Cyclopia extracts act as ERα antagonists and ERβ agonists, in vitro and in vivo

Cyclopia extracts act as selective estrogen receptor subtype downregulators in estrogen receptor positive breast cancer cell lines: Comparison to standard of care breast cancer endocrine therapies and a selective estrogen receptor agonist and antagonist

Breast cancer is the most diagnosed type of cancer amongst women in economically developing countries and globally. Most breast cancers express estrogen receptor alpha (ERα) and are categorized as positive (ER+) breast cancer. Endocrine therapies such as, selective estrogen receptor modulators (SERMs), aromatase inhibitors (AIs), and selective estrogen receptor downregulators (SERDs) are used to treat ER+ breast cancer. However, despite their effectiveness, severe side-effects and resistance are associated with these endocrine therapies. Thus, it would be highly beneficial to develop breast cancer drugs that are as effective as current therapies, but less toxic with fewer side effects, and less likely to induce resistance. Extracts of Cyclopia species, an indigenous South African fynbos plant, have been shown to possess phenolic compounds that exhibit phytoestrogenic and chemopreventive activities against breast cancer development and progression. In the current study, three well characterized Cyclopia extracts, SM6Met, cup of tea (CoT) and P104, were examined for their abilities to modulate the levels of the estrogen receptor subtypes, estrogen receptor alpha and estrogen receptor beta (ERβ), which have been recognized as crucial to breast cancer prognosis and treatment. We showed that the Cyclopia subternata Vogel (C. subternata Vogel) extracts, SM6Met and cup of tea, but not the C. genistoides extract, P104, reduced estrogen receptor alpha protein levels while elevating estrogen receptor beta protein levels, thereby reducing the ERα:ERβ ratio in a similar manner as standard of care breast cancer endocrine therapies such as fulvestrant (selective estrogen receptor downregulator) and 4-hydroxytamoxifen (elective estrogen receptor modulator). Estrogen receptor alpha expression enhances the proliferation of breast cancer cells while estrogen receptor beta inhibits the proliferative activities of estrogen receptor alpha. We also showed that in terms of the molecular mechanisms involved all the Cyclopia extracts regulated estrogen receptor alpha and estrogen receptor beta protein levels through both transcriptional and translational, and proteasomal degradation mechanisms. Therefore, from our findings, we proffer that the C. subternata Vogel extracts, SM6Met and cup of tea, but not the C. genistoides extract, P104, selectively modulate estrogen receptor subtypes levels in a manner that generally supports inhibition of breast cancer proliferation, thereby demonstrating attributes that could be explored as potential therapeutic agents for breast cancer.

Combinatorial treatments of tamoxifen and SM6Met, an extract from Cyclopia subternata Vogel, are superior to either treatment alone in MCF-7 cells

Synergistic drug combinations are not only popular in antibiotic, anti-microbial, immune disease (i.e., AIDS) and viral infection studies, but has also gained traction in the field of cancer research as a multi-targeted approach. It has the potential to lower the doses needed of standard of care (SOC) therapeutic agents, whilst maintaining an effective therapeutic level. Lower dosages could ameliorate the fundamental problems such as drug resistance and metastasis associated with current SOC therapies. In the current study, we show that the combination of SM6Met with (2)-4-hydroxytamoxifen (4-OH-Tam, the active metabolite of tamoxifen) produces a strong synergistic effect in terms of inhibiting MCF7 ER-positive (ER⁺) breast cancer cell proliferation and that a 20 times lower dose of 4-OH-Tam in combination with SM6Met is required to produce the same inhibitory effect on cell proliferation as 4-OH-Tam on its own. Cell cycle analyses of the best combination ratios of SM6Met and 4-OH-Tam also suggests that the combination results in increased accumulation of cells in the S-phase and in the apoptotic phase. Moreover, the best combination ratio (20:1) of SM6Met with 4-OH-Tam displayed greater anti-metastatic potential in terms of inhibiting ER⁺ breast cancer cell migration, invasion, and colony formation than the SOC therapy alone, suggesting that SM6Met together with 4-OH-Tam could be a viable drug combination for not only delaying resistance and ameliorating the negative side-effects associated with current SOC therapies, like tamoxifen, but could also provide a novel, more affordable therapeutic alternative for treating or preventing ER⁺ breast cancer metastasis.

Chemoprevention of LA7-Induced Mammary Tumor Growth by SM6Met, a Well-Characterized Cyclopia Extract

