Probing the Interaction of Cisplatin with the Human Copper Chaperone Atox1 by Solution and In-Cell NMR Spectroscopy

Reactions of Cisplatin with Thioredoxin-1 Regulate Intracellular Redox Homeostasis

Cisplatin is a widely used anticancer drug. In addition to inducing DNA damage, increased levels of reactive oxygen species (ROS) play a significant role in cisplatin-induced cell death. Thioredoxin-1 (Trx1), a redox regulatory protein that can scavenge ROS, has been found to eliminate cisplatin-induced ROS, while elevated Trx1 levels are associated with cisplatin resistance. However, it is unknown whether the effect of Trx1 on the cellular response to cisplatin is due to its direct reaction and how this reaction influences the activity of Trx1. In this work, we performed detailed studies of the reaction between Trx1 and cisplatin. Trx1 is highly reactive to cisplatin, and the catalytic motif of Trx1 (CGPC) is the primary binding site of cisplatin. Trx1 can bind up to 6 platinum moieties, resulting in the structural alteration and oligomerization of Trx1 depending on the degree of platination. Platination of Trx1 inhibits its interaction with ASK1, a Trx1-binding protein that regulates cell apoptosis. Furthermore, the reaction with cisplatin suppresses drug-induced ROS generation, which could be associated with drug resistance. This study provides more insight into the mechanism of action of cisplatin.

The p53 protein is a suppressor of Atox1 copper chaperon in tumor cells under genotoxic effects

The p53 protein is crucial for regulating cell survival and apoptosis in response to DNA damage. However, its influence on therapy effectiveness is controversial: when DNA damage is high p53 directs cells toward apoptosis, while under moderate genotoxic stress it saves the cells from death and promote DNA repair. Furthermore, these processes are influenced by the metabolism of transition metals, particularly copper since they serve as cofactors for critical enzymes. The metallochaperone Atox1 is under intensive study in this context because it serves as transcription factor allegedly mediating described effects of copper. Investigating the interaction between p53 and Atox1 could provide insights into tumor cell survival and potential therapeutic applications in oncology. This study explores the relationship between p53 and Atox1 in HCT116 and A549 cell lines with wild type and knockout TP53. The study found an inverse correlation between Atox1 and p53 at the transcriptional and translational levels in response to genotoxic stress. Atox1 expression decreased with increased p53 activity, while cells with inactive p53 had significantly higher levels of Atox1. Suppression of both genes increased apoptosis, while suppression of the ATOX1 gene prevented apoptosis even under the treatment with chemotherapeutic drugs. The findings suggest that Atox1 may act as one of key elements in promotion of cell cycle under DNA-damaging conditions, while p53 works as an antagonist by inhibiting Atox1. Understanding of this relationship could help identify potential targets in cell signaling pathways to enhance the effectiveness of combined antitumor therapy, especially in tumors with mutant or inactive p53.

The mechanism of copper transporters in ovarian cancer cells and the prospect of cuproptosis

Copper transporters can not only carry copper (Cu) to maintain the homeostasis of Cu in cells but also transport platinum-based chemotherapy drugs. The effect of copper transporters on chemosensitivity has been demonstrated in a variety of malignancies. In addition, recent studies have reported that copper transporters can act as vectors to induce cuproptosis. Therefore, copper transporters can act on cells through different mechanisms to achieve different purposes. This review mainly describes the current research progress of the intracellular transport mechanism of copper transporters and cuproptosis, and prospects for the application of them in the treatment of ovarian cancer (OC).

Copper chaperone antioxidant 1: multiple roles and a potential therapeutic target

Copper (Cu) was recently demonstrated to play a critical role in cellular physiological and biochemical processes, including energy production and maintenance, antioxidation and enzymatic activity, and signal transduction. Antioxidant 1 (ATOX1), a chaperone of Cu previously named human ATX1 homologue (HAH1), has been found to play an indispensable role in maintaining cellular Cu homeostasis, antioxidative stress, and transcriptional regulation. In the past decade, it has also been found to be involved in a variety of diseases, including numerous neurodegenerative diseases, cancers, and metabolic diseases. Recently, increasing evidence has revealed that ATOX1 is involved in the regulation of cell migration, proliferation, autophagy, DNA damage repair (DDR), and death, as well as in organism development and reproduction. This review summarizes recent advances in the research on the diverse physiological and cytological functions of ATOX1 and the underlying mechanisms of its action in human health and diseases. The potential of ATOX1 as a therapeutic target is also discussed. This review aims to pose unanswered questions related to ATOX1 biology and explore the potential use of ATOX1 as a therapeutic target.

In-cell NMR: Why and how?

