Interactions between anticancer trans-platinum compounds and proteins: crystal structures and ESI-MS spectra of two protein adducts of trans-(dimethylamino)(methylamino)dichloridoplatinum(II)

Tyrosine kinase inhibitors (TKIs) for ovarian cancer treatment: from organic to inorganic chemotherapeutics towards selectivity-a perspective overview

Ovarian cancer (OC) is a lethal gynecologic cancer in industrialized countries. Treatments for OC include the surgical removal and chemotherapy. In the last decades, improvements have been made in the surgery technologies, drug combinations and administration protocols, and in diagnosis. However, mortality from OC is still high owing to recurrences and insurgence of drug resistance. Accordingly, it is urgent the development of novel agents capable to effectively target OC. In this respect, tyrosine kinase inhibitors (TKIs) may play an important role. Most of TKIs developed and tested so far are organic. However, owing to their chemical versatility, also metals can be exploited to design selective and potent TKIs. We provide a short and easy-to-read overview on the main organic TKIs with a summary of those that entered clinical trials. Additionally, we describe the potential of metal-based TKIs, focusing on this overlooked family of compounds that may significantly contribute towards the concept of precision-medicine.

Anti-Her2 affibody-decorated arsenene nanosheets induce ferroptosis through depleting intracellular GSH to overcome cisplatin resistance

Ferroptosis, a form of regulated cell death induced by excessive accumulation of reactive oxygen species and lipid peroxidation, has recently attracted extensive attention due to its ability to effectively suppress tumors and overcome drug resistance. Unlike previously reported metal nanomaterials that induce ferroptosis via the Fenton reaction, arsenene nanosheets can effectively deplete intracellular glutathione and then induce ferroptosis by inhibiting glutathione peroxidase 4. In this study, we designed target-modified arsenene nanosheets loaded with cisplatin (Her2-ANs@CDDP), which are capable of selective uptake by tumor cells. Her2-ANs@CDDP promotes both apoptosis and ferroptosis through a reciprocal cascade reaction between cisplatin and the carrier, respectively, and we demonstrate that it can significantly inhibit the activity of drug-resistant cells. Arsenene nanosheets kill drug-resistant tumor cells by inducing ferroptosis and restoring the sensitivity of drug-resistant cells to cisplatin. Cisplatin-loaded arsenene nanosheets can be prepared simply, and exert synergistic effects that overcome drug resistance. They show great potential for applications in the clinical treatment of chemotherapy-insensitive osteosarcoma, expanding the uses of arsenic in the treatment of solid tumors.

Chemical Modification of Auranofin Yields a New Family of Anticancer Drug Candidates: The Gold(I) Phosphite Analogues

A panel of four novel gold(I) complexes, inspired by the clinically established gold drug auranofin (1-Thio-β-D-glucopyranosatotriethylphosphine gold-2,3,4,6-tetraacetate), was prepared and characterized. All these compounds feature the replacement of the triethylphosphine ligand of the parent compound auranofin with a trimethylphosphite ligand. The linear coordination around the gold(I) center is completed by Cl^-, Br^-, I^- or by the thioglucose tetraacetate ligand (SAtg). The in-solution behavior of these gold compounds as well as their interactions with some representative model proteins were comparatively analyzed through ³¹PNMR and ESI-MS measurements. Notably, all panel compounds turned out to be stable in aqueous media, but significant differences with respect to auranofin were disclosed in their interactions with a few leading proteins. In addition, the cytotoxic effects produced by the panel compounds toward A2780, A2780R and SKOV-3 ovarian cancer cells were quantitated and found to be in the low micromolar range, since the IC₅₀ of all compounds was found to be between 1 μM and 10 μM. Notably, these novel gold complexes showed large and similar inhibition capabilities towards the key enzyme thioredoxin reductase, again comparable to those of auranofin. The implications of these results for the discovery of new and effective gold-based anticancer agents are discussed.

