A cell-impermeable luminogenic probe for near-infrared imaging of prostate-specific membrane antigen in prostate cancer microenvironments

Dual-color and specific luminescence detection of Pd2+ ions using iridium(III) complex-based probes in food samples

The toxicity of palladium (Pd) is highly associated with its oxidative states, thus it is important to develop specific detection methods for Pd2+ ions in food and environmental systems. However, the reliable and selective detection of Pd2+ ions remains challenging. Here, we report two iridium(III) complexes with dual colors (717 nm and 637 nm) for the specific detection of Pd2+ ions, with the 3,3'-diamino group being used as a specific recognition unit for Pd2+ ions for the first time. The dual-color probes showed a luminescence quenching response to Pd2+ ions in aqueous solution within 1 min, along with an obvious color change under UV irradiation. Moreover, complexes 1-2 allow sensitive and selective detection of Pd2+ ions with a limit of detection (LOD) of 0.69 μM and 0.26 μM, respectively, showing a good linear response for Pd2+ ions in the range of 1-13 μM (R2 = 0.985) and 1-9 μM (R2 = 0.996). Finally, the probes were successfully applied for the detection of Pd2+ ions in food and environmental samples with good recoveries ranging from 85.4 to 118.7 %, providing a robust analytical tool for Pd2+ ions quantification for onsite setting.

Inhibiting Glycolysis and Disrupting the Mitochondrial HK2-VDAC1 Protein-Protein Interaction Using a Bifunctional Lonidamine-Conjugated Metal Probe for Combating Triple-Negative Breast Cancer

Triple-negative breast cancer (TNBC) relies primarily on aerobic glycolysis for energy and rapid cancer cell proliferation. Hexokinase 2 (HK2), a key enzyme regulating glycolysis, is overexpressed in TNBC, promoting tumor cell proliferation and apoptosis resistance by interacting with the mitochondrial membrane's voltage-dependent anion channel 1 (VDAC1). However, the development of bioactive molecules for effectively disrupting the HK2-VDAC1 interaction remains challenging. Herein, we have modified londamine (LND) with an iridium(III) complex to create bifunctional far-red probe 1. This complex not only has the ability to distinguish TNBC cells from normal cells by probing HK2 in mitochondria, but also significantly enhances antitumor activity by inhibiting mitochondrial glycolysis and effectively disrupting the HK2-VDAC1 interaction. This led to increased Bax-VDAC1 interaction, opening of the mitochondrial permeability transition pores (MPTPs), and generation of ROS, ultimately leading to mitochondrial dysfunction and enhanced cancer cell apoptosis. Probe 1 also demonstrated stronger antiproliferative activity than LND alone in a TNBC mouse model by targeting the HK2-VDAC1 interaction without causing overt toxicity. This work showcases the potential of probe 1 as an effective therapeutic agent for TNBC by inhibiting the mitochondrial HK2-VDAC1 interaction.

A Bivalent Iridium(III) Complex Toolkit for Mitochondrial DNA G-Quadruplex-Targeted Theranostics

The G-quadruplex (G4) is an important diagnostic and therapeutic target in cancers, but the development of theranostic probes for subcellular G4 s remains challenging. In this work, we report three G4-targeted theranostic probes by conjugating a pyridostatin-derived G4 ligand to G4-specific iridium(III) complexes with desirable photophysical properties. These probes showed specifically enhanced luminescence to mitochondrial G4 in triple-negative breast cancer (TNBC) cells. Of note, complex 3 exhibited NIR emission and the ability to discriminate TNBC cells and normal breast cells. Furthermore, these probes showed much higher PDT toxicity in TNBC cells through ROS-induced apoptosis, where complex 3 exhibited a type I/II hybrid PDT effect with the potential to overcome hypoxia. These results demonstrate that these complexes are multicolor and modular phototheranostic probes for DNA G4s. We believe that this work offers a multifunctional theranostic toolkit for unmasking subcellular DNA G-quadruplex functions.

Selective detection of mitochondrial Cu2+ in living cells by a near-infrared iridium(III) complex

The widespread use of copper (Cu) has raised concerns about environmental pollution and adverse effects on human health, highlighting the need to develop copper detection methods. Developing near-infrared (NIR) luminescent probes for imaging subcellular Cu2+ is still a challenge. In this work, we have developed a luminescence probe based on a NIR iridium(III) complex, which rapidly detects Cu2+ by combining salicylaldehyde and amine groups through a simple Schiff base reaction on the N^N ligand. The probe exhibits strong luminescence with a quantum yield of 0.66 and is able to detect Cu2+ with a limit of detection (LOD) of 0.31 μM, without interference from other metal ions. Mechanistic studies showed that the probe coordinated Cu2+ ions with a molar ratio of 1:1 and binding constant as low as 4.02 × 10-2 μM, and operated through photoinduced electron transfer (PeT) for luminescence quenching. Importantly, the photostability experiments confirmed the desirable photostability of the probe in aqueous solution and in cellulo compared with a commercial organic dye. Furthermore, cellular imaging experiments demonstrated its capability for the visualization of Cu2+ in the mitochondria of living cells, which paves the way for the study of the subcellular distribution of Cu2+ and related toxicity analysis.