NMR spectroscopy has been applied to cells and tissues analysis since its beginnings, as early as 1950. We have attempted to gather here in a didactic fashion the broad diversity of data and ideas that emerged from NMR investigations on living cells. Covering a large proportion of the periodic table, NMR spectroscopy permits scrutiny of a great variety of atomic nuclei in all living organisms non-invasively. It has thus provided quantitative information on cellular atoms and their chemical environment, dynamics, or interactions. We will show that NMR studies have generated valuable knowledge on a vast array of cellular molecules and events, from water, salts, metabolites, cell walls, proteins, nucleic acids, drugs and drug targets, to pH, redox equilibria and chemical reactions. The characterization of such a multitude of objects at the atomic scale has thus shaped our mental representation of cellular life at multiple levels, together with major techniques like mass-spectrometry or microscopies. NMR studies on cells has accompanied the developments of MRI and metabolomics, and various subfields have flourished, coined with appealing names: fluxomics, foodomics, MRI and MRS (i.e. imaging and localized spectroscopy of living tissues, respectively), whole-cell NMR, on-cell ligand-based NMR, systems NMR, cellular structural biology, in-cell NMR… All these have not grown separately, but rather by reinforcing each other like a braided trunk. Hence, we try here to provide an analytical account of a large ensemble of intricately linked approaches, whose integration has been and will be key to their success. We present extensive overviews, firstly on the various types of information provided by NMR in a cellular environment (the "why", oriented towards a broad readership), and secondly on the employed NMR techniques and setups (the "how", where we discuss the past, current and future methods). Each subsection is constructed as a historical anthology, showing how the intrinsic properties of NMR spectroscopy and its developments structured the accessible knowledge on cellular phenomena. Using this systematic approach, we sought i) to make this review accessible to the broadest audience and ii) to highlight some early techniques that may find renewed interest. Finally, we present a brief discussion on what may be potential and desirable developments in the context of integrative studies in biology.

In-Cell Structural Biology by NMR: The Benefits of the Atomic Scale

In-cell structural biology aims at extracting structural information about proteins or nucleic acids in their native, cellular environment. This emerging field holds great promise and is already providing new facts and outlooks of interest at both fundamental and applied levels. NMR spectroscopy has important contributions on this stage: It brings information on a broad variety of nuclei at the atomic scale, which ensures its great versatility and uniqueness. Here, we detail the methods, the fundamental knowledge, and the applications in biomedical engineering related to in-cell structural biology by NMR. We finally propose a brief overview of the main other techniques in the field (EPR, smFRET, cryo-ET, etc.) to draw some advisable developments for in-cell NMR. In the era of large-scale screenings and deep learning, both accurate and qualitative experimental evidence are as essential as ever to understand the interior life of cells. In-cell structural biology by NMR spectroscopy can generate such a knowledge, and it does so at the atomic scale. This review is meant to deliver comprehensive but accessible information, with advanced technical details and reflections on the methods, the nature of the results, and the future of the field.

FGF13 enhances resistance to platinum drugs by regulating hCTR1 and ATP7A via a microtubule-stabilizing effect

Platinum‐based regimens are the most widely used chemotherapy regimens, but cancer cells often develop resistance, which impedes therapy outcome for patients. Previous studies have shown that fibroblast growth factor 13 (FGF13) is associated with resistance to platinum drugs in HeLa cells. However, the mechanism and universality of this effect have not been clarified. Here, we found that FGF13 was associated with poor platinum‐based chemotherapy outcomes in a variety of cancers, such as lung, endometrial, and cervical cancers, through bioinformatics analysis. We then found that FGF13 simultaneously regulates the expression and distribution of hCTR1 and ATP7A in cancer cells, causes reduced platinum influx, and promotes platinum sequestration and efflux upon cisplatin exposure. We subsequently observed that FGF13‐mediated platinum resistance requires the microtubule‐stabilizing effect of FGF13. Only overexpression of FGF13 with the ‐SMIYRQQQ‐ tubulin‐binding domain could induce the platinum resistance effect. This phenomenon was also observed in SK‐MES‐1 cells, KLE cells, and 5637 cells. Our research reveals the mechanism of FGF13‐induced platinum drug resistance and suggests that FGF13 can be a sensibilization target and prognostic biomarker for chemotherapy.

Interference between copper transport systems and platinum drugs

Cisplatin, or cis-diamminedichloridoplatinum(II) cis-[PtCl₂(NH₃)₂], is a platinum-based anticancer drug largely used for the treatment of various types of cancers, including testicular, ovarian and colorectal carcinomas, sarcomas, and lymphomas. Together with other platinum-based drugs, cisplatin triggers malignant cell death by binding to nuclear DNA, which appears to be the ultimate target. In addition to passive diffusion across the cell membrane, other transport systems, including endocytosis and some active or facilitated transport mechanisms, are currently proposed to play a pivotal role in the uptake of platinum-based drugs. In this review, an updated view of the current literature regarding the intracellular transport and processing of cisplatin will be presented, with special emphasis on the plasma membrane copper permease CTR1, the Cu-transporting ATPases, ATP7A and ATP7B, located in the trans-Golgi network, and the soluble copper chaperone ATOX1. Their role in eliciting cisplatin efficacy and their exploitation as pharmacological targets will be addressed.

