title: Mass spectrometry studies of the binding of the minor groove-directed alkylating agent alkamin to AT-tract oligonucleotides.
abstract: Minor groove binding alkylating agents, which have potential as cancer drugs, generate cytotoxic DNA adducts that are relatively resistant to repair as a consequence of locating covalent attachment at purine N3 nitrogen atoms. Recently, we used electrospray and matrix-assisted laser desorption ionization mass spectrometry to study the binding of the minor groove-directed polybenzamide bis-half-mustard alkamin, and its monofunctional analogue alkamini, to the oligonucleotide d(CGCGAATTCGCG)(2), identifying a number of inter- and intrastrand alkamin cross-links involving the GAATTC sequence [ Abdul Majid , A. M. S. , Smythe , G. , Denny , W. A. , and Wakelin , L. P. G. ( 2007 ) Mol. Pharmacol. 71 , 1165 - 1178 ]. Here, we extend these studies to d(CGCAAATTTGCG)(2), A3T3, and d(CGCAAAAAAGCG).d(CGCTTTTTTGCG), A6/T6, in which the opportunity for both inter- and intrastrand cross-linking is enhanced. We find that both ligands alkylate all adenines in the longer AT-tracts, as well as the abutting guanines, whether they are in the same strand as the adenines or not, in a manner consistent with covalent attack on purine N3 atoms from the minor groove. Alkamin forms intrastrand cross-links involving A4 and A6 and A6 and G10 in A3T3 and all of the purines in the A6/T6 purine tract, including G10. In addition, it forms interstrand cross-links between A4, A5, A6 and A4', A5', A6', between G10 and the latter adenines in A3T3, and between G22 and adenines A5 and A6 in A6/T6. The reactivity of the abutting guanines provides unexpected opportunities for both inter- and intrastrand cross-linking by alkamin, such as the interstrand cross-link in the CAAAAAAG sequence. We conclude that positioning monofunctional mustard groups on either end of a minor groove-directed polybenzamide has the capacity to enhance interstrand cross-links at all manner of AT-tracts, including most in which the adenines are all in one strand.
authors.affiliation: School of Molecular Sciences, Department of Pharmacology, and Bioanalytical Mass Spectrometry Facility, University of New South Wales, NSW 2052, Australia. aminmalikshah@usm.my
authors.forename: Amin M S
authors.initials: AM
authors.lastname: Abdul Majid
authors.forename: George
authors.initials: G
authors.lastname: Smythe
authors.forename: William A
authors.initials: WA
authors.lastname: Denny
authors.forename: Laurence P G
authors.initials: LP
authors.lastname: Wakelin
mesh_terms: D000225:Adenine / Q000737:chemistry; D000477:Alkylating Agents / Q000737:chemistry* / Q000633:toxicity; D000813:Anilides / Q000737:chemistry* / Q000633:toxicity; D018736:DNA Adducts / Q000737:chemistry; D009588:Nitrogen Mustard Compounds / Q000737:chemistry* / Q000633:toxicity; D009841:Oligonucleotides / Q000737:chemistry*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization / Q000379:methods*; D013941:Thymine / Q000737:chemistry
chemical_list: D000477:Alkylating Agents; D000813:Anilides; D018736:DNA Adducts; D009588:Nitrogen Mustard Compounds; D009841:Oligonucleotides; C539372:alkamin; D000225:Adenine; D013941:Thymine