Sl. Mee et al., Cellular resistance to the antitumor DNA topoisomerase II inhibitor S16020-2: Importance of the N-[2(dimethylamino)ethyl] carbamoyl side chain, MOLEC PHARM, 58(4), 2000, pp. 709-718
The new olivacine derivative S16020-2 (NSC-659687) is a DNA topoisomerase I
I inhibitor endowed with a remarkable antitumor activity against various ex
perimental tumors. In vitro physicochemical properties of this compound, in
particular its interaction with DNA and DNA topoisomerase II, were very si
milar to those of ellipticine derivatives, except for a strictly ATP-depend
ent mechanism of cleavable complex induction. From the Chinese hamster lung
fibroblast cell line DC-3F, a subline resistant to S16020-2, named DC-3F/S
16, was selected by adding stepwise increasing concentrations of the drug t
o the cell growth medium. Whereas DC-3F/9-OH-E cells, a DC-3F subline resis
tant to 9-hydroxy-ellipticine, are cross-resistant to S16020-2, DC-3F/S16 c
ells are only very weakly cross-resistant to ellipticine derivatives, indic
ating that, despite their structural similarity, these compounds may differ
in their mechanisms of action. Uptake and efflux rates of S16020-2 were id
entical in the resistant and the sensitive cells. Topoisomerase II alpha wa
s expressed at the same level in both sensitive and resistant cells, wherea
s expression of the beta-enzyme was approximately 50% lower in the resistan
t cells. Sequencing of both alpha- and beta-isoform cDNAs revealed a point
mutation that converts Arg(486) to a Gly in the alpha cDNA, whereas the bet
a cDNA was not modified. This amino acid substitution in a highly conserved
sequence of the enzyme appears to be responsible for the resistance to S16
020-2. Comparative analysis of the properties of the ellipticine and S16020
-2- resistant cells suggests that S16020-2, which is a DNA intercalator, mi
ght also interact with this enzyme amino acid sequence through its side cha
in.