Mechanism of action of the copper(I) complex of 2,9-dimethyl-1,10-phenanthroline on Mycoplasma gallisepticum

Copper Complexes with 1,10-Phenanthroline Derivatives: Underlying Factors Affecting Their Cytotoxicity

The interpretation of in vitro cytotoxicity data of Cu(II)-1,10-phenanthroline (phen) complexes normally does not take into account the speciation that complexes undergo in cell incubation media and its implications in cellular uptake and mechanisms of action. We synthesize and test the activity of several distinct Cu(II)-phen compounds; up to 24 h of incubation, the cytotoxic activity differs for the Cu complexes and the corresponding free ligands, but for longer incubation times (e.g., 72 h), all compounds display similar activity. Combining the use of several spectroscopic, spectrometric, and electrochemical techniques, the speciation of Cu-phen compounds in cell incubation media is evaluated, indicating that the originally added complex almost totally decomposed and that Cu(II) and phen are mainly bound to bovine serum albumin. Several methods are used to disclose relationships between structure, activity, speciation in incubation media, cellular uptake, distribution of Cu in cells, and cytotoxicity. Contrary to what is reported in most studies, we conclude that interaction with cell components and cell death involves the separate action of Cu ions and phen molecules, not [Cu(phen)_n] species. This conclusion should similarly apply to many other Cu-ligand systems reported to date.

Differential Susceptibility of Mycoplasma and Ureaplasma Species to Compound-Enhanced Copper Toxicity

Rationale

Mycoplasmas represent important etiologic agents of many human diseases. Due to increasing antimicrobial resistance and slow rate of novel discovery, unconventional methods of drug discovery are necessary. Copper ions are utilized in host microbial killing, and bacteria must regulate intracellular Cu concentrations to avoid toxicity. We hypothesized that human mollicutes may have susceptibility to Cu-induced toxicity, and compounds that augment copper-dependent killing.

Methods

Mycoplasma pneumoniae (Mpn), Ureaplasma parvum (Up), Ureaplasma urealyticum (Uu), and Mycoplasma hominis (Mh) were exposed to CuSO₄ to determine minimal inhibitory concentrations (MICs). Once inhibitory concentrations had been determined, bacteria were treated with an FDA-approved drug disulfiram (DSF), glyoxal bis(4-methyl-3-thiosemicarbazone) (GTSM), and 2,9-dimethyl-1,10-phenanthroline (neocuproine), with or without Cu²⁺, to determine compound MICs.

Results

Ureaplasma species and Mh were able to tolerate 30–60 μM CuSO₄, while Mpn tolerated over 10-fold higher concentrations (>1 mM). GTSM inhibited growth of all four organisms, but was unaffected by Cu²⁺ addition. Inhibition by GTSM was reduced by addition of the cell-impermeant Cu chelator, bathocuproine disulfonate (BCS). Neocuproine exhibited Cu-dependent growth inhibition of all organisms. DSF exhibited Cu-dependent growth inhibition against Mh at low micromolar concentrations, and at intermediate concentrations for Mpn.

Conclusion

MICs for CuSO₄ differ widely among human mollicutes, with higher MICs for Mpn compared to Mh, Uu, and Up. DSF and Neocuproine exhibit Cu-dependent inhibition of mollicutes with copper concentrations between 25 and 50 μM. GTSM has copper-dependent anti-microbial activity at low levels of copper. Drug enhanced copper toxicity is a promising avenue for novel therapeutic development research with Mycoplasma and Ureaplasma species.

Copper and Antibiotics: Discovery, Modes of Action, and Opportunities for Medicinal Applications

Copper is a ubiquitous element in the environment as well as living organisms, with its redox capabilities and complexation potential making it indispensable for many cellular functions. However, these same properties can be highly detrimental to prokaryotes and eukaryotes when not properly controlled, damaging many biomolecules including DNA, lipids, and proteins. To restrict free copper concentrations, all bacteria have developed mechanisms of resistance, sequestering and effluxing labile copper to minimize its deleterious effects. This weakness is actively exploited by phagocytes, which utilize a copper burst to destroy pathogens. Though administration of free copper is an unreasonable therapeutic antimicrobial itself, due to insufficient selectivity between host and pathogen, small-molecule ligands may provide an opportunity for therapeutic mimicry of the immune system. By modulating cellular entry, complex stability, resistance evasion, and target selectivity, ligand/metal coordination complexes can synergistically result in high levels of antibacterial activity. Several established therapeutic drugs, such as disulfiram and pyrithione, display remarkable copper-dependent inhibitory activity. These findings have led to development of new drug discovery techniques, using copper ions as the focal point. High-throughput screens for copper-dependent inhibitors against Mycobacterium tuberculosis and Staphylococcus aureus uncovered several new compounds, including a new class of inhibitors, the NNSNs. In this review, we highlight the microbial biology of copper, its antibacterial activities, and mechanisms to discover new inhibitors that synergize with copper.

