named CA-Re, that not only performs type-I and type-II photodynamic therapy (PDT) with high efficiency under hypoxia (nanomolar-level phototoxicity), but also evokes gasdermin D (GSDMD) mediated pyroptotic cell death to effectively stimulate tumor immunogenicity. CA-Re could disrupt and self-report the loss of membrane integrity simultaneously. This promoted the maturation and antigen-presenting ability of dendritic cells (DCs), and fully activated T cells dependent adaptive immune response in vivo, eventually eliminating distant tumors at the same time as destroying primary tumors. To the best of our knowledge, CA-Re is the first metal complex-based pyroptosis inducer.

Recent progress in metal-based molecular probes for optical bioimaging and biosensing

Biological imaging and biosensing from subcellular/cellular level to whole body have enabled non-invasive visualisation of molecular events during various biological and pathological processes, giving great contributions to the rapid and impressive advances in chemical biology, drug discovery, disease diagnosis and prognosis. Optical imaging features a series of merits, including convenience, high resolution, good sensitivity, low cost and the absence of ionizing radiation. Among different luminescent probes, metal-based molecules offer unique promise in optical bioimaging and biosensing in vitro and in vivo, arising from their small sizes, strong luminescence, large Stokes shifts, long lifetimes, high photostability and tunable toxicity. In this review, we aim to highlight the design of metal-based molecular probes from the standpoint of synthetic chemistry in the last 2 years for optical imaging, covering d-block transition metal and lanthanide complexes and multimodal imaging agents.

Novel recognition mechanism based on oxidative addition of Pt(II) complex-based luminescent probes for hypochlorite ion detection

Platinum(II) complexes are the most commonly used anticancer drugs and potential optical materials, but the detectability of Pt(II) complex-based probes is seldom reported. In our previous work, a tetradentate Pt(II) complex Pt-CHO was utilised as a 'turn-off' probe to detect ClO^- and image cancer cells. However, the recognition mechanism has not been completely clarified and there are still doubts. In this work, three Pt(II) complexes, Pt-H, Pt-CHO and Pt-COOH, were developed to elucidate the mechanism of this class of complexes and refine their property studies. As a result, the UV-visible absorption and luminescence emission experiments, as well as the mass spectrum, proved that the oxidation of Pt(II) to Pt(IV) was the real reason for luminescence quenching, which has nothing to do with aldehyde groups. This first reported mechanism introduces a new type of ClO^- probe based on Pt(II) complexes, thereby expanding the application fields of platinum complexes. Moreover, the quantum yield measurements, the effect of biomolecules and reversibility were studied to improve the properties of the probes. Theoretical calculations were used to gain an in-depth understanding of optical characteristics and related mechanisms. The cell imaging of RAW264.7 cells under endogenous ClO^- proved the potential of the probes in bioimaging.

Intracellular Dynamic Assembly of Deep-Red Emitting Supramolecular Nanostructures Based on the Pt…Pt Metallophilic Interaction

Many drug delivery systems end up in the lysosome because they are built from covalent or kinetically inert supramolecular bonds. To reach other organelles, nanoparticles hence need to either be made from a kinetically labile interaction that allows re-assembly of the nanoparticles inside the cell following endocytic uptake, or, be taken up by a mechanism that short-circuits the classical endocytosis pathway. In this work, the intracellular fate of nanorods that self-assemble via the Pt…Pt interaction of cyclometalated platinum(II) compounds, is studied. These deep-red emissive nanostructures (638 nm excitation, ≈700 nm emission) are stabilized by proteins in cell medium. Once in contact with cancer cells, they cross the cell membrane via dynamin- and clathrin-dependent endocytosis. However, time-dependent confocal colocalization and cellular electron microscopy demonstrate that they directly move to mitochondria without passing by the lysosomes. Altogether, this study suggests that Pt…Pt interaction is strong enough to generate emissive, aggregated nanoparticles inside cells, but labile enough to allow these nanostructures to reach the mitochondria without being trapped in the lysosomes. These findings open new venues to the development of bioimaging nanoplatforms based on the Pt…Pt interaction.

