title: Cellular events involved in the sensitization of etoposide-resistant cells by inhibitors of calcium-calmodulin-dependent processes. Role for effects on apoptosis, DNA cleavable complex, and phosphorylation.
abstract: Inhibitors of calcium-calmodulin-dependent processes, 1-[N,O-bis(1,5-isoquinolinesulfonyl)-N-methyl-L-tyrosyl]-4-piperazine KN-62 and trifluoperazine (TFP), at non-cytotoxic concentrations (2 and 5 microM, respectively) enhanced etoposide (VP-16) cytotoxicity in Adriamycin-resistant (HL-60/ADR0.05) cells (3- to > 50-fold). In contrast to TFP, the inhibitor KN-62 was able to reverse resistance in HL-60/ADR0.05 cells at VP-16 concentrations that produced equivalent cytotoxicity in sensitive (HL-60/S) cells. Unlike TFP, the cellular accumulation of VP-16 in the presence of KN-62 was enhanced 1.5- to 2-fold in HL-60/S (MDR1 -ve) and HL-60/ADR0.05 (MDR1 +ve) cells. To achieve equivalent cytotoxicity, levels of VP-16 in the resistant cells were > 4-fold lower in the presence of KN-62 compared with treatment with VP-16 alone. The sensitizing effects of both KN-62 and TFP were due to enhancement (2- to 4-fold) of VP-16-induced topoisomerase II (TOPO II)-mediated DNA cleavable complex formation, and depletion of the 170 kDa (alpha) TOPO II isoform. The DNA damage induced by VP-16 in the presence of KN-62 or TFP resulted in the rapid induction of apoptosis and depletion of cells in "S" phase of the cell cycle. Both 5 microM TFP and 2 microM KN-62 enhanced the phosphorylation of 170 kDa TOPO II 1.6-fold and 1.5-fold, respectively. Results suggest that the inhibitory effect of KN-62 or TFP on calcium-calmodulin-dependent processes may be mechanistically involved in sensitizing resistant cells to VP-16 by enhancing TOPO II-mediated DNA damage.
authors.affiliation: Department of Cancer Biology, Cleveland Clinic Foundation, OH 44195, USA.
authors.forename: K
authors.initials: K
authors.lastname: Kawamura
authors.forename: D
authors.initials: D
authors.lastname: Grabowski
authors.forename: K
authors.initials: K
authors.lastname: Krivacic
authors.forename: H
authors.initials: H
authors.lastname: Hidaka
authors.forename: R
authors.initials: R
authors.lastname: Ganapathi
mesh_terms: D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine / Q000031:analogs & derivatives / Q000494:pharmacology; D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D002118:Calcium / Q000502:physiology*; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000037:antagonists & inhibitors*; D002147:Calmodulin / Q000502:physiology*; D004250:DNA Topoisomerases, Type II / Q000378:metabolism*; D004351:Drug Resistance; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005047:Etoposide / Q000494:pharmacology*; D018922:HL-60 Cells; D006801:Humans; D059005:Topoisomerase II Inhibitors; D014268:Trifluoperazine / Q000494:pharmacology
chemical_list: D000970:Antineoplastic Agents; D002147:Calmodulin; D004791:Enzyme Inhibitors; D059005:Topoisomerase II Inhibitors; D014268:Trifluoperazine; C063302:KN 62; D005047:Etoposide; D019307:1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D004250:DNA Topoisomerases, Type II; D002118:Calcium