The copper export pump ATP7B modulates the cellular pharmacology of carboplatin in ovarian carcinoma cells

Copper homeostasis and cuproptosis in gynecological disorders: Pathogenic insights and therapeutic implications

This review comprehensively explores the complex role of copper homeostasis in female reproductive system diseases. As an essential trace element, copper plays a crucial role in various biological functions. Its dysregulation is increasingly recognized as a pivotal factor in the pathogenesis of gynecological disorders. We investigate how copper impacts these diseases, focusing on aspects like oxidative stress, inflammatory responses, immune function, estrogen levels, and angiogenesis. The review highlights significant changes in copper levels in diseases such as cervical, ovarian, endometrial cancer, and endometriosis, underscoring their potential roles in disease mechanisms and therapeutic exploration. The recent discovery of 'cuproptosis,' a novel cell death mechanism induced by copper ions, offers a fresh molecular perspective in understanding these diseases. The review also examines genes associated with cuproptosis, particularly those related to drug resistance, suggesting new strategies to enhance traditional therapy effectiveness. Additionally, we critically evaluate current therapeutic approaches targeting copper homeostasis, including copper ionophores, chelators, and nanoparticles, emphasizing their emerging potential in gynecological disease treatment. This article aims to provide a comprehensive overview of copper's role in female reproductive health, setting the stage for future research to elucidate its mechanisms and develop targeted therapeutic strategies.

Cuproptosis in cancer: biological implications and therapeutic opportunities

Cuproptosis, a newly identified copper (Cu)-dependent form of cell death, stands out due to its distinct mechanism that sets it apart from other known cell death pathways. The molecular underpinnings of cuproptosis involve the binding of Cu to lipoylated enzymes in the tricarboxylic acid cycle. This interaction triggers enzyme aggregation and proteotoxic stress, culminating in cell death. The specific mechanism of cuproptosis has yet to be fully elucidated. This newly recognized form of cell death has sparked numerous investigations into its role in tumorigenesis and cancer therapy. In this review, we summarized the current knowledge on Cu metabolism and its link to cancer. Furthermore, we delineated the molecular mechanisms of cuproptosis and summarized the roles of cuproptosis-related genes in cancer. Finally, we offered a comprehensive discussion of the most recent advancements in Cu ionophores and nanoparticle delivery systems that utilize cuproptosis as a cutting-edge strategy for cancer treatment.

Establishment and Characterization of Carboplatin-Resistant Retinoblastoma Cell Lines

Carboplatin-based chemotherapy is the primary treatment option for the management of retinoblastoma, an intraocular malignant tumor observed in children. The aim of the present study was to establish carboplatin-resistant retinoblastoma cell lines to facilitate future research into the treatment of chemoresistant retinoblastoma. In total, two retinoblastoma cell lines, Y79 and SNUOT-Rb1, were treated with increasing concentrations of carboplatin to develop the carboplatin-resistant retinoblastoma cell lines (termed Y79/CBP and SNUOT-Rb1/CBP, respectively). To verify resistance to carboplatin, the degree of DNA fragmentation and the expression level of cleaved caspase-3 were evaluated in the cells, following carboplatin treatment. In addition, the newly developed carboplatin-resistant retinoblastoma cells formed in vivo intraocular tumors more effectively than their parental cells, even after the intravitreal injection of carboplatin. Interestingly, the proportion of cells in the G0/G1 phase was higher in Y79/CBP and SNUOT-Rb1/CBP cells than in their respective parental cells. In line with these data, the expression levels of cyclin D1 and cyclin D3 were decreased, whereas p18 and p27 expression was increased in the carboplatin-resistant cells. In addition, the expression levels of genes associated with multidrug resistance were increased. Thus, these carboplatin-resistant cell lines may serve as a useful tool in the study of chemoresistance in retinoblastoma and for the development potential therapeutics.

Sensitization of cancer cells towards Cisplatin and Carboplatin by protein kinase D inhibitors through modulation of ATP7A/B (copper transport ATPases)

Drug resistance of cancer cells is a significant impediment to effective chemotherapy. One primary reason for this is copper exporters - ATPase copper transporting alpha (ATP7A) and ATPase copper transporting beta (ATP7B). These molecular pumps belong to P-type ATPases and dispose off the Platinum (Pt) based anticancer drugs from cancer cells, causing resistance in them. For the disposal of Pt-drugs, copper exporters require phosphorylation mediated by protein kinase D (PKD) for their activation and trafficking. Even though various research works are underway to overcome resistance to anticancer drugs, the role of PKD is mainly ignored. In this study, we have found a significant upregulation of ATP7A and ATP7B in cervical cancer cells (HeLa) and Liver Hepatocellular Carcinoma cells (HepG2) in the presence of Cisplatin or Carboplatin; both at transcriptional as well as translational levels. Interestingly, the expression of ATP7A and ATP7B were significantly downregulated in the presence of a PKD inhibitor (CID2011756), resulting in the reduction of PKD mediated phosphorylation of ATP7A/7B. This causes enhancement of proteasome-mediated degradation of ATP7A/7B and thereby sensitizes the cells towards Cisplatin and Carboplatin. Similarly, the treatment of Cisplatin resistant HepG2 cells with PKD inhibitor causes enhanced sensitivity towards Cisplatin drug. However, the presence of proteasome inhibitor (MG132) reversed the effect of the PKD inhibitor on the expression level of ATP7A/7B, indicating the necessity of phosphorylation for its stability. Hence, we conclude that the combinatorial usage of Cisplatin with drugs targeting PKD can be developed as an effective chemotherapeutic approach to overcome drug resistance.

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.

Altered cisplatin pharmacokinetics during nonalcoholic steatohepatitis contributes to reduced nephrotoxicity

Disease-mediated alterations to drug disposition constitute a significant source of adverse drug reactions. Cisplatin (CDDP) elicits nephrotoxicity due to exposure in proximal tubule cells during renal secretion. Alterations to renal drug transporter expression have been discovered during nonalcoholic steatohepatitis (NASH), however, associated changes to substrate toxicity is unknown. To test this, a methionine- and choline-deficient diet-induced rat model was used to evaluate NASH-associated changes to CDDP pharmacokinetics, transporter expression, and toxicity. NASH rats administered CDDP (6 mg/kg, i.p.) displayed 20% less nephrotoxicity than healthy rats. Likewise, CDDP renal clearance decreased in NASH rats from 7.39 to 3.83 mL/min, renal secretion decreased from 6.23 to 2.80 mL/min, and renal CDDP accumulation decreased by 15%, relative to healthy rats. Renal copper transporter-1 expression decreased, and organic cation transporter-2 and ATPase copper transporting protein-7b increased slightly, reducing CDDP secretion. Hepatic CDDP accumulation increased 250% in NASH rats relative to healthy rats. Hepatic organic cation transporter-1 induction and multidrug and toxin extrusion protein-1 and multidrug resistance-associated protein-4 reduction may contribute to hepatic CDDP sequestration in NASH rats, although no drug-related toxicity was observed. These data provide a link between NASH-induced hepatic and renal transporter expression changes and CDDP renal clearance, which may alter nephrotoxicity.

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.

