Antiprogestin-induced regression of experimental breast carcinomas transplanted in mouse brains.

ROJAS P; DE LA FUENTE V; BOLADO J; VANZULLI S ; LANARI C

San Diego

Congreso; Advances in Breast Cancer Research: Genetics, Biology, and Clinical Applications; 2009

AACR

Metastatic disease represents a challenging issue in breast cancer treatment being lymph nodes, brain and bone, the preferential organ sites for breast cancer metastasis in humans. In mice, most of the experimental models available metastasize in lung and occasionally in lymph nodes. We have developed a murine model of breast cancer progression in which ductal carcinomas transit through different stages of hormone responsiveness retaining the expression of high levels of estrogen and progesterone receptors (PR). Interestingly, tumors implanted sc metastasize in lymph nodes and lungs. We have reported previously that these tumors with higher levels of PR isoform A (PR-A) than isoform B, and their metastasis may experience complete regression after treatment with estrogens or antiprogestins. The aim of this study was to evaluate the effect of the antiprogestin RU-486 on tumors implanted in the brains of BALB/c female mice. C4-HI tumors were transplanted by trocar into the brains of adult BALB/c female mice (n=10/group). Mice were operated under deeply anesthesia (ketamine and xylazine). Briefly, one small drill hole was performed in the mouse skull, at coordinates A −1.94, L -1.2 (left hemisphere), in accordance with the atlas of Paxinos and Franklin (Paxinos and Franklin, 2001. The mouse brain in stereotaxic coordinates, 2nd ed. Academic Press, San Diego). Tumor pieces (2 mm2) were introduced, using a trocar, between the skull and the dorsal cortex. Holes were filled in with dental acrylic, and boundary skull covered with the same material. RU-486 was administered as sc silastic pellets (5mg) implanted the same day as the tumors (RU-0) or 10 days later (RU-10). Untreated mice remained as controls. Animals were perfused under anesthesia, euthanized and brains removed 20 days after tumor implantation. Only tumors of the control group had macroscopically visible tumors. RU-486-treated mice showed almost no visible tumors. C4-HI tumors growing in the brain were poorly differentiated ductal carcinomas with solid nests and small cribiform areas. No tumors were registered in RU-0 treated mice while RU10 mice showed small tumors with pathological marked response evidenced by scanty remaining cancer cells within an increased fibrous stroma. An increased apoptotic index and a decreased mitotic index was observed in RU10-treated mice (p<0.0001) as compared with the control mice. All quantifications were performed in 20 (100X) fields/section. Ki67 immunostaining, a proliferation marker, confirmed the decrease in mitosis observed in treated tumors and the increase in activated caspase-9 immunostaining suggests the involvement of the instrinic apoptotic pathway in antiprogestin-induced inhibition of tumor growth. In conclusion, our studies support the excellent effects of antiprogestins inducing the regression of tumors which have high levels of PR-A, even when they are growing in the brain, a site with limited drug delivery due to the hematoencephalic barrier. This model may be a useful tool to evaluate therapeutic options in mammary tumors growing in brain.