The use of bidirectional transcription footprinting to detect platinum-DNA crosslinks by acridine-tetheredplatinum diamine complexes and cisplatin

Bidirectional transcription footprinting has been used to probe the platination of DNA by cisplatin, and to examine the modulation of these interactions by (a) cyclisation of the non-reactive amino group by either ethyl or propyl groups, and (b) the further addition of a pendant intercalator (9-amino acridine) linked by either phenylethyl or phenylpentyl groups. Intrastrand crosslinking was detected for all derivatives at all 5'-GG and 5'-AG sequences on the template strand, but the same sites did not result in transcriptional blockages when on the non-template strand. There was little effect of cyclysation of the amino groups, but the further addition of an intercalator resulted in three responses: a time-dependent increase of the blocked transcript by one and three nucleotides; a reduction of the sequence selectivity of platination; a decrease of apparent interstrand crosslinking for these derivatives with a pendant intercalator tethered to the amino moiety of cisplatin.