Digging into protein metalation differences triggered by fluorine containing-dirhodium tetracarboxylate analogues

Catalytic and biological properties of dirhodium tetracarboxylates ([Rh2(μ-O2CR)4L2], L=axial ligand, R=CH3-, CH3CH2-, etc) largely depend on the nature of the bridging carboxylate equatorial μ-O2CR ligands, which can be easily exchanged...

Interaction of Platinum-based Drugs with Proteins: An Overview of Representative Crystallographic Studies

Pt-based drugs are widely used in clinics for the treatment of cancer. The mechanism of action of these molecules relies on their interaction with DNA. However, the recognition of these metal compounds by proteins plays an important role in defining pharmacokinetics, side effects and their overall pharmacological profiles. Single crystal X-ray diffraction studies provided important information on the molecular mechanisms at the basis of this process. Here, the molecular structures of representative adducts obtained upon reaction with proteins of selected Pt-based drugs, including cisplatin, carboplatin and oxaliplatin, are briefly described and comparatively examined. Data indicate that metal ligands play a significant role in driving the reaction of Pt compounds with proteins; non-covalent interactions that occur in the early steps of Pt compound/protein recognition process play a crucial role in defining the structure of the final Pt-protein adduct. In the metallated protein structures, Pt centers coordinate few protein side chains, such as His, Met, Cys, Asp, Glu and Lys residues upon releasing labile ligands.

Preclinical Advances in Theranostics for the Different Molecular Subtypes of Breast Cancer

Breast cancer is the most common cancer in women worldwide. The heterogeneity of breast cancer and drug resistance to therapies make the diagnosis and treatment difficult. Molecular imaging methods with positron emission tomography (PET) and single-photon emission tomography (SPECT) provide useful tools to diagnose, predict, and monitor the response of therapy, contributing to precision medicine for breast cancer patients. Recently, many efforts have been made to find new targets for breast cancer therapy to overcome resistance to standard of care treatments, giving rise to new therapeutic agents to offer more options for patients with breast cancer. The combination of diagnostic and therapeutic strategies forms the foundation of theranostics. Some of these theranostic agents exhibit high potential to be translated to clinic. In this review, we highlight the most recent advances in theranostics of the different molecular subtypes of breast cancer in preclinical studies.

Mustards-Derived Terpyridine-Platinum Complexes as Anticancer Agents: DNA Alkylation vs Coordination

The development of bifunctional platinum complexes with the ability to interact with DNA via different binding modes is of interest in anticancer metallodrug research. Therefore, we report platinum(II) terpyridine complexes to target DNA by coordination and/or through a tethered alkylating moiety. The platinum complexes were evaluated for their in vitro antiproliferative properties against the human cancer cell lines HCT116 (colorectal), SW480 (colon), NCI-H460 (non-small cell lung), and SiHa (cervix) and generally exhibited potent antiproliferative activity although lower than their respective terpyridine ligands. ¹H NMR spectroscopy and/or ESI-MS studies on the aqueous stability and reactivity with various small biomolecules, acting as protein and DNA model compounds, were used to establish potential modes of action for these complexes. These investigations indicated rapid binding of complex PtL3 to the biomolecules through coordination to the Pt center, while PtL4 in addition alkylated 9-ethylguanine. PtL3 was investigated for its reactivity to the model protein hen egg white lysozyme (HEWL) by protein crystallography which allowed identification of the N^δ1 atom of His15 as the binding site.

The first step of arsenoplatin-1 aggregation in solution unveiled by solving the crystal structure of its protein adduct

Arsenoplatin-1 (AP-1) is an innovative dual-action anticancer agent that contains a platinum(ii) center coordinated to an arsenous acid moiety. We found that AP-1 spontaneously aggregates in aqueous solutions generating oligomeric species of increasing length. Afterward, we succeeded in solving the crystal structure of the adduct formed between the model protein lysozyme and an early AP-1 oligomer that turned out to be a trimer. Remarkably, this crystal structure traps an early stage of AP-1 aggregation offering detailed insight into the molecular process of the oligomer's growth.