NMR spectroscopy to study the fate of metallodrugs in cells

Metal-based drugs can modulate various biological processes and exhibit a rich variety of properties that foster their use in biomedicine and chemical biology. On the way to intracellular targets, ligand exchange and redox reactions can take place, thus making metallodrug speciation in vivo a challenging task. Advances in NMR spectroscopy have made it possible to move from solution to live-cell studies and elucidate the transport of metallodrugs and interactions with macromolecular targets in a physiological setting. In turn, the electronic properties and supramolecular chemistry of metal complexes can be exploited to characterize drug delivery nanosystems by NMR. The recent evolution of in-cell NMR methodology is presented with special emphasis on metal-related processes. Applications to paradigmatic cases of platinum and gold drugs are highlighted.

Rapid desalting during electrospray ionization mass spectrometry for investigating protein-ligand interactions in the presence of concentrated salts

Investigation of protein-ligand interactions in physiological conditions is crucial for better understanding of biochemistry because the binding stoichiometry and conformations of complexes in biological processes, such as various types of regulation and transportation, could reveal key pathways in organisms. Nanoelectrospray ionization mass spectrometry is widely used in studies of biological processes and systems biology. However, non-volatile salts in biological fluid may adversely interfere with nanoelectrospray ionization mass spectrometry. In this study, the previously developed method of induced nanoelectrospray ionization was used to facilitate in situ desalting of protein in solutions with high concentrations of non-volatile salts, and direct investigation of protein-ligand interactions for the first time. In situ desalting occurred at the tip of emitters within a short period lasting for a few to tens of milliseconds, enabling the maintenance of nativelike conditions compatible with mass spectrometry measurements. Induced nanoelectrospray ionization was driven by pulsed potential and exhibited microelectrophoresis effect in each spray cycle, which is not observed in conventional nanoelectrospray ionization because the continuous spray procedure is driven by direct current. Microelectrophoresis caused desalting through micron-sized spray emitters (1-20 μm), as confirmed experimentally with proteins in 100 mM NaCl solution. The method developed in this study has been further illustrated as a potential option for fast and direct identification of protein-ligand (small molecules or metal ions) interactions in complex samples. The results of this study demonstrate that the newly developed method may represent a reliable approach for investigations of proteins and protein complexes in biological samples.

The Multifaceted Roles of Copper in Cancer: A Trace Metal Element with Dysregulated Metabolism, but Also a Target or a Bullet for Therapy

In the human body, copper (Cu) is a major and essential player in a large number of cellular mechanisms and signaling pathways. The involvement of Cu in oxidation-reduction reactions requires close regulation of copper metabolism in order to avoid toxic effects. In many types of cancer, variations in copper protein levels have been demonstrated. These variations result in increased concentrations of intratumoral Cu and alterations in the systemic distribution of copper. Such alterations in Cu homeostasis may promote tumor growth or invasiveness or may even confer resistance to treatments. Once characterized, the dysregulated Cu metabolism is pinpointing several promising biomarkers for clinical use with prognostic or predictive capabilities. The altered Cu metabolism in cancer cells and the different responses of tumor cells to Cu are strongly supporting the development of treatments to disrupt, deplete, or increase Cu levels in tumors. The metallic nature of Cu as a chemical element is key for the development of anticancer agents via the synthesis of nanoparticles or copper-based complexes with antineoplastic properties for therapy. Finally, some of these new therapeutic strategies such as chelators or ionophores have shown promising results in a preclinical setting, and others are already in the clinic.

A recombinant platform to characterize the role of transmembrane protein hTMEM205 in Pt(II)-drug resistance and extrusion

Platinum-coordination complexes are among the most effective chemotherapeutic drugs used in clinics for the treatment of cancer. Despite their efficacy, cancer cells can develop drug resistance leading to treatment failure and relapse. Cellular uptake and extrusion of Pt(ii)-complexes mediated by transmembrane proteins are critical in controlling the intracellular concentration of Pt(ii)-drugs and in developing pre-target resistance. TMEM205 is a human transmembrane protein (hTMEM205) overexpressed in cancer cells that are resistant to cisplatin, but its molecular function underlying - resistance remains elusive. We developed a low-cost and high-throughput recombinant expression platform coupled to in vivo functional resistance assays to study the molecular mechanism by which the orphan hTMEM205 protects against Pt(ii)-complex toxicity. Based on the original observation by the Rosenberg group, which led to the discovery of cisplatin, we performed quantitative analysis of the effects of Pt(ii)-coordination complexes on cellular growth and filamentation in E. coli cells expressing hTMEM205. By coupling our methods with Pt quantification and cellular profiling in control and hTMEM205-expressing cells, we demonstrate that hTMEM205 mediates Pt(ii)-drug export selectively towards cisplatin and oxaliplatin but not carboplatin. By mutation analysis, we reveal that hTMEM205 recognizes and allows Pt(ii)-extrusion by a putative sulfur-based translocation mechanism, thereby resulting in pre-target resistance. Thus, hTMEM205 represents a new potential target that can be exploited to reduce cellular resistance towards Pt(ii)-drugs.

