An Antitumor Bis(N-Heterocyclic Carbene)Platinum(II) Complex That Engages Asparagine Synthetase as an Anticancer Target

New anticancer platinum(II) compounds with distinctive modes of action are appealing alternatives to combat the drug resistance and improve the efficacy of clinically used platinum chemotherapy. Herein, we describe a rare example of an antitumor Pt^II complex targeting a tumor-associated protein, rather than DNA, under cellular conditions. Complex [(bis-NHC)Pt(bt)]PF₆ (1 a; Hbt=1-(3-hydroxybenzo[b]thiophen-2-yl)ethanone) overcomes cisplatin resistance in cancer cells and displays significant tumor growth inhibition in mice with higher tolerable doses compared to cisplatin. The cellular Pt species shows little association with DNA, and localizes in the cytoplasm as revealed by nanoscale secondary ion mass spectrometry. An unbiased thermal proteome profiling experiment identified asparagine synthetase (ASNS) as a molecular target of 1 a. Accordingly, 1 a treatment reduced the cellular asparagine levels and inhibited cancer cell proliferation, which could be reversed by asparagine supplementation. A bis-NHC-ligated Pt species generated from the hydrolysis of 1 a forms adducts with thiols and appears to target an active-site cysteine of ASNS.

TriplatinNC and Biomolecules: Building Models Based on Non-covalent Interactions

The class of polynuclear platinum(II) compounds have demonstrated a great interest because their high activity against cancer cells. Among these new compounds, the TriplatinNC also called AH78, demonstrated surprising antitumor activity, in some cases equivalent to cisplatin. It is well-known that complex charge +8 favors interaction with DNA and other biomolecules non-covalently, through the hydrogen bonds with phosphate and sulfate groups present in these structures. The hydrogen atoms of the amine interact with the oxygen atoms of the phosphate and sulfate groups present in the DNA strand and heparan sulfate, respectively. These interactions can cause significant twists in double helix and inhibit the activity of these biomolecules. The present investigation is an attempt to provide a benchmark theoretical study about TriplatinNC. We have described the non-covalent interactions through small reliable mimetic models. The non-covalent interactions were also evaluated on larger models containing DNA fractions with six nitrogenous base pairs (CGCGAA) and fractions of the disaccharide that makes the HS evaluated by the hybrid QM/MM ONIOM methodology.

Substitution-Inert Polynuclear Platinum Complexes with Dangling Amines: Condensation/Aggregation of Nucleic Acids and Inhibition of DNA-Related Enzymatic Activities

The substitution-inert polynuclear platinum complexes (SI-PPCs) are now recognized as a distinct subclass of platinum anticancer drugs with high DNA binding affinity. Here, we investigate the effects of SI-PPCs containing dangling amine groups in place of NH₃ as ligands to increase the length of the molecule and therefore overall charge and its distribution. The results obtained with the aid of biophysical techniques, such as total intensity light scattering, gel electrophoresis, and atomic force microscopy, show that addition of dangling amine groups considerably augments the ability of SI-PPCs to condense/aggregate nucleic acids. Moreover, this enhanced capability of SI-PPCs correlates with their heightened efficiency to inhibit DNA-related enzymatic activities, such as those connected with DNA transcription, catalysis of DNA relaxation by DNA topoisomerase I, and DNA synthesis catalyzed by Taq DNA polymerase. Thus, the addition of the dangling amine groups resulting in structures of SI-PPCs, which differ so markedly from the derivatives of cisplatin used in the clinic, appears to contribute to the overall biological activity of these molecules.

Arsenoplatin-1 Is a Dual Pharmacophore Anticancer Agent

Arsenoplatins are adducts of two chemically important anticancer drugs, cisplatin and arsenic trioxide, that have a Pt(II) bond to an As(III) hydroxide center. Screens of the NCI-60 human tumor cell lines reveal that arsenoplatin-1 (AP-1), [Pt(μ-NHC(CH3)O)2ClAs(OH)2], the first representative of this novel class of anticancer agents, displays a superior activity profile relative to the parent drugs As2O3 or cisplatin in a majority of cancer cell lines tested. These activity profiles are important because the success of arsenic trioxide in blood cancers (such as APL) has not been seen in solid tumors due to the rapid clearance of arsenous acid from the body. To understand the biological chemistry of these compounds, we evaluated interactions of AP-1 with the two important classes of biomolecules-proteins and DNA. The first structural studies of AP-1 bound to model proteins reveal that platinum(II) binds the Nε of His in a manner that preserves the Pt-As bond. We find that AP-1 readily enters cells and binds to DNA with an intact Pt-As bond (Pt:As ratio of 1). At longer incubation times, however, the Pt:As ratio in DNA samples increases, suggesting that the Pt-As bond breaks and releases the As(OH)2 moiety. We conclude that arsenoplatin-1 has the potential to deliver both Pt and As species to a variety of hematological and solid cancers.

Unfolded Protein Response is Involved in Trans-Platinum (II) Complex-Induced Apoptosis in Prostate Cancer Cells via ROS Accumulation

BACKGROUND

Prostate cancer is one of the most common cancer types and it is the sixth leading cause of cancer-related death in men worldwide. Even though novel treatment modalities have been developed, it still a lifethreatening disease. Therefore novel compounds are needed to improve the overall survival.

METHODS

In our study, it was aimed to evaluate the anti-cancer activity of newly synthesized Platinum (II) [Pt(II)] complex on DU145, LNCaP and PC-3 prostate cancer cell lines. The cytotoxic activity of Pt(II) complex was tested by SRB and ATP cell viability assays. To detect the mode of cell death; fluorescent staining, flow cytometry and western blot analyses were performed.

