Nuclear (PET/SPECT) and optical imaging probes targeting the CXCR4 chemokine receptor

The chemokine receptor CXCR4 has been found to be highly expressed in a wide variety of cancer types, including breast, colorectal, melanoma, nasopharyngeal, oesophageal, osteosarcoma, and non-small-cell lung carcinoma. It has been shown that these elevated expression levels are yet further increased upon metastasis. This receptor therefore represents a highly attractive target which could facilitate the diagnostic imaging of many aggressive cancers. Since 2005, there have been a wide assortment of CXCR4-targeting imaging probes spanning both nuclear (PET/SPECT) and optical imaging modalities. This review highlights a wide variety of pertinent examples from the recent literature, placing special focus on the chemical aspects of probe design.