Kinetic study on the reaction of cisplatin with metallothionein

Jones A, Romero-Canelon I, Erxleben A. Multiaction Pt(IV) Complexes: Cytotoxicity in Ovarian Cancer Cell Lines and Mechanistic Studies

Ovarian cancer has the worst case-to-fatality ratio of all gynecologic malignancies. The main reasons for the high mortality rate are relapse and the development of chemoresistance. In this paper, the cytotoxic activity of two new multiaction platinum(IV) derivatives of cisplatin and oxaliplatin in a panel of ovarian cancer cells is reported. Cis,cis,trans-[Pt(NH3)2Cl2(IPA)(DCA)] (1) and trans-[Pt(DACH)(OX)(IPA)(DCA)] (2) (IPA = indole-3-propionic acid, DCA = dichloroacetate, DACH = 1R,2R-1,2-diaminocyclohexane, OX = oxalate) were synthesized and characterized by elemental analysis, ESI-MS, FT-IR, and 1H, 13C, and195Pt NMR spectroscopy. The biological activity was evaluated in A2780, PEA1, PEA2, SKOV3, SW626, and OVCAR3 cells. Both complexes are potent cytotoxins. Remarkably, complex 2 is 14 times more active in OVCAR3 cells than cisplatin and is able to overcome cisplatin resistance in PEA2 and A2780cis cells, which are models of post-treatment patient-developed and laboratory-induced resistance. This complex also shows activity in 3D cancer models of the A2780 cells. Mechanistic studies revealed that the complexes induce apoptosis via DNA damage and ROS generation.

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.

Studies on the Complexation of Platinum(II) by Some 4-Nitroisoxazoles and Testing the Cytotoxic Activity of the Resulting Complexes

Two novel platinum(II) complexes (1 and 2) were synthesized by the reaction of the appropriate 3,5-dimethyl-4-nitroisoxazole with K₂PtCl₄ and characterized by elemental analysis, ESI MS spectrometry, ¹H NMR and far-IR spectroscopy. The structure of trans complex 2 was additionally confirmed by X-ray diffraction. The cytotoxicity of the investigated compounds was examined in vitro on three human cancer cell lines (MCF-7 breast, ES-2 ovarian and A-549 lung adenocarcinomas) in both normoxia and hypoxia conditions. LogPs of complexes were measured using the shake-flask method. The trans complex 2 showed much better cytotoxic activity than cisplatin for all the tested cancer cell lines. Cis complex 1 was inferior to its trans isomer against all the cancer lines tested in normoxia conditions but proved superior to the reference cisplatin against the MCF-7 and A549 lines, and showed similar activity to cisplatin against the ES-2 line. To gain additional information that may facilitate the explanation of the pharmacological activity of the tested compounds, cellular platinum uptake and stability in L-glutathione solution were determined for both compounds 1 and 2.

Novel cis-Pt(II) Complexes with Alkylpyrazole Ligands: Synthesis, Characterization, and Unusual Mode of Anticancer Action

One concept of improving anticancer effects of conventional platinum-based antitumor drugs consists of conjugating these compounds with other biologically (antitumor) active agents, acting by a different mechanism. Here, we present synthesis, physicochemical characterization, biological effects, and mechanisms of action of four new analogs of conventional cisplatin, namely, cis-Pt(II) complexes containing either methyl or ethyl pyrazole N-donor ligands and chlorido or iodido ligands. It is noteworthy that while chlorido complexes display activity in a variety of cancer cell lines comparable to cisplatin, iodido complexes are considerably more potent due to their enhanced hydrophobicity and consequently enhanced cellular accumulation. Moreover, all of the studied Pt(II) alkylpyrazole complexes display a higher selectivity for tumor cells and effectively overcome the acquired resistance to cisplatin. Further results focused on the mechanism of action of the studied complexes and showed that in contrast to cisplatin and several platinum-based antitumor drugs, DNA damage by the investigated Pt(II)-alkylpyrazole complexes does not play a major role in their mechanism of action. Our findings demonstrate that inhibition of the tubulin kinesin Eg5, which is essential for forming a functional mitotic spindle, plays an important role in their mechanism of antiproliferative action.

Selective synergistic anticancer effects of cisplatin and oridonin against human p53-mutant esophageal squamous carcinoma cells

Oridonin (ORI) is known to pose anticancer activity against cancer, which could induce the therapeutic impact of chemotherapy drugs. However, such simple combinations have numerous side effects such as higher toxicity to normal cells and tissues. To enhance the therapeutic effects with minimal side effects, here we used ORI in combination with cisplitin (CIS) against different esophageal squamous cell carcinoma (ESCC) cell lines in vitro, to investigate the synergistic anticancer effects of the two drugs against ESCC. Calcusyn Graphing Software was used to assess the synergistic effect. Apoptosis, wound healing and cell invasion assay were conducted to further confirm the synergistic effects of ORI and CIS. Intracellular glutathione (GSH) and reactive oxygen species assay, immunofluorescence staining and western blot were used to verify the mechanism of synergistic cytotoxicity. ORI and CIS pose selective synergistic effects on ESCC cells with p53 mutations. Moreover, we found that the synergistic effects of these drugs are mediated by GSH/ROS systems, such that intracellular GSH production was inhibited, whereas the ROS generation was induced following ORI and CIS application. In addition, we noted that DNA damage was induced as in response to ORI and CIS treatment. Overall, these results suggest that ORI can synergistically enhance the effect of CIS, and GSH deficiency and p53 mutation, might be biomarkers for the combinational usage of ORI and CIS.

