Mammary Fat Pad Xenograft Mouse Model

All mouse procedures were approved by the University of Illinois at Chicago Animal Care Committee. HCC1806 (1 × 10⁶), MCF7 (3 × 10⁶), MCF7-EMPTY (5 × 10⁶) and MCF7-PSAT1 (5 × 10⁶) cells were injected into the fat pad of the #4 mammary glands of 6 to 8-week-old athymic nude-foxn1_nu female mice (Envigo). Cell suspensions were injected in a volume of 50 μL growth factor-reduced Matrigel (Corning). Estrogen (E2) was administered via silastic capsules implanted subcutaneously as previously described (Molloy et al., 2014 (link)). Even though not required for HCC1806 tumor growth, E2 was provided for all experiments to maintain constant conditions. All tumors were monitored by caliper measurements over time and tumor volume was calculated using the formula ½ (width² x length). Mice were euthanized according to institutional guidelines. Serine and glycine free (TD.160752) and control (TD.110839) diets were purchased from Envigo and diet formulations are listed as reported (Sullivan et al., 2019b (link)). Custom diets were administered five days after surgery and replaced at least weekly.