Antagonistic activity of acolbifene, fulvestrant, tamoxifen, and raloxifene on cancer-associated genes in the mouse mammary gland.

10583 Background: The efficacy and exceptionally good tolerance of estrogen blockade in the treatment of breast cancer is well recognized. Acolbifene (ACOL) is a novel and unique SERM completely free of estrogen-like activity in both the mammary gland and uterus. To better understand the specificity of ACOL, we have investigated its effect on the expression of a set of genes modulated by estradiol (E2) in the mouse mammary gland. Methods: ACOL, tamoxifen (TAM), raloxifene (RALOX) and fulvestrant (FULV) were administered (0.01 mg/mouse; sc) to ovariectomized (OVX) mice or to OVX mice simultaneously treated with E2 (0.05 µg/mouse; single sc injection). Microarray screening followed by Q_RTPCR was used to identify a reproducible set of E2 responsive genes. Results: From 128 genes significantly modulated by E2, 108 genes were up-regulated and 20 were down-regulated. Forty-nine of these genes were associated with tumorigenesis while 22 are known to be associated with breast cancer. This set of 49 genes were used to determine the specificity of ACOL compared to another pure antiestrogen in the mammary gland and uterus, namely FULV, as well as to the mixed estrogen antagonists/agonists TAM and RALOX, in their ability to block the effect of E2. Efficacy of reversal of the effect of E2 was 94%, 63%, 45% and 90% for ACOL, FULV, TAM and RALOX, respectively. The overlap between all treatments was 30.6% (15/49). ACOL reversed the effect of E2 on 42 of the 49 (85.7%) cancer-related genes. Between the genes up-regulated by E2 and reversed by ACOL, seven are considered as prognostic markers in breast cancer, namely Fgfr3, Fos12, Junb, Jdp2, Gdf15, Greb1 and Tgm2. On the other hand, two genes down‑regulated by E2, namely Foxa1 and Fgfr2, were restored by ACOL. Conclusions: Taken together, these data offer new information for a better understanding of the previously demonstrated potent tumoricidal action of ACOL in human breast cancer xenografts. The data also suggest, under the tested conditions, superiority of ACOL over TAM and the other compounds to reverse the effect of E2 on specific gene expression, thus supporting the interest of this new 3rd generation SERM for the hormonal therapy and prevention of breast cancer.

Activation of Central, But Not Peripheral, Estrogen Receptors Is Necessary for Estradiol’s Anorexigenic Effect in Ovariectomized Rats

Estradiol appears to exert its anorexigenic effect by activating nuclear estrogen receptors (ERs), which are expressed widely in peripheral tissues and in the brain. Here, we used ICI-182,780 (ICI), a pure antiestrogen with limited ability to cross the blood-brain barrier, to assess the relative involvement of peripheral vs. central ERs to estradiol’s anorexigenic effect. Food intake was measured after peripheral (sc) administration of ICI or vehicle in ovariectomized rats treated with acute injections of estradiol benzoate and sesame oil over a 2-wk period. Uterine weight was assessed as a biological assay of peripheral ER activation. In a second experiment, food intake was measured after central (lateral ventricular) administration of ICI or vehicle in ovariectomized rats receiving acute injections of estradiol benzoate and oil over a period of 10 d. In order to assess the possible spread of ICI from the brain to the periphery, vaginal cytology samples were examined as a biological assay of peripheral ER activation. Peripherally administered ICI failed to attenuate estradiol’s anorexigenic effect at a dose that was sufficient to block estradiol’s uterotrophic effect. This suggests that peripheral activation of ERs is not necessary for estradiol’s anorexigenic effect. Although central infusion of 4 nm ICI blocked estradiol’s anorexigenic effect, it did not attenuate estradiol’s ability to increase the presence of cornified cells in vaginal cytology samples, suggesting that ICI did not leak into the periphery. We conclude that activation of central, but not peripheral, ERs is necessary for estradiol’s anorexigenic effect.

Activity of Fulvestrant 500 mg Versus Anastrozole 1 mg As First-Line Treatment for Advanced Breast Cancer: Results From the FIRST Study

Purpose To compare the clinical activity of the pure antiestrogen fulvestrant at 500 mg/mo (double the approved dose) with the aromatase inhibitor anastrozole as first-line endocrine therapy for advanced hormone receptor–positive breast cancer in postmenopausal women. Patients and Methods FIRST (Fulvestrant First-Line Study Comparing Endocrine Treatments) is a phase II, randomized, open-label, multicenter study of a fulvestrant high-dose (HD) regimen (500 mg/mo plus 500 mg on day 14 of month 1) versus anastrozole (1 mg/d). The primary efficacy end point was clinical benefit rate (CBR), defined as the proportion of patients experiencing an objective response (OR) or stable disease for ≥ 24 weeks. The primary analysis was performed 6 months after the last patient was randomly assigned. Results CBR was similar for fulvestrant HD (n = 102) and anastrozole (n = 103), 72.5% v 67.0%, respectively (odds ratio, 1.30; 95% CI, 0.72 to 2.38; P = .386). Objective response rate (ORR) was also similar between treatments: fulvestrant HD, 36.0%; anastrozole, 35.5%. Time to progression (TTP) was significantly longer for fulvestrant versus anastrozole (median TTP not reached for fulvestrant HD v 12.5 months for anastrozole; hazard ratio, 0.63; 95% CI, 0.39 to 1.00; P = .0496). Duration of OR and CB also numerically favored fulvestrant HD. Both treatments were well tolerated, with no significant differences in the incidence of prespecified adverse events. Conclusion First-line fulvestrant HD was at least as effective as anastrozole for CBR and ORR and was associated with significantly longer TTP. Fulvestrant HD was generally well tolerated, with a safety profile similar to that of anastrozole.

Peripheral estrogen receptor-α selectively modulates the waveform of GH secretory bursts in healthy women

Estradiol (E2) drives growth hormone (GH) secretion via estrogen receptors (ER) located in the hypothalamus and pituitary gland. ERα is expressed in GH releasing hormone (GHRH) neurons and GH-secreting cells (somatotropes). Moreover, estrogen regulates receptors for somatostatin, GHR peptide (GHRP, ghrelin), and GH itself, while potentiating signaling by IGF-I. Given this complex network, one cannot a priori predict the selective roles of hypothalamic compared with pituitary ER pathways. To make such a distinction, we introduce an investigative model comprising 1) specific ERα blockade with a pure antiestrogen, fulvestrant, that does not penetrate the blood-brain barrier; 2) graded transdermal E2 administration, which doubles GH concentrations in postmenopausal women; 3) stimulation of fasting GH secretion by pairs of GHRH, GHRP-2 (a ghrelin analog), and l-arginine (to putatively limit somatostatin outflow); and 4) implementation of a flexible waveform deconvolution model to estimate the shape of secretory bursts independently of their size. The combined strategy unveiled that 1) E2 prolongs GH secretory bursts via fulvestrant-antagonizable mechanisms; 2) fulvestrant extends GHRH/GHRP-2-stimulated secretory bursts; 3) l-arginine/GHRP-2 stimulation lengthens GH secretory bursts whether or not E2 is present; 4) E2 limits the capability of l-arginine/GHRP-2 to expand GH secretory bursts, and fulvestrant does not inhibit this effect; and 5) E2 and/or fulvestrant do not alter the time evolution of l-arginine/GHRH-induced GH secretory bursts. The collective data indicate that peripheral ERα-dependent mechanisms determine the shape (waveform) of in vivo GH secretory bursts and that such mechanisms operate with secretagogue selectivity.