THE 1'-SUBSTITUENT ON THE ANILINO RING OF THE ANTITUMOR DRUG AMSACRINE IS A CRITICAL ELEMENT FOR TOPOISOMERASE-II INHIBITION AND CYTOTOXICITY

The mechanism of action of the antitumor drug amsacrine involves inter calation of the acridine chromophore into DNA and inhibition of topois omerase II. The substituent at position 1' on the aniline is believed to be essential to the formation of the topoisomerase II/DNA cleavable complex and therefore to the cytotoxicity of the drug. To further del ineate the role of the 1'-substituent, we investigated the effects on topoisomerase II activities of three anilinoacridine derivatives that differ only by the nature of the substituent at position 1'. The resul ts of the cytotoxicity assays performed with cells sensitive (DC-3F) a nd resistant [DC-3F/9-hydroxy-ellipticine (9-OH-E)] to topoisomerase i nhibitors are correlated with the effects of the drugs on topoisomeras e II-mediated DNA cleavage in vitro. The influence of topoisomerase II alpha on the mechanism of action of the drugs was examined using resi stant DC-3F/9-OH-E cells transfected with a plasmid carrying a wild-ty pe human topoisomerase II alpha cDNA. Depending on the nature of the 1 '-substituent of the drugs, the restoration of normal topoisomerase II alpha catalytic activity in human topoisomerase II alpha cDNA-transfe cted DC-3F/9-OH-E cells either does not modify the susceptibility of t he cells to the drug or partially reverses the resistance phenotype. T he molecular and cellular studies reveal that topoisomerase II alpha i s implicated in the cytotoxicity of amsacrine and confirm that the sub stituent at position 1' on the anilino ring of amsacrine governs the i nteraction with topoisomerase II.