Advances in Our Understanding of the Molecular Mechanisms of Action of Cisplatin in Cancer Therapy

Cisplatin and other platinum-based chemotherapeutic drugs have been used extensively for the treatment of human cancers such as bladder, blood, breast, cervical, esophageal, head and neck, lung, ovarian, testicular cancers, and sarcoma. Cisplatin is commonly administered intravenously as a first-line chemotherapy for patients suffering from various malignancies. Upon absorption into the cancer cell, cisplatin interacts with cellular macromolecules and exerts its cytotoxic effects through a series of biochemical mechanisms by binding to Deoxyribonucleic acid (DNA) and forming intra-strand DNA adducts leading to the inhibition of DNA synthesis and cell growth. Its primary molecular mechanism of action has been associated with the induction of both intrinsic and extrinsic pathways of apoptosis resulting from the production of reactive oxygen species through lipid peroxidation, activation of various signal transduction pathways, induction of p53 signaling and cell cycle arrest, upregulation of pro-apoptotic genes/proteins, and down-regulation of proto-oncogenes and anti-apoptotic genes/proteins. Despite great clinical outcomes, many studies have reported substantial side effects associated with cisplatin monotherapy, while others have shown substantial drug resistance in some cancer patients. Hence, new formulations and several combinational therapies with other drugs have been tested for the purpose of improving the clinical utility of cisplatin. Therefore, this review provides a comprehensive understanding of its molecular mechanisms of action in cancer therapy and discusses the therapeutic approaches to overcome cisplatin resistance and side effects.

Phase I study of metformin in combination with carboplatin/paclitaxel chemotherapy in patients with advanced epithelial ovarian cancer

Background Metformin use is associated with reduced cancer risk in epidemiological studies and has preclinical anti-cancer activity in ovarian cancer models. The primary objective of this phase I study was to determine the recommended phase II dose (RP2D) of metformin in combination with carboplatin/paclitaxel in patients with ovarian cancer. Secondary objectives were to describe safety and pharmacokinetics. Methods In this single-center trial the RP2D of metformin in combination with carboplatin area under the concentration-time curve (AUC) 6 and paclitaxel 175 mg/m2 every 3 weeks (q3w) in patients with advanced epithelial ovarian cancer was determined using a 3 + 3 escalation rule at three fixed dose levels: 500 mg three times daily (tds), 850 mg tds and 1000 mg tds. Metformin was commenced on day 3 of cycle 1 and continued until 3 weeks after the last chemotherapy administration. The RP2D was defined as the dose level at which 0 of 3 or ≤ 1 of 6 evaluable subjects experienced a metformin-related dose-limiting toxicity (DLT). Safety was assessed according to CTCAE v4.0. Plasma and serum samples for pharmacokinetic (PK) analyses were collected during treatment cycles 1 and 2. Results Fifteen patients with epithelial ovarian cancer and an indication for neo-adjuvant (n = 5) or palliative (n = 10) treatment were included. No DLTs were observed. Three patients discontinued study treatment during cycle 1 for other reasons than DLT. Six patients were treated at the RP2D of metformin 1000 mg tds. The most frequent low-grade toxicities were anemia, hypomagnesemia and diarrhea. Grade 3 adverse events (AEs) occurred in ten patients, most common were leucopenia (n = 4), thrombocytopenia (n = 3) and increased GGT (n = 3). There were no grade 4 AEs. Metformin increased the platinum (Pt) AUC (Δ22%, p = 0.013) and decreased the Pt clearance (Δ-28%, p = 0.013). Metformin plasma levels were all within the therapeutic range for diabetic patients (0.1-4 mg/L). Conclusion The RP2D of metformin in combination with carboplatin and paclitaxel in advanced ovarian cancer is 1000 mg tds. This is higher than the RP2D reported for combination with targeted agents. A potential PK interaction of metformin with carboplatin was identified.

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.

Synthetic Lethality Screening Identifies FDA-Approved Drugs that Overcome ATP7B-Mediated Tolerance of Tumor Cells to Cisplatin

Tumor resistance to chemotherapy represents an important challenge in modern oncology. Although platinum (Pt)-based drugs have demonstrated excellent therapeutic potential, their effectiveness in a wide range of tumors is limited by the development of resistance mechanisms. One of these mechanisms includes increased cisplatin sequestration/efflux by the copper-transporting ATPase, ATP7B. However, targeting ATP7B to reduce Pt tolerance in tumors could represent a serious risk because suppression of ATP7B might compromise copper homeostasis, as happens in Wilson disease. To circumvent ATP7B-mediated Pt tolerance we employed a high-throughput screen (HTS) of an FDA/EMA-approved drug library to detect safe therapeutic molecules that promote cisplatin toxicity in the IGROV-CP20 ovarian carcinoma cells, whose resistance significantly relies on ATP7B. Using a synthetic lethality approach, we identified and validated three hits (Tranilast, Telmisartan, and Amphotericin B) that reduced cisplatin resistance. All three drugs induced Pt-mediated DNA damage and inhibited either expression or trafficking of ATP7B in a tumor-specific manner. Global transcriptome analyses showed that Tranilast and Amphotericin B affect expression of genes operating in several pathways that confer tolerance to cisplatin. In the case of Tranilast, these comprised key Pt-transporting proteins, including ATOX1, whose suppression affected ability of ATP7B to traffic in response to cisplatin. In summary, our findings reveal Tranilast, Telmisartan, and Amphotericin B as effective drugs that selectively promote cisplatin toxicity in Pt-resistant ovarian cancer cells and underscore the efficiency of HTS strategy for identification of biosafe compounds, which might be rapidly repurposed to overcome resistance of tumors to Pt-based chemotherapy.

ATP7B Binds Ruthenium(II) p-Cymene Half-Sandwich Complexes: Role of Steric Hindrance and Ru-I Coordination in Rescuing the Sequestration

Ruthenium(II/III) complexes are predicted to be efficient alternatives to platinum drug-resistant cancers but have never been investigated for sequestration and efflux by Cu-ATPases (ATP7A or ATP7B) overexpressed in resistant cancer cells, although a major cause of platinum drug resistance is found to be sequestration of platinum chemotherapeutic agents by thiol donors glutathione (GSH) or the Cys-X-X-Cys (CXXC) motifs in the Cu-ATPases in cytosol. Here, we show for the first time that ATP7B efficiently sequesters ruthenium(II) η⁶-p-cymene complexes. We present seven complexes, [Ru^II(η⁶-p-cym)(L)X](PF₆) (1-7; L = L1-L3, X = Cl, Br, and I), out of which two resists deactivation by the cellular thiol, glutathione (GSH). The results show that Ru-I coordination and a moderate steric factor increase resistance to GSH and the CXXC motif. Ru^II-I-coordinated 3 and 7 showed resistance to sequestration by ATP7B. 3 displays highest resistance against GSH and does not trigger ATP7B trafficking in the liver cancer cell line. It escapes ATP7B-mediated sequestration and triggers apoptosis. Thus, with a suitable bidentate ligand and iodido leaving group, Ru^II(η⁶-p-cym) complexes may display strong kinetic inertness to inhibit the ATP7B detoxification pathway. Inductively coupled plasma mass spectrometry data show higher retention of 3 and 7 inside the cell with time compared to 4, supporting ATP7B-mediated sequestration.

Gene expression and single nucleotide polymorphism of ATP7B are associated with platinum-based chemotherapy response in non-small cell lung cancer patients

Objectives: Platinum-based chemotherapy is first-line treatment for non-small cell lung cancer (NSCLC) patients. The efficacy is limited by drug resistance. Recent studies suggest that ATP7B, a copper efflux transporter, may be involved in platinum resistance. However, the clinical significance of ATP7B expression in NSCLC is controversial. Moreover, the effects of single nucleotide polymorphisms (SNPs) in ATP7B gene on the response to platinum-based chemotherapy are scarcely understood. The aim of our study is to evaluate the clinical value of ATP7B in NSCLC patients and explore the interrelationships between ATP7B SNPs and protein expression, and their association with chemotherapy response.

