Fulvestrant

Fulvestrant is a drug treatment of hormone receptor-positive metastatic breast Y in post-menopausal women with disease progression following anti-estrogen therapy. It is an estrogen receptor antagonist with no agonist effects, which works both by down-regulating and by degrading the estrogen receptor.(In Vitro):Fulvestrant (ICI 182780; ZD 9238; ZM 182780) is a potent and specific inhibitor of estrogen action and demonstrates excellent growth-inhibitory effects in both cell and animal models of human breast cancer. Fulvestrant inhibits MCF-7 human breast cancer cells growth with the IC50 of 0.29 nM. The relative binding affinities of Fulvestrant is 0.89. Fulvestrant has significantly increased antiestrogenic potency and retains pure estrogen antagonist activity. Fulvestrant is the first of a new type of endocrine treatment-an oestrogen receptor (ER) antagonist that downregulates the ER. Treatment of MCF-7 cells with 1 μM ICI 47699 has no effect on the expression of ERα, whereas 100 nM Fulvestrant completely inhibits ERα expression.\n(In Vivo):When administered alone, parenterally (s.c.), to immature female rats Fulvestrant (ICI 182,780) is devoid of uterotropic activity. Complete antagonism of Estrogen action is achieved with a dose of 0.5 mgFulvestrant/kg/day s.c. The effects of Fulvestrant administered p.o. are qualitatively similar but potency is reduced by an order of magnitude compare with s.c. dosing (ED50 0.46 and complete antagonism at 5 mg/kg/day p.o.). The anti-tumor activity of Fulvestrant is first demonstrated in two models of human breast cancer in nude mice. In one of these models, the growth of MCF-7 tumor xenografts is completely blocked for at least 4 weeks following a single injection of Fulvestrant 5 mg. Similar reductions in growth are seen in the Br10 human tumor model. In other studies in nude mice bearing MCF-7 xenografts, Fulvestrant suppresses the growth of established tumours for twice as long and tumor growth is delayed to a greater extent than is observed with ICI 47699 treatment. ICI 47699-resistant breast tumors, which grow in nude mice after long-term treatment with ICI 47699, remain ensitive to growth inhibition by Fulvestrant. These are comparable to the tumor growth inhibition (TGI) observed for ICI 47699 and Fulvestrant, which on day 40 are 86 and 88%, respectively.