Fluorescence Imaging with mvGlu-AB2 and mvGlu-AB3. 4T1 cells were trypsinized, neutralized with growth media, and counted on the Countess II FL Cell Counter (Invitrogen, Thermo Fisher Scientific). Cells were spun down, media was aspirated, and a solution was made in 1:1 serumfree RPMI media to VitroGel® hydrogel. Mice were injected in the mammary fat pad with 300,000 cells (50 µL) of the cell solution. Tumors grew for around 1.5-2 weeks and the mice were imaged once tumors reached 100 mm3. Dyes (1.2 mg/kg) were dissolved in 0.9% saline (5% DMSO) and injected retroorbitally. Mice were imaged using the CRi Maestro In-Vivo Fluorescence Imaging System at timepoints = 0, 6, 8, 12, 16, and 48 hours. Excitation occurred at 680 nm, and light was collected from 690-850 nm.