De-intercalation of ethidium bromide and acridine orange by xanthine derivatives and their modulatory effect on anticancer agents: a study of DNA-directed toxicity enlightened by time correlated single photon counting

Time Correlated Single Photon Counting (TCSPC) was used for the first time to analyze the effect/changes in the mode of intercalation of ethidium bromide (EtBr) and acridine orange (AO) to calf thymus DNA brought about due to interaction of naturally occurring methylxanthines such as theophylline (X1), theobromine (X2) and caffeine (X3). UV absorption and fluorescence studies were also carried to observe the behaviour of these xanthines on the modulation of the binding mode of anticancer agents (cisplatin, novantrone, and actinomycin D) and certain intercalating dyes (EtBr and AO) to DNA. In TCSPC analysis we found that when the concentration of the drugs (X1, X2 and X3) increased from 0.025 mM to 2 mM i.e. P/D 2.4 to P/D 0.03 reduction in intercalation of EtBr and AO was observed, suggesting that xanthine derivatives could play very important role in reducing the DNA-directed toxicity in a dose dependent manner. In TCSPC, the amplitude of smaller lifetime component A(1) and higher lifetime component A(2) are attributed to free and intercalated dye concentration and their variation could indicate the process of intercalation or reduced intercalation of EtBr and AO by xanthine derivatives. We found that at the maximum drug concentration the smaller lifetime component A(1) was increased by 7-8% and 17-37% in EtBr and AO intercalated complex respectively. Also the changes in lifetime and fluorescence decay profile were observed for the DNA-intercalated dyes before and after treatment with xanthines. Especially, at maximum P/D 0.03 the lifetime of DNA-intercalated EtBr and AO reduced by 1-2 ns. The present analysis reveals that xanthines are able to interact with free dyes and also with intercalated dyes, suggesting that when they interact with free dyes they might inhibit the further intercalation of dye molecules to DNA and the interaction with intercalated dyes might lead to displacement of the dyes resulting in de-intercalation. The results obtained from UV and fluorescence spectroscopy also support the present investigation of probable interaction of xanthines with the DNA damaging agents in modulating/reducing the DNA-directed toxicity.     

Further fluorospectrophotometric studies on the binding of acridine orange with DNA. Effects of thermal denaturation of DNA and additions of spermine, kanamycin, dihydrostreptomycin, methylene blue and chlorpromazine

Fluorospectrophotometric studies on the binding of acridine orange (AO) with calf thymus DNA showed that the thermal denaturation of DNA reduced markedly the fluorescence of Complex II and the extent of this decrease depended on the temperature to which the DNA solutions were heated. The denaturation was carried out in the absence and presence of AO (methods A and B, respectively), and then fluorescence measurements of solutions were carried out at 23 °C. The fluorescence intensity-heating temperature curves obtained by methods A and B were similar in shape to the usual melting curves of DNA and AO-DNA solutions, respectively. The higher midpoint value obtained with method B indicates the stabilizing activity of AO against denaturation. These findings support an intercalation model for Complex II and an external self-association binding model for Complex I.A high concentration of ethylene diamine (EDA) restored the fluorescence of denatured Complex II to about 80% of the intensity value of native Complex II. The effects of spermine, kanamycin and dihydrostreptomycin were much stronger than that of EDA.Methylene blue (MB) and chlorpromazine (CP) reduced the fluorescence of native Complex II markedly. Since the analysis of the difference absorption spectra declared that MB and CP were intercalated without release of bound AO, the interacting MB and CP were considered to weaken the interaction between AO and DNA bases, that made AO more fluorescent. Free radical (CP·) of CP was prepared by a new method using H₂O₂, peroxidase, and ascorbic acid. Intercalated CP· showed a much stronger quenching effect on Complex II, indicating that unpaired electron spin contained in the costacking unit between CP· and DNA bases might affect the fluorescence of the adjacent AO molecule by paramagnetic perturbation.     