Characterization of a hyaluronic acid and folic acid-based hydrogel for cisplatin delivery: Antineoplastic effect in human ovarian cancer cells in vitro

We successfully prepared and characterized a hyaluronic acid- and folic acid-based hydrogel for the delivery of cisplatin (GEL-CIS) with the aim to induce specific and efficient incorporation of CIS into ovarian cancer (OC) cells, improve its antineoplastic effect and avoid CIS-resistance. The slow and controlled release of the drug from the polymeric network and its swelling degree at physiologic pH suggested its suitability for CIS delivery in OC. We compared here the effects of pure CIS to that of GEL-CIS on human OC cell lines, either wild type or CIS-resistant, in basal conditions and in the presence of macrophage-derived conditioned medium, mimicking the action of tumor-associated macrophages in vivo. GEL-CIS inhibited OC cell growth and migration more efficiently than pure CIS and modulated the expression of proteins involved in the Epithelial Mesenchymal Transition, a process playing a key role in OC metastatic spread and resistance to CIS.

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.

Synthesis of Platinum(II) Complexes with Some 1-Methylnitropyrazoles and In Vitro Research on Their Cytotoxic Activity

A series of eight novel platinum(II) complexes were synthesized by the reaction of the appropriate 1-methylnitropyrazole derivatives with K₂PtCl₄ and characterized by elemental analysis, ESI MS spectrometry, ¹H NMR, ¹⁹⁵Pt NMR, IR and far IR spectroscopy. Thermal isomerization of cis-dichloridobis(1-methyl-4-nitropyrazole)platinum(II) 1 to trans-dichloridobis(1-methyl-4-nitropyrazole)platinum(II) 2 has been presented, and the structure of the compound 2 has been confirmed by X-ray diffraction method. Cytotoxicity of the investigated compounds was examined in vitro on three human cancer cell lines (MCF-7 breast, ES-2 ovarian and A-549 lung adenocarcinomas) and their logP was measured using a shake-flask method. The trans complex 2 showed better antiproliferative activity than cisplatin for all the tested cancer cell lines. Additionally, trans-dichloridobis(1-methyl-5-nitropyrazole)platinum(II) 4 has featured a lower IC₅₀ value than reference cisplatin against MCF-7 cell line. To gain additional information that may facilitate the explanation of the mode of action of tested compounds cellular platinum uptake, stability in L-glutathione solution, influence on cell cycle progression of HL-60 cells and ability to apoptosis induction were determined for compounds 1 and 2.

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

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

Synthesis, antiproliferative activity in cancer cells and DNA interaction studies of [Pt(cis-1,3-diaminocycloalkane)Cl2] analogs

The search for more effective platinum anticancer drugs has led to the design, synthesis, and preclinical testing of hundreds of new platinum complexes. This search resulted in the recognition and subsequent FDA approval of the third-generation Pt(II) anticancer drug, [Pt(1,2-diaminocyclohexane)(oxalate)], oxaliplatin, as an effective agent in treating colorectal and gastrointestinal cancers. Another promising example of the class of anticancer platinum(II) complexes incorporating the Pt(1,n-diaminocycloalkane) moiety is kiteplatin ([Pt(cis-1,4-DACH)Cl₂], DACH = diaminocyclohexane). We report here our progress in evaluating the role of the cycloalkyl moiety in these complexes focusing on the synthesis, characterization, evaluation of the antiproliferative activity in tumor cells and studies of the mechanism of action of new [Pt(cis-1,3-diaminocycloalkane)Cl₂] complexes wherein the cis-1,3-diaminocycloalkane group contains the cyclobutyl, cyclopentyl, and cyclohexyl moieties. We demonstrate that [Pt(cis-1,3-DACH)Cl₂] destroys cancer cells with greater efficacy than the other two investigated 1,3-diamminocycloalkane derivatives, or cisplatin. Moreover, the investigated [Pt(cis-1,3-diaminocycloalkane)Cl₂] complexes show selectivity toward tumor cells relative to non-tumorigenic normal cells. We also performed several mechanistic studies in cell-free media focused on understanding some early steps in the mechanism of antitumor activity of bifunctional platinum(II) complexes. Our data indicate that reactivities of the investigated [Pt(cis-1,3-diaminocycloalkane)Cl₂] complexes and cisplatin with glutathione and DNA binding do not correlate with antiproliferative activity of these platinum(II) complexes in cancer cells. In contrast, we show that the higher antiproliferative activity in cancer cells of [Pt(cis-1,3-DACH)Cl₂] originates from its highest hydrophobicity and most efficient cellular uptake.

Interplay between Carbonic Anhydrases and Metallothioneins: Structural Control of Metalation

Carbonic anhydrases (CAs) and metallothioneins (MTs) are both families of zinc metalloproteins central to life, however, they coordinate and interact with their Zn2+ ion cofactors in completely different ways. CAs and MTs are highly sensitive to the cellular environment and play key roles in maintaining cellular homeostasis. In addition, CAs and MTs have multiple isoforms with differentiated regulation. This review discusses current literature regarding these two families of metalloproteins in carcinogenesis, with a dialogue on the association of these two ubiquitous proteins in vitro in the context of metalation. Metalation of CA by Zn-MT and Cd-MT is described. Evidence for protein-protein interactions is introduced from changes in metalation profiles of MT from electrospray ionization mass spectrometry and the metalation rate from stopped-flow kinetics. The implications on cellular control of pH and metal donation is also discussed in the context of diseased states.

Identification of Cisplatin and Palladium(II) Complexes as Potent Metallo-β-lactamase Inhibitors for Targeting Carbapenem-Resistant Enterobacteriaceae

The emergence and prevalence of carbapenem-resistant bacterial infection have seriously threatened the clinical use of almost all β-lactam antibacterials. The development of effective metallo-β-lactamase (MβL) inhibitors to restore the existing antibiotics efficacy is an ideal alternative. Although several types of serine-β-lactamase inhibitors have been successfully developed and used in clinical settings, MβL inhibitors are not clinically available to date. Herein, we identified that cisplatin and Pd(II) complexes are potent broad-spectrum inhibitors of the B1 and B2 subclasses of MβLs and effectively revived Meropenem efficacy against MβL-expressing bacteria in vitro. Enzyme kinetics, thermodynamics, inductively coupled plasma atomic emission spectrometry (ICP-AES), matrix-assisted laser desorption/ionization-time of flight-mass spectrometry (MALDI-TOF-MS), and site-directed mutation assays revealed that these metal complexes irreversibly inhibited NDM-1 through a novel inhibition mode involving binding to Cys208 and displacing one Zn(II) ion of the enzyme with one Pt(II) containing two NH₃'s or one Pd(II) ion. Importantly, the combination therapy of Meropenem and metal complexes significantly suppressed the development of higher-level resistance in bacteria producing NDM-1, also effectively reduced the bacterial burden in liver and spleen of mice infected by carbapenem-resistant Enterobacteriaceae producing NDM-1. These findings will offer potential lead compounds for the further development of clinically useful inhibitors targeting MβLs.