RESULTS

The Pt(II) complex treatment resulted in a decrease in cell viability and increasing levels of apoptotic markers (pyknotic nuclei, annexin-V, caspase 3/7 activity) and a decrease in mitochondrial membrane potential in a dose dependent manner. Among cell types, tested PC-3 cells were found to be more sensitive to Pt(II) complex, demonstrating elevation of DNA damage in this cell line. In addition, Pt(II) complex induced Endoplasmic Reticulum (ER) stress by triggering ROS generation. More importantly, pre-treatment with NAC alleviated Pt(II) complex-mediated ER stress and cell death in PC-3.

CONCLUSION

These findings suggest an upstream role of ROS production in Pt(II) complex-induced ER stressmediated apoptotic cell death. Considering the ROS-mediated apoptosis inducing the effect of Pt(II) complex, it warrants further evaluation as a novel metal-containing anticancer drug candidate.

Synthesis, characterization and biological investigation of platinum(ii) complexes with asparagusic acid derivatives as ligands

After more than 50 years of platinum-based anticancer research only three compounds are in clinical use worldwide. The use of the well-known lead compound of this class of anticancer agents, cisplatin, is limited by its side effects and varying resistance mechanisms. Therefore, we report on platinum(ii) compounds with asparagusic acid derivatives as ligands which show interesting anticancer results on cisplatin resistant cell lines.

Nanoparticles of Metal-Organic Cages Overcoming Drug Resistance in Ovarian Cancer

A long-standing challenge in the treatment of ovarian cancer is drug resistance to standard platinum-based chemotherapy. Recently, increasing attention has been drawn to the use of self-assembled metal-organic complexes as novel therapeutics for cancer treatment. However, high hydrophobicity that is often associated with these structures lowers their solubility and hinders their clinical translation. In this article, we present a proof-of-concept study of using nanoprecipitation to formulate the hydrophobic metal-organic cages and facilitate their use in treating chemoresistant ovarian cancer. The Pt₆L₄ Cage 1 is an octahedral cage formed by self-assembly of six 1,10-phenanthroline-Pt(II) centers and four 2,4,6-tris(4-pyridyl)-1,3,5-triazine ligands (L). Cage 1 is able to trigger DNA damage and exhibits promising in vitro potency against a panel of human ovarian cancer cell lines. However, due to the large portion of aromatic components, this cage structure has very limited solubility in cell culture media (<20μM). Notably, upon nanoformulation by using fluorescein (2) and a pegylated anionic polymer (3), the concentration of Cage 1 can reach up to 0.4 mM. Production of the nanoparticles of metal-organic cages (nMOC) is driven by the formation of the 1:1 host-guest complex of 1 and 2 in aqueous solution, which then form nanoprecipitation in presence of poly glutamic acid-b-poly ethylene glycol (3). The resulted nMOC are about 100 nm in diameter, and they serve as a delivery platform that slowly releases the therapeutic content. The use of fluorescein facilitates monitoring cell entry of nMOC and drug release using flow cytometry. Finally, comparing to cisplatin, the nMOC exhibit comparable in vitro efficacy against a panel of human cancer cell lines, and notably, it shows a much lower resistance factor against chemoresistant ovarian cancer cell lines.

Molecular methods for assessment of non-covalent metallodrug-DNA interactions

The binding of small molecule metallodrugs to discrete regions of nucleic acids is an important branch of medicinal chemistry and the nature of these interactions, allied with sequence selectivity, forms part of the backbone of modern medicinal inorganic chemistry research. In this tutorial review we describe a range of molecular methods currently employed within our laboratories to explore novel metallodrug-DNA interactions. At the outset, an introduction to DNA from a structural perspective is provided along with descriptions of non-covalent DNA recognition focusing on intercalation, insertion, and phosphate binding. Molecular methods, described from a non-expert perspective, to identify non-covalent and pre-associative nucleic acid recognition are then demonstrated using a variety of techniques including direct (non-optical) and indirect (optical) methods. Direct methods include: X-ray crystallography; NMR spectroscopy; mass spectrometry; and viscosity while indirect approaches detail: competitive inhibition experiments; fluorescence and absorbance spectroscopy; circular dichroism; and electrophoresis-based techniques. For each method described we provide an overview of the technique, a detailed examination of results obtained and relevant follow-on of advanced biophysical/analytical techniques. To achieve this, a selection of relevant copper(ii) and platinum(ii) complexes developed within our laboratories are discussed and are compared, where possible, to classical DNA binding agents. Applying these molecular methods enables us to determine structure-activity factors important to rational metallodrug design. In many cases, combinations of molecular methods are required to comprehensively elucidate new metallodrug-DNA interactions and, from a drug discovery perspective, coupling this data with cellular responses helps to inform understanding of how metallodrug-DNA binding interactions manifest cytotoxic action.