Intramolecular platinum migration on a peptide in gas phase during collision-induced dissociation

We report the migration of platinum ligand unit {Pt(en)}₂ (en = ethylenediamine) on a short peptide during collision-induced dissociation fragmentation combined with the characterization of the same species by 2D [¹H,¹⁵N] HSQC (Heteronuclear Single Quantum Coherence) NMR spectroscopy. The NMR spectrum showed that the cysteine is platinated while the MS/MS (Tandem mass spectrometry) showed the platination at glutamic acid. Our results provide the first experimental evidence of platinum migration on peptide during collision-induced dissociation.

Oxidation of Human Copper Chaperone Atox1 and Disulfide Bond Cleavage by Cisplatin and Glutathione

Cancer cells cope with high oxidative stress levels, characterized by a shift toward the oxidized form (GSSG) of glutathione (GSH) in the redox couple GSSG/2GSH. Under these conditions, the cytosolic copper chaperone Atox1, which delivers Cu(I) to the secretory pathway, gets oxidized, i.e., a disulfide bond is formed between the cysteine residues of the Cu(I)-binding CxxC motif. Switching to the covalently-linked form, sulfur atoms are not able to bind the Cu(I) ion and Atox1 cannot play an antioxidant role. Atox1 has also been implicated in the resistance to platinum chemotherapy. In the presence of excess GSH, the anticancer drug cisplatin binds to Cu(I)-Atox1 but not to the reduced apoprotein. With the aim to investigate the interaction of cisplatin with the disulfide form of the protein, we performed a structural characterization in solution and in the solid state of oxidized human Atox1 and explored its ability to bind cisplatin under conditions mimicking an oxidizing environment. Cisplatin targets a methionine residue of oxidized Atox1; however, in the presence of GSH as reducing agent, the drug binds irreversibly to the protein with ammine ligands trans to Cys12 and Cys15. The results are discussed with reference to the available literature data and a mechanism is proposed connecting platinum drug processing to redox and copper homeostasis.

Coordination of Platinum to α-Synuclein Inhibits Filamentous Aggregation in Solution

Accumulation of filamentous aggregates of α-synuclein (AS) in Lewy bodies and neurites is characteristic of neurodegenerative diseases such as Parkinson's disease. Inhibition of AS fibrillation is helpful for understanding of AS aggregate structure and for developing chemical therapies. Herein, we report that the Pt^II -containing antitumor drug cisplatin suppresses filamentous aggregation of AS in solution. Pt^II thus contrasts strongly with reported transition-metal ions such as Mn^II , Fe^III , and Cu^II , which accelerate AS aggregation. Interaction between Pt^II and the side chains of methionine and histidine residues was essential for inhibition of AS fibrillation. Binding of Pt^II to AS did not change the protein's overall random coil structure, as indicated by solution-state two-dimensional NMR and circular dichroism spectroscopy; and a solution of the AS⋅Pt^II complex remained free of filamentous aggregates. Our results constitute interesting new information about the biological chemistry of metal ions in Parkinson's disease and might open new lines of research into the suppression of filamentous aggregation.

Copper trafficking in eukaryotic systems: current knowledge from experimental and computational efforts

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The main copper transporter, Ctr1, can transfer Cu(I) in the cell, through two different intracellular domains.

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Conformational flexibility of the copper metallochaperone Atox1 controls copper transfer mechanism in the cell.

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Each metal binding domain in ATP7B has a specific role.

Copper plays a vital role in fundamental cellular functions, and its concentration in the cell must be tightly regulated, as dysfunction of copper homeostasis is linked to severe neurological diseases and cancer. This review provides a compendium of current knowledge regarding the mechanism of copper transfer from the blood system to the Golgi apparatus; this mechanism involves the copper transporter hCtr1, the metallochaperone Atox1, and the ATPases ATP7A/B. We discuss key insights regarding the structural and functional properties of the hCtr1-Atox1-ATP7B cycle, obtained from diverse studies relying on distinct yet complementary biophysical, biochemical, and computational methods. We further address the mechanistic aspects of the cycle that continue to remain elusive. These knowledge gaps must be filled in order to be able to harness our understanding of copper transfer to develop therapeutic approaches with the capacity to modulate copper metabolism.

Mass spectrometric quantification of the binding ratio of metal-based anticancer complexes with protein thiols

RATIONALE

The binding ratio of metal complexes with cysteinyl thiols in proteins plays an important role in deciphering the mechanisms of action of therapeutic metal complexes, but its analysis is still a significant challenge. In this work, a quantitative mass spectrometry method is developed to determine the binding ratio of metal-based anticancer complexes with cysteines in human copper chaperone protein Atox1.

METHODS

A novel strategy based on a thiol-specific stable isotopic labelling reagent was developed to determine the binding ratio of metal-based anticancer complexes, namely cisplatin and organometallic ruthenium complex [(η⁶ -biphenyl)RuCl(en)]PF₆ (en = ethylenediamine), with the cysteinyl residues of Atox1.

