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Cancer Res. 2007 Oct 15;67(20):9929-36.

Progestin-dependent progression of human breast tumor xenografts: a novel model for evaluating antitumor therapeutics.

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  • 1Dalton Cardiovascular Research Center, Veterinary Pathobiology, and Department of Biomedical Sciences, University of Missouri, Columbia, Missouri 65211, USA.


Recent clinical trials indicate that synthetic progestins may stimulate progression of breast cancer in postmenopausal women, a result that is consistent with studies in chemically-induced breast cancer models in rodents. However, progestin-dependent progression of breast cancer tumor xenografts has not been shown. This study shows that xenografts obtained from BT-474 and T47-D human breast cancer cells without Matrigel in estrogen-supplemented nude mice begin to regress within days after tumor cell inoculation. However, their growth is resumed if animals are supplemented with progesterone. The antiprogestin RU-486 blocks progestin stimulation of growth, indicating involvement of progesterone receptors. Exposure of xenografts to medroxyprogesterone acetate, a synthetic progestin used in postmenopausal hormone replacement therapy and oral contraception, also stimulates growth of regressing xenograft tumors. Tumor progression is dependent on expression of vascular endothelial growth factor (VEGF); growth of progestin-dependent tumors is blocked by inhibiting synthesis of VEGF or VEGF activity using a monoclonal anti-VEGF antibody (2C3) or by treatment with PRIMA-1, a small-molecule compound that reactivates mutant p53 into a functional protein and blocks VEGF production. These results suggest a possible model system for screening potential therapeutic agents for their ability to prevent or inhibit progestin-dependent human breast tumors. Such a model could potentially be used to screen for safer antiprogestins, antiangiogenic agents, or for compounds that reactivate mutant p53 and prevent progestin-dependent progression of breast disease.

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