Tyrosine Kinases in experimental Pulmonary Hypertension

P ulmonary arterial hypertension (PAH) is a progressive pulmonary vascular disorder with high morbidity and mortality. 1 Current therapeutic approaches for the treatment of PAH mainly provide symptomatic relief, as well as some improvement in prognosis. Pathological changes observed in vascular remodeling include endothelial injury, proliferation, and migration of pulmonary arterial smooth muscle cells (PASMCs), causing medial hypertrophy of the intraacinar muscular resistance vessels, muscularization of the normally nonmuscular precapillary arterioles, and an increase in connective tissue deposition in the medial layer. 2 Over recent years, considerable evidence has been accumulated suggesting the involvement of receptor tyrosine kinases (RTK), such as the platelet-derived growth factor (PDGF) receptor, in the pathogenesis of pulmonary vascu-lar remodeling. A complete analysis of the pathogenic role of PDGF in PAH demonstrated an increased expression of PDGF ligands and receptors (PDGFR) in pulmonary arteries of idiopathic PAH lungs. 3,4 In addition, PDGF was shown to primarily contribute to the proliferative and migratory phenotype of PASMCs. 5 Administration of imatinib, a small molecular inhibitor that inhibits PDGFR/Abl and c-Kit, 6 was shown to reverse vascular remodeling in severe experimental Objective—Pulmonary arterial hypertension is a progressive pulmonary vascular disorder with high morbidity and mortality. Compelling evidence suggests that receptor tyrosine kinases, such as platelet-derived growth factor (PDGF) are closely involved in the pathogenesis of pulmonary arterial hypertension. We investigated the effects of 2 novel PDGF inhibitors, nilotinib/AMN107 (Abl kinases/PDGF receptor inhibitor) and dasatinib/BMS-354825 (Abl kinases/PDGF receptor/Src inhibitor), on the proliferation and migration of pulmonary arterial smooth muscle cells (PASMCs) and on the hemodynamics and pulmonary vascular remodeling in experimental pulmonary hypertension, and determined the expression and regulation of Src family kinases. Methods and Results—Human PASMCs were stimulated by PDGF alone or multiple growth factors to induce proliferation and migration in vitro. Dasatinib (0.03 mol/L), nilotinib (0.3 mol/L), and imatinib (1 mol/L) potently inhibited PDGF-induced signal transducer and activator of transcription 3 and Akt phosphorylation. All 3 inhibitors decreased PDGF-induced proliferation, cell cycle gene regulation, and migration. In contrast, only dasatinib inhibited multiple growth factor–induced PASMC proliferation, and this was associated with the inhibition of Src phosphorylation. Combination of specific Src inhibitors (phosphoprotein phosphatase 1, phosphoprotein phosphatase 2) with either imatinib or nilotinib reduced multiple growth factor–induced proliferation to a similar extent as dasatinib. Importantly, Src phosphorylation increased in pulmonary arterial hypertension PASMCs compared with control PASMCs. Finally, in vivo dasatinib (15 mg/kg per body weight) treatment caused a …