RESULTS

Both cisplatin and the ruthenium complex were reactive not only to Cys15 and/or Cys18, the copper(I) binding site of Atox1, but also to Cys44. The binding ratios of the ruthenium complex with the cysteinyl residues were much higher than those of cisplatin. However, the addition of copper(I) could markedly increase the binding ratios of cysteinyl residues of Atox1 with cisplatin, but not with the ruthenium complex.

CONCLUSIONS

This strategy can not only precisely determine the binding ratios of metal complexes to protein thiols, but also be helpful in distinguishing thiol-binding sites from other binding sites of metal complexes in proteins. We expect wide application of this method to the research of covalent/coordinative interactions between metal complexes and protein thiols.

Tandem mass spectrometry characterization of a conjugate between oleuropein and hydrated cis-diammineplatinum(II)

RATIONALE

Oleuropein (Ole) has been claimed to mitigate cisplatin (CP)-induced acute injury in kidney and liver of mice. In vitro reactivity of hydrated CP species with Ole, and an Ole metabolite, hydroxytyrosol (HT), is of great interest as the preliminary step for gathering in vivo information on the possible physiological role of the Ole/HT-cis-diammineplatinum(II) (Ole/HT-cis-DAP) conjugate.

METHODS

Reversed-phase liquid chromatography coupled to electrospray ionization mass spectrometry using a linear ion trap instrument (RPLC/ESI-MS) and tandem mass (MS/MS) measurements, both in positive and negative ion mode, revealed the molecular identity of platinum-based conjugates.

RESULTS

The Ole-cis-DAP conjugate (i.e., C₂₅ H₃₆ N₂ O₁₃ Pt^II ) features two cis-ammine non-leaving ligands and a bidentate catechol ligand moiety belonging to Ole; the coordination of the central Pt(II) is square-planar with non-equivalent bond angles compared with the ideal arrangement of 90°. HT, the free Ole metabolite excreted in human urine, acts as bidentate O,O-donor ligand of cis-DAP as well.

CONCLUSIONS

The first evidence, together with structural information, is provided about the in vitro formation of a conjugate between cis-DAP and Ole or its urinary metabolite HT. Presuming that such conjugates are also generated in vivo, the mechanisms by which they might contribute to reduce CP toxicity remain to be elucidated.

Fate of cisplatin and its main hydrolysed forms in the presence of thiolates: a comprehensive computational and experimental study

Thiolations and bidentations drive the chemical fate of cisplatin compounds in intracellular medium.

Probing the interaction of a quercetin bioconjugate with Bcl-2 in living human cancer cells with in-cell NMR spectroscopy

In-cell NMR spectroscopy has emerged as a powerful technique for monitoring biomolecular interactions at an atomic level inside intact cells. However, current methodologies are inadequate at charting intracellular interactions of nonlabeled proteins and require their prior isotopic labeling. Herein, we describe for the first time the monitoring of the quercetin-alanine bioconjugate interaction with the nonlabeled antiapoptotic protein Bcl-2 inside living human cancer cells. STD and Tr-NOESY in-cell NMR methodologies were successfully applied in the investigation of the binding, which was further validated in vitro. In-cell NMR proved a very promising strategy for the real-time probing of the interaction profile of potential drugs with their therapeutic targets in native cellular environments and could, thus, open a new avenue in drug discovery.

Response of Cisplatin Resistant Skov-3 Cells to [Pt(O,O'-Acac)(γ-Acac)(DMS)] Treatment Revealed by a Metabolomic ¹H-NMR Study

The novel [Pt(O,O′-acac)(γ-acac)(DMS)], Ptac2S, Pt(II) complex has recently gained increasing attention as a potential anticancer agent for its pharmacological activity shown in different tumor cell lines, studied both in vitro and in vivo. The mechanism of action of Ptac2S, operating on non-genomic targets, is known to be very different from that of cis-[PtCl₂(NH₃)₂], cisplatin, targeting nucleic acids. In this work, we evaluated the cytotoxicity of Ptac2S on the cisplatin resistant Epithelial Ovarian Carcinoma (EOC), SKOV-3 cells, by the MTT assay. A ¹H-NMR metabolomic approach coupled with multivariate statistical analysis was used for the first time for Ptac2S to figure out the biological mechanisms of action of the complex. The metabolic variations of intracellular metabolites and the composition of the corresponding extracellular culture media were compared to those of cisplatin (cells were treated at the IC₅₀ doses of both drugs). The reported comparative metabolomic analysis revealed a very different metabolic profile between Ptac2S and cisplatin treated samples, thus confirming the different mechanism of action of Ptac2S also in the Epithelial Ovarian Carcinoma (EOC), SKOV-3 cells line. In particular, higher levels of pyruvate were observed in Ptac2S treated, with respect to cisplatin treated, cells (in both aqueous and culture media). In addition, a very different lipid expression resulted after the exposure to the two drugs (Ptac2S and cisplatin). These results suggest a possible explanation for the Ptac2S ability to circumvent cisplatin resistance in SKOV-3 cells.

