C-122, a novel antagonist of serotonin receptor 5-HT2B, prevents monocrotaline-induced pulmonary arterial hypertension in rats

Pulmonary arterial hypertension (PAH) is a chronic disease characterized by sustained elevation of pulmonary arterial pressure that leads to right ventricle failure and death. Pulmonary resistance arterioles in PAH undergo progressive narrowing and/or occlusion. Currently approved therapies for PAH are directed primarily at relief of symptoms by interfering with vasoconstrictive signals, but do not halt the microvascular cytoproliferative process. In this study we show that C-122 (2-amino-N-(2-{4-[3-(2-trifluoromethyl-phenothiazin-10-yl)-propyl]-piperazin-1-yl}-ethyl)-acetamide trihydrochloride, a novel antagonist of serotonin receptor 5-HT2B (Ki = 5.2 nM, IC50 = 6.9 nM), when administered to rats for three weeks in daily oral 10 mg/kg doses, prevents not only monocrotaline (MCT)-induced elevations in pressure in the pulmonary arterial circuit (19 ± 0.9 mm Hg vs. 28 ± 2 mm Hg in MCT-vehicle group, P < 0.05) and hypertrophy of the right ventricle (right ventricular wt./body wt. ratio 0.52 ± 0.02 vs. 0.64 ± 0.04 in MCT-vehicle group, P < 0.05), but also muscularization of pulmonary arterioles (23% vs. 56% fully muscularized in MCT-vehicle group, P < 0.05), and perivascular fibrosis in the lung. C-122 is orally absorbed in the rat, and partitions strongly into multiple tissues, including heart and lung. C-122 has significant off-target antagonist activity for histamine H-1 and several dopamine receptors, but shows no evidence of crossing the blood-brain barrier after a single 10 mg/kg oral dose in rats. We conclude that C-122 can prevent microvascular remodeling and associated elevated pressures in the rat MCT model for PAH, and offers promise as a new therapeutic entity to suppress vascular smooth muscle cell proliferation in PAH patients.