Elucidation of the Mechanism of Action for Metal Based Anticancer Drugs by Mass Spectrometry-Based Quantitative Proteomics

The discovery of the anticancer activity of cisplatin and its clinical application has opened a new field for studying metal-coordinated anticancer drugs. Metal-based anticancer drugs, such as cisplatin, can be transported to cells after entering into the human body and form metal–DNA or metal–protein adducts. Then, responding proteins will recognize adducts and form stable complexes. The proteins that were binding with metal-based anticancer drugs were relevant to their mechanism of action. Herein, investigation of the recognition between metal-based anticancer drugs and its binding partners will further our understanding about the pharmacology of cytotoxic anticancer drugs and help optimize the structure of anticancer drugs. The “soft” ionization mass spectrometric methods have many advantages such as high sensitivity and low sample consumption, which are suitable for the analyses of complex biological samples. Thus, MS has become a powerful tool for the identification of proteins binding or responding to metal-based anticancer drugs. In this review, we focused on the mass spectrometry-based quantitative strategy for the identification of proteins specifically responding or binding to metal-based anticancer drugs, ultimately elucidating their mechanism of action.

Substitution-Inert Polynuclear Platinum Complexes Act as Potent Inducers of Condensation/Aggregation of Short Single- and Double-Stranded DNA and RNA Oligonucleotides

Compounds condensing DNA and RNA molecules can essentially affect important biological processes including DNA replication and transcription. Here, this work shows with the aid of total intensity light scattering, gel electrophoresis, and atomic force microscopy (AFM) that the substitution-inert polynuclear platinum complexes (SI-PPCs), particularly [{trans-Pt(NH₃ )₂ (NH₂ (CH₂ )₆ - NH₃ ⁺ )}₂ -μ-{trans-Pt(NH₃ )₂ (NH₂ (CH₂ )₆ NH₂ )₂ }]⁸⁺ (Triplatin NC), exhibit an unprecedented high potency to condense/aggregate fragments of DNA and RNA as short as 20 base pairs. SI-PPCs condensates are distinctive from those generated by the naturally occurring polyamines (commonly used DNA compacting/condensing agents). Collectively, the results further confirm that SI-PPCs are very efficient inducers of condensation of DNA and RNA, including their short fragments that might have potential in gene therapy, biotechnology, and bionanotechnology. Moreover, the data confirm the structural advantages of the phosphate clamp, with a well-defined rigid DNA recognition motif in initiating condensation and aggregation phenomena on oligonucleotides.

Rhomboidal Pt(II) metallacycle-based NIR-II theranostic nanoprobe for tumor diagnosis and image-guided therapy

Fluorescent theranostics probes at the second near-IR region (NIR-II; 1.0-1.7 µm) are in high demand for precise theranostics that minimize autofluorescence, reduce photon scattering, and improve the penetration depth. Herein, we designed and synthesized an NIR-II theranostic nanoprobe 1 that incorporates a Pt(II) metallacycle 2 and an organic molecular dye 3 into DSPE-mPEG5000 (1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy(polyethylene glycol)-5000]). This design endows 1 with good photostability and passive targeting ability. Our studies show that 1 accurately diagnoses cancer with high resolution and selectively delivers the Pt(II) metallacycle to tumor regions via an enhanced permeability and retention effect. In vivo studies reveal that 1 efficiently inhibits the growth of tumor with minimal side effects. At the same time, improved fluorescent imaging quality and signal-to-noise ratios are shown due to the long emission wavelengths. These studies demonstrate that 1 is a potential theranostic platform for tumor diagnosis and treatment in the NIR-II region.

Toward Multi-Targeted Platinum and Ruthenium Drugs-A New Paradigm in Cancer Drug Treatment Regimens?

While medicinal inorganic chemistry has been practised for over 5000 years, it was not until the late 1800s when Alfred Werner published his ground-breaking research on coordination chemistry that we began to truly understand the nature of the coordination bond and the structures and stereochemistries of metal complexes. We can now readily manipulate and fine-tune their properties. This had led to a multitude of complexes with wide-ranging biomedical applications. This review will focus on the use and potential of metal complexes as important therapeutic agents for the treatment of cancer. With major advances in technologies and a deeper understanding of the human genome, we are now in a strong position to more fully understand carcinogenesis at a molecular level. We can now also rationally design and develop drug molecules that can either selectively enhance or disrupt key biological processes and, in doing so, optimize their therapeutic potential. This has heralded a new era in drug design in which we are moving from a single- toward a multitargeted approach. This approach lies at the very heart of medicinal inorganic chemistry. In this review, we have endeavored to showcase how a "multitargeted" approach to drug design has led to new families of metallodrugs which may not only reduce systemic toxicities associated with modern day chemotherapeutics but also address resistance issues that are plaguing many chemotherapeutic regimens. We have focused our attention on metallodrugs incorporating platinum and ruthenium ions given that complexes containing these metal ions are already in clinical use or have advanced to clinical trials as anticancer agents. The "multitargeted" complexes described herein not only target DNA but also contain either vectors to enable them to target cancer cells selectively and/or moieties that target enzymes, peptides, and intracellular proteins. Multitargeted complexes which have been designed to target the mitochondria or complexes inspired by natural product activity are also described. A summary of advances in this field over the past decade or so will be provided.

Water soluble, optically active monofunctional Pd(ii) and Pt(ii) compounds: promising adhesive and antimigratory effects on human prostate PC-3 cancer cells

Water soluble, enantiomerically pure “rule breakers” Pd(ii) and Pt(ii) compounds with promising anticancer potential are reported.