Interaction between tryptophan‐Sm(III) complex and DNA with the use of a acridine orange dye fluorophor probe

The interaction of the Trp–Sm(III) complex with herring sperm DNA (hs‐DNA) was investigated with the use of acridine orange (AO) dye as a spectral probe for UV‐vis spectrophotometry and fluorescence spectroscopy. The results showed that the both the Trp–Sm(III) complex and the AO molecule could intercalate into the double helix of the DNA. The Sm(III)–(Trp)₃ complex was stabilized by intercalation into the DNA with binding constants: K^?_25°C = 7.14 × 10⁵ L·mol^?1 and K^?_37°C = 5.28 × 10⁴ L·mol^?1, and it could displace the AO dye from the AO–DNA complex in a competitive reaction. Computation of the thermodynamic functions demonstrates that Δ_rH_m^? is the primary driving power of the interaction between the Sm(III)(Trp)₃ complex and the DNA. The results from Scatchard and viscometry methods suggested that the interaction mode between the Sm(III)(Trp)₃ complex and the hs‐DNA is groove binding and weak intercalation binding. Copyright © 2015 John Wiley & Sons, Ltd.     

Acridine orange interaction with DNA: Effect of ionic strength

BackgroundThe study of acridine orange (AO) spectral characteristics and the quenching of its singlet and triplet excited states by TEMPO radical at its binding to DNA in the function of the DNA concentration and in the absence and presence of NaCl is reported.MethodsThe study was performed using steady-state and time resolved optical absorption and florescence, fluorescence correlation spectroscopy and resonant light scattering techniques.ResultsThe presence of different species in equilibrium: AO monomers and aggregates bound to DNA, has been demonstrated, their relative content depending on the DNA and the AO concentrations. At high DNA concentration the AO monomers are protected against the contact with other molecules, thus reducing the AO excited state quenching. The addition of NaCl reduces the AO binding constant to DNA, thus reducing the AO and DNA aggregation.ConclusionsThe interaction of AO with DNA is a complex process, including aggregation and disaggregation of both components. This modifies the AO excited state characteristics and AO accessibility to other molecules. The salt reduces the DNA effects on the AO excited state characteristics thus attenuating its effects on the AO efficacy in applications.General significanceThis study demonstrates that the interaction of photosensitizers with DNA, depending on their relative concentrations, can both decrease and increase the photosensitizer efficacy in applications. The salt is able to attenuate these effects.     

Mechanism of acridine orange interaction with phospholipids and proteins in renal microvillus vesicles

The mechanism of interaction of acridine orange (AO), a fluorescent, weak base, with rabbit kidney brush border membrane vesicles (BBMV) has been studied by absorption, and steady-state and time-resolved fluorescence spectroscopy. Equilibrium binding experiments indicate that AO binds to an apparent single class of sites on BBMV with a dissociation constant of 90 microM and site stoichiometry of 810 nmol/mg protein. The absorption spectra AO indicate that BBMV induces aggregation of AO; experiments with lipid vesicles show that the aggregation requires BBMV membrane proteins. Fluorescence stopped-flow experiments in which 0.15 mg/ml BBMV is mixed with increasing concentrations of AO result in a time course of fluorescence enhancement for [AO] less than 1.5 microM, and of fluorescence quenching for [AO] greater than 1.5 microM. Similar stopped-flow experiments with phosphatidylcholine lipid vesicles result only in a fluorescence enhancement time course. These results indicate the presence of two parallel pathways for AO binding to BBMV: one for AO binding to BBMV lipid, the other for AO binding to BBMV protein. Nanosecond lifetime measurements and fluorescence titration experiments confirm the presence of two environments for AO in BBMV. Fluorescence stopped-flow experiments indicate that AO responds to the imposition of an outwardly directed proton gradient by a rapid (less than 0.5 s) decrease in fluorescence, corresponding to re-equilibration of AO into the acidic intravesicular compartment, followed by an increase in fluorescence, corresponding to proton flux across the membrane. These findings have been incorporated into a stepwise mechanism for AO interaction with BBMV which have direct implications for the use of AO as a pH indicator in biological systems.     

DNA Binding Studies of Hematoxylin-Dy(Ш) Complex by Spectrometry Using Acridine Orange as a Probe

The interaction of a hematoxylin(HE)-Dy(Ш) complex with herring sperm DNA(hsDNA) was studied using acridine orange(AO) as a probe by UV-vis absorption, circular dichroism(CD), fluorescence spectroscopy and viscosity measurements. From the results of the probe experiment, we found that the HE-Dy(Ш) complex could compete with AO for intercalating into hsDNA. The binding constants of the HE-Dy(Ш) complex to hsDNA was obtained by the double reciprocal method and indicated that the affinity between hsDNA and the complex is weaker than that between hsDNA and classical intercalators. The thermodynamic parameters(ΔH°, ΔG°, ΔS°) were calculated from the UV-vis absorption data measured at two different temperatures. Further experimental results suggested that there exist groove binding and partial intercalation binding between hsDNA and HE-Dy(Ш) complex.     

