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  1. Abstract

    The mitochondrial calcium uniporter (MCU) is a transmembrane protein that is responsible for mediating mitochondrial calcium (mCa2+) uptake. Given this critical function, the MCU has been implicated as an important target for addressing various human diseases. As such, there has a been growing interest in developing small molecules that can inhibit this protein. To date, metal coordination complexes, particularly multinuclear ruthenium complexes, are the most widely investigated MCU inhibitors due to both their potent inhibitory activities as well as their longstanding use for this application. Recent efforts have expanded the metal‐based toolkit for MCU inhibition. This concept paper summarizes the development of new metal‐based inhibitors of the MCU and their structure‐activity relationships in the context of improving their potential for therapeutic use in managing human diseases related tomCa2+dysregulation.

     
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    Free, publicly-accessible full text available June 15, 2024
  2. Ischemia-reperfusion injury (IRI), which describes the cell damage and death that occurs after blood and oxygen are restored to ischemic or hypoxic tissue, is a significant factor within the mortality rates of heart disease and stroke patients. At the cellular level, the return of oxygen triggers an increase in reactive oxygen species (ROS) and mitochondrial calcium (mCa2+) overload, which both contribute to cell death. Despite the widespread occurrence of IRI in different pathological conditions, there are currently no clinically approved therapeutic agents for its management. In this Perspective, we will briefly discuss the current therapeutic options for IRI and then describe in great detail the potential role and arising applications of metal-containing coordination and organometallic complexes for treating this condition. This Perspective categorizes these metal compounds based on their mechanisms of action, which include their use as delivery agents for gasotransmitters, inhibitors of mCa2+ uptake, and catalysts for the decomposition of ROS. Lastly, the challenges and opportunities for inorganic chemistry approaches to manage IRI are discussed. 
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  3. Abstract

    The mitochondrial calcium uniporter (MCU) mediates uptake of calcium ions (Ca2+) into the mitochondria, a process that is vital for maintaining normal cellular function. Inhibitors of the MCU, the most promising of which are dinuclear ruthenium coordination compounds, have found use as both therapeutic agents and tools for studying the importance of this ion channel. In this study, six Co3+cage compounds with sarcophagine‐like ligands were assessed for their abilities to inhibit MCU‐mediated mitochondrial Ca2+uptake. These complexes were synthesized and characterized according to literature procedures and then investigated in cellular systems for their MCU‐inhibitory activities. Among these six compounds, [Co(sen)]3+(3, sen=5‐(4‐amino‐2‐azabutyl)‐5‐methyl‐3,7‐diaza‐1,9‐nonanediamine) was identified to be a potent MCU inhibitor, with IC50values of inhibition of 160 and 180 nM in permeabilized HeLa and HEK293T cells, respectively. Furthermore, the cellular uptake of compound3was determined, revealing moderate accumulation in cells. Most notably,3was demonstrated to operate in intact cells as an MCU inhibitor. Collectively, this work presents the viability of using cobalt coordination complexes as MCU inhibitors, providing a new direction for researchers to investigate.

     
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  4. The neurovascular unit (NVU) is composed of vascular cells, glia, and neurons that form the basic component of the blood brain barrier. This intricate structure rapidly adjusts cerebral blood flow to match the metabolic needs of brain activity. However, the NVU is exquisitely sensitive to damage and displays limited repair after a stroke. To effectively treat stroke, it is therefore considered crucial to both protect and repair the NVU. Mitochondrial calcium (Ca2+) uptake supports NVU function by buffering Ca2+and stimulating energy production. However, excessive mitochondrial Ca2+uptake causes toxic mitochondrial Ca2+overloading that triggers numerous cell death pathways which destroy the NVU. Mitochondrial damage is one of the earliest pathological events in stroke. Drugs that preserve mitochondrial integrity and function should therefore confer profound NVU protection by blocking the initiation of numerous injury events. We have shown that mitochondrial Ca2+uptake and efflux in the brain are mediated by the mitochondrial Ca2+uniporter complex (MCUcx) and sodium/Ca2+/lithium exchanger (NCLX), respectively. Moreover, our recent pharmacological studies have demonstrated that MCUcxinhibition and NCLX activation suppress ischemic and excitotoxic neuronal cell death by blocking mitochondrial Ca2+overloading. These findings suggest that combining MCUcxinhibition with NCLX activation should markedly protect the NVU. In terms of promoting NVU repair, nuclear hormone receptor activation is a promising approach. Retinoid X receptor (RXR) and thyroid hormone receptor (TR) agonists activate complementary transcriptional programs that stimulate mitochondrial biogenesis, suppress inflammation, and enhance the production of new vascular cells, glia, and neurons. RXR and TR agonism should thus further improve the clinical benefits of MCUcxinhibition and NCLX activation by increasing NVU repair. However, drugs that either inhibit the MCUcx, or stimulate the NCLX, or activate the RXR or TR, suffer from adverse effects caused by undesired actions on healthy tissues. To overcome this problem, we describe the use of nanoparticle drug formulations that preferentially target metabolically compromised and damaged NVUs after an ischemic or hemorrhagic stroke. These nanoparticle-based approaches have the potential to improve clinical safety and efficacy by maximizing drug delivery to diseased NVUs and minimizing drug exposure in healthy brain and peripheral tissues.

