Melting Temperature Of DNA Research Articles

Empirical and Theoretical Evaluation of a Tree-Shaped DNA Nanostructure with a Looped Arm (L-DNA)

Several nanostructures have been created with the advent of nanotechnology. DNA has been recognized as a new building block material in addition to its genetic coding role because of its unique features (e.g., intrinsic biocompatibility, precise tenability, specific selectivity). DNA can be organized into a variety of self-assembled nanomaterials including a sphere, a ball, and even an emoticon. In particular, a tree-shaped DNA structure possessing characteristic fractural patterns is easily controlled by size and functionality and can be exploited in various fields. Here, we report an empirical and theoretical evaluation of a Y-shaped tree DNA nanostructure with a looped arm (L-DNA). The synthesized L-DNAs were analyzed for thermal and structural stability. The melting temperature (Tm) of a Y-shaped DNA (Y-DNA) as a core unit and a model DNA nanostructure comprising of central Y-DNA and looped arm were measured individually. According to the complexity (e.g., increased length of the single stranded DNA (ssDNA) used), its yield suddenly decreased with the generation of ssDNAs with distinctive secondary structures. A complicated DNA product is predicted by considering the Tm of expected secondary structures, with increased Tm with respect to variation in salt concentrations. Therefore, the new DNA nanostructure may be utilized as a platform for various practical applications.

Interacting mechanism of benzo(a)pyrene with free DNA in vitro

Polycyclic aromatic hydrocarbons are environmental pollutants with strong carcinogenicity, indirect teratogenicity, and mutagenicity. This study explored the interaction mechanism of benzo(a)pyrene with free DNA in vitro by using various analytical methods. UV–vis spectra showed that benzo(a)pyrene and DNA formed a new benzo(a)pyrene–DNA complex. The thermal melting temperature of DNA increased by 12.7 °C, showing that the intercalation of benzo(a)pyrene into DNA could promote the stability of the DNA double helix structure. The intercalation of benzo(a)pyrene with DNA in vitro was further confirmed by fluorescence microscopy with magnetic beads. Fluorescence spectra showed that the interaction between DNA and benzo(a)pyrene decreased the fluorescence intensity of benzo(a)pyrene, and the maximum quenching rate was 27.89%. The quenching mode of benzo(a)pyrene was static quenching. Thermodynamic data showed that the main driving forces were van der Waals forces and hydrogen bonds, and the reaction was spontaneous. The results of this study provided a novel insight for the establishment of polycyclic aromatic hydrocarbon capture and elimination through polycyclic aromatic hydrocarbon–DNA intercalation.

Removal of 1,2-benzanthracene via the intercalation of 1,2-benzanthracene with DNA and magnetic bead-based separation

In this study, DNA-functionalize-magnetic beads were investigated as sorbent materials for effective removing 1,2-benzanthracene (BaA) from water. In order to reveal the removal mechanism, the interaction mode between BaA and DNA was evaluated by using various characterization tools such as UV-visible and circular dichroism spectroscopy, fluorescence and resonance scattering spectroscopy, and agarose gel electrophoresis. In the presence of BaA, the melting temperature of DNA increased from 76.2 °C to 82.3 °C, which closely related to the intercalating of BaA. It was found that a part of the ethidium bromide (EB) binding sites to DNA were occupied by BaA in EB competing study. The results indicated that a new complex appeared between hsDNA and BaA, and the number of the binding sites (n) and the binding constants (KA) at different temperatures were obtained. DNA binding saturation value (≈0.80) was obtained by resonance scattering spectra study. BaA could be enriched and removed by DNA-functionalize-magnetic beads via the intercalation, and the removal efficiency was 97.73% when the initial concentration was 2.45 x10−6 mol·L−1 (559.31 μg/L).

Thiophene-benzothiazole dyad ligand and its Ag(I) complex – Synthesis, characterization, interactions with DNA and BSA

