PRX-08066 Maleic acid is a selective 5-hydroxytryptamine receptor 2B (5-HT2BR) antagonist . 5-HT receptors are a group of G protein-coupled receptors and play an important role in schizophrenia, feeding disorders, perception, depression, migraines, hypertension, anxiety, hallucinogens, and gastrointestinal dysfunctions. In NET cell line, KRJ-I, PRX-08066 inhibited 5-HT secretion and cell proliferation and decreased ERK1/2 phosphorylation and profibrotic growth factor synthesis and secretion (TGFβ1, CTGF and FGF2). In the KRJ-I:HEK293 coculture system, PRX-08066 significantly reduced 5-HT release, Ki67, CTGF, TGFβ1 and FGF2 transcription in the KRJ-I cell line. 5-HT itself stimulated HEK293 proliferation . PRX-08066 has preclinical safety profile, good bioavailability, and low acute toxicity, which is under phase II clinical trials for the treatment of hypoxia-induced pulmonary hypertension syndromes and pulmonary hypertension . In the monocrotaline (MCT)-induced PAH male rats model, PRX-08066 (100 mg/kg) significantly increased right ventricular ejection fraction and reduced peak PA pressure at 50 and 100 mg/kg. Morphometric assessment of pulmonary arterioles showed PRX-08066 significantly reduced medial wall thickening, lumen occlusion and RV hypertrophy. Also, PRX-08066 diminished pulmonary vascular remodeling .