Mitochondria-Targeted Chemotherapeutics: The Rational Design of Gold(I) N-Heterocyclic Carbene Complexes That Are Selectively Toxic to Cancer Cells and Target Protein Selenols in Preference to Thiols
26 Aug 2008-Journal of the American Chemical Society (American Chemical Society)-Vol. 130, Iss: 38, pp 12570-12571
TL;DR: A family of lipophilic, cationic Au(I) complexes of N-heterocyclic carbenes (NHCs) have been designed as new mitochondria-targeted antitumor agents that combine both selective mitochondrial accumulation and selective thioredoxin reductase inhibition properties within a single molecule.
Abstract: A family of lipophilic, cationic Au(I) complexes of N-heterocyclic carbenes (NHCs) have been designed as new mitochondria-targeted antitumor agents that combine both selective mitochondrial accumulation and selective thioredoxin reductase inhibition properties within a single molecule. Two-step ligand exchange reactions with cysteine (Cys) and selenocysteine (Sec) occur with release of the NHC ligands. At physiological pH the rate constants for the reactions with Sec are 20- to 80-fold higher than those with Cys. The complexes are selectively toxic to two highly tumorigenic breast cancer cell lines and not to normal breast cells, and the degree of selectivity and potency are optimized by modification of the substituent on the simple imidazolium salt precursor. The lead compound is shown to accumulate in mitochondria of cancer cells, to cause cell death through a mitochondrial apoptotic pathway and to inhibit the activity of thioredoxin reductase (TrxR) but not the closely related and Se-free enzyme glutat...
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TL;DR: A concise overview of N-heterocyclic carbenes in modern chemistry is provided, summarizing their general properties and uses and highlighting how these features are being exploited in a selection of pioneering recent studies.
Abstract: The successful isolation and characterization of an N-heterocyclic carbene in 1991 opened up a new class of organic compounds for investigation. From these beginnings as academic curiosities, N-heterocyclic carbenes today rank among the most powerful tools in organic chemistry, with numerous applications in commercially important processes. Here we provide a concise overview of N-heterocyclic carbenes in modern chemistry, summarizing their general properties and uses and highlighting how these features are being exploited in a selection of pioneering recent studies.
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2,594 citations
TL;DR: The quest for alternative drugs to the well-known cisplatin and its derivatives, which are still used in more than 50% of the treatment regimes for patients suffering from cancer, is highly needed, and organometallic compounds have recently been found to be promising anticancer drug candidates.
Abstract: The quest for alternative drugs to the well-known cisplatin and its derivatives, which are still used in more than 50% of the treatment regimes for patients suffering from cancer, is highly needed.1,2 Despite their tremendous success, these platinum compounds suffer from two main disadvantages: they are inefficient against platinum-resistant tumors, and they have severe side effects such as nephrotoxicity. The latter drawback is the consequence of the fact that the ultimate target of these drugs is ubiquitous: It is generally accepted that Pt anticancer drugs target DNA, which is present in all cells.3,4 Furthermore, as a consequence of its particular chemical structure, cisplatin in particular offers little possibility for rational improvements to increase its tumor specificity and thereby reduce undesired side effects.
In this context, organometallic compounds, which are defined as metal complexes containing at least one direct, covalent metal−carbon bond, have recently been found to be promising anticancer drug candidates. Organometallics have a great structural variety (ranging from linear to octahedral and even beyond), have far more diverse stereochemistry than organic compounds (for an octahedral complex with six different ligands, 30 stereoisomers exist!), and by rational ligand design, provide control over key kinetic properties (such as hydrolysis rate of ligands). Furthermore, they are kinetically stable, usually uncharged, and relatively lipophilic and their metal atom is in a low oxidation state. Because of these fundamental differences compared to “classical coordination metal complexes”, organometallics offer ample opportunities in the design of novel classes of medicinal compounds, potentially with new metal-specific modes of action. Interestingly, all the typical classes of organometallics such as metallocenes, half-sandwich, carbene-, CO-, or π-ligands, which have been widely used for catalysis or biosensing purposes, have now also found application in medicinal chemistry (see Figure Figure11 for an overview of these typical classes of organometallics).
Figure 1
Summary of the typical classes of organometallic compounds used in medicinal chemistry.
In this Perspective, we report on the recent advances in the discovery of organometallics with proven antiproliferative activity. We are emphasizing those compounds where efforts have been made to identify their molecular target and mode of action by biochemical or cell biology studies. This Perspective covers more classes of compounds and in more detail than a recent tutorial review by Hartinger and Dyson.(5) Furthermore, whereas recent reviews and book contributions attest to the rapid development of bioorganometallic chemistry in general,6,7 this Perspective focuses on their potential application as anticancer chemotherapeutics. Another very recent review article categorizes inorganic anticancer drug candidates by their modes of action.(8) It should be mentioned that a full description of all currently investigated types of compounds is hardly possible anymore in a concise review. For example, a particularly promising class of organometallic anticancer compounds, namely, radiolabeled organometallics, has been omitted for space limitations. Recent developments of such compounds have been reviewed in detail by Alberto.(9)
1,364 citations
TL;DR: This work presents a meta-analysis of multi-NHCs Linked by Spacers and its applications in Catalysis and Nanomaterials, which shows clear trends in both the number and complexity of the components and their applications.
