title: Characterisation of VP-16-induced DNA cleavage in oestrogen-stimulated human breast cancer cells.
abstract: Cycling cells are recognised to be more susceptible than quiescent cells to the cytotoxic action of many commonly used cancer chemotherapeutic agents. We have found that oestrogen stimulation of T-47D human breast cancer cells is accompanied by a two-fold increase in VP-16-induced DNA cleavage as measured by alkaline DNA unwinding, and that this increase in DNA cleavage is accompanied by a corresponding enhancement of drug-induced cytostasis. The enhancement of VP-16-induced DNA cleavage seen with oestrogen exposure is antagonised both by antioestrogen treatment and by cycloheximide, an inhibitor of protein synthesis, but not by the DNA synthesis inhibitor aphidicolin. Increased c-myc protein synthesis is detectable within an hour of oestrogen exposure, while increased VP-16-induced DNA cleavage is detectable within 4h and increased DNA synthesis within 16h. Only small changes in cell-cycle distribution occur with oestrogen stimulation. In the absence of VP-16, oestrogen does not reduce DNA double-strandedness, nor does it induce changes in chromatin structure as measured by alterations in DNA superhelicity or chromatin accessibility. These findings suggest that oestrogen enhances VP-16-induced DNA damage in asynchronously growing G1-phase cells and that this enhancement may be dependent at some point upon de novo protein synthesis. Oestrogen pre-treatment of T-47D human breast cancer cells improves the therapeutic index of VP-16 without the need for cell synchronisation or highly precise drug scheduling.
authors.affiliation: MRC Unit, MRC Centre, Cambridge, UK.
authors.forename: R J
authors.initials: RJ
authors.lastname: Epstein
authors.forename: P J
authors.initials: PJ
authors.lastname: Smith
authors.forename: J V
authors.initials: JV
authors.lastname: Watson
authors.forename: N M
authors.initials: NM
authors.lastname: Bleehen
mesh_terms: D001943:Breast Neoplasms / Q000473:pathology*; D002455:Cell Division / Q000187:drug effects; D002843:Chromatin / Q000187:drug effects; D004249:DNA Damage; D004273:DNA, Neoplasm / Q000187:drug effects*; D004305:Dose-Response Relationship, Drug; D004357:Drug Synergism; D004958:Estradiol / Q000494:pharmacology*; D005047:Etoposide / Q000494:pharmacology*; D005260:Female; D006801:Humans; D066298:In Vitro Techniques; D013997:Time Factors; D014407:Tumor Cells, Cultured / Q000187:drug effects
chemical_list: D002843:Chromatin; D004273:DNA, Neoplasm; D004958:Estradiol; D005047:Etoposide