In vivo MMTV-Wnt-1 transgenic mouse study

Animal studies and procedures were approved and monitored by the University of Texas Institutional Animal Care and Use Committee. Female MMTV-Wnt-1 mice on a C57BL/6 background (n=30) were obtained from the Hursting laboratory’s breeding colony and ovariectomized at 12 weeks of age. Following a 1-week recovery period, the mice were randomized to receive one of two diets, both fed ad libitum: a control regimen or a diet-induced obesity (DIO) regimen (n=15/diet group) as previously described (18). Mice were followed for up to 42 weeks and euthanized when tumor diameter was >1.5 cm in any direction or at study termination, whichever occurred first. Mice that died or were euthanized for non-tumor related cause prior to study termination were censored from the survival analysis. Mice were palpated weekly for mammary tumors, and tumors were measured (2 dimensions) with calipers twice weekly after detection. Mice were fasted for 4-6 hours before blood collection. Tumor (when present), distal mammary fat pad, and blood were collected, processed, and stored as previously described (19). Body fat and lean mass were assessed after euthanization using a Lunar PIXImus Dual Emission X-Ray Absorptiometer (GE Medical Systems, Ontario, CA). One DIO mouse and 4 control mice died from nontumor-related causes, were censored at the time of death in body weight and survival analyses, and excluded from serum and tissue analyses.