Computational insight into the interaction of oxaliplatin with insulin

In an organism, cisplatin and its derivatives are known to interact with proteins besides their principal DNA target. These off-target interactions have major therapeutic consequences including undesired side effects, loss of bioavailability and emergence of resistance. Insulin is one of the prototypical protein targets of platinum drugs as it has been seen to be involved in bioavailability reduction and might also determine resistance in certain cancer lines. However, despite the interest in understanding the nature of the oxaliplatin-insulin adducts, no 3D models have been achieved so far. In this study, we apply our recent computational multiscale protocol optimized for bioinorganic interactions to provide structural insights into these systems. To do so, the initial structures are predicted by blind protein-metalloligand docking calculations optimized to account for a metal-containing species, and then refined using a Molecular Dynamics (MD) and Quantum Mechanics/Molecular Mechanics (QM/MM) integrated protocol. The results are consistent with experimental information obtained from fragment analysis, and also provide novel structural information like conformational changes occurring upon binding and potential effects on the biological functions of the protein. This study opens an avenue towards applying similar strategies to a wide ensemble of metallodrug-protein/peptide systems for which no structural data are available.

The asymmetry of plasma membranes and their cholesterol content influence the uptake of cisplatin

The composition of the plasma membrane of malignant cells is thought to influence the cellular uptake of cisplatin and to take part in developing resistance to this widespread anti-cancer drug. In this work we study the permeation of cisplatin through the model membranes of normal and cancer cells using molecular dynamics simulations. A special attention is paid to lipid asymmetry and cholesterol content of the membranes. The loss of lipid asymmetry, which is common for cancer cells, leads to a decrease in their permeability to cisplatin by one order of magnitude in comparison to the membranes of normal cells. The change in the cholesterol molar ratio from 0% to 33% also decreases the permeability of the membrane by approximately one order of magnitude. The permeability of pure DOPC membrane is 5-6 orders of magnitude higher than one of the membranes with realistic lipid composition, which makes it as an inadequate model for the studies of drug permeability.

Platinum Resistance in Ovarian Cancer: Role of DNA Repair

Epithelial ovarian cancer (EOC) is the most lethal gynecological cancer. It is initially responsive to cisplatin and carboplatin, two DNA damaging agents used in first line therapy. However, almost invariably, patients relapse with a tumor resistant to subsequent treatment with platinum containing drugs. Several mechanisms associated with the development of acquired drug resistance have been reported. Here we focused our attention on DNA repair mechanisms, which are fundamental for recognition and removal of platinum adducts and hence for the ability of these drugs to exert their activity. We analyzed the major DNA repair pathways potentially involved in drug resistance, detailing gene mutation, duplication or deletion as well as polymorphisms as potential biomarkers for drug resistance development. We dissected potential ways to overcome DNA repair-associated drug resistance thanks to the development of new combinations and/or drugs directly targeting DNA repair proteins or taking advantage of the vulnerability arising from DNA repair defects in EOCs.

Platinum Resistance in Ovarian Cancer: Role of DNA Repair

Epithelial ovarian cancer (EOC) is the most lethal gynecological cancer. It is initially responsive to cisplatin and carboplatin, two DNA damaging agents used in first line therapy. However, almost invariably, patients relapse with a tumor resistant to subsequent treatment with platinum containing drugs. Several mechanisms associated with the development of acquired drug resistance have been reported. Here we focused our attention on DNA repair mechanisms, which are fundamental for recognition and removal of platinum adducts and hence for the ability of these drugs to exert their activity. We analyzed the major DNA repair pathways potentially involved in drug resistance, detailing gene mutation, duplication or deletion as well as polymorphisms as potential biomarkers for drug resistance development. We dissected potential ways to overcome DNA repair-associated drug resistance thanks to the development of new combinations and/or drugs directly targeting DNA repair proteins or taking advantage of the vulnerability arising from DNA repair defects in EOCs.

Platinum Resistance in Ovarian Cancer: Role of DNA Repair

Epithelial ovarian cancer (EOC) is the most lethal gynecological cancer. It is initially responsive to cisplatin and carboplatin, two DNA damaging agents used in first line therapy. However, almost invariably, patients relapse with a tumor resistant to subsequent treatment with platinum containing drugs. Several mechanisms associated with the development of acquired drug resistance have been reported. Here we focused our attention on DNA repair mechanisms, which are fundamental for recognition and removal of platinum adducts and hence for the ability of these drugs to exert their activity. We analyzed the major DNA repair pathways potentially involved in drug resistance, detailing gene mutation, duplication or deletion as well as polymorphisms as potential biomarkers for drug resistance development. We dissected potential ways to overcome DNA repair-associated drug resistance thanks to the development of new combinations and/or drugs directly targeting DNA repair proteins or taking advantage of the vulnerability arising from DNA repair defects in EOCs.

Metallothionein: An Aggressive Scavenger-The Metabolism of Rhodium(II) Tetraacetate (Rh2(CH3CO2)4)

Anthropogenic sources of xenobiotic metals with no physiological benefit are increasingly prevalent in the environment. The platinum group metals (Pd, Pt, Rh, Ru, Os, and Ir) are found in marine and plant species near urban sources, and are known to bioaccumulate, introducing these metals into the human food chain. Many of these metals are also being used in innovative cancer therapy, which leads to a direct source of exposure for humans. This paper aims to further our understanding of nontraditional metal metabolism via metallothionein, a protein involved in physiologically important metal homeostasis. The aggressive reaction of metallothionein and dirhodium(II) tetraacetate, a common synthetic catalyst known for its cytotoxicity, was studied in detail in vitro. Optical spectroscopic and equilibrium and time-dependent mass spectral data were used to define binding constants for this robust reaction, and molecular dynamics calculations were conducted to explain the observed results.

