title: Potential mechanisms for the synergistic cytotoxicity elicited by 4-hydroxytamoxifen and epigallocatechin gallate in MDA-MB-231 cells.
abstract: Potential mechanisms for the synergistic cytotoxicity elicited by epigallocatechin gallate (EGCG) (25 microM) and 4-hydroxytamoxifen (4-OHT) (1 microM) in MDA-MB-231 human breast cancer cells were investigated. The role of apoptosis was determined using chromatin condensation and Annexin-V staining. Condensed chromatin was visible following 24 h of combination treatment while flow cytometry experiments demonstrated that apoptosis was 2-fold greater following 36 h of combination treatment compared to EGCG. The temporal appearance of cells in G1-arrest did not correlate with apoptosis and thus was not considered to be a viable mechanism for the enhancement of apoptosis. While 4-OHT was a weak competitive inhibitor of microsomal UGT activity (Ki 95 microM), it did not alter the metabolism of EGCG as the rate of disappearance of EGCG from the media was the same for cells treated with either EGCG or EGCG + 4-OHT. Additionally, the metabolism of EGCG was not shifted toward the production of active methylated metabolites, as neither 4''-MeEGCG nor 4',4''-diMeEGCG (2.5-25 microM) were cytotoxic toward MDA-MB-231 cells. In conclusion, the synergistic cytotoxicity elicited by the combination of EGCG and 4-OHT results from an earlier induction of apoptosis but this was not caused by an increase in G1-arrest or 4-OHT-mediated changes in the metabolism of EGCG.
authors.affiliation: Department of Pharmacology and Toxicology, University of Otago, Dunedin, New Zealand.
authors.forename: Emma C
authors.initials: EC
authors.lastname: Stuart
authors.forename: Lesley
authors.initials: L
authors.lastname: Larsen
authors.forename: Rhonda J
authors.initials: RJ
authors.lastname: Rosengren
mesh_terms: D000971:Antineoplastic Combined Chemotherapy Protocols / Q000378:metabolism / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects; D001943:Breast Neoplasms / Q000188:drug therapy* / Q000473:pathology*; D002392:Catechin / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology; D002453:Cell Cycle / Q000187:drug effects; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D004357:Drug Synergism; D005434:Flow Cytometry; D006801:Humans; D013629:Tamoxifen / Q000031:analogs & derivatives* / Q000378:metabolism / Q000494:pharmacology
chemical_list: D013629:Tamoxifen; C016601:afimoxifene; D002392:Catechin; C045651:epigallocatechin gallate