In vitro activities of 2,2'-bipyridyl analogues against Mycobacterium avium and M. tuberculosis

SETTING

Because of widespread emergence of resistant Mycobacterium tuberculosis and the high incidence of opportunistic infection caused by M. avium (MAC) in AIDS patients, there is an urgent need for new drugs against these organisms.

OBJECTIVE

To evaluate the activity of newly synthesized 2,2'-bipyridyl analogues against MAC and M. tuberculosis.

DESIGN

Susceptibility of MAC and M. tuberculosis to VUF-8514 and VUF-8842 were determined by both tube dilution method using 7H9 broth and radiometric (BACTEC) method using 14C-palmitic acid.

RESULTS AND CONCLUSIONS

The MICs of 8514 against MAC and M. tuberculosis wee 1 microgram/ml and 0.5 microgram/ml respectively, while for 8842 the respective values were 8 micrograms/ml and 2 micrograms/ml. In general, the MBC values for both drugs were two-fold higher than their corresponding MIC values. However, both drugs exhibited high bactercidal activities against both organisms. The MICs of clinical isolates of both organisms were in the same range as reference strains; furthermore, two isolates of M. tuberculosis that showed resistance to rifampicin were found to be susceptible to 8514. Thus, these two bipyridyl analogues show great promise in chemotherapy of tuberculosis and M. avium infection.

Investigation into the mechanism of copper uptake by Mycoplasma gallisepticum in the presence of 2,9-dimethyl-1,10-phenanthroline

In the presence of copper certain 2,2'-bipyridyls show antimycoplasmal activity, whereas copper itself causes a toxic effect. In this paper results are presented to elucidate the mechanism of copper uptake in the presence of 2,9-dimethyl-1,10-phenanthroline. The time course of copper and/or ligand uptake under the applied conditions is consistent with a carrier transport mechanism in which 2,9-dimethyl-1,10-phenanthroline operates as a carrier for copper ions. The influence of valinomycin on copper uptake indicates that the transmembrane potential is not the driving force in the carrier process.

Copper modulation of macrophage cyclooxygenase metabolite synthesis

The effect of copper on the release of cyclooxygenase metabolites from starch elicited, rat, peritoneal macrophages was investigated. Copper sulphate, in the range 10(-6)-10(-5) M, inhibited the formation of prostaglandin (PG) E2 and thromboxane (Tx) B2, the stable metabolite of TxA2, in a dose dependent manner but had no effect on the production of 6-keto-PGF1 alpha, the stable product of prostacyclin. At higher concentrations (5 x 10(-5) and 10(-4) M) the synthesis of all three metabolites of arachidonic acid (AA) was stimulated as was the release of radioactivity from macrophages prelabelled with 14C AA. Copper had no effect on the metabolism of exogenous AA however. At 10(-4) M copper also stimulated secretion of the lysosomal enzyme, beta-glucuronidase (GUR). Copper nitrate (10(-4) M), but not zinc sulphate, also stimulated eicosanoid formation and lysosomal enzyme release. Our results are consistent with the idea that copper stimulates eicosanoid formation via an effect on PL activity.

Inhibition of NADH oxidase and lactate dehydrogenase of Mycoplasma gallisepticum by copper complexes of 2,2'-bipyridyl analogues

In the presence of copper, 2,2'-bipyridyl analogues possess growth-inhibitory activity against Mycoplasma gallisepticum. Inhibition of the energy yielding metabolism plays a role in the mechanism of action. We showed that probably inhibition of lactate dehydrogenase and NADH oxidase is involved. Both enzymes were inhibited in vitro and in vivo by several copper 2,2'-bipyridyl complexes. A two-step mechanism of action is proposed, i.e. first a copper complex enters the cell, then after dissociation of the complex the enzymes are inhibited by free copper.

Biological studies of a new class of technetium complexes: the hexakis(alkylisonitrile)technetium(I) cations

This study describes the preparation and synthesis of a new class of cationic technetium compounds, the hexakis(alkylisonitrile)technetium(+ 1) complexes, at both carrier added and no carrier added concentrations in aqueous media from pertechnetate. Biological distribution and imaging data in animals indicate that certain members of this class may be effective for cardiac imaging in man. The usefulness of these lipophilic water-soluble species for labeling mammalian cells is also reported.

Determination of formation constants of copper(II) complexes of Adler medium components with a solid-state copper(II) ion-selective electrode

A general method for the determination of overall conditional formation constants of copper(II) complexes of mycoplasma growth medium (Adler) constituents together with the protonation constants of the complexing ligands was developed. In Adler medium a total of 0.204 +/- 0.004 molar copper binding sites proved to be present with log beta 2 = 8.14 +/- 0.05 (mu = 0.11) and log Ka = 6.14 +/- 0.004. Conditional overall formation constants were calculated at various pH values. Free copper(II) ion concentrations were calculated as a function of the total added amount of copper(II) and pH. The consequences of these findings for the determination of the growth inhibition of mycoplasmas by copper complexes of 2,2'-bipyridyl analogues are stressed.