Materials and Methods: A total of 247 NSCLC patients were recruited in this study. Among them, 158 patients who received platinum-based chemotherapy were used to explore the interrelationships between ATP7B SNPs, protein expression and chemotherapy response, while 89 patients who underwent surgical resection were used to further investigate the association between ATP7B SNPs and expression level. We genotyped 15 SNPs of ATP7B by Sequenom MassARRAY and determined ATP7B protein levels by immunohistochemistry.

Results: Patients with ATP7B-negative tumors had improved chemotherapeutic response (p=0.025) and better overall survival (p=0.044) compared with the patients with ATP7B-positive tumors. The multivariate Cox regression analysis revealed that ATP7B expression was an independent prognostic factor (HR=0.639, 95%CI=0.424-0.962, p=0.032). Moreover, we found that the rs9526814 GG genotype was significantly associated with favorable response to platinum-based chemotherapy when compared with TT+TG genotypes (OR=0.362, 95CI%=0.140-0.935, p=0.036). Mechanistically, rs9526814 GG genotype showed a strong trend towards reduced expression level of ATP7B compared with the TT+TG genotypes (p= 0.048).

Conclusion: Our findings indicate that ATP7B rs9526814 may contribute to platinum resistance by influencing ATP7B gene expression and can be used as a potential biomarker to predict the sensitivity of platinum-based chemotherapy in NSCLC patients.

Desferal regulates hCtr1 and transferrin receptor expression through Sp1 and exhibits synergistic cytotoxicity with platinum drugs in oxaliplatin-resistant human cervical cancer cells in vitro and in vivo

The development of resistance to platinum drugs in cancer cells severely reduces the efficacy of these drugs. Thus, the discovery of novel drugs or combined strategies to overcome drug resistance is imperative. In addition to our previous finding that combined D-penicillamine with platinum drugs exerts synergistic cytotoxicity, we recently identified a novel therapeutic strategy by combining an iron chelating agent desferal with platinum drugs to overcome platinum resistance in an oxaliplatin-resistant human cervical cancer cell line, S3. Further study demonstrated that the level of platinum–DNA adduct formation positively correlated with cell death in combination of desferal with platinums than that of each drug alone in S3 cells. Decrement of human copper transporter 1 (hCtr1) and transferrin receptor 1 (TfR1) expression involved in the development of platinum resistance in S3 cells. Moreover, desferal promoted the expression of hCtr1 through the upregulation of Sp1. The overexpression of Sp1 increased the expression of NF-κB and translocated it into the nucleus to bind to the TfR1 promoter region, which subsequently increased the expression of TfR1. Importantly, the cotreatment of oxaliplatin with desferal significantly potentiated the oxaliplatin-elicited antitumoral effect in the oxaliplatin-resistant xenograft animal model without any toxic effect observed. Taken together, these results demonstrated that the combination of desferal with oxaliplatin can overcome oxaliplatin resistance through the regulation of hCtr1 and TfR1, and may have beneficial effect for treatment of patient with oxaliplatin-refractory tumors.

Copper efflux transporters ATP7A and ATP7B: Novel biomarkers for platinum drug resistance and targets for therapy

Platinum-based chemotherapy agents are widely used in the treatment of various solid malignancies. However, their efficacy is limited by drug resistance. Recent studies suggest that copper efflux transporters, which are encoded by ATP7A and ATP7B, play an important role in platinum drug resistance. Over-expressions of ATP7A and ATP7B are observed in multiple cancers. Moreover, their expressions are associated with cancer prognosis and treatment outcomes of platinum-based chemotherapy. In our review, we highlight the roles of ATP7A/7B in platinum drug resistance and cancer progression. We also discuss the possible mechanisms of platinum drug resistance mediated by ATP7A/7B and provide novel strategies for overcoming resistance. This review may be helpful for understanding the roles of ATP7A and ATP7B in platinum drug resistance. © 2018 IUBMB Life, 70(3):183-191, 2018.

Organic cation transporter 3 mediates cisplatin and copper cross-resistance in hepatoma cells

Platinum-based drugs are first-line compounds in the treatment of many solid cancers. Major obstacles are tumors that become resistant and toxic side effects, both largely due to the expression of transporters that mediate the cellular processing of platinum. In this study, we addressed the establishment of cisplatin resistance in the absence of copper transporter ATP7B that has been previously found to be overexpressed in various resistant cells. Cisplatin sensitivity, induction of apoptosis, drug accumulation, and transporter gene expression were determined in hepatoma cell lines. Knockout or overexpression of copper transporter ATP7B did not affect cisplatin sensitivity. Cisplatin resistant cells showed a stably reduced cisplatin accumulation and a downregulation of organic cation transporter 3 (OCT3). In contrast, OCT3 overexpression could reverse resistance. Reduced MT1 expression was detected in the resistant cell line, however transient and highly dependent on the presence of cisplatin. Cross-resistance to copper was also associated with OCT3 downregulation. Our results suggest that a decreased level of OCT3 expression results in resistance to cisplatin and copper. OCT3 may represent a novel target for improved prognosis and anticancer therapy, including HCC.

The role of copper transporter ATP7A in platinum-resistance of esophageal squamous cell cancer (ESCC)

Purpose: Platinum derivatives, such as cisplatin (DDP), carboplatin and oxaliplatin, are widely used components of modern cancer chemotherapy including esophageal squamous cell cancer (ESCC). However, their roles are limited by the impact of intrinsic/acquired resistance mechanisms on tumor responses. Recent studies have shown that the mammalian copper transporters CTR1, ATP7A and ATP7B are involved in cisplatin-resistance to some cancers.

Methods: The cytotoxicities of DDP in different cell lines were determined using the MTT assay. To determine whether knockdown the expression of ATP7A could reverse the platinum-resistance of EC109/DDP cells or not, we used RNA interference system to explore the role of ATP7A in platinum resistance.

Results: We found that DDP-resistant cell sublines EC109/DDP (8.490 folds) showed cross-resistance to carboplatin (5.27 folds) and oxaliplatin (4.12 folds). ATP7A expressions in DDP-resistant cell sublines (EC109/DDP) were much higher than DDP-sensitive cell lines (EC109) at both mRNA and protein levels. ATP7A targeted small interfering RNA duplex at 100nM final concentration added into DDP-resistant cancer cells (EC109/DDP) markedly inhibited the expression of ATP7A as determined by Western blot (83.0%) and partially reversed DDP-resistance (37.09%), moreover, it also increased cell apoptosis at different DDP concentrations. Conclusions: These findings indicate that ATP7A high expression plays an important role in platinum-resistance of ESCC. This study sheds light on platinum resistance in ESCC patients and may have implications for therapeutic reversal of drug resistance.