Role of ZIP8 in regulation of cisplatin sensitivity through Bcl-2

ZIP8 is a membrane transporter that facilitates the uptake of divalent metals (e.g., Zn, Mn, Fe, Cd) and the mineral selenite in anionic form. ZIP8 functionality has been recently reported to regulate cell proliferation, migration and cytoskeleton arrangement, exhibiting an essential role for normal physiology. In this study, we report a ZIP8 role in chemotherapy response. We show ZIP8 regulates cell sensitivity to the anti-cancer drug cisplatin. Overexpression of ZIP8 in mouse embryonic fibroblast (MEF) cells induces cisplatin sensitivity, while knockout of ZIP8 in leukemia HAP1 cells leads to cisplatin resistance. In ZIP8 altered cells and transgenic mice, we show cisplatin is not a direct ZIP8 substrate. Further studies demonstrate that ZIP8 regulates anti-apoptotic protein Bcl-2. ZIP8 overexpression decreases Bcl-2 levels in cultured cells, mice lung and liver tissue while loss of ZIP8 elevates Bcl-2 expression in HAP1 cells and liver tissue. We also observe that ZIP8 overexpression modulates cisplatin-induced cell apoptosis, manifested by the increased protein level of cleaved Caspase-3. Since Bcl-2 elevation was previously discovered to induce cisplatin drug resistance, our results suggest ZIP8 may modulate cisplatin drug responses as well as apoptosis through Bcl-2. We therefore conclude ZIP8 is a new molecule to be involved in cisplatin drug responses and is predicted as a genetic factor to be considered in cisplatin therapy.

Unravelling the mechanistic details of metal binding to mammalian metallothioneins from stoichiometric, kinetic, and binding affinity data

Metallothioneins (MTs) are small, cysteine-rich proteins, found throughout Nature. Their ability to bind a number of different metals with a range of stoichiometric ratios means that this protein family is critically important for essential metal (Zn²⁺ and Cu⁺) homeostasis, metal storage, metal donation to nascent metalloenzymes as well as heavy metal detoxification. With its 20 cysteines, metallothionein is also considered to protect cells against oxidative stress. MT has been studied by a large number of researchers over the last 6 decades using a variety of spectroscopic techniques. The lack of distinguishing chromophores for the multitude of binding sites has made the evaluation of stoichiometric properties for different metals challenging. Initially, only ¹¹³Cd-NMR spectroscopy could provide strong evidence for the proposed cluster formation of Cd-MT. The extraordinary development of electrospray ionization mass spectrometry (ESI-MS), where all coexisting species in solution are observed, revolutionized MT research. Prior to the use of ESI-MS data, a range of "magic numbers" representing metal-to-MT molar ratios were reported from optical spectroscopic studies. The availability of ESI mass spectral data led to (i) the confirmation of cluster formation, (ii) a conceptual understanding of the cooperativity involved in multiple metal binding events, (iii) the presence of domain specificity between regions of the protein and (iv) mechanistic details involving both binding affinities and rate constants. The kinetic experiments identified the presence of multiple individual binding sites, each with a unique rate constant and an analogous binding affinity. The almost linear trend in rate constants as a function of bound As³⁺ provided a unique insight that became a critical step in the complete understanding of the mechanistic details of the metalation of MT. To fully define the biological function of this sulfur-rich protein it is necessary to determine kinetic rate constants and binding affinities for the essential metals. Recently, Zn²⁺ competition experiments between both of the isolated fragments (α and β) and the full-length protein (βα-MT 1a) as well as Zn²⁺ competition between βα-MT 1a and carbonic anhydrase were reported. From these data, the trend in binding affinities and the values of the K_f of the 7 bimolecular reactions involved in metalation were determined. From the analysis of ESI-MS data for Cu⁺ binding to βα-MT 1a at different pH-values, a trend in the 20 binding affinities for the complete metalation mechanism was reported. This review details a personal view of the historical development of the determination of stoichiometry for metal binding, the structure of the binding sites, the rates of the metalation reactions and the underlying binding affinities for each metalation step. We have attempted to summarize the experimental developments that led to the publication in May 2017 of the experimental determination of the 20 binding constants for the 20 sequential bimolecular reactions for Cu⁺ binding to the 20 Cys of apoMT as a function of pH that show the appearance and disappearance of clusters. We report both published data and in a series of tables an assembly of stoichiometries, and equilibrium constants for Zn²⁺ and Cu⁺ for many different metallothioneins.

Immunohistochemically detectable metallothionein expression in malignant pleural mesotheliomas is strongly associated with early failure to platin-based chemotherapy

Background

Malignant pleural mesothelioma (MPM) is a biologically highly aggressive tumor arising from the pleura with a dismal prognosis. Cisplatin is the drug of choice for the treatment of MPM, and carboplatin seems to have comparable efficacy. Nevertheless, cisplatin treatment results in a response rate of merely 14% and a median survival of less than seven months. Due to their role in many cellular processes, methallothioneins (MTs) have been widely studied in various cancers. The known heavy metal detoxifying effect of MT-I and MT-II may be the reason for heavy metal drug resistance of various cancers including MPM.

Methods

105 patients were retrospectively analyzed immunohistochemically for their MT expression levels. Survival analysis was done by Cox-regression, and statistical significance determined using likelihood ratio, Wald test and Score (logrank) tests.

Results

Cox-regression analyses were done in a linear and logarithmic scale revealing a significant association between expression of MT and shortened overall survival (OS) in a linear (p=0.0009) and logarithmic scale (p=0.0003). Reduced progression free survival (PFS) was also observed for MT expressing tumors (linear: p=0.0134, log: p=0.0152).