Breast cancer (BC) is the leading cause of cancer-related deaths in women. Chemoprevention of BC by using plant extracts is gaining attention. SM6Met, a well-characterized extract of Cyclopia subternata with reported selective estrogen receptor subtype activity, has shown tumor suppressive effects in a chemically induced BC model in rats, which is known to be estrogen responsive. However, there is no information on the estrogen sensitivity of the relatively new orthotopic model of LA7 cell-induced mammary tumors. In the present study, the potential chemopreventative and side-effect profile of SM6Met on LA7 cell-induced tumor growth was evaluated, as was the effects of 17β-estradiol and standard-of-care (SOC) endocrine therapies, such as tamoxifen (TAM), letrozole (LET), and fulvestrant (FUL). Tumor growth was observed in the tumor-vehicle control group until day 10 post tumor induction, which declined afterward on days 12-14. SM6Met suppressed tumor growth to the same extent as TAM, while LET, but not FUL, also showed substantial anti-tumor effects. Short-term 17β-estradiol treatment reduced tumor volume on days prior to day 10, whereas tumor promoting effects were observed during long-term treatment, which was especially evident at later time points. Marked elevation in serum markers of liver injury, which was further supported by histological evaluation, was observed in the vehicle-treated tumor control, TAM, LET, and long-term 17β-estradiol treatment groups. Alterations in the lipid profiles were also observed in the 17β-estradiol treatment groups. In contrast, SM6Met did not augment the increase in serum levels of liver injury biomarkers caused by tumor induction and no effect was observed on lipid profiles. In summary, the results from the current study demonstrate the chemopreventative effect of SM6Met on mammary tumor growth, which was comparable to that of TAM, without eliciting the negative side-effects observed with this SOC endocrine therapy. Furthermore, the results of this study also showed some responsiveness of LA7-induced tumors to estrogen and SOC endocrine therapies. Thus, this model may be useful in evaluating potential endocrine therapies for hormone responsive BC.

A comparative characterization of estrogens used in hormone therapy via estrogen receptor (ER)-α and -β

Conventional hormone therapy (HT) containing estrogens such as ethinylestradiol (EE) have been associated with an increased risk of breast cancer and cardiovascular disease resulting in women seeking safer alternatives that are claimed to have fewer health risks. One such alternative gaining popularity, is custom-compounded bioidentical (b)HT formulations containing bioidentical estradiol (bE₂) and estriol (bE₃). However, the preparation of these custom-compounded estrogens is not regulated, and depending on the route of synthesis, steroid mixtures with differing activities may be produced. Thus, an investigation into the activities of estrogens prepared by custom-compounded pharmacies is warranted. The aim of this study was therefore to directly compare the pharmacological properties of bE₂ and bE₃ of unknown purity relative to commercially available, pure E₂, E₃ and estrone (E₁) standards as well as synthetic EE used in conventional HT via the human estrogen receptor (ER)-α and -β. We determined precise equilibrium dissociation constants (K_d or K_i values) and showed that bE₂ and bE₃ display similar binding affinities to the E₂ and E₃ standards, while EE had a higher affinity for ERα, and E₁ a lower affinity for ERβ. Furthermore, all the estrogens display similar agonist efficacies, but not potencies, for transactivation on a minimal ERE-containing promoter via the individual ER subtypes. Although E₂ and E₃ were equally efficacious and potent on the endogenous ERE-containing pS2 promoter in the MCF-7 BUS breast cancer cell line co-expressing ERα and ERβ, E₁ was less efficacious and potent than E₂. This study is the first to demonstrate that the bioidentical estrogens, commercially available estrogen standards and synthetic EE are full agonists for transrepression on both minimal and endogenous NFκB-containing promoters. Moreover, we showed that these estrogens all increase proliferation and anchorage-independent growth of MCF-7 BUS cells to a similar extent, suggesting that custom-compounded bHT may in fact not be a safer alternative to conventional HT. Furthermore, our results showing that E₃ and E₁ are not weak estrogens, and that E₃ does not antagonize the activity of E₂, suggest that the rationale behind the use of E₃ and E₁ in custom-compounded bHT formulations should be readdressed. Taken together, the results indicating that there is mostly no difference between the custom-compounded bioidentical estrogens, commercially available estrogen standards and synthetic EE, at concentrations reflecting serum levels in women using estrogen-containing HT, suggest that there is no clear advantage in choosing bHT above conventional HT.

The phytoestrogenic Cyclopia extract, SM6Met, increases median tumor free survival and reduces tumor mass and volume in chemically induced rat mammary gland carcinogenesis

SM6Met, a phytoestrogenic extract of Cyclopia subternata indigenous to the Western Cape province of South Africa, displays estrogenic attributes with potential for breast cancer chemoprevention. In this study, we report that SM6Met, in the presence of estradiol, induces a significant cell cycle G0/G1 phase arrest similar to the selective estrogen receptor modulator, tamoxifen. Furthermore, as a proof of concept, in the N-Methyl-N-nitrosourea induced rat mammary gland carcinogenesis model, SM6Met increases tumor latency by 7days and median tumor free survival by 42 days, while decreasing palpable tumor frequency by 32%, tumor mass by 40%, and tumor volume by 53%. Therefore, the current study provides proof of concept that SM6Met has definite potential as a chemopreventative agent against the development and progression of breast cancer.