Platinum(II) O,S Complexes Inhibit the Aggregation of Amyloid Model Systems

Platinum(II) complexes with different cinnamic acid derivatives as ligands were investigated for their ability to inhibit the aggregation process of amyloid systems derived from Aβ, Yeast Prion Protein Sup35p and the C-terminal domain of nucleophosmin 1. Thioflavin T binding assays and circular dichroism data indicate that these compounds strongly inhibit the aggregation of investigated peptides exhibiting IC₅₀ values in the micromolar range. MS analysis confirms the formation of adducts between peptides and Pt(II) complexes that are also able to reduce amyloid cytotoxicity in human SH-SY5Y neuroblastoma cells. Overall data suggests that bidentate ligands based on β-hydroxy dithiocinnamic esters can be used to develop platinum or platinoid compounds with anti-amyloid aggregation properties.

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.

Platinum(ii) O,S complexes as potential metallodrugs against Cisplatin resistance

We report on platinum(ii) complexes with different cinnamic acid derivatives as ligands with cytotoxic activity against Cisplatin resistant ovarian cancer cell line subcultures of SKOV3 and A2780. A typical mechanism of action for platinum(ii) complexes as Cisplatin itself is binding to the DNA and inducing double-strand breaks. We examined the biological behavior of these potential drugs with 9-methylguanine using NMR spectroscopic methods and their DNA damage potential including γH2AX-foci analyses. X-ray diffraction methods have been used to elucidate the molecular structures of the platinum(ii) complexes. Interactions with the model protein lysozyme have been evaluated by different techniques including UV-Vis absorption spectroscopy, fluorescence and X-ray crystallography.

Reactions of a tetranuclear Pt-thiosemicarbazone complex with model proteins

The tetranuclear Pt complex (PtL)₄ (where L^2- is the anion derived from para-isopropyl thiosemicarbazone) was first described in A.G. Quiroga et al., J. Med. Chem. 41, 1998, 1399-1408. (PtL)₄ manifests antiproliferative properties toward various cancer cell lines being a promising anticancer drug candidate. Yet, details of its reactivity with biomolecules have not been elucidated. To this end, we investigated the reactions of (PtL)₄ with a few model proteins, i.e. bovine pancreatic ribonuclease (RNase A), cytochrome c (Cyt c) and hen egg white lysozyme (Lysozyme), through electrospray ionization mass spectrometry and other biophysical methods. A rich reactivity of (PtL)₄ with the above-mentioned model proteins is observed, leading to the formation of numerous metallodrug-protein adducts. The tetranuclear complex breaks down and various fragments bind proteins up to high metal/protein ratios; this typically results into very complicated mass spectral patterns. However, some of the main mass peaks could be assigned in the case of the Lysozyme adduct. In addition, crystallographic data were obtained for the (PtL)₄/Lysozyme and (PtL)₄/RNase A adducts pointing at His side chains as the primary binding sites for monometallic Pt fragments. Notably, a few selected features of the interactions observed in the (PtL)₄/protein adducts were reproduced by reacting (PtL)₄ with a small molecule, i.e. N-methylimidazole. In conclusion, the present study confirms the prodrug nature of the tetraplatinum complex, clarifies one possible pathway for its activation through cluster disassembly and allows initial identification of adducts formed with a representative protein.

Ru-Based CO releasing molecules with azole ligands: interaction with proteins and the CO release mechanism disclosed by X-ray crystallography

Structural data on the adducts formed upon reaction of Ru-based CO releasing molecules containing azole ligands with model proteins are reported.

A Novel Platinum(II)-Based Bifunctional ADC Linker Benchmarked Using 89Zr-Desferal and Auristatin F-Conjugated Trastuzumab

