Cisplatin binds human copper chaperone Atox1 and promotes unfolding in vitro

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.

Cuproptosis: unveiling a new frontier in cancer biology and therapeutics

Copper plays vital roles in numerous cellular processes and its imbalance can lead to oxidative stress and dysfunction. Recent research has unveiled a unique form of copper-induced cell death, termed cuproptosis, which differs from known cell death mechanisms. This process involves the interaction of copper with lipoylated tricarboxylic acid cycle enzymes, causing protein aggregation and cell death. Recently, a growing number of studies have explored the link between cuproptosis and cancer development. This review comprehensively examines the systemic and cellular metabolism of copper, including tumor-related signaling pathways influenced by copper. It delves into the discovery and mechanisms of cuproptosis and its connection to various cancers. Additionally, the review suggests potential cancer treatments using copper ionophores that induce cuproptosis, in combination with small molecule drugs, for precision therapy in specific cancer types.

Development of Integrated Bioorthogonal Self-Catalyzed NO Donor/Platinum(IV) Prodrugs for Synergistical Intervention against Triple-Negative Breast Cancer

The platinum(IV) prodrug strategy is attractive for the synergistic antitumor effect. High levels (>400 nM) of nitric oxide (NO) exert promising cancer inhibition effects via multiple mechanisms. Herein, we designed and synthesized a new group of integrated bioorthogonal self-catalyzed NO donor/Pt(IV) prodrugs bearing long alkyl chains to enhance the stability in circulation, while the cytoplasmic reductants trigger cascade activation to release Pt and NO in tumor cells. Specifically, compound 10c exhibited an improved stability, favorable pharmacokinetic properties (AUC(0-t) of 2210.10 h*ng/mL), potent anti-triple-negative breast cancer (TNBC) effects (71.08% tumor growth inhibition (TGI) against the MDA-MB-231 xenograft model), potent in vivo anti-TNBC lung metastasis activity, and acceptable low toxicity. Importantly, NO released from 10c leads to the S-nitrosation of metal transporters Atox1&ATP7a in TNBC cells, which increases the Pt retention and inhibits lysyl oxidase, generating synergistic tumoricidal and antimetastatic activity. These results may inspire further study on the synergistical therapy of Pt and NO for the treatment of TNBC.

Copper homeostasis and cuproptosis in cancer immunity and therapy

Copper is an essential nutrient for maintaining enzyme activity and transcription factor function. Excess copper results in the aggregation of lipoylated dihydrolipoamide S-acetyltransferase (DLAT), which correlates to the mitochondrial tricarboxylic acid (TCA) cycle, resulting in proteotoxic stress and eliciting a novel cell death modality: cuproptosis. Cuproptosis exerts an indispensable role in cancer progression, which is considered a promising strategy for cancer therapy. Cancer immunotherapy has gained extensive attention owing to breakthroughs in immune checkpoint blockade; furthermore, cuproptosis is strongly connected to the modulation of antitumor immunity. Thus, a thorough recognition concerning the mechanisms involved in the modulation of copper metabolism and cuproptosis may facilitate improvement in cancer management. This review outlines the cellular and molecular mechanisms and characteristics of cuproptosis and the links of the novel regulated cell death modality with human cancers. We also review the current knowledge on the complex effects of cuproptosis on antitumor immunity and immune response. Furthermore, potential agents that elicit cuproptosis pathways are summarized. Lastly, we discuss the influence of cuproptosis induction on the tumor microenvironment as well as the challenges of adding cuproptosis regulators to therapeutic strategies beyond traditional therapy.

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 in cancer: From pathogenesis to therapy

One of the basic trace elements for the structure and metabolism of human tissue is copper. However, as a heavy metal, excessive intake or abnormal accumulation of copper in the body can cause inevitable damage to the organism because copper can result in direct injury to various cell components or disruption of the redox balance, eventually leading to cell death. Interestingly, a growing body of research reports that diverse cancers have raised serum and tumor copper levels. Tumor cells depend on more copper for their metabolism than normal cells, and a decrease in copper or copper overload can have a detrimental effect on tumor cells. New modalities for identifying and characterizing copper-dependent signals offer translational opportunities for tumor therapy, but their mechanisms remain unclear. Therefore, this article summarizes what we currently know about the correlation between copper and cancer and describes the characteristics of copper metabolism in tumor cells and the prospective application of copper-derived therapeutics.