A Continuous Add-On Probe Reveals the Nonlinear Enlargement of Mitochondria in Light-Activated Oncosis

Oncosis, depending on DNA damage and mitochondrial swelling, is an important approach for treating cancer and other diseases. However, little is known about the behavior of mitochondria during oncosis, due to the lack of probes for in situ visual illumination of the mitochondrial membrane and mtDNA. Herein, a mitochondrial lipid and mtDNA dual-labeled probe, MitoMN, and a continuous add-on assay, are designed to image the dynamic process of mitochondria in conditions that are unobservable with current mitochondrial probes. Meanwhile, the MitoMN can induce oncosis in a light-activated manner, which results in the enlargement of mitochondria and the death of cancer cells. Using structured illumination microscopy (SIM), MitoMN-stained mitochondria with a dual-color response reveals, for the first time, how swelled mitochondria interacts and fuses with each other for a nonlinear enlargement to accelerate oncosis into an irreversible stage. With this sign of irreversible oncosis revealed by MitoMN, oncosis can be segregated into three stages, including before oncosis, initial oncosis, and accelerated oncosis.

Long-term live-cell lipid droplet-targeted biosensor development for nanoscopic tracking of lipid droplet-mitochondria contact sites

Background: Lipid droplets (LDs) establish a considerable number of contact sites with mitochondria to enable energy transfer and communication. In this study, we developed a fluorescent biosensor to image LD-mitochondria interactions at the nanoscale and further explored the function of LD-mediated matrix transmission in processes involving multi-organelle interactions. Methods: A fluorescent probe called C-Py (C21H19N3O2, 7-(diethylamino) coumarin-3-vinyl-4-pyridine acetonitrile) was designed and synthesized. Colocalization of C-Py and the commercial LD stain Nile Red was analyzed in HeLa cells. The fluorescence stability and signal to background ratio of C-Py under structured illumination microscopy (SIM) were compared to those of the commercial probe BODIPY493/503. The cytotoxicity of C-Py was assessed using CCK-8 assays. The uptake pattern of C-Py in HeLa cells was then observed under various temperatures, metabolic levels, and endocytosis levels. Contact sites between LDs and various organelles, such as mitochondria, nuclei, and cell membrane, were imaged and quantitated using SIM. Physical changes to the contact sites between LDs and mitochondria were monitored after lipopolysaccharide induction. Results: A LD-targeted fluorescent biosensor, C-Py, with good specificity, low background signal, excellent photostability, low cytotoxicity, and high cellular permeability was developed for tracking LD contact sites with multiple organelles using SIM. Using C-Py, the subcellular distribution and dynamic processes of LDs in living cells were observed under SIM. The formation of contact sites between LDs and multiple organelles was visualized at a resolution below ~200 nm. The number of LD-mitochondria contact sites formed was decreased by lipopolysaccharide treatment inducing an inflammatory environment. Conclusions: C-Py provides strategies for the design of ultra-highly selective biosensors and a new tool for investigating the role and regulation of LDs in living cells at the nanoscale.

Selectivity and Targeting of G-Quadruplex Binders Activated by Adaptive Binding and Controlled by Chemical Kinetics

G-quadruplexes (G4s) are prevalent in oncogenes and are potential antitumor drug targets. However, binding selectivity of compounds to G4s still faces challenges. Herein, we report a platinum(II) complex (Pt1), whose affinity to G4-DNA is activated by adaptive binding and selectivity controlled by binding kinetics. The resolved structure of Pt1/VEGF-G4 (a promoter G4) shows that Pt1 matches 3'-G-tetrad of VEGF-G4 through Cl^- -dissociation and loop rearrangement of VEGF-G4. Binding rate constants are determined by coordination bond breakage/formation, correlating fully with affinities. The selective rate-determining binding step, Cl^- -dissociation upon G4-binding, is 2-3 orders of magnitude higher than dsDNA. Pt1 potently targets G4 in living cells, effectively represses VEGF expression, and inhibits vascular growth in zebrafish. We show adaptive G4-binding activation and controlled by kinetics, providing a complementary design principle for compounds targeting G4 or similar biomolecules.

