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Bereznyak EG, Gladkovskaya NA, Khrebtova AS, Dukhopelnikov EV, Zinchenko AV. Peculiarities of DNA-proflavine binding under different concentration ratios. Biophysics (Nagoya-shi) 2010. [DOI: 10.1134/s0006350909050030] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
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el-Subbagh HI, Abadi AH, al-Khamees HA. Synthesis and antitumor activity of 9-anilino, phenylhydrazino, and sulphonamido analogs of 2- or 4-methoxy-6-nitroacridines. Arch Pharm (Weinheim) 1997; 330:277-84. [PMID: 9396385 DOI: 10.1002/ardp.19973300903] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Synthesis of several new 9-anilino, phenylhydrazino, and sulphonamido analogs of 2- or 4-methoxy-6-nitroacridine derivatives is described. The prepared compounds were tested for their in vitro antitumor activity against 60 human tumor cell lines by the National Cancer Institute (NCI) and showed a potential anticancer activity. Compounds 9-(phenylhydrazino)-2-methoxy-6-nitroacridine (8a) and 9-(4-chlorophenylhydrazino)-4-methoxy-6-nitroacridine (9b) exhibited a broad spectrum antitumor activity with full panel (MG-MID) median growth inhibition (GI50), of 16.1 and 10.9 microM and total growth inhibition (TGI) of 66.7 and 37.9 microM, respectively. Meanwhile, compounds 15a and 15b showed moderate selectivity toward leukemia cell lines. As a trial to explore the mode of action of their antitumor activity, the 6-nitroacridine analogs were evaluated for their inhibitory effect on major cell cycle control proteins cdc2 kinase and cdc25 phosphatase as possible molecular targets that may account for antimitotic potency. None of the tested compounds proved to exert their activity via this antimitotic mode of action.
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Affiliation(s)
- H I el-Subbagh
- Department of Pharmaceutical Chemistry, College of Pharmacy, King Saud University, Riyadh, Saudi Arabia
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Chen T, Voelk E, Platz MS, Goodrich RP. Photochemical and photophysical studies of 3-amino-6-iodoacridine and the inactivation of lambda phage. Photochem Photobiol 1996; 64:622-31. [PMID: 8863468 DOI: 10.1111/j.1751-1097.1996.tb03115.x] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
The photochemistry and photophysics of 3-amino-6-iodoacridine (Acr-I) was studied. Photolysis (350 nm) of Acr-I (free base) generates products consistent with a free radical intermediate in methanol, benzene and carbon tetrachloride. The Acr-I hydrochloride is shown to bind to calf thymus DNA and to the self-complementary dinucleotide cytidylyl-(3'-5')-guanosine (CpG) miniduplex in a manner similar to that of proflavine (Acr-NH2), a known DNA intercalator. The Acr-I is shown to more efficiently nick supercoiled plasmid DNA pBR322 upon 350 nm or 420 nm photolysis than Acr-NH2. The efficiency of Acr-I-sensitized DNA nicking is not oxygen dependent. Photolysis of the Acr-I/(CpG)2 complex leads to cleavage of the dinucleotide and to cytidine base release by selective damage to a specific ribose moiety. Dinucleotide cleavage occurs equally well in the presence or absence of oxygen, thereby eliminating a singlet oxygen- or peroxyl radical-mediated process. Photolysis of Acr-I in the presence of a mononucleotide (GMP) or a non-self-complementary dinucleotide (uridylyl-[3'-5']-cytidine-UpC) does not lead to fragmentation and base release. Similarly, photolysis of the Acr-NH2/(CpG)2 complex does not lead to fragmentation and base release. The data indicate that photolysis of an iodinated intercalator bound to CpG or plasmid DNA generates an intercalated aryl radical and that the reactive intermediate initiates a sequence of reactions that efficiently nick nucleic acids. The inactivation of lambda phage sensitized by Acr-I with UV (350 nm) light is oxygen independent but with visible (420 nm) light is strongly oxygen dependent. The Acr-I fluoresces more intensely when excited at 446 than at 376 nm. Thus, UV photolysis may lead to C-I bond homolysis and free radical formation, a process that is not energetically feasible with visible light. The results demonstrate the difficulty of extrapolating model studies involving simple molecules and DNA to understanding the mechanism of viral inactivation with a particular sensitizer.
