DNA Condensing Effects and Sequence Selectivity of DNA Binding of Antitumor Noncovalent Polynuclear Platinum Complexes

Monomeric copper(II) complexes with unsymmetrical salen environment: Synthesis, characterization and study of biological activities

Three new ONNO-donor tetradentate unsymmetrical salen ligands were synthesized by using o-phenyl diamine with substituted salicylaldehydes followed by a two-step reaction methodology. These three ligands by reaction with Cu(OAc)2.4H2O produced three new monomeric Cu(II) complexes, [CuII(L1-3)] (1-3). Elemental analysis, IR, UV-vis, NMR, and HR-ESI-MS techniques were used to analyze and characterize all the synthesized ligands and their corresponding metal complexes. Molecular structures of 1-3 were confirmed by the single-crystal-XRD analysis. Furthermore, the DNA binding ability of these complexes was checked through UV-vis, fluorescence spectroscopy, and also by circular dichroism studies. All the complexes were found to show an intercalation mode of binding with the Kb value in the range of 104-105 M-1. Finally, 1-3 was tested against two malignant (HeLa and A549) and non-cancerous (NIH-3T3) cell lines to check their in vitro antiproliferative activities. Among all, 1 is the most cytotoxic of the series having IC50 values of 5.7 ± 0.9 and 6.0 ± 0.3 μM against HeLa and A549 cell lines, respectively. This result is also consistent with the DNA binding order. Furthermore, the apoptotic mode of cell death of all the complexes was also evaluated by DAPI, AO/EB, and Annexin V-FITC/PI double staining assays.

Glycosaminoglycan-directed cobalt complexes

The biological activity of the 6+ Co containing Werner's Complex has been described and mechanistic considerations suggest that the highly anionic glycosaminoglycans (heparan sulfate, HS, GAGs) are implicated in this activity [Paiva et al. 2021]. To examine in detail the molecular basis of Werner's Complex biological properties we have examined a selection of simple mononuclear Co3+ compounds for their interactions with HS and Fondaparinux (FPX). FPX is a highly sulfated synthetic pentasaccharide used as a model HS substrate [Mangrum et al. 2014, Peterson et al. 2017]. The Co complexes were chosen to be formally substitution-inert and/or have the potential for covalent binding to the biomolecule. Using both indirect competitive inhibition assays and direct mass spectrometric assays, formally substitution-inert complexes bound to FPX with protection from multiple sulfate loss in the gas phase through metalloshielding. Covalent binding of Co-Cl complexes as in [CoCl(NH3)5]2+ and cis-[CoCl2(en)2]+ was confirmed by mass spectrometry. Interestingly, the former complex was shown to be an effective inhibitor of bacterial heparinase enzyme activity and to inhibit heparanase-dependent cellular invasion through the extracellular matrix (ECM). Pursuing the theme of metalloglycomics, we have observed the hitherto unappreciated biological activity of the simple [CoCl(NH3)5]2+ compound, a staple of most inorganic chemistry lab curricula.

Water-Soluble Dioxidovanadium(V) Complexes of Aroylhydrazones: DNA/BSA Interactions, Hydrophobicity, and Cell-Selective Anticancer Potential

Five new anionic aqueous dioxidovanadium(V) complexes, [{VO₂L^1,2}A(H₂O)_n]_α (1-5), with the aroylhydrazone ligands pyridine-4-carboxylic acid (3-ethoxy-2-hydroxybenzylidene)hydrazide (H₂L¹) and furan-2-carboxylic acid (3-ethoxy-2-hydroxybenzylidene)hydrazide (H₂L²) incorporating different alkali metals (A = Na⁺, K⁺, Cs⁺) as countercation were synthesized and characterized by various physicochemical techniques. The solution-phase stabilities of 1-5 were determined by time-dependent NMR and UV-vis, and also the octanol/water partition coefficients were obtained by spectroscopic techniques. X-ray crystallography of 2-4 confirmed the presence of vanadium(V) centers coordinated by two cis-oxido-O atoms and the O, N, and O atoms of a dianionic tridentate ligand. To evaluate the biological behavior, all complexes were screened for their DNA/protein binding propensity through spectroscopic experiments. Finally, a cytotoxicity study of 1-5 was performed against colon (HT-29), breast (MCF-7), and cervical (HeLa) cancer cell lines and a noncancerous NIH-3T3 cell line. The cytotoxicity was cell-selective, being more active against HT-29 than against other cells. In addition, the role of hydrophobicity in the cytotoxicity was explained in that an optimal hydrophobicity is essential for high cytotoxicity. Moreover, the results of wound-healing assays indicated antimigration in case of HT-29 cells. Remarkably, 1 with an IC₅₀ value of 5.42 ± 0.15 μM showed greater activity in comparison to cisplatin against the HT-29 cell line.