Conclusion

Since both, overall survival and progression-free survival are negatively correlated with detectable MT expression in MPM, our results indicate a possible resistance to platin-based chemotherapy associated with MT expression upregulation, found exclusively in progressive MPM samples. Initial cell culture studies suggest promoter DNA hypomethylation and expression of miRNA-566 a direct regulator of copper transporter SLC31A1 and a putative regulator of MT1A and MT2A gene expression, to be responsible for the drug resistance.

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

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

Capturing platinum in cisplatin: kinetic reactions with recombinant human apo-metallothionein 1a

Detailed mass spectra data show the stepwise sequence of cisplatin deconstruction by apo-metallothionein.

Advances in nano-based inner ear delivery systems for the treatment of sensorineural hearing loss

Sensorineural hearing loss (SNHL) is one of the most common diseases, accounting for about 90% of all hearing loss. Leading causes of SNHL include advanced age, ototoxic medications, noise exposure, inherited and autoimmune disorders. Most of SNHL is irreversible and managed with hearing aids or cochlear implants. Although there is increased understanding of the molecular pathophysiology of SNHL, biologic treatment options are limited due to lack of noninvasive targeted delivery systems. Obstacles of targeted inner ear delivery include anatomic inaccessibility, biotherapeutic instability, and nonspecific delivery. Advances in nanotechnology may provide a solution to these barriers. Nanoparticles can stabilize and carry biomaterials across the round window membrane into the inner ear, and ligand bioconjugation onto nanoparticle surfaces allows for specific targeting. A newer technology, nanohydrogel, may offer noninvasive and sustained biotherapeutic delivery into specific inner ear cells. Nanohydrogel may be used for inner ear dialysis, a potential treatment for ototoxicity-induced SNHL.

Enhanced anti-cancer efficacy to cancer cells by a novel monofunctional mononuclear platinum(ii) complex containing a mixed S,N,S-donor ligand

A novel platinum–intercalator hybrid complex (1) exhibits a cytotoxicity comparable to that of cisplatin against MCF-7 cell lines, and more potent activities against HeLa and A-549 cell lines, especially against the former.

Selective speciation improves efficacy and lowers toxicity of platinum anticancer and vanadium antidiabetic drugs

Improving efficacy and lowering resistance to metal-based drugs can be addressed by consideration of the coordination complex speciation and key reactions important to vanadium antidiabetic drugs or platinum anticancer drugs under biological conditions. The methods of analyses vary depending on the specific metal ion chemistry. The vanadium compounds interconvert readily, whereas the reactions of the platinum compounds are much slower and thus much easier to study. However, the vanadium species are readily differentiated due to vanadium complexes differing in color. For both vanadium and platinum systems, understanding the processes as the compounds, Lipoplatin and Satraplatin, enter cells is needed to better combat the disease; there are many cellular metabolites, which may affect processing and thus the efficacy of the drugs. Examples of two formulations of platinum compounds illustrate how changing the chemistry of the platinum will result in less toxic and better tolerated drugs. The consequence of the much lower toxicity of the drug, can be readily realized because cisplatin administration requires hospital stay whereas Lipoplatin can be done in an outpatient manner. Similarly, the properties of Satraplatin allow for development of an oral drug. These forms of platinum demonstrate that the direct consequence of more selective speciation is lower side effects and cheaper administration of the anticancer agent. Therefore we urge that as the community goes forward in development of new drugs, control of speciation chemistry will be considered as one of the key strategies in the future development of anticancer drugs.

Comparative analysis of gene expression between renal cortex and papilla in nedaplatin-induced nephrotoxicity in rats

To elucidate the mechanism of nephrotoxicity caused by anti-neoplastic platinum complex, nedaplatin (NDP), treatment with a particular focus on the renal papillary toxicity, we analysed the gene expression profiles of two renal regions, the cortex (RC) and the papilla (RP) in rat kidneys. Male Wistar rats received a single administration of 10 mg/kg intravenous NDP or vehicle alone (5% xylitol solution) and were sacrificed six days later. The kidneys were dissected into the RC and RP and used for histopathological and microarray analyses. Histopathologically, NDP caused characteristic renal lesions, such as necrosis, single cell necrosis (with TUNEL TdT-mediated dUTP-biotin nick end labelling-positive) and regeneration/hyperplasia of the epithelial cells in both renal regions. Global gene expression analysis revealed that several genes involved in various functional categories were commonly deregulated in both renal regions, such as apoptosis, cell cycle regulation, DNA metabolism, cell migration/adhesion and cytoskeleton organization or genes induced as a perturbation of oxidative status and calcium homeostasis. Comparative analysis of gene expression between RC and RP revealed that genes encoding several subtypes of cytokeratins were identified as being specifically overexpressed in RP by the NDP treatment. Differential expression patterns of these selected genes observed by microarray analysis were further confirmed by quantitative real time RT-PCR and immunohistochemistry, which demonstrated increased expression of cytokeratins (CKs) 14 and 19 at the epithelium covering RP and/or collecting duct epithelium. Overall, the results contribute to understanding the renal molecular events of NDP-induced nephrotoxicity including novel potential biomarker genes encoding CKs 14 and 19 that may serve as indicators of renal papillary toxicity. Human & Experimental Toxicology (2007) 26, 767—780

Destructive interactions of dirhodium(ii) tetraacetate with β metallothionein rh1a

The four bridging acetates of dirhodium(ii) tetraacetate are removed in a stepwise manner by human-metallothionein 1a β-fragment, a reaction captured by electrospray ionization mass spectrometry.

Assessing the contribution of the two protein disulfide isomerases PDIA1 and PDIA3 to cisplatin resistance

Intracellular binding of cisplatin to non-DNA partners, such as proteins, has received increasing attention as an additional mode of action and as mechanism of resistance. We investigated two cisplatin-interacting isoforms of protein disulfide isomerase regarding their contribution to acquired cisplatin resistance using sensitive and resistant A2780/A2780cis ovarian cancer cells. Cisplatin cytotoxicity was assessed after knockdown of either protein disulfide isomerase family A member 1 (PDIA1) or protein disulfide isomerase family A member 3 (PDIA3). Whereas PDIA1 knockdown led to increased cytotoxicity in resistant A2780cis cells, PDIA3 knockdown showed no influence on cytotoxicity. Coincubation with propynoic acid carbamoyl methyl amide 31 (PACMA31), a PDIA1 inhibitor, resensitized A2780cis cells to cisplatin treatment. Determination of the combination index revealed that the combination of cisplatin and PACMA31 acts synergistically. Our results warrant further evaluation of PDIA1 as promising target for chemotherapy, and its inhibition by PACMA31 as a new therapeutic approach.

