Synthesis of Acridines from o-Aminoaryl Ketones and Arylboronic Acids by Copper Trifluoroacetate-Mediated Relay Reactions

An efficient and practical method for the synthesis of medicinally important acridines from readily available o-aminoaryl ketones and arylboronic acids was developed using copper(II)-mediated relay reactions that involve intermolecular Chan-Lam cross-coupling and subsequent intramolecular Friedel-Crafts-type reactions. A sole promoter, i.e., Cu(OTf)₂, was used; therefore, strongly acidic and basic conditions, nonreadily available or expensive substrates, additives, and noble-metal catalysts were not needed.

General analysis of competitive binding in drug-interceptor-DNA systems

A general model of competitive binding in drug-interceptor-DNA systems has been developed in order to quantify both the interceptor and protector mechanisms. The model involves full parameterization of the basic equations governing the mutual competition between drugs binding to DNA and incorporates as partial cases various similar models existing in the literature. The generality of the model results from strict accounting of the statistical effects of the binding of the drug and interceptor with DNA according to the McGhee-von Hippel formalism, and to the strict treatment of hetero-association between the drug and interceptor, which includes formation of all possible types of self- and hetero-complexes in solution. Indirect experimental evidence is provided for the importance of the protector mechanism in drug-caffeine-DNA systems, which is sometimes ignored in the literature because of the small magnitude of the CAF-DNA binding constant.

Macrocyclic DNA-mismatch-binding ligands: structural determinants of selectivity

A collection of 15 homodimeric and 5 heterodimeric macrocyclic bisintercalators was prepared by one- or two-step condensation of aromatic dialdehydes with aliphatic diamines; notably, the heterodimeric scaffolds were synthesized for the first time. The binding of these macrocycles to DNA duplexes containing a mispaired thymine residue (TX), as well as to the fully paired control (TA), was investigated by thermal denaturation and fluorescent-intercalator-displacement experiments. The bisnaphthalene derivatives, in particular, the 2,7-disubstituted ones, have the highest selectivity for the TX mismatches, as these macrocycles show no apparent binding to the fully paired DNA. By contrast, other macrocyclic ligands, as well as seven conventional DNA binders, show lesser or no selectivity for the mismatch sites. The study demonstrates that the topology of the ligands plays a crucial role in determining the mismatch-binding affinity and selectivity of the macrocyclic bisintercalators.

On the electronic structure of ethidium

The electronic structure of the common intercalating agent ethidium bromide (3,8-diamino-5-ethyl-6-phenylphenanthridinium bromide) is dominated by an interplay of electron donating and withdrawing effects mediated by its nitrogen atoms. X-ray crystallography, UV/Vis and IR absorption, fluorescence emission, and NMR spectroscopy are used to probe the electronic properties of the phenanthridinium "core" of ethidium as well as its exocyclic amines and 6-phenyl groups. Interestingly, despite its positive charge, most of ethidium's aromatic carbon and hydrogen atoms have high electron densities (compared to both 6-phenylphenanthridine and benzene). The data suggest that electron donation by ethidium's exocyclic amines dominates over the electron withdrawing effects of its endocyclic iminium in their combined influence on the electron densities of these atoms. Ethidium's nitrogen atoms are, conversely, electron deficient where the 5-position is the most electropositive, followed by the 3-amino, and lastly the 8-amino group. These results have been used to generate an empirically-based pi-electron density map of ethidium that may prove useful to understanding its nucleic acid binding specificity.

Relaxation technique for kinetic measurements of dye accumulation at the mitochondria of HeLa cells in situ

The lipophilic cationic fluorescent dye ESI4 specifically stains the mitochondria in living cells. It was used to determine the kinetics of vital staining of mitochondria in single selected HeLa cells by quantitative microfluorometry in the concentration range CD = 6 x 10(-8) to 4 x 10(-6) M. The experiments were performed using the concentration jump method. They were evaluated with a quantitative staining model which considers dye binding as well as dye release at mitochondrial binding sites. The kinetic equations of the model are discussed in terms of the relaxation technique. The predictions of the theory agree well with the experimental results. The staining model was used to determine the rate constant k1 = 7.6 x 10(2)s-1 M-1 and k2 = 1.6 x 10(-3) s-1 for dye binding and dye release respectively, and the binding constant K = 4.8 x 10(5) M-1 of dye molecules at the mitochondria in HeLa cells (values according to relaxation experiments). The constants are discussed in detail. In addition, some experiments were performed on dye accumulation under the influence of antimycin, nigericin and oligomycin.