Research progress of azido-containing Pt(IV) antitumor compounds

Cancer is a long-known incurable disease, and the medical use of cisplatin has been a significant discovery. However, the side-effects of cisplatin necessitate the development of new and improved drug. Therefore, in this study, we focused on the photoactivatable Pt(IV) compounds Pt[(X₁)(X₂)(Y₁)(Y₂)(N₃)₂], which have a completely novel mechanism of action. Pt(IV) can efficiently overcome the side-effects of cisplatin and other drugs. Here, we have demonstrated, summarized and discussed the effects and mechanism of these compounds. Compared to the relevant articles in the literature, we have provided a more detailed introduction and a made comprehensive classification of these compounds. We believe that our results can effectively provide a reference for the development of these drugs.

On the Biology of Werner's Complex

Werner's Complex, as a cationic coordination complex (CCC), has hitherto unappreciated biological properties derived from its binding affinity to highly anionic biomolecules such as glycosaminoglycans (GAGs) and nucleic acids. Competitive inhibitor and spectroscopic assays confirm the high affinity to GAGs heparin, heparan sulfate (HS), and its pentasaccharide mimetic Fondaparinux (FPX). Functional consequences of this affinity include inhibition of FPX cleavage by bacterial heparinase and mammalian heparanase enzymes with inhibition of cellular invasion and migration. Werner's Complex is a very efficient condensing agent for DNA and tRNA. In proof-of-principle for translational implications, it is demonstrated to display antiviral activity against human cytomegalovirus (HCMV) at micromolar concentrations with promising selectivity. Exploitation of non-covalent hydrogen-bonding and electrostatic interactions has motivated the unprecedented discovery of these properties, opening new avenues of research for this iconic compound.

Monofunctional Platinum(II) Anticancer Agents

Platinum-based anticancer drugs represented by cisplatin play important roles in the treatment of various solid tumors. However, their applications are largely compromised by drug resistance and side effects. Much effort has been made to circumvent the drug resistance and general toxicity of these drugs. Among multifarious designs, monofunctional platinum(II) complexes with a general formula of [Pt(3A)Cl]⁺ (A: Ammonia or amine) stand out as a class of "non-traditional" anticancer agents hopeful to overcome the defects of current platinum drugs. This review aims to summarize the development of monofunctional platinum(II) complexes in recent years. They are classified into four categories: fluorescent complexes, photoactive complexes, targeted complexes, and miscellaneous complexes. The intention behind the designs is either to visualize the cellular distribution, or to reduce the side effects, or to improve the tumor selectivity, or inhibit the cancer cells through non-DNA targets. The information provided by this review may inspire researchers to conceive more innovative complexes with potent efficacy to shake off the drawbacks of platinum anticancer drugs.

Molecular dynamics simulation of non-covalent interactions between polynuclear platinum(II) complexes and DNA

Several studies with substitution-inert polynuclear platinum(II) complexes (SI-PPC) have been carried out in recent years due to the form of DNA binding presented by these compounds. This form of bonding is achieved by molecular recognition through the formation of non-covalent structures, commonly called phosphate clamps and forks, which generate small extensions of the major and minor grooves. In this work, we use molecular dynamics simulations (MD) to study the formation of these cyclical structures between six different SI-PPCs and a double DNA dodecamer, here called 24_bp_DNA. The results showed the influence of the complex expressed on the number of phosphate clamps and forks formed. Based on the conformational characterization of the DNA fragment, we show that the studied SI-PPCs interact preferentially in the minor groove, causing groove spanning, except for two of them, Monoplatin and AH44. The phosphates of C-G pairs are the main sites for such non-covalent interactions. The Gibbs interaction energy of solvated species points out to AH78P, AH78H, and TriplatinNC as the most probable ones when coupled with DNA. As far as we know, this work is the very first one related to SI-PPCs which brings MD simulations and a complete analysis of the non-covalent interactions with a double DNA dodecamer.

Different Effects of Cisplatin and Transplatin on the Higher-Order Structure of DNA and Gene Expression

Despite the effectiveness of cisplatin as an anticancer agent, its trans-isomer, transplatin, is clinically ineffective. Although both isomers target nuclear DNA, there is a large difference in the magnitude of their biological effects. Here, we compared their effects on gene expression in an in vitro luciferase assay and quantified their effects on the higher-order structure of DNA using fluorescence microscopy (FM) and atomic force microscopy (AFM). The inhibitory effect of cisplatin on gene expression was about 7 times that of transplatin. Analysis of the fluctuation autocorrelation function of the intrachain Brownian motion of individual DNA molecules showed that cisplatin increases the spring and damping constants of DNA by one order of magnitude and these visco-elastic characteristics tend to increase gradually over several hours. Transplatin had a weaker effect, which tended to decrease with time. These results agree with a stronger inhibitory effect of cisplatin on gene expression. We discussed the characteristic effects of the two compounds on the higher-order DNA structure and gene expression in terms of the differences in their binding to DNA.

DNase I-Responsive Calixpyridinium-Mediated DNA Aggregation

In this work, cationic macrocyclic calixpyridinium was employed as a new strategy to condense DNA. Moreover, the degradation of DNA by DNase I could lead to the calixpyridinium-DNA supramolecular aggregates being dissipated. Therefore, the present system is potentially applicable as the targeted drug delivery model at DNase I-overexpressed sites.

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.

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.