Multi-scale imaging of anticancer platinum(iv) compounds in murine tumor and kidney

Nano-scale secondary ion mass spectrometry (NanoSIMS) enables trace element and isotope analyses with high spatial resolution. This unique capability has recently been exploited in several studies analyzing the subcellular distribution of Au and Pt anticancer compounds. However, these studies were restricted to cell culture systems. To explore the applicability to the in vivo setting, we developed a combined imaging approach consisting of laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), NanoSIMS and transmission electron microscopy (TEM) suitable for multi-scale detection of the platinum distribution in tissues. Applying this approach to kidney and tumor samples upon administration of selected platinum(iv) anticancer prodrugs revealed uneven platinum distributions on both the organ and subcellular scales. Spatial platinum accumulation patterns were quantitatively assessed by LA-ICP-MS in histologically heterogeneous organs (e.g., higher platinum accumulation in kidney cortex than in medulla) and used to select regions of interest for subcellular-scale imaging with NanoSIMS. These analyses revealed cytoplasmic sulfur-rich organelles accumulating platinum in both kidney and malignant cells. Those in the tumor were subsequently identified as organelles of lysosomal origin, demonstrating the potential of the combinatorial approach for investigating therapeutically relevant drug concentrations on a submicrometer scale.

Gene expression of membrane transporters: Importance for prognosis and progression of ovarian carcinoma

Membrane transporters (such as ABCs, SLCs and ATPases) act in carcinogenesis and chemoresistance development, but their relevance for prognosis of epithelial ovarian cancer (EOC) remains poorly understood. We evaluated the gene expression profile of 39 ABC and 12 SLC transporters and three ATPases in EOC tissues and addressed their putative role in prognosis and clinical course of EOC patients. Relative gene expression in a set of primary EOC (n=57) and in control ovarian tissues (n=14) was estimated and compared with clinical data and survival of patients. Obtained data were validated in an independent set of patients (n=60). Six ABCs and SLC22A18 gene were significantly overexpressed in carcinomas when compared with controls, while expression of 12 ABCs, five SLCs, ATP7A and ATP11B was decreased. Expression of ABCA12, ABCC3, ABCC6, ABCD3, ABCG1 and SLC22A5 was higher in high grade serous carcinoma compared with other subtypes. ABCA2 gene expression significantly associated with EOC grade in both sets of patients. Notably, expression level of ABCA9, ABCA10, ABCC9 and SLC16A14 significantly associated with progression-free survival (PFS) of the disease in either pilot or validation sets. ABCG2 level associated with PFS in the pooled set of patients. In conclusion, ABCA2, ABCA9, ABCA10, ABCC9, ABCG2 and SLC16A14 present novel putative markers of EOC progression and together with the revealed relationship between ABCA12, ABCC3, ABCC6, ABCD3, ABCG1 and SLC22A5 expression, and high grade serous type of EOC should be further examined by larger follow-up study.

Cisplatin-Induced Ototoxicity: Effects, Mechanisms and Protection Strategies

Cisplatin is a highly effective chemotherapeutic agent that is widely used to treat solid organ malignancies. However, serious side effects have been associated with its use, such as bilateral, progressive, irreversible, dose-dependent neurosensory hearing loss. Current evidence indicates that cisplatin triggers the production of reactive oxygen species in target tissues in the inner ear. A variety of agents that protect against cisplatin-induced ototoxicity have been successfully tested in cell culture and animal models. However, many of them interfere with the therapeutic effect of cisplatin, and therefore are not suitable for systemic administration in clinical practice. Consequently, local administration strategies, namely intratympanic administration, have been developed to achieve otoprotection, without reducing the antitumoral effect of cisplatin. While a considerable amount of pre-clinical information is available, clinical data on treatments to prevent cisplatin ototoxicity are only just beginning to appear. This review summarizes clinical and experimental studies of cisplatin ototoxicity, and focuses on understanding its toxicity mechanisms, clinical repercussions and prevention strategies.

Role of transporters in the distribution of platinum-based drugs

Platinum derivatives used as chemotherapeutic drugs such as cisplatin and oxaliplatin have a potent antitumor activity. However, severe side effects such as nephro-, oto-, and neurotoxicity are associated with their use. Effects and side effects of platinum-based drugs are in part caused by their transporter-mediated uptake in target and non target cells. In this mini review, the transport systems involved in cellular handling of platinum derivatives are illustrated, focusing on transporters for cisplatin. The copper transporter 1 seems to be of particular importance for cisplatin uptake in tumor cells, while the organic cation transporter (OCT) 2, due to its specific organ distribution, may play a major role in the development of undesired cisplatin side effects. In polarized cells, e.g., in renal proximal tubule cells, apically expressed transporters, such as multidrug and toxin extrusion protein 1, mediate secretion of cisplatin and in this way contribute to the control of its toxic effects. Specific inhibition of cisplatin uptake transporters such as the OCTs may be an attractive therapeutic option to reduce its toxicity, without impairing its antitumor efficacy.

The Hippo pathway transcriptional co-activator, YAP, confers resistance to cisplatin in human oral squamous cell carcinoma

Cisplatin (CDDP) is widely used to treat oral squamous cell carcinoma (OSCC), however, many patients exhibit acquired drug resistance. Yes-associated protein (YAP) is a transcriptional co-activator of the Hippo pathway that regulates organ size and promotes cell proliferation. YAP overexpression correlates with epithelial-mesenchymal transition and nodal metastasis, resulting in anti-tubulin drug resistance. Whether YAP overexpression is the cause of CDDP resistance in cancer cells is unclear, therefore, we investigated the correlation between YAP expression and CDDP sensitivity. We established three CDDP-resistant cell lines (OSC-19-R, SCCKN-R and HSC-3-R) from the OSCC parental cell lines. We also examined the expression levels of ATP7B, GST-π and ERCC1, which are strongly associated with CDDP resistance, and Hippo pathway-related proteins by western blotting. Using immunocytochemistry, we examined the cellular localization of YAP. Additionally, following knockdown of YAP using short interfering RNAs (siRNAs), we analyzed changes in sensitivity to CDDP. Compared with parental OSC-19 cells, OSC-19-R cells were obviously larger. Expression levels of YAP were not significantly different between OSC-19 and OSC-19-R. However, expression levels of phosphorylated YAP in OSC-19-R were decreased. We observed translocation of YAP from the cytoplasm to the nucleus in OSC-19-R cells. Knockdown of YAP using siRNAs revealed that sensitivity to CDDP was significantly increased. Translocation of YAP correlated with the acquisition of CDDP resistance. YAP could be a new therapeutic target for the treatment of patients with cancer that are resistant to CDDP.

Mechanistic basis of a combination D-penicillamine and platinum drugs synergistically inhibits tumor growth in oxaliplatin-resistant human cervical cancer cells in vitro and in vivo

The platinum-based regimen is the front-line treatment of chemotherapy. However, development of platinum resistance often causes therapeutic failure in this disease. We previously have generated an oxaliplatin-resistant subline, named S3, from human cervical carcinoma SiHa cells, and its resistant phenotype was well-characterized. In the present study, we aimed to identify the novel therapeutic strategy by combining copper chelator D-penicillamine with oxaliplatin, and to elucidate the underlying mechanisms for overcoming oxaliplatin resistance. As the result, D-penicillamine exerted synergistic killing effects only in S3 cells when combined with oxaliplatin and cisplatin by using Chou-Talalay method. Further study showed that the amounts of platinum DNA adduct formed were positively correlated to the percentage of cell death in S3 cells when co-treated D-penicillamine with oxaliplatin and cisplatin. D-penicillamine promoted copper influx transporter hCtr1 expression through upregulation of Sp1. Sp1 overexpression induced p53 translocation from nucleus to cytosol and caused p53 degradation through ubiquitination, which subsequently suppressed the expression of the copper efflux transporter ATP7A. Importantly, co-treatment of cisplatin with D-penicillamine enhanced oxaliplatin-elicited antitumor effect in the oxalipatin-resistant S3 xenograft tumors, but not found in SiHa xenograft model. Notably, Mice received D-penicillamine alone or in combination of D-penicillamine ad oxalipatin, increased hCtrl protein level in S3 xenograft tumor, however, the protein level of ATP7A was decreased. Taken together, this study provides insight into that the co-manipulation of hCtrl and ATP7A by D-penicillamine could increase the therapeutic efficacy of platinum drugs in oxaliplatin resistant tumors, especially in resistant phenotype with downexpression of hCtrl and overexpression of ATP7A.