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Affiliation(s)
- T Chen
- Department of Chemistry, Ohio State University, Columbus 43210, USA
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Kimura M, Okabayashi I, Kato A. Acridine derivatives.V. Synthesis and P388 antitumor activity of the novel 9-anilino-2,3-ethylenedioxyacridines. J Heterocycl Chem 1993. [DOI: 10.1002/jhet.5570300446] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
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Kimura M, Kato A, Okabayashi I. Acridine derivatives.IV. Synthesis, molecular structure, and antitumor activity of the novel 9-anilino-2,3-methylenedioxyacridines. J Heterocycl Chem 1992. [DOI: 10.1002/jhet.5570290112] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022]
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Gilbert DE, Feigon J. The DNA sequence at echinomycin binding sites determines the structural changes induced by drug binding: NMR studies of echinomycin binding to [d(ACGTACGT)]2 and [d(TCGATCGA)]2. Biochemistry 1991; 30:2483-94. [PMID: 2001374 DOI: 10.1021/bi00223a027] [Citation(s) in RCA: 49] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
The complexes formed between the cyclic octadepsipeptide antibiotic echinomycin and the two DNA octamers [d(ACGTACGT)]2 and [d(TCGATCGA)]2 have been investigated by using one- and two-dimensional proton NMR spectroscopy techniques. The results obtained for the two complexes are compared to each other, to the crystal structures of related DNA-echinomycin complexes, and to enzymatic and chemical footprinting results. In the saturated complexes, two echinomycin molecules bind to each octamer by bisintercalation of the quinoxaline moieties on either side of each CpG step. Binding of echinomycin to the octamer [d(ACGTACGT)]2 is cooperative so that only the two-drug complex is observed at lower drug-DNA ratios, but binding to [d(TCGATCGA)]2 is not cooperative. At low temperatures, both the internal and terminal A.T base pairs adjacent to the binding site in the [d(ACGTACGT)]2-2 echinomycin complex are Hoogsteen base paired (Gilbert et al., 1989) as observed in related crystal structures. However, as the temperature is raised, the internal A.T Hoogsteen base pairs are destabilized and are observed to be exchanging between the Hoogsteen base-paired and an open (or Watson-Crick base-paired) state. In contrast, in the [d(TCGATCGA)]2-2 echinomycin complex, no A.T Hoogsteen base pairs are observed, the internal A.T base pairs appear to be stabilized by drug binding, and the structure of the complex does not change significantly from 0 to 45 degrees C. Thus, the structure and stability of the DNA in echinomycin-DNA complexes depends on the sequence at and adjacent to the binding site. While we conclude that no single structural change in the DNA can explain all of the footprinting results, unwinding of the DNA helix in the drug-DNA complexes appears to be an important factor while Hoogsteen base pair formation does not.
