Formation Of Diadducts Research Articles

Investigation of nucleic acid damage induced by a novel ruthenium anti-cancer drug using multiple analytical techniques: Sequence specificity and damage kinetics.

Cis-diacetonitrilo-bis(bipyridine) ruthenium(II) chloride is a recently introduced cis-platin analogue that has anti-cancer properties with lower side effects. However, the sequence dependence of its DNA damaging mechanism is unclear. Here, we present a simple, sensitive, multiplexed mix-and-read assay for ascertaining the molecular mechanism of DNA damage induced by the studied ruthenium complex (Ru-complex). The damage kinetics and sequence specificity for the Ru-complex induced DNA damage are examined by studying the induced damage in various oligonucleotide sequences by EvaGreen-DNA intercalator probe. High-through-put measurements were established using a 96-well microplate platform that allows multiple sequences to be measured simultaneously. The results show that the extent of damage increases with an increasing number of guanines, with considerable amount of damage at GA, GT and GC sites, in particular. Furthermore, the interaction of Ru-complex with DNA was confirmed using thermal analysis and MALDI-TOF-MS. Results indicate that the activated Ru-complex preferentially binds via both mono- and di-adduct formation at G and GG sites, respectively. Moreover, the developed method was successfully applied for the determination of the potency of the studied Ru-complex to induce DNA damage in K-Ras and N-Ras family of genes, one of the most common oncogenic events in cancer.

Oxaliplatin effects on the DNA molecule studied by force spectroscopy

In the present study we investigated the binding of the anticancer compound Oxaliplatin to DNA. Using optical tweezers to perform single molecule force spectroscopy, we determined the changes of the mechanical parameters of DNA complexes formed with Oxaliplatin, at high and low ionic strengths. The interaction mechanism and the physical chemistry of the binding were determined from these measurements. In addition, kinetic information on covalent diadduct formation and on DNA compaction by Oxaliplatin were also obtained. All these results were critically compared to those obtained for the related anti-neoplastic compounds Cisplatin and Carboplatin, previously determined under similar experimental conditions. These results provide new information about the action of platinum-based compounds on DNA, being useful to the improvement of current chemotherapies and to the design of novel correlated drugs.

Ammonium Chloride/B(C6F5)3System Catalyzed Selective Addition of Acids to Alkynes

Development of straightforward and selective approaches to functionalize vinyl groups is an important and continuing goal. A novel convenient route to vinylhalides or enol esters by a Markovnikov regioselective addition of hydrogen chloride or carboxylic acid to the C≡C bond of alkynes in the presence of an ammonium hydrochloride/B(C6F5)3 catalytic system is reported. Thus, when treated with catalytic amounts of ammonium hydroborate ([TMPH]+[Cl-B(C6F5)3] ), equimolar mixtures of hydrogen chloride and alkynes are converted into a variety of chloroalkenes as monoadducts. The yields of the monoadducts are usually higher than 90% for terminal aromatic alkynes, while for the terminal aliphatic alkynes they are considerably lower, with the worst observed for sterically hindered tert-butylacetylene (only 67%). NMR monitoring of the reaction mixtures reveals that under ambient conditions the main by-products are the corresponding diadducts (gem-dihalides). At higher temperatures (50 °C) for equimolar alkyne/HCl mixtures or at ambient temperature for alkyneenriched mixtures, the diadduct formation can be nearly completely suppressed. Noteworthy, that both ammonium and borane (-ate) components of the catalytic system are essential for the conversion success. In the case of trifuoroacetic acid addition to alkynes, presence of the ammonium component is not required, with the reaction yields usually exceeding 95% for terminal aromatic alkynes and being modest to good for the aliphatic ones. The reported catalytic system presents the first example of the “metal-free” catalysts for the selective addition of acids to alkynes.

Oxaliplatin and its enantiomer induce different condensation dynamics of single DNA molecules.

The interactions of DNA with oxaliplatin (Pt(R,R-DACH)) or its enantiomer (Pt(S,S-DACH)) were investigated using magnetic tweezers and atomic force microscope. In the process of DNA condensation induced by Pt-DACH, only diadducts and micro-loops are formed at low Pt-DACH concentrations, while at high Pt-DACH concentrations, besides the diadducts and micro-loops, long-range cross-links are also formed. The diadduct formation rate of Pt(R,R-DACH) is higher than that of Pt(S,S-DACH). However, the proportions of micro-loops and long-range cross-links for Pt(S,S-DACH) are higher than those for Pt(R,R-DACH). We propose a model to explain these differences between the effect of Pt(R,R-DACH) and that of Pt(S,S-DACH) on DNA condensation. The study has strong implications for the understanding of the effect of chirality on the interaction between Pt-DACH and DNA and the kinetics of DNA condensation induced by platinum complexes.

