PET Imaging of Cardiac Inflammation in Viral Myocarditis Using a DPP4-Targeted Probe

Myocarditis, primarily induced by viral infection, lacks reliable non-invasive imaging for early diagnosis. We developed a novel PET probe, ⁶⁸Ga-DOTA-linagliptin (abbreviated as ⁶⁸Ga-linagliptin), which targets dipeptidyl peptidase-4 (DPP4), to assess its potential in detecting myocarditis. Western blotting and immunostaining showed an elevated cardiac DPP4 expression in mice with Coxsackievirus B3 (CVB3) myocarditis. Single-cell sequencing analysis and cardiac flow cytometry further revealed that the elevated DPP4 expression predominantly originated from infiltrating immune cells, including T cells, dendritic cells, and B cells. Molecular docking and dynamics simulations, together with a DPP4 enzyme inhibition assay, demonstrated high-affinity and direct binding between ⁶⁸Ga-linagliptin and DPP4. ⁶⁸Ga-linagliptin showed favorable pharmacokinetics in vivo and shows significantly higher probe uptake in DPP4-overexpressing cells in vitro and in vivo. PET/CT imaging revealed pronounced ⁶⁸Ga-linagliptin accumulation within the inflamed myocardium of mice with myocarditis, with minimal uptake in control animals. The PET/CT signal distribution closely matched histologically identified inflammatory regions. Moreover, pretreatment with the unlabeled precursor drug linagliptin effectively attenuated inflammation and improved cardiac function in CVB3-infected mice. These findings indicate that ⁶⁸Ga-linagliptin enables sensitive and non-invasive visualization of cardiac inflammation and may offer combined diagnostic and therapeutic benefits for viral myocarditis.