Recent advances in small-molecule fluorescent probes for studying ferroptosis.

Ferroptosis is an iron-dependent, non-apoptotic form of programmed cell death driven by excessive lipid peroxidation (LPO). Mounting evidence suggests that the unique modality of cell death is involved in the development and progression of several diseases including cancer, cardiovascular diseases (CVDs), neurodegenerative disorders, etc. However, the pathogenesis and signalling pathways of ferroptosis are not fully understood, possibly due to the lack of robust tools for the highly selective and sensitive imaging of ferroptosis analytes in complex living systems. Up to now, various small-molecule fluorescent probes have been applied as promising chemosensors for studying ferroptosis through tracking the biomolecules or microenvironment-related parameters in vitro and in vivo. In this review, we comprehensively reviewed the recent development of small-molecule fluorescent probes for studying ferroptosis, with a focus on the analytes, design strategies and bioimaging applications. We also provided new insights to overcome the major challenges in this emerging field.

Multifunctional Fluorescent Probe for Simultaneously Detecting Microviscosity, Micropolarity, and Carboxylesterases and Its Application in Bioimaging.

Based on OR logic gate, we proposed a smart near-infrared (NIR) fluorescent probe, named VPCPP, for simultaneously monitoring local microviscosity, micropolarity, and carboxylesterases (CEs) in living cells through blue and red channels. This proposed probe was capable of distinguishing cancer cells from normal cells and had good potential for identifying living liver cell lines. Furthermore, the fluctuations of the three analytes of interest in different cell status was successfully explored. Particularly, facilitated with high-content analysis (HCA) and VPCPP, a simple and efficient high-throughput screening (HTS) platform was first constructed for screening antitumor drugs and studying their effect on the analytes. For the first time, we found that sorafenib-induced ferroptosis led to an increase in the microviscosity and up-regulation of CEs at the same time. Additionally, the procedure that aristolochic acid (AA) induced the overexpression of CEs was verified. Besides, VPCPP was utilized for imaging the variations of the two microenvironment parameters and CEs in the inflammation model. Finally, VPCPP was able to image the tumor ex vivo and in vivo through two channels and one channel separately, as well as to visualize the kidneys and liver ex vivo with dual emissions, which indicated that the probe had great potential for imaging applications such as medical diagnosis, preclinical research, and imaging-guided surgery.

Two birds with one stone: a NIR fluorescent probe for mitochondrial protein imaging and its application in photodynamic therapy.

Mitochondrial proteins, most of which are encoded in the nucleus and the rest of which are regulated by the mitochondrial genome, play pivotal roles in essential cellular functions. However, fluorescent probes that can be used for monitoring mitochondrial proteins have not yet been widely developed, thereby severely limiting the exploration of the functions of proteins in mitochondria. Towards this end, here we propose a near-infrared (NIR) fluorescence probe MPP to effectively illuminate the dynamic changes in mitochondrial proteins in live cells under oxidative stress, with excellent temporal and spatial resolution. Of particular importance, MPP extends the study of the pharmacology involved in apoptosis induced by anti-cancer drugs (hydroxycamptothecin (HCPT), epirubicin (Epi) and cyclophosphamide (CPA)) for the first time. Furthermore, employing a protein-activatable strategy, this probe could serve as an excellent phototherapeutic agent in photodynamic therapy (PDT). Finally, in vivo experiments suggest that this versatile probe can be used to image tumors in HeLa tumor-bearing mice for 24 h, which demonstrates that our probe could play a dual role as a robust phototherapeutic and imaging agent.

An Activatable and Switchable Nanoaggregate Probe for Detecting H2 S and Its Application in Mice Brains.

Employing a sequentially activated probe design method, an activatable, switchable and dual-mode probe was designed. This nanoprobe, HSDPP, could be effectively activated by H2 S to form H-type aggregates with green emission; subsequently, the aggregates could bind to mtDNA to form monomers and the emIssion color switched from green to deep-red. We exploited HSDPP to image exogenous and endogenous H2 S in living cells. Of note, for the first time, this novel nanoprobe with an optimal partition coefficient value (LogP=1.269) was successfully applied for tracking the endogenous H2 S upregulation stimulated by cystathionase activator S-adenosyl-L-methionine (SAM) in mice brains. Finally, our work provides an invaluable chemical tool for probing endogenous H2 S upregulation in vitro/vivo and, importantly, affords a prospective design strategy for developing switchable chemosensors to unveil the relationship between biomolecules and DNA in mitochondria in many promising areas.

A turn-on fluorescent sensor for selective detection of hydrazine and its application in Arabidopsis thaliana.

In this work, a primary method was constructed for detecting hydrazine in plant, thus accomplished the closed-loop monitoring of hydrazine circulation within manufacture, environment, plants, animals and human. From a series of sensors, QYL-1 was selected to present the hydrazine sensing properties. As a preliminary tool, QYL-1 suggested the ultra-wide linear range (0-20.0 equivalent) and high selectivity, which were extremely essential for linking the monitoring in various scale and field. For the first time, concentration-dependent tracking of hydrazine was successfully performed in Arabidopsis Thaliana root tips. Afterwards applications in water samples and living MCF-7 cells then fulfilled the demonstration of closing the loop by linking both the upstream and downstream nodes. More than raising a practical method, this work offered initial information for the closed-loop monitoring of hydrazine circulation, which might be significant for the ideal systematic managing in future.

An umbelliferone-derivated fluorescent sensor for selective detection of palladium(II) from palladium(0) in living cells.

Palladium (Pd) has drawn worldwide attentions because its connections to industry, chemistry, biological material and public health. Quantitative and selective detection tools for Pd and its ion forms are in urgent necessity. Here an umbelliferone derivative Umb-Pd2 was provided as a small, steady, safe and selective sensor for detecting Pd(II). It indicated advantages including sensitive (LOD 1.1 nM), wide pH tolerance (5.0-10.0), applicable linear range (0-1.8 equivalent) and low toxicity. The most attractive point was its explicit selectivity towards Pd(II) from Pd(0) in both independent and coexistence systems. This distinguishing ability was further utilized in imaging in living cells, raising this work as a rare and important example among all the published papers on palladium sensing. Thus, Umb-Pd2 supplied a potential approach for further improvement and applications in both daily chemistry and public health.

Design, synthesis, and biological evaluation of 2,3-diphenyl-cycloalkyl pyrazole derivatives as potential tubulin polymerization inhibitors.

Several novel cycloalkyl-fused 2,3-diaryl pyrazole derivatives were designed, synthesized, and evaluated as potential anti-tubulin agents. Compound A10 exhibited the most potent antiproliferative activity against a panel of cancer lines (IC50  = 0.78-2.42 µM) and low cytotoxicity against 293T & L02 (CC50 values of 131.74 and 174.89 µM, respectively). Moreover, A10 displayed inhibition of tubulin polymerization in vitro, arrested the G2/M phase of the cell cycle, changed morphology of tubulin, increased intracellular reactive oxygen species, and induced apoptosis of HeLa cells. Docking simulation and 3D-QSAR models were performed to elaborate on the anti-tubulin mechanism of the derivatives. The inhibition of monoclonal colony formation provided more intuitional data to verify the possibility of A10 as a novel tubulin assembling inhibitor.