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Affiliation(s)
- D E Gilbert
- Department of Chemistry and Biochemistry, University of California, Los Angeles 90024
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Prabhakaran M, Harvey SC. Molecular dynamics of structural transitions and intercalation in DNA. Biopolymers 1988; 27:1239-48. [PMID: 3219395 DOI: 10.1002/bip.360270805] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
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8
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Kimura M. Acridine Derivatives. I. Molecular Structure of the Novel Acridinyl-Substituted Uracil, 5-(9-Acridinyl)-6-amino-1,3-dimethyluracil. BULLETIN OF THE CHEMICAL SOCIETY OF JAPAN 1987. [DOI: 10.1246/bcsj.60.447] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/12/2022]
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9
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Kimura M, Okabayashi I. Formation and molecular structure of the novel acridine substituted uracil derivatiLves. J Heterocycl Chem 1986. [DOI: 10.1002/jhet.5570230363] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022]
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Lybrand T, Kollman P. Molecular mechanical calculations on the interaction of ethidium cation with double-helical DNA. Biopolymers 1985; 24:1863-79. [PMID: 4074844 DOI: 10.1002/bip.360241003] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
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Constant JF, Carden BM, Lhomme J. Synthetic models related to DNA intercalating molecules: Preparation of 9-aminoacridines linked to the nucleotide bases adenine, guanine and thymine. J Heterocycl Chem 1985. [DOI: 10.1002/jhet.5570220422] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/07/2022]
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Assa-Munt N, Leupin W, Denny WA, Kearns DR. 1H NMR study of the binding of bis(acridines) to d(AT)5.d(AT)5. 2. Dynamic aspects. Biochemistry 1985; 24:1449-60. [PMID: 12096754 DOI: 10.1021/bi00327a025] [Citation(s) in RCA: 27] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Measurements of the 1H NMR spectra and relaxation rates were used to study the dynamic properties of 9-aminoacridine (9AA) and four bis(acridine) complexes with d(AT)5.d(AT)5. The behavior of the 9AA (monointercalator) and that of C8 (bisintercalator containing an eight-carbon atom linker chain) are entirely similar. For both compounds, the lifetime of the drug in a particular binding site is 2-3 ms at approximately 20 degrees C, and neither affects the A.T base pair opening rates. The complex with C10 (bisintercalator containing a 10-carbon atom linker chain) is slightly more stable than the C8 complex since its estimated binding site lifetime is 5-10 ms at 29 degrees C. Base pairs adjacent to the bound C10 are destabilized, relative to free d(AT)5.d(AT)5, but other base pairs in the C10 complex are little affected. Bis(acridine) pyrazole (BAPY) and bis(acridine) spermine (BAS) considerably stabilize those base pairs that are sandwiched between the two acridine chromophores, but in the BAS complex proton exchange from the two flanking base pairs appears to be accelerated, relative to free d(AT)5.d(AT)5. The lifetime of these drugs in specific binding sites is too long (>10 ms) to be manifested in increased line widths, at least up to 41 degrees C. An important conclusion from this study is that certain bisintercalators rapidly migrate along DNA, despite having large binding constants (K>10(6) M-1). For C8 and C10 complexes, migration rates are little different from those deduced for 9AA. The rigid linker chain in BAPY and the charge interactions in BAS retard migration of these two bisintercalators. These results provide new parameters that are useful in understanding the biochemical and biological properties of these and other bisintercalating drugs.
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Affiliation(s)
- N Assa-Munt
- Department of Chemistry, University of California, San Diego, La Jolla, California 92093, USA
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Newlin DD, Miller KJ, Pilch DF. Interactions of molecules with nucleic acids. VII. Intercalation and T.A specificity of daunomycin in DNA. Biopolymers 1984; 23:139-58. [PMID: 6696975 DOI: 10.1002/bip.360230111] [Citation(s) in RCA: 26] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
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Neidle S, Abraham Z. Structural and sequence-dependent aspects of drug intercalation into nucleic acids. CRC CRITICAL REVIEWS IN BIOCHEMISTRY 1984; 17:73-121. [PMID: 6094101 DOI: 10.3109/10409238409110270] [Citation(s) in RCA: 139] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
Information gained from X-ray crystallographic studies on drug-nucleic acid complexes is described, with emphasis on the intercalation process. Relevant data from NMR experiments are examined in order to highlight similarities and differences between solution and solid-state structures. Theoretical analyses of intercalation complexes are also discussed and evaluated, with respect to the structural methods, with special reference being made to nucleic acid conformation and positions of drug molecules in the binding sites.