Interactions of the DNA intercalator acridine orange, with itself, with caffeine, and with double stranded DNA

Caffeine (CAF) inhibits the intercalation of acridine orange (AO) into cellular DNA. Optical absorption and fluorescence spectroscopy were employed to determine the molecular interactions of AO with itself, with CAF, and with double stranded herring sperm DNA (dsDNA). AO dimerization was observed at concentrations >2 micromol. The sharp increase in fluorescence (lambda(em)=530 nm) at 5 micromol of AO was attributed to AO multimer formation. From 0.5 to 5.0 micromol, the AO self-association binding constant (K(assoc)) was determined to be 38620 mol(-1), however, the presence of 150 mmol NaCl increased K(assoc) to 118000 mol(-1) attributed to the charge neutralization. The K(assoc) for AO with CAF was confirmed to be 256 mol(-1). K(assoc) for the binding of AO with 20 micromol DNA ranged from, 32000 mol(-1) at 2 micromol AO, to approximately 3700 mol(-1) at 10 micromol AO, in the absence of NaCl. This AO concentration dependency of K(assoc) value with DNA was attributed to AO intercalation into dsDNA at high dsDNA/AO ratios, and electrostatic binding of AO to dsDNA at low AO ratios. The findings provide information used to explain fluorescence intensity values at lambda(em) at 530 nm from studies that combine AO, caffeine, and dsDNA.     

Interactions of acridine orange with double stranded nucleic acids. Spectral and affinity studies

Spectral properties of acridine orange (AO) alone or in complexes with natural and synthetic nucleic acids of various base composition have been studied in aqueous solutions by absorption and fluorescence spectroscopy. The dimerization constant and absorption spectra of the dye in monomeric and dimeric form were established; dimerization of AO resulted in quenching of its fluorescence. Complexes of the dye with synthetic nucleic acids differed in the degree of enhancement of fluorescence quantum yield, varying between 1.42 to 2.38 fold as compared to AO monomer; these differences, however, were not base-dependent. Affinity of the dye to natural and synthetic polymers was studied and analyzed using McGhee-von Hippel model of polymer-ligand interactions. Because the sterical requirement for intercalative binding assumes interaction of dye monomer, the correction for AO dimerization was made in all calculations. All studied DNAs (natural and synthetic ones, the latter being homopolymer pairs or alternating copolymers of A,T or G,C or I,C base composition) had similar intrinsic association constants (KI = 5 X 10(4) - 1 X 10(5), M-1) and binding site size (n = 2.0-2.4 b.p.). The exception was poly(dA).poly(dT), having KI = 1.2 X 10(4) and n = 19.3 b.p. The results of KI measurement for calf thymus DNA and AO in different sodium ion concentration were in good agreement with predictions of the counterion condensation theory. The intercalation of AO into DNA is discussed in view of recent theoretical models of DNA-ligand interactions.     

Caffeine and other xanthines as cytochemical blockers and removers of heterocyclic DNA intercalators from chromatin

Caffeine (CAF) and other xanthines non-covalently bind with the cationic fluorescent dye acridine orange (AO) and with other heterocyclic mutagens and carcinogens that are known to intercalate into double-stranded DNA (dsDNA). Fluorescence microscopy and spectrofluorometry studies were employed to test the ability of caffeine and certain other methyl substituted xanthines, with different binding affinities for AO, to inhibit and to reverse the intercalation of AO and other heterocyclic agents from intercalation with the DNA of nuclear chromatin of air-dried cells. Results indicated that xanthines with binding affinity for AO greater than 150 m(-1) block the AO molecule in a concentration dependent manner and comply with mass action kinetics. Thus CAF and other xanthines can be used to either inhibit intercalation of AO into nuclear DNA or to remove AO once intercalated into nuclear DNA. The interactions between other planar heterocyclics, xanthines, and nuclear chromatin dsDNA were also found to be non-covalent. Studies are needed to determine the ability of CAF and other xanthines to block and/or remove polyaromatic hydrocarbon (PAH) intercalators from the DNA of living cells.     