Toxicological studies with primary cultures of chick embryo cells: DNA fragmentation under the influence of DNase I-inhibitors

Chicken embryo brain and liver cells in vitro exhibited spontaneous DNA fragmentation as determined by viscometry of alkaline cell lysates. Ca2+ and Mg2+ enhanced, while Zn2+, the Ca2+ chelator ethylenglycol-bis(beta-aminoethyl-ether)-N,N,N'-tetraacetic acid (EGTA), spermine and--to a lesser extent--spermidine and Hoechst 33,258 inhibited spontaneous DNA fragmentation. Under the same conditions chromatin condensation, as assessed by nucleoid sedimentation, increased. Exposure of chicken embryo cells to various genotoxic agents, i.e. doxorubicin, bleomycin, methyl methanesulfonate, thiyl radicals, H2O2, UV light, and X-rays, increased DNA fragmentation in a dose dependent manner. Zn2+ or EGTA diminished DNA fragmentation in cells exposed to bleomycin, thiyl radicals, H2O2 and UV light. An apparent sensitisation to X-irradiation has been observed in Zn2+ or EGTA-pretreated cells. It is suggested by the present investigations that, with agent specific peculiarities, apoptotic phenomena are implicated when nucleotoxicity is assessed in chicken embryo cells by physico-chemical short-term tests in vitro.

Ring-substituted diaqua(1,2-diphenylethylenediamine)platinum(II) sulfate reacts with DNA through a dissociable complex

Ring-substituted diaqua(1,2-diphenylethylenediamine)platinum(II) sulfate shows unusual kinetics in its reaction with salmon testis DNA. The mechanism for diaqua[meso-1,2-bis(2,6-dichloro-4- hydroxyphenyl)ethylenediamine]platinum(II) sulfate, [Pt(H2O)2(meso-6)]2+SO4(2-), a representative of this series, has been investigated and compared with that for cis-[Pt(NH3)2(H2O)2]2+. Reactions were followed by atomic absorption, analytical HPLC of Pt-DNA digests, arrest of enzymatic DNA synthesis/degradation, ultraviolet and fluorescence spectrophotometry. Except for the formation of monofunctional DNA adducts, the kinetics of the platinum(II) complexes are comparable. The pseudo-first-order rate constant for the attack of DNA by [Pt(H2O)2(meso-6)]2+ follows the concentration of DNA in a hyperbolic fashion, which is in contrast to the linear dependence for cis-[Pt(NH3)2(H2O)2]2+. The hyperbolic dependence is typical for a dissociable DNA/drug complex preceding the coordination reaction. By studying the binding of free ligand to DNA, and by correlating ligand structures and electrostatic charges with effects on adduct formation, both the phenyl residues and the positive charge of the platinum(II) complex are shown to be crucial for the stability of the dissociable complex. A non-intercalative mode of binding to the DNA backbone is suggested. At the high concentrations of DNA found in cell nuclei, the reaction of the dissociable complex can, principally, become rate-limiting in the attack of DNA and thus reduce the cytotoxic efficiency of a drug.

Viscometry of alkaline cell lysates--the hitherto simplest short-term test for chromatin-interactive agents? Investigations in rat thymic and splenic cells

Alkaline (AL) lysates from thymic cells (T-cells) and splenic cells (S-cells) of the rat were measured by low-shearing glass capillary viscometry. AL-viscometry was compared to the nucleoid sedimentation technique and the alkaline unwinding method. The results obtained in cells treated by (a) DNA strand breaking agents (X-rays, UV-light, doxorubicin, bleomycin, hydrogenperoxide, methylmethanesulfonate (MMS)), (b) intercalating and/or cross-linking substances (ethidium bromide, actinomycin D, mitomycin C, bisbenzimide), (c) the DNA repair inhibitor 3-aminobenzamide (3-AB) and (d) hyperthermia suggest that AL-viscometry may be considered as a very simple, rapid and inexpensive preliminary short-term test for detecting chromatin-interactive agents. Whereas agent- and cell-specific characteristics can be also revealed by AL-viscometry, quantification of specific lesions and conclusions as to the mechanisms of action require additional assays.