The PERK/ATF4/CHOP signaling branch of the unfolded protein response mediates cisplatin-induced ototoxicity in hair cells

Cisplatin is a widely used chemotherapeutic agent. However, its clinical application remains limited due to the high incidence of severe ototoxicity. It has been reported that the unfolded protein response (UPR) is involved in cisplatin-induced ototoxicity. However, the specific mechanism underlying its effect remains unclear. Therefore, the present study aimed to explore the sequential changes in the key UPR signaling branch and its potential pro-apoptotic role in cisplatin-induced ototoxicity. The hair cell-like OC-1 cells were treated with cisplatin for different periods and then the expression levels of the UPR- and apoptosis-related proteins were determined. The results showed that the apoptotic rate of cells was gradually increased with prolonged cisplatin treatment. Furthermore, the sequential changes in three UPR signaling branches were evaluated. The expression levels of activating transcription factor 4 (ATF4) and C/EBP homologous protein (CHOP) were gradually increased with up to 12 h of cisplatin treatment. The aforementioned expression profile was consistent with that observed for the apoptosis-related proteins. Subsequently, the proportion of apoptotic cells was notably decreased in CHOP-silenced hair cell-like OC-1 cells following treatment with cisplatin. Moreover, we found significant hair cells loss and a higher level of CHOP in cisplatin-treated cochlear explants in a time-dependent manner. Overall, the present study demonstrated that the protein kinase RNA‑like endoplasmic reticulum kinase (PERK)/ATF4/CHOP signaling branch could play an important role in cisplatin-induced cell apoptosis. Furthermore, the current study suggested that CHOP may be considered as a promising therapeutic target for cisplatin-induced ototoxicity.

Crossroads between copper ions and amyloid formation in Parkinson's disease

Copper (Cu) ion dys-homeostasis and α-synclein amyloid deposits are two hallmarks of Parkinson's disease (PD). Here, I will discuss the connections between these features, with a major focus on the role of Cu in the α-synuclein (aS) amyloid formation process. The structurally disordered aS monomer can bind to both redox states of Cu (i.e., oxidized Cu(II) and reduced Cu(I)) with high affinity in vitro. Notably, the presence of Cu(II) (in absence of aS N-terminal acetylation) and Cu(I) (when in complex with the copper chaperone Atox1) modulate aS assembly into β-structured amyloids in opposite directions in vitro. Albeit the link to biological relevance is not fully unraveled, existing observations clearly emphasize the need for more knowledge on this interplay and its consequences to eventually combat destructive reactions that promote PD.

Ovarian Cancer: Treatment and Resistance to Pharmacotherapy

Despite advances in surgical techniques and chemotherapy, ovarian cancer is still a leading cause of death among gynecological cancers. In addition to the late detection of the disease, the main reason for poor prognosis is resistance to pharmacotherapy, mostly platinum compounds. About a third of patients do not respond to primary platinum-based chemotherapy treatment, and over time, eventually, 80% of other patients develop chemoresistance, which makes the recurrence of disease incurable. In this review, we describe a difficult clinical hurdle faced in ovarian cancer therapy as a result of platinum resistance, as well as resistance to newer targeted therapy with PARP inhibitors and bevacizumab. We, furthermore, give attention also to the role of the tumor microenvironment as it is less well understood than the tumor cell-intrinsic mechanism. Because a central goal in ovarian cancer research is the development of novel strategies to overcome chemoresistance, treatment for cancer is moving toward personalized therapy.

