EXPRESS: Application of [18F]FLT-PET in Pulmonary Arterial Hypertension (PAH): A clinical study in PAH patients and unaffected BMPR2 mutation carriers
Background: Pulmonary arterial hypertension (PAH) is a heterogeneous group of diseases characterized by vascular cell proliferation leading to pulmonary vascular remodelling and ultimately right heart failure. Previous data indicated that 3'-deoxy-3'-[18F]-fluorothymidine (18FLT) positron emission tomography (PET) scanning was increased in PAH patients, hence providing a possible biomarker for PAH as it reflects vascular cell hyperproliferation in the lung. This study sought to validate 18FLT-PET in an expanded cohort of PAH patients in comparison to matched healthy controls and unaffected bone morphogenetic protein receptor type 2 (BMPR2) mutation carriers. Methods and Results: 18FLT-PET scanning was performed in 21 PAH patients (15 hereditary PAH and 6 idiopathic PAH), 11 unaffected mutation carriers and 9 healthy control subjects. In-depth kinetic analysis indicated that there were no differences in lung 18FLT k3 phosphorylation among PAH patients, unaffected BMPR2 mutation carriers and healthy controls. Lung 18FLT uptake did not correlate with hemodynamic or clinical parameters in PAH patients. Sequential 18FLT-PET scanning in three patients demonstrated uneven regional distribution in 18FLT uptake by 3D parametric mapping of the lung, although this did not follow the clinical course of the patient. Conclusion: We did not detect significantly increased lung 18FLT uptake in PAH patients, nor in the unaffected BMPR2 mutation carriers, as compared to healthy subjects. The conflicting results with our preliminary human 18FLT report may be explained by a small sample size previously and we observed large variation of lung 18FLT signals between patients, challenging the application of 18FLT-PET as a biomarker in the PAH clinic.