Anti-Proliferative and Anti-Migration Activity of Arene–Ruthenium(II) Complexes with Azole Therapeutic Agents

The efficacy of organoruthenium complexes containing ergosterol biosynthesis inhibitors (CTZ: clotrimazole, KTZ: ketoconazole and FCZ: fluconazole) against tumor cells, and their interaction with important macro-biomolecules such as human serum albumin and DNA have been investigated here. Our experimental results indicated that these ruthenium(II) complexes present spontaneous electrostatic interactions with albumin, and act as minor groove binders with the DNA. The ability of these Ru(II)–azole complexes to inhibit the proliferation of selected human tumor and non-tumor cell lines was determined by MTT assay. Complexes [RuCl(CTZ)(η6-p-cymene)(PPh3)]PF6 (3) and [RuCl(KTZ)(η6-p-cymene)(PPh3)]PF6 (4) were shown to be between 3- and 40-fold more cytotoxic than the free ligands and the positive control cisplatin. Complex 3 was selected to continue studies on the triple negative breast tumor cell line MDA-MB-231, inducing morphological changes, loss of adhesion, inhibition of colony formation, and migration through Boyden chambers, cell cycle arrest in the sub-G1 phase, and a mechanism of cell death by apoptosis. All these interesting results show the potential of this class of organometallic Ru(II) complexes as an antiproliferative agent.

Synthesis, Reactivity Studies, and Cytotoxicity of Two trans-Iodidoplatinum(II) Complexes. Does Photoactivation Work?

trans-Platinum complexes have been the landmark in unconventional drugs prompting the development of innovative structures that might exhibit chemical and biological profiles different to cisplatin. Iodido complexes signaled a new turning point in the platinum drug design field when their cytotoxicity was reevaluated and reported. In this new study, we have synthesized and evaluated diodidoplatinum complexes trans-[PtI2(amine)(pyridine)] bearing aliphatic amines (isopropylamine and methylamine) and pyridines in trans configuration. X-ray diffraction data support the structural characterization. Their cytotoxicity has been evaluated in tumor cell lines such as SAOS-2, A375, T-47D, and HCT116. Moreover, we report their solution behavior and reactivity with biological models. Ultraviolet-a (UVA) irradiation induces an increase in their reactivity towards model nucleobase 5′-GMP in early stages, and promotes the release of the pyridine ligand (spectator ligand) at longer reaction times. Density Functional calculations have been performed and the results are compared with our previous studies with other iodido derivatives.

Pyriplatin-Boron-Dipyrromethene Conjugates for Imaging and Mitochondria-Targeted Photodynamic Therapy

Monofunctional pyriplatin analogues cis-[Pt(NH₃)₂(L)Cl](NO₃) (1-3) having boron-dipyrromethene (BODIPY) pendants (L) with 1,3,5,7-tetramethyl-8-(4-pyridyl)-4,4'-difluoroboradiazaindacene moieties were designed and synthesized, and their photocytotoxic properties were studied. The Pt-BODIPY conjugates displayed an absorption band within 505-550 nm and a green emissive band near 535 nm in 1% DMSO/DMEM (Dulbecco's modified Eagle's medium) buffer. Complex cis-[Pt(NH₃)₂(4-Me-py)Cl](NO₃) (4) was used as a control for determining the structural aspects by X-ray crystallography. The mono- and diiodinated BODIPY complexes 2 and 3 showed generation of singlet oxygen on light activation as evidenced from the 1,3-diphenylisobenzofuran (DPBF) titration experiments. The cytotoxicity of the BODIPY complexes was tested against A549 (human lung cancer), MCF-7 (human breast cancer), and HaCaT (human skin keratinocyte) cells in dark and visible light (400-700 nm, 10 J cm^-2). While complexes 2 and 3 showed excellent photocytotoxicity (IC₅₀ ≈ 0.05 μM), they remained essentially nontoxic in the dark (IC₅₀ > 100 μM). The emissive bands of 1 and 2 were used for cellular imaging by confocal microscopy study, which showed their mitochondrial localization. This was further supported by platinum estimation from isolated mitochondria and mitochondrial depolarization through a JC-1 assay. The photomediated apoptotic cell death was evidenced from flow cytometric assays, annexin-V/FITC-PI (fluorescein isothiocyanate-propidium iodide) and cell cycle arrest in sub-G1 and G2/M phases. The complexes bind to 9-ethylguanine as a model nucleobase to form monoadducts. A mechanistic study on DNA photocleavage activity using pUC19 DNA showed singlet oxygen as the reactive oxygen species (ROS). The combination of photodynamic therapy with DNA cross-linking property enhanced the anticancer potential of the monofunctional BODIPY-conjugates of pyriplatins.

Hyaluronic Acid Grafted Nanoparticles of a Platinum(II)-Silicon(IV) Phthalocyanine Conjugate for Tumor and Mitochondria-Targeted Photodynamic Therapy in Red Light

Herein, we report novel hyaluronic acid formulated nanoparticles containing a platinum(II) conjugated silicon(IV) phthalocyanine (SiPc-Pt-HA) for tumor targeted red light photodynamic therapy and chemotherapy. The SiPc-Pt-HA conjugate showed specific uptake, photo-enhanced cytotoxicity (~1500 fold) and mitochondrial accumulation in breast cancer over normal cells.

Stimuli-Responsive Therapeutic Metallodrugs

The success of platinum-based anticancer agents has motivated the exploration of novel metal-based drugs for several decades, whereas problems such as drug-resistance and systemic toxicity hampered their clinical applications and efficacy. Stimuli-responsiveness of some metal complexes offers a good opportunity for designing site-specific prodrugs to maximize the therapeutic efficacy and minimize the side effect of metallodrugs. This review presents a comprehensive and up-to-date overview on the therapeutic stimuli-responsive metallodrugs that have appeared in the past two decades, where stimuli such as redox, pH, enzyme, light, temperature, and so forth were involved. The compounds are classified into three major categories based on the nature of stimuli, that is, endo-stimuli-responsive metallodrugs, exo-stimuli-responsive metallodrugs, and dual-stimuli-responsive metallodrugs. Representative examples of each type are discussed in terms of structure, response mechanism, and potential medical applications. In the end, future opportunities and challenges in this field are tentatively proposed. With diverse metal complexes being introduced, the foci of this review are pointed to platinum and ruthenium complexes.