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Ornstein RL, Fresco JR. Correlation of Tm, sequence, and delta H of complementary RNA helices and comparison with DNA helices. Biopolymers 1983; 22:2001-16. [PMID: 6193821 DOI: 10.1002/bip.360220812] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
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Ornstein RL, Fresco JR. Correlation of Tm and sequence of DNA duplexes with delta H computed by an improved empirical potential method. Biopolymers 1983; 22:1979-2000. [PMID: 6616016 DOI: 10.1002/bip.360220811] [Citation(s) in RCA: 44] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/21/2023]
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17
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Delbarre A, Gourevitch MI, Gaugain B, Le Pecq JB, Roques BP. 1H NMR study of an ethidium dimer poly(dA-dT) complex: evidence of a transition between bis and monointercalation. Nucleic Acids Res 1983; 11:4467-82. [PMID: 6866771 PMCID: PMC326059 DOI: 10.1093/nar/11.13.4467] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/22/2023] Open
Abstract
Comparative 1H NMR and optical studies of the interaction between poly(dA-dT), ethidium bromide (Et) and ethidium dimer (Et2) in 0.7 M NaCl are reported as a function of the temperature. Denaturation of the complexes followed at both polynucleotide and drug levels leads to a biphasic melting process for poly(dA-dT) complexed with ethidium dimer (t1/2 = 75 degrees C; 93 degrees C) but a monophasic one in poly(dA-dT): ethidium bromide complex (t1/2 = 74 degrees C). In both cases drug signals exhibit monophasic thermal dependence (Et = 81 degrees C; Et2 = 95 degrees C). Evidence is presented showing that the ethidium dimer bisintercalates into poly(dA-dT) in high salt, based on the observation that i) dimer and monomer ring protons exhibit similar upfield shifts upon DNA binding, ii) upfield shifts of DNA sugar protons are twice as large with the dimer than with ethidium bromide. Comparison between native DNA fraction and bound drug fraction indicates that ethidium covers, n = 2.5-3 base pairs. The dimer bisintercalates and covers, n = 5.7 base pairs when the helix fraction is high but as the number of available sites decreases the binding mode changes and the drug monointercalates (n = 2.9).
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Dougherty G. A comparison of the base-pair specificities of three phenanthridine drugs using solution spectroscopy. THE INTERNATIONAL JOURNAL OF BIOCHEMISTRY 1982; 14:493-504. [PMID: 7106349 DOI: 10.1016/0020-711x(82)90117-3] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/23/2023]
Abstract
1. The absorption spectrum of three phenanthridine drugs (ethidium, dimidium and prothidium bromide) bound to natural DNAs of differing G-C content were obtained using a novel mixing scheme and analysed according to the excluded site binding model. 2. Ethidium bromide shows a strong G-C specificity at low binding ratios. especially at low ionic concentration. 3. Dimidium bromide shows a less strong G-C specificity. 4. For both drugs, the binding site size reflects a situation close to nearest-neighbour exclusion. 5. Prothidium shows no specificity in its binding. The binding modes are different than for the other two phenanthridines, and it is suggested that the primary mode is "sideways" intercalation.
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Patel DJ, Kozlowski SA, Rice JA. Hydrogen bonding, overlap geometry, and sequence specificity in anthracycline antitumor antibiotic.DNA complexes in solution. Proc Natl Acad Sci U S A 1981; 78:3333-7. [PMID: 6267584 PMCID: PMC319562 DOI: 10.1073/pnas.78.6.3333] [Citation(s) in RCA: 55] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
We have deduced structural aspects of the intercalation complex of the anthracycline antitumor antibiotic daunomycin and its analogs with the synthetic DNA poly(dA-dT) by 1H and 31P NMR in high-salt solution. We demonstrate that the base pairs are intact at the antibiotic binding site and that the anthracycline phenolic hydroxyls form intramolecular hydrogen bonds with the quinone carbonyls and are shielded from solvent in the intercalation complex. The complexation shifts of the exchangeable phenolic and nonexchangeable aromatic protons demonstrate that rings B and C of the anthracycline chromophore overlap with adjacent base pairs, while anthracycline ring D passes right through the intercalation site in the complex. We observe two resolved 31P resonances attributable to the dA-dT and dT-dA phosphodiester linkages in the phosphorus spectra of the neighbor-exclusion daunomycin.poly(dA-dT) complex. This suggests that the anthracycline antitumor antibiotic exhibits a sequence specificity in its intercalation complex with alternating purine-pyrimidine synthetic DNAs in solution. These conclusions on hydrogen bonding and overlap geometry at the intercalation site and sequence specificity for the daunomycin.poly(dA-dT) complex in solution are in agreement with the structure of the daunomycin.dC-dG-dT-dA-dC-dG hexanucleotide duplex crystalline complex at atomic resolution published recently [Quigley, G. J., Wang, A. H.-J., Ughetto, G., van der Marel, G., van Boom, J. H. & Rich, A. (1980) Proc. Natl. Acad. Sci. USA 77, 7204-7208].
