Biomedical applications of copper ionophores

Leveraging disulfiram to treat cancer: Mechanisms of action, delivery strategies, and treatment regimens

Disulfiram (DSF) has been used as an alcoholism drug for 70 years. Recently, it has attracted increasing attention owing to the distinguished anticancer activity, which can be further potentiated by the supplementation of Cu²⁺. Although encouraging anticancer results are obtained in lab, the clinical outcomes of oral DSF are not satisfactory, which urges an in-depth understanding of the underlying mechanisms, bottlenecks, and proposal of potential methods to address the dilemma. In this review, a critical summarization of various molecular biological anticancer mechanisms of DSF/Cu²⁺ is provided and the predicament of orally delivering DSF in clinical oncotherapy is explained by the metabolic barriers. We highlight the recent advances in the DSF/Cu²⁺ delivery strategies and the emerging treatment regimens for cancer treatment. Last but not the least, we summarize the clinical trials regarding DSF and make a prospect of DSF/Cu-based cancer therapy.

Ionophore Ability of Carnosine and Its Trehalose Conjugate Assists Copper Signal in Triggering Brain-Derived Neurotrophic Factor and Vascular Endothelial Growth Factor Activation In Vitro

l-carnosine (β-alanyl-l-histidine) (Car hereafter) is a natural dipeptide widely distributed in mammalian tissues and reaching high concentrations (0.7-2.0 mM) in the brain. The molecular features of the dipeptide underlie the antioxidant, anti-aggregating and metal chelating ability showed in a large number of physiological effects, while the biological mechanisms involved in the protective role found against several diseases cannot be explained on the basis of the above-mentioned properties alone, requiring further research efforts. It has been reported that l-carnosine increases the secretion and expression of various neurotrophic factors and affects copper homeostasis in nervous cells inducing Cu cellular uptake in keeping with the key metal-sensing system. Having in mind this l-carnosine ability, here we report the copper-binding and ionophore ability of l-carnosine to activate tyrosine kinase cascade pathways in PC12 cells and stimulate the expression of BDNF. Furthermore, the study was extended to verify the ability of the dipeptide to favor copper signaling inducing the expression of VEGF. Being aware that the potential protective action of l-carnosine is drastically hampered by its hydrolysis, we also report on the behavior of a conjugate of l-carnosine with trehalose that blocks the carnosinase degradative activity. Overall, our findings describe a copper tuning effect on the ability of l-carnosine and, particularly its conjugate, to activate tyrosine kinase cascade pathways.

Zinc ionophores: chemistry and biological applications

Zinc can play a pathophysiological role in several diseases and can interfere in key processes of microbial growth. This evidence justifies the efforts in applying Zinc ionophores to restore Zinc homeostasis and treat bacterial/viral infections such as coronavirus diseases. Zinc ionophores increase the intracellular concentration of Zinc ions causing significant biological effects. This review provides, for the first time, an overview of the applications of the main Zinc ionophores in Zinc deficiency, infectious diseases, and in cancer, discussing the pharmacological and coordination properties of the Zinc ionophores.

Membrane Transporters Involved in the Antimicrobial Activities of Pyrithione in Escherichia coli

Pyrithione (2-mercaptopyridine-N-oxide) is a metal binding modified pyridine, the antibacterial activity of which was described over 60 years ago. The formulation of zinc-pyrithione is commonly used in the topical treatment of certain dermatological conditions. However, the characterisation of the cellular uptake of pyrithione has not been elucidated, although an unsubstantiated assumption has persisted that pyrithione and/or its metal complexes undergo a passive diffusion through cell membranes. Here, we have profiled specific membrane transporters from an unbiased interrogation of 532 E. coli strains of knockouts of genes encoding membrane proteins from the Keio collection. Two membrane transporters, FepC and MetQ, seemed involved in the uptake of pyrithione and its cognate metal complexes with copper, iron, and zinc. Additionally, the phenotypes displayed by CopA and ZntA knockouts suggested that these two metal effluxers drive the extrusion from the bacterial cell of potentially toxic levels of copper, and perhaps zinc, which hyperaccumulate as a function of pyrithione. The involvement of these distinct membrane transporters contributes to the understanding of the mechanisms of action of pyrithione specifically and highlights, more generally, the important role that membrane transporters play in facilitating the uptake of drugs, including metal-drug compounds.

