Specificity of platinum-DNA adduct repair

Cell lines with resistance to cisplatin and carboplatin often retain sensit ivity to platinum complexes with different carrier ligands (e.g., oxaliplat in and JM216). HeLa cell extracts were shown to excise cisplatin, oxaliplat in, and JM216 adducts with equal efficiency, suggesting that nucleotide exc ision repair does not contribute to the carrier-ligand specificity of plati num resistance. We have shown previously that the extent of replicative byp ass in vivo is influenced by the carrier ligand of the platinum adducts. Th e specificity of replicative bypass may be determined by the DNA polymerase complexes that catalyze translesion synthesis past Pt-DNA adducts, by the mismatch-repair system that removes newly synthesized DNA opposite Pt-DNA a dducts, and/or by DNA damage-recognition proteins that bind to the Pt-DNA a dducts and block translesion synthesis. Primer extension on DNA templates c ontaining site-specifically placed cisplatin, oxaliplatin, or JM216 Pt-GG a dducts revealed that the eukaryotic DNA polymerases beta, zeta, gamma and H IV-1 RT had a similar specificity for translesion synthesis past Pt-DNA add ucts (oxaliplatin greater than or equal to cisplatin > JM216). In addition, defects in the mismatch-repair proteins hMSH6 and hMLH1 led to increased r eplicative bypass of cisplatin adducts, but not of oxaliplatin adducts. Fin ally, primer extension assays performed in the presence of HMG1, which is k nown to recognize cisplatin-damaged DNA, revealed that inhibition of transl esion synthesis by HMG1 also depended on the carrier ligand of the Pt-DNA a dduct (cisplatin > oxaliplatin = JM216). These studies show that DNA polyme rases, the mismatch-repair system and damage-recognition proteins can all i mpart specificity to replicative bypass of Pt-DNA adducts. Replicative bypa ss, in turn, may influence the carrier-ligand specificity of resistance. (C )1999 Elsevier Science Inc. All rights reserved.