Fig. 2

Subtype-specific integrin PET imaging in arthritic mice. a, b α5β1 integrin PET using ⁶⁸Ga-Aquibeprin. c, d αvβ3 integrin PET using ⁶⁸Ga-Avebetrin. Each of the images a–d shows two independent scans of the same mouse (different animals are shown in a–d). The arthritic joints are indicated by the arrows. The saturation of the receptor binding capacity by means of co-injection of a large dose (30 nmol) of unlabeled compound (blockade) resulted in a virtually complete reduction of the uptake in arthritic joints for both tracers, confirming the specificity of the PET imaging (a, c). The cross-blockade experiments confirmed the subtype-selectivity of α5β1- and αvβ3 integrin PET: The co-injection of 30 nmol Avebetrin did not substantially affect the α5β1 integrin imaging with ⁶⁸Ga-Aquibeprin, while the minuscule reduction of the signal is likely related to a residual α5β1 activity (39 nM) of Avebetrin (b). The co-injection of 30 nmol Aquibeprin did not affect αvβ3 integrin imaging with ⁶⁸Ga-Avebetrin (d)