ACTA1 and atrial fibrillation: In the present study we demonstrate that SP02SP26-ABD: (1) binds specifically to PDGFRβ, and not to PDGFRα, without activating PDGFRβ; (2) shows cross-species binding with similar nM affinity for human, mouse and rat PDGFRβ, facilitating clinical translation of preclinical findings; (3) is taken up by PDGFRβ-positive cells, which is important for intracellular drug delivery as showcased with SP02SP26-ABD-AF in vitro; (4) binds to human and murine fibrotic livers, and co-localizes to areas with increased α-SMA staining (marker for activated myofibroblasts) and collagen deposition.