Orthotopic MDA-MB-231 breast tumor xenografts

All animal experiments were approved by the Johns Hopkins Institutional Animal Care and Use Committee. Approximately, 2×10⁶ MDA-MB-231 breast cancer cells were orthotopically implanted into the fourth right mammary fat pad of 6 weeks old female athymic nu/nu mice (NCI) as previously described by us (27, 28). Tumor growth was monitored with standard calipers. Tumors reached their experimental size of approximately 600 mm³ within 8 weeks of inoculation. Three mice with one MDA-MB-231 tumor each were assessed with in vivo CEST-MRI as described below.