DNA Interaction and Topoisomerase II Inhibition by the Antitumor Agent 3′-(9-Acridinylamino)-5′-hydroxymethylaniline and Derivatives

Cleavage and cytotoxicity assays have been used to show that 3′-(9-acridinylamino)-5′-hydroxymethylaniline (AHMA) is a potent antileukemic agent that inhibits topoisomerase II-mediated relaxation of supercoiled DNA and promotes the topoisomerase II-mediated cleavage of DNA at a subset of the cleavage sites of 4′-(9-acridinylamino)-methanesulfon-m-anisidide (m-AMSA). Equilibrium binding data show a larger binding constant for the more cytotoxic derivatives for binding to poly(dA-dT)2as compared to poly(dG-dC)2, but greater cooperativity for binding to poly(dG-dC)2and a steric barrier to binding caused by the size of the 5′-hydroxymethyl substituent. Circular dichroism shows a more intercalated binding geometry on poly(dG-dC)2for 1′-substituted derivatives when compared to AHMA and derivatives with a free 1′-amino group, which is absent with poly(dA-dT)2and calf thymus DNA and is indicative of specific interactions with GC-rich areas in natural DNA for AHMA and derivatives with free 1′-amino groups which may stabilize the drug–DNA complex.