Substitution-Inert Polynuclear Platinum Complexes That Inhibit the Activity of DNA Polymerase in Triplex-Forming Templates

The formation of triple-helical DNA is implicated in the regulation of gene expression. The triplexes are, however, unstable under physiological conditions so that effective stabilizers for the triplex formation are needed. Herein, we describe a new strategy for the stabilization of such triplexes that is based on antitumor substitution-inert polynuclear platinum complexes (SI-PPCs). These compounds were previously shown to bind to DNA through the phosphate clamp-a discrete mode of DNA-ligand recognition distinct from the canonical intercalation and minor-groove binding. We have found that SI-PPCs efficiently inhibit DNA synthesis by DNA polymerase in sequences prone to the formation of pyrimidine- and purine-motif triplex DNAs. Moreover, the results suggest that SI-PPCs are able to induce the formation of triple-helical DNA between duplexes and strands that are not completely complementary to each other. Collectively, these data provide evidence that SI-PPCs are very efficient stabilizers of triple-stranded DNA that might exert their action by stabilizing higher-order structures such as triple-helical DNA.

In-vivo evaluation of the response of Galleria mellonella larvae to novel copper(II) phenanthroline-phenazine complexes

Herein we report the in-vivo characterisation and metabolic changes in Galleria mellonella larvae to a series of bis-chelate copper(II) phenanthroline-phenazine cationic complexes of [Cu(phen)₂]²⁺ (Cu-Phen), [Cu(DPQ)(Phen)]²⁺ (Cu-DPQ-Phen) and [Cu(DPPZ)(Phen)]²⁺ (Cu-DPPZ-Phen) (where phen = 1,10-phenanthroline, DPQ = dipyrido[3,2-ƒ:2',3'-h]quinoxaline and DPPZ = dipyrido[3,2-a:2',3'-c]phenazine). Our aim was to investigate the influence of the systematic extension of the ligated phenazine ligand in the G. mellonella model as a first step towards assessing the in-vivo tolerance and mode of action of the complex series with respect to the well-studied oxidative chemical nuclease, Cu-Phen. The Lethal Dose₅₀ (LD₅₀) values were established over dose ranges of 2 - 30 μg at 4-, 24-, 48- and 72 h by mortality assessment, with Cu-Phen eliciting the highest mortality at 4 h (Cu-Phen, 12.62 μg < Cu-DPQ-Phen, 21.53 μg < Cu-DPPZ-Phen, 26.07 μg). At other timepoints, a similar profile was observed as the phenazine π-backbone within the complex scaffold was extended. Assessment of both cellular response and related gene expression demonstrated that the complexes did not initiate an immune response. However, Label-Free Quantification proteomic data indicated the larval response was associated with upregulation of key proteins such as Glutathione S-transferase, purine synthesis and glycolysis/gluconeogenesis (e.g. fructose-bisphosphate aldolase and glyceraldehyde-3-phosphate). Both Cu-Phen and Cu-DPQ-Phen elicited a similar in-vivo response in contrast to Cu-DPPZ-Phen, which displayed a substantial increase in nitrogen detoxification proteins and proteins with calcium binding sites. Overall, the response of G. mellonella larvae exposure to the complex series is dominated by detoxification and metabolic proteome response mechanisms.

Metal transport capabilities of anticancer copper chelators

In the present study, several Cu chelators [2,2'-biquinoline, 8-hydroxiquinoline (oxine), ammonium pyrrolidinedithiocarbamate (APDTC), Dp44mT, dithizone, neocuproine] were used to study Cu uptake, depletion and localization in different cancer cell lines. To better understand the concentration dependent fluctuations in the Cu intracellular metal content and Cu-dependent in vitro antiproliferative data, the conditional stability constants of the Cu complex species of the investigated ligands were calculated. Each investigated chelator increased the intracellular Cu content on HT-29 cells causing Cu accumulation depending on the amount of the free Cu(II). Copper accumulation was 159 times higher for Dp44mT compared to the control. Investigating a number of other transition metals, intracellular accumulation of Cd was observed only for two chelators. Intracellular Zn content slightly decreased (cca. 10%) for MCF-7 cells, while a dramatic decrease was observed on MDA-MB-231 ones (cca. 50%). A similar decrease was observed for HCT-116, while Zn depletion for HT-29 corresponded to cca. 20%. The IC₅₀ values were registered for the investigated four cell lines at increasing external Cu(II) concentration, namely, MDA-MB-231 cells had the lowest IC₅₀ values for Dp44mT ranging between 7 and 35 nM. Thus, Zn depletion could be associated with lower IC₅₀ values. Copper depletion was observed for all ligands being less pronounced for Dp44mT and neocuproine. Copper localization and its colocalization with Zn were determined by μ-XRF imaging. Loose correlation (0.57) was observed for the MCF-7 cells independently of the applied chelator. Similarly, a weak correlation (0.47) was observed for HT-29 cells treated with Cu(II) and oxine. Colocalization of Cu and Zn in the nucleus of HT-29 cells was observed for Dp44mT (correlation coefficient of 0.85).