Greater control is desirable in the stochastic conjugation technology used to synthesize antibody-drug conjugates (ADC). We have shown recently that a fluorescent dye can be stably conjugated to a mAb using a bifunctional platinum(II) linker. Here, we describe the general applicability of this novel linker technology for the preparation of stable and efficacious ADCs. The ethylenediamine platinum(II) moiety, herein called Lx, was coordinated to Desferal (DFO) or auristatin F (AF) to provide storable "semifinal" products, which were directly conjugated to unmodified mAbs. Conjugation resulted in ADCs with unimpaired mAb-binding characteristics, DAR in the range of 2.5 to 2.7 and approximately 85% payload bound to the Fc region, presumably to histidine residues. To evaluate the in vivo stability of Lx and its effect on pharmacokinetics and tumor targeting of an ADC, Lx-DFO was conjugated to the HER2 mAb trastuzumab, followed by radiolabeling with ⁸⁹Zr. Trastuzumab-Lx-DFO-⁸⁹Zr was stable in vivo and exhibited pharmacokinetic and tumor-targeting properties similar to parental trastuzumab. In a xenograft mouse model of gastric cancer (NCI-N87) or an ado-trastuzumab emtansine-resistant breast cancer (JIMT-1), a single dose of trastuzumab-Lx-AF outperformed its maleimide benchmark trastuzumab-Mal-AF and FDA-approved ado-trastuzumab emtansine. Overall, our findings show the potential of the Lx technology as a robust conjugation platform for the preparation of anticancer ADCs. Cancer Res; 77(2); 257-67. ©2016 AACR.

Effect of temperature on the interaction of cisplatin with the model protein hen egg white lysozyme

The products of the reaction between cisplatin (CDDP) and the model protein hen egg white lysozyme (HEWL) at 20, 37 and 55 °C in pure water were studied by UV-Vis absorption spectroscopy, intrinsic fluorescence and circular dichroism, dynamic and electrophoretic light scattering and inductively coupled plasma mass spectrometry. X-ray structures were also solved for the adducts formed at 20 and 55 °C. Data demonstrate that high temperature facilitates the formation of CDDP-HEWL adducts, where Pt atoms bind ND1 atom of His15 or NE2 atom of His15 and NH1 atom of Arg14. Our study suggests that high human body temperature (fever) could increase the rate of drug binding to proteins thus enhancing possible toxic side effects related to CDDP administration.

Oxaliplatin vs. cisplatin: competition experiments on their binding to lysozyme

The model protein hen egg white lysozyme was challenged with oxaliplatin and cisplatin. ESI mass spectrometry, surface plasmon resonance and thermal shift analyses demonstrate the formation of a bis-platinum adduct, though in very small amounts. Crystals of the bis-platinum adduct were obtained using two different preparations and the X-ray structures were solved at 1.85 Å and 1.95 Å resolution. Overall, the obtained data point out that, under the analyzed conditions, the two Pt drugs have similar affinities for the protein, but bind on its surface at two non-overlapping sites. In other words, these two drugs manifest a significantly different reactivity with this model protein and do not compete for the same protein binding sites.

Cisplatin binding to human serum albumin: a structural study

The reaction between cisplatin and human serum albumin (HSA) was investigated by X-ray crystallography and crystal structures of the cisplatin/HSA adduct were eventually solved for the first time. Structural data unambiguously prove that cisplatin mainly binds to His105 and Met329 side chains; additional binding sites are detected at His288, Met298, and Met548 and at His535, His67 and His247.

Unusual mode of protein binding by a cytotoxic π-arene ruthenium(ii) piano-stool compound containing an O,S-chelating ligand

A new π-arene Ru(ii) piano-stool compound, showing significant cytotoxic activityin vitro, was synthesized. The X-ray structure of this compound and that of its complex with RNase A were determined.

Platinum(II) Complexes with O,S Bidentate Ligands: Biophysical Characterization, Antiproliferative Activity, and Crystallographic Evidence of Protein Binding