The molecular and cellular basis of copper dysregulation and its relationship with human pathologies

Copper (Cu) is an essential micronutrient required for the activity of redox-active enzymes involved in critical metabolic reactions, signaling pathways, and biological functions. Transporters and chaperones control Cu ion levels and bioavailability to ensure proper subcellular and systemic Cu distribution. Intensive research has focused on understanding how mammalian cells maintain Cu homeostasis, and how molecular signals coordinate Cu acquisition and storage within organs. In humans, mutations of genes that regulate Cu homeostasis or facilitate interactions with Cu ions lead to numerous pathologic conditions. Malfunctions of the Cu⁺ -transporting ATPases ATP7A and ATP7B cause Menkes disease and Wilson disease, respectively. Additionally, defects in the mitochondrial and cellular distributions and homeostasis of Cu lead to severe neurodegenerative conditions, mitochondrial myopathies, and metabolic diseases. Cu has a dual nature in carcinogenesis as a promotor of tumor growth and an inducer of redox stress in cancer cells. Cu also plays role in cancer treatment as a component of drugs and a regulator of drug sensitivity and uptake. In this review, we provide an overview of the current knowledge of Cu metabolism and transport and its relation to various human pathologies.

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.

My journey in academia: things not on the CV

I am a professor at Chalmers University of Technology in Sweden. I trained in chemistry in Sweden but went to the USA for my postdoc. I remained there for 12 years, being faculty at two American universities, before I returned to Sweden for a professorship in the northern city of Umeå. More recently, I returned to my alma mater Chalmers University of Technology in Gothenburg, where I have taken on senior leadership roles. On paper, my career trajectory looks straightforward, but there are many detrimental aspects and lucky coincidences that are not listed on my CV. Life in academia is never easy, and one is never ‘done’. But working in academia is wonderful, as it provides so much freedom and creativity, including being very accommodating towards having kids. Here, I will describe my own personal journey, with the hope of inspiring young women to follow their own path in academia. Yes, there is still bias against women in academia, but change is happening, and the many benefits of being an academic beat such drawbacks.

Inhibition of copper chaperones sensitizes human and canine osteosarcoma cells to carboplatin chemotherapy

Osteosarcoma (OSA) is the most common primary bone cancer in children, adolescents and dogs. Current combination surgical and chemotherapeutic treatments have increased survival. However, in recurrent or metastatic disease settings, the prognosis significantly decreases, representing an urgent need for better second-line and novel chemotherapeutics. The current gold standard for combination chemotherapy in OSA often includes a platinum agent, for example, cisplatin or carboplatin. These platinum agents are shuttled within the cell via copper transporters. Recent interest in targeting copper transport has been directed towards antioxidant protein 1 (Atox1) and copper chaperone for superoxide dismutase 1 (CCS), with Atox1 demonstrating the ability to aggregate platinum agents, preventing them from forming DNA adducts. DC_AC50 is a small molecule inhibitor of both Atox1 and CCS. To assess the impact of targeting these pathways on chemotherapy response, two human and two canine OSA cell lines were utilized. After treatment with single agent or combination drugs, cell viability was evaluated and pharmacological synergism calculated using the combination index method. Apoptosis, cell cycle distribution, clonogenic survival and migration were also evaluated. DC_AC50 synergised with carboplatin in combination treatment of human and canine OSA cells to reduce cancer cell viability. DC_AC50-treated cells were significantly less mitotically active, as demonstrated by decreased expression of phospho-histone H3 and cell cycle analysis. DC_AC50 also potentiated carboplatin-induced apoptosis in OSA cells and decreased clonogenic survival. Finally, DC_AC50 reduced the migratory ability of OSA cells. These results justify further investigation into inhibiting intracellular copper chaperones as a means of reducing/preventing acquired chemotherapy resistance.

Links between cancer metabolism and cisplatin resistance

Cisplatin is one of the most potent and widely used chemotherapeutic agent in the treatment of several solid tumors, despite the high toxicity and the frequent relapse of patients due to the onset of drug resistance. Resistance to chemotherapeutic agents, either intrinsic or acquired, is currently one of the major problems in oncology. Thus, understanding the biology of chemoresistance is fundamental in order to overcome this challenge and to improve the survival rate of patients. Studies over the last 30 decades have underlined how resistance is a multifactorial phenomenon not yet completely understood. Recently, tumor metabolism has gained a lot of interest in the context of chemoresistance; accumulating evidence suggests that the rearrangements of the principal metabolic pathways within cells, contributes to the sensitivity of tumor to the drug treatment. In this review, the principal metabolic alterations associated with cisplatin resistance are highlighted. Improving the knowledge of the influence of metabolism on cisplatin response is fundamental to identify new possible metabolic targets useful for combinatory treatments, in order to overcome cisplatin resistance.

