In vivo molecular imaging of chemokine receptor CXCR 4 expression in patients with advanced multiple myeloma

CXCR4 is a G-protein-coupled receptor that mediates recruitment of blood cells toward its ligand SDF-1. In cancer, high CXCR4 expression is frequently associated with tumor dissemination andpoor prognosis. We evaluated the novel CXCR4 probe [$^{68}$Ga]Pentixafor for invivo mapping of CXCR4 expression density in mice xenografted with human CXCR4-positive MM cell lines and patients with advanced MM by means of positron emission tomography (PET). [$^{68}$Ga]Pentixafor PET provided images with excellent specificity and contrast. In 10 of 14 patients with advanced MM [$^{68}$Ga]Pentixafor PET/CT scans revealed MM manifestations, whereas only nine of 14 standard [$^{18}$F]fluorodeoxyglucose PET/CT scans were rated visually positive. Assessment of blood counts and standard CD34$^{+}$ flow cytometry did not reveal significant blood count changes associated with tracer application. Based on these highly encouraging data on clinical PET imaging of CXCR4 expression in a cohort of MM patients, we conclude that [$^{68}$Ga]Pentixafor PET opens a broad field for clinical investigations on CXCR4 expression and for CXCR4-directed therapeutic approaches in MM and other diseases