CYTOGENETIC EVALUATION OF THE MECHANISM OF CELL-DEATH INDUCED BY THE NOVEL ANTHRACENYL-AMINO ACID TOPOISOMERASE-II CATALYTIC INHIBITOR NU ICRF-500/

Anthracenyl-amino acid/dipeptides are novel topoisomerase (topo) inhib itors which can be actively cytotoxic in the low mu M range. The prese nt studies have been performed to determine whether cells treated with the topo II catalytic inhibitor NU/ICRF 500 (serine derivative) would manifest cytogenetic lesions consistent with its proposed mechanism o f enzyme inhibition. Three other compounds were included for compariso n: NU/ICRF 505 (tyrosine) which stabilises topo I cleavable complexes, NU/ICRF 602 (gly-gly) a non-cytotoxic catalytic inhibitor of topo I a nd II and NU/ICRF 502 (alanine) a non-cytotoxic non-topo inhibitor. Ch romosomal damage was measured using the micronucleus test, NU/ICRF 500 (7.5-30 mu M) induced an increase in CREST negative micronuclei (11-1 5 per 500 cells) in human lymphocytes (HL) and blocked the traverse of HL through the cell cycle, with cells accumulating in G2/M at 15 mu M drug and G1/S at 30 mu M drug. NU/ICRF 502 was without effect in the micronucleus test. NTJ/ICRF 500 and 602 (90-150 mu M) caused no block in passage of synchronised metaphase Chinese hamster ovary cells throu gh mitosis whereas NU/ICRF 505 produced a significant delay. DNA measu rements of post-mitotic cells revealed that after NU/ICRF 500 treatmen t nuclei had a 4C DNA content, indicative of a lack of chromosomal seg regation. Normal (2C) DNA content was observed with NU/ICRF 505 and 60 2. Overall, the data for NU/ICRF 500 are consistent with the cytogenet ic modifications expected after catalytic inhibition of topo II and su ggest that cell death may be mediated, at least in part, through this mechanism.