Targeting of copper-trafficking chaperones causes gene-specific systemic pathology in Drosophila melanogaster: prospective expansion of mutational landscapes that regulate tumor resistance to cisplatin

Copper, a transition metal, is an essential component for normal growth and development. It acts as a critical co-factor of many enzymes that play key roles in diverse cellular processes. The present study attempts to investigate the regulatory functions decisively controlling copper trafficking during development and aging of the Drosophila model system. Hence, through engagement of the GAL4/UAS genetic platform and RNAi technology, we herein examined the in vivo significance of Atox1 and CCS genes, products of which pivotally govern cellular copper trafficking in fly tissue pathophysiology. Specifically, we analyzed the systemic effects of their targeted downregulation on the eye, wing, neuronal cell populations and whole-body tissues of the fly. Our results reveal that, in contrast to the eye, suppression of their expression in the wing leads to a notable increase in the percentage of malformed organs observed. Furthermore, we show that Atox1 or CCS gene silencing in either neuronal or whole-body tissues can critically affect the viability and climbing capacity of transgenic flies, while their double-genetic targeting suggests a rather synergistic mode of action of the cognate protein products. Interestingly, pharmacological intervention with the anti-cancer drug cisplatin indicates the major contribution of CCS copper chaperone to cisplatin's cellular trafficking, and presumably to tumor resistance often acquired during chemotherapy. Altogether, it seems that Atox1 and CCS proteins serve as tissue/organ-specific principal regulators of physiological Drosophila development and aging, while their tissue-dependent downregulation can provide important insights for Atox1 and CCS potential exploitation as predictive gene biomarkers of cancer-cell chemotherapy responses.

Summary: We demonstrate the essential roles of Atox1 and CCS copper-trafficking chaperones in Drosophila development and aging. We also provide insights for their therapeutic exploitation as cisplatin regulators during cancer chemotherapy.

Activity and Trafficking of Copper-Transporting ATPases in Tumor Development and Defense against Platinum-Based Drugs

Membrane trafficking pathways emanating from the Golgi regulate a wide range of cellular processes. One of these is the maintenance of copper (Cu) homeostasis operated by the Golgi-localized Cu-transporting ATPases ATP7A and ATP7B. At the Golgi, these proteins supply Cu to newly synthesized enzymes which use this metal as a cofactor to catalyze a number of vitally important biochemical reactions. However, in response to elevated Cu, the Golgi exports ATP7A/B to post-Golgi sites where they promote sequestration and efflux of excess Cu to limit its potential toxicity. Growing tumors actively consume Cu and employ ATP7A/B to regulate the availability of this metal for oncogenic enzymes such as LOX and LOX-like proteins, which confer higher invasiveness to malignant cells. Furthermore, ATP7A/B activity and trafficking allow tumor cells to detoxify platinum (Pt)-based drugs (like cisplatin), which are used for the chemotherapy of different solid tumors. Despite these noted activities of ATP7A/B that favor oncogenic processes, the mechanisms that regulate the expression and trafficking of Cu ATPases in malignant cells are far from being completely understood. This review summarizes current data on the role of ATP7A/B in the regulation of Cu and Pt metabolism in malignant cells and outlines questions and challenges that should be addressed to understand how ATP7A and ATP7B trafficking mechanisms might be targeted to counteract tumor development.

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.

Folding of copper proteins: role of the metal?

