Radiolabelled antimicrobial peptides for imaging of infections: a review

At present, it is difficult to distinguish between bacterial infections and sterile inflammatory processes using radiopharmaceuticals. This is so for a variety of reasons, including binding to bacteria with low affinity (e.g. infection) and binding to a specific micro-organism (e.g. radiolabelled monoclonal antibodies or F(ab)2 fragments thereof against micro-organisms). In this review, we propose that radiolabelled antimicrobial peptides should be the first choice in the development of new radiopharmaceuticals for imaging of bacterial infections. Antimicrobial peptides are a recently discovered component of the innate defence system of plants, animals and humans. These peptides, which now number more than 100, with proven microbicidal activity against a variety of micro-organisms, share certain properties, such as their small size and cationic charge. The latter allows them to bind preferentially to a broad spectrum of micro-organisms. We have recently demonstrated that radiolabelled human defensins allow the rapid visualization of bacterial infections in mice. Furthermore, binding of this antimicrobial peptide to bacteria is the major factor contributing to the accumulation of this tracer in bacterial infections. Based on these considerations, we believe that radiolabelled antimicrobial peptides will be an important asset in the imaging of infections in patients.