Abstract: 2.3.5. Multi-NHCs Linked by Spacers 3568 2.4. The Ag2O Route 3570 2.4.1. Feasibility 3570 2.4.2. Complications 3571 2.4.3. Theoretical Consideration 3572 2.5. Applications 3572 2.5.1. Ag(I)-NHCs in NHC Transfer 3572 2.5.2. Ag(I)-NHCs in Catalysis 3572 2.5.3. Ag(I)-NHCs in Medicine 3572 2.5.4. Ag(I)-NHCs in Nanomaterials 3573 3. Au(I)and Au(III)-NHCs 3573 3.1. Historical Background 3573 3.2. General Synthetic Methods 3573 3.3. Formation of Au(I)and Au(III)-NHCs 3574 3.3.1. Neutral [Au(NHC)L] 3574 3.3.2. Ionic [Au(NHC)L][Anion] 3576 3.3.3. Multinuclear Au(I)-NHCs 3578 3.3.4. Other Classes of Au(I)-NHCs 3578 3.3.5. Au(III)-NHC Complexes 3579 3.4. Applications 3579 3.4.1. Au(I)and Au(III)-NHCs in Catalysis 3579 3.4.2. Au(I)-NHCs in Medicine 3580 4. Cu(I)and Cu(II)-NHCs 3581 4.1. Historical Background 3581 4.2. General Synthetic Methods 3582 4.3. Formation of Cu(I)and Cu(II)-NHCs 3583 4.3.1. Complexes Containing the Cu(NHC)2 Core 3583 4.3.2. [Cu(NHC)(Halide)] 3583 4.3.3. [Cu(NHC)(Ligand)] 3584 4.3.4. Multinuclear Cu(I)and Cu(II)-NHCs 3589 4.4. Catalysis 3591 4.4.1. Past Events 3591 4.4.2. Recent Advancements 3591 5. Photoluminescence 3592 6. Conclusions 3594 7. Abbreviations 3594 8. Acknowledgments 3595 9. References 3595
906 citations
TL;DR: The physicochemical basis for mitochondrial accumulation of lipophilic cations, synthetic chemistry strategies to target compounds to mitochondria, mitochondrial probes, and sensors, and examples of mitochondrial targeting of bioactive compounds are described.
Abstract: Mitochondria are recognized as one of the most important targets for new drug design in cancer, cardiovascular, and neurological diseases. Currently, the most effective way to deliver drugs specifically to mitochondria is by covalent linking a lipophilic cation such as an alkyltriphenylphosphonium moiety to a pharmacophore of interest. Other delocalized lipophilic cations, such as rhodamine, natural and synthetic mitochondria-targeting peptides, and nanoparticle vehicles, have also been used for mitochondrial delivery of small molecules. Depending on the approach used, and the cell and mitochondrial membrane potentials, more than 1000-fold higher mitochondrial concentration can be achieved. Mitochondrial targeting has been developed to study mitochondrial physiology and dysfunction and the interaction between mitochondria and other subcellular organelles and for treatment of a variety of diseases such as neurodegeneration and cancer. In this Review, we discuss efforts to target small-molecule compounds to mitochondria for probing mitochondria function, as diagnostic tools and potential therapeutics. We describe the physicochemical basis for mitochondrial accumulation of lipophilic cations, synthetic chemistry strategies to target compounds to mitochondria, mitochondrial probes, and sensors, and examples of mitochondrial targeting of bioactive compounds. Finally, we review published attempts to apply mitochondria-targeted agents for the treatment of cancer and neurodegenerative diseases.
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References
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TL;DR: N-Heterocyclic carbenes have become universal ligands in organometallic and inorganic coordination chemistry as mentioned in this paper, and they not only bind to any transition metal, be it in low or high oxidation states, but also to main group elements such as beryllium, sulfur, and iodine.
Abstract: N-Heterocyclic carbenes have become universal ligands in organometallic and inorganic coordination chemistry. They not only bind to any transition metal, be it in low or high oxidation states, but also to main group elements such as beryllium, sulfur, and iodine. Because of their specific coordination chemistry, N-heterocyclic carbenes both stabilize and activate metal centers in quite different key catalytic steps of organic syntheses, for example, C-H activation, C-C, C-H, C-O, and C-N bond formation. There is now ample evidence that in the new generation of organometallic catalysts the established ligand class of organophosphanes will be supplemented and, in part, replaced by N-heterocyclic carbenes. Over the past few years, this chemistry has been the field of vivid scientific competition, and yielded previously unexpected successes in key areas of homogeneous catalysis. From the work in numerous academic laboratories and in industry, a revolutionary turning point in oraganometallic catalysis is emerging.
3,388 citations
TL;DR: The therapeutic induction of MOMP may restore apoptosis in cancer cells in which it is disabled, and the general rules governing the pathophysiology and controversial issues regarding its regulation are discussed.
Abstract: In the mitochondrial pathway of apoptosis, caspase activation is closely linked to mitochondrial outer membrane permeabilization (MOMP). Numerous pro-apoptotic signal-transducing molecules and pathological stimuli converge on mitochondria to induce MOMP. The local regulation and execution of MOMP involve proteins from the Bcl-2 family, mitochondrial lipids, proteins that regulate bioenergetic metabolite flux, and putative components of the permeability transition pore. MOMP is lethal because it results in the release of caspase-activating molecules and caspase-independent death effectors, metabolic failure in the mitochondria, or both. Drugs designed to suppress excessive MOMP may avoid pathological cell death, and the therapeutic induction of MOMP may restore apoptosis in cancer cells in which it is disabled. The general rules governing the pathophysiology of MOMP and controversial issues regarding its regulation are discussed.
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1,003 citations
TL;DR: The use of N-heterocyclic carbenes as ligands for transition metals has increased dramatically in the last few years, spurred on by their remarkable successes in the areas of metathesis chemistry and coupling reactions as discussed by the authors.
901 citations
TL;DR: A comprehensive overview of the progress in this area can be found in this paper, where the N-heterocyclic carbene-based organometallic chemistry has drawn increasing attention to this class of ancillary ligands.
763 citations