Glyceollins and dehydroglyceollins isolated from soybean act as SERMs and ER subtype-selective phytoestrogens

Seven prenylated 6a-hydroxy-pterocapans and five prenylated 6a,11a-pterocarpenes with different kinds of prenylation were purified from an ethanolic extract of fungus-treated soybean sprouts. The activity of these compounds toward both human estrogen receptors (hERα and hERβ) was determined in a yeast bioassay and the activity toward hERα was additionally tested in an U2-OS based hERα CALUX bioassay. In the yeast bioassay, compounds with chain prenylation showed in general an agonistic mode of action toward hERα, whereas furan and pyran prenylation led to an antagonistic mode of action. Five of these antagonistic compounds had an agonistic mode of action in the U2-OS based hERα CALUX bioassay, implying that these compounds can act as SERMs. The yeast bioassay also identified 8 ER subtype-selective compounds, with either an antagonistic mode of action or no response toward hERα and an agonistic mode of action toward hERβ. The ER subtype-selective compounds were characterized by 6a-hydroxy-pterocarpan or 6a,11a-pterocarpene backbone structure. It is suggested that either the extra D-ring or the increase in length to 12-13.5Å of these compounds is responsible for an agonistic mode of action toward hERβ and, thereby, inducing ER subtype-selective behavior.

Non-clinical toxicity studies on bioactive compounds within the framework of nutritional and health claims

The growing presence of products on the market with added value in terms of health makes essential their regulation and harmonization in critical aspects such as safety. The toxicology applied to the bioactive compounds should demonstrate the absence of toxic effects at doses advised for consumption, as well as evaluate the potential toxic effects in the assumption that the products are used in quantities superior to those recommended. The specific strategy should be defined case by case; therefore, prior to any toxicological development, it is essential to study all the information regarding the bioactive compounds (BACs) characterization, nutridynamics and nutrikinetics, that is available. In this guideline, a general strategy to be applied in the development of BACs is proposed. It includes a first in vitro phase to discard genotoxicity and endocrine effects and a second in vivo phase with different possibilities regarding the duration and the extension of the studies.

Divide and Conquer May Not Be the Optimal Approach to Retain the Desirable Estrogenic Attributes of the Cyclopia Nutraceutical Extract, SM6Met

The genus Cyclopia, an indigenous South African fynbos plant used to prepare honeybush tea, contains phytoestrogenic compounds. An extract from C. subternata, SM6Met, displays three desirable estrogenic attributes for future development of a phytoestrogenic nutraceutical, namely, ERα antagonism, ERβ agonism, and also antagonism of E₂-induced breast cancer cell proliferation. Activity-guided fractionation of SM6Met was used in an attempt to isolate and identify compounds conferring the desirable estrogenic profile to SM6Met. Initial liquid-liquid fractionation of SM6Met yielded a polar fraction (PF) and a non-polar fraction (NPF), with the desirable estrogenic attributes retained in the NPF. Subsequent high performance counter-current chromatography (HPCCC) fractionation of the NPF yielded three fractions (F1-F3). Interestingly, the fractions revealed separation of the previously demonstrated positive estrogenic attributes of the NPF into separate fractions, with F1 and F2 acting as ERα antagonists, only F2 inducing antagonism of E₂-induced breast cancer cell proliferation and only F3 retaining robust ERβ agonist activity. In terms of major polyphenols, quantitative HPLC and liquid chromatography tandem mass spectrometry (LC-MS/MS) indicated that HPCCC fractionation resulted in a divergence of polyphenolic classes, with F1 emerging as the dihydrochalcone-rich fraction and F2 as the flavanone- and benzophenone-rich fraction, while the xanthones, flavones and phenolic acids were retained in F3. F3 was re-engineered into F3R by reassembling the major polyphenols identified in the fraction. F3R could, however, not replicate the effect of F3. In conclusion, although activity-guided fractionation results suggest that retention of all the desirable estrogenic attributes of the original SM6Met in one fraction is not an attainable goal, fractionation is a useful tool to enhance specific desirable estrogenic attributes.

Effects of nemorosone, isolated from the plant Clusia rosea, on the cell cycle and gene expression in MCF-7 BUS breast cancer cell lines

BACKGROUND

Breast cancer is the cause of considerable morbidity and mortality in women. While estrogen receptor antagonists have been widely used in breast cancer treatment, patients have increasingly shown resistance to these agents and the identification of novel targeted therapies is therefore required. Nemorosone is the major constituent of the floral resin from Clusia rosea and belongs to the class of polycyclic polyisoprenylated benzophenones of the acylphloroglucinol group. The cytotoxicity of nemorosone in human cancer cell lines has been reported in recent years and has been related to estrogen receptors in breast cancer cells.

METHODS

Changes induced by nemorosone in the cell cycle and gene expression of the MCF-7 BUS (estrogen-dependent) breast cancer cell line were analyzed using flow cytometry and the RT(2) Profiler PCR array, respectively.

RESULTS

In comparison to breast cancer cells without treatment, nemorosone induced discrete cell cycle arrest in the G1 phase and significant depletion in the G2 phase. Moreover, the compound altered the expression of 19 genes related to different pathways, especially the cell cycle, apoptosis and hormone receptors.

CONCLUSION

These promising results justify further studies to clarify mechanisms of action of nemorosone, in view of evaluate the possible use of this benzophenone as adjuvant in the treatment of breast cancer.