title: Modulation of the cell cycle-dependent cytotoxicity of adriamycin and 4-hydroperoxycyclophosphamide by novobiocin, an inhibitor of mammalian topoisomerase II.
abstract: Centrifugal elutriation was used to obtain synchronized cell populations in various cell cycle phases without prior growth-perturbing manipulation. Treatment of these subpopulations with novobiocin (NOVO), a putative inhibitor of the mammalian topoisomerase II enzyme, revealed a unique cell cycle phase-dependent cytotoxicity for this agent. At a concentration of 0.3 mM, NOVO was cytotoxic only to a specific cell subpopulation in the G1-S phase boundary. Cells in other cell cycle phases were completely unaffected. Additionally, S and G2M phase cells progressed through the cell cycle relatively unaffected by NOVO but were blocked at the G1-S boundary. NOVO treatment protected tumor cells from Adriamycin (ADR)-induced lethality but sensitized them to the toxic action of 4-hydroperoxycyclophosphamide, and alkylating agent. These opposing effects of NOVO were demonstrated in all of the four tumor cell lines investigated: A431 and HEp3 (derived from human squamous cell carcinomas); MLS, a human ovarian cancer cell line; and a Chinese hamster ovary cell line. The degree of protection against ADR was the greatest for S-phase cells, intermediate for cells in early G1 and M phases, and the least for late G1 cells. This cell cycle-dependent protection by NOVO, which is identical to the cell cycle-dependent cytotoxicity of ADR, was consistent with the idea that NOVO interfered directly with the cell-killing mechanism of ADR. In contrast, even though the cytotoxic activity of 4-hydroperoxycyclophosphamide exhibited significant cell cycle dependency, NOVO enhanced 4-hydroperoxycyclophosphamide lethality equally for all cell cycle phases.
authors.affiliation: Tumor Biology Division, University of Rochester Cancer Center, New York 14642.
authors.forename: F Y
authors.initials: FY
authors.lastname: Lee
authors.forename: D J
authors.initials: DJ
authors.lastname: Flannery
authors.forename: D W
authors.initials: DW
authors.lastname: Siemann
mesh_terms: D000818:Animals; D002453:Cell Cycle / Q000187:drug effects; D002460:Cell Line; D002470:Cell Survival / Q000187:drug effects; D003520:Cyclophosphamide / Q000031:analogs & derivatives* / Q000494:pharmacology; D004317:Doxorubicin / Q000494:pharmacology*; D005978:Glutathione / Q000378:metabolism; D009675:Novobiocin / Q000494:pharmacology*; D059004:Topoisomerase I Inhibitors
chemical_list: D059004:Topoisomerase I Inhibitors; D009675:Novobiocin; D004317:Doxorubicin; D003520:Cyclophosphamide; D005978:Glutathione; C011272:perfosfamide