Serum metallothionein in patients with testicular cancer

PURPOSE

Metallothioneins (MTs) have been disclosed as a useful diagnostic factor for tumour progression and drug resistance in a variety of malignancies. Increased levels of MT in blood serum have been found in patients with several types of cancer, but there is no available information on serum MT levels in patients with testicular germ cell tumour (TGCT). The aim of the study was to determine MT levels in serum of patients with TGCT and to evaluate the portion of platinum (Pt) that binds to MT after cisplatin administration since MTs could be involved in drug resistance.

METHODS

Concentration of total MT was determined in serum of 25 men with newly diagnosed TGCT by differential pulse voltammetry. The fractionation of serum was carried out by size exclusion high-performance liquid chromatography (SE-HPLC), while concentration of Pt in collected fractions was determined by inductively coupled plasma mass spectrometry.

RESULTS

Concentration of serum MT was significantly higher in TGCT patients than in healthy volunteers. The results of SE-HPLC analysis showed that only a small amount of Pt was bound to proteins in the area of MT elution.

CONCLUSIONS

Significant increase in MT levels in individuals with TGCT indicates certain health problem and, in combination with other commonly used diagnostic tools, could improve early diagnosis.

Biological activity of a series of cisplatin-based aliphatic bis(carboxylato) Pt(IV) prodrugs: how long the organic chain should be?

The biological properties of a series of cisplatin-based Pt(IV) prodrug candidates, namely trans,cis,cis-[Pt(carboxylato)2Cl2(NH3)2], where carboxylato=CH3(CH2)nCOO(-) [(1), n=0; (2), n=2; (3), n=4; (4), n=6] having a large interval of lipophilicity are discussed. The stability of the complexes was tested in different pH conditions (i.e. from 1.0 to 9.0) to simulate the hypothetical conditions for an oral route of administration, showing a high stability (>90%). The transformation into their active Pt(II) metabolites was demonstrated in the presence of ascorbic acid, with a pseudo-first order kinetics, the half-time of which smoothly decreases as the chain length of carboxylic acid increases. Their antiproliferative activity has been evaluated in vitro on a large panel of human cancer cell lines. As expected, the potency increases with the chain length: 3 and 4 resulted by far more active than cisplatin on all cell lines of about one or two orders of magnitude, respectively. Both complexes retained their activity also on cisplatin-resistant cell line, and exhibited a progressive increase of the selectivity compared with non-tumor cells. These results were confirmed with more prolonged treatment (up to 14days) studied on multicellular tumor spheroids (MCTSs). In this case the Pt(IV) complexes exert a protracted antiproliferative action, even if the drug is removed from the culture medium. Finally, in a time-course experiment of the total platinum evaluation in mice blood (after a single oral administration of the title complexes), 2 gave the best results, representing a good compromise between lipophilicity and water solubility, that increase and decrease respectively on passing from 1 to 4.

Conformation and recognition of DNA damaged by antitumor cis-dichlorido platinum(II) complex of CDK inhibitor bohemine

A substitution of the ammine ligands of cisplatin, cis-[Pt(NH3)2Cl2], for cyclin dependent kinase (CDK) inhibitor bohemine (boh), [2-(3-hydroxypropylamino)-6-benzylamino-9-isopropylpurine], results in a compound, cis-[Pt(boh)2Cl2] (C1), with the unique anticancer profile which may be associated with some features of the damaged DNA and/or its cellular processing (Travnicek Z et al. (2003) J Inorg Biochem94, 307-316; Liskova B (2012) Chem Res Toxicol25, 500-509). A combination of biochemical and molecular biology techniques was used to establish mechanistic differences between cisplatin and C1 with respect to the DNA damage they produce and their interactions with critical DNA-binding proteins, DNA-processing enzymes and glutathione. The results show that replacement of the NH3 groups in cisplatin by bohemine modulates some aspects of the mechanism of action of C1. More specifically, the results of the present work are consistent with the thesis that, in comparison with cisplatin, effects of other factors, such as: (i) slower rate of initial binding of C1 to DNA; (ii) the lower efficiency of C1 to form bifunctional adducts; (iii) the reduced bend of longitudinal DNA axis induced by the major 1,2-GG intrastrand cross-link of C1; (iv) the reduced affinity of HMG domain proteins to the major adduct of C1; (v) the enhanced efficiency of the DNA adducts of C1 to block DNA polymerization and to inhibit transcription activity of human RNA pol II and RNA transcription; (vi) slower rate of the reaction of C1 with glutathione, may partially contribute to the unique activity of C1.

Serum metallothioneins in childhood tumours-a potential prognostic marker

Metallothioneins (MT) are low molecular weight, cysteine-rich proteins maintaining metal ions homeostasis. They play a role in carcinogenesis and may also cause chemoresistance. The aim of the study was to explore the importance of MT serum levels in children suffering from malignant tumours. This prospective study involves examination of 865 samples from 172 patients with malignant tumours treated from 2008 to 2011 at University Hospital Motol. MT serum levels were determined using differential pulse voltammetry-Brdicka reaction. Mean MT level was 2.7 ± 0.5 μM. There was no statistically significant difference between MT levels in different tumours. We also did not find any correlation between MT levels and response to therapy or clinical stages. However, we found a positive correlation between MT levels and age (p = 0.009) and a negative correlation with absolute lymphocyte number (p = 0.001). The fact that patients who had early disease recurrence had lower MT levels during the treatment (complete remission 2.67 vs. recurring 2.34, p = 0.001) seems to be important for clinical practice. Accordingly we believe that there is benefit in further studies of serum MT levels in tumours.

