Cell cycle phase specificity in the potentiation of etoposide-induced DNA damage and apoptosis by KN-62, an inhibitor of calcium-calmodulin-dependentenzymes

The cell cycle phase-dependent induction of DNA damage and apoptosis by eto poside (VP-16) and its modulation by 1-[N,O-bis(1,5-isoquinolinesulfonyl)-N -methyl-1-tyrosyl] -4-piperazine (KN-62), an inhibitor of calcium-calmoduli n-dependent enzymes, were examined in sensitive (HL-60/S) and VP-16-resista nt (HL-60/DOX0.05) HL-60 cells. Cells from exponential-phase cultures were enriched by centrifugal elutriation into G(1), S, and G(2) + M fractions. M odulation of VP-16-induced apoptosis by KN-62 in HL-60/S cells was apparent only in the S phase at the IC50 concentration. However, in the HL-60/DOX0. 05 cells, significant (P < 0.001) potentiation of VP-16-induced apoptosis b y a non-cytotoxic concentration of 2 <mu>M KN-62 was apparent in cells in t he G(1), S, and G(2) + M phases, as well as over the entire concentration r ange tested. VP-16-induced apoptosis and its potentiation by a non-cytotoxi c concentration of 2 muM KN-62 were correlative with drug-stabilized DNA cl eavable complex formation based on a band depletion assay. In agreement wit h the results on apoptosis in the resistant HL-60/DOX0.05 cells, the enhanc ed depletion of the a and P isoforms of topoisomerase II by VP-16 + KN-62 w as observed in G(1), S, and G(2) + M cells. Results suggest that the effect s of KN-62 in reversing resistance are based on its role as a potent sensit izer of VP-16-induced DNA damage and apoptosis in a cell cycle phase-indepe ndent manner. (C) 2000 Elsevier Science Inc. All rights reserved.