18F-labelling of a cyclic pentapeptide inhibitor of the chemokine receptor CXCR4

The chemokine receptor CXCR4 is overexpressed in a variety of cancers including breast, prostate and lung cancer. Expression is also associated with invasion and metastasis. The possibility to image and quantify CXCR4 expression in vivo would be a valuable tool in the clinic to aid treatment regimens and to potentially understand the underlying biology of metastasis. Herein we describe the synthesis and the radiolabelling of an 18F-labelled cyclic pentapeptide, [18F]CCIC-0007 designed to bind to the extracellular domains of CXCR4. Radiolabelling was performed via conjugation of [18F]fluorobenzaldehyde with an aminooxy functionalised cyclopentapeptide. Typically, starting with 1.10 GBq (30 mCi) of aqueous [18F]fluoride, 105 MBq (2.85 mCi) of the formulated tracer was obtained within 2.5 h (23 ± 8% dc rcy, 8% EOS yield). Tissue pharmacokinetic studies in mice demonstrated rapid blood clearance, together with biliary and renal elimination.