G-quadruplex targeting chemical nucleases as a nonperturbative tool for analysis of cellular G-quadruplex DNA

G-quadruplex structures are associated with various biological activities, while in vivo evidence is essential to confirm the formation of G-quadruplexes inside cells. Most conventional agents that recognize G-quadruplex, including antibodies and small-molecule G-quadruplex ligands, either stabilize the G-quadruplex or prevent G-quadruplex unfolding by helicase, thereby artificially increasing the G-quadruplex levels in cells. Unambiguous study of G-quadruplexes at natural cellular levels requires agents that do not enhance the stability of G-quadruplex. Herein, we report the first example of nonperturbative chemical nucleases that do not influence the stability of G-quadruplex telomeric DNA but can selectively cleave G-quadruplex DNA over duplex DNA. These chemical nucleases can be readily taken up by cells and promote selective cleavage of telomeric DNA with low levels of nonselective DNA cleavage of other regions of the genome. The cleavage of G-quadruplex telomeric DNA by nonperturbative chemical nucleases confirms the formation of G-quadruplex telomeric DNA in live cells.

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Novel chemical nucleases exhibit no effect on G-quadruplex telomeric DNA stability

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Selective nucleases cleave G-quadruplex DNA over duplex DNA

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Cleavage of G-quadruplex telomeric DNA motifs confirms their existence in cells

Length-Dependent Distinct Cytotoxic Effect of Amyloid Fibrils beyond Optical Diffraction Limit Revealed by Nanoscopic Imaging

Fibrillar species have been proposed to play an essential role in the cytotoxicity of amyloid peptide and the pathogenesis of neurodegenerative diseases. Discrimination of Aβ aggregates in situ at high spatial resolution is therefore significant for the development of a therapeutic method. In this work, we adopt a rhodamine-like structure as luminescent centers to fabricate carbonized fluorescent nanoparticles (i.e., carbon dots, RhoCDs) with tunable emission wavelengths from green to red and burst-like photoblinking property for localization-based nanoscopic imaging. These RhoCDs contain lipophilic cationic and carboxyl groups which can specifically bind with Aβ_1-40 aggregates via electrostatic interaction and hydrogen bonding. According to the nanoscopic imaging in the Aβ_1-40 fibrillation and disaggregation process, different types of Aβ_1-40 aggregates beyond the optical diffraction limit have been disclosed. Additionally, length-dependent toxic effect of Aβ_1-40 aggregates beyond the optical diffraction limit is unveiled. Short amyloid assemblies with length of 187 ± 3.9 nm in the early stage are more toxic than the elongated amyloid fibrils. Second, disassembly of long fibrils into short species by Gramicidin S (GS-2) peptide might enhance the cytotoxicity. These results lay the foundation to develop functional fluorophore for nanoscopic imaging and also provide deep insight into morphology-dependent cytotoxicity from amyloid peptides.

Transporting mitochondrion-targeting photosensitizers into cancer cells by low-density lipoproteins for fluorescence-feedback photodynamic therapy

Low-density lipoproteins (LDLs) are an endogenous nanocarrier to transport lipids in vivo. Owing to their biocompatibility and biodegradability, reduced immunogenicity, and natural tumor-targeting capability, we, for the first time, report the reconstitution of native LDL particles with saturated fatty acids and a mitochondrion-targeting aggregation-induced emission (AIE) photosensitizer for fluorescence-feedback photodynamic therapy (PDT). In particular, a novel AIE photosensitizer (TPA-DPPy) with a donor-acceptor (D-A) structure and a pyridinium salt is designed and synthesized, which possesses typical AIE and twisted intramolecular charge transfer (TICT) characteristics as well as reactive oxygen species (ROS)-sensitizing capability. In view of its prominent photophysical and photochemical properties, TPA-DPPy is encapsulated into LDL particles for photodynamic killing of cancer cells that overexpress LDL receptors (LDLRs). The resultant LDL (rLDL) particles maintain a similar morphology and size distribution to native LDL particles, and are efficiently ingested by cancer cells via LDLR-mediated endocytosis, followed by the release of TPA-DPPy for mitochondrion-targeting. Upon light irradiation, the produced ROS surrounding mitochondria lead to efficient and irreversible cell apoptosis. Interestingly, this process can be fluorescently monitored in a real-time fashion, as reflected by the remarkably enhanced luminescence and blue-shifted emission, indicating the increased mechanical stress during apoptosis. Quantitative cell viability analysis suggests that TPA-DPPy exhibits an outstanding phototoxicity toward LDLR-overexpressing A549 cancer cells, with a killing efficiency of ca. 88%. The rLDL particles are a class of safe and multifunctional nanophototheranostic agents, holding great promise in high-quality PDT by providing real-time fluorescence feedback on the therapeutic outcome.

