Dinucleotides adduct

The adduct formed between oxaliplatin and DNA diguanosine dinucleotides is conformationally distinct from the adduct formed with cisplatin. Specifically, whereas the cisplatin diguanosine dinucleotide adduct bends the DNA by 60 to 80° and presents a relatively wide minor groove, the oxaliplatin adduct produces a 31° bend with a comparatively narrow minor groove (34). 

Fig. 8. Reaction mechanism of (6-4) photolyase. The enzyme binds to DNA containing a (6-4) photoproduct and flips out the dinucleotide adduct into the active site cavity, where the open form of the photoproduct is converted to the oxetane intermediate by a light-independent general acid-base mechanism. Catalysis is initiated by light MTHF absorbs a photon and transfers energy to FADH , which then transfers an electron to the oxetane intermediate bond rearrangement in the oxetane radical regenerates two canonical pyrimidines, and back-electron transfer restores the flavin radical to catalytically competent FADH form. The repaired dipyrimidine flips back into the DNA duplex, and the enzyme is dissociated from the substrate.

The fact that the 3,P-NMR signal of 183a can only be observed in pyridine-containing solution provides food for thought124). Viewed in conjugation with the idea that alkyl metaphosphates could form adducts such as 173 and 174 U9,120) as discussed above, formulation as a zwitterionic pyridine/metaphosphate adduct (188) seems reasonable. Similar adducts have also been found in the reaction of TPS with dinucleotides and trinucleoside diphosphate 126). In any case, the reactions of 183 or 188 are in full accord with the expected properties of a monomeric metaphosphate and its reactivity towards alcohols is far greater than that of all other reactive phosphorylation intermediates which can arise on reaction of TPS with oligonucleotides 126). 

The prodrug isoniazid (34) targets M. tuberculosis InhA [3] after activation by a mycobacterial catalase-peroxidase by reacting irreversibly with the cofactor nicotinamide adenine dinucleotide (NAD). This covalent adduct... 

With the dinucleotide d(GG), initial binding of the dinuclear Pt(II) compounds (l,l/t,t n = 2-6) is relatively fast compared to the ring closure into the macrochelate adduct [94]. In addition, the rate of ring... 

Reddy MV, Bleicher WT, Blackburn GR, et al. 1990. DNA adduction by phenol, hydroquinone, or benzoquinone in vitro but not in vivo Nuclease PI-enhanced 32P-postlabeling of adducts as labeled nucleoside bisphosphates, dinucleotides and nucleoside monophosphates. Carcinogenesis 11 1349-1357. 

During in vivo studies under biologically relevant conditions, the cis-Pt loading of the DNA is much lower than for the above-mentioned in vitro studies. It has been calculated that mortality of HeLa cells occurs at an value of 10 5 (i.e., one bound cis-Pt molecule per 105 nucleotides) (64a). This excludes atomic absorption spectroscopy for identification of the in vivo adducts. Immunochemical techniques, however, have shown to be very promising, and high sensitivity and selectivity levels have been reached. At the moment, only a few studies in which antibodies are raised against cis-Pt-treated DNA (64) or against synthetic cis-Pt adducts with mono- or dinucleotides are available (64a). With the latter method, quantitation of the different platinum-DNA adducts formed under in vivo conditions is possible. At the moment, femtomole (10-15 mol) amounts of the adducts can be detected with competitive enzyme-linked immunosorbent assay (ELISA) techniques. It has been demonstrated in this manner that the GG-Pt adduct is also the predominant adduct under in vivo conditions. 

As said above, only a summary of the many reported studies can be given here, and for details the reader is referred to the reviews (49-53) and the papers of the groups mentioned in Section III, B (55). A complete conformational NMR analysis of the solution structure of the adduct with a dinucleotide, i.e. cis-Pt(NH3)2 d(GpG)-N7(l),N7(2) ], has been available for some time (50b). The main features of this structure can be summarized as follows ... 

A second point of interest is the question of the stoichiometry. For example when cisplatin is reacted with the dinucleotide CG in a 1 1 ratio, the resulting product maybe a 1 1 adduct, but also cw-Pt(NH3)2(CG-N7)2 may be formed (leaving unreacted cisplatin in solution). A detailed study of this system by Chottard8 has made clear that in dilute solutions the 1 1 product is formed only when the concentration of CG is high, is the 1 2 product formed. This agrees with earlier observations of Jordanov66 and Kidani67) for the reactions of cisplatin and CG and GC, respectively. 

NMR and ultraviolet (UV) methods have been used to study the interesting adducts formed between the antituberculous drug isoniazid and cofactor NAD (nicotinamide adenine dinucleotide) <20050BC670>. Studies... 

Figure 8.23. Mechanism-Based (Suicide) Inhibition. Monoamine oxidase, an enzyme important for neurotransmitter synthesis, requires the cofactor FAD (flavin adenine dinucleotide). AA -Dimethylpropargylamine inhibits monoamine oxidase by covalently modifying the flavin prosthetic group only after the inhibitor is first oxidized. The N-5 flavin adduct is stabilized by the addition of a proton.

DNA polymerase incorporation of the mutagenic 2-hydroxy-dA has been examined and found to lead to GC- AT transition mutations." The synthesis, incorporation and repair of etheno-dA adducts have been reported." The use of a C2-alkaryl modified adenosine gave rise to enhanced stability towards a mutant UlA protein in which a conserved phenylalanine was substituted for alanine. ° 2-Aminopurine (2-AP) has been widely used because of its fluorescent properties. However, 2-AP dinucleotide also exhibits a distinct positive CD band at 326 nm, and this property has been used to probe changes in local conformation of ODNs containing (2-AP)2 by CD measurements." ... 

Acetone-sensitized irradiation of uracil (107) with ethene affords the adduct (108) in 75% yield. This compound can be transformed into the cyclobutane derivative (109) in an overall yield of 52%. The intramolecular cyclization of the dinucleotide model (110) has been investigated. The reaction affords the cycloadduct (111) by irradiation using wavelengths > 300 nm. The use of an anionic template for photochemical dimerization of a thymine system has been demonstrated. The thymine forms an assembly (112) with pyrophosphate. Irradiation of this brings about syn- 2 + 2)-cycloaddition of the thymine units. ... 

P 4394 Cis-diammineplatinum(ll) dichloride (cisplatin) Forms cytotoxic adducts with the DNA dinucleotide d(pGpG) induces apoptosis. 

---