Carboplatin: molecular mechanisms of action associated with chemoresistance

Carboplatin is a derivative of cisplatin; it has a similar mechanism of action, but differs in terms of structure and toxicity. It was approved by the FDA in the 1980s and since then it has been widely used in the treatment of several tumor types. This agent is characterized by its ability to generate lesions in DNA through the formation of adducts with platinum, thereby inhibiting replication and transcription and leading to cell death. However, its use can lead to serious inconvenience arising from the development of resistance that some patients acquire during treatment, limiting the scope of its full potential. Currently, the biochemical mechanisms related to resistance are not precisely known. Therefore, knowledge of pathways associated with resistance caused by carboplatin exposure may provide valuable clues for more efficient rational drug design in platinum-based therapy and the development of new therapeutic strategies. In this narrative review, we discuss some of the known mechanisms of resistance to platinum-based drugs, especially carboplatin.

Biochemical characterization of P-type copper ATPases

Copper ATPases, in analogy with other members of the P-ATPase superfamily, contain a catalytic headpiece including an aspartate residue reacting with ATP to form a phosphoenzyme intermediate, and transmembrane helices containing cation-binding sites [TMBS (transmembrane metal-binding sites)] for catalytic activation and cation translocation. Following phosphoenzyme formation by utilization of ATP, bound copper undergoes displacement from the TMBS to the lumenal membrane surface, with no H⁺ exchange. Although PII-type ATPases sustain active transport of alkali/alkali-earth ions (i.e. Na⁺, Ca²⁺) against electrochemical gradients across defined membranes, PIB-type ATPases transfer transition metal ions (i.e. Cu⁺) from delivery to acceptor proteins and, prominently in mammalian cells, undergo trafficking from/to various membrane compartments. A specific component of copper ATPases is the NMBD (N-terminal metal-binding domain), containing up to six copper-binding sites in mammalian (ATP7A and ATP7B) enzymes. Copper occupancy of NMBD sites and interaction with the ATPase headpiece are required for catalytic activation. Furthermore, in the presence of copper, the NMBD allows interaction with protein kinase D, yielding phosphorylation of serine residues, ATP7B trafficking and protection from proteasome degradation. A specific feature of ATP7A is glycosylation and stabilization on plasma membranes. Cisplatin, a platinum-containing anti-cancer drug, binds to copper sites of ATP7A and ATP7B, and undergoes vectorial displacement in analogy with copper.

Cellular transport mechanisms of cytotoxic metallodrugs: an overview beyond cisplatin

The field of medicinal inorganic chemistry has grown consistently during the past 50 years; however, metal-containing coordination compounds represent only a minor proportion of drugs currently on the market, indicating that research in this area has not yet been thoroughly realized. Although platinum-based drugs as cancer chemotherapeutic agents have been widely studied, exact knowledge of the mechanisms governing their accumulation in cells is still lacking. However, evidence suggests active uptake and efflux mechanisms are involved; this may be involved also in other experimental metal coordination and organometallic compounds with promising antitumor activities in vitro and in vivo, such as ruthenium and gold compounds. Such knowledge would be necessary to elucidate the balance between activity and toxicity profiles of metal compounds. In this review, we present an overview of the information available on the cellular accumulation of Pt compounds from in vitro, in vivo and clinical studies, as well as a summary of reports on the possible accumulation mechanisms for different families of experimental anticancer metal complexes (e.g., Ru Au and Ir). Finally, we discuss the need for rationalization of the investigational approaches available to study metallodrug cellular transport.

The ATP7B genetic polymorphisms predict clinical outcome to platinum-based chemotherapy in lung cancer patients

This study aims to investigate the influence of ATP7B genetic polymorphism to platinum-based chemotherapy in Chinese Han lung cancer patients. A total of 338 Chinese Han lung cancer patients were enrolled in this study. All patients underwent at least two cycles of platinum-based chemotherapy. Four tag SNPs of ATP7B (rs1061472, rs9535826, rs7999812, and rs9535828) were selected to evaluate their impacts to platinum-based chemotherapy in these patients. ATP7B rs9535828 and rs9535826 were found to be associated with platinum resistance in Chinese Han lung cancer patients. Patients with A allele in ATP7B rs9535828 presented an increased susceptibility to platinum drugs (OR 1.96, 95 % CI 1.17-3.30, p < 0.01). Patients with G allele in ATP7B rs9535826 had the highest susceptibility to platinum drugs (OR 2.05, 95 % CI 1.19-3.52, p < 0.01). Our findings suggest that ATP7B genetic polymorphisms could affect the therapeutic efficacy of platinum-based chemotherapy, and ATP7B gene might be considered as predictive markers for the efficacy evaluation of platinum-based chemotherapy in Chinese Han lung cancer patients.

The role of metal binding and phosphorylation domains in the regulation of cisplatin-induced trafficking of ATP7B

The copper (Cu) exporter ATP7B mediates cellular resistance to cisplatin (cDDP) by increasing drug efflux. ATP7B binds and sequesters cDDP in into secretory vesicles. Upon cDDP exposure ATP7B traffics from the trans-Golgi network (TGN) to the periphery of the cell in a manner that requires the cysteine residues in its metal binding domains (MBD). To elucidate the role of the various domains of ATP7B in its cDDP-induced trafficking we expressed a series of mCherry-tagged variants of ATP7B in HEK293T cells and analyzed their subcellular localization in basal media and after a 1 h exposure to 30 μM cDDP. The wild type ATP7B and a variant in which the cysteines in the CXXC motifs of MBD 1-5 were converted to serines trafficked out of the trans-Golgi (TGN) when exposed to cDDP. Conversion of the cysteines in all 6 of the CXXC motifs to serines, or in only the sixth MBD, rendered ATP7B incapable of trafficking on exposure to cDDP. Truncation of MBD1-5 or MBD1-6 resulted in the loss of TGN localization. Addition of the first 63 amino acids of ATP7B to these variants restored TGN localization to a great extent and enabled the MBD1-5 variant to undergo cDDP-induced trafficking. A variant of ATP7B in which the aspartate 1027 residue in the phosphorylation domain was converted to glutamine localized to the TGN but was incapable of cDDP-induced trafficking. These results demonstrate that the CXXC motif in the sixth MBD and the catalytic activity of ATP7B are required for cDDP-induced trafficking as they are for Cu-induced redistribution of ATP7B; this provides further evidence that cDDP mimics Cu with respect to the molecular mechanisms by they control the subcellular distribution of ATP7B.

Nanocarriers for delivery of platinum anticancer drugs

Platinum based anticancer drugs have revolutionized cancer chemotherapy, and continue to be in widespread clinical use especially for management of tumors of the ovary, testes, and the head and neck. However, several dose limiting toxicities associated with platinum drug use, partial anti-tumor response in most patients, development of drug resistance, tumor relapse, and many other challenges have severely limited the patient quality of life. These limitations have motivated an extensive research effort towards development of new strategies for improving platinum therapy. Nanocarrier-based delivery of platinum compounds is one such area of intense research effort beginning to provide encouraging preclinical and clinical results and may allow the development of the next generation of platinum chemotherapy. This review highlights current understanding on the pharmacology and limitations of platinum compounds in clinical use, and provides a comprehensive analysis of various platinum-polymer complexes, micelles, dendrimers, liposomes and other nanoparticles currently under investigation for delivery of platinum drugs.

