PT  - JOURNAL ARTICLE
AU  - Susan E. Morgan
AU  - Rhonda S. Cadena
AU  - Susana C. Raimondi
AU  - William T. Beck
TI  - Selection of Human Leukemic CEM Cells for Resistance to the DNA Topoisomerase II Catalytic Inhibitor ICRF-187 Results in Increased Levels of Topoisomerase IIα and Altered G<sub>2</sub>/M Checkpoint and Apoptotic Responses
DP  - 2000 Feb 01
TA  - Molecular Pharmacology
PG  - 296--307
VI  - 57
IP  - 2
4099  - http://molpharm.aspetjournals.org/content/57/2/296.short
4100  - http://molpharm.aspetjournals.org/content/57/2/296.full
SO  - Mol Pharmacol2000 Feb 01; 57
AB  - ICRF-187 is a bisdioxopiperazine anticancer drug that inhibits the catalytic activity of DNA topoisomerase (topo) II without stabilizing DNA-topoII cleavable complexes. To better understand the mechanisms of action of and resistance to topoII catalytic inhibitors, human leukemic CEM cells were selected for resistance to ICRF-187. The clones CEM/ICRF-8 and CEM/ICRF-18 are approximately 40- and 69-fold resistant to ICRF-187, and 12- and 67-fold cross-resistant to ICRF-193, respectively, but are sensitive to other topoII catalytic inhibitors (merbarone and aclarubicin), as well as collaterally sensitive to the DNA-topoII complex-stabilizing drug etoposide (VP-16). Both the number of VP-16- induced DNA-topoII complexes formed and the amount of in vitro topoII catalytic activity are enhanced in the drug-resistant cells. The ICRF-187-resistant clones contain ∼5-fold increase in topoIIα protein levels and ∼2.2-fold increase in topoIIα mRNA levels. Furthermore, CEM/ICRF-8 expresses ∼3.5-fold increase in topoIIα promoter activity, suggesting that up-regulation of topoIIα in this clone occurs at the transcriptional level. Treatment of the drug-resistant or -sensitive cells with equitoxic doses of merbarone or teniposide results in a G2/M arrest. In marked contrast, when treated with equitoxic ICRF-187 doses, the drug-resistant clones exhibit either a transient arrest or completely lack the G2/M checkpoint compared with the drug-sensitive cells. This aberrant cell cycle profile is associated with a 48-h delay in drug-induced apoptotic cell death, as revealed by fluorescent-end labeling of DNA and poly (ADP-ribose) polymerase cleavage. In summary, resistance to ICRF-187 in CEM cells is associated with increased levels of catalytically active topoIIα and altered G2/M checkpoint and apoptotic responses. The American Society for Pharmacology and Experimental Therapeutics