Toremifene–atamestane; alone or in combination: Predictions from the preclinical intratumoral aromatase model

Abstract

Since most breast cancers occur in post-menopausal women and are hormone dependent, we developed a model system that mimics this situation. In this model, tumors of human estrogen receptor ER positive breast cancer cells stably transfected with aromatase (Ac-1) are grown in immune compromised mice. Using this model we have explored a number of therapeutic strategies to maximize the antitumor efficacy of antiestrogens (AEs) and aromatase inhibitors (AIs). This intratumoral aromatase xenograft model has proved accurate in predicting the outcome of several clinical trials. In this current study we compared the effect of an AE toremifene and steroidal AI atamestane, alone or in combination, on growth of hormone dependent human breast cancer. We have also compared toremifene plus atamestane combination with tamoxifen in this study.The growth of Ac-1 cells was inhibited by tamoxifen, toremifene and atamestane in vitro with IC 50 values of 1.8±1.3μM, 1±0.3μM and 60.4±17.2μM, respectively. The combination of toremifene plus atamestane was found to be better than toremifene or atamestane alone in vitro. The effect of this combination was then studied in vivo using Ac-1 xenografts grown in ovariectomized female SCID mice. The mice were injected with toremifene (1000μg/day), atamestane (1000μg/day), tamoxifen (100μg/day), or the combination of toremifene plus atamestane. In this study, our results indicate that the combination of toremifene plus atamestane was as effective as toremifene or tamoxifen alone but may not provide any additional benefit over toremifene alone or tamoxifen alone.

Supplementary Methods from Functional Activation of the Estrogen Receptor-α and Aromatase by the HDAC Inhibitor Entinostat Sensitizes ER-Negative Tumors to Letrozole

“…Tumor xenografts of MDA-MB-231 cells were grown in the mice as previously described with minor modifications (3)(4)(5)(6)(7)(8). Each mouse received subcutaneous (sc) inoculations in one site per flank with 100µL of cell suspension containing ~ 2.5Χ10 7 cells suspension mixed 1:1 with Matrigel (BD Biosciences, San Jose, CA).…”

Preclinical modeling of endocrine response and resistance

“…(C) The effect of anastrozole (200 μg per day) and the combination of anastrozole and fulvestrant (1 mg per day) on the growth of Ac1 breast tumor xenografts in female, ovariectomized, athymic, nude mice. Animals were inoculated with Ac1 cells6 at 1 site on each flank and were supplemented with androstenedione (100 μg per day) for the duration of the experiment, as described previously 7, 8. When tumors reached approximately 300 mm 3 , animals were divided into 3 groups and injected subcutaneously daily with vehicle (control; n = 5), anastrozole (200 μg per day; n = 8), or anastrozole (200 μg per day) plus fulvestrant (1 mg per day; n = 5).…”

“…Unlike tamoxifen, AIs do not have estrogenic activity, which may account for their clinical advantage. To compare the effectiveness of AIs and AEs and to determine the best strategy for their optimal use, we used a mouse model with tumors of human ER‐positive cancer cells stably transfected with the aromatase gene (MCF‐7Ca or Ac1 cells) 4–8. The cells synthesize estrogens, which stimulates the proliferation and development of tumors in ovariectomized, immunosuppressed mice.…”

“…The cells synthesize estrogens, which stimulates the proliferation and development of tumors in ovariectomized, immunosuppressed mice. The tumors are responsive to the antiproliferative effects of both AEs and AIs 4, 7, 8. This model simulates the postmenopausal breast cancer patient, because the source of estrogen after menopause is from nonovarian tissue (including the breast and breast cancers) and is not under regulation by gonadotropins.…”

Synthesis of a Novel Antiestrogen Radioligand (99mTc-TOR-DTPA)

“…3 TOR is a chlorinated synthetic analog of tamoxifen (TAM) and, like TAM, is bound specifically to ER. [4][5][6] It is an orally administered triphenylethylene derivative with antiestrogenic activity that is primarily used in the treatment of patients with metastatic breast cancer. [7][8][9][10][11] The radiolabeled compounds of TAM and TAM derivatives specific to the ERs were prepared in numerous studies.…”