Chemical and biochemical properties of abasic site adducts and 6-thioguanine DNA cross-links in DNA

Abstract

DNA is a macromolecular complex, composed of the nucleotides adenine, thymine, guanine and cytosine interconnected by a phosphate backbone, that contains the genetic code for living organisms and viruses. Spontaneous and enzymatic hydrolysis of the glycosidic bonds that hold the coding nucleobases to the 2-deoxyribose-phosphate backbone of DNA results in the production of abasic (Ap) sites. These lesions are abundant in cellular DNA, and cellular Ap-containing DNA is damaging and may lead to cellular destruction if left unrepaired. Thus, efficient cellular DNA repair mechanisms that repair Ap sites have evolved in DNA containing organisms. The studies in this report examine the interaction between small molecules or naturally occurring DNA residues with Ap sites in duplex DNA. Experiments provide evidence that hydralazine binds to and forms a stable DNA lesion in single- and double-stranded DNA. Also, the hydralazine-DNA lesion is found to be a poor substrate for mammalian base excision repair enzymes such as Ap endonuclease and 8-oxoguanine DNA glycosylase. In addition, these studies provide preliminary evidence that hydralazine may potentiate the cytotoxicity of temozolomide in U87 cells. The investigation of the formation of cross-links between canonical DNA residues deoxyadenosine (dA) and deoxyguanosine (dG) with Ap sites is also explored. These experiments suggest that sequence effects contribute majorly to the cross-link yield in both dA- and dG-Ap site cross-links, especially when comparing central versus terminal cross-link locations. Here, this manuscript provides novel studies involving the interaction between DNA analog 6-thioguanine and opposing DNA bases in duplex oligonucleotide DNA.