DNA interaction with low molecular ligands of different structure. II. Complexes of DNA with actinomine and its analogs

DNA-complexes with actinomine and its analogues containing omega-dialkylaminoalkyl groups at 1,9 positions of the phenoxazone moiety were studied by technique of spectrophotometry, viscometry and flow birefringence. In the process of spectrophotometry titration two groups of spectra corresponding to different DNA--ligand ratio in a complex were observed. According to the experimental data the investigated compounds are bounded to DNA by means of intercalation and external binding. There within a region of low degrees of binding the intercalation type of the ligand--DNA interaction prevails. In virtue of the spectrophotometry data the intercalation binding share was calculated. The intrinsic viscosity of a complex increases in the case of ligand intercalation and does not change as it joins to the DNA double-helix from outside. Optical anisotropy of DNA molecule increases linearly irrespective of the way of ligand binding. Data on the flow birefringence permits to conclude that under external binding the angle between the normal to the ligand chromophore plane and the axis of DNA double-helix is about zero. During ligand intercalation the equilibrium rigidity of DNA molecules increases.     

Nuclear chromatin changes during erythroid differentiation of friend virus induced leukemic cells

Friend leukemia (FL) cells grown in the presence of dimethylsulfoxide (DMSO) undergo erythroid differentiation. Acridine orange (AO) binding to DNA and thermal denaturation of DNA in situ were studied in differentiated and non-differentiated FL cells using flow-through cytofluorometry. The differentiated cells bind less AO than do the non-differentiated ones. The difference in AO binding is higher in the spectrum of emission characteristic for AO intercalation (at 530 nm) than for AO stacking (>600 nm) and depends on AO concentration. The difference is abolished after extraction of acid-soluble macromolecules from cells. During stepwise extraction by lowering pH, there is a progressive increase of AO binding to DNA. Most of the increase in AO binding of the non-differentiated cells occurs at pH 2.5-2.0; of the differentiated cells at pH 1.75-1.50. There are differences in sensitivity of DNA in situ to heat-denaturation between differentiated and non-differentiated cells, as evidenced by the variation in height and in position of the melting bands on derivative melting profiles. The changes described suggest that a profound modulation of chromatin structure, perhaps involving altered DNA-histone interactions, occurs during the DMSO-induced erythroid differentiation of FL cells.     

Acridine orange distribution and fluorescence spectra in myoblasts and single muscle fibers

Acridine orange (AO) fluorescence spectra in nuclei and cytoplasm of living myoblasts L6J1 and frog single muscle fibers have been studied using spectral scanning system of Leica TCS SL confocal microscope. AO fluorescence spectra in salt solutions dependent on free AO concentrations or in complex with DNA have also been obtained. Myoblast nuclei fluoresced in the green spectral region with maximum at about 530 nm; nucleoli had the brightest fluorescence. The fluorescence of nuclear chromatin was not uniform. Similar fluorescence of nuclei and nucleoli was observed in frog single muscle fibers. Uniform, weak, green fluorescence was observed in the myoblast cytoplasm. In the sarcoplasm of muscle fibers, AO green fluorescence was seen in A discs. In the cytoplasm of myoblasts and muscle fibers stained with AO, different red, yellow, and green fluorescent granules, which were acidic organelles, were visualized. The comparison of AO fluorescence spectra in living cells with AO fluorescence spectra in buffer solutions with different AO concentrations and AO in complex with DNA enables the estimation of the AO concentration in acidic granules. It is important for the evaluation of these cellular organelles functions in intracellular transport, adaptation, and apoptosis, as well as in a number of pathological processes.     

Spectroscopic, viscositic and electrochemical studies of DNA interaction with a novel mixed-ligand complex of nickel (II) that incorporates 1-methylimidazole and thiocyanate groups

A novel mixed-ligand nickel(II) complex that contains 1-methylimidazole and thiocyanate, Ni(NCS)(2)(Mim)(4) (Mim=1-methylimidazole), was synthesized and its structure was determined by X-ray crystallography, IR spectrum and elemental analysis, etc. Its DNA-binding properties were studied by electronic absorption spectral, viscositive and electrochemical measurements. The absorption spectral and viscositive results suggest that the nickel(II) complex binds to DNA via partial intercalation. The addition of DNA results in the decrease of the peak current of the nickel(II) complex proved their interaction. The slight differences of peak profiles and electrochemical parameters between free and DNA-bound Ni(NCS)(2)(Mim)(4) showed the formation of an electrochemical inactive complex between Ni(NCS)(2)(Mim)(4) and DNA. The binding site and binding constant of the complex to DNA were determined by electrochemical titration method.     

