Ellipticine derivatives have been shown to induce
DNA strand breaks by trapping
DNA-topoisomerase II (
Topo II) in an intermediary covalent complex between
Topo II and
DNA which could be related to their cytotoxic effects. We report here that
Celiptium and
Detalliptinium, two
ellipticine derivatives clinically used for their antitumoral properties against
breast cancer, exhibit the highest in vitro activity on
Topo II DNA cleavage reaction and decatenation among a series of 14
ellipticine derivatives. The in vitro cleavage site specificity in pBR 322 plasmid
DNA and in a human c-myc gene inserted in a lambda phage
DNA is identical for both
ellipticines, but different from
m-AMSA, another
Topo II related antitumoral agent. Recently, it has been shown that the
ellipticine derivative
Celiptium presents a strong cytotoxic activity in vitro on different human
tumors including
small cell lung carcinoma (SCLC). However, the studies that involved
Topo II as a target for
ellipticine derivatives have been performed only by using animal tumor cell lines. Therefore we have studied the in vivo DNA cleavage activity of
Celiptium and
Detalliptinium on a human SCLC cell line, NCI N417, comparatively to that obtained with
m-AMSA. The respective IC50 on cell growth are 9, 8 and 1 microM for
Celiptium,
Detalliptinium and
m-AMSA, respectively. Using the alkaline elution technique, we have observed that
Celiptium and
Detalliptinium exhibit a weak cleavage activity on genomic
DNA from whole cells. The
ellipticines are about 50 times less potent than
m-AMSA in inducing
DNA strand breaks. Analysis of in vivo c-myc gene cleavage by Southern blot hybridization also demonstrates a lack of activity of the
ellipticine derivatives as no gene cleavage could be detected up to 50 microM of the
drug. With
m-AMSA, c-myc gene cleavage is detected at a concentration of 0.2 microM, which indicates that this methodology is less sensitive in detecting
DNA strand breaks than is the alkaline elution. Further studies of the
drug effect on isolated nuclei by alkaline elution also show that the DNA cleavage activity of
Celiptium and
Detalliptinium is increased when compared to whole cells. Our data indicate that these two drugs have a weaker cytotoxic effect than
m-AMSA on NCI N417 cell line, due to a limited access to the cell nucleus rather than to a lack of activity on
Topo II as assessed by in vitro and isolated nuclei experiments.