Synthesis, cytotoxic activity and DNA interaction studies of new dinuclear platinum(ii) complexes with an aromatic 1,5-naphthyridine bridging ligand: DNA binding mode of polynuclear platinum(ii) complexes in relation to the complex structure

The synthesis, spectroscopic characterization, cytotoxic activity and DNA binding evaluation of seven new dinuclear platinum(ii) complexes Pt1-Pt7, with the general formula [{Pt(L)Cl}2(μ-1,5-nphe)](ClO4)2 (1,5-nphe is 1,5-naphthyridine; while L is two ammines (Pt1) or one bidentate coordinated diamine: ethylenediamine (Pt2), (±)-1,2-propylenediamine (Pt3), trans-(±)-1,2-diaminocyclohexane (Pt4), 1,3-propylenediamine (Pt5), 2,2-dimethyl-1,3-propylenediamine (Pt6), and 1,3-pentanediamine (Pt7)), were reported. In vitro cytotoxic activity of these complexes was evaluated against three tumor cell lines, murine colon carcinoma (CT26), murine mammary carcinoma (4T1) and murine lung cancer (LLC1) and two normal cell lines, murine mesenchymal stem cells (MSC) and human fibroblast (MRC-5) cells. The results of the MTT assay indicate that all investigated complexes have almost no cytotoxic effects on 4T1 and very low cytotoxicity toward LLC1 cell lines. In contrast to the effects on LLC1 and 4T1 cells, complexes Pt1 and Pt2 had significant cytotoxic activity toward CT26 cells. Complex Pt1 had a much lower IC50 value for activity on CT26 cells compared with cisplatin. In comparison with cisplatin, all dinuclear Pt1-Pt7 complexes showed lower cytotoxicity toward normal MSC and MRC-5 cells. In order to measure the amount of platinum(ii) complexes taken up by the cells, we quantified the cellular platinum content using inductively coupled plasma mass spectrometry (ICP-QMS). Molecular docking studies performed to evaluate the potential binding mode of dinuclear platinum(ii) complexes Pt1-Pt7 and their aqua derivatives W1-W7, respectively, at the double stranded DNA showed that groove spanning and backbone tracking are the most stable binding modes.

Photoactivatable Cell-Selective Dinuclear trans-Diazidoplatinum(IV) Anticancer Prodrugs

A series of dinuclear octahedral Pt^IV complexes trans,trans,trans-[{Pt(N₃)₂(py)₂(OH)(OC(O)CH₂CH₂C(O)NH)}₂R] containing pyridine (py) and bridging dicarboxylate [R = −CH₂CH₂– (1), trans-1,2-C₆H₁₀– (2), p-C₆H₄– (3), −CH₂CH₂CH₂CH₂– (4)] ligands have been synthesized and characterized, including the X-ray crystal structures of complexes 1·2MeOH and 4, the first photoactivatable dinuclear Pt^IV complexes with azido ligands. The complexes are highly stable in the dark, but upon photoactivation with blue light (420 nm), they release the bridging ligand and mononuclear photoproducts. Upon irradiation with blue light (465 nm), they generate azidyl and hydroxyl radicals, detected using a 5,5-dimethyl-1-pyrroline N-oxide electron paramagnetic resonance spin trap, accompanied by the disappearance of the ligand-to-metal charge-transfer (N₃ → Pt) band at ca. 300 nm. The dinuclear complexes are photocytotoxic to human cancer cells (465 nm, 4.8 mW/cm², 1 h), including A2780 human ovarian and esophageal OE19 cells with IC₅₀ values of 8.8–78.3 μM, whereas cisplatin is inactive under these conditions. Complexes 1, 3, and 4 are notably more photoactive toward cisplatin-resistant ovarian A2780cis compared to A2780 cells. Remarkably, all of the complexes were relatively nontoxic toward normal cells (MRC5 lung fibroblasts), with IC₅₀ values >100 μM, even after irradiation. The introduction of an aromatic bridging ligand (3) significantly enhanced cellular uptake. The populations in the stages of the cell cycle remained unchanged upon treatment with complexes in the dark, while the population of the G2/M phase increased upon irradiation, suggesting that DNA is a target for these photoactivated dinuclear Pt^IV complexes. Liquid chromatography–mass spectrometry data show that the photodecomposition pathway of the dinuclear complexes results in the release of two molecules of mononuclear platinum(II) species. As a consequence, DNA binding of the dinuclear complexes after photoactivation in cell-free media is, in several respects, qualitatively similar to that of the photoactivated mononuclear complex FM-190. After photoactivation, they were 2-fold more effective in quenching the fluorescence of EtBr bound to DNA, forming DNA interstrand cross-links and unwinding DNA compared to the photoactivated FM-190.

Novel all-trans dinuclear Pt^IV complexes bridged by a dicarboxylate linker, highly stable in the dark, generate azidyl and hydroxyl radicals upon irradiation with blue light. They are photocytotoxic to human cancer cells, whereas cisplatin was inactive under these conditions and more photoactive toward cisplatin-resistant ovarian cancer cells compared to wild-type cells. Remarkably, the dinuclear complexes were relatively nontoxic toward normal human cells. Cell cycle and DNA binding experiments suggested that DNA is a target.

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.

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.