Toxicity in tumor cells, DNA binding mode, and resistance to decomposition by sulfur nucleophiles of new dinuclear bifunctional trans-PtII complexes containing long alkane linkers

In an effort to design dinuclear PtII compounds that maintain the target (DNA) binding profile of the trans-oriented dinuclear bifunctional PtII complexes containing aliphatic linker chains but are less susceptible to metabolic decomposition, the new, long-chain dinuclear PtII complexes—[{trans-PtCl(dien)}2-μ-(CH2)n]2+ (n = 7,10,12, dien = diethylenetriamine)—were synthesized. The toxicity of these metallodrugs was examined in ovarian tumor cell lines. The results showed that the activity of these complexes increased with growing length of the linker; the activity of complex containing the longest linker (n = 12) was comparable with that of cis-diamminedichloridoplatinum(II) (cisplatin). This observation correlated with the results of DNA binding studies performed in cell-free media. The results of these studies demonstrated that the growing length of the aliphatic bridge promoted more distorting conformational alterations induced in DNA. Attention was also paid to the reactivity of {[Pt(dien)Cl]2-alkane} compounds with glutathione (GSH). The results of these experiments support the thesis that the dinuclear structure of {[Pt(dien)Cl]2-alkane} complexes remains stable in the presence of S-containing compounds without undergoing chemical degradation as previously observed for some di/trinuclear bifunctional PtII complexes. This enhanced stability represents a favorable property which may contribute to reduce side effects and increase therapeutic efficacy of the dinuclear {[Pt(dien)Cl]2-alkane} compounds.

Retained platinum uptake and indifference to p53 status make novel transplatinum agents active in platinum-resistant cells compared to cisplatin and oxaliplatin

Despite the clinical success of platinum-containing drugs in the treatment of solid tumors, acquired resistance remains a major obstacle. We previously identified a group of novel transplanaramine or transplatinum compounds based on distinct activity profiles in the NCI-60 panel. In the present study, parental KB-3.1 cells with wild-type p53 and its cisplatin- and oxaliplatin-resistant sublines harboring mutant p53 proteins were used to contrast several transplatinum compounds with cisplatin and oxaliplatin. The transplatinum compounds retained cytotoxic activity in the resistant cell lines. While intracellular accumulation and DNA platination of cisplatin and oxaliplatin was decreased in the resistant cells, the transplatinum compounds both accumulated intracellularly and platinated DNA at comparable levels in all cell lines. Cytoflow analysis confirmed that cisplatin and oxaliplatin alter the cell cycle distribution and result in apoptosis; however, at comparably toxic concentrations, the transplatinum compounds did not alter the cell cycle distribution. Analysis of the cytoplasmic fraction treated with acetone showed that cisplatin and oxaliplatin readily bound to macromolecules in the pellet, whereas a larger percentage of the transplatinum compounds remained in the supernatant. We concluded that, distinct from platinum compounds currently in use, transplatinum compounds accumulate intracellularly in resistant cells at levels comparable to those in drug-sensitive cells, do not affect the cell cycle and thus retain cytotoxicity independent of p53 status and likely have cytoplasmic targets that are important in their activity.

Comparative nephrotoxicity of Cisplatin and nedaplatin: mechanisms and histopathological characteristics

The antineoplastic platinum complexes cisplatin and its analogues are widely used in the chemotherapy of a variety of human malignancies, and are especially active against several types of cancers. Nedaplatin is a second-generation platinum complex with reduced nephrotoxicity. However, their use commonly causes nephrotoxicity due to a lack of tumor tissue selectivity. Several recent studies have provided significant insights into the molecular and histopathological events associated with nedaplatin nephrotoxicity. In this review, we summarize findings concerning the renal histopathology and molecular pathogenesis induced by antineoplastic platinum complexes, with a particular focus on the comparative nephrotoxicity of cisplatin and nedaplatin in rats.

The anticancer drug cisplatin can cross-link the interdomain zinc site on human albumin

Cisplatin, cis-[Pt(Cl(2)(NH(3))(2)], can crosslink residues His67 of domain I and His247 of domain II in human albumin, occupying the major binding site for the essential metal zinc on the protein.

Studies on cellular accumulation of satraplatin and its major metabolite JM118 and their interactions with glutathione

Before the active form of a Pt drug reaches its major pharmacological target in the cell nucleus, the Pt complex has to accumulate in cells, and during its transportation into cells and inside cells, it reacts with various biomolecules. Satraplatin is the first orally administered Pt drug under active clinical investigation. The major metabolite of this Pt(IV) complex is its Pt(II) analogue (JM118), which also has significant anticancer properties. Here we report the role of active transport in cellular entry of satraplatin and JM118 and interactions of these Pt complexes with glutathione. The results reveal that the organic cation transporters may play a more important role in the mechanism of cytotoxicity of JM118 than in the cytotoxicity of cisplatin. In contrast, satraplatin is a poor substrate of these transporters. In addition, satraplatin reacts with glutathione with the rate markedly lower than JM118 and cisplatin. Interestingly, satraplatin can be activated by glutathione allowing it to react with DNA, although to a much lower extent than in the case of another Pt(IV) drug tetraplatin.

Ergothioneine protects against neuronal injury induced by cisplatin both in vitro and in vivo

The neuroprotective effects of ergothioneine (EGT) against cisplatin toxicity were investigated both in vitro and in vivo. For in vitro study, two types of neuronal cells, primary cortical neuron (PCN) cells and rat pheochromocytoma (PC12) cells, were incubated with EGT (0.1-10.0 μM) for 2 h followed by incubation with 0.5 μM cisplatin for 72 h. Results show that cisplatin markedly decreased the proliferation of PC12 cells and strongly inhibited the growth of axon and dendrite of PCN cells, but these effects were significantly prevented by EGT. For in vivo study, CBA mice were orally administered with 2 or 8 mg EGT/kg body weight for 58 consecutive days and were injected i.p. with 5mg cisplatin/kg body weight on days 7, 9 and 11. We found that EGT significantly restored the learning and memory deficits in mice treated with cisplatin evaluated by active and passive avoidance tests. EGT also significantly prevented brain lipid peroxidation, restored acetylcholinesterase (AChE) activity and maintained glutathione/glutathione disulfide ratio in brain tissues of mice treated with cisplatin. These results demonstrate that EGT protects against cisplatin-induced neuronal injury and enhances cognition, possibly through the inhibition of oxidative stress and restoration of AChE activity in neuronal cells.