We recently characterized a series of novel platinum(II) compounds bearing a conserved O,S binding moiety as a bifunctional ligand and evaluated their solution behavior and antiproliferative properties in vitro against a representative cancer cell line. On the whole, those platinum compounds showed an appreciable stability in mixed dimethyl sulfoxide-aqueous buffers and promising in vitro cytotoxic effects; yet they manifested a rather limited solubility in aqueous media making them poorly suitable for further pharmaceutical development. To overcome this drawback, four new derivatives of this series were prepared and characterized based on a careful choice of substituents on the O,S bidentate ligand. The solubility and stability profile of these novel compounds in a reference buffer was determined, as well as the ligands' log P(o/w) value (P(o/w) = n-octanol-water partition coefficient) as an indirect measure for the complexes' lipophilicity. The antiproliferative properties were comparatively evaluated in a panel of three cancer cell lines. The protein binding properties of the four platinum compounds were assessed using the model protein hen egg white lysozyme (HEWL), and the molecular structures of two relevant HEWL-metallodrug adducts were solved. Overall, it is shown that a proper choice of the substituents leads to a higher solubility and enables a selective fine-tuning of the antiproliferative properties. The implications of these results are thoroughly discussed.

Interactions of carboplatin and oxaliplatin with proteins: Insights from X-ray structures and mass spectrometry studies of their ribonuclease A adducts

Oxaliplatin and carboplatin are two platinum(II) drugs in widespread clinical use for the treatment of various types of cancers; yet, structural information on their interactions with proteins is scarce. Here, the X-ray structures of the adducts formed upon reaction of carboplatin and oxaliplatin with bovine pancreatic ribonuclease (RNase A) are reported and compared with results obtained for the structure of the RNase A-cisplatin adduct derived from isomorphous crystals, under the same experimental conditions. Additional details on the binding mode of these metallodrugs toward RNase A are provided by electrospray ionization mass spectrometry (ESI MS) measurements, thus offering insight on the occurring metal-protein interactions. Notably, while carboplatin and cisplatin mainly bind the side chain of Met29, oxaliplatin also binds the side chains of Asp14, of catalytically important His119 and, to a lesser extent, of His105. On the basis of the available data, a likely mechanism for oxaliplatin hydrolysis and binding to the protein is proposed. These results are potentially useful for a better understanding of the biological chemistry, toxicity and side effects of this important class of antitumor agents.

Interactions of gold-based drugs with proteins: the structure and stability of the adduct formed in the reaction between lysozyme and the cytotoxic gold(III) compound Auoxo3

The structure and stability of the adduct formed in the reaction between Auoxo3, a dinuclear gold(iii) compound, and the model protein hen egg white lysozyme (HEWL) are investigated by X-ray crystallography, UV-Vis absorption spectroscopy and circular dichroism (CD). It is found that Auoxo3 breaks down completely, undergoes reduction and produces reactive gold(i) species able to bind the protein and form stable derivatives. The behaviour of Auoxo3 is compared with that of two analogous gold(iii) complexes previously studied: a few significant differences are highlighted. The general implications of these new results for the mode of action of cytotoxic gold complexes are discussed.

Platinated oligomers of bovine pancreatic ribonuclease: Structure and stability

The reaction between cis-diamminedichloroplatinum(II) (CDDP), cisplatin, a common anticancer drug, and bovine pancreatic ribonuclease (RNase A), induces extensive protein aggregation, leading to the formation of one dimer, one trimer and higher oligomers whose yields depend on cisplatin/protein ratio. Structural and functional properties of the purified platinated species, together with their spontaneous dissociation and thermally induced denaturation, have been characterized. Platinated species preserve a significant, although reduced, ribonuclease activity. The high resistance of the dimers against dissociation and the different thermal unfolding profiles suggest a quaternary structure different from those of the well-known swapped dimers of RNase A.

Design and biological evaluation of new platinum(II) complexes bearing ligands with DNA-targeting ability

A novel series of platinum(II) complexes bearing aliphatic amines and ligands with DNA-targeting properties was synthesized to achieve more potent and selective metallodrugs. We developed six new platinum-based drugs, which contain methylamine, 1a-c, and isopropylamine, 2a-c, both in the trans position to a selected targeting ligand: naphthalimide. The activity of the complexes has been evaluated in order to confirm the improvements from our proposed approach, and the complexes demonstrate better cytotoxic activity on cancer cell lines when compared with the ligands and, importantly, with cisplatin. Further studies were performed to assess their subcellular localization and binding mode to DNA.