Small-Molecule Fluorescent Ligands for the CXCR4 Chemokine Receptor

[Image: see text] The C–X–C chemokine receptor type 4, or CXCR4, is a chemokine receptor found to promote cancer progression and metastasis of various cancer cell types. To investigate the pharmacology of this receptor, and to further elucidate its role in cancer, novel chemical tools are a necessity. In the present study, using classic medicinal chemistry approaches, small-molecule-based fluorescent probes were designed and synthesized based on previously reported small-molecule antagonists. Here, we report the development of three distinct chemical classes of fluorescent probes that show specific binding to the CXCR4 receptor in a novel fluorescence-based NanoBRET binding assay (pK(D) ranging 6.6–7.1). Due to their retained affinity at CXCR4, we furthermore report their use in competition binding experiments and confocal microscopy to investigate the pharmacology and cellular distribution of this receptor.