Bacterial Cytological Profiling Reveals the Mechanism of Action of Anticancer Metal Complexes

Target identification and mechanistic studies of cytotoxic agents are challenging processes that are both time-consuming and costly. Here we describe an approach to mechanism of action studies for potential anticancer compounds by utilizing the simple prokaryotic system, E. coli, and we demonstrate its utility with the characterization of a ruthenium polypyridyl complex [Ru(bpy)₂dmbpy²⁺]. Expression of the photoconvertible fluorescent protein Dendra2 facilitated both high throughput studies and single-cell imaging. This allowed for simultaneous ratiometric analysis of inhibition of protein production and phenotypic investigations. The profile of protein production, filament size and population, and nucleoid morphology revealed important differences between inorganic agents that damage DNA vs more selective inhibitors of transcription and translation. Trace metal analysis demonstrated that DNA is the preferred nucleic acid target of the ruthenium complex, but further studies in human cancer cells revealed altered cell signaling pathways compared to the commonly administrated anticancer agent cisplatin. This study demonstrates E. coli can be used to rapidly distinguish between compounds with disparate mechanisms of action and also for more subtle distinctions within in studies in mammalian cells.

Effect of cisplatin on the transport activity of PII-type ATPases

Cisplatin (cis-diamminedichlorido-Pt(ii)) is extensively used as a chemotherapeutic agent against various types of tumors. However, cisplatin administration causes serious side effects, including nephrotoxicity, ototoxicity and neurotoxicity. It has been shown that cisplatin can interact with P-type ATPases, e.g., Cu⁺-ATPases (ATP7A and ATP7B) and Na⁺,K⁺-ATPase. Cisplatin-induced inhibition of Na⁺,K⁺-ATPase has been related to the nephrotoxic effect of the drug. To investigate the inhibitory effects of cisplatin on the pumping activity of P_II-type ATPases, electrical measurements were performed on sarcoplasmic reticulum Ca²⁺-ATPase (SERCA) and Na⁺,K⁺-ATPase embedded in vesicles/membrane fragments adsorbed on a solid-supported membrane. We found that cisplatin inhibits SERCA and Na⁺,K⁺-ATPase only when administered without a physiological reducing agent (GSH); in contrast, inhibition was also observed in the case of Cu⁺-ATPases in the presence of 1 mM GSH. Our results indicate that cisplatin is a much stronger inhibitor of SERCA (with an IC₅₀ value of 1.3 μM) than of Na⁺,K⁺-ATPase (with an IC₅₀ value of 11.1 μM); moreover, cisplatin inhibition of Na⁺,K⁺-ATPase is reversible, whereas it is irreversible in the case of SERCA. In the absence of a physiological substrate, while Cu⁺-ATPases are able to translocate cisplatin, SERCA and Na⁺,K⁺-ATPase do not perform ATP-dependent cisplatin displacement.

Platinum transfer from hCTR1 to Atox1 is dependent on the type of platinum complex

In spite of their wide application, the cellular uptake of platinum based anticancer drugs is still unclear. The copper transport protein, hCTR1, is proposed to facilitate the cellular uptake of cisplatin, whereas organic cation transport (OCT) is more important for oxaliplatin. It has been reported that both N-terminal and C-terminal metal binding motifs of hCTR1 are highly reactive to cisplatin, which is the initial step of protein assisted cellular uptake of cisplatin. It is still unknown how the platinum drugs in hCTR1 transfer to cytoplasmic media, and whether various platinum complexes possess different activities in this process. Herein, we investigated the reaction of the platinated C-terminal metal binding motif of hCTR1 (C8) with the down-stream protein Atox1. Results show that Atox1 is highly reactive to the platinated C8 adducts of cisplatin and transplatin, whereas the oxaliplatin/C8 adduct is much less reactive. The platinum transfer from C8 to Atox1 occurs in the reaction, which results in the protein unfolding of Atox1. These results demonstrated that the platinated intracellular-domain of hCTR1 is reactive to Atox1, and the reactivity is dependent on the ligand and the coordination structure of platinum complexes. The different reactivity is consistent with the hypothesis that hCTR1 is more significant in the transport of cisplatin than that of oxaliplatin.

Protein metalation by metal-based drugs: X-ray crystallography and mass spectrometry studies

The combined use of X-ray crystallography and mass spectrometry represents a valuable strategy to investigate and characterize protein metalation induced by anticancer metal-based drugs. Here, we summarize a series of significant results recently obtained in our laboratories upon the examination of the structures of several adducts of proteins with representative metallodrugs (mostly containing ruthenium, gold and platinum). The general mechanisms of protein metalation that emerge from a careful comparative analysis of these structures are illustrated and their mechanistic implications are discussed. Possible directions for future work in the field are delineated.

Tetrathiomolybdate inhibits the reaction of cisplatin with human copper chaperone Atox1

Tetrathiomolybdate inhibits the platination of Cu–Atox1 and prevents the protein unfolding and aggregation induced by cisplatin.