Self-Assembly of a [1 + 1] Ionic Hexagonal Macrocycle and Its Antiproliferative Activity

A unique irregular hexagon was self-assembled using an organic donor clip (bearing terminal pyridyl units) and a complementary organometallic acceptor clip. The resulting metallamacrocycle was characterized by multinuclear NMR, mass spectrometry, and elemental analyses. Molecular modeling confirmed hexagonal shaped cavity for this metallamacrocycle which is a unique example of a discrete hexagonal framework self-assembled from only two building blocks. Cytotoxicity of the Pt-based acceptor tecton and the self-assembled Pt^II-based macrocycle was evaluated using three cancer cell lines and results were compared with cisplatin. Results confirmed a positive effect of the metallamacrocycle formation on cell growth inhibition.

Synthesis and antiproliferative activity of a series of new platinum and palladium diphosphane complexes

New organometallic complexes [M(dppe)(R)₂] {where M = Pt or Pd, dppe = 1,2-bis(diphenylphosphano)ethane, and R = C₆F₄H-x (x = 6,5,4), C₆F₃H₂-3,5, C₆F₃H₂-5,6, C₆F₃H₂-3,6, C₆F₄(OMe)-4, and C₆F₄(cyclo-C₅H₁₀N)-4, the numbers x refer to the positions of the protons in the polyfluoroaryl ligands} were synthesised either through transmetalation from the dichlorido complexes [M(dppe)Cl₂] or through ligand exchange using [M(diene)Cl₂] precursor complexes with diene = 1,5-cyclooctadiene (cod) or 1,5-hexadiene (hex). Alternatively, [M(dppX)Cl(R)] complexes with dppX = dppm (1,1-bis(diphenylphosphano)methane), dppe, dppp (1,3-bis(diphenylphosphano)propane), and dppb (1,4-bis(diphenylphosphano)butane) were prepared in decarboxylation reactions from thallium(i) carboxylates Tl(O₂CR). The different preparative methods were compared in terms of yield and purity. Structural and spectroscopic data are reported for the new dppX- and diene-M(R)₂ complexes. Antiproliferative activity was investigated for these new complexes against the HT-29 (colon carcinoma) and MCF-7 (breast adenocarcinoma) cell lines, and the active compounds of this first series together with organometallic dppX or hex Pt^II or Pd^II complexes were then included in cell tests using L1210 (leukaemia cells) and the cisplatin-resistant L1210/DDP cell line. Remarkably, promising antiproliferative results were found for a few Pt^II and Pd^II complexes, while structurally closely related compounds were essentially nontoxic.

Photoactivation of the Cytotoxic Properties of Platinum(II) Complexes through Ligand Photoswitching

The development of photoactivatable metal complexes with potential anticancer properties is a topical area of current investigation. Photoactivated chemotherapy using coordination compounds is typically based on photochemical processes occurring at the metal center. In the present study, an innovative approach is applied that takes advantage of the remarkable photochemical properties of diarylethenes. Following a proof-of-concept study with two complexes, namely, C1 and C2, a series of additional platinum(II) complexes from dithienylcyclopentene-based ligands was designed and prepared. Like C1 and C2, these new coordination compounds exhibit two thermally stable, interconvertible photoisomers that display distinct properties. The photochemical behavior of ligands L3-L7 has been analyzed by ¹H NMR and UV-vis spectroscopies. Subsequently, the corresponding platinum(II) complexes C3-C7 were synthesized and fully characterized, including by single-crystal X-ray diffraction for some of them. Next, the interaction of each photoisomer (i.e., containing the open or closed ligand) of the metal complexes with DNA was examined thoroughly using various techniques, revealing their distinct DNA-binding modes and affinities, as observed for the earlier compounds C1 and C2. The antiproliferative activity of the two forms of the complexes was then assessed with five cancer cell lines and compared with that of C1 and C2, which supported the use of such diarylethene-based systems for the generation of a new class of potential photochemotherapeutic metallodrugs.

Comparison of Metal-Ammine Compounds Binding to DNA and Heparin. Glycans as Ligands in Bioinorganic Chemistry

We present spectroscopic and biophysical approaches to examine the affinity of metal-ammine coordination complexes for heparin as a model for heparan sulfate (HS). Similar to nucleic acids, the highly anionic nature of heparin means it is associated in vivo with physiologically relevant cations, and this work extends their bioinorganic chemistry to substitution-inert metal-ammine compounds (M). Both indirect and direct assays were developed. M compounds are competitive inhibitors of methylene blue (MB)-heparin binding, and the change in the absorbance of the dye in the presence or absence of heparin can be used as an indirect reporter of M-heparin affinity. A second indirect assay uses the change in fluorescence of TAMRA-R₉, a nonaarginine linked to a fluorescent TAMRA moiety, as a reporter for M-heparin binding. Direct assays are surface plasmon resonance (SPR) and isothermal titration calorimetry (ITC). The K_d values for TriplatinNC-heparin varied to some extent depending on the technique from 33.1 ± 2 nM (ITC) to 66.4 ± 1.3 nM (MB absorbance assay) and 340 ± 30 nM (SPR). The differences are explained by the nature of the technique and the use of heparin of differing molecular weight. Indirect probes using the displacement of ethidium bromide from DNA or, separately, fluorescently labeled oligonucleotide (DNA-Fl) can measure the relative affinities of heparin and DNA for M compounds. These assays showed essentially equivalent affinity of TriplatinNC for heparin and DNA. The generality of these methods was confirmed with a series of mononuclear cobalt, ruthenium, and platinum compounds with significantly lower affinity because of their smaller overall positive charge but in the order [Co(NH₃)₆]³⁺ > [Ru(NH₃)₆]³⁺ > [Pt(NH₃)₄]²⁺. The results on heparin can be extrapolated to glycosoaminoglycans such as HS, emphasizing the relevance of glycan interactions in understanding the biological properties of coordination compounds and the utility of the metalloglycomics concept for extending bioinorganic chemistry to this class of important biomolecules.