Exploring the interactions between model proteins and Pd(ii) or Pt(ii) compounds bearing charged N,N-pyridylbenzimidazole bidentate ligands by X-ray crystallography

X-ray structure of the adducts formed between lysozyme and Pd(ii) and Pt(ii) compounds bearing N,N-pyridylbenzimidazole derivatives with an alkylated sulfonate or phosphonium side chain are reported.

Interfering with DNA High-Order Structures using Chiral Ruthenium(II) Complexes

In this work, it was found that DNA can undergo B-Z transformational changes and compaction in the presence of DNA intercalators such as ruthenium(II) polypyridyl complexes. The link between B-Z transition and condensation is weak but can be strengthened under certain circumstances with slight alterations to the structures of the ruthenium(II) complexes. Here, following on from previous research, this work reports a series of ruthenium(II) complexes with imidazophenanthroline ligands, which vary in size and planarity. The complexes exhibit distinct effects on DNA structures, ranging from little impact to the transformation of DNA secondary structures to the formation of higher-order DNA structures. Further studies on DNA morphological changes induced by chiral ruthenium(II) complexes are observed by atomic force microscopy and transmission electron microscopy.

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.

Kinetic analysis of and platinum(II) migration in the reactions of tetrazolato-bridged dinuclear platinum(II) complexes with nucleotides

The series of tetrazolato-bridged complexes with the formula [{cis‑Pt(NH₃)₂}₂(μ-OH)(μ-5-H-tetrazolato-N1,N2)]²⁺ (5-H-X) or [{cis‑Pt(NH₃)₂}₂(μ-OH)(μ-5-R-tetrazolato-N2,N3)]ⁿ⁺ (R=H (5-H-Y), CH₃ (1), CH₂COOCH₂CH₃ (2), CH₂COO^- (3), n=2 (5-H-Y, 1, 2) or 1 (3)) are promising candidate complexes for formulation as next-generation platinum-based anticancer drugs that form multimodal bindings with DNA molecules. These multimodal bindings involve both non-covalent and covalent interactions, the latter of which are acknowledged to be essential for platinum-based drugs to exert their anticancer activity. In the present study, the tetrazolato-bridged complexes reacted with two molar equivalents of guanosine-5'-monophosphate (GMP) to yield the 1:2 reaction products [{cis‑Pt(NH₃)₂(GMP-N7)}₂(μ-5-R-tetrazolato-N1,N3)]^{2- or 1-}. This reaction was accompanied by an intramolecular Pt(II) migration that contributed to the formation of diverse DNA crosslinking, such as interhelical crosslinks. The second-order reaction rate constants for the reactions performed in phosphate-buffered D₂O solution showed that the reactivity of the complexes decreased in the order 5-H-X≳5-H-Y>2≳1>3 and that reactivity was correlated with the cytotoxicity of the complexes. A similar result was obtained for the reaction of the complexes with calf thymus DNA in which the formation of covalent DNA adducts was quantified by means of inductively coupled plasma mass spectrometry. These results suggest that overall charge affects the kinetics of the reactions of platinum complexes with GMP and calf thymus DNA. Thus, the positive charge of the complexes affects not only the non-covalent but also the covalent interactions between the complexes and nucleotides and DNA, which are negatively charged molecules.

Impact of the Pd2Spermine Chelate on Osteosarcoma Metabolism: An NMR Metabolomics Study

A metabolomics study of Pd₂Spermine(Spm) on osteosarcoma MG-63 and osteoblastic HOb cells is presented to assess the impact of the potential palladium drug on cell metabolism compared with cisplatin (cDDP). Despite its higher cytotoxicity, Pd₂Spm induced lower (and reversible) metabolic impact on MG-63 cells and the absence of apoptosis; conversely, it induced significant deviations in osteoblastic amino acid metabolism. However, when in combination with doxorubicin and methotrexate, Pd₂Spm induced strong metabolic deviations on lipids, choline compounds, amino acids, nucleotides, and compounds related to antioxidative mechanisms (e.g., glutathione, inositol, hypoxanthine), similarly to the cDDP cocktail. Synergetic effects included triggering of lipid biosynthesis by Pd₂Spm in the presence of doxorubicin (and reinforced by methotrexate) and changes in the glycosylation substrate uridine diphosphate acetylgalactosamine and methionine and serine metabolisms. This work provides promising results related to the impact of Pd₂Spm on osteosarcoma cellular metabolism, particularly in drug combination protocols. Lipid metabolism, glycosylation, and amino acid metabolisms emerge as relevant features for targeted studies to further understand a potential anticancer mechanism of combined Pd₂Spm.

