Differential expression of FGF family members in a progestin-dependent BT-474 human breast cancer xenograft model.

Members of the fibroblast growth factor (FGF) family have been associated with tumor progression and angiogenesis, though the mechanism through which they affect the progression of breast cancer remains elusive. We recently showed that progestins increase the production of the potent angiogenic factor VEGF in an in vivo BT-474 human breast cancer cell-derived xenograft model. In this study we sought to determine the effect of progesterone (P) on regulation of specific FGF family members (FGF-2, FGF-4 and FGF-8) in the same model. Using immunohistochemistry we found that treatment with P significantly reduced FGF-2 and FGF-8 levels, while modestly increasing the levels of FGF-4 in tumors collected at the termination of the study or soon after P treatment began. The in vivo observations with FGF-2 were confirmed in cultured BT-474 cells, though the P-mediated reduction in FGF-2 was not blocked by the anti-progestin RU-486, suggesting that classical progesterone receptors (PR) are not involved in FGF-2 down-regulation. Also, P did not affect levels of FGF-2 mRNA in BT-474 cells, indicating that P exerts its effects on FGF-2 post-transcriptionally. Our observations suggest that the in vivo stimulation of BT-474 cell growth by P is associated with down-regulation of FGF-2 and FGF-8. Furthermore, since FGF-4 levels increased during P-treatment, FGF-4 may be required for tumor growth and maintenance and might therefore be a potential therapeutic target through which to suppress P-dependent tumor growth.

Apigenin prevents development of medroxyprogesterone acetate-accelerated 7,12-dimethylbenz(a)anthracene-induced mammary tumors in Sprague-Dawley rats.

The use of progestins as a component of hormone replacement therapy has been linked to an increase in breast cancer risk in postmenopausal women. We have previously shown that medroxyprogesterone acetate (MPA), a commonly administered synthetic progestin, increases production of the potent angiogenic factor vascular endothelial growth factor (VEGF) by tumor cells, leading to the development of new blood vessels and tumor growth. We sought to identify nontoxic chemicals that would inhibit progestin-induced tumorigenesis. We used a recently developed progestin-dependent mammary cancer model in which tumors are induced in Sprague-Dawley rats by 7,12-dimethylbenz(a)anthracene (DMBA) treatment. The flavonoid apigenin, which we previously found to inhibit progestin-dependent VEGF synthesis in human breast cancer cells in vitro, significantly delayed the development of, and decreased the incidence and multiplicity of, MPA-accelerated DMBA-induced mammary tumors in this animal model. Whereas apigenin decreased the occurrence of such tumors, it did not block MPA-induced intraductal and lobular epithelial cell hyperplasia in the mammary tissue. Apigenin blocked MPA-dependent increases in VEGF, and suppressed VEGF receptor-2 (VEGFR-2) but not VEGFR-1 in regions of hyperplasia. No differences were observed in estrogen or progesterone receptor (ER/PR) levels, or the number of estrogen receptor-positive cells, within the mammary gland of MPA-treated animals administered apigenin, MPA-treated animals, and placebo treated animals. However, the number of progesterone receptor-positive cells was reduced in animals treated with MPA or MPA and apigenin compared with those treated with placebo. These findings suggest that apigenin has important chemopreventive properties for those breast cancers that develop in response to progestins.