Randomised placebo-controlled safety and tolerability trial of FK506 (tacrolimus) for pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a devastating disease characterised by occlusive pulmonary vasculopathy. Activation of bone morphogenetic protein receptor 2 (BMPR2) signalling by FK506 (tacrolimus) reverses occlusive vasculopathy in rodent PAH models. Here, we determined the safety and tolerability of low-level FK506 therapy in stable PAH patients. We performed a randomised, double-blind, placebo-controlled, 16-week, single-centre, phase IIa trial in PAH patients with New York Heart Association functional class II/III symptoms using three FK506 target levels (<2, 2-3 and 3-5 ng mL-1). 23 patients were randomised and 20 patients completed the trial. FK506 was generally well tolerated, with nausea/diarrhoea being the most commonly reported adverse event and no observation of line infections in patients on intravenous prostacyclin therapy. PAH patients had significantly lower BMPR2 expression in peripheral blood mononuclear cells versus healthy controls (n=13; p=0.005), which improved after FK506 treatment. While we observed that some patients responded with a pronounced increase in BMPR2 expression as well as improvement in 6-min walk distance, and serological and echocardiographic parameters of heart failure, these changes were not significant. Low-level FK506 is well tolerated and increases BMPR2 in subsets of PAH patients. These results support the study of FK506 in a phase IIb efficacy trial.