Estrogenic and Anticarcinogenic Properties of Kurarinone, a Lavandulyl Flavanone from the Roots of Sophora flavescens An De Naeyer, † Wim Vanden Berghe, ‡ Victoria Pocock, § Stuart Milligan, § Guy Haegeman, ‡ and Denis De Keukeleire* ,† Laboratory of Pharmacognosy and Phytochemistry, Faculty of Pharmaceutical Sciences, Ghent University, Harelbekestraat 72, B-9000 Ghent, Belgium, Laboratory of Eukaryotic Gene Expression and Signal Transduction, Faculty of Sciences, Department of Molecular Biology, Ghent University, Ledeganckstraat 35, B-9000 Ghent, Belgium, and Endocrinology and Reproduction Research Group, School of Biomedical Sciences, King’s College, London SE1 1UL, U.K. Received March 16, 2004 Kurarinone, a lavandulyl flavanone, was isolated from a polyphenolic extract of the roots of Sophora flavescens using fractionation guided by estrogenic activity, which was determined by recombinant yeast and Ishikawa Var-I bioassays. Kurarinone showed weak estrogenic activity both in the yeast screen and in the Ishikawa Var-I assay with EC 50 values of 4.6 and 1.66 µM, respectively. Furthermore, kurarinone was found to have potent cytotoxic activity (IC 50 value ) 22.2 µM) against human MCF-7/6 breast cancer cells in the sulforhodamine-B assay. Despite decades of accumulated observational evidence, the balance of risks and benefits for hormone use in healthy postmenopausal women remains uncertain. Recent evi- dence convincingly demonstrated increased risks for breast cancer 1 and cardiovascular diseases 2 associated with hor- mone replacement therapy (HRT). There is a renewed interest in naturally occurring phytoestrogens as potential alternatives to HRT, and also in the use of selective estrogen receptor modulators. Various phytotherapeuticals with a claimed hormonal activity are recommended for prevention of discomforts related to a disturbed hormonal balance. 3 Unlike xenobiotic estrogens (environmental pollutants with estrogenic activity) that have a negative impact on the development of human reproductive organs and male fertility, 4-6 phytoestrogens are believed to have mainly health-beneficial effects. 7,8 Although phytotherapy for pre- vention of menopausal ailments gained much interest and appreciation during the past few years, its benefits have been questioned. 9,10 It is clear that we need to know much more about the molecular mechanisms, safety, and efficacy of bioactive natural compounds before they can be generally applied to the benefit of postmenopausal women. 11 Previous investigations on the health-protective effects of a soy-rich diet (soybeans and soy-derived products) have shown that isoflavone-type constituents are beneficial with respect to menopausal symptoms (hot flushes, osteoporo- sis), hormone-dependent cancers, and cardiovascular diseases. 7,12-14 Together with lignans, coumestans, fla- vones, and flavanones, isoflavones belong to the larger group of nonsteroidal phytoestrogens. Although phytoestro- gens can function as typical estrogens through ERR, it was found that most representatives have a stronger binding affinity for ER. 15,16 Besides their estrogenic properties, phytoestrogens exert a wide variety of pharmacological effects in animal cells, including inhibition of tyrosine kinases and DNA topoisomerases, antioxidative effects, interference in a plethora of signaling pathways, cell cycle, and apoptosis events, synergism with growth factors by inducing synthesis or activating receptors, and modulation of important enzymatic activities. 17,18 Sophora flavescens Ait. (Leguminosae) is a perennial shrub occurring wild as well as cultivated in Northeast Asia. The plant is known as “ku shen”, which literally means “the bitter root”. This oriental crude drug is used in traditional Chinese medicine as an antipyretic, analge- sic, anthelmintic, and stomachic drug. Phytochemical stud- ies of S. flavescens have described the isolation of quino- lizidine alkaloids, triterpenoids, and a number of flavo- noids. 19-22 The occurrence of flavonoids carrying one or multiple prenyl units incited us to investigate their poten- tial estrogenic properties, since we discovered very potent estrogenicity in prenylated flavonoids present in hops, Humulus lupulus L. 23-25 Previous research has demon- strated favorable effects of these plant components in relation to hormone-dependent cancers, 26-29 cardiovascular diseases, 14 and (post)menopausal symptoms such as os- teoporosis and hot flushes. 11,30,31 Results and Discussion Screening for Estrogenic Activity. Kurarinone, a lavandulyl flavanone present in S. flavescens, has been shown to exhibit antiandrogenic activity, 19 but its potential estrogenicity was not investigated. Thus, we embarked on a study aimed at identifying the estrogenic activity by bioactivity-guided fractionation of a polyphenolic fraction of S. flavescens, using an estrogen-inducible yeast screen and the Ishikawa Var-I bioassay. It was readily shown that estrogenic activity was present at concentrations above 0.02% with respect to the original polyphenolic extract * To whom correspondence should be addressed. Tel: +32-9-264-80-55. Fax: +32-9-264-81-92. E-mail: denis.dekeukeleire@UGent.be. † Laboratory of Pharmacognosy and Phytochemistry, UGent. ‡ Laboratory of Eukaryotic Gene Expression and Signal Transduction, UGent. § Endocrinology and Reproduction Research Group, King’s College. 1829 J. Nat. Prod. 2004, 67, 1829-1832 10.1021/np040069a CCC: $27.50 © 2004 American Chemical Society and American Society of Pharmacognosy Published on Web 10/20/2004