CXCR4 and neoplasm: U87-stb-CXCR4/U87 (targeted-tumor/control tumor) ratios were higher for [111In]G5-X4 compared to [111In]G5-Ctrl in particular at 1 h 1.83 ± 0.13 vs. 1.25 ± 0.22 and 3 h 1.93 ± 0.02 vs. 1.35 ± 0.11, respectively (Figure 3C), suggesting relatively faster uptake of [111In]G5-X4 in CXCR4-expressing tumors.