     
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    Free, publicly-accessible full text available July 7, 2024
  5. An analogue of the mitochondrial calcium uniporter (MCU) inhibitor Ru265 containing axial ferrocenecarboxylate ligands is reported. This new complex exhibits enhanced cellular uptake compared to the parent compound Ru265.

     
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  6. We have investigated the biological properties of the osmium analogue of a potent ruthenium-based mitochondrial calcium uniporter inhibitor and have found it to possess distinct properties.

     
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  7. Infrared spectroscopy has drawn considerable interest in biological applications, but the measurement of live cells is impeded by the attenuation of infrared light in water. Metasurface-enhanced infrared reflection spectroscopy (MEIRS) had been shown to mitigate the problem, enhance the cellular infrared signal through surface-enhanced infrared absorption, and encode the cellular vibrational signatures in the reflectance spectrum at the same time. In this study, we used MEIRS to study the dynamic response of live cancer cells to a newly developed chemotherapeutic metal complex with distinct modes of action (MoAs): tricarbonyl rhenium isonitrile polypyridyl (TRIP). MEIRS measurements demonstrated that administering TRIP resulted in long-term (several hours) reduction in protein, lipid, and overall refractive index signals, and in short-term (tens of minutes) increase in these signals, consistent with the induction of endoplasmic reticulum stress. The unique tricarbonyl IR signature of TRIP in the bioorthogonal spectral window was monitored in real time, and was used as an infrared tag to detect the precise drug delivery time that was shown to be closely correlated with the onset of the phenotypic response. These results demonstrate that MEIRS is an effective label-free real-time cellular assay capable of detecting and interpreting the early phenotypic responses of cells to IR-tagged chemotherapeutics. 
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  8. Abstract

    Inhibitors of the mitochondrial calcium uniporter (MCU) are valuable tools for studying the role of mitochondrial Ca2+in various pathophysiological conditions. In this study, a new fluorogenic MCU inhibitor,RuOCou, is presented. This compound is an analogue of the known MCU inhibitor Ru265 that contains fluorescent axial coumarin carboxylate ligands. Upon aquation ofRuOCouand release of the axial coumarin ligands, a simultaneous increase in its MCU‐inhibitory activity and fluorescence intensity is observed. The fluorescence response of this compound enabled its aquation to be monitored in both HeLa cell lysates and live HeLa cells. This fluorogenic prodrug represents a potential theranostic MCU inhibitor that can be leveraged for the treatment of human diseases related to MCU activity.

     
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  9. Abstract

    Inhibitors of the mitochondrial calcium uniporter (MCU) are valuable tools for studying the role of mitochondrial Ca2+in various pathophysiological conditions. In this study, a new fluorogenic MCU inhibitor,RuOCou, is presented. This compound is an analogue of the known MCU inhibitor Ru265 that contains fluorescent axial coumarin carboxylate ligands. Upon aquation ofRuOCouand release of the axial coumarin ligands, a simultaneous increase in its MCU‐inhibitory activity and fluorescence intensity is observed. The fluorescence response of this compound enabled its aquation to be monitored in both HeLa cell lysates and live HeLa cells. This fluorogenic prodrug represents a potential theranostic MCU inhibitor that can be leveraged for the treatment of human diseases related to MCU activity.

     
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