A photostable luminescent iridium(III) complex probe for imaging endogenous mitochondrial sulfur dioxide in living cells

Sulfur dioxide (SO2) is an important signaling gas molecule, but its aberration is highly associated with inflammatory diseases and cancers. Luminescence probes for SO2 have emerged as essential instruments for elucidating its biological roles and facilitating disease diagnosis, owing to their high sensitivity and capabilities for real-time detection. Nevertheless, the majority of current probes lack subcellular selectivity and suffer from limited photostability. In this work, we develop an Ir(III)-based luminescence probe (Ir3) for the rapid, real-time, and accurate detection of SO2 in aqueous solution. This probe exhibits low cytotoxicity and provides exceptional imaging of mitochondrial SO2 in living cells. We anticipate that this probe will serve as a foundational tool for the advancement of effective imaging technologies for SO2, thereby enhancing the clinical and biomedical applications of Ir(III) complex-based detection probes.

Current Context of Designing Phototheranostic Cyclometalated Iridium (III) Complexes to Open a New Avenue in Cancer Therapy

Photo-induced chemotherapy offers the best option for the selective treatment of cancer among all the prevailing modalities. Iridium (III) complexes, flourished with excellent photophysical and photochemical properties, have been considered to be superior for undergoing photo-responsive cancer therapy. Large Stokes shift, long-lived triplet excited state, photostability, and tuneable emission have rendered its excellence as a phototheranostic agent. In particular, the cyclometalated Ir (III) complexes and their respective nanoparticles have made a strong niche in the arena of cancer therapy. In recent years, Ir (III) based complexes have shown promising utilities as both imaging and therapeutic agents as well. Therefore, this review summarises the recent advances in the strategic designing of cyclometalated Ir(III) complexes to augment their phototheranostic applications in precision medicine.

Shining New Light on Biological Systems: Luminescent Transition Metal Complexes for Bioimaging and Biosensing Applications

Luminescence imaging is a powerful and versatile technique for investigating cell physiology and pathology in living systems, making significant contributions to life science research and clinical diagnosis. In recent years, luminescent transition metal complexes have gained significant attention for diagnostic and therapeutic applications due to their unique photophysical and photochemical properties. In this Review, we provide a comprehensive overview of the recent development of luminescent transition metal complexes for bioimaging and biosensing applications, with a focus on transition metal centers with a d6, d8, and d10 electronic configuration. We elucidate the structure-property relationships of luminescent transition metal complexes, exploring how their structural characteristics can be manipulated to control their biological behavior such as cellular uptake, localization, biocompatibility, pharmacokinetics, and biodistribution. Furthermore, we introduce the various design strategies that leverage the interesting photophysical properties of luminescent transition metal complexes for a wide variety of biological applications, including autofluorescence-free imaging, multimodal imaging, organelle imaging, biological sensing, microenvironment monitoring, bioorthogonal labeling, bacterial imaging, and cell viability assessment. Finally, we provide insights into the challenges and perspectives of luminescent transition metal complexes for bioimaging and biosensing applications, as well as their use in disease diagnosis and treatment evaluation.

Covalent inhibition of epidermal growth factor receptor using a long-lived iridium(III)-afatinib probe

The overexpression and overactivation of epidermal growth factor receptor (EGFR) are frequently observed in human cancers, including squamous cell carcinoma and adenocarcinoma. In this study, a covalent EGFR probe was developed by conjugating afatinib to an iridium(III) scaffold. Complex 1 showed enhanced luminescence in living epidermoid squamous carcinoma A431 cells compared to other cell lines, via engaging EGFR as confirmed via CETSA and knockdown experiments. Moreover, complex 1 inhibited downstream targets of EGFR in cellulo with repression persisting after removal of the complex, indicating an irreversible mode of inhibition. Finally, complex 1 showed potent antiproliferative activity against A431 cells with comparable potency to afatinib alone. To our knowledge, complex 1 is the first EGFR covalent inhibitor based on an iridium scaffold reported in the literature, with the potential to be further explored as a theranostic agent in the future.