A Theoretical Rationale why Furan‐side Monoadduct is More Favorable Toward Diadduct Formation in 8‐Methoxypsoralen and Thymine Complexes

The photoinduced mechanism of formation of mono- and diadducts between 8-MOP and thymine bases is studied using the ONIOM(MPWB1K/6-31 + G(d,p):B3LYP/6-31G(d,p):UFF) and B3LYP/6-31 + G(d,p) methods. The relevant cycloaddition displays favorable energy barriers and reaction energies in the triplet excited state, which involves the initial formation of a diradical followed by ring closure via singlet-triplet interaction. The monoadduct on the pyrone side is favored over the furan side when comparing reaction energies. The distinguishing feature in the formation of the monoadducts is that the furan-side adduct displays a better photostability, which is a relatively high-barrier exothermic reaction, and thus the energy balance of the monoadduct on the furan side toward final diadduct formation is favored.

Third strand-mediated psoralen-induced correction of the sickle cell mutation on a plasmid transfected into COS-7 cells

A significant level of correction of the mutation responsible for sickle cell anemia has been achieved in monkey COS-7 cells on a plasmid containing a beta-globin gene fragment. The plasmid was treated in vitro with a nucleic acid 'third strand' bearing a terminal photoreactive psoralen moiety that binds immediately adjacent to the mutant base pair. Following covalent attachment of the psoralen by monoadduct or diadduct formation to the mutant T-residue on the coding strand, the treated plasmid was transfected into the cells, which were then incubated for 48 h to allow the cellular DNA repair mechanisms to remove the photoadducts. Upon re-isolation and amplification of the transfected plasmid, sickle cell mutation correction, as determined by sequence analysis of both complementary strands, was established in a full 1%. This result encourages extension of the approach to correct the mutation directly on the chromosome.

Different Reaction Patterns in the Baylis-Hillman Reaction of Aryl Aldehydes with Phenyl Vinyl Ketone, Phenyl Acrylate and Phenyl Thioacrylate

In the Baylis-Hillman reaction of aryl aldehydes with phenyl vinyl ketone we have observed exclusive formation of diadducts 4, and that the yields of diadduct can reach 80% with increasing amounts of phenyl vinyl ketone. On the other hand, for phenyl acrylate and phenyl thioacrylate, only the normal Baylis-Hillman adduct was obtained. The effects of substituents were also examined and a plausible reaction mechanism is proposed for the formation of compounds 4.

Thienocoumarin derivatives: interaction with nucleic acids and synthetic polydeoxyribonucleotides

This paper reports the photobiological properties of two new thienocoumarins, 4,6,9-trimethyl-2 H-thieno[3,2-g]-1-benzopyran-2-one (compound I) and the 6,9-dimethyl-4-methoxymethyl-2 H-thieno[3,2-g]-1-benzopyran-2-one (compound II). Cell growth inhibition studies have revealed significant antiproliferative potency on human tumor cell lines. The photoaddition process of these tritium-labeled derivatives was investigated using various nucleic acid structures (calf thymus DNA, bacterial DNA, and synthetic polydeoxyribonucleotides). The results obtained show that both compounds photobind to DNA to a higher extent than 8-MOP, taken as the reference drug. The capacity to form interstrand crosslinks into DNA helix was also evaluated. Interestingly, notwithstanding the lack of cutaneous phototoxicity, II revealed a good ability to induce diadduct formation.

Effects of thiourea and ammonium bicarbonate on the formation and stability of bifunctional cisplatin-DNA adducts: Consequences for the accurate quantification of adducts in (cellular) DNA

Cisplatin reacts with DNA by forming mainly bifunctional adducts via reactive monofunctional intermediates. When freshly platinated DNA was postincubated with thiourea (10 mM, at 23 or 37°C) for periods of up to 24 h, followed by determination of mono- and diadducts, a rapid initial decrease was seen in the fraction of diadducts, followed by a much slower decrease. About 40% diadducts were found after 10-min postincubation at 23°C, which dropped to some 14% after 24 h at 37°C; total platination was hardly affected. Postincubation of “aged” platinated DNA (no reactive monoadducts) only showed the slower decrease. The rapid process is likely to represent monoadduct inactivation, preventing the formation of diadducts, whereas the slow reaction must be interpreted as diadduct-to-monoadduct conversion. Similar reactions, but less efficient than with thiourea, occurred during dialysis against NH 4HCO 3 (0.1–1 M). Pt-containing (di)nucleotides in digested DNA were hardly affected by thiourea. Rapid reduction of the measured level of bifunctional adducts also occurred when cisplatin-treated Chinese hamster ovary cells were postincubated with thiourea, with concomitant increase in survival. It is concluded that quantification of the real levels of mono- and diadducts in freshly platinated DNA requires a posttreatment with thiourea of 30–60 min at 37°C.

Molecular dynamics simulations of chlorambucil/DNA adducts. A structural basis for the 5'-GNC interstrand DNA crosslink formed by nitrogen mustards.