Endoplasmic reticulum stress is involved in the response of human laryngeal carcinoma cells to Carboplatin but is absent in Carboplatin-resistant cells

The major obstacle of successful tumor treatment with carboplatin (CBP) is the development of drug resistance. In the present study, we found that following treatment with CBP the amount of platinum which enters the human laryngeal carcinoma (HEp2)-derived CBP-resistant (7T) cells is reduced relative to the parental HEp2. As a consequence, the formation of reactive oxidative species (ROS) is reduced, the induction of endoplasmic reticulum (ER) stress is diminished, the amount of inter- and intrastrand cross-links is lower, and the induction of apoptosis is depressed. In HEp2 cells, ROS scavenger tempol, inhibitor of ER stress salubrinal, as well as gene silencing of ER stress marker CCAAT/enhancer-binding protein (CHOP) increases their survival and renders them as resistant to CBP as 7T cell subline but did not influence the survival of 7T cells. Our results suggest that in HEp2 cells CBP-induced ROS is a stimulus for ER stress. To the contrary, despite the ability of CBP to induce formation of ROS and activate ER stress in 7T cells, the cell death mechanism in 7T cells is independent of ROS induction and activation of ER stress. The novel signaling pathway of CBP-driven toxicity that was found in the HEp2 cell line, i.e. increased ROS formation and induction of ER stress, may be predictive for therapeutic response of epithelial cancer cells to CBP-based therapy.

Is ATP7B a predictive marker in patients with ovarian carcinoma treated with platinum-taxane combination chemotherapy?

OBJECTIVE

This study examined the prognostic significance of copper-transporting P-type adenosine triphosphatase (ATP7B) expression in patients with ovarian carcinoma treated with platinum-taxane combination chemotherapy.

METHODS

Expression of ATP7B in ovarian carcinoma was assessed by immunohistochemistry and clinical data collected by retrospective review of medical charts.

RESULTS

Overexpression of ATP7B was identified in 25 (29.1%) of 86 ovarian carcinomas. The frequency of ATP7B expression in clear cell carcinomas was significantly higher than that in serous high-grade carcinomas (P < 0.05). We observed no statistically significant correlations between high ATP7B protein expression and either disease-free survival (P = 0.722) or overall survival (P = 0.389).

CONCLUSIONS

Our study is the first to demonstrate a lack of statistically significant differences between ATP7B positive and negative cases with respect to prognosis of patients with ovarian carcinoma treated with a platinum-taxane combination regimen. However, that ATP7B expression in clear cell carcinomas was significantly higher than that in serous carcinomas may partially explain the difference in chemotherapeutic response and prognosis between patients with these 2 types of carcinomas.

Comparison of 18F-fluoroazomycin-arabinofuranoside and 64Cu-diacetyl-bis(N4-methylthiosemicarbazone) in preclinical models of cancer

Hypoxic regions are present in different types of cancer and are a negative prognostic factor for disease progression and response to therapy. (18)F-fluoroazomycin-arabinofuranoside ((18)F-FAZA) and (64)Cu-diacetyl-bis(N4-methylthiosemicarbazone) ((64)Cu-ATSM) have been widely used to visualize hypoxic regions in preclinical and clinical studies. Although both these radioligands have high signal-to-noise ratios, (64)Cu-ATSM may be suitable for use in in vivo imaging and as a radiotherapeutic agent. Despite encouraging results suggesting that it may have a role as a prognostic tracer, (64)Cu-ATSM was recently shown to display cell line-dependent kinetics of oxygen-dependent uptake. We set out to evaluate the kinetics of (64)Cu-ATSM distribution in different cancer models, using (18)F-FAZA as the gold standard.

METHODS

(18)F-FAZA and (64)Cu-ATSM uptake were compared ex vivo using dual-tracer autoradiography and in vivo using PET in different xenograft mouse models (FaDu, EMT-6, and PC-3). (18)F-FAZA uptake was compared with (64)Cu-ATSM uptake in PET studies acquired at early (2 h after injection) and delayed time points (24 h after injection). To evaluate the presence of hypoxia and copper pumps, the tumors from animals submitted to PET were harvested and analyzed by an immunohistochemical technique, using antibodies against carbonic anhydrase IX (CAIX) and copper pumps (Ctr1 and ATP7B).

RESULTS

(64)Cu-ATSM showed a higher tumor-to-muscle ratio than did (18)F-FAZA. In the FaDu mouse model, radioactivity distribution profiles were overlapping irrespective of the hypoxic agent injected or the time of (64)Cu acquisition. Conversely, in the EMT-6 and PC-3 models there was little similarity between the early and delayed (64)Cu-ATSM images, and both the radiotracers showed a heterogeneous distribution. The microscopic analysis revealed that (18)F-FAZA-positive areas were also positive for CAIX immunostaining whereas immunolocalization for copper pumps in the 3 models was not related to radioactivity distribution.

CONCLUSION

The results of this study confirm the cell-dependent distribution and retention kinetics of (64)Cu-ATSM and underline the need for proper validation of animal models and PET acquisition protocols before exploration of any new clinical applications.

ATP11B mediates platinum resistance in ovarian cancer

Platinum compounds display clinical activity against a wide variety of solid tumors; however, resistance to these agents is a major limitation in cancer therapy. Reduced platinum uptake and increased platinum export are examples of resistance mechanisms that limit the extent of DNA damage. Here, we report the discovery and characterization of the role of ATP11B, a P-type ATPase membrane protein, in cisplatin resistance. We found that ATP11B expression was correlated with higher tumor grade in human ovarian cancer samples and with cisplatin resistance in human ovarian cancer cell lines. ATP11B gene silencing restored the sensitivity of ovarian cancer cell lines to cisplatin in vitro. Combined therapy of cisplatin and ATP11B-targeted siRNA significantly decreased cancer growth in mice bearing ovarian tumors derived from cisplatin-sensitive and -resistant cells. In vitro mechanistic studies on cellular platinum content and cisplatin efflux kinetics indicated that ATP11B enhances the export of cisplatin from cells. The colocalization of ATP11B with fluorescent cisplatin and with vesicular trafficking proteins, such as syntaxin-6 (STX6) and vesicular-associated membrane protein 4 (VAMP4), strongly suggests that ATP11B contributes to secretory vesicular transport of cisplatin from Golgi to plasma membrane. In conclusion, inhibition of ATP11B expression could serve as a therapeutic strategy to overcome cisplatin resistance.

Membrane transporters as mediators of Cisplatin effects and side effects

Transporters are important mediators of specific cellular uptake and thus, not only for effects, but also for side effects, metabolism, and excretion of many drugs such as cisplatin. Cisplatin is a potent cytostatic drug, whose use is limited by its severe acute and chronic nephro-, oto-, and peripheral neurotoxicity. For this reason, other platinum derivatives, such as carboplatin and oxaliplatin, with less toxicity but still with antitumoral action have been developed. Several transporters, which are expressed on the cell membranes, have been associated with cisplatin transport across the plasma membrane and across the cell: the copper transporter 1 (Ctr1), the copper transporter 2 (Ctr2), the P-type copper-transporting ATPases ATP7A and ATP7B, the organic cation transporter 2 (OCT2), and the multidrug extrusion transporter 1 (MATE1). Some of these transporters are also able to accept other platinum derivatives as substrate. Since membrane transporters display a specific tissue distribution, they can be important molecules that mediate the entry of platinum derivatives in target and also nontarget cells possibly mediating specific effects and side effects of the chemotherapeutic drug. This paper summarizes the literature on toxicities of cisplatin compared to that of carboplatin and oxaliplatin and the interaction of these platinum derivatives with membrane transporters.