Specific Conformational Change in Giant DNA Caused by Anticancer Tetrazolato-Bridged Dinuclear Platinum(II) Complexes: Middle-Length Alkyl Substituents Exhibit Minimum Effect

Derivatives of the highly antitumor-active compound [{cis-Pt(NH₃)₂}₂(μ-OH)(μ-tetrazolato-N2,N3)]²⁺ (5-H-Y), which is a tetrazolato-bridged dinuclear platinum(II) complex, were prepared by substituting a linear alkyl chain moiety at C5 of the tetrazolate ring. The general formula for the derivatives is [{cis-Pt(NH₃)₂}₂(μ-OH)(μ-5-R-tetrazolato-N2,N3)]²⁺, where R is (CH₂)_nCH₃ and n = 0 to 8 (complexes 1-9). The cytotoxicity of complexes 1-4 in NCI-H460 human non-small-cell lung cancer cells decreased with increasing alkyl chain length, and those of complexes 5-9 increased with increasing alkyl chain length. That is, the in vitro cytotoxicity of complexes 1-9 was found to have a U-shaped association with alkyl chain length. This U-shaped association is attributable to the degree of intracellular accumulation. Although circular dichroism spectroscopic measurement indicated that complexes 1-9 induced comparable conformational changes in the secondary structure of DNA, the tetrazolato-bridged complexes induced different degrees of DNA compaction as revealed by a single DNA measurement with fluorescence microsopy, which also had a U-shaped association with alkyl chain length that matched the association observed for cytotoxicity. Complexes 7-9, which had alkyl chains long enough to confer surfactant-like properties to the complex, induced DNA compaction 20 or 1000 times more efficiently than 5-H-Y or spermidine. A single DNA measurement with transmission electron microscopy revealed that complex 8 formed large spherical self-assembled structures that induced DNA compaction with extremely high efficiency. This result suggests that these structures may play a role in the DNA compaction that was induced by the complexes with the longer alkyl chains. The derivatization with a linear alkyl chain produced a series of complexes with unique cellular accumulation and DNA conformational change profiles and a potentially useful means of developing next-generation platinum-based anticancer drugs. In addition, the markedly high ability of these complexes to induce DNA compaction and their high intracellular accumulation emphasized the difference in mechanism of action from platinum-based anticancer drugs.

C 3-symmetric opioid scaffolds are pH-responsive DNA condensation agents

Herein we report the synthesis of tripodal C₃-symmetric opioid scaffolds as high-affinity condensation agents of duplex DNA. Condensation was achieved on both supercoiled and canonical B-DNA structures and identified by agarose electrophoresis, viscosity, turbidity and atomic force microscopy (AFM) measurements. Structurally, the requirement of a tris-opioid scaffold for condensation is demonstrated as both di- (C₂-symmetric) and mono-substituted (C₁-symmetric) mesitylene-linked opioid derivatives poorly coordinate dsDNA. Condensation, observed by toroidal and globule AFM aggregation, arises from surface-binding ionic interactions between protonated, cationic, tertiary amine groups on the opioid skeleton and the phosphate nucleic acid backbone. Indeed, by converting the 6-hydroxyl group of C₃-morphine (MC3) to methoxy substituents in C₃-heterocodeine (HC3) and C₃-oripavine (OC3) molecules, dsDNA compaction is retained thus negating the possibility of phosphate—hydroxyl surface-binding. Tripodal opioid condensation was identified as pH dependent and strongly influenced by ionic strength with further evidence of cationic amine-phosphate backbone coordination arising from thermal melting analysis and circular dichroism spectroscopy, with compaction also witnessed on synthetic dsDNA co-polymers poly[d(A-T)₂] and poly[d(G-C)₂]. On-chip microfluidic analysis of DNA condensed by C₃-agents provided concentration-dependent protection (inhibition) to site-selective excision by type II restriction enzymes: BamHI, HindIII, SalI and EcoRI, but not to the endonuclease DNase I.

Anti-Invasive and Anti-Proliferative Synergism between Docetaxel and a Polynuclear Pd-Spermine Agent

The present work is aimed at evaluating the antitumour properties of a Pd(II) dinuclear complex with the biogenic polyamine spermine, by investigating: i) the anti-angiogenic and anti-migration properties of a Pd(II) dinuclear complex with spermine (Pd2Spm); ii) the anti-proliferative activity of Pd2Spm against a triple negative human breast carcinoma (MDA-MB-231); and finally iii) the putative interaction mediated by combination of Pd2Spm with Docetaxel. Anti-invasive (anti-angiogenic and anti-migratory) as well as anti-proliferative capacities were assessed, for different combination schemes and drug exposure times, using the CAM assay and VEGFR2 activity measurement, the MatrigelTM method and the SRB proliferation test. The results thus obtained evidence the ability of Pd2Spm to restrict angiogenesis and cell migration: Pd2Spm induced a marked inhibition of migration (43.8±12.2%), and a higher inhibition of angiogenesis (81.8±4.4% for total length values, at 4 μM) as compared to DTX at the clinical dosage 4x10-2 μM (26.4±14.4%; n = 4 to 11). Combination of Pd2Spm/DTX was more effective as anti-invasive and anti-proliferative than DTX or Pd2Spm in sole administration, which is compatible with the occurrence of synergism: for the anti-angiogenic effect, IC50(Pd2Spm/DTX) = 0.5/0.5x10-2 μM vs IC50(DTX) = 1.7x10-2 μM and IC50(Pd2Spm) = 1.6 μM. In conclusion, the reported effects of Pd2Spm on angiogenesis, migration and proliferation showed that this compound is a promising therapeutic agent against this type of breast cancer. Moreover, combined administration of Pd2Spm and DTX was found to trigger a substantial synergetic effect regarding angiogenesis inhibition as well as anti-migratory and anti-proliferative activities reinforcing the putative use of Pd(II) complexes in chemotherapeutic regimens. This is a significant outcome, aiming at the application of these combined strategies towards metastatic breast cancer (or other type of resistant cancers), justifying further studies that include pre-clinical trials.