Ligand-controlled and nanoconfinement-boosted luminescence employing Pt(ii) and Pd(ii) complexes: from color-tunable aggregation-enhanced dual emitters towards self-referenced oxygen reporters

In this work, we describe the synthesis, structural and photophysical characterization of four novel Pd(ii) and Pt(ii) complexes bearing tetradentate luminophoric ligands with high photoluminescence quantum yields (Φ L) and long excited state lifetimes (τ) at room temperature, where the results were interpreted by means of DFT calculations. Incorporation of fluorine atoms into the tetradentate ligand favors aggregation and thereby, a shortened average distance between the metal centers, which provides accessibility to metal-metal-to-ligand charge-transfer (3MMLCT) excimers acting as red-shifted energy traps if compared with the monomeric entities. This supramolecular approach provides an elegant way to enable room-temperature phosphorescence from Pd(ii) complexes, which are otherwise quenched by a thermal population of dissociative states due to a lower ligand field splitting. Encapsulation of these complexes in 100 nm-sized aminated polystyrene nanoparticles enables concentration-controlled aggregation-enhanced dual emission. This phenomenon facilitates the tunability of the absorption and emission colors while providing a rigidified environment supporting an enhanced Φ L up to about 80% and extended τ exceeding 100 μs. Additionally, these nanoarrays constitute rare examples for self-referenced oxygen reporters, since the phosphorescence of the aggregates is insensitive to external influences, whereas the monomeric species drop in luminescence lifetime and intensity with increasing triplet molecular dioxygen concentrations (diffusion-controlled quenching).

Simultaneous Zn2+ tracking in multiple organelles using super-resolution morphology-correlated organelle identification in living cells

Zn²⁺ plays important roles in metabolism and signaling regulation. Subcellular Zn²⁺ compartmentalization is essential for organelle functions and cell biology, but there is currently no method to determine Zn²⁺ signaling relationships among more than two different organelles with one probe. Here, we report simultaneous Zn²⁺ tracking in multiple organelles (Zn-STIMO), a method that uses structured illumination microscopy (SIM) and a single Zn²⁺ fluorescent probe, allowing super-resolution morphology-correlated organelle identification in living cells. To guarantee SIM imaging quality for organelle identification, we develop a new turn-on Zn²⁺ fluorescent probe, NapBu-BPEA, by regulating the lipophilicity of naphthalimide-derived Zn²⁺ probes to make it accumulate in multiple organelles except the nucleus. Zn-STIMO with this probe shows that CCCP-induced mitophagy in HeLa cells is associated with labile Zn²⁺ enhancement. Therefore, direct organelle identification supported by SIM imaging makes Zn-STIMO a reliable method to determine labile Zn²⁺ dynamics in various organelles with one probe. Finally, SIM imaging of pluripotent stem cell-derived organoids with NapBu-BPEA demonstrates the potential of super-resolution morphology-correlated organelle identification to track biospecies and events in specific organelles within organoids.

Subcellular Zn²⁺ compartmentalisation is essential for cell biology. Here the authors make a turn-on fluorescent Zn²⁺ probe that localises to multiple organelles, and correlate its location using organelle morphology derived from structured illumination microscopy.