title: Sequence specificity of alkylation for a series of nitrogen mustard-containing analogues of distamycin of increasing binding site size: evidence for increased cytotoxicity with enhanced sequence specificity.
abstract: The covalent sequence specificity of a series of nitrogen mustard-containing analogues of distamycin was determined using modified sequencing techniques. The analogues tether benzoic acid mustard (BAM) and possess either one, two, or three pyrrole-amide units. Previous characterization of the biological profile of the series revealed an increase in cytotoxicity for each corresponding increase in the number of pyrrole units, while showing poor cross-link formation in isolated and cellular DNA. Examination of the sequence specificity revealed that BAM produced guanine-N7 lesions in similar manner to other conventional nitrogen mustards. The monopyrrole BAM conjugate also produced guanine-N7 alkylation in a similar pattern to BAM. However, alkylation of adenines was also seen that was found to be minor groove adenine-N3 lesions. The dipyrrole and tripyrrole conjugates did not produce detectable guanine-N7 alkylation but only alkylated in AT tracts. In addition, the tripyrrole conjugate preferentially alkylated only a subset of those sites alkylated by the monopyrrole and dipyrrole conjugates. Two sites, 5'-TTTTGG and 5'-TTTTGA, confirmed as guanine-N3 and adenine-N3 lesions, respectively, were strongly alkylated by the tripyrrole conjugate in preference to other similar sites including three occurrences of 5'-TTTTAA. Footprinting studies comparing distamycin and the tripyrrole conjugate showed identical non-covalent recognition of AT-rich sites. Hence, the drug that possessed the most enhanced sequence specificity for alkylation was also the most cytotoxic of this series.
authors.affiliation: Department of Oncology, University College London Medical School, UK.
authors.forename: M D
authors.initials: MD
authors.lastname: Wyatt
authors.forename: M
authors.initials: M
authors.lastname: Lee
authors.forename: B J
authors.initials: BJ
authors.lastname: Garbiras
authors.forename: R L
authors.initials: RL
authors.lastname: Souhami
authors.forename: J A
authors.initials: JA
authors.lastname: Hartley
mesh_terms: D018906:Antineoplastic Agents, Alkylating / Q000737:chemistry*; D001483:Base Sequence; D001565:Benzoates / Q000737:chemistry; D019817:Benzoic Acid; D004247:DNA / Q000096:biosynthesis / Q000737:chemistry*; D018736:DNA Adducts / Q000737:chemistry; D004249:DNA Damage; D017931:DNA Primers / Q000737:chemistry; D004214:Distamycins / Q000737:chemistry*; D008466:Mechlorethamine / Q000737:chemistry*; D008969:Molecular Sequence Data; D009588:Nitrogen Mustard Compounds / Q000737:chemistry*; D013329:Structure-Activity Relationship
chemical_list: D018906:Antineoplastic Agents, Alkylating; D001565:Benzoates; D018736:DNA Adducts; D017931:DNA Primers; D004214:Distamycins; D009588:Nitrogen Mustard Compounds; D008466:Mechlorethamine; C066900:tallimustine; D019817:Benzoic Acid; D004247:DNA