Conformational studies of Escherichia coli ribosomes with the use of acridine orange as a probe

The interaction of E. coli vacant ribosomes with acridine orange (AO) was studied, to obtain conformational information about rRNAs in ribosomes. Acridine orange binds to an RNA in two different modes: cooperative outside binding with stacking of bound AO's and intercalation between nucleotide bases. Free 16S and 23S rRNAs have almost identical affinities to AO. At 1 mM Mg2+, AO can achieve stacking binding on about 40% of rRNA phosphate groups. The number of stacking binding sites falls to about 1/3 in the 30S subunit in comparison with free 16S rRNA. In the 50S subunit, the number of stacking binding sites is only 1/5 in comparison with free 23S rRNA. Mg2+ ions are more inhibitory for the binding of AO to ribosomes than to free rRNAs. The strength of stacking binding appears to be more markedly reduced by Mg2+ in active ribosomes than in rRNAs. "Tight couple" 70S particles are less accessible for stacking binding than free subunits. The 30S subunits that have irreversibly lost the capability for 70S formation under low Mg2+ conditions have an affinity to AO that is very different from that of active 30S but similar to that of free rRNA, though the number of stacking binding sites is little changed by the inactivation. 70S and 30S ribosomes with stacking bound AO's have normal sedimentation constants, but the 50S subunits reversibly form aggregates.     

86 Characterization and differentiation of binding modes of water-soluble porphyrins at complexation with DNA

The influence of water-soluble cationic meso-tetra-(4?N-oxyethylpyridyl)porphyrin (H₂TOEPyP4) and it’s metallocomplexes with Ni, Cu, Co, and Zn on hydrodynamic and spectral behavior of DNA solutions has been studied by UV/Vis absorption and viscosity measurement. It was shown that the presence of planar porphyrins such as H₂TOEPyP4, NiTOEPyP4, and СuTOEPyP4 leads to an increase in viscosity at relatively small concentrations, and then decrease to stable values. Such behavior is explained by intercalation of these porphyrins in DNA structure because the intercalation mode involves the insertion of a planar molecule between DNA base pairs which results in a decrease in the DNA helical twist and lengthening of the DNA. Further decrease of viscosity is explained by the saturation intercalation sites and occurs outside the binding mode. But, in the case of porphyrins with axial ligands such as CoTOEPyP4 and ZnTOEPyP4, the hydrodynamic parameters decrease, which is explained by self-stacking of these porphyrins in DNA surface. This data are proved by spectral measurements. The results obtained from titration experiments were used for calculation of binding parameters: the binding constant K _b and the number of binding sites per base pair n. Obtained data reveal that K _b varies between 3.4 and 5.4?×?10⁶?M^?1 for a planar porphyrins, a range typical for intercalation mode interactions, and 5.6?×?10⁵?M^?1 and 1.8?×?10⁶?M^?1 for axial porphyrins. In addition, the exclusion parameter n also testifies that at intercalation, (n～2) the adjacent base pairs are removed to place the planar molecules, and for outside binders to pack on the surface needs too few places (n～0.5–1). It is apparent that the binding is somewhat stronger at intercalation. The viscometric and spectrophotometric measurements are in good agreement.     

87 The melting of DNA in the presence of meso-tetra-pyridyl porphyrins with different peripheral substituents

The influence of water-soluble cationic 3N- and 4N-pyridyl porphyrins with different peripheral substituents (oxyethyl, buthyl, allyl, and metallyl) on melting parameters of DNA has been studied. Results indicate that the presence of porphyrin changes the shape and parameters of DNA melting curve. The increase of porphyrins concentration results in the increase of the melting temperature (Tm) and the melting interval (ΔT) of DNA. At the porphyrin-DNA concentration ratio r?=?0.01, changes in the melting temperature have not been observed. The melting intervals almost do not change upon adding of the 4N-porphyrins, while the decrease of ΔT, in the presence of 3N-porphyrins, is observed. Because the intercalation binding mechanism occurs in GC-rich regions of DNA, we assume that 3N-porphyrins, intercalated in GC-rich regions, reduce the thermal stability of these sites, bringing them closer to the thermal stability of the AT-sites, which is the reason for the decrease in the melting interval. While at the relative concentration r?=?0.01 for 4-N porphyrins, already the external binding mechanism “turns on” and the destabilizing effect of porphyrins on GC-pairs compensates stabilizing effect on AT-pairs, as a result of which change in the melting of DNA upon complexation with these porphyrins is not observed. The decrease of the hypochromic effect also indicates the intercalation of investigated porphyrins in the DNA structure, which weakens the staking interaction of base pairs of DNA. The increase of the hypochromic effect of DNA upon binding with porphyrin depends on the type of peripheral substituents of the porphyrin. The results show that porphyrins with butyl and allyl substituents weaken staking interaction of base pairs less than porphyrins with other substituents. The largest change was observed for metallyl porphyrins. It can be the result of bulky peripheral substituents, which make significant local changes in DNA structure.     

