INDUCTION OF APOPTOSIS IN HUMAN CANCER CELL-LINES BY THE NOVEL ANTHRACENYL AMINO-ACID TOPOISOMERASE-I INHIBITOR NU ICRF-505/

Anthracenyl-amino acid conjugates represent, a novel chemical class of topoisomerase (topo) inhibitor. NU/ICRF 505 is a lead compound that s tabilises topo I cleavable complexes and is actively cytotoxic at low mu M concentrations. In this study, endonucleolytic DNA cleavage was u sed as a marker of apoptosis to investigate mechanisms of cell death p roduced by this compound. NU/ICRF 505 (5 mu M) induced a substantial i ncrease in the level of DNA fragmentation in HL60 cells (up to 30% of total extracted DNA) but only after a 48 and 72 h drug exposure (compa red with 6 h after treatment with camptothecin), as determined qualita tively by conventional gel electrophoresis and quantitatively by spect rofluorimetry. This effect was substantially reversed by co-treatment with zinc (1 mM). Subsequent studies with the human lung (NX002), ovar ian (A2780) and colon (HT29) cancer cell Lines yielded evidence of for mation of higher molecular weight DNA fragments in NX002 and A2780 cel ls in response to NU/ICRF 505 (5 mu M). Co-treatment with zinc (1 mM) caused a small decrease in DNA fragmentation. These data suggest that the induction of apoptosis may play an important role in the mechanism of cytotoxicity of NU/ICRF 505 in HL60 cells and that other pathways of cell death may also be operative in NX002 and A2780 in conjunction with apoptosis.