Cellular responses to Cisplatin-induced DNA damage

Cisplatin is one of the most effective anticancer agents widely used in the treatment of solid tumors. It is generally considered as a cytotoxic drug which kills cancer cells by damaging DNA and inhibiting DNA synthesis. How cells respond to cisplatin-induced DNA damage plays a critical role in deciding cisplatin sensitivity. Cisplatin-induced DNA damage activates various signaling pathways to prevent or promote cell death. This paper summarizes our current understandings regarding the mechanisms by which cisplatin induces cell death and the bases of cisplatin resistance. We have discussed various steps, including the entry of cisplatin inside cells, DNA repair, drug detoxification, DNA damage response, and regulation of cisplatin-induced apoptosis by protein kinases. An understanding of how various signaling pathways regulate cisplatin-induced cell death should aid in the development of more effective therapeutic strategies for the treatment of cancer.

Cytotoxicity, cellular uptake, glutathione and DNA interactions of an antitumor large-ring Pt II chelate complex incorporating the cis-1,4-diaminocyclohexane carrier ligand

Earlier studies have described promising antitumor activity of a large-ring chelate complex [PtCl(2)(cis-1,4-DACH)] (DACH=diaminocyclohexane). Encouraging antitumor activity of this analogue of cisplatin prompted us to perform studies focused on the mechanistic basis of pharmacological effects of this complex. Four early steps in the mechanism of biological activity of cisplatin have been delineated: cell entry, reactions with sulfur-containing compounds, platinum-DNA binding along with processing platinated DNA by proteins (enzymes) and DNA repair. Here, we describe comparative experiments (involving also cisplatin) revealing: (i) improved cytotoxicity (3.4-5.4-fold) of [PtCl(2)(cis-1,4-DACH)] in human tumor ovarian cell lines; (ii) enhanced cellular uptake (approximately 1.5-fold) of [PtCl(2)(cis-1,4-DACH)]; (iii) somewhat enhanced rate of reactions of [PtCl(2)(cis-1,4-DACH)] with glutathione (approximately 1.5-fold), but a similar rate of reactions with metallothionenin-2; (iv) enhanced rate of DNA binding of [PtCl(2)(cis-1,4-DACH)] in cell-free media (approximately 2-fold); (v) similar sequence preference of DNA binding of [PtCl(2)(cis-1,4-DACH)] in cell-free media; (vi) identical DNA interstrand cross-linking efficiency (6%); (vii) similar bending (32 degrees) and enhanced local unwinding (approximately 1.5-fold) induced in DNA by the major 1,2-GG-intrastrand cross-link; (viii) markedly enhanced inhibiting effects of DNA adducts of [PtCl(2)(cis-1,4-DACH)] on processivity of DNA polymerase; and (ix) a slightly lower efficiency of DNA repair systems to remove the adducts of [PtCl(2)(cis-1,4-DACH)] from DNA.

Analytical methodologies for metallomics studies of antitumor Pt-containing drugs

Pt-containing drugs are nowadays essential components in cancer chemotherapy. However, drug resistance and side effects limit the efficiency of the treatments. In order to improve the response to Pt-based drugs, different administration strategies or new Pt-compounds have been developed with little success. The reason for this failure could be that the mechanism of action of these drugs is not completely understood. In this way, metallomics studies may contribute to clarify the interactions of Pt-containing drugs within the organism. This review is mainly focused on the role of Analytical Chemistry on the study of the interactions between Pt-based drugs and biomolecules. A summary of the analytical techniques and the most common sample treatment procedures currently used in metallomics studies of these drugs is presented. Both are of paramount importance to study these complex samples preserving the drug-biomolecule interaction. Separation and detection techniques must be carefully selected in order to achieve the intended goals. The use of multidimensional hyphenated techniques is usually necessary for a better understanding of the Pt-based drugs interactions in the organism. An overview of Pt-drugs biological interactions is presented, considering the different sample matrices and the drugs course through the organism. Samples analysed in the included studies are blood, urine, cell cytosol, DNA as well as the drugs themselves and their derivatives. However, most of these works are based on in vitro experiments or incubations of standards, leading in some cases to contradictory results depending on the experimental conditions used. Though in vivo experiments represent a great challenge due to the high complexity and the low concentrations of the Pt-adducts in real samples, these studies must be undertaken to get a deeper understanding of the real interactions concerning Pt-containing drugs.

Conformation and recognition of DNA modified by a new antitumor dinuclear PtII complex resistant to decomposition by sulfur nucleophiles

Reported herein is a detailed biochemical and molecular biophysics study of the molecular mechanism of action of antitumor dinuclear Pt(II) complex [{PtCl(DACH)}(2)-mu-Y](4+) [DACH=1,2-diaminocyclohexane, Y=H(2)N(CH(2))(6)NH(2)(CH(2))(2)NH(2)(CH(2))(6)NH(2)] (complex 1). This new, long-chain bifunctional dinuclear Pt(II) complex is resistant to metabolic decomposition by sulfur-containing nucleophiles. The results show that DNA adducts of 1 can largely escape repair and yet inhibit very effectively transcription so that they should persist longer than those of conventional cisplatin. Hence, they could trigger a number of downstream cellular effects different from those triggered in cancer cells by DNA adducts of cisplatin. This might lead to the therapeutic effects that could radically improve chemotherapy by platinum complexes. In addition, the findings of the present work make new insights into mechanisms associated with antitumor effects of dinuclear/trinuclear Pt(II) complexes possible.