CXCR4 and cancer: The CXC chemokine receptor type 4 (CXCR4) is a rhodopsin-like GPCR with seven transmembrane (TM) helices, which can trigger a series of signal pathways upon binding its agonist ligands [3], leading to many physiological functions including hematopoiesis [4], embryogenesis [5], and vascularization [6] and being implicated in human diseases such as cancer growth and metastasis [7–9] and HIV-1 infection [10].