Phytoestrogenic extracts of Cyclopia modulate molecular targets involved in the prevention and treatment of breast cancer

Visser, Jacobus Albertus Koch (2014-04)

Thesis (PhD)--Stellenbosch University, 2014.

Thesis

ENGLISH ABSTRACT: Phytoestrogen containing extracts of Cyclopia, an indigenous South African fynbos plant used to prepare honeybush tea, may serve as a source of new estrogen analogues. It would be of great benefit if these new analogues would not only prevent the development and progression of breast cancer which, globally, is responsible for the highest number of cancer associated deaths among females, but also have a reduced side-effect profile when compared to current treatments and, in addition, also alleviate menopause associated symptoms. In this study three extracts, P104, SM6Met, and cup-of-tea, from two species of Cyclopia, C. genistoides and C. subternata, were evaluated for their potential to modulate molecular targets involved in prevention and treatment of breast cancer. We show that the phytoestrogenic extracts of Cyclopia antagonise estrogen-induced cell proliferation both in vitro as well as in vivo. Furthermore, our study presents various molecular mechanisms whereby the Cyclopia extracts may be eliciting this effect. Importantly, we show, for the first time, that the Cyclopia extracts behave as ERα antagonists and ERβ agonists which, with respect to the known role of the ER subtypes in breast cancer, where the ERα subtype is associated with the stimulation of cell proliferation and the occurrence of breast cancer, while ERβ ameliorates the action of ERα in breast cancer and could act as an inhibitor of breast cancer development, may be beneficial for the prevention or treatment of breast cancer. In addition, we also show that the extracts of Cyclopia behave as selective estrogen receptor degraders by down-regulating ERα protein levels while stabilising ERβ protein levels, which not only provides a possible molecular explanation for the observed ERα antagonism and ERβ agonism, but, in addition, may be beneficial as higher ERα levels are associated with malignant breast cancer tumours, while higher ERβ levels are associated with benign tumours. Furthermore, we show that the Cyclopia extracts affect the nuclear localization and distribution of both ER subtypes in a manner that provides an additional molecular explanation for the observed ERα antagonism and ERβ agonism. Investigation of the molecular processes involved in the promotion and progression of breast cancer, such as the distribution of cells between the phases of the cell cycle, cancer cell invasion, and the regulation of genes governing these processes provides evidence that the Cyclopia extracts are not as proliferative as estrogen. In addition, Cyclopia extracts display anti-inflammatory properties, which may be beneficial as inflammation is an enabling characteristic in cancer development and progression. Furthermore, this study, for the first time, shows that the phytoestrogenic extracts of Cyclopia are absorbed, are not toxic, and display biological ERα antagonist activity in vivo by retarding uterine growth. Thus, we propose that the Cyclopia extracts act as selective estrogen receptor subtype modulators with potential to be developed as a nutraceutical for the treatment or prevention of breast cancer.

AFRIKAANSE OPSOMMING: Fitoëstrogeen-bevattende ekstrakte van Cyclopia, ‘n inheemse Suid Afrikaanse fynbosplant wat gebruik word vir die voorbereiding van heuningbostee, mag as ‘n bron van nuwe estrogeen-analoë dien. Dit sal baie voordelig wees indien hierdie nuwe analoë nie net die ontwikkeling en progressie van borskanker sal voorkom nie, aangesien borskanker wêreldwyd verantwoordelik is vir die grootste getal kankerverwante sterftes onder vroue, maar ook ‘n verminderde newe-effek profiel vertoon in vergelyking met huidige behandelings en ook, boonop, simptome wat met menopouse geassosieer word, sal verlig. In hierdie studie is drie ekstrakte, P104, SM6Met, en cup-of-tea, vanaf twee spesies van Cyclopia, C. genistoides en C. subternata, geëvalueer vir hul potensiaal om die molekulêre teikens betrokke by die voorkoming en behandeling van borskanker te moduleer. Ons wys dat die fitoëstrogeniese ekstrakte van Cyclopia antagoniseer estrogeen-geïnduseerde selproliferasie beide in vitro as ook in vivo. Verder bied ons studie ook verkskeie molekulêre meganismes aan oor hoe die Cyclopia ekstrakte hierdie effek mag ontlok. ‘n Belangrike bevinding is dat ons vir die eerste keer wys dat die Cyclopia ekstrakte hulself as ERα -antagoniste en ERβ-agoniste gedra wat, met betrekking tot die erkende rol van die ER-subtipes in borskanker, waar die ERα-subtipe geassosieer word met die stimulasie van selproliferasie en die gebeurtenis van borskanker, terwyl ERβ die aksie van ERα onderdruk en as ‘n inhibeerder van borskankerontwikkeling kan dien, voordelig mag wees vir die voorkoming of behandeling van borskanker. Ons wys boonop ook dat die ekstrakte van Cyclopia hulself soos selektiewe estrogeen- reseptor-degradeerders gedra deurdat hul ERα-proteïnvlakke verlaag terwyl hul ERβ-proteïnvlakke stabiliseer. Dit verksaf nie net ‘n moontlike molekulêre verduideliking vir die waargeneemde ERα-antagonisme en ERβ-agonisme nie, maar mag ook voordelig wees in borskanker aangesien hoër ERα-vlakke geasosieer word met kwaadaardige borskankertumors en hoër ERβ-vlakke met nie-kwaadaardige tumors. Verder wys ons dat die Cyclopia ekstrakte die lokalisering en verspreiding van beide ER-subtipes in die selkern op so ‘n wyse beïnvloed dat dit ‘n addisionele molekulêre verduideliking bied vir die ERα-antagonisme en ERβ-agonisme wat waargeneem is. Verdere ondersoek van die molekulêre prosesse betrokke by die promosie en progressie van borskanker, soos die verspreiding van selle tussen die fases van die selsiklus, die beweging van kankerselle na omliggende weefsels, en die regulering van gene wat hierdie prosesse beheer, verskaf bewyse dat die Cyclopia-ekstrakte nie so proliferatief is soos estrogeen nie. Die ekstrakte van Cyclopia vertoon boonop ook anti-inflamatoriese eienskappe, wat voordelig mag wees aangesien inflammasie ‘n bydraende eienskap in kankerontwikkeling en -progressie is. Verder wys hierdie studie vir die eerste keer dat die fitoëstrogeniese ekstrakte van Cyclopia geabsorbeer word, nie toksies is nie, en dat hulle biologiese ERα-antagonis aktiwiteit vertoon deurdat hulle uterus-groei vertraag in vivo. Dus stel ons voor dat die Cyclopia-ekstrakte optree soos selektiewe-estrogeen-reseptor-subtipe-moduleerders met die potensiaal om ontwikkel te word as ‘n nutraseutiese middel vir die behandeling of voorkoming van borskanker.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/86718
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