Since the average age of the population in the United States is rising, there are an increasing number of menopausal women. Menopause is often associated with hot flashes, night sweats, mood changes, urogenital atrophy and loss of bone density that have traditionally been treated with hormone therapy (HT) to restore estrogen levels. The Women’s Health Initiative (WHI) trial, however, found that estrogen plus progestin increased a woman’s risk of heart disease, breast cancer, and dementia [1
]. In addition, a second arm of the WHI found that using estrogen alone increased the risk of stroke and dementia [6
]. While some of the unfavorable results on heart disease from the WHI are likely due to the late time when HT was initiated in relation to the onset of menopause [8
] the adverse impact of HT on breast cancer and blood clots indicated that new strategies are needed to treat menopausal symptoms.
Alternative drugs to traditional HT could potentially include selective estrogen receptor modulators (SERMs), such as tamoxifen and raloxifene. However, while current SERM therapy has some favorable effects, such as improved bone mineral density [9
] and the prevention of breast cancer, SERMs exacerbate hot flashes [11
]. Other pharmacological options for hot flashes include antidepressant therapy using serotonin and norepineprhine reuptake inhibitors, as well as other neuro-modulators, such as gabapentin [12
]. However, the overall benefit of these treatments is unclear considering their moderate efficacy [13
], potential significant side effects [14
] and lack of benefits on other menopausal symptoms, such as vaginal atrophy and osteoporosis.
Many patients rely on botanical dietary supplements (BDS) used in Traditional Chinese Medicine (TCM) to relieve their menopausal symptoms. It has been reported that about 25% of women use botanical extracts to treat menopausal symptoms [16
]. Recently, there has been an increased interest in using isoflavones, which are one of several classes of phytoestrogens, as an alternate therapy for menopausal symptoms. Daidzein and genistein, the major isoflavones found in soy products, have been studied at length with inconclusive results from clinical trials. Some studies with daidzein have shown modest improvement in menopausal symptoms as compared to placebo [17
], while a large meta-analysis did not show that daidzein-rich isoflavones improved symptoms over placebo [19
]. Similarly, studies with genistein, have shown inconclusive results [19
]. The selective estrogen receptor (SERM) DT56a is an enzymatic isolate of soybeans that has been shown to improve vasomotor symptoms and increased bone mineral density in post-menopausal women, with no effect on sex hormone levels or endometrial thickness [21
]. While these data suggest that phyto-SERMs from soy have promise to safely treat menopausal symptoms and osteoporosis their effectiveness still needs to be evaluated in larger placebo-controlled randomized trials.
In addition to soy, it has been found that Chinese herbs contain compounds that have estrogenic activity [24
]. We have been performing basic and clinical research on one botanical extract, MF101, which is composed of 22 individual plants [25
]. A Phase 2 clinical trial with 217 postmenopausal women found that 5 gm and 10 gm MF101 were safe for short term use and more effective than placebo after 12 weeks of treatment (data not shown). We also demonstrated that MF101 acted as an ERβ-selective agonist by regulating gene transcription via ERβ pathways [25
]. In addition, we showed that MF101 does not stimulate MCF-7 breast cancer cell proliferation or uterine growth in a mouse xenograft model [25
]. These findings suggested that plants used in TCM might be a source for the discovery of estrogen receptor subtype selective drugs to safely treat menopausal symptoms.
The estrogens used in current HT regimens activate both known estrogen receptor subtypes, ERα and ERβ. Although the precise roles of both ERs are not known, the specific activation of each subtype results in different biological outcomes. ERα and ERβ knockout mice have different phenotypes [26
]. In addition, estradiol (E2
,) activation of ERα versus ERβ results in different gene regulation patterns [27
]. Estrogen acts as an agonist on ERα and ERβ in all tissue types, which likely explains the beneficial aspects of HT, but this non-selective action also likely causes the adverse side effects unveiled by the WHI. On the other hand, drugs that selectively activate ERα or ERβ might mimic some of the beneficial effects while avoiding the untoward effects. Since ERα has been shown to cause the proliferation of breast cancer cells and ERβ has been demonstrated to be a tumor suppressor [28
], it is conceivable that ERβ-selective agonists may serve as safer long-term alternative treatment to traditional HT.
Due to the large unmet need encountered as a result of the WHI, we have developed a parallel strategy to discover drugs for the treatment of menopausal symptoms. Our first approach was to determine the mechanism of action of standardized crude plant extracts and to test them in controlled clinical trials. To this end, we showed that MF101 had ERβ-selective properties [25
] and a Phase 2 clinical trial with MF101 for the treatment of hot flashes was done to further evaluate its safety and efficacy (http://clinicaltrials.gov/show/NCT00119665
). Our next step was to isolate and characterize individual chemical entities from MF101 as potential drugs for menopausal symptoms. This paper summarizes the results from a study representing our second approach as we isolated an ERβ-selective compound, liquiritigenin, from the root of G. uralensis
, and determined its biologic activity on estrogen receptors in cells and animal models.