Mouse Model of Metastatic Breast Cancer

All animal work was approved by the OHSU Institutional Animal Use and Care Committee. Immune-compromised 8- to 10-week-old female nu/nu mice were purchased from Jackson Labs. Growth factor-reduced Matrigel (BD) with 400 ng/ml recombinant human bFGF (Millipore) was injected subcutaneously in nu/nu mice. Mice were injected intravenously (i.v.) with 7C1 nanoparticles containing miR-494 or control miR (~1 mg/kg, i.v) 3 or 4 days after plugs were implanted. At day 7 mouse tissues were harvested and processed to obtain RNA or frozen in OCT for tissue staining. 4T1 cells (1 × 10⁴) were implanted into the mammary fat pad #4 of 6- to 8-week-old female Balb/C mice in 100 μl Matrigel. Mice were randomized into groups once the average tumor volume reached 150 mm³, approximately 10 days after implantation. Mice were treated with 7C1 nanoparticles containing miR-494 or control miR (0.7 mg/kg, i.v.). Mice were euthanized ~day 18–20 for analysis of metastatic burden in lungs. Additional experiments were carried out in postpubertal female FVB/n mice (10–12 weeks), which received injections of 50 000 PyMT-derived tumor cells into the right lower mammary fat pad for induction of orthotopic tumors as described in ref. ^{47 (link)}.