PET imaging was performed four weeks after tumor inoculation with a method described previously.20 (link), 22 (link) Briefly, each mouse was given 3.7 MBq of 64Cu-DOTA-Pab-IR800 or 64Cu-DOTA-IgG via the tail vein injection. The PET images were acquired at 4, 24, and 48 h post injection using a small animal PET/CT system (GE eXplore Vista) while the mice were under isoflurane-induced anesthesia. The regions of interest (ROIs) were calculated to percentage injected dose per gram tissue (%ID/g) based on the assumption of 1g/mL tissue density. Biodistribution study was performed in nude mice bearing NCI/ADR-RES tumors. Mice were given intravenously approximate 5.5 MBq of 64Cu-DOTA-Pab-IR800 and 64Cu-DOTA-IgG, and were sacrificed 48h post injection. Tissues and organs of interest were excised and weighed. Radioactivity was measured by a γ-counter (PerkinElmer) and the tracer uptake was calculated as %ID/g.