The aim of the reported research is to evaluate the significance and potential role of the thiophene moiety in potential DNA and BSA targeting drugs. For this purpose a Thiophene-BenzoThiazole tandem molecule (TBT) and its mononuclear silver(I) complex [Ag(TBT)2]+ was synthesized. The research was carried out using spectroscopic techniques such as circular dichroism (CD), UV–Vis and fluorescence. Based on the presented results the intercalating type of binding to DNA by complex [Ag(TBT)2]+ and ligand TBT was observed. The binding is spontaneous in both cases and the Kb values of both compounds are similar (Kb = 6.40 × 105 and Kb = 5.83 × 105 for ligand TBT and complex [Ag(TBT)2]+, respectively). Yet, this type of interaction was confirmed in ethidium bromide competitive binding experiments and a special emphasis should be put on the higher KSV value for complex [Ag(TBT)2]+ (5.1 × 104) than ligand TBT (3.4 × 104), since it may be the result of the bisintercalation of the complex. It has found confirmation in the increase of the melting temperature (Tm) of DNA treated with complex [Ag(TBT)2]+ of ~5 °C, while in analogues experiment with ligand TBT Tm was only ~1 °C higher. The bisintercalation of the complex is possible since two TBT ligands are bound to the metallic center with planar thiophene moieties placed on the same site. Furthermore, the complex [Ag(TBT)2]+ caused more significant changes in the secondary structures of the model protein BSA than the ligand TBT as determined by CD (reduction of α-helix content by 95 times in presence of the complex vs. stabilization of BSA structure with TBT). It needs to be emphasized, that both compounds bind to BSA via static quenching mechanism, however [Ag(TBT)2]+ has a higher affinity to it than the ligand itself (as evidenced by the extent of hyperchromism). Both compounds interact in hydrophobic site of the protein, however [Ag(TBT)2]+ exhibits higher Stern-Volmer constant KSV = 1.66 × 105 in comparison to TBT KSV = 1.24 × 105. The Scatchard equation allowed one to estimate the compound:BSA binding ratio as 1:1 and 2:3 for ligand and complex, respectively. Moreover, the binding constant Kb is higher for complex (Kb = 4.05 × 107) than ligand (Kb = 3.70 × 105). It confirms that, indeed, both compounds may be distributed by albumins in the body, however the {(BSA)3 - [Ag(TBT)2]+2} adduct is more stable. The synchronous fluorescence spectra indicated that both compounds bind better in Trp than Tyr residues, therefore they may serve as potential molecular targets.

Femtosecond Laser Pulse Excitation of DNA-Labeled Gold Nanoparticles: Establishing a Quantitative Local Nanothermometer for Biological Applications.

Femtosecond (fs) laser pulsed excitation of plasmonic nanoparticle (NP)-biomolecule conjugates is a promising method to locally heat biological materials. Studies have demonstrated that fs pulses of light can modulate the activity of DNA or proteins when attached to plasmonic NPs; however, the precision over subsequent biological function remains largely undetermined. Specifically, the temperature the localized biomolecules "experience" remains unknown. We used 55 nm gold nanoparticles (AuNPs) displaying double-stranded (ds) DNA to examine how, for dsDNA with different melting temperatures, the laser pulse energy fluence and bulk solution temperature affect the rate of local DNA denaturation. A universal "template" single-stranded DNA was attached to the AuNP surface, and three dye-labeled probe strands, distinct in length and melting temperature, were hybridized to it creating three individual dsDNA-AuNP bioconjugates. The dye-labeled probe strands were used to quantify the rate and amount of DNA release after a given number of light pulses, which was then correlated to the dsDNA denaturation temperature, resulting in a quantitative nanothermometer. The localized DNA denaturation rate could be modulated by more than threefold over the biologically relevant range of 8-53 °C by varying pulse energy fluence, DNA melting temperature, and surrounding bath temperature. With a modified dissociation equation tailored for this system, a "sensed" temperature parameter was extracted and compared to simulated AuNP temperature profiles. Determining actual biological responses in such systems can allow researchers to design precision nanoscale photothermal heating sources.

Development of the Genus and Species Determination Method for Histamine Producing Bacteria Isolated from Fishery Product with High-Resolution Melting Analysis

