Non-Invasive Assessment of Locally Overexpressed Human Adenosine 2A Receptors in the Heart of Transgenic Mice

A(2A) adenosine receptors (A(2A)-AR) have a cardio-protective function upon ischemia and reperfusion, but on the other hand, their stimulation could lead to arrhythmias. Our aim was to investigate the potential use of the PET radiotracer [(18)F]FLUDA to non-invasively determine the A(2A)-AR availability for diagnosis of the A(2A)R status. Therefore, we compared mice with cardiomyocyte-specific overexpression of the human A(2A)-AR (A(2A)-AR TG) with the respective wild type (WT). We determined: (1) the functional impact of the selective A(2A)R ligand FLUDA on the contractile function of atrial mouse samples, (2) the binding parameters (B(max and) K(D)) of [(18)F]FLUDA on mouse and human atrial tissue samples by autoradiographic studies, and (3) investigated the in vivo uptake of the radiotracer by dynamic PET imaging in A(2A)-AR TG and WT. After A(2A)-AR stimulation by the A(2A)-AR agonist CGS 21680 in isolated atrial preparations, antagonistic effects of FLUDA were found in A(2A)-AR-TG animals but not in WT. Radiolabelled [(18)F]FLUDA exhibited a K(D) of 5.9 ± 1.6 nM and a B(max) of 455 ± 78 fmol/mg protein in cardiac samples of A(2A)-AR TG, whereas in WT, as well as in human atrial preparations, only low specific binding was found. Dynamic PET studies revealed a significantly higher initial uptake of [(18)F]FLUDA into the myocardium of A(2A)-AR TG compared to WT. The hA(2A)-AR-specific binding of [(18)F]FLUDA in vivo was verified by pre-administration of the highly affine A(2A)AR-specific antagonist istradefylline. Conclusion: [(18)F]FLUDA is a promising PET probe for the non-invasive assessment of the A(2A)-AR as a marker for pathologies linked to an increased A(2A)-AR density in the heart, as shown in patients with heart failure.