Copper complexation screen reveals compounds with potent antibiotic properties against methicillin-resistant Staphylococcus aureus

Survival in amoeba--a major selection pressure on the presence of bacterial copper and zinc resistance determinants? Identification of a "copper pathogenicity island"

The presence of metal resistance determinants in bacteria usually is attributed to geological or anthropogenic metal contamination in different environments or associated with the use of antimicrobial metals in human healthcare or in agriculture. While this is certainly true, we hypothesize that protozoan predation and macrophage killing are also responsible for selection of copper/zinc resistance genes in bacteria. In this review, we outline evidence supporting this hypothesis, as well as highlight the correlation between metal resistance and pathogenicity in bacteria. In addition, we introduce and characterize the "copper pathogenicity island" identified in Escherichia coli and Salmonella strains isolated from copper- and zinc-fed Danish pigs.

Disulfiram and Copper Ions Kill Mycobacterium tuberculosis in a Synergistic Manner

Tuberculosis is a severe disease affecting millions worldwide. Unfortunately, treatment strategies are hampered both by the prohibitively long treatment regimen and the rise of drug-resistant strains. Significant effort has been expended in the search for new treatments, but few options have successfully emerged, and new treatment modalities are desperately needed. Recently, there has been growing interest in the synergistic antibacterial effects of copper ions (Cu(II/I)) in combination with certain small molecular compounds, and we have previously reported development of a drug screening strategy to harness the intrinsic bactericidal properties of Cu(II/I). Here, we describe the copper-dependent antimycobacterial properties of disulfiram, an FDA-approved and well-tolerated sobriety aid. Disulfiram was inhibitory to mycobacteria only in the presence of Cu(II/I) and exerted its bactericidal activity well below the active concentration of Cu(II/I) or disulfiram alone. No other physiologically relevant bivalent transition metals (e.g., Fe(II), Ni(II), Mn(II), and Co(II)) exhibited this effect. We demonstrate that the movement of the disulfiram-copper complex across the cell envelope is porin independent and can inhibit intracellular protein functions. Additionally, the complex is able to synergistically induce intracellular copper stress responses significantly more than Cu(II/I) alone. Our data suggest that by complexing with disulfiram, Cu(II/I) is likely allowed unfettered access to vulnerable intracellular components, bypassing the normally sufficient copper homeostatic machinery. Overall, the synergistic antibacterial activity of Cu(II/I) and disulfiram reveals the susceptibility of the copper homeostasis system of Mycobacterium tuberculosis to chemical attacks and establishes compounds that act in concert with copper as a new class of bacterial inhibitors.

Disulfiram and Copper Ions Kill Mycobacterium tuberculosis in a Synergistic Manner

Tuberculosis is a severe disease affecting millions worldwide. Unfortunately, treatment strategies are hampered both by the prohibitively long treatment regimen and the rise of drug-resistant strains. Significant effort has been expended in the search for new treatments, but few options have successfully emerged, and new treatment modalities are desperately needed. Recently, there has been growing interest in the synergistic antibacterial effects of copper ions (Cu(II/I)) in combination with certain small molecular compounds, and we have previously reported development of a drug screening strategy to harness the intrinsic bactericidal properties of Cu(II/I). Here, we describe the copper-dependent antimycobacterial properties of disulfiram, an FDA-approved and well-tolerated sobriety aid. Disulfiram was inhibitory to mycobacteria only in the presence of Cu(II/I) and exerted its bactericidal activity well below the active concentration of Cu(II/I) or disulfiram alone. No other physiologically relevant bivalent transition metals (e.g., Fe(II), Ni(II), Mn(II), and Co(II)) exhibited this effect. We demonstrate that the movement of the disulfiram-copper complex across the cell envelope is porin independent and can inhibit intracellular protein functions. Additionally, the complex is able to synergistically induce intracellular copper stress responses significantly more than Cu(II/I) alone. Our data suggest that by complexing with disulfiram, Cu(II/I) is likely allowed unfettered access to vulnerable intracellular components, bypassing the normally sufficient copper homeostatic machinery. Overall, the synergistic antibacterial activity of Cu(II/I) and disulfiram reveals the susceptibility of the copper homeostasis system of Mycobacterium tuberculosis to chemical attacks and establishes compounds that act in concert with copper as a new class of bacterial inhibitors.

Inhibition of respiratory complex I by copper(ii)-bis(thiosemicarbazonato) complexes

Several copper(ii) complexes of bis(thiosemicarbazones) [Cu(btsc)s] show promise as therapeutics for the treatment of neurological diseases, cancers and bacterial infections. These complexes are thought to act primarily as copper ionophores or "copper boosting" agents, whereby the Cu(II) centre is reduced by cytosolic reductants and Cu(I) is released as "free" or "bioavailable" ion. It is then assumed that the dissociated Cu(I) ion is the species responsible for many of the observed biological effects of Cu(btsc)s. We recently showed that Cu(btsc) complexes inhibited NADH dehydrogenases in the bacterial respiratory chain. In this work, we demonstrate that Cu(btsc) complexes also inhibit mitochondrial respiration and that Complex I in the mitochondrial electron transport chain is a specific target of inhibition. However, bioavailable Cu ions do not appear to contribute to the action of Cu(btsc) as a respiratory inhibitor. Instead, an intact Cu(btsc) molecule may bind reversibly and competitively to the site of ubiquinone binding in Complex I. Our results add to the growing body of evidence that the intact complex may be important in the overall cellular activity of Cu(btsc) complexes and further the understanding of their biological effects as a potential therapeutic.