Copper is a redox-active transition metal ion required for the function of many essential human proteins. For biosynthesis of proteins coordinating copper, the metal may bind before, during or after folding of the polypeptide. If the metal binds to unfolded or partially folded structures of the protein, such coordination may modulate the folding reaction. The molecular understanding of how copper is incorporated into proteins requires descriptions of chemical, thermodynamic, kinetic and structural parameters involved in the formation of protein-metal complexes. Because free copper ions are toxic, living systems have elaborate copper-transport systems that include particular proteins that facilitate efficient and specific delivery of copper ions to target proteins. Therefore, these pathways become an integral part of copper protein folding in vivo. This review summarizes biophysical-molecular in vitro work assessing the role of copper in folding and stability of copper-binding proteins as well as protein-protein copper exchange reactions between human copper transport proteins. We also describe some recent findings about the participation of copper ions and copper proteins in protein misfolding and aggregation reactions in vitro.

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.

Tetrathiomolybdate induces dimerization of the metal-binding domain of ATPase and inhibits platination of the protein

Tetrathiomolybdate (TM) is used in the clinic for the treatment of Wilson’s disease by targeting the cellular copper efflux protein ATP7B (WLN). Interestingly, both TM and WLN are associated with the efficacy of cisplatin, a widely used anticancer drug. Herein, we show that TM induces dimerization of the metal-binding domain of ATP7B (WLN4) through a unique sulfur-bridged Mo₂S₆O₂ cluster. TM expels copper ions from Cu-WLN4 and forms a copper-free dimer. The binding of Mo to cysteine residues of WLN4 inhibits platination of the protein. Reaction with multi-domain proteins indicates that TM can also connect two domains in the same molecule, forming Mo-bridged intramolecular crosslinks. These results provide structural and chemical insight into the mechanism of action of TM against ATPase, and reveal the molecular mechanism by which TM attenuates the cisplatin resistance mediated by copper efflux proteins.

Tetrathiomolybdate (TM) and Cu-ATPases, e.g. Wilson (WLN) protein, affect the efficacy of common anticancer drug cisplatin. Here, the authors show that TM generates a protein dimer with a WLN domain by expelling copper and provide insight into the synergy of TM and cisplatin in cancer chemotherapy.

Modulating Chemosensitivity of Tumors to Platinum-Based Antitumor Drugs by Transcriptional Regulation of Copper Homeostasis

Platinum (Pt)-based antitumor agents have been effective in treating many human malignancies. Drug importing, intracellular shuffling, and exporting—carried out by the high-affinity copper (Cu) transporter (hCtr1), Cu chaperone (Ato x1), and Cu exporters (ATP7A and ATP7B), respectively—cumulatively contribute to the chemosensitivity of Pt drugs including cisplatin and carboplatin, but not oxaliplatin. This entire system can also handle Pt drugs via interactions between Pt and the thiol-containing amino acid residues in these proteins; the interactions are strongly influenced by cellular redox regulators such as glutathione. hCtr1 expression is induced by acute Cu deprivation, and the induction is regulated by the transcription factor specific protein 1 (Sp1) which by itself is also regulated by Cu concentration variations. Copper displaces zinc (Zn) coordination at the zinc finger (ZF) domains of Sp1 and inactivates its DNA binding, whereas Cu deprivation enhances Sp1-DNA interactions and increases Sp1 expression, which in turn upregulates hCtr1. Because of the shared transport system, chemosensitivity of Pt drugs can be modulated by targeting Cu transporters. A Cu-lowering agent (trientine) in combination with a Pt drug (carboplatin) has been used in clinical studies for overcoming Pt-resistance. Future research should aim at further developing effective Pt drug retention strategies for improving the treatment efficacy.

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.

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.