Glucose-Appended Platinum(II)-BODIPY Conjugates for Targeted Photodynamic Therapy in Red Light

Platinum(II) complexes [Pt(L¹)(R-BODIPY)]Cl (1) and [Pt(L²)(R-BODIPY)]Cl (2), where R-BODIPY is 8-(4-ethynylphenyl)-distyryl-4,4-difluoro-5,7-dimethyl-4-bora-3a,4a-diaza-s-indacene-3, L¹ is 4'-phenyl-2,2':6',2″-terpyridine, and L² is (2,2':6',2″-terpyridin-4'-oxy)ethyl-β-d-glucopyranoside, were synthesized and characterized, and their photocytotoxicity was studied. The phenylacetylide complex [Pt(L¹)(C≡CPh)]Cl (3) was prepared and used as a control. Complexes 1 and 2 showed near-IR absorption bands at 713 nm (ε = 3.47 × 10⁴ M^-1 cm^-1) and 715 nm (3.2 × 10⁴ M^-1 cm^-1) in 10% dimethyl sulfoxide (DMSO)-Dulbecco's Modified Eagle's Medium (DMEM) (pH 7.2). The BODIPY complexes are emissive in 10% DMSO-DMEM at pH 7.2 with λ_em (λ_ex, Φ_f) = 822 nm (710 nm, 0.022) for complex 1 and λ_em (λ_ex, Φ_f) = 825 nm (710 nm, 0.026) for complex 2. They generated singlet oxygen (¹O₂) in red light as evidenced from 1,3-diphenylisobenzofuran (DPBF) titration experiments. The singlet oxygen quantum yield (Φ_Δ) values for 1 and 2 were ∼0.6 signifying their photosensitizing ability. They were remarkably photodynamic therapy (PDT) active in red light showing significant red light-induced cytotoxicity in cervical HeLa, lung cancer A549, and breast cancer MCF-7 cells (IC₅₀: 2.3-24.7 μM in light) with negligible dark toxicity (IC₅₀ > 100 μM). A significant enhancement in cellular uptake was observed for 2 having glucose-appended terpyridine ligand compared to 1. The confocal microscopy showed significant mitochondrial localization of the complexes as evidenced from the JC-1 assay. The complexes released the photoactive R-BODIPY ligand upon red light-irradiation as evidenced from the mass and ¹H NMR spectral studies. Complex 2 is remarkable in satisfying the essential requirements of targeted PDT in red light.

Platinum complexes as light promoted anticancer agents: a redefined strategy for controlled activation

Site-specific delivery and amenable activation of prodrugs are indispensible criteria for designing novel anticancer agents. Platinum based drugs vanguard the chemotherapeutic regimes and over the years significant attention has been paid to achieve more efficacious drugs with fewer adverse effects. The switch from platinum(ii) drugs to the inert platinum(iv) analogues proved advantageous but the new prodrugs still suffered from unspecific cytotoxic actions. Thus the photoactivation of an inert platinum prodrug specifically within neoplastic cells provided the desired spatio-temporal control over drug activation by means of illumination, thereby limiting the cytotoxic events to only at the targeted tumors. This article collates research on platinum complexes which exhibit potential light mediated anticancer effects and provides insights into the underlying mechanisms of activation. Fine tuning of the coordination sphere results in dramatic alteration of the redox and spectral properties of both ground and excited states and the cellular properties of the molecules. This concise article highlights the various light promoted strategies employed to attain a controlled release of active platinum(ii) and/or reactive oxygen species such as photoreduction, photocaging, photodissociation and photosensitization. Such dual action photoactive metal complexes with improved aqueous solubility and versatility are promising candidates for combination therapy which is likely to be the future of anticancer research.

Metal–azole fungistatic drug complexes as anti-Sporothrix spp. agents

Metal–antifungal drug complexes were investigated against fungus causing of sporotrichosis. They were more active against fungal cells than to mammalian cells.

Synthesis, structures and mechanistic pathways of anticancer activity of palladium(ii) complexes with indole-3-carbaldehyde thiosemicarbazones

Palladium(ii) complexes featuring bidentate heterocyclic thiosemicarbazones have been synthesized, characterized and evaluated for their biomolecular interactions. The complexes induced in vitro anticancer activity through apoptosis.

Mitochondria-localizing BODIPY–copper(ii) conjugates for cellular imaging and photo-activated cytotoxicity forming singlet oxygen

BODIPY–copper(ii) conjugates are prepared and characterized and the complexes showed mitochondrial localization with singlet oxygen mediated visible light-induced apoptotic cell death.

