Cisplatin adducts inhibit 1,N-6-ethenoadenine repair by interacting with the human 3-methyladenine DNA glycosylase

The human 3-methyladenine DNA glycosylase (AAG) is a repair enzyme that rem oves a number of damaged bases from DNA, including adducts formed by some c hemotherapeutic agents. Cisplatin is one of the most widely used anticancer drugs. Its success in killing tumor cells results from its ability to form DNA adducts and the cellular processes triggered by the presence of those adducts in DNA. Variations in tumor response to cisplatin may result from a ltered expression of cellular proteins that recognize cisplatin adducts. Th e present study focuses on the interaction between the cisplatin intrastran d cross-links and human AAG. Using site-specifically modified oligonucleoti des containing each of the cisplatin intrastrand cross-links, we found that AAG readily recognized cisplatin adducts. The apparent dissociation consta nts for the 1,2-d(GpG), the 1,2-d(ApG), and the 1,3-d(GpTpG) oligonucleotid es were 115 nM, 71 nM, and 144 nM, respectively. For comparison, the appare nt dissociation constant for an oligonucleotide containing a single 1,N-6-e thenoadenine (epsilon A), which is repaired efficiently by AAG, was 26 nM. Despite the affinity of AAG for cisplatin adducts, AAG was not able to rele ase any of these adducts from DNA. Furthermore, it was demonstrated that th e presence of cisplatin adducts in the reactions inhibited the excision of EA by AAG. These data suggest a previously unexplored dimension to the toxi cological response of cells to cisplatin. We suggest that cisplatin adducts could titrate AAG away from its natural substrates, resulting in higher mu tagenesis and/or cell death because of the persistence of AAG substrates in DNA.