The six metal binding domains in human copper transporter, ATP7B: molecular biophysics and disease-causing mutations

Wilson Disease (WD) is a hereditary genetic disorder, which coincides with a dysfunctional copper (Cu) metabolism caused by mutations in ATP7B, a membrane-bound P1B-type ATPase responsible for Cu export from hepatic cells. The N-terminal part (~ 600 residues) of the multi-domain 1400-residue ATP7B constitutes six metal binding domains (MBDs), each of which can bind a copper ion, interact with other ATP7B domains as well as with different proteins. Although the ATP7B's MBDs have been investigated in vitro and in vivo intensively, it remains unclear how these domains modulate overall structure, dynamics, stability and function of ATP7B. The presence of six MBDs is unique to mammalian ATP7B homologs, and many WD causing missense mutations are found in these domains. Here, we have summarized previously reported in vitro biophysical data on the MBDs of ATP7B and WD point mutations located in these domains. Besides the demonstration of where the research field stands today, this review showcasts the need for further biophysical investigation about the roles of MBDs in ATP7B function. Molecular mechanisms of ATP7B are important not only in the development of new WD treatment but also for other aspects of human physiology where Cu transport plays a role.

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.

Binding of Copper and Cisplatin to Atox1 Is Mediated by Glutathione through the Formation of Metal-Sulfur Clusters

Copper is an essential nutrient required for many biological processes involved in primary metabolism, but free copper is toxic due to its ability to catalyze formation of free radicals. To prevent toxic effects, in the cell copper is bound to proteins and low molecular weight compounds, such as glutathione, at all times. The widely used chemotherapy agent cisplatin is known to bind to copper-transporting proteins, including copper chaperone Atox1. Cisplatin interactions with Atox1 and other copper transporters are linked to cancer resistance to platinum-based chemotherapy. Here we analyze the binding of copper and cisplatin to Atox1 in the presence of glutathione under redox conditions that mimic intracellular environment. We show that copper(I) and glutathione form large polymers with a molecular mass of approximately 8 kDa, which can transfer copper to Atox1. Cisplatin also can form polymers with glutathione, albeit at a slower rate. Analysis of simultaneous binding of copper and cisplatin to Atox1 under physiological conditions shows that both metals are bound to the protein through copper-sulfur-platinum bridges.

Roles of Copper-Binding Proteins in Breast Cancer

Copper ions are needed in several steps of cancer progression. However, the underlying mechanisms, and involved copper-binding proteins, are mainly elusive. Since most copper ions in the body (in and outside cells) are protein-bound, it is important to investigate what copper-binding proteins participate and, for these, how they are loaded with copper by copper transport proteins. Mechanistic information for how some copper-binding proteins, such as extracellular lysyl oxidase (LOX), play roles in cancer have been elucidated but there is still much to learn from a biophysical molecular viewpoint. Here we provide a summary of copper-binding proteins and discuss ones reported to have roles in cancer. We specifically focus on how copper-binding proteins such as mediator of cell motility 1 (MEMO1), LOX, LOX-like proteins, and secreted protein acidic and rich in cysteine (SPARC) modulate breast cancer from molecular and clinical aspects. Because of the importance of copper for invasion/migration processes, which are key components of cancer metastasis, further insights into the actions of copper-binding proteins may provide new targets to combat cancer.

The C-Terminus of Human Copper Importer Ctr1 Acts as a Binding Site and Transfers Copper to Atox1

Uptake of copper (Cu) ions into human cells is mediated by the plasma membrane protein Ctr1 and is followed by Cu transfer to cytoplasmic Cu chaperones for delivery to Cu-dependent enzymes. The C-terminal cytoplasmic tail of Ctr1 is a 13-residue peptide harboring an HCH motif that is thought to interact with Cu. We here employ biophysical experiments under anaerobic conditions in peptide models of the Ctr1 C-terminus to deduce Cu-binding residues, Cu affinity, and the ability to release Cu to the cytoplasmic Cu chaperone Atox1. Based on NMR assignments and bicinchoninic acid competition experiments, we demonstrate that Cu interacts in a 1:1 stoichiometry with the HCH motif with an affinity, KD, of ∼10(-14) M. Removing either the Cys residue or the two His residues lowers the Cu-peptide affinity, but site specificity is retained. The C-terminal peptide and Atox1 do not interact in solution in the absence of Cu. However, as directly demonstrated at the residue level via NMR spectroscopy, Atox1 readily acquires Cu from the Cu-loaded peptide. We propose that Cu binding to the Ctr1 C-terminal tail regulates Cu transport into the cytoplasm such that the metal ion is only released to high-affinity Cu chaperones.

