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) inhibitors which can be actively cytotoxic in the low microM range. The present 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 of enzyme inhibition. Three other compounds were included for comparison: NU/ICRF 505 (tyrosine) which stabilises topo I cleavable complexes, NU/ICRF 602 (gly-gly) a non-cytotoxic catalytic inhibitor of topo I and II and NU/ICRF 502 (alanine) a non-cytotoxic non-topo inhibitor. Chromosomal damage was measured using the micronucleus test. NU/ICRF 500 (7.5-30 microM) induced an increase in CREST negative micronuclei (11-15 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 microM drug and G1/S at 30 microM drug. NU/ICRF 502 was without effect in the micronucleus test. NU/ICRF 500 and 602 (90-150 microM) caused no block in passage of synchronised metaphase Chinese hamster ovary cells through mitosis whereas NU/ICRF 505 produced a significant delay. DNA measurements of post-mitotic cells revealed that after NU/ICRF 500 treatment nuclei had a 4C DNA content, indicative of a lack of chromosomal segregation. Normal (2C) DNA content was observed with NU/ICRF 505 and 602. Overall, the data for NU/ICRF 500 are consistent with the cytogenetic modifications expected after catalytic inhibition of topo II and suggest that cell death may be mediated, at least in part, through this mechanism.