Claudin-3 and claudin-4 regulate sensitivity to cisplatin by controlling expression of the copper and cisplatin influx transporter CTR1

Claudin-3 (CLDN3) and claudin-4 (CLDN4) are the major structural molecules that form tight junctions (TJs) between epithelial cells. We found that knockdown of the expression of either CLDN3 or CLDN4 produced marked changes in the phenotype of ovarian cancer cells, including an increase in resistance to cisplatin (cDDP). The effect of CLND3 and CLDN4 on cDDP cytotoxicity, cDDP cellular accumulation, and DNA adduct formation was compared in the CLDN3- and CLDN4-expressing parental human ovarian carcinoma 2008 cells and CLDN3 and CLDN4 knockdown sublines (CLDN3KD and CLDN4KD, respectively). Knockdown of CLDN3 or CLDN4 rendered human ovarian carcinoma 2008 cells resistant to cDDP in both in vitro culture and in vivo xenograft model. The net accumulation of platinum (Pt) and the Pt-DNA adduct levels were reduced in CLDN3KD and CLDN4KD cells. The endogenous mRNA levels of copper influx transporter CTR1 were found to be significantly reduced in the knockdown cells, and exogenous expression of CTR1 restored their sensitivity to cDDP. Reexpression of an shRNAi-resistant CLDN3 or CLDN4 up-regulated CTR1 levels, reversed the cDDP resistance, and enhanced TJ formation in the knockdown cells. Baseline copper (Cu) level, Cu uptake, and Cu cytotoxicity were also reduced in CLDN3KD and CLDN4KD cells. Cu-dependent tyrosinase activity was also markedly reduced in both types of CLDN knockdown cells when incubated with the substrate l-DOPA. These results indicate that CLDN3 and CLDN4 affect sensitivity of the ovarian cancer cells to the cytotoxic effect of cDDP by regulating expression of the Cu transporter CTR1.

The CXXC motifs in the metal binding domains are required for ATP7B to mediate resistance to cisplatin

The copper (Cu) exporter ATP7B mediates resistance to cisplatin (cDDP) but details of the mechanism are unknown. We explored the role of the CXXC motifs in the metal binding domains (MBDs) of ATP7B by investigating binding of cDDP to the sixth metal binding domain (MBD6) or a variant in which the CXXC motif was converted to SXXS. Platinum measurement showed that cDDP bound to wild type MBD6 but not to the SXXS variant. Wild type ATP7B rendered ovarian 2008 cells resistant to cDDP. In 2008 and in HEK293T cells, wild type ATP7B trafficked from TGN to peripheral locations in response to Cu or cDDP. A variant in which the CXXC motifs in all 6 MBDs were converted to SXXS localized correctly to the TGN but failed to traffic when exposed to either Cu or cDDP. Deletion of either the first 5 MBDs or all 6 MBDs resulted in failure to localize to the TGN. Neither the SXXS variant nor the deletion variant was able to mediate resistance to cDDP. We conclude that cDDP binds to the CXXC motifs of ATP7B and that this interaction is essential to the trafficking of ATP7B and to its ability to mediate resistance to cDDP.

Mechanism of tumor resistance to cisplatin mediated by the copper transporter ATP7B

The Wilson disease protein (ATP7B) is a copper-transporting ATPase that is responsible for regulating copper homeostasis in human tissues. ATP7B is associated with cancer resistance to cisplatin, one of the most widely used anticancer drugs. This minireview discusses the possible mechanisms of tumor resistance to cisplatin mediated by ATP7B. Cisplatin binds to the N-terminal cytosolic domain of ATP7B, which contains multiple copper-binding sites. Active platinum efflux catalyzed by ATP7B is unlikely to significantly contribute to cisplatin resistance in vivo. Transient platinum sequestration in the metal-binding domain followed by transfer to an acceptor protein or a low molecular weight compound is proposed as an alternative mechanism of cisplatin detoxification in the cell.

Nanomedicine for targeted cancer therapy: towards the overcoming of drug resistance

Anticancer drug resistance almost invariably emerges and poses major obstacles towards curative therapy of various human malignancies. In the current review we will distinguish between mechanisms of chemoresistance that are predominantly mediated by ATP-driven multidrug resistance (MDR) efflux transporters, typically of the ATP-binding cassette (ABC) superfamily, and those that are independent of such drug efflux pumps. In recent years, multiple nanoparticle (NP)-based therapeutic systems have been developed that were rationally designed to overcome drug resistance by neutralizing, evading or exploiting various drug efflux pumps and other resistance mechanisms. NPs are being exploited for selective drug delivery to tumor cells, to cancer stem/tumor initiating cells and/or to the supportive cancer cell microenvironment, i.e. stroma or tumor vasculature. Some of these NPs are currently undergoing preclinical in vivo studies as well as advanced stages of clinical evaluation with promising results. Nanovehicles harboring a payload of therapeutic drug combinations for the selective targeting and elimination of tumor cells as well as the simultaneous overcoming of mechanisms of drug resistance are a subject of intense research efforts, some of which are expected to enter clinical trials in the near future. In the present review we highlight novel approaches to selectively target cancer cells and overcome drug resistance phenomena, through the use of various nanometric drug delivery systems. In the near future, it is anticipated that innovative theragnostic nanovehicles will be developed which will harbor four major components: (1) a selective targeting moiety, (2) a diagnostic imaging aid for the localization of the malignant tumor and its micro- or macrometastases, (3) a cytotoxic, small molecule drug(s) or novel therapeutic biological(s), and (4) a chemosensitizing agent aimed at neutralizing a resistance mechanism, or exploiting a molecular "Achilles hill" of drug resistant cells. We propose to name these envisioned four element-containing nanovehicle platform, "quadrugnostic" nanomedicine. This targeted strategy holds promise in paving the way for the introduction of highly effective nanoscopic vehicles for cancer therapeutics while overcoming drug resistance.

Differential expression of ATP7A, ATP7B and CTR1 in adult rat dorsal root ganglion tissue

BACKGROUND

ATP7A, ATP7B and CTR1 are metal transporting proteins that control the cellular disposition of copper and platinum drugs, but their expression in dorsal root ganglion (DRG) tissue and their role in platinum-induced neurotoxicity are unknown. To investigate the DRG expression of ATP7A, ATP7B and CTR1, lumbar DRG and reference tissues were collected for real time quantitative PCR, RT-PCR, immunohistochemistry and Western blot analysis from healthy control adult rats or from animals treated with intraperitoneal oxaliplatin (1.85 mg/kg) or drug vehicle twice weekly for 8 weeks.