Unresolved questions in human copper pump mechanisms

Copper (Cu) is an essential transition metal providing activity to key enzymes in the human body. To regulate the levels and avoid toxicity, cells have developed elaborate systems for loading these enzymes with Cu. Most Cu-dependent enzymes obtain the metal from the membrane-bound Cu pumps ATP7A/B in the Golgi network. ATP7A/B receives Cu from the cytoplasmic Cu chaperone Atox1 that acts as the cytoplasmic shuttle between the cell membrane Cu importer, Ctr1 and ATP7A/B. Biological, genetic and structural efforts have provided a tremendous amount of information for how the proteins in this pathway work. Nonetheless, basic mechanistic-biophysical questions (such as how and where ATP7A/B receives Cu, how ATP7A/B conformational changes and domain-domain interactions facilitate Cu movement through the membrane, and, finally, how target polypeptides are loaded with Cu in the Golgi) remain elusive. In this perspective, unresolved inquiries regarding ATP7A/B mechanism will be highlighted. The answers are important from a fundamental view, since mechanistic aspects may be common to other metal transport systems, and for medical purposes, since many diseases appear related to Cu transport dysregulation.

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.

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.

A comparative study on the interactions of human copper chaperone Cox17 with anticancer organoruthenium(II) complexes and cisplatin by mass spectrometry

Herein we report investigation of the interactions between anticancer organoruthenium complexes, [(η(6)-arene)Ru(en)(Cl)]PF6 (en=ethylenediamine, arene=p-cymene (1) or biphenyl (2)), and the human copper chaperone protein Cox17 by mass spectrometry with cisplatin as a reference. The electrospray ionization mass spectrometry (ESI-MS) results indicate much weaker binding of the ruthenium complexes than that of cisplatin to apo-Cox172s-s, the functional state of Cox17. Up to tetra-platinated Cox17 adducts were identified while only mono-ruthenated and a little amount of di-ruthenated Cox17 adducts were detected even for the reactions with 10-fold excess of the Ru complexes. However, ESI-MS analysis coupled with liquid chromatography of tryptic digests of metalated proteins identified only three platination sites as Met4, Cys27 and His47 residues, possibly due to the lower abundance or facile dissociation of Pt bindings at other sites. Complexes 1 and 2 were found to bind to the same three residues with Met4 as the major site. Inductively coupled plasma mass spectrometry results revealed that ~7mol Pt binding to 1mol apo-Cox172s-s molecules, compared to only 0.17 (1) and 0.10 (2) mol Ru to 1mol apo-Cox172s-s. This is in line with the circular dichroism results that much larger unfolding extent of α-helix of apo-Cox172s-s was observed upon cisplatin binding than that upon organoruthenium bindings. These results collectively indicate that Cox17 might not participate in the action of these anticancer organoruthenium complexes, and further verify the distinct anticancer mechanism of the organoruthenium(II) complexes from cisplatin.

Copper transporters and chaperones CTR1, CTR2, ATOX1, and CCS as determinants of cisplatin sensitivity

The development of resistance to cisplatin (cDDP) is commonly accompanied by reduced drug uptake or increased efflux. Previous studies in yeast and murine embryonic fibroblasts have reported that the copper (Cu) transporters and chaperones participate in the uptake, efflux, and intracellular distribution of cDDP. However, there is conflicting data from studies in human cells. We used CRISPR-Cas9 genome editing to individually knock out the human copper transporters CTR1 and CTR2 and the copper chaperones ATOX1 and CCS. Isogenic knockout cell lines were generated in both human HEK-293T and ovarian carcinoma OVCAR8 cells. All knockout cell lines had slowed growth compared to parental cells, small changes in basal Cu levels, and varying sensitivities to Cu depending on the gene targeted. However, all of the knockouts demonstrated only modest 2 to 5-fold changes in cDDP sensitivity that did not differ from the range of sensitivities of 10 wild type clones grown from the same parental cell population. We conclude that, under basal conditions, loss of CTR1, CTR2, ATOX1, or CCS does not produce a change in cisplatin sensitivity that exceeds the variance found within the parental population, suggesting that they are not essential to the mechanism by which cDDP enters these cell lines and is transported to the nucleus.