Effective platinum(IV) prodrugs conjugated with lonidamine as a functional group working on the mitochondria

Platinum-based anticancer drugs are one of the most widely used anticancer chemotherapeutics in oncology. Lonidamine (LND) could increase the response of human tumor cells to platinum(II) drugs in preclinical studies by working on the mitochondria. Herein, five platinum(IV) prodrugs conjugated with their potentiator LND are prepared, and most of the target complexes achieve improved anticancer activities compared with their platinum(II) precursors. Notably, Pt(NH₃)₂(LND)Cl₃ (complex 1) derived from cisplatin achieve significantly improved anticancer activities against LNCaP cells and could trigger cancer cell death via an apoptotic pathway and the cell cycle arrest mainly at S phases. And the induction of apoptosis by complex 1 in LNCaP cells is closely associated with mitochondrial function disruption and reactive oxygen species (ROS) accumulation. Moreover, it is possessed of the ability to overcome cisplatin-resistance. Further research revealed that complex 1 could be easily reduced to release its platinum(II) precursor and axial ligand by ascorbic acid. All the results provid evidence to support the design strategy of conjugating platinum complexes with its potentiator to improve their anticancer effect.

Potent Anticancer Activity with High Selectivity of a Chiral Palladium N-Heterocyclic Carbene Complex

Five enantiomeric pairs of palladium complexes of 1,2,4-triazole-derived chiral N-heterocyclic carbene ligands were investigated to probe the influence of chirality on the compound's anticancer activity. Although no chirality-related influence was observed for any of the enantiomeric pair, strong anticancer activity was seen for a particular pair, (1S,2S,5R)-1c and (1R,2R,5S)-1c, which was significantly more active than the benchmark drug cisplatin for human breast cancer cells, MCF-7 (ca. 24-27-fold), and human cervical cancer cells, HeLa (ca. three- to fourfold). Broadening its scope of application, (1R,2R,5S)-1c also exhibited antiproliferative activity against lung cancer (A549), skin cancer (B16F10), and multidrug-resistant mammary tumor (EMT6/AR1) cell lines. Interestingly, (1R,2R,5S)-1c displayed 8- and 16-fold stronger antiproliferative activity toward B16F10 and MCF-7 relative to their respective noncancerous counterparts, L929 (fibroblast skin cells) and MCF10A (epithelial breast cells), thereby upholding the potential of these complexes for further development as anticancer agents. (1R,2R,5S)-1c inhibited tumor-cell proliferation by blocking the cells at the G2 phase. (1R,2R,5S)-1c caused DNA damage in MCF-7 cells, leading to mitochondrial reactive oxygen species production and subsequently cell death. We also present evidence indicating that (1R,2R,5S)-1c induced p53-dependent programmed cell death in MCF-7 cells.

Monofunctional BODIPY-Appended Imidazoplatin for Cellular Imaging and Mitochondria-Targeted Photocytotoxicity

Monofunctional platinum(II) complexes of formulation cis-[Pt(NH₃)₂(L)Cl](NO₃), where L is an imidazole base conjugated to 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) with emissive (L¹ in 1) and nonemissive (L² in 2) moieties were prepared and characterized, and their singlet oxygen-mediated photoinduced cytotoxicity was studied. The 1-methylimidazole (1-MeIm) complex 3 was prepared as a control and for structural characterization by X-ray crystallography. Complexes 1 and 2 showed strong visible absorption bands at 500 nm (ε = 2.7 × 10⁴ M^-1 cm^-1) and 540 nm (1.4 × 10⁴ M^-1 cm^-1). Complex 1 is emissive with a band at 510 nm (Φ_F = 0.09) in 1% dimethyl sulfoxide/Dulbecco's Modified Eagle's Medium (pH 7.2). Singlet oxygen generation upon photoirradiation with visible light (400-700 nm) was evidenced from 1,3-diphenylisobenzofuran titration experiments showing significant photosensitizing ability of the BODIPY complexes. Both 1 and 2 were remarkably photocytotoxic in visible light (400-700 nm, 10 J cm^-2) in skin keratinocyte HaCaT and breast cancer MCF-7 cells giving IC₅₀ values in nanomolar concentration. The complexes were, however, essentially nontoxic to the cells in the dark (IC₅₀ > 80 μM). Complex 2 having a diiodo-BODIPY unit is nonemissive but an efficient photosensitizer with high singlet oxygen generation ability in visible light (400-700 nm). Confocal microscopy using the emissive complex 1 showed significant mitochondrial localization of the complex. Cell death via apoptotic pathway was observed from the Annexin-V-FITC/PI assay. The formation of Pt-DNA adducts was evidenced from the binding experiments of the complexes 1 and 2 with 9-ethylguanine as a model nucleobase from ¹H NMR and mass spectral studies.

9,9-Difluorobispidine Analogues of Cisplatin, Carboplatin, and Oxaliplatin

As part of a comprehensive study of N-unsubstituted bispidines, the novel 9,9-difluorobispidine (D) has been synthesized. The compound crystallizes from pentane below 0 °C in the ordered-crystalline phase D-II and undergoes at 0-30 °C a stepwise endothermic phase transition to a dynamically disordered crystalline phase D-I; melting occurs at 227 °C. Single crystalline D-II has been subjected to X-ray structure analysis, revealing association of the molecules to form chains. Reaction of (1,5-hexadiene)PtCl₂ with D affords {C₇H₁₀F₂(NH)₂}PtCl₂ (D1), which can be converted by conventional routes to {C₇H₁₀F₂(NH)₂}Pt(cbdca)·5H₂O (D2) and {C₇H₁₀F₂(NH)₂}Pt(C₂O₄) (D3). Compound D1 crystallizes solvent-free from water and is isomorphous to the solvent-free parent bispidine analogue (A1). The pentahydrate D2 is isomorphous to the bispidine and 9-oxabispidine homologues (A2 and C2), as shown by X-ray structure analyses. An increased polarity of the bispidine skeleton as a consequence of the high electronegativity of fluorine is seen as the reason for low cytotoxic potency of D1-D3.