Abstract 16555: ML290, an Allosteric Agonist of RXFP1, Attenuates Experimental Pulmonary Hypertension

IntroductionRelaxin prevents fibrosis in animal models of heart failure and pulmonary fibrosis, but its role in pulmonary hypertension (PH) is unknown. Development of relaxin peptide is limited by the need of continuous administration. ML290, a biased small molecule allosteric agonist of RXFP1 receptor, has favorable pharmacokinetics and anti-fibrotic effects. ML290 interacts only with human RXFP1. Humanized RXFP1 knock-in (KI) mice but not WT mice are sensitive to the acute hemodynamic effects of ML290.HypothesisModulation of relaxin-RXFP1 signaling via ML290 may attenuate PH in humanized RXFP1 KI mice subjected to SU5416 and hypoxia.MethodsRXFP1 expression was analyzed in PH patient and control lung, and in cultured pulmonary vascular cells. Rats were exposed to monocrotaline (MCT) and treated with recombinant relaxin (250 μg/kg/day) via osmotic pump for 3 weeks. RXFP1 KI mice were exposed to SU5416 (20 mg/kg sc) and hypoxia (FIO2=0.1) for 3 weeks while receiving ML290 (10 or 30 mg/kg/day ip) or vehicle. Invasive hemodynamics, Fulton’s ratio and pulmonary vascular remodeling were assessed.ResultsImmunohistochemistry revealed RXFP1 expression in vascular media but not intima of normal human pulmonary arteries, and abundant expression in the hypertrophied media of pulmonary arteries in PAH patients. Expression of RXFP1 mRNA was detected in cultured primary pulmonary arterial smooth muscle cells (PASMCs) from normal and PAH lungs, but not in endothelial cells. In human PASMCs, relaxin induced transient activation of ERK1/2, inhibited TGFβ-mediated SMAD3 activation, and attenuated the contractile or fibrogenic phenotype. Relaxin did not attenuate PH in MCT-rats, but was associated with development of neutralizing antibodies. In contrast, ML290 attenuated PH, RV hypertrophy and vascular remodeling in Sugen-hypoxia exposed humanized RXFP1 KI mice in a dose-dependent manner (Figure).ConclusionsRXFP1 is expressed in human PASMC. Relaxin inhibits canonical TGFβ-mediated signaling and myogenic-fibrogenic differentiation. Small molecule RXFP1 agonist ML290 ameliorates PH in RXFP1 KI mice, suggesting that relaxin-RXFP1 signaling contributes to pulmonary vascular homeostasis and may be a potential therapeutic target in PAH.