Purpose: Antiestrogens are used to treat estrogen receptor (ER)-α-positive breast cancers and cause a p27-dependent G 1 arrest. Estrogen-bound ER recruits Src to mediate proteolysis of p27 and drive cell proliferation. Here, we tested the antitumor efficacy of combined Src and aromatase inhibition for ER-positive breast cancer. Experimental Design: Antiproliferative effects of the aromatase inhibitor, anastrozole, and Src inhibitor, AZD0530, alone or in combination were tested in vitro and in vivo on aromatase-transfected MCF-7Arom5 xenografts. Xenografts were analyzed by immunohistochemistry and proteomic analysis to identify potential biomarkers of drug response and resistance. Results: AZD0530 and anastrozole together increased p27 and caused greater G 1 cell cycle arrest than either drug alone. AZD0530 monotherapy initially retarded xenograft growth in vivo, but drug resistance rapidly emerged. Combined anastrozole/AZD0530 reduced drug resistance and showed greater antitumor efficacy in vivo with greater Src and epidermal growth factor receptor inhibition and a greater increase in p27 and reduction of Ki-67 than either drug alone, supporting further evaluation of these putative predictors of response to combined Src/aromatase inhibition in vivo. Anastrozole alone stimulated Src activity both in vitro and in vivo. AZD0530-resistant tumors showed activation of bypass pathways including MEK and phosphatidylinositol 3-kinase (PI3K)/Akt/mammalian target of rapamycin, raising the possibility that MEK, mammalian target of rapamycin (mTOR), or PI3K inhibitors may augment Src inhibitor efficacy. Conclusions: These data support clinical investigation of anastrozole-AZD0530 therapy for postmenopausal ER-positive breast cancer. Loss of p27 and increased Ki-67 may predict response and further clinical studies should evaluate for activation of bypass pathways including MEK and PI3K pathways during Src inhibitor therapy.Estrogen is a potent mitogen and a survival factor for many estrogen receptor (ER)-α-positive human breast cancer lines and appears to play a role in the genesis and progression of a majority of breast cancers. ER blockade and drug-mediated estrogen deprivation are used in ER-positive breast cancer both as adjuvant treatments to prevent recurrence after initial breast surgery and for metastatic disease (1). Aromatase inhibitors such as anastrozole and letrozole have significantly improved the efficacy of endocrine therapy (2). Adrenal androstenedione and testosterone undergo peripheral conversion to estrogen by aromatase. Aromatase inhibitors block the last biosynthetic step in estrogen production (2) and cause >90% reduction in circulating estrogens in postmenopausal women (1). Anastrozole was the first aromatase inhibitor tested in large clinical trials in both metastatic and adjuvant settings and showed superior antitumor activity compared with tamoxifen (1, 2).Oncogenic activation of the Src tyrosine kinase regulates proliferation, motility, and survival in many human cancers (3). We observed t...
Antiestrogen therapies arrest susceptible estrogen receptor (ER)-positive breast cancers by increasing p27. Since Src phosphorylates p27 to promote p27 proteolysis, Src activation observed in up to 40% of ER-positive cancers may contribute to antiestrogen resistance. In this article, we show that treatment with the Src-inhibitor saracatinib (AZD0530) together with ER-blocking drugs increased breast cancer cell cycle arrest via p27. Saracatinib and fulvestrant together more effectively increased p27, reduced Ki67, and impaired MDA-MB-361 xenograft tumor growth in vivo than either of the drugs alone. In contrast, saracatinib monotherapy rapidly gave rise to drug resistance. Since combined ER and Src inhibition delays development of resistance in vivo, these data support further clinical investigation of saracatinib in combination with fulvestrant for women with ER-positive breast cancer. Proteomic analysis revealed striking bypass activation of the mTOR pathway in saracatinib-resistant tumors. mTORC1 activation also arose following long-term culture of ER-positive breast cancer lines in the presence of saracatinib. These data indicate the utility of proteomic analysis of drug-resistant tumors to identify potential means of drug resistance. The use of mTOR kinase inhibitors with saracatinib may subvert drug resistance and prove to be more effective than saracatinib alone.
Breast cancers are routinely assessed for estrogen receptor status using immunohistochemical assays to assist in patient prognosis and clinical management. Specific assays vary between laboratories, and several antibodies have been validated and recommended for clinical use. As numerous factors can influence assay performance, many laboratories have opted for ready-to-use assays using automated stainers to improve reproducibility and consistency. Three commonly used autostainer vendors-Dako, Leica, and Ventana-all offer such estrogen receptor assays; however, they have never been directly compared. Here, we present a systematic comparison of three platform-specific estrogen receptor ready-to-use assays using a retrospective, tamoxifen-treated, breast cancer cohort from patients who were treated in Calgary, Alberta, Canada from 1985 to 2000. We found all assays showed good intra-observer agreement. Inter-observer pathological scoring showed some variability: Ventana had the strongest agreement followed closely by Dako, whereas Leica only showed substantial agreement. We also analyzed each estrogen receptor assay with respect to 5-year disease-free survival, and found that all performed similarly in univariate and multivariate models. Determination of measures of test performance found that the Leica assay had a lower negative predictive value than Dako or Ventana, compared with the original ligand-binding assay, while other measures-sensitivity, specificity, positive predictive value, and accuracywere comparable between the three ready-to-use assays. When comparing against disease-free survival, the difference in negative predictive value between the vendor assays were not as extreme, but Dako and Ventana still performed slightly better than Leica. Despite some discordance, we found that all ready-to-use assays were comparable with or superior to the ligand-binding assay, endorsing their continued use. Our analysis also allowed for exploration of estrogen receptor-negative, progesterone receptor-positive cases, and we discovered that this phenotype was not consistent across the assays, suggesting this might be an artifact. Endocrine therapy is standard treatment for hormone receptor-positive breast cancers that can improve patient survival. 1-3 Estrogen receptor and progesterone receptor analysis is routinely performed by immunohistochemical assays on breast cancer specimens to classify hormone receptor status and determine patient prognosis and management. [1][2][3][4] Eventually, immunohistochemical-based testing replaced the ligand-binding assay as the standard method for determining hormone receptor status. 5 The switch from ligand-binding assay to immunohistochemistry did not occur at a specific time point, and varied by location and laboratories between the mid-90s and early 2000s. Although estrogen and progesterone receptor are both routinely evaluated, patient management decisions are typically made on the basis of estrogen receptor results alone as the role of progesterone receptor in breast cancer patie...
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