Figure 5 reports the chemical structures of NOTA-CP01 (cyclo[Phe-Tyr-Lys-(iPr)-d-Arg-2-Nal-Gly-d-Glu]-Lys-(iPr)-butane-1,4-diamine-bis-t-butyl NOTA-NH2, 5) and LY2510924 6, which is a potent cyclopeptide CXCR4 antagonist developed for the noninvasive visualization of CXCR4 expression in metastatic ESCC. Here, CXCR4 is linked to esophageal squamous cell carcinoma.