Nucleotides platination

Kratochwil NA, Parkison JA, Bednarski PJ, Sadler PJ. Nucleotide platination induced by visible light. Angew Chem Int Ed Eng 1999 38 1460-3. 

From these experiments it can be concluded that the closure of the monofunctional adducts depends upon the presence of other adducts in its vicinity. Although a systematic study has not yet been done, the interference between two or more adducts is expected to be a function of several parameters, such as the nature and the number of base pairs between the adducts, the DNA supercoiling, the local environment of the DNA, in addition to the distortions of the DNA double helix induced by the adducts, which are also function of these parameters. DNA has to be platinated at a low drug-to-nucleotide residue ratio when in vitro and in vivo experiments are compared. This holds also for cisplatin-modified DNA, but is masked by the preferential binding of cisplatin to runs of guanine residues and the ability of the monofunctional adducts to react with the adjacent residues. 

More work is needed to clearly establish the role of outer-sphere association in DNA-platination. We can infer its influence on the rate of platination according to the relation kp = kK0 [N]/(l + K0 [N]) (with N = nucleotide-binding sites of Pt, i.e., N G, [N] [Pt]) (Scheme 3). It could also influence the selectivity of platination via selective association between the cationic species and the sites of higher negative electrostatic potential. To test this hypothesis one will have to analyze the influence of various sequences, of different types of platinum ligands, and of the ionic status of the DNA medium. 

Figure 14 Stereoviews of the NMR solution structures of platinated DNA sequences iUiistrating the deformation of the normal double-helical structure, (a) intrastrand cis-GG crosslink in d(CCTCTG G TCTCC)-d(GGAGACCAGAGG) (b) interstrand cis-GG crosslink in the palindromic sequence d(CATAG CTATG)-d(CATAG CTATG) represents the donor nucleotides. (Reprinted with permission from Ref 90. 1999 American Chemical Society)...

Garcia, S.D., Montes-Bayon, M., Blanco, G.E., Sanz-Medel, A. Speciation studies of cis-platin adducts with DNA nucleotides via elemental specific detection (P and Pt) using liquid chromatography-inductively coupled plasma-mass spectrometry and structural characterization by electrospray mass spectrometry. J. Anal. At. Spectrom. 21, 861-868 (2006)... 

A plot of gel mobility versus the amount of platinum bound. Figure 5> demonstrates this difference. We compare gel mobilities of samples platinated with a formal ratio of one cis-DDP per nucleotide, for samples containing either no ethidium or three ethidium molecules per ten nucleotides. The gel mobilities are normalized to 0 for form II and 1.0 for form I DNA in the control sample. Note that there is about a 35% decrease in mobility where forms I and II comigrate in the gel when platinum is bound in the presence of saturating amounts of ethidium. 

The bottom micrograph is of pBR522 platinated to a level of 23 platinum atoms per lOO nucleotides in the presence of saturating amounts of ethidium. It is clear that this DNA is more similar to control DNA than are the samples platinated with no ethidium present. There is some compacting and "shrinking seen, but not to the extent seen in the sample platinated in the absence of ethidium. 

Diagram illustrating the replication mapping experiment. To a single-stranded, platinated template is annealed a short primer for DNA synthesis using DNA polymerase I (Klenow fragment) and radiolabeled nucleotides. Sites of platinum binding are revealed as bands on gel electrophoresis where chain termination occurs (see text for details). 

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