The alkylation of DNA by chlorambucil has been studied using a computational approach. Molecular dynamics simulations were performed on the fully solvated non-covalent complex, two monoadducts and a crosslinked diadduct of chlorambucil with the d(CGG3G2CGC).-d(GCG1CCCG) duplex, in which the N7 atoms of G1, G2 and G3 are potential alkylation sites. The results provide a structural basis for the preference of nitrogen mustards to crosslink DNA duplexes at a 5'-GNC site (a 1,3 crosslink, G1-G3) rather than at a 5'-GC sites (a 1,2 crosslink, G1-G2). In the non-covalent complex simulation the drug reoriented from a non-interstrand crosslinking location to a position favorable for G1-G3 diadduct formation. It proved possible to construct a G1-G3 diadduct from a structure from the non-covalent simulation, and continue the molecular dynamics calculation without further disruption of the DNA structure. A crosslinked diadduct developed with four BII conformations on the 3' side of each alkylated guanine and of their respective complementary cytosine. In the first monoadduct simulation the starting point was the same DNA conformation used in the crosslinked diadduct simulation with alkylation at G1. In this simulation the DNA deformation was reduced, with the helix returning to a more canonical form. A second monoadduct simulation was started from a canonical DNA conformation alkylated at G3. Here, no significant motion towards a potential crosslinking conformation occurred. Collectively, the results suggest that crosslink formation is dependent upon the drug orientation prior to alkylation and the required deformation of the DNA to permit 1,3 crosslinking can largely be achieved in the non-covalent complex.

Derivatives of sorbic acid-thiol adducts

Ethyl and methyl sorbate react with thiols in the corresponding alcohol as solvent and with sodium alkoxide as catalyst. Nucleophilic attack by alkylthiols leads to the formation of diadducts (2,3- and 4,5-addition of H + RS −) whilst reaction with mercaptoethanol, esters of 2-mercaptoacetic acid, and cysteine ethyl ester gives the 2,5-addition product. Detailed consideration is given to the location of the double bond in position 3. Attempted hydrolysis of the esters causes dissociation of monoadducts liberating sorbic acid. However, if sorbic acid is allowed to react with cysteine in a predominantly aqueous medium, and the product esterified, it is identical to that formed from the esters of sorbic acid and of cysteine.

Interstrand DNA crosslinking by 4,5′,8-trimethylpsoralen plus monochromatic ultraviolet light. Studies by alkaline elution in mouse L1210 leukemia cells

DNA crosslinking by 4,5′,8-trimethylpsoralen plus monochromatic ultraviolet light of wavelength 365 nm was studied in mouse L1210 leukemia cells. DNA breaks and crosslinking were evaluated by alkaline elution of DNA from poly(vinyl chloride) filters. Trimethylpsoralen plus 365 nm light produced DNA crosslinks but not breaks. The kinetics of crosslinking were linear with respect to concentration and second-order with respect to light exposure time. The latter finding supports the proposed two photon mechanism for the formation of diadducts. In contrast to DNA crosslinking agents such as nitrogen mustard, nitrosoureas and platinums, trimethylpsoralen crosslinks were resistant to proteolytic digestion. Thus, trimethylpsoralen plus 365 nm light produced interstrand crosslinks, as proposed for a bifunctional agent binding to bases on opposite DNA strands.

Mono- and di-pyridine adducts of bis(3-substituted 2,4-pentanedionato)copper(II) complexes

Adduct formation constants, K1, for equilibria of the type, CuL2+ py ⇌ CuL2(py), where L =(MeCO·CR·COMe; R = Me, H, Cl, Ac, CO2Et, CN, and NO2) and py = pyridine, have been determined in benzene, acetone, and acetonitrile solution at 22 °C. The values of K1 are correlated with the electronic nature of the substitutent, R, and the dielectric constant of the solvent. In two cases, R = CN and NO2, further equilibria of type CuL2py + py ⇌ CuL2(py)2 have been observed at high pyridine concentrations and diadduct formation constants, K2 have been determined.

Vinylamines—VIII : The reaction of cyclohexanone enamines with 1- and 2-nitropropene

Enamines containing a trisubstituted double bond were obtained by reaction of morpholine, piperidine and pyrrolidine enamines of cyclohexanone with 1-nitropropene. Different results were obtained in the reaction of the same enamines with 2-nitropropene. A cycloaddition reaction occurred between 1-N-morpholino-cyclohexene and 2-nitropropene in ether at 0°, leading to an oxazine derivative. The structures of the products were determined by spectral and chemical evidence. In acetonitrile at 0° or in ether at room temperature the same enamine reacted with 2-nitropropene to give an enaminic mixture, where the less substituted alkylated isomer appeared to be the minor component. Analogous behaviour was shown by piperidine and pyrrolidene enamines. The mechanism and the stereochemistry of these reactions have been discussed. The formation of diadducts of a different nature from morpholine and pyrrolidine enamines with excess 2-nitropropene is also reported.