title: Sensitization to doxorubicin resistance in breast cancer cell lines by tamoxifen and megestrol acetate.
abstract: Acquired drug resistance is a major factor in the failure of doxorubicin-based chemotherapy in breast cancer. We determined the ability of megestrol acetate and/or tamoxifen to reverse doxorubicin drug resistance in a doxorubicin-resistant breast cancer line (the human MCF-7/ADR). The cytotoxicity of doxorubicin, megestrol acetate, and/or tamoxifen was determined in the sensitive and resistant cell lines utilizing the sulphorhodamine B assay. Tamoxifen alone produced an IC50 (concentration resulting in 50% inhibition of control growth) of 10.6 microM, whereas megestrol acetate alone resulted in an IC50 of 48.7 microM in the MCF-7/ADR cell line. The IC50 of doxorubicin in MCF-7/ADR was 1.9 microM. Neither megestrol acetate alone nor tamoxifen alone at 1 or 5 microM altered the IC50 of doxorubicin. However, the combination of tamoxifen (1 or 5 microM) and megestrol acetate (1 or 5 microM) synergistically sensitized MCF-7/ADR cells. Additionally, megestrol acetate and tamoxifen inhibited iodoarylazidoprazosin binding to P-glycoprotein, and, in their presence, there was an increased doxorubicin accumulation in the MCF-7/ADR cells. Furthermore, the combination of tamoxifen and megestrol acetate had much less effect on the cytotoxicity of doxorubicin in MCF-7 wild-type cells. Clinically achievable concentrations of tamoxifen and megestrol acetate can largely sensitize MCF-7/ADR to doxorubicin. The combination of these three drugs in a clinical trial may be informative.
authors.affiliation: Lady Davis Institute, Montreal, Quebec, Canada.
authors.forename: L
authors.initials: L
authors.lastname: Panasci
authors.forename: B J
authors.initials: BJ
authors.lastname: Jean-Claude
authors.forename: D
authors.initials: D
authors.lastname: Vasilescu
authors.forename: A
authors.initials: A
authors.lastname: Mustafa
authors.forename: S
authors.initials: S
authors.lastname: Damian
authors.forename: Z
authors.initials: Z
authors.lastname: Damian
authors.forename: E
authors.initials: E
authors.lastname: Georges
authors.forename: Z
authors.initials: Z
authors.lastname: Liu
authors.forename: G
authors.initials: G
authors.lastname: Batist
authors.forename: B
authors.initials: B
authors.lastname: Leyland-Jones
mesh_terms: D001943:Breast Neoplasms / Q000188:drug therapy*; D004317:Doxorubicin / Q000494:pharmacology*; D019008:Drug Resistance, Neoplasm; D005260:Female; D006801:Humans; D019290:Megestrol Acetate / Q000494:pharmacology*; D013629:Tamoxifen / Q000494:pharmacology*; D014407:Tumor Cells, Cultured / Q000187:drug effects
chemical_list: D013629:Tamoxifen; D004317:Doxorubicin; D019290:Megestrol Acetate