title: Apigenin inhibits antiestrogen-resistant breast cancer cell growth through estrogen receptor-alpha-dependent and estrogen receptor-alpha-independent mechanisms.
abstract: Breast cancer resistance to the antiestrogens tamoxifen (OHT) and fulvestrant is accompanied by alterations in both estrogen-dependent and estrogen-independent signaling pathways. Consequently, effective inhibition of both pathways may be necessary to block proliferation of antiestrogen-resistant breast cancer cells. In this study, we examined the effects of apigenin, a dietary plant flavonoid with potential anticancer properties, on estrogen-responsive, antiestrogen-sensitive MCF7 breast cancer cells and two MCF7 sublines with acquired resistance to either OHT or fulvestrant. We found that apigenin can function as both an estrogen and an antiestrogen in a dose-dependent manner. At low concentrations (1 mumol/L), apigenin stimulated MCF7 cell growth but had no effect on the antiestrogen-resistant MCF7 sublines. In contrast, at high concentrations (>10 mumol/L), the drug inhibited growth of MCF7 cells and the antiestrogen-resistant sublines, and the combination of apigenin with either OHT or fulvestrant showed synergistic, growth-inhibitory effects on both antiestrogen-sensitive and antiestrogen-resistant breast cancer cells. To further elucidate the molecular mechanism of apigenin as either an estrogen or an antiestrogen, effects of the drug on estrogen receptor-alpha (ERalpha); transactivation activity, mobility, stability, and ERalpha-coactivator interactions were investigated. Low-dose apigenin enhanced receptor transcriptional activity by promoting interaction between ERalpha and its coactivator amplified in breast cancer-1. However, higher doses (>10 mumol/L) of apigenin inhibited ERalpha mobility (as determined by fluorescence recovery after photobleaching assays), down-regulated ERalpha and amplified in breast cancer-1 expression levels, and inhibited multiple protein kinases, including p38, protein kinase A, mitogen-activated protein kinase, and AKT. Collectively, these results show that apigenin can function as both an antiestrogen and a protein kinase inhibitor with activity against breast cancer cells with acquired resistance to OHT or fulvestrant. We conclude that apigenin, through its ability to target both ERalpha-dependent and ERalpha-independent pathways, holds promise as a new therapeutic agent against antiestrogen-resistant breast cancer.
authors.affiliation: Medical Sciences, Indiana University School of Medicine, 302 Jordan Hall, 1001 East 3rd Street, Bloomington, IN 47405-4401, USA.
authors.forename: Xinghua
authors.initials: X
authors.lastname: Long
authors.forename: Meiyun
authors.initials: M
authors.lastname: Fan
authors.forename: Robert M
authors.initials: RM
authors.lastname: Bigsby
authors.forename: Kenneth P
authors.initials: KP
authors.lastname: Nephew
mesh_terms: D047310:Apigenin / Q000494:pharmacology*; D001943:Breast Neoplasms / Q000201:enzymology / Q000473:pathology*; D045744:Cell Line, Tumor; D049109:Cell Proliferation / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D019008:Drug Resistance, Neoplasm / Q000187:drug effects*; D004354:Drug Screening Assays, Antitumor; D004357:Drug Synergism; D004958:Estradiol / Q000031:analogs & derivatives / Q000494:pharmacology; D020847:Estrogen Receptor Modulators / Q000494:pharmacology*; D047628:Estrogen Receptor alpha / Q000235:genetics / Q000378:metabolism*; D005260:Female; D036681:Fluorescence Recovery After Photobleaching; D000077267:Fulvestrant; D017930:Genes, Reporter; D051548:Histone Acetyltransferases / Q000378:metabolism; D006801:Humans; D006915:Hydroxytestosterones / Q000494:pharmacology; D056921:Nuclear Receptor Coactivator 3; D011485:Protein Binding / Q000187:drug effects; D011494:Protein Kinases / Q000378:metabolism; D021381:Protein Transport / Q000187:drug effects; D015534:Trans-Activators / Q000378:metabolism; D014158:Transcription, Genetic / Q000187:drug effects
chemical_list: C506487:ESR1 protein, human; D020847:Estrogen Receptor Modulators; D047628:Estrogen Receptor alpha; D006915:Hydroxytestosterones; D015534:Trans-Activators; D000077267:Fulvestrant; D004958:Estradiol; D047310:Apigenin; D051548:Histone Acetyltransferases; C538866:NCOA3 protein, human; D056921:Nuclear Receptor Coactivator 3; D011494:Protein Kinases