Histamine in foods with a high histidine content may be produced by bacteria with histidine decarboxylase activity. Consumption of food enriched in histamine can produce symptoms of histamine poisoning that include flushing, headache, and urticaria. The number of histamine poisoning cases in Japan has decreased with developments in food hygiene management technology. However, approximately 10 cases are still reported each year. In addition, there have been cases where histamine was detected in the end products, prompting large product recalls. To prevent and identify causes of histamine toxicity, manufacturers must identify the bacteria causing the illness. A simple method of identification is needed, since sequence-based identification is complicated to perform and the analysis takes a long time. High-Resolution Melting Analysis (HRMA) is a method that detects differences in the base sequences of PCR products manifested as varied melting temperatures of double-stranded DNA. The present study was intended to develop a rapid identification method for major histamine-producing bacteria using HRMA. Species-specific HRMA primers were designed that specifically targeted the hdcA gene of 20 Gram-negative histamine-producing bacterial strains. The designed primers were used for HRM analysis of the 20 histamine-producing bacterial strains. The strains were divided into three groups (A, B, and C) based on differences in melting temperature values obtained by Tm Calling analysis program. Group A comprised terrestrial bacteria, such as Morganella, Enterobacter, and Raoultella, while Groups B and C comprised marine bacteria, such as those belonging to the genera Vibrio and Photobacterium. The melting profiles obtained in Group A by HRMA were used to identify the aforementioned terrestrial bacteria. The findings indicated that HRMA can easily identify the major gram-negative histamine-producing bacteria. A flow chart was created to identify histamine-producing bacterial species. This method enables the identification of histamine-producing bacterial species more quickly and easily than conventional sequence-based methods. Therefore, the method could be valuable for food companies to screen raw materials and products and track the source of contamination, which will in turn contribute to the prevention of histamine-food poisoning and investigation of its causes.

Binding-Induced 3D-Bipedal DNA Walker for Cascade Signal Amplification Detection of Thrombin Combined with Catalytic Hairpin Assembly Strategy.

As an important biomarker, thrombin (TB) is a major player in thrombosis and hemostasis and has attracted increasing attention involving its determination. Herein a universal and ultrasensitive fluorescence biosensor based on a binding-induced 3D-bipedal DNA walker and catalytic hairpin assembly (CHA) strategy has been proposed for cascade signal amplification detection of thrombin. In this study, we designed two proximity probes (foot 1 and foot 2) which include a specific affinity ligand for TB binding and a Pb2+-dependent DNAzyme tail sequence. In the presence of TB, the simultaneous binding of TB to foot 1 (F1) and foot 2 (F2) via TB aptamer (TBA) brings the tail sequences into close proximity and the melting temperature for tail sequences and track DNA is increased, allowing the Pb2+-dependent DNAzyme to cleave the track DNA into two short fragments which have lower affinities for the DNAzyme and, finally, leading to the release of trigger DNA (T-DNA) for subsequent CHA reaction. In the meantime, the dissociated DNA walkers (F1 and F2) explore adjacent unwound track DNA, and the walking procedure is conducted. Unlike the conventional unipedal DNA walkers that anchor foot DNA and track DNA on the same sensing surface, the proposed 3D-bipedal DNA walking machine can not only increase the local concentration of track DNA but can also improve the walking efficiency and expand the range of the walkers to some extent due to the two free feet. Moreover, with the advantages of superior sensitivity and excellent specificity, this biosensing platform exhibits a huge potential in practical application in biomedical research and clinical diagnosis.

Synthesis and antileishmanial evaluation of thiazole orange analogs

Cyanine compounds have previously shown excellent in vitro and promising in vivo antileishmanial efficacy, but the potential toxicity of these agents is a concern. A series of 22 analogs of thiazole orange ((Z)-1-methyl-4-((3-methylbenzo[d]thiazol-2(3H)-ylidene)methyl)quinolin-1-ium salt), a commercial cyanine dye with antileishmanial activity, were synthesized in an effort to increase the selectivity of such compounds while maintaining efficacy. Cyanines possessing substitutions on the quinolinium ring system displayed potency against Leishmania donovani axenic amastigotes that differed little from the parent compound (IC50 12–42 nM), while ring disjunction analogs were both less potent and less toxic. Changes in DNA melting temperature were modest when synthetic oligonucleotides were incubated with selected analogs (ΔTm ≤ 5 °C), with ring disjunction analogs showing the least effect on this parameter. Despite the high antileishmanial potency of the target compounds, their toxicity and relatively flat SAR suggests that further information regarding the target(s) of these molecules is needed to aid their development as antileishmanials.