RESULTS

In DRG tissue from healthy control animals, ATP7A mRNA was clearly detectable at levels similar to those found in the brain and spinal cord, and intense ATP7A immunoreactivity was localised to the cytoplasm of cell bodies of smaller DRG neurons without staining of satellite cells, nerve fibres or co-localisation with phosphorylated heavy neurofilament subunit (pNF-H). High levels of CTR1 mRNA were detected in all tissues from healthy control animals, and strong CTR1 immunoreactivity was associated with plasma membranes and vesicular cytoplasmic structures of the cell bodies of larger-sized DRG neurons without co-localization with ATP7A. DRG neurons with strong expression of ATP7A or CTR1 had distinct cell body size profiles with minimal overlap between them. Oxaliplatin treatment did not alter the size profile of strongly ATP7A-immunoreactive neurons but significantly reduced the size profile of strongly CTR1-immunoreactive neurons. ATP7B mRNA was barely detectable, and no specific immunoreactivity for ATP7B was found, in DRG tissue from healthy control animals.

CONCLUSIONS

In conclusion, adult rat DRG tissue exhibits a specific pattern of expression of copper transporters with distinct subsets of peripheral sensory neurons intensely expressing either ATP7A or CTR1, but not both or ATP7B. The neuron subtype-specific and largely non-overlapping distribution of ATP7A and CTR1 within rat DRG tissue may be required to support the potentially differing cuproenzyme requirements of distinct subsets of sensory neurons, and could influence the transport and neurotoxicity of oxaliplatin.

Expression of Drug-Resistant Factor Genes in Hepatocellular Carcinoma Patients Undergoing Chemotherapy with Platinum Complex by Arterial Infusion

This study investigated gene expression of drug resistance factors in biopsy tissue samples from hepatocellular carcinoma (HCC) patients undergoing chemotherapy by platinum complex. Liver biopsy was performed to collect tissue from the tumor site (T) and the non-tumor site (NT) prior to the start of treatment. For drug-resistant factors, drug excretion transporters cMOAT and MDR-1, intracellular metal binding protein MT2, DNA repair enzyme ERCC-l and inter-nucleic cell transport protein MVP, were investigated. The comparison of the expression between T and NT indicated a significant decrease of MT2 and MDR-1 in T while a significant increase in ERCC-1 was noted in T. Further, expression was compared between the response cases and non-response cases using the ratios of expression in T to those in NT. The response rate was significantly low in the high expression group when the cutoff value of cMOAT and MT2 was set at 1.5 and 1.0, respectively. Furthermore, when the patients were classified into A group (cMOAT ≧ 1.5 or MT2 ≧ 1.0) and B group (cMOAT < 1.5 and MT2 < 1.0), the response rate of A group was significantly lower than B group when we combined the cutoff values of cMOAT and MT2. It is considered possible to estimate the therapeutic effect of platinum complex at a high probability by combining the expression condition of these two genes.

ATP7B expression is associated with in vitro sensitivity to cisplatin in non-small cell lung cancer

Copper-transporting P-type adenosine triphosphatase (ATP7B) is reportedly associated with platinum drug resistance in various solid tumors. However, the impact of ATP7B on platinum drug resistance in non-small cell lung cancer (NSCLC) remains unclear. We investigated in vitro cisplatin (CDDP) sensitivity using the collagen gel-droplet embedded culture drug sensitivity test. The ATP7B mRNA expression level in each specimen was also examined using real-time polymerase chain reaction. The relationship between ATP7B expression and in vitro CDDP sensitivity was then evaluated. The ATP7B mRNA expression levels in CDDP-resistant tumors were significantly higher than those in the CDDP-sensitive group (p=0.015; Mann-Whitney U test). Our results suggested that ATP7B expression is a promising chemoresistance marker for cisplatin.

Copper transporters and the cellular pharmacology of the platinum-containing cancer drugs

Multiple lines of evidence indicate that the platinum-containing cancer drugs enter cells, are distributed to various subcellular compartments, and are exported from cells via transporters that evolved to manage copper homeostasis. The cytotoxicity of the platinum drugs is directly related to how much drug enters the cell, and almost all cells that have acquired resistance to the platinum drugs exhibit reduced drug accumulation. The major copper influx transporter, copper transporter 1 (CTR1), has now been shown to control the tumor cell accumulation and cytotoxic effect of cisplatin, carboplatin, and oxaliplatin. There is a good correlation between change in CTR1 expression and acquired cisplatin resistance among ovarian cancer cell lines, and genetic knockout of CTR1 renders cells resistant to cisplatin in vivo. The expression of CTR1 is regulated at the transcriptional level by copper via Sp1 and at the post-translational level by the proteosome. Copper and cisplatin both trigger the down-regulation of CTR1 via a process that involves ubiquitination and proteosomal degradation and requires the copper chaperone antioxidant protein 1 (ATOX1). The cisplatin-induced degradation of CTR1 can be blocked with the proteosome inhibitor bortezomib, and this increases the cellular uptake and the cytotoxicity of cisplatin in a synergistic manner. Copper and platinum(II) have similar sulfur binding characteristics, and the presence of stacked rings of methionines and cysteines in the CTR1 trimer suggest a mechanism by which CTR1 selectively transports copper and the platinum-containing drugs via sequential transchelation reactions similar to the manner in which copper is passed from ATOX1 to the copper efflux transporters.

Potential predictive markers of chemotherapy resistance in stage III ovarian serous carcinomas

BACKGROUND

Chemotherapy resistance remains a major obstacle in the treatment of women with ovarian cancer. Establishing predictive markers of chemoresponse would help to individualize therapy and improve survival of ovarian cancer patients. Chemotherapy resistance in ovarian cancer has been studied thoroughly and several non-overlapping single genes, gene profiles and copy number alterations have been suggested as potential markers. The objective of this study was to explore genetic alterations behind chemotherapy resistance in ovarian cancer with the ultimate aim to find potential predictive markers.

METHODS

To create the best opportunities for identifying genetic alterations of importance for resistance, we selected a homogenous tumor material concerning histology, stage and chemotherapy. Using high-resolution whole genome array comparative genomic hybridization (CGH), we analyzed the tumor genomes of 40 fresh-frozen stage III ovarian serous carcinomas, all uniformly treated with combination therapy paclitaxel/carboplatin. Fisher's exact test was used to identify significant differences. Subsequently, we examined four genes in the significant regions (EVI1, MDS1, SH3GL2, SH3KBP1) plus the ABCB1 gene with quantitative real-time polymerase chain reaction (QPCR) to evaluate the impact of DNA alterations on the transcriptional level.

RESULTS

We identified gain in 3q26.2, and losses in 6q11.2-12, 9p22.3, 9p22.2-22.1, 9p22.1-21.3, Xp22.2-22.12, Xp22.11-11.3, and Xp11.23-11.1 to be significantly associated with chemotherapy resistance. In the gene expression analysis, EVI1 expression differed between samples with gain versus without gain, exhibiting higher expression in the gain group.

CONCLUSION

In conclusion, we detected specific genetic alterations associated with resistance, of which some might be potential predictive markers of chemotherapy resistance in advanced ovarian serous carcinomas. Thus, further studies are required to validate these findings in an independent ovarian tumor series.

Novel strategies for reversing platinum resistance

Platinum-based drugs continue to be the mainstay of therapy for ovarian cancer. Along with adverse effects, chemoresistance (intrinsic or acquired) has become a major limitation in the management of recurrent disease. Even though much is known about the effects of platinum drugs on cancer cells, the mechanisms underlying resistance are poorly understood. In this review, we summarize the current data on chemoresistance and discuss novel strategies to reverse resistance to platinum-based drugs. The most important targets highlighted here include Aurora kinases, PARP, ATP7B, and ERCC1. Furthermore, we discuss the implications of these novel approaches for ovarian cancer treatment.