Recent progress in fluorine-18 labelled peptide radiopharmaceuticals

The application of biologically active peptides labelled with positron-emitting nuclides has emerged as a useful and interesting field in nuclear medicine. Small synthetic receptor-binding peptides are currently the preferred agents over proteins and antibodies for diagnostic imaging of various tumours. Due to the smaller size of peptides, both higher target-to-background ratios and rapid blood clearance can often be achieved with radiolabelled peptides. Hence, short-lived positron emission tomography (PET) isotopes are potential candidates for labelling peptides. Among a number of positron-emitting nuclides, fluorine-18 appears to be the best candidate for labelling bioactive peptides by virtue of its favourable physical and nuclear characteristics. The major disadvantage of labelling peptides with F-18 is the laborious and time-consuming preparation of the F-18 labelling agents. In recent years, various techniques have been developed which allow efficient labelling of peptides with F-18 without affecting their receptor-binding properties. Moreover, the development of a variety of prosthetic groups has facilitated the efficient and site-specific labelling of peptides with F-18. The F-18-labelled peptides hold enormous clinical potential owing to their ability to quantitatively detect and characterise a wide variety of human diseases when using PET. Recently, a number of F-18-labelled bioactive peptides have shown great promise as diagnostic imaging agents. This review presents the recent developments in F-18-labelled biologically active peptides used in PET.