DNA binding interaction studies of flavonoid complexes of Cu(II) and Fe(II) and determination of their chemotherapeutic potential

The present study is based on molecular level investigation of DNA binding of three flavonoids (Fls), morin (mor), quercetin (quer) and primuletin (prim) and their metal (Cu (II) and Fe (III)) complexes through UV–Vis spectroscopy, fluorescence spectroscopy, thermal analysis and cyclic voltammetry (CV). The spectroscopic experiments were performed by titrating compounds with DNA and the results were in good agreement with those obtained from titration of DNA by the compounds. The Fe-mor, Cu-quer, Fe-quer and prim which exhibited hypsochromic/hyperchromic shifts in UV–Vis spectra, showed negligible effects over florescent spectra of NR-DNA (intercalating Neil red dye–DNA complex), intact Tm (thermal melting temperature) of DNA and the shift of peak potential (Ep) towards less positive value were designated to exhibit electrostatic mode of binding with dsDNA having binding constant, Kb ≈ 102 M−1. The mor, Cu-mor, Cu-prim and Fe-prim showed intercalating mode of interaction with dsDNA which was recognized from hypochromic/bathochromic shifts in the spectra, Ep shifts towards higher potential in CV, significant decay in fluorescence intensity, distinct shift in Tm of DNA and binding constant (Kb) of the order of 104 M−1. The mor exhibited mixed binding mode (intercalation and groove binding) at different concentrations. The quer displayed increase in peak current and hyperchromism thus depicted groove binding into dsDNA (Kb ≈ 103 M−1). The binding modes were found to be correlated with the apoptotic activity of the Fls and M-Fls (flavonoids and metal-flavonoids) assayed against human breast cancer cell lines (MCF-7) and human uterine cervical cancer cell lines (HeLa). The correlation is interpreted in terms of, the intercalation mode as cytostatic activity and the groove binding with no apoptosis. However, electrostatic binding of (M-)Fls to dsDNA did not produce significant anti-proliferation activity against Hela cell lines with exception of Fe-mor (cytostatic activity) and Cu-quer (cytotoxicity) against MCF-7 cell line.

Synthesis, structure, and DNA-binding study of a novel Zn (II) complex with fleroxacin and 1,10-phenanthroline monohydrate

A novel metal-based compound of zinc complexing with fleroxacin (flrx) was prepared in the presence of 1,10-phenanthroline (phen) monohydrate and characterized by various techniques. The crystal structure of the complex ([Zn(flrx)(phen)(H2O)](NO3)·2H2O) was successfully disclosed through single-crystal X-ray diffraction, and Zn(II) connected with pyridone oxygen and the carboxylic oxygen atom of flrx by coordination bonds. The complex showed a square pyramid, and its structure was stabilized by intermolecular hydrogen bonding and π–π stacking. The interaction between the complex and calf thymus DNA (ctDNA) was studied. Results indicated that [Zn(flrx)(phen)(H2O)](NO3)·2H2O bound to ctDNA through a static mechanism, and the hydrophobic force was the main driving force in the binding process. Circular dichroism spectra, iodide quenching studies, and DNA melting temperature experiments indicated that the complex bound to ctDNA in the groove. Molecular docking further verified the groove binding mode and provided a visualized view for the interactions between the complex and ctDNA.

Fluorophore-Quencher Interactions Effect on Hybridization Characteristics of Complementary Oligonucleotides.

Nucleic acids are often covalently modified with fluorescent reporter molecules to create a hybridization state-dependent optical signal. Designing such a nucleic acid reporter involves selecting a fluorophore, quencher, and fluorescence quenching design. This report outlines the effect that these choices have on the DNA hybridization characteristics by examining six fluorophores in four quenching schemes: a quencher molecule offset from the fluorophore by 0, 5, or 10 bases, and nucleotide quenching. The similar binding characteristics of left-handed L-DNA were evaluated in comparison with right-handed DNA to quantify the effect of each quenching scheme. These results were applied to the Adaptive PCR method, which monitors fluorescently-labeled L-DNA as a sentinel for analogous unlabeled D-DNA in the reaction. All of the tested fluorophores and quenching schemes increased the annealing temperature of the oligonucleotide pairs by values ranging from 0.5 to 8.5 °C relative to unlabeled oligonucleotides. The design with the smallest increase (0.5 °C) was a sense strand with a FAM fluorophore and an anti-sense strand with Black Hole Quencher 2 offset by 10 bases from the FAM. An identical design that did not offset the quencher molecules resulted in a shift in annealing temperature of 5 °C. PCR was performed using temperature switching based on each of these L-DNA designs, and efficiency was significantly increased for the 10-base offset design, which had the smallest shift in annealing temperature. These results highlight the importance of selecting an appropriate fluorescence quenching scheme for nucleic acid optical signals.