Platinum Binds Proteins in the Endoplasmic Reticulum of S. cerevisiae and Induces Endoplasmic Reticulum Stress

Pt(II)-based anticancer drugs are widely used in the treatment of a variety of cancers, but their clinical efficacy is hindered by undesirable side effects and resistance. While much research has focused on Pt(II) drug interactions with DNA, there is increasing interest in proteins as alternative targets and contributors to cytotoxic and resistance mechanisms. Here, we describe a chemical proteomic method for isolation and identification of cellular protein targets of platinum compounds using Pt(II) reagents that have been modified for participation in the 1,3 dipolar cycloaddition "click" reaction. Using this method to visualize and enrich for targets, we identified 152 proteins in Pt(II)-treated Saccharomyces cerevisiae. Of interest was the identification of multiple proteins involved in the endoplasmic reticulum (ER) stress response, which has been proposed to be an important cytoplasmic mediator of apoptosis in response to cisplatin treatment. Consistent with possible direct targeting of this pathway, the ER stress response was confirmed to be induced in Pt(II)-treated yeast along with in vitro Pt(II)-inhibition of one of the identified proteins, protein disulfide isomerase.

Magnetic Resonance Spectroscopy as a Tool for Assessing Macromolecular Structure and Function in Living Cells

Investigating the structure, modification, interaction, and function of biomolecules in their native cellular environment leads to physiologically relevant knowledge about their mechanisms, which will benefit drug discovery and design. In recent years, nuclear and electron magnetic resonance (NMR) spectroscopy has emerged as a useful tool for elucidating the structure and function of biomacromolecules, including proteins, nucleic acids, and carbohydrates in living cells at atomic resolution. In this review, we summarize the progress and future of in-cell NMR as it is applied to proteins, nucleic acids, and carbohydrates.

Interactions of cisplatin and the copper transporter CTR1 in human colon cancer cells

There is much interest in understanding the mechanisms by which platinum-based anticancer agents enter cells, and the copper transporter CTR1 has been the focus of many recent studies. While there is a clinical correlation between CTR1 levels and platinum efficacy, cellular studies have provided conflicting evidence relating to the relationship between cisplatin and CTR1. We report here our studies of the relationship between cisplatin and copper homeostasis in human colon cancer cells. While the accumulation of copper and platinum do not appear to compete with each other, we did observe that cisplatin perturbs CTR1 distribution within 10 min, a far shorter incubation time than commonly employed in cellular studies of cisplatin. Furthermore, on these short time-scales, cisplatin caused an increase in the cytoplasmic labile copper pool. While the predominant focus of studies to date has been on CTR1, these studies highlight the importance of investigating the interaction of cisplatin with other copper proteins.

Towards understanding cellular structure biology: In-cell NMR

To watch biological macromolecules perform their functions inside the living cells is the dream of any biologists. In-cell nuclear magnetic resonance is a branch of biomolecular NMR spectroscopy that can be used to observe the structures, interactions and dynamics of these molecules in the living cells at atomic level. In principle, in-cell NMR can be applied to different cellular systems to achieve biologically relevant structural and functional information. In this review, we summarize the existing approaches in this field and discuss its applications in protein interactions, folding, stability and post-translational modifications. We hope this review will emphasize the effectiveness of in-cell NMR for studies of intricate biological processes and for structural analysis in cellular environments.

Developing drugs targeting transition metal homeostasis

Metal dyshomeostasis is involved in the pathogenesis and progression of diseases including cancer and neurodegenerative diseases. Metal chelators and ionophores are well known modulators of transition metal homeostasis, and a number of these molecules are in clinical trials. Metal-binding compounds are not the only drugs capable of targeting transition metal homeostasis. This review presents recent highlights in the development of chelators and ionophores for the treatment of cancer and neurodegenerative disease. Moreover, we discuss the development of small molecules that alter copper and iron homeostasis by inhibiting metal transport proteins. Finally, we consider the emergence of metal regulatory factor 1 as a drug target in diseases where it mediates zinc-induced signalling cascades leading to pathogenesis.

Mass spectrometry based strategy for studies of binding sites and structural changes of cisplatin binding to myoglobin

RATIONALE

It is of great significance to investigate the interaction of the metallodrug cisplatin (cis-[PtCl₂ (NH₃ )₂ ]) with myoglobin for understanding of the mechanism of action of cisplatin and the overexpression of myoglobin in tumor cells.

METHODS

The reactions of cisplatin and myoglobin were incubated under different conditions. A mass spectrometry (MS)-based strategy combining full proteolysis and limited proteolysis was developed for comprehensive studies of cisplatin-myoglobin interaction.

RESULTS

The binding sites of cisplatin on myoglobin were identified as Trp14, His64, His81, His113 and His116 using electrospray ionization multiple-stage tandem mass spectrometry (ESI-MSⁿ ) without liquid chromatography (LC) separation. The relative abundances of digested peptides from platinated myoglobin were obviously higher than those from native samples by limited proteolysis.

CONCLUSIONS

An alternative and simple approach was developed to successfully monitor conformational changes of myoglobin induced by cisplatin binding using an ESI-MS-based quantification method combined with limited proteolysis. Meanwhile, His64 was firstly found to coordinate to platinum, which was likely to affect hydrogen bonds with the oxygen in the heme group. Copyright © 2016 John Wiley & Sons, Ltd.

