title: Observation of a single-stranded DNA/pyrrolobenzodiazepine adduct.
abstract: Pyrrolobenzodiazepine (PBD) antitumor agents have, to date, only been observed to bind to duplex DNA, apparently requiring a minor groove environment for covalent bond formation between their C11-position and the C2-NH(2) functionality of a guanine base. Using an HPLC/MS assay we have now observed and isolated for the first time PBD adducts with single-stranded DNA fragments. Surprisingly, these adducts could only be formed through dissociation of duplex DNA adducts and not by direct interaction of PBDs with single-stranded DNA. They were sufficiently stable for characterization by MALDI-TOF-MS and remained intact after storing at -20 °C for at least 20 days, although the PBD became detached from the DNA within 7 days if stored at room temperature. Furthermore, addition of a complementary strand allowed the duplex adduct to reform. The relative stability of single-stranded PBD/DNA adducts despite a complete loss of minor groove structure was further confirmed by CD spectroscopic analysis. The CD signal induced by the presence of a PBD molecule in the single-stranded adducts remained prominent despite heating for 2 h at 50-60 °C, thus indicating their relatively robust nature.
authors.affiliation: Gene Targeted Drug Design Research Group, The School of Pharmacy, University of London, 29/39 Brunswick Square, London WC1N 1AX, UK.
authors.forename: Khondaker M
authors.initials: KM
authors.lastname: Rahman
authors.forename: Colin H
authors.initials: CH
authors.lastname: James
authors.forename: Tam T T
authors.initials: TT
authors.lastname: Bui
authors.forename: Alex F
authors.initials: AF
authors.lastname: Drake
authors.forename: David E
authors.initials: DE
authors.lastname: Thurston
mesh_terms: D000970:Antineoplastic Agents / Q000032:analysis* / Q000494:pharmacology; D001483:Base Sequence; D001569:Benzodiazepines / Q000032:analysis* / Q000494:pharmacology; D018736:DNA Adducts / Q000032:analysis* / Q000378:metabolism; D004277:DNA, Single-Stranded / Q000737:chemistry / Q000378:metabolism*; D008958:Models, Molecular; D009690:Nucleic Acid Conformation / Q000187:drug effects; D011758:Pyrroles / Q000032:analysis* / Q000494:pharmacology; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
chemical_list: D000970:Antineoplastic Agents; D018736:DNA Adducts; D004277:DNA, Single-Stranded; D011758:Pyrroles; C438462:pyrrolo(2,1-c)(1,4)benzodiazepine; D001569:Benzodiazepines