Clinical trials and epidemiological evidence show that combined estrogen (E) and progestin (P) hormone replacement therapy (HRT) increases the risk of breast cancer in postmenopausal women, whereas HRT containing E alone does not. Tumor progression is dependent on angiogenesis, which provides nutrients vital to the developing cancer. We previously showed, both in vitro and in vivo, that natural and synthetic P (including the widely used progestin Medroxyprogesterone acetate, MPA), increase production of vascular endothelial growth factor (VEGF), a potent angiogenic factor, in human breast cancer cells (Cancer Res., 1998, 58:392). This effect is blocked by the anti-progestin RU-486, suggesting involvement of progesterone receptors in the process (Int J Cancer, 2001, 92:469). Evidence from our laboratory using in vivo breast cancer models suggests that P accelerates the development of tumors from latent tumorigenic cells. This leads to the formation of palpable tumors and tumor metastasis, processes that may be attributed to increased production of VEGF (Cancer Res., 2007, 67:9929; Menopause, 2010, 17:1040). RU-486 blocks P-dependent VEGF production and thereby reduces tumor growth; however, the anti-progestin has severe side-effects averting its long-term use. Recently, we have studied less toxic naturally-occurring compounds for their ability to antagonize P-dependent VEGF induction and block tumor progression. In this study, we tested the effects of luteolin, a flavonoid commonly found in fruits and vegetables, on proliferation of BT-474 and T47-D breast cancer cells and their P-dependent production of VEGF. Luteolin treatment (25-100 μM) for 24-48 h reduced in vitro tumor cell viability and induced apoptosis. Interestingly, treatment with a lower concentration of luteolin (10 μM) blocked the production of P-dependent VEGF, indicating that VEGF suppression precedes luteolin-mediated loss of cell viability. Furthermore, luteolin (20 mg/kg, i.p.) suppressed the growth of MPA-dependent T47-D human xenograft tumors in nude mice. Immunohistochemical analysis showed that luteolin reduced P-induced VEGF in tumor sections (p<0.05). These findings strongly suggest that the flavonoid disrupts tumor progression by blocking P-dependent angiogenesis and preventing tumor cell proliferation. Furthermore, luteolin blocked the MPA-induced acquisition of stem cell like properties by breast cancer cells; CD44 expression, ALDH activity and mammosphere formation were all reduced by the flavonoid. We contend therefore that luteolin is a compound with valuable therapeutic properties. Its ability to reduce levels of VEGF, coupled with its capacity to interfere with the acquisition of stem-cell like properties by breast cancer cells, make luteolin a compound with significant clinical potential in the battle against P-dependent human breast cancer.

Supported by a COR award from the College of Veterinary Medicine and in part by funds from generous donors to the Ellis Fischel Cancer Center, University of Missouri.

Citation Format: Hyder SM, Cook MT, Besch-Williford C, Liang Y. Luteolin inhibits progestin-dependent VEGF induction, stem-cell like characteristics, and tumor progression of human breast cancer cells. [abstract]. In: Proceedings of the Thirty-Eighth Annual CTRC-AACR San Antonio Breast Cancer Symposium: 2015 Dec 8-12; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2016;76(4 Suppl):Abstract nr P1-16-06.