Accelerated Redox Reaction of Hydrogen Peroxide by Employing Locally Concentrated State of Copper Catalysts on Polymer Chain

Copper complexes act as catalysts for redox reactions to generate reactive oxygen species that destroy biomolecules and, therefore, are utilized to design drugs including antitumor and antibacterial medicines. Especially, catalytic reaction for hydrogen peroxide decomposition is important because it includes the process for generating highly toxic hydroxyl radical, i.e., Fenton-like reaction. Considering that multicoppers/hydrogen peroxide species are the important intermediates for the redox reaction, herein a polymer having copper complexes in the side chains is designed to facilitate the formation of the intermediates by building locally concentrated state of the copper complexes. The polymer increases their catalytic activities for hydrogen peroxide decomposition and promotes reactive oxygen species' generation, eventually leading to higher antibacterial activity. This reveals the virtue of building a locally concentrated state of catalysts on polymers toward drug design with low amounts of transition metals.

Structure prediction of neutral physiological copper(II) compounds with l-cysteine and l-histidine

Bis(aminoacidato)copper(II) [Cu^II(aa)₂] coordination compounds are the physiological species of copper(II) amino acid compounds in blood plasma. Since there are no experimental data in the literature about the geometries that physiological Cu^II(aa)₂ could form with l-cysteine (Cys), that is, for bis(l-cysteinato)copper(II) [Cu(Cys)₂] and the ternary (l-histidinato)(l-cysteinato)copper(II) [Cu(His)(Cys)], this paper computationally examines the possible conformations that the two compounds could form with the Cys ligand having a protonated sulfur, as in the conventional zwitterion, which was determined to be prevailing in aqueous solution. These two amino acids can bind metals in a tridentate fashion and thus form many possible coordination patterns. Density functional calculations were performed for the conformational analyses in the gas phase and in implicitly modeled aqueous solution using a polarizable continuum model. Additionally, we examine which coordination mode, with thiol or thiolate group, is more stable. The Cys coordination via the amino N and carboxylato O atoms (a glycinato mode) is obtained as the most stable one in aqueous Cu(Cys)₂, and also in Cu(His)(Cys) when the His glycinato or histaminato mode combines with the intact thiol group. Whereas the conformers with N and thiol S as the copper(II) donor atoms are predicted to be the least stable, those with the Cu-N and Cu-S(thiolate) bonding (and protonated carboxylato group) are the most stable. The differences are explained by different covalent and ionic contributions of Cu-S(thiol) vs. Cu-S(thiolate). The study can contribute to the insight into formation and reactivity of the copper(II) cysteinato complexes in solution.

Copper: An Intracellular Achilles' Heel Allowing the Targeting of Epigenetics, Kinase Pathways, and Cell Metabolism in Cancer Therapeutics

Copper is an essential transition metal frequently increased in cancer known to strongly influence essential cellular processes. Targeted therapy protocols utilizing both novel and repurposed drug agents initially demonstrate strong efficacy, before failing in advanced cancers as drug resistance develops and relapse occurs. Overcoming this limitation involves the development of strategies and protocols aimed at a wider targeting of the underlying molecular changes. Receptor Tyrosine Kinase signaling pathways, epigenetic mechanisms and cell metabolism are among the most common therapeutic targets, with molecular investigations increasingly demonstrating the strong influence each mechanism exerts on the others. Interestingly, all these mechanisms can be influenced by intracellular copper. We propose that copper chelating agents, already in clinical trial for multiple cancers, may simultaneously target these mechanisms across a wide variety of cancers, serving as an excellent candidate for targeted combination therapy. This review summarizes the known links between these mechanisms, copper, and copper chelation therapy.

Protein Folding Stability Changes Across the Proteome Reveal Targets of Cu Toxicity in E. coli

The ability of metal ionophores to induce cellular metal hyperaccumulation endows them with potent antimicrobial activity; however, the targets and mechanisms behind these outcomes are not well understood. This work describes the first utilization of proteome-wide measurements of protein folding stability in combination with protein expression level analysis to identify protein targets of copper, thereby providing new insight into ionophore-induced copper toxicity in E. coli. The protein folding stability analysis employed a one-pot protocol for pulse proteolysis (PP) in combination with a semi-tryptic peptide enrichment strategy for proteolysis procedures (STEPP) to generate stability profiles for proteins in cell lysates derived from E. coli exposed to copper with and without two ionophores, the antimicrobial agent pyrithione and its β-lactamase-activated prodrug, PcephPT. As part of this work, the above cell lysates were also subject to protein expression level analysis using conventional quantitative bottom-up proteomic methods. The protein folding stability and expression level profiles generated here enabled the effects of ionophore vs copper to be distinguished and revealed copper-driven stability changes in proteins involved in processes spanning metabolism, translation, and cell redox homeostasis. The 159 differentially stabilized proteins identified in this analysis were significantly more numerous (∼3×) than the 53 proteins identified with differential expression levels. These results illustrate the unique information that protein stability measurements can provide to decipher metal-dependent processes in drug mode of action studies.