Thermodynamic and Kinetic Studies of Tiopronin Gold Nanoparticles Binding With Extracted DNA of Rheumatoid Arthritis

Nanomaterial can interact with biological systems in different way, using their surface functionalities and depending on the particle size, shape, and aggregation .The present work aims to characterize the binding of tiopronin gold nanoparticles with extracted DNA from blood patients with rheumatoid arthritis kinetically and thermodynamically. A total of 19 patients with rheumatoid arthritis attending Baghdad Teaching Hospital / Medical City were included in this study. Tiopronin monolayer-protected gold nanoparticles) were prepared by chemical methods and a partial purification of DNA extracted was preceded using negative ions exchange column chromatography. Characterization of Tio Au NPs binding with DNA was investigated by using TEM,SEM,FTIR,EDX and UV-VIS. techniques.The results indicated that the average size of Tio Au NPs was 48 nm.,and there is a different binding affinity of DNA to tiopronin gold nanoparticles depending on pH. Also the melting temperature of DNA was decreased 5C0 when binding with tiopronin gold nanoparticles. Thermodynamic studies indicated that the reaction was endothermic, less order, and non spontaneous.

Carbohydrates and Charges on Oligo(phenylenethynylenes): Towards the Design of Cancer Bullets.

Two new tetralkylammonium-OPEs, bearing one or two positively charged groups directly linked to the aromatic residues and two β-d-glucopyranose terminations, were synthesized. Their peculiar structural features, joining the biologically relevant sugar moieties, flat aromatic cores and positive charges, make these luminescent dyes soluble in aqueous media and able to strongly interact with DNA. As a result of UV/Vis spectral variations, DNA melting temperature measures, viscometric titrations and induced CD, we propose a partial insertion of the OPEs aromatic core into the helix, stabilized by glucose H-bonding with the groups accessible from the grooves. This interaction leads to the quenching of the OPE luminescence due to guanine reduction. The biocompatibility of the monocationic OPE with healthy and cancer cells, and the reduction of proliferation in HEp-2 cancer cells induced by the dicationic one, make this class of compounds promising for future biological applications.

1H-[1,2,4]Triazolo[4,3-a]pyridin-4-ium and 3H-[1,2,4]triazolo[4,3-a]quinolin-10-ium derivatives as new intercalating agents for DNA

AbstractTwo new cationic DNA intercalators, 3-phenyl-1-(6-phenylpyridin-2-yl)-1H-[1,2,4]triazolo[4,3-a]pyridin-4-ium (1a)+and 1-phenyl-3-(6-phenylpyridin-2-yl)-3H-[1,2,4]triazolo[4,3-a]quinolin-10-ium (1b)+, were synthesized from 2-chloropyridine and 2-chloroquinoline, respectively, in a four-step procedure. Generation of the hydrazine, followed by condensation with an aldehyde to give a hydrazone and subsequent Buchwald-Hartwig amination gave a mixture ofE- andZ-configuredN,N-functionalized hydrazones. Finally, oxidative cyclisation gave rise to the formation of the cationic DNA intercalators, whose molecular structures were determined by single-crystal X-ray diffraction analysis of the hexafluorophosphate and tribromide salt of (1a)+and (1b)+, respectively. The intercalative binding of (1a)PF6and (1b)PF6to ctDNA was confirmed by means of UV, CD and luminescence spectroscopy, determination of the DNA melting temperature and by rheology measurements.

INFLUENCE OF X-RADIATION ON STRUCTURE OF DNA OF YEASTS C. guilliermondii NP-4

Investigation of fluorescence, electrophoretic and melting parameters of DNA of yeasts Candida guilliermondii NP-4 after X-radiation and posradiation repair was carried out. It was shown that under influence of X-radiation the rate of saturation of DNA by ethidium bromide and the melting temperature of yeast DNA was increased, and the melting interval was decreased. After repair period the rate of saturation of DNA by ethidium bromide and the melting temperature of yeast DNA were the highest, and the melting interval was the lowest, and in the electrophoregramms or repaired DNA there were additional low molecular fractions which testify about possible changes in DNA primary and secondary structures under influence of X-radiation and postradiation repair.

Preliminary study on effect of nano-hydroxyapatite and mesoporous bioactive glass on DNA

Abstract

Application of spectral methods for studying DNA damage induced by gamma-radiation

Spectral methods can provide a variety of possibilities to determine several types of radiation-induced DNA damage, such as nucleobase destruction and local denaturation. DNA UV absorption and CD spectra measured at room temperature undergo noticeable alteration under the action of γ-radiation. We have applied the Spirin method of total nucleobases determination, and have measured the molar extinction coefficient of DNA and DNA CD spectra for solutions with different NaCl concentrations (3mM–3.2M) and containing MgCl2, exposed to γ-radiation with the doses of 0–103Gy. The melting temperatures of DNA in irradiated solutions at the doses of 0–50Gy were obtained with the help of spectrophotometric melting. It was found that the amount of destructed nucleobases and radiation-induced loss of DNA helicity significantly decreases with the rise of the ionic strength of the irradiated solution. Substitution of a portion of Na+ ions on Mg2+ while keeping the total ionic strength constant (μ=5mM) does not affect the considered radiation effects. The role of the structure and composition of the DNA secondary hydration layer in the radiation-induced damages is discussed.

DNA binding and cleavage properties of ponicidin.

Ponicidin, an effective component isolated from Isodon rubescens, possesses anticancer properties. In the present study, we proved its ability to bind to and cleave DNA. DNA binding and cleavage properties are important for designing the rational construction of new and more efficient drugs targeted to DNA, because DNA is the biological target with which many anti-tumor drugs and potential antineoplastic agents interact. The characterization of interaction of ponicidin not only provides insights into its biology, but also gives the opportunity for developing effective therapeutic agents for control of gene expression. The interaction of ponicidin with DNA has been explored by using absorption spectroscopy, fluorescence spectroscopy, viscosity measurement, thermal denaturation and electrophoresis measurement. Firstly, adding ponicidin to a DNA solution could shift the absorption spectra to red. Secondly, ponicidin also raised the melting temperature and viscosity of DNA. Moreover, fluorescence of DNA binding with ethidium bromide was quenched by ponicidin. Finally, ponicidin showed nuclease activity. We propose that the DNA binding and cleavage properties of ponicidin may underlie the mechanism of its cell toxic effects.

Application of Electrochemical Devices to Characterize the Dynamic Actions of Helicases on DNA.

Much remains to be understood about the kinetics and thermodynamics of DNA helicase binding and activity. Here, we utilize probe-modified DNA monolayers on multiplexed gold electrodes as a sensitive recognition element and morphologically responsive transducer of helicase-DNA interactions. The electrochemical signals from these devices are highly sensitive to structural distortion of the DNA produced by the helicases. We used this DNA electrochemistry to distinguish the details of the DNA interactions of three distinct XPB helicases, which belong to the superfamily-2 of helicases. Clear changes in DNA melting temperature and duplex stability were observed upon helicase binding, shifts that could not be observed with conventional UV-visible absorption measurements. Binding dissociation constants were estimated in the range from 10 to 50 nM and correlated with observations of activity. ATP-stimulated DNA unwinding activity was also followed, revealing exponential time scales and distinct time constants associated with conventional and molecular wrench modes of operation further confirmed by crystal structures. These devices thus provide a sensitive measure of the structural thermodynamics and kinetics of helicase-DNA interactions.

Effects of cytotoxic cis- and trans-diammine monochlorido platinum(II) complexes on selenium-dependent redox enzymes and DNA

Here we present the preparation of 14 pairs of cis- and trans-diammine monochlorido platinum(II) complexes, coordinated to heterocycles (i.e., imidazole, 2-methylimidazole and pyrazole) and linked to various acylhydrazones, which were designed as potential inhibitors of the selenium-dependent enzymes glutathione peroxidase 1 (GPx-1) and thioredoxin reductase 1 (TrxR-1). However, no inhibition of bovine GPx-1 and only weak inhibition of murine TrxR-1 was observed in in vitro assays. Nonetheless, the cis configured diammine monochlorido Pt(II) complexes exhibited cytotoxic and apoptotic properties on various human cancer cell lines, whereas the trans configured complexes generally showed weaker potency with a few exceptions. On the other hand, the trans complexes were generally more likely to lack cross-resistance to cisplatin than the cis analogues. Platinum was found bound to the nuclear DNA of cancer cells treated with representative Pt complexes, suggesting that DNA might be a possible target. Thus, detailed in vitro binding experiments with DNA were conducted. Interactions of the compounds with calf thymus DNA were investigated, including Pt binding kinetics, circular dichroism (CD) spectral changes, changes in DNA melting temperatures, unwinding of supercoiled plasmids and ethidium bromide displacement in DNA. The CD results indicate that the most active cis configured pyrazole-derived complex causes unique structural changes in the DNA compared to the other complexes as well as to those caused by cisplatin, suggesting a denaturation of the DNA structure. This may be important for the antiproliferative activity of this compound in the cancer cells.