Vol. 58, Issue 4, 709-718, October 2000

Cellular Resistance to the Antitumor DNA Topoisomerase II Inhibitor S16020-2: Importance of the N-[2(Dimethylamino)ethyl]carbamoyl Side Chain

Sandrine Le Mée, Françoise Chaminade, Charlotte Delaporte, Judith Markovits, Jean-Marie Saucier, and Alain Jacquemin-Sablon

Centre National de la Recherche Scientifique UMR 8532, Physico-chimie et Pharmacologie des Macromolécules Biologiques, Institut Gustave Roussy, Villejuif, France

The new olivacine derivative S16020-2 (NSC-659687) is a DNA topoisomerase II inhibitor endowed with a remarkable antitumor activity against various experimental tumors. In vitro physicochemical properties of this compound, in particular its interaction with DNA and DNA topoisomerase II, were very similar to those of ellipticine derivatives, except for a strictly ATP-dependent mechanism of cleavable complex induction. From the Chinese hamster lung fibroblast cell line DC-3F, a subline resistant to S16020-2, named DC-3F/S16, was selected by adding stepwise increasing concentrations of the drug to the cell growth medium. Whereas DC-3F/9-OH-E cells, a DC-3F subline resistant to 9-hydroxy-ellipticine, are cross-resistant to S16020-2, DC-3F/S16 cells are only very weakly cross-resistant to ellipticine derivatives, indicating that, despite their structural similarity, these compounds may differ in their mechanisms of action. Uptake and efflux rates of S16020-2 were identical in the resistant and the sensitive cells. Topoisomerase II was expressed at the same level in both sensitive and resistant cells, whereas expression of the -enzyme was approximately 50% lower in the resistant cells. Sequencing of both - and -isoform cDNAs revealed a point mutation that converts Arg⁴⁸⁶ to a Gly in the  cDNA, whereas the  cDNA was not modified. This amino acid substitution in a highly conserved sequence of the enzyme appears to be responsible for the resistance to S16020-2. Comparative analysis of the properties of the ellipticine and S16020-2-resistant cells suggests that S16020-2, which is a DNA intercalator, might also interact with this enzyme amino acid sequence through its side chain.