Fig. 2

RP-HPLC chromatograms of [¹¹¹In]In-Ex4, [¹¹¹In]In-MVK-Ex4, [¹¹¹In]In-MV-MVK-Ex4 and [¹¹¹In]In-MVK-MVK-Ex4 at different times after incubation with human plasma. In red, stability given as percentage of intact peptide, while the fraction of the secondary peak (blue) is shown next to the arrow. The reference compound Ex4 shows high plasma stability over 4 h with over 96% Ex4 intact, with a consequent drop to 80% intact radiotracer after 24 h. In contrast, Ex4 derivatives equipped with MVK display only 63–76% intact tracer after 24 h and quickly show the generation of an unidentified secondary peak after 1 h exposure to plasma