title: Cell cycle phase specificity in the potentiation of etoposide-induced DNA damage and apoptosis by KN-62, an inhibitor of calcium-calmodulin-dependent enzymes.
abstract: The cell cycle phase-dependent induction of DNA damage and apoptosis by etoposide (VP-16) and its modulation by 1-[N,O-bis(1, 5-isoquinolinesulfonyl)-N-methyl-l-tyrosyl]-4-piperazine (KN-62), an inhibitor of calcium-calmodulin-dependent enzymes, were examined in sensitive (HL-60/S) and VP-16-resistant (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. Modulation of VP-16-induced apoptosis by KN-62 in HL-60/S cells was apparent only in the S phase at the IC(50) concentration. However, in the HL-60/DOX0.05 cells, significant (P < 0.001) potentiation of VP-16-induced apoptosis by a non-cytotoxic concentration of 2 microM KN-62 was apparent in cells in the G(1), S, and G(2)+M phases, as well as over the entire concentration range tested. VP-16-induced apoptosis and its potentiation by a non-cytotoxic concentration of 2 microM KN-62 were correlative with drug-stabilized DNA cleavable complex formation based on a band depletion assay. In agreement with the results on apoptosis in the resistant HL-60/DOX0.05 cells, the enhanced depletion of the alpha and beta isoforms of topoisomerase II by VP-16 + KN-62 was observed in G(1), S, and G(2)+M cells. Results suggest that the effects of KN-62 in reversing resistance are based on its role as a potent sensitizer of VP-16-induced DNA damage and apoptosis in a cell cycle phase-independent manner.
authors.affiliation: Experimental Therapeutics Program, Taussig Cancer Center (R40), Cleveland Clinic Foundation, 9500 Euclid Avenue, 44195, Cleveland, OH, USA.
authors.forename: M
authors.initials: M
authors.lastname: Aoyama
authors.forename: D R
authors.initials: DR
authors.lastname: Grabowski
authors.forename: K A
authors.initials: KA
authors.lastname: Holmes
authors.forename: L A
authors.initials: LA
authors.lastname: Rybicki
authors.forename: R M
authors.initials: RM
authors.lastname: Bukowski
authors.forename: M K
authors.initials: MK
authors.lastname: Ganapathi
authors.forename: R
authors.initials: R
authors.lastname: Ganapathi
mesh_terms: D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine / Q000031:analogs & derivatives* / Q000494:pharmacology*; D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology*; D017209:Apoptosis; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000037:antagonists & inhibitors; D002453:Cell Cycle / Q000187:drug effects; D004247:DNA / Q000187:drug effects / Q000378:metabolism; D004249:DNA Damage; D004250:DNA Topoisomerases, Type II / Q000378:metabolism; D004357:Drug Synergism; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005047:Etoposide / Q000494:pharmacology*; D018922:HL-60 Cells; D006801:Humans
chemical_list: D000972:Antineoplastic Agents, Phytogenic; D004791:Enzyme Inhibitors; C063302:KN 62; D005047:Etoposide; D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; D004247:DNA; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D004250:DNA Topoisomerases, Type II