Fluorescent zinc(ii) complexes for gene delivery and simultaneous monitoring of protein expression

Two new zinc(ii) complexes, [Zn(l-His)(NIP)]+(1) and [Zn(acac)2(NIP)](2) (where NIP is 2-(naphthalen-1-yl)-1H-imidazo[4,5-f][1,10]phenanthroline, acac = acetyl acetone), have been synthesized and characterized by elemental analysis, UV-vis, fluorescence, IR, 1H NMR and electron spray ionization mass spectroscopies. Gel retardation assay, atomic force microscopy and dynamic light scattering studies show that 1 and 2 can induce the condensation of circular plasmid pBR322 DNA into nanometer size particles under ambient conditions. Treatment of 2 with 5 mM EDTA restored 30% of the supercoiled form of DNA, revealing partial reversibility of DNA condensation. The in vitro transfection experiment demonstrates that the complexes can be used to deliver pCMV-tdTomato-N1 plasmid which expresses red fluorescent protein. The confocal studies show that the fluorescent nature of complexes is advantageous for visualizing the intracellular delivery of metal complexes as well as transfection efficiency using two distinct emission windows.

In vitro DNA binding profile of enantiomeric dinuclear Cu(II)/Ni(II) complexes derived from l-/d-histidine-terepthaldehyde reduced Schiff base as potential chemotherapeutic agents

New chiral reduced Schiff base ligands, L1 and L2 derived from l-/d-histidine and terepthaldehyde, and their Cu(II) and Ni(II) dinuclear complexes 1 &2 (a and b) were synthesized and thoroughly characterized by various spectroscopic techniques. Comparative binding profile of both l-/d-enantiomeric Cu(II) and Ni(II) complexes with ct-DNA was studied by employing optical and spectroscopic techniques to evaluate their enantiopreferential selectivity towards molecular target DNA and thereby explore their relative chemotherapeutic potential. Quantitative assessment of DNA binding propensity was ascertained by calculating K_b, K and K_sv values of 1 &2 (a and b) which demonstrated higher binding affinity of l-enantiomeric Cu(II) complex, 1a and followed the order as 1a>1b>2a>2b. Scanning electron microscopy (SEM) was used to analyze the morphological changes of the DNA condensate in presence of complexes 1 (a and b). The SEM micrographs condensates revealed morphological transitions and formation of different structural features implicating the condensation process between the complexes and biomolecule occurred to form compact massive structures. The gel electrophoretic assay of complex 1a was carried out with pBR322 plasmid DNA which revealed an efficient cleaving ability of the complex via oxidative pathway with the involvement of singlet oxygen (¹O₂) and the superoxide anion (O₂^•-) radicals as the ROS responsible the cleavage reactions. Molecular docking studies of 1 (a and b) with DNA revealed selective recognition of G-C residues of the narrow minor groove of the DNA duplex and complex 1a demonstrated binding affinity towards DNA ascertained from its higher binding energy values. Furthermore, the cytotoxic assessment of 1a was examined on a panel of cancer cell lines of different histological origin employing SRB assay which revealed remarkably good cytotoxic activity towards HL60, HeLa and MCF7 cancer cell lines.

A Simple Zn2+ Complex-Based Composite System for Efficient Gene Delivery

Metal complexes might become a new type of promising gene delivery systems because of their low cytotoxicity, structural diversity, controllable aqua- and lipo-solubility, and appropriate density and distribution of positive charges. In this study, Zn2+ complexes (1-10) formed with a series of ligands contained benzimidazole(bzim)were prepared and characterized. They were observed to have different affinities for DNA, dependent on their numbers of positive charges, bzim groups, and coordination structures around Zn2+. The binding induced DNA to condensate into spherical nanoparticles with ~ 50 nm in diameter. The cell transfection efficiency of the DNA nanoparticles was poor, although they were low toxic. The sequential addition of the cell-penetrating peptide (CPP) TAT(48-60) and polyethylene glycol (PEG) resulted in the large DNA condensates (~ 100 nm in diameter) and the increased cellular uptake. The clathrin-mediated endocytosis was found to be a key cellular uptake pathway of the nanoparticles formed with or without TAT(48-60) or/and PEG. The DNA nanoparticles with TAT(48-60) and PEG was found to have the cell transfection efficiency up to 20% of the commercial carrier Lipofect. These results indicated that a simple Zn2+-bzim complex-based composite system can be developed for efficient and low toxic gene delivery through the combination with PEG and CPPs such as TAT.