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Prado F, Giessner-Prettre C. Parameters for the calculation of the ring current and atomic magnetic anisotropy contributions to magnetic shielding constants: Nucleic acid bases and intercalating agents. ACTA ACUST UNITED AC 1981. [DOI: 10.1016/0166-1280(81)85115-9] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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Miller KJ, Brodzinsky R, Hall S. Interactions of molecules with nucleic acids. IV. Binding energies and conformations of acridine and phenanthridine compounds in the two principal and in several unconstrained dimer-duplex intercalation sites. Biopolymers 1980; 19:2091-122. [PMID: 7437502 DOI: 10.1002/bip.1980.360191111] [Citation(s) in RCA: 33] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
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Tyler Burt C, Wyrwicz AM. 31P Nuclear magnetic resonance observations in biological systems II. Nucleic acids and proteins. Trends Biochem Sci 1979. [DOI: 10.1016/0968-0004(79)90299-8] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
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Ornstein RL, Rein R. Energetic and structural aspects of ethidium cation intercalation into DNA minihelices. Biopolymers 1979; 18:2821-47. [PMID: 508904 DOI: 10.1002/bip.1979.360181112] [Citation(s) in RCA: 46] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
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Broyde S, Hingerty B. Conformational origin of the pyrimidine (3'-5') purine base sequence preference for intercalation into RNAs. Biopolymers 1979; 18:2905-10. [PMID: 508906 DOI: 10.1002/bip.1979.360181117] [Citation(s) in RCA: 22] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
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Neidle S. The molecular basis for the action of some DNA-binding drugs. PROGRESS IN MEDICINAL CHEMISTRY 1979; 16:151-221. [PMID: 95595 DOI: 10.1016/s0079-6468(08)70188-7] [Citation(s) in RCA: 97] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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Patel DJ, Canuel LL. Anthracycline antitumor antibiotic nucleic-acid interactions. Structural aspects of the daunomycin poly(dA-dT) complex in solution. EUROPEAN JOURNAL OF BIOCHEMISTRY 1978; 90:247-54. [PMID: 710429 DOI: 10.1111/j.1432-1033.1978.tb12597.x] [Citation(s) in RCA: 28] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
The helix-to-coil transition of the synthetic DNA poly(dA-dT) in the presence of the anthracycline antitumor antibiotic daunomycin has been investigated by high-resolution proton nuclear magnetic resonance (NMR) spectrocopy in 1 M salt solution. The dissociation of the complex, containing molar ratios of phosphate to daunomycin (Pi/drug) of 50, 25, 9 and 5, with increasing temperature can be monitored independently at the nucleic acid and the antibiotic resonances under conditions of fast exchange. The antibiotic complex formation shifts suggest that either ring B and/or C of the intercalated anthracycline chromophore of daunomycin overlaps with adjacent nucleic acid base pairs. Ultraviolet/visible melting studies of daunomycin complexes with a series of synthetic DNAs substituted with halogen atoms (Br, I) at position 5 of the pyrimidine ring suggest that intercalation of the antibiotic into poly(dA-dU) is not perturbed by bulky substituents at this position. A comparison of the melting curves for the daunomycin . poly(dA-dT) complex with an analog of the antibiotic where the NH3 + group is replaced by dimethylglycine demonstrates the important contributions of electrostatic interactions between the amino sugar and backbone phosphates to the stability of the complex in low salt solution. The ultraviolet/visible and NMR studies monitor biphasic melting transitions at the nucleic acid markers in the daunomycin . poly(dA-dT) complexes, Pi/drug = 50--9, so that antibiotic-free base-pair regions and those centered about bound daunomycin can be independently studied at the synthetic DNA level in solution.
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