Interactions of the organogold(III) compound Aubipyc with the copper chaperone Atox1: a joint mass spectrometry and circular dichroism investigation

The so called "copper trafficking system" in mammalian cells is primarily devoted to the regulation of copper transport and homeostasis. This system, now well characterized, consists of a few strictly interconnected proteins that assist copper entrance inside cells and then promote metal transfer and delivery to essential copper-dependent cellular proteins (Boal and Rosenzweig 2009a; Banci et al., Mol Life Sci 67:2563-2589, 2010). Yet, the "copper trafficking system" may also facilitate the entrance inside cells of non-physiological metal species such as clinically established platinum drugs. ESI and MALDI MS methods are exploited here to characterize the interactions occurring between the experimental anticancer organogold(III) drug, Aubipyc, and the copper chaperone Atox1, a key protein of the copper trafficking system. The nature of the adducts that are formed when reacting Aubipyc with Atox1 is elucidated in detail. Characterization of the Aubipyc/Atox1 system is further supported by circular dichroism experiments. Binding competitions with mercury and bismuth ions were also explored. The relevance and the biological implications of the present results are discussed.

Computational metallomics of the anticancer drug cisplatin

Cisplatin, cis-diamminedichlorido-platinum(II), is an important therapeutic tool in the struggle against different tumors, yet it is plagued with the emergence of resistance mechanisms after repeated administrations. This hampers greatly its efficacy. Overcoming resistance problems requires first and foremost an integrated and systematic understanding of the structural determinants and molecular recognition processes involving the drug and its cellular targets. Here we review a strategy that we have followed for the last few years, based on the combination of modern tools from computational chemistry with experimental biophysical methods. Using hybrid Quantum Mechanics/Molecular Mechanics (QM/MM) simulations, validated by spectroscopic experiments (including NMR, and CD), we have worked out for the first time at atomic level the structural determinants in solution of platinated cellular substrates. These include the copper homeostasis proteins Ctr1, Atox1, and ATP7A. All of these proteins have been suggested to influence the pre-target resistance mechanisms. Furthermore, coupling hybrid QM/MM simulations with classical Molecular Dynamics (MD) and free energy calculations, based on force field parameters refined by the so-called "Force Matching" procedure, we have characterized the structural modifications and the free energy landscape associated with the recognition between platinated DNA and the protein HMGB1, belonging to the chromosomal high-mobility group proteins HMGB that inhibit the repair of platinated DNA. This may alleviate issues relative to on-target resistance process. The elucidation of the mechanisms by which tumors are sensitive or refractory to cisplatin may lead to the discovery of prognostic biomarkers. The approach reviewed here could be straightforwardly extended to other metal-based drugs.

Glutathione selectively modulates the binding of platinum drugs to human copper chaperone Cox17

The copper chaperone Cox17 (cytochrome c oxidase copper chaperone) has been shown to facilitate the delivery of cisplatin to mitochondria, which contributes to the overall cytotoxicity of the drug [Zhao et al. (2014) Chem. Commun. 50: , 2667-2669]. Kinetic data indicate that Cox17 has reactivity similar to glutathione (GSH), the most abundant thiol-rich molecule in the cytoplasm. In the present study, we found that GSH significantly modulates the reaction of platinum complexes with Cox17. GSH enhances the reactivity of three anti-cancer drugs (cisplatin, carboplatin and oxaliplatin) to Cox17, but suppresses the reaction of transplatin. Surprisingly, the pre-formed cisplatin-GSH adducts are highly reactive to Cox17; over 90% platinum transfers from GSH to Cox17. On the other hand, transplatin-GSH adducts are inert to Cox17. These different effects are consistent with the drug activity of these platinum complexes. In addition, GSH attenuates the protein aggregation of Cox17 induced by platination. These results indicate that the platinum-protein interactions could be substantially influenced by the cellular environment.