Kinetics of the daunomycin--DNA interaction

The kinetics of the interaction of daunomycin with calf thymus DNA are described. Stopped-flow and temperature-jump relaxation methods, using absorption detection, were used to study the binding reaction. Three relaxation times were observed, all of which are concentration dependent, although the two slower relaxations approach constant values at high reactant concentrations. Relaxation times over a wide range of concentrations were gathered, and the data were fit by a minimal mechanism in which a rapid bimolecular association step is followed by two sequential isomerization steps. The six rate constants for this mechanism were extracted from our data by relaxation analysis. The values determined for the six rate constants may be combined to calculate an overall equilibrium constant that is in excellent agreement with that obtained by independent equilibrium measurements. Additional stopped-flow experiments, using first sodium dodecyl sulfate to dissociate bound drug and second pseudo-first-order conditions to study the fast bimolecular step, provide independent verification of three of the six rate constants. The temperature dependence of four of the six rate constants was measured, allowing estimates of the activation energy of some of the steps to be made. We speculate that the three steps in the proposed mechanism may correspond to a rapid "outside" binding of daunomycin to DNA, followed by intercalation of the drug, followed by either conformational adjustment of the drug or DNA binding site or redistribution of bound drug to preferred sites.     

Dependence of mode of DNA binding to benzo crown derivatives of actinocin on the size and distance from the chromophore of crown fragments

Complexes of DNA with benzocrown derivatives of actinocin were studied by viscometry and dynamic birefringence. Changes in the macromolecular structure of DNA caused by complex formation were determined. Models of DNA binding to the studied compounds were suggested on the basis of data obtained. The intercalation of actinocin chromophore of benzocrown derivatives of actinocin was shown to occur only when benzocrown groups were bound to the chromophore via glycine fragment. A change in the distance between the crown group and the chromophore prevents ligand intercalation. Increase in medium ionic strength results in appearance of new nonintercalational binding mode for crown-containing compounds with DNA caused by interaction of the crown groups with DNA.     

Modulation of DNA intercalation by resveratrol and genistein

Time correlated Single Photon Counting study (TCSPC) was performed for the first time to evaluate the effect of resveratrol (RES) and genistein (GEN) at 10–100 μM and 10–150 μM respectively, in modulating the DNA conformation and the variation induced due to intercalation by the dyes, ethidium bromide (EtBr) and acridine orange (AO). It is demonstrated using UV-absorption and fluorescence spectroscopy that RES and GEN, at 50 μM and 100 μM respectively can bind to DNA resulting in significant de-intercalation of the dyes, preventing their further intercalation within DNA. Hyperchromicity with red/blue shifts in DNA when bound to dyes was reduced upon addition of RES and GEN. DNA-dependent fluorescence of EtBr and AO was quenched in the presence of RES by 87.97% and 79.13% respectively, while similar quenching effect was observed for these when interacted with GEN (85.52% and 83.85%). It is found from TCSPC analysis that the higher lifetime component or constituent of intercalated dyes (τ₂, A ₂) decreased with the subsequent increase in smaller component or constituent of free dye (τ₁, A ₁) after the interaction of drugs with the intercalated DNA. Thus these findings signify that RES and GEN can play an important role in modulating DNA intercalation, leading to the reduction in DNA-directed toxicity.     

Dependence of Mode of DNA Binding to Benzocrown Derivatives of Actinocin on the Size and Distance from the Chromophore of Crown Fragments

Complexes of DNA with benzocrown derivatives of actinocin were studied by viscometry and dynamic birefringence. Changes in the macromolecular structure of DNA caused by complex formation were determined. Models of DNA binding to the studied compounds were suggested on the basis of data obtained. The intercalation of actinocin chromophore of benzocrown derivatives of actinocin was shown to occur only when benzocrown groups were bound to the chromophore via the glycine spacer. A change of the distance between the crown group and the chromophore prevented ligand intercalation. Increase of the ionic strength resulted in appearance of a new, nonintercalative binding mode for crown-containing compounds determined by interaction of the crown groups with DNA.