2.8. Xenograft Mouse Model of Breast Cancers

Female BALB/c-nu/nu mice (8 weeks old) were subjected to subcutaneous transplantation of MDA-MB-231 cells. Cells were cultured under the standard culture condition and treated with vehicle (DMSO), RA (1 μM), and/or PD0325901 (0.3 μM) for 9 days. After detachment by trypsinization, cells were first suspended in PBS, and then mixed in a 1:1 ratio with Matrigel. A 0.1 mL cell suspension containing 2 × 10⁵ cells was subcutaneously injected into the flank of mice. The tumors were allowed to grow for up to 16 weeks. After euthanasia of mice, the developed tumors were excised and weighed. This study was approved by the institutional animal care and use committee of Hokkaido University.