Characterisation of the DNA sequence specificity, cellular toxicity and cross-linking properties of novel bispyridine-based dinuclear platinum complexes

Background

The anti-tumour activity of cisplatin is thought to be a result of its capacity to form DNA adducts which prevent cellular processes such as DNA replication and transcription. These DNA adducts can effectively induce cancer cell death, however, there are a range of clinical side effects and drug resistance issues associated with its use. In this study, the biological properties of three novel dinuclear platinum-based compounds (that contain alkane bridging linkers of eight, ten and twelve carbon atoms in length) were characterised to assess their potential as anticancer agents.

Methods

The properties of these compounds were determined using a DNA template containing seven tandem telomeric repeat sequences. A linear amplification reaction was used in combination with capillary electrophoresis to quantify the sequence specificity of DNA adducts formed by these compounds at base pair resolution. The DNA cross-linking ability of these compounds was assessed using denaturing agarose gel electrophoresis and cytotoxicity was determined in HeLa cells using a colorimetric cell viability assay.

Results

The dinuclear compounds were found to preferentially form DNA adducts at guanine bases and they exhibited different damage intensity profiles at the telomeric repeat sequences compared to that of cisplatin. The dinuclear compounds were found to exhibit a low level of cytotoxicity relative to cisplatin and their cytotoxicity increased as the linker length increased. Conversely, the interstrand cross-linking efficiency of the dinuclear compounds increased as the linker length decreased and the compound with the shortest alkane linker was six-fold more effective than cisplatin.

Conclusions

Since the bifunctional compounds exhibit variation in sequence specificity of adduct formation and a greater ability to cross-link DNA relative to cisplatin they warrant further investigation towards the goal of developing new cancer chemotherapeutic agents.

The Next Generation of Platinum Drugs: Targeted Pt(II) Agents, Nanoparticle Delivery, and Pt(IV) Prodrugs

The platinum drugs, cisplatin, carboplatin, and oxaliplatin, prevail in the treatment of cancer, but new platinum agents have been very slow to enter the clinic. Recently, however, there has been a surge of activity, based on a great deal of mechanistic information, aimed at developing nonclassical platinum complexes that operate via mechanisms of action distinct from those of the approved drugs. The use of nanodelivery devices has also grown, and many different strategies have been explored to incorporate platinum warheads into nanomedicine constructs. In this Review, we discuss these efforts to create the next generation of platinum anticancer drugs. The introduction provides the reader with a brief overview of the use, development, and mechanism of action of the approved platinum drugs to provide the context in which more recent research has flourished. We then describe approaches that explore nonclassical platinum(II) complexes with trans geometry or with a monofunctional coordination mode, polynuclear platinum(II) compounds, platinum(IV) prodrugs, dual-threat agents, and photoactivatable platinum(IV) complexes. Nanoparticles designed to deliver platinum(IV) complexes will also be discussed, including carbon nanotubes, carbon nanoparticles, gold nanoparticles, quantum dots, upconversion nanoparticles, and polymeric micelles. Additional nanoformulations, including supramolecular self-assembled structures, proteins, peptides, metal-organic frameworks, and coordination polymers, will then be described. Finally, the significant clinical progress made by nanoparticle formulations of platinum(II) agents will be reviewed. We anticipate that such a synthesis of disparate research efforts will not only help to generate new drug development ideas and strategies, but also will reflect our optimism that the next generation of approved platinum cancer drugs is about to arrive.

Cooperative interaction between metallosurfactants, derived from the [Ru(2,2'-bpy)3](2+) complex, and DNA

With the idea of improving and advancing the design and preparation of new reagents based on cationic surfactants for gene therapy, two luminescent metallosurfactants derived from the [Ru(2,2'-bpy)3](2+) complex were synthesized. Their interaction with DNA and the effect they exert on the conformation of the polynucleotide were studied by using different techniques. The equilibrium binding constants, Kb, of the two surfactants to DNA were obtained at different molar ratios X=[surfactant]/[DNA]. The observed sigmoidal dependence of Kb on X confirms the cooperative character of the binding. After the addition of a determined surfactant concentration, the condensation of the polymer was observed. The amount of surfactant needed to produce this conformational change is lower for the double stranded surfactant than for the single chain surfactant due to a stronger hydrophobic interaction. The addition of α-cyclodextrin molecules to the metallosurfactant/DNA solutions results in polynucleotide decompaction, which confirms the importance of the hydrophobic interactions in the condensation of the polynucleotide. Results also show the importance of choosing both a proper system to study and the most seeming measuring technique to use. It is demonstrated that, in some cases, the use of several techniques is desirable to obtain reliable and accurate results.

A dendritic nano-sized hexanuclear ruthenium(II) complex as a one- and two-photon luminescent tracking non-viral gene vector

Fluorescent tracking gene delivery could provide us with a better understanding of the critical steps in the transfection process. However, for in vivo tracking applications, a small diameter (<10 nm) is one of the rigorous requirements for tracking vectors. Herein, we have demonstrated a new paradigm for two-photon tracking gene delivery based on a dendritic nano-sized hexanuclear ruthenium(II) polypyridyl complex. Because this metallodendrimer has a multivalent periphery, the complex, which is 6.1 nm, showed high stability and excellent dispersibility and could stepwise condense DNA in vitro. With the outstanding photochemical properties of Ru(II) polypyridyl, this complex could track gene delivery in vivo using one- and two-photon imaging.

