Relaxin promotes differentiation of human breast cancer cells MCF-7 transplanted into nude mice

Previous studies showed that the hormone relaxin acts on human breast cance r MCF-7 cells in vitro by modulating cell proliferation and promoting cell differentiation toward a duct epithelial phenotype. The present study was d esigned to investigate whether relaxin retains these properties when acting in vivo on MCF-7 cell tumors developed in athymic nude mice. Mice bearing MCF-7 cell tumors transplanted under the mammary fat pad and estrogenized t o sustain tumor growth were treated systemically with relaxin (10 mu g/day) for 19 days. Vehicle-treated mice were used as controls. Thirty days later , the mice were sacrificed and tumor fragments were analyzed by light and e lectron microscopy and immunocytochemistry. Measurements of tumor volume we re recorded weekly for the overall experimental period. The results obtaine d indicate that relaxin treatment promotes differentiation of tumor cells t owards both myoepithelial-like and epithelial-like cells, as judged by the ultrastructural features of the cells and by the increased expression of sm ooth muscle actin and cadherins. Measurements of tumor size and of the numb er of cycling cells show that relaxin, at the doses and times of exposure u sed in this study, does not significantly influence tumor growth and cell p roliferation.