Anilino analogues of
amsacrine showed increased activity against
amsacrine (
AMSA)-resistant cell lines when compared with the parent compound, but the mechanisms of
amsacrine resistance in these lines were unknown (Finlay, G. J., Baguley, B. C., Snow, K., and Judd, W., J. Natl.
Cancer Inst., 82: 662-667, 1990). We tested the cytotoxic and
DNA-cleaving activities of two
amsacrine analogues which were derivatives of
9-anilinoacridine (1'-methylcarbamate and 1'-benzenesulfonamide) against an
amsacrine-resistant human
leukemia cell line (HL-60/
AMSA) whose resistance is due to an
amsacrine-resistant
topoisomerase II. Neither agent could overcome the
amsacrine resistance of HL-60/
AMSA. Neither agent could induce HL-60/
AMSA topoisomerase II-mediated cleavage of
DNA in an isolated biochemical system, although at high concentrations the two analogues could inhibit HL-60/
AMSA topoisomerase II-mediated
DNA strand passage. Both analogues were at least as active, if not more active, than
amsacrine against
amsacrine-sensitive HL-60 and its
topoisomerase II. Comparison of the cellular and biochemical results with those from computer simulation of the energy-minimized structures of
amsacrine, its inactive isomer
o-AMSA, and the two new active analogues suggests the following possibilities: (a) the positioning of the potential
topoisomerase II-binding site (1'-anilino group) of the two new drugs resembles the positioning of this site in
amsacrine; (b) the HL-60
topoisomerase II has a binding site which interacts with
amsacrine and the two anilino analogues but not with
o-AMSA, an analogue with altered positioning of the methoxy group; (c) the HL-60/
AMSA topoisomerase II interacts with reduced affinity with
amsacrine and the two anilino analogues, although HL-60/
AMSA topoisomerase II still interacts with the structurally distinct
topoisomerase II-reactive nonintercalator,
etoposide; (d) because of their higher
DNA binding affinity or the greater possible positions of their side groups in comparison to
amsacrine, the two analogues can, at high concentrations, inhibit the strand-passing activity of HL-60/
AMSA topoisomerase II.