Iron(II) supramolecular helicates condense plasmid DNA and inhibit vital DNA-related enzymatic activities

The dinuclear iron(II) supramolecular helicates [Fe2 L3 ]Cl4 (L=C25 H20 N4 ) bind to DNA through noncovalent (i.e., hydrogen-bonding, electrostatic) interactions and exhibit antimicrobial and anticancer effects. In this study, we show that the helicates condense plasmid DNA with a much higher potency than conventional DNA-condensing agents. Notably, molecules of DNA in the presence of the M enantiomer of [Fe2 L3 ]Cl4 do not form intermolecular aggregates typically formed by other condensing agents, such as spermidine or spermine. The helicates inhibit the activity of several DNA-processing enzymes, such as RNA polymerase, DNA topoisomerase I, deoxyribonuclease I, and site-specific restriction endonucleases. However, the results also indicate that the DNA condensation induced by the helicates does not play a crucial role in these inhibition reactions. The mechanisms for the inhibitory effects of [Fe2 L3 ]Cl4 helicates on DNA-related enzymatic activities have been proposed.

Competitive formation of DNA linkage isomers by a trinuclear platinum complex and the influence of pre-association

2D [(1)H, (15)N] HSQC NMR spectroscopy has been used to monitor the reaction of fully (15)N-labelled [{trans-PtCl(NH3)2}2(μ-trans-Pt(NH3)2{NH2(CH2)6NH2}2)](4+) (BBR3464 ((15)N-1)) with the 14-mer duplex (5'-{d(ATACATG(7)G(8)TACATA)}-3'·5'-{d(TATG(18)TACCATG(25)TAT)}-3' or I) at pH 5.4 and 298 K, to examine the possible formation of 1,4 and 1,5-GG adducts in both 5'-5' and 3'-3' directions. In a previous study, the binding of the dinuclear 1,1/t,t to I showed specific formation of the 5'-5' 1,4 G(8)G(18) cross-link, whereas in this case a mixture of adducts were formed. Initial (1)H NMR spectra suggested the presence of two pre-associated states aligned in both directions along the DNA. The pre-association was studied in the absence of covalent binding, by use of the "non-covalent" analog [{trans-Pt(NH3)3}2(μ-trans-Pt(NH3)2{NH2(CH2)6NH2}2)](6+) (AH44, 0). Chemical shift changes of DNA protons combined with NOE connectivities between CH2 and NH3 protons of 0 and the adenine H2 protons on I show that two different molecules of 0 are bound in the minor groove. Molecular dynamic simulations were performed to study the interaction of 0 at the two pre-association sites using charges derived from density functional theory (DFT) calculations. Structures where the central platinum is located in the minor groove and the aliphatic linkers extend into the major groove, in opposite directions, often represent the lowest energy structures of the snapshots selected. In the reaction of (15)N-1 and I, following the pre-association step, aquation occurs to give the mono aqua monochloro species 2, with a rate constant of 3.43 ± 0.03 × 10(-5) s(-1). There was evidence for two monofunctional adducts (3, 4) bound to the 3' (G8) and 5' (G7) residues and the asymmetry of the (1)H,(15)N peak for 3 suggested two conformers of the 3' adduct, aligned in different directions along the DNA. The rate constant for combined monofunctional adduct formation (0.6 ± 0.1 M(-1)) is ca. 2-fold lower for 1 compared to 1,1/t,t, whereas the rate constant for conversion of the combined monofunctional species to combined bifunctional adducts (5) (8.0 ± 0.2 × 10(-5) s(-1)) is two-fold higher.

Solution studies on DNA interactions of substitution-inert platinum complexes mediated via the phosphate clamp

The phosphate clamp is a distinct mode of ligand-DNA binding where the molecular recognition is manifested through ("non-covalent") hydrogen-bonding from am(m)ines of polynuclear platinum complexes to the phosphate oxygens on the oligonucleotide backbone. This third mode of DNA binding is unique to the "classical" DNA intercalators and minor groove binding agents and even the closely related covalently binding mononuclear and polynuclear drugs. 2D (1)H NMR studies on the Dickerson-Drew dodecamer (DDD, d(CGCGAATTCGCG)2) showed significant A-T contacts mainly on nucleotides A6, T7 and T8 implying a selective bridging from C9G10 in the 3' direction to C9G10 of the opposite strand. {(1)H, (15)N} HSQC NMR spectroscopy using the fully (15)N-labelled compound [{trans-Pt(NH2)3(H2N(CH2)6NH3}2μ-(H2N(CH2)6NH2)2(Pt(NH3)2](8+) (TriplatinNC) showed at pH 6 significant chemical shifts and (1)J((195)Pt-(15)N) coupling constants for the free drug and DDD-TriplatinNC at pH 7 indicative of formation of the phosphate clamp. (31)P NMR results are also reported for the hexamer d(CGTACG)2 showing changes in (31)P NMR chemical shifts indicative of changes around the phosphorus center. The studies confirm the DNA binding modes by substitution-inert (non-covalent) polynuclear platinum complexes and help in further establishing the chemotype as a new class of potential anti-tumour agents in their own right with a distinct profile of biological activity.