Ctr1 Intracellular Loop Is Involved in the Copper Transfer Mechanism to the Atox1 Metallochaperone

Understanding the human copper cycle is essential to understand the role of metals in promoting neurological diseases and disorders. One of the cycles controlling the cellular concentration and distribution of copper involves the copper transporter, Ctr1; the metallochaperone, Atox1; and the ATP7B transporter. It has been shown that the C-terminus of Ctr1, specifically the last three amino acids, HCH, is involved in both copper coordination and the transfer mechanism to Atox1. In contrast, the role of the intracellular loop of Ctr1, which is an additional intracellular segment of Ctr1, in facilitating the copper transfer mechanism has not been investigated yet. Here, we combine various biophysical methods to explore the interaction between this Ctr1 segment and metallochaperone Atox1 and clearly demonstrate that the Ctr1 intracellular loop (1) can coordinate Cu(I) via interactions with the side chains of one histidine and two methionine residues and (2) closely interacts with the Atox1 metallochaperone. Our findings are another important step in elucidating the mechanistic details of the eukaryotic copper cycle.

A ratiometric fluorescent sensor for the mitochondrial copper pool

Copper plays a key role in the modulation of cellular function, defence, and growth. Here we present InCCu1, a ratiometric fluorescent sensor for mitochondrial copper, which changes from red to blue emission in the presence of Cu(i). Employing this probe in microscopy and flow cytometry, we show that cisplatin-treated cells have an impaired ability to accumulate copper in the mitochondria.

Cisplatin inhibits MEK1/2

Cisplatin (cDDP) is known to bind to the CXXC motif of proteins containing a ferrodoxin-like fold but little is known about its ability to interact with other Cu-binding proteins. MEK1/2 has recently been identified as a Cu-dependent enzyme that does not contain a CXXC motif. We found that cDDP bound to and inhibited the activity of recombinant MEK1 with an IC₅₀ of 0.28 μM and MEK1/2 in whole cells with an IC₅₀ of 37.4 μM. The inhibition of MEK1/2 was relieved by both Cu⁺¹ and Cu⁺² in a concentration-dependent manner. cDDP did not inhibit the upstream pathways responsible for activating MEK1/2, and did not cause an acute depletion of cellular Cu that could account for the reduction in MEK1/2 activity. cDDP was found to bind MEK1/2 in whole cells and the extent of binding was augmented by supplementary Cu and reduced by Cu chelation. Molecular modeling predicts 3 Cu and cDDP binding sites and quantum chemistry calculations indicate that cDDP would be expected to displace Cu from each of these sites. We conclude that, at clinically relevant concentrations, cDDP binds to and inhibits MEK1/2 and that both the binding and inhibitory activity are related to its interaction with Cu bound to MEK1/2. This may provide the basis for useful interactions of cDDP with other drugs that inhibit MAPK pathway signaling.

Total Cellular RNA Modulates Protein Activity

RNA constitutes up to 20% of a cell's dry weight, corresponding to ∼20 mg/mL. This high concentration of RNA facilitates low-affinity protein-RNA quinary interactions, which may play an important role in facilitating and regulating biological processes. In the yeast Pichia pastoris, the level of ubiquitin-RNA colocalization increases when cells are grown in the presence of dextrose and methanol instead of methanol as the sole carbon source. Total RNA isolated from cells grown in methanol increases β-galactosidase activity relative to that seen with RNA isolated from cells grown in the presence of dextrose and methanol. Because the total cellular RNA content changes with growth medium, protein-RNA quinary interactions can alter in-cell protein biochemistry and may play an important role in cell adaptation, critical to many physiological and pathological states.

Identification of binding sites of cisplatin to human copper chaperone protein Cox17 by high-resolution FT-ICR-MS

RATIONALE

Cox17 is a key copper chaperone protein responsible for delivery of cuprous ions to mitochondria and has been demonstrated to be involved in the anticancer action of cisplatin. However, the binding sites of the drug to the protein have not yet been directly identified.

METHODS

The recombinant protein apo-Cox172s-s , the functional state of Cox17 transferring Cu(I), was reacted with an excess of cisplatin to produce platinated Cox17 adducts, of which the platination sites were identified by high-resolution Fourier transform ion cyclotron tandem mass spectrometry (FT-ICR-MS/MS) through electron capture dissociation (ECD).

RESULTS

Primary FT-ICR-MS showed that mono-platinated Cox17 adducts were the main products, and top-down MS/MS results indicated that cisplatin bound to the Cys26 or Cys27 residue which is the binding site of cuprous ions in apo-Cox172s-s .

CONCLUSIONS

This is the first report for identification of the main binding sites of cisplatin to Cox17 by top-down high-resolution mass spectrometry, providing direct evidence for the competitive coordination with Cox17 of cisplatin and cuprous ions. These findings will also be helpful to understand further how Cox17 facilitates cisplatin accumulation in mitochondria, and how cisplatin disturbs the transportation of cuprous ions. Copyright © 2016 John Wiley & Sons, Ltd.