CXCR4 and glioma: Plerixafor, another small molecule CXCR4 antagonist, binds to the three acidic residues of the CXCR4 ligand-binding pocket (Fricker, 2008) and impairs the proliferation of glioma cells by inhibiting the invasion of CXCR4/CXCR7-expressing GSCs in vitro (Mercurio et al., 2016; Hira et al., 2017).