Vasorelaxant and anti-proliferative effects of lefluomide - 09/03/22

Leflunomide (LEF) is a immunomodulator indicated in various diseases including rheumatoid arthritis. Recently, a link between this drug and pulmonary arterial hypertension (PAH) has been suggested (Lacoste Palasset et al., 2021, Ann Am Thorac Soc). Our aim was to examine the effect of LEF on pulmonary artery (PA) tone, whose abnormality is associated with PAH.

Distal intralobar PAs and mesenteric arteries (MA) were isolated from male Wistar rats. PA were also collected from subjects with lung cancer, distal from tumor areas. PAs segments were mounted on a myograph for measurement of isometric tension and stimulated with various contractile agents and inhibitors. Experiments were conducted in the presence of LEF, its metabolite teriflunomide (TER) or vehicle (DMSO) (<0.7%).

LEF (100μM) dramatically inhibited the contractile response to high K⁺, phenylephrine (PE) and U46619 in rat PAs. LEF decreased E_max of PE by 77% and induced a 3-fold increase in EC₅₀ compared to vehicle. Similar effects were observed in MA. Effect of LEF was unaffected by endothelium removal and was relieved after LEF wash out. Concentrations >10μM of LEF produced a dose-dependent relaxation of PAs precontracted with U46619. TER had intermediary effect on K⁺ response in PA and MA. TER exerted similar inhibition as LEF on PE-evoked contraction in MA, but had a milder effect in PA. In the latter, TER decreased E_max by 42% and did not change EC₅₀ of PE. With calcium-free solution or nifedipine LEF still inhibited response to PE, suggesting the effect is not caused by Ca²⁺ influx inhibition. Preliminary data showed that LEF inhibited contractile responses to K⁺ and PE in human PAs, but surprisingly had no effect on U46619 response. Concentrations ≥100μM inhibit proliferation of human pulmonary arterial smooth muscle cells(hPASMCs)

LEF evoked a robust inhibitory effect of rat and human vascular tone at high, yet clinically relevant concentrations. Experiments are currently ongoing in order to clarify the actual mechanism.