Binding of Ru(bpy)3(2+) and Ru(phen)3(2+) to polynucleotides and DNA: effect to added salts on the absorption and luminescence properties

The interactions of tris(2,2'-bipyridyl)ruthenium(II) chloride and tris-(1,10-phenanthroline)ruthenium(II) chloride, Ru(bpy)3Cl2 and Ru(phen)3Cl2 respectively, with nucleic acids were studied by means of absorption spectroscopy and time-resolved and steady state luminescence techniques in unbuffered aqueous solution at room temperature as a function of added salt, oxygen and the [nucleotide]/[sensitizer] ratio (N/S). The hypochromicity of the visible absorption band of Ru(ligand)3(2+) and the changes in the luminescence intensity and luminescence decay kinetics are considerably larger in the presence of double-stranded calf thymus DNA (dsDNA) than in the presence of single-stranded DNA and polynucleotides. This is suggested to be the result of partial intercalation of the ruthenium complex into the dsDNA rather than just its higher charge density with respect to ssDNA. Spectral changes in the presence of dsDNA increase with increasing N/S ratio (maximum changes reached at N/S = 10-12, half-value 3-4). This is postulated to be due to a transition from mainly electrostatic binding to a binding in which partial intercalation plays an increased role. Addition of alkali or alkaline earth salts at very low concentrations stabilizes partial intercalation whereas higher salt concentrations lead to a release of the ruthenium complex from the strand. This effect of the salt cation increases in the order Cs less than Rb less than K less than Na less than Li less than Ba less than Sr less than Ca less than Mg less than Be. For Ru(bpy)3(2+) the presence of 0.5 mM Mg(ClO4)2 or 6 mM NaClO4 are sufficient to release 50% of the ruthenium complexes which are bound to the dsDNA (N/S = 10); the corresponding half-concentrations for Ru(phen)3(2+) are 0.8 mM and 40 mM respectively. The half-concentrations for release increase with increasing N/S ratio and decrease with the ionic radius of the added salt.

Staining kinetics in single cells. Part I. Influence of convective diffusion on the staining rate

The staining kinetics of single cells have been investigated using a perfusion cuvette in combination with a computer controlled microscope spectrometer. The physicochemical hydrodynamics of staining are characterized. Using a steady-state laminar flow parallel to the cell surface a hydrodynamic and a diffusional boundary layer are observed which are determined by the flow rate. The thickness of the diffusional boundary layer revealed by experimental data is in agreement with theoretically calculated values. At certain well-defined hydrodynamic conditions convective diffusion has no further effect on the staining rate.

[The vital staining of nuclear chromatin and the chromosomes of HeLa cells with the fluorochrome AMHA binding to DNA]

The fluorochrome AMHA (3-amino-6-methoxy-9-(2-hydroxyethylamino)acridine) stains the nuclear chromatin and the chromosomes of living HeLa cells. At relatively low dye concentrations CF less than or equal to 10(-4) M and short incubation periods tI less than or equal to 2 h cell growth is not affected by the drug. But at higher CF and longer tI the population doubling time of the cell cultures rapidly increases, and finally the cells die. In vital staining experiments the dye AMHA preferentially binds to the DNA of the nuclei and to the chromosomes of the cells, respectively. The dye binding to DNA has been proved by the absorption and emission microspectra of the stained cells, and by the comparison with authentic spectra of AMHA bound to DNA in aqueous solutions. Within the limits of experimental errors both types of spectra are identical. The spectra of DNA-bound AMHA show a characteristic gap of ca. 3500 cm-1 between the 0-0-transitions of the long wave length 1La absorption and the fluorescence. AMHA molecules dissolved in the polar solvent water have a gap of even 4100 cm-1. This energy gap shows that the electron distribution of AMHA is strongly changed by light absorption and emission. Finally, using absorption spectroscopy, we investigated the binding of AMHA to DNA in aqueous solutions over a wide range of concentrations of the dye, of nucleic acid (calf thymus), and of the competitor NaCl respectively. The Scatchard binding isotherms were determined. With the method of competitive salt effect three different bonds of AMHA to DNA can be distinguished even at low dye concentrations: The intercalation 1 of the fluorochrome F, binding constant KF1 = 1.1.10(5) M-1, binding parameter n1 = 0.15; the pre-intercalative or external binding 2, KF2 = 6.9.10(5) M-1, n2 = 0.21; the external binding 3, KF3 = 2.8.10(5) M-1, n3 = 0.55. Externally bound dye molecules 2 and 3 occupy two phosphodiester residues of the DNA. A detailed discussion of the data and the competitive salt effect shows that in living cells only intercalated and small amounts of pre-intercalatively bound molecules 1 and 2 exist. The binding constant KF1 = 1.1.10(5) M-1 of AMHA is unusual high in comparison with the constants of intercalation of other dyes, KF1 = (1-4).10(4) M-1.(ABSTRACT TRUNCATED AT 400 WORDS)

[Romanowsky dyes and the Romanowsky-Giemsa effect. 4. Binding of azure B to DNA]

We investigated the binding of azure B to DNA (calf thymus) over a wide range of concentrations of the dye (CF) and the nucleic acid (CN) using absorption spectroscopy [CF and CN represent the total concentrations of the ye (F) and the mononucleotide units (N) of the DNA, respectively]. The binding isotherms of the dye to DNA in aqueous solutions were determined. In addition, we analysed the composition of insoluble DNA/azure B precipitates that are formed in presence of an excess of azure B. These precipitates are of particular interest, because Giemsa staining is usually performed using high dye concentrations. Azure B easily forms dimers in aqueous solutions. When determining the binding isotherms, the equilibrium between free monomers and dimers must be taken into account. Therefore, we determined the dimerisation constant (Kd) of azure B from the concentration dependency of its absorption spectra in water at the standard temperature T = 298 K (25 degrees C), Kd = 6.5 X 10(3) M-1 (experimental conditions: tris buffer, pH 7.2; concentration of Na ions, CNa = 0.002 M). As the CNa value increases, the dimerisation constant rises rapidly. When the azure B concentration is very low and there is an excess of DNA, ordinary Scatchard and Langmuir isotherms are observed. Monomer dye cations are bound to DNA, these cations being in equilibrium with free monomers in the solution. In order to obtain the Scatchard binding constant (Ks) and the binding parameter (n) spectroscopically, it is necessary to determine the extinction coefficient (epsilon Fb) of the monomer bound (b) dye molecules (F) at one analytical wave number (upsilon a). The three constants can be determined simultaneously using an iterative technique that combines Scatchard isotherms and the Benesi-Hildebrand extrapolation, CN----infinity. We obtained Ks = 1.8 X 10(5) M-1 and n = 0.18 (25 degrees C; tris buffer, pH 7.2; CNa = 0.002 M). At very low dye (CF) and competitor (CNa) concentrations, only 18% of the anionic binding sites of the DNA are capable of binding the dye cations. With increasing CNa values the concentration of bound azure B cations decreases rapidly. The Na cations displace the bound dye cations and act as a competitor. The Ks value also greatly depends on the competitor concentration (CNa).(ABSTRACT TRUNCATED AT 400 WORDS)

Effects of ethidium bromide, tetramethylethidium bromide and betaine B on the ultrastructure of HeLa cell mitochondria in situ. A comparative binding study

Several investigators have described the ultrastructural changes that occur in the mitochondria of cells in tissue cultures after treatment with the drug ethidium bromide (E). The mitochondria swell and the cristae become greatly altered and finally disappear; in the cristae-free region of the matrix electron-dense granules can be observed. It has been assumed that intercalation of E between the base pairs of the mitochondrial DNA induces the formation of the granular inclusions. To investigate whether intercalation is really the initial step in the generation of dense granules inside the matrix, we performed a comparative incubation study of HeLa-cell mitochondria in situ using three closely related dyes (D), i.e., E, tetramethylethidium bromide (TME) and betaine B (B). They strongly differ with regard to their affinity for DNA and their ability to cross membranes. E was used as a reference dye. TME does not intercalate, but is externally bound to DNA only weakly. The neutral B is not bound at all, but can cross membranes more easily than the cation E. Moreover, in aqueous solutions at pH approximately equal to 7.0, B is in equilibrium with its protonated cation BH. BH and E have almost equal affinities for DNA. Therefore B may quickly pass the inner mitochondrial membranes and the cristae, and should then be bound inside the matrix, thus forming a BH-DNA complex. On the assumption that intercalation is necessary for the generation of intramitochondrial electron-dense bodies, we predicted that BH/B should be more efficient than E, while TME should be relatively ineffective.(ABSTRACT TRUNCATED AT 250 WORDS)