Potential applications of designed ankyrin repeat proteins in diagnostics and therapeutics

Designed ankyrin repeat proteins (DARPins) represent a novel binding scaffold class with binding characteristics comparable to immunoglobulins. However, in contrast to immunoglobulins, their small molecular size and structural nature may offer advantages, particularly regarding intracellular stability, expression yield and tissue penetration. DARPins against a wide range of targets, including the cancer marker HER2, intracellular MAPKs, cysteine proteases, a caspase and a bacterial drug exporter have been isolated. In principle, these binders allow selective tissue targeting, intracellular pathway modulation, anti-infective applications and open new possibilities for agonistic and antagonistic approaches. In this review, the potential of DARPins as a diagnostic and therapeutic tool is evaluated.