Nitracrine (
Ledakrin) is an
antitumor drug which is activated by cellular
enzymes and binds covalently to
DNA. Previous studies have shown that covalent binding and crosslinking of
DNA is associated with the cytotoxic and antitumor activities of this compound. In this study, cell cycle perturbations, effects on
DNA synthesis and the cell death process initiated by
Nitracrine were studied in murine
leukemia L1210 cells. We show that exposure of L1210 cells to
Nitracrine at the IC(99) concentration delayed progression through the S phase and transiently arrested cells in G(2)/M as found by flow cytometry. Higher
drug concentration (2 x IC(99)) inhibited cell cycle progression in the S phase and induced rapid cell death. Both studied concentrations of the
drug produced different effects on
DNA synthesis as determined by
bromodeoxyuridine incorporation, with a delay in the S phase progression at EC(99) concentration and irreversible arrest in early S phase at the higher dose (2 x IC(99)). At both concentrations of
Nitracrine cell death occurred preferentially in the S phase as revealed by the TUNEL assay. When cells treated with the
drug for 4 hours were post-incubated in the presence of 1 mM
caffeine this led to rapid cell death and suppression of the G(2) arrest. This was associated with a about 10-fold increase in the cytotoxicity of
Nitracrine. Similar effects were observed for another
DNA crosslinking agent,
cis-platinum, and to a lesser extent, for
DNA topoisomerase I inhibitor,
camptothecin. Together, our studies show that suppression of